Improvement of Refrigerant Flow Control Method in Automotive Air Conditioners

This paper describes the improvement of the refrigerant flow control method under transient conditions in automotive air conditioners. First, the mathematical model to analyze the dynamic characteristics of the refrigeration cycle is explained, then by using this model, it is demonstrated that the evaporator performance deteriorates at an initial stage of starting because of the shortage of the refrigerant flow caused by the response delay of the thermostatic expansion valve. Second, for improving this disadvantage, a refrigerant flow control method is proposed which uses an electronic expansion valve and compensates the response delay in the feedback control by means of the feedforward control. By using this control method, the evaporator capacity has been extracted effectively under the thermostatic on/off operation performed for the freeze protection, and consequently the evaporator discharge air temperature has become approximately 3°C lower than that of the conventional thermostatic expansion valve system.