fre/uencies .1 to & H2!. #his is not compatible with the high fre/uency re/uirements of a camless engine. Earlier wor$ by ;o$ota and +$utu 8! results in an on%off poppet%type valve that operates at higher speeds. However, actuation is limited to & $H2 and simple binary function 3 open or closed. #his is also not compatible with the re/uirements of variable timing and lift needed for the camless engine. +nother, more recent, advance in high operating fre/uency pie2oelectrically%driven hydraulic actuators was completed by 4oberts et al 9!. #heir system provides actuation at fre/uencies up to &( $H2, but valve stro$e is limited to ( µm.
References
1! ould, <: 4icheson, =: and Eric$son, -., 1991, 6>erformance Evaluation of a Camless Engine sing ?alve +ctuation with >rogrammable #iming,7 0+E > aper o. 91(). &! @obson, . and "uddell, ., 199', 6+ctive ?alve #rain 0ystem >romises to Eliminate Camshafts,7 +utomotive Engineer -ebruary A "arch 199'. '! +nderson, ": #sao, #%C: and aper o. 981&9 (! Bim, @: +nderson, ": #sao, #%C: and aper o. 95&(8 )! +shhab, "%0: and 0tefanopoulou, +., &, 6Control%riented "odel for Camless Inta$e >rocess 3 >art 1,7 #ransactions of the +0"E ?ol 1&&, "arch & *! +shhab, "%0: and 0tefanopoulou, +., &, 6Control of a Camless Inta$e >rocess 3 >art II,7 +0"E Dournal of @ynamic 0ystems, "easurement, and Control 3 "arch & 5! "auc$, <: "enchaca, D: and ie2oelectric Hydraulic >ump @evelopment,7 >roceedings of 0>IE 3 #he International 0ociety for ptical Engineering '98) "ar *%9, & 8! ;o$oat, 0: and +$utu, B., 1991, 6-ast%acting Electro%hydraulic @igital #ransducer. + >oppet%type n%off ?alve sing a "ultilayered >ie2oelectric @evice!,7 D0"E International Dournal, 0eries & -luids Engineering, Heat #ransfer, >ower, Combustion, #hermophysical >roperties ?ol. '( o. (, ov. 1991
9! 4oberts, @: Hagood, : 0u, ;%H: ie2oelectrically%driven Hydraulic +mplification "icrovalve for High >ressure, High -re/uency +pplications,7 >roceedings of 0>IE 3 #he International 0ociety for ptical Engineering '98) "ar *%9, &
Camless Engine Homepage
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0ince the origination of the automobile, the internal combustion engine ICE! has evolved considerably. However, one constant has remained throughout the decades of internal combustion engine development. #he camshaft has been the primary means of controlling the valve actuation and timing, and therefore, influencing the overall performance of the vehicle. #he camshaft is attached to the cran$shaft of an ICE and rotates relative to the rotation of the cran$shaft. #herefore, as the vehicle increases is velocity, the cran$shaft must turn more /uic$ly, and ultimately the camshaft rotates faster. #his dependence on the rotational velocity of the cran$shaft provides the primary limitation on the use of camshafts. +s the camshaft rotates, cam lobes, attached to the camshaft, interface with the engineFs valves. #his interface may ta$e place via a mechanical lin$age, but the result is, as the cam rotates it forces the valve open. #he spring return closes the valve when the cam is no longer supplying the opening force. -igure 1 shows a schematic of a single valve and cam on a camshaft.
