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

Abstract

<div class="htmlview paragraph">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.</div> <div class="htmlview paragraph">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.</div> <div class="htmlview paragraph">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.</div> <div class="htmlview paragraph">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.</div>