GB2403770A

GB2403770A - I.c. engine valve gear

Info

Publication number: GB2403770A
Application number: GB0315246A
Authority: GB
Inventors: Christopher Paulet Mel Walters
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-06-30
Filing date: 2003-06-30
Publication date: 2005-01-12
Also published as: GB0315246D0

Abstract

Valve gear for an internal combustion engine comprises a pair of fingers 30, 32 interposed between a cam 10 and an associated valve stem 20. The upper finger 30 has a recess 48 along which moves a roller 62 carried by the lower finger 32. The profile of the surface of the recess 48 is such that rotation of the cam 10 is converted into a desired acceleration profile of the valve stem 20, without requiring a re-entrant profile of the cam 10.

Description

VALVE GEAR

This invention relates to valve gear for operating a valve in an internal combustion engine.

In many overhead camshaft engines, valves are operated by cams on a camshaft by buckets which slide in guides under the action of the cams. GB 2190140 discloses valve gear of this kind in which the valve lift, duration and timing can be adjusted while the engine is running. Developments of this concept are disclosed in GB 2341659 and GB 2359608. The adjustment of valve operation is achieved by varying the profile of each cam along its axis, so that part of the cam surface, as viewed from the side, is inclined to the axis about which the cam rotates. The camshaft is axially displaceable to move the cam across the bucket so as to vary the effect of the cam on valve operation. To accommodate the varying inclination of the cam surface as it passes over the bucket, the bucket has a half- roller having a flat surface which contacts the cam and a cylindrical surface which engages the bucket, so that the half-roller can rock relatively to the bucket as the cam rotates.

Many modern overhead camshaft engines, particularly those used in high performance applications, do not employ buckets as cam followers but instead use a so- called finger follower. A finger follower is a lever which is pivotable about a pivot axis parallel to that of the camshaft. The finger follower is acted upon by the cam at a position between its ends. The end of the finger follower away from the pivot axis acts on a valve stem to operate the valve.

Finger followers provide a mechanical advantage between the cam and the valve so enabling a greater valve lift area for a given cam angle duration due to the higher velocities that are possible with this system. Finger followers also allow greater freedom in cylinder head design, since the camshafts do not need to be positioned directly above the valve.

Finger followers usually have a roller which is acted upon by the cam to pivot the finger follower. It is difficult to incorporate such a roller into a system as disclosed in GB 2190140. Furthermore, finger follower arrangements sometimes require a re-entrant cam profile if required valve velocities, accelerations and lift are to be achieved, and such profiles cannot cooperate satisfactorily with a flat follower surface as is disclosed in GB 2190140.

According to the present invention there is provided valve gear for operating a valve in an internal combustion engine, the valve gear comprising a camshaft carrying a cam which acts on a first pivotable finger, the first finger having an actuating surface which contacts a second pivotable finger, the second pivotable finger being in driving engagement with the valve.

In one practical embodiment in accordance with the present invention, the pivotable fingers are each pivotable about a respective axis which is parallel to the axis of the camshaft. The pivot axis of the first finger may lie in a plane extending transversely of the direction of valve movement, which plane lies between the axis of the camshaft and the contact point between the base circle of the cam and the first finger. The pivot axis of the second finger may lie in a plane extending transversely of the direction of valve movement and be positioned so that the point of contact between the second finger and the valve moves across that plane as the valve opens and closes.

The valve gear may include a mechanism for varying the valve lift, duration and timing, for example in accordance with GB 2190140, GB 2341659 or GB 2359608.

Thus, the cam may have a profile which varies in the direction of the camshaft axis, the camshaft being axially displaceable to vary the action of the cam on the first finger. The first finger may thus have a cam engaging element which is pivotable with respect to the finger about an axis which lies in a plane perpendicular to the camshaft axis. The cam engaging element preferably has a flat cam contact surface which is engaged by the cam. The cam engaging element may be in the form of a halfroller.

The actuating surface of the first finger is preferably in the form of a profiled track along which travels a contact element carried by the second finger. The track is preferably at least partly concave and, in a preferred embodiment, comprises a first convex then concave arcuate portion at a radially inner end of the track with respect to the pivot axis of the first finger. A straight region of the track extends generally radially outwardly from the first arcuate portion and, in the embodiment, terminates at a second concave arcuate portion at the radially outer end of the track. The straight portion of the track may be inclined to the cam contact surface so that the distance between the track and the cam contact surface increases in the direction away from the pivot axis of the first finger. I In an engine having two inlet valves per cylinder, the second finger may have two valve engaging portions for engaging the two valves. The contact element on the second finger may comprise a cylindrical roller which extends parallel to the pivot axis of the second finger between the valve engaging portions.

