Temperature Field Analysis And Cooling Structure Design Of In-Wheel Motor Driving System

Under the pressure of energy shortage and environmental pollution,new energy vehicles is energy-saving and environmental-protection and have become a trend in the development of the automotive industry.In recent years,the in-wheel motor(IWM)driving electric vehicle has obvious technical advantages in the overall layout of the vehicle,active control of the chassis and the convenience of control,so it is highly favored by professionals in the industry.However,for IWM driving system,the driving motor,the speed reducer,the brake and so on are highly integrated in the wheels,while the air circulation is poor and the heat radiation is difficult in the narrow-closed space;meanwhile,the motor volume is decreased in order to pursue the high torque and power density of the driving motor.Though the power density can be increased,the loss density is also increased,which lead to the overheat of the IWM.It will not only damage the winding insulation and reduce the life,but also cause irreversible demagnetization of permanent magnet and threaten the safety and stability of the IWM and vehicles.Therefore,the correct calculation and analysis of the temperature field distribution of the IWM driving system and the design of an efficient cooling structure are of great significance for extending the service life of the IWM and improving the overall vehicle performance.Based on the summarization of the related domestic and foreign research results,taking a 15 kW built-in permanent magnet synchronous IWM driving system as the research object,the model of IWM driving system was established to analyze and calculate the loss of each component in the motor.Then,the temperature field characteristics of the IWM driving system under various working conditions were studied,and a axial water cooling and spray cooling structure were designed to compare and analyze the cooling performance of the two schemes.The main research contents of the paper are as follows:(1)Research and analysis of temperature field characteristics of IWM driving system.Based on the related theories of electromagnetism and electromagnetic fields,the losses of the stator core,stator winding,rotor core,and permanent magnet of the motor were calculated and solved.Based on the loss calculation,the thermal performance parameters of various parts of the motor are determined,including the heat generation rate,thermal conductivity,heat dissipation coefficient.At the same time,a three-dimensional temperature field simulation model of the IWM driving system was established.And the transient temperature field characteristics of the IWM driving system under rated operating conditions and peak operating conditions were analyzed.The results show that: 1)under the rated condition,the temperature of the motor stator area is obviously higher than the temperature of the motor rotor area,especially the temperature change of the stator winding of the motor is most significant,and the temperature of the end of stator winding is the highest;2)under the peak condition,the highest temperature of the motor has reached 170.94°C,which exceeds the insulation level requirements of the motor(155°C).(2)Research on temperature field characteristics of IWM driving system under different working conditions.Through the analysis of the vehicle operating conditions,the typical operating conditions that have the most significant effect on the temperature rise of the IWM are obtained.Based on this,according to the actual driving process of the vehicle,the losses of each component of the IWM under various typical operating conditions are calculated,and then the temperature field characteristics of IWM driving system under various working conditions are studied and analyzed.The results show that under the typical working conditions,the operation state of IWM is changed with the change of the working condition,which leads to the remarkable temperature rise of the IWM,even exceeding the insulation level of the motor,and the temperature of the end of stator winding is the highest,affecting the safe and stable operation of the motor.(3)Design and analysis of cooling structure of IWM driving system.According to the distribution of the temperature field of the IWM driving system under various typical working conditions,the axial water cooling and spray cooling structure were designed.Based on the basic theory of computational fluid dynamics and heat transfer,it is modeled and analyzed by fluid dynamics software to compare and analyze theirs cooling performance.The results show that both cooling structures can achieve good cooling effects,so that the temperature rise of the motor is controlled within the range of insulation requirements.In comparison,the cooling effect of the spray cooling structure is better,which can more effectively control the temperature rise of the motor and ensure the normal operation of the motor and the safe driving of the vehicle.