GB2200952A - Adjustable valve gear - Google Patents

Abstract

A valve 1 is operable by two cams 21, 22 through respective followers 25 (32, Fig. 2) which have their pivots 26 independently adjustable to vary the movement which is imparted to the opposite ends of a rocker (10) between zero and a maximum. The cams 21, 22 are out of phase or of different angular extent (Fig. 6) whereby the valve timing and/or lift can be altered by selective adjustment of the follower pivots. The cams may be located inside the followers (Figs. 8 and 9). <IMAGE>

Description

Description of Invention "Improvements in or relating to a valve arrangement." THIS INVENTION relates to a valve arrangement, and, more particularly, to the control of poppet valves as found in internal combustion engines.

The present invention seeks to provide a valve arrangement which offers a means of achieving variation in lift, dwell and timing, together with the ability to extend the event of a valve in either direction or, if required, in both directions at the same time.

According to this invention there is provided a valve arrangement comprising a linearly movable valve member, a pair of rotatable eccentric members having different eccentric properties, and means for converting rotary motion of both eccentric members into linear movement of the valve member, the converting means being adjustable to vary the relative effectiveness with which the rotary motion of the eccentric members is converted into linear movement of the valve member, so as to vary a characteristic of the movement of the valve member and to enable progressive adjustment of the effectiveness of each eccentric member independently of the effectiveness of the other eccentric member, wherein the converting means comprises, for each eccentric member, a pivotally movable follower which is pivoted for movement about a pivot axis parallel to the axis of rotation of the eccentric member and has a follower surface held in contact with the eccentric member, and means for angularly adjusting the pivot axis about a datum axis parallel to the axis of rotation of the eccentric member so that the effectiveness of the eccentric varies progressively in dependence upon the angular position of the pivot axis about the datum axis.

Preferably the eccentric member is a cam having a cam profile and the follower has a follower surface held in contact with the cam profile.

Conveniently the follower surface is an external surface of the follower.

Alternatively the follower is a hollow member inside which the cam is rotatable.

Advantageously the follower surface is provided with a cam lobe.

Alternatively the follower is a hollow member having an internal cam profile which is held in contact with the eccentric member wherein the eccentric member has a roller which contacts the cam profile of the follower.

Conveniently the follower is a substantially ringshaped member.

Preferably the converting means includes a lever which extends transversely of the direction of movement of the valve member and which is operatively engaged with the valve member, and means for applying effort to the lever from the rotation of the two eccentric members at two spaced apart locations along the length of the lever.

Advantageously the lever comprises a member which is pivotally or rockably mounted on an element connected to the valve for movement therewith.

Conveniently the pair of eccentric members are carried by a single shaft for rotation therewith.

In order that the present invention may be more readily understood, embodiments thereof will now be described by way of example, with reference to the accompanying drawings in which: Figure 1 is a section through a valve assembly in accordance with the invention; Figure 2 is a side view of the valve assembly of Figure 1; Figure 3 is a side view showing the camshaft for actuation of the assembly of Figures 1 and 2; Figure 4 is an enlarged, perspective view of a rocker used in accordance with the invention; Figure 4'A' is a side view of the rocker of Figure 4; Figure 4'B' is an end view of the rocker of Figure 4; Figure 4'C' is a top plan view of the rocker of Figure 4; Figure 4'D' is a bottom view of the rocker of Figure 4; Figure 5 is a side view showing the rocker of Figure 4 in use;; Figure 6 is a sectional view of a camshaft for use in an alternative embodiment of the invention; Figure 7 is a simplified view corresponding to Figure 2 of a modified embodiment of the invention; Figure 8 is a sectional view showing an alternative embodiment of the present invention; and Figure 9 is a sectional view illustrating another embodiment of the present invention.

Referring initially to Figures 1 and 2 of the accompanying drawings a valve arrangement according to the present invention comprises a conventional poppet valve 1 having a head 2 and an elongate stem 3. The poppet valve is of the type which is conventional as found in an internal combustion engine. The poppet valve is intended to cooperate with a valve seat (not shown).

