AU714090B2 - Valve operating system - Google Patents

Description

WO 97/19260 PCT/AU96/00756 1 VALVE OPERATING SYSTEM Technical Field The present invention relates to a system for controlling the operation of internal combustion engine inlet and exhaust valves. The invention provides a system and method for hydraulic or pneumatic actuation and electronic control of individual valves.

Background Art It is well known that the timing of the opening and closing of inlet and exhaust valves has a major effect on the performance of engines.

The ability to totally control the operation of inlet and exhaust valves brings with it other possibilities including the ability to shut-off the operation of certain cylinders when they are not required, thus bringing about variable displacement to an engine. Auxiliary controllable valves can be used to allow air from one cylinder to be cycled to another cylinder or chamber and vice-versa during a period of cylinder close-down. When a blower mechanism for scavenging purposes is used it becomes possible to switch an engine between 2 and 4 cycle at will. This can be carried out with conventional valves or in combination with two-cycle type exhaust ports at the bottom of each cylinder which are only brought into operation during two-cycle operation by means of auxiliary valves.

When combined with suitable forced induction, it is possible to employ the cycle known as the "Miller Cycle", as desired It also brings about the possibility of starting the engine as a 4-cycle, allowing the pressure from a turbocharger to build up and then switching to 2-cycle operation using the forced induction for the turbocharger to scavenge and charge the cylinder with air during the 2-cycle operation.

It also brings about the possibility of greatly reducing pumping losses and gaining thermodynamic advantages by totally or substantially eliminating the throttle and controlling the amount of air drawn into the cylinder and remaining during the compression of the air by early closure of the inlet valve or by delaying the closing of the inlet valve to a greater or lesser degree during the compression stroke. It also brings about the ability to flatten the torque curve throughout the rev range of an engine.

Actuation of automotive valves by conventional hydraulic or pneumatic pumps and with control by electronic means, through conventional hydraulic or pneumatic valves, brings with it problems such as Scr'/u 9 0 7 RECEIVED 1 0 1997 2 the effect of Helmholtz or shock waves in the hydraulic system at high speeds or the complexity and expense of conventional electronically controlled hydraulic valves and other hydraulic components and the difficulty of getting the system to operate at the required speed. In the case of pneumatic systems there is the problem of energy losses due to the irreversible energy processes involved in the compression of gases.

Preferably, a valve control system should optionally make provision for variable stroke or opening of valves and should optionally make provision for safety factors to prevent poppet valves operating in the wrong part of the cycle and hitting the piston. Preferably the system should optionally make provision for force imparted by the cam on the force stroke to be partially returned to the cam on the closing stroke. Preferably the system should optionally make provision for 2-way positive operation of poppet valves with similar effects to desmodronic valves. Preferably the system should optionally make provision for delayed closing of the inlet valve as a means of controlling the air/fuel ratio. Preferably a valve control system should optionally make provision for partial dual mechanisms to facilitate operation at high speed. Preferably a valve control system should optionally make provision for a hydraulic or pneumatic lock or passive or active dampening mechanisms to eliminate or minimise valve bounce. The invention disclosed herein, in various of its embodiments, is designed to be adaptable to provide for the above abilities and/or to ameliorate the above problems.

In the case of hydraulic systems, the greater the distance the piston and cylinder arrangement is from the source of hydraulic power and the more complex the mechanical layout of the hydraulic system, then the greater the likelihood of shock waves or random changes within the system causing problems to the operation of the system at high RPM of the engine and/or the system being too costly and complex to be practical. In the system of the present invention it is possible to keep the source of hydraulic or pneumatic power physically close to the actuating piston and the control valve arrangement can be kept relatively simple.

Disclosure of Invention The broadest form of the present invention utilises motive means such as a rotating crank, cam or cams that are similar to conventional cams used with 4 cycle internal combustion engine poppet valve systems except Sthat the profile of the cam is of a different shape to that employed for C j AMENDED SHEET

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R E C E I V E00 RECEhPIJ O 3 operating conventional engine poppet valve systems. The speed of rotation of the camn can be the usual half-speed of the engine's crankshaft or it can be another speed which could typically be the same as or one quarter of the speed of rotation of the engine's crankshaft. Each cam in this system is used to generate hydraulic or pneumatic power which is then controlled by a valve to operate an inlet or exhaust valve. The cam is shaped such that there is a continual rise from the smallest radius to the largest radius during that period of rotation in which the valve would normally be operated or the cam can rise rapidly during the period in which the valve would normally open and rise slowly or not at all until it drops rapidly to minimum rise.

The system of this invention employs variable valve timing totally controlled by an engine management system wherein the valve timing can be varied to optimise performance under varying conditions. This invention goes beyond variable valve timing in that the operation of each individual valve is controlled by the engine management system. In a preferred embodiment of the invention a cam system is used to apply force to pressurises fluid to actuate valves and which pressurised fluid can also be used to generate hydraulic pressure for direct fuel injection.

The valve operation in this system is hydraulically or pneumatically actuated and electronically controlled.

In accordance with one aspect of the present invention there is provided a system for controlling the operation of combustion chamber valves in an internal combustion engine wherein the opening and closing commands originate from an engine management system and which system employs hydraulic or pneumatic operation wherein a power is adapted to move within a power cylinder via the action of motive means such as a crank or a cam which continually rises and then falls on each rotation of said cam, said power piston having a larger diameter and/or stroke than the piston/s of an associated slave cylinder/s and wherein the hydraulic or pneumatic force generated by the piston within the power cylinder operates the slave cylinder/s which, in turn, opens and closes the valve/s in the cylinder head, and further wherein pressure to open the valve/s in the cylinder head against the pressure exerted on the valve by biasing means is controlled until a controlled shut-off means closes a passage and stops flow of fluid to allow sufficient pressure to build to open said valve and where fluid spills from the ower cylinder against a source of fluid under lower pressure than the 0MEiE SHEE %NT OAMENUED

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P 7 r 11 V RrCE!VED !7 4 pressure within the power cylinder, until the controlled shut-off means closes the passage, preventing such spill, characterised in that a main control piston is provided such that movement of the power piston within the power cylinder causes pressure on the fluid to act on the main control piston causing the main control piston to compress resilient means whereby the main control piston acts on a secondary source of fluid through a secondary control piston of smaller cross-sectional area than the main control piston and which secondary control piston is movable until movement of the secondary fluid is blocked preventing further movement of the secondary control piston and hence the main control piston so as to allow pressure to build within the fluid and for this fluid pressure to operate the slave cylinder/s so that the spill of fluid and prevention of movement of such fluid which controls the actuation of the valves occurs external to the fluid.

