Design And Research Of Direct Drive Permanent Magnet In-wheel Motor For Medium-speed Electric Vehicle

In recent years, researching and developing electric cars is becoming a hot trend around the world, and electric-vehicle technologies are also valued as one of the key research projects in China. At present, it is the conventional inner rotor motor instead of the internal combustion engine that is adopted by most of electric cars. But compared to the traditional centralized driving pattern, cars adopting distributed direct driving pattern have higher drive efficiency and more stable handling. On this background, this paper designed a kind of direct-drive outer rotor applied for middle or low speed electric cars based on the optimized parameters obtained through finite element analysis, and analyzed the electromagnetic field, the temperature field and mechanical properties of the motor, and at last verified the validity of the simulation through experimental determination.At first, based on an appointed car, this paper calculated some key parameters of the motor such as motor torque and motor speed in three kinds of working conditions. And then based on these calculated data, this paper calculated sizes of the stator core, the permanent magnet and the rotor. After that, this paper optimized the pole-arc coefficient and the gas length by RMxprt module in ANSOFT Maxwell software, and obtained a improved electromagnetic scheme at last.Secondly, this paper conducted a finite element analysis on the electromagnetic field of the designed electromagnetic scheme above. By analyzing static magnetic field characteristics, it was found that the field distribution was rational and the air gap flux density was about sinusoidal. By analyzing transient magnetic field characteristics of the no-load motor, it was found that the back EMF was about sinusoidal and the cogging torque waved by 1.13%. By analyzing electromagnetic transient load characteristics, it was found that the magnetic torque satisfied electric cars' performance requirements well. Meanwhile, this paper analyzed the gap flux density and the radial electromagnetic force and found that they accorded with features of the permanent magnetic outer rotor motor, and thus these conclusions could serve as the basis for the subsequent modal analysis of the motor.Thirdly, this paper established the 3D model of a hub motor using 3D software and analyzed the stress conditions, strain conditions and fatigue life of the hub in three different kinds of using ANSYS Workbench software, and the conclusions showed that the strength, stiffness and reliability can meet performance requirements. This paper analyzed modal vibrations of the hub motor, and the conclusions showed that external excitations and self-conditions of the motor will not cause motor resonance.Finally, this paper determined thermal loads of the motor and thermal conductivity of assembly parts, calculated heat extraction coefficient of surfaces and simulated static temperature field distributions of motor parts, which showed that the temperature waved in a stable and reliable range. At last, based on all of those obtained data, this paper conducted machining operation, set up an experimental system, measured the motor temperature rise and compared the simulation results. The conclusions showed that temperature rise distributions and trends obtained from experiments and simulations were identical, and thus verified the validity of simulations.