Engine Lubrication, Part I With the correct oil friction losses in an engine are reduced to a minimum. This is done by taking into consideration circumstances as engine usage, ambient temperature, time of year and climate, location and engine design. The engine manufacturer usually recommends a certain type of oil to use regarding different circumstances. Lubricating oil plays an important part in the life of the engine and during maintenance it will be replaced, on certified aircraft the pilot can only replenish it. Without lubricating oil the engine would fail within minutes, keeping a watchful eye during flight is therefore important. Engine oil comes in many forms: synthetic or mineral or a combination of both. Each with their own unique properties and the most important one is viscosity, which determines its readiness to flow at different temperatures. To enhance the properties of the oil, special formulated additives are added which contain friction reducers, high pressure and anti wear compounds to name a few. Having a basic understanding of engine oil is a must for the professional and private pilot, here we can only scratch on the surface of a very interesting subject.
Oil properties Engine oil performs a number of functions in the engine: lubrication, cooling, cleaning, sealing, corrosion protection, noise reduction and propeller operation. The most important being lubrication. Without oil all moving parts of the engine would be in direct contact and wear out very rapidly. Oil forms a layer between the parts and reduces friction. You can visualize oil as millions of tiny, molecular size, ball bearings rolling between the moving parts of the engine. The size of these balls is determined by the clearances in the engine and dictates which viscosity the oil must have for a long service life. To perform its task, oil must be able to withstand high temperatures, pressure and shear loads. It has certain properties as viscosity and contains additives to clean the engine as zinc and other compounds. Oil is either mineral (from oil wells), semisynthetic (part mineral part synthetic) or of full synthetic (man made) srcin. Each type has its own unique properties and specific purposes.
Viscosity For pilots the most important property is oil viscosity, its readiness to flow under different temperatures.
During a cold start in wintertime oil will be thicker than during a warm start in summertime. In both cases it is important that oil pressure is attained within 30 seconds after start to prevent any damage.
Multigrade Oil is said to be of a certain viscosity or grade. Multigrade oils are capable of keeping their specific viscosity under a wide temperature range, for example: -10°C to + 40°C, important during startup of the engine. Oil with higher grades are used at higher startup/ambient temperatures and not really usable in freezing arctic conditions where a synthetic multigrade like 0W or 5W would be best. Aircraft engines used to use a single grade oil as a 80 grade (SAE40) or even a 100 grade (SAE50). Although multigrades (for summer and winter use) like 15W50 or 20W50 are more common these days. Some diesel engines and more modern gasoline engines (Centurion, Wilksch, Rotax, Subaru) tend to use the 10W40 or 15W40 viscosity oils, where Rotax even recommends a motorbike oil as it contains additives for gears. When replenishing, you can add oil of a different viscosity but keep in mind that the final viscosity will end up in between the two. For example: 50% of SAE80 mixed with 50% SAE100 results in SAE90. Mixing multigrades as 10W40 and 15W50 should get 12W45, the final result depends on the mixing ratio. Be sure not to mix mineral, semisynthetic or full synthetic oils.
Cooling As oil is pumped around in the engine lubricating gears, bearings, pistons and valves its temperature rises. Especially near the pistons and cylinders. To make sure the oil stays within the operating limits it will need to be cooled by running it through an oil cooler. Some of which are thermostatically controlled, which is a must as it keeps the engine oil on a preset constant temperature regardless the ambient temperature. The oil temperature indicator shows the temperature of the oil when it leaves the cooler and is about to enter the engine. It must be within a certain range so that all parts are cooled properly and do not overheat. Too low an oil temperature isn't good either as any moisture collected by the oil needs to dry out. Furthermore, the engine is only operating on design specifications when at its proper operating temperature.
Cleaning and corrosion protection Using the correct ashless dispersant oil keeps the interior of the engine clean if used continuously after the first hours of initial break-in. These oils contain specific additives which keep dirt suspended so that the oil filter can collect them. During the time the engine is running, oil is collecting combustion byproducts as: soot, coke produced by hot areas, blowby gases add acids, water vapour and gasoline dilution from priming.
All these products form their own composition as sludge, varnish and corrosive acids. Oil is capable to handle all of this without problem but it will need regular changes as the additives in new fresh oil are 'used up'. The aircraft maintenance program dictates how many hours can be flown before the oil and filter will need changing, usually every 50 or 100 hours. After the engine is shutdown the oil will eventually collect in the sump, leaving a thin film on all internal parts preventing corrosion. But if the engine is shutdown with oil that was in service for quite some time and isn't flown for the next couple of weeks or months, there is a change that contaminants in the oil could corrode the metals. It is wise to change the oil before putting an aircraft in storage or even using preservation oil in the cylinders to prevent any possible corrosion.
Sealing and noise reduction Thin oil films provide the necessary gas tight seals between piston rings and cylinder walls preventing gas blowby. Lubricating oil on the valve train cushions the valves which open and closes at 20 times per second at 2400 RPM cruise power reducing valve noise. With the correct oil friction losses in an engine are reduced to a minimum. This is done by taking into consideration circumstances as engine usage, ambient temperature, time of year and climate, location and engine design. The engine manufacturer usually recommends a certain type of oil to use regarding different circumstances. Lubricating oil plays an important part in the life of the engine and during maintenance it will be replaced, on certified aircraft the pilot can only replenish it. Without oil the engine would fail within minutes, keeping a watchful eye during flight is therefore important. Having a basic understanding of engine oil is a must for the professional and private pilot, here we can only scratch on the surface of a very interesting subject. The oil system in an aircraft engine is very reliable and needs little maintenance, changing oil and filters in regular intervals plus visual inspection. The pilot must keep an eye on levels, pressures and temperatures during operation. Sponsor the site!
Oil system
A typical aircraft engine oil system has a dry or wet sump. A dry sump means that oil is collected in a separate tank and these are normally used in radial, aerobatic and the well known four stroke Rotax engines. A wet sump system as most Lycoming or Continental engine uses has the oil in the sump underneath attached to the engine.
Oil pump Oil is being kept in the sump and flows around through a cooler (sometimes with a thermostat), a filter and to the high pressure oil pump (with regulating valve) which pumps the oil through galeries to spray and splash the lubrication points. Dry sump engines contain a scavenge pump to remove the oil from the engine to the separate tank. Oil pumps are usually two gears (gerotor) driven by the camshaft.
Oil pressure and temperature An oil pressure gauge is connected in the high pressure line after the oil pump as an indicator for the pilot and a oil temperature gauge shows temperature after being cooled en before entering the engine again. Some oil pressure sensors are equipped with an extra switch which closes the moment oil pressure is build up by the pump. This can be indicated by a light on the instrument panel.
Screens and filters A screen is used in the sump to act as a coarse filter and a screw on type external oil filter is used as the main filter. This filter sometimes contains a pressure relieve valve to let oil through should the filter become clogged and this valve makes sure that the oil keeps flowing.
Oil cooler A radiator type cooler, is basically an air/oil heat exchanger. Outside air is led through the cooler and the cool air picks up the heat from the tubes and fins in the cooler. Can be equiped with an thermostat and or bypass valve should the cooler become blocked. Those models with a thermostat (either internally or as addon) keep the oil on a preset temperature, regardless. This is much better than having to keep the engine warm with a winterization kit which blocks part of the air flow into the cowling. The engine will reach operating temperatures much quicker after a cold start and maintain it during a long descent. With the correct oil friction losses in an engine are reduced to a minimum. This is done by taking into consideration circumstances as engine usage, ambient temperature, time of year and climate, location and engine design. The engine manufacturer usually recommends a certain type of oil to use regarding different circumstances.
Lubricating oil plays an important part in the life of the engine and during maintenance it will be replaced, on certified aircraft the pilot can only replenish it. Without oil the engine would fail within minutes, keeping a watchful eye during flight is therefore important. Having a basic understanding of engine oil is a must for the professional and private pilot, here we can only scratch on the surface of a very interesting subject. The oil system in an aircraft engine is very reliable and needs little maintenance, changing oil and filters in regular intervals plus visual inspection. The pilot must keep an eye on levels, pressures and temperatures during operation.
Oil maintenance Oil maintenance you say? Yes. Regular oil changes form the basis of good preventive maintenance. Oil should be changed during each 50 hour check, it also gives the maintenance engineer the opportunity to have a look under the cowling (as some pilots would care less) and see if things are still as they should be. And if you are doing it the proper way, have an oil sample analyzed. This will give you insight in what is going on inside the engine related to the wear and tear of bearings, pistons, cylinders, valves and more. Engine oil has a number of important functions: • • • • • •
lubrication, reducing friction of moving parts cooling, of internal engine hot spots cleaning, keeping sludge, dirt and other contaminants suspended sealing, pistons in cylinders cushioning, reducing sound and dampening noise corrosion protection
Oil must carry out all these functions under harsh conditions as low and high temperatures, pressure and shearing effects without any side effect. In part I of Engine Lubrication we discussed al off the above but cleaning. During an oil change, the oil together with suspended contaminants is being removed from the engine and it forms a very important part of preventive maintenance.
Changing oil Normally ashless dispersant type oils are used after the first 100 hours of engine run in. These oils contain additives capable of holding dirt in the engine suspended so that they can be collected by the oil filter, if large enough, or removed during an oil change. This is very important since there are many small passages in the engine which could clog up and cause oil starvation.
During engine operation the oil collects dirt from different places, from the atmosphere through the air filter, soot during start and idling, hot areas cause coke, blowby gasses produce sulfuric acids and water vapor is attracted after engine shutdown and startup. Acids are corrosive, but only in combination with water. Thus it is very important that the oil reaches it correct operating temperature during each flight so that any water gets 'boiled off'. The oil dries out and the vapor leaves the engine through the crankcase breather or water/oil separator. The amount of water condensation depends on the humidity of the ambient air, the higher the temperature (summer) the more water vapor it can contain and the location of the aircraft.
Oil change Any good brand ashless dispersant oil contains additives as acid neutralizers, zinc and more to combat contaminant, sludge, dirt and varnish. There is a reserve of additives in new oil which is 'used up' during the time the engine runs. Just adding extra additives will not work as the oil itself is subject to very high temperatures and shearing action which have their effect on quality. Oil therefore need to be changed after a certain amount of time.
Oil and air filters A filter can only remove particles of a certain specified size and larger. No filter is able to remove everything 100%, for such a filter would even block the oil. For example a 10 micron filter should remove all particles of 10 micron and larger, but what usually is forgotten is the effectiveness of the filter. And the longer the filter is on the engine, the more dirt it collects the more it starts loosing it effectiveness and it will need replacement which is done during the 100 hour check.
Engine break-in Every engine is run-in or broken-in at the factory on a test stand, but it is generally accepted that the first 100 hours are considered the final break in period. In the first 25 hours (or when oil consumption stabilizes) straight mineral oil should be used, this is oil without the additives found in ashless dispersant oil. This aids in the break-in. If normal ashless dispersant oil would be used during the break-in period the additives would cause the break-in to fail and the piston rings will never properly seat in the cylinders resulting in a higher than normal oil consumption and possible a higher cylinder wall wear rate and the engine not reaching its recommended TBO.
Oil brands When on a cross country and the engine needs an oil top up, don't worry about the brand. Just make sure that it is the same type: straight mineral or ashless dispersant. The viscosity should be the same you would use, but if it is not available, you may mix a 20W50 with a 15W50. The result will be a 17W50, depending on the ratio of the mix. Just make sure not to mix synthetic oil with mineral oil.
With the correct oil friction losses in an engine are reduced to a minimum. This is done by taking into consideration circumstances as engine usage, ambient temperature, time of year and climate, location and engine design. The engine manufacturer usually recommends a certain type of oil to use regarding different circumstances. Lubricating oil plays an important part in the life of the engine and during maintenance it will be replaced, on certified aircraft the pilot can only replenish it. Without oil the engine would fail within minutes, keeping a watchful eye during flight is therefore important. As oil is used to reduce friction and wear it eventually picks up metals from the engine, measured parts per million analysis we can determine and which type. If theinconcentration of a (ppm). certain Through metal rises its a good indication thathow wearmuch is increasing and maintenance action might be needed before the engine fails. Sponsor the site!
Oil analysis Spectrographic oil analysis is a popular way of identifying wear characteristics of an engine, it is adopted by the military, commercial and general aviation. Engines are designed with various metals and alloys, the oil system provides oil under pressure or splashes oil to the areas needed and subject to friction. During the normal course of operation these parts undergo minimal and minute wear. Submicroscopic material is released and suspended in the oil. Oil analysis identifies this and gives a good view of the engine internals regarding wear during its operation.
Analysis methods There are two ways of analysis: atomic absorbtion and atomic emissions. Both will identify submicroscopic particles in the oil in ppm. But with atomic absorption particles smaller than 5 micron will be detected and with atomic emission particles smaller than 10 micron are detected. Either method is good, but they should not be used together on the same engine. Comparing these different reports will have little meaning. It mustthe be same said that allprocedures) the oil analysis your should be carried out by same lab oil (as to assure work and of even anengine one time analysis of a batch of the fresh engine should be done to set up a base line for the engine. It goes without saying that the engine should be run on the same type and brand of the oil for the results to have any meaning.
Oil analysis is an extra tool which can help identify problems in the engine before they develop into threating issues during flight. It gives the technician insight information in the normal wear of the engine and any deviations from the normal trend should be investigated.
Engine Oil use The frequency of aircraft / engine use is one of the prime factors in determining how the oil will perform and how often it should be changed. Frequently flown aircraft, think one hour a week and regular (50 hour) oil changes will make any oil look good. This behavior keeps the oil covering all internal parts. There is some debate that oil will 'run off' engine parts after a while, but oil will always stick to metal and keep it covered. This, however, could not be the case of piston oil compression and scraper rings as they are subject to high temperatures and oil does tend to get burned off, although this is only in minute quantities. Engines flown less than 100 hours a year are candidates for corrosion formation (my personal opinion is that in this day of age engine corrosion can be properly taken care of by good metallurgy and modern engine oil and I wonder why the established engine manufacturers do not apply modern alloys in their engines to combat corrosion).
Protective coatings Between aircraft use, engine oil should maintain a coating on all internal parts, if not, the surfaces will begin to oxidate within a short period of time. If left unattended longer, the oxidation will damage the steel parts of the engine. Frequent oil and filter changes is a good way to minimize these effects. Thicker oil would help too as it 'sticks' better to the metal. But this has the disadvantage that it takes a couple of seconds for the oil to be up to pressure and reaching all parts moving, especially in winter. Hence the need for multigrade oils in which we have 15W50 and 20W50 which are thinner at lower temperatures facilitating quicker oil pressure but are able to be 'thick' enough at engine operating temperatures.
Moisture formation Moisture is formed when the engine oil cools and water condenses. Regular flying with oil temperatures reaching 100°C will make sure that all water is boiled off. Ground running is just not enough. Its too short for all parts to get up to operating temperatures and in the end will do harm. It increases water formation and corrosive attack.
Acids Engine combustion are pickup oil and form, when mixedinwith condensation, acids byproducts capable of etching intoby thethe metals of will the engine. Resulting more corrosion. Frequent oil changes, even on a four monthly basis when not flying frequently (time limited as opposed to hour limited), will help against acid formation.
Location The location where the aircraft is used or parked, coastal and or high humidity places, will contribute to corrosion. As said above, if flying infrequently are your are in said locations, do more oil changes to minimize possible corrosion and this will help in keeping the engine in good health.
Finally Oil and filter should be changed regularly but the use of the aircraft (or the lack of) and other factors dictates if the oil must be changed sooner than prescribed by the manufacturer to prevent any corrosion formation in the engine. Oil analysis is a great tool to see if the oil is up to the task its designed for in your engine and particular use of the aircraft. Lubrication is needed to overcome friction caused by surfaces sliding or rolling over each other. No matter how polished or closely machined a surface is, on a microscopic level there are always small jagged edges or uneven spots. If these surface irregularities come into contact they may break off or even seize and become attached together. With further movement tiny parts will break and float around in the oil and eventually may cause damage if the oil is not filtered or oil filters not changed at the proper interval. In an engine, be it diesel or spark ignited, oil is used to lubricate all moving parts so that durability and reliability is assured for many thousands of hours of trouble free service life. Sponsor the site!
Types of Lubrication The amount of friction between two parts depends on several factors: • •
• • •
Temperature, either ambient and in the engine itself has an effect on friction Surface finish, the better the surface is machined or polish the lower the coefficient friction the surfaces have Load, the heavier the load on a surface the more friction there is Speed of movement, the increase of speed of sliding surface will increase the friction Nature of movement, sliding or rolling motion have different friction characteristics
•
Type of lubricant, the type of oil and its characteristics also have an effect on friction (viscosity)
If we want to reduce friction we need to change or remove the factors which may have an adverse effect on the surfaces in motion. There's a number of ways to do just that. In case of sliding friction use a rolling element like a ball or needle bearing elements. The use of sacrificial surfaces can be used to, think of lead/copper journal bearings. Last but not least, the changing of viscosity, different or improved additives or even changing from oil to grease can reduce friction. In the small area where the sliding or rolling surfaces are lubricated this happens in one of three modes of lubrication: • • •
Boundary lubrication Hydrodynamic lubrication, HDL Elastohydrodynamic lubrication, EHL
We will discuss each of these.
