EP0205527A1

EP0205527A1 - Arrangements for converting rotary motion to linear motion

Info

Publication number: EP0205527A1
Application number: EP86900206A
Authority: EP
Inventors: Frederick Michael Stidworthy
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-12-12
Filing date: 1985-12-12
Publication date: 1986-12-30
Also published as: WO1986003550A1; GB2172653A; GB8530660D0; GB8431407D0; AU5310486A; GB2172653B; JPS62501863A

Abstract

Dispositif convertisseur du mouvement rotatif d'une came (9) sur un arbre à cames (1) en un mouvement linéaire périodique d'une soupape en champignon (8) dont le mouvement linéaire est guidé par un guide (7). La soupape possède un godet (5) sollicité par un ressort de soupape (non illustré) et pourvu d'une semelle conique (4) présentant une surface courbe de contact. Un suiveur de came (3) est monté de manière pivotante sur un pivot (2) définissant un axe de pivot parallèle à l'axe de rotation de l'arbre à cames (11). Le suiveur de came (3) est sollicité élastiquement (CS) de manière à être en contact avec la came (9) et la semelle (4). Le pivot (2) est réglable angulairement autour d'un axe donné (D) parallèle à l'axe de rotation de l'arbre à cames, de sorte que le déplacement linéaire de la soupape (8) est variable en fonction de la position angulaire séléctionnée du pivot (2). Dans une variante, l'arbre à cames traverse un suiveur de came annulaire pivotant sur un pivot réglable angulairement et l'arbre à cames agit de concert avec une surface interne du suiveur de came pour déplacer la soupape.Device for converting the rotary movement of a cam (9) on a camshaft (1) into a periodic linear movement of a mushroom valve (8), the linear movement of which is guided by a guide (7). The valve has a cup (5) biased by a valve spring (not shown) and provided with a conical sole (4) having a curved contact surface. A cam follower (3) is pivotally mounted on a pivot (2) defining a pivot axis parallel to the axis of rotation of the camshaft (11). The cam follower (3) is resiliently biased (CS) so as to be in contact with the cam (9) and the sole (4). The pivot (2) is angularly adjustable around a given axis (D) parallel to the axis of rotation of the camshaft, so that the linear movement of the valve (8) is variable depending on the position selected angular of the pivot (2). Alternatively, the camshaft passes through an annular cam follower pivoting on an angularly adjustable pivot and the camshaft acts in concert with an internal surface of the cam follower to move the valve.

Description

Description of Invention

Title: Arrangements for converting rotary motion to linear motion

THIS INVENTION relates to arrangements for converting rotary motion of a rotatable member into linear motion of a linearly movable member.

Arrangements in accordance with the present invention find application particularly, but not exclusively, in the operation of poppet valves in internal combustion engines, in which environment embodiments of the invention may provide the ability to advance and/or retard the onset of the opening and closing movements of such valves, variation of the valve lift from zero to a maximum value, prolongation of the dwell at peak opening, throttling of the engine operation by the valve and disablement of the operation of a cylinder or cylinders in which such valves are incorporated.

It has long been appreciated that an ability to vary the timing and other operating parameters of the inlet and exhaust valves of an internal combustion engine would provide considerable advantages, in that power and economy could be achieved simultaneously, together with much cleaner engine exhaust. The complexities of variable valve timing devices as proposed until now have, however, meant that mass production of such devices has not been feasible. The present invention provides a relatively simple solution to the problem of providing such variable valve timing.

According to the present invention, there is provided an arrangement for converting rotary motion to linear motion, in which a linearly movable member is displaceable, in response to rotation of a rotatable member, by a pivotally movable member which is pivotable about a pivot axis parallel to the axis of rotation of the rotatable member and is held in contact with the rotatable member, the said pivot axis being angularly adjustable about a datum axis parallel to the axis of rotation of the rotatable member so that the movement of the linearly movable member is variable depending upon the angular position of the pivot axis about the datum axis.

In one embodiment of the invention, the rotatable member is a cam having a cam profile and the pivotable member is a cam follower having a follower surface held in contact with the cam profile.