In an embodiment of this invention it is possible to continually vary the timing of inlet and exhaust valves via the engine management system; but there is a limit to the amount of timing that can, in practice, be used for the opening of both inlet and exhaust valves. For the inlet valve this would typically be close to the top dead centre position of the piston at the commencement of the inlet stroke to the bottom of that stroke but, in this system, when the timing of the inlet valve is used to control the air/fuel ratio, the duration of opening may be delayed to close to top dead centre on the compression stroke. Thus for this system, when used with conventional timing of the inlet valve, the period during which the inlet valve may be opened and remain open is close to one half of a revolution of the crankshaft or one quarter of a revolution of the camshaft if the camshaft is driven at one half of crankshaft speed, that is close to the full period of the inlet stroke. In an alternate embodiment providing for control of air/fuel ratio by means of delayed closing of the inlet valve, the period of opening can be up to close to the time of opening of the inlet and compression stroke ie. close to one full revolution of the crankshaft and one half of a revolution of the camshaft if the camshaft is driven at half engine speed. For the exhaust valve the period of opening would be typically close to the bottom position of the piston on the exhaust stroke, ie. close to one half revolution of the crankshaft.

The cam of an embodiment of the present invention is in close contact with a cam follower and the force transmitted by the change in shape Oof the lobe of the cam as it rotates is transmitted to, say, a piston and cylinder k AMENDED SHEET OT

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PCT'.A Q n( RECEIVED i 0 O 19 97 4/1 arrangement filled with fluid. This cylinder will be hereinafter referred to as the "power cylinder". The fluid would typically but not necessarily be engine oil. The cam follower is kept biased against the lobe of the cain by a resilient means such as a spring. The systems described herein will be for systems in which the camshaft turns at half crankshaft speed. The camshaft can turn at one quarter or the same speed as the crankshaft, provided the shape of the cam and the mechanisms are modified to suit.

In one embodiment the fluid outlet from the power cylinder is connected to the inlet of a second hydraulic or pneumatic cylinder which can be formed from part of the housing of the power cylinder or can be a separate assembly. This second hydraulic or pneumatic cylinder will be hereinafter A0 AMENDED 8HE

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WO 97/19260 PCT/AU96/00756 referred to as the "slave cylinder". The piston of the slave cylinder is mechanically connected to the stem of a poppet valve and, when the piston travels under the effects of fluid under pressure, it opens the poppet valve.

The poppet valve is biased to the closed position by a resilient means which would typically be a spring. The word spring will be used herein but other resilient means can be used in place of a spring. The diameter and/or stroke of the power cylinder would typically be larger than that of the slave cylinder/s. The ratio of the diameter and/or stroke of the power cylinder relative to those of the slave cylinder is determined by the requirement that sufficient fluid must be available from the operation of the power cylinder to open the slave cylinder at a suitably rapid rate when the control system is actuated to commence the valve opening operation.

A spill port is provided which joins to the inlet of the slave cylinder and an electrically operated solenoid valve which is controlled by an electric current generated by a computerised engine management system is able to allow or prevent flow of fluids to the outlet of the spill port. Whilst flow through the spill port is allowed then pressure is prevented from building up in the slave cylinder and the piston in the slave cylinder will not exert any significant force on the stem of the poppet valve. As the poppet valve is biased, by a resilient means, to the closed position, the poppet valve will remain closed whilst fluid flow occurs to the spill port. When the solenoid valve is actuated to a position where it prevents the flow of fluid to the outlet of the spill port, then pressure builds up in the slave cylinder which forces the piston to travel and open the poppet valve. When the solenoid operated hydraulic or pneumatic valve is actuated or released so that flow to the spill port is again allowed, the pressure on the piston in the slave cylinder drops and the force of the valve spring acting on the valve stem and then on the piston will return the piston to its initial position.

The engine management system can thus exercise complete control over the opening and closing of the valves and can determine whether the valve will open at all on that cycle and at what point it will open and at what point it will close.

The slave cylinder can be designed so that one or more spill ports are provided such that after a pre-determined amount of travel the spill port is exposed by the piston of the slave cylinder and fluid will be released out of the spill port and the travel of the piston will thereby be limited. When WO 97/19260 PCT/AU96/00756 6 multiple spill ports are provided the first spill port or ports exposed may be closed from passage of oil by one or more electro-mechanical valves. When passage of fluid is closed then the piston travel will continue until a port is exposed which will allow passage of fluid at which point piston travel will cease. The amount of valve opening can be controlled by this means.

The slave cylinder can be designed with fluid on both sides of the piston and so that the section of the cylinder closest to the poppet valve is provided with one ore more ports which can be opened or closed to the passage of fluids. The ports are disposed so that, depending on which part is open allowing fluids to enter or exit a particular port, then more or less fluid can be trapped in this section of the cylinder, preventing travel of the piston beyond a certain point and limiting the travel of the piston. A relief valve is provided at the inlet to the slave cylinder so that, when movement of the piston is prevented by the trapped fluid then the relief valve will open and allow excess pressure to be dissipated. Thus a means of controlling the amount of valve lift which can be varied by the engine management system under differing operating regimes of the engine is provided.

When more than one inlet and/or exhaust valve is used per cylinder then one power cylinder can be used for each valve or one power cylinder can provide power from fluid under pressure to actuate more than one slave cylinder.

When speed of operation is a problem then multiple mechanisms per valve can be used with the mechanisms being operated in sequence by the engine management system.

The speed of return of the engine's poppet valve can be too rapid and cause problems from impact upon the valve seat at high speeds and a means of damping the return is described herein. A means of varying the dampening of the return action relative to temperature and/or viscosity of the actuating fluid is also described.

