Method for slip power management of a controllable viscous fan drive
AssigneeGeneral Motors Corporation
InventorsAnthony L. Smith, Patrick Benedict Usoro
Life of this patent
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Abstract
A method is disclosed for controlling the slip power of a viscous fluid fan drive clutch, especially of a cooling fan drive for an automotive vehicle. Data is prepared correlating slip power generation with clutch input and output speeds for the clutch and fan design. A maximum slip power for the operation of the cooling fan is specified by considering, for one, fan drive durability requirements. During operation of a computer based, fan speed control module, a desired fan drive speed is continually determined for the cooling requirements of the vehicle and the desired fan speed is compared, and adjusted, if appropriate, to avoid excessive slip power.
Claims11
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, ωF, (y-axis) and the rotational speed of said rotating input member, ωI, (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 ωI and ωF values below said maximum slip power level and an operation region of ωI and ωF values above said pre-determined maximum slip power level, said curved linear path having a vertex at input member speed ωI1 with all operating values of ωF at ωI less than ωI1 lying below said pre-determined maximum slip power level, said curved linear path having a first border portion at ωI values greater than ωI1 where corresponding ωF1 (ωI) values are at a lower border of ωF values in said maximum slip power level and a second border portion at ωI values greater than ωI1 where corresponding ωF3 (ωI) values are at an upper border of ωF 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, ωF2, and a rotating input member speed ωI2>ωI1;
- 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.
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 magnetorheological 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 being controlled through application of a magnetic field to said fluid by command of a programmed controller;
- said method comprising:
- pre-determining a mathematical relationship using, in graphical form, orthogonal x-y coordinates between the rotational speed of said fan stator member, ωF, (y-axis) and the rotational speed of said rotating input member, ωI, (x-axis) at a pre-determined maximum slip power level for operation of said fan clutch drive, said mathematical relationship, in graphical form, comprising a curved linear path defining a border between an operating region of ωI and ωF values below said maximum slip power level and an operation region of ωI and ωF values above said pre-determined maximum slip power level, said curved linear path having a vertex at input member speed ωI1 with all operating values of ωF at ωI less than ωI1 lying below said pre-determined maximum slip power level, said curved linear path having a first border portion at ωI values greater than ωI1 where corresponding ωF1 (ωI) values are at a lower border of ωF values in said maximum slip power level and a second border portion at ωI values greater than ωF1 where corresponding ωF3(ωI) values are at an upper border of ωF 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, ωF2, and a rotating input member speed, ωI2>ωI1;
- said programmed controller determining a desired rotational speed of said fan stator member, ωF desired at a current speed of said rotating input member, ωI;
- and, before changing said current speed,
- said programmed controller comparing said current speed, ωI, of said rotating input member with ωI1 or ωI2 as provided in sub-steps (a)-(c);
- and
- (a) if ωI<ωI1, then changing the current rotational speed of said stator member to ωF desired, or
- (b) if ωI1<ωI<=ωHI2, then determining whether ωF1 (ωI)<ωdesired<ωF3 (ωI) and, if so, adjusting ωF desired to either ωF1 (ωI) or ωF3 (ωI) to operate at or below said pre-determined maximum slip power level, or
- (c) if ωI>ωI2, then determining whether ωF desired is within said pre-determined maximum slip power level and, if so, adjusting ωF desired to ωF1 (ωI) to operate at or below said pre-determined maximum slip power level.
Dependencies are inferred from the claim text.