In one embodiment, the follower surface may constitute an external surface of the cam follower. Alternatively, the cam follower may be a ring-shaped member inside which the cam is rotatable.

In another form of the invention, the pivotable member is a ring- shaped follower member having an internal cam profile and the rotatable member is in the form of an eccentric with which the cam profile of the follower is held in contact.

In order that the invention may be readily understood, embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, in which:

FIGURES 1 to 3 illustrate diagrammatically, partly in side elevation and partly in cross section, a first embodiment of an arrangement according to the present invention for operating a poppet valve in an internal combustion engine;

FIGURE 4 illustrates, again partly a cross section and partly in side elevation, incorporation of the arrangement of Figures 1 to 3 in a twin valve system for an internal combustion engine;

FIGURE 5 is a plan view, partly in section, of the twin valve arrangement shown in Figure 4;

FIGURE 6 is a front elevation of a half worm wheel employed in the arrangement of Figures 4 and 5.

FIGURE 7 diagrammatically illustrates a modified form of the arrangement shown in Figures 1 to 3 indicating a possible alternative positioning within the arrangement; FIGURES 8 to 10 diagrammatically illustrate another possible modification of the arrangement shown in Figures 1 to 3;

FIGURES 1 1 to 13 show in diagrammatic form, partly in side elevation and partly in cross section, a second embodiment of an arrangement according to the present invention for operating a poppet valve of an internal combustion engine;

FIGURE 14 illustrates the incorporation of the arrangement of Figures 1 1 to 13 in a twin valve system in an internal combustion engine;

FIGURES 15 to 17 illustrate in diagrammatic form a third embodiment of an arrangement according to the invention for operating a poppet valve in an internal combustion engine;

FIGURE 18 illustrates a possible modification of the third embodiment shown in Figures 15 to 17; and

FIGURE 19 illustrates a possible modification of a follower member included in the embodiments of the invention described in Figures 1 to 18.

Figures 1 to 3 illustrate a first embodiment of an arrangement in accordance with the present invention, in which rotary movement of a cam 9 rotatable with a camshaft 1 is converted into linear movement of a poppet valve 8 constrained for linear movement by a valve guide 7. The conversion of the movement of the cam 9 about the axis of rotation of the camshaft 1 is converted into linear movement of the valve 8 by a follower member 3 mounted for pivoting movement about a pivot 2 and acting on a curved contact surface of a tapered contact shoe 4 provided on the free end of a valve spring bucket 5 of the poppet valve. The pivot axis defined by pivot 2 is parallel to the axis of rotation of the camshaft 1 and is angularly adjustable about a datum axis D parallel to the axis of rotation of the camshaft 1 which, in this embodiment, is a usual kind of solid camshaft carrying a solid cam lobe 9.

The arrow CS in Figure 1 subsequent Figures indicates the action of a contact spring arrangement (not shown) which is required to hold the follower 3 in contact with the shoe 4 and the cam 9.

In Figures 1 to 3, the line X-X extending perpendicularly to both the axis of rotation of the camshaft and the direction of displacement of the valve 8 represents the centre line datum for camshaft 1 and also indicates the position of the pivot axis defined by pivot 2 when such a pivot axis has been rotated anti-clockwise through 90 from the position shown in Figure

Figures 4 and 5 show the application of the valve-operating arrangement of Figures 1 to 3 to a twin valve arrangement for an internal combustion engine. The same reference numeral is given to like components of the two valve operating arrangements shown in the twin valve system of Figures 4 and 5, with the addition of the suffix "a" to differentiate the components associated with one from the components associated with the other. Although the components of the operating arrangement are, in general, the same for each valve, there may be differences, in that one arrangement may require a right-hand component while the other may require the left-hand version of the same component in some cases. In general, the detailed description will be confined to only one of the two illustrated valve-operating arrangements.

