GB2214578A - A differential mechanism - Google Patents

Abstract

The differential comprises a drive input element 40 two outputs cam members 16, 17 rotatable about an axis A, each said member having a single annular cam surfaces 22, 23 thereon of undulating form arranged such that the cam surfaces on the cam members converge towards each other, and a plurality of cam followers 28. The followers have cam engaging end surfaces 29, 30, 32, 33 for imparting drive from the input element 40 to said output cam members. Relative contra rotation of said output cam members causes the cam followers to slide axially. The cam followers 28 are elongate in the direction of axis A and are slidably supported throughout virtually their entire length by the drive input element 40. The followers 28 may be arranged closely adjacent each other to provide a degree of mutual support. The angle P of the line cam faces may be different to provide different torque outputs. The cam may consist of a pattern which repeats around the cams periphery. <IMAGE>

Description

A DIFFERENTIAL MECHANISM The invention relates to a differential mechanism particularly but not exclusively for use in motor vehicles.

Differential mechanisms commonly used on vehicles are of the sun and planet gear type and have a well known disadvantage that when one wheel is on a slippery surface such as mud or ice and the other wheel is on a firm surface capable of providing traction, the first wheel will simply spin as it receives all the available power transmitted to the differential.

Limited slip differential mechanisms have been proposed in an attempt to overcome this problem which restrict the extent to which one wheel can spin relative to the other but such differentials are more complex therefore more costly to produce.

It has also been proposed to provide a lockable differential which enables the differential effect to be prevented completely when necessary thereby ensuring that the speed of each wheel is the same enabling the maximum available traction to be obtained at each wheel. However if the user of the vehicle overlooks the fact that the differential has been locked and drives the vehicle in normal conditions for any length of time, abnormal wear of tyres and excessive transmission stresses will result.

Alternative differential mechanisms were proposed many years ago in U.S. Patents Nos.1,568,358, 2,034,318, 2,220,432 and U.K. Patent No.431,020.

In the aforesaid patents the differentials each comprise an input, two outputs rotatable about an axis, a cam member connected to each of the outputs, said cam members including annular cam surfaces of undulating form coaxial with the outputs, a plurality of cam followers having surfaces which engage the cam surfaces to impart drive to the outputs, the cam followers being drivable from the input and the arrangement being such that relative contra-rotation of said outputs causes the cam followers to slide axially. Such arrangements are normally non-reversible so that rotation of one output cannot be transmitted through the cam followers so as to impart drive to the other output. In that manner drive will always be transmitted to one of the outputs from the input even if the other output is connected to a wheel which is spinning on a slippery surface.

The construction of the differential mechanisms described in the foregoing patents is not particularly compact and in some cases, e.g., U.S.

No.2,220,432 and U.K. No.431,020 a relatively low area of contact between the cam and cam followers can lead to high cam surface stress which is obviously undesirable.

A more recent development of the foregoing kind of differential is described in the January 1988 edition of Eureka published by Innopress Limited where the form of the cam followers helps to spread the driving load over a substantial area of the cam.

An object of the present invention is to provide an improved differential mechanism.

According to one aspect of the present invention there is provided a differential mechanism comprising an input, two outputs rotatable about an axis, two cam members one of which is connected to one said output and the other of which is connected to the other output, said cam members having annular cam surfaces of undulating form coaxial with said outputs, a plurality of cam followers having cam engaging surfaces for imparting drive to the outputs and side surfaces extending between the cam engaging surfaces, said or a number of said cam followers side by side with the side surfaces of adjacent cam followers lying closely adjacent the arrangement being such that relative contra rotation of said outputs causes the cam followers to slide axially with substantial portions of said closely adjacent surface of the or said member of the adjacent cam followers facing each other continuously during the full axial sliding movement thereof.

The positioning of the cam followers in this way enables a large number of cam followers to occupy the available space and the closely adjacent cam followers may provide a degree of support for each other, in use, through the adjacent side surfaces.

The use of a large number of cam followers enables driving load transmitted from the input to be applied over a substantial area of the cam.

According to another aspect of the invention there is provided a differential mechanism comprising an input, two outputs rotatable about an axis, two cam members one of which is connected to one said output and the other of which is connected to the other output, said cam members having annular cam surfaces of undulating form coaxial with said outputs, a plurality of cam followers having cam engaging surfaces for imparting drive to the outputs, and a drive input element for imparting drive from the input to the cam followers, said drive input element comprising first and second sections which are drivably interconnected so as to define openings extending in the axial direction in which the cam followers are located, the arrangement being such that relative contra-rotation of said outputs causes the cam followers to slide axially.

Such a drive input element is easier to produce than that shown in the Eureka article where the drive input element comprises a single member formed with axial through-slots for receiving the cam followers.

