This invention relates to vehicle differentials and particularly to differentials for inclusion in axles for agricultural or industrial tractors or similar vehicles.

With the requirement to provide tractors capable of higher road speeds to reduce transportation times there is a requirement to increase the braking capacity of such tractors over and above the normal rear axle braking only, which is conventionally provided on most tractors.

Various proposals have been made to provide additional braking capacity. For example, separate multi-plate wet disc brakes have been provided in each front wheel drive hub to provide the possibility of independent braking on each front wheel of the tractor to assist with tight turns. However- such wet brake arrangements are by their nature fully enclosed within the drive hub within a relatively small volume of oil within which the final drive gear of the hub also runs. Problems are thus experienced with an inability to dissipate the considerable amount of heat which may be generated when, for example, braking a tractor with a heavy trailer which is descending a hill. This may lead to severe brake failure and/or damage to the final drive gear of the hub.

Other solutions have involved the provision of a disc brake which operates on the drive shaft to the front wheels. This solution suffers from the problem that because the brake operates on a part of the drive train before the differential, the braking effect can be lost

if one of the front wheels is on ground with poor adherence. Also problems can arise due to the brake being exposed to contamination by mud and water etc. and it is also impossible to provide independent braking on the front wheels to reduce the turning circle of the tractor.

Also with the increasing trend to more sophisticated automatic electronic control of various tractor functions, such as the engagement and disengagement of differential locks, there is a requirement for a differential lock with an actuating system which is reliable in operation and which employs an actuating system which lends itself to remote installation (in a front axle for example) and which can readily be operated by an electronic system.

It is an object of the present invention to provide a differential with a braking function which is not susceptible to the braking problems outlined above and which can be easily adapted to include a differential lock function.

Thus according to the present invention there is provided a vehicle differential comprising an oil containing casing within which is disposed a pinion, a crown wheel meshing with the pinion, a planet carrier supported on the crown wheel, planet gears mounted on the carrier, at least two sun gears meshing with the planet gears and each drivingly connected to a respective drive shaft, characterised in that the differential also comprises separate multi-plate oil immersed disc brakes disposed within the casing around each respective drive shaft, each brake acting between the casing and its respective drive shaft.

By including the brakes within the differential casing the brakes are immersed in a much larger volume of oil than if the brakes are included within the drive hubs and the surface area of the casing is also significantly larger further improving the ability of the differential to dissipate the heat generated by the brakes.

In a preferred arrangement each brake comprises one or more non-rσtatable discs held against rotation relative to the casing and one or more interleaved discs connected for rotation with the associated drive shaft by a sleeve which encircles the drive shaft and is splined to or otherwise connected to the drive shaft for rotation therewith.

Preferably the brakes are each independently actuated by separate hydraulic piston and cylinder assemblies.

Each brake may be housed within a separate support arch which is secured to the casing and which encircles the brake discs, holds the non-rotatable discs against rotation relative to the casing, includes the hydraulic piston and cylinder assembly and supports a bearing for the associated drive shaft.

A differential lock function may be built into the differential by providing the sleeve with a first locking formation which is engageable with a second locking formation on the crown wheel or carrier, the locking formations being engageable on axial displacement of the sleeve by an actuator.

Such an arrangement enables a manufacturer to provide very economically versions of the differential

with and without a differential lock simply by fitting different versions of the sleeve with and without the first locking formation and by adding a differential lock actuator.

Preferably the first and second locking formations are held disengaged by a spring means and are engaged by an hydraulic piston and cylinder assembly. The supply of hydraulic fluid to the piston and cylinder assembly may be controlled by a solenoid operated fluid flow control. valve which may receive its electric signal from an electronic control system and/or from a manually operated switch.

Several embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:-

Figure 1 is a horizontal section through a differential in accordance with the present invention;

Figure 2 is a view in the direction of the arrow A of Figure 1;

Figure 3 is a view in the direction of the arrow B of Figure 1;

Figure 4 is a view in the direction of the arrow C of Figure 1; and

Figure 5 is a horizontal section through a further form of differential in accordance with the present inventio .

Referring to Figure 1, this shows the central part of a tractor front axle having a casing 10 which encloses an inter-wheel differential 11 and a pair of internal oil-immersed multi-plate disc brakes 12 and 13 situated one on each side of the differential 11. The disc brakes when operated act to brake drive shafts 15 and 16 respectively relative to the casing 10. Casing 10 is provided with an integral spigot 10B which together with other support surfaces (not shown) mounts the axle for pivotting relative to the remainder of the tractor about a horizontal fore and aft axis X-X.

Referring to the differential 11 this includes an input pinion 17 on a front wheel drive shaft 18, a crown wheel 19, which meshes with pinion 17, and a planet carrier 20 which is secured to the crown wheel 19 via bolts 21. Mounted on the carrier 20, via a cross pin 22, is a pair of planet gears 23. The planet gears 23 mesh with sun gears 24 and 25 which are respectively splined on to the ends of drive shafts 15 and 16 via splines 26 and 27.

