GB2183770A

GB2183770A - Rotary drive arrangements

Info

Publication number: GB2183770A
Application number: GB08620899A
Authority: GB
Inventors: Frederick Michael Stidworthy
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-08-31
Filing date: 1986-08-29
Publication date: 1987-06-10
Also published as: CN86106074A; EP0235229A1; AU6333586A; GB8620899D0; GB8521718D0; WO1987001423A1

Abstract

A rotary drive arrangement for rotating a camshaft (13) so that the speed of rotation oscillates during a revolution of the camshaft comprises a driving sprocket wheel (19) driving a follower (1) mounted on a square-section shaft (4) driven by the sprocket wheel. The follower is slidable on the shaft (4) transversely of the axis of rotation of the sprocket wheel and is held in contact with a cam surface of a stationary hollow cam member. A pin (6) fixed to the follower (1) eccentrically of the axis of rotation is drivingly engaged in an aperture (15) in a drive arm (12) fixed to the camshaft, so that there is imparted to the camshaft a rotational motion which oscillates during a revolution of the driven member in accordance with the sliding motion of the follower resulting from its contact with the cam surface.

Description

SPECIFICATION Rotary drive arrangements THIS INVENTION relates to a rotary drive arrangement for rotating a driven member so that the speed of rotation increases and decreases, or "oscillates" during a revolution of the driven member.

The drive arrangement finds particular application in applying oscillatory pulses to the rotation of a camshaft, but the basic principles can be applied to any shaft, component or axle arrangement wherein such rotational characteristics are deemed desirable.

According to the invention, there is provided a rotary drive arrangement for rotating a driven member so that the speed of rotation oscillates during a revolution of the driven member, which arrangement comprises a rotatable driving member, a follower member rotatable with the driving member and slidable relative to the driving member transversely of the axis of rotation of the driving member, a cam member having a cam surface with which the follower member is held in contact during its rotation, and means coupling a point on the follower member located eccentrically of the axis of rotation of the driving member to the driven member to impart to the driven member a rotational movement which oscillates during a revolution of the driven member in accordance with the sliding motion of the follower member resulting from its contact with the cam surface.

In order that the invention may be readily understood, embodiments thereof will now be described by way of example, with reference ot the accompanying drawings, in which: Figure 1 is an end elevation, partly in section, of part of one embodiment of rotary drive arrangement according to the invention; Figure 2 is a side elevation partly in section, of the Figure 1 embodiment of rotary drive arrangement; Figure 3 is a plan view, partly in section, of the rotary drive arrangement of Figure 2; Figure 4 is a view like Figure 1 of a rotary drive arrangement having a modified follower member; Figure 5 is a side elevation, partly in section, of another embodiment of a rotary drive arrangement according to the invention; Figure 6 is an end elevation of a rotary drive embodying the invention and illustrating a modified coupling between the follower member and a driven member; and Figure 7 is a side elevation, partly in section, of the arrangement of Figure 6.

While this invention will be particularly described in terms relating to motor vehicles, it should be understood that the principles involved can be used in any situation wherein a oscillatory motion is required. However, as the control of valve timing in internal combustion engines is an extremely important area of endeavour this particular description is based upon examples of the rotary drive arrangement concerned with the timing and rotational characteristics of a camshaft and capable of defining, not only the event, but also the shape of the envelope concerned.

The present invention offers a simple solution to the problem of providing variable valve timing and behaviour in internal combustion engines, in that the necessary components are, in themselves, extremely basic in mechanical realisation and, therefore, cost effective.

Referring now to Figures 1 to 3, a rotary drive arrangement comprises a reciprocable follower 1 mounted upon a square-section drive-shaft 4 within an annular cam 9. The follower 1 contacts the annular cam 9 via a free-running roller 2, but this roller could be replaced by a solid follower point. Follower 1 is provided with a slotted centre 3. The sides of the slot 3 are parallel wth the side walls of the square-section shaft 4, and are shown to be in bearing maintained communication.

The amount of travel which is permitted to the follower 1 relative to the shaft 4 is, in this example, restricted by the length of slot 3.

The lateral axis i.e. the sliding axis, of follower 1 is, in Figure 1, shown at 90" to a datum line "X"--"X".

If the follower 1 is allowed to reciprocate upon the shaft 4, it will be seen that the lever arm 5, which is fixed to or part of follower 1, will also be caused to reciprocate.

The centre-line axis X"-"X' of lever 5 is at 90" to the main reciprocal centre datum of follower 1, as both datums meet at the centre of rotation of the shaft 4. It will be seen, that any reciprocating movement of follower 1 will have the effect of lengthening, or shortening the effective length of lever 5.

