GB2237851A

GB2237851A - Axle drive unit using unequal torque split bevel gear differential

Info

Publication number: GB2237851A
Application number: GB8925510A
Authority: GB
Inventors: Harry Balmforth
Original assignee: GKN Axles Ltd
Current assignee: Dana Spicer Europe Ltd
Priority date: 1989-11-10
Filing date: 1989-11-10
Publication date: 1991-05-15
Also published as: GB8925510D0

Abstract

An axle drive unit, for use in a tri-axle drive, has disposed in its casing an unequal-torque-split bevel gear differential gear (26 to 36) whose outputs are connected respectively to an equal-torque-split inter-wheel differential gear (51, 53) in the casing and to an output member (42) for connection to a further inter-axle differential gear. In the tri-axle drive the unit enables torque to be split equally between the three axles. The bevel gear differential gear preferably splits torque in the ratio 1/3 : 2/3. <IMAGE>

Description

AXLE DRIVE UNIT This invention relates to an axle drive unit for use in a tri-axle drive, i.e. a drive wherein input torque is split between three driving axles.

In our published UK patent application no. 2 208 530 there is disclosed a tri-axle drive and a drive unit therefor. In order that the torque received from the engine of a vehicle is split substantially equally between the three axles, the drive unit includes an unequal-torque-split first differential gear with an input element which receives torque from the vehicle's engine and two output elements one of which has a driving connection with an equal-torque-split inter-wheel second differential gear incorporated in the axle drive unit and the other of which provides an output for connection to a further inter-axle differential gear. In the tri-axle drive, this last mentioned differential gear splits torque equally between two further axles of the vehicle, each of which incorporates a respective further inter-wheel differential gear.

The first differential gear in the axle drive unit splits torque in the ratio approximately : between the first output element leading to the inter-wheel second differential gear in the unit and the second output element for connection to the equal-torque-split inter-axle differential gear. The result is thus the required approximately equal torque split between the three axles in the complete tri-axle drive. The first inter-axle differential gear, in the drive unit, is a spur gear epicyclic differential gear, whose planet carrier is connected to the input of the unit. This necessitates a generally U-section driving connection passing around the outside of the annulus gear of the differential gear, and the overall arrangement is thus relatively complex.

According to the present invention, an axle drive unit which is generally of the type disclosed in our patent application aforesaid has, instead of the spur gear epicyclic first differential gear in the casing of the unit, an unequal-torque-split bevel gear differential gear whose outputs are connected respectively to the inter-wheel second differential gear in the casing and to the output member for connection to the other axles in a tri-axle drive.

Preferably the bevel gear differential gear provides an approximately : torque split, between the output leading to the inter-wheel second differential gear in the casing of the unit, and the output for connection to the other axles of a tri-axle drive.

The unequal torque split in the bevel gear first differential gear may be achieved by providing each of a number of circumferentially spaced planet bevel gear supporting pins of the differential with two planet bevel gears connected together, one of which planet bevel gears meshes with a bevel side gear of larger diameter and the other of which meshes with a bevel side gear of smaller diameter. The side gear of larger diameter is connected to the output for connection to the other axles of the tri-axle drive whilst the smaller side gear is connected to the inter-wheel second differential gear in the casing.

As in our published patent application aforesaid, the drive to the inter-wheel differential may be by way of a tubular shaft and hollow gear supported by bearing means in the casing of the unit.

The invention will now be described by way of example with reference to the accompanying drawing, which is a diagrammatic sectional view of an axle drive unit according to the invention.

The illustrated axle drive unit comprises a casing which is formed of a number of parts secured to one another by bolts and studs some of which are visible and some of which are not shown in the drawing. At one end, the input end of the casing, there is an end casing part 10 secured to a first intermediate casing part 11 which is itself secured to a second intermediate casing part 12. The part 12 is secured to a second end casing part 13. The free end of the first casing part 10 is closed by a bearing carrier sleeve 14 which carries, by taper roller bearings 15, an input member 16 which is of tubular form and has a drive flange 17 for bolted driving connection to, e.g., the output from a gearbox. A double oil seal 18 is supported within a seal carrier sleeve 19 secured with the bearing carrier sleeve 14 to the end of the casing part 10.

