GB2272022A - Variable timing valve gear. - Google Patents

Abstract

Rockers 16, 22 operated by respective cams 11, 12 or a circular lobe and a cam are rocked in opposite directions about respective fulcrums 14, 26. When the piston fulcrum 26 is hydraulically actuated at higher engine speeds and/or loads the higher lift cam 12 or the cam is operative to open the valve 27. In the actuated position of the fulcrum 26 pistons in the fulcrum (Figs. 6 and 7) or in the surrounding cylinder head (Figs. 8 to 13) are projected hydraulically to hold the fulcrum in position. The maximum outward fulcrum movement may be determined by a pin (120, Fig. 10) in its mounting bore or by a stepped fulcrum formation (Fig. 14). A third rocker (32, Fig. 3) may be operated by a cam 13 providing a lift intermediate that of the cams 11, 12 and operate a respective engine inlet or exhaust valve in the same or an adjacent cylinder to the valve 27. <IMAGE>

Description

CAM MECHANISM The invention relates to cam mechanisms for controlling valve means and relates in particular to valve cam mechanisms for controlling the inlet and/or exhaust valve of an internal combustion engine, with the aim of improving the torque, fuel economy and emissions output of said engine.

Traditional cam mechanisms for engines use a cam shaft with a single cam profile to drive the inlet and exaust valves of the engine. However, this arrangement is disadvantageous since the cam profile used to drive the valves is the same at all engine speeds and loads.

However, to optimise engine efficiency, valve motion should be varied with engine speed and load. Typically high lift and high duration cam profiles are suited for high speed and high load conditions and low lift low duration cams are ideal for low speeds/low load operation of an engine. It is beneficial to vary the opening period of inlet and exhaust valves in terms of degrees of crankshaft rotation with varying engine speed, since the total time of each engine cycle varies considerably with engine speed.

In the International application PCT/GB 91/00232, published as WO 91/12415, a solution to the problems of traditional cam shaft engines is proposed. The specification describes a cam mechanism for controlling the inlet and/or exhaust valve of an internal combustion engine. The cam mechanism describes cam shaft means with first and second cam means mounted thereon for rotation therewith. First and second finger followers are provided having first and second follower means respectively arranged to follow the surface of the first and second cam means. The first and second finger followers are rockable about fulcrum means which hold the finger followers in engagement with the cam means.

The finger followers engage a valve to permit control of the valve by the cam means. The first cam means has a different cam profile to the second cam means.

Therefore, the first cam means, the first follower means and the first finger follower together act as a first short duration cam mechanism for low speeds of the engine, with the fulcrum means being in a first position at low speeds of the engine wherein the first cam follower is in engagement with the first cam means. At higher engine speeds the fulcrum means is moved to a second position where the second cam follower is in engagement with the second cam means, the second follower means and the second finger follower acting as a long duration cam mechanism for the engine.

In internal combustion engines with the technology of the present day there is a trend towards using multi-valve engines and therefore space at the cylinder head is very limited. It is accordingly important to ensure that cam mechanisms at the cylinder head are kept as compact in size as possible. It is also very important to keep the arrangement as simple as possible. In particular, it is important to keep the number of oil galleries required for operation of the cam mechanism to a minimum, due to machining difficulties involved.

Cam mechanisms operate at high operating frequencies and therefore it is important to keep frictional losses in the mechanism as low as possible.

This is especially important in a cam operating mechanism since if surfaces wear down the timing of the operated valve can be altered.

In a first aspect, the present invention provides a cam mechanism for controlling the valve means of an internal combustion engine or compressor comprising camshaft means having first and second cam means mounted thereon for rotation therewith and first and second finger followers respectively arranged to be engageable directly or indirectly with the first and second cam means, the first and second finger followers being rockable about fulcrum means operable to engage the first and second finger followers with the cam means and the valve means to thereby permit control of the valve means by the cam means, in which the first cam means and the first finger follower operate as a first short duration and/or low lift cam mechanism for low speeds and/or loads of the engine, the fulcrum means being in a first position at low speeds and/or loads wherein the first finger follower is in engagement with the first cam means and the valve means is controlled by the first cam means, and in which the second cam means and the second finger follower operate as a second long duration and/or high lift cam mechanism for high speeds and/or loads of the engine, the fulcrum means being in a second position at high speeds and/or loads of the engine wherein the second finger follower is in engagement with the second cam means and the valve means is controlled by the second cam means, characterised in that the first finger follower rocks about the fulcrum means in the opposite rotational sense to the rocking motion of the second finger follower.

In the first aspect of the invention the first and second cam means will all have cam profiles, the cam profile of the first cam means being suited to low speed and/or low load operation of the engine and the cam profile of the second cam means being suited to high speed and/or high load operation of the engine.

The present invention provides in a second aspect a cam mechanism for controlling the valve means of an internal combustion engine or compressor comprising camshaft means having circular lobe means and cam means mounted thereon for rotation therewith and first and second finger followers respectively arranged to be engageable directly or indirectly with the circular lobe means and the cam means, the first and second finger followers being rockable about fulcrum means operable to engage the first and second finger followers with the circular lobe means, the cam means and the valve means to thereby permit activation and deactivation of the valve means, in which the circular lobe means and the first finger follower operate as a valve deactivation mechanism at low speeds and/or loads of the engine, the fulcrum means being in a first position at low speeds and/or loads wherein the first finger follower is in engagement with the circular lobe means and the valve means is deactivated, and in which the cam means and the second finger follower operate as a second long duration and/or high lift cam mechanism for high speeds and/or loads of the engine, the fulcrum means being in a second position at high speeds and/or loads of the engine wherein the second finger follower is in engagement with the cam means and the valve means is activated and the motion of the valve means is controlled by the cam means, characterised in that the first finger follower rocks about the fulcrum means in the opposite rotational sense to the rocking motion of the second finger follower.

