The present invention concerns a differential gear.

Differential gears permit the relative rotation of two shafts driven by a third drive shaft, the sum of the rotation rates of the driven shafts being constant. Differential gears typically comprise a drive shaft which rotates a cage containing a planetary bevel wheel or wheels which mesh with two bevel wheels, one on each of the driven shafts. The meshed bevel wheels cause the sum of the rotation rates of the driven shafts to be constant, although they may rotate at different rates.

Such differential gears are widely used, for example in cars, but the manufacture of the cage and bevel wheels is expensive and places a price barrier upon goods containing differential gears.

The present invention overcomes the problems of the prior art, at least in part, and provides a simple, convenient, less expensive differential gear.

According to the present invention there is provided a differential gear comprising an input member constituting a cage for rolling means and rolling means in the cage and having drive input means and being mounted for rotation about an output axis, and output half-shafts each axial side of the input member, each half-shaft having a clutch plate, the clutch plates being disposed each axial side of the input member and being urgeable together so as to clutch against said rolling means, whereby a differential

output effect is achieved by the clutch plates rolling over the rolling means.

The differential may comprise at least one rolling means and may comprise for example up to or even more than 6 rolling means.

At least two rolling means may be at different radii from the output axis.

The rolling means, which may be balls, may be of a width greater than that of the cage.

The cage may comprise a perforated plate..

Hence the present invention may comprise a plate with, say, 6 perforations, the perforations being at different radii from the output axis, and housing balls of a width greater than that of the plate.

The clutch plates may be urged together by angular contact bearings and belleville washer arrangements, or by any other convenient means.

The differential may be lubricated, and may be lubricated by oil or be self- lubricating.

The input member may comprise a self-lubricating plastic.

Hence a self-lubricating differential may be made according to the invention, which may be a sealed unit.

The drive input means may comprise a worm wheel, a spur gear, a bevel gear, a friction drive, a V-belt or a toothed belt, or any other convenient means.

A differential gear according to the present invention may be easily manufactured and may be used to advantage in applications e.g. golf trollies which would not use a conventional differential gear due to the additional cost it would impose.

Particular applications may include those which would impose relatively low forces (i.e. power/torque) upon the differential gear.

The invention will be further apparent from the following description, with reference to the figures of the accompanying drawing, which show, by way of example only, one form of differential gear.

Figure 1 shows an aerial axial/half section of a differential gear and

Figure 2 is a view along the gear axis of a cage of the gear.

A differential gear according to the present invention comprises an input member (10) constituting a cage for rolling means (21; 22; 23) and having drive input

means (30) and being mounted for rotation about an output axis, the output axis comprising output half-shafts (41; 42) either side of the input member (10), each half- shaft having a clutch plate (51 ; 52), the clutch plates (51 ; 52) being disposed either side of the input member (10) and being urgeable together so as to clutch against said rolling means (21 ; 22), whereby a differential output effect is achieved by the clutch plates (51 ; 52) rolling over the rolling means (21; 22; 23).

The differential comprises three rolling means (21; 22; 23 j, which comprise balls at different radii from the ouput axis.

The balls (21; 22; 23) are of a width greater than that of the cage (10).

The cage (10) comprises a perforated plate..

The clutch plates (51 ; 52) are urged together by angular contact bearings and belleville washer arrangements (61 ; 62), though other loading arrangements may be used.

The differential is lubricated, as by oil or grease, but may also be self- lubricating. The input member (10) may comprise a self-lubricating plastic.

The drive input means (30) comprises a worm wheel.

The differential is contained within a casing (71).

The input member (10) is mounted on supporting means (81) which are attached to clutch plate (51) such that the input member (10) rotates about the output axis independently of the supporting means (81) and any rotation thereof.

The clutch plates could be nitrided or surface coated to increase hardness. It is preferred to have the rolling means somewhat harder than the clutch plates. For example the rolling means could have a hardness of 65 - 68 Rockwell C, while the clutch plates have a hardness of 50 - 55 Rockwell C. This, for one particular application, has been found to minimise wear (which results in grooving of the plates) yet to afford good frictional contact, especially with grease or oil lubrication, possibly because the pressure is high enough to cut through the lubricant film.

It will be appreciated that it is not intended to limit the invention to the above example only, many variations being possible, such as might readily occur to one skilled in the art, without departing from the scope thereof.