WO1987003335A1

WO1987003335A1 - Variable rotary drives

Info

Publication number: WO1987003335A1
Application number: PCT/GB1985/000548
Authority: WO
Inventors: Frederick Michael Stidworthy
Original assignee: Stidworthy Frederick M
Priority date: 1985-11-29
Filing date: 1985-11-29
Publication date: 1987-06-04
Also published as: EP0246225A1

Abstract

A camshaft (2) is driven from a sprocket shaft (1) via an arrangement of bevel gears (a, b, c, d). Bevel gear (a) is rotatable with the sprocket wheel and bevel gear (b) is rotatable with a sleeve shaft (6) disposed coaxially on the camshaft. The gears (a, b) permanently mesh with the pair of idler gears (c, d) rotatably carried on stub shafts (4, 5) on the camshaft. A wormwheel (e) is rotatable with the sleeve shaft (6) and is engaged by a worm (f) to form a unidirectional drive in which movement can be transmitted from the worm to the wormwheel but not vice versa. The resulting resistance of the sleeve shaft (6) to rotation by the sprocket wheel effects rotation of the camshaft at a speed and phase which can be varied by rotating or displacing the sleeve shaft by means of the worm.

Description

"Variable Rotary Drives"

This invention relates to variable rotary drive arrangements which find application inter alia but not exclusively, i n achieving variable valve timing in internal combustion engines.

The ability to vary the breathing cycle, or cycles, of an internal combustion engine, while it is actually running, will provide a flexibility of operation capable of allowing the engine to realise its full potential.

The running characteristics of any engine are always determined by just how far the valves open, for how' long they remain open, and by how much the intake and exhaust sequences are allowed to overlap. In general, the bigger and longer the opening and the greater the overlap, the more powerful an engine will be at the top end of its speed range, and the more restricted the valve openings with little or no overlap, the better the efficiency at low engine revolutions.

With mechanical solid metal cams, it is almost impossible to break away from the accepted compromise designs incorporated in almost every production internal combustion engine at present under manufacture. How¬ ever, some attention to the problem has been paid by such devices as the one developed by the Alfa Romeo Company, which comprises a sliding helical spline arrangement on the inlet valve camshaft situated between the drive sprocket and the shaft itself. This spring-loaded device enabled (by way of oil pressure variation) the drive-sprocket to be rotated relative to the shaft itself accordingto engine revolution speed, thereby changing the timing of the camshaft relative to crankshaft speed and situation, and relative to the exhaust valve camshaft which remains in fixed relationship with the crankshaft.

The fist versions of the Alfa Romeo device allowed for only 10 degrees of movement, but later developments include up to 16 degrees of movement. However, it is a case of 'all or nothing¹, i.e.; the device is not fully variable over that 16 degrees. Nevertheless, considerable fuel efficiencies have been realised. Embodiments of the present invention allow for a possible 360 degrees of fully variable operation, i.e. the camshaft can, if required, be advanced, or retarded, through a full 360 degrees relative to the drive- sprocketj furthermore, the camshaft can, if required, be brought to a perfectly stationary situation (while the drive sprocket is still rotating) and reversed, if required.

It is clear therefore, that this invention has considerable applicability beyond internal combustion engine design, and could be included in any type of rotating or partially rotating device, wherein it is considered necessary to vary the relative rotational association of one or more rotatable members, such as shafts.

According to the present invention, there is provided a variable rotary drive arrangement in which first and second rotatable members are permanently coupled for rotation of the second member by the first member, the first member is permanently coupled to a third rotatable member rotation of which by the first member is precluded to effect rotation of the second member by the first member, and control drive means are provided for imparting rotational movement to the third member to vary a rotational relationship between the first and second members.

In one application of the invention, the control drive means serves to rotate the third member at a selected speed to vary the speed of rotation of the second member for a given rotational speed of the first member.

In another application of the invention, the control drive means serves to impart to the third member a selected rotational displacement from a datum position of the third member to vary the rotational phase relationship between the first and second members.

Conveniently, the first and second members are coupled by a first drive element rotatable with the first member and drivingly engaging a second drive element rotatably carried by the second member, and the first and third members are coupled by a third drive element rotatable with the third member and drivingly engaging the second drive element. Preferably, a pair of second drive elements are rotatably carried by the second member and each such second drive element drivingly engages each of the first and third drive efements.