In the second aspect of the invention the valve means is deactivated at low engine speeds and/or low engine loads since the circular lobe means provides no valve lift. At higher engine speeds and/or loads the valve will be activated by the lift profile of the cam means.

The present invention also provides in a third aspect a cam mechanism for controlling the valve means of an internal combustion engine or compressor comprising cam shaft means having first and second cam means mounted thereon for rotation therewith and first and second finger followers respectively arranged to be engageable directly or indirectly with the first and second cam means, the first and second finger followers being rockable about fulcrum means operable to engage the first and second finger followers with the cam means and the valve means to thereby permit control of the valve means by the cam means, in which the first cam means and the first finger follower operate as a first short duration and/or low lift cam mechanism for low speeds and/or loads of the engine, the fulcrum means being in a first position at low speeds and/or loads wherein the first finger follower is in engagement with the first cam means and the valve means is controlled by the first cam means, and in which the second cam means and the second finger follower operate as a second long duration and/or high lift cam mechanism for high speeds and/or loads of the engine, the fulcrum means being in a second position at high speeds and/or loads of the engine wherein the second cam follower is in engagement with the second cam means and the valve means is controlled by the second cam means, wherein the fulcrum means for the second finger follower is moveable and comprises a piston moveable in a piston bore in a cylinder head of the engine or compressor under the influence of oil pressure supplied to the piston bore by a first oil passage in the cylinder head, locking means being provided to releasably secure the piston relative to the cylinder head, the locking means being characterised by a locking pin moveable in a chamber in the cylinder head from a first position in which the locking pin is at least partially withdrawn into the cylinder head and does not engage the piston to a second position in which the locking pin extends into the piston bore to engage the piston.

In the third aspect of the invention the first and second cam means will have cam profiles different to one another and the cam profile of the first cam means will be suited to low speed and/or high load engine operating conditions and the cam profile of the second cam means will be suited to high speed and/or high load operating conditions.

The present invention provides in a fourth aspect a cam mechanism for controlling the valve means of an internal combustion engine or compressor comprising cam shaft means having circular lobe means and cam means mounted thereon for rotation therewith and first and second finger followers respectively arranged to be engageable directly or indirectly with the circular lobe means and the cam means, the first and second finger followers being rockable about fulcrum means operable to engage the first and second finger followers with the circular lobe means, the cam means and the valve means to thereby permit activation and deactivation of the valve means, in which the circular lobe means and the first finger follower operate as a valve deactivation mechanism at low speeds and/or loads of the engine, the fulcrum means being in a first position at low speeds and/or loads wherein the first finger follower is in engagement with the circular lobe means and the valve means is deactivated, and in which the cam means and the second finger follower operate as a second long duration and/or high lift cam mechanism for high speeds and/or loads of the engine, the fulcrum means being in a second position at high speeds and/or loads of the engine wherein the second cam follower is in engagement with the cam means and the valve means is activated and the motion of the valve means is controlled by the cam means, wherein the fulcrum means for the second finger follower is moveable and comprises a piston moveable in a piston bore in a cylinder head of the engine or compressor under the influence of oil pressure supplied to the piston bore by a first oil passage in the cylinder head, locking means being provided to releasably secure the piston relative to the cylinder head, the locking means being characterised by a locking pin moveable in a chamber in the cylinder head from a first position in which the locking pin is at least partially withdrawn into the cylinder head and does not engage the piston to a second position in which the locking pin extends into the piston bore to engage the piston.

In the fourth aspect of the invention the controlled valve will be deactivated at low engine speeds and/or low engine loads since the circular lobe will provide no lift. At high engine speeds and/or high engine loads the valve will be activated by the lift of the cam means.

In both of the third and fourth aspects of the invention the locking pin is arranged to ease installation of the cam mechanism and keep the reciprocating mass in the mechanism to a minimum.

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings in which; Figure 1 is a cross-sectional view of a cam mechanism according to the invention in a first operating condition, Figure 2 is a cross-sectional view of the cam mechanism of Figure 1 in a second operating condition, Figure 3 is a simplified plan view of the cam mechanism shown in Figure 1, Figure 4 is a side elevational view of one component of the cam mechanism shown in Figures 1 and 2, Figure 5 is a side elevation of a second component of the cam mechanism shown in Figures 1 and 2, Figure 6 is a schematic representation of a first embodiment of fulcrum means suitable for use in the cam mechanism of Figures 1 and 2, Figure 7 is a schematic representation of a second embodiment of fulcrum means suitable for use in the cam mechanism of Figures 1 and 2, Figure 8 is a schematic representation of a third embodiment of the fulcrum means suitable for use in the cam mechanism shown in Figures 1 and 2, Figure 9 is a schematic representation of a fourth embodiment of fulcrum means suitable for use in the cam mechanism shown in Figures 1 and 2, Figures 10a and lOb are schematic representations of a fifth embodiment of fulcrum means suitable for use in the cam mechanism of Figures 1 and 2, Figures 11 and lia are schematic representations of a sixth embodiment of fulcrum means suitable for use in the cam mechanism ofFigures 1 and 2, Figure 12 is a schematic representation of a seventh embodiment of fulcrum means suitable for use in the cam mechanism of Figures 1 and 2, Figure 13 is a schematic representation of an eighth embodiment of fulcrum means suitable for use in the cam mechanism of Figures 1 and 2, Figure 14 is a schematic representation of a ninth embodiment of fulcrum means suitable for use in the cam mechanism of Figures 1 and 2.

