A Hybrid Electric Vehicle Motor Cooling System-Design, Model, and Control

Hybrid electric vehicle motors offer propulsion while accelerating and charge the battery pack when braking or decelerating. Though electric motors have high operating efficiency, considerable heat is generated based on required operating torque and speed. Thus, an efficient motor cooling system is needed to maintain the temperature within a prescribed range. The traditional motor liquid cooling system is effective but consumes energy to run the coolant pump and radiator fan. This paper examines the performance of a hybrid cooling system, combining heat pipes with conventional liquid cooling in a compact thermal cradle. This innovative design allows heat removal via an integrated thermal pathway by regulating various actuators (e.g., centrifugal fans, radiator pump, and fan) to minimize energy consumption. A reduced order thermal model predicts the motor's internal temperatures. Cooling performance is evaluated based on the Urban Assault driving cycle for different conditions. Numerical results show that the electric motor temperature is maintained at approximately the target value of 70 degrees C. Additionally, up to approximately 370 kJ of energy is saved as compared to a conventional liquid cooling system for a specific 85 kW e-motor within 1500 s run time.