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Trucks and sport utility class vehicles are established as choice of daily transportation in the US. A new breed of vehicles, commonly referred as “crossover vehicles”, based on passenger car derived platforms, are rapidly filling in the ranks between trucks and automobiles. Most of these vehicles are equipped with relatively sophisticated all wheel drive systems. This sophistication is necessary to fulfill the target mission of these vehicles, to provide an automatic and effortless all wheel drive capability while retaining refined on road comfort. Building on some of the existing systems and sensors, and integrating with other vehicle systems such as ABS, traction control and stability control systems, it is possible to enhance handling response by creating a moment along yaw axis. Pitch and roll movements can also be indirectly influenced. Further possibilities and enhancements will be feasible when drive by wire systems and active suspensions will become available.

Hydraulically actuated, friction disc type couplings are capable of being utilized as direct drive limited slip devices for use on auxiliary drive axles. These couplings can be excited to function at wheel speed Δn levels due to their high torque transfer density and high torque transfer capacity. The utilization of these hydraulic couplings eliminates the need for torque multiplication through speed reduction. The common differential element is replaced by two independent, but communicating couplings to facilitate direct drive of the wheels on the auxiliary axle. The arrangement described in this paper provides a built in limited slip differential (LSD) effect as well as a simple and powerful all wheel drive (AWD) system. This paper will compare the performances of such systems with classic architectures under various driving conditions.