Method for slip power management of a controllable viscous fan drive

A method of controlling slip power generation in a cooling fan clutch drive for a cooling system in an automotive vehicle, said fan clutch drive comprising a rotating input member and a rotatable fan stator member separated by a gap filled with a viscous fluid, said fluid serving to transmit torque between said input member and said fan stator member such that the rotational speed of said fan stator member is a function of the viscosity of said fluid, and the viscosity of said fluid is controlled through application of a magnetic field to said fluid by command of a programmed controller;

• said method comprising
• pre-determining a maximum slip power level for operation of said fan clutch drive,
• said controller thereafter continually determining one or more current stator member slip power control rotational speed values for keeping current slip power at or below said maximum slip power level as a function of current input member rotational speed, the torque constant of said fan, and said maximum slip power level, and
• said controller continually controlling said stator rotational speed, through control of said magnetic field, consistent with said current slip power control rotational speed value and the cooling requirements of said fan so as to minimize slip power excursions above said maximum slip power level.

A method of controlling slip power generation in a cooling fan clutch drive for a cooling system in an automotive vehicle, said fan clutch drive comprising a rotating input member and a rotatable fan stator member separated by a gap containing a viscous fluid, said fluid serving to transmit torque between said input member and said fan stator member such that the rotational speed of said fan stator member is a function of the volume of said fluid in said gap, and said volume of said fluid is controlled by command of a programmed controller;

• said method comprising
• pre-determining a maximum slip power level for operation of said fan clutch drive,
• said controller thereafter continually determining one or more current stator member slip power control rotational speed values, for keeping current slip power at or below said predetermined maximum slip power level, as a function of current input member rotational speed, the torque constant of said fan, and said maximum slip power level, and
• said controller continually controlling said stator rotational speed, through control of said volume of said fluid, consistent with said current slip power control rotational speed value and the cooling requirements of said fan so as to minimize slip power excursions above said maximum slip power level.