GB2215414A - 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 two cam faces may be difficult to provide different torque outputs. The cam may consist of a pattern which repeats around the axis 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 an 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 each said cam having a single annular cam surface thereon of undulating form coaxial with the outputs and arranged such that cam surfaces on the cam members converge towards each other, and a plurality of cam followers which are elongate in the direction of said axis and which have cam engaging surfaces for imparting drive from the input to said outputs, the arrangement being such that relative contra rotation of said outputs causes the cam followers to slide axially.

The use of single annular cam surfaces is particularly advantageous, e.g., over U.S.

Nos.2,034,318 and 2,220,432 where the cam surfaces are defined by grooves which are less straithtforward to manufacture.

Each cam follower may be of elongate strut-like form having end surfaces which engage the cam surfaces, said end surfaces terminating at relatively longer side surfaces. Such followers are advantageous over those described in U.S. Nos.2,034,318 and 2,220,432 where the cam engaging end surfaces are formed on spaced apart teeth projecting from beneath a connecting bar. In the latter case, compressive forces on the teeth axially of the bar will create cyclic bending stresses in the bar which are undesirable.

Preferably the or a number of said cam followers lie side by side with the side surfaces of the cam followers or the cam followers of said number lying closely adjacent or in interengagement.

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.

Means may be provided for imparting drive from the input to the cam followers and such means may be non-interposed between the side surfaces of the cam followers or the cam followers of said member.

According to a second 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 from the input 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.

In this other aspect the arrangement of the drive means so as to be non-interposed in that way enables the maximum number of cam followers to be located in the available circumferential space.

Preferably each cam follower has an arcuate embrace of 360/n degrees where n is the number of cam followers.

During said contra rotation of the outputs, substantial portions of said side surfaces of the or said number of the adjacent cam followers overlap each other continuously during full axial sliding movement thereof.

According to a third 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 side surfaces extending between the cam engaging surfaces, said or a number of said cam followers being 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 overlapping each other continuously during the full axial sliding movement thereof.

By arranging for overlap in that way, each follower is able to provide support for the other during drive over the substantial portions of said closely adjacent surfaces.

Preferably 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.

Resilient means may be provided for urging the cam surfaces and the cam engaging surfaces of the cam followers against each other. The resilient means may tend to urge the cam followers radially outwardly relative to the cam surfaces.

According to a fourth 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, each said cam having an annular cam surface thereon of undulating form coaxial with the outputs and arranged such that cam surfaces on the cam members converge towards each other, and resilient means for urging the cam surfaces and the cam engaging surfaces against each other so as to urge the cam followers radially outwardly relative to the converging cam surfaces, the arrangement being such that relative contra rotation of said outputs causes the cam followers to slide axially.

The resilient means is advantageous as it pre-loads the differential to ensure firm inter-engagement of the cam surfaces and cam follower members and to reduce backlash.

Preferably the resilient means acts between part of said input and one of said cam members so as to urge said one cam member towards the other. The resilient means may apply load to the cam member through a thrust bearing. Conveniently, the resilient means nay take the form of a Belleville Washer.

In order to support the cam followers, particularly during assembly of the differential, support means may be provided for biasing the cam followers towards a drive input element through which drive is transmitted to the cam followers from the input.

According to a fifth 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 can 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, and support means for biasing the cam followers towards a drive input element, the arrangement being such that relative contra-rotation of said outputs causes the cam followers to slide axially.

The support means ideally takes the form of a spring which may be generally cylindrical in shape and, e.g., coaxial with the outputs. The support means preferably serves to hold the cam follower members in the drive input element during assembly of the differential.

Where a drive input element is provided it may comprise first and second sections which are drivably interconnected so as to define openings in which the cam followers are slidably located.

According to a sixth 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 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 cam followers described therein comprise elongate bodies with relatively larger end sections fon.ledwith 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.

The first section of the drive input element may include a plurality of radial projections with the cam followers disposed therebetween. The second section may comprise a sleeve coaxial with the first section, the radial projections drivably engaging the sleeve.

The radial projections may locate in grooves in the sleeves.

In one embodiment, the cam surface of one of the cam members converges towards the cam surface of the 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 of relative rotation between the outputs.

According to a seventh 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 of one of the cam members converging towards the cam surface of the other and the cam engaging surfaces of the cam followers being complementary thereto, each cam surface having a 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.

The ratio may be substantially constant.

The cam surface on one cam member may comprise 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.

According to an eighth 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 substantially symmetrically to the cam surface to create a balanced axial loading on the cam member, the arrangement being such that relative contra rotation of said outputs causes the cam followers to slide axially.

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 two immediately preceding paragraphs helps to avoid that.

Both of the cams may be formed with at least two tracks so that balanced axial loading is applied to both tracks.

In the various aspects of the invention and consistory clauses set out above, the cam followers may be arranged in batches each of which may comprise an equal number of cam follower members.

Where the drive input element is formed so as to define openings in which the cam followers are located, a batch of followers may be provided in each opening.

