GB2310249A

GB2310249A - I.c.engine poppet valve and valve guide

Info

Publication number: GB2310249A
Application number: GB9602952A
Authority: GB
Inventors: James Wilfred Gennard
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1996-02-13
Filing date: 1996-02-13
Publication date: 1997-08-20
Anticipated expiration: 2016-02-13
Also published as: GB9602952D0; GB2310249B

Description

A VALVE AND VALVE GUIDE ASSEMBLY FOR AN INTERNAL COMBUSTION ENGINE The invention relates to a valve and valve guide assembly for an internal combustion engine, the valve having a head which seals against the seat and a stem extending from the head which is slidable within the valve guide.

During operation of an internal combustion engine, it is known that deposits of combustion such as carbon will tend to build up on valve stem and, where the deposits become substantial, they can slow down closing of the valve or can cause the valve to stick in an open position.

Exhaust valves are particularly prone to that problem.

Hitherto, it has been proposed to form an annular undercut in the valve stem at an appropriate position or to form a counterbore in the valve guide to minimise the risk of sticking but neither is entirely satisfactory. Where the undercut is formed, it is located in a section of the valve stem between the head and the valve guide and, therefore, is located in a highly stressed region.

Moreover, the forming of a counterbore in the valve guide does not necessarily prevent the build up of deposits on that part of the valve stem which moves into and out of the remainder of the valve guide.

One object of the present invention is to provide an improved valve and valve guide assembly which helps to reduce the likelihood of valve closing problems and valve sticking due to build up of deposits of combustion on the valve stem.

According to a first aspect of the invention there is provided a valve and valve guide assembly for an internal combustion engine, the valve having a head which seals against a seat and a stem extending from the head which is slidable within the valve guide, one of the valve stem and valve guide being formed with a groove which follows a substantially helical path and which co-operates with the other of the valve stem and guide so as to reduce build-up of deposits of combustion on the valve stem.

The helical groove provides a break in the continuity of the surface in which it is formed which will assist in the removal of the deposits as the valve stem moves in and out of the valve guide.

The groove has a wall which preferably forms an edge at a surface of the valve stem or valve guide in which the groove is formed. The edge will co-operate with the valve guide or valve stem respectively so that the deposits will be removed by a scraping action.

Preferably, the groove extends helically by a plurality of turns.

In one embodiment, the groove is formed in the valve stem. The valve stem may terminate at an annular recess formed in the valve stem. Preferably the annular recess is positioned in part of the valve stem which normally slides within the valve guide and which, therefore, is not subjected to the high stresses experienced by that part of the valve stem which, hitherto, has been formed with the annular undercut as described above.

In another embodiment, the groove is formed in the valve guide and commences at an end surface of the valve guide nearest the valve head. In that way, the groove can form an edge near the point where the valve stem enters the valve guide and the edge can effectively scrape deposits from the valve stem as the valve stem moves into the guide.

The groove in the valve guide preferably extends completely through the valve guide and terminates at an opposite end surface thereof. In that way, deposits removed from the valve stem can gradually work their way through the groove and exit the opposite end.

Whilst we prefer to form the groove in either the valve stem or the valve guide, it is envisaged that both the valve stem and the valve guide could be formed with respective grooves. In such a case, the grooves may have respective pitches which are different from each other and may be of opposite hand.

According to a second aspect of the invention there is provided a valve for use in a valve and valve guide assembly according to the first aspect of the invention, the valve stem being provided with the groove.

According to a third aspect of the invention there is provided a valve guide for use in a valve guide assembly according to the first aspect of the invention, the valve guide being formed with the groove.

A valve and valve guide in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which: Fig 1 is a cross section through the cylinder head of an internal combustion engine showing a valve and valve guide assembly in accordance with the invention, Fig 2 is a view of part of the valve and valve guide shown in Fig 1 drawn to a larger scale and showing the valve stem in longitudinal cross section, Fig 3 is a perspective view of a valve guide formed with an internal helical groove and shown partly broken away and Fig 4 is a view of one end of the valve guide of Fig 3 drawn to a larger scale and illustrating details of the groove.

Referring to Fig 1, a cylinder head 10 of an internal combustion engine is provided with a guide 12 for a valve generally indicated at 14. The valve has a head 16 which can seal against a seat 18 formed on the cylinder head 10.

The valve 14 has a stem 20 which passes slidably through the valve guide 12 in known manner. The upper end of the valve stem 20 as viewed in Fig 1 is formed with a peripheral groove 22 for locating projections 24 formed on the interior surfaces of two collets 26. The collets locate within an annular valve spring cap 28 and a valve spring 30 extends in compression between the valve spring cap 28 and spring locator 32 in abutment with a shoulder 34 on the cylinder head 10. The valve 14 is operated by means of a cam 36 on a cam shaft 38 via a tappet 40.

The valve stem 14 is formed with a helical groove 42.

