Viscous fluid coupling device

A viscous fluid coupling device for driving a cooling fan of a vehicle, comprising an input shaft including a rotor and driven by an engine, output means connected to said cooling fan and made of a metal material whose coefficient of thermal expansion is relatively large, a valve plate dividing an interior of said output means into a reservoir chamber and an operating chamber in which said rotor is positioned, said reservoir chamber being in communication with said operating chamber, said rotor and said output means having opposed spaced surfaces providing a fluid shear space therebetween and cooperable with a viscous fluid in said shear space in order to transmit rotational torque from said rotor to said output means, a first bearing set interposed between said input shaft and said output means, a stationary member secured to a fixed part of the vehicle and made of a metal material whose coefficient of thermal expansion is relatively small, and a second bearing set interposed between said output means and said stationary member;

• whereby, at a temperature of a predetermined value, the output means is compressed thereby locking the second bearing set such that said second bearing set acts as a braking mechanism preventing rotation of the cooling fan.