Turning to Figure 1, there can be seen a cam shaft 10 having three cams 11, 12 and 13. The cam profile of cam 11 is of a first lift, the cam profile of cam 13 (shown in dotted lines) is a cam profile surface with greater lift than the surface 11. The cam profile surface of cam 12 is the cam profile surface of highest lift. The three cams 11, 12 and 13 are spaced axially along the cam shaft 10. The high lift cam 12 is located adjacent to and in between the two cams 11 and 13.

A rocker shaft 14 is provided which has an oil gallery 15 running axially therethrough.

In Figure 1 it can be seen that a finger follower 16 is mounted for rotation about the rocker shaft 14. A roller 17 is rotatably mounted to the finger follower 16.

The finger follower 16 can be seen in greater detail in Figure 4, which shows the component of the cam mechanism in isolation from the other components of the cam mechanism. The aperture 18 shown in Figure 4 allows the finger follower 16 to be rotatably mounted on the rocker shaft 14.

A hydraulic lash adjuster 19 is mounted in a recess provided in the finger follower 16. The hydraulic lash adjuster is supplied by oil through an oil gallery shown in dotted lines in Figure 4. The oil gallery 20 communicates with the aperture 18 and in use will communicate with an aperture in the rocker shaft 14 which allows oil to flow from the oil passage 15 to the oil passage 20.

A cylindrical bore 21 can be seen in dotted lines in Figure 4. The cylindrical bore is designed to receive a locating pin of a second finger follower 22 shown in Figure 1.

The second finger follower 22 is shown in detail in Figure 5. The locating pin 23 of the finger follower can be seen clearly in Figure 5 and in use of the cam mechanism the connecting pin 23 is engaged in the cylindrical bore 21 of the first finger follower.

The second finger follower 22 has a wear pad 24 located on its upper surface. A roller 25 is rotatably mounted to the finger follower 22 at one end thereof.

In use, the wear pad 24 of the second finger follower 22 is arranged such that it can be brought into and out of contact with the central high lift cam 12.

The roller 25 is positioned on fulcrum means 26 which will be described later.

In Figure 1 an inlet or exhaust valve 27 of an engine can be seen with a valve stem 28. The top of the valve stem 28 contacts the hydraulic lash adjuster 19 of the finger follower 16. A collar 29 is attached to the valve stem 28 and a biasing spring 30 acts between the engine block and the collar 29 to bias the valve 27 into engagement with its valve seat and to bias the valve stem 28 into engagement with the bottom of the hydraulic lash adjuster 19.

In Figure 1 there can be seen an oil gallery 31 which is machined in the cylinder head of the engine to provide oil to the fulcrum means 26.

Looking now at Figure 3 which is a plan view of the embodiment shown in Figure 1, the rocker shaft 14 can be clearly seen as can the first and second finger followers previously described. The plan view clearly shows the connecting pin 23 located in the recess 21 of the first finger follower 16.

In the plan view of Figure 3 a third finger follower 32 can be seen. The third finger follower 32 is virtually a mirror image of the first finger follower 16. Like the first finger follower 16, the third finger follower 32 has a hydraulic lash adjuster 33 (shown in dotted lines) and a roller 34. In use of the cam mechanism the roller 34 will contact the surface of the cam 13 (which is shown in dotted lines in Figure 1).

There is an important difference between the cam follower 32 and the cam follower 16. The important difference is the provision of a slot 35 which is shown in dotted lines in Figure 1. The connecting pin 23 of the finger follower 22 extends on both sides of the finger follower. As previously mentioned, one side of the connecting pin 23 is securely engaged in a cylindrical bore 21 of the finger follower 16. The other side of the connecting pin 23 is located in a slot 35 machined in the third finger follower 32. The slot 35 is a lost motion slot, the purpose of which will be described later.

The hydraulic lash adjuster 33 of the finger follower 32 will have a lower surface in contact with an inlet or exhaust valve (not shown) which is in line with the valve 27, but spaced from the valve 27 along the length of the rocker shaft 14. The second valve could be a valve of the same cylinder of the internal combustion engine (for instance two inlet valves might be controlled one each by the finger followers 16 and 32). Alternatively, the valves controlled could be valves of different cylinders of the engine.

The method of operation of the cam mechanism of the invention will now be described. When the valve cam mechanism is used in an internal combustion engine the cam shaft 10 will be driven to rotate at a speed equal to or proportional to the speed of the crankshaft of the engine. The three cams 11, 12 and 13 on the cam shaft 10 will rotate at the same speed. In Figure 1, the cam mechanism is shown in its configuration for high engine speed loads, in which the fulcrum means 26 is located in an upper position to bring the wear pad 24 into contact with the cam 12.Since the cam 12 is the cam of highest lift and since the finger followers 22, 16 and 32 are all linked, the finger followers 16 and 32 will both be displaced by the cam 12 and accordingly both of the valves engaged by the finger followers 16 and 32 will be controlled by the profile of the cam 12, with the wear pad 24 engaging and following the surface of the cam 12. The finger followers 16 and 32 are constrained to rotate about the rocker shaft 14. Therefore during the rocking motion of the finger followers the finger follower 22 rotates with respect to the finger followers 16 and 32 in the opposite rotational sense of rocking.

The central finger follower 22 will also be displaced in relation to the fulcrum means 26, with such motion allowed by the roller 25, which rolls back and forth along the top surface of the fulcrum means 26. The frictional losses of the arrangement and the wear of the fulcrum means 26 are both minimised by the provision of the roller 25.

