A viscous clutch includes a shaft, a rotor disk, a housing having a base, a working chamber, a reservoir fluidically connected to the working chamber, a valve, an electromagnetic coil, and a flux guide that passes through the housing. The rotor disk includes a conductive portion made of a magnetic flux conductive material that forms a hub of the rotor disk that contacts the shaft and another portion. The base includes a hub with an axially-extending ring, and an armature of the valve is located radially outward of the axially-extending ring. The electromagnetic coil is located at an opposite side of the rotor disk from the reservoir. A magnetic flux circuit extends from the electromagnetic coil to the flux guide, then to the armature of the valve, then to the conductive portion of the rotor disk, then to the shaft, and then back to the electromagnetic coil.

A cooling control system includes a prime mover, a fan to be rotated under rotational power of an output shaft of the prime mover, a housing to which the fan is attached, a rotor to be rotated under rotational power of the prime mover, the rotor and the housing, under the agency of a fluid, rotating together, a fluid setting circuit to determine an injection quantity of the fluid to be introduced into the gap, a fan rotation detection device to detect a fan actual rotation speed, a target rotation obtaining circuit to obtain a fan target rotation speed. The integral controlling circuit does not execute the integral control with a difference between the fan actual rotation speed and a fan target rotation speed being greater than or equal to a threshold, and executes the integral control with the difference being less than the threshold.

A liquid cooled viscous fan clutch transfers torque from a driving plate driven by an engine crankshaft to a driven plate connected to a cooling fan. Heat generated in a working fluid is transferred to a second fluid, such as engine coolant or transmission fluid, flowing through a cooling jacket. The cooling jacket is located in a stationary housing which may be fixed to the engine. The working fluid circulates through a working zone, a passageway in the stationary housing, and a passageway in the driving plate. Rotation of the driving plate provides the motive force to circulate the fluid, independent of the rotation speed of the driven plate. A controllable valve may be closed to block circulation, trapping working fluid in a reservoir, to disengage the clutch.

A liquid cooled viscous fan clutch transfers torque from a driving plate driven by an engine crankshaft to a driven plate connected to a cooling fan. Heat generated in a working fluid is transferred to a second fluid, such as engine coolant or transmission fluid, flowing between the driven plate and a stationary housing. A controllable valve may be closed to block circulation of working fluid, trapping working fluid in a reservoir, to disengage the clutch. Rotation of the driven plate provides the motive force to circulate the coolant or transmission fluid.