Patent ID: 6648115
Filing Date: 2003-11-18
Classification: F16D

Abstract:
A method of controlling slip power generation in a cooling fan clutch drive 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; determining a mathematical relationship using, in graphical form, orthogonal x-y coordinates between the rotational speed of said fan stator member, &ohgr;F, (y-axis) and the rotational speed of said rotating input member, &ohgr;I, (x-axis) at said pre-determined maximum slip power level, said mathematical relationship comprising, in graphical form, a curved linear path defining a border between an operating region of &ohgr;I and &ohgr;F values below said maximum slip power level and an operation region of &ohgr;I and &ohgr;F values above said pre-determined maximum slip power level, said curved linear path having a vertex at input member speed &ohgr;I1 with all operating values of &ohgr;F at &ohgr;I less than &ohgr;I1 lying below said pre-determined maximum slip power level, said curved linear path having a first border portion at &ohgr;I values greater than &ohgr;I1 where corresponding &ohgr;F1 (&ohgr;I) values are at a lower border of &ohgr;F values in said maximum slip power level and a second border portion at &ohgr;I values greater than &ohgr;I1 where corresponding &ohgr;F3 (&ohgr;I) values are at an upper border of &ohgr;F values in said maximum slip power level, and said fan stator member having a maximum speed curve intersecting said curved linear path at a stator member fan speed, &ohgr;F2, and a rotating input member speed &ohgr;I2>&ohgr;I1; said controller thereafter continually determining a current stator member slip power control rotational speed value using said mathematical relationship for keeping current slip power below said predetermined maximum slip power level as a function of current input member rotational speed, the torque constant of said fan clutch drive, 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.