As mentioned above, Figure 1 shows the high engine speed/high engine load configuration of the cam mechanism, with the fulcrum means 26 in the upper position. Figure 2 shows the cam mechanims in its low engine speed/low engine configuration, with the fulcrum means 26 lowered to its lowermost position. The lowering of the fulcrum means 26 has caused lowering of the wear pad 24 and has taken the wear pad 24 out of engagement with the cam 12. In this configuration the valve 27 is driven by the finger follower 16 following cam 11 and also the valve driven by the finger follower 32 is driven by engagement of the roller 34 with the cam 13. The rollers 17 and 34 follow the cam profile surface of the cams 11 and 13 and the finger followers 16 and 32 rock about the rocker shaft 14 under the influence of the cams 11 and 13 to displace the valves of the engine.

It will be noted that the lift of the cam 13 is greater than the lift of the cam 11. The difference in cam lift is accomodated by the lost motion slot 35.

Whilst the locating pin 23 of the central finger follower 22 is securely located in a bore in the cam finger follower 16, it is slidable in the lost motion slot 35 and therefore relative motion between the finger follower 16 and finger follower 32 is allowed by sliding of the connecting pin 23 in the lost motion slot 35.

Embodiments of the fulcrum means 26 will now be described with reference to Figures 6 to 12. In Figure 6 there can be seen fulcrum means 26 which comprises the piston member 60 slidable within a bore 61 provided in the cylinder head of the engine. An oil gallery 62 is provided which communicates with the bore 61. Two locking pins 63 and 64 are provided in the piston 60 which are slidable radially of the piston 60 in radial slots provided in the piston 60. A circumferential recess 65 is provided in the cylinder head in communication with an oil gallery 66.

To operate the fulcrum means of Figure 6 it is necessary to provide valves controlling the supply of oil pressure to the galleries 66 and 62. To bring the fulcrum means into the uppermost position and to lock it in that position full oil pressure is supplied in the gallery 62 and this has the effect of forcing the piston 60 upward in the bore 61 and also has the effect of forcing the locking pins 63 and 64 radially outwardly of the piston 60 to lock in the annular recess 65. To hold the pins in the annular recess 65 raised oil pressure is maintained in the oil gallery 62.

To allow the fulcrum means to return to its lower position, oil pressure is supplied in the gallery 66 which communicates with the circumferential recess 65.

The oil pressure in the oil gallery 62 is reduced to zero. In this way, the locking pins 63 and 64 are forced radially inward of the piston 60 and the piston 60 is forced downward in the bore 61 under the force of the roller 25 when the wear pad 24 is next in contact with the high lift portion of the cam 12.

The fulcrum means shown in Figure 6 corresponds to the fulcrum means shown in PCT/GB 91/00232. It is disadvantageous in two respects. In the first respect, problems with lash adjustment can arise if the low pressure condition of the oil gallery 62 is too high and a force is applied to the finger followers which tends to compress the lash adjusters in the mechanism. It is also disadvantageous since the locking pins need aligning with the circumferential recess 65, which can cause complexity of manufacture.

The embodiment of the fulcrum means shown in Figure 7 solves the problem of compression of the lash adruetee. In the embodiment a piston 70 is moveable in a bore 71 in the cylinder head. An oil gallery 72 is provided which communicates with the bore 71 and an oil gallery 73 is provided which communicates with a circumferential recess 74 surrounding the bore 71. Pins 75 and 76 are provided in the piston 70 which are moveable radially of the piston 70 in radial slots provided in the piston. A spring 77 is fitted between the locking pins 75 and 76.

To bring the fulcrum means to its uppermost position full oil pressure is supplied in the oil gallery 72 which forces the piston 70 upwardly in the bore 71. The force of spring 77 and the pressure of oil in the bore 71 both force the locking pins 75 and 76 outwardly of the piston 70 to engage the circumferential recess 74.

To maintain the fulcrum means in the uppermost position it is not necessary to apply any oil pressure to the gallery 72, since the biasing spring 77 maintains the locking pin 75 and 76 in secure engagement with the circumferential recess 74.

To allow the fulcrum means to be displaced downwardly full oil pressure is supplied in the gallery 73, with the oil pressure in the gallery 72 being kept at zero. The pins 75 and 76 are displaced radially inwardly of the piston 70 by the oil pressure in the gallery 73, against the biasing force of the spring 77.

Downward motion of the piston 70 in the bore 71 is thus allowed.

The embodiment of the fulcrum means shown in Figure 7 does not have the tendency to cause unwanted compression of the hydraulic lash adjusters present in the cam mechanism since no oil pressure is needed to keep the fulcrum means in its uppermost position.

The embodiments of the fulcrum means shown in Figures 6 and 7 both require complex machining operations since the pistons 60 and 70 will be small components and therefore machining is difficult.

Furthermore, the presence of the locking pins within the pistons 60 and 70 necessitate the use of pistons of a certain diameter and this can be disadvantageous since it is beneficial to keep the cam mechanism as compact as possible. Solutions to these problems are provided by the embodiments of Figures 8 and 9.

In Figure 8 a piston 80 is provided which is slidable in a bore 81 provided in the cylinder head of the engine. An oil gallery 82 is provided in communication with the bore 81. A cicumferential recess 83 is machined in the exterior surface of the piston 80. Cylindrical bores 84 and 85 extend radially of the bore 81 in the cylinder head.

Pistons 86 and 87 are respectively provided in the bores 84 and 85. Oil galleries 88 and 89 are respectively provided in communication with the bores 84 and 85. Springs 90 and 91 are provided in the bores 84 and 85 to bias the pistons 86 and 87 radially outwardly of the bore 81.

To bring the fulcrum means to its uppermost position pressure is supplied to the oil galleries 82, 88 and 89. Thus the oil pressure in the bore 81 forces the piston 80 upwardly and the oil pressure in the bores 84 and 85 forces the locking pins 86 and 87 radially inwardly, the locking pins 86 and 87 engaging the circumferential recess 83 of the piston 80 to lock it in position. To hold the fulcrum means in the uppermost position oil pressure is required in the oil galleries 88 and 89 only. Thus there is no tendency for the piston 80 to be forced upwardly in the bore 81 when held in the uppermost position and unwanted compression of hydraulic lash adjusters in the cam mechanism is avoided.