In another embodiment of the invention, the first and third members are coupled by a first drive element rotatable with the first member and drivingly engaging a third drive element rotatably carried by the third member, and the first and second members are coupled by driving engage¬ ment between the third drive element and a second drive element rotatable with the second member. According to a preferred feature of this embodiment, a pair of third drive elements are rotatably carried by the third member and each drivingly engages a respective one of the first and second drive elements'.

Desirably, rotation of the third member by the first member is precluded by the control drive means driving of which by the third member is precluded and preferably the control drive means comprises a driving element rotatable with the third member and a unidirectional actuating member capable, when driven, of rotating the driving element but capable of resisting driving of itself by the driving element.

In order that the invention may be readily understood, embodiments thereof will now be described, by way of example, with reference to the accompanying drawing, which illustrates three basic representative embodi¬ ments of the invention and in which:

FIGURE I illustrates a first embodiment of the invention in axial cross-section;

FIGURE 2 is an axial cross-section through a second embodiment of the invention;

FIGURE 3 illustrates in axial cross-section a third embodiment of the invention;

FIGURES 4 and 5 are end views of the third embodiment in two different conditions; and FIGURES 6 and 7 are axial and transverse cross-sectional views of a modified form of the third embodiment.

The enclosed drawing "VARIABLE TIMING DEVICES", contains three basic layouts of hypothetical realisations of the invention, these are not intended to be definitive designs but are merely, reasonably realistic representations of possible embodiments.

O Figure I shows a simple version of the invention, in which the basic assembly includes a four gear differential type of device.

Throughout this description all 'solid' black areas depict bearing surfaces and/or devices etc.

COMPONENT LISTING

Sprocket-Shaft ( I ); Camshaft (2); Worm-Shaft (3); Idler Stub-Axles (4 and 5); Sleeve-Shaft (6); Location-Shaft (7); Backing-Plate (8); Sprocket- Wheel (9); End-Caps ( 10 and I I); Sprocket Chain-Teeth ( 12 and 13); Locking Nuts ( 14 and 15); Support Pillars ( 16; 17 and 18); Base (Cylinder Head, or Block etc) (19); Differential Hub (20); Sprocket Location Shaft (la).

GEAR LISTING

Gears (a/b/c/d) are all similar sized bevelled gears as shown, how¬ ever, as in any bevelled differential arrangement, these can be of varying sizes, in that, the two Idlers (c and d) can be of a different tooth count to gears (a and b). Gear (f) is a worm-gear and gear (e) is a worm-wheel. The lead angle between the worm and worm-wheel is decided as being a 'locking' angle, e.g., about 10 degrees - this can be anything between say, 5 and 15 degrees but must retain a drive capability from worm to worm-wheel but an irreversible characteristic from worm-wheel to worm.

The worm (f) will be provided with a drive means; e.g; an electric motor or hydraulic motor (or motors) or pump drive etc., or any suitable, and/or controlable means of rotational instigation.

ASSEMBLIES Gear (a) is fixed to, or part of, Shaft ( I); Backing-Plate (8) is fixed to, or part of, Shaft (I); Sprocket- Wheel (9) is fixed to, or part of, Backing- Plate (8); the whole assembly (la/!/8/9/a/ l 2/l 3/!4/ ! 5) is a free-running unit,located concentrically upon datum 'x' - 'y', and could, if required, be machined from one single piece of material.

Stub-Axles (4 and 5) are fixed to, or part of, Camshaft (2); End-Caps (10 and 1 1) are fixed to, or part of, Stub-Axles (4 and 5); Location Shaft (7) is fixed to, or part of, Camshaft (2); with the whole assembly located concentrically along datum 'x' - 'x' and providing a free- running carrier for the bearing located bevelled-gears (c and d).

Gear (b) is fixed to, or part of, Sleeve-Shaft (6); Sleeve-Shaft (6) is fixed to, or part of, Worm-Whee! (e); again, this free-running assembly could be manufactured from a single item of material if required. Assembly (b/6/e) is also located concentrically along datum 'x' - 'y' and concentrically external of shaft (2), around which it is concentrically bearing located in free-running but constant communication.

The Chain-Drive Sprocket assembly (9/ 12/ 13) could be replaced by any type of suitable device; e.g; a gear-wheel; Pulley; etc.

