Temperature compensated closed loop control of a hydraulically controlled clutch and APU starting system

A control system for a hydraulically controlled clutch for coupling a source of rotary power to a load for accelerating the load from a first velocity to a second velocity within a time interval measured from a beginning of the acceleration and ending between first and second times measured from the beginning of acceleration with the load being variable during the acceleration of the load from the first velocity to the second velocity comprising:

• a source of pressurized hydraulic fluid;
• a temperature sensor coupled to the hydraulic fluid which provides a temperature signal of a temperature of the hydraulic fluid;
• a servo valve, having an inlet coupled to the source of pressurized fluid and an outlet coupled to the hydraulically controlled clutch, the servo valve being responsive to a control signal to vary the pressure of hydraulic fluid applied to the hydraulically controlled clutch to vary the coupling between the source of rotary power and an output shaft which is coupled to the load;
• a sensor for producing a velocity signal proportional to the velocity of the output shaft;
• a stored program controlling a programmed acceleration of the load from the first velocity to the second velocity within a time interval measured from the beginning of the acceleration and ending between the first and second times;
• and
• a controller, responsive to the stored program, the velocity signal and the temperature signal, for producing the control signal which is a function of a difference between the velocity signal and a desired velocity of the output shaft during acceleration from the first velocity to the second velocity by the stored program and a gain control signal which is a function of the temperature signal.