As the followers described therein comprise elongate bodies with relatively. larger end sections formed with cam-engaging end surfaces, the bodies need to be made in two halves which are inserted into the slots from opposite ends. The use of a two section drive input element enables similar followers to be made in one piece and to be located in the openings during assembly of the drive input element.

According to a further aspect of the invention there is provided a differential mechanism comprising an input, two outputs rotatable about an axis, two cam members one of which is connected to one said output and the other of which is connected to the other output, said cam members having annular cam surfaces of undulating form coaxial with said outputs, a plurality of cam followers having cam engaging surfaces for imparting drive to the outputs, the cam surfaces on each cam member converging towards each other and the cam engaging surfaces of the cam followers being complementary thereto, each cam surface having a number of mutually inclined faces which is different from the number of mutually inclined faces of the other cam surface, and the angles of convergence of the cam surface being different whereby the torque delivered to the outputs will be divided between the outputs at a desired ratio or ratios for both directions of relative rotation between the outputs.

This feature is particularly useful as it enables the ratio to be selected by selecting appropriate angles of convergence. In that way the ratio can be constant for both directions of relative rotation or may be different in one direction than in the other.

According to a still further aspect of the invention there is provided a differential mechanism comprising an input, two outputs rotatable about an axis, two cam members one of which is connected to one said output and the other of which is connected to the other output, said cam members having annular cam surfaces of undulating form coaxial with said outputs, a plurality of cam followers having cam engaging surfaces for imparting drive to the outputs, the cam surface on one cam member comprising at least two identical tracks which form the complete annular cam surface whereby axial loading applied thereto by the cam followers during drive is applied symmetrically to the cam surface to create a balanced axial loading on the cam member.

Non-symmetrical loading of the cams will exert extra loading on bearings for the cam members and the differential mechanism as set out in the immediately preceding aspect avoids that.

According to yet another aspect of the invention there is provided a differential mechanism comprising an input, two outputs rotatable about an axis, two cam members one of which is connected to one of the outputs and the other of which is connected to the other output, said cam members including annular cam surfaces of undulating form coaxial with said outputs, a plurality of cam followers of elongate strut-like form, said cam followers having end surfaces which engage the cam surfaces to impart drive to the outputs, said end surfaces terminating at relatively longer side surfaces, the or a number of said cam followers lying side by side with side surfaces of the cam followers or the cam followers of said number lying closely adjacent or in inter-engagement and means for imparting drive to the cam followers from the input positioned so as to be non-interposed between the side surfaces of the cam followers or the cam followers of said number , the arrangement being such that relative contra-rotation of said outputs causes the cam followers to slide axially.

Differential mechanisms in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which: Fig.l is a cross-section through a differential mechanism in accordance with the invention taken through the outputs, Fig.2 is an end view of the differential of Fig.l shown partly broken away, Fig.3 is a development of cam members on the outputs with cam followers shown in positions therebetween, Fig.4 is an elevation of a cam follower of the differential in Figs.l to 3, Fig.5 is an end view of the cam follower in Fig.4, Fig.6 is a cross-section of the'cam follower on line VI-VI in Fig.4, Figs.7 to 9 are views similar to Figs.l to 3 showing a different embodiment of differential mechanism, Fig.lO is an elevation of an alternative form of cam follower for the differentials, Fig.ll is an end view of the cam follower in Fig.10, Fig.12 is a cross-section of the cam follower of Fig.lO on the line XII-XII in Fig.lO.

Fig.13 is part cross-section showing a differential mechanism in accordance with the invention having a different form of construction using the follower of Figs.10 to 12.

Fig .14 is an end view of part of the differential shown in Fig.13, Fig.15 is a part cross-section of the differential constructed as shown in Fig.13 but having the follower members shown in Figs.4 to 6, Fig.16 is an end view of part of the differential shown in Fig.15 and Fig.17 is a diagrammatic end view of a follower of the kind shown in Figs.4 to 5 showing the way in which loading is applied thereto in use.

Fig.l8 is a cross-section through a further form of differential in accordance with the invention, Fig.l9 is an end view of the differential of Fig.18 shown partly in cross-section, Fig.20 is a development of cam members on the outputs of the differential in Fig.l9 with cam followers shown in positions therebetween.

Fig.21 is a cross-section through another form of differential in accordance with the invention, Fig.22 is an end view of the differential of Fig.21 shown partly in cross-section, and Fig.23 is a development of cam members on the outputs of the differential in Fig.22 with cam followers shown in positions therebetween, In Figs.l to 6 the differential comprises a drive input 10 in the form of a crown bevel gear 12 which receives drive from a. pinion (not shown) in known manner. The gear 12 is drivably connected to drive input members 13, 14 which are interconnected by circumferentially spaced bolts 15.

