HYDRAULIC VALVE OPERATING SYSTEM FOR OPERATING A POPPET VALVE OF AN INTERNAL COMBUSTION ENGINE

Abstract

With reference to FIG. 1, the present invention provides valve operating system for operating a pair of poppet valves (10, 32) of an internal combustion engine. The system comprises a source of pressurised hydraulic fluid (22), a fluid return (23), a first hydraulic actuator (13) which the first poppet valve (10) and a second hydraulic actuator (13) acts on the second poppet valve (32). A first valve (21) is connected to both the source of pressurised fluid and the fluid return (23). A second valve (20) is connected between the first valve (21) and the first hydraulic actuator (13). A third valve (30) is connected between the first valve (21) and the second hydraulic actuator (31). An electronic controller (40) controls operation of the valves (20, 21, 30) to open and close the pair of poppet valves (10, 32).

Description

The present invention relates to a valve operating system for operating a poppet valve of an internal combustion engine.

It is typical for an internal combustion engine to use poppet valves as inlet and exhaust valves controlling flow of fuel/air charge into and combusted gases out of a combustion chamber. Traditionally, these have been cam driven. While such a system is robust, it does not allow any (or only limited) variation of valve motion with changes in engine speed and load. Therefore, more recently it has been proposed to use hydraulic actuators to open and close internal combustion engine poppet valves. The actuators are electronically controlled and allow variation of the valve opening and closing points (measured in terms of degrees of crankshaft rotation) from engine cycle to engine cycle.

In WO2004/033861 the applicant has described a hydraulic actuator for opening and closing a poppet valve. In WO2004/011833 the applicant has disclosed a valve for connecting a hydraulic actuator to either a source of pressurised fluid or to a fluid return. The applicant has researched how best to control operation of a system using the previously described hydraulic actuator and the previously described valve.

In a first aspect, the present invention provides a valve operating system for operating a poppet valve of an internal combustion engine comprising:

a source of pressurised hydraulic fluid;

a fluid return;

a hydraulic actuator which acts on the poppet valve;

a first valve connected to both the source of pressurised fluid and the fluid return;

a second valve which is connected between the first valve and the hydraulic actuator, which is a bistable switching valve and which operates to either connect the hydraulic actuator with the first valve or to disconnect the hydraulic actuator from the first valve;

a sensor which provides a signal indicative of position of the poppet valve; and

an electronic controller which receives the signal indicative of poppet valve position and which controls operation of both the first and second valves to:

open the poppet valve by connecting the hydraulic actuator to the source of pressurised fluid via the first and second valves;

close the poppet valve by connecting the hydraulic actuator to the fluid return via the first and second valves; or

maintain the poppet valve in position by using the second valve to disconnect the hydraulic actuator from the first valve.

In a second aspect the present invention provide a valve operating system for operating a pair of poppet valves of an internal combustion engine comprising:

a source of pressurised hydraulic fluid;

a fluid return;

a first hydraulic actuator which acts on a first of the poppet valves;

a second hydraulic actuator which acts on a second of the poppet valves;

a first valve connected to both the source of pressurised fluid and the fluid return;

a second valve which is connected between the first valve and the first hydraulic actuator, which is a bistable switching valve and which operates to either connect the first hydraulic actuator with the first valve or to disconnect the first hydraulic actuator from the first valve;

a third valve which is connected between the first valve and the second hydraulic actuator, which is a bistable switching valve and which operates to either connect the second hydraulic actuator to the first valve or to disconnect the second hydraulic actuator from the first valve;

a first sensor which provides a signal indicative of position of the first poppet valve;

a second sensor which provides a signal indicative of position of the second poppet valve; and

an electronic controller which receives the signals indicative of positions of the first and second poppet valves and which controls operation of all of the first, second and third valves to:

open the first poppet valve by connecting the first hydraulic actuator to the source of pressurised fluid via the first and second valves;

close the first poppet valve by connecting the first hydraulic actuator to the fluid return via the first and second valves;

maintain the first poppet valve in position by using the second valve to disconnect the hydraulic actuator from the first valve;

open the second poppet valve by connecting the second hydraulic actuator to the source of pressurised fluid via the first and third valves;

close the second poppet valve by connecting the second hydraulic actuator to the fluid return via the first and third valves; and/or

maintain the second poppet valve in position by using the third valve to disconnect the hydraulic actuator from the second valve.