As will be seen from Figures 4 and 5, the camshaft 1 is supported for rotation about its axis in suitable journals 16 and 17 in support pillars 13 provided on the cylinder head casting or the like 6. The journals 16 and 17 may be centrally divided in a plane perpendicular to the plane of the drawing, if required. The pivot 2 on which the follower 3 is pivotally mounted is constituted by an eccentric portion of a cranked adjustment shaft 10 which ϊs supported for rotation about the datum axis X-X in suitable bearings in support pillars 13 provided on the casting 6. The adjustment shaft 10 also carries for rotation therewith a half worm wheel 15 constructed as part of a crank 14. This worm wheel 15 is in constant engagement with a worm 1 1 , the lead angle of which is selected to be a "locking angle", in this case approximately 10 . This 10 interface between the worm 1 1 and the worm wheel 15 means that it is possible to rotate the worm wheel 15 by the worm 1 1 but impossible to rotate the worm by rotating the worm wheel. A drive source (not shown) such as an electric motor is connected to the worm 1 1 to rotate the same, and it is thereby possible to rotate the adjustment shaft 10 whilst, once the supply of power to the drive source is terminated, the locking angle engagement ensures that the chosen position of the worm wheel, once reached, is thereafter securely maintained until the drive source is again energised. Any other suitable manner of rotating and locking the adjustment shaft 10 in its adjusted position could of course be used.

A centre bearing housing 18 is provided between the two valves and their operating arrangments to rotatably support the adjacent ends of the two adjustment shafts 10 and 10a. Should it be desireable to couple the shafts 10 and 10a together, then a single worm and worm wheel drive would serve both valves 8 and 8a.

In the Figures of the drawings, emboldened lines indicated bearing surfaces or components.

The basic operation of the first embodiment of a valve-operating arrangement as shown in Figures 1 to 6 will now be described, more particularly with reference to Figures 1 to 3.

The outer peripheral surface or profile of the cam 9 remains in constant, but sliding contact with the outer peripheral surface or follower surface of the follower 3. This sliding contact between the cam and its follower is maintained throughout the entire 360° rotation (in either direction) of the camshaft 1.

In Figure 1 , the angular position of the camshaft is such that the cam lobe, which extends over 124 of rotation, is just about to act on the circular follower surface of the follower 3. However, with the pivot 2 in the illustrated position such that the line connecting the pivot axis and the datum axis D is at 90 to the datum line X-X, the maximum cam effect, as shown in Figure 2, only serves to displace the follower 3 across the curved surface of the shoe 4 without any force being applied to the shoe 4. In this neutral condition, the action of the cam 9 is negated by virtue of the fact that the pivot axis defined by pivot 2 is compatible with the arcuate contour of the contact surface of the shoe 4, the radial distance between the pivot axis and the shoe remaining constant throughout the movement of the follower.

With the pivot 2 in the position illustrated in Figures 1 and 2, the valve 8 therefore will remain closed regardless of the rotation of the cam and such positioning of the pivot 2 would enable the cylinder of an engine associated with the valve 8 to be disabled.

In Figure 3, the pivot 2 is shown as having been rotated anticlockwise from the Figure 1 position through 90º so that the pivot axis coincides with the datum line X-X. As a result, the result of the action of the cam 9 upon location of the camshaft 1 is very different in Figure 3 from that of Figure 2. As shown in Figure 2, rotation of the camshaft now causes the follower 3 to exert a downward pressure upon the shoe 4 with resulting movement of the valve 8. Moreover, assuming the lobe of the cam 9 provides a hypothetical lift. of .228" at maximum, it will be seen that, due to the leverage inherent in the system and the ramp effect of the shoe, the lift capability of the cam is increased to .425".

Accordingly, the two extreme adjusted positions of the pivot 2 dipicted in Figures 1 and 3 respectively represent zero movement of the valve 8 and about .425" of movement of valve 8. Between the two extremes illustrated, i.e., across the 90 of angular adjustment between these positions, there exists a fully variable range of valve movement.

The layout illustrated in Figures 4 and 5 assumes a twin valve engine design with two inlet and two exhaust valves. However, the invention is, of course, equally applicable to single valve applications, such as in two-stroke internal combustion engines, two valve applications with a single inlet and single exhaust valve per cylinder, and engines with multiple inlet and exhaust valves. It will be noted that, in the twin valve arrangment shown, the valves 8 and 8a are provided with individual adjustment shafts 10 and 10a, thereby allowing each valve to be adjusted separately.

