Research On Ride Comfort Of In-Wheel Motor Drive Electric Vehicle Under Rotor Eccentricity

In recent years,with the increasingly serious problems of energy shortage and environmental pollution,in order to reduce the ecological environment damage caused by exhaust emissions,the realization of the transformation of traditional fuel vehicles to electric and intelligent has become one of the important development trends of the automobile industry.In-wheel drive electric vehicles have attracted wide attention from many scholars and enterprises in the automotive field due to its advantages such as compact structure,high transmission efficiency,fast torque response,and flexible drive system layout.However,its special arrangement also brings inevitable vehicle dynamics problems.The high integration of the electric wheel causes the unsprung mass of the vehicle to increase,which aggravates the vibration of the unsprung parts.In addition,the in-wheel motor is easy to cause rotor eccentricity under external disturbances such as road excitation and driving behavior,which leads to the imbalance of radial electromagnetic force and deteriorates the output performance of the motor,further affecting the dynamic response of the vehicle.As a rare earth-free motor,switched reluctance motor has the advantages of simple structure and low cost,and has great application potential in the field of in-wheel drive electric vehicles.Aiming at the problem of vehicle ride comfort deterioration under road excitation and unbalanced radial force coupling excitation of in-wheel motor,this thesis takes an 8/6 four-phase in-wheel switched reluctance motor as the research object,considers the electromagnetic coupling effect of in-wheel switched reluctance motor,and uses its nonlinear model to obtain the electromagnetic distribution characteristics of the motor under different rotor space angles and currents.The electromagnetic characteristics of the motor under different eccentric conditions are analyzed by finite element method.Considering the influence of electromagnetic excitation on vehicle ride comfort under motor eccentricity,a 1/4 vehicle vertical dynamic model is established to study the ride comfort response of vehicles under uniform and accelerated conditions.Based on the established vehicle vertical dynamics model,the structure parameters of the in-wheel switched reluctance motor are optimized to improve the ride comfort of the in-wheel drive electric vehicle.The main research contents are as follows :(1)The basic structure,operation principle and control mode of switched reluctance motor are expounded.Through finite element simulation,the variation characteristics of inductance with current in special position of the motor are analyzed.The nonlinear model of switched reluctance motor is obtained by Fourier series method,and the variation law of electromagnetic characteristics with rotor space angle and current in a single cycle is further obtained,which lays a foundation for the follow-up research work of this thesis.(2)Aiming at the problem that the rotor eccentricity causes the electromagnetic characteristics of the motor to change.Two basic types of eccentricity during the operation of the motor are described,and the finite element models of the normal state and the eccentric state are established according to the structural parameters of the switched reluctance motor.The response of the electromagnetic characteristics of the motor under different structures is analyzed by means of the established finite element model.In order to study the electromagnetic characteristics of the motor under eccentric conditions,the static and transient characteristics of switched reluctance motor are analyzed respectively,and the response law of electromagnetic characteristics of switched reluctance motor under different eccentricity,eccentricity direction and eccentricity type is obtained.(3)Aiming at the deterioration of vehicle ride comfort under road excitation and unbalanced radial force coupling excitation of in-wheel motor.The filtering white noise method is used to establish different road grade models.Based on the traditional twodegree-of-freedom 1/4 vehicle model,a three-degree-of-freedom 1/4 vehicle model including the in-wheel motor is constructed.From the three aspects of vehicle speed,random road grade and load,the ride comfort response of in-wheel drive electric vehicle considering electromagnetic excitation under uniform speed and acceleration conditions is analyzed by time domain simulation.(4)Because the change of the structural parameters of the in-wheel switched reluctance motor will cause the change of the output performance of the motor,which will affect the ride comfort of the vehicle,the structural parameters of the motor which have great influence on the ride comfort of the vehicle are selected by sensitivity analysis.In order to improve the ride comfort of the vehicle,the collaborative optimization method of the in-wheel switched reluctance motor and the ride comfort of the vehicle is studied.The structural parameters of the in-wheel motor are further optimized and analyzed to achieve a good match between the in-wheel motor and the ride comfort of the electric vehicle.