The groove 42 is substantially rectangular in cross section with a pitch p of approximately 5mm. The groove 42 commences on a section 44 of the valve stem 14 which always lies outside the valve guide 12 during reciprocal movement of the valve. The groove 42 continues its helical upward path and eventually runs out or terminates at an annular recess 46 formed in the valve stem 14. As shown in Fig 2, the groove 42 has a wall 43 which forms an edge 47 at the outer surface of the valve stem 20. As the valve 14 reciprocates, the annular recess 46 moves over a central area of the valve guide. During reciprocation of the valve 14, the edge 47 of the groove 42 and a lower annular end surface 48 of the valve guide 12 co-operate so that carbon deposited on the grooved area of the valve stem 20 is effectively scraped from the valve stem.The valve 14 will typically move through approximately 8 to 12 mm. Therefore with a pitch p of 5 mm, approximately two turns of the groove 42 will pass the end surface 48 of the valve guide 12 during reciprocation of the valve.

In Fig 2, a carbon deposit d, exaggerated in thickness in the drawing, is shown on the valve stem 20. As the valve 14 moves into the valve guide 12 in the direction of arrow A, the end surface 48 of the valve guide 12 effectively scraps off the deposit d as the edge 47 of the groove 42 moves past the end surface 48. In that way, the risk of the valve 14 sticking because of carbon deposits is minimised.

Carbon actually deposited within the groove 42 will tend to break away from the groove from time to time and it is anticipated that the groove 42 will not become clogged with carbon deposits.

Although the groove 42 commences at a relatively highly stressed region 44 of the valve 14, the helical groove will have considerably less adverse effect on the strength of the valve in that region than the annular undercut as proposed hitherto.

Fig 3 shows the way in which the valve guide 12 can itself be formed with an internal groove 50 instead of forming a groove on the valve 14. The groove 50 begins at the end face 48 of the valve guide 12 and extends completely through the valve guide to an opposite end face 52.

Looking at Fig 4, it will be seen that the groove 50 has a wall 51 which effectively forms a scraping edge 54 at the inner circumference of the valve guide which will help to remove carbon deposits from the valve stem 20 during reciprocation of the valve 14. Should carbon deposits not fall away from the end of the valve guide 12 during scraping, they may gradually move along the groove 50. The termination of the groove 50 at the upper end 52 of the valve guide 12 would, in such a case, allow the carbon to move completely through the groove 50 and exit the groove at the surface 52.

The pitch s of the groove 50 is preferably around 5 mm so that during valve movement (approximately 8-12 mm) the portion of the valve stem 20 which moves into the valve guide 12 will pass approximately two turns of the groove 50 to ensure cleaning of substantially the whole circumference of that portion of the valve stem.

If desired, both the valve guide 12 and the valve stem 20 may be provided with respective grooves 42, 50. In such a case, the grooves 42, 50 should be of different pitch if of the same hand. Alternately the grooves can be of opposite hand in which case similarly of pitch is permissible.

During reciprocation of the valve 14, the valve also has a tendency to rotate which will assist further the clearing of deposits from the entire circumference of the valve stem 20.

Claims

1. A valve and valve guide assembly for an internal combustion engine, the valve having a head which seals against a seat and a stem extending from the head which is slidable within the valve guide, one of the valve stem and valve guide being formed with a groove which follows a substantially helical path and which co operates with the other of the valve stem and guide so as to reduce build-up of deposits of combustion on the valve stem.

2. A valve and valve guide assembly according to Claim 1 in which the groove extends helically by a plurality of turns.

3. A valve and valve guide assembly according to Claim 1 or 2 in which the groove has a wall which forms an edge at a surface of the valve stem or valve guide in which the groove is formed.

4. A valve and valve guide assembly according to Claim 1, 2 or 3 in which the groove has a pitch of approximately 5 mm.

5. A valve and valve guide assembly according to any preceding claim in which the groove is formed in the valve stem.

6. A valve and valve guide assembly according to Claim 5 in which the groove in the valve stem commences at a point spaced from the valve head and terminates at a position within the valve guide.

7. A valve and valve guide assembly according to Claim 6 in which the groove in the valve stem terminates at an annular recess formed in the valve stem.

8. A valve and valve guide assembly according to any of Claims 1 to 4 in which the groove is formed in the valve guide and commences at an end surface of the valve guide nearest the valve head.

9. A valve and valve guide assembly according to Claim 8 in which the groove in the valve guide extends completely through the valve guide and terminates at an opposite end surface thereof.

10. A valve and valve guide assembly according to any preceding Claim in which both the valve stem and the valve guide are formed with respective grooves.

11. A valve and valve guide assembly according to Claim 10 in which the grooves follow respective helical paths of opposite hand.

12. A valve and valve guide assembly according to Claim 10 or 11 in which the grooves have respective pitches which are different from each other.

13. A valve and valve guide assembly constructed and arranged substantially as described herein with reference to the Figures 1 and 2 of the accompanying drawings.

14. A valve for use in a valve and valve guide assembly according to any preceding claim, the valve having the features as set out in Claim 6, 7 or 8.

15. A valve constructed and arranged substantially as described herein with reference to Figure 1 or 2 of the accompany drawings.

16. A valve guide for use in a valve and valve guide assembly according to any of Claims 1 to 12, the valve guide having the features as set out in Claim 8 or 9.

17. A valve guide constructed and arranged substantially as described herein with reference to Figures 3 and 4 of the accompanying drawings.