Planetary gear transmission systems or components – Differential planetary gearing – Bevel gear differential
Patent
1993-12-16
1996-04-16
Marmor, Charles A.
Planetary gear transmission systems or components
Differential planetary gearing
Bevel gear differential
475184, 475236, F16H 4828, F16H 4806
Patent
active
055077021
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to differential mechanisms and in particular to a torque proportioning or "limited slip" differential having inherent frictional torque bias.
The invention has been developed primarily for use in automotive applications, and will be described hereinafter with reference to this application. However, it will be appreciated that the invention is not limited to this particular field of use.
BACKGROUND ART
When a vehicle is cornering, the outside wheel rotates with higher angular velocity than the inside wheel. The conventional differential mechanism accommodates this difference in angular velocity while, in the case of a differential having 100% efficiency, transmitting equal torque to both driving wheels at all times.
However, if one driving wheel loses traction, for example on a slippery surface, this wheel will spin freely and support little or no torque and therefore the conventional differential mechanism will transmit little or no driving torque to the wheel with traction and the vehicle will remain motionless.
One solution to this problem is to provide a torque proportioning or "limited slip" differential whereby torque is biased or transferred to the wheel with the most traction to control loss of drive. The resultant ratio of torques is known as torque bias and is defined in the following equation: ##EQU1##
Torque proportioning differentials are known. However, many of these known differentials do not provide sufficient range of torque bias for all design applications. These limitations are particularly significant in heavy vehicles. Other known torque proportioning differentials have employed preloading springs and frictional clutches as a means of increasing the torque bias. However, these designs have limited operational life due to excessive clutch wear which occurs whenever there is differential motion as a result of the inherent frictional preload which is applied to the clutches. Furthermore, the inherent friction preload in the clutches resists relative wheel rotation during normal turning manoeuvres thereby adversely affecting vehicle handling under normal driving conditions and giving rise to a further problem of increased tire wear. These problems are particularly significant in front wheel drive vehicular applications.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a relatively simple torque proportioning differential which overcomes or substantially ameliorates at least some of these disadvantages of the prior art.
According to one aspect of the invention there is provided a torque proportioning differential mechanism for transmitting drive to at least two wheels of a vehicle, said differential including a carrier adapted to be rotatably driven about a first axis and having a plurality of inner peripherally spaced pinion locating formations defining respective inwardly directed carrier thrust surfaces, a pair of spaced apart bevel side gears respectively adapted for connection to said wheels and supported for rotation about a common axis fixed with respect to said carrier, a plurality of peripherally spaced floating shaftless bevel pinions each in meshing engagement with both said side gears and having a complementary outer pinion thrust surface nestingly disposed closely adjacent a respective one of said locating formations, said pinions being rotatably supported by said locating formations such that under normal driving conditions when both wheels have substantial traction said pinions are permitted to rotate with minimal frictional resistance in response to relative rotation of the side gears, and such that under conditions of wheel slip a separating force component tends to urge the pinions away from the side gears and into engagement with the respective locating formations to create a temporary frictional reaction force between said carrier and the outer pinion thrust surfaces, said frictional reaction force resisting rotation of the pinions relative to the carrier and thereby providing temporary to
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Joachim Clifford A.
Spryszynski Stanislaw
BTR Engineering (Australia) Limited
Jensen Nathan O.
Marmor Charles A.
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