Lever 5 is provided with a pin 6 located eccentrically of the axis of rotation of shaft 4, and the eccentric pin 6 is provided with a flange 20. Therefore, if the pin 6 is brought into contact with a resistive loading, any rotation of the shaft 5 will result in the follower 1 being caused to rotate, with roller 2 maintained in forced contact with annular cam 9.

If annular cam 9 were perfectly circular, then there would be no change in the attitude of the follower 1, i.e. it would simply describe a perfectly circular motion. However, annular cam 9 is provided with an undulating inner cam surface provided, in this example, with four lobes 8. Therefore, if contact is maintained between the roller 2 and the annular cam 9, a reciprocating motion will be experienced by follower 1, relative to the shaft 4.

In the end elevation of Figure 1 the direction of rotation of the shaft 4 is important. If the shaft 4 as shown in Figure 1 were rotated in a clockwise fashion, with an anti-clockwise resistance applied to the pin 6, then the follower 1 would be driven linearly transversely of the shaft with the roller 2 coming out of contact with annular cam 9, after the roller 2 passes the crest of the first lobe 8 of the cam surface that it passes the follower 1 then remaining in a "static" mode not engaging the cam surface as the shaft 4 rotates as long as the situation described is maintained.

If, however, the shaft 4 is rotated in an anti-clockwise direction, with a clockwise resistive loading applied to the pin 6, then the original status as described is maintained; i.e.

the roller 2 will be forced into contact with annular cam 9 and a reciprocating motion will be generated by the follower, with the resultant change in effective lever length felt by item 5.

Referring to Figures 2 and 3, it will be seen that the shaft 4 is fixed to or part of an input shaft 18 which, in turn, is fixed to or part of a mounting flange 16, to which is fixed a driving sprocket wheel 19. Therefore, any rotational movement of sprocket wheel 19 will result in similar rotational movement of shaft 4. Input shaft 18 is bearing located within a journal assembly 1.

Follower 1 is indicated as being a free-sliding component, located upon the shaft 4 and maintained in correct location by two side mounted guides 10 and 11, these preventing any sideways movement away from the desired reciprocative attitude of follower 1. The two guides are fixed to, or part of shaft assembly 18, 4.

Figure 3 shows that the eccentric pin 6 is located within a slightly elongated aperture situated in a cranked arm 12 which is fixed to, or part of, a camshaft 13. Thus, as the shaft 4 is rotated the pin 6 will follow a generally circular path and will cause the camshaft 13 to rotate. Any change in the effective length of the lever 5 to which the eccentric pin 6 is attached, will therefore have a considerable effect upon the instantaneous speed of rotation of the camshaft, for the repeated lengthening and shortening of the effective parameters will change the constant rotational motion of the driving assembly 18, 4 to one of oscillatory rotational motion of the driven assembly 12, 13.

This will, for any rotational input via shaft 18 cause a speeding up and slowing down of shaft 13, the size and frequency of the undulations or lobes of the annular cam determining the number of oscillatory pulses felt by shaft 13. If annular cam 9 were a fixed component, the number of pulses (four as indicated in Figure 1), would remain constant and will occur (peak) at 450, 315 , 225 and 135".

It will be seen, however, that annular cam 9 is carried by an annular carrier 7 which is capable of being rotated concentrically of the axis of rotation of shaft 4. The oscillatory pulse sequence can thus be advanced and/or retarded in relation to the basic rotary input timing by adjusting the angular position of the carrier 7. The carrier 7 is provided with a means (not shown) for rotating it and locking it in the adjusted position. A worm/wormwheel assembly having the necessary "locking" lead angle is one example of a suitable adjusting means, but any suitable repositioning means can be incorporated, and the necessary control (manual or otherwise) mechanism (not shown) can be added in order to maintain a desired functional envelope.

It is clear, therefore, that there are two options presented by this particular device; i.e.

fixed annular cam arrangement or an annular cam unit capable of repositioning.

As shown in Figure 1, the annular cam 9, has four undulations, or lobes, each equal in size, shape and profile and with a similar rise and fall. In other embodiments any desired number of cam lobes may be provided, each having a desired size and shape. The lobes may thus all be the same, or may all be different. The positioning, profile and general intention can be designed to suit any desired pulse "shape", and in this respect, the eventual event as described by the individual valve, can be designed according to oscillatory accelerations and declerations of a repositional nature.

This gives the internal combustion engine engineer the ability to design valve operating envelopes without structure or compromise, and regulate valve openings, closings, dwells and sequences etc., to suit any revolution, power or emission consideration, and if used in aeroplane internal combustion engines, the full benefits of adjustment according to altitude etc., could have significant effects upon all aspects of safety, range and economy etc.

A bearing journal 14 is responsible for supporting the camshaft 13.