In one embodiment, the pivot axis of the first finger is fixed with respect to the cylinder head which supports the valve gear.

In an alternative embodiment, the pivot axis of the first finger may be movable with respect to the cylinder head. For example, the pivot axis of the; first finger may be defined by contact between the first finger and a movable support element. Thus, the first finger may have a recess with which the movable support element cooperates to define the pivot axis. t The movable support element may be moved in dependence on the position of the second finger. For example, the movable support element may comprise a support cam; which is pivotable about a fixed axis by means of an operating lever which moves with the second finger about the pivot axis of the second finger.

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 shows valve gear of an internal combustion engine in a first position; Figure 2 shows the valve gear of Figure 1 in a second position; Figure 3 is a view in the direction of the arrow 3 in Figure 1; Figure 4 is a view in the direction of the arrow 4 in Figure 1; Figures 5a to 5d are views of a component of the valve gear; Figures 6a to 6c are views of another component of the valve gear; Figure 7 is a perspective view of the component shown in Figures 5a to Ed; Figure 8 is a perspective view of the component shown in Figures 6a to 6c; Figure 9 corresponds to Figure 1 but shows an alternative embodiment; Figures 10 to 12 correspond respectively to Figures 1, 3 and 4 but show a further alternative embodiment. I Figures 1 to 4 show a cylinder block 2 having a cylinder 4, and a cylinder head 5 which, in the embodiment illustrated, has a separate cam carrier 6.

A camshaft 8 is supported by the cam carrier 6, and has a series of cams 10 distributed along it, only one of which is shown in Figures 1 to 3. The camshaft is rotatable about a camshaft axis 12.

The admission of fuel-air mixture into the cylinder 4 is controlled by two inlet valves 14 (see Figures 3 and 4) and the exhaust of combustion products is controlled by two exhaust valves 16. Each inlet valve comprises a valve head 18 and a valve stem 20. The valve stems move in valve guides 22 and are biased to the closed position (upwardly as shown in Figure 1) by valve springs 24 in a conventional manner.

As shown in Figure 3, the cam 10 varies in profile along the axis 12. Although the base circle 26 is parallel to the axis 12, parts of the cam which extend beyond the base circle, as exemplified by the line 28 in Figure 3, vary in distance from the axis 12 in the axial direction. The cam 10, or the entire camshaft 8, is movable axially so that the part of the cam 10 that is effective to operate the valves 14 changes to alter the valve lift, duration and timing. The mechanism for displacing the camshaft 8 may be as described in GB 2190140, GB 2341659 or GB 2359608.

The action of the cam 10 is transferred to the valves 14 through a first pivotable finger 30 and a second pivotable finger 32. The first finger 30 is pivotaLle about an axis 34 which is fixed to the cam carrier 6.

The axis 34 is defined by a pivot pin 36. The first finger 30 is cranked, having a first portion 38 which, in the valve-closed condition shown in Figure 1, extends obliquely from the pivot pin 36 towards the valve stem 20, and a second portion 40 which extends substantially transversely of the lengthwise direction of the valve stem 20.

The first finger 30 is shown in greater detail in Figures 5a to Ed and Figure 7. It comprises a bore 42 for receiving the pin 36. The portion 40 includes a part cylindrical recess 44 which extends in the lengthwise direction of the portion 40 and receives a cam engaging element 46 (Figures 1 and 2) which is in the form of a half roller having a part cylindrical surface cooperating with the recess 44 and a flat surface which engages the cam 10. The cam engaging element 46 is thus able to rock in the recess 44 so that the flat surface can align with the engaging surface of the cam 10 which, as will be appreciated from Figure 3, varies in inclination relatively to the axis 12 as the cam rotates.

The surface of the portion 40 of the first finger 30 includes, on the side opposite the recess 44, a recess 48 which acts as a guide track as will be described below.

The second finger 32 is mounted for pivotal movement about an axis 50 defined by pivot pins 52 mounted in the cam carrier 6. The second finger is shown in more detail in Figures 6a to 6c and Figure 8. The second finger 32 extends generally radially of the axis 50 from aligned bores 54 for receiving the pins 52. At the end away from the bores 54, the second finger 32 terminates at a downwardly directed foot 56. At the transition between the radially extending part of the second finger 32 and the foot 56, there is a second bore 58, parallel to the bores 54 and half way along this bore 58 there is a notch 60 which is sufficiently wide to receive the portion 40 of the first finger 30.

