Abstract: A pressure transducer is disclosed which produces a variable fluid pressure level in correspondence with the level of a varying electrical signal. The particular application of the pressure transducer disclosed is for a vacuum modulator for producing a variable level vacuum pressure for operating an actuator utilized to position a blend air door in an automatic temperature control system for automotive passenger compartments. The pressure variation is accomplished by controlled communication of either a low pressure or a high pressure source with an interior chamber of the transducer housing, such controlled communication being produced by a pair of heated bimetal actuator devices, each including a bimetal arm which is normally biased to seal the respective inlet port associated with each of the low pressure and high pressure sources.

Abstract: 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.

Abstract: An automatic control system for regulating the temperature of the passenger compartment in automotive vehicles is disclosed of the type in which a vacuum operated actuator is utilized to control the position of a blend air door, the position of the blend air door in turn controlling the temperature of the air circulated into the passenger compartment by proportioning the flow of cooled air circulated through a heater prior to entering the passenger compartment. This air flow is utilized to correct the temperature level in the passenger compartment. The disclosed control system features a nulling pressure signal feedback loop in which the error signal developed by the difference in the temperature selector and sensor signals acts on a vacuum modulator to generate an actuator pressure level which is sensed and a corresponding electrical signal used to null the temperature error signal, to provide a stabilizing feedback loop in the control system.