GB2213873A

GB2213873A - Engine valve actuation system

Info

Publication number: GB2213873A
Application number: GB8827908A
Authority: GB
Inventors: Ronald Phillips; Robert Keith Cross
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1987-12-19
Filing date: 1988-11-30
Publication date: 1989-08-23
Also published as: FR2624911A1; JPH01262308A; DE3841997A1; GB8827908D0; GB8729657D0

Description

1 k % VALVE A(--ruA-itor-4 5"Y'STEM This invention relates to an actuating

system for a valve of a reciprocating piston internal combustion engine.

)2 13873 Ir It is known from British patent specifications 2107393B and 1578019, to open an inlet or exhaust valve of a spark ignition engine or compression ignition engine using hydraulic pressure which is applied to a piston, the piston effecting movement of the valve against the action of the valve spring. The application of hydraulic pressure to the piston or the like is effected by means of an electromagnetic valve which is under the control of an electronic control system. Closing of the engine valve is effected by closing the aforesaid valve and opening a further such valve which allows the valve spring to move the engine valve to the closed position during which movement the piston is also displaced. Such an actuating system allows the timing of the engine valves to be varied to suit the particular operating requirements of the engine.

In order to open an engine valve the force developed upon the piston by the hydraulic pressure must be sufficient to overcome the force exerted by the valve spring, any forces acting on the engine valve due to the pressure within the engine cylinder and the inertia forces. Once the valve has started to open the force required to move the engine valve to its fully open position will diminish. If the original force is maintained the engine valve during its movement will achieve too high a velocity and although the velocity of the valve can be controlled, the volume of liquid utilised in moving the engine valve to the open position will be that required to displace the piston and this will be substantially unaffected by the rate of movement of the engine valve.

71 The object of the present invention is to provide an actuating system for an engine valve in a simple and convenient form.

According to the invention an actuating system for an engine valve comprises a fluid pressure operable device defining first and second surfaces which can be exposed to a fluid pressure under the action of an electromagnetic valve means, said device including an output member operatively connected to an engine valve which is spring biased to a closed position, the fluid pressure acting on the first and second surfaces causing movement of said output member to achieve the initial movement of the engine valve against the action of the spring, the device being constructed so that after said initial movement the engine valve is moved to the open position by the action of the fluid pressure on one only of said surfaces.

An example of an actuating system in accordance with the invention will now be described with reference to the accompanying drawings in which:Figure 1 is a diagrammatic representation of the system, and Figure 2 shows a modification to the system shown in Figure 1.

With reference to Figure 1, part of an engine cyli-nder head 9 is shown with two engine valves being indicated at 10, the valves being the exhaust valves of one cylinder of an engine having four valves per cylinder. The valves 10 are biased to the closed position by conventional valve springs 12 and the valves are movable to the open position by a fluid pressure operable device 13 which will be describei in 1 3 _f greater detail. Fluid under pressure can be supplied to the device 13 by way of an electromagnetically operable valve 14 which is a normally closed valve and allowed to escape from the device by way of an electromagnetically operable valve 15 which is a normally open valve. The fluid escaping from the device flows to a drain and the fluid is a liquid which is pressurised by an engine driven pump 16.

The device 13 comprises a cylinder housing 17 in which is formed a stepped cylinder 18. The housing defines a pair of ears 19 which carry threaded studs 20 aligned with the stems 21 of the valves. The ears ar recessed to accommodate the ends of the valve st.ems. Extending into the cylinder 18 and having sliding engagement with the narrower portion of the cylinder is an outwardly flanged spigot 22 which is mounted in the cylinder head of the engine.

The spigot defines a control axial drilling 22B and cross drillings 22A which open into an intermediate portion of the cylinder and slidable in the wider portion of the cylinder is an annular member 23 which in the closed position of the engine valves, abuts against the adjacent step in the cylinder and a step defined on the spigot 22.