Two output members 16, 17 are splined, in use, to output shafts (not shown) which extend through bearings (not shown) in bores 18 in the input members 13, 14. The output members 16, 17 are rotatable about an axis A relative to the input members 13, 14. The output members 17 have respective flanges 19, 20 thereon on which are formed respective annular face cams 22, 23. The cam 22 defines a zig-zag surface shown in detail in Fig.3 made up from seven pairs of mutally inclined surfaces 24, 25. The cam 23 also defines a zig-zag surface apparent from Fig.3 but is made up from eight pairs of mutually inclined surfaces 26, 27.

As shown in Fig.l the undulating cam surfaces are inclined at identical angles P to the axis A whereby each cam surface converges towards the other.

Fifteen cam followers 28 are positioned between the cams 22, 23. Each cam follower is of strut-like elongate form and comprises two sets of mutually inclined end surfaces 29, 30 and 32, 33 which terminate at relatively longer side surfaces 34, 35.

The angle of inclination Q between the end surfaces 29, 30 corresponds to the angle of inclination between the end surfaces 32, 33 and the angle of inclination S between the end surfaces 32, 33 corresponds to the angle of the inclination between the cam surfaces 26, 27. The end surfaces 29, 30 and 32, 33 are also inclined at the angle P as apparent from Figs. 1 and 4. When viewed from the end as in Fig.5, it can be seen that the cam follower is arcuate which enables the followers to be assembled together as viewed in Fig.2 Each cam follower is formed with a drive dog 36 having mutually inclined side surfaces 37, 38. The drive dogs 36 locate complementary shaped grooves 39 formed in the inner periphery of a cylindrical driving element 40 through which the bolts 15 pass so as to connect the element 40 drivably to the input members 13, 14.

As apparent from Figs.2 and 3 the assembly of the cam followers is such as to place the side surfaces 34, 35 of adjacent followers so that they interengage or lie closely adjacent. In that way maximum use is made of the available circumferential space for the cam followers, the followers together forming a substantially continuous annular array as viewed in Fig.2.

When drive input is applied through element 40, and assuming that a vehicle having the differential is being driven in a straight line, the cam followers apply a load to the surfaces of cams 22, 23 so as to rotate the output members 16, 17 at equal speeds. As apparent from Fig.3, with driving load applied in direction X the cam follower on the extreme left has its end surfaces 30, 33 in driving engagement with surfaces 24, 26 and alternate followers are similarly in driving engagement with the cams 22, 23. However intermediate cam followers have their surfaces in non- driving engagement with the cam surfaces.

The driving force F applied by the followers 28 to the inclined surfaces 24, 26 is illustrated in Fig.l7 The inclination of the end surfaces of the cam follower at angle P causes the application of force F to create an outward force G thereby producing a resultant force R which passes approximately through the line of intersection L at a corner between the drive dog 36 and the adjacent part of the follower. In that way the loading on the cam follower tends to wedge it firmly against a corner of the element 40 in such a way that tipping of the follower about its edge E is avoided.

The differential effect can best be appreciated by considering the driving element 40 as being stationary and by applying contra rotary movement to the cams 22, 23 in directions J, K, respectively in Fig.3. The cam surface 26 will move to the left and cam surface 24 to the right. Such movement of cam surface 26 causes the associated follower to move axially towards cam 22. If both cams 22, 23 and the driving element 40 are all given an additional rotational movement in direction of arrow J, it will be appreciated that the cams 22 and 23 will be rotating respectively faster and slower than element 40. The difference in speeds between the two cams 22, 23 and the element 40 will be different because of the different number of cam surfaces on the cams.

As there is a considerable amount of friction between the followers and the cams, torque will be transmitted to one cam even when the other is drivably connected to a wheel spinning on a slippery surface.

As mentioned above, the adjacent cam followers may be arranged with their side surfaces 34, 35 closely adjacent or in inter-engagement. Where the side surfaces interengage, driving force F applied to any follower in non-driving engagement with cam surfaces will transmit driving load applied thereto to the next driving cam through its interengaging surfaces.

Also the use of interengaging surfaces further inhibits the cam followers tipping relative to the cams. Interengagement of the surfaces will take place over substantially their entire length.

Axial thrust applied to the cams by the followers is transmitted to the input members 13, 14 through thrust needle bearings 8. Shims 9 may be used to adjust the relative axial positions of the cams. If desired resilient elements may be used instead of shims to urge the cams axially against the followers In Figs. 7 to 9 parts corresponding to parts in Figs.l to 6 carry the same reference numbers and are not described in detail.

