Research On Electromagnetic Clutch Device And System For Wheel Motor Drive

Because of the compact structure and flexible control,wheel motor is recognized as the ideal drive mode for electric vehicles.However,the rigid connection is usually used between the hub and the motor to transmission the energy,which results in mechanical shock and electromagnetic impulsion,especially in the starting and braking process.In this paper,a novel bistable permanent magnet electromagnetic clutch device with a compact structure is presented,the controllable clutch unit can be integrated with the motor to achieve a flexible connection between the motor and hub.Accordingly,the mechanical shock and electromagnetic impulsion in starting and braking are released,which improves the reliability and comfort of the vehicle greatly.This paper focuses on the design,manufacturing of the clutch prototype and the overall integration of the clutch system.The feasibility and advance of the new solution of “no-load starting,variable-idle shifting and detached braking” are demonstrated.The design theory and engineering specifications of the novel clutch system are built.Then,a more competitive solution for the wheel electric vehicle drive is provided.The main contents are summarized as follows:Firstly,the magnetic field distribution of the clutch unit is analyzed,the variation of the magnetic field of the clutch is studied.Meanwhile,by comparing the calculation results of the three-dimensional model and the two-dimensional model,a simplified 2D model is proposed.On this basis,the boundary conditions of the magnetic leakage domain are established,then the analytical expression of the scalar magnetic potential is derived.Furthermore,the analytical solution of magnetic leakage coefficient is proposed by using the magnetic circuit model,which reveals the influence of the main dimensions of the clutch on the magnetic flux leakage coefficient.The results show that the error between the analytical solution and the FEA simulation result is less than 5%,which lays the foundation for the optimal design of the clutch unit.On the basis of the magnetic field analysis,the optimal design of the clutch unit is carried out.With the guiding ideology of less consumables and high energy efficiency,the optimal structure size of the clutch is determined by investigating the flux leakage coefficient and the steady-state holding force.Based on the design criteria,a universal experimental platform for the prototype is built for the experimental study on the static performance of the clutch unit.The results show that the error between the analytical calculation results and the experimental results is less than 5%,and the clutch has good steady state self-sustainability.The optimal design lays the foundation for the integrated embedded design of the clutch system.Based on the determined basic size of the clutch,the design of the power supply system is carried out.Firstly,the layout of the coils is proposed by micro-topology analysis.Then through the study on the dynamic performance of the clutch unit,the relationship between the force and motion,the upper,lower boundaries,the minimum pulse width of the magnetizing current are obtained.Furthermore,a pulsed power supply is proposed,and its matching design method is improved.Based on the above analysis,the slideway and coils of the unit prototype are made to carry out the test of the dynamic characteristics of the clutch unit.The experimental results show that the clutch actuation is reliable when it is powered by the pulsed power supply.The actuation time is 16 ms and the current can be self-turn-off after the capacitor is discharged for 30 ms,which meets the requirement of the application.Based on the clutch unit structure and power supply design,with the integrated and embedded design ideas,the integration scheme of the clutch group and the rotor is proposed,and the different engagement modes of the clutch system are determined.By carrying out the engagement processes analysis,the key size requirement of the putter type clutch system is proposed,and the related indicators requirement of the clutch in friction type clutch system is obtained.Furthermore,to improve the reliability of the clutch system,the rotor harmonic power generation and wireless remote control solution are proposed,the synchronous operation of the clutch group is also studied.Finally,the integrated experimental prototype is set up,the experiments validate the advancement and the feasibility of the design.The introduction of the clutch makes it possible to implement the idle speed start-up strategy.By studying the idle start mode,the control laws of the optimal idle speed shifting are revealed,the superiority of the idle speed control strategy is highlighted,the advantages of variable-idle shifting are proved.Besides,the adaptive control method for further improving the load capacity of the driving motor when the idle speed reaches its upper limit is proposed.Then,a special experimental platform is built,the experimental results show that the peak value of the wheel jerk is only 1/3 of the direct start when starting at variable idle speed,which greatly improves the starting comfort.Furthermore,by implementing the adaptive control,the load capacity is doubled.