Thermal Management of a Hybrid Vehicle Using a Heat Pump

This paper presents the thermal management of a hybrid vehicle (HV) using a heat pump system in cold weather. One advantage of an HV is the high efficiency of the vehicle system provided by the coupling and optimal control of an electric motor and an engine. However, in a conventional HV, fuel economy degradation is observed in cold weather because delivering heat to the passenger cabin using the engine results in a reduced efficiency of the vehicle system. In this study, a heat pump, combined with an engine, was used for thermal management to decrease fuel economy degradation. The heat pump is equipped with an electrically driven compressor that pumps ambient heat into a water-cooled condenser. The heat generated by the engine and the heat pump is delivered to the engine and the passenger cabin because the engine needs to warm up quickly to reduce emissions and the cabin needs heat to provide thermal comfort. To control the heat flow from the engine and the heat pump, switching between coolant circuits was used. An optimal way to control the engine and the heat pump to minimize the fuel consumption was found. To this end, a 1-D thermal vehicle model was used for optimization, and the fuel economy of the optimized system was measured on a prototype vehicle. Compared to a conventional HV, the fuel economy of the optimized system improved by 10%.