-igure 1 0ingle Cam and ?alve 0ince the timing of the engine is dependent on the shape of the cam lobes and the rotational velocity of the camshaft, engineers must ma$e decisions early in the automobile development process that affect the engineFs performance. #he resulting design represents a compromise between fuel efficiency and engine power. 0ince maGimum efficiency and maGimum power re/uire uni/ue timing characteristics, the cam design must compromise between the two eGtremes. #his compromise is a prime consideration when consumers purchase automobiles. 0ome individuals value power and lean toward the purchase of a high performance sports car or towing capable truc$s, while others value fuel economy and vehicles that will provide more miles per gallon. 4ecogni2ing this compromise, automobile manufacturers have been attempting to provide vehicles capable of cylinder deactivation, variable valve timing ??#!, or variable camshaft timing ?C#!. #hese new designs are mostly mechanical in nature. +lthough they do provide an increased level of sophistication, most are still limited to discrete valve timing changes over a limited range.
4+>H
versity of 0outh Carolina
International Patents trends on VVA ‘s including Camless Engines
#he above graph shows a steady increase in Camless engine patent applications in the early 9Fs, while there was not too much going on throughout the 5Fs and most of the 8Fs. + li$ely cause for this trend is a more stabili2ed economy during the 8Fs and a leaping step in software, hardware and computing technology during the late 8Fs and 9Fs. #hese advances in computer technology allow for faster calculations by the Engine Control nit EC! therefore controlling more precisely and effectively the high%speed valve actuators. +dvances in material research and development have surely had their share of importance.
>reviously wire valve springs have been used, they use a coil spring 1'! to return the valve 1! to a closed position after the cam has retarded. #hey re/uired huge amounts of the detail development on their shape and material to reach the rev limits of around 1)$ 4>". #he pressure to deliver power from '.)l and later '.l engines re/uired ever higher rev ceilings and metal springs could not longer be developed at the same rate as the rest of the engine.
Pneumatic valve spring
>neumatic systems use conventional cams operating the valve (! via a shimbuc$et or finger follower, the valve spring poc$et is replaced with a chamber &8! pressurised with nitrogen held within a cylinder in the sidepods! that runs at a constant pressure to return the valve when the cam timing retards. ;ou often see the teams suffer a loss of pressure in the races through lea$s in the system, the driver comes in and mechanics re%pressurises the pneumatic circuit, this rarely wor$s for more than few laps. +lso when Engines are changed the un%installed engine needs a remote gas cylinder connected in order for the valves not to drop and hit the pistons.
Wire spring vs Pneumatic valve comparision
Renault Electro-Hydraulic (Camless valve actuation Camless Engines
I was reading up on this, and I thought it was pretty cool to share the info.
Cams, lifters, pushrods... all these things have up until now been associated with the internal combustion engine. But the end is near or these lovely shiny metal objects that comprise the valve train hardware in your pride and joy (Owners of the technically far more advanced rotary are excluded! Camless engine technology is soon to be a reality for mass"produced vehicles. In the camless valvetrain, the valve motion is controlled directly by a valve actuator " there#s no camshaft or connecting mechanisms. $arious studies have shown that a camless valve train can eliminate many otherwise necessary engine design trade"offs. %utomotive engines e&uipped with camless valvetrains of the electro"hydraulic and electro" mechanical type have been studied for over twenty years, but production vehicles with such engines are still not available. 'he issues that have had to be addressed in the actuator design include • • • •
reliable valve performance cost pac)aging power consumption
•
noise and vibration
*oise has been identified as the main problem with the electromechanical actuator technology, arising from high contact velocities of the actuator#s moving parts. +or this noise to be reduced, a so"called soft"landing of the valves has to be achieved. In a conventional valvetrain, the soft"landing is mechanically embedded into the shape of the camshaft lobe. One lectromechanical $alve 'rain (-$'!, developed by iemens %utomotive ystems has already been demonstrated at full load in a /0"valve four"cylinder engine. 1acobs $ehicle &uipment Co is another company involved in this f ield of research, but in diesel truc) engines. 'heir direction is towards the lectrohydraulic $alve %ctuation 'echnology (2$'!. International 'ruc) and ngine Corp is another engine manufacturer poised to ta)e a huge step forward in diesel engine design, announcing that it will eliminate camshafts from its diesel engines and replace them with electronic"valve timing systems by the year 3445. 'he long 0" year delay by International is due to testing. 6here mechanical systems can be put on a dyno and tested for a couple of thousand hours, electronic testing must be done in such places as %las)a and 7eath $alley, where e&uipment can be subjected to temperature extremes. ngineers say they need two summers and two winters of testing to be satisfied they#ve got all the bugs out. Conventional Valvetrain
