Temperature responsive, pneumatically actuated, fluid shear, cooling fan clutch and a control providing three step variation thereof

Claim 1

A cooling fan device for use with an internal combustion engine, comprising a viscous fluid coupling means which includes an input means drivingly connected to the engine, an output means provided with a fan for cooling a radiator of the engine and rotatable relative to said input means, a fluid-tight chamber, a partition plate for dividing said chamber into a viscous fluid working chamber and a viscous fluid reservoir chamber, said input means being on the working chamber side of said partition plate, said partition plate having a first and a second hole for permitting viscous fluid communication between said reservoir chamber and said working chamber to hydrodynamically transmit rotational power from said input means to said output means, and stepwise control means for controlling the amount of viscous fluid in said working chamber, said stepwise control means including means for sensing the temperature of cooling water in the engine, a slidable plug on the reservoir chamber side of said partition plate, an inner cover secured to said input means to form an air chamber therein, said inner cover having a center opening through which said slidable plug extends in sealing relationship therewith, a diaphragm dividing said air chamber into two opposed chambers, the outer periphery of said diaphragm being fixed to said input means and the inner periphery of said diaphragm being attached to an inner end of said slidable plug, a first valve plate secured to an outer end of said plug to open or close said first hole of said partition plate, a second valve plate positioned to be engaged by said outer end of said plug to open or close said second hole of said partition plate, first and second changeover valve means connected to a source of suction air pressure and a source of atmospheric air pressure, first passage means connecting said first changeover valve means and a first one of said opposed chambers, second passage means connecting said second changeover valve means and said first opposed chamber, each said change-over valve means being for regulating in accordance with the temperature of the engine cooling water the supply of suction pressure and atmospheric pressure through each respective passage means into said first opposed chamber defined by said diaphragm for moving said plug and each said valve plate secured thereto to effect a three stepwise control of viscous fluid flowing to said working chamber and provide a three stepwise variation in the speed of rotation of said fan.