Secured to the ears 19 of the cylinder housing by means of nuts engaged with the studs 20, is a stop member 24 which defines an annular stop flange 25 spaced outwardly of the spigot and which in the closed position of the engine valve is axially spaced from the annular member 23.

In operation when it is required to open the engine valves 10, the valve 15 is closed and the valve 14 opened by supplying electric current to the respective solenoids associated with the valves. Fluid under pressure is supplied to the device and acts upon a first surface defined by the end wall of the cylinder 18 and by way of the cross drillings 22A, upon a second surface which is defined by the steps in the cylinder. The force generated by the fluid pressure acting on the two surfaces causes movement of the engine valves 10 against the action of the springs 12. The pressure acting on the annular member 23 urges it against the step defined on the spigot 22.

When the clearance between the member 23 and stop flange 25 has been taken up, the fluid pressure actingon the aforesaid second surface, is no longer effective to move the cylinder housing and the further opening movement of the engine valves 10 is due only to the fluid pressure acting on the first surface. During the continued movement of the engine valves and the cylinder housing, the annular member moves with the cylinder housing.

During the movement of the cylinder housing before the aforesaid clearance is taken up, a substantial force is generated which is more than sufficient to open the valves against the prevailing pressure in the engine cylinder and the forces exerted by the valve springs, and to accelerate the valves. When contact is established between the stop flange 25 and the annular member 23, the force is reduced and the acceleration is also reduced. Moreover, the consumption of liquid for a given movement of the engine valves is reduced.

The lift of the engine valves is determined by the length of time the electromagnetically operable valve 14 is opened. The flow of current to the solenoids of - -j, the valves 14 and 15 is controlled by an electronic control system which is responsive to the engine crankshaft position and may be responsive to other engine operating parameters. When the electromagnetic valve 14 is closed an hydraulic lock is created which prevents further movement of the engine valves. A displacement transducer can be used to monitor the lift of the engine valves and to adjust the duration of opening of the electromagnetic valve 14. A non-return valve 14A is connected in parallel with the valve 14 and can open to relieve excess pressure which may be developed in the system due for example to the engine piston striking the val When it is required to close the engine valves, the electromagnetic valve 15 is de-energised to allow the fluid to escape from the cylinder. The initial rate of flow of fluid before the annular member 23 engages the step on the spigot, is small and therefore the valves move quickly towards their closed positions. However, when the annular member 23 engages the step on the spigot the rate of flow of liquid is increased and this slows the movement of the engine valves onto their seatings. This helps to minimise valve bounce and damage to the seatings.

In both the opening and closing sequences it is possible to control the rate of engine valve movement by pulsing the electromagnetic valves 14 and 15. In fact it has proved necessary during the engine valve opening sequence to control the movement of the engine valves before maximum lift is attained since it has been found that mere closure of the electromagnetic valve 14 when the desired lift has been achieved, causes cavitation of the liquid to occur. Pulsing the electromagnetic valve 14 can achieve the required h degree of control but such pulsing requires very short pulse widths which might be difficult to maintain over the operating life of the system. As an alternative to pulsing it is possible to restrict the flow by using the electromagnetic valve 14 as a flow restrictor by gradually decreasing the current flow in its solenoid. This again however requires very careful control and the better solution seems to be the provision of a damper.

Figure 2 shows part of the system shown in Figure 1 but incorporating a damper which is in the form of a piston 26 slidable within a cylinder 27 from which extends a passage containing an orifice 28, the passage leading to a drain. Liquid can be supplied to the cylinder from the pressurised source of liquid by way of a non-return valve 29. The arrangement is such that when the cylinder housing 17 approaches the maximum stroke, it contacts a reduced end portion of the piston 26 which damps the final movement of the cylinder housing and therefore the engine valves.