Brief Description of the Drawings The present invention will now be described, by way of example, with reference to the accompanying drawings in which:- Figs 1 and 2 are schematic representations of an embodiment of a valve control system of the present invention with the power and slave cylinders adjoined to each other;

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WO 97/19260 PCT/AU96/00756 7 Fig. 3 is a schematic representation showing alternate embodiment in which one cam is operating two power cylinders which are disposed above the cam; Fig. 4 shows an alternate embodiment generally similar to that shown in Fig. 3 but depicting only one of the two valve operating systems operated by a cain; Fig. 5 is a schematic representation of a valve control system in which two power cylinders are set above the cam and the cam rises over more than 180 degrees of retation of the camshaft; Fig. 6 is identical to Fig. 5, except that it shows detail only on the left hand power and slave cylinders and the solenoid control valve in the open position, allowing the valve to return to the closed position; Fig. 7 is identical to Fig. 6 except that the cam is shown in a position where the cam follower/piston is extended to the extreme open position; Fig. 8 is a schematic representation of an embodiment of the invention which has a cam with the lobe rising over approximately one quarter of a revolution of the camshaft and utilising two power cylinders for the intake valve and one power cylinder for the exhaust valve; Fig. 9 is a schematic representation of a system in which the force from fluid under pressure is generated by a crankshaft and piston and cylinder arrangement and with an arrangement that provides positive movement in both directions to the piston in the slave cylinder which opens and closes the valve; Fig. 10 is a schematic representation of a variation of the system depicted in Figs 1 and 2 in which a third control piston and cylinder is incorporated external to the power and slave cylinders; Fig. 11 is a schematic representation of a variation of the system depicted in Fig. 10, in which the control piston is incorporated into the power cylinder; Fig. 12 is a schematic representation of a variation of the system depicted in Fig. 11.

Best Modes of Carrying Out The Invention Fig. 1 shows the cam in a position where it is not exerting force on the piston the power cylinder and the solenoid valve is open so that the slave cylinder will not actuate.

i_ jlr WO 97/19260 PCT/AU96/00756 8 Figure 2 shows the cam in a position where it is exerting force on the piston of the power cylinder and the solenoid control valve is in the closed position causing the piston of the slave cylinder to move. Fig. 2 also shows an optional second spill port and control valve in the slave cylinder and an optional positive stop to the travel of the piston of the slave cylinder.

Referring to Figs 1 and 2, the central axis of the camshaft 1 is provided with a cam 2 which has a profile with a continually rising radius relative to the central axis until it reaches a maximum dimension within approximatcly on. quarter of a revolution and the radius then rapidly reduces to a minimum.

The cam, as it rotates and rises, is able to exert pressure on piston of power cylinder 3 and force piston 5 down into cylinder 3, thus tending to exert pressure on fluid 22. Piston 5 is kept engaged to cam 2 by means of spring 6 which is located partly with recess 13 of piston 5. Passage of fluid 22 from port 29 can be allowed or prevented by electrically operated solenoid valve 15 at position 16. Fluid under comparatively low pressure from a pressure source not shown but which could be the engine's lubricating oil system is provided to point The slave cylinder 17 is fitted with piston 18 of a lesser diameter than piston 5 and piston 18 is connected to valve stem 19, which is fitted with a valve spring (not shown) which tends to move valve stem 19 in a direction such that piston 18 would move into cylinder 17.

Referring to Fig. 1, the cam moves in the direction of rotation shown and forces piston 5 into cylinder 3, thereby exerting pressure on fluid 22, which flows out port 29 through position 16 to the source of fluid under pressure 30. This source is low pressure and is provided with an accumulator allowing excess fluid, forced out by piston 5, to flow against the pressure tending to move fluid in the direction of the arrow in Fig. 1. The pressure at point 30 is not sufficient to move piston 18 against the pressure of the valve spring (not shown).

If control valve 15 were to fail and keep point 16 closed, piston 18 would return when the cam lobe releases the pressure within cylinder 3. An additional safety factor could be built in the form of a port at position 72, which releases pressure to source 30 when the piston is in the extreme open position or by a cam-operated valve which prevents pressure from building up in the slave valve when the cam is in a position in the cycle where an

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WO 97/19260 PCT/AU96/0056 9 open valve could hit the piston. The port at position 72 can also be used for the purpose of sending fluid back to the reservoir for the purpose of circulating fluid to prevent the temperature of the fluid rising beyond acceptable operating temperatures.

Referring to Fig 2, the control solenoid 15 has been activated by an electric current provided by the engine management system (not shown) and has blocked passage of fluid at point 16. The fluid 22 now exerts sufficient pressure on piston 18 to overcome the force of the valve spring and cause valve stem 19 to travel and open the valve. Piston 18 travels to a point where it uncovers port 20, allowing fluid 22 to travel through port 20 to a source of low pressure fluid 30 where it overcomes pressure at that point and travels in the direction of the arrow in Fig. 2. An alternate configuration is for port to be connected to the reservoir to allow fluid to flow back to the reservoir for the purpose of allowing the system to operate at lower temperatures. The valve will not open beyond this point as the fluid escaping through port prevents any further build-up of pressure. Neither can the valve close under these conditions as when piston 18 covers port 20 it cannot move back against the fluid in cylinder 17.

When the valve is required to close, the engine management system (not shown) actuates solenoid valve 15 and allows passage of fluid at point 16. The pressure of the valve spring exerts force on valve stem 19 against piston 18 and forces oil 22 through port 29 against low pressure fluid source and allows piston 18 to move into cylinder 17 and the valve to close. As piston 5 rises due to the changing cam profile low pressure from source flows through point 16 to port 29 and fills cylinder 3 with fluid. The cycle is now ready to be repeated.

Fig 2 shows optional additional port 21 in slave cylinder 17 with optional valve lift control solenoid 80 which can allow or prevent passage of oil through port 21. When passage of fluid is blocked from passage through port 21 the piston 18 moves until it uncovers port 20. When passage of fluid is allowed through port 21 then fluid will flow through port 21 and the movement of piston 18 will cease at that point. Thus the amount of the travel of piston 18 and the amount of the valve opening can be controlled by the operation of control solenoid Fig. 2 shows an alternate housing for slave cylinder 17, which provides for a positive stop to the travel of piston 18 at position WO 97/19260 PCT/AU96/00756 Fig. 3 shows the profile in the cam, in the case of Fig. 3 which rises continually over more than one half of a revolution of the camshaft to provide for a delayed closing of the inlet valve to enable control of the air/fuel ratio by means of control of the inlet valve one cam providing the movement to generate force from fluid under pressure for two power cylinders which are disposed at approximately 90 degrees to each other at the top of the cam. The profile of the cam in this embodiment can rise the same as in Fig. 1, ie. approximately one quarter of a camshaft revolution but is shown in this case as rising over approximately one half of a camshaft revolution (or more, as drawn) to ensure that there is a supply of fluid under pressure to allow the inlet valve to stay open for close to a full crankshaft revolution or half of a camshaft revolution, so that the air/fuel ratio can be controlled by means of the timing of closure of the inlet valve.