In a typical six cylinder engine, there would be 24 valves ( 12 inlet and

12 exhaust) assuming that there are four valves per cylinder. On the assumption that all twelve valves of each kind were to be adjusted in use, then a single, multi-cranked adjustment shaft 10 would be provided and only a single angular adjusting and locking control means (e.g. worm and worm wheel) would be required. If a certain cylinder or cylinders were selected as being suitable for disablement or other modification during running of the engine, then a separate adjustment shaft would be required for this particular cylinder or cylinders.

A possible variation in the arrangement of Figures 1 to 6 is illustrated in Figure 7, which shows that the datum line X-X need not be the same for the datum axis of the follower 3 and the axis of rotation of the camshaft 1. Thus, in the arrangement shown schematically and partially in Figure 7, the axis of rotation of the camshaft 1 lies on a new higher datum line Z-Z and the pivot axis (in the 90º position) lies on a lower datum line Y-Y. The datum axis D of the follower 3 lies on the datum line X-X. The position assumed by the follower 3 upon rotation of the camshaft with the pivot 2 in the neutral 90º position is indicated in dashed lines and by reference 3b for the case of the maximum cam effect on the follower 3.

The two cams 9 and 9a in Figures 4 and 5 are shown as identical and similarly positioned. However, these cams could be staggered, for example in order to cause opening of the two valves 8 and 8a at slightly different times.

The arrangements of Figures 1 to 7 are, therefore, capable of providing complete control of individual valves, or groups of valves, in that the valve lift can be adjusted between zero lift and a maximum lift while the engine or other mechanism in which they are included is running, this being achieved without alteration to the valve timing in this first embodiment of the invention.

Control springing may included at any suitable contact point or points to ensure continuous contact between the cam and the follower and the follower and the shoe, if necessary.

A modified form of the first embodiment of the invention is illustrated by Figures 8 to 10, in which the construction of the arrangment is substantially the same as in Figures 1 to 7, except that the circular follower surface of the follower 3 is also provided with a lobe 3c. Also, in Figures 8 to 10, the datum line Z-Z on which the axis of rotation of the camshaft 1 lies is disposed between the datum lines Y-Y and X-X on which the pivot (in its 90° position ) and the datum axis D lie. The disposition of the datum line Z-Z above the datum line X-X provides for control of the follower 3 by retaining contact between the follower and the cam 9 when the datum line of the pivot 2 is swung from datum Y-Y to X-X.

The lobe 3c formed on the follower surface of the follower 3 is, in the example of Figures 8 to 10, formed in such a way as to remain within the radial confines of the follower's maximum distance from the pivot axis defined by pivot 2, thereby to allow a neutral position with zero valve movement to be obtained (see Figure 10).

Figure 9 indicates an extended dwell at peak displacement of the valve and retard overlap made possible by the arrangement of Figures 8 to 10. Such an arrangement, for example, permits the camshaft 1 to be advanced by several degrees, say half of the degrees of operation available due to the lobe 3c, and this would provide for an overall extension of the whole valve opening, together with a dwell period at the peak opening. The dwell period at the peak of operation is indicated in Figure 9 as having been increased by 2.1.5° from 16° to 37.5 º .

Figures 1 1 to 14 illustrate a second embodiment of the present invention, in which a camshaft 101 is rotatable within a ring-shaped or hollow follower member 103 which is pivotally mounted on a pivot 102 constituted by an eccentric portion of a hollow adjustment shaft disposed concentrically of the camshaft 101.

A contact roller 1 19 is mounted on the camshaft 101 and engages a profiled inner follower surface of the follower 103, which surface exhibits a lobe 109. The hollow shaft 1 10 carries for rotation therewith a worm wheel 1 15 which engages a worm 1 11. A spacer portion 102b interconnects the two pivots 102 and 102a in the twin valve arrangement illustrated in Figure 14.

