Fuel Injection Pump

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D ESEL ENGINE FUNDAMENTALS

4 M E C H A N I C A L F U E L I N J E C T I O N S Y S T E M S

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MECHANICAL FUEL INJECTION SYSTEMS

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4.1 FUEL SUPPLY SYSTEMS

Overview Fuel supply systems In-line p ump Rotary pump C ommon rail Unit injec tion

Fuel supply pumps Plunger pump Diaphragm pump G ea r pump Roller cell

Fuel filters Filtering material Types of filters Fuel pipes Water separators Filter service Injec tor filters Revision questions

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4 .1 F UE L S UP PL Y S YS TE MS

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Fuel return line Injector Fuel tank

Fuel flter

Distributor pump Glow plug

Fig 2. Schematic diagram of a distributor pump fuel injection system C ou rtesy of Bosch

C ommon Rail Fuel System A general fuel system layout of a common rail fuel system is shown in Fig 3. In a c ommon rail system an elec tric or gear pump is used to supp ly fuel to the high p ressure pump. Elec tric supp ly pumps are mainly used on c ars and the gear pump is used on all other co mmerc ial app lic ations. The elec tric fuel supp ly pump is loc ated inside the fuel tank and operates as soon as the ignition switc h is turned on. This ensures fast engine starting as the low pressure fue l circuit is c harge d p rior to engine being started.

The gea r supp ly pump on the o ther hand is flanged to the b ac k of the high pressure c ommon rail pump and is driven by it’s input shaft. Both fuel supp ly pump s draw fuel via a pre filter in the fuel tank then pump the fuel through the fuel filter before d elivering it to the high pressure pump . Fuel bypa ssed from the fuel rail helps to supplement the fuel flow in the low pressure circuit and leak off fuel from within the high pressure pump returns to the fuel tank.

Fuel rail (common rail)

Fuel flter

Common rail fuel pump

High pressure fuel line

Fuel supply pump

Return line

Injector

Fuel tank

Fig 3. Schematic diagram of a common rail fuel injection system. C o u rt e sy o f M A N N u t zf a h r ze u g e

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4.2 INJECTORS

Overview Injector operation Injector nozzles Multi hole nozzles Pintle nozzles

Mechanical unit injector operation Electronic unit injector operation Common rail injector Injector service (conventional) Injector service (common rail) Injec tor testing Isolating a faulty injector Revision questions Industry updates Related web sites Additional diagrams/ photos

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4.2 INJECTORS

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The injector section consists of a nozzle body and needle valve assembly. The operation of the nozzle assembly is identic al to that o f a c onventiona l injector in that fuel pressure acts on the needle valve shoulder lifting the nee dle valve o ff its sea t allowing fuel to p ass throug h the multi spray holes and a tomise into the c ombustion c hamber. Injec tor ope ration is de sc ribed under the following headings: •

No injection

•

Start of injec tion

•

End o f injection Solenoid valve spring

Ball valve & seat

Fuel - (from c ommon rail) Command piston

Solenoid coil Valve body Orifice plate

Control chamber

Start of injection When the solenoid coil is energised by the electronic control module, the electromagnetic force draws the valve body upward allowing the ba ll sea t to o pe n. Fuel in the c ontrol chamber now passes through the orifice plate and flows to the fuel tank. With the p ressure of the fuel in the c ontrol c hamber now reduced, the fuel pressure a c ting on the underside of the nozzle needle shoulder is great e nough to lift the nozzle needle o ff it sea t. Fuel under pressure now flows through the nozzle spray ho les and is atomised as it enters into the combustion chamber as shown in Fig 13. Note: A s fuel flow into and o ut of the c ontrol chamber is controlled by inlet and outlet restricting orifii, rail pressure is not noticea bly red uc ed during injec tion by the small qua ntity of fuel returning to the fuel tank.

