Patent ID: 7137267

Claim:
An apparatus for controlling a variable displacement compressor that forms a refrigeration circuit with an external refrigerant circuit, the compressor including a rotary shaft, a piston for compressing refrigerant gas drawn into a compression chamber, a crank chamber for accommodating a crank mechanism that converts rotation of the rotary shaft into reciprocation of the piston, a separation chamber located on a discharge passage that extends from the compression chamber to the external refrigerant circuit, wherein lubricating oil in the refrigerant gas is separated in the separation chamber, an oil return passage for connecting the separation chamber with the crank chamber, and a control valve located on the oil return passage, wherein the control valve varies the opening degree of the oil return passage based on an external command, and wherein the displacement of the compressor is varied by controlling the pressure of the crank chamber through controlling the opening degree of the oil return passage, the apparatus comprising: an information detector for detecting information about a thermal load on the refrigeration circuit; and a controller, wherein the controller determines a target value that reflects the displacement of the compressor based on the information about the thermal load detected by the information detector, and outputs the target value as a command value, and wherein, when determining that the compressor is in a heavy load state based on information about a load on the compressor, the controller changes the command value to a value that causes the displacement of the compressor to become smaller than a displacement that corresponds to the determined target value.