The fulcrum means is allowed to return to its lowermost position by simply switching off the oil pressure in the three Oil galleries , aa and a9. The locking pins 87 and 86 will be forced radially outwardly by the biasing springs 90 and 91.

It will be appreciated that the fulcrum means shown in Figure 8 is very simply controlled, requiring a simple on/off of oil pressure.

Figure 9 shows a fourth embodiment of the fulcrum means for the cam mechanism. The fourth embodiment illustrated comprises a piston 100 moveable in a bore 101. An oil gallery 102 is provided in the cylinder head in communication with the bore 101. A circumferential recess 103 is machined in the exterior of the piston 100.

Two bores 104 and 105 are machined in the cylinder head and extend radially of the bore 101. Two locking pins 106 and 107 are respectively located in the bore 104 and 105. Biasing springs 108 and 109 are provided to bias the locking pins 106 and 107 radially inwardly towards the cylinder bore 101.

The bores 104 and 105 are machined in two portions; portions 104A and 105A are of first heights and portions 104B and 105B are of second reduced heights. The locking pins 106 and 107 are formed with portions of corresponding heights 107A, 107B and 106A and 106B. As can be seen in Figure 9 chambers 112 and 113 are formed between the locking pins 107 and 106 and the bores 104 and 105. These chambers communicate with two oil galleries 110 and 111.

To bring the fulcrum means to the uppermost position pressure is supplied in the oil gallery 102 which forces the piston 100 upwardly. The two locking pins 106 and 107 are forced inwardly by the springs 108 and 109 to lock in the recess 103 of the piston 100. To hold the piston 100 in its uppermost position oil pressure is turned off to all three oil galleries 110, 111 and 102. The biasing springs 108 and 109 hold the locking pins 107 and 106 in engagement with the piston 100.

To allow the piston 100 to return to its lowermost position oil is supplied to the two galleries 110 and 111, with the oil pressure in the oil gallery 102 being held at zero. The oil pressure in the galleries 110 and 111 communication with the chambers 112 and 113 forces the locking pins radially outward of the piston 100 to disengage the annular recess 103.

Since oil pressure is not required to hold the piston 100 in its uppermost position there is no tendency for the actuator piston 100 to cause unwanted retraction of the hydraulic lash adjusters of the cam mechanism. The system has a very simple oil control, with on/off control to the three oil galleries being required.

All of the above described arrangements of fulcrum means have two disadvantages. First, each requires at least two oil galleries for operation. Secondly, each has a problem of alignment since there are two contradictory requirements for the locking pins and the recesses in which they lock. To prevent unwanted motion of the fulcrum means in its locked state there should not be excessive clearance between the locking pins and the recesses. However, certain clearances must be allowed for the locking pins to move into the recesses during motion of the piston. Both of these problems can be solved by a principle as illustrated in Figure 10a and 10b.

In Figure 10a and lOb it can be seen that a pin 120 is provided in the actuator bore 121 provided in the cylinder head. A piston 122 of the fulcrum means is provided with a suitable abutment surface for engagement with the pin 120. By provision of the pin 120 and the abutment surface on the piston 122 it is possible to allow full oil pressure to remain present acting on the bottom surface of the piston 122 when it is in its uppermost position without risking the overriding or compression of hydraulic lash adjusters present in the cam mechanism system. Therefore the operation of the fulcrum means shown in Figure 10 can be quite simple with full oil pressure- being supplied to one oil passage 123 in communication with the bore 121 both when the actuator piston 122 should be moved upwardly and also when the actuator piston 122 should be maintained in position.When the actuator piston should be allowed to return to its lowermost position then the oil pressure in the gallery 123 is reduced to zero.

The provision of the pin in the bore 121 and an abutment surface on the piston 122 of the fulcrum means and also allows direct and secure alignment of locking pins with recesses and therefore locking pins can be provided which are a tight fit (ie. with little clearance) in a bore. Thus negligible movement of the piston of the fulcrum means is allowed when locked in place. Such an arrangement can be seen in Figures lia and lib.

In Figure lla the piston 130 is slidable in a bore 131 machined in the cylinder head. The piston 130 has a bore 132 therethrough. The piston 130 has an abutment surface for abutting a pin 133 secured to the cylinder head (see Figure llb).

A single oil gallery 134 is provided which communicates with the bore 131 and also communicates through tubes 135 and 136 with two bores 137 and 138 which extend radially of the bore 131. Located in the bores 137 and 138 are two locking pins 139 and 140 which are slidable in the bores. The locking pins 139 and 140 are biased away from the bore 131 by two biasing springs 141 and 142.

When activation of the fulcrum means is required, full oil pressure is supplied to the oil gallery 134 which is communicated to the bore 131 and by the passages 135 and 136 to the bores 137 and 138. The oil pressure causes the piston 130 to move upwardly within the bore 131. The oil pressure also causes the locking pins 139 and 140 to move inwardly to engage the bore 132 of the piston 130. The locking pins 139 and 140 will engage with the bore 132 when the piston 130 comes up against the pin 133 extending across the bore 131.

To hold the piston 130 in its uppermost position full oil pressure is maintained in the oil gallery 134.

There is no danger of the piston 130 moving upwardly to cause unwanted compression of hydraulic lash adjuster elements since the piston 130 is held firmly in abutment with the locking pin 133.