Boundary lubrication This occurs when an engine is started, at low speed or even in high load conditions. At this time the two moving (rolling or sliding) surfaces may come into real contact and damage could result. Some specialist say that 70% of all wear in an engine occurs in this regime. To make sure that no damage is done during these regimes, is to use a lubricant which is formulated with antiwear or even extreme pressure additives. These additives react with the surfaces in contact due to the high pressure and temperature and form a chemical film on those surfaces. This film is then sacrificed as the surfaces come into contact so that the film wears off and not the metal surface. By increasing the viscosity of the lubricant, ie increasing its thickness, boundary friction can be minimized in some situations. Although care must be taken not to increase viscosity too much as the internal friction of the lubricant increases too and can give rise to higher temperatures.
Hydrodynamic lubrication This is when a full film of oil has separated an engine shaft (crank or camshaft) from its support and no contact exists between the parts. The oil is keeping the shaft and bearing apart by viscosity. Also, during hydrodynamic lubrication there is no friction except in the lubricant itself, where molecular structures shear during operation.
HDL requires that the machined surfaces have a high degree of geometric conformity and relatively low pressure. This situation can be found between rotating crank or camshafts and the journal or sleeve bearings. Once the engine is at operating temperature and shafts are at normal engine speeds it should be possible to remain in hydrodynamic regime forever so that friction is at minimum.
Elastohydrodynamic lubrication This type of lubrication occurs where surfaces have a low degree of conformity combined with high contact pressures as found in gear drives (Rotax) and rolling bearing elements (wheel bearings). The lubricants are caught by the moving surfaces and under high pressure the viscosity increase to such a high level that it forms a semisolid film separating the two moving surfaces. And as long as these conditions do not change, the metal surfaces will not come into contact. In fact these surfaces may actually deform long before the semisolid oil or grease film breaks, due to this remarkable property of the lubricant. With the correct oil friction losses in an engine are reduced to a minimum. This is done by taking into consideration circumstances as engine usage, ambient temperature, time of year and climate, location and engine design. The engine manufacturer usually recommends a certain type of oil to use regarding different circumstances. Lubricating oil plays an important part in the life of the engine and during maintenance it will be replaced, on certified aircraft the pilot can only replenish it. Without oil the engine would fail within minutes, keeping a watchful eye during flight is therefore important. Having a basic understanding of engine oil is a must for the professional and private pilot, here we can only scratch on the surface of a very interesting subject. Before flight the pilot checks the oil level and adds any if needed, during flight he (or she) must pay close attention to temperature and pressure.
Operational Aspects Engine oil systems are usually very reliable but the daily (and in between flights) checks of the oil level can not be forgotten as aircraft engines will use a bit of oil during operation. During preflight the pilot should check the oil cooler for obvious blockages by foreign matter and leaks (under the engine on the ground). Make sure to check under the cowling for oil stains, it could indicate a minor oil leak from the sump or oil lines. When topping up, make sure not to add too much oil. For example: the PA-28-180 runs perfectly on 6 quarts but will throw out anything above that (min is 2 quarts), a Rotax should be kept at
maximum level for optimum cooling. Make sure to top up with the correct quantity, type and grade of oil. After engine start the first and most important item to check is the oil pressure, it must register within 30 seconds (60 when in cold to freezing conditions). Check your POH for precise details.
Oil system malfunctions Oil system faults are rare and usually are related to pressure and or temperature, make sure that you are familiar with the normal indications for your engine.
Fluctuating oil pressure This can be an indication that the oil level is getting low and the pump is drawing air from either the in or external sump. A failing scavenge pump may cause oil not being transferred to the external sump. On the Rotax 9 series engine the oil pressure sensor is a resistive type mounted on the engine near the oil pump and due to vibrations from the engine the sensor will eventually fail while indicating fluctuating pressures.
High pressure Usually caused by a faulty pressure relief valve or failing oil pressure sensor (more likely). Oil pressure too high may cause seals to blow out resulting in a loss of oil.
Low pressure Maybe be caused by a low oil level, loss of pressure by a failing pump, broken oil line or relief valve or even a faulty pressure gauge or oil pressure sensor may cause a low oil pressure indication. Keep in mind that a high oil temperature will cause oil viscosity to be lower and that oil pressure will drop slightly.
High oil temperature Extended climbs in high OAT will cause oil temperature to rise and pressure to drop slightly. If oil temperature rises with a large oil pressure loss then a oil leak can be expected. High power settings combined with low airspeeds (extended climb) will increase the oil pressure due to a higher RPM. If combined with a low or reducing oil pressure this may indicate an oil leak with a resulting engine failure closeby. Keep an eye on the oil pressure and temperature as these are indications of general engine health, if in doubt land asap and consult your or any aircraft engineer.
Lubrication System in I.C. Engines
2.12.1 Need for Lubrication In an I.C. engine, moving parts rub against each other causing frictional force. Due to the frictional force, heat is generated and the engine parts wear easily. Power is also lost due to friction, since more power is required to drive an engine having more friction between rubbing surfaces. To reduce the power lost and also wear and tear of the moving part substance called lubricant is introduced between, the rubbing surfaces.
2.12.2 Function of Lubrication (a)
Lubricant reduces friction between moving part
(b)
It reduces wear and tear of the moving parts.
(c)
It minimizes power loss due to friction.
(d) It provides cooling effect. While lubricating it also carries some heat from the moving parts and delivers it to the surroundings through the bottom of the engine (crank case). (e)
It helps reduce noise created by the moving parts.
2.12.3 Engine parts which are lubricated The following are some engine parts that require adequate lubrication. 1. Crank shaft
2. Crank pin
3. Big and small end of the connecting rode
4. Piston pin
5. Internal surfaces of cylinder walls
6. Piston rings
7. Valve mechanisms 8. Cam shaft etc.
2.12.4 Lubrication Systems The main lubrication systems are: 1. Petrol lubrication system or Mist lubrication system. 2. Wet sump lubrication system.
2.12.5 Petrol Lubrication System or Mist Lubrication System.
This system of lubrication is used in scooters and motor cycles. About 3% to 6% of lubricating oil is added with petrol in the petrol tank. The petrol evaporates when the engine is working. The lubricating oil is left behind in the form of mist. The parts of the engine such as piston cylinder walls, connecting rod are lubricated by being wetted with the oil mist Disadvantage
(i) If the added oil is less, there will not be sufficient lubrication and even result in seizure of the engine, (ii) If the added oil is more, it will lead to excess exhaust smoke and carbon deposits in the cylinder, exhaust parts and spark plugs.
2.12.6 Wet sump Lubrication System Engine Lubrication
Two types of engine lubrication systems are used in internal-combustion engines: the splash system and the pressure-feed system. The pressure-feed system, with small modifications, is the more popular for more popular for modern automobile engines. The splash system is used on most lawn mower and outboard engines.
2.12.7 Pressure-Feed System. In the pressure-feed system, oil is forced by the oil pump through oil lines and drilled passageways. The oil, passing through the drilled passageways under pressure, supplies the necessary lubrication for the crankshaft main bearings, the connecting-rod bearings piston-pin bushings, camshaft bearings, valve lifters, valve push rods, and rocker studs. Oil passing through the oilThe linescylinder is directed to are the lubricated timing gears the valve shafts in orderand to piston-pin lubricate these parts. walls by and oil thrown offrocker the connecting-rod bearings. Some engines have oil spit holes in the connecting rods that line up with drilled holes in the crankshaft journal during each revolution, and through or spit a steam of oil onto the cylinder walls.
Pressure-Feed System
To enable the oil to pass from the drilled passageways in the engine block to the rotating crankshaft, the main bearings must have oil feed holes or grooves that line up with the drilled holes in the crankshaft each time the crankshaft rotates. The same is true in the case of the connecting-rod bearings and the drilled passageways in the connecting rods. Since the oil in the passageways is under pressure, each time the drilled holes in the crankshaft and connecting rod line up with the holes in the bearings, the pressure forces the oil through these drilled passages into the crankshaft and connecting rod, lubricating their respective bearings. After the oil has been forced to the area requiring lubrication, it falls back down into the oil pan ready to be picked up again and returned through the system. As the oil falls, it is frequently splashed by the moving parts onto some other part requiring lubrication.
2.12.8 The Splash system The splash system is used only on small four-stroke-cycle engines such as lawn mower engines. As the engine is operating, dippers on the ends of the connecting rods enter the oil supply, pick up sufficient oil to lubricate the connecting-rod bearing, and splash oil to the upper parts of the engine. The oil is thrown up as droplets, or fine spray, which lubricates the cylinder walls, piston pins and valve mechanism.
The Splash system
Dry sump lubrication in F1 engines The dry sump lubrication system is a design that intends to lubricate the engine's internal parts to provide optimal performance of the engine itself. It is currently the best system for high performance engines and is widely used in Formula One, Le Mans, IRL and other well known racing series. Lubrication systems for a four-stroke, reciprocating piston engine can be categorised in just two groups: the wet sump design and the dry sump system. Both systems rely on an oil reservoir from which oil is drawn with a pump and spread around the engine for lubrication and cooling purposes. All oil is then allowed to flow back to the reservoir from where the cycle restarts.
Wet sump lubrication is the most widely used system as it is more cost efficient and perfectly adequate for normal passenger vehicles. In this design, the oil of the engine is stored in a sump located under the crankshaft as an integral part of the engine block. The oil pans' capacity can range from 3 to 7 litre, depending on the engine's size and purpose. From this pan, the oil is pumped up a pick-up tube and supplied to the engine under pressure. A wet sump design has several advantages, including its low cost, low weight and its simplicity. Because the sump is an internal part of the engine, there is no need for tubes to circulate the oil from the reservoir to the engine, reducing chances of leaks. Despite its advantages, a wet sump system is unsuitable for racing purposes.Formula One cars for example experience ofpossibly up to 3Gleaving in mid the corner. Such centrifugal would pull all oil to one lateral side ofG-forces the sump, engine without oil foraccelleration a short period. The latter phenomenon is also known as oil starvation. When performance and reliability matter, such a situation is unacceptable. To resolve this issue, the dry sump system was designed and is now in use in all major racing series. The dry sump system literally keeps the sump of the engine dry and allows for it to be produced small, giving a further advantage to lower the engine's centre of gravity and reduce its empty weight. The design differs from a wet sump in its external oil tank. Again, the oil is pumped into the engine at elevated pressure and then flows down to the engine's sump. While it was previously held there, the oil is now sucked away from the engine by one or more scavenger pumps, run by belts or gears from the crankshaft, usually at around half the crank speed. In most designs, the oil reservoir is tall and narrow and specially designed with internal baffles. The pump itself consists of at least two stages with as many as 5 or 6. With two stages, one is for scavenging while the second is a pressure stage. The three-stage dry sump pump has one pressure sectionsections. and two The scavenge sections, the feeds four-stage has one pressure and three scavenge pressure sectionwhile of each oil topump the block, while the scavenge sections pull oil from special pickups in the dry sump oil pan. The latter system is connected similar to the three stage while the extra line of the scavenge section is routed to pull oil from the lifter valley. This prevents excess oil to slosh in the top of the engine, reducing windages and increasing horsepower. In some cases, a fifth stage is added to provide extra suction in the crankcase area.
Application in Formula One As mentioned, all current F1 engines include a dry sump system, quite simply because it is impossible to create a similar high revving engines with a wet sump system. Due to the engine freeze, all engines also have a similar layout as the fuel tank is located ahead of the engine, just behind the driver. The oil pump that rotates the oil through the engine is - as required by the regulations driven by the crankshaft through gears.
One of the providers of the required high performing lubricants is Shell, the supplier of Ferrari. Shell Technology Manager for Ferrari, Dr. Lisa Lilleyexplains: “Engine lubricant is critical. The very lifeblood of the engine, its job is to protect the moving parts from mechanical wear, reduce friction and power loss and cool the engine as it endures extreme track conditions. It takes a good engine lubricant to achieve just the right balance of these characteristics, while ensuring the car’s performance is optimised, no energy is wasted and maximum power is delivered to the engine.” The first job of Shell Helix is to protect all the moving parts that rub together from mechanical wear. The oil is fed to the bearings of the camshafts to lubricate, minimising friction and wear, thereby the engine’s reliability. The forces required to open the valvesand quickly enhancing enough at 19,000 rev/min must also be enormous transmitted through a lubricant effectively without failure. The engine is exposed to extreme conditions and high temperatures as it turns. The ‘multitasking’ lubricant is designed to take away the heat, controlling the engine temperature and preventing the heat from having a detrimental affect. The ability of an engine oil to cool as well as lubricate is often overlooked. Pistons can exceed temperatures of 300°C; engine oil is sprayed on the underside of the pistons to keep them cool - without this extra protection they would undoubtedly fail in a race. “When you consider that the oil flow around the engine is faster than the speed of the Ferrari Formula One car, this gives you an idea of the extreme conditions in a Formula One engine,” says Dr. Lilley. “At Shell we have a team dedicated to tailoring Shell Helix engine oil for the Ferrari so that we can ensure reliability and protection but we can also guarantee the car is receiving the most horsepower possible.”
Oil is pumped from the “dry sump” oil tank on the front of the engine into the “distribution
Lubricant is fed to the bearings of the camshafts to minimise friction and wear and also to
network” within the cylinder block and heads, which ensures it gets directly to all critical engine components
lubricate the critical cam-to-follower interfaces, where the enormous forces required to open the valves quickly enough at 19,000 rev/min must be transmitted through a layer of lubricant
efficiently and without failure
The lubricant is fed down the middle of the crankshaft, coming out inside the bearings to keep them working. The lubricant flung off these The lubricant squirts onto the underside of the bearings then creates a film on the cylinder walls, pistons from small nozzles on the distribution on which the pistons and rings run smoothly to network, to take away heat ensure minimum power losses and mechanical wear
The used lubricant is sucked away from the bottom of the crankcase by the scavenge pumps, The “camera” exits the engine, showing a fully to be cooled in radiators and returned to the oil lubricated engine tank, refreshed and ready to start its circuit of the engine again What major functions do lubricants perform in aviation engines?
Lubricants are used to reduce friction and wear, whether it's in an aviation engine or the wheel bearing on a car.
Other major functions of a lubricant include cleaning, cooling and sealing, in addition to helping fight corrosion and rust in the engine. Airplanes that are used infrequently especially need the corrosion and rust protection that good aviation lubricants can provide. Unused aircraft have a high potential for rust and corrosion, among other downtime problems. The more frequently and consistently an airplane is flown, the easier it is to properly maintain and lubricate. What are the benefits of using a lubricant that cleans the engine? All aviation oils clean. When we say an aviation oil cleans, we think of removing sludge,
varnishes, and grunge accumulations in the itoilalso pan,means on plugs, or in thebelt screen. a lubricant keeps your airplane engine clean, a clean ring area However, and better when control of the combustion process. When those rings are able to move freely, your engine operates at higher efficiencies, has better ring seal, produces less blow-by, and consumes less oil. A dirty ring belt restrains the movement of the rings within the grooves and they can't seal. This may create pressure between the ring face and the cylinder wall — leading to wear, scarring or scuffing. How do aviation lubricants keep an engine cool? Air-cooled aircraft engines rely on their oil for cooling far more than water-cooled automotive engines. Automotive oil typically accounts for about 40 percent of the engine's cooling capacity. In aviation engines, the oil must carry off a greater percentage of the engine's heat.
Principles of aircraft engine lubrication Oil is a heat-transfer medium which flows through the crankcase and oil coolers, and dissipates the heat from moving parts, thus constantly cooling engine bearings and piston rings. Without the cooling oil film on a cylinder wall, the rings wouldn't have a good heat transfer path. This can lead to melting, galling, or scarring problems. Oil also cools the valve springs and the whole valve train. How does oil seal an aviation engine? Aviation oil not only provides a seal between the rings and cylinder walls, but also helps seal the gasketed areas and the rubber or synthetic seals for the crankshaft. When oil washes around those areas, it helps retain a seal. Thus, aviation oil must be of a blend or formulation that is compatible with the seal materials so that the seal itself lasts longer. What about the job we think of first when we think of oil — lubrication? Lubricating properties are among the most important physical characteristics of aviation oil. Proper lubrication requires a strong enough and thick enough oil film between moving parts to keep friction and wear to a minimum.
Oil properties can include boundary or mixed film, dynamic, hydrodynamic, and elastohydrodynamic forms.
Boundary or mixed film lubrication is found in the upper cylinder area in the outer boundary of an aircraft engine. This is the most remote engine area to lubricate because the oil rings scrape most of the oil film off the cylinder walls before it reaches the upper cylinder. However, there must be a residual amount of lubrication in the upper cylinder to protect the engine on startup. Also, if an engine has been sitting idle for a month, some lifters have been pressed against cam faces and loaded under maximum spring pressure. Most of the oil has been squeezed out of that junction. When the engine is fired up, it takes a while to get oil to all those surfaces again. So, for that crucial moment, you need good boundary or mixed film strength at those critical boundary areas. Oil film retention is not as critical on startup in cam and crank journal areas.