A stub shaft 20 is supported within the tubular input member 16 and held therein by a nut 21. Interengaging splines 22 provided for torque transmission between the input member and stub shaft. Within the casing part 10 and integral with the stub shaft 20 there is a somewhat cup-shaped differential housing 23 of an unequal torque split inter-wheel bevel gear differential gear. Where the stub shaft 20 expands into the differential housing 23, it will be noted that there is a shoulder 24 which abuts the inner race of one of the taper roller bearings 15, so that the position of the differential housing 23 within the casing part 10, in the direction along the axis of the stub shaft 20, is accurately determined and can be adjusted by the insertion of suitable shims between the bearing carrier sleeve 14 and the end of the casing part 10, where indicated at 25.This serves to adjust and set the backlash between the side gears and planet bevel pinions of the differential, to be described hereafter.

The unequal-torque-split inter-axle differential gear comprises four planet bevel support pins 26 in cruciform disposition, joined at their innermost ends by a collar 28 and carried at their outermost ends by the differential housing 23 which constitutes the input element of the differential gear. Visible in the drawing is one bolt 29 of a number thereof securing a removable end part 30 of the differential housing 23 to the main part thereof, by which the assembly of support pins 26 is connected and held to the differential housing. Each pin 26 carries two planet bevel pinions 31, 32 of which the pinion 32 is rotatable on the pin and the pinion 31 is rotationally fast with the pinion 32, being engaged therewith by splines 33.Pinion 31 meshes with a bevel side gear 34 and pinion 32 meshes with a bevel side gear 35 which is of larger diameter than the side gear 34 so that torque is split approximately in the ratio : between the side gears 34 and 35. The back of side gear 35 abuts an axially presented internal surface of the differential gear housing 23 with the interposition of a thrust washer 36.

Bevel side gear 35 is splined to a shaft 37 which extends through the unit to the output end of the casing, where it is supported by a bearing 38. A splined portion 39 of the shaft protrudes outwardly of the casing of the unit, through a closure cap 40 with seal 41, to receive a yoke 42 of a Hookes universal joint for driving connection, by way of a suitable intermediate shaft, to the two further axles of a tri-axle drive.

The smaller bevel side gear 34 has a tubular portion 43 surrounding the shaft 37 and having splined engagement at 44 with a hollow gear 45 supported by bearings 46, 47.

Bearing 46 is carried by a carrier flange 48 bolted to the casing part 11, whilst bearing 47 is supported in the casing part 12.

Gear 45 meshes with a gear 49 splined to a stub shaft 50 having a bevel pinion 51. Shaft 50 is supported in bearings 52 in the casing part 12. Bevel pinion 51 meshes with a crown wheel 53 which is shown in outline only and is associated with an equal-torque-split interwheel differential gear whose outputs, on a transverse axis at 54, would be connected to the wheels of the axle associated with the axle drive unit in the tri-axle drive.

A dog clutch arrangement indicated generally at 55 and substantially the same as that described in our patent application aforesaid is provided for locking the hollow gear 45 to the shaft 37 so that the differential action of the bevel gear differential gear in the unit can be rendered inoperative, i.e. the differential gear is locked.

The unit thus provides an unequal-torque-split bevel gear differential gear whose outputs are connected to an inter-wheel second differential gear in the casing and to an output member for connection to the other axles in a tri-axle drive.

Claims

1. An axle drive unit comprising: a casing having opposite first and second ends; an input member at the first end of the casing; an unequal-torque-split bevel gear first differential gear in the casing, comprising an input connected to said input member, and two outputs; an equal-torque split inter-wheel second differential gear in the casing and having an input element; first driving means interposed between a first output of the first differential gear and said input element of the second differential gear, and including a tubular shaft; an output member at the second end of the casing; and second driving means connecting the second output of the first differential gear to said output member, said second driving means including a driving shaft within and rotatable with respect to said tubular shaft.

2. An axle drive unit according to Claim 1 wherein the first differential gear provides an approximately : torque split between its output leading to the inter-wheel second differential gear and the output leading to the output member.

3. An axle drive unit according to Claim 2 wherein said bevel gear first differential gear comprises a number of circumferentially spaced planet bevel gear supporting pins each provided with two bevel gears connected together, and two bevel side gears of different diameter from one another meshing with said planet bevel gears and connected to said outputs of the differential gear.

4. An axle drive unit substantially as hereinbefore described with reference to the accompanying drawing.