The locking pins 139 and 140 can be circular in the embodiment of Figure 11 since the arrangement will not allow rotation of the piston 130 and alignment of the piston is not a problem. Thus a tight and secure engagement of the locking pins can be achieved.

To allow the piston 130 to be returned to its lowermost position the oil pressure in the gallery 134 is to be brought to zero so that the locking pins 139 and 140 are brought out of engagement with piston 130 by the biasing springs 141 and 142.

The embodiment of the Figure lla and llb can be modified as shown in Figure 12. In Figure 12 a slidable pin 150 is provided which is slidable radially of a piston 151 mounted to be slidable in a bore 152 in the cylinder head. A single oil gallery 153 communicates by a passage 154 with a bore 155 extending radially of the bore 152. In the bore 155 a slidable locking element 156 is located. On the opposite side of the bore 152 in alignment with the bore 155 is a second bore 162 which contains a slidable piston 157 urged towards the bore 152 by a spring 158. The locking member 157 has a stop member 159 which engages a shoulder portion of bore 162 to prevent the locking element 157 from extending into the bore 152.

To bring the fulcrum means to its uppermost position oil pressure is supplied in the gallery 153 which acts in the bores 152 and 155. The pressure in bore 152 causes upward motion of the piston 151 and causes radially inward motion of the locking element 156. The locking element 156 engages the bore in the piston 151 and pushes the locking element 150 out of the bore in the piston 151. The piston 150 abuts the piston 157 and causes it to move radially outwardly of the bore 152 against the biasing force of the spring 158.

The piston 151 is held in its uppermost position by maintaining full oil pressure in the gallery 153.

The piston 151 is allowed to return to its lowermost position when the pressure in the oil gallery 153 is brought back to zero and the biasing spring 158 forces the piston 157 radially inwardly towards the piston 151, forcing the locking pin 150 back within the piston 151 and forcing the locking pin 156 back within the bore 155.

The locking pin 150 shown in the Figure 12 has two spherical ends 160 and 161 at each end to allow for inaccuracies in alignment.

The embodiment of Figure 12 will have a pin extending across the bore 152 and an engagement surface provided on the piston 151 in a similar fashion to the embodiment of Figures lla and b.

The embodiment shown in Figures 11a and b and in Figure 12 will have the advantage of requiring just one oil gallery and simple on/off control of oil pressure to the oil gallery.

Figure 13 shows a fulcrum means comprising a piston 170 slidable within a bore 171. An oil gallery 181 communicates with the bore 171. Two bores 174 and 175 extend radially of the bore 171 and locking pins 172 and 173 are slidable in the bores. Oil passages 176 and 177 are provided to allow fluid communication between the oil passage 181 and the two bores 174 and 175.

A bore is provided in the piston 170 which extends through the piston 170. Two biasing members 178 and 179 are slidable in the bore of the piston 170. Each biasing member 178 and 179 has a hemispherical end portion. A biasing spring 180 acts between the two biasing members.

The piston 170 is brought to its upper position and locked there by supplying oil pressure to the oil gallery 181. The oil pressure in gallery 181 is communicated via the passages 176 and 177 to the bores 174 and 175 and the locking pins 172 and 173 are forced radially inwardly.

A pin will be provided in the bore 181 and a mating abutment surface provided on the piston 170 to limit the upward motion of the piston 170. When the piston 170 reaches its upper limit of motion the locking pins 172 and 173 align with the biasing members 172 and 173 and push them radially inwardly against the biasing force of spring 180. The locking pins 172 and 173 thus lock the piston 170 in position.

The piston 170 is held in its uppermost position by maintaining oil pressure in oil gallery 181.

Unwanted compression of hydraulic lash adjuster elements is avoided by limiting the upward motion of the pistons 170.

To allow the piston 170 to be pushed downwardly in the bore 171, the oil pressure in the gallery 181 is brought to zero and the locking pins 172 and 173 are pushed radially outwardly by the biasing spring 180.

The operation of the fulcrum means of Figure 13 is simple, requiring only an ON/OFF supply of oil pressure.

Rather than using a pin 133 which extends tangentially of a bore, the bore in which the fulcrum piston moves can be provided with a stepped diameter, as shown in figures 14a and 14b. In figures 14a and 14b a piston 190 is provided with a first portion 190a of a first diameter and second portion 190b of second increased diameter. Figure 14a shows the piston 190 in its lowermost position in use and figure 14b shows the piston in its uppermost position. The bore 191 is provided with two different portions of corresponding diameters. The stepped diameter of the bore 191 provides an abutment surface which is abutted by the shoulder provided by the stepped diameter of the piston 190 when the piston 190 is in its uppermost portion (see figure 14b). The upward motion of the piston 190 is thus limited and the problem of compression of hydraulic lash adjusters is avoided.The alignment of locking pins for the piston 190 is also eased. The locking pins arrangement for piston 190 could be of any form but wuld preferably be as shown in figures gila, llb, 12 and 13.

In all of the above-noted embodiments suitable valve means will be provided to control the pressure of oil to the oil galleries for the fulcrum means. The valve means will typically be servo-valves controlled by an electronic engine management system. The electronic management system will cause switching of the fulcrum means from one position to the other with changes in engine speed and load.

The cam mechanism described in Figures 1 to 5 in detail could have any of the above-noted switching fulcrum means or could have any other fulcrum means. It is also possible to replace the wear pad 24 of the finger follower 22 of the cam mechanism with a roller.

Conversely, it is possible to replace the roller 25 with a surface acting on a wear pad provided on the fulcrum means 26. However, it is more beneficial to have the roller provided at the point of contact with the fulcrum means than a roller provided at the point of contact with the cam means. This is because contact will exist between the finger follower 22 and the fulcrum means 26 for all operating conditions of the mechanism, whilst contact will only exist between the wear pad 24 and the cam 12 at high speed conditions.

