Patent ID: 6681583
Filing Date: 2004-01-27
Classification: B60H,F04B,F25B

Abstract:
A control unit for a clutchless, variable displacement compressor used in air conditioning systems for vehicles, said compressor having a solenoid, such that discharge displacement of said compressor is controlled by adjusting a pressure in said compressor by a control valve operated by controlling a current flowing in said solenoid, said control unit comprising:solenoid drive means comprising switching elements for adjusting said current flowing in said solenoid; voltage detection means for detecting a voltage applied to said solenoid; current detection means for detecting said current flowing in said solenoid; and control means for delivering current to said solenoid drive means for a first predetermined time period when said air conditioning system for vehicles is not operating and after said solenoid has been isolated from flowing current for a second predetermined time; for calculating a resistance of a coil of said solenoid from a voltage detected by said voltage detection means and a current detected by said current detection means; for calculating a temperature of said compressor from said calculated resistance based on a predetermined relationship between said calculated resistance and a temperature of said coil of said solenoid; and for operating said variable displacement compressor by supplying current to said solenoid when said calculated temperature exceeds a set value.