As can be seen from Figures 1, 3 and 4 each multi-plate brake 12, 13 comprises a support arch 28, which is secured to a flat internal surface 29 of casing 10 via a pair of dowells 30 and two pairs of bolts 31 and 32. A pair of non-rotatable brake discs 33 and a reaction member 33A are located within support arch 28 against rotation by projections 34 (see Figure 3) which engage corresponding cut-outs 35 in the support. A locating ring 44 prevents axially outward movement of reaction member 33A. Inter-leaved between the discs 33 and reaction member 33A is a second pair of discs 36 with friction pads 36A. The inner peripheries of discs 36 are splined onto a sleeve 37 which is itself splined onto

the associated drive shaft 15 or 16 via splines 26 or 27. The internal splining on sleeve 37 has a tapering lead-in 37A to facilitate the assembly of the brake during which the drive shafts 15 and 16 are introduced down arms 10A of the axle casing from the outer ends of the axle.

Without the use of sleeve 37 with its tapering lead-in 37A this assembly operation would be much more difficult.

Each brake has an actuator in the form of an annular piston 38 which is axially displaceable in an annular cylinder 39 cut in the support arch. Fluid is admitted into a chamber 40 behind the piston 38 via a drilling 41 and an hydraulic union 42. A bleed nipple 43 is also provided for each chamber 40.

When the chamber 40 of each brake is pressurised by hydraulic fluid using any form of suitable operating pedal and master cylinder arrangement, the inter-leaved brake discs 33 and 36 are compressed between the piston 38 and the reaction member 33A to apply the respective brake.

Each support arch 28 also carries a bearing 45 which supports the planet carrier 20 and hence the inner-end of each drive shaft 15, 16. Thus the brakes 12 and 13, the differential 11 and the inner ends of the drive shafts 15 and 16 are all supported from surface 29 via support arches 28.

As will be appreciated, if desired, each brake 12, 13 can be arranged to be independently operable by providing a separate pedal and master cylinder for each chamber so that each drive shaft 15, 26 can be braked independently in order to improve the turning circle of

the tractor under certain operating conditions when it is desirable to brake only the inside wheel when making the turn. Conveniently, the separate pedals and master cylinders provided for the operation of the left and right-hand rear wheel brakes of a tractor can also be coupled to the left and right-hand front axle brakes respectively, so that one pedal controls both the front and rear left-hand brakes and the other pedal controls both the front and rear right-hand brakes.

As is conventional, the front axle casing 10 contains a significant volume of oil in which the differential 11 and the brakes 12 and 13 are at least partially immersed. Typically the casing 10 and its arms 10A are approximately half full of oil (say 5 or 6 litres of oil). Oil is prevented from escaping from the ends of casing arms 10A near the outer ends of drive shafts 15 and 16 by sealing arrangement (not shown).

As will be appreciated, the casing 10 with its arms 10A has a considerable surface area through which the heat generated by the brakes 12 and 13 can be dissipated. Cooling of the brakes is also greatly improved by the relatively large volume of oil within the casing 10 and its arms 10A.

Figure 5 shows an alternative form of differential in accordance with the present invention in which component parts equivalent to the parts used in the differential shown in Figures 1 to 4 have been similarly numbered.

The main difference between the arrangements shown in Figures 1 and 5 is that the right hand brake 13 has been modified to also include a differential lock

function 50. This modification is easily achieved by replacing the sleeve 37 onto which brake discs 36 of brake 13 are splined with an alternative form of sleeve 51, which is provided with dog teeth 52 at its axially inner end. These dog teeth are engageable with corresponding teeth 53 provided on the carrier 20. The reaction member 33A of brake 13 is also replaced by an end cap 54 which includes a bore 55 in which a stepped piston 56 is slidable. The piston and cylinder assembly 55, 56 provides an acutator to engage the dogs 52 and 53. Piston 56 acts on the end of sleeve 51 to bring dogs 52 and 53 into engagement when hydraulic fluid is admitted into a chamber 57 via an inlet 58. A spring 59 acts between the piston 56 and an abutment 60 secured in the bore 55 by a circlip 61. Conveniently, pressurised fluid can be supplied to chamber 57 under the control of a solenoid-operated fluid flow valve, the electrical signal required to operate the solenoid being generated either automatically by an electronic control system or manually by an operator closing a switch.

As will be appreciated when dogs 52 and 53 are brought into engagement, this locks the carrier 20 against relative rotation with respect to the sun gear 25 so that differential action is prevented.

Thus the arrangement shown in Figure 5 provides a basis for a simple modification of one of the brakes of the differential to include a differential lock function simply by replacing the brake disc splining sleeve 37 with an adapted sleeve 51 and by adding an additional hydraulic actuator to axially displace the sleeve. The dog teeth 53 required on planet carrier 20 may be included unnecessarily in the planet carrier used in the Figure 1 construction to avoid the necessity for two

types of carrier, or a modified form of carrier may be used in Figure 5.

It is thus possible for a manufacturer to provide a basic differential of the form shown in Figure 1 in which no differential lock is provided and also to offer a differential of the form shown in Figure 5 which includes a differential lock and in which most of the brake and differential parts are common with those used in Figure 1. Both forms of differential could be designed to be housed within the same external housing 10, thus achieving further economies.