Principles of aircraft engine lubrication Dynamic lubrication is produced through the pressure generated by an oil pump and this pressure provides an adequate flow of oil to the lubrication system. Hydrodynamic lubrication is like water skiing — it provides a smooth surface for any moving part to ride on and prevents any direct contact between moving parts. Hydrodynamic lubrication is full-film lubrication that keeps moving parts from contacting one another. In true hydrodynamic lubrication, as with water skiing, contact pressure is much lower and is spread over a large surface area. A constant supply of oil is required between the parts for hydrodynamic lubrication. When everything is operating properly in an aircraft engine, there is a constant lubricating film between any parts that might rub together. Any wear that the lubricant flow itself could cause is so slight that it would take several lifetimes to wear out a component — like a river wearing away the rocks. If that's true, why do engines wear out? Your biggest problems are on surfaces where there is no oil. That usually happens after an engine has been sitting for a while.
You need the right viscosity and the right velocity between moving parts to keep oil where it needs to be. Think about what happens inside your engine whenever you do something like a cold start. If it's very cold when you fire up your engine, there is maximum velocity between metal parts and maximum oil viscosity. The oil isn't going to provide good hydrodynamic lubrication until the engine warms up. With bearings, the clearances are so close and so contained that they will sometimes keep a good lubricating film on that bearing for years.
Principles of aircraft engine lubrication
In elastohydrodynamic lubrication, an oil can act like a solid — as in areas of very fast, extreme force, such as where the rocker arm contacts the valve stem. The contact happens so quick that the oil can't get out of the way. When engine parts hit that fast, the oil literally acts like a solid. Elastohydrodynamic lubrication provides effective protection for the instant it's needed. The oil acts as a shock absorber, and hence, exhibits elastohydrodynamic properties. What does viscosity have to do with lubrication? All of these lubrication types — the mixed film, dynamic, hydrodynamic, and elastohydrodynamic, all relate to and depend on oil viscosity. Viscosity is a measure of a fluid's resistance to flow. All fluids flow better when they are warm — cold oil is thick, but thins and flows better as it gets hot. Oil viscosity is more important in an aviation engine than in an automobile engine. The fewer additives in the oil, the more dependent it is on its viscometrics (viscosity properties). Straight, untreated base oil can be limited in its lubrication without supplemental additives. Aviation oil will assist in boundary or mixed film lubrication, detergency and other lubrication aspects. Ash cannot be added to aviation piston engine oils. Regulations prohibit the use of ash-bearing detergents and anti-wear, zinc-dithio-phosphate that are used in automotive or diesel truck engine oils because they may cause pre-ignition or detonation in an aircraft engine. What is an oil's viscosity index? While viscosity is an oil's internal resistance to flow, its viscosity index is simply its resistance to changing flow characteristics due to changes in temperature. If an oil's viscosity changes very little, despite significant temperature changes, the oil has a high viscosity index.
Viscosity index is an arbitrary numbering system. Higher numbers mean an oil's viscosity changes little temperature, and90lower numbers means it changes more. Single grade oils typically havewith a viscosity index of to 110. Multi-grade oils, with a viscosity index of 150 or higher, can tolerate extreme temperature changes and better retain their viscosity characteristics. Some automatic transmission fluid is so multi-graded that it may have a viscosity index of 200. Multi-grade oils are common in applications such as aviation oil, automatic transmission fluid, power steering fluid, gear oil, and hydraulic fluids. How can an oil's viscosity index be improved? Viscosity index can be increased by adding viscosity modifiers, or viscosity index improvers, to base oils. Several types of polymers are used to change the viscosity index of aviation oils.
Viscosity modifiers are available in different molecular weights, so oil formulators can select those with the most desirable performance and cost characteristics. What other oilhelp characteristics be changed with components. additives? Some additives the oil, whilecan others protect engine
Dispersants, flow-improvers, anti-foam, anti-rust, anti-corrosion, and oxidation inhibitors can all be found in aviation oils, as can some ashless, anti-wear additives. Dispersants isolate minute particles to prevent sludge and deposit formation. Ashless dispersants in aviation oil are important because they encapsulate these very small particles of contamination and keep them from clumping and getting big enough to cause internal problems such as contributing to deposits or sludge, oil thickening, and oil screen restrictions. Flow improvers help prevent wax crystal formations and slow viscosity increases that occur when oil gets cold. Sometimes you can improve the pour point of an oil significantly for a cold engine or cold starts by adding a little flow improver or flow modifier. Anti-foam additives allow small bubbles in oil to burst, preventing excessive foam formation. Reducing foam improves oil cooling and lubrication. If an oil is foaming, it can't adhere to an engine's surface and can't cool as effectively. Oxidation inhibitors reduce reactions of oxygen with oil molecules and thereby minimize engine deposits.
Principles of aircraft engine lubrication Rust and corrosion inhibitors help protect the metal engine components from corrosive contaminants introduced by typical engine operation. Oxidation inhibitors, as the name implies, tend to fortify the oil against oxidation. Final thoughts •Change your aircraft engine oil frequently, based on manufacturer recommendations. •Fly your plane monthly to reduce the effects of rust and corrosion on engine components. That doesn't mean starting-up and idling the engine for 10 minutes. You must fly the plane to allow the moisture to dissipate. •Use only approved aviation oils in aircraft engines.
Grease is the word....... Grease is the word
July / August 1998 Although not in the same category as aviation oils, greases are derivatives of oils that provide the same types of protection to other parts of the aircraft. The following information on grease is from the Sky Ranch Engineering Manual by John Schwaner (916) 421-7672. Greases are thickened oils that seal, protect, cushion, and provide long service life. Greases are often referred to by the type of thickener used. Calcium (lime) is the srcinal type of thickener, but is becoming less popular. It has high water resistance but poor high-temperature performance.
Lithium thickeners are used in Aeroshell Grease 7 (MIL-G-23827D) and Aeroshell Grease 17 (MIL-G-21164D). These have high melting points ("drop out") and adequate water resistance. Inorganic gels, as used in Aeroshell Grease 22(MIL-G-81322D), AeroShell Grease 5 (MIL-G3545C) and AeroShell Grease 16 (MIL-G-5760), offer superior high temperature performance over lithium or calcuim thickeners. Inorganic gel does not melt and the grease does not soften at high temperatures. The high temperature point of the grease is often governed by the flash point of the oil portion. These greases burn, rather than melt, if subjected to excessive temperatures. Clay-based greases (bentonite) are sometimes used in high temperature greases. The type of oil that makes up the grease can either be synthetic or mineral oil. AeroShell Grease 7, 16, and 17, are all synthetic oil greases. AeroShell Grease 5 is the most common mineral oil grease. It is not good practice to mix a synthetic oil grease with a mineral oil grease. AeroShell Grease 5 and 22 are both used as a wheel bearing grease. AeroShell Grease 22, an inorganic gel synthetic grease, has superior high and low temperature performance and is specified in higherperformance aircraft wheel bearings. AeroShell Grease 5, a mineral oil grease, is also used in wheel bearings. AeroShell Grease 5 offers superior water and corrosion resistance. Greases are separated by their usage. A low-speed, high pressure gear requires different grease characteristics than a high-speed, roller bearing grease. High pressure sliding surfaces require extreme pressure additives such as Molybdemum Disulfide. These "Moly" greases form a solidfilm lubricant. Low or moderate pressure sliding surfaces may require a grease that will not evaporate, prevent water wash off, and prevent corrosion. Moly is not desired in roller bearings because of its coating property. Roller bearings require a clean grease that has excellent thermal stability. a roller will be grease, pushed causing from the race by the action of the balls. If grease is tooGrease thin orin melts, thebearing race fills with churning of the grease and adding friction and heat to the bearing. If the grease is too thick or dries out, the grease will be displaced to the side and therefore perform no lubricating action. Grease of the proper thickness will come in contact with the side of the ball as it passes and impart a thin film of oil onto the ball. High-speed ball bearing greases should be kept clean. Five gallon pails of grease are subject to dirt contamination because of the length of time it takes to use up that much grease. Ball bearing greases
MIL-PRF-81322E (AeroShell Grease 22, Royco 22CF, Mobilgrease 28) A synthetic inorganic gel grease, used in low or high temperature applications. Wide temperature performance makes it a preferred grease in jet aircraft. MIL-G-3545C (AeroShell Grease 5, Royco 45) A mineral oil-based, inorganic gel grease, the most common wheel bearing grease used. Not as temperature stable as MIL-PRF-81322E, but it has superior water resistance at high temperature.
MIL-G-25760A (AeroShell Grease 16, Royco 25) A synthetic inorganic gel grease with the similar temperature applications as MIL-PRF-81322E.
It has moderate water resistance (between MIL-PRF-81322E and MIL-G-3545), but has superior oxidation and corrosion resistance. Used in amphibious wheel bearings.
MIL-G-25537C (AeroShell Grease 14) A calcium-based mineral oil grease with excellent anti-fretting and oxidation protection. It is used where ball bearings are subject to static vibration that may cause fretting and corrosion. It is used in helicopter main and tail rotor bearings.
Principles of aircraft engine lubrication Mobil Aviation Grease SHC 100 (No mil-spec) Mobil Aviation Grease SHC 100's synthetic base oil, combined with selected additives, provide outstanding protection against wear, rust, corrosion, and high-temperature degradation. It is recommended for aviation applications which need a lubricant that can perform normal functions, yet go far beyond that in terms of high and low temperatures, long-life performance. It is particularly suitable for the lubrication of commercial aircraft wheel bearings. General purpose grease
MIL-G-23827B (AeroShell Grease 7, Royco 27) A Microgel® grease (AeroShell Grease 7) and a lithium soap (Royco 27), synthetic grease with a broad temperature range (-100 to 250 F). It has low evaporation loss, moderate-load wear index (lower than the moly-based greases), relatively poor water resistance but excellent corrosion resistance. This is a good, all-purpose airframe grease. MIL-G-81827A (Royco 22MS) An inorganic gel, molybdenum disulfide synthetic grease with a higher temperature range. It has the greatest load carrying ability of any of the listed greases. It has better water resistance than MIL-G-23827 or MIL-G-21164. Oxidation and evaporation rate are greater than MIL-G-23827. Used where high water-resistance, high temperature, and high load carrying is required. MIL-G-7711A or MIL-G-24139 (AeroShell Grease 6) An inorganic gel mineral oil grease with superior water-resistance than for other listed greases. It is used as a general purpose airframe grease where water-resistance and corrosion prevention is important. It is also available with molybdenum disulfide under Royco 11MS part number. Used with high load, slow moving sliding surfaces, such as landing gear bogie pivot assemblies, where water and corrosion resistance are required. MIL-G-21164D (AeroShell Grease 17, Royco 64) A Microgel® grease (AeroShell Grease 17) and a lithium soap (Royco 64) synthetic oil molybdenum disulfide grease. It is the same as MIL-G-23827 but contains moly. It is used in jet aircraft where parts are exposed to low temperatures. It is not as good as Royco 11MS in waterresistance and load carrying ability.
TM10-3930-660-10 LUBRICATION AND SYSTEMS. PUMP. Located 1-13. on theENGINE front housing cover side. The COOLING pump draws oil fromOIL the oil pan and sends it through the oil cooler, and then through the oil filter. From the filter, the oil enters the cylinder block to lubricate the engine and is then returned to the oil pan. From the filter, oil is also sent through the turbocharger and then returned to the oil pan. OIL PAN. Contains the oil that lubricates moving parts in the engine. It is attached to the bottom of the engine. ENGINE OIL COOLER. Engine oil flows through the plates of the oil cooler. As the oil warms, the heat is transferred to the coolant which flows from the radiator. The coolant flows across the plates of the oil cooler. OIL FILTER. Removes particles from the oil which could cause damage to the internal parts of the engine. WATER PUMP. Draws coolant from the radiator and sends it through the oil cooler cavity and cylinder block to cool the engine. The coolant then returns to the radiator. FAN. The fan is turned by the engine drive belt. It creates air flow through the radiator to lower the temperature of the coolant as it passes through the radiator
TM10-3930-660-10 1-13. ENGINE LUBRICATION AND COOLING SYSTEMS. OIL PUMP. Located on the front housing cover side. The pump draws oil from the oil pan and sends it through the oil cooler, and then through the oil filter. From the filter, the oil enters the cylinder block to lubricate the engine and is then returned to the oil pan. From the filter, oil is also sent through the turbocharger and then returned to the oil pan. OIL PAN. Contains the oil that lubricates moving parts in the engine. It is attached to the bottom of the engine. ENGINE OIL COOLER. Engine oil flows through the plates of the oil cooler. As the oil warms, the heat is transferred to the coolant which flows from the radiator. The coolant flows across the plates of the oil cooler. OIL FILTER. Removes particles from the oil which could cause damage to the internal parts of the engine. WATER PUMP. Draws coolant from the radiator and sends it through the oil cooler cavity and cylinder block to cool the engine. The coolant then returns to the radiator. FAN. The fan is turned by the engine drive belt. It creates air flow through the radiator to lower the temperature of the coolant as it passes through the radiator
TM10-3930-660-10 1-13. ENGINE LUBRICATION AND COOLING SYSTEMS. OIL PUMP. Located on the front housing cover side. The pump draws oil from the oil pan and sends it through the oil cooler, and then through the oil filter. From the filter, the oil enters the cylinder block to lubricate the engine and is then returned to the oil pan. From the filter, oil is also sent through the turbocharger and then returned to the oil pan. OIL PAN. Contains the oil that lubricates moving parts in the engine. It is attached to the bottom of the engine. ENGINE OIL COOLER. Engine oil flows through the plates of the oil cooler. As the oil warms, the heat is transferred to the coolant which flows from the radiator. The coolant flows across the plates of the oil cooler. OIL FILTER. Removes particles from the oil which could cause damage to the internal parts of the engine. WATER PUMP. Draws coolant from the radiator and sends it through the oil cooler cavity and cylinder block to cool the engine. The coolant then returns to the radiator. FAN. The fan is turned by the engine drive belt. It creates air flow through the radiator to lower the temperature of the coolant as it passes through the radiator
Properties Most motor oils are made from a heavier, thicker petroleum hydrocarbon base stock derived from crude oil, with additives to improve certain properties. The bulk of a typical motor oil consists of hydrocarbons with between 18 and 34 carbon atoms per molecule.[6] One of the most important properties of motor oil in maintaining a lubricating film between moving parts is its viscosity. The viscosity of a liquid can be thought of as its "thickness" or a measure of its resistance to flow. The viscosity must be high enough to maintain a lubricating film, but low enough that the oil can flow around the engine parts under all conditions. The viscosity index is a measure of how much the oil's viscosity changes as temperature changes. A higher viscosity index indicates the viscosity changes less with temperature than a lower viscosity index. Motor oil must be able to flow adequately at the lowest temperature it is expected to experience in order to minimize metal to metal contact between moving parts upon starting up the engine. The pour point defined first this property of motor oil, as defined by ASTM D97 as "...an index
of the lowest temperature of its utility..." for a given application,[7] but the "cold cranking simulator" (CCS, see ASTM D5293-08) and "Mini-Rotary Viscometer" (MRV, see ASTM D3829-02(2007), ASTM D4684-08) are today the properties required in motor oil specs and define the SAE classifications. Oil is largely composed of hydrocarbons which can burn if ignited. Still another important property of motor oil is its flash point, the lowest temperature at which the oil gives off vapors which can ignite. It is dangerous for the oil in a motor to ignite and burn, so a high flash point is desirable. At a petroleum refinery, fractional distillation separates a motor oil fraction from other crude oil fractions, removing the more volatile components, and therefore increasing the oil's flash point (reducing its tendency to burn). Another manipulated property of motor oil is its Total Base Number (TBN), which is a measurement of the reserve alkalinity of an oil, meaning its ability to neutralize acids. The resulting quantity is determined as mg KOH/ (gram of lubricant). Analogously, Total Acid Number (TAN) is the measure of a lubricant's acidity. Other tests include zinc, phosphorus, or sulfur content, and testing for excessive foaming. The NOACK volatility (ASTM D-5800) Test determines the physical evaporation loss of lubricants in high temperature service. A maximum of 15% evaporation loss is allowable to meet API SL and ILSAC GF-3 specifications. Some automotive OEM oil specifications require lower than 10%.
[edit] Grades
Range of motor oils on display in Kuwait The Society of Automotive Engineers (SAE) has established a numerical code system for grading motor oils according to their viscosity characteristics. SAE viscosity gradings include the following, from low to high viscosity: 0, 5, 10, 15, 20, 25, 30, 40, 50 or 60. The numbers 0, 5, 10, 15 and 25 are suffixed with the letter W, designating their "winter" (not "weight") or coldstart viscosity, at lower temperature. The number 20 comes with or without a W, depending on whether it is being used to denote a cold or hot viscosity grade. The document SAE J300 defines the viscometrics related to these grades.
Kinematic viscosity is graded by measuring the time it takes for a standard amount of oil to flow through a standard orifice, at standard temperatures. The longer it takes, the higher the viscosity and thus higher SAE code. Note that the SAE has a separate viscosity rating system for gear, axle, and manual transmission oils, SAE J306, which should not be confused with engine oil viscosity. The higher numbers of a gear oil (eg 75W-140) do not mean that it has higher viscosity than an engine oil.
