Viscous fluid clutch

Claim 1

A viscous fluid clutch comprising first and second relatively rotatable drive members, said first drive member including front and rear walls and defining a fluid cavity therebetween, a cooling fan mounted on an outer surface of said first drive member, a divider wall sealed between said front and rear walls in said fluid cavity and dividing said fluid cavity into first and second chambers, said second drive member being rotatable in said first chamber, said second drive member and said rear wall having opposed spaced parallel surfaces defining a fluid shear space therebetween and cooperable with a fluid medium in said shear space to provide a shear-type fluid drive therebetween, a first opening formed in said divider wall for providing communication between said first chamber and said second chamber, a dam element formed on said divider wall in said first chamber adjacent said first opening for causing said fluid medium to flow through said first opening for varying the volume of fluid medium in said shear space to vary the torque transmitted between said first and second drive members, a second opening formed in said divider wall for at times communicating said fluid medium from said second chamber to said first chamber, valve means for controlling the flow of said fluid medium through said second opening to further vary the torque transmitted between said first and second drive members, a drive slot formed in said valve means, a hollow disk having a hollow stem formed thereon and extended through and secured within an opening formed in said front wall, the interiors of said hollow disk and said hollow stem being in communication with one another, a bourdon tube connected at one open end thereof to said hollow stem in said second chamber, the interiors of said hollow stem and said bourdon tube being in communication with one another, a drive pin formed on the other closed end of said bourdon tube and extended through said drive slot, and a thermal-sensitive expandable fluid contained in said hollow disk, said hollow stem and said bourdon tube for causing said bourdon tube to straighten out in response to increased ambient temperature and corresponding increased pressure of said expandable fluid and, thereby, causing said valve means to uncover said second opening to permit said fluid medium to flow from said second chamber to said first chamber to provide said shear-type fluid drive between said first and second drive members and thus drive said cooling fan.