'he valvetrain in a typical internal combustion engine comprises several moving components. ome are rotating and some are moving in a linear manner. Included Included are poppet valves that are operated by roc)er arms or tappets, with valve springs used to return the valves to their seats. In such a system the parasitic power losses are major " power is wasted in accelerating and decelerating the components of the valvetrain. +riction of the camshaft, springs, cam belts, etc also robs us of precious power and worsens fuel economy, not to mention contributing to wear and tear. 'he power draw on the cran)shaft to operate the conventional valve train is 8 to /4 percent of total power output. %nother factor wor)ing against the conventional valve train is that of the cam profile. 9sually , it is fixed to deliver only one specific cam timing. 'he cam lobes have to be shaped such that when the valve travels up and down at the engines maximum speed it should still be able to slow down and gently contact the valve seat. :ou don#t want valves crashing down on their valve seats. It results in an engine that is real noisy and has a short life expectancy. :ou are all aware that having different cam profiles will result in different engine characteristics. 6hile high"rpm power and low rpm"tor&ue can be each optimised, a compromise is re&uired to obtain the best of both in the same engine. 6ith $ariable $alve 'iming ($$'! technologies the compromise is getting better and better " reasonable low down tor&ue and high"speed power are being produced by many sub 3"litre engines. But the problem remains that the cam grind is still a fixed &uantity " or two fixed &uantities in the case of 2onda $"'C engines. 'hat#s why the lectromechanical $alve 'rain is considered the next evolution of $$'. 6ith the potential to dial in any conceivable valve timing at any point of the combustion cycle for each individual cylinder, valves can be opened with more lift and;or duration , as the computer deems necessary. 1ust imagine that you have your latest 3" litre /0"valve -$' powered engine on the dyno after installing an exhaust. imply changing a
couple of numbers [Maybe lots of numbers! - Ed] on the computer will have a set of completely revised valve timing maps to suit your exhaust " or cold air inta)e for that mater. 'here will be no need for expensive cam changes that may not even give the results you are after. lectronically altering valve events will have a f ar more major impact on engine performance than any current electronically"controlled item. Camless Valvetrain Operation 'he types of camless variable valve actuating systems being developed can be classed in two groups electrohydraulic and electromechanical. 6hen it comes to electromechanical valve trains, there are several designs that are being trialed. -ost developers are using the conventional poppet valve system (ie valves that loo) the same as in today#s engines! but an alternative is a ball valve set up. Both use electromagnets in one way or another to open and close the valve. Originally created for the %pollo space program, the electrohydraulic valve actuator wor)s by sending pressurised hydraulic fluid to the engine valve to move it open or closed. 'hese systems are mainly retain poppet valves and are preferred by truc) engine manufacturers. 1. Electromechanical Poppet Valves 'his type of system uses an armature attached to the valve stem.'he outside casing contains a magnetic coil of some sort that can be used to either attract or repel the armature, hence opening or closing the valve.
-ost early systems employed solenoid and magnetic attraction;repulsion actuating principals using an iron or f erromagnetic armature. 'hese types of armatures limited the performance of the actuator because they resulted in a variable air gap. %s the air gap becomes larger (ie when the distance between the moving and stationary magnets or electromagnets increases!, there is a reduction in the force. 'o maintain high forces on the armature as the si
is an armature"position sensor. 'his sensor ensures the exact position of the armature is )nown to the C9 at all times and allows the magnetic coil current to be adjusted to obtain the desired valve motion.
