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Viscous coupling unit
From Wikipedia, the free encyclopedia
A viscous coupling is made up of alternating circular plates. The plates have tabs or perforations in them. The plates are mounted in a sealed drum, which are located very close to each other. The drum is filled with silicone or other dilatant fluid. When the two sets are plates are rotating in unison, the fluid stays cool and remains in a liquid state. When the plates start rotating at two different speeds, the shear effect of the tabs or perforations on the fluid will cause it to heat up and solidify (Silicone when heated will turn into a near solid; the viscosity of dilatant fluids rapidly increases with shear). The fluid in this state will essentially glue the plates together and transmit power from one set of plates to the other. The size of the tabs or perforations on the plates, along with the number of plates and fluid used will determine the strength and onset of when this mechanical transfer will happen. Viscous couplings can be found in the center differential of some AWD vehicles, and also in the differential of limited slip rear axles and limited slip differentials (LSD).