A preferred embodiment of the present invention will be described with reference to the accompanying drawings, in which:

FIG. 1 is a schematic drawing of a pair of poppet valves operated by hydraulic actuators and controlled by a combination of switching valves and a flow direction control valve;

FIG. 2 is an illustration of an actuator of FIG. 1;

FIG. 3 is an illustration of a flow direction control valve of FIG. 1;

FIG. 4 illustrates a first valve lift profile of one of the poppet valves of FIG. 1 during an engine cycle and also the control signals sent to the switching and flow direction control valves at different points of the engine cycle;

FIG. 5 is a simplified control diagram of the control system used to control the operation of the poppet valves of FIG. 1; and

FIG. 6 illustrates a second valve lift profile of one of the poppet valves of FIG. 1 during an engine cycle at low engine speeds and also the control signals sent to the switching and flow direction control valves at different points of the engine cycle.

Turning firstly to FIG. 1, there can be seen an inlet valve 10 of an internal combustion engine which controls flow of fuel/air charge from an inlet passage 11 into a combustion chamber 12. The inlet valve 10 is a poppet valve. It is opened by a hydraulic actuator 13 against the force of a biasing spring 14, the spring acting to close the poppet valve 10.

The actuator 13 is of the type described in WO2004/033861 and is shown in more detail in FIG. 2. In the Figure the inlet valve 10 can be seen and it can be seen that the valve spring 14 shown schematically in FIG. 1 actually comprises a pair of springs 104 and 105 acting between a surface 106 in the cylinder head and a collar 107 provided on the valve stem of the poppet valve 10. The actuator comprises a lower piston 15 and an upper piston 16. The operation of the actuator is described in detail in WO2004/033861 and therefore will not be described in detail in this patent specification. The actuator 13 operates during opening of the valve 10 by the piston 16 moving downwardly under application of fluid pressure until it reaches an end stop, with the piston 16 engaging and moving the piston 15. Then, the lower piston 15 moves under the application of fluid pressure. The piston 15 acts on the top of the valve stem 10. The larger area of the piston 16 means that the force applied by the piston 16 to the valve 10 is greater for a given system pressure than the force applied by the piston 15 with its smaller surface area. For a given amount of fluid flow, the movement of the piston 15 is greater than the movement of the piston 16 by reason of the difference in areas.

Operation of the actuator 13 is controlled by a bistable switching valve 20 and a bistable flow direction control valve 21 which is of the type described in WO2004/011833 and is shown in detail in FIG. 3. The valve 21 controls flow of fluid from a source of pressurised fluid 22 (e.g. a pump, see FIG. 1) via a pressure line 214 and also controls flow of fluid to a fluid return (e.g. a sump 23—see FIG. 1), via a fluid return line 215. The operation of the valve 21 has been described in detail in WO2004/011833 and therefore will not be described in detail in the specification. Suffice to say that the valve 21 can connect the valves, 20, 30 to either the source of pressurised fluid 22 or the return for pressurised fluid 23. In other words, the valve 21 is a bistable two-position valve and the two positions are graphically illustrated in FIG. 1. The valve 21 is a fast acting switching valve which switches between two conditions; it is not a metering valve for regulating the rate of fluid flow through the valve, i.e. the valve 21 controls direction of flow, not rate of flow.

As shown in FIG. 1, the flow direction control valve 21 controls flow of fluid to bistable switching valve 20 which in turn controls flow of fluid to and from the actuator 13. The valve 21 also controls flow of fluid to a second bistable switching valve 30, identical to valve 20, which controls flow of fluid to and from a second actuator 31, identical to actuator 13. The switching valves 20,30 are fast acting bistable switching valves which switch between two conditions; neither are metering valves for regulating rate of flow fluid, i.e. they switch flow on or off, but do not control rate of flow therethrough.

The actuator 31 acts on a second poppet valve 32, which is an exhaust valve controlling flow of combusted gases from the combustion chamber 12 to an exhaust runner 33. A valve spring 34 acts on the poppet valve 32 to close the poppet valve.