>eferring now to +igures / to ?, an electromechanical valve actuator of the poppet valve variety is illustrated in conjunction with an inta)e or exhaust valve (33!. 'he valve (33! includes a valve closure member 3@ having a cylindrical valve stem (A4! and a cylindrical valve head (A3! attached to the end of the stem (A4!. 'he valve actuator (34! of the poppet valve system generally includes a housing assembly (A?! consisting of upper and lower tubular housing members (A0! and (?3!, a magnetic field generator consisting of upper and lower field coils (?@! and (83!, a core (80! consisting of upper and lower core member (8@! and (0@!, and an armature (5@! suitably connected to the valve stem (A4!. 'he armature coil is preferably made from aluminium wire or other electrically conductive lightweight material, which is highly conductive for its mass. -inimising the armature mass is especially important in view of the rapid acceleration forces placed on it in both directions. 'he ability of the electromechanical valve actuator to generate force in either direction and to vary the amount of force applied to the armature in either direction is an important advantage of this design. +or instance, varying the value of the current through the armature coil and;or changing the intensity of the magnetic field can control the speed of opening and closing of the valve. 'his method can also be used to slow the valve closure member to reduce the seating velocity, thereby lessening wear as well as reducing the resulting noise.
'his system is able to operate without valve springs as shown in +igure / or can e&ually be e&uipped with them as shown in +igures 0 5. iemens report that a special software algorithm is used to control the actuator coil currents such that the valves are decelerated to a speed near
>eferring to +igure /4, the valve housing (5! is shown in two pieces. Ball valve (@! has two rigidly attached pivots (/3!. 'he disc (/4! is permanently attached and indexed to the ball valve and contains permanent magnets around its perimeter. 'he electromagnets (//! are situated on both sides of the ball valve (@! and they are fixed to the valve housing. 'he electromagnets are controlled through the C9. % cran) trigger sensor on the cran)shaft provides information about the position of the pistons relative to top dead centre. 'hus, at top dead centre of the power stro)e, the C- could be used to fix the polarity of both electromagnets so that they are of opposite polarity to the magnets in the ball valve, rotating the ball valve to the closed position. 'he substitution of a simple, efficient ball valve and valve housing arrangement in a a four stro)e reciprocation piston engine eliminates all the independent moving parts in the valve train. 'his may even be an improvement over the poppet valve camless system " the ball valve needs only to rotate on its axis to achieve the desired flow conditions, rather than be accelerated up and down in a linear fashion. % partially open ball valve state may also be able to be used to create more turbulence.
lectromechanical valve train implementation would not be possible with a normal /3$ electrical system. %s has been covered previously in %utopeed (Doodbye /3 volts... hello ?3 voltsD!, the automotive industry has chosen a ?3$ electrical system as the next automotive standard. Conse&uently, the energy demand of -$' can be optimally matched by a cran)shaft"mounted starter"generator (E " in iemens spea)! operating at ?3$F it is integrated in the flywheel and designed for the starting process as well as generator operation. Electrohydraulic Poppet Valves In general terms, present designs of electrohydraulic valves comprise poppet valves moveable between a first and second position. 9sed is a source of pressurised hydraulic fluid and a hydraulic actuator coupled to the poppet valve. 'he motion between a f irst and second position is responsive to the flow of the pressurised hydraulic fluid. %n electrically operated hydraulic valve controls the flow of the pressurised hydraulic fluid to the hydraulic actuator. In one design, the provision is made for a three"way electrically operated valve to control the flow of the pressurised hydraulic fluid to the actuator. 'his supplies pressure when electrically pulsed open, and dumps actuator oil to the engine oil sump when the valve is electrically pulsed to close. 'he use of engine oil as the hydraulic fluid simplifies and lowers the cost of the design by removing the need for a separate hydraulic system.