In Fig. 3 the central axis of the camshaft 1 is provided with cam 2 which rises as described above. Power cylinders 3 and 4 are disposed so that cam 2 can provide force to the extremities of pistons 5 and force them to move and tend to compress fluid 22. As in the system depicted in Figs 1 and 2, the fluid 22 will exert pressure on piston 18 and overcome the force of the spring unless it is allowed by solenoid valve 15 to pass fluid through position 16 to source of low pressure fluid 30. Power cylinder 4 is depicted with its solenoid valve 15 in the open position and its slave cylinder 18 has not commenced movement. Power cylinder 3 is depicted with its solenoid valve in the closed position and fluid cannot flow at its point 16 so that pressure builds in fluid 22 and exerts pressure through port 28 and gallery 12 on piston 18 and the resultant force overcomes the pressure of the spring (not shown) on valve stem 19 and forces the valve stem 19 to move and open the valve. In this case a positive stop 25 is depicted and this positively stops the travel of piston 18. Power cylinder 3 is still exerting pressure and the buildup of pressure in fluid 22 is relieved by the opening of pressure relief valve 26, which allows fluid to flow through to source of low pressure fluid The fluid being vented is at a higher pressure than fluid at 30 and therefore flows into this system. If optional port 27, shown on the slave cylinder operated by power cylinder 3, were fitted and operated as described under Figs 1 and 2 then the pressure relief valves 26 and positive stops 25 would not be necessary.

WO 97/19260 PCT/AU96/00756 11 In the case of Fig. 4 the power cylinder has a rod protruding through both ends and connected at one end to a device upon which pressure is exerted by the cam. Fluid flows from one end of the cylinder to the other and a one-way valve in the piston facilitates return of fluid on the return (non-power) stroke.

Fig. 4 depicts one power/slave cylinder arrangement which is generally similar to that depicted in Fig. 3 except that the cylinder is doubleended and fluid can flow on both sides of the piston, slave cylinder 17 does not have a positive stop for piston 18, and there are other changes as described. Fig. 4 does not show a spring, which tends to keep cam follower 36 engaged to cam 2 and it is assumed that it can be installed internally in the power cylinder 3 or at either end of rod 35, externally to cylinder 3. A source of constant low pressure fluid is provided at location Cam 2 exerts pressure on cam follower 36, which exerts force through rod 35 to piston 5. Piston 5 exerts force on fluid at 43. Fluid from chamber 43 flows through gallery 31 to the opposite end of the power cylinder 3 unless its passage is blocked by solenoid valve 15 at point 16. Due to the fact that rod 35 protrudes through both ends of cylinder 3, the volume of fluid can flow backwards and forwards with the requirement of a spill or addition of fluid until slave cylinder 17 is actuated. Unless passage of fluid is blocked at 16, insufficient pressure will build up in fluid 22 to overcome the pressure of the valve spring (not shown) on valve stem 19, by means of piston 18.

When passage of fluid is blocked at point 16 by operation of the solenoid valve 15, then pressure builds up in passage 32 and sufficient force is exerted on piston 18 to overcome the pressure which the valve spring is exerting on piston 18 and the piston travels thereby moving valve stem 19 and making the valve open. When piston 18 uncovers port 20 fluid will escape and overcome the pressure of fluid at 30 and further movement of the valve will cease.

When control valve 15 is actuated so that passage of fluid can flow at point 16, the pressure of fluid in cylinder 17 will drop as fluid flows and overcomes the low pressure at point 30 and the pressure of the valve spring (not shown) on valve stem 19 will cause piston 18 to force fluid out of piston 17 and the valve will close.

An alternate is that passage 37 be eliminated and alternate passage 42, which is fitted with one-way valve 41 and a source of low pressure fluid WO 97/19260 PCT/AU96/00756 12 be installed. Fluid can flow through one-way valve 41 only when the pressure at source 40 is higher than fluid on the other side of the valve.

When position 16 is blocked and piston 5 forces fluid into cylinder 17 there is not sufficient fluid to fill chamber 39 and a partial vacuum is created in this chamber. When passage of fluid is allowed at position 16, fluid can flow from cylinder 17 and restore fluid to chamber 39. The vacuum will help the flow of fluid. In either alternate or optional one-way valve 33 can be fitted into piston 4 and biased against piston 4 by spring 34. When valve 33 is opened fluid can flow from chamber 43 to chamber 39 through piston 5 by means of valve 33. On the return stroke of piston 5, valve 33 will open and facilitate the return of fluid to chamber 43.

Fig. 5 depicts an optional means of returning part of the force exerted by the cam on the piston. The schematic depicts the left hand cylinder at full depression by the cam and with the solenoid control valve at the closed position with the result that its slave cylinder has forced the valve to the open position the camshaft rotation provides power from fluid under pressure for a sufficiently long duration to enable delayed closing of the inlet valve and thus bring about the ability to control the air/fuel ratio by means of the timing of the closing of the inlet valve. Camshaft 1 is fitted with a cam 2 which rises as described and exerts force on cam follower/piston 5 in the process. Pistons 5 are close fits in bores 7 of power cylinders 3 and 4 and are kept biased against cam 2 by means of resilient means 6 which in this case are springs. Piston 5 will exert force on fluid 22 when forced to move by cam 2, provided that solenoid control valve 15 is closed and passage of fluid through position 16 is prevented. The force on fluid 22 is transmitted to accumulator piston 10 which, in turn, exerts force, depressing spring 11 and exerting force on the fluid in the area of spring 11 and through fluid in passage 12 to slave cylinder 17 to piston 18, forcing piston 18 to move and move valve stem 19, overcoming the force exerted by valve spring (not shown) on valve stem 19 and forcing the valve to open. One-way valve 14 remains closed. Piston 18 moves until it uncovers port 20, allowing fluid to flow and overcome the low pressure of fluid at source 30 and prevent further movement of piston 18. If solenoid control valve 44 is operated and allows passage of fluid then the motion of the piston will cease when port 21 is uncovered by piston 18.

WO 97/19260 PCT/AU96/00756 13 Referring to Fig. 6, solenoid control valve 15 is shown at the open position, allowing fluid to flow through position 16, overcoming the low pressure of fluid at 30 and allowing fluid to flow through 30, releasing pressure on fluid throughout the system. This allows the pressure from the valve spring (not shown), on valve stem 19 to move piston 18 and force it to move, closing the valve. The pressure from the valve spring exerts force on piston 18, which exerts force on fluid and thus on piston 10. This force, combined with energy stored in springs 11 and 6, exerts pressure on piston/cam follower 5 which exerts pressure on cam 2 and when that cam has moved to a point where the lobe is diminishing in height and thus returns some of the energy to the cam that was imparted to the cam in the opening phase.

