Vehicle cooling system with system motor control apparatus

A control apparatus for a motor that selectively drives a vehicle cooling system fan, the apparatus comprising:

• a controller that generates motor control signals in response to sensed system operating parameters;
• and
• a switching device that receives the motor control signals from the controller and that drives the motor in response thereto;
• the controller being operative to generate the motor control signals at a highest target duty ratio among target duty ratios calculated based on the sensed system operating parameters, the highest target duty ratio causing an input power provided to the motor by the switching device to be below a rated input power of the motor when the sensed system operating parameters are below a predetermined level, and to remain above the rated input power only for a predetermined time period when one or more of the sensed system operating parameters is above the predetermined level.

A method of controlling a motor that drives a vehicle cooling system fan, comprising the steps of:

• sensing cooling system operating parameters;
• calculating target duty ratios for the sensed cooling system operating parameters;
• driving the motor via a motor input power based on a final duty ratio selected as a highest one of the calculated duty ratios;
• varying values of the target duty ratios within predetermined duty ratio ranges based on changing operating parameters, the duty ratio ranges each having generated an associated motor input power having a maximum value less than a rated input power of the motor;
• increasing the final duty ratio to generate a motor input power that is greater than the rated input power only for a predetermined time period when one or more of the cooling system operating parameters increases to a predetermined high level;
• and
• returning the final duty ratio to a level below a level that increases the input power to a level higher than the rated input power after the predetermined time period lapses.