[edit] Single-grade A single-grade engine oil, as defined by SAE J300, cannot use a polymeric Viscosity Index Improver (also referred to as Viscosity Modifier) additive. SAE J300 has established eleven viscosity grades, of which six are considered Winter-grades and given a W designation. The 11 viscosity grades are 0W, 5W, 10W, 15W, 20W, 25W, 20, 30, 40, 50, and 60. These numbers are often referred to as the 'weight' of a motor oil. For single winter grade oils, the dynamic viscosity is measured at different cold temperatures, specified in J300 depending on the viscosity grade, in units of mPa·s or the equivalent older nonSI units, centipoise (abbreviated cP), using two different test methods. They are the Cold Cranking Simulator (ASTMD5293) and the Mini-Rotary Viscometer (ASTM D4684). Based on the coldest temperature the oil passes at, that oil is graded as SAE viscosity grade 0W, 5W, 10W, 15W, 20W, or 25W. The lower the viscosity grade, the lower the temperature the oil can pass. For example, if an oil passes at the specifications for 10W and 5W, but fails for 0W, then that oil must be labeled as an SAE 5W. That oil cannot be labeled as either 0W or 10W. For single non-winter grade oils, the kinematic viscosity is measured at a temperature of 100 °C (212 °F) in units of mm²/s or the equivalent older non-SI units,Stokes (unit|centistokes]] (abbreviated cSt). Based on the range of viscosity the oil falls in at that temperature, the oil is graded as SAE viscosity grade 20, 30, 40, 50, or 60. In addition, for SAE grades 20, 30, and 40, a minimum viscosity measured at 150 °C (302 °F) and at a high-shear rate is also required. The higher the viscosity, the higher the SAE viscosity grade is. For some applications, such as when the temperature ranges in use are not very wide, singlegrade motor oil is satisfactory; for example, lawn mower engines, industrial applications, and vintage or classic cars.
[edit] Multi-grade The temperature range the oil is exposed to in most vehicles can be wide, ranging from cold temperatures in the winter before the vehicle is started up, to hot operating temperatures when the vehicle is fully warmed up in hot summer weather. A specific oil will have high viscosity when cold and a lower viscosity at the engine's operating temperature. The difference in viscosities for most single-grade oil is too large between the extremes of temperature. To bring the difference in viscosities closer together, special polymer additives called viscosity index improvers, or VIIs are added to the oil. These additives are used to make the oil a multi-grade motor oil, though it is possible to have a multi-grade oil without the use of VIIs. The idea is to
cause the multi-grade oil to have the viscosity of the base grade when cold and the viscosity of the second grade when hot. This enables one type of oil to be generally used all year. In fact, when multi-grades were initially developed, they were frequently described as all-season oil. The viscosity of a multi-grade oil still varies logarithmically with temperature, but the slope representing the change is lessened.[8] This slope representing the change with temperature depends on the nature and amount of the additives to the base oil. The SAE designation for multi-grade oils includes two viscosity grades; for example, 10W-30 designates a common multi-grade oil. The two numbers used are individually defined by SAE J300 for single-grade oils. Therefore, an oil labeled as 10W-30 must pass the SAE J300 viscosity grade requirement 30, and all limitations placed on if theanviscosity (for example, a 10W-30for oilboth must10W fail and the J300 requirements at 5W). Also, oil does grades not contain any VIIs, and can pass as a multi-grade, that oil can be labelled with either of the two SAE viscosity grades. For example, a very simple multi-grade oil that can be easily made with modern base oils without any VII is a 20W-20. This oil can be labeled as 20W-20, 20W, or 20. Note, if any VIIs are used however, then that oil cannot be labeled as a single grade. The real-world ability of an oil to crank or pump when cold is potentially diminished soon after it is put into service. The motor oil grade and viscosity to be used in a given vehicle is specified by the manufacturer of the vehicle (although some modern European cars now have no viscosity requirement), but can vary from country to country when climatic or fuel efficiency constraints come into play.
[edit] Standards [edit] American Petroleum Institute The American Petroleum Institute (API) sets minimum for performance standards for lubricants. Motor oil is used for the lubrication, cooling, and cleaning of internal combustion engines. Motor oil may be composed of a lubricant base stock only in the case of non-detergent oil, or a lubricant base stock plus additives to improve the oil's detergency, extreme pressure performance, and ability to inhibit corrosion of engine parts. Lubricant base stocks are categorized into five groups by the API. Group I base stocks are composed of fractionally distilled petroleum which is further refined with solvent extraction processes to improve certain properties such as oxidation resistance and to remove wax. Group II base stocks are composed of fractionally distilled petroleum that has been hydrocracked to further refine and purify it. Group III base stocks have similar characteristics to Group II base stocks, except that Group III base stocks have higher viscosity indexes. Group III base stocks are produced by further hydrocracking of Group II base stocks, or of hydroisomerized slack wax, (a byproduct of the dewaxing process). Group IV base stock are polyalphaolefins (PAOs). Group V is a catch-all group for any base stock not described by Groups I to IV. Examples of group V base stocks include polyol esters, polyalkylene glycols (PAG oils), and perfluoropolyalkylethers (PFPAEs). Groups I and II are commonly referred to as mineral oils, group III is typically referred to as synthetic (except in Germany and Japan, where they must not be called synthetic) and group IV is a synthetic oil. Group V base oils are so diverse that there is no catch-all description.
The API service classes[9] have two general classifications: S for "service" (srcinating from spark ignition) (typical passenger cars and light trucks using gasoline engines), and C for "commercial" (srcinating from compression ignition) (typical diesel equipment). Engine oil which has been tested and meets the API standards may display the API Service Symbol (also known as the "Donut") with the service designation on containers sold to oil users.[9] The API oil classification structure has eliminated specific support for wet-clutch motorcycle applications in their descriptors, and API SJ and newer oils are referred to be specific to automobile and light truck use. Accordingly, motorcycle oils are subject to their own unique standards. The latest API service standard designation is SN for gasoline automobile and light-truck engines. The SN standard refers to a group of laboratory and engine tests, including the latest series for control of high-temperature deposits. Current API service categories include SN,SM, SL and SJ for gasoline engines. All previous service designations are obsolete, although motorcycle oils commonly still use the SF/SG standard. All the current gasoline categories (including the obsolete SH), have placed limitations on the phosphorus content for certain SAE viscosity grades (the xW-20, xW-30) due to the chemical poisoning that phosphorus has on catalytic converters. Phosphorus is a key anti-wear component in motor oil and is usually found in motor oil in the form of Zinc dithiophosphate. Each new API category has placed successively lower phosphorus and zinc limits, and thus has created a controversial issue obsolescing oils needed for older engines, especially engines with sliding (flat/cleave) tappets. API, and ILSAC, which represents most of the worlds major automobile/engine manufactures, states API SM/ILSAC GF-4 is fully backwards compatible, and it is noted that one of the engine tests required for API SM, the Sequence IVA, is a sliding tappetbackwards design to compatibility, test specificallyand forincam wear protection. However, not everyone in agreement with addition, there are special situations, such asis"performance" engines or fully race built engines, where the engine protection requirements are above and beyond API/ILSAC requirements. Because of this, there are specialty oils out in the market place with higher than API allowed phosphorus levels. Most engines built before 1985 have the flat/cleave bearing style systems of construction, which is sensitive to reducing zinc and phosphorus. Example; in API SG rated oils, this was at the 1200-1300 ppm level for zincs and phosphorus, where the current SM is under 600 ppm. This reduction in anti-wear chemicals in oil has caused pre-mature failures of camshafts and other high pressure bearings in many older automobiles and has been blamed for pre-mature failure of the oil pump drive/cam position sensor gear that is meshed with camshaft gear in some modern engines. There are six diesel engine service designations which are current: CJ-4, CI-4, CH-4, CG-4, CF2, and CF. Some manufacturers continue to use obsolete designations such as CC for small or stationary diesel engines. In addition, API created a separated CI-4 PLUS designation in conjunction with CJ-4 and CI-4 for oils that meet certain extra requirements, and this marking is located in the lower portion of the API Service Symbol "Donut". It is possible for an oil to conform to both the gasoline and diesel standards. In fact, it is the norm for all diesel rated engine oils to carry the "corresponding" gasoline specification. For example,
API CJ-4 will almost always list either SL or SM, API CI-4 with SL, API CH-4 with SJ, and so on.
[edit] ILSAC The International Lubricant Standardization and Approval Committee (ILSAC) also has standards for motor oil. Introduced in 2004, GF-4 [10] applies to SAE 0W-20, 5W-20, 0W-30, 5W30, and 10W-30 viscosity grade oils. A new set of specifications, GF-5,[11] took effect in October 2010. The industry has one year to convert their oils to GF-5 and in September 2011, ILSAC will no longer offer licensing for GF-4. In general, ILSAC works with API in creating the newest gasoline oil specification, with ILSAC adding an extra requirement of fuel economy testing to their specification. For GF-4, a Sequence VIB Fuel Economy Test (ASTM D6837) is required that is not required in API service category SM. A key new test for GF-4, which is also required for API SM, is the Sequence IIIG, which involves running a 3.8 L (232 in³), GM 3.8 L V-6 at 125 hp (93 kW), 3,600 rpm, and 150 °C (300 °F) oil temperature for 100 hours. These are much more severe conditions than any APIspecified oil was designed for: cars which typically push their oil temperature consistently above 100 °C (212 °F) are most turbocharged engines, along with most engines of European or Japanese srcin, particularly small capacity, high power output. The IIIG test is about 50% more difficult [12] than the previous IIIF test, used in GF-3 and API SL oils. Engine oils bearing the API starburst symbol since 2005 are ILSAC GF-4 compliant.[13] To help consumers recognize that an oil meets the ILSAC requirements, API developed a "starburst" certification mark.
[edit] ACEA The ACEA (Association des Constructeurs Européens d'Automobiles) performance/quality classifications A3/A5 tests used in Europe are arguably more stringent than the API and ILSAC standards. CEC (The Co-ordinating European Council) is the development body for fuel and lubricant testing in Europe and beyond, setting the standards via their European Industry groups; ACEA, ATIEL, ATC and CONCAWE.
[edit] JASO The Japanese Automotive Standards Organization (JASO) has created their own set of performance and quality standards for petrol engines of Japanese srcin. For 4-stroke gasoline engines, the JASO T904 standard is used, and is particularly relevant to motorcycle engines. The JASO T904-MA and MA2 standards are designed to distinguish oils that are approved for wet clutch use, and the JASO T904-MB standard is not suitable for wet clutch use.
For 2-stroke gasoline engines, the JASO M345 (FA, FB, FC) standard is used, and this refers particularly to low ash, lubricity, detergency, low smoke and exhaust blocking. These standards, especially JASO-MA and JASO-FC, are designed to address oil-requirement issues not addressed by the API service categories.
[edit] OEM standards divergence By the early 1990s, many of the European srcinal equipment manufacturer (OEM) car manufacturers felt that the direction of the American API oil standards was not compatible with the needs of a motor oil to be used in their motors. As a result many leading European motor manufacturers created and developed their own "OEM" oil standards. Probably the most well known of these are the VW50*.0* series from Volkswagen Group, and the MB22*.** from Mercedes-Benz. Other European OEM standards are from General Motors, for the Vauxhall, Opel and Saab brands, the Ford "WSS" standards, BMW Special Oils and BMW Longlife standards, Porsche, and the PSA Group of Peugeot and Citroën. General Motors also has the 4718M standard that is used for the Chevrolet Corvette, a standard that is used in North America for selected North American performance engines, with a "Use Mobil 1 only" sticker usually placed on those cars. [citation needed] In recent times, very highly specialized "extended drain" "longlife" oils have arisen, whereby, taking Volkswagen Group vehicles, a petrol engine can now go up to 2 years or 30,000 km (~18,600 mi), and a diesel engine can go up to 2 years or 50,000 km (~31,000 mi) - before requiring an oil change. Volkswagen (504.00), BMW, GM, Mercedes and PSA all have their own similar longlife oil standards.[citation needed] Another trend of today represent midSAP (sulfated ash <0,8 wt.-%) and lowSAP (sulfated ash <0,5 wt.-%) engine oil (see specifications: Renault RN 0720, FORD WSS-M2C934-A). The ACEA specifications C1 to C4 reflect the midSAP and lowSAP needs of automotive OEMs. Furthermore, virtually all European OEM standards require a long drains of 30.000 km and up by using HTHS (High Temperature, High Shear) viscosity, many around the 3.5 cP (3.5 mPa·s). In Japan, the HTHS figures are low as >2.6 mPas. Because of the real or perceived need for motor oils with unique qualities, many modern European cars will demand a specific OEM-only oil standard. As a result, they may make no reference at all to API standards, nor SAE viscosity grades. They may also make no primary reference to the ACEA standards, with the exception of being able to use a "lesser" ACEA grade oil for "emergency top-up", though this usually has strict limits, often up to a maximum of ½ a litre of non-OEM oil.
[edit] Other additives In addition to the viscosity index improvers, motor oil manufacturers often include other additives such as detergents and dispersants to help keep the engine clean by minimizing sludge buildup, corrosion inhibitors, and alkaline additives to neutralize acidic oxidation products of the oil. Most commercial oils have a minimal amount of zinc dialkyldithiophosphate as an anti-wear additive to protect contacting metal surfaces with zinc and other compounds in case of metal to
metal contact. The quantity of zinc dialkyldithiophosphate is limited to minimize adverse effect on catalytic converters. Another aspect for after-treatment devices is the deposition of oil ash, which increases the exhaust back pressure and reduces over time the fuel economy. The socalled "chemical box" limits today the concentrations of sulfur, ash and phosphorus (SAP). There are other additives available commercially which can be added to the oil by the user for purported additional benefit. Some of these additives include: •
•
•
• •
Zinc dialkyldithiophosphate (ZDDP) additives, which typically also contain calcium sulfonates, are available to consumers for additional protection under extreme-pressure conditions or in heavy performance ZDDP calcium added to protect motor duty oil from oxidativesituations. breakdown and toand prevent the additives formationare of also sludge and varnish deposits. In the 1980s and 1990s, additives with suspended PTFE particles were available e.g. "Slick50" to consumers to increase motor oil's ability to coat and protect metal surfaces. There is controversy as to the actual effectiveness of these products as they can coagulate and clog the oil filters. Some molybdenum disulfide containing additives to lubricating oils are claimed to reduce friction, bond to metal, or have anti-wear properties. They were used in WWII in flight engines and became commercial after WWII until the 1990s. They were commercialized in the 1970s (ELF ANTAR Molygraphite) and are today still available (Liqui Moly MoS2 10 W-40, www.liqui-moly.de). Various other extreme-pressure additives and antiwear additives. Many patents proposed use perfluoropolymers to reduce friction between metal parts, such as PTFE (Teflon), or micronized PTFE. However, the application obstacle of PTFE is insolubility in lubricant oils. Their application is questionable.
[edit] Synthetic oil and synthetic blends Synthetic lubricants were first synthesized, or man-made, in significant quantities as replacements for mineral lubricants (and fuels) by German scientists in the late 1930s and early 1940s because of their lack of sufficient quantities of crude for their (primarily military) needs. A significant factor in its gain in popularity was the ability of synthetic-based lubricants to remain fluid in the sub-zero temperatures of the Eastern front in wintertime, temperatures which caused petroleum-based lubricants to solidify owing to their higher wax content. The use of synthetic lubricants widened through the 1950s and 1960s owing to a property at the other end of the temperature spectrum, the ability to lubricate aviation engines at temperatures that caused mineral-based lubricants to break down. In the mid 1970s, synthetic motor oils were formulated and commercially applied for the first time in automotive applications. The same SAE system for designating motor oil viscosity also applies to synthetic oils. Instead of making motor oil with the conventional petroleum base, "true" synthetic oil base stocks are artificially synthesized. Synthetic oils are derived from either Group III mineral base oils, Group IV, or Group V non-mineral bases. True synthetics include classes of lubricants like synthetic esters as well as "others" like GTL (Methane Gas-to-Liquid) (Group V) and polyalphaolefins (Group IV). Higher purity and therefore better property control theoretically means
synthetic oil has good mechanical properties at extremes of high and low temperatures. The molecules are made large and "soft" enough to retain good viscosity at higher temperatures, yet branched molecular structures interfere with solidification and therefore allow flow at lower temperatures. Thus, although the viscosity still decreases as temperature increases, these synthetic motor oils have a much improved viscosity index over the traditional petroleum base. Their specially designed properties allow a wider temperature range at higher and lower temperatures and often include a lower pour point. With their improved viscosity index, true synthetic oils need little or no viscosity index improvers, which are the oil components most vulnerable to thermal and mechanical degradation as the oil ages, and thus they do not degrade as quickly as traditional motor oils. However, they still fill up with particulate matter, although at a lower rate compared to conventional oils, thewith oil filter still fills andsome clogs synthetic up over time. periodic oil and filter changes should still beand done synthetic oil; but oil So, suppliers suggest that the intervals between oil changes can be longer, sometimes as long as 16,000-24,000 km (10,000–15,000 mi) primarily due to reduced degredation by oxidation. Tests[citation needed] do show that fully synthetic oil is superior in extreme service conditions to conventional oil. But in the vast majority of vehicle applications, mineral oil based lubricants, sometimes fortified with synthetic additives and with the benefit of over a century of development, continues to be the predominant and satisfactory lubricant for most internal combustion engine applications.