Figure 4 shows a variation of the arrangement of Figures 1 to 3, in which the main reciprocative axis is parallel with the axis passing through the centres of the eccentric pin 6 and the roller 2. All other components are similar to those of Figure 1. However, it will be seen that there are only three lobes 8 indicated in this drawing. Figure 4 illustrates that the reciprocating axis can be varied in order to benefit from angles of mechanical advantage, or disadvantage, depending upon the requirements. It is assumed that annular cam carrier 7 is either fixed or adjustable. The three lobes 8 are situated 1200 apart. The direction of rotation of the shaft 4 is assumed to be anti-clockwise.

The in-line six cylinder internal combustion engine presents certain difficulties in respect of "nose" mounted devices, i.e. devices mounted at the end of the camshaft, in that, the six events (intake or exhaust) have a certain degree of overlap. Therefore, it is necessary to divide the camshaft 13 into two separate shafts, and provide, for example, a concentric quill shaft down the inside of the first "half" camshaft.

The quill shaft would then drive the squaresection shaft between the two "half" camshafts. In order that the two "half" camshafts receive the correctly timed pulse sequences etc., there would be two coupled squaresection shafts, the second of which would be out of phase with the first, thereby allowing for the event differences. This would require, either one shared annular cam, or two separate annular cams, and two separate followers. In this way, the six cylinder requirements can be met by this type of oscillatory installation.

Figure 5 shows another embodiment of the invention, which includes two annular cams.

However, unlike the version required for the in-line six, these two annular cams 7 and 7a are intended to serve a single camshaft 13. It will be seen, that input shaft 18 is provided with a square section 2, and a follower guide 4. Follower 1 is mounted upon the squaresection 2 in the usual way; i.e. it is free to reciprocate. Follower 1 has an eccentric pin 6 which is located in the elongated slot situated in cranked are 12, this being fixed to, or part of, the small concentric lay camshaft 21. The assembly comprising cranked coupling arm 12, the second square-section 2a, follower guide 4a and internal, concentric shaft 21 is a free-running, bearing located assembly, with shaft 21 mounted within the main camshaft 13.

A second follower 1a is mounted upon square-section 2a and is provided with its own annular cam 7a, annular cam 7 being provided for follower 1. An output eccentric pin 6a is located, in free but constant communication within the elongated slot situated in the cranked arm 1 2a which is fixed to, or part of, the main camshaft 13. Any rotation of shaft 18 will result in the reciprocation of both followers 1 and la, with their effects being felt upon shaft 13.

As they are controlled by two separate annular cams 7 and 7a, the two followers can be subjected to separate pulse sequence timing changes, in that the lobes present upon one annular cam can be angularly moved in relation to those of the other. Either or both can be adjustable.

This means that one set of lobes could, if required, be used to negate those of the other, extend those of the other, or complement, or detract effects as required. Furthermore, one annular cam could be used to generate basic advance/retard of the overall camshaft assembly, while the second annular cam is used to generate the oscillatory pulse sequence variations required in order to change event profile. Event profile is the main cam profile event present upon the cams responsible for operating the valves. The Figure 5 embodiment therefore provides extreme flexibility of operation for minimum complexity.

The examples described by with reference to Figures 1 to 5 rely upon leverage and sliding surfaces in order to create the reciprocating/oscillatory output from the drive shaft to the camshaft 13. This simple method of producing the desired results is only one way of applying the reciprocative action, and Figures 6 and 7 illustrate a further possibility.

Figures 6 and 7 illustrate an embodiment in which there is a rack and pinion comprising between the input shaft and the camshaft. A rack 22 is formed integrally with the follower 1. A pinion gear 24 meshes with the rack 22.

The gear 24 is mounted on a long shaft 23, which, as will be described, transmits a drive to the camshaft 13.

The rack and pinion coupling of Figures 6 and 7 is able to offer extremely positive coupling between the input shaft (sprocket shaft) and the camshaft 13, in that the gear tooth engagement between rack 22 and pinion 24 ensures maximum mechanical advantage. The reciprocative action created by the follower 1 and annular cam 9 is directly transferred to the pinion.

It will be seen, that the pinion gear 24 is fixed to, or part of, the lay-shaft 23, this being bearing located within the elongated guide members 10 and 11. Lay-shaft 23 is also provided with a compound pinion gear 25 which, serves as a planet engaging a sun gear 26 is fixed to, or part of, the camshaft 13. The engagement ratio indicated i.e. gear 25 being larger than gear 26 would suggest that the oscillatory motion created in the pinion 24 will be exaggerated. However, any suitable ratio between the rack and pinion, and/or compound pinion and camshaft sun gear can be contemplated according to design requirements.