Referring to Fig. 7, cam 2 has moved to a point where cam follower/piston 5 has opened to its full extremity. Solenoid control valve is in the open position and fluid flows through position 16 and replenishes fluid under piston 5. Should fluid in the area of spring 11 need replenishing, one-way valve 14 will open, allowing fluid to flow to that area.

Fig. 8 is a schematic representation of an embodiment of the invention in which the lobe of cam 2 rises over approximately one quarter of a revolution of camshaft 1 and there are two power cylinders, 3 and 45, to provide power from fluid under pressure to the slave cylinder 17 of the intake valve and one power cylinder 45, to provide power to the slave cylinder 46 of the exhaust valve.

This embodiment is configured so as to provide power from fluid under pressure for the duration required to allow the intake valve to remain open for a period sufficiently long enough to enable it to exercise control of the air/fuel ratio by means of delayed closing of the inlet valve. This embodiment allows delayed closing of the inlet valve using lesser rise of the cam lobe and, consequently, lesser movements of fluid in each power cylinder.

Cam 2 exerts pressure on each cam follower/piston 5 as it rises and this exerts pressure on fluid 22 in each power cylinder. Each cam follower/piston 5 is biased to cam 2 by springs 6. One-way check valves 47 and 48 allow flow of fluid only in the direction of arrows at each valve. Fluid under pressure from power cylinder 45 opens check valve 48 and, when flow is prevented at position 16 by electric solenoid valve 15, pressure is exerted

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WO 97/19260 PCT/AU96/00756 14 on piston 18 and piston 18 moves and moves valve stem 19 to open the intake valve. Piston 18 moves until it uncovers port 20 and allows pressure to escape to source of low pressure 30 where it overcomes that pressure or to the reservoir; and no further movement of piston 18 occurs. As the lobe of the cam continues to move, pressure is generated within power cylinder 3 and pressure diminishes within power cylinder 45. Check valve 48 closes and check valve 47 opens under the pressure from low pressure source and replenishes the fluid in power cylinder 45 as piston 5 returns under pressure from spring 6. Power cylinder 3 then continues to supply fluid under pressure to actuate the intake valve whilst flow at position 16 is blocked. When solenoid valve 15 is actuated to allow flow at position 16, fluid from slave cylinder 17 has pressure exerted on it by piston 18 by means of valve spring (not shown) on valve stem 19 and this pressure overcomes the pressure at source of low pressure 30 and allows the intake valve to close.

Fluid from source 30 will replenish the fluid in cylinder 3 as its piston returns. The operation of power cylinder 4 and slave cylinder 46 is identical to that of power cylinder 3 and slave cylinder 17 if power cylinder 45 is isolated.

The previous embodiments have all incorporated camshafts as a means of generating power from fluid under pressure. An alternate means is to make use of a crankshaft and piston arrangement to generate power. One embodiment of this is shown in Fig 9. In this particular embodiment a connecting rod 49 connects to a rod 50, which exerts force on piston 51. The connecting rod could also be connected directly to piston 51 by means of a suitable wrist pin. The central axis of the crankshaft 52 is fitted with crank or cranks 53 and rotation of crankshaft 52 causes the crank 53 to move piston 51 within power cylinder 54, thereby tending to exert force on fluid 22 during that part of the stroke where the piston moves into the cylinder.

Electric solenoid control valve 56 is capable of blocking or allowing the passage of fluids at points 57 and 58. When 57 is blocked, 58 is open and vice versa. Similarly, valve 60 controls fluid at points 61 and 62. When valve 60 allows flow at point 60, fluid 22 flows through point 60 to source of low pressure fluid 71 and overcomes the low pressure so that there will be no significant pressure exerted on piston 69 and therefore it will not move. The schematic shows points 57 and 62 open and 58, 60 and 61 closed. In this configuration fluid flows through port 55, through point 57, and enters slave

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WO 97/19260 PCT/AU96/00756 cylinder 68, forcing piston 69 to move and move valve stem 67, thereby opening the valve. Fluid at point 70 is forced through port 66, through point 62 to source of low pressure fluid 71, where it overcomes the low pressure and exits the system. When piston 69 uncovers port 64, fluid flows through that port through point 62 to 71 and movement of the piston ceases. When control valves 59 and 60 are actuated and points 58 and 61 allow flow and flow is blocked at points 57 and 62, fluid 22 under pressure flows through point 58 through point 66 to chamber 70 and forces piston 69 into a reverse movement thereby.closing the valve. When port 65 is uncovered, fluid flows through 65 through point 61 to source 71 and movement of piston 69 ceases.

Valve 60 is then actuated so that point 60 allows flow and the chamber at point 60 is replenished with fluid from source 71. On the downward stroke, point 60 is left open until the engine management system gives a command to close point 60 and allows the movement of piston 69 to commence. Thus the timing of the valve can be controlled and the valve can be prevented from opening if the engine management system so commands.

Fig. 10 depicts a schematic representation of a variation of the system depicted in Figs 1 and 2, the main variation being the addition of an external control piston and cylinder arrangement. The general arrangement and principles of operation are identical to the system in Figs 1 and 2, apart from the action of the control piston. An external control cylinder 84 abuts power cylinder 3 so that fluid can move through a large aperture from power cylinder 3 to control cylinder 84. When cam 2 exerts force on cam follower/piston 5, fluid 22 tends to be compressed and pressure is exerted on control piston 79 which moves and compresses spring 81. The area around spring 81 contains no fluid other than air and the chamber at that end of control piston 79 is vented to atmosphere. A plunger 80 is attached to control piston 79 and plunger 80 exerts force on fluid at position 85 which overcomes the pressure exerted by the source of low pressure fluid which is provided at position 30 and control piston 79 is thus allowed to move when electrically operated valve 15 is open and there is no restriction at position 16. As the pressure exerted by spring 81 does not allow the pressure in oil 22 to build to a point where it will exert sufficient pressure on piston 18 to overcome the pressure of the valve spring (not shown) on valve stem 19, piston 18 will not move whilst electric control valve 15 is in the open position. Control cylinder 84 can be a larger diameter than power cylinder 3, WO 97/19260 PCT/AU96/00756 16 in which case, the movement of control piston 79 will be less than that of power camn follower/piston 5. This is beneficial in that the movement of both control cylinder 79 and plunger 80 is minimised and the volumes of fluid to be moved around position 85 is minimised. If control valve 15 stays in the open position, control piston 79 will oscillate backwards and forwards as cam 2 rotates and piston 18 and valve stem 19 will not move and the poppet valve in the cylinder head will stay closed. Optional port 87 is uncovered at the extremity of movement of cam follower/piston 5 and fluid is bled to the reservoir to keep fluid circulating and the temperature of the fluid to be minimised during a period of operation in which control valve 15 is not actuated to close position 16, ie. during a cycle in which the variable displacement capabilities of the system are utilised. A pressure relief valve can be incorporated after optional port 87, to keep pressure to a predetermined value.

