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The viscous coupling is known mainly as a driveline component in four wheel drive vehicles. Developments in recent years, however, point toward the probability that this device will become a major player in mainstream front-wheel drive application. Production applications in European and Japanese front-wheel drive cars have demonstrated that viscous couplings provide substantial improvements not only in traction on slippery surfaces but also in handling and stability even under normal driving conditions. This paper presents a series of proving ground tests which investigate the effects of a viscous coupling in a front-wheel drive vehicle on traction and handling. Testing demonstrates substantial traction improvements while only slightly influencing steering torque. Factors affecting this steering torque in front -wheel drive vehicles during straight line driving are described.

Under normal conditions, on high friction surfaces such as tarmac or concrete, a single driving axle (front or rear) is more than adequate. The traction potential of the tires generally exceeds the torque applied. However, on low friction surfaces, such as ice, snow or wet roads, and in off-road conditions the traction potential of the wheels can be easily exceeded. In these circumstances the improved traction provided by four-wheel drive is most noticeable. This study concerns the optimization of the recently developed Visco-Lok limited-slip differential and coupling for use in four-wheel drive vehicles. In addition to the traction improvement, the influence on the vehicle handling and stability was investigated.