A hybrid oil cooling strategy for thermal management of high power density PMSMs

With the ongoing trend toward higher power-density and increased integration in electric drive systems for new-energy vehicles, the energy density per unit volume of drive motors continues to rise, intensifying the challenge of thermal management. However, existing motor cooling schemes struggle to simultaneously and effectively cool both the middle stator region and the end windings. To address this limitation, this study proposes a hybrid oil-cooling scheme that combines oil-channel cooling with oil-spray cooling to enhance the thermal performance of drive motors. Using a permanent magnet synchronous motor (PMSM) as a case study, the electromagnetic losses of each component are obtained via coupled electric-magnetic simulations. A three-dimensional thermal model is then established to obtain the temperature distribution based on these losses. Focusing on the severely heated middle stator region and end windings, a stator cooling channel and spray cooling channels are designed, and the optimal configuration is determined according to thermal–fluid coupling analysis. The stator cooling channel adopts a rounded folded geometry with a 180° inlet–outlet angle, while the spray cooling channel employs an 8-nozzle spray layout with a spray angle of 120°. Finally, an electric-magnetic-thermal-fluid coupled model of the motor and its thermal management system is developed to evaluate the cooling performance under different operating conditions. The results show that, under both rated and peak operating conditions, the average temperature of key components remains below 40 °C, corresponding to a reduction of more than 70% compared with natural cooling condition. The maximum temperature difference among internal components is less than 10 °C, a reduction of approximately 36%. These findings demonstrate that the proposed hybrid oil-cooling scheme delivers efficient, uniform, and stable cooling effect over a wide range of conditions, confirming its feasibility for high-performance electric drive systems and its strong potential for engineering application.