'he basic design of the electrohydraulic valvetrain hardware is illustrated in +igure //. 'he engine poppet valves (33! and the valve springs (3?! that are used to reset them are shown. 'he poppet valves are driven by hydraulic actuators (30!, which are controlled by electrically operated electro"hydraulic valves (3@! supplying hydraulic fluid to the actuators via conduit (3G!. 'he preferred hydraulic fluid is engine oil, supplied to the electro"hydraulic valves by the pressure rail (A4!. %n engine"driven hydraulic pump (A3! supplies the oil pressure, receiving the oil from the engine oil sump (A?!. 'he pump output pressure is also limited by an unloader valve (A0!, as controlled by an accumulator (A@! connected to the oil pressure rail. 6ith this design the hydraulic pump could be periodically disconnected, such as under bra)ing, so that the valve train would run off the stored accumulator hydraulic pressure. %s is the trend with all modern engine systems, the camless engine has an even greater reliance on sensors. 'he valve actuation and control system typically needs a manifold pressure sensor, a manifold temperature sensor, a mass flow sensor, a coolant temperature sensor, a throttle position sensor, an exhaust gas sensor, a high resolution engine position encoder, a valve;ignition timing decoder controller, injection driver electronics, valve coil driver electronics, ignition coil driver electronics, air idle speed control driver electronics and power down control electronics. % valve developed by turman Industries is said to be about six times faster than conventional hydraulic valves. 'o achieve such speeds, it uses a tiny spool sandwiched between two electrical coils. By passing current bac) and forth between the coils, a microprocessor"based controller can &uic)ly move the spool bac) and forth, thereby actuating the engine valves in accordance. 2owever, electrohydraulic systems are mostly being developed for diesel truc) use because it
is currently not clear whether the technology will have the speed needed for higher revving passenger car engines. Benefits of Camless Engines 'he benefits of camless valve actuator systems are numerous. =et#s begin with the most obvious one " infinitely variable valve timing. -ore tor&ue is made available through out the rev"range due to the valve timing changes enabling optimal volumetric efficiency. 'his increases engine performance and decreases fuel consumption, also decreasing harmful emissions, increasing durability and engine life, and allowing compensation for different types of fuel and varying altitudes. iemens claims that even today, fuel savings of at least ten per cent can be obtained in the uropean test cycle by using a camless valvetrain. Cylinder deactivation (ie an eight cylinder can become a six as needed! is also possible, with the associated reduction in emissions. +urther fuel consumption reductions could be obtained by combining camless valve technology with a high"pressure direct fuel injection system. (iemens has also developed this type of system and its expected to be part of the camless valve train engine when it does reach production readiness.! 'he amount of engine oil re&uired would also be dramatically reduced because no lubrication would be re&uired for the traditional complex camshaft valve system. Cold start wear would also be minimal to the valve train hardware. 'here is also a general consensus that electromechanical valve actuation will increase overall valvetrain efficiency by eliminating the frictional losses of the camshaft mechanism, the weight of the mechanism and the cam mechanism#s drain of power from the cran)shaft.