When control valve 15 is actuated and closes position 16, fluid at position 85 cannot move and therefore plunger 81 is prevented from moving towards position 16 and thus piston 79 is prevented from moving. Pressure builds in fluid 22, exerting sufficient pressure on piston 18 to force it to open to a point where port 20 is uncovered and oil flows through position 20 to the return line to the reservoir 82 (or to position 30 in an alternate configuration), thus limiting further movement of piston 18. When control valve 15 is actuated to again open position 16, movement is again allowed to control cylinder 79. Pressure from the spring (not shown), on valve stem 19, forces piston 18 to close and, prior to cam 2 reaching a position where it allows the start of the return of cam follower/piston 5, the fluid displaced by the return movement of piston 18 moves control piston 79 towards position 16. When cam 2 allows cam follower/piston 5 to move towards shaft 1, the fluid displaced by the movement of cam follower/piston 5 is provided by the movement of control piston 79 towards power cylinder 3. Fluid from source 30 passes through one-way valve 86 and replenishes fluid lost through position 20. If the movement of fluid through 29 is not sufficiently rapid to allow cam follower/piston 5 to move as rapidly as required, the fluid to allow this to happen is provided by movement of control piston 79 which will move beyond the point where it will settle, once the flow of fluid through point 29 brings the system into equilibrium prior to the start of the next cycle.

WO 97/19260 PCT/AU96/00756 17 An optional arrangement is that a port can be incorporated in control cylinder 84, which is uncovered at the extremity of the movement of control piston 79 toward point 16, to bleed fluid back to the reservoir to aid in the cooling of the fluid and to aid the return of piston 18. Similarly, a port can optionally be incorporated so that it is uncovered by the movement of plunger 80 at its extreme movement towards power cylinder 3, to bleed fluid back to the reservoir at that point and aid in the cooling of fluid around point The advantage of this arrangement over that depicted in Figures 1 and 2 is that the volume of fluid 22 will remain constant during periods when control valve 15 allows position 16 to remain open, or nearly constant if optional ports as described above are provided; movement of fluid between cylinders 3 and 84 is subject to minimum restriction, the limitation potentially caused by the speed of movement of fluid through position 29 to replenish fluid lost through position 20 is overcome by the ability of control piston 79 to over-run its movement and provide a temporary supply of fluid which is then replenished before the next cycle commences and the volume of fluid moved around position 80 can be kept to a minimum.

The system schematically depicted in Figure 11 works on the same principles as the system depicted in Figure 10, except that the control cylinder is eliminated and the control piston in incorporated within the power cylinder.

Referring to Fig. 11, cam follower/piston 5 slides in a close tolerance fit in an aperture at the centre of control piston 79 and is also supported by a suitable bearing area in cylinder cap 88. Control piston 79 has a circular ring 76 incorporated into it which slides in a close tolerance fit in ring incorporated into cylinder cap 88 such that movement of control piston 79 can exert pressure on fluid at position 89. When cam 2 forces cam follower/piston 5 to move the resulting pressure on fluid 22 exerts pressure on control piston 79. When control valve 15 allows position 16 to be open, fluid 89 can flow through position 16 and the pressure exerted by control piston 79 overcomes the pressure of low pressure source 30 and control piston 79 can move and compress spring 81. The area around position 81 is vented to atmosphere. Whilst position 16 remains open, the rotation of cam 2 will move cam follower/piston 5 in and out of power cylinder 3, aided by the pressure exerted by spring 6 and the resulting pressure on fluid 22 will i Ilf -IXi WO 97/19260 PCT/AU96/00756 18 force control piston 79 to oscillate in a reverse movement to cam follower/piston 5, and the volume of fluid 22 will remain constant or, if strategies to cool fluid are used as in the system depicted in Fig. 10, the volume will remain nearly constant. When position 16 is closed by control valve 15, movement of control piston 79 is prevented by fluid at 89 and pressure builds in fluid 22, movement of fluid is prevented through position 29 by one-way valve 78, and the pressure moves piston 18 in a similar manner to that described in the system in Fig. 10 and the poppet valve in the cylinder head opens. When position 16 is again opened, control piston 79 can again move and fluid flows essentially in the same manner as described in the system in Fig. 10 and the valve in the cylinder head closes.

In an alternate embodiment, ring 76 can abut cam follower/piston and slide 75 will abut ring 76. In another alternate embodiment a plunger or plungers can be incorporated into control piston 79 and move in an aperture provided in cylinder cap 88 so that the operation of the plunger is similar to that described for the plunger in the system depicted in Fig. An alternate configuration is schematically shown in Fig. 12 which is similar in most ways to the system depicted in Fig. 11 except that the fluid that is used to control the movement of control piston 79 provides a double hydraulic or pneumatic lock and control piston 79 is positively prevented from moving in both directions under conditions of closure of position 16.

The same principle can be used in the system depicted in Fig. The system in Fig. 12 is configured so that chambers are formed at 89 and 90 so that fluid can move from chamber 89 to chamber 90 when position 16 is open and control piston 79 is forced to move by pressure in fluid 22.

When position 16 is closed then fluid cannot move from chamber 89 to chamber 90 and control piston 79 is prevented from moving in either direction so that slave piston 18 is forced to move as described in the system depicted in Fig. 11. An optional one-way valve 91 can be incorporated, leading to a source of low-pressure fluid 30 so that fluid can move in the direction indicated when pressure at 30 exceeds the pressure at chamber 89.

Optionally the solenoid in control valve 15 can also control a second valve which can be opened when position 16 is open and closed when position 16 is closed. This valve can be used to allow fluid from chamber 89 to spill (optionally through a small orifice or pressure relief valve) to the reservoir.