[edit] Bio-based oils Bio-based oils existed prior to the development of petroleum-based oils in the 19th Century. They have become the subject of renewed interest with the advent of bio-fuels and the push for green products. The development of canola-based motor oils began in 1996 in order to pursue environmentally friendly products. Purdue University has funded a project to develop and test such oils. Test results indicate satisfactory performance from the oils tested.[14]
[edit] Maintenance
Oil being drained from a car In engines, there is inevitably some exposure of the oil to products of internal combustion, and microscopic coke particles from black soot accumulate in the oil during operation. Also the rubbing of metal engine parts inevitably produces some microscopic metallic particles from the
wearing of the surfaces. Such particles could circulate in the oil and grind against the part surfaces causing wear. The oil filter removes many of the particles and sludge, but eventually the oil filter can become clogged, if used for extremely long periods. The motor oil and especially the additives also undergo thermal and mechanical degradation. For these reasons, the oil and the oil filter need to be periodically replaced. While there is a full industry surrounding regular oil changes and maintenance, an oil change is fairly simple and something car owners can do themselves. Some vehicle manufacturers may specify which SAE viscosity grade of oil should be used, but different viscosity motor oil may perform better based on the operating environment. Many manufacturers have and haveintervals designations for motor oil they used. Some quick oilvarying changerequirements shops recommended of 5,000 km (3,000 mi) require or everyto3be months which is not necessary according to many automobile manufacturers. This has led to a campaign by the California EPA against the 3,000 mile myth, promoting vehicle manufacturer's recommendations for oil change intervals over those of the oil change industry. Motor oil is changed on time in service or distance vehicle has traveled. Actual operating conditions and engine hours of operation are a more precise indicator of when to change motor oil. Also important is the quality of the oil used especially when synthetics are used (synthetics are more stable than conventional oils). Some manufactures address this (IE. BMW and VW with their respective long-live standards) while others do not. The viscosity can be adjusted for the ambient temperature change, thicker for summer heat and thinner for the winter cold. Lower viscosity oils are used in many newer American market vehicles. Time-based intervals account for the short trip driver who drives fewer miles, but builds up more contaminants. It is advised by manufacturers to not exceed their time or distance driven on a motor oil change interval. Many modern cars now list somewhat higher intervals for changing of oil and filter, with the constraint of "severe" changes driving; this applies to short trips ofservice under requiring 16 km (10more mi), frequent where the oil doeswith not less-than get to fullideal operating temperature long enough to burn off condensation, excess fuel, and other contamination that leads to "sludge", "varnish", "acids", or other deposits. Many manufacturers have engine computer calculations to estimate the oil's condition based on the factors which degrade it such as RPMs, temperatures, and trip length; and one system adds an optical sensor for determining the clarity of the oil in the engine. These systems are commonly known as Oil Life Monitors or OLMs. In the 1960s typical cars took heavy 20W-50 oil. By the early 1980s recommended viscosities had moved down to 10W-30, primarily to improve fuel efficiency. A modern typical application would be Honda Motor's use of 5W-20 viscosity oil for 12,000 km (7,500 mi) while offering increased fuel efficiency. Engine designs are evolving to allow the use of low viscosity oils without the risk of high rates of metal to metal abrasion, prinicipally in the cam and valve mechanism areas.
[edit] Future A new process to break down polyethylene, a common plastic product found in many consumer containers, is used to make wax with the correct molecular properties for conversion into a lubricant, bypassing the expensive Fischer-Tropsch process. The plastic is melted and then pumped into a furnace. The heat of the furnace breaks down the molecular chains of
polyethylene into wax. Finally, the wax is subjected to a catalytic process that alters the wax's molecular structure, leaving a clear oil. (Miller, et al., 2005) Biodegradable Motor Oils based on esters or hydrocarbon-ester blends appeared in the 1990s followed by formulations beginning in 2000 which respond to the bio-no-tox-criteria of the European preparations directive (EC/1999/45).[15] This means, that they not only are biodegradable according to OECD 301x test methods, but also the aquatic toxicities (fish, algae, daphnie) are each above 100 mg/L. Another class of base oils suited for engine oils represents the polyalkylene glycols. They offer [16]
zero-ash, bio-no-tox properties and lean burn characteristics.
[edit] Re-refined motor oil The oil in a motor oil product does not break down or burn as it is used in an engine—it simply gets contaminated with particles and chemicals that make it a less effective lubricant. Re-refining cleans the contaminants and used additives out of the dirty oil. From there, this clean “base stock” is blended with some virgin base stock and a new additives package to make a finished lubricant product that can be just as effective as lubricants made with all virgin oil.[17] The US Environmental Protection Agency defines re-refined products as containing at least 25% rerefined base stock,[18] but other standards are significantly higher. The California State public contract code define a re-refined motor oil as one that contains at least 70% re-refined base stock.[19]
General classification of lubricants Mineral lubricants •
Fluid lubricants (Oils)
Mineral fluid lubricants are based on mineral oils. Mineral oils (petroleum oils) are products of refining crude oil. There are three types of mineral oil: paraffinic, naphtenic and aromatic.
Paraffinic oils are produced either by hydrocracking or solvent extraction process. Most hydrocarbon molecules of paraffinic oils have non-ring long-chained structure. Paraffinic oils are relatively viscous and resistant to oxidation. They possess high flash point and high pour point. Paraffinic oils are used for manufacturing engine oils, industrial lubricants and as processing oils in rubber, textile, and paper industries. Naphtenic oils are produced from crude oil distillates. Most hydrocarbon molecules of naphtenicnic oils have saturated ring structure. Paraffinic oils possess low viscousity, low flash point, low pour point and low resistance to oxidation. Naphtenic oils are used in moderate temperature applications, mainly for manufacturing transformer oils and metal working fluids. Aromatic oils are products of refining process in manufacture of paraffinic oils.
Most hydrocarbon molecules of aromatic oils have non-saturated ring structure. Aromatic oils are dark and have high flash point. Aromatic oils are used for manufacturing seal compounds, adhesives and as plasiticezers in rubber and asphalt production. •
Semi-fluid lubricants (greases)
Semi-fluid lubricants (greases) are produced by emulsifying oils or fats with metallic soap and water at 400-600°F (204-316°C). Typical mineral oil base grease is vaseline. Grease are determined a type (mineral, synthetic, vegetable, animal(extra fat), type of soap properties (lithium, sodium, calcium,by etc. saltsof ofoil long-chained fatty acids) and additives pressure, corrosion protection, anti-oxidation, etc.). Semi-fluid lubricants (greases) are used in variety applications where fluid oil is not applicable and where thick lubrication film is required: lubrication of roller bearings in railway car wheels, rolling mill bearings, steam turbines, spindles, jet engine bearings and other various machinery bearings. •
Solid lubricants
Solid lubricants possess lamellar structure preventing direct contact between the sliding surfaces even at high loads. Graphite and molybdenum disulfide particles are common Solid lubricants. Boron nitride, tungsten disulfide and polytetrafluorethylene (PTFE) are other solid lubricants. Solid lubricants are mainly used as additives to oils and greases. Solid lubricants are also used in form of dry powder or as constituents of coatings. to top Synthetic lubricants •
Polyalphaolefins (PAO)
Polyalphaoleins are the most popular synthetic lubticant. PAO’s chemical structure and properties are identical to those of mineral oils. Polyalphaoleins (synthetic hydrocarbons) are manufactured by polymerization of hydrocarbon molecules (alphaoleins). The process occurs in reaction of ethylene gas in presence of a metallic catalyst. •
Polyglycols (PAG)
Polyglycols are produced by oxidation of ethylene and propylene. The oxides are then polymerized resulting in formation of polyglycol. Polyglycols are water soluble. Polyglycols are characterized by very low coefficient of friction. They are also able to withstand high pressures without EP (extreme pressure) additives.
•
Ester oils
Ester oils are produced by reaction of acids and alcohols with water. Ester oils are characterized by very good high temperature and low temperature resistance. •
Silicones
Silicones are a group of inorganic polymers, molecules of which represent a backbone structure built from repeated chemical units (monomers) containing Si=O moieties. Two organic groups are attached to each Si=O moiety: eg. methyl+methyl ( (CH3)2 ), methyl+phenyl ( CH3 + C6H5 ), 6 5 2 phenyl+phenyl ( (C H ) ). is polydimethylsiloxane (PDMS). Its monomer is (CH 3)2SiO. PDMS is The most popular silicone produced from silicon and methylchloride. Other examples of silicones are polymethylphenylsiloxane and polydiphenylsiloxane. Viscosity of silicones depends on the length of the polymer molecules and on the degere of their cross-linking. Short non-cross-linked molecules make fluid silicone. Long cross-linked molecules result in elastomer silicone. Silicone lubricants (oils and greases) are characterized by broad temperature range: -100ºF to +570ºF (-73ºC to 300ºC).
to top Vegetable lubricants
Vegetable lubricants are based on soybean, corn, castor, canola, cotton seed and rape seed oils. Vegetable oils are environmentally friendly alternative to mineral oils since they are biodegradable. Lubrication properties lubricants of vegetable identical to temperature those of mineral oils. The main disadvantages of vegetable arebase theiroils loware oxidation and stabilities. to top Animal lubricants
Animal lubricants are produced from the animals fat. There are two main animal fats: hard fats (stearin) and soft fats (lard). Animal fats are mainly used for manufacturing greases. to top
Classification of lubricants by application • • • • • •
Engine oils Gear oils oils Hydraulic Cutting fluids (coolants) Way lubricants Compressor oils
• • • • • •
Quenching and heat transfer oils Rust protection oils Transformer oils (insulating oils) Turbine oils Chain lubricants Wire rope lubricants
to top
Classification of lubricants by additives • • • • • • • • • • • •
• •
• •
Extreme pressure (EP) Anti-wear (AW) Friction modifiers Corrosion inhibitors Anti-oxidants Dispersants Detergents Compounded Anti-foaming agents Pour point depressant CLASSIFICATION OF LUBRICATING OILS The Navy identifies lubricating oils by number symbols. Each identifying symbol consists of four digits and, in some cases, appended letters. The first digit shows the series of oil according to type and use; the last three digits show the viscosity of the oil. The viscosity digits indicate the number of seconds required for a 60-milliliter (ml) sample of oil to flow through a standard orifice at a certain temperature. Symbol 9250,
for example, shows that the oil is a series 9 oil which is specified for use in diesel engines. It also shows that a 60-milliliter sample should flow through a standard orifice in 250 seconds when the temperature of the oil is 210°F. Another example is symbol 2135 TH. This symbol shows that the oil is a series 2 oil, which is suitable for use as a forcefeed lubricant or as a hydraulic fluid. It also shows that a 60-milliliter sample should flow through a standard orifice in 135 seconds when the oil is at a certain temperature (130°F, in this case). The letters H, T, TH, or TEP added to a basic number indicate a primary specific usage within the general category. PROPERTIES OF LUBRICATING OILS Lubricating oils used by the Navy are tested for a number of properties. These include (1) viscosity, (2) pour point, (3) flash point, (4) fire point, (5) auto-ignition point, (6) demulsibility, (7) neutralization number, and (8) precipitation number. Standard test methods are used for each test. The properties of lube oil are briefly explained in the following paragraphs. 1. VISCOSITY-The viscosity of an oil is its tendency to resist flow. A liquid of high viscosity flows very slowly. In variable climates, for example, automobile owners change oil to prevailing changes are necessary heavy oil becomes too according thick or sluggish in coldseasons. weather,Oil and light oil becomes toobecause thin in hot weather. The higher the tem-perature of an oil, the lower its viscosity becomes; lowering the temperature increases the viscosity. On a cold morning, it is the high viscosity or stiff-
•
•
•
•
•
•
•
•
•
ness of the lube oil that makes an automobile engine difficult to start. The viscosity must always be high enough to keep a good oil film between the moving parts. Otherwise, friction will increase, resulting in power loss and rapid wear on the parts. Oils are graded by their viscosities at a certain temperature. Grading is set up by noting the number of seconds required for a given quantity (60 ml) of the oil at the given temperature to flow through a standard orifice. The right grade of oil, therefore, means oil of the proper viscosity. Every oil has a viscosity index based on the slope of the temperature-viscosity curve. The viscosity index depends on the rate of change in viscosity of a given oil with a change in temperature. A low index figure means a steep slope of the curve, or a great variation of viscosity with a change in temperature; a highinindex figure means a flatter slope, or lesser variation of viscosity with the same changes temperatures. If you are using an oil with a high viscosity index, its viscosity or body will change less when the temperature of the engine increases. 2. POUR POINT-The pour point of an oil is the lowest temperature at which the oil will barely flow from a container. At a temperature below the pour point, oil congeals or solidifies. Lube oils used in cold weather operations must have a low pour point. (NOTE: The pour point is closely related to the viscosity of the oil. In general, an oil of high viscosity will have a higher pour point than an oil of low viscosity.) 3. FLASH POINT-The flash point of an oil is the temperature at which enough vapor is given off to flash when a flame or spark is present. The minimum flash points allowed for Navy lube oils are all above 300°F. However, the temperatures of the oils are always far below 300°F under normal operating conditions. 4. FIRE POINT-The fire point of an oil is the temperature at which the oil will continue to burn when it is ignited. 5. AUTOIGNITION POINT-The auto-ignition point of an oil is the temperature at which the flammable vapors given off from the oil For willmost burn.lubricating This kind oils, of burning will occur is without the application of a spark or flame. this temperature in the range of 465° to 815°F. 6. DEMULSIBILITY-The demulsibility, or emulsion characteristic, of an oil is its ability to separate cleanly from any water present- an important factor in forced-feed systems. You should keep water (fresh or salt) out of oils. 7. NEUTRALIZATION NUMBER-The neutralization number of an oil indicates its acid content and is defined as the number of milligrams of potassium hydroxide (KOH) required to neutralize 1 gram of the oil. All petroleum products deteriorate (oxidize) in air and heat. Oxidation produces organic acids which, if present in sufficient concentrations, will cause deterioration of (1) alloy bearings at elevated temperatures, (2) galvanized surfaces, and (3) demulsibility of the oil with respect to fresh water and salt water. The increase in acidity with use is an index of deterioration and is measured as a part of the work factor test. This test is not applicable to 9250 oil. 8. PRECIPITATION NUMBER-The pre-cipitation number of an oil is a measure of the amount of solids classified as asphalts or carbon residue contained in the oil. The number is reachedby when a known amount of oil diluted with naphtha precipitatenumber. is separated centrifuging-the volume ofisseparated solids equalsand the the precipitation This test detects the presence of foreign materials in used oils. An oil with a high
precipitation number may cause trouble in an engine. It could leave deposits or plug up valves and pumps. ) SYSTEM COMPONENTS It must be remembered that the lubricating system is actually an integral part of the engine and the operation of one depends upon the operation of the other. Thus the lubricating system, in actual practice, cannot be considered as a separate and independent system; it is part of the engine. The lubricating system basically consists of the following: Oil Pan—reservoir or storage area for engine oil. Oil Level Gauge—checks the amount of oil in the oil pan. Oil Pump—forces oil throughout the system. Oil Pickup and Strainers—carries oil to the pump and removes large particles. Oil Filters—strains out impurities in the oil. Oil Galleries—oil passages through the engine. Oil Pressure Indicator—warns the operator of low oil pressure. Oil Pressure Gauge—registers actual oil pressure in the engine. Oil Temperature
Lubrication Systems Classification of Lubricants Animal Vegetable Mineral Synthetic Animal Lubricants Lubricants with animal srcin: – Tallow – Tallow oil – Lard oil – Neat’s foot oil – Sperm oil – Porpoise oil These are highly stable at normal temperatures Animal lubricants may not be used for internal combustion because they produce fatty acids Vegetable
Lubricants Examples of vegetable lubricants are: – Castor oil – Olive oil – Cottonseed oil Animal and vegetable oils have a lower
coefficient of friction than most mineral oils but they rapidly wear away steel Mineral Lubricants These lubricants are used to a large extent in the lubrication of aircraft internal combustion engines There are
three classifications of mineral lubricants: – Solid – Semisolid – Fluid Synthetic Lubricants Because of the high operating temperatures of gas-turbine engines, it became necessary to
develop lubricants which would retain their characteristics at
temperatures that cause petroleum lubricants to evaporate and break down Synthetic lubricants do not break down easily and do not produce coke or
other deposits Lubricating Oil Properties Gravity Flash Point Viscosity Cloud Point Pour Point CarbonResidue Test Ash Test Precipitation Number Corrosion and Neutralization Number
Oiliness ExtremePressure (Hypoid) Lubricants Chemical and Physical Stability Gravity The gravity of petroleum oil is a numerical value which serves as an index of the weight of a measured volume of this product
There are two scales generally used by petroleum
engineers: – Specificgravity scale – American Petroleum Institute gravity scale Flash Point The flash point of an oil is the temperature to which the oil must be heated in order to give off enough vapor to form a combustible mixture above the surface that will momentarily flash or burn when the vapor is brought into contact with a very small flame Viscosity