The basic difference in the embodiment of Figs.l to 6 and that of Figs.7 to 9 is the shape of the cams and the shape and mounting of the cam followers.

As apparent from Fig.7 the face cams 22, 23 have part radial cam surfaces 24, 25 and 26, 27. In the embodiment shown cam 22 has twelve pairs of surfaces 24, 25 and cam 23 has thirteen pairs of surfaces 26, 27.

The cam followers 128 are again of strut-like elongate form having end surfaces 29, 30, 32, 33 and side surfaces 34, 35. The side surfaces are mutually inclined radially as shown in Fig.8 so that when the followers are arranged side by side in batches with adjacent surfaces 34, 35 in engagement or closely adjacent, the batches form part annular arrays of followers. In the embodiment illustrated five batches 42, 43, 44, 45, 46 of four followers are provided. The end surfaces 29, 30 and 32, 33 of the followers are mutually inclined at the same angle as that of the inclined surfaces of the associated cams 22, 23.

Drive is transmitted to the batches of followers through a drive element 40 comprising a first section 47a in the form of a spider having five radial legs 48, and a second section 47b which receives drive from drive input members 13, 14and is formed with slots 42 in which the radially outer ends of legs 48 are located. As in the previous embodiment, alternate followers 28 in the batch will always be in driving engagement with the cams. When driving load is applied in direction F to the cam follower at the far left in each batch and when that cam follower is in non-driving engagement with cam surfaces, driving load is transmitted through it to the adjacent driving follower and so on through the batch so that a plurality of cam followers in each batch will always be in driving engagement with the cam surfaces.

The transverse of cross-section each follower 128 may be varied as indicated at 49 so that each has a radially inner rib 50 slidably located in an axial groove 51 in the hub of the spider 47 and a radially outer rib 52 slidably located in a groove 153 in the driving element 40.

Reference is now made to Figs.13 to 16 and, again, parts corresponding to parts in the previous embodiments carry the same reference numerals.

In Fig.l3 the bolts 15 present in the embodiments of Figs.l and 7 are omitted and the input members 13, 14 are held together axially by a sleeve 53. The sleeve 53 has flanges 54 at one end bolted to the input member 13, the opposite end of the sleeve being beam welded to a cylindrical extension 55 on the input member 13.

Cam followers 228 as shown in detail in Figs.10 to 12 are used in Fig.l3. The cam follower 228 has the same basic shape in plan as the cam follower 28 and has mutually inclined end surfaces 29, 30, 32 and 33 for engagement with the cam surfaces. However, as viewed if Figs.ll and 14, the radially inner half of each follower has side surfaces 34, 35 inclined as in Fig.5 and the driving dog 61 has two inclined upper side surfaces 62, 63 which locate in grooves 64 in the sleeve 53.

The resultant force R created during operation of the differential using the cam follower 228 may pass inboard of one of the radially inner edges 64 of each groove 64 as indicated in Fig.l4 to prevent tipping of the follower. The cam follower 228 enables radially deeper end faces 29, 30, 32, 33 to be used. Therefore, as shown in Fig.l3, the cam surfaces (surface 24 being shown) can also be deeper than those in Fig.l which helps the driving load from the cam followers to be spread over an even larger cam area. This is a useful feature as it reduces wear between the mating cam and follower surfaces.

Alternatively, the inner periphery of the sleeve 53 can' be formed with grooves 56 as in Fig.16 identical to the grooves 39 in Fig.2 to receive the driving dogs 36 of the cam followers 28 shown in Figs.4 to 6.

In Figs. 18 to 20 parts corresponding to parts in Fig.l3 carry the same reference numerals and only the differences will be described.

The sleeve 53 forms the outer section of 'a drive element 70 which is formed with axial grooves 72.

Alternate grooves 72 receive radially outer ends of legs 73 of a spider constituting an inner section 74 of the drive element. The inner and outer sections 53, 74 of the drive elements define therebetween openings 75 in which fifteen cam followers 428 are slidably received.

Each cam follower 328 comprises an elongate strut-like body 76 having two heads 77, 78. The head 78 has end surfaces 79, 80 which are mutually inclined for engagement with similarly inclined surfaces 24, 25 of-a cam 22 and the head 78 has mutually inclined end surfaces 82, 83 engageable with similarly inclined surfaces 26, 27 of a cam 23. The head 77 has side surfaces 84, 85 and the head 78 has side surfaces 86, 87. The side surfaces of adjacent heads lie closely adjacent each other and during use, a cam follower in non drive-transmitting engagement with the cam surfaces may transmit driving load to the adjacent cam follower in drive transmitting engagement with the cam surfaces. Radially outer sections 71 of the cam followers 328 locate slidably in grooves 72 not occupied by the legs 73.

