Abstract: The degree of opening of the expansion valve in refrigeration system is controlled by means of PID control such that a refrigerant superheat at the outlet of the evaporator approaches a target valve. Since an elapsed time after the start of the refrigeration system varies in response to a change of a heat load of air to be cooled by the evaporator, if the control constant of the PID control is designed so that the expansion valve can be controlled adequately for high evaporator heat load, or for low evaporator heat load, adequate control cannot be achieved in the opposite case not taken into consideration in design. According to the present invention, the control constant of the PID control is varied when an elapsed time after the start of the refrigeration system reaches a reference time which is determined on the basis of a heat load of air to be cooled by the evaporator.

Abstract: A refrigeration system for use in an automotive air conditioning system has a vane type variable displacement refrigerant compressor drivingly connectable by an electromagnetic clutch to an automotive engine, a refrigerant evaporator through which air is caused to flow by a blower, and a pressure check valve which prevents the refrigerant pressure in the evaporator from lowering under the predetermined pressure, so that frost or icing is not formed on the evaporator fins. The compressor is provided with one or two unloading ports for releasing the refrigerant being compressed and with a valve member or members associated with the unloading port. The refrigerator temperature and the pressure of the refrigerant in the conduit between a throttling valve and the compressor are detected. A signal is emitted to an electric circuit for actuating the valve member or members so that the unloading port is selectively opened to vary the compressor displacement to provide a multi-stage compressor displacement control.

Abstract: A refrigeration system for use in an automotive air conditioning system has a variable displacement refrigerant compressor drivingly connectable by an electromagnetic clutch to an automotive engine, a refrigerant evaporator through which air is caused to flow by a blower, and a throttling valve which prevents the refrigerant pressure in the evaporator from lowering over the predetermined pressure, so that frost or icing is not formed on the evaporator fins.The compressor is provided with one or two unloading ports for releasing the refrigerant being compressed and with a valve member or members associated with the unloading port. The operation of the throttling valve is detected by a sensor which emits a signal to an electric circuit for actuating the valve member or members so that the unloading port is selectively or gradually opened to vary the compressor displacement to provide a multi-stage or continuous compressor.

Abstract: A refrigeration system for use in an automotive air conditioning system has a vane type variable displacement refrigerant compressor drivingly connectable by an electromagnetic clutch to an automotive engine and a refrigerant evaporator through which air is caused to flow by a blower. The compressor is provided with one or two unloading ports for releasing the refrigerant being compressed and with a valve member or members associated with the unloading port or ports. The air temperature just downstream of the evaporator is detected by a sensor which emits a signal to an electric circuit for actuating the valve member or members so that the unloading port or ports are selectively opened to vary the compressor displacement to provide a multistage compressor displacement control. The electric circuit is also operative to control the electromagnetic clutch to selectively connect and disconnect the compressor to and from the engine.