Applications of Viscous Couplings for Traction Control in Passenger Cars

THIS ARTICLE DESCRIBES the wide range of potential applications of the viscous coupling, not only as a lock in two and four-wheel drive differentials, but also as an assembly that facilitates low-cost implementation of permanent four-wheel drive concepts with one directly driven axle. In such systems, the viscous coupling combines the functions of a locked transfer box and/or axle differential in a single component.

Operating according to the principle of fluid friction, the coupling represents a differential slip control: the linear to degressive dependence between locking torque and speed difference provides optimized torque distribution.

The article also describes a method of calculating the coupling's characteristic in advance. A max.-traction-characteristic is used to determine the coupling's dimensions at the early vehicle design stage. For handling and ABS-compatibility reasons a fine adjustment will be done later on by vehicle testing.