Displacement control apparatus and method for variable displacement compressor

A displacement control apparatus for a variable displacement compressor used in a refrigerant circuit of a vehicle air conditioner, wherein the compressor is driven by a drive source of a vehicle, the apparatus comprising:

• a displacement control mechanism, which controls the displacement of the compressor based on the pressure difference between the pressures at two pressure monitoring points located in the refrigerant circuit, the pressure difference representing the displacement of the compressor;
• a first device for detecting external information representing the required cooling performance of the refrigerant circuit;
• a second device for detecting information representing the load acting on the external drive source;
• a determining means for determining a target value of the pressure difference in accordance with the external information detected by the first device, wherein the displacement control mechanism controls the displacement of the compressor such that the pressure difference seeks the target value;
• a judging means for judging whether to set a limit value of the pressure difference based on the external information detected by the second device, and
• a means for using the limit value as the target value of the pressure difference to limit the compressor displacement when the limit value is set and a compressor displacement that corresponds to the target value is greater than a compressor displacement that corresponds to the limit value.

A method for controlling the displacement of a variable displacement compressor used in a refrigerant circuit of a vehicle air conditioner, wherein the compressor is driven by a drive source of a vehicle, the method comprising:

• determining a target value of the pressure difference between the pressures at two pressure monitoring points located in the refrigerant circuit based on external information that represents the required cooling performance of the refrigerant circuit, the pressure difference representing the displacement of the compressor;
• controlling the compressor displacement such that the pressure difference seeks the target value;
• judging whether to set a limit value of the pressure difference based on external information that represents the load acting on the drive source;
• and
• using the limit value as the target value of the pressure difference when the limit value is set and when a compressor displacement that corresponds to the target value is greater than a compressor displacement that corresponds to the limit value.