WO 97/19260 PCT/AU96/00756 19 This arrangement would allow fluid to be continually replenished in chambers 89 and 90 to prevent heat build up.

In the Fig. 12 embodiment control of the movement of the control piston is positive in both directions, a damping mechanism is provided to dampen the return of the slave piston and wherein a mechanism is depicted to provide variable valve lift. Also a means of venting fluid is depicted to prevent pressure build-up. The Fig. 12 embodiment incorporates a system to continually vary the stroke of slave piston 1 and hence to achieve variable valve lift. A slidable cylinder 92 is incorporated, adjacent to slave piston 18, so that piston 18 moves in a close tolerance fit within cylinder 92. Cylinder 92 is fitted with a spill port 22 which is adjacent to an elongated spill port 94 such that fluid from spill port 22 can exit spill port 94 when cylinder 92 slides. A chamber is formed at the top of cylinder 92 at 96 and fluid under pressure from fluid in control line 97 exerts a pressure in chamber 96 and forces cylinder 92 against the pressure of spring 93. The pressure in control line 97 is determined by a remote controlling device not shown. As previously described, slave piston 18 moves until it uncovers spill port and the position of spill port 20 moves as cylinder 92 moves and thus variable valve lift is achieved, depending on the pressure in control line 97.

There are various other means of moving cylinder 92, eg mechanical cam action.

The system depicted in Fig 12 also provides a means of dampening the return action of slave piston 18. The slave piston 18 incorporates an extension 98 which optionally can be tapered. The last portion of the return movement is damped by the provision of a porting device 99 which inhibits the movement of fluid which is being forced by pressure from slave piston 18. Optionally, porting device 99 can be active rather than passive with two sliding sections which can be made to move together or apart by various means such as the expansion of material which expands under increasing temperature, including bi-metallic materials or by servo-mechanisms, the action of which can be linked to and relative to the viscosity of fluid 22. The objective is that the aperture provided the movement of the segments of porting device 99 is smaller at higher temperatures or decreased viscosity of fluid 22 to provide variable damping characteristics of the return of slave piston 22, relative to temperature and/or the viscosity of fluid 22.

WO 97/19260 PCT/AU96/00756 The system Fig. 12 embodiment incorporates a spill port 100 which vents fluid optionally through a pressure relief valve 101 to the reservoir with the objective of preventing pressure build-up in fluid 22 and to also help in the circulation of fluid 22 to prevent heat build-up. The spill port 100 can optionally vent to the source of low pressure fluid 30. The spill port 100 can be incorporated elsewhere in the power cylinder by alterations to the configuration, eg a plunger of smaller diameter than the power cylinder could extend below the power cylinder to slide within a cylinder to uncover a port or the power cylinder could partially slide within a cylinder incorporated in the lower part of the main housing 3 to uncover a port for venting purposes.

The pressure relief valve 101 can optionally be made variable by a servomechanism or by the action of a temperature-reactive material exerting additional pressure on the spring with the objective of varying the pressure within the system to compensate for varying viscosity of the actuating fluid under varying conditions of temperature.

Control valve 15 in Fig. 12 can be in the form of a slidable cylinder fitted in a close tolerance fit around valve body 3 and both valve body 3 and the cylinder be fitted with suitable porting so that the action of sliding the cylinder can allow or prevent movement of fluid between chambers 89 and 90. The benefit of such a system is that multiple ports can be provided to minimise the restriction to the flow of fluid between chambers 89 and A power cylinder such as cylinder 54 in Fig. 9 could be used to actuate slave cylinders to operate both inlet and exhaust valves for one cylinder, in a system such as that Fig. 5, if fluid was present on both sides of piston 51, with suitable porting provided, and the fluid at point 22 was used on the downward stroke to provide power to actuate an intake slave cylinder including the ability to delay closing of the intake cylinder to control the air/fuel ratio and the fluid at the opposite end of piston 51 was used on the reverse stroke to actuate the exhaust slave cylinder.

To simplify an understanding of the depicted embodiments, not all options are shown in each embodiment, but options shown on some embodiments can be incorporated into other embodiments as required.

If the slave cylinder is configured so that fluid is present on both sides of the piston and suitable venting provided for fluid on the side of the piston closest to the valve stem, a secondary solenoid valve can be incorporated into the venting system so as to momentarily block fluid flow WO 97/19260 PCT/AU96/00756 21 upon return of the piston, ie closure of the poppet valve, so that the piston is momentarily prevented from returning, the objective being to eliminate or minimise valve bounce and enable weaker valve springs to be used, thereby saving on the energy required to compress the valve springs during the opening phase.

The type of cam described herein can also be used to provide a source of fuel under pressure for direct injection systems. Power cylinders described herein can be readily modified to provide fuel under pressure with a pressure relief valve providing constant pressure and the fuel being fed to an injector where it is fed directly into the cylinder under moderate to very high pressure.

The configurations of Figs 10, 11 and 12 can have elements from systems depicted elsewhere herein incorporated into them, for example the cam can be open for a longer period, the mechanisms can be mounted above the cam, and one cam can operate two or more power/slave cylinder combinations, all of these elements as in the system depicted in Fig. 3. The cam profile can be a different shape to that described. The rise in profile can occur to maximum or close to maximum height in the period of rotation in which the valve would open in its designed maximum advance or retard position and continue at maximum height in the former case and with a slight rise in the latter case to a point where the latest designed closing point of the valve would occur, at which point it would rapidly diminish to minimum height. The advantage of this profile is that the ratio of diameter of the power valve relative to the slave valve can be lessened and still achieve a rapid opening of the valve.

The position of the camshaft if shown as overhead to the cylinder but it can also be mounted low in the engine with the power cylinder mounted adjacent to the cam as illustrated, except inverted, and the slave cylinder operating a push rod in lieu of directly acting on the valve. In low mounting of the cam the power cylinder can be mounted adjacent to the cam with a hydraulic or hydraulic/mechanical link connection to the slave cylinder/s.

An example of a hydraulic/mechanical link would be that a hydraulically actuated push rod would convey force for part of the distance to minimise shock waves that may otherwise occur in a fully hydraulic link.

The systems depicted in Figs 10, 11 and 12 have a one-way valve 78 to prevent fluid escaping when pressure builds, due to action of the cam on WO 97/19260 PCT/AU96/00756 22 the power cylinder. An alternate method is to provide an electrically operated solenoid valve, which can be a second or third element in the control valve 15, which allows flow when control valve 15 is not activated and prevents flow when control valve 15 is activated. The flow would be to the source of low pressure 30 and the venting system 100 may be omitted if this valve is incorporated, as this system would allow the pressure in the actuating system to drop.