In the assembled condition, the second bore 58 receives a track engaging contact element in the form of a roller 62. As shown in Figures 1 and 2, the roller 62 engages the track 48 in the first finger 30. Also, the foot 56 engages the end of the valve stem 20. The pivot axes 34 and 50 and that of the roller 62 are parallel to the camshaft axis.

In the position shown in Figure 1, the base circle 26 of the cam 10 contacts the half roller 46. The first finger 30 is consequently in its uppermost position about the pivot axis 34. Since the position of the second finger 32 is determined by abutment of the pin 36 with the track 48, the second finger 32 is also in its uppermost position about the axis 50 under the influence of the valve spring 24. The valve 14 is thus I closed.

Rotation of the camshaft causes the nose of the cam 10 to come into contact with the half roller 46, so pivoting it in a clockwise direction about the axis 34. ! This in turn causes the second finger 32 to rotate about the pivot axis 50, also in a clockwise direction, ! to cause the valve to begin to open. Eventually, as shown in Figure 2, the valve 14 reaches its fully open position, "hereafter further rotation of the camshaft 8 will cause the valve 14 to close again under the action of the spring 24.

The profile of the track 48 governs the relationship between the motion of the first finger 30 and the second finger 32. It will be appreciated that the track can be any shape commensurate with the-valve motion required and acceptable track/roller contact stress. In a preferred embodiment as shown in Figure 5b, the track 48 is largely concave, and comprises a convex arcuate transmission 63 into a first arcuate portion 64 at the radially inner end of the track 48 with respect to the bore 42, a straight portion 66 which extends radially outwardly from the arcuate portion 64, and a second arcuate portion 68 at the radially outer end of the track 48. The straight portion 66 is inclined to the lengthwise direction of the portion 40 and thus, as viewed in the plane of Figure 1, to the flat surface of the half roller 46.

The effect of this profile of the track 48 is that, from the position shown in Figure 1, the initial pivoting of the first finger 30 produces a lower rate Of pivoting of the second finger 32 as the roller 62 moves along the first arcuate portion 64.

Subsequently, when the roller 62 reaches the straight portion 66, the motion of the second finger 32 accelerates with respect to the first finger 30, under - the influence of the inclination of the straight portion 66 and because the point of contact between the roller 62 and the track 48 moves further from the pivot axis 34 of the first finger 30. Further acceleration of the second finger 32, and consequently of the valve 14, is achieved as the roller 62 travels over the second arcuate portion 68. Consequently, rapid opening of the valve 14 to its full extent can be achieved without requiring a re-entrant profile on the cam 10.

A similar effect is achieved on further rotation of the camshaft 8 as the valve returns to the closed position.

Figure 9 shows an arrangement similar to that of Figures 1 to 8, except that the second finger is supported by a hydraulic adjuster 70 instead of the pivot pin 52. On start-up of the engine, the adjuster receives oil under pressure to take up any clearance between the foot 56 of the second finger 32 when the valve is fully closed.

The adjuster 70 has a pin 72 which is moved upwardly under hydraulic pressure. The pin 72 has a hemispherical tip which is received in a correspondingly-shaped recess in the second finger 32.

More than one adjuster 70 may be provided along the pivot axis 50 in order to provide stability to the second finger 32. In this embodiment the foot 56 is notched at 90 to receive the ends of the valve stems to enhance lateral location of the front of the second finger 32 against the valve stems 20.

A further embodiment of the valve gear is shown in Figures 10 to 12. In these Figures, the parts corresponding to those of the preceding embodiments are designated by the same reference numbers.

In the embodiment of Figures 10 to 12, the pivot axis 34 for the first finger 30 is defined by a pivot 74 with sideways locating end plates integral with body 30 on a lever 76 which is mounted in the cam carrier on a pin 78 for rotation about an axis 80. The lever 76 also has a lug 82 which is retained between the arms of a yoke 84 secured to the second finger 32.

A clearance recess 86 is provided in the first finger 30 to accommodate the lever 76 as the finger 30 moves.

Unlike the cranked first finger 30 of the embodiments of Figures 1 to 9, the first finger 30 of the embodiment of Figures 10 to 12 is generally straight although it is profiled at its lower surface (ie the surface closest to the valve stem 20) to provide the track 48. In this embodiment, the track 48 comprises a convex transmission 63 into a concave radially inner arcuate portion 64 and a straight portion 66, but the straight portion 66 merges into a convex transition 88 extending to the free end of the first finger 30. It will be appreciated that the straight portion 66, both in this embodiment and the embodiments of Figures 1 to 9, may not be perfectly straight, but may instead be slightly convex or concave.