In Figs. 21 to 23 parts corresponding to parts in the earlier drawings carry the same reference numerals.

In Fig.21 it can be seen that the angles of inclination to the axis A of the cams 22, 23 are different, the surface of cam 22 being inclined at angle V and the surface of cam 23 being inclined at angle W. The cam followers 428 have similarly inclined end surfaces 90, 91 and 92, 93. The end surfaces 90, 91 are also mutually inclined at the same angle as surfaces 24, 25 of cam 22 and end surfaces 92, 93 are inclined at the same angle as surfaces 26, 27 of cam 23. Each cam follower has side surfaces 95, 96. The side surfaces of adjacent cam followers face each other for the full axial travel thereof and preferably engage each other over the full axial travel.In that way the cam followers (which are driven through projections 97 located in grooves 98 in a drive input sleeve 53) give each other maximum support and, as described above, a cam follower in non-driving engagement with the cam surfaces can transmit driving load to the adjacent cam follower.

As the angle of inclination between surfaces 24, 25 is different from that between surfaces 26, 27 the division of torque between the output shafts (indicated at 5, 6 in Fig.21) splined to the cams 22, 23 will be different when the cams are turning relative to each other in one direction than when they are turning relatively in the opposite direction.

It has been found that appropriate selection of angles V and W will enable the ratio of torques transmitted to the shafts to be selected either to provide a constant ratio for both directions of relative rotation or a different ratio for each direction as required. It has also been found that for a given set of angles V, W and angles of inclination between the cam surfaces, a variation in the coefficient of friction between the cam surfaces and the cam followers arising from selection of alternative materials will not significantly alter the torque ratio.

In Fig.23, it can be seen that the cam surfaces and the arrangement of followers is such as to provide two identical patterns over lengths J and K, each length extending for exactly half of the length of the cam surface. With differentials using axially displaceable cam followers, differential rotation between the cams can result in a non-symmetrical axial loading on the cams which will, in turn, place extra loading on the bearings in the bores 18. However by arranging the cam surfaces and cam followers in a repeating pattern as in Fig.23 the axial loading will be applied symmetrically to the cams (in the present case at diametrically opposite positions at all times). It will be understood that three or more repeating patterns could be used in a similar way to give symmetrical axial loading.

The different angles of inclination W, V and the repeating pattern of cam surfaces and followers can also be applied to the differentials illustrated in Figs.l to 20.

Claims (83)

1. A differential mechanism comprising an input, two outputs rotatable about an axis, two cam members one of which is connected to one said output and the other of which is connected to the other output, said cam members having annular cam surfaces of undulating form coaxial with said outputs, a plurality of cam followers having cam engaging surfaces for imparting drive to the outputs and side surfaces extending between the cam engaging surfaces, said or a number of said cam followers bing arranged side by side with the side surfaces of adjacent cam followers lying closely adjacent the arrangement being such that relative contra rotation of said outputs causes the cam followers to slide axially with substantial portions of said closely adjacent surfaces of the or said number of the adjacent cam followers facing each other continuously during the full axial sliding movement thereof.

2. A differential mechanism according to Claim 1 in which said adjacent surfaces interengage in use and drive from the input is transmitted from a cam follower in non-driving engagement with the cam surface to a cam follower in driving engagement with the cam surface.

3. A differential mechanism according to Claim 1 or 2 in which said number of cam followers forms a batch of cam followers arranged adjacent a similar batch.

4. A differential mechanism according to Claim 3 in which each batch comprises an equal number of cam follower members.

5. A differential mechanism according to Claim 1 in which a drive input element is provided for imparting drive from the input to the cam followers, said drive input element comprising first and second sections which are drivably interconnected so as to define openings in which the cam followers are slidably located.

6. A differential mechanism according to Claim 5 in which the first section includes a plurality of radial projections with the cam followers disposed therebetween.

7. A differential mechanism according to Claim 6 and where said number of cam followers forms a batch of cam followers arranged adjacent a similar batch, in which the batches of cam followers are disposed between the radial projections.

8. A differential mechanism according any of Claims 3 to 7 in which the batches and means for imparting drive together form a substantially continuous annular set of components coaxial with the outputs.

9. A differential mechanism according to Claim 1 or 2 in which the cam follower members are driven by a driving element which extends circumferentially around the cam follower members.

10. A differential mechanism according to Claim 9 in which said driving element and cam follower members interengage through projection and socket means.

11. A differential mechanism according to Claim 9 in which the projections and sockets are tapered in the radial direction.

12. A differential mechanism according to Claim 9, 10 or 11 in which the cam surfaces on each cam member converge towards the other cam member and the end surfaces of the follower members are complementary thereto whereby during drive of said output members through the follower members, a radially outward force is created which urges the follower members towards said driving member.