Operation of the system previously described will now be explained with reference to FIGS. 4 and 5. FIG. 4 shows the lift of the valve 10 plotted against time during one opening event. Also shown in the Figure are the control signals used to control the switching valve 20 (shown at SV) and the flow direction control valve 21 (shown at FCV). The L₀ position shows the poppet valve 10 closed. At point A the poppet valve 10 starts to lift away from its valve seat. This is achieved by controlling the flow direction control valve 21 so that it connects the switching valve 20 to the source of pressurised fluid 22 and then opening the switching valve 20 to allow flow of hydraulic fluid from the source of pressurised fluid 22 via the flow direction control valve 21 to the hydraulic actuator 13. The switching valve 20 is bistable and the impulse shown in FIG. 5 associated with point A switches the valve to its open condition. The valve remains open until a second control signal is supplied to it (described later). The flow direction control valve is switched to the source 22 prior to opening of the switching valve 20, as can be seen from the impulse on line FCV. Between A and B the valve opening is occasioned by movement of the piston 16, whilst between B and C the valve movement is occasioned by movement of the piston 15. This is the reason for the varying gradient between A and B and between B and C.

At C, the switching valve 20 is switched to a closed position to stop fluid flow and to maintain the poppet valve 10 in its maximum open position with the maximum valve lift L2. The maximum valve lift L2 will vary from engine cycle to engine cycle with varying engine speed and load.

Between C and D the valve 10 is maintained in its maximum lift valve open condition. It remains stationary during this period. In advance of the point D the control signal FCV is controlled so that the flow direction control valve 21 switches to connect the switching valve 20 to the sump 23. Then at D, the switching valve is switched to an open condition to allow flow of fluid out of the actuator 13 via the switching valve 20 and the flow direction control valve 21 to the sump 23. The valve spring 14 applies the biasing force which forces the fluid from the actuator 13. Between D and E the piston 15 moves alone within the actuator 13 and then at E the piston 15 engages the piston 16 and both pistons 15, 16 move together between E and F as the poppet valve 10 approaches its closed position. For this reason, the gradient between D and E is different to the gradient between E and F.

At F, the switching valve 20 is controlled and switched to the closed position to keep the poppet valve 10 closed until it is next opened. Then, the flow direction control valve 21 is switched back to the source of pressurised fluid, ready for actuating the valve 32 via the actuator 31.

The exhaust poppet valve 32 will be similarly controlled using a combination of the metering valve 21 and the switching valve 30.

The switching valves 21 and 30 are very fast acting and allow precise control of the time of starting and stopping of valve motion. In order to control the valve motion the control system has to control the start point A, the period α2 to the point C, the period α3 to the point D and then the period α5 to the point F. The points B and E are not specifically controlled but will result from the characteristics of the actuator during opening and closing. In this way, both the valve lift and the valve opening duration are controlled. Although the FIG. 5 shows crank angle α on the X axis, it could also show time since time will be directly related to crank angle for any given speed of rotation.

FIG. 5 shows the control diagram for the engine valve operating system. The controller 40 (see FIG. 1) receives a signal indicative of engine speed, typically from a crankshaft rotation sensor, a signal indicative of engine load, e.g. from a manifold depression sensor and feedback signals showing the positions of the poppet valves 10 and 32 as measured by two position sensors 41 and 42 associated respectively with the actuators 13 and 31. The crankshaft position sensor can be differentiated with respect to time to give an indication of engine speed. The position sensors 41 and 42 could be replaced with velocity sensors, whose output could then be integrated with respect to time to give position. The controller 40 uses a look-up table 50 (see FIG. 5) to determine for a given engine speed and engine load a desired valve opening duration and valve lift and a lift demand signal is generated. This is then used to generate an error signal at 54 (described later) and this is converted at 51 into control signals controlling the switching valve and flow direction control valve as previously described. In FIG. 5 the combination of flow direction control valve, switching valve and actuator is shown as 51. The control signals input at 51 result in a lift. The valve lift is then measured, (e.g. by the sensor 41) and this feedback signal is then fed to a feedback loop 53, which contains a Proportional, Integral, Differential (PID) signal processor 52, which can be used to modify the feedback signal. The feedback lift signal is combined with the lift demand signal at 54. In this way a closed loop system is provided which during the lifetime of the system compensates for wear of the components and for variations in operation due to changes in ambient temperature, system pressure, etc. For instance, for a given system pressure there will be a maximum flow capability and the timing of opening and closing of the switching valve will have to be varied to accommodate e.g. a lower system pressure than expected by the system. The error signal from the valve lift gives this possibility.

