This device is made up of a number of circular plates with tabs or perforations that are fitted very close to each other in a sealed drum. Every other plate is connected to a driving shaft at one end of the assembly and a driven shaft at the opposite end. The drum is full of a dilatant fluid which is often silicone – based. When the two sets of plates are rotate in unity, the fluid stays cool and stays liquid but as the plates hit different speeds for rotating, the shear effect of the tabs or perforations on the fluid causes it to heat and changes it to nearly a solid as the viscosity of dilatant fluids speedily increases with shear. The fluid in this state effectively glues the plates together and transmits power through one set of plates to the other. To determine the strength and onset of this mechanical transfer the size of the tabs or perforations, the number of plates, and the fluid used are taken into account. When the engine is below standard working temperature, a silicone fluid is permitted into the chamber between the fan and its belt – driven coupling by the means of a thermostatic valve, and like the fluid in a torque converter, it takes up the drive.
Viscous couplings are used as the center differential in certain four – wheel – drive (4WD) automobiles. The first majorly produced viscous couplings for a permanent 4WD off – roading capable vehicle was inside the AMC Eagle, which was manufactured from 1980 to 1988 model years. Viscous couplings offer a cheaper way to execute four – wheel – drives than othrt technologies like the Torsen differentials’ mechanical – transfer used by Audis.
Automobile manufacturers like Vaxhall/ Opel, Subaru, Volvo, Range Rover, and many others have brought viscous couplings into use in their respective drivelines at many times. Though, they are now mostly outdated by electronically controlled devices.