If the square-section shaft is considered as being rotated in an anticlockwise direction then it will be understood that the resistance in the camshaft 13 will cause compound pinion 25 to attempt to "walk" around sun gear 26. However, this will cause gear 25 to rotate in an anti-clockwise direction, turning the lay-shaft 23 in the same anti-clockwise direction, and causing rack 22 to move in a radially outwards direction, thereby forcing the follower 1 to apply pressure, via the roller 2 upon the internal face of annular cam 9. This illustrates the contact loading necessary to ensure pressured communicatian between roller 2 and the undulating internal cam 9.The four lobes of cam 9 are shown to be in the 45 ; 135 ; 225 and 315 positions, with lobe 8 at 315 , however, this is only a hypothetical layout and the positional locations can be situated at any point, and the contours of the lobes can be designed to any set of angular requirements, thereby making the pulse shape suitable for any valve event characteristics as may be required.

It is assumed that annular cam carrier 7 can be either fixed or repositional, and the methods of rotating and locking can be of any suitable kind. A peripheral worm-wheel fixed to, or part of, the outer face of the annular carrier 7 engaged with a worm with say a 10 lead angle, will satisfy both requirements.

Input shaft 18 can be a shaft connected directly to the sprocket wheel (not shown) or to any other rotational device.

It is possible to suggest that two pinions could be engaged with a single rack gear, one out of phase with the other and thereby provide a device capable of satisfying the splitshaft in line six requirements, etc.

In all the examples given above, it is possible to rotate the annular assembly 7, 9 in order that the oscillatory pulses created, are caused to occur during negative periods; i.e.

during the periods when a particular valve is closed, thereby causing no direct effect upon the event. This would allow the oscillatory effects to be completely negated.

A double rack and pinion, twin annular assembly version, as suggested by the single annulus version of Figures 6 and 7 could be constructed in order to produce a device similar to that illustrated by Figure 5, i.e. one section responsible for overall advance/retard, and the second section concerned with pulse generation. Both sections may be variable one against the other, or in any conflicting or compatible overlapping of function.

All of the devices herein described, as hypothetical and variations, and combinations of their various characteristics etc, can be contemplated, however, they offer to the engine designer, a very easy method of including complete control and variation of valve timing and event profile/envelope etc. The mechanical components required are of basic engineering requirement, and there are no "new material" requirements.

The ability to inciude these inventions to any internal combustion engine does not demand a redesign of the original engine, and after-market "add-on" examples can be contemplated.

Lubrication requirements would be in line with present camshaft demands.

While return springs are not shown, their inclusion may be necessary.

The square-section is, in all examples given, indicated as being the "drive" shaft, however, it is possible to construct negatives of all examples, in which the "slot" is the drive section, and the square-section is part of the follower etc.

Claims

1. A rotary drive arrangement for rotating a driven member so that the speed of rotation oscillates during a revolution of the driven member, which arrangement comprises a rotatable driving member, a follower member rotatable with the driving member and slidable relative to the driving member transversely of the axis of rotation of the driving member, a cam member having a cam surface with which the follower member is held in contact during its rotation, and means coupling a point on the follower member located eccentrically of the axis of rotation of the driving member to the driven member to impart to the driven member a rotational movement which oscillates during a revolution of the driven member in accordance with the sliding motion of the follower member resulting from its contact with the cam surface.

2. A rotary drive arrangement according to claim 1, wherein the coupling means comprises a pin fixed to the follower member eccentrically of the axis of rotation and drivingly engaged with a drive arm extending transversely of the axis of rotation of the driven member.

3. A rotary drive arrangement according to claim 1, wherein the coupling means comprises a rack attached to the follower member parallel to the direction of sliding of the follower member, the rack engaging a pinion rotatable with a lay-shaft which is drivingly coupled to the driven member.

4. A rotary drive arrangement according to claim 3, wherein the layshaft carries a planet gear wheel drivingly engaged with a sun gear wheel carried by the driven member.

5. A rotary drive arrangement according to any preceding claim, wherein the cam member has a fixed angular orientation about the axis of rotation of the driving member.

6. A rotary drive arrangement according to any one of claims 1 to 4, wherein the angular orientation of the cam member about the axis of rotation of the driving member is adjustable to vary the timing of the oscillations in the speed of rotation of the driven member.

7. A rotary drive arrangement according to any preceding claim, wherein the driven member carries a second follower member rotatable with the driving member and slidable relative to the driven member transversely of the axis of rotation of the driven member, the second follower member is held in contact with a cam surface of a second cam during its rotation, and a point on the second follower member located eccentrically of the axis of rotation of the driven member is coupled to a second driven member to impart to the second driven member a rotational movement which oscillates during a revolution thereof in accordance with the superimposed sliding motions of the two follower members.

8. A rotary drive arrangement according to any preceding claim, wherein the follower member is formed with a rectangular slot which receives a portion of the driving member of rectangular cross-sectional shape.

9. A rotary drive arrangement according to any peceding claim, wherein the driving member is a sprocket wheel and the driven member is a camshaft.

10. A rotary drive arrangement substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

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