Viscosity is technically defined as the fluid friction of an oil To put it more simply, it is the resistance an oil offers to flowing Heavy-bodied oil is high in viscosity and pours or flows slowly Cloud Point The cloud
point is the temperature at which the separation of wax
becomes visible in certain oils under prescribed testing conditions When such oils are tested, the cloud point is slightly above the solidification point Pour Point The pour point of an oil is the temperature at which the oil will just flow without disturbance when chilled Carbon-Residue Test The purpose of the carbonresidue test is to study the carbonforming
properties of a lubricating oil There are two methods: – The Ramsbottom carbon-residue test – The Conradson test Ash Test The ash test is an extension of the carbonresidue test If an unused
oil leaves almost no ash, it is regarded as pure The ash
content is a percentage (by weight) of the residue after all carbon and all carbonaceous matter have been evaporated and burned Precipitation Number The precipitation number recommended by the ASTM is the number of milliliters of precipitate formed when 10 mL of lubricating oil is mixed with 90 mL of petroleum naphtha under specific
conditions and then centrifuged Lubricant Requirements and Functions
Characteristics of Aircraft Lubricating Oil Functions of Engine Oil Straight Mineral Oil Ash-less Dispersant Oil Multi
viscosity Oil Characteristics of Aircraft Lubricating Oil
It should have the proper body (viscosity) High antifriction characteristics Maximum fluidity at low temperatures Minimum changes in viscosity with changes in temperature High antiwear properties Maximum cooling abilities Maximum resistance to oxidation Noncorrosive Functions of Engine Oil Lubrication, thus reducing
friction Cools various engine parts Seals the combustion chamber Cleans the engine Aids in preventing corrosion Serves as a cushion between impacting parts Straight Mineral Oil
Straight mineral oil is one of many types of oil used in
aircraft reciprocating engines It is blended from selected high-viscosityindex base stocks These oils do not contain additives, except for a small amount of pourpoint depressant for improved fluidity at cold temperatures Ashless Dispersant Oil Most aircraft oils other than straight mineral oils contain a dispersant that suspends contamination such as carbon,
lead compound and dirt The dispersant helps prevent these contaminants from gathering into clumps and forming sludge or plugging oil passageways Multiviscosity Oil In certain circumstances, all single-grade
oils have short comings In coldweather starts,
single grade oil generally flows slowly to the upper reaches and vital parts of the engine Multigrade oils have viscosity characteristics that allow for better flow characteristics at engine start
Characteristics of Lubrication Systems Pressure Lubrication Splash Lubrication and Combination Systems Principal Components of a
Lubrication System Oil Capacity In a pressure lubrication system, a mechanical pump supplies oil under pressure to the bearings Oil flows into the inlet of the pump through the pump and into an oil manifold which distributes
it to the crankshaft bearings Splash
Lubrication and Combination Systems Although pressure lubrication is the principle method of lubrication on all aircraft engines, some engines use splash lubrication also Splash lubrication is never used by itself All lubrication systems are pressure systems or combination pressure/splash systems Components of Lubrication Systems
Plumbing for Lubrication Systems Temperature Regulator (Oil Cooler) Oil Viscosity Valve Oil Pressure Relief Valves Oil Separator Oil Pressure Guage Oil Temperature Guage
Oil Pressure Pumps Scavenge Pumps
Oil Dilution System Plumbing for Lubrication Systems Oil plumbing is essentially the same as is used in oil and hydraulic
systems When the lines will not be subject to bending, aluminum tubing is used Synthetic hose is often used near the engine and other places on the aircraft that are subject to vibration or other movement Temperature
Regulator (Oil Cooler) An oil temperature regulator is designed to maintain the temperature of the oil for an operating engine at the correct level These regulators are often called oil coolers since
cooling of engine oil is one of their main functions Oil Viscosity
Valve The oil viscosity valve is generally considered a part of the oil temperature regulator unit and is employed in some oil systems The viscosity valve consists essentially of an aluminum alloy housing and a thermostatic control element The oil viscosity valve works with the oil cooler valve to maintain a desired temperature and keep the viscosity within
required limits Oil Pressure Relief Valves The purpose of the oil pressure relief valve is to control and limit the lubricating pressure in the oil system This is necessary to prevent damage caused by excessive system
pressure and to ensure that engine parts are not deprived of
fuel due to a system failure Oil Separator Air systems where oil of oil mist is present may require the use of an oil separator These are
often used on vacuum pump outlets The oil separator contains baffle plates which cause the air to swirl and it deposits on the baffles Oil Pressure Gauge An oil pressure gauge is an essential
component of any engine oil system These gauges generally use a bourdon tube to measure the pressure They are designed to measure a wide range of pressures Oil Temperature Gauge
The temperature probe for the oil temperature
gauge in the oil inlet line or passage between the pressure pump and the engine system On some installations the temperature probe is located
in the oil filter housing These are normally electric or electronic Oil Pressure Pumps Oil pressure pumps may either be of the gear type or vane type The gear type pump is used in the majority of
reciprocating engines and uses close fitting gears that rotate and push the oil through the system
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Engine Lubrication : Lubrication system components • • • • • • • • • •
Sump Oil collection pan Oil tank Pickup tube Oil pump Oil pressure relief valve Oil filters Spurt holes & galleries Oil indicators Oil cooler
Sump
The sump is bolted to the engine under the crankcase. It is a reservoir, or storage container, for the engine lubricating oil, and a collector for oil returning from the engine lubricating system. The sump can be formed as a thin sheet metal pressing, and shaped to ensure that oil will return to its deepest section. The oil pickup tube and strainer are located in this deep section to ensure they stay submerged in oil, and to prevent air being drawn into the oil pump. Some high performance vehicles have a windage tray fitted to prevent churning of the oil by the rotation of the crankshaft. Baffles prevent oil from surging away from the pickup during cornering, braking and accelerating. The sump’s large external surface area helps heat transfer from the oil to the outside air. In some designs, the sump is an aluminum alloy casting with fins and ribs to assist in this heat transfer.
Oil collection pan
The oil collection pan is part of the dry sump system which is used in some motorcycles. It replaces the sump in the wet sump system, but it is much smaller. It collects the oil after it has circulated through the engine, and directs it to the pick-up strainer on the scavenge pump. Since no oil is stored in the engine in this system, a dipstick that is normally used to check oil levels in the sump is not needed.
Oil tank
The oil tank is part of the dry sump lubrication system. It is usually positioned away from the heat of the engine, and the large surface area improves cooling. It receives oil from the scavenge pump and allows it to settle and cool. The main oil pump then pumps it back through the lubrication system. A dipstick is often provided to measure the oil level.
Pickup tube
Between the sump and oil pump is a pickup tube with a flat cup and a strainer immersed in the oil. The strainer stops large particles of dirt and carbon entering the pump and damaging it. The pickup tube leads to the inlet of the oil pump, on the low pressure side of the pump.
Oil pump
Oil pumps may be driven from the camshaft or the crankshaft. In a rotor-type oil pump, an inner rotor drives an outer one. As they turn, the volume between them increases. This larger volume lowers the pressure at the pump inlet. Outside atmospheric pressure is then higher. This forces oil into the pump, and it fills the spaces between the rotor lobes. As the lobes of the inner rotor move into the spaces in the outer rotor, oil is squeezed out through the outlet. The crescent pump uses a similar principle. It is mounted on the front of the cylinder block. The inner gear is on the end of the crankshaft which then drives the pump directly. An external toothed gear meshes with this inner one. Some gear teeth are meshed but others are separated by the crescent-shaped part of the pump housing. The increasing volume between gear teeth causes pressure to fall. Oil is then taken through the intake port, and carried around between the gears and crescent, then discharged to the outlet port. Similarly in a geared oil pump, the driving gear meshes with a second gear. As both gears turn, their teeth separate, creating a low pressure area. Higher atmospheric pressure outside forces oil up into the inlet. The spaces between the teeth fill with oil. The gears rotate, and carry oil around the chamber. The teeth mesh again, and oil is forced from the outlet toward the oil filter.
Oil pressure relief valve
A normal pump is capable of delivering more oil than an engine needs. It’s a safety measure to ensure the engine is never starved for oil. As the pump rotates, and engine speed increases, the volume of oil delivered also increases. The fixed clearances between the moving parts of the engine prevent oil escaping back to the sump, and pressure builds up in the system. An oil pressure relief valve stops excess pressure developing. It’s like a controlled leak, releasing just enough oil back to the sump to regulate the pressure of the whole system.
Oil filters
There are 2 basic oil-filtering systems - full-flow, and by-pass. The full-flow type filters all of the oil before delivering it to the engine. The by-pass type only filters some of the oil. The full-flow type is the more common. Its filter uses pleated filtering paper in a metal housing, to collect harmful particles. Normally all oil goes through the filter before it gets to the engine, but if the filter clogs up, it can starve an engine of oil. As a safety measure, full-flow filters have a bypass valve. If the filter clogs, this valve opens and directs unfiltered oil to the engine. Dirty oil is better than none at all. Most oil-filters on diesel engines are larger than those on similar gasoline engines, and some diesel engines have 2 oil filters. Diesel engines produce more carbon particles than gasoline engines, so the oil filter can have a full-flow element to trap larger impurities, and a bypass element to collect sludge and carbon soot. In a by-pass system, the bypass element filters only some of the oil from the pump by tapping an oil line into an oil passage. It collects finer particles than a full-flow filter. After this oil is filtered, it goes back to the sump.
Spurt holes & galleries
Pistons, rings and pins are lubricated by oil thrown onto the cylinder walls from the connecting rod bearings. Some connecting rods have oil spurt holes. These holes are positioned to receive oil from similar holes in the crankshaft. Oil can then spurt out at the point in the engine cycle when the largest area of cylinder wall is exposed. It lubricates the walls and gudgeon pin, and also cools the underside of the piston. Oil feeds to the cylinder head, and through a gallery to the camshaft bearings and valve-train. As well as lubricating these moving parts, it also gathers heat from the engine so its temperature keeps rising. Finally it drains back to the sump to cool, and start again.
Oil indicators
If a lubrication system fails it’s serious, so it’s crucial to know it’s working. If oil pressure falls too low, a pressure sensor in a gallery can light up a warning light, or register on a gauge. Low oil pressure can mean a lack of oil. It may have leaked away, or it may have been burned. This can be caused by worn piston rings which let oil into the combustion chamber. Some engines even use an automatic cut-out that turns off the engine if oil pressure falls too low. Too little oil in the engine is a problem but so is too much. The crankshaft can whip it into foam, and cause leaks by flooding the seals.. Of course, the simplest indicator of oil level is still the dip stick.
Oil cooler
Engines which operate under severe conditions may use an oil cooler to cool the oil in the engine. In diesel engines, the oil cooler and oil filter are often on the same mounting , on the cylinder block. The oil cooler is a heat exchanger. It transfers heat from the oil to coolant from the cooling system. Coolant circulates through tubes in the cooler, and oil fed from the lubrication system surrounds the tubes. As the coolant circulates, heat is removed from the oil. In another design, the oil cooler is mounted in the airstream at the front of the vehicle. This type of oil cooler uses the flow of air passing across its fins to cool the air circulating through it. It is called an oil-to air heat exchanger. An engine lubrication system in which the lubricating oil is carried in an external tank and not internally in a sump. The sump is kept relatively free from oil by scavenging pumps, which return the oil to the tank after cooling. The opposite of a wet sump system. The pumping capacity of scavenge pumps is higher than that of the engine-driven pumps supplying oil to the system.
Read more: http://www.answers.com/topic/dry-sump-lubrication-system#ixzz1Ie7IXwF1
The Dry Sump System
The dry sump lubrication system is the ultimate oiling system for internal combustion engines. The simple fact that all Formula One, Indy cars, Le Mans and Sports Racing cars as well as Super Speedway Stock Cars use dry sumps, proves this point. In order to have a good understanding of the dry sump system, let’s first examine the wet sump system. Wet sump oiling systems are used on 99% of all street cars. They utilize a conventional oil pan with dipstick, where the oil is stored and supplied to the oil pump. The pans capacity can range from 3 quarts to 20 quarts or more, depending on the engine. The oil is sucked up a pickup tube into the stock oil pump, where it is filtered and supplied to the engine under pressure. While this system is very adequate for highway use, it presents problems under racing conditions. Aside from the size of the and necessity of the a deep sump, oiland is subjected tothe extreme cornering forces racing, the pan, oil simply “crawls” up sides of thethe pan away from pick-up. Although thereinare manyand good designs, with trap doors, etc., racing cars generate lateral and acceleration/deceleration forces that overcome the best wet sump designs. Aside from the obvious pressure loss, this also results in a reduction in horsepower as well as oil aeration. These are the reasons dry sumps were developed. I will discuss other advantages later. The main purpose of the dry sump system is to contain all the stored oil in a separate tank, or reservoir. This reservoir is usually tall and round or narrow and specially designed with internal baffles, and an oil outlet (supply) at the very bottom for uninhibited oil supply. The dry sump oil pump is a minimum of 2 stages, with as many as 5 or 6. One stage is for pressure and is supplied the oil from the bottom of the reservoir, and along with an adjustable pressure regulator, supplies the oil under pressure through the filter and into the engine. The remaining stages “scavenge” the oil out of the dry sump pan and return the oil (and air) to the top of the tank or reservoir. If an oil cooler is used usually it is mounted inline between the scavenge outlets and the tank. The dry sump pump is usually driven by a Gilmer or HTD timing belt and pulleys, off the frontof the crankshaft, at approximately one halfcrank speed. The dry sumpresults pump in is removing designed excess with multiple stages, to insure that is scavenged from the pan. This also air from the crankcase, andall is the the oil reason they are called “dry sump” meaning the oil pan is essentially dry. Increased engine reliability from the consistent oil pressure provided by the dry sump system is the reason dry sumps were invented. The many other benefits I mentioned earlier are, shallower oil pan allowing engine to be lowered in chassis, horsepower increase due to less viscous drag (oil resistance due to sloshing into rotating assembly) and cooler oil. We have also increased these advantages further through advanced designs of windage trays, and scavenge pickup designs and locations, as well as our utilization of precision machined alloy castings, which add stiffness to the block and afford better sealing. All in all, the dry sump system came out of necessity to maintain oil pressure, and evolved into a very sophisticated system which increases reliability as well as horsepower while allowing the engines to be mounted with the lowest center of gravity. Gary Armstrong, S.A.E
Wet Sump vs. Dry Sump Oiling Systems
A wet sump system is based on the srcinal equipment oiling system, and can be enhanced with certain components to improve oil control and increase power.
The use of a wet or dry sump oiling system is often determined by the level of competition and the racer’s budget. A wet sump system is based on the srcinal equipment oiling system, and can be enhanced with certain components to improve oil control and increase power. A dry sump system is designed for the top levels of racing where maximum power and oil control are absolutely essential. Oil Pan Capacities
Capacities listed for Moroso Wet Sump Oil Pans include the capacity of the pan only, measured at or below the normal fill mark on a stock dipstick. Additional oil must be added to compensate for filters, coolers, tanks, etc. Unlike a wet sump system where oil is stored in the pan, a Dry Sump Oiling system stores oil in a separate tank -- leaving the pan essentially "dry." An externally-mounted pump, generally with three or four stages, is used to "scavenge" or remove oil from the pan, deliver it to the storage tank, and send it back through the engine. In a typical setup, all but one of the stages is used to scavenge oil from the pan. A single pressure stage is normally used to return oil from the tank to the engine. The primary advantage of a dry sump system is its ability to make more power. With very little oil in the pan, the rotating assembly is not burdened with the weight of excess oil (a phenomenon commonly referred to as "windage"). And because there is no internal pump, the windage tray or screen which serves to isolate sump oil from the rotating assembly, is allowed to run the full length of the pan. Keeping the rotating assembly free of windage allows it to spin freely and make more power. In addition, the extra crankcase vacuum created by the dry sump pump helps to improve ring seal for additional power gain. Other advantages of a dry sump system include increased oil capacity, more consistent oil pressure, the ability to easily add remote coolers, and adjustable oil pressure. And because the pan doesn’t store oil, it can be relatively shallow in depth to allow lower engine placement for improved weight distribution and handling. Moroso manufactures a full range of Dry Sump Oiling System components, all of which are engineered to be fully compatible with one another. This allows the engine builder to select the best combination of equipment and avoid the costly problems that often occur when "mixing and matching" components from various manufacturers.
Note: Oil pan rules vary from track to track. Check with your race track and/or sanctioning body before selecting your Moroso Oil Pan.