Heat build-up in the actuating and control fluids is a potential problem and can be eliminated or minimised by the spill of fluids from the spill port 20 under conditions of valve actuation. As one of the objectives of this system is to be able to shut down cylinders by means of the valves in those cylinders being shut down, the spill will not occur during this part of the operation. A strategy can be adapted by the engine management system to sequentially shut down different cylinders so that any one cylinder does not spend long periods in a shut-down state. In this way the spill will occur regularly and will aid in the process of keeping fluids within acceptable temperature ranges.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims (18)

1. A system for controlling the operation of combustion chamber valves in an internal combustion engine wherein the opening and closing commands originate from an engine management system and which system employs hydraulic or pneumatic operation wherein a power piston is adapted to move within a power cylinder via the action of motive means, such as a crank or a cam which continually rises and then falls on each rotation, said power piston having a larger diameter and/or stroke than the piston of an associated slave cylinder/s and wherein the hydraulic or pneumatic force generated by the piston within the power cylinder operates the slave cylinder/s which, in turn, opens and closes the valve/s in the cylinder head, and further wherein pressure to open the valve/s in the cylinder head against the pressure exerted on the valve by biasing means is controlled until a controlled shut-off means closes a passage and stops flow of fluid to allow sufficient pressure to build to open said valve and where fluid spills from the power cylinder against a source of fluid under lower pressure than the pressure within the power cylinder, until the controlled shut-off means closes the passage, preventing such spill, characterised in that a main control piston is provided such that movement of the power piston within the power cylinder causes pressure on the fluid to act on the main control piston causing the main control piston to compress resilient means whereby the main control piston acts on a secondary source of fluid through a secondary control piston of smaller cross-sectional area than the main control piston and which secondary control piston is movable until movement of the secondary fluid is blocked preventing further movement of the secondary control piston and hence the main control piston so as to allow pressure to build within the fluid and for this fluid pressure to operate the slave cylinder/s so that the spill of fluid and prevention of movement of such fluid which controls the actuation of the valves occurs external to the fluid.

2. A system as claimed in claim 1 wherein the secondary control piston is adapted to be blocked from moving either by preventing movement of fluid in one direction or by the secondary control piston being double-ended and preventing fluid from moving at both ends of such secondary control piston. 6< AMiENDED SHEET 'PRAIADJ 24

3. A system as claimed in claim 1 or 2, wherein one camn operates more than one power/slave cylinder combination.

4. A system as claimed in any one of claim 1 to 3, wherein each power cylinder operate more than one slave cylinder.

5. A system as claimed in any one of claims 1 to 4, wherein the period of rise of the cam is equivalent to approximately one revolution of an engine's crankshaft, so that each inlet valve can be kept in the open position during part of the compression stroke.

6. A system as claimed in any one of claims 3 to 5, wherein a one-way valve is incorporated into the power piston so as to allow movement of fluid from one side of the power piston to the other, in one direction of stroke.

7. A system as claimed in any one of claims 3 to 5, wherein a separate accumulator piston and cylinder is provided to exert pressure against resilient means so as to store energy in said resilient means, which energy can be releasable to exert pressure on the power piston which, in turn, is adapted to exert pressure on the cam during the period of rotation in which the lobe of the cam falls, so as to return part of the energy exerted by the camn in the period during which the lobe of the cam rises.

8. A system as claimed in any one of claims 1 to 4 or 6 and 7 wherein the lobe of the cam rises over approximately one half of a revolution of a engine's crankshaft and wherein two power cylinders are provided for each cam to drive slave cylinder/s to operate inlet valve/s and wherein one power cylinder is provided to drive slave cylinder/s to operate exhaust valve.

9. A system as claimed in any one of claims 1 to 8 wherein the movement of each piston within a slave cylinder is limited by the action of the slave piston Luncovering a port allowing the primary fluid to spill therefromi.

A system as claimed in any one of claims 1 to 9 wherein more than one spill port is provided and one or more of these spill ports is adapted to be closed so as to allow variable amounts of movement of the slave piston and hence vary the amount of lift of the combustion chamber valve/s.

11. A system as claimed in any one of claims 1 to 8 wherein the movement of the slave piston is limited and spillage of fluid occurs against a pressure relief valve to allow further movement of the power piston when the lobe of the cam is still rising. RA44 AMNE~ SHEET VT )7 RECEIVED 1 0 .V I' 37

12. A system as claimed in any one of claims 1 to 11 wherein fluid is present on both sides of the slave piston.

13. A system as claimed in any one of claims 1 to 12 wherein the closing of the inlet valve is adapted to occur early during the inlet stroke or during the compression stroke.

14. A system as claimed in any of claims 1 to 13 wherein the rate of return of the slave cylinder piston is dampened at the end of the return stroke via a main control solenoid for at or just prior to the last period of the return stroke.

15. A system as claimed in any one of claims 1 to 13 wherein the rate of return of the slave cylinder piston is dampened at the end of the return stroke via an extension at the top of the slave cylinder, which extension passes through an orifice at the end of the return stroke, causing fluid to be throttled through the orifice and dampen the rate of return prior to the end of the stroke.

16. A system as claimed in claim 15 wherein the rate orifice is a variable orifice.

17. A system as claimed in any one of claims 1 to 9 and 14 wherein the movement of the slave piston within the slave cylinder is limited by the action of the slave piston uncovering a port allowing the primary fluid to spill therefrom and wherein that port is incorporated in a slidable cylinder in a close tolerance fit around the slave cylinder with the slidable cylinder being adapted to be slid along the slave cylinder with ports being arranged such that the port in the slidable cylinder is uncovered by the slave piston at varying lengths of travel of the slave piston such that fluid can spill from the of ports within predetermined limits of travel of the slave piston, whereby varying lengths of travel of the slave piston vary the lift of the valve within the cylinder head.

18. A system as claimed in any one of claims 1 to 17 wherein a passage is in incorporated in the power piston with a port towards the end of the power piston closest to the cam, such port being able to transfer actuating fluid to a port in the power cylinder body or cylinder cap and such fluid being able to exit either unimpeded to a reservoir or impeded by a pressure relief valve to the reservoir such transfer to fluid taking place at the extremity of the stroke RA f the power cylinder at or close to the minimum rise of the cam where tact is made between the power cylinder and the cam. fMEV SHEET