The Bendix Corporation

Jeri A Betts

Van P Spiker

A closed loop control circuit for regulating the response of an automatic temperature control system is disclosed. The temperature control system provides automatic regulation of the temperature for the passenger compartment of a vehicle by positioning a blend air door in response to three control parameters. Two of the control parameters, the actual temperature of the passenger compartment and the desired temperature of the passenger compartment, are serially combined in one leg of a bridge circuit and compared against another leg of the bridge presenting the third control parameter, the position of the blend door. An unbalanced condition in the bridge circuit is corrected by the repositioning of the blend door until the error between the two legs is nulled. Repositioning is accomplished by a pair of differential amplifiers which detect the sense of the error and thereafter provide an interrupter control function to a vacuum modulator. The interrupter control function is accomplished by current limiting open collector output devices in the amplifiers. The interrupter function regulates the vacuum level in the modulator which positions the blend air door through a vacuum actuator.

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Utica, MI, United States of America

Jeri A Betts