Tech Tip courtesy of Moroso. A wet sump is a lubricating oil management design for four-stroke piston internal combustion engines which uses a built-in reservoir for oil, as opposed to an external or secondary reservoir used in a dry sump design. Four-stroke engines are lubricated by oil which is pumped into various bearings, and thereafter allowed to drain to the ofsump the engine under In mostinproduction automobiles motorcycles, which usebase a wet system, the gravity. oil is collected a 3 to 10 litres (0.66 to and 2.2 imp gal; 0.79 to 2.6 USgal) capacity pan at the base of the engine, known as the sump or oil pan, where it is pumped back up to the bearings by the oil pump, internal to the engine. A wet sump offers the advantage of a simple design, using a single pump and no external reservoir. Since the sump is internal, there is no need for hoses or tubes connecting the engine to an external sump which may leak. An internal oil pump is generally more difficult to replace, but that is dependent on the engine design. A wet sump design can be problematic in a racing car, as the large g force pulled by drivers going around corners causes the oil in the pan to slosh, gravitating away from the oil pick-up, briefly starving the system of oil and damaging the engine. However, on a motorcycle this difficulty does not arise, as a bike leans into corners and the oil is not displaced sideways. Nevertheless, racing motorcycles usually benefit from dry sump lubrication, as this allows the engine to be mounted lower in the frame; and a remote oil tank can permit better lubricant cooling. Early stationary engines employed a small scoop on the extremity of the crankshaft or connecting rod to assist with the lubrication of the cylinder walls by means of a splashing action. Modern small engines, such as those used in lawnmowers, use a "slinger" (basically a paddle wheel) to perform the same function.
CHAPTER 5 LUBRICATING SYSTEMS Although the oil system of the modern gas turbine engine is varied in design and plumbing most have units which perform similar functions. In most cases a pressure pump or system furnishes oil to the engine to be lubricated and cooled. A scavenging system returns the oil to the tank for reuse. The problem of overheating is more severe after the engine has stopped than while it is running. Oil flow would normally have cooled bearings has stopped. Heat stored in the turbine wheel willwhich raise the bearing temperature muchthe higher than that reached during operation. Most systems will include a heat exchanger (air or fuel) to cool the oil. Many are designed with
pressurized sumps. Some incorporate a pressurized oil tank. This ensures a constant head pressure to the pressure-lubrication pump to prevent pump cavitation at high altitude. Oil consumption in a gas turbine engine is low compared to that in a reciprocating engine of equal power. Oil consumption on the turbine engine is affected by the efficiency of the seals. However, oil can be lost through internal leakage and on some engines by malfunction of the pressurizing or venting system. Oil scaling is very important in a jet engine. Any wetting of the blades or vanes by oil vapor will encourage the accumulation of dust and dirt. A dirty blade or vane represents high friction-to-airflow. This decreases engine efficiency, and results in a noticeable decrease in thrust or increase in fuel consumption. Since oil consumption is so low, oil tanks canhave be made relatively small. This a decrease in weight andmay storage Tanks may capacities ranging from l/2 causes to 8 gallons. System pressures varyproblems. from 15 psig at idle to 200 psig during cold starts. Normal operating pressures and bulk temperatures are about 50 to 100 psig and 200oF, respectively. GENERAL
In general, the parts to be lubricated and cooled include the main bearings and accessory drive gears and the propeller gearing in the turboprop. This represents again in gas turbine engine lubrication simplicity over the complex oil system of the reciprocating engine. The main rotating unit can be carried by only a few bearings. In a piston power plant there are hundreds more moving parts to be lubricated. On some turbine engines the oil may also be used-• • •
To operate the servo mechanism of some fuel controls. To control the position of the variable area exhaust-nozzle vanes. To operate the thrust reverser.
Because each bearing in the engine receives its oil from a metered or calibrated orifice, the system is generally known as the calibrated type. With a few exceptions the lubricating system used on the modem turbine engine is of the dry-sump variety. However, some turbine engines are equipped with a combination dry- and wet-type lubrication system. Wet-sump engines store the lubricating oil in the engine proper. Dry-sump engines utilize an external tank usually mounted on or near the engine. Although this chapter addresses dry-sump systems, an example of the wet-sump design can be seen in the Solar International T-62 engine. In this engine the oil reservoir is an integral part of the accessory-drive gear case. An example of a combination dryand wet-sump lubrication can be found in the Lycoming T-55-series engines.
TURBINE ENGINE DRY-SUMP LUBRICATION In a turbine dry-sump lubrication system, the oil supply is carried in a tank mounted externally on or near the engine. With this type of system, a larger oil supply can be carried and the oil temperature can be controlled An oil cooler usually is included in a dry-sump oil system (Figure 5-l ). Thistocooler air-cooled orsmall fuel-cooled. The dry-sump allows thetank axial-flow engines retain may theirbe comparatively diameter. This is done oil by system designing the oil and the oil cooler to conform to the design of the engine.
The following component descriptions include most of those found in the various turbine lubrication systems. However, not all of these components will be found in any one system. The dry-sump systems use an oil tank which contains most of the oil supply. However, a small sump usually is included on the engine to hold a supply of oil for an emergency system. The drysump system usually contains-• • • • • •
Oil pump. Scavenge and pressure inlet strainers. Scavenge return connection. Pressure outlet ports. Oil filter. Mounting bosses for the oil pressure transmitter.
•
Temperature bulb connections.
A typical oil tank is shown in Figure 5-2. It is designed to furnish a constant supply of oil to the engine. This is done by a swivel outlet assembly mounted inside -the tank a horizontal baffle
mounted in the center of the tank, two flapper check valves mounted on the baffle, and a positive-vent system.
The swivel outlet fitting is controlled by a weighted end, which is free to swing below the baffle. The flapper valves in the baffle are normally open. They close only when the oil in the bottom of the tank rushes to the top of the tank during deceleration. This traps the oil in the bottom of the tank where it is picked up by the swivel fitting A sump drain is located in the bottom of the tank. The airspace is vented at all times. All oil tanks have expansion space. This allows for oil expansion after heat is absorbed from the bearings and gears and after the oil foams after circulating through the system. Some tanks also incorporate a deaerator tray. The tray separates air from the oil returned to the top of the tank by the scavenger system. Usually these deaerators are the "can" type in which oil enters a tangent. The air released is carried out through the vent system in the top of the tank. Inmost oil tanks a pressure buildup is desired within the tank. This assures a positive flow of oil to the oil pump inlet. This pressure buildup is made possible by running the vent line through an adjustable check-relief valve. The check-relief valve normally is set to relieve at about 4 psi pressure on the oil pump inlet. There is little need for an oil-dilution system. If the air temperature is abnorrnally low, the oil may be changed to a lighter grade. Some engines may provide for the installation of an immersion-type oil heater.
TURBINE ENGINE WET-SUMP LUBRICATION
In some engines the lubrication system is the wet-sump type. Because only a few models of centrifugal-flow engines are in operation, there are few engines using a wet-sump type of oil system. The components of a wet-sump system are similar to many of a dry-sump system. The oil reservoir location is the major difference. The reservoir for the wet-sump oil system may be the accessory gear case, which consists of the accessory gear casing and the front compressor bearing support casing. Or it may be a sump mounted on the bottom of the accessory case. Regardless of configuration reservoirs for wetsump systems are an integral part of the engine and contain the bulk of the engine oil supply. The following components are included in the wet-sump reservoir: • •
• •
•
A bayonet-type gage indicates the oil level in the sump. Two or more finger strainers (filters) are inserted in the accessory case for straining pressure and scavenged oil before it leaves or enters the sump. These strainers aid the main oil strainer. A vent or breather equalizes pressure within the accessory casing. A magnetic drain plug may be provided to drain the oil and to trap any ferrous metal particles in the oil. This plug should always be examined closely during inspections. The presence of metal particles may indicate gear or bearing failure. A temperature bulb and an oil pressure fitting may be provided.
This system is typical of all engines using a wet-sump lubrication system. The bearing and drive gears in the accessory drive casing are lubricated by a splash system. The oil for the remaining points of lubrication leaves the pump under pressure. It passes through a filter to jet nozzles that direct the oil into the rotor bearings and couplings. Most wet-sump pressure systems are variable-pressure systems in which the pump outlet pressure depends on the engine RPM. The scavenged oil is returned to the reservoir (sump) by gravity and pump suction. Oil from the front compressor bearing in the accessory-drive coupling shaft drains directly into the reservoir. Oil from the turbine coupling and the remaining rotor shaft bearings drains into a sump. The oil is then pumped by the scavenge element through a finger screen into the reservoir.
OIL SYSTEM COMPONENTS The oil system components used on gas turbine engines are-• • •
• • • •
Tanks. Pressure pumps. Scavenger pumps. Filters. Oil coolers. Relief valves. Breathers and pressurizing components.
• • • • •
Pressure and temperature gages lights. Temperature-regulating valves. Oil-jet nozzle. Fittings, valves, and plumbing. Chip detectors.
Not all of the units will be found in the oil system of any one engine. But a majority of the parts listed will be found in most engines. Oil Tanks
Tanks can be either an airframe or engine-manufacturer-supplied unit. Usually constructed of welded sheet aluminum or steel, it provides a storage place for the oil. In most engines the tank is pressurized to ensure a constant supply of oil to the pressure pump. The tank can contain-• • • • • •
Venting system. Deaerator to separate entrained air from the oil. Oil level transmitter or dipstick. Rigid or flexible oil pickup. Coarse mesh screens. Various oil and air inlets and outlets.
Pressure Pumps
Both gear- and Gerotor-type pumps are used in the lubricating system of the turbine engine. The gear-type pump consists of a driving and a driven gear. The engine-accessory section drives the rotation of the pump. Rotation causes the oil to pass around the outside of the gears in pockets formed by the gear teeth and the pump casing. The pressure developed is proportional to engine RPM up to the time the relief valve opens. After that any further increase in engine speed will not result in an oil pressure increase. The relief valve may be located in the pump housing or elsewhere in the pressure system for both types of pumps. The Gerotor pump has two moving parts: an inner-toothed element meshing with an outertoothed element. The inner element has one less tooth than the outer. The missing tooth provides a chamber to move the fluid from the intake to the discharge port. Both elements are mounted eccentrically to one another on the same shaft. Scavenger Pumps
These pumps are similar to the pressure pumps but have a much larger total capacity. An engine is generally provided with several scavenger pumps to drain oil from various parts of the engine. Often one or two of the scavenger elements are incorporated in the same housing as the pressure pump (Figure 5-3). Different capacities can be provided for each system despite the common driving shaft speed. This is accomplished by varying the diameter or thickness of the gears to vary the volume of the tooth chamber. A vane-type pump may sometimes be used.
Oil Filters and Screens or Strainers
To prevent foreign matter from reaching internal parts of the engine, filters and screens or stainers are provided in the engine lubricating system. The three basic types of oil filters for the jet engine are the cartridge screen-disc and screen (Figures 5-4, 5-5 and 5-6). The cartridge filter is most commonly used and must be replaced periodically. The other two can be cleaned and reused. In the screen-disc filter there are a series of circular screen-type filters. Each filter is comprised of two layers of mesh forming a chamber between mesh layers. The filters are mounted on a common tube and arranged to provide a space between each circular element. Lube oil passes through the circular mesh elements and into the chamber between the two layers of mesh. This chamber is ported to the center of a common tube which directs oil out of the filter. Screens or strainers are placed at pressure oil inlets to bearings in the engine. This aids in preventing foreign matter from reaching the bearings.
To allow for oil flow in the event of filter blockage, all filters incorporate a bypass or relief valve as part of the filter or in the oil passages. When the pressure differential reaches a specified value (about 15 to 20 psi), the valve opens and allows oil to bypass the filter. Some filters incorporate a check valve. This prevents reverse flow or flow through the system when the engine is stopped Filtering characteristics vary, but most filters will stop particles of approximately 50 microns. Magnetic Chip Detector
One or more magnetic chip detectors are installed on gas turbine engines. They are used to detect and attract ferrous material (metal with iron as its basic element) which may come from inside the engine. This ferrous material builds up until it bridges a gap. Whenever there is a requirement, the chip detectors may be collected and analyzed to determine the condition of the engine. Most engines utilize an electrical chip detector, located in the scavenger pump housing or in the accessory gearbox. Should the engine oil become contaminated with metal particles, the detector will catch some of them. This causes the warning light on the caution panel to come on. Tubing, Hose, and Fittings
Tubing, hose, and fittings are used throughout the lubricating system. Their purpose is to connect apart into a system or to connect one part to another to complete a system. Oil Pressure Indicating System
In a typical engine oil pressure indicating system the indicator receives inlet oil pressure indications from the oil pressure transmitter and provides readings in pounds per square inch
Electrical power for oil pressure indicator and transmitter operation is supplied by the 28-volt AC system. Oil-Pressure-Low Caution Light
Most gas turbine engine lubricating systems incorporate an engine oil-pressure-low caution light warning device into the system for safety purposes. The light is connected to a low-pressure switch. When pressure drops below a safe limit, the switch closes an electrical circuit causing the caution light to burn. Power is supplied by the 28-volt DC system. Oil Temperature Indicating System
In a typical engine oil temperature indicating system, the indicator is connected to and receives temperature indications from an electrical resistance-type thermocouple or thermobulb. These are located in the pressure pump oil inlet side to the engine. Power to operate this circuit is supplied by the 28-volt DC system. Oil Coolers
The oil cooler is used to reduce oil temperature by transmitting heat from the oil to another fluid usually fuel. Since the fuel flow through the cooler is much greater than the oil flow, the fuel is able to absorb a considerable amount of heat. This reduces the size and weight of the cooler. Thermostatic or pressure-sensitive valves control the oil temperature by determining whether the oil passes through or bypasses the cooler. Oil coolers are also cooled by air forced through them by a blower/fan. Breathers and Pressurizing Systems
Internal oil leakage is kept to a minimum by pressurizing the bearing sump areas with air that is bled off the compressor (Figure 5-7). The airflow into the sump minimizes oil leakage across the seals in the reverse direction.
The oil scavenge pumps exceed thethan capacity of the lubrication pressure pump are capable of handling considerably more oil actually exists in the bearing sumps andThey gearboxes. Because the pumps area constant-displacement type, they make up for the lack of oil by pumping air from the sumps. Large quantities of air are delivered to the oil tank. Sump and tank pressures are maintained close to one another by a line which connects the two. If the sump pressure exceeds the tank pressure, the sump vent check valve opens, allowing the excess sump air to enter the oil tank. The valve allows flow only into the tank; oil or tank vapors cannot back up into the sump areas. Tank pressure is maintained little above ambient. The scavenge pumps and sump-vent check valve functions result in relatively low air pressure in the sumps and gearboxes. These low internal sump pressures allow air to flow across the oil seals into the sumps. This airflow minimizes lube oil leakage across the seals. For this reason it is necessary to maintain sump pressures low enough to ensure seal-air leakage into the sumps. Under some conditions, the ability of the scavenge pumps to pump air forms a pressure low enough to cavitate the pumps or cause the sump to collapse. Under other conditions, too much air can enter the sump through worn seals. If the seal leakage is not sufficient to maintain proper internal pressure, check valves in the sump and tank pressurizing valves open and allow ambient air to enter the system. Inadequate internal sump and gearbox pressure may be caused by seal leakage. If that occurs, air flows from the
sumps, through the sump-vent check valve, the oil tank, the tank and sump pressurizing valves to the atmosphere. Tank pressure is always maintained a few pounds above ambient pressure by the sump and tank pressurizing valve. The following addresses two types of lubrication systems used in the Army today: the General Electric T-701 turboshaft engine and the International/Solar T-62-series engine.
TYPICAL OIL SYSTEM FOR T-701 The lubrication system in the T-700-GE-701 engine distributes oil to all lubricated parts (Figure 5-8). In emergencies it supplies an air-oil mist to the main shaft bearings in the A- and B-sumps. The system is a self-contained, recirculating dry-sump system. It consists of the following subsystems and components: • • • • • • • • • •
Oil supply and scavenge pump. Seal pressurization and sump venting. Emergency lube system. Oil filtration and condition monitoring. Tank and air-oil cooler. Oil cooler. Oil pressure monitoring. Cold oil-relief and cooler-bypas valves. Chip detector. Integral accessory gearbox
Lube Supply System
The oil tank, integral with the mainframe, holds approximately 7.3 quarts of oil (Figure 5-9). This is a sufficient quantity to lubricate the required engine parts without an external oil supply. The tank is filled using a 3-inch, gravity-fill port on the right-hand side. Visual indication of oil level is supplied by a fluid level indicator installed on each side of the tank. A coarse pickup screen located near the tank bottom keeps sizable debris form entering the lube supply pump inlet. A drain plug is located at the bottom of the tank.
