Apparatus and method for controlling variable displacement compressor

An apparatus for controlling a variable displacement compressor used in a refrigerant circuit of an air conditioner, wherein the refrigerant circuit includes the compressor and an external circuit, which is connected to the compressor, wherein the compressor compresses refrigerant sent from the external circuit and discharges the compressed refrigerant to the external circuit, wherein the refrigerant circuit has a high pressure zone, which is exposed to the pressure of refrigerant that is compressed by the compressor, wherein the compressor includes a tiltable drive plate, which is located in a crank chamber and changes its inclination angle in accordance with the pressure in the crank chamber, and wherein the inclination angle of the drive plate determines the displacement of the compressor, wherein the minimum displacement of the compressor is greater than zero, wherein the refrigerant circuit includes a shutoff valve, which is actuated according to the pressure in the high pressure zone, wherein the shutoff valve stops circulation of refrigerant in the refrigerant circuit when the compressor displacement is minimum, and wherein, when the shutoff valve stops refrigerant circulation in the refrigerant circuit, refrigerant circulates within the compressor, the apparatus comprising:

• a control valve, which adjusts the pressure in the crank chamber;
• and
• a controller for controlling the control valve, wherein the controller sends a command value that represents cooling performance required for the refrigerant circuit to the control valve, wherein the control valve operates to adjust its opening according to the sent command value, wherein, when the pressure in the high pressure zone is equal to or higher than a predetermined threshold value, the controller sends a command value that can minimize the displacement of the compressor to the control valve thereby limiting the pressure in the high pressure zone.

A method for controlling a variable displacement compressor used in a refrigerant circuit of an air conditioner, wherein the refrigerant circuit includes the compressor and an external circuit, which is connected to the compressor, wherein the compressor compresses refrigerant sent from the external circuit and discharges the compressed refrigerant to the external circuit, and wherein the refrigerant circuit has a high pressure zone, which is exposed to the pressure of refrigerant that is compressed by the compressor, wherein the compressor includes a tiltable drive plate, which is located in a crank chamber, and a drive shaft for driving the drive plate, wherein the drive shaft is directly coupled to an external drive source so that the drive shaft is always rotated when the external drive source is running, wherein the drive plate changes its inclination angle in accordance with the pressure in the crank chamber, and wherein the inclination angle of the drive plate determines the displacement of the compressor, the method comprising:

• adjusting the pressure in the crank chamber by a control valve, wherein the control valve operates according to a command value, which represents cooling performance required for the refrigerant circuit;
• and
• sending a command value that can minimize the displacement of the compressor to the control valve thereby limiting the pressure in the high pressure zone when the pressure in the high pressure zone is equal to or higher than a predetermined threshold value.