Research On In-wheel Drive Axial Flux Permanent Magnet Motor Of Pure Electric Vehicles

New energy vehicles play a decisive role in the global energy revolution.In order to get rid of technological dependence on advanced countries for core components such as engines and transmissions,China continues to launch numerous policies to promote the development of the new energy vehicle industry.Electric drive system plays a vital role in the performance of the vehicles as a core component.In-wheel drive system can replace mechanical differential,the stability and maneuverability of the vehicles can be greatly improved by electronic differential.Axial Flux Permanent Magnet(AFPM)motor is superior to radial flux motor in terms of power density.To sum up,in-depth research on in-wheel-driven AFPM motor is of great significance to the development of new energy vehicles.Due to the special rotor structure of AFPM motor,eddy current loss of permanent magnet caused by magnetic field harmonics is large and the dissipation of heat is difficult,there are risks of demagnetization due to high temperature.The blocking and slotting methods of permanent magnets proposed by some scholars will introduce magnetic field harmonics,withal,this paper puts forward technology for permanent magnet,such as parallel blocking at diagonal,and parallel slotting at double sides,the effects of different spacing and different directions of block and slot methods on eddy current loss suppression and magnetic field harmonics of permanent magnets were studied,and the best way of blocking or slotting is summarized by defining the coefficient.There is radial diffusion of armature magnetic field in the stator core of AFPM motor,resulting in radial flux component.There are few relevant studies on the difference of eddy current loss of stator core caused by this,and the efficiency of iterative calculation of motor loss and temperature rise by three-dimensional finite element method is low.The increased iron loss at the direction of radial caused by armature magnetic field of AFPM motor were analyzed creatively,the analytical calculation method was deduced,and improvement points ring method was put forward,the fast calculation method of loss of AFPM motor was obtained,combined with the thermal network,rapid iteration model is set up,finally,the two-way coupling,fast iterative calculation of the magnetic heat loss-temperature rise was realized.The distribution of high efficiency area of motor has great influence on vehicle range,and electronic differential control will cause the difference of running conditions of the each side of in-wheel motor,resulting in the change of average efficiency,based on the road spectrum of typical working conditions,the vehicle dynamics model was established to conduct matching analysis between vehicle working conditions and motor high efficiency area,the reasons and trends of the influence of different parameters on high efficiency area were studied.The yaw stability of vehicle under steering condition was analyzed.Based on the characteristics of distributed drive that can control torque distribution flexibly,the influence of torque distribution control on motor operation efficiency under yaw stability priority principle was studied,and the optimization method of motor high efficiency area was obtained.After calculation and analysis of the main performance by analytical method and finite element method(FEM),such as,output characteristic,loss,temperature,stress and so on,a liquid-cooled AFPM motor test prototype was designed and produced.The test bench was built to test torque,current,back EMF,loss,temperature rise and so on.The calculation results and analyze results were compared at variety of conditions,to correct the calculation method is verified.