Controller for reversible air conditioning and heat pump HVAC system for electric vehicles

A control system for controlling a temperature of a motor vehicle having a passenger compartment, the control system comprising:

• a heat pump having an electric compressor for circulating a refrigerant in a direction, said electric compressor having a rotating speed related to a duty cycle of a compressor control signal and a suction pressure related to the rotating speed, first and second heat exchangers for transferring heat energy between an outside environment and the passenger compartment, a refrigerant flow switching device for switching the direction of refrigerant flow towards the first heat exchanger in a heating mode and towards the second heat exchanger in a cooling mode, and a flow management center for supplying pressure reduced refrigerant to the first heat exchanger in the cooling mode and to the second heat exchanger in the heating mode, said flow management center including an electronic expansion valve having a flow rate related to a duty cycle of an EXV control signal;
• a controller for controlling the duty cycle of the EXV control signal such that efficient operation of the first and second heat exchangers is maintained and for controlling the duty cycle of the compressor control signal such that a desired quantity of heat is transferred between the outside environment and the passenger compartment;
• a first sensor coupled to the controller to sense a refrigerant parameter reflective of an evaporator refrigerant saturation temperature during the heating mode and the cooling mode;
• and
• a second sensor coupled to the controller to sense a refrigerant parameter reflective of an evaporator outlet refrigerant temperature;
• wherein the controller calculates a refrigerant superheat temperature based on the evaporator refrigerant saturation temperature and the evaporator outlet refrigerant temperature;
• said controller controls the duty cycle of the EXV control signal such that the refrigerant superheat temperature is maintained substantially at a predetermined superheat temperature, whereby the evaporator is efficiently used for transferring heat energy.