The system as described besides allowing the timing of the engine valves to be varied, also permits the use of lighter valve springs since the mass of the moving parts associated with the engine valves is considerably reduced.

it will of course be appreciated that whilst the system has been described as applied to the operation of two exhaust valves of a cylinder having four valves, it is equally applicable to the operation of a single exhaust valve or the inlet valve or valves.

The ability to alter the engine valve timing can be used during engine overrun, to enhance the braking T 111 1 0 7 effect provided by the engine. For example if the exhaust valve or valves is/are opened at Top Dead Centre, the engine braking effect is enhanced since there is no energy recovery during the downward stroke of the engine piston. It has been found that the exhaust valves can be opened by a small amount, up to 900 before Top Dead Centre. The increasing pressure in the engine cylinder as the piston continues to move upwardly will close the exhaust valve or valves against the compliance provided by the fluid in the actuating device. AS the piston passes Top Dead Centre and the cylinder pressure starts to fall, the valve or valves reopen and the cylinder pressure falls.

It is also possible in order to enhance the engine braking effect, to cause a four stroke engine to operate in the two stroke mode.

The lift of the engine valve or valves can be varied and in the case of the inlet valve this can be partially opened to increase the air velocity across the valve seat thereby improving swirl in the engine cylinder. In the case of a spark ignition engine the partial opening of the inlet valves of the engine can be utilised to replace the action of the normal butterfly valve which controls the air or air/fuel flow to the engine cylinder.

In the case of a turbo supercharged engine it is possible to open the exhaust valves of the engine earlier than usual in order to increase the energy supplied to the turbocharger. This can help to reduce "turbo lag" in such an engine.

VP 8

Claims

1. An actuating system for an engine valve comprising a fluid pressure operable device defining first and second surfaces which can be exposed to a fluid pressure under the action of an electromagnetic valve means, said device including an output member operatively connected to an engine valve which is spring biased to a closed position, the fluid pressure acting on the first and second surfaces causing movement of said output member to achieve the initial movement of the engine valve against the action of the spring, the device being constructed so that after saia initial movement the engine valve is moved to the open position by the action of the fluid pressure on one only of said surfaces.

2. A system according to Claim 1 in which said output member defines a stepped cylinder, a spigot slidably located in the inner and narrower oortion of said cylinder, said spigot being secured to the cylinder head of the engine, the inner end of the cylinder defining said one surface, an annular member slidably mounted about said spigot and slidable within the outer and wider portion of the cylinder passage means for conveying liquid to and from the inner end and an intermediate portion of, the cylinder, a step defined on said spigot and against which said annular member rests in the closed position of said valve and stop means carried by said operating member and engageable with said annular member after said initial movement of the valve.

3. A system according to Claim 2 in which said stop means comprises a stop flange which extends over the wider end of the cylinder.

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4. A system according to Claim 3 in which said passage means comprises an axial passage in said spigot and cross drillings formed in said spigot connecting the axial passage with said intermediate portion of the cylinder.

5. A system according to Claim 2 in which said intermediate portion of the cylinder defines an annular space about said spigot.

6. A system according to Claim 2 including first and second electromagnetically operable valves for controlling the flow of liquid through said passage means, said first valve being a normally closed Valve which is opened to allow liquid flow from a source of liquid under pressure to said passage means and the second valve being a normally open valve which allows flow of liquid from said passage means to a drain.

7. A system according to Claim 6 including damping means operable to damp the final movement of the valve towards the open position.

8. A system according to Claim 7 in which said damping means comprises a piston slidable within a cylinder, a restricted outlet from the cylinder and a non-return valve through which liquid can be admitted to the cylinder from a source of liquid under pressure.

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9. An actuating system for an engine valve compris. the combination and arrangement of parts substantially as hereinbefore described.

Published 1988 at The Patent Office. State House, 66771 High Holborn, London WCIR 4TP Firther copies may be obtained from The Patent Office, Wes Branch, St Mary Cray. Orpington, Kent BM 3RD Printed by Multiplex techniques ltd, St Mary Cray. Kent Con. 1'87