GB2171454A - An adjustable valve actuator for an engine - Google Patents

Abstract

The actuator (10) comprises a body (11), which defines a fluid chamber (12); an output piston (13) disposed in a cylinder (14) opening onto the chamber (12) and connected to a push rod (15), which lifts a respective valve; a first input piston (16) disposed in the cylinder (17) a second input piston (18) disposed in a cylinder (19) and an adjusting device generally indicated at (20). The adjusting device controls the inward and outward movement of the second input piston (18) and hence the timing of the stroke of the output piston (13) to provide advanced exhaust valve opening timing at low engine speed without increasing the valve lift or the opening period determined by the cam (21). <IMAGE>

Description

SPECIFICATION An Adjustable valve actuator for an engine This invention relates to an adjustable valve actuator for an engine. In turbo diesel truck engines there are considerable problems in driving the turbo efficiently at low engine speeds because the mass flow from cylinder at low speeds is too low and typically the turbos operate at as little as 10% full power.

However, it is not possible to alter the gearing of the valve gear train so as to increase the mass flow at low speeds, because the stresses in the gear train at higher speeds would be quite unacceptable. In addition it is realised that the operation of an engine can be enhanced by suitable adjustment of the valve timing or total valve lift, but again there are problems in achieving this in a practical manner.

It is one object of the invention to provide an improved device or system for opening a valve of an engine.

From one aspect the invention consists in a device for opening a valve of an engine, comprising means for opening the valve in accordance with the engine cycle and means for modifying a property or parameter of the opening at at least one engine speed or in one engine speed range.

Thus the property or parameter modified may be the valve lift, valve timing or the rate of lift of the valve or any combination of these. Preferably the modifying means is adjustable with engine speed to vary the degree by which the property or parameter is modified. Additionally or alternatively the modifying means may be inhibited or rendered inoperative above a certain engine speed.

In one embodiment, at least, the modifying means may operate to modify the property or parameter in one part of the valve open period, in which case the modifying means may compensate for the initial modification of the property or parameter in another part of the valve open period. The object of this arrangement is to leave the total effect of the property the same, whatever the speed of the engine.

From another aspect the invention consists in a device for varying the rate of lifting of an engine valve at at least one engine speed or in one engine speed range.

In a preferred embodiment the rate of lifting the valve is higher in a lower speed range of an engine than it would be in the absence of the device and the total lifting of the valve is independent of engine speed. The device may include a hydraulic, mechanical, electric or electromechanical valve actuator. For example, it may include a hydraulic actuator comprising a hydraulic chamber, a first piston connected to lift the valve in accordance with the hydraulic pressure in the chamber, second and third pistons acting on the fluid in the chamber to vary the pressure thereof, a first cam means operable by the engine for moving the second piston, second cam means operable by the engine and operably connected to the third piston and means for adjusting the action of the second cam means on the third piston.

The third piston may be operated by a rocker arm and the adjustment means may vary the pivot of the rocker arm. For example, the adjustment means may be constituted by a rotatable control shaft and a crank mounted on the control shaft to pivotaily support the rocker arm so that rotation of the control shaft causes movement of the pivot of the rocker arm. In this case the rocker arm may be profiled to maintain a constant engagement with the third piston as the location of its pivot is adjusted. The adjustment means may be inhibited or rendered inoperative above a predetermined speed and the effect of the adjustment means may be varied in accordance with engine speed.

The first and second cam means may be profiled and located such that the second cam adds to the effect of the first cam during a first part of the valve open period and subtracts during a second part. Thus the cams may be arranged so that there is no overall change in the property with engine speed.

From another aspect the invention consists in a hydraulic control device comprising a fluid chamber, an output piston in hydraulic communication with fluid in the chamber, first and second input pistons and means for driving the first and second pistons into and out of the chamber such that during one part of the first piston cycle the second piston adds to the effect of the first piston and in a second part it subtracts from the effect of the first piston.

