Fluid coupling for engine cooling system

Claim 1

A fluid coupling for an engine cooling system, comprising: a driving member; a driven member having an engine cooling element and enclosing a sealed working chamber, wherein said driving member comprises a rotor fitted in said working chamber and having input means drivable by an engine to be cooled; rotational torque coupling means between said driving member and said driven member, wherein said torque coupling means comprise a viscous fluid in said working chamber and engaging said rotor, whereby viscous shear in said viscous liquid transfers torque between said rotor and said driven member; an engine coolant liquid temperature sensor; and means for controlling said torque coupling means as a function of a sensed engine coolant liquid temperature, whereby said engine cooling element is driven as a function of the engine coolant liquid temperature, wherein said driven member comprises a casing rotatably supported by said driving member and a cover sealingly mounted to said casing, and wherein said means for controlling said torque coupling means comprise a plate sealingly held in said driven member and rotating therewith, said plate cooperating with said driven member to define said working chamber, said plate being movable toward and away from said rotor, whereby a volume of said working chamber varies so as to vary both an area of contact of said viscous liquid on said rotor and the torque transferred from said rotor to said driven member; wherein said means for controlling said torque coupling means further comprise: spring means for normally biasing said plate towards said rotor so as to decrease the volume of said working chamber, and means for applying a negative gas pressure to a pressure chamber at a side of said plate opposite said working chamber so as to increase the volume of said working chamber.