Battery Thermal Management System for PHEV by using Air Conditioning Heater System

At Toyota Motor Corporation, we are pursuing an omnidirectional strategy that includes BEVs, PHEVs, and FCEVs to accelerate electrification. One of the technical challenges with our xEV batteries, which feature good degradation resistance and long battery life, is that regenerative braking cannot be fully effective due to the decrease in regenerative power in some situations, such as low battery temperature. For the electrified vehicles with an internal combustion engine such as PHEVs, the solution has been starting the engine to increase deceleration through engine braking during coasting. In this context, PHEVs are expected to extend their cruising range and enhance EV driving experience as "Practical BEVs". While several manufacturers including us are increasing battery capacity and enhancing convenience, restrictions on EV driving opportunity due to low battery temperature will affect the appeal of these electrified vehicles. However, introducing a battery heater is considered system redundant, costly, and negatively impacts battery pack size. Another alternative solution has been ripple heating of the battery to control battery temperature, but with the concern to deteriorate degradation resistance and shorten battery life. 　This paper is to present a technology to warm up the battery and increase regeneration by utilizing only the air conditioning heater system as the heat source, to maintain coasting deceleration while minimizing the engine start. In addition, a heater and water valve control system has been developed and will be implemented in the next-generation PHEV for the thermal management that considers the impact on cabin heating performance and EV driving range in winter.