This invention relates to vehicle differential mechanisms of the automatic de-clutching type in which drive to one of the two output members of the mechanism is automatically declutched upon overrunning or underrunning of either output member.

Disclosure of t ^~~ e Invention Differential mechanisms of this type are well known and examples can be found, for example, in US Patent 2329θ59.To date, such mechanisms have been of a relatively complex and thus expensive construction.

It is an object of the present invention to provide an improved form of vehicle differential mechanism which is of a relatively simple and reliable construction.

Thus, according to the present invention there is provided a vehicle differential mechanism comprising a rotatable input member for connection with a drive means, the input member having oppositely directed faces extending in planes generally at right angles to the axis of rotation of the input member; a pair of rotatable output members for connection with components to be driven by the mechanism, the output members being located co-axially one on each side of the input member; a pair of rotatable clutch members located coaxially one on each side of the input member between the input member and the output members and slidable relative thereto in directions parallel to said axis of rotation, each clutch member having separate first and second cjrcumferentially-spaced axi ally-pro ecting cam formations for engagement with first and second cam formations on the nput and output jnembers respectively, said com foi τ.ations being shaped to result in axial dip] accTic-nt of the clulch member on relative rotation between i ntere.wgaui ng c m form._l.jons; and blocking means for

controlling the maximum possible rotational movement of the clutch members relative to the input member ; the arrangement being such that when the output members rotate in synchronism the first cam formations force both sets of second cam formations into engagement to transmit drive to each output member from the input member via the first and second cam formations, and when relative rotation occurs between the output members by virtue of their connection with said components, the second cam formations of the faster rotating output member cause axial and rotational displacement of the associated clutch member thus disconnecting drive between the associated first and second cam formations to disconnect drive between the input member and the faster rotating output member, the blocking means controlling the rotational displacement of said clutch member to prevent re-establishment of contact between the disconnected first cam formations whilst relative rotation occurs between the output members.

One of the main applications for a differential mechanism in accordance with the present invention is as an inter-wheel differential. When used in this application the output members are connected with respective wheels of a vehicle axle so that when the vehicle is driven substantially in a straight line (when the wheels and thus the output members rotate substantially in synchronism) both output members are driven, but when the vehicle makes a turn, the output member connected with the outer wheel of the turn will rotate faster than the other output member so that drive to the outer wheel is disconnected during the turn and the outer wheel simply over-runs.

The blocking means may comprise a blocker member supported co-axially with the clutch members and provided with two series of circumferentially-spaced blocker formations, each

respective series of formations engaging a mating set of blocker formations on a respective one of the clutch members, the circumferential spacing between adjacent blocker formations on the blocker member and clutch members limiting the maximum possible relative rotation between the clutch members and hence controlling the maximum possible relative rotation between either clutch member and the input member.

The input member and clutch members are all preferably of annular form and surround central axially-adjacent portions of the output members. The blocker member is also preferably of annular form and lies radially between the clutch members and said central portions of the output members. This gives a particularly compact arrangement.

Preferably a torsional friction drive is provided between each clutch member and its associated output member to assist in re-establishing drive to a disconnected output member on re-establishment of synchronous output member rotation.

The friction drive may be provided by a friction member which is axially slidably connected for rotation with each clutch member, each friction member being spring-biassed into frictional contact with a corresponding friction surface on its associated output member. Preferably the friction members are biassed axially apart into contact with their respective output members by a spring which surrounds said axially-adjacent central portions of the output members.

Means are preferably provided for preventing the simultaneous disconnection of drive to both output members .

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The invention also provides a vehicle axle including a differential mechanism in accordance with the invention employed as an inter-wheel differential with each output member connected with a respective wheel-driving shaft. Description of the Drawings

One embodiment of the present invention, as applied to tractor front axle, will now be described, by way of example only, with reference to the accompanying drawings in which:-

Figure 1 shows a horizontal section through the centre portion of the tractor front axle;

Figure 2 shows the differential mechanism used in the axle of Figure 1 on a larger scale;

Figure 3 shows a side view of the input member of the differential mechanism;

Figure 4 shows a part-section on the line IV - IV of Figure 3;

Figure 5 shows a side view of the clutch member of the differential mechanism;

Figure 6 shows a part-section on the line VI - VI of Figure 5;

Figure 7 is a diametral section through the blocker member of the differential mechanism;

Figure 8 is a diametral section through an output member of the differential mechanism;

Figures 9 and 10 show, for the purpose of explanation of the

operation of the differential mechanism, diagrammatic developments of the differential mechanism in straight-ahead and turn conditions respectively, and

Figure 11 shows a modification to the differential mechanism of Figure 2.