In operation of the embodiment of Figures 10 to 11, pivoting of the second finger 32 causes rotation of the lever 76 by means of the yoke 84 engaging the lug 82.

This changes the position of the pivot axis 34 in the cam carrier and so adjusts the position of the first - finger 30, and consequently the track 48, for any particular position of the cam 10.

Thus, starting from the position shown in Figure 10 which corresponds to the position shown in Figure 1, clockwise displacement of the first finger 30 causes corresponding clockwise movement of the second finger 32. This causes anti-clockwise rotation of the lever 76, so moving the pivot axis 34 downwards and to the left as seen in Figure 10. Since the first finger 30 can be regarded as pivoting about a fulcrum constituted by the contact point between the cam 10 and the half roller 46, a vertical component of movement of the track 48 is superimposed on the overall clockwise movement of the first finger 30, so effectively changing the speed of rotation of the second finger 32.

Thus, the lever 76 provides a further facility for adjusting the speed and timing of valve travel.

The present invention thus enables use of the same conical (swathed or unswashed) cam and rectangular half-roller design as with the variable lift duration and timing bucket system of, for example, GB2190140 in a finger follower actuation system that employs two fingers. A variable track in the bottom of the top rocker is acted upon by a roller in the top of the bottom rocker, the effect of which is to modify the motion between the valve and cam such that the cam profile always remains convex so that it effectively becomes a bucket actuation system at the cam with the cam acting on a flat surface.

This allows the more advantageous higher velocity (and lower friction) reentrant cam/finger follower system type lift to be obtained at the valve but with a flat follower system at the cam and the retention of all the valve lift, duration and timing variability that was achievable with the bucket systems disclosed in GB2190140, GB 2341659 and GB 2359608.

In the embodiments described above, the lower, second rocker 32 is radiussed and is shaped in plan view to allow two valves of a 4-valve combustion chamber to be ! opened and closed simultaneously when acted upon by the vertical movement of the upper, first rocker 30 which communicates its motion to the roller.62 and lower rocker 32 via the upper rocker track 48.

The lower rocker 32 can accept lateral loads from the upper rocker halfroller 46 communicated through the forward lower vertical side faces of the upper rocker to the slot 60 in the lower rocker top surface and is itself wide-based for efficient distribution of these loads into the cam carrier/cylinder head structure 5,6.

The lower rocker 32 has suitably high vertical stiffness deriving from the vertical material at the front of the rocker and above the valves and the structure is further stiffened by being made as a 1- ; piece component which is tied-together" in the middle by the horizontal surface 92 formed between the two rocker halves which also provides an excellent bearing carrier for the roller 62 in its central slot 60.

The lower rocker 32 has only to accept the fairly low lateral loads communicated from the half-roller 46 to the upper rocker 30 and then the lower rocker 32.

The lower rocker has also only to accept relatively low loads in its structure between the wide based double shear pivot pins 52 and the roller 62 because the roller 62 is disposed near the valve stem 20 and this structure can therefore be made lighter than the two conventional finger followers which it replaces - each conventional follower has to accept all the loading at each valve.

Owing to the effect of the supporting pivot and the actuation of the two valves being effected by the single cam lobe 10 and half-roller 46 acting on the single upper rocker 30, the effective mass of the upper rocker 30 at each valve is low and the lower rocker mass can be reduced compared with two conventional rockers. Therefore the total mass at the valve of this system is approximately equivalent to a conventional roller rocker finger system at each valve.

As the valves lift the disparate radial arcs of movement at the roller 62 resulting from the pivoting of the two rockers about their respective axes are such that a large differential motion occurs between the track 48 and the roller 62 which allows the design of the track/roller to be disposed in such a way that the desired valve motion can be achieved by a combination of asymmetric cam design and track shape, which ensures that the complex conical camshaft profile always remains convex so that it operates with 100 contact across the half-roller face.

The contact stress between the roller 62 and the track 48 can be kept within reasonable bounds and this design lends itself to good roller support, bearing action and lubrication.

By suitable design of the components, valve lift velocities can match those of roller/finger follower systems (which tend to be higher than those of than bucket systems) whilst retaining the half-roller concept that uses flat follower tangential variable valve lift, duration and timing. With this system lift at the cam normally associated with a bucket system can be translated into a valve lift that can normally only be obtained-with a re-entrant finger follower cam/convex finger pad system.

