Control method for a variable displacement refrigerant compressor in a high-efficiency AC system

Abstract

A high efficiency air conditioning system includes a pneumatically-controlled variable displacement compressor and a compressor clutch that is selectively cycled on and off to minimize series re-heating of conditioned air. Conditioned air is discharged after passing through an evaporator core, and a target value for the evaporator outlet air temperature is determined based on the desired air discharge temperature. The compressor clutch is cycled off when the evaporator outlet air temperature falls below the target value by at least a calibrated amount, and is thereafter cycled on again when the evaporator outlet air temperature rises above the target value. The target value is preferably biased to prevent compressor operation when the desired air discharge temperature exceeds outside air temperature by at least a calibrated amount and to prevent the relative humidity in the air-conditioned space from rising above a desired level.

Description

TECHNICAL FIELD[0001]The present invention relates to a motor vehicle air conditioning system in which the capacity of a refrigerant compressor is controlled for high efficiency, and more particularly to a capacity control method for a variable displacement refrigerant compressor in such an air conditioning system.BACKGROUND OF THE INVENTION[0002]Vehicle fuel efficiency studies have shown that a traditional air conditioning system with a fixed displacement compressor cycled on and off in the usual fashion can account for the consumption of nearly twenty-five gallons of gasoline per vehicle annually. As described in the U.S. Pat. No. 6,293,116 to Forrest et al., however, air conditioning efficiency can be significantly improved by regulating the compressor capacity in a way that eliminates over-dehumidification and minimizes series re-heating of conditioned air. Whereas compressor capacity is traditionally regulated so as maximize cooling by the evaporator without ice formation on th...

AI Technical Summary

Benefits of technology

[0004]The present invention provides an improved control methodology for achieving an efficient compressor capacity control with a pneumatically-controlled variable displacement compressor and a compressor clutch that is selectively cycled on and off to minimize series re-heating of conditioned air. Conditioned air is discharged after passing through an evaporator core, and a target value for the evaporator outlet air temperature is determined based on the desired air discharge temperature. The compressor clutch is cycled off when the evaporator outlet air temperature falls below the target value by at least a calibrated amount, and is thereafter cycled on again when the evaporator outlet air temperature rises above the target value. The target value is preferably biased to prevent compressor operation when the desired air discharge temperature exceeds outside air temperature by at least a calibrated amount and to prevent the relative humidity in the air-conditioned space from rising above a desired level.

Problems solved by technology

Nevertheless, using an electronically controlled variable displacement compressor usually results in higher overall system cost because of the modulating control valve and the required control electronics.

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