Differential gear assembly

Details Differential gear assembly Differential gear assembly

1993-07-23

1995-09-26

Wright, Dirk

Planetary gear transmission systems or components

Differential planetary gearing

Planet pinion is worm gear

F16H 4828

Patent

active

054530628

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to a differential gear assembly as is used to transmit drive torque from a power source to driven road wheels of a vehicle, and is more specifically concerned with a differential gear assembly having resistance to wheel spin and generally referred to in the art as a limited slip differential.


STATE OF THE ART

The conventional differential gear is a `free` differential which divides the driving torque equally between the driven ground wheels whilst compensating for differences in the ground speed of the wheels caused by the vehicle cornering or surface irregularities of the ground, or variations in tire sizes.
The free differential is a standard assembly on all but the more expensive motor vehicles. However it has the disadvantage that a loss of traction and driving torque on one wheel results in a corresponding loss in driving torque on the other driving wheel. Surplus torque from the power source will only generate spin in the wheel which has lost traction.
There have been many proposals to design a assembly which would permit unbalanced output torques in the event of loss of traction at one wheel. One such assembly is described in Gleasman U.S. Pat. No. 2,859,641 and is commercially known as the TORSEN differential. This differential utilises inefficient gearing combined with internal friction to generate torque imbalance between output shafts when one driving wheel cannot maintain a required driving torque due to poor ground adhesion.
The limited slip differential assembly taught by Gleasman in the above patent is a complex structure reliant upon efficiency of drive characteristics of worm-wheel gearing or what may be better described as modified crossed helical gearing. The number of tooth engagements is such a layout is limited and this combined with the nature of contact between the teeth of crossed-helical gearing significantly limits the load capacity of such differentials. In recent times the TORSEN differential assembly has found application in vehicles having constant four-wheel drive where axle loading is obviously much less than in conventional two-wheel drive vehicles.
In our earlier U.S. Pat. No. 5,071,395 hereby inserted by way of reference, is described a non-slip differential gear assembly in which intermediate shafts mounted in a housing each carry gearing in mesh with respective axle gears. The set of meshing gears to one output shaft are conventional spur or helical gears having teeth of opposite hand respectively, and the set of meshing gears to the other output shaft are helical gears of the same hand having zero or a very low efficiency of drive between them. In the assembly described in our above patent, reliance is placed on the zero or low efficiency of drive between the set of helical gears of the same hand to prevent wheel spin, whilst the different rotational characteristics of the two sets of meshing gears allows differentialling between axles to occur. The inherent asymmetry of this differential assembly of the prior art, has not found commercial acceptance in private motor cars or trucks as difficulties in its performance reliability and handling characteristics have posed problems which have not yet been solved.


OBJECT OF THE INVENTION

An object of this invention is to provide an improved limited slip differential gear assembly.


SUMMARY OF THE INVENTION

In accordance with the present invention a limited slip differential gear assembly comprises a housing mounted for rotation about a first axis, means for coupling a rotational drive to said housing, two coaxial and spaced gear members having external teeth and respectively mounted in opposite sides of said housing, and pairs of gear elements meshing respectively with each of the gear members and interconnected by spur gears which rotate with respective gear elements; in which gear assembly the axes of rotation of the gear members, the gear elements and spur gears extend parallel to one another and to the axis of rotation of the housing, and the gear elements and gear m

REFERENCES:
patent: 2462000 (1949-02-01), Randall
patent: 2972265 (1961-02-01), Walter
patent: 3481215 (1969-12-01), Howell
patent: 5071395 (1991-12-01), Fahy et al.
patent: 5169370 (1992-12-01), Dye et al.
patent: 5302159 (1994-04-01), Dye et al.

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