GB2333322A

GB2333322A - A cam mechanism for an I.C. engine

Info

Publication number: GB2333322A
Application number: GB9800679A
Authority: GB
Inventors: Jeffrey Allen; Paul Burke
Original assignee: Lotus Cars Ltd
Current assignee: Lotus Cars Ltd
Priority date: 1998-01-13
Filing date: 1998-01-13
Publication date: 1999-07-21
Anticipated expiration: 2018-01-13
Also published as: GB9800679D0; GB2333322B

Abstract

A cam mechanism for operating a gas exchange valve of an internal combustion engine comprises a cam 10, a rocker shaft 17 and a rocker arm 16. The rocker arm 16 is formed in two sections; a cam follower section (15, figure 2) - which engages and is driven by the cam 10 - and a valve actuation section 18 - which engages the gas exchange valve. The cam follower and valve actuation 18 sections are independently mounted on the rocker shaft 17. A locking mechanism 26 is provided which can either selectively inter-engage the cam follower section and the valve actuation section 18 so that they are locked and therefore rotate together, thus allowing the valve to be opened, or selectively disengage the cam follower section from the valve actuation section 18 so that the cam follower section can rotate about the rocker shaft relative to the valve actuation section 18, thus deactivating the valve. The locking means (see figure 2) comprises two pins which are moved between the engaged position and disengaged position by hydraulic pressure.

Description

CAM MECHANISM This invention relates to a cam mechanism for controlling valve means. In particular, it relates to a cam mechanism for controlling an inlet or an exhaust valve of an internal combustion engine.

It is a common requirement now in multicylinder engines to provide deactivation of certain cylinders of the engine in certain operating conditions. For instance, it may be desired to deactivate four cylinders of a V8 engine so that the engine becomes effectively a V4 engine at low vehicle speeds in order to improve engine economy. It is also a common requirement for engines which have two or more valves per cylinder for there to be a facility to deactivate one or more valves, again in certain engine operating conditions. For instance, in a four-valve per cylinder engine, it may be advantageous to operate only two valves per cylinder at low engine speeds, in order to improve overall engine efficiency.

The need for cam mechanisms which can deactivate inlet or exhaust valves has been well recognised in the prior art and there are many systems which provide for valve deactivation. For instance, in EP-A-0515528 there is provided a cam mechanism for controlling a valve which comprises a finger-follower arrangement and in which valve deactivation is provided. In the finger-follower arrangement, the finger-follower is pivotably mounted at one end to a shaft and engages at the other end an inlet or exhaust valve. An intermediate portion of the finger-follower is then engaged by a cam. Other such systems can be seen, for instance, in GB-A-2185784, EP-A-0405927, EP-A-0265282.

The present invention provides a cam mechanism for operating an engine valve of an internal combustion engine, comprising: a cam; a rocker shaft; and a rocker arm having a cam follower section which engages and is driven by the cam as the cam rotates and a valve actuator section which engages the engine valve and can drive the engine valve to open and close, wherein: the cam follower and the valve actuator sections of the rocker arm are independently mounted on the rocker shaft each for free rotation about the rocker shaft; and a locking mechanism is provided which can selectively interengage the cam follower section with the valve actuator section so that the sections are locked to rotate together and which can selectively disengage the cam follower section from the valve actuator section to allow the cam follower section to rotate about the rocker shaft relative to the valve actuator section; whereby: when the cam follower and the valve actuator sections of the rocker arm are interengaged by the locking mechanism then the rocker arm activates the engine valve and drives the engine valve to open and close under the control of the cam during rotation of the cam; and when the cam follower and the valve actuator sections of the rocker arm are disengaged by the locking mechanism then the cam when rotating drives only the cam follower section to rotate about the rocker shaft and the valve actuator section remains inactive and thus the engine valve is de-activated.

A preferred embodiment of the present invention will be described with reference to the accompanying drawings in which: Figure 1 is a schematic elevational view of a cam mechanism according to the present invention; Figure 2 is a cross-section through the line A-A' in Figure 1 showing the mechanism in a first operating condition; and Figure 3 is a detail view showing a part of the mechanism of Figures 1 and 2 taken in cross-section through line B-B', the mechanism being shown in a second operating condition.

