Research On Dynamic Characteristics And Vibration Control Of Electric Vehicle Driven By In-wheel Motors With Semi-active Suspension

As the development direction and key technology of electric vehicle(ab.EV) in the future, the EV driven by in-wheel motors because of its obvious technical advantages has become a hot research topic for the global auto industry. But currently, the research and development of EV driven by in-wheel motors are still in their infancy, some key technologies have not completely solved. There are still some deficiencies that are mainly focused on the design of hub motor itself with integrated development of in-wheel motor system, the ride comfort deterioration caused by in-wheel motors driving mode and imperfect control strategy, etc.Focusing on solving the problem of the ride comfort deterioration caused by in-wheel motors driving mode,in virtue of improving the transmission of vibration, a multifunctional in-wheel motor system with embedded magneto-rheological(ab.MR) semi-active suspension is proposed.In theory, the EV driven by in-wheel motors based on semi-active suspension is a kind of complex intelligent mechanical and electrical system, at present, there is still no relevant deciphering technology report about this system at home and abroad, the influence of electromagnetic excitation of the wheel motor on the dynamic characteristics has not caused wide attention, and the application of semi active suspension is mainly concentrated in the traditional vehicle driven by internal combustion engine, but also has some problems to be solved, what is more, the application research of semi-active suspension on the EV driven by in-wheel motors is less. Therefore, study on the dynamic characteristics and vibration control based on the semi-active suspension not only has an important theoretical research value, but also has a wide application prospects. The details of the research are presented as follows:(1) Firstly, reviews the development and research status of the EV independently driven by the in-wheel motors at home and abroad, then analyses the two existing problems of this EV, which are the negative effect of vertical vibration caused by the increase of the non sprung mass and ride comfort deterioration as a result of electromagnetic vibration caused by the in-wheel motors. In order to solve these problems,a high efficient and integrated motorized wheel system with many functions of power, vibration reduction, braking and travelling is proposed. According to the power and vibration requirements of electric vehicles, and considering the constraint of wheel’ssize, the structure scheme and dimension parameters of the hub motor and MR damper are determined respectively.After that, the mathematical model of MR damper is established based on Bingham viscoplastic model and viscous hydrodynamics theory, the working performance of the MR damper is simulated and analyzed. Finally, the virtual prototype model of this multifunctional in-wheel motor system is established.These research works provide the entity model of in-wheel motor and the parameters of basic vehicle for the following dynamics analysis.(2) A new system involving road, in-wheel motor, vehicle and passengers is proposed to make ride comfort analysis for the EV independently driven by the in-wheel motors.After making some simplify to this type EV, dynamic models of two degrees of freedom quarter-car and seven degrees of freedom full car are established respectively using the basic dynamic theory and method of the system state space. The models of roughness excitation of various roads are established. Based on the theory of electromagnetic field and magnetic circuit method, the electromagnetic torque and the tangential force of the disc hub motor are analyzed, and then the vertical component of electromagnetic excitation force of the hub motor is obtained by using the mechanics principle and the numerical calculation method. The above research provides the model for the dynamic characteristics analysis and vibration control for the EV independently driven by the in-wheel motors.(3)Based on the dynamics model of electric wheel vehicle, the transfer function of ride comfort performance indexes such as vertical acceleration of vehicle body, the suspension deflections and wheel’s dynamic displacement with respect to road roughness’ s displacement input are derived using the Laplace transform method,furthermore the root-mean-square of three response indexes are calculated. Afterwards the influence of the changes of system parameters on the ride comfort are analyzed comprehensively associate with the amplitude frequency characteristic and time domain response of root-mean-square response, and the sensitivity analysis of ride comfort indicators with respect to these important structural parameters are performed using perturbation method,so the main parameters affecting the ride comfort are found out. In addition, the influence of the motor’s electromagnetic vibration on the ride comfort of EV driven by in-wheel motors is studied. The ride comfort performance of quarter-car and full car is simulated and analyzed under the combined excitation of the road roughness and theelectromagnetic force of hub motor. The simulation results show that the electromagnetic force of the wheel motor has a negative effect on the ride comfort of the vehicle. The above research on the dynamic characteristics provides the theoretical basis and direction for study on the vibration control strategy of EV driven by in-wheel motors.(4)The fuzzy reasoning model based on single input rule modules(ab. SIRMs) is applied to the semi-active suspension control strategy. Firstly, the fuzzy control algorithm of semi-active suspension of quarter-car based SIRMs is studied. The simulation results show that compared with the passive suspension and classical fuzzy controller, the fuzzy control strategy based on SIRMs has better control on vibration of the vehicle body, which is more effective and easy to conduct. Then the control strategy is popularized to vibration control of whole EV driven by in-wheel motors. In view of the structure features four independent driving EV with in-wheel motor, and making analysis on the principle of vehicle vibration, two kinds of controllers for whole vehicle vibration are designed, which one is fuzzy controller based on classical fuzzy control strategy and the other is double loop fuzzy controller based on SIRMs fuzzy control strategy, then dynamic simulation of whole vehicle vibration system under the different operating conditions is conducted. The simulation results show that compared with the passive suspension and classical fuzzy controller, double loop fuzzy controller based on SIRMs can restrain the body vibration evidently, and improve the ride comfort effectively in the premise of ensuring the safety of driving, its comprehensive performance is better, and has better adaptability and robustness to the changes of driving condition.