Although the invention has been defined above, it will be appreciated that it includes any inventive combination of the features set out above or in the following description. One object of the invention has been stated, but the invention is not limited to devices which fulfil this object.

The invention may be performed in various ways and a specific embodiment will now be described, with modifications, by way of example with reference to the accompanying drawings, in which: Figure 1 is a part sectional side view of a valve actuator; Figure 2 is a view on the arrow A in Figure 1; Figure 3 illustrates graphically the performance of the actuator; Figures 4a,b and c illustrate graphically the use of actuators of this type to achieve variable timing, rate and lift; and Figure 5 is a schematic representation of a mechanical equivalent to the actuator of Figure 1.

As has been previously explained there is a problem with providing sufficient mass flow to the turbo of a diesel engine at low speeds.

The exhaust pulse energy is a function of the rate at which the outlet valves in the engine lift and engine speed. The applicant has realised that because of the stress in the valve gear train it is not possible to increase the rate of lift for all engine speeds, and accordingly he has developed a device which will allow the valve to lift at its normal rate near the top of the engine design speed range, but will increase the rate of lift, with respect to the normal design, at lower engine speeds. A device for achieving this is illustrated in Figures 1 and 2.The device 10 comprises a body 11 which defines a fluid chamber 12; an output piston 13 disposed in a cylinder 14 opening onto the chamber 12 and connected to a push rod 15 which lifts a respective valve; a first input piston 16 disposed in a cylinder 17; a second input piston 18 disposed in a cylinder 19 and a variable actuating device generally indicated at 20.

The actuating device controls the inward and outward movement of the input pistons 16 and 18 and hence the pressure within the chamber 12. As this increases the output piston 13 is lifted and the valve opened. This opening takes place against a valve spring, not shown, which in turn pressurizes the fluid in the chamber 12 to return the input pistons 16 and 18.

Thus the actuating device 20 comprises a pair of cams 21,22 mounted on the engine cam shaft or a shaft connected thereto, a pivotai rocker arm 23 and means 24 for adjusting the position of the pivot of the rocker arm 23.

The main cam 21 is located and profiled to lift and lower the first input piston 16 in such a way that the push rod opens and closes the valve at the desired rate at the top speed of the engine,say 2,000 r.p.m.. This lift is shown in Figure 3 at line 1. The corresponding lift profile at 1,000 r.p.m. is shown at line 2.

The secondary cam 22 is profiled and located such that in association with the rocker arm 23 and adjustment means 24 the lift of the valve is adjusted to that shown in line 3 of Figure 3, over at least a wide range of engine speeds. Thus the secondary cam accelerates the rate of lift initially as compared with that provided at low speeds by the main cam lift so that the overall valve lift is the same whatever the engine speed (see the flat portion of the graph) and the lowering of the valve takes place totally in accordance with the main cam.

The secondary cam causes an addition to the lift followed by a subtraction, because it initially drives the second input piston 18 into its cylinder 19 and subsequently allows the return of that piston during the lift part of the first input piston stroke.

It will be seen from Figure 1 that the movement of the input piston 18 is dictated by the movement of the rocker arm 23. The extent to which the contact head part 25 of the rocker arm 23 drives the second input piston 18 depends on the position of the rocker arm pivot 26. Thus whilst the pivot 26 is in the position shown in Figure 1 the secondary cam will move the head part 25, and hence the second input piston 18, considerably. However, as the pivot 26 moves upwardly (as indicated in Figure 1) to its uppermost position, in which it lies on the longitudinal axis of the second input piston 18, the effect of the secondary cam is progressively reduced to zero.

This adjustment of the pivot and hence of the affect of the secondary cam 22 can be made speed dependent by mounting the pivot 26 on a rotatable control shaft 27 by means of cranks 28 and adjusting the rotational position of the control shaft in accordance with engine speed.