Turning first to Figure 1, in Figure 1 a cam mechanism according to the invention can be seen to comprise a cam 10 mounted on a cam shaft (not shown) and rotating in use of the engine. The cam 10 is engaged by a roller follower 11 which is mounted on a spindle 12. The spindle 12 extends between two spaced arms (see Figure 2) 13 and 14 of a cam follower section 15 of a rocker arm 16. The cam follower section 15 of the rocker arm 16 is mounted for rotation about a rocker shaft 17. The rocker shaft 17 is parallel to, but spaced from, the cam shaft 10.

The spindle 12 is mounted parallel to and spaced apart from the rocker shaft 17.

Also mounted on the rocker shaft 17 is a valve actuator section 18 of the rocker arm 16. The valve actuator section 18 has a bore 19 at an end remote from the rocker shaft 17. The bore 19 accommodates a hydraulic lash adjuster 20. The hydraulic lash adjuster 20 has a lower portion 21 which abuts the top of an engine valve 22. The engine valve 22 could be either an inlet valve or an exhaust valve of an internal combustion engine. A spring retainer 23 encircles the engine valve 22 and a spring 24 acts between the top of the cylinder head 25 of the engine and the spring retainer 23. The valve spring 24 biases the engine valve 22 into abutment with the hydraulic lash adjuster 20.

A locking mechanism 26 is provided to selectively interengage the cam follower section 15 with the valve actuator section 18 of the rocker arm 16 so that both sections are locked together to move together or to disengage the valve actuator section 18 from the cam follower section 15 to allow the cam follower section 15 to rotate relative to the valve actuator section 18, which can remain still.

The locking mechanism 26 comprises two locking pins 27 and 28 which are mounted respectively in bores 29 and 30 which are respectively provided in the spaced-apart parallel arms 13 and 14 of the cam follower section 15 of the rocker arm 16. A spring 31 is provided to bias the locking pin 27 inwardly.

Similarly, a spring 32 is provided to bias the locking pin 28 inwardly.

Parallel to the rocker shaft 17, two bores 33a and 33b extend into opposed sides of the valve actuator section 18, the locking pins 27, 28 respectively extending into the bores 33a and 33b when biased to do so by the springs 29 and 30. Two pistons 50 and 51 are respectively slidable in the bores 33a and 33b.

Running centrally through the rocker shaft 17 is a passage 34 for hydraulic fluid. The passage 34 communicates via an aperture 35 in the rocker shaft 17 with a passage 36 which runs lengthwise along the valve actuator section 18 to connect the passage 34 with the bore 19 in which the hydraulic lash adjuster 20 is located. Hydraulic fluid supplied from the passage 34 along passage 36 to lash adjuster 20 feeds the lash adjuster 20 and enables the lash adjuster 20 to extend to compensate for any wear in the cam mechanism. The aperture 35 extends around the circumference of the rocker shaft 17 a little way so that fluid communication can be maintained between the passage 34 and the passage 36 despite rotation of the valve actuator section 18 relative to the rocker shaft 17.

Somewhere in the hydraulic fluid supply system there will be provided a pressure modulator for controlling the pressure of the hydraulic fluid supplied in passage 34 and therefore passage 36. The controller will be able to switch the pressure between a first low level and a second higher level. The pressure of the hydraulic fluid at both levels will be sufficient to supply the needs of the lash adjuster 20.

The pressure of the hydraulic fluid in the passage 36 acts upon the innermost ends of the pistons 50 and 51 by means of radial drillings connecting the bores 33a and 33b to the passage 36. The pistons 50 and 51 abut the locking pins 27 and 28 and the locking pins 27 and 28 are held in abutment with the pistons 50 and 51 by the springs 31 and 32.

When the oil pressure in the passage 34 is switched to a high oil pressure then the pressurized oil in passage 36 will apply a force to the ends of the pistons 50 and 51 sufficient to enable the pistons 50 and 51 to force the locking pins back into the bores 29 and 30 and out of engagement with the bores 33a and 33b. Vents 37 and 38 are provided to vent the bores 29 and 30 in order to prevent the build-up of a hydraulic lock which could prevent locking pins 27 and 28 being forced by oil pressure fully back into their bores 29 and 30. When the locking pins 27 and 28 are forced fully back into their respective bores 29 and 30 then they do not engage the bores 33a and 33b and thus the locking mechanism 26 disengages the cam follower section 15 from the valve actuator 18. This condition is shown in Figure 3. Stops will be machined in the bores 33a and 33b to limit the pistons 50 and 51 from moving beyond the positions shown in Figure 3 to positions where they could interfere with bores 29 and 30. In the operating condition shown in Figure 3 the cam follower section 15 is rotated first clockwise and then anti-clockwise cyclically by engagement of the cam 10 with the roller follower 11, but no motion is transmitted from the cam follower section 15 to the valve actuator section 18, which therefore remains inactive. The inactive valve actuator section 18 passes no motion onto the engine valve 22 and thus the engine valve 22 is deactivated.