Preferably the batches and means on the drive input element for imparting drive thereto together form a substantially continuous annular set of components coaxial with the outputs.

Instead of arranging the cam followers in batches, they may be arranged as a continuous series forming an annulus of components coaxial with the outputs.

Where a drive input element is provided, it may extend circumferentially around the cam followers, e.g., in the form of a sleeve.

The drive input element and cam follower members may interengage through projection and socket means.

The projections and sockets may be tapered in the radial direction.

Where the cam surfaces on the cam members converge towards each other, the cam-engaging surfaces of the follower members may be complementary thereto whereby during drive of said output members through the follower members, a force is created which urges the follower members radially outwards towards a drive input element.

Where a projection and socket means is used to transmit drive, the force which urges a said follower radially combines with a reaction 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 input element to inhibit tipping of the cam follower.

The undulating surfaces of each cam comprises a multiplicity of mutually inclined helical surfaces e.g., of zig-zag form.

The number of surfaces on one cam may be different from the number of faces on the other cam.

Preferablythe cam engaging surfaces of the cam followers comprise two inclined helical surfaces at each end for engagement with the respective cam surfaces.

Each cam follower may include 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.

Drive from said input may be transmitted to a drive input element for imparting drive to the cam followers by removable bolts extending between spaced apart sections of the input. Alternatively the drive can be transmitted to the drive input element by a sleeve extending between and drivably secured to sections of the input. In the latter case, the sleeve may be drivably secured by screw threading or welding.

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 follcwer 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.10 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.10 on the line XII-XII in Fig.10.

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.18 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, and 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, 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 has an arcuate embrace of 360/n degrees where n is the number of cam followers.

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 drive input 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.

To assist assembly of the cam followers 26, a light circular spring 28a may be used to bias the followers radially against the drive input element 40.

When drive input is applied through drive input 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.17 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 drive input 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 drive input 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 drive input element 40 will result from 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. Preferably the angles Q, S which, as stated above, correspond to the angles between the associated cam surfaces are selected so that relative rotation between the two cams 22, 23 will drive the cam followers axially but when one of the cams 22, 23 is associated with a first wheel in tractive engagement with the ground and the second wheel associated with the other cam is on a slippery surface, it is not possible for the cam followers to drive the second wheel relative to the first wheel, i.e., the drive path through the differential is non-reversible. However, if desired, the angles Q, S can be selected to provide a degree of reversibility.

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 he input members 13, 14 through thrust needle bearings 8. Shims 9 may be used to adjust the relative axial positions of the cams. A Belleville Washer 9a may be arranged to urge the followers into firm engagement with the cams. The urging of the followers against the cams also creates a radially outward force Z on the followers 28 resulting from the angles of inclination P and, in addition helps to reduce backlash.

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 radialiy 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 input 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, 14 and 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 camfollower 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 groovel53 in the drive input element 40.

Reference is now made to Figs.l3 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 screwed 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.13. 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 uinclined 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.14 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.13, 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.13 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 turng relative to each other in onedirection than when they are turning relatively in the opposite direction.

It has been found that appropriate selection of angles V and IV 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. Once a given relationship has been achieved between the torque ratio in one direction and the torque ratio in the other direction using 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 relationship.For example; if a torque ratio of 4:1 in each direction is achieved with selected materials, the selection of alternative materials may give a torque ratio of 3:1 in both directions, the relationship between the torque ratios therefore remaining constant.

In Fig.23, it can be seen that the cam surfaces anc 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.

The present application is related to our G.B.

Patent Application No.8801401.

Claims (49)

1. A differential mechanism comprising an input, two outputs rotatable about an axis, two cam members one of which is connected to one output and the other of which is connected to the other output, each said cam having a single annular cam surface thereon of undulating form coaxial with the outputs and arranged such that cam surfaces on the cam members converge towards each other, and a plurality of cam followers which are elongate in the direction of said axis and which have cam engaging surfaces for imparting drive from the input to said outputs, the arrangement being such that relative contra rotation of said outputs causes the cam followers to slide axially.

2. A differential mechanism according to Claim 1 in which each cam follower is of strut-like form having end surfaces which engage the cam surfaces, said end surfaces terminating at relatively longer side surfaces.

3. A differential mechanism according to Claim 2 or 3 in which the or a number of said cam followers lie side by side with the side surfaces of the cam followers or the cam followers of said number lying closely adjacent or in interengagement.

4. A differential mechanism according to Claim 2 or 3 in which means is provided for imparting drive to the cam followers.

5. A differential mechanism according to Claim 4 in which the means for imparting drive is non-interposed between the side surfaces of the cam followers or the cam followers of said member.

6. 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 from the input 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.

7. A differential mechanism according to any of Claims 2 to 6 in which during said contra rotation of the outputs, substantial portions of said side surfaces of the or said number of the adjacent cam followers overlap each other continuously during full axial sliding movement thereof.

8. 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 being 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 overlapping each other continuously during the full axial sliding movement thereof.