The error signal is used to vary the timing of closing and opening of the switching valve, the periods α₂, α₃ and α₅ in FIG. 4.

At very low engine speeds the range of control provided by the method of control previously described may not be sufficient to provide the desired valve lift. Instead, a method of operation illustrated graphically by FIG. 6 could be used. The valve lift is occasioned solely by movement of the pistons 16 and 15 together—piston 15 does not move separately. Rather than the piston 16 moving the whole length of its stroke as described previously, the piston 16 is moved incrementally by switching on and switching off the switching valve 20. At α₁ the switching valve 20 is switched on and it is then switched off again at α₂ before the piston 16 has completed its maximum stroke. It is switched on again at α₃ and off at α₄, on at α₅ and off at α₆. In this way, the piston 16 is moved down in stages. Similarly, the piston is returned under the action of the valve spring in stages, the switching valve 20 being switched on at α₇ and off at α₈, then on at α₉ and off at α₁₀, then on at α₁₁ and off at α₁₂. In this way, a slower lifting and slower closing of the poppet valve 10 can be achieved. The bigger area of the piston 16 allows for better control of the motion of the piston 16 than the piston 15 and therefore enables the control illustrated in FIG. 6. The total movement under the control of the larger piston 16 will be around 0.9 mm.

The crank angle position will typically be provided by a crank sensor which reads teeth on a toothed wheel. Typically, there are provided 58 teeth, spaced as if there were 60 teeth with two gaps. The two gaps indicate top dead centre of the piston within the cylinder. The teeth that are present are spaced (other than at the gaps) by an equivalent of 3 degrees of crankshaft rotation. Sometimes, this does not give sufficient resolution of crank angle. Typically, this allows resolution of crank angle to 0.5 degrees. However, it is often desired to have resolution to 0.1 degree of crank angle position. The applicant envisages that the crank angle sensor could be modified to provide such a resolution without providing extra teeth. This could be done by using software to interpolate between actual measured points of crank shaft rotation.

Claims

1-19. (canceled)

20. A valve operating system for operating a poppet valve of an internal combustion engine comprising: a source of pressurised hydraulic fluid;a fluid return;a hydraulic actuator which acts on the poppet valve;a first valve connected to both the source of pressurised fluid and the fluid return;a second valve which is connected between the first valve and the hydraulic actuator, which is a bistable switching valve and which operates to either connect the hydraulic actuator with the first valve or to disconnect the hydraulic actuator from the first valve;a sensor which provides a signal indicative of position of the poppet valve; andan electronic controller which receives the signal indicative of poppet valve position and which controls operation of both the first and second valves to:open the poppet valve by connecting the hydraulic actuator to the source of pressurised fluid via the first and second valves;close the poppet valve by connecting the hydraulic actuator to the fluid return via the first and second valves; ormaintain the poppet valve in position by using the second valve to disconnect the hydraulic actuator from the first valve, wherein:the hydraulic actuator comprises a first piston having a pressure face on which supplied hydraulic fluid applies pressure, anda second piston also having a pressure face on which supplied hydraulic fluid applies pressure;the pressure face of the first piston is larger than the pressure face of the second piston; andduring opening of the poppet valve the first and second pistons initially move together and then latterly the second piston moves alone.

21. A valve operating system as claimed in claim 20 wherein the first valve is a bistable valve which operates to either connect the second valve to the source of pressurised fluid or to connect the second valve to the fluid return.

22. A valve operating system as claimed in claim 20 which comprises a valve spring which applies a closing force on the poppet valve.

23. A valve operating system as claimed in claim 20 wherein the electronic controller controls valve lift by control of the second valve and by controlling duration of connection of the hydraulic actuator to the first valve.

24. A valve operating system as claimed in claim 20 wherein the electronic controller switches the first valve between connection to the source of pressurised fluid and connection to the fluid return only while the second valve disconnects the hydraulic actuator from the first valve.