13. A differential mechanism according to Claim 12 and where a projection and socket means is used to transmit drive in which the radial force is combined with a cam driving force at the undulating cam surface to give a resultant outward force which urges a corner section of the cam follower against a substantially complementary corner section of the drive element to inhibit tipping of the cam follower.

14. A differential mechanism according to any of Claims 8 to 13 in which the cam follower members are arranged as a continuous series forming an annul us of components coaxial with the outputs.

15. A differential mechanism according to any preceding claim in which drive from said input is transmitted to means for imparting drive to the cam followers by removable bolts extending between spaced apart sections of the input.

16. A differential mechanism according to any of Claims 1 to 14 in which the drive from said input is transmitted to means for imparting drive to the cam followers by a sleeve extending between and rotatably secured to sections of the input.

17. A differential mechanism according to any preceding claim in which the undulating surfaces of each cam comprises a multiplicity of zig-zag faces.

18. A differential mechanism according to any preceding claim in which the number of faces on one cam is different from the number of faces on the other cam.

19. A differential mechanism according to any preceding Claim in which the cam engaging surfaces of the cam followers comprise two inclined helical surfaces at each end for engagement with the respective cam surfaces.

20. A differential mechanism according to any preceding Claim in which each cam follower includes a radially inner first portion, and a radially outer second portion to which driving load is imparted, said end surfaces extending over both said first and second portions.

21. A differential mechanism according to any preceding claim in which the cam surface on one cam member comprises at least two identical tracks which form the complete annular cam surface whereby axial loading applied thereto by the cam followers during drive is applied symmetrically to the cam surface to create a balanced axial loading on the cam member.

22. A differential mechanism according to any preceding claim in which the cam surfaces on each cam member converge towards each other and the cam engaging surfaces of the cam followers are complementary thereto, each cam surface having a number of mutually inclined faces which is different from the number of mutually inclined faces of the other cam surface, the angles of convergence of the cam surfaces being different whereby the torque delivered to the outputs will be divided between the outputs at a desired ratio or ratios for both directions of relative rotation between the outputs.

23. A differential mechanism according to Claim 22 in which the ratio is substantially constant.

24. A differential mechanism comprising an input, two outputs rotatable about an axis, two cam members one of which is connected to one said output and the other of which is connected to the other output, said cam members having annular cam surfaces of undulating form coaxial with said outputs, a plurality of cam followers having cam engaging surfaces for imparting drive to the outputs, and a drive input element for imparting drive from the input to the cam followers, said drive input element comprising first and second sections which are drivably interconnected so as to define openings extending in the axial direction in which the cam followers are located, the arrangement being such that relative contra-rotation of said outputs causes the cam followers to slide axially.

25. A differential mechanism according to Claim 24 in which said adjacent surfaces interengage in use and drive from the input is transmitted from a cam follower in non-driving engagement with the cam surface to a cam follower in driving engagement with the cam surface.

26. A differential mechanism according to Claim 24 or 25 in which said number of cam followers forms a batch of cam followers arranged adjacent a similar batch.

27. A differential mechanism according to Claim 26 in which each batch comprises an equal number of cam follower members.

28. A differential mechanism according to any of Claims 24 to 27 in which drive from said input is transmitted to means for imparting said drive input element by removable bolts extending between spaced apart sections of the input.

29. A differential mechanism according to any of Claims 24 to 28 in which the undulating surfaces of each cam comprises a multiplicity of zig-zag faces.

30. A differential mechanism according to any of Claims 24 to 29 in which the number of faces on one cam is different from the number of faces on the other cam.

31. A differential mechanism according to any of Claims 24 to 30 in which the cam engaging surfaces of the cam followers comprise two inclined helical surfaces at each end for engagement with the respective cam surfaces.

32. A differential mechanism according to any of Claims 24 to 31 in which each cam follower includes a radially inner first portion, and a radially outer second portion to which driving load is imparted, said end surfaces extending over both said first and second portions.

33. A differential mechanism according to any of Claims 24 to 32 in which the cam surface on one said cam member comprises at least two identical tracks which form the complete annular cam surface whereby axial loading applied thereto by the cam followers during drive is applied symmetrically to the cam surface to create a balanced axial loading on the cam member.

34. A differential mechanism according to any of Claims 24 to 33 in which the cam surfaces on each cam member converge towards each other and the cam engaging surfaces of the cam followers are complementary thereto, each cam surface having a number of mutually inclined faces which is different from the number of mutually inclined faces of the other cam surface, the angles of convergence of the cam surfaces being different whereby the torque delivered to the outputs will be divided between the outputs at a desired ratio or ratios for both directions of relative rotation between the outputs.