The elongate stem 3 of the valve passes through a conventidnal valve guide 4, and the upper end of the stem 3 is received within a recess formed in the underside of a bucket 5. The bucket is slidably received within an aperture 6 formed in part of a conventional cylinder head 7. The'upper surface of the bucket 5 is provided with a transverse rib 8 which, as can be seen in Figure 2, has a depressed upper surface 9 of arcuate form.

Received within the recess 9 is a rocker unit 10.

The rocker unit is illustrated more clearly in Figure 4 and it can be seen that the rocker unit 10 comprises two parallel spaced apart cylindrical portions 11, 12, the mid-regions of which are interconnected by a saddle 13 which presents an arcuate undersurface 14.

The arcaute undersurface 14 has a configuration corresponding to that of the arcuate recess 9, and is received within that arcuate-recess. The rocker unit 10 may thus effect a rocking motion about the centre of curvature of the arcuate undersurface 14.

The upper -part of each cylindrical arm 11, 12 engages a respective shoe 15, 16. Each shoe has a part curved 17 and part linear undersurface 18. When the rocker unit 10 is in a horizontal position, the peripheries of the arms 11, 12 are received in the arcuate portions 17 of the undersurface of each respective shoe 15, 16 but, if the rocker unit rocks, the peripheries of the arms 11, 12 will traverse the linear portions 18 of the undersurface. The arrangement may then be in the condition illustrated in Figure 5.

The upper surface of each shoe is of arcuate form, the plane of the arc being transverse to the plane of the arcuate surface 9 formed on the bucket 5.

As can be seen in Figure 2, the described apparatus incorporates two valves 1, 1'.

The described valve is adapted to be controlled by means of a cam shaft 20 which is provided with a plurality of cam lobes 21, 22, 23, 24 thereon at axially spaced positions. The cam lobes are of the same configuration, but they have different angular orientations.

Each cam lobe, such as a cam lobe 21, engages a cam follower 25. Each cam follower is of substantially circular outer configuration, and is pivotally supported on a trunion 26 for movement about a pivot axis which is parallel with the axis of the camshaft 20. However, the pivot axis is not located at the centre of the circular follower 25, but instead is off-set. Thus the follower 25 is mounted for eccentric rotation. The trunion 26 is mounted on an arm 27 which, in turn, is mounted on a shoe 28 of arcuate form. The shoe 28 is slidable, about a datum- axis in an arcuate manner, as indicated by the arrow 29 over a range of approximately 900 between a first condition (as illustrated) which is turned to the 900 position, and a second position, which is turned to the 3600 position.Adjustment of the -position of the shoe results in adjustment of the pivot axis about the datum axis parallel to the axis of the camshaft.

A fixedly mounted stop 30 is provided which is adajcent the shoe 28 when it is in the illustrated 900 position, the stop having a portion 31 which engages the periphery of the cam follower 25.

A lower portion of the periphery of the cam follower 25 engages the arcuate upper surface of the shoe 15.

From Figure 2 it can be seen that, for the two illustrated valves, there are four cam followers 25, 32, 33 and 34 each mounted on a respective trunion, and each associated with a respective shoe. Thus each follower is independently adjustable. As mentioned above each follower is acted upon by a respective cam 21, 22, 23, 24.

It is to be understood that the valve springs have been omitted from the illustrations for the sake of clarity.

In operation of the described arrangement the camshaft rotates in an anti-clockwise direction. The cam lobe 21 engages the follower 25 and causes the follower 25 to swing away from the camshaft 20 about a pivot axis defined by the trunion 26. Because, when the arrangement is in the condition illustrated in Figure 1, the axis of the trunion 26 is located at the centre of curvatur-e of the arcuate upper surface of the shoe 15, the follower 25 can execute this movement without imparting any downward force upon the shoe 15.However, it. is to be understood that if the shoe 28 were moved in the direction of arrow 29, the follower 25 would then not rotate about an axis which is coincident with the centre of curvature of the upper surface of the shoe 15, and then, when the follower 25 moves in response to pressure applied thereto by the cam lobe 21, the shoe 15 will move downwardly.

