Torque calculation apparatus and torque calculation method of variable capacitance compressor

A torque calculation apparatus of a variable capacitance compressor which is provided in a refrigeration cycle of a vehicular air conditioning system, which controls discharge capacity of refrigerant based on an external control signal, and which can estimate compressor suction side pressure based on the external control signal and compressor discharge side pressure, the torque calculation apparatus comprising:

• a compressor torque calculator which calculates a torque of the variable capacitance compressor based on evaporator upstream and downstream temperature difference data which is a temperature difference between inlet side air temperature of an evaporator and outlet side air temperature of the evaporator, compressor discharge side pressure data, external control signal data, and compressor's number of revolution data;
• an outside air temperature detector which detects temperature of outside air;
• an inside air temperature detector which detects temperature in a passenger room;
• and
• a memory which stores a torque calculation equation in which at least one of the evaporator upstream and downstream temperature difference data, the compressor discharge side pressure data, the external control signal data, and the compressor's number of revolution data is defined as a variable, and other data is defined as a constant value that is determined based on measurements under various conditions, wherein
• the compressor torque calculator defines the outside air temperature detected by the outside air temperature detector as the inlet side air temperature of the evaporator in an outside air introduction mode, and defines the passenger room temperature detected by the inside air temperature detector as the inlet side air temperature of the evaporator in an inside air circulation mode,
• each of the data defined as the variable and the constant value is input to the torque calculation equation to carry out calculation for calculating the torque, and
• the torque calculation equation is Tc=A·LN(Pd/Δt)+B, wherein
• Tc represents the torque of the variable capacitance compressor, Δt represents the evaporator upstream and downstream temperature difference data, Pd represents the compressor discharge side pressure data, the compressor's number of revolution data is defined as the constant value, LN represents logarithm natural, and A and B represent values determined based on the external control signal data and the evaporator upstream and downstream temperature difference data,
• the external control signal is a duty ratio for controlling an open/close duty ratio of a control valve of the variable capacitance compressor, and
• the constant value is determined based on measurements under various conditions of the duty ratio and the evaporator upstream and downstream temperature difference data.