25. A valve operating system as claimed in claim 20 comprising a sensor which produces a signal indicative of crankshaft rotation position which is used by the electronic controller to determine timing of operation of the first and second valves.

26. A valve operating system as claimed in claim 20 wherein the electronic controller uses a look-up table to determine a valve lift demand which is then used to control operation of the first and second valves.

27. A valve operating system as claimed in claim 26 wherein the electronic controller uses the signal indicative of poppet valve position to provide a feedback signal which is used to modify the valve lift demand in closed loop control of the hydraulic actuator.

28. A valve operating system for operating a pair of poppet valves of an internal combustion engine comprising: a source of pressurised hydraulic fluid;a fluid return;a first hydraulic actuator which acts on a first of the poppet valves;a second hydraulic actuator which acts on a second of the poppet valves;a first valve connected to both the source of pressurised fluid and the fluid return;a second valve which is connected between the first valve and the first hydraulic actuator, which is a bistable switching valve and which operates to either connect the first hydraulic actuator with the first valve or to disconnect the first hydraulic actuator from the first valve;a third valve which is connected between the first valve and the second hydraulic actuator, which is a bistable switching valve and which operates to either connect the second hydraulic actuator to the first valve or to disconnect the second hydraulic actuator from the first valve;a first sensor which provides a signal indicative of position of the first poppet valve;a second sensor which provides a signal indicative of position of the second poppet valve; andan electronic controller which receives the signals indicative of positions of the first and second poppet valves and which controls operation of all of the first, second and third valves to:open the first poppet valve by connecting the first hydraulic actuator to the source of pressurised fluid via the first and second valves;close the first poppet valve by connecting the first hydraulic actuator to the fluid return via the first and second valves;maintain the first poppet valve in position by using the second valve to disconnect the hydraulic actuator from the first valve;open the second poppet valve by connecting the second hydraulic actuator to the source of pressurised fluid via the first and third valves;close the second poppet valve by connecting the second hydraulic actuator to the fluid return via the first and third valves; and/ormaintain the second poppet valve in position by using the third valve to disconnect the hydraulic actuator from the second valve, wherein:each hydraulic actuator comprises a first piston having a pressure face on which supplied hydraulic fluid applies pressure, anda second piston also having a pressure face on which supplied hydraulic fluid applies pressure;the pressure face of the first piston is larger than the pressure face of the second piston; andduring opening of the first and second poppet valves the first and second pistons initially move together and then latterly the second piston moves alone.

29. A valve operating system as claimed in claim 28 wherein the first valve is a bistable switching valve which operates to either connect the second and third valves to the source of pressurised fluid or to connect the second and third valves to the fluid return.

30. A valve operating system as claimed in claim 28 which comprises a first valve spring which applies a closing force on the first poppet valve and a second valve spring which applies a closing force on the second poppet valve.

31. A valve operating system as claimed in claim 28 wherein the electronic controller controls valve lift of the first poppet valve by control of the second valve and by controlling duration of connection of hydraulic actuator to the first valve and the electronic controller controls valve lift of the second poppet valve by control of the third valve and by controlling duration of connection of the hydraulic actuator to the first valve.

32. A valve operating system as claimed in claim 28 wherein the electronic controller switches the first valve between connection to the source of pressurised fluid and connection to the fluid return only while the second valve disconnects the first hydraulic actuator from the first valve and only while the third valve disconnects the second hydraulic actuator from the first valve.

33. A valve operating system as claimed in claim 32 wherein the second valve connects the first actuator to the first valve only while the third valve disconnects the second actuator from the first valve and the third valve connects the second actuator to the first valve only while the second valve disconnects the first actuator from the first valve.

34. A valve operating system as claimed in claim 28 comprising a sensor which produces a signal indicative of crankshaft rotational position which is used by the electronic controller to determine timing of operation of the first, second and third valves.

35. A valve operating system as claimed in claim 28 wherein the electronic controller uses a look-up table to determine valve lift demands for the first and second poppet valves which then are used to control operation of the first, second and third valves.

36. A valve operating system as claimed in claim 35 wherein the electronic controller uses the signals indicative of poppet valve positions to provide feedback signals which are used to modify the valve lift demands in closed loop control of the hydraulic actuators.