Other components in Figures 1 1 to 14 which correspond to like components in the first embodiment are designated by the same reference numerals.

Referring more particularly now to Figures 1 1 to 13, the operation of the embodiment of the invention illustrated therein is as follows.

If the camshaft 1 is rotated in an anti-clockwise direction, with the pivot 102 in the position illustrated in Figure 1 1 , then it will be seen that a neutral position exists, in which the follower 3 is simply pivoted about pivot 102 and no displacement of valve 8 is caused. This would, of course, also be true if camshaft 1 were rotated in a clockwise direction.

Figure 12 shows a condition of the arrangement in which the pivot 2 has been rotated by 90 about the datum axis D which coincides with the axis of rotation of camshaft 1. Roller 1 19 is about to come into contact with an opening ramp of the cam lobe 9 of the follower surface of the follower 103. If clockwise rotation of the camshaft 13 is continued to the position shown in Figure 13, displacement of the follower 103 results, with consequent displacement of the valve 8. As illustrated in Figures 12 and 13, the maximum potential lift of .350" provided by the cam lobe 9 is translated into a maximum valve lift of .360".

As in the case of the first embodiment, angular adjustment of the pivot 102 between the respective position shown in Figures 1 1 and 12 permits the valve lift to be varied between zero lift and a lift of .360", in this particular case.

However, in the arrangement illustrated in Figures 11 to 14, unlike the first embodiment of Figures 1 to 7, the timing of the valve movement is changed together with the lift, since the cam lobe 9 is angularly adjusted along with the follower 103 upon adjustment of pivot 102.

It should be noted that, in the embodiment of Figures 1 1 to 14, adjustment of a pivot 102 from the neutral to the fully operative position also provides benefits with regard to "wiping" forces, in that the follower 103 produces a considerable wiping action across the shoe 104 in the neutral position but, as the amount of lift increases, the wiping action decreases as can be seen in Figures 12 and 13. This would indicate that lightweight materials can be considered for the bucket tappet, thereby reducing the mass be moved to acceptable levels.

Control springing similar to the externally contacting springing proposed for the embodiment of Figure 1 can also be employed with the second embodiment shown in Figures 1 1 to 14. It is noted, however, that adjustment of the pivot 102 also changes the loading as regards the valve -closing spring as against the control spring, in that the loading of both springs changes during adjustment from one end position of the pivot to the other. The overall loading will, however, remain constant.

Figures 15 to 18 show a third embodiment of the present invention which is, however, similar to the second embodiment of Figures 1 1 o 14, in that the camshaft 1 extends through a ring - shaped follower 103. The camshaft is, in the case of Figures 15 to 18, a normal camshaft 1 provided with a cam 9 as in the case of the first embodiment of Figures 1 to 7. Contact between the cam 9 and the follower 103 is established by means of a roller 200, the contact pressure being maintained as a result of the valve spring (not shown) pressing the bucket and shoe assembly 4 and 5 into contact with the external periphery of the follower 103.

Figure 16 illustrates the adjusted position of the pivot 2 which provides neutral operation with zero valve lift.

Figures 15 and 17 illustrate an adjusted position of pivot 2 which provides maximum valve lift, Figure 15 showing the cam 9 in an inoperative position during its rotation with the roller 200 kept in firm contact with the circular portion of the cam profile as a result of the valve spring pressure. Figure 17 illustrates a position in which the camshaft has been rotated to bring the lobe of the cam 9 into contact with the roller 200 and thereby cause displacement of the follower 103 and the valve 8. The potential lift of .288" provided by the lobe of cam 9 is translated, in this arrangement, into a resultant maximum valve lift of .3 12".

A fully spring - controlled version of the arrangement embodied in Figures 15 to 17 is shown schematically in Figure 18, in which the follower 203 is formed with a spring housing 24 which accommodates a control spring 23 acting between a closed end of the housing 24 and a piston carrying a roller 21 which engages the cam 9 at a position diametrically opposite the roller 200 carried by the internal follower surface of the follower 203. Such a spring - loaded arrangement keeps the follower under control at all times, whilst still enabling the arrangement to be fully variable as regar ds timing and lift. The Figure 18 modification would also render possible a Desmodromic arrangement in which the follower 3 is attached directly to the valve 8, thereby eliminating the need for a bucket 5 or a valve spring.