It is to be understood that the downward force applied to the shoe on rotation of the camshaft 20 can be regulated from a minimum of zero, when the shoe 28 is at the 900 position, to a maximum when the shoe 28 is at the 360O position. It is to be understood that the downward force can be adjusted in a totally stepless fashion.

The downward pressure applied to the shoe 15 is, as will be readily understood, transferred to one arm 11 of the rocker 10, but the downward force applied by the rocker 10 to the bucket 5 does also depend upon the pressure applied to the other arm 12 of the rocker 10 by the cam follower 32. It is to be appreciated that the cam follower 32 is acted upon by the cam lobe 22 which has a different angular position to the cam lobe 21.

Thus the cam lobes 21, 22 can be considered to be a pair of rotatable eccentric members having different eccentric properties, which are associated with cam followers, shoes and a rocker which serves to convert rotary motion of the eccentric members into linear movement of the valve. Of course, these converting means are adjustable to vary the relative effectiveness with which the rotary motion of the eccentric member is converted into linear movement of the valve member, so as to vary a characteristic of the movement of the valve member and to enable progressive adjustment of the effectiveness of each eccentric member independently of the effectiveness of the other eccentric member.

It is to be understood that if both of the cam followers 25, 32 associated with rocker 10 were mounted on trunions mounted at - the 900 position, on rotation of the camshaft 20, the cam followers 25 would move about their respective axes of rotation, as defined by the trunions, but there would be no force applied to the arcuate upper surfaces of the shoes 15, 16. Thus the valve would not move at all.

If, for example, the cam follower 25 is activated, by moving the shoe 28 towards the 3600 position, then, on rotation of the camshaft, and on movement of the follower 25 due to operation of the cam lobe 21, a downward force will be applied to the arm 11 of the rocker 10. The other arm 12 of the rocker will be maintained in the stationary position, and thus the arm 11 will be moved downwardly, causing the rocker to pivot about the axis defined by the arm 12. The undersurface 14 of the saddle 13 will slide relative to the arcuate recess 9 formed by the rib 8, and a downward pressure will be applied to the bucket 5, thus moving the valve stem 3 downwardly, separating the valve head 2 from the valve seat. It is, of course, assumed that the shoe supporting the trunion of the follower 32 is in the 900 position and is engaged with a stop corresponding to the stop 30.

It is to be understood, therefore, that if the cam follower 32 has its supporting shoe in the 900 position, it is effectively inoperative, whereas if the cam follower 25 has its shoe in any position other than the 900 position, it will be operative. Thus only the profile of cam lobe 21 will influence the operation of the valve.

However, if the reversed situation obtains, the cam follower 25 has its shoe 28 in the 900 position, and the cam follower 32 has its shoe in a position other than the 900 position, then the cam follower 25 will be inoperative, and the cam follower 32 will be operative, and thus only the profile of the cam lobe 22 will influence the operation of the valve.

It is, of course, to be understood that both the supporting shoes of the followers 25 and 32 may be moved away from the 900 or inoperative position, and then both the followers will be operative, and both will apply a downward force to the respective arms of the rocker unit 10, thus serving to open the valve. It is thus to be appreciated- that by adjusting the positions of the shoes supporting the followers 25, 32, the operating characteristic of the valve may be selectively adjusted.

The rocker unit 10 thus effectively comprises a lever which extends transversely of the direction of movement of the valve. A force is applied to the lever from two spaced eccentrics at spaced positions along the lever. the lever is operatively engaged with the valve member to transfer such face of the valve member.

As shown in the accompanying drawings, the cam lobes 21 and 22 have the same profile but are out of phase by 180. Thus, in an internal combustion engine, by having cam follower 32 active, and cam follower 25 inactive, a low speed running situation can be envisaged.

However, by deactivating cam follower 32 and activating cam follower 25 an 180 advance in the timing can be realised, whilst having no direct effect on the amount of lift being generated. Thus, by activating a selected follower, a timing change can be accomplished.

It will be understood that if both cam followers are activated, the degree of lift of the valve can be greater than if only one cam follower is activated.

Also, the amount of movement of the shoe supporting the particular cam follower away from the 900 position towards the 3600 position will help in determining the degree of lift provided by the valve.

