Design And Research Of Permanent Magnet In-wheel Motor For Electric Vehicle

Electric vehicle(EV) is the road vehicle in the new century. Compared to the traditional vehicle, electric vehicle has many advantages, including clean and green, energy-efficient, renewable and sustainable development. As the new type road vehicle with electric propulsion, it involves many subjects and a wide range of technical knowledge. At this stage energy technology and drive technology are the key issues of drive system development of EV. It is particularly important to develop high-performance drive system when there is a bottleneck in the development of energy technology. Along with the development of drive technology both in C hina and abroad, the direct drive system with in- wheel motor gets wide attention. It has the advantages of simple mechanical structure, high transmission efficiency, high control flexibility and easily integrate design. It is an inevitable trend of development. The in-wheel motor of drive system used in EV has been studied and analyzed emphatically in this paper.The in-wheel motor will be mounted inside the wheel. It increases the unsprung mass and hence deteriorates ride comfort and reduces the road holding capability of the automobile. In addition to meets the general need of the drive technology of EV, the in-wheel motor also need to meet high power density and high torque density.According to the structure size of automobile wheel hub and the running performance of automobile, an in-wheel motor is designed in this paper. The rated power of the in- wheel motor is 8.5 kW, the peak power is 20 kW. In order to improve the force index of the motor and the material utilization. The exterior rotor structure is chose. The stator winding is designed as fractional-slot concentrated winding to satisfy the space limitation of the wheel.The performance parameters of the motor prototype are calculated based on the magnetic circuit method. O n the basis of calculation results, the optimization design of the motor is carried out. The evolutionary strategy(ES) is proposed to optimize the permanent magnet shape. The structure parameter of the permanent magnet is set as the optimal variables and the performance parameters of the motor as the optimal objective during the optimization process. The finite element analysis(FEA) model of the in-wheel motor is also established in this paper. The optimal design of in- wheel motor with multivariable and multiobjective is achieved by ES and finite element method(FEM). It is also applied to optimize the in-wheel motor with Halbach permanent magnet array successfully.The accurate thermal analysis of in- wheel motor is quite important to its safety operation and performance improvement. The equivalent thermal network method and the FEM are used to calculate temperature rise of the in-wheel motor. The heat dissipation problem of in- wheel motor with exterior rotor and inner stator is validated. The calculate results also show that the two methods are adaptable and compatible to calculate the temperature field of motor. According to the structure of in-wheel motor used in EV, the inner-oil cooling method is proposed. The 3-D finite element analysis models were established for the in-wheel motor with natural cooling and inner-oil cooling. By comparing the calculation results with measurement results, the correctness of the FEA and the validity of inner-oil cooling method were verified. This is conducive to reduce temperature rise, improve running efficiency, improve the power density and the torque density of the in-wheel motor.