Again, it should be appreciated that the rollers 17 and 34 could be replaced by wear pads. Furthermore, the cam mechanism shown in the drawings need not have hydraulic lash adjusters as shown and instead adjustment could be provided for by using shims.

Whilst in the cam mechanism embodiment described in Figures 1 to 5 the profile of cam 11 is different to the profile of cam 13, the profiles of both cams could be chosen to be identical, in which the lost motion slot 35 would not be required and the locating pin 23 of the follower 22 would engage cylindrical bores in both of the finger followers 16 and 32.

It should also be appreciated that the cam 11 could be replaced with a circular lobe member, in which case one valve operated by the cam mechanism would remain inactive at low engine speeds/loads.

Whilst the fulcrum means described in Figures 6 to 12 have been described in use in the cam mechanism embodiment of Figures 1 to 5 it should be appreciated that the fulcrum means could be used in any suitable cam mechanism, eg. the cam mechanism of PCT/GB 91/00232.

Claims (20)

CLAIMS:

1. A cam mechanism for controlling the valve means of an internal combustion engine or compressor comprising camshaft means having first and second cam means mounted thereon for rotation therewith and first and second finger followers respectively arranged to be engageable directly or indirectly with the first and second cam means, the first and second finger followers being rockable about fulcrum means operable to engage the first and second finger followers with the cam means and the valve means to thereby permit control of the valve means by the cam means, in which the first cam means and the first finger follower operate as a first short duration and/or low lift cam mechanism for low speeds and/or loads of the engine, the fulcrum means being in a first position at low speeds and/or loads wherein the first finger follower is in engagement with the first cam means- and the valve means is controlled by the first cam means, and in which the second cam means and the second finger follower operate as a second long duration and/or high lift cam mechanism for high speeds and/or loads of the engine, the fulcrum means being in a second position at high speeds and/or loads of the engine wherein the second finger follower is in engagement with the second cam means and the valve means is controlled by the second cam means, characterised in that the first finger follower rocks about the fulcrum means in the opposite rotational sense to the rocking motion of the second finger follower.

2. A cam mechanism as claimed in Claim 1 wherein the first finger follower is rockable about fixed fulcrum means and the second finger follower is rockable about moveable fulcrum means, the fixed and moveable fulcrum means being spaced apart on opposite sides of the axis of rotation of the camshaft means.

3. A cam mechanism as claimed in Claim 2 wherein the second finger follower is rotatably connected to the first finger follower for rotation about an axis which is fixed with respect to the first finger follower and which rotates about the fixed fulcrum means with rocking of the first finger follower.

4. A cam mechanism as claimed in Claim 3 wherein roller means is provided on the second finger follower and a reaction surface provided on the moveable fulcrum means, the roller means rolling back and forth on the reaction surface to allow motion of the second finger follower relative to the moveable fulcrum means.

5. A cam mechanism as claimed in any one of the preceding claims 2 to 4 wherein the moveable fulcrum means comprises a piston moveable within a piston bore in the cylinder head of an engine or compressor and locking pins located in bores in the cylinder head which are moveable into and out of the piston bore to engage and disengage the piston the locking pins thereby being operable to secure the piston in a fixed position relative to the cylinder head or release the piston from its fixed position.

6. A cam mechanism as claimed in any one of Claims 2 to 5 wherein the fulcrum means for the first finger follower is a rocker shaft with an oil passage therethrough and the first finger follower has a hydraulic lash adjuster mounted therein supplied by oil through a passage extending through the first finger follower to align with an aperture in the rocker shaft which allows oil to flow out of the rocker shaft from the oil passage therein.

7. A cam mechanism as claimed in any one of the preceding claims comprising additionally third cam means mounted on the cam shaft means for rotation therewith, the third cam means having a lift greater than the first cam means and less than the second cam means, and a third finger follower arranged to be engageable with the third cam means, the third finger follower being rockable about the fulcrum means with the fulcrum means in the first position thereof engaging the third finger follower with the third cam means and the valve means thereby permitting control of the valve means by the third cam means, wherein the first and third finger followers are rockable about fixed fulcrum means, and the second finger follower is rotatably connected to the first follower and has a locating pin slidable in a slot provided in the third finger follower, the locating pin sliding in the slot to allow relative motion between the first and third finger followers when the fulcrum means is in the first position and the locating pin engaging an end of the slot when the fulcrum means is in its second position whereby both the first and third finger followers transmit motion from the second cam means to the valve means.

8. A cam mechanism for controlling the valve means of an internal combustion engine or compressor comprising cam shaft means having first and second cam means mounted thereon for rotation therewith and first and second finger followers respectively arranged to be engageable directly or indirectly with the first and second cam means, the first and second finger followers being rockable about fulcrum means operable to engage the first and second finger followers with the cam means and the valve means to thereby permit control of the valve means by the cam means, in which the first cam means and the first finger follower operate as a first short duration and/or low lift cam mechanism for low speeds and/or loads of the engine, the fulcrum means being in a first position at low speeds and/or loads wherein the first finger follower is in engagement with the first cam means and the valve means is controlled by the first cam means, and in which the second cam means and the second finger follower operate as a second long duration and/or high lift cam mechanism for high speeds and/or loads of the engine, the fulcrum means being in a second position at high speeds and/or loads of the engine wherein the second cam follower is in engagement with the second cam means and the valve means is controlled by the second cam means, wherein the fulcrum means for the second finger follower is moveable and comprises a piston moveable in a piston bore in a cylinder head of the engine or compressor under the influence of oil pressure supplied to the piston bore by a first oil passage in the cylinder head, locking means being provided to releasably secure the piston relative to the cylinder head, the locking means being characterised by a locking pin moveable in a chamber in the cylinder head from a first position in which the locking pin is at least partially withdrawn into the cylinder head and does not engage the piston to a second position in which the locking pin extends into the piston bore to engage the piston.