Spring Ball valve (open)

Fuel - (from c ommon rail)

Nozzle spring Nozzle needle

Command piston

Solenoid coil Valve body Reduced pressure in control chamber Fuel - (to fuel tank)

Nozzle spring Nozzle needle

Fig 12. Schematic diagram of a common rail injector showing ‘no injection’ C ou rtesy o f M itsub ishi Hea vy Ind ustries Ltd

No injection With the solenoid coil not energised, the solenoid valve spring presses the valve body and valve ball onto the b all sea t of the orific e p late c losing off fuel flow through the orifice plate. Inside the control c hambe r the pressure rises to that of the fuel rail. The same p ressure is also a pp lied to the nozzle needle shoulder. The fuel pressure now acting on the nozzle need le shoulder ca nnot overco me the c ombined forces of the fuel pressure a c ting on top of the c ommand p iston and the nozzle spring. Therefore, the nozzle needle stays sea ted on the nozzle seat as shown in Fig 12. © 2011 DEFS

Fig 13. Schematic diagram of a common rail injector showing ‘start of injec tion’ C o urtesy of M itsub ishi Hea vy Ind ustries Ltd

The engine c ontrol unit determines the length of the injection period by energising the injector’s elec trica l solenoid c oil for the pre-injection, main and possibly post-injection periods. In order to achieve multiple injections during the power stroke, some injectors are using a sec ond solenoid c oil to assist in the rapid opening and closing of the nozzle needle. 4.2 INJECTORS

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4.3 FLANGE & IN-LINE INJECTION

PUMPS

Overview Function of injec tion pump Flange mounted injection pumps C onstruc tion Pumping p rinc iple Plunger and helix Delivery valve function

In-line injection pump C onstruc tion Camshaft design Pump lubric ation Automatic ad vance unit

Pump servicing Pump to engine timing Mark method Spill time method Ad vanc ed and retarted timing

Revision questions Industry updates Related web sites

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Inlet port

Spill port

Plunger helix C harging cycle

Port closing (start of delivery)

Delivery

Spill port opening (end of delivery)

Fig 5. Charging and delivery cycle (maximum fuel position) Co urtesy o f Bosch

Delivery of fuel ceases when the plunger helix passes the barrel spill port (or c ontrol po rt), and the delivery valve returns to its seat. During the remainder of the stroke, the fuel displaced by the plunger simply returns to the gallery via the vertica l slot, cut away area and spill po rt. Thus fuel c ea ses to b e injected when the helix unco vers the spill port.

Metering the fuel charge Since the plunge r is c am driven, its stroke is c onstant and c annot be varied to c ontrol the quantity of fuel injected per stroke. However, the effec tive pa rt of the p umping stroke c an be

varied to c ontrol the qua ntity of fuel injec ted per stroke simply by rotating the plunger in the barrel.

Fuel delivery begins at the instant the top of the plunge r c ove rs the b arrel ports and c ontinues until the helix edge uncovers the spill port, at which po int fuel trapp ed abo ve the plunger is allowe d to return to the fue l ga llery. Thus the effe c tive pumping stroke c ea ses when the spill port is uncove red , and is direc tly c ontrolled by the distanc e through which the plunger must travel before the edge of the helix pa sses the bottom of the spill port.

Spill port

Inlet port

Plunger helix

No delivery

Partial delivery

Maximum delivery

Fig 6. Control of fuel delivery C ou rtesy of Bosch © 2011 DEFS

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4.4 DISTRIBUTOR TYPE INJECTION PUMP

Overview VE Pump Construction and operation Fuel supply pump Pumping and fuel distribution Fuel metering Delivery va lve

Mechanical governor Variable speed

Solenoid shut off valve Automatic advance unit Air-fuel ratio control Pump timing Revision questions Industry updates Related web sites Additional diagrams/ photos

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Overow restriction orifce

Maximum fuel adjust screw

Governor assembly

Soleno id shut off valve

Pressure control valve

Distributor head with high pressure pump Fuel supply pump

Cam plate

Automatic advance unit

Fig 2. Cut away section of a VE fuel injection pump Co urtesy of Bosc h

Fuel Supply Pump Low pressure c harging o f the pump ho using is accomplished, by a vane type fuel supply pump situated at the drive end of the distributor pump. Fuel flow is from the fuel tank through the fuel filter and into the vane pump, from here it enters the pump housing at pressures that va ry be twee n 360 kPa and 810 kPa. Generally there is no fuel feed pump fitted to this fuel system, a s the vane p ump serves this purpose. Being a c onstant displac ement pump, the fuel supply pump can deliver several times the amount of fuel required for injection. Fuel from tank Pressure c ontrol valve piston To pump housing Rotor Vane

