Study On The Stability Of Automotive Air Conditioning System

Variable displacement compressors with internal control valve ate widely used in automobile air conditioning systems.However,the system has problems of evaporator frosting,high oil consumption and system hunting.In this paper,the application of externally controlled compressors is used as the starting point.And the integration of theoretical analysis and experimental investigation are used to investigate control characteristics of the valve,variable displacement compressor and its refrigeration system are also studied.To oprimize externally controlled compressors system,the control strategy is presented,the paper has sound theoretical meaning and application value.On internal control variable displacement compressor control mechanism and structural characteristics of the foundation,the research on control control valve for variable displacement compressor,establish mathematical model of external control valve and test verification.The mathematic model is used to analyze the control characteristics,including crankcase pressure changes with open ratio of external control valve,discharge pressure and suction pressure respectively.Steady state simulation model of externally controlled compressors is built by combination of the mathematical model of external control valve,the dynamice model of movable components and the model of compress process.The experimental system is built to observe the dynamic characteristics of externally controlled compressors.And the dynamic characteristics of the external control compressor are tested and verified.Externally controlled variable displacement compressor as the latest generation of compressor,is able to be electronically driven from zero to its maximum displacement.The cooling power can be adjusted to the exact need and this way the fuel aonsumption of the automotive air conditioning loop and be reduced.Unfortunately,for the mean and low thermal loads on the evaporator,this new opportunity is limited by air conditioning loop operation instabilities.Based on a great deal of experiments of thermal expansion valve,the flow correlation coefficient and the adjusted coeddicient of the refrigerant in the both liquid and two phase state at the inlet of thermal expansion valve are obtained respectiovely.The coefficients,together with the models of evapotator and condenser,are adopted to build the steady state simulation model of sutomobile air conditioning system with externally controlled compressors.Thanks to an automatic approach of the coupling thermal expansion valve – evaporator,it can explain the origin of these instabilities and we can show the involvement of this new compressor generation.This can explain the origin of this instability and can show the new generation of compressor to join the situation.