GB2279719A

GB2279719A - An adjustable cam follower

Info

Publication number: GB2279719A
Application number: GB9314207A
Authority: GB
Inventors: John Ian Westwood; Keith Trevor Simons
Original assignee: CLANCEY G Ltd
Current assignee: CLANCEY G Ltd
Priority date: 1993-07-09
Filing date: 1993-07-09
Publication date: 1995-01-11
Also published as: GB9314207D0

Abstract

The valve clearance of a cam follower 10 in an internal combustion engine, is adjusted by selecting a drive element 30 with a first suitable portion 33 of length L. The first portion 33 abuts a spacer part 18 having a recess 31 that may be a friction fit with second part 34 of the drive element 30. A valve stem R engages on a bearing surface on the first portion 33 of drive element 30 so as to urge, via spring 19, the cam follower 10 towards cam C. Bearing part 15, having a bearing surface 16, is recessed to receive a projecting portion 12 of body part 11. The recess and the portion 12 are a close fit, eg friction fit, which may be achieved by precision forming and/or subsequent finishing although packing may be used, if required. Bearing surface 16 is hardened or made of a hard material to provide good wear characteristics. <IMAGE>

Description

Title: Cam Follower Description of Invention This invention relates to a cam follower and to a method of making a cam follower and to a method of achieving a desired valve clearance in an internal combustion engine.

According to a first aspect of the invention we provide a cam follower comprising a body including a bearing surface which in use bears on a cam, and means to engage a drive member which, in use, is moved via the cam follower in response to rotation of the cam, the engagement means comprising a separate drive element connected to the remainder of the body.

Thus by selecting a drive element of an appropriate size and configuration the positional relationship between the cam and the cam follower can be varied.

In a preferred arrangement, the cam follower includes a spacer part which spaces the engagement means away from the bearing surface. The spacer part may comprise a recess in which at least a part of the drive element is received. In one arrangement, the drive element comprises a first portion which lies exteriorally of the spacer part and has an engagement face which in use is engaged with the drive member, and a second portion of reduced cross sectional dimension which is received within the recess of the spacer part. The dimension of the first portion between the spacer part and the engagement surface may be selected to achieve the desired positional relationship between the cam and cam follower.

The recess of the spacer part and the first and second portions of the drive element may each be generally cylindrical, centred on a common axis which extends generally perpendicularly to a plane containing the bearing surface.

The bearing surface may be provided by a bearing part connected to the remainder of the body. For example the bearing part may have a recess to receive a projecting portion of the body part of the cam follower to which the drive element is connected, as described in our co-pending application No.

9312116.8 filed on the 11th June 1993 or the bearing part may be received in a recess of a body part as in a conventional arrangement.

According to a second aspect of the invention we provide an internal combustion engine comprising a cam shaft having one or more cams and a cam follower in accordance with the first aspect of the invention mounted for bearing on the or one of the cams.

The engine may comprise a valve having a valve stem which comprises the drive member, which is moved in response to rotation of the cam shaft. The valve may be biased into a closed position for example by means of a spring. Thus the drive member and hence the cam follower is urged towards the cam.

According to a third aspect of the invention we provide a method of making a cam follower in accordance with the first aspect of the invention including the steps of making a body part and separately manufacturing a drive element, and connecting the drive element to the body part such that in use, the drive element engages a drive member which is moved via the cam follower in response to rotation of the cam.

The method may include selecting a drive element of appropriate size and configuration to achieve a desired positional relationship between the cam and cam follower.

According to a fourth aspect of the invention, we provide a method of achieving a desired valve clearance in an internal combustion engine, comprising selecting a drive element from a plurality of drive elements of different dimensions and/or configurations, connecting the drive element to a body part of a cam follower to provide a cam follower in accordance with the first aspect of the invention.

The invention will now be described with reference to the accompanying drawing which is a side sectional illustrative view of a cam follower in accordance with the invention in use in an internal combustion engine.

Referring to the drawing, there is shown a cam follower 10 which is adapted to be mounted in an internal combustion engine and directly to operate a valve of the engine in response to rotation of a cam C of a cam shaft. For example, the valve of the engine may have a valve stem R of rod like configuration which bears on the cam follower 10 as hereinafter described.

The cam follower 10 comprises a body including a body part 11, a bearing part 15 and a drive element 30. The body part 11 comprises a projecting part 12, in this example of a generally circular configuration, which in use projects towards the cam C.

The bearing part 15 is also of circular configuration and in this example is of generally cup shaped configuration, at least a bearing surface 16 of which is treated so as to be suitably hardened, or is made of a suitably hard metal to provide good wear characteristics in use whilst bearing on the cam C.

The bearing part 15 has an internal recess opening away from the bearing surface 16, preferably oppositely and the recess is configured to receive the projecting portion 12 of the body part 11. Preferably the internal surface of the recess and the external surface of the projecting portion 12 are a close fit which may be achieved by precision forming and/or subsequent finishing although if necessary packing may be provided between projecting portion 12 and the recess to ensure a close fit.

Hence the body part 11 and bearing part 15 are connected together and preferably the bearing part 15 is retained on the projecting portion 12 by friction with a side wall of the bearing part and by virtue of the bearing part 15 bearing on the cam C of the cam shaft. No fasteners or the like are required.

The body part 11 includes an integrally formed spacer part 18 which extends away from the bearing part 15 into a hollow of body part 11 of the body of the cylindrical cam follower 10 and the spacer part 18 is itself hollowed out as indicated at H, both to reduce weight and to provide a recess 31 to receive the drive element 30.