9. A differential mechanism according to Claim 7 or 8 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.

10. A differential mechanism according to any preceding Claim in which resilient means is provided for urging the cam surfaces and the cam engaging surfaces of the cam followers against each other.

11. A differential mechanism according to Claim 10 in which the resilient means tends to urge the cam followers radially outwardly relative to the cam surfaces.

12. 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, each said cam having an annular cam surface thereon of undulating form coaxial with the outputs and arranged such that cam surfaces on the cam members converge towards each other, and resilient means for urging the cam surfaces and the cam engaging surfaces against each other so as to urge the cam followers radially outwardly relative to the converging cam surfaces, the arrangement being such that relative contra rotation of said outputs causes the cam followers to slide axially.

13. A differential mechanism according to Claim 10, 11 or 12 in which the resilient means acts between part of said input and one of said cam members so as to urge said one cam member towards the other.

14. A differential mechanism according to Claim 13 in which the resilient means applies load to the cam member through a thrust bearing.

15. A differential mechanism according to any of Claims 10 to 14 in which the resilient means is a Belleville washer.

16. A differential mechanism according to any preceding Claim which support means is provided for biasing the cam followers towards a drive input element through which drive is transmitted to the cam followers from the input.

17. 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, and support means for biassing the cam followers towards a drive input element, the arrangement being such that relative contra-rotation of said outputs causes the cam followers to slide axially.

18. A differential mechanism according to Claim 16 or 17 in which the support means is a spring.

19. A differential mechanism according to Claim 18 in which the spring is cylindrical.

20. A differential mechanism according to Claim 18 or 19 in which the spring is coaxial with the outputs.

21. A differential mechanism according to any preceding Claim 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.

22. 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 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.

23. A differential mechanism according to Claim 21 or 22 in which the first section includes a plurality of radial projections with the cam followers disposed therebetween.

24. A differential mechanism according to Claim 23 in which second section comprises a sleeve coaxial with the first section, the radial projections drivably engaging the sleeve.

25. A differential mechanism according to Claim 24 in which the radial projections locate in grooves in the sleeves.

26. A differential mechanism according to any preceding claim in which the cam surface of one of the cam members converges towards the cam surface of the 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 of relative rotation between the outputs.

27. 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 of one of the cam members converging towards the cam surface of the other and the cam engaging surfaces of the cam followers being complementary thereto, each cam surface having a 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.

28. A differential mechanism according to Claim 26 or 27 in which the ratio is substantially constant.

29. 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.

30. A differential mechanism comprising an input, two outputs rotatable about an axis, two cam members one of which is connected to one said putput and the other of which is connected to the other output, said cam members having annular cam surfaces or 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 substantially symmetrically to the cam surface to create a balanced axial loading on the cam member, the arrangement being such that relative contra rotation of said outputs causes the cam followers to slide axially.

31. A differential mechanism according to Claim 29 or 30 in which both of the cams are formed with at least two tracks so that balanced axial loading is applied to both tracks.

32. A differential mechanism according to any preceding Claim in which the cam followers are arranged in adjacent batches.

33. A differential mechanism according to Claim 32 in which each batch comprises an equal number of cam follower members.

34. A differential mechanism according to Claim32 or 33 and where said drive input element defines openings wherein the cam followers are located, in which a batch of cam followers is disposed in each opening.

35. A differential mechanism according to Claim 34 in which the batches and means on the drive input element for imparting drive thereto together form a substantially continuous annular set of components coaxial with the outputs.

36. A differential mechanism according to any of Claims 1 to 31 in which the cam followers are arranged as a continuous series forming an annulus of components coaxial with the outputs.

37. A differential mechanism according to any preceding Claim in which a drive input element extends circumferentially around the cam follower members.

38. A differential mechanism according to Claim 37 in which said drive input element and cam follower members interengage through projection and socket means.

39. A differential mechanism according to Claim 38 in which the projections and sockets are tapered in the radial direction.

40. A differential mechanism according to any preceding Claim and where the cam surfaces on the cam members converge towards each other, in which cam-engaging surfaces of the follower members are complementary thereto whereby during drive of said output members through the follower members, a force is created which urges the follower members radially outwards towards a drive input element.

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41. A differential mechanism according to Claim 40 and where a projection and socket means is used to transmit drive in which the force which urges a follower member radially is combined with a reaction 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 input element to inhibit tipping of the cam follower.

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

43. A differential mechanism according to Claim 42 in which the number of faces on one cam is different from the number of faces on the other cam.

44. 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.

45. 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.

46. A differential mechanism a-ccording to any preceding Claim in which drive from said input is transmitted to a drive input element for imparting drive to the cam followers by removable bolts extending between spaced apart sections of the input.

47. A differen.ial mechanism according to any of Claims 1 to 45 in which the drive from said input is transmitted to a drive input element for imparting drive to the cam followers by a sleeve extending between and drivably secured to sections of the input.

48. A differential mechanism according to Claim 47 in which the sleeve is drivably secured by screw threading.

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