I. Introduction
With the development of society and the improvement of people's living standard, ownership and use of vehicle has been exponential growth, which is leading to energy consumption and environmental pollution deterioration. So each country is very concerned about energy efficiency and emissions, policies also are further promoting the development of new energy vehicles [1]–[2]. According to the development trend of vehicles, the electric vehicles will completely replace the traditional ICE cars in the near future because of its lowest emissions and zero fuel consumption. Internal permanent magnet synchronous motor is very important in electrical vehicles because of its known higher power density, higher torque density and wider speed range[3]. But these requirements make the IPM motor more temperature rise. Overheating will lead to degradation of insulation materials, magnet demagnetization and this will impact the efficiency and life of the machine. Therefore, it is very important how to predict and avoid the excessive temperature rise of the E-motor in design stage by using thermal simulation method[4]. The thermal behavior of an electric machine can be predicted using multiple methods, two general methods are the thermal circuit and the FEM method. But these two methods have their different advantages and disadvantages. The thermal circuit method can calculate faster, it is more useful than the 3D FEM method in the concept design phase of the E-motor[2]. And this model has been established to calculate the temperature of the IPM [5]–[10]. However, 3D thermal simulation can get more detail temperature and liquid distribution of the motor assembly. In order to calculate the temperature of disc-type PM electric machines accurately, the method of computational fluid dynamic (CFD) is adopted [11]–[12]. However, little study has been done on the multi - physics coupling thermal analysis method. For the purpose of stability and reliability application of the IPM in the EV, this paper investigated how to couple liquid, structure and heat fields in two-way to analyze the detail temperature and liquid distribution of the motor assembly.