Oil from the pickup screen enters a cast passage in the mainframe. It is then conducted to the top of the engine to a point beneath the lube supply pump. A short connector tube transfers the oil from the mainframe to the accessory gearbox pump inlet port. The connector tube contains a domed, coarse-debris screen. The screen keeps foreign objects out of the passage when the accessory module is not installed on the mainframe. Oil flows through the connector tube to the pump inlet. There it enters the pump tangentially in alignment with pump rotational direction. The lube supply pump, a Geroter-type pumping element assembly, is comprised of an inner and outer element. The element assembly is located adjacent to the drive spline end of the pump. Six scavenge elements are also located in tandem on the common drive shaft. The stack of pump elements is retained in a cast tubular hosing having an integral end plate. The complete pump slides into a precision bore in the gearbox casing. Oil from the supply pump flows to the lube
filter inlet and through the filter, a 3-micron filter element. Oil flow passes from outside to inside of the filter element. It then passes through the open bore of the bypass valve and into the gearbox outlet passage. Bypass valve opening occurs when filter differential pressure unseats a spring-loaded poppet from its seat. The filter bowl contains an impending bypass warning button which will provide an indication for filter servicing. An electrical bypass sensor for cockpit indication of filter bypass tits into an AGB boss adjacent to the lube filter. A differential pressure of 60-80 psi across the filter will actuate this sensor. A spring-loaded poppet-type, cold oil relief valve is incorporated in this system. This valve prevents excessive supply pressure during cold starts when high oil viscosity creates high line pressures. is set for 120-180 psid and reset is 115 minimum. When apart of theCracking lube flowpressure is discharged into the AGB where churning in psid the gears will assist inopen, reducing warm-up time. Oil leaving the filter branches in three directions. It goes to the to of the emergency oil reservoirs in the A and B-sumps, the AGB, and C-sump jets.
Scavenge System. After the oil has lubricated and cooled the parts, the scavenge system returns it to the oil tank (Figure 5-10). In addition, fuel-oil and air-oil coolers and a chip detector are located in the scavenge return path.
Scavenge Inlet Screens. Each scavenge pump inlet is fitted with a relatively coarse screen (Figure 5-11). This screen is designed to protect the pumps from foreign object damage and to provide for fault isolation. Scavenge oil (and air) enters the bore of each screen axially on the
open inner end. It exits into a cast annulus which discharges directly into the scavenge pump inlet.
These screens may be removed for inspection if chip generation is suspected
Scavenge pumps. Six scavenge pumps are in line with the lube supply pump on a common shaft (Figure5-10). Positioning of the pump elements is determined by these factors: •
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The lube supply element is placed in the least vulnerable location and isolated from scavenge elements at one end. The B-sump element is placed at the other end of the pump to help isolate it from the other scavenge elements. This element is the only one with an elevated inlet pressure. Pump windmilling experience on other engine scavenge pumps shows that adjacent pumps tend to cut each other off due to interelement leaks at very low speed Therefore, the two A-sump elements are placed adjacent, as are the three C-sump elements, to reduce the possibility of both elements in a sump being inoperative simultaneously. Porting simplification for the gearbox coring determines relative positions of A- sump, B-sump, and C-sump elements.
Scavenge Discharge Passage. The common discharge of all six scavenge pumps is cast into the gearbox at the top of the pump cavity. Top discharge facilitates priming by clearing air bubbles and by wetting all pumping elements from the discharge of first pumps to prime. The discharge
cavity is tapered to enlarge as each pump enters the flow steam. This keeps discharge velocity relatively constant. It also tends to avoid air traps which could short-circuit pumping at windmilling speeds. This discharge plenum flows into the core to the chip detector. Flow leaving the chip detector passes to the fuel-oil cooler in series with the air-oil cooler. To promote faster warm-up and guard against plugged coolers, a bypass valve is provided which bypasses both coolers. Air-oil cooling is an integral part of the mainframe casting. Scavenge oil enters a manifold at the tank top. It then flows in a serpentine fashion in and out through the hollow scroll vanes and box-sectioned hub. Air for the particle separator is pulled across the vanes by the scavenge air blower providing the oil cooling process. Exit from the air-oil cooler is through three holes at the top of the tank. These outlets disperse the oil over the tank surfaces on both sides to settle in the tank. The oil tank vents to the AGB. Emergency Oil System
The T-700-GE-701 engine is designed to have two oil jets to provide each main bearing with oil for lubricating and cooling (Figure 5-12).
In addition to being designed for normal engine operation, the system provides for operation if the normal oil supply from the primary system is interrupted. The AGB and C-sump components can continue operateand at least minutes with residual oil present. The No. 4 bearing in the Bsump and theto bearings gears6 in the A-sump are provided with emergency air-oil mist systems located in each sump. The emergency oil system forms part of the normal full-time lubrication system and incorporates one full set of main bearing oil jets operating in parallel with
the primary jets. The dual-jet system also provides redundancy to minimize the effect of oil jet plugging. A small reservoir, curved to tit the A- and B-sumps, retains a sufficient amount of oil to provide air-oil mist when normal lubrication is interrupted The total sump oil supply is fed into the reservoir at the top. Top feed prevents reservoir drainage if the supply line is damaged. Primary oil jets, squeeze film damper, and uncritical lube jets are connected to a standpipe at the top of the tank. Secondary or emergency jets are similarly connected to the lowest point in the tank. Secondary jets are only located at points where lubrication is vital for short-duration emergency operation. Each oil the jet has a companion air air jet jets or air sourceoil which the oil end of the oil jet andsecondary impinges on lubricated part. The aspirate mistflows when over normal supply pressure is lost. They are pressurized from the seal pressurization cavities and operate continuously with no valving required. Component Description
The oil filter (Figure 5-13) consists of three subassemblies: • • •
Filter element. Bowl and impending bypass indicator. Bypass valve and inlet screen.
Filter Element. Media used in this filter are high-temperature materials containing organic and inorganic fibers. The layered media are faced on both sides with stainless steel mesh. This mesh provides mechanical support to resist collapse when pressure loads become high. Pleating of the faced media adds surface area and mechanical rigidity. A perforated steel tube in the bore also adds rigidity and retains the circular shape of the element. The media and support tube are epoxy-bonded to formed sheet metal and caps. These end caps include an O-ring groove which seals inlet to outlet leak paths at each end.
Filtration level selected is 100 percent of all particles three microns or larger and is disposable when saturated with debris. Support of the filter element is provided by the bypass valve on one end and the impending bypass indicator on the other. The indicator end has a spring-loaded sleeve which restrains the filter axially.
Bowl and Bypass Indicator. An aluminum bowl houses the element and contains the impending bypass indicator at the end. Mounting is horizontal to fit the space available and provide ready access for servicing Impending bypass indication is provided by a small unit which is part of the bowl assembly. The indicator is installed from the inside of the bowl. It is retained in place with an external retaining ring. Basic mechanics of operation are as follows: •
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Different pressure between filter inlet and outlet acts to move a piston against a spring at 44 to 60 psi. Piston contains a magnet which normally attracts a redbutton assembly and holds it seated against its spring. When the piston moves, the button is released. It extends 3/16 inch to visually indicate an impending bypass condition. Button is physically reattained from tripping by a cold lockout bimetallic latch if temperature is less than 100 to 130°F. This prevents a false trip during cold starts. As the button is released, a small spring-loaded ball also moves out of position to latch the button and block reset. The internal piston assembly automatically resets on shutdown; however, the indicator remains latched out. After removing the filter element and the bowl from the gearbox, a springloaded sleeve around the indicator moves aft and pulls the piston assembly to a tripped position. This causes the button to trip if operation is attempted with no filter in the bowl. To react the indicator, the bowl is held vertically so the button latch ball can roll out of the latched position. The button is then manually reset.
If the bowl is reassembled with no filter, the indicator will trip when the temperature exceeds the 100 to 130°F lock-out level. The internal latch mechanism prevents resetting the button without disassembling the bowl. Resetting must be done with the bowl removed from the accessory gearbox and held vertically, button up, to release the latch.
Oil Filter Bypass Sensor. The oil filter bypass sensor is a differential-pressure switch which senses filter inlet minus outlet pressure. The sensor consists of a spring-loaded piston which moves aft at high filter differential pressure (60 to 80 psi) and magnetically releases a microswitch lever. The switch is in a sealed cavity separated from the oil and is wired to a hermetically sealed electrical connector. The switch connects 28-VDC aircraft power when tripped and reopens the circuit at 15 psi minimum differential No latch is used in the sensor so resetting is automatic. Also, there is no cold lockout. The pilot will be informed of filter bypassing during cold start warm-ups. Sensor tolerance range is set slightly below the tolerance range of bypass valve cracking pressure. Therefore, bypassing will not occur without pilot warning. The impending bypass indicator will show need-to-change filter elements. This sensor provides backup warning if maintenance action is not taken.
Lubrication and Scavenge Pump. The lube and scavenge pump is a Gerotor-type pump of cartridge design, located on the forward side of the accessory gearbox (refer back to Figure 510). It fits into a precision bore in the gearbox casing. The Gerotor-type pump was chosen because of its wear resistance and efficiency. Gerotor elements are similar to male gear inside a female (internal) gear with one less tooth on the inner member. The inner Gerotors are keyed to the drive shaft, and the outer Gerotors are pocketed in individual eccentric rings. AS the assembly rotates, oil is drawn into an expanding cavity between teeth on one side. The oil is expelled when the cavity contracts approximately 180° away. Inlet and discharge ports are cast into the port plates. They are shaped and positioned to fill and empty at proper timing for maximum volumetric efficiency and resistance to inlet cavitation. There are seven different elements in the pump from the spline end forward. They are the lube supply element, C-sump cover, C-sump aft, C-sump forward, A-sump forward, A-sump aft, and B-sump Delta scavenge elements. The port plate eccentric rings and Gerotors are assembled into a surrounding concentric aluminum tubular housing The housing maintains all elements in proper alignment. The oil suction and discharge pas-sages from the Gerotors are brought radially through the housing. They match the appropriate locations of the mating passages in the engine gearbox casing. The entire stack of port plates is retained in the housing with the retaining rings at the spline end. The outermost end of the housing has an integrally cast cover. The cover bolt holes are arranged to orient the pump assembly in the gearbox housing during installation.
Cold Oil Relief Valve. The cold oil relief valve protects the oil supply system from overpressure during cold starts (refer back to Figure 5-9). It is a conventional poppet-type valve with a crackingsacking pressure of 120-180 psi.adjustment Valve tolerances held sufficiently desired pressure without shims are or selective fitting ofclose parts.to achieve the The valve includes a No. 10-32 threaded hole on the outside. This allows for the use of a bolt as a pulling handle during valve removal from the AGB.
Oil Cooler. The fuel-oil cooler is a tube and shell design (Figure 5-14). It cools the combined output of the scavenge discharge oil that is ported through gearbox-cored passages to the cooler. The cooler is mounted adjacent to the fuel-boost pump on the forward side of the gearbox. Oil and fuel porting enter on the same end via face porting to the gearbox. Fuel is used as the coolant. It is provided to the cooler via the boost pump, fuel filter, and hydromechanical control unit. A counterparallel flow, miltipass cooler design is used to minimize pressure drop while obtaining maximum cooler effectiveness. Fuel flows through the tubes, while the oil flows over the tubes resulting in the counterparallel flow arrangement.
Oil Cooler Bypass Valve. Design of the oil cooler bypass valve is identical to the cold oil relief valve with an exception (refer back to Figure 5-9). A lighter spring is utilized to obtain a lower cracking pressure of 22-28 psi. Housing modifications prevent inadvertent interchange with the cold oil relief valve. Chip Detector. The chip detector in the common scavenge line is the engine diagnostic device most likely to provide first warning of impending part failure (Figure 5-15).
The chip detector magnetically attracts electrically conductive ferrous chips. The chips bridge the gap between the detector's electrodes and close a circuit in series with the aircraft cockpit indicator (warning light). The chip detecting gap has a magnetic field induced in tapered pose pieces at each end of a cylindrical permanent magnet. A single ferrous chip 0.090 inch in length or longer will be indicated if magnetically attracted to bridge the pole pieces. The local mangetic field is intense at the gap and tends to orient particles in the bridging direction. Smaller particles tend to form chains until the pole pieces are bridged Nonconductive particles greater than 0.015 inch are trapped inside the screen for visual examination. Smaller particles will be found either in the lube tank or in the lube supply filter. The detector housing pushes into the accessory gearbox It is retained by two captive bolts used in common with other accessories. Self-locking inserts in the gearbox ensure retention of these bolts if assembly torque is improperly low. Venting System
A-Sump. The A-sump centervent handles air-oil separation and overboard venting from these sources: • • • •
A-sump seals and emergency air system. Scavenge pumped air from the lube tank. Accessory gearbox vent (no air sources). B-sump centervent flow which passes through the intershaft seal.
Path of this vent is into the bore of the power turbine shaft and torque-reference tube and out the aft end of the engine through the C-sump cover. The centrifugal air-oil separator vent holes in
the power turbine shaft are located under the forward end of the high-speed shaft. Windage from PTO gear locknut wrenching slots assists in turning oil back into the sump. Air from the sump and intershaft seal flows inward radially through these holes in the power turbine shaft. The air must flow forward in the annulus between the power turbine shaft and the torque-reference tube. Movement of air is blocked by a standoff ring on the reference tube OD. The forward axial passage of the air centrifuges oil droplets outward to the bore of the power turbine shaft. They either flow back into the sump at the centervent or at small weep holes forward of the PT shaft spline. Dried air then exits through multiple rows of holes in the reference tube and out the aft Csump cover. Some remaining oil in this air is spun into the C-Sump if it has condensed in transit. Any additional accumulated oil is then scavenged through the C-sump cover.
B-Sump. A centervent on the forward side of the No. 4 bearing accommodates air entering the sump at the labyrinth seals at each end Two rows of small holes are drilled in a radially thickened section of the forward seal runner. Use of many small holes increases the surface area of metal in contact with exiting oil droplets. These small holes also reduce effective window area for any droplets which may have a trajectory aimed directly at the holes. After the air is inside these holes, it follows a tortuous path through additional rows of holes in the turbine shaft and compressor rear shaft. The air then enters the annulus between the high-and low-speed shafts. In doing this, remaining oil is spun back into the sump. About 70 percent of B-sump centervent flow moves forward through the bore of the compressor tiebolt and intershaft seal. It exits at the A-sump centervent. Oil weep holes are provided near the aft end of the compressor tiebolt. These weep holes keep oil out of the rotor by returning it to the sump. A rotor seal is provided hereto keep any weepage out of the seal air. This airflow keeps the compressor tiebolt relatively cool and uniformly clamped. The remaining percent centervent air joins the inner balance piston seal leakage flow. It exits aft30under the of gasB-sump generator turbine wheels.
C-Sump. Centerventing the C-sump is a passage between the aft end of the PT shaft and a stationary standpipe built into the C-sump cover. Windage at the torque and speed-sensor teeth and in the annulus between the reference tube and the standpipe will return oil droplets to the sump. Weep holes are provided through the reference tube, shaft, and bearing spacer to allow oil from C-or A-sumps to enter the C-sump. C-sump cover scavenging through the C-sump housing removes remaining oil accumulation from the centerventing process during locked PT rotor operation and normal operation. Oil Tank. After being routed through air-oil cooler passages into the oil tank, air from the scavenge pumps flows down the radial drive shaft passage (Axis A) into the A-sump. Centerventing occurs after air enters the A-sump. Accessory Gearbox. The accessory gearbox is vented through the Axis A pad via the mainframe oil eventually the are A-sump. The AGB, tank, and A-sump essentially operate at the tank sameand pressure levelsthrough since they interconnected.
LUBRICATION SYSTEM FOR T-62
The lubrication system consists of-• • • • • • •
Pump. Internal oil passages. Oil filter assembly. Filter bypass relief valve. Pressure switch (mounted externally). Oil jet ring. Sump.
The oil filter cavity, oil passages, and oil sump are built into the reduction drive housing. Two oil separator plates are installed on the accessory drive gear. Lubrication system capacity is 3 quarts and is a wet-sump system. Oil is drawn out of the sump into the pump housing. The oil is carried between the pump gear teeth and pump housing wall. It is then forced through drilled passages to the oil filter housing. Oil under pump pressure enters the bottom of the filter housing and passes through the filter element (from outside to inside). It then flows out the housing through a passage in the filter element cap. A relief valve in the filter element cap unseats at a differential pressure of 15 to 25 psi. This allows oil to flow from outside the filter element, through a passage in the filter element cap, to the filter outlet passage. If the filter element becomes clogged, the valve will open and allow oil to bypass the filter element. From the filter, oil is forced into a passage to the system relief valve and to four oil jets. The oil jet ring, which encircles the high-speed input pinion, contains three of these jets. It sprays oil to the points where the high-speed input pinion meshes with the three planetary gears. One jet directs a spray between the end of the output shaft and the high-speed pinion to create a mist for lubrication of the rotor shaft bearings. The remaining gears and bearings are lubricated by air-oil mist created when oil strikes the planetary gears and high-speed pinion. System pressure is maintained at 15 to 25 psi by a system relief valve. The valve regulates pressure by bypassing excessive pressure directly into the reduction drive housing. The bypassed oil strikes the inside surface of the air inlet housing, aiding in cooling the oil. Bypassed oil returns to the sump by gravity flow through an opening in the bottom of the planet carrier. The normally open contacts of the low oil pressure switch close on increasing oil pressure at 5 to 7 psi. When the switch contacts close, the low oil pressure circuit is deenergized. At rated engine speed a drop in oil pressure below 5 to 7 psi will open the low oil pressure switch contacts. Through electrical circuitry, the drop in oil pressure will also close the main fuel solenoid valve and shut down the engine.
