Vehicle air conditioner with auxiliary heat exchanger

A vehicle air conditioner comprising:

• an air conditioning duct through which air discharged to a vehicle interior flows;
• a refrigeration cycle unit that includes
• a compressor configured to compress an intake refrigerant and discharge the compressed refrigerant,
• a condenser configured to condense the refrigerant discharged from the compressor by heat exchange with outside air,
• a decompressor configured to decompress the refrigerant in a liquid phase condensed by the condenser, and
• an evaporator disposed in the air conditioning duct and configured to cool the air flowing in the air conditioning duct by heat exchange with the refrigerant decompressed by the decompressor;
• a heater core that is disposed in a heating passage located downstream of the evaporator in the air conditioning duct with respect to an airflow, the heater core being configured to heat the air cooled by the evaporator by heat exchange with a heat medium, the heat medium receiving heat from an internal combustion engine of the vehicle to cool the internal combustion engine;
• a cool air bypass passage that is located downstream of the evaporator in the air conditioning duct with respect to the airflow, the air bypassing the heater core via the cool air bypass passage;
• an air volume ratio regulator that is configured to regulate a ratio of a volume of air passing through the heating passage to a volume of air passing through the cool air bypass passage;
• an auxiliary heat exchanger that is provided in the refrigeration cycle unit and configured to change enthalpy of refrigerant having flowed out of the condenser and to flow into the evaporator by heat exchange;
• and
• a controller configured to determine a target cooling temperature that is a temperature target value of air flowing out of the evaporator, wherein
• the compressor is driven by the internal combustion engine,
• the evaporator includes a cold energy storage configured to store cold energy, the cold energy storage being configured to store cold energy when the compressor is in operation, the cold energy storage being configured to dissipate cold energy while the compressor stops,
• the auxiliary heat exchanger is located downstream of the evaporator and upstream of the heater core in the air conditioning duct with respect to the airflow,
• the auxiliary heat exchanger is configured to change enthalpy of refrigerant, which is in the liquid phase having been condensed by the condenser and to be evaporated by the evaporator, by heat exchange between the refrigerant and air having been cooled by the evaporator and to be heated by the heater core, and
• the controller is programmed to:
• obtain a second target cooling temperature based on an outside air temperature, the second target cooling temperature being a temperature at which an effect on improving fuel economy of the internal combustion engine is improved, the fuel economy being calculated by synthesizing an effect on power saving of the compressor obtained when the auxiliary heat exchanger changes enthalpy of the refrigerant in the liquid phase, and an improving effect on fuel economy of the internal combustion engine obtained when the evaporator dissipates cold energy;
• and
• control the compressor such that temperature of the air flowing out of the evaporator is to be the second target cooling temperature.