It will thus be understood that the described device can achieve a variation in timing and/or a variation in lift, either simultaneously or independently.

Figure 2, as has been mentioned above, illustrates a twin valve assembly. It is to be understood that the valves depicted could be two inlet valves or two exhaust valves, as used in a four valve head assembly. However, it is to be understood that equally the two illustrated valves might comprise one inlet valve and one exhaust valve. Since the timing of the valves can be varied without recourse to varying the timing of the operation.

of the camshaft, both inlet and exhaust valves could be driven off a single camshaft.

It will be apparent, from Figure 2, that the construction of the rocker and the shoes and the cam followers associated with the second valve is precisely the same as the construction of the corresponding components associated with the first valve. Of course, the specific configuration and angular position of the cam lobes 23, 24 may be adjusted in the light of the particular circumstances.

It is to be understood that if the valves are two inlet valves, the cam lobes 21, 22, 23, 24 could all have a similar profile, but each be out of phase, with regard 0 to the adjacent cam lobe by 18 . Thus, if all cam followers 25, 32, 33, 34 were active at once, the whole event, across both valves, could be increased from approximately 1340 to 1800. It will also be understood that if the cam lobes 22 and 23 were in phase with each other, the overall event across both arms will be approximately 1520. The valve 1 can be advanced by activating follower 25 and the valve 1' can be retarded by activating follower 34. However, if only followers 32 and 33 are active, then the total events be approximately 1340. However, the advance and/or retard elements can be included independently.

Whilst, in the above description, specific angular values are given, it is to be appreciated that in modified embodiments of the invention, different angular values could be obtained.

Figure 6 illustrates a modified camshaft 20', having a pair of cam lobes 35, 36. Cam lobe 35 is designed to have an event angle of 1200, whilst cam lobe 36, is of large configuration, and has an extended event angle of 1400. If a camshaft 20 having such cam lobes, is utilised with the cam lobes engaging cam followers 25 and 32 as described above, by activating each cam lobe in concert, or separately, a high speed or low speed breathing cycle can be instigated. Also, by using both cam lobes together, increased lift can be generated.

Thus, if cam 35 were active, and cam 36 were brought into play without deactivating cam 35, the lift could be increased at, or around, the point of mid-dwell.

Therefore, by applying modest amounts of lift by way of the followers 25 and 32, the activation of both cams will automatically produce more lift during the most extensive event.

It will therefore be appreciated that embodiments of the invention may be devised which are of considerable flexibility to valve operation, without being complexed.

Figure 7 illustrates a modified embodiment of the invention in which, instead of shoes being interposed between the cam followers and the arms 11, 12 of the rocker 10, modified followers 37, 38 are provided, the lower peripheral portions of which are configured to have a part linear and part arcuate undersurface, corresponding to the configuration of the undersurfaces of the shoes described above. Of course, it is-only part of the periphery of each follower 37, 38 which engages the arms 11, 1? of the rocker 10 during operation of the device, and it is these parts of the peripheries of the followers which have the described configuration. Otherwise the embodiment illustrated in Figure 7 is the same as that described with reference to Figures 1 to 4.

Whilst, in the above-described embodiments of the invention, a camshaft is provided with external lobes which engage the outer periphery of the cam follower, it is possible to devise embodiments of the invention in which the camshaft passes through the centre of a ringlike cam follower. Reference may be .made to Figure 8 which shows a camshaft 40 provided with cam lobes 41, 42 which passes through a ring-shaped cam follower 43 having an inwardly directed projection 44 for engagement with the cam lug 42. The cam follower 43 is mounted pivotally on a trunion 45 which is mounted for adjustment in an angular way, such as the adjustment of the trunion 26 described above. The outer periphery of the ring-shaped cam follower 43 engages on the upper surface of a shoe 46, which corresponds with the shoe 15. In Figure 8 the cam follower 43 is shown at the 3600 maximum lift position.It is to be noted that the two cam lobes 41, 42 are shown as being out of phase by 900, and for the simplicity of illustration the ring-shaped cam follower for the lobe 41 is not illustrated.