35. A differential mechanism according to Claim 22 in which the ratio is substantially constant.

36. A differential mechanism comprising an input, two outputs rotatable about an axis, two cam members one of which is connected to one said output and the other of which is connected to the other output, said cam members having annular cam surfaces of undulating form coaxial with said outputs, a plurality of cam followers having cam engaging surfaces for imparting drive to the outputs, the cam surfaces on each cam member converging towards each other and the cam engaging surfaces of the cam followers being complementary thereto, each cam surface having a number of mutually inclined faces which is different from the number of mutually inclined faces of the other cam surface, and the angles of convergence of the cam surface being different whereby the torque delivered to the outputs will be divided between the outputs at a desired ratio or ratios for both directions of relative rotation between the outputs.

37. A differential mechanism according to Claim 36 in which the ratio is substantially constant.

38. A differential mechanism according to Claim 37 in which said adjacent surfaces interengage in use and drive from the input is transmitted from a cam follower in non-driving engagement with the cam surface to a cam follower in driving engagement with the cam surface.

39. A differential mechanism according to Claim 37 or 38 in which said number of cam followers forms a batch of cam followers arranged adjacent a similar batch.

40. A differential mechanism according to Claim 39 in which each batch comprises an equal number of cam follower members.

41. A differential mechanism according to Claim 36 in which a drive input element is provided for imparting drive from the input cam followers, the drive input element comprising first and second sections which are drivably interconnected so as to define openings in which the cam followers are slidably located.

42. A differential mechanism according to Claim 41 in which the first section includes a plurality of radial projections with the cam followers disposed therebetween.

43. A differential mechanism according to Claim 42 and where said number of cam followers forms a batch of cam followers arranged adjacent a similar batch, in which the batches of cam followers are disposed between the radial projections.

44. A differential mechanism according to any of Claims 39 to 43 in which the batches and means for imparting drive together form a substantially continuous annular set of components coaxial with the outputs.

45. A differential mechanism according to Claim 36, 37 or 38 in which the cam follower members are driven by a driving element which extends circumferentially around the cam follower members.

46. A differential mechanism according to Claim 45 in which said driving element and cam follower members interengage through projection and socket means.

47. A differential mechanism according to Claim 45 in which the projections and sockets are tapered in the radial direction.

48. A differential mechanism according to Claim 45, 46, or 47 in which the cam surfaces on each cam member converge towards the other cam member and the end surfaces of the follower members are complementary thereto whereby during drive of said output members through the follower members, a radially outward force is created which urges the follower members towards said driving member.

49. A differential mechanism according to Claim 48 and where a projection and socket means is used to transmit drive in which the radial force is combined with a cam driving force at the undulating cam surface to give a resultant outward force which urges a corner section of the cam follower against a substantially complementary corner section of the drive element to inhibit tipping of the cam follower.

50. A differential mechanism according to any of Claims 44 to 49 in which the cam follower members are arranged as a continuous series forming an annul us of components coaxial with the outputs.

51. A differential mechanism according to any of Claims 36 to 50 in which drive from said input is transmitted to means for imparting drive to the cam followers by removable bolts extending between spaced apart sections of the input.

52. A differential mechanism according to any of Claims 36 to 50 in which the drive from said input is- transmitted to means for imparting drive to the cam followers by a sleeve extending between and rotatably secured to sections of the input.

53. A differential mechanism according to any of Claims 36 to 52 in which the undulating surfaces of each cam comprises a multiplicity of zig-zag faces.

54. A differential mechanism according to any of Claims 36 to 53 in which the number of faces on one cam is different from the number of faces on the other cam.

55. A differential mechanism according to any of Claims 36 to 54 in which the cam engaging surfaces of the cam followers comprise two inclined helical surfaces at each end for engagement with the respective cam surfaces.

56. A differential mechanism according to any of Claims 36 to 55 in which each cam follower includes a radially inner first portion, and a radially outer second portion to which driving load is imparted said end surfaces extending over both said first and second portions.

57. A differential mechanism according to any of Claims 36 to 56 in which the cam surface on one cam member comprises at least two identical tracks which form the complete annular cam surface whereby axial loading applied thereto by the cam followers during drive is applied symmetrically to the cam surface to create a balanced axial loading on the cam member.

58. A differential mechanism comprising an input, two outputs rotatable about an axis, two cam members one of which is connected to one said output ~ and the other of which is connected to the other output, said cam members having annular cam surfaces of undulating form coaxial with said outputs, a plurality of cam followers having cam engaging surfaces for imparting drive to the outputs, the cam surface on one cam member comprising at least two identical tracks which form the complete annular cam surface whereby axial loading applied thereto by the cam followers during drive is applied symmetrically to the cam surface to create a balanced axial loading on the cam member.