Best Mode of Carrying Out Invention

Figure 1 shows the centre portion of a tractor front axle having a casing 15 into which drive is transmitted via a bevel wheel 10 which meshes with a crownwheel 11 which is bolted to a differential housing 12. Drive is transmitted from the differential housing 12 to one or both front wheel drive shafts 13, 14 via a differential mechanism in accordance with the present invention.

The differential mechanism, shown on a larger scale in Figure 2, has the following main components :-

An Input member 16 which bolted between left and right hand parts (12a, 12b) of the differential housing 12 by a series of six circumferentially spaced bolts 50 and a series of six circumferentially spaced dowells 51 which are circumferentially inter-leaved between the bolts;

Left and right hand output members 17 and 18 which are splined onto left and right hand drive shafts 13 and 14 respectively;

Left and right hand clutch members 19 and 20 which, when engaged, transmit drive from the central input member 16 to the left and right hand output members 17 and 18 respectively, and

A blocker member in the form of a ring 21 which controls the maximum possible relative rotation between

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clutch members 19 and 20 and hence the maximum possible rotation of either clutch member relative to the input member.

As can be seen from Figures 2, 3 and 4, the input member 16 has cam teeth 22 on each side which are engageable with cam teeth 23 on the adjacent faces of clutch members 19 and 20 shown in Figures 5 and 6. Cam teeth 23 are inclined at approximtely 45 degrees to the general planes of rotation of clutch members 19 and 20. The other faces of the clutch members have smaller cam teeth 24 engageable with cam teeth 25 on the output members 17 and 18, shown in Figure 8. Cam teeth 24 are inclined at approximately 60 degrees to the general planes of rotation of clutch members 19 and 20. The angles of cam teeth 23 and 24 ensure that the separating force between the input member 16 and the clutch members 19 and 20 due to a given input torque is greater than the separating force between the clutch members and the output members 17 and 18 for the same torque. This ensures that engagement is maintained between the clutch members and the output members in the driving condition described below.

Each clutch member 19,20 is also provided on its inside diameter with blocker formations in the form of teeth 26,27 respectively for co-operation with two series of blocker formations in the blocker ring 21 in the form of slots 28 and 29 to limit the relative rotational movement possible between the two clutch members as will be described below.

Referring to Figure 9, this shows a diagrammatic development of the view from the inside of the differential mechanism looking radially outwards (i.e., in the direction of arrow A of Figure 1) with the blocker ring 21 shown in dotted detail for clarity and those portions of the output members 17 and 18 radially inward of the blocker ring removed.

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Figure 9 shows the normal straight-ahead driving condition in which the differential housing 12 is rotating so that input member 16 moves in effect in direction X. Drive is therefore transmitted via the contact zones 22a and 22b of cam teeth 22 and 23 from input member 16 to both clutch members 19 and 20 and hence via cam teeth 24 and 25 to both output members 17 and 18 and hence both drive shafts 13 and 14. Thus both drive shafts are driven in this condition.

If the vehicle now makes a turn which results in the outside wheel (the left-hand wheel as shown in Figure 10) rotating faster than the inside (right-hand) wheel, the contact between input member 16 and clutch member 19 will be lost since the clutch member will tend to rotate in the forward drive direction relative to the input member 16 as indicated by arrow Y.

Rotation in direction Y of clutch member 19 relative to input member 16 is limited by contact between the blocker teeth 26 on clutch member 19 and the sides 40 of the slots

28 in blocker ring 21 and by contact between the blocker teeth 27 on clutch member 20 and the sides 41 of the slots

29 in blocker ring 21.