A system in accordance with the present invention can be designed to occupy the same packaging space as a conventional roller finger follower system.

Also, the ability to employ only a single cam lobe and half-roller upper follower 30 and a single 1-piece lower follower 32 and a cam profile having no re- entrant profile to operate two valves provides a relatively inexpensive mechanism.

A system in accordance with the present invention has approximately the same friction (or slightly higher) as a roller finger follower system as only a single cam lobe/bucket is required for two valves. Possibly slightly higher friction resulting from the wider cam lobe with its slightly wider half-roller type bucket giving slightly greater sliding friction than a roller, is approximately offset by the need for only a single cam/follower for two valves). The overall friction is likely to be lower than occurs in a bucket system. - !

Claims

Claims 1. Valve gear for operating a valve in an internal combustion

engine, the valve gear comprising a camshaft carrying a cam which acts on a first pivotable finger, the first finger having an actuating surface which contacts a second pivotable finger, the second pivotable finger being in driving engagement with the valve.
2. Valve gear as claimed in claim 1, in which the pivotable fingers are each pivotable about a À:. respective axis which is parallel to the axis of À.

the camshaft. me À. -

À ..
3. Valve gear as claimed in claim 2, in which the pivot axis of the first finger lies in a plane extending transversely of the direction of valve I:. movement, which plane lies between the axis of the À .. 20 camshaft and the contact point between the base circle of the cam and the first finger. i
4. Valve gear as claimed in claim 2 or 3, in which the pivot axis of the second finger lies in a plane extending transversely of the direction of valve movement and positioned so that the point of contact between the second finger and the valve moves across that plane as the valve opens and closes.
5. Valve gear as claimed in any one of the preceding claims, in which the cam has a profile which varies in the direction of the camshaft axis, the camshaft being axially displaceable to vary the action of the cam on the first finger.
6. Valve gear as claimed in claim 5, in which the first finger has a camengaging element which is pivotable with respect to the first finger about an axis which lies in a plane perpendicular to the camshaft axis.
7. Valve gear as claimed in claim 6, in which the cam engaging element has a flat cam contact surface which is engaged by the cam.

À:. :
8. Valve gear as claimed in claim 7, in which the cam Àe- engaging element is in the form of a half-roller. I À. e. À e À À

A.
9. Valve gear as claimed in any one of the preceding claims, in which the actuating surface of the first À:: finger is in the form of a profiled track along À eeee 20 which travels a contact element carried by the second finger. i
10. Valve gear as claimed in claim 9, in which the track is at least partly concave.
11. Valve gear as claimed in claim 10, in which the track comprises a first convex then concave arcuate portion at a radially inner end of the track with respect to the pivot axis of the first finger, a straight region of the track extending generally radially outwardly from the first arcuate portion and terminating at a second concave arcuate portion at the radially outer end of the track.
12. Valve gear as claimed in claim 11, in which the straight portion of the track is inclined to the cam contact surface so that the distance between the track and the cam contact surface increases in the direction away from the pivot axis of the first finger.
13. Valve gear as claimed in any one of the preceding claims, in an engine having two inlet valves per cylinder, in which the second finger has two valve engaging portions for engaging the two valves.

.
14. Valve gear as claimed in claim 13, in which the . contact element on the second finger comprises a cylindrical roller which extends parallel to the À. - À .. pivot axis of the second finger between the valve À. engaging portions.

À
15. Valve gear as claimed in any one of the preceding I:: 20 claims, in which the pivot axis of the first finger is fixed with respect to a cylinder head which supports the valve gear.
16. Valve gear as claimed in any one of claims 1 to 14, in which the pivot axis of the first finger is movable with respect to a cylinder head which supports the valve gear.
17. Valve gear as claimed in claim 16, in which the pivot axis of the first finger is defined by contact between the first finger and a movable support element.
18. Valve gear as claimed in claim 17, in which the first finger has a recess with which the movable support element cooperates to define the pivot axis.
19. Valve gear as claimed in claim 18, in which the movable support element is movable in dependence on the position of the second finger.
20. Valve gear as claimed in claim 19, in which the movable support element comprises a support cam which is pivotable about a fixed axis by means of I. an operating lever which moves with the second . finger about the pivot axis of the second finger. À. À. .e

À ..
21. Valve gear substantially as described herein with reference to, and as shown in, Figures 1 to 8 or Figures 9 to 12 of the accompanying drawings. a.-. À:

À .. 20
22. An internal combustion engine provided with valve gear in accordance with any one of the preceding claims.