The Bendix Corporation

Van P Spiker

George T Bata

Patrick D Harper

Jeri A Betts

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. One or the other of the bimetal arms is heated if the pressure level differs from the level corresponding to the electrical signal value by means of a bimetal heater circuit associated with each bimetal arm with the varying electrical signal to be transduced causing activation of the heater current in one or the other respective bimetal heater circuit depending on whether the pressure level is to be increased or decreased, until the pressure level reaches the corresponding level to that of the electrical signal. The electrical signal is disclosed as an error signal in an automatic control system which causes either a vacuum pressure or atmospheric vent port to be placed in communication with the interior chamber of the pressure transducer housing so as to either increase or decrease the vacuum pressure within the enclosure.

Bimetal controlled actuator

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.

Closed loop control for automatic temperature control system

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. A particular vacuum modulator structure is also disclosed in which a pair of heated bimetal actuator devices are utilized to control communication of a vent port and a source of vacuum pressure with an interior chamber, the resulting pressure communicated to the vacuum operated actuator. The heater circuit for the heated bimetals is controlled to develop the proper actuator pressure and also features an interrupted heater current mode of operation in which the heater current is interrupted after a predetermined deflection of the heated bimetals to thereby improve their response and to simplify the design thereof.

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Newport News, VA, United States of America

Van P Spiker