When the pressure of oil in the passage 34 is switched to a low pressure then the locking pins 27 and 28 are slid into the bores 33a and 33b by the springs 31 and 32 when the bores 33a and 33b first align with the locking pins 27 and 28. The locking pins 33a and 33b will force the pistons 50 and 51 inwardly towards each other under the influence of the springs 31 and 32. The mechanism will be constructed so that the locking pins 27 and 28 can only be slid into the bores 33a and 33b when the roller follower 11 is running along the base circle portion of the cam 10. This ensures that there is smooth switching between valve activation and valve deactivation and that the valve 22 is always abutted against its valve seat (not shown) when switching between activation and deactivation takes place.

When the locking pins 27 and 28 are slid into the bores 33a and 33b then the locking mechanism 26 interengages the cam follower section 15 and the valve actuator section 18 of the rocker arm 16 and locks the two sections to move together. Thus, the rotating cam 10 by engagement with the roller follower 11 causes the cam follower section 15 of the rocker arm 16 to pivot about the rocker shaft 17 and this motion is transmitted by the pins 27 and 28 to the valve actuator section 18 which pivots along with the cam follower section 15. The pivoting valve actuator section 18 pivots cyclically clockwise and anticlockwise about the rocker shaft 17 and this pivoting motion is relayed via the hydraulic lash adjuster 20 to the engine valve 22 which is activated and is cyclically lifted from its valve seat.

A spring (not shown) will be incorporated into the cam mechanism to act between the cam follower section 15 and the valve actuator section 18. The spring will bias the roller follower 11 of the cam follower section 15 into engagement with the cam 10, whilst simultaneously biasing the hydraulic lash adjuster 20 of the valve actuator section 18 into contact with the top of the engine valve 22. Thus, both cam/roller follower contact and valve spring/lash adjuster contact is maintained even when the cam follower section 15 and the valve actuator section 18 are disengaged by the locking mechanism 26.

A stop (not shown) will be provided on one of the valve actuator and cam follower sections of the rocker arm. The stop will limit relative pivoting between the two sections of the rocker arm 16. The stop is necessary so that the hydraulic lash adjuster 20 will have a defined position to work from. In use when the rocker arm 16 is first mounted on the rocker shaft 17 then the cam follower and valve actuator sections of the rocker arm 16 will be held by the biasing spring (not shown) acting therebetween in a position in which one abuts the stop (not shown) defined on the other.

The rocker arm will be rotated as a whole by the lash adjuster 20 as it extends until the roller follower 11 engages the cam 10 and the lash adjuster 20 to the top of the engine valve 22. As well as providing a definite position from which the lash adjuster 20 can work, the stop (not shown) is important in ensuring that there is a defined limit position in which the locking pins 27 and 28 align with the bores 33a and 33b.

Whilst above the valve actuator section 18 engages only one engine valve 22, in an alternative embodiment the end of the valve actuator section 18 could be bifurcated and two side-by-side engine valves engaged by a single valve actuator 18. Two lash adjusters would be provided, one for each engine valve, but both would be fed hydraulic fluid through a single passage 36.

Whilst in the described embodiment two locking pins 27 and 28 are used, it is possible to use only one locking pin. Whilst in the embodiments described the locking pins are retracted into bores in the cam follower section 15 when the valve 22 is deactivated, the pins could equally well be withdrawn into the bores in the valve actuator section 18 to achieve deactivation (e.g. a tension spring or springs could be provided to pull the locking pins 27 and 28 back into the bores in the valve actuator section 18 - perhaps a spring could extend between the two locking pins themselves, the spring being extended by the application of hydraulic fluid to force the locking pins outwardly to engage the bores in the cam follower section).

Whilst it is advantageous to include a hydraulic lash adjuster in the mechanism, this is not necessary and mechanical shim adjustment would suffice.

It is possible to replace the locking pin arrangement altogether and provide an alternative locking mechanism, such as a clutch arrangement, acting between the two sections of the rocker arm.