Figure 9 illustrates a further modified embodiment of the invention in which a ring-shaped cam follower 43 is pivotally mounted on a trunion 45 and has an inwardly directed projection 44, whilst the exterior of the ringshaped cam follower 43 engages on a shoe 46. A camshaft 40' is rotatably mounted passing through the centre of the ring-shaped cam follower 43 and it carries a plurality of rollers 47, 48 which act as cam lobes. The roller 47, for example, engages the internal periphery of the ring-shaped cam follower 43, and when the roller 47 engages the inwardly directed projection 44, the cam follower 43 executes an eccentric pivotal motion about the axis defined by the trunion 45, thus causing the shoe 46 to be moved downwardly. The cam follower to cooperate with the roller 48 is not illustrated.

It is to be understood that appropriate arrangements will be provided to lubricate the components of the arrangements described above. In modified embodiments of the invention the rocker device can be attached to a fixed pivot point mounted on the top of the bucket if required, and the shoes can be also be captive upon the rocker if required. It is to be appreciated that any number of valves can be used in conjunction with a single camshaft. However, if the cam lobes are to be situated in a very close approximity to one another, it must be assumed that a fabricated camshaft will be used in commercial embodiments of the invention, since machining solid integral cams in close proximity is extremely difficult in mass production.

In modified embodiments of the invention the shoes can be restricted from lateral movement, as shown in the accompanying drawings. However, lateral movements can be included with fixed bucket pivots. Further modifications may be effected and the rocker, instead of contacting a conduit contact surface formed in the top of the bucket, may instead engage a rocker contact point.

A valve arrangement as described above may, of course, be incorporated in an internal combustion engine, but may also find other applications.

Claims (15)

CLAIMS:

1. A valve arrangement comprising a iinearly movable valve member, a pair of rotatable eccentric members having different eccentric properties, and means for converting rotary mqtion of both eccentric members into linear movement of the valve member, the converting means being adjustable to vary the relative effectiveness with which the rotary motion of the eccentric members is converted into linear movement of the valve member, so as to vary a characteristic of the movement of the valve member and to enable progressive adjustment of the effectiveness of each eccentric member independently of the effectiveness of the other eccentric member, wherein the converting means comprises, for each eccentric member, a pivotally movable follower which is pivoted for movement about a pivot axis parallel to the axis of rotation of the eccentric member and has a follower surface held in contact with the eccentric member, and means for angularly adjusting the pivot axis about a datum axis parallel to the axis of rotation of the eccentric member so that the effectiveness of the eccentric varies progressively in dependence upon the angular position of the pivot axis about the datum axis.

2. A valve arrangement according to claim 1, wherein the eccentric member is a cam having a cam profile and the follower has a follower surface held in contact with the cam profile.

3. A valVe arrangement according to claim 2, wherein the follower surface is an external surface of the follower.

4. A valve arrangement according to claim 2, wherein the follower is a hollow member inside which the cam is rotatable.

5. A valve arrangement according to claim 2, 3 or 4, wherein the follower surface is provided with a cam lobe.

6. A valve arrangement according to claim 1, wherein the follower is a hollow member having an internal cam profile which is held in contact with the eccentric member.

7. A valve arrangement according to claim 6, wherein the eccentric member has a roller which contacts the cam profile of the follower.

8. A valve arrangement according to claim 4, 6 or 7, wherein the follower is a substantially ring-shaped member.

9. A valve arrangement according to any preceding claim, wherein the converting means includes a lever which extends transversely of the direction of movement of the valve member and which is operatively engaged with the valve member; and means for applying effort to the lever from the rotation of the two eccentric members at two spaced apart locations along the length of the lever.

10. A valve arrangement according to claim 9, wherein the lever comprises a member which is pivotally or rockably mounted on an element connected to the valve for movement therewith.

11. A valve arrangement according to any preceding claim, wherein the pair of eccentric members are carried by a single shaft for rotation therewith.

12. A valve arrangement substantially as hereinbefore described with reference to the accompanying drawings.

13. A valve arrangement according to any one of the preceding claims incorporated -in an internal combustion engine.

14. An internal combustion engine incorporating a valve arrangement -according to any one of claims 1 to 12.

15. Any novel feature or combination of features described herein.