Therefore, when the pump housing pressure reaches a predetermined level, excess fuel delivery is relieved via a pressure control valve and returned ba c k to the inlet side of the fuel supply pump, as shown in Fig 3. The pressure c ontrol valve is loc ated be side the fuel supply pump and is of the spring loaded piston type. This valve is pre-set on ma nufac ture a nd requires no further adjustment. For the purpo se o f self bleed ing a nd c oo ling of the entire pump, fuel circulates through an overflow restricting orifice back to the fuel tank. The overflow restricting orifice is 0.6 mm in diameter and is situated in the ba njo bolt in the fue l return line on top of the pump housing a s shown in Fig 2. While this orifice allows fuel to return to the fuel tank, it offers suffic ient restriction to fuel flow from the fuel supply pump to c ause the injection p ump housing to be pressurised . Further, in c onjunc tion with the fuel supp ly pump pressure c ontrol valve, the o rific e is responsible for the pump housing fuel pressure necessary for the charging of the high pressure c hamber and the o peration of the automatic injection advance unit.

Drive shaft

Fig 3. Schematic diagram of the operation of a vane type fuel supply pump © 2011 DEFS


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4.5 GOVERNORS

Overview Function of a governor Classification of governors Types of governors Governor terminology Graphs of governor control and engine fuelling Mechanical governors C onstant spe ed Variable speed Idle maximum speed

Pneumatic governor Electronic governor Revision questions

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Control rack

Control lever

Governor spring

As the shaft rotates, centrifugal force causes the flyweights to mo ve o utwards from the shaft, the lever arm thrusting against the sleeve. Thus the sleeve is ba lanc ed between spring force on the one end and the force e xerted by the flyweights on the other. The gove rnor mec hanism conne c ts to the pump rac k via the pivoted fork, one e nd of whic h enga ge s in a g roo ve in the sleeve with the o ther end c onnec ting to the rac k via a link. Should the engine speed drop due to an increase in engine load, the centrifugal force acting on the weights will dec rea se, a llowing the spring to p ush the slee ve a long the shaft. This move ment will move the rack, via the pivoted fork, to increase the fuel supply to the engine.

Centrifugal weights

Fig 3. Mechanical governor with centrifugal weights C ou rtesy o f Bosch

Simple C onstant Speed G overnor C onstant spe ed go vernors are fitted to e ngines that are required to run at a set or constant speed, and are governed to this set speed. Ap plic ations include engines that p ower alternator sets, water pumps, conveyors, etc. The simple c onstant spe ed go vernor as shown in Figs 4 c onsists of two pivoted flyweights, fixed to a pivot plate, which rotates with the pump camshaft, a sliding control sleeve, a pivoted fork and a governor spring. Spring force acts against the sleeve, forcing it against the lever arm of the flyweights, which are forced in towards the shaft.

On the o ther hand , should the engine spe ed inc rea se due to a lightening o f the loa d, the subsequent increase in centrifugal force will fling the flyweights outwards and the leve r arms will force the sleeve along the shaft against the spring. Movement in this direction will move the rack to red uce the fuel de livery from the pump. Thus any cha nge in the eng ine spe ed will ca use a n immediate c hang e in the q uantity of fuel injec ted, whic h will co mpensate fo r the speed c hange.

Simple Variable Speed Governor In applic ations where e ngines may be req uired to operate at a ny selec ted speed, variab le speed go vernors are used . These g ove rnors govern the engine at any set engine speed, from idle to ma ximum. G ove rnors of this type are used extensively in engines for earthmoving equipment and farm tractors.

Fuel control rack Fixed throttle position C entrifuga l weights

Ma ximum fuel rack stop screw

Fulc rum lever G ove rnor spring

Pumping element

Sliding sleeve

Fig 4. A simple constant speed governor © 2011 DEFS

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Fuel Injection Pump

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