The use of a roller follower 11 is preferred to cut down frictional forces, but it is not essential.

A multi-valve engine would typically-have a plurality of valves each controlled by a cam mechanism as illustrated in Figure 1 and 2 and described above.

A single rocker shaft would be used for rocker arms engaging a plurality of valves and a single hydraulic fluid passage would be used to convey fluid to a plurality of locking mechanisms, each one used to control a single engine valve or a pair of side-by side engine valves. Thus a number of engine valves could be simultaneously activated or simultaneously deactivated by a single pressure modulator controlling pressure of fluid in the passage in the rocker shaft.

The term "simultaneously" should be understood to include changes between activation and de-activation within a given time period of a change in pressure since changing between states can only occur when the relevant valve is against its valve seat.

Claims

CLAIMS 1. A cam mechanism for operating an engine valve of an internal combustion engine, comprising: a cam; a rocker shaft; and a rocker arm having a cam follower section which engages and is driven by the cam as the cam rotates and a valve actuator section which engages the engine valve and can drive the engine valve to open and close, wherein: the cam follower and the valve actuator sections of the rocker arm are independently mounted on the rocker shaft each for free rotation about the rocker shaft; and a locking mechanism is provided which can selectively interengage the cam follower section with the valve actuator section so that the sections are locked to rotate together and which can selectively disengage the cam follower section from the valve actuator section to allow the cam follower section to rotate about the rocker shaft relative to the valve actuator section; whereby: when the cam follower and the valve actuator sections of the rocker arm are interengaged by the locking mechanism then the rocker arm activates the engine valve and drives the engine valve to open and close under the control of the cam during rotation of the cam; and when the cam follower and the valve actuator sections of the rocker arm are disengaged by the locking mechanism then the cam when rotating drives only the cam follower section to rotate about the rocker shaft and the valve actuator section remains inactive and thus the engine valve is de-activated.
2. A cam mechanism as claimed in claim 1, wherein the rocker shaft is parallel to and spaced apart from the camshaft and the cam follower section of the rocker arm extends radially from the rocker shaft to engage the cam in a first radial direction and the valve actuator section of the rocker arm extends radially from the rocker shaft to engage the valve in a second radial direction substantially opposite to the first radial direction.
3. A cam mechanism as claimed in claim 1 or claim 2 wherein the locking mechanism comprises a locking pin which is slidably mounted in a first bore in one of the cam follower and valve actuator sections of the rocker arm and which can be aligned with a second bore in the other of cam follower and valve actuator sections of the rocker arm and then slid into the second bore to link and thereby interengage the cam follower and valve actuator sections.
4. A cam mechanism as claimed in claim 3 wherein biasing means is provided in the first bore to bias the locking pin to slide into the second bore.
5. A cam mechanism as claimed in claim 4 wherein the biasing means comprises a spring.
6. A cam mechanism as claimed in any one of claims 3 to 5 wherein pressurised hydddraulic fluid is used to slide the locking pin out of the second bore to disengage the cam follower and valve actuator sections of the rocker arm.
7. A cam mechanism as described in claim 6 wherein a piston is provided in the second bore which can abut the locking pin and wherein the piston can be slid along the second bore under pressure applied by the pressurised hydraulic fluid, the sliding piston forcing the locking pin out of the second bore.
8. A cam mechanism as claimed in claim 7, wherein a stop is provided to limit motion of the piston in the second bore and to prevent the piston extending out of the second bore.
9. A cam mechanism as claimed in any one of claims 6 to 8 wherein the rocker shaft has a passage extending axially therethrough and through the pressurised hydraulic fluid can be supplied.
10. A cam mechanism as claimed in claim 9 wherein the first bore is provided in the cam follower section of the rocker arm and the second bore is provided in the valve actuation section of the rocker arm and the valve actuation section has a passage through which the pressurised hydraulic fluid is supplied, the passage in the valve actuation section extending radially out from the rocker shaft and being connected with the axially extending passage in the rocker shaft via an aperture in the rocker shaft which connects the axially extending passage in the rocker shaft with the exterior of the rocker shaft.
11. A cam mechanism as claimed in claim 10 wherein a hydraulic lash adjuster is provided in a bore in the valve actuator section of the rocker shaft, the hydraulic lash adjuster extending between the valve actuator section and the engine valve and the hydraulic lash adjuster being supplied with hydraulic fluid via the passage in the valve actuator section which supplies also the pressurised hydraulic fluid used to apply pressure on the locking pin.
