Development of a coefficient of performance to evaluate the oil cooling methods in electric vehicle motors

This study developed performance coefficients to evaluate oil cooling in electric vehicle motors. The coefficients, incorporating oil flow field, heat removal capacity, and temperature as input parameters, are used to optimize motor cooling conditions. The flow field coefficient, defined by comparing dripping and churning oil volumes, was influenced by flow complexity and improved by 85 % at higher coolant flow rates, lower rotor speed, and lower inlet oil temperature. The heat removal capacity coefficient, representing the ratio of cooling capacity to heat generation, increased up to 70 % with colder oil supply. The overall cooling performance coefficient, combining flow field and heat removal effects, showed a 55 % performance increase by enhancing the flow field and a 74 % increase by improving heat removal. Thus, inlet temperature adjustment proves to be the most effective temperature management strategy. The proposed coefficients provide a framework for optimizing motor cooling performance.