When further rotation of clutch memnber 19 relative to input member 16 is prevented by contact between teeth 26 and the slot sides 40 as described above,the continued rotation of output member 17 due to its conection with the associated wheel causes a cam action between teeth 24 and 25 which results in the axial displacement of clutch member 19 (as indicated by arrow Z) until teeth 24 and 25 are disengaged as shown in Figures 2 and 10. This disengagement of teeth 24 and 25 allows the outer (left-hand) faster rotating wheel o idle, the wheel being driven by its contact with the

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ground so that it overruns the other wheel until the turn is completed.

The above described limitation of the maximum possible relative rotation between clutch member 19 and input member 16 is arranged to prevent contact between sides 23d of teeth 23 and sides 22d of teeth 22 during a turn (which would cam clutch member 19 outwardly to re-engage teeth 24 and 25).

As will be appreciated,blocker ring 21 and cooperating teeth 26 and 27 directly limit the maximum possible relative rotation between the two clutch members.However, since one of the clutch members always remains in driving engagement with the input member 16 during a turn,the blocker member 21 and teeth 26 and 27 are capable of limiting the maximum possible rotation of either clutch member relative to the input member depending on the direction of the turn.

On completion of the turn the speed differential between output members 17,18 disappears and the clutch member 19 moves in the opposite direction to arrow Y to re-establish contact with the teeth 22 of input member 16 so that teeth 22 and 23 co-operate to axially displace clutch member 19 in the opposite direction to arrow Z to re-engage teeth 24 and 25 and reconnect drive to output member 17.

It will be noted that the axial distance W (See Figure 10) between the bottoms of the slots 28 and 29 in the blocker ring 21 limits the minimum possible distance between the two sets of blocker teeth 26 and 27 and hence the clutch members to prevent the simultaneous disconnection of drive from both outside members 17 and 18. It will be seen from Figure 10 that with clutch member 19 disconnected from output member 17, the blocker teeth 26 are in contact with the bottoms of slots 28 whilst the axial clearance between the blocker

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teeth 27 and the bottoms of slots 29 is less than the axial movement of clutch member 20 required to disconnect the drive from output member 18. Thus at least one of the output members is always connected with the input member.

If desired, in order to assist in re-establishing contact between teeth 22 and 23 when a turn is completed, a light friction drive may be provided between the clutch members 19 and 20 and their respective output members 17 and 18. Figure 11 shows such and arrangement in which the differential mechanism of Figure 2 is modified by the provision of friction members 60 and 61. Friction members 60 and 61 are splined onto blocker teeth 26 and 27 respectively for rotation with their associated clutch members and are provided with frusto-conical friction surfaces 60a and 61a respectively for frictional contact with corresponding frusto-conical surfaces 17a and 18a on the output members 17 and 18. A spring 62 biasses the friction members 60 and 61 apart to provide the necessary level of frictional drive in a torsional sense between the clutch members and the output members via surfaces 60a, 17a and 61a, 18a respectively, whilst allowing the clutch members to move axially without friction.

Thus in operation the differential mechanism will cause one or both wheels to be driven by the crownwheel, but at any time either wheel (but not both) can over-run if the tractor is turning a corner. If the tractor is descending a steep hill, and the transmission is resisting the forward movement, this device will cause one or both wheels to be resisted by the crownwheel, but either wheel can "under-run" when turning a corner.

In the drive condition during a turn only the inside wheel is driven whilst in an overrunning condition during a turn

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only the outside wheel is resisted.

It will be appreciated from the above that the present invention provides an improved form of vehicle differential mechanism which is of a relatively simple construction and which is reliable in operation. The differential mechanism is compact with the input member 16, clutch members 19,20 and blocker member 21 all being of annular form and surrounding the central axially-adjacent portions 17b, 18b of the output members with the spring 62 (when used) between the blocker member 21 and the central portions 17b, 18b of the output members.

Also since none of the teeth used in the mechanism have re-entrant angles, the toothed components can be produced by forming processes such as casting, forging or sintering without the need for expensive tooth machining.

Although the invention has been described above in relation to a tractor front axle inter-wheel differential, it will be evident that it has wider application. For example, it is also suitable for use as an inter-wheel differential in the rear axle of a four wheel drive vehicle and also as an inter-axle differential.

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