Shafts ( 1/2/6) are all bearing located within the Pillars, or supports, thereby enabling free-running operation.

The differential type unit (a/b/c/d) will, as in all such four-gear differentials of such proportions, provide a 2 : I ratio envelope of operation; i.e; If gear (b) were held fast, and Gear (a) rotated (in either direction), then Assembly (2/20/4/5/ 10/ 1 1 /7) together with the free running idlers (c and d) would be caused to rotate, in a similar direction to (a) but at half the speed and twice the torque.

This 2 : I operating characteristic can be used as a bonus in relation to a camshaft realisation of the invention, in that, it is usual for the camshaft of I.C. engines to rotate at half the speed of the Crankshaft, therefore, if gear (b) is held fast, then the chain drive coupling between the Camshaft and Crankshaft (not shown) Sprocket Assemblies can remain a 1 : I with the necessary 2 : I reduction being accomplished by the differential's natural operating mode.

In order to hold Gear (b) 'fast', i.e; stationary; it is provided, as will be seen, with a Worm- Wheel, this in turn, is engaged with a Worm-Gear (f). If, as already explained, the lead, or interface, angle between (e) and (f) is a locking angle, then gear (b) can be restrained providing no rotational movement is fed to Worm-Gear (f); i.e; as (e) cannot drive (f) (a) via fdlers (c and d) cannot cause (b) to rotate as it will, via Sleeve-Shaft (6) be ocked' in position by Worm-Wheel (e); therefore, whatever rotational input is fed to gear (a) from the chain drive assembly, will cause only assembly (2/20/4/5/ 10/ 1 1/7) to rotate at half the speed of (a) but in a similar direction to that of Gear (a).

Therefore, with Worm-Gear (f) providing the only means of rotating Worm-Wheel (e), it is clear that the Chain-Drive introduced via Sprocket Assembly (9/ 12/ 13) will, via Bevelled gears (a/b/c), provide Cam-Shaft (2) with a standard 2 : I rotational ability.

In order to appreciate the variability of the device, it is necessary to understand that if gear (a) were rotated, in either direction, and gear (b) were rotated by exactly the same amount but in the opposite direction, then Assembly (2/20/4/5/ 10/1 1/7) would remain perfectly stationary. £ this status were in vogue and (a and b) were indeed rotating by equal and opposite amounts, with Assembly (2/20/4/5/ 10/ 1 1 /7) stationary; by decreas¬ ing the drive to gear (b), Assembly (2/20/4/5/ 10/ 1 1 /7) would begin to rotate In a direction similar to that of Gear (a) but at a reduced speed. If the rotation of (b) is restricted to the point where it becomes stationary, then the 2 : I drive status between (a) and (2/20/4/5/ 10/ 1 1 /7) is established; therefore, if this situation; i.e.; one with (b) stationary, is assumed as being 'normal', or 'standard', then this is the point when it could be decided that the Cams contained upon Camshaft (2) were neither advanced or retarded but in their mid range situation.

As (b) can so effect the rotational qualities of Camshaft (2), it will be seen, that If it were rotated in a similar direction to (a) and at the same speed, then there would be a I : I drive situation between Sprocket -o-

Assembly (9/ 12/ 13) and Camshaft (2); if (b) were driven faster than (a) but in a similar direction) then Camshaft (2) would be rotating faster than I : I in comparison to (a). This wide range envelope provides an ability to close down; i.e; Disable; selective Engine Cylinders - in that, if a device as shown by Figure I were interposed between any of the cylinders, or cylinder combinations etc., by rotating Gear (b)in an equal and opposite direction to that of Gear (a), that selected cylinder or group of cylinders etc., c uld be closed down, with no effective cam action taking place.

ADVANCE/RETARD

If as described above, the 'normal' Crankshaft to Camshaft status quo is established with (b) stationary, and all cam lobe calculations being established by timing marks in the usual way; i.e; by totally disregarding the fact that (b) can be made to rotate; then, in every respect other than the fact that the 2 : I speed drop is achieved by four bevelled gears rather than a 2 : I chain sprocket combination; this would be a standard camshaft device, however, whatever the status quo established at onset; i.e; when timing the engine etc., with the 'fixed' relationship between (a) and (2) determined with (b) is a stationary 'fixed' position; the relationship es¬ tablished between (a) and (2) can be altered; i.e; advanced and/or retarded by any amount by simply rotating (b) slightly (any degree) in either direction. If (b) is caused to rotate only .50 degrees away from the original 'fixed' setting-up situation, in either direction, then the previous juxta¬ position of the two items (a) and (2) will be altered. (NOTE: the .50 degree example is only included as a means of description, as any amount of rotation will cause a change in a relationship).