9. A cam mechanism as claimed in Claim 8 wherein the locking pin is moveable in a chamber connected to an oil passage and the control means is provided to control the pressure of oil in the chamber.

10. A cam mechanism as claimed in Claim 9 wherein a biasing spring is provided in the chamber to bias the locking pin therein out of engagement with the piston, the locking pins being engaged with the piston by the supply of oil pressure to the chamber in which the locking pin is moveable.

11. A cam mechanism as claimed in Claim 9 wherein a biasing spring is provided in the chamber which biases the locking pin in the chamber into engagement with the piston, oil pressure being supplied to the chamber to disengage the locking pin from the piston.

12. A cam mechanism as claimed in Claim 8 wherein an abutment member is provided extending radially inwardly into the piston bore, which abutment member is engageable with an abutment surface provided on the piston to limit the motion of the piston.

13. A cam mechanism as claimed in Claim 8 wherein a shoulder is defined by the exterior of the piston and an abutment surface defined by the inwardly facing surface of the piston bore, the shoulder of the piston being engageable with the abutment surface of the piston bore to limit the motion of the piston.

14. A cam mechanism as claimed in Claim 13 wherein the piston is cylindrical and has a stepped diameter and the piston bore is cylindrical with a corresponding stepped diameter, the shoulder of the piston being defined by the stepped diameter of the piston and the abutment surface of the piston bore being defined by the stepped diameter of the piston bore.

15. A cam mechanism as claimed in any one of Claims 12, 13 or 14 wherein the locking pin is moveable in a chamber extending radially of the piston bore and the first oil passage is connected by passage means in the cylinder head to the chamber for the locking pin whereby supply of oil pressure to the first oil passage causes upward motion of the piston in the cylinder bore and urges the locking pin into engagement with the piston.

16. A cam mechanism as claimed in any one of Claims 8 to 15 wherein the piston has a radially extending bore therein, a biasing member is slidable in the radial bore in the piston, biasing means is provided to act on the biasing member, and when the locking pin aligns with the biasing member the piston the locking pin pushes the biasing member inwardly against the force of the biasing means to lock the piston in position.

17. A cam mechanism as claimed in any one of Claims 8 to 16 wherein the piston is provided with a radially extending bore therethrough and a locking member slidable in the bore, a first chamber is provided in the cylinder head with a biasing member located therein urged radially inwardly towards the piston bore by a biasing spring, a second chamber is provided in the cylinder head with a locking pin moveable therein under the influence of oil pressure supplied through a passage connected to the first, and supply of oil pressure to the first oil passage causes the piston to move to a position in which the locking pin, the locking member and the biasing member are in alignment, supply of pressure to the second chamber then causing the locking pin to push the locking member out of the bore in the piston which in turn pushes the biasing member radially outwardly of the piston bore against the biasing force of the biasing spring.

18. A cam mechanism for controlling the valve means of an internal combustion engine or compressor comprising camshaft means having circular lobe means and cam means mounted thereon for rotation therewith and first and second finger followers respectively arranged to be engageable directly or indirectly with the circular lobe means and the cam means, the first and second finger followers being rockable about fulcrum means operable to engage the first and second finger followers with the circular lobe means, the cam means and the valve means to thereby permit activation and deactivation of the valve means, in which the circular lobe means and the first finger follower operate as a valve deactivation mechanism at low speeds and/or low loads of the engine, the fulcrum means being in a first position at low speeds and/or loads wherein the first finger follower is in engagement with the circular lobe means and the valve means is deactivated, and in which the cam means and the second finger follower operate as a cam mechanism for high speeds and/or loads of the engine, the fulcrum means being in a second position at high speeds and/or loads of the engine wherein the second finger follower is in engagement with the second cam means and the valve means is activated and the motion of the valve means is controlled by the second cam means, characterised in that the first finger follower rocks about the fulcrum means in the opposite rotational sense to the rocking motion of the second finger follower.

19. A cam mechanism for controlling the valve means of an internal combustion engine or compressor comprising cam shaft means having circular lobe means and cam means mounted thereon for rotation therewith and first and second finger followers respectively arranged to be engageable directly or indirectly with the circular lobe means and the cam means, the first and second finger followers being rockable about fulcrum means operable to engage the first and second finger followers with the circular lobe means, the cam means and the valve means to thereby permit activation and deactivation of the valve means, in which the circular lobe means and the first finger follower operate as a valve deactivation mechanism at low speeds and/or low loads of the engine, the fulcrum means being in a first position at low speeds and/or loads wherein the first finger follower is in engagement with the circular lobe means and the valve means is deactivtated, and in which the cam means and the second finger follower operate as a cam mechanism for high speeds and/or loads of the engine, the fulcrum means being in a second position at high speeds and/or loads of the engine wherein the second cam follower is in engagement with the cam means and the valve means is activated and the motion of the valve means is controlled by the second cam means, wherein the fulcrum means for the second finger follower is moveable and comprises a piston moveable in a piston bore in a cylinder head of the engine or compressor under the influence of oil pressure supplied to the piston bore by a first oil passage in the cylinder head, locking means being provided to releasably secure the piston relative to the cylinder head, the locking means being characterised by a locking pin moveable in a chamber in the cylinder head from a first position in which the locking pin is at least partially withdrawn into the cylinder head and does not engage the piston to a second position in which the locking pin extends into the piston bore to engage the piston.

20. A cam mechanism substantially as hereinbefore described with reference to and as shown in the accompanying drawings.