Development of an Intelligent Thermal Management System for BYD DM-i Hybrid Engine

BYD recently introduced its new DM-i (Dual Mode-Intelligent) plug-in hybrid architecture with a new dedicated 1.5NA (Naturally Aspirated) high-efficiency engine, which can reach a peak of 43% brake thermal efficiency. With this architecture, the vehicle is mainly driven by motors and engine only starts when required. This requires that once started, the engine can reach its best working temperature as quick as possible. To achieve this target, a new intelligent thermal management system was designed. This system adopted an advanced split cooling strategy to control the flow ratio between cylinder block and head, which was realized by the combination of one electronic thermostat and one wax thermostat. An electronic water pump was used to actively control the coolant flow rate. Together with the intelligent control of thermal needs under all working conditions, the new thermal management system realized the following benefits: faster engine warm-up, better fuel economy and lower pollutant emissions. 1D (One Dimensional) simulation was used to optimize the flow ratio between cylinder block and head. By analyzing the flow distribution, temperature level and pressure drop of each component in the HT (High Temperature) loop and LT (Low Temperature) loop, the cooling performance of this new thermal management system was evaluated and optimized. 3D (Three Dimensional) simulation was used to optimize the flow channel design. Finally, the performance of the thermal management cooling system was validated on the engine test bench and the coolant temperature was calibrated for the whole engine map.