This can be understood if, for the sake of explanation, it is assumed that (a) is stationary, and (b) is rotated in either direction. By whatever amount (b) is. rotated. Assembly (2/20/4/5/ 10/ 1 1 /7) will be rotated half as much but in a similar direction, therefore, if this is done while (a) is running, the same degree of variation between (a) and (2) can be achieved regardless of the fact that (a) is rotating, as it must be remembered that (2) was timed In conjunction with (a) with (b) in an established juxtaposition also.

By allowing (b) to rotate even slightly, say between its initial established juxtaposition and a .50 degree variation of that point, the retative relationship or timing, of the items (a) and (2) will alter. It is not necessary to have (b) under continuos rotation but merely to move it by only a desired amount in order to change the camshaft timing. It will be seen, however, that any degree of alteration is possible and is achieved by way of continous variation rather than 'all or nothing' parameters, as in the Alf Romeo device. Q

The ratio between the Worm (f) and Worm-Wheel (e) can be such, that only a very small electric motor need be employed. Furthermore, control of said motor (not shown) can be instigated by way of an engine management system and the variation required can be determined in conjunction with all other known or required parameters etc.

If a device such as that shown in Figure 2 were used in conjunction with normal camshaft devices etc., then special design attention would be made to the cam lobes in order to realise as much of the variable benefits available, however, certain compromises ^"would still be made if the cams themselves were not of the Annular or Reciprocating types. These particular innovative devices can take full advantage of this invention, while standard 'solid' fixed cams can only obtain certain of the considerable benefits available, however, as demonstrated by the restricted Alfa Romeo device, these can be considerable in their own right.

Figure 2 is a further variation of the invention, in that the gear type used is of the spur epicylic (sun and planet/annulus) arrangement rather than bevelled. All reference Numbers maintain with the exceptions as follows:-

Dϊfferential Hub (20) in Figure I is now, in Figure 2 a Free-Running Carrier (20); Support Pillars ( 16/ 17 and 18) are reduced in number; i.e; Figure 2 contains only two such items; Support Pillars ( 16 and 17); A carrier has also been added to carry Annular Gear (b), this item is shown as Carrier (21 ) and is fixed to, or part of Sleeve-Shaft (6);

The Gears shown in Figure 2 are as follows:-

Gear (a) is a 'sun' Gear; Gears (c and d) are Idler Planet Gears (Free- Running upon Stub-Axles (4 and 5); and Gear (b) is an Annular, or Internal- Gear, which is fixed to, or part of, Carrier (21 ).

The gear ratios chosed are hypothetical, in that, it is not restricted to one particular set, but the design Indicated would be a 2 : I train; i.e; for every single revolution of the 'sun' gear ta), the Carrier (20) would rotate 1 /2 of a single revolution in the same direction. Therefore, any suitable tooth count can be included, providing the outcome is as defined above.

If alternative gear ratios are to be included, then compensation can be made across the Chain-Drive Sprocket assembly, thereby enabling almost any suitable epicyclic combination to be used. This, of course, depends upon the through rotational relationship required between the Sprockett Assembly and the Camshaft (2).

All other principles of operation are the same as described for Figure

Figure 3 together with Figures 4 to 7 depict a further alternative embodiment of the same basic invention.

This variation Includes the use of two Sun Gears (a and b), together with a compound Planet arrangement consisting Gears (c and d).

COMPONENT LISTING

Sprocket Sleeve-Shaft ( I ); Camshaft (2); Worm Lay-Shaft (3); Com¬ pound Planet Lay-Shaft (4); Carrier Centre-Line Lay-Shaft (5); Location- Shaft (7); Backing Plate (8); Sprocket- Wheel (9); Sprocket Chain-Teeth ( 12 and 13); Locking-Nuts ( 14 and 1 5); Support Pillars ( 16/ 17 and 1 8); Base (Cylinder-head or Block etc) ( 19); Free-Running Planet Carrier (20); Bearing Housing (22); Angled Bracket Support (24); (Datum shown as 'z' - 'z').

