Reducing powertrain losses is essential for enhancing electrified vehicle efficiency and achieving carbon neutrality. In recent years, the use of oil-cooled systems in transaxles(T/A) has increased, where insulating oil is supplied directly to the gears and motors for lubrication and cooling. However, to supply lubrication oil to high-speed gears and motors, significant losses occur due to stirring and dragging caused by oil viscosity. Therefore, to significantly reduce these losses in T/A, an ultra-low viscosity transaxle fluid has developed. Another advantage of using lower viscosity oil is the improvement in cooling performance. This study investigates the impact of the developed ultra-low viscosity oil on the cooling performance of motors by evaluating the heat dissipation from the motor and the heat exchange performance of the oil cooler related to the oil supply temperature using actual components. The results shows that the surface temperature of the stator with oil flow is on average 4°C lower compared to ATF (Automatic Transmission Fluid), and the evaluation of the oil cooler indicates an expected improvement of about 12% in heat exchange performance compared to ATF.
Ikeda et al. (Wed,) studied this question.