The drive element 30 comprises a first portion 33 which is generally cylindrical in configuration, and provides a bearing surface for engagement with the valve stem R. The first portion 33, when the drive element 30 is connected to spacer part 18, is located exteriorally of the recess 31. The drive element 30 comprises a second portion 34 which is also of generally cylindrical configuration but of a smaller diameter than the first portion 33, the second part 34 being received within the recess 31 when the drive element 30 is connected to the remainder of the body. The second portion 34 of the drive element 30, is preferably a simple friction fit in the recess 31.

The first and second portions 33,34, of the drive element 30 and the spacer part 18 of the body part 11, are all centred on a common axis B, which extends generally perpendicularly to the bearing surface 16.

The valve stem R engages directly on the bearing surface of the drive element 30 and is urged by spring 19 in an upward direction as seen in the drawing, to close the valve of the engine.

Hence the cam follower 10 is biased towards the cam C by the spring 19.

It will be appreciated by those skilled in the art that it is essential to provide a small clearance between the cam C and the bearing surface 16 of the cam follower 10 at least whilst the cam C and cam follower 10 are at ambient temperature, at least when the cam tip indicated at 20 is rotated 1800 from the position shown in the drawings about axis E, to accommodate thermal expansion.

By utilising the arrangement of the invention, the valve clearance i.e.

the positional relationship between the tip 20 of the cam C and the bearing surface 16 of the cam follower 10, can be varied by selecting different drive elements 30 with first portions 33 of differing lengths L in a direction along axis A between the bearing surface of the first portion 33 and the second portion 34.

Hence by selecting a drive element 30 with a first part 33 of an appropriate length L, a desired valve clearance can be achieved.

Various modifications are possible without departing from the scope of the invention. For example, although the cam follower 10 described above is of the type described in our co-pending patent application 9312116.8 filed on the 11th June 1993, in which the bearing part 15 provides a recess for the projecting portion 12 of the remainder of the body of the cam follower 10, if desired, a bearing part may be received within a recess of the remainder of the cam follower, or indeed, a cam follower having an integral bearing surface 16 could alternatively be provided.

Although as described, the spacer part 18, and the first and second portions 33,34, of the drive element 30 are each of cylindrical configuration, other arrangements are no doubt possible.

The cam follower 10 need not be of generally cylindrical configuration having an internal hollow into which the spacer element 18 extends, but other arrangements are possible.

Although the invention has been described with reference to a cam follower for an internal combustion engine, the invention has wider application and may be applied to any cam follower, made of metal or any other material, in which it is desired to achieve a desired positional relationship between the cam and the cam follower.

The features disclosed in the foregoing description or the accompanying drawing, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, or a class or group of substances or compositions, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1. A cam follower comprising a body including a bearing surface which in use bears on a cam, and means to engage a drive member which in use is moved via the cam follower in response to rotation of the cam, the engagement means comprising a separate drive element connected to the remainder of the body.

2. A cam follower according to Claim 1 including a spacer part which spaces the engagement means away from the bearing surface.

3. A cam follower according to Claim 2 wherein the spacer part comprises a recess in which part of the drive element is received.

4. A cam follower according to Claim 3 wherein a drive element comprises a first portion which lies exteriorly of the spacer part and has an engagement face which in use is engaged with the drive member, and a second portion of reduced cross-sectional dimension which is received within the recess of the spacer part.

5. A cam follower according to Claim 4 wherein the dimension of the first portion between the spacer part and the engagement surface is selected to achieve the desired positional relationship between the cam and the cam follower.

6. A cam follower according to one of Claims 4 and 5 wherein the recess of the spacer part and the first and second portions of the drive element are each generally cylindrical, centred on a common axis which extends generally perpendicularly to a plane containing the bearing surface.

7. A cam follower according to any one of the preceding claims wherein the bearing surface is provided by a bearing part connected to the remainder of the body.

8. A cam follower according to Claim 7 wherein the bearing part has a recess to receive a projecting portion of the body part of the cam follower to which the drive element is connected.

9. A cam follower according to Claim 7 wherein the bearing part is received in a recess of a body part.

10. An internal combustion engine comprising a cam shaft having one or more cams and a cam follower in accordance with any one of the preceding claims mounted for bearing on the or one of the cams.

11. An internal combustion engine according to Claim 10 comprising a valve having a valve stem which comprises the drive member, which is moved in response to rotation of the cam shaft.

12. An engine according to Claim 11 wherein the valve is biased to a closed position by means of a spring.

13. A method of making a cam follower in accordance with any one of Claims 1 to 9 including the steps of making a body part and separately manufacturing a drive element, and connecting the drive element to the body part such that in use, the drive element engages a drive member which is moved via the cam follower in response to rotation of the cam.

14. A method according to Claim 13 involving the step of selecting a drive element of appropriate size and configuration to achieve a desired positional relationship between the cam and the cam follower.

15. A method of achieving a desired valve clearance in an internal combustion engine, comprising selecting a drive element from a plurality of drive elements of different dimensions and/or configurations, and connecting the drive element to a body part of a cam follower to provide a cam follower in accordance with any one of Claims 1 to 9.

16. A cam follower constructed and arranged substantially hereinbefore described with reference to the accompanying drawings.

17. An internal combustion engine constructed and arranged substantially hereinbefore described with reference to the accompanying drawings.

18. A method of making a cam follower when carried out substantially as hereinbefore described with reference to the accompanying drawings.

19. A method of achieving a desired valve clearance in an internal combustion engine when carried out substantially as hereinbefore described with reference to the accompanying drawings.

20. Any novel feature or novel combination of features described herein and/or in the accompanying drawings.