Research On Coupling Dynamics Of In-wheel Motor Driving Electric Vehicles

Under the pressure of energy shortage and environment pollution, high efficiency, energy saving, environmental protection of electric vehicles has become a hot research topic in global automatic industry. In recent years, the independent drive electric vehicles based on in-wheel motor will have broad research prospects. The target vehicle has a unique structure and arrangement, cancelled the mechanical transmission device, clutch, transmission shaft and other parts, which simplifies the transmission system, reduces the weight, improves the transmission efficiency, increases effective use of space and improve the performance of vehicles through. For a new structure form of in-wheel motor driving electric vehicles(IWMDEV), it has become an important direction of the development of electric vehicles. Due to the introduction of the in-wheel motor, the unsprung mass of IWMDEV was significantly increased, which seriously affects the dynamic characteristics of the vehicle. Meanwhile, the in-wheel motor was further deteriorated by the uneven road surface excitation, which causes the change of the stator and rotor clearance. These factors eventually bring adverse effects on vehicle dynamics. Therefore, it is of great importance to study the coupling dynamics of IWMDEV.Based on the domestic and foreign correlation research results, an electric vehicle driven by two rear in-wheel motor was taken as the research object in this paper, whose vehicle nonlinear coupling dynamics model was established. The coupling dynamics of IWMDEV was analyzed under simultaneous acting of road and electromagnetic excitation. The hierarchical coordination control of Active Front Steering(AFS), Direct Yaw Moment Control(DYC), and Active Suspension System(ASS) was studied. The integrated optimization design of the structure and the controller parameters of the vehicle system are carried out. The main research contents are as follows:(1) The establishment and verification of the coupling dynamics model of IWMDEV. Considering the vehicle dynamics of the longitudinal, lateral and vertical coupling relation, a relatively complete model of 16 degree-of-freedom nonlinear dynamic was established for IWMDEV. In the process of vehicle modeling, the time domain model for road roughness excitation was established based on the lag of the front and rear wheels and the relative degree of the left and right wheels. Vehicle coupling dynamics simulation model was established by using Matlab/Simulink, whose accuracy was verified by using Adams/Car. It will build foundation for the further study of subsequent dynamic simulation and dynamic control.(2) Research on coupling dynamics of IWMDEV under simultaneous acting of road and electromagnetic excitation. Based on permanent magnet synchronous motor prototype structure, a uniform/uneven air gap length model of in-wheel motor was established. The analytical expressions were derived for the electromagnetic force of in-wheel motor by Maxwell stress tensor method. And the coupling dynamics of IWMDEV was analyzed under simultaneous acting of road and electromagnetic excitation.(3) Research on hierarchical coordination of IWMDEV. In order to eliminate the influence of coupling between the various subsystems of the vehicle on the dynamic control performance, the subsystems controller and coordinated controller were designed respectively for AFS, DYC and ASS. The specific coordination control strategy and the distribution of the weight of each subsystem were established. Compared with the single control system, the validity of hierarchical coordination control was confirmed. It provides a new idea for the hierarchical coordination control of multi-system integration.(4) Integrated optimization of mechanical structure and controller parameters of IWMDEV. Based on analysis of the system parameters influence on the dynamic indicators, the sensitivity analysis of the dynamic indicators to the stiffness and damping of suspension, the mass ratio of the body to the in-wheel motor, the mass ratio of the stator to the rotor, the stiffness ratio of the bearing to the tire and the relative displacement between the stator and the rotor were conducted by adopting the perturbation method. Based on the results of the sensitivity analysis, the structural parameters of the larger impact were chosen as the optimization variables. For vehicle dynamics system global performance of the optimal problems, an integrated optimization design of mechanical structure and coordination controller parameters based on particle swarm optimization algorithm is proposed. Compared with the coordination control and structure optimization, the results show that the integration and optimization of the system structure and the coordination controller parameters further improve the vehicle safety, ride comfort and handling stability. The research results provide reference significance for the realization of the overall optimal performance of the vehicle coupling dynamics system.