Temperature Field Analysis For In-Wheel PMSM In Electric Vehicle Cooled By Oil

Nowadays, the production and sales of private cars increase rapidly with the social development and the increase of living standard. It makes people's life convenient, but suffers from serious environmental and energy problems. Fortunately, electric vehicles were successfully developed to saves energy and reduce pollution. The in-wheel motor is widely used in electric vehicle by virtue of its small in size and nice efficiency presented by complex control strategies. Normally, permanent magnet synchronous motor(PMSM) is the best choice for in-wheel motor. But the characteristics of permanent magnet and insulating materials are affected by the temperature of motor. In fact, the high temperature caused by the heat generated from motor could lead to insulating materials aging and permanent magnet demagnetizing, and even motor burning. Thus, the efficient removal of the generated heat by cooling is the goal of this study. In this paper, the method of closed oil cooling is employed to study on the motor cooling system as following:Firstly, the cooling efficiency of oil cooling and natural cooling methods has been comparatively researched by Finite Element Method(FEM) on the basis of electromagnetic field theory and hydrodynamics theory. The motor model is established by finite element simulation software. The convective heat transfer coefficient between the stator and rotor is deduced by the heat transfer theory and hydrodynamics equations at different speeds or in different fluid media. According to the coefficients obtained from the two cooling methods,the simulating experiments were carried out. The temperature distribution of motor and the cooling efficiency of the two cooling methods were then discussed with the simulating results.Secondly, the influences of motor speed and overload current to the efficiency of oil cooling method were investigated. The distribution of heat sources at different speed or overload current, the temperature distribution of motor at steady-state operation were analyzed. The relationship among temperature rise, heat and speed, and the relationship among overload capacity of motor, overload current and temperature rise were established.Thirdly, the relationship between the oil amount and the cooling efficiency was investigated. The relationship between speed and temperature rise in the case of less oil cooling was examined. The motion state of oil was studied by hydrodynamic theory in the case of less oil. The cooling efficiency at different speed was obtained. The conclusions were verified by simulation. Comparison study on the cooling efficiency between 1/3 and full oil amount was carried out.Finally, the temperature rising experiments of full oil cooling were carried out.Comparing the experimental results and the simulating results demonstrated that the results from the model and magnet-thermal coupling FEM simulation are correct in this paper.