59. A differential mechanism according to Claim 58 in which both of the cams are formed with at least two tracks so that balanced axial loading is applied to both tracks.

60. A differential mechanism according to Claim 58 or 59 in which said adjacent surfaces interengage in use and drive from the input is transmitted from a cam follower in non-driving engagement with the cam surface to a cam follower in driving engagement with the cam surface.

61. A differential mechanism according to Claim 58, 59 or 60 in which said number of cam followers forms a batch of cam followers arranged adjacent a similar batch.

62. A differential mechanism according to Claim 61 in which each batch comprises an equal number of cam follower members.

63. A differential mechanism according to Claim 58 or 59 in which a drive input element is provided for imparting drive from the input cam followers, drive input element comprising first and second sections which are drivably interconnected so as to define openings in which the cam followers are slidably located.

64. A differential mechanism according to Claim 63 in which the first section includes a plurality of radial projections with the cam followers disposed therebetween.

65. A differential mechanism according to Claim 64 and where said number of cam followers forms a batch of cam followers arranged adjacent a similar batch, in which the batches of cam followers are disposed between the radial projections.

66. A differential mechanism according any of Claims 61 to 65 in which the batches and means for imparting drive together form a substantially continuous annular set of components coaxial with the outputs.

67. A differential mechanism according to Claims 58, 59 or 60 in which the cam follower members are driven by a driving element which extends circumferentially around the cam follower members.

68. A differential mechanism according to Claim 67 in which said driving element and cam follower members interengage through projection and socket means.

69. A differential mechanism according to Claim 68 in which the projections and sockets are tapered in the radial direction.

70. A differential mechanism according to Claims 67, 68 or 69 in which the cam surfaces on each cam member converge towards the other cam member and the end surfaces of the follower members are complementary thereto whereby during drive of said output members through the follower members, a radially outward force is created which urges the follower members towards said driving member.

71. A differential mechanism according to Claim 70 and where a projection and socket means is used to transmit drive in which the radial force is combined with a cam driving force at the undulating cam surface to give a resultant outward force which urges a corner section of the cam follower against a substantially complementary corner section of the drive element to inhibit tipping of the cam follower.

72. A differential mechanism according to any of Claims 66 to 71 in which the cam follower members are arranged as a continuous series forming an annul us of components coaxial with the outputs.

73. A differential mechanism according to any of Claims 58 to 72 in which drive from said input is transmitted to means for imparting drive to the cam followers by removable bolts extending between spaced apart sections of the input.

74. A differential mechanism according to any of Claims 58 to 72 in which the drive from said input is transmitted to means for imparting drive to the cam followers by a sleeve extending between and rotatably secured to sections of the input.

75. A differential mechanism according to any of Claims 58 to 74 in which the undulating surfaces of each cam comprises a multiplicity of zig-zag faces.

76. A differential mechanism according to any of Claims 58 to 75 in which the number of faces on one cam is different from the number of faces on the other cam.

77. A differential mechanism according to any of Claims 58 to 76 in which the cam engaging surfaces of the cam followers comprise two inclined helical surfaces at each end for engagement with the respective cam surfaces.

78. A differential mechanism according to any of Claims 58 to 77 in which each cam follower includes a radially inner first portion, and a radially outer second portion to which driving load is imparted, said end surfaces extending over both said first and second portions.

79. A differential mechanism according to any of Claims 58 to 67 in which the cam surface on each cam member comprises at least two identical tracks which form the complete annular cam surface whereby axial loading applied thereto by the cam followers during drive is applied symmetrically to the cam surface to create a balanced axial loading on the cam member.

80. A differential mechanism according to Claim 22 in which the ratio is substantially constant.

81. A differential mechanism according to any preceding claim in which each cam follower is of elongate strut-like form having end surfaces which engage the cam surfaces, said end surfaces terminating at relatively longer said side surfaces.

82. A differential mechanism comprising an input, two outputs rotatable about an axis, two cam members one of which is connected to one of the outputs and the other of which is connected to the other output, said cam members including annular cam surfaces of undulating form coaxial with said outputs, a plurality of cam followers of elongate strut-like form, said cam followers having end surfaces which engage the cam surfaces to impart drive to the outputs, said end surfaces terminating at relatively longer side surfaces, the or a number of said cam followers lying side by side with side surfaces of the cam followers or the cam followers of said number lying closely adjacent or in inter-engagement and means for imparting drive to the cam followers from the input positioned so as to be non-interposed between the side surfaces of the cam followers or the cam followers of said number, the arrangement being such that relative contra-rotation of said outputs causes the cam followers to slide axially.

83. A differential mechanism constructed and arranged substantially as described with reference to any of the accompanying drawings.