12. A cam mechanism as claimed in any one of claims 3 to 11 wherein the valve actuator section of the rocker arm is an arm which extends radially out from the rocker shaft and which is sandwiched between two spaced apart radially extending arms of the cam follower section of the rocker arm.
13. A cam mechanism as claimed in claim 10 which has first and second locking pins, the first locking pin being slidable to link the valve actuator section with a first of the spaced apart arms of the cam follower section and the second locking pin being slidable to link the valve actuator section with the second of the spaced apart arms of the cam follower section.
14. A cam mechanism as claimed in claim 13 wherein the first locking pin is slidable in a first pair of bores provided one each in the first spaced apart arm and the valve actuator section, the first locking pin being slidable in both of the first pair of bores when the first pair of bores are aligned.
15. A cam mechanism as claimed in claim 12 wherein the second locking pin is slidable in a second pair of bores provided one each in the second spaced apart arm and the valve actuator section, the second locking pin being slidable in both of the second pair of bores when the second pair of bores are aligned.
16. A cam mechanism as claimed in claim 15 wherein the two bores of the first and second pairs of bores which are provided in the valve actuator section lie on a common axis.
17. A cam mechanism as claimed in claim 16 wherein the two bores of the first and second pairs of bores which are provided in the first and second spaced apart arms of the cam follower section lie on a common axis.
18. A cam mechanism as claimed in any one of claims 14 to 17 wherein the first and second locking pins are biased by biasing means to slide toward each other into the bores in the valve actuator section.
19. A cam mechanism as claimed in claim 18 wherein the first and second locking pins are slid out of the bores in the valve actuator section by applying pressure using pressurised hydraulic fluid and the pressurised hydraulic fluid used to apply pressure to both of the locking pins is supplied via a common passage in the valve actuator section which extends along the valve actuator section radially out from the rocker shaft.
20. A cam mechanism as claimed in claim 19 wherein first and second pistons are provided one in each of the two bores provided in valve actuator section, the first and second pistons being respectively abuttable with the first and second locking pins and the first and second pistons being respectively slidable along the said two bores under pressure applied by the pressurised hydraulic fluid, the sliding pistons forcing the locking pins out of the said two bores.
21. A cam mechanism as claimed in claim 20 wherein a stop is provided in each of the said two bores in the valve actuator section, each stop limiting motion of one of the pistons in the bore associated therewith and each stop preventing one of the pistons from extending out of the bore associated therewith.
22. A cam mechanism as claimed in any one of the preceding claims comprising biasing means which acts between the cam follower and valve actuator sections of the rocker arm to bias the cam follower section into engagement with the cam and the valve actuator section with engagement within the engine valve.
23. A cam mechanism as claimed in claim 22 wherein a stop is provided on one of the cam follower and valve actuator sections against which the other of the cam follower and valve actuator sections is biased by the biasing means acting between the cam follower and valve actuator sections, the stop providing a limit to the range of possible rotation of one of the cam follower and valve actuator sections relative to the other.
24. A cam mechanism as claimed in any one of the preceding claims wherein the cam follower section of the rocker arm comprises a roller follower which is mounted on a spindle secured to the remainder of the cam follower section, the roller follower making direct contact with the cam.
25. A cam mechanism as claimed in any one of the preceding claims wherein the locking mechanism is activated and deactivated by hydraulic pressure and the cam mechanism comprises supply means for supplying pressurised hydraulic fluid and pressure modulating means for modulating the pressure of the supplied hydraulic fluid between a first pressure level for controlling the locking mechanism to interengage the valve activating and cam follower sections of the rocker arm and a second level for controlling the locking mechanism to disengage the valve activating and cam follower sections of the rocker arm.
26. A multiple valve internal combustion engine wherein: a plurality of engine valves are operated by cam mechanisms according to claim 25; a single rocker shaft is used to carry a plurality of rocker arms, each of which engages an engine valve or valves different to the engine valve or valves engaged by the other rocker arms; a passage is provided in the rocker shaft extending axially therethrough and transferring hydraulic fluid from the supply means to the plurality of locking mechanisms associated with the plurality of rocker arms; and modulation of pressure of the hydraulic fluid in the passage in the rocker shaft can simultaneously activate a plurality of engine valves or simultaneously de-activate a plurality of engine valves.
27. A cam mechanism substantially as hereinbefore described with reference to and as shown in the accompanying drawings.