'he improvement in the speed of operation valve actuation and control system can be readily appreciated with reference to +igure /3. It shows a comparison between valve speeds of a mechanical camshaft engine and the camless engine valve actuation. 'he length of the valve stro)e in inches versus degrees of rotation of a mechanical camshaft is illustrated. 6hen graphed, the cycle of opening and closing of a valve driven by a mechanical camshaft will display a shape similar to a sine curve. 'he opening period (as measured in cran)shaft degrees! remains constant for any engine load or rpm. 2owever, the cycle of opening and closing of valves driven by the electromechanical valve actuators operates much faster. 7esigned to match valve"opening rates at the maximum engine rpm, the electromechanical valve actuators open the valve at this same rate regardless of engine operating conditions. Because of this improved speed, greater flexibility in programming valve events is possible, allowing for improved low"end tor&ue, lower emissions and improved fuel economy. 'he massive opening period for the electromechanically driven valve can also be seen Controlling the inta)e valve event can also eliminate the need for throttled operation in petrol engines, thereby reducing pumping losses and improving fuel economy " the throttle butterfly becomes redundant In the un"throttled camless engine, the inta)e valves# opening duration is used for cylinder airflow regulation, rather than a throttle or air"bypass valve. % simplification of the induction system results and a more compact engine design is thus possible. 'his leads to valve specific inta)e trumpets with less restriction to give the best breathing capabilities. %lthough, it needs to be said that there are reported problems with respect to idle control of a throttleless design, with stable unthrottled engine operation difficult to achieve during low load, and more precisely, during idle conditions. %n internal > (exhaust gas recirculation! function can be created by increasing valve
overlap as appropriate. imilarly, the inta)e valve may be opened and closed several times during the inta)e or exhaust se&uence to promote scavenging and later to f ollow the piston to promote inta)e volumetric optimisation, and inta)e and exhaust valves may be dithered to control engine throttling and bra)ing. 9sing camless valve actuators permits reprogramming to allow the engine to operate in reverse . 'his can be done by simply inverting one input wire pair. >everse operation is advantageous in marine e&uipment having dual outdrives or '"drives. 'his feature would also eliminate the need for reverse gear in the transmission since forward gears would be used to operate in either vehicle direction. 'his provides an opportunity for multiple reverse gears without the added hardware. 2owever, the future is not necessarily as rosy as the above states. 'here are many problems to be overcome with the electronically controlled valves. 'he problems lie not only in the software re&uired but also the mechanisms of the actuators. Coil transient response times and saturation effects at high rpm are just some of the issues. HI-file;;;C;7OC9-J5/;Owner;=OC%=J5/;'emp;mo<"screenshot"/.jpgH;I- HI-file;;;C;7OC9-J5/;Owner;=OC%=J5/;'emp;mo<"screenshot.jpgH;I-
4enault have not planned an Electro%mechanical system, which was commonly believed to use actively controlled magnetic coils to open and close the valves. Clearly the electrical and 4>" performance re/uired from the this system were not ready or suitable for a -1 engine. =hat 4enault have is an Electro%hydraulic system, where two pressurised circuits operate the valve 1*!. ?alve return is still handled by the pneumatic system )&, &!, but the
opening of the valves discards cams for a hydraulic circuit )! controlled by a electronic valve )8!. +s this system can use high pressure hydraulics already on the car to operate the valve at the re/uired 4>" ceiling, the system seems almost too simple.. Infinitely variable valve timing plus the loss of the reciprocating weight of the cams and drive gears ma$es this an enticing solution. #his solution has yet to race or to my $nowledge even be tested in a car, 4enault have admitted that as a broader automotive organisation, that this systems has been tried.
!rig"ton #ulti-Cylinder Camless Engine Contact$ @r 0teve Jegg
' Cylinder asoline Camless Engine #he Jrighton "ulti%Cylinder Camless Engine is a 4icardo%developped in%line ' cylinder camless @I research engine. #he four independently controlled hydraulically actuated valves per cylinder allow for research into advanced engine cycles and combustion modes. #his engine was originally commissioned at the Jrighton 0H4< for the &A( 0IH# proect. It produced the first ever controlled operating mode switches from ( stro$e to & stro$e and bac$! and demonstrated outstanding & stro$e performance of 1) mAl at 1 rpm and &' mAl at &) rpm than$s to its innovative combustion chamber. #he concept of the &A( cycle engine illustrated in -ig. 1 below! relies on using the traditional cylinder poppet valves found commonly in ( stro$e engines to be used in & stro$e mode also by switching to a different valve opening fre/uency. ni/ue valve, fuel and air handling control strategies ensure a smooth mode switch and good scavenging in & stro$e operation. + demonstration of mode switching can be seen in the video in -ig. &.
-ig 1 >rinciple of operation in & stro$es mode
-ig & &A( cycle engine switch demonstration
@epartment of "echanical Engineering &&
