Fan drives

Claim 1

A cooling fan assembly including a rotary input drive member located at one axial end of the assembly and formed with means for attachment to a drive shaft or pulley, a friction clutch including a clutch input element secured to said input drive member, and a clutch output element, a viscous fluid clutch arranged torsionally in ''''series'''' with said friction clutch and including a rotary clutch casing secured to said friction clutch output element, and a rotary clutch driven member located within said casing and spaced by a small clearance from the internal wall surfaces of said casing, and sealing means acting between said clutch casing and said clutch driven member providing an enclosed sealed fluid chamber, a hub having means for attaching a plurality of fan blades thereto and secured to said rotary clutch driven member, bearing means acting between said hub and said input drive member and supporting said hub for rotatiOn and axial movement relative to said input drive member, a fluid operated ram including two axially movable operative ram elements, namely a ram cylinder and a ram piston, one of said ram elements being connected to said hub and the other ram element being connected to said input drive member, whereby relative axial displacement of said ram elements causes relative axial displacement of said hub relative to said input drive member, and consequent relative axial displacement between said friction clutch input and output elements, spring means acting in an axial direction between said friction clutch input and output elements in a direction to cause engagement of said friction clutch, and a non-rotary pressure fluid supply conduit located at the end of said hub remote from said rotary input drive member, and communicating with said ram cylinder.