GB2148418A - Differential gear - Google Patents

Abstract

A differential gear for a land vehicle final drive, comprises two mutually oppositely disposed epicyclic gear trains, the planet carriers of which are mutually joined to define a hollow cylindrical body 16 housing the gear trains and forming a drive input, the respective planet gears 19, 19A being drivingly inter-connected by first mutually meshed gears 23, 24, and the respective annular gears being drivingly inter-connected by second mutually meshed gears 25, 26, whereby with said single carrier held stationary, the sun wheels 17, 18 can turn in one to one ratio and in mutually opposite directions being drivingly inter-connected by the first and second mutually meshed gears. Thus, with positive road wheel loads on the sun wheels and with the single carrier as a drive input, drive is transmitted to the sun wheels simultaneously with the possibility that either one of the sun wheels may reduce speed with a simultaneous and equal increase in speed of the other so providing for differential action. In the event that positive traction is lost at one wheel, the one to one ratio between the off-side and near-side is no longer controlled or constrained by normal road wheel behaviour, and the first and second mutually meshed gears lock against any tendency to vary the one to one ratio mentioned and positive drive is transmitted to the other road wheel. <IMAGE>

Description

SPECIFICATION Differential gear This invention relates to differential gears for land vehicle final drives.

Conventional final drives for road vehicles incorporate a differential gear to transmit drive to near-side and off-side road wheels whilst permitting a near-side/off-side speed difference. A disadvantage associated with previously proposed uncontrolled differential gears is that loss of traction at one road wheel stops or reduces drive to the other road wheel.

An object of the present invention is to provide a differential gear for a land vehicle final drive in which the said disadvantage is obviated or mitigated.

According to the present invention, there is provided a differential gear for a land vehicle final drive, comprising two mutually oppositely disposed epicyclic gear trains each having a sun gear, a planet gear on a planet carrier, and an annular gear, the planet carriers being mutually joined to constitute a single carrier and being adapted as a drive input, the respective planet gears being drivingly inter-connected by first mutually meshed gears, and the respective annular gears being drivingly inter-connected by second mutually meshed gears.

Preferably, each annular gear is freely carried by its associated planet carrier.

The arrangement is such that with said single carrier held stationary, the sun wheels can turn in one to one ratio and in mutually oposite directions being drivingly interconnected through both the first and the second mutually meshed gears. Thus, with positive road wheel loads on the sun wheels and with the single carrier as a drive input, drive is transmitted to the sun wheels simultaneously with the possibility that either one of the sun wheels may reduce speed with a simultaneous and equal increase in speed of the other so providing for differential action. The one road wheel can turn less only if the other road wheel is simultaneously positively and equally turned more by virtue of contact with the road.In the event that positive traction is lost at one wheel, the one to one ratio between the off-side and near-side is no longer controlled or constrained by normal road wheel behaviour. The resulting action in the differential gear is that the first and second mutually meshed gears lock against any tendency to vary the one to one ratio mentioned. Accordingly, positive drive is transmitted to the other road wheel.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawing which is a diagramatic part-sectional elevation of a differential gear in accordance with the present invention.

In the drawing, shafts 10 and 11 represent near-side and off-side drives to near-side and off-side road wheels (not shown) respectively.

The shafts 10 and 11 are journalled coaxially with a generally cylindrical hollow casing 1 2 which carries an integral crown gear 1 3 and is thus adapted as a drive input through a drive pinion 14. The casing 12 with its integral crown wheel 1 3 and the gear trains about to be described together consitute a final drive suitable for driving a road vehicle.

The shafts 10 and 11 are connected respectively to mutually oppositely disposed epicyclic gear trains 1 5 and 1 6 by way of sun gears 1 7 and 18. In addition to the sun gear 17, the epicyclic train 1 5 further comprises a planet gear 1 9 and an annular gear 20. The planet gear 1 9 is journalled in a planet carrier 21, and the annular gear 20 is rotatable freely with respect to the carrier 21 by means of a spigot and socket configuration indicated at 22. The construction of the epicyclic train 1 6 is similar to that of train 1 5 and its components are given the reference numerals of train 1 5 suffixed by letter A.The respective planet carriers 21 and 21A on each side of the assembly are in fact mutually joined by virtue of being part of the housing 1 2 so forming a single carrier.

The planet wheels 1 9 and 1 9A are drivingly interconnected by first mutually meshed gears 23 and 24. These gears are disposed in the space between the epicyclic trains 1 5 and 16; and it will be understood that they are disposed on the same pitch circle and have mutually equal diameters. The manner of presentation in the drawing is simply for clarity of illustration. It will further be appreciated that the planet gears 1 9 and 1 9A are circumferentiall off-set, and that the gears 23, 24 constitute reversing gears. Each annular gear 20, 20A, in addition to internal gear teeth, also has external teeth.Thus, the annular gear 20 is drivingly connected to the annular gear 20A by second mutually meshed gears 25 and 26 which are respectively associated with pinions 27 and 28 each journalled in the single carrier 21, 21A.

It is to be understood that the design of the foregoing gear train would provide for equally circumferentially spaced duplicates of the planet gears and first and second mutually meshing gears.

By inspection, or by trial, it can be assertained that with the single carrier 1 2 held stationary, rotation of shaft 10 in one direction produces an opposite rotation of shaft 11 in one to one ratio since the mutually meshed gears 23, 24 and 25, 26 are of mutually equal diameters. Accordingly if the entire assembly including the casing 1 2 is rotating on the axis of the shafts 10, 11, then a differential action between shafts 10 and 11 is possible on the basis that a reduction in turns of one shaft must equal an increase in turns of the other shaft. Such an action will be imparted to the shafts 10, 11 in accordance with the behaviour of the road wheels of a road vehicle negotiating a curved path. However, in the event that one road wheel loses traction, this removes constraint to the one to one ratio between shafts 10 and 11 with the result that the mutually meshing gears 23, 24 and 25, 26 lock the final drive and the road wheel remaining in contact with the road surface still receives positive drive.

Claims (6)

1. A differential gear for a land vehicle final drive, comprising two mutually oppositely disposed epicyclic gear trains each having a sun gear, a planet gear on a planet carrier, and an annular gear, the planet carriers being mutually joined to constitute a single carrier and being adapted as a drive input, the respective planet gears being drivingly interconnected by first mutually meshed gears, and the respective annular gears being drivingiy interconnected by second mutually meshed gears.

2. A differential gear according to claim 1, wherein each annular gear is freely carried by its associated planet carrier.

3. A differential gear according to claim 1 or 2, wherein the said single carrier defines a hollow cylindrical body housing the said epicyclic gear trains.

4. A differential gear according to claim 3, wherein the said hollow cylindrical body carries a crown gear of said final drive.

5. A differential gear for a land vehicle final drive, substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

6. A land vehicle final drive incorporating a differential gear according to any one of the preceding claims.