Note: Figure 2 - Datum shwon as 'y' - 'y'.

GEAR LISTING Spur-Geαr (α) and Spur-Gear (b) form, as shown, a I : I coupling, while Compound Planet Spur-Gear (d) Is half the tooth count of Sun Gear (b). This four gear train produces an overall 2 : I through-drive.

The carrier (20) is provided with Worm-Wheel (e) which is gear-cut around only 180 degrees of its periphery. This can be seen to advantage in Figures 4 and 5 in that the amount of advance/retard adjustment ϊs^assumed to be less than 360 degrees, and therefore, the Carrier (20) has only been provided with 90 degrees of rotation in each direction either side of zero. (i.e.; 'normal' or standard setting etc).

Figures 6 and 7 contain a further variation to the basic Worm/Worm- Wheel drive input, in that the Worm-Gear is replaced by a Rack (g) type gear and this would be engaged with a pinion gear in place of the Worm- Wheel (e). The Rack is threaded down the internal centre and a drive screw (h) is provided upon shaft (3). The Rack is prevented from rotating by way of side mounted lugs, these running in slots or channels along the side of the Rack component (see Figure 7). Therefore, if Shaft (3) is rotated, then the Screw Thread section of Shaft (3) will cause the Pack assembly (23) to move along the slotted grooves present in fixed Pillars ( 16a and 17a). As the angle of the thread (exaggerated in the drawing) would be very similar to that of the Worm, as originally used, there would be a 'locking' effect from Rack unit to Threaded Shaft, thereby again creating a drive/lock situation.

Several alternative means of driving the Carrier (20) can be used; e.g; a Motor coupled directly would suffice, providing a method of 'locking' once the new position is reached, can be incorporated,; a ratchet device would suit this kind of approach. Therefore, any suitable means of driving Carrier (20) in Figure 3 the Annular Carrier (21 ) in Figure 2 or the Bevelled-Gear (b) in Figure I and holding these items in their various desired positions can be contemplated.

The device described hypothetical I y by Figure 3 has a 180 degree adjustment, however, if a 360 degree ability is required, then a slightly different Carrier arrangement could be used which would enable full rotation. In Figure 2 it can be seen that only one Planet-Gear is necessary, and in Figure f , only one of the Idler Bevelled Gears is really required.

In applications wherein the loadings would be reasonably light, it is possible to replace the gear components with friction wheels, or rollers etc.

Figures 4 and 5 show the Carrier (20) in the 'normal', OQ neutral adjustment position (Figure 4) and in a position of half (45 degrees of adjustment) adjustment (Figure 5).

As already described, this device can be used in many different applications other than the fully variable Camshaft, and as it can be shown that by causing the correct rotation of the input-gear (a) and the secondary gear (b) (or the Carrier in Figure 3) a totally negative rotation of Shaft (2) can be achieved; therefore, this indicates that the device offers a Clutching ability; i.e; it could be situated between the engine (powerplant) and the Gearbox (transmission) and by driving, say, Gear (a) by way of the engine, and Gear (b), say, electrically, in the opposite direction and at the^"~same speed etc., there would be no drive to the output via Shaft (2), but by cutting the power to Gear (b) on a gradual basis, a 'slipping' type of engagement could be achieved, thereby clutching the engine to the trans¬ mission. This type of installation would be extremely useful in motor vehicles as the drive unit feeding the Worm and Gear (b) could also be used to start the engine against the load; i.e.; if power were supplied to the Worm, and subsequently to Gear (b) (or the Carrier in Figure 3) and Shaft (2) were loaded (and presumably locked via a hand-brake etc) then the least resistance would be represented by the engine which would be rotated and started. Once firing, the increase in revolutions could be followed by the Gear (b) remaining compatable with Gear (a) and thereby remaining in rotational unison. This would, therefore, retain negative output via Shaft (2) and not until the power was reduced, or cut, to Gear (b) would drive be available via Shaft (2). This offers a perfect clutching and started device of extremely controllable means.

This ability to have drive or negative drive can be used in steering assemblies, where, for example, a Tracked vehicle requires one track_j or the other, to be driven by more, or less, of the power output, at different, or the same time; i.e; in order to steer by speed of the track rather than deflection. This device, or a combination of such devices can offer this type of ability.

