1993-03-01

A New Form of Limited Slip Differential 930672

Improved performance creates a need for a limited slip differential for widespread application. Existing types suffer from the disadvantage of high cost and they are generally not well suited to front wheel drive applications.The ‘Suretrac’ differential meets this enhanced requirement. In this new design torque is transmitted through the unit using a cam and follower principle. Any relative rotation of the cams on the output shafts is opposed by friction forces which generate a torque ratio between the output shafts. The design is novel in using helical faces to give large contact areas and avoid high Hertzian stresses.The performance of this type of differential differs from viscous types or traction control because the torque difference is established before any relative motion takes place. The tyre dynamics dictate the torques generated so that the differential always provides the optimum torque balance. This maintains tyre adhesion and enhances directional stability and safety.The complexity of the shapes involved precludes machining as an economic production process, so nett shape forming methods are used. This also has to apply to the prototype phase, and so simultaneous engineering has been implemented throughout the product development.The operation of the differential should normally not impinge on the driver's consciousness, so the performance can only be established by special tests carried out with full instrumentation. These tests include acceleration with the wheels on different surfaces, “split mu”, and acceleration on a curve to give unequal wheel loading. Test results are presented. Durability tests have also been completed.The differential is shown to give substantial advantages in operation, is capable of being installed in the same space as a conventional differential and has a minimum additional cost and so should gain widespread acceptance in all types of vehicle.

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