of the front cover 77 is designed to avoid magnetic flux saturation and simultaneously to minimize the amount of material used as permitted by mechanical strength requirements this optimizes on the overall weight of the clutch more specifically the area of the flux path is relatively thick while the center of the front cover 77 is dished out on the outside the front cover 77 and the rear cover 78 act as the output clutch plates and are made of conventional steel coil 76 comprises a plurality of turns of wire and is held in the output section of the fan clutch 75 the coil wire is energized through slip rings not shown either on the input shaft 70 or the rear cover 78 the two clutch covers are magnetically joined through the core piece 100 that is made of conventional steel for magnetic permeability for purposes of the present invention the magnetorheological fluid contained in cavity 98 carries a selected volume percent of solid particles that permit substantially complete slippage between the input clutch plate 79 and the output clutch plates comprising front cover 77 and rear cover 78 when the clutch is disengaged a gradually increasing torque transfer is effected between input and output plates as the clutch is engaging and substantially complete coupling is provided when the clutch is fully engaged with minimal slippage between the input and output plates the coil 76 is supplied with a variable current signal through a conductor not illustrated magnetic flux generated by.