Furthermore, as described throughout this Specification, the input has been defined via Shaft ( I), however, there is no reason why, say, Shaft (2) cannot be considered the 'input' with shaft (!) the Camshaft, aQoutput. Providing one section, or part, of the device is controllable and able to be •locked' or held, then any of the rotating sections can be considered either the Input or the output. Compensatory ratios can be included in any of the devices in order to achieve almost any desirable speed abilities etc.

Claims

CLA1MS

I. A variable rotary drive arrangement in which first and second rotatable members are permanently coupled for rotation of the second member by the first member, the first member is permanently coupled to a third rotatable member rotation of which by the first member is precluded to effect rotation of the second member by the first member, and control drive means are provided for imparting rotational movement to the third member to vary a rotational relationship .between the first and second members.

2. A drive arrangement according to Claim 1 , in which the control drive means serves to rotate the third member at a selected speed to vary the speed of rotation of the second member for a given rotational speed of the first member.

3. A drive arrangement according to Cjaim I , in which the control drive means serves to Impart to the third member a selected rotational displace¬ ment from a datum position of the third member to vary the rotational phase relationship between the first and second members.

4. A drive arrangement according to any preceding claim, in which the first and second members are coupled by a first drive element rotatable with the first member and drivingly engaging a second drive element rotatably carried by the second member, and the first and third members are coupled by a third drive element rotatable with the third member and drivingly engaging the second drive element.

5. A drive arrangement according to Claim 4, in which a pair of second drive elements are rotatably carried by the second member and each such second drive element drivingly engages each of the first and third drive elements.

6. A drive engagement according to Claim 4 or 5, in which the first drive element comprises a first gear wheel, the or each second drive element comprises a second gear wheel, and the third drive element comprises α third gear wheel.

7. A drive arrangement according to Claim 6, in which each of the first, second and third drive elements is a bevel gear.

8. A drive arrangement according to Claim 6, in which the first drive element comprises a sun gear wheel, the or each second drive element

V_»* comprises a planet gear wheel and the third drive element comprises an annular gear.

9. A drive arrangement according to any one of Claims 1 to 3, in which the first and third members are coupled by a first drive element rotatable with the first member and drivingly engaging a third^" drive element rotatably carried by the third member, and the first and second members are coupled by driving engagement between the third drive element and a second drive element rotatable with the second member.

10. A drive arrangement according to Claim 9, in which a pair of third drive elements are rotatably carried by the third member and each drivingly engages a respective one of the first and second drive elements.

1 1. A drive arrangement according to Claim 10, in which the pair of third drive elements are rotatable about a common axis of rotation.

12. A drive arrangement according to Claim 9, 10 or I I , in which the first drive element comprises a first gear wheel, the second drive element comprises a second gear wheel and the or each third drive element comprises a third gear wheel.

13. A drive arrangement according to Claim 12, in which each of the first, second and third drive elements in a spur gear.

14. A drive arrangement according to any preceding claim, in which rotation of the third member by the first member is precluded by the control drive means driving of which by the third member is precluded.

15. A drive arrangement according to Claim 14, in which the control _ , .

drive means comprises a driving element rotatable with the third member and a unidirectional actuating member capable, when driven, of rotating the driving element but capable of resisting driving of itself by the driving element.

^'

16. A drive arrangement according to Claim 15, in which the driving element of the control drive means is a worm-wheel and the actuating element is a worm.

17. A drive arrangement according to Claim 15, in which the driving element of the control drive means is a pinion gear wheel and the actuating element is a rack.

18. A drive arrangement according to any preceding claim, in which the first, second and third members are rotatable about a common axis of rotation.

19. A drive arrangement according to any preceding claim, in which the second member is a camshaft and the first member is a sprocket shaft or the like driving the camshaft.

20. A drive arrangement according to Claim 19, in which the third member comprises a hollow shaft coaxial with the camshaft.

21. A drive arrangement according to Claim 19, in which the third member is rotatably interposed between the first and second members.

22. A variable rotary drive arrangement substantially as hereinbefore described with reference to, and as illustrated in Figure I of the accom¬ panying drawings.

23. . A variable rotary drive arrangement substantially as hereinbefore described with reference to, and as illustrated in Figure 2 of the accom¬ panying drawings.

24. A variable rotary drive arrangement substantially as hereinbefore described with reference to, and as illustrated in, Figure 3 of the σccom- pαnying drawings.

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