In the above described embodiments of the invention, it has been assumed that the contact surface between the cam and the follower and the contact surface between the follower and the shoe is one and the same. However, this need not be the case and Figure 19 illustrates a possible arrangement in which the surface of the follower responsible for following the cam 9 is separate from the surface responsible for acting on the shoe 4 or shoes 4 and 4a.

The arrangement illustrated in Figure 19 is intended for inclusion in cm arrangement such as the twin valve device shown in Figure 4. To this end, a single cam follower 3 is provided with two outp ut rings 3b and 3c which act on respective valve buckets 5 and 5a (not shown in Figure 19). As a result, the valves 8 and 8a would operate in unison, unless as might be required the two output rings 3b and 3c were provided with different external contours in some way. Only one pivot 2 is required for the pair of valves in this form of arrangement , but two separate pivots 2 and 2a could be provided as in Figure 4 and, if required, a single output ring 3b or 3c could be provided on each of two separate followers 3 and 3a, if this is preferred.

It is envisaged that embodiments of the present invention will enable an internal combustion engine to be provided with the benefits of variable lift and timing and valve throttling with relatively little alteration to the existing engine design.

Claims

1. An arrangement for converting rotary motion to linear motion, in which a linearly movable member is displaceable, in response to rotation of a rotatable member, by a pivotally movable member which is pivotable about a pivot axis parallel to the axis of rotation of the rotatable member and is held in contact with the rotatable member, the said pivot axis being angularly adjustable about a datum axis parallel to the axis of rotation of the rotatable member so that the movement of the linearly movable member is variable depending upon the angular position of the pivot axis about the datam axis.

2. An arrangement according to Claim I , in which the rotatable member is a cam having a cam profile and the pivotable member is a cam follower having a follower surface held in contact with the cam profile.

3. An arrangement according to Claim 2, in which the follower surface is an external surface of the cam follower.

4. An arrangement according to Claim 2 in which the cam follower is a ring-shaped member inside which the cam is rotatable.

5. An arrangement according to Claim I , in which the pivotable member is a ring-shaped follower member having an internal cam profile and the rotatable member is in the form of an eccentric with which the cam profile of the follower is held in contact.

6. An arrangement according to Claim 5 in which the eccentric is in the form of a roller which contacts the cam profile of the follower.

7. An arrangement according to Claim 3 or 4, in which the follower surface of the follower is provided with a cam lobe.

8. An arrangement according to Claim 5, in which the cam follower surface has a roller mounted thereon in contact with the cam profile.

9. An arrangement according to Claim 8, in which the contact roller of the follower surface is angularly spaced by 90º from the pivot axis of the follower.

10. An arrangement according to Claim 9 in which the follower has a second contact roller which is movable radially of and resiliently biased towards the datum axis.

1 1. An arrangement according to Claim 10, in which the first and second contact rollers of the follower are diametrically opposed.

12. An arrangement according to any preceding claim, in which the pivot axis of the follower is defined by a pivot carried eccentrically of an adjustment shaft the axis of rotation of which constitutes the datum axis, the angular position of the shaft being adjustable by means for rotating the adjustment shaft and holding such shaft in its adjusted position.

13. An arrangement according to Claim 12, in which the adjustment means comprises a driven member rotatable with the adjustment shaft and a driving member adapted to be driven by a power source, the driving engagement between the driving and driven members being such that motion can be transmitted from the driving member to the driven member but not vice versa.

14. An arrangement according to Claim 13, in which the driven member is a worm wheel and a driving member is a worm.

15. An arrangement according to any preceding claim, in which the rotatable member is carried or constituted by a camshaft and the linearly movable member is a valve member.

16. An arrangement converting rotary motion into linear motion substantially as hereinbefore described with reference to the accompanying drawings.

17. An internal combustion engine having an arrangement according to any one of the preceding claims for converting motion of a camshaft into motion of the valves of the engine.

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