1996-02-01

VISCO-LOK: A Speed-Sensing Limited-Slip Device with High-Torque Progressive Engagement 960718

It can be noted that there is an increasing demand for simple, self-controlling, speed-sensing limited-slip devices with progressive locking characteristics and high torque capacity, in particular in Sport Utility Vehicle and light truck axle and transfer case applications. Existing speed-sensing systems mostly have a degressive locking characteristic curve; other designs are too complex for high volume production. Torque-sensing Limited-Slip Differentials (LSD) that are fully ABS-compatible, provide an insufficient locking effect under extreme surface conditions.
Visco-Lok (“the system”) is a new speed-sensing limited-slip device with high-torque progressive engagement and is tuned to minimize driveline windup. This new LSD allows a wide range of calibration in specifying the level of torque transfer at any particular speed difference. This self-controlling stand-alone system consists of a unique shear pump design creating a pressure proportional to a speed difference, which engages a friction clutch to transmit the torque. A unique feature of the shear pump is that it is self-contained and independent, requiring no external source of hydraulic fluid. The viscous shear pump, which is filled with silicone fluid, provides significant benefits in packaging, temperature stability, durability, and weight.
By simple mechanical means, various torque characteristics ranging from degressive to progressive can be realized to optimize both traction and handling. Asymmetrical characteristics are possible with minimum additional effort; the device can be switched off by simple speed-actuated or an externally controlled valve.
This system can be used as a differential biasing device in conjunction with an open differential or as an “on-demand” torque transfer between the axles of the vehicle, resulting in the system as a basis for a comprehensive limited-slip system.

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