The actuating device 10 need not be hydraulic, but it may be mechanical, electric or electromechanical, depending on the valve drive system. Figure 4 illustrates a schematically mechanical arrangement in which the cams 21 and 22 act on a pair of pivotally connected levers and the valve lift is derived from the upper lever. By adjusting the point of the pivot 26 (as indicated), the effect of the secondary cam 22 can be modified. If the valve is moved by a helinoid a suitable electronic control system could be provided for modifying the current supplied to the coil spring.

It will be appreciated that the use of a secondary cam to modify the effect of the main cam in a speed dependent way has many applications. Figures 4a,b and c show how this system can be utilised to vary the timing, the rate and the lift of a valve. One important feature of the system is that the secondary cam cam be used to compensate for the initial modification so that, for example, the total lift is the same whatever the engine speed.

Claims (21)

1. A device for opening a valve of an engine comprising means for opening the valve in accordance with the engine cycle and means for modifying a property or parameter of the opening at at least one engine speed or in one engine speed range.

2. A device as claimed in Claim 1, wherein the property or parameter modified is valve lift, valve timing or the rate of lift of the valve or a combination of these.

3. A device as claimed in Claim 1 or Claim 2, wherein the modifying means is adjustable with engine speed to vary the degree by which the property or parameter is modified.

4. A device as claimed in any one of the preceding claims, wherein the modifying means is inhibited or rendered inoperative above a certain engine speed.

5. A device as claimed in any one of the preceding claims, wherein the modifying means operates to modify the property or parameter in one part of the valve open period.

6. A device as claimed in Claim 5, wherein the modifying means compensates for the initial modification of the property or parameter in another part of the valve open period.

7. A device for varying the rate of lifting of an engine valve at at least one engine speed or in one engine speed range.

8. A device as claimed in Claim 7, wherein the rate of lifting the valve is higher in a lower speed range of the engine, than it would be in the absence of the device.

9. A device as claimed in Claim 7 or Claim 8, wherein the total lifting of the valve is independent of engine speed.

10. A device ss claimed in any one of Claims 7 to 9 having a hydraulic, mechanical, electric or electro-mechanical valve actuator.

11. A device as claimed in any one of Claims 7 to 9, wherein the device includes a hydraulic actuator, comprising a hydraulic chamber, a first piston connected to lift the valve in accordance with the hydraulic pressure in the chamber, second and third pistons acting on the fluid in the chamber to vary the pressure thereof, a first cam means operable by the engine for moving the second piston, second cam meana operable by the engine and operably connected to the third piston and means for adjusting the action of the second cam means on the third piston.

12. A device as claimed in Claim 11, wherein the third piston is operated by a rocker arm and the adjustment means varies the pivot of the rocker arm.

13. A device as claimed in Claim 11 or Claim 12, wherein the adjustment means is constituted by a rotatable control shaft and a crank mounted on the control shaft to pivotally support the rocker arm so that rotation of the control shaft causes movement of the pivot of the rocker arm.

14. A device as claimed in Claim 13,wherein the rocker arm is profiled to maintain a constant engagement with the third piston as the location of its pivot is adjusted.

15. A device as claimed in any one of Claims 11 to 14, wherein the adjustment means is inhibited or rendered inoperative above a predetermined speed.

16. A device as claimed in any one of Claims 11 to 15, wherein the effect of the adjustment means is varied in accordance with engine speed.

17. A device as claimed in any one of Claims 11 to 16, wherein the first and second cams are profiled and located such that the second cam adds to the effect of the first cam during a first part of the valve open period and subtracts during a second part.

18. A device as claimed in Claim 17 wherein the cams are so arranged that there is no overall change in the property with engine speed.

19. A hydraulic control device comprising, a fluid chamber, an output piston in hydraulic communication with fluid in the chamber, first and second input pistons and means for driving the first and second pistons into and out of the chamber such that during one part of the first piston's cycle and the second piston adds to the effect of the first piston and in a second part it subtracts from the effect of the first piston.

20. A device for opening a valve of an engine substantially as hereinbefore described with reference to the accompanying drawings.

21. A hydraulic control device substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.