Study On Handling Stability Analysis And Control For 8 In-Wheel Motor Drive Vehicle

All-Electric Combat Vehicle(AECV) is a hot issue in the research of military vehicle, and the in-wheel motor drive technology is an important development tendency of AECV. For armoured wheeled vehicle, whose driving conditions are always complex and varied, handling stability is crucial for improving safety under the extreme driving conditions. The in-wheel motor-driven system exploits performance potential of AECV with technology innovation. On the other hand, the in-wheel motor-driven system changes vehicle parameters and provides more actuators, significant changes on vehicle dynamics characteristics and control are resulted. It is necessary to research the handling stability for the AECV with in-wheel motor-driven system.Based on the research project of in-wheel motor drive technology in an 8-wheeled vehicle, the handling stability characteristics of the 8-wheeled vehicle with in-wheel motor-driven system are analyzed, the handling stability control strategy is studied, and off-line simulations and real-time simulations are used to verify the proposed control strategy.A full vehicle model with 23 degrees of freedom(DOF), including 6DOF for body, 1DOF for steering, 8DOF for tires vertical hopping and 8DOF for wheels rolling, and driver lateral model, is established for the research of stability control strategy. The precision of the full vehicle model is experimentally validated to reflect vehicle dynamics characteristics.The influences of in-wheel motor-driven system on the vehicle handling stability are analyzed in different perspectives. The response characteristics, including stable and transient characteristics, to the steering angle input are analyzed based on the linear 2DOF model. Further more, the steering angle is taken as a state variable, and the response characteristics to the steering torque input are analyzed based on the linear 3DOF model. In addition, the trajactory following performance of driver-vehicle system is investigated based on the ‘preview optimal lateral acceleration’ driver model. The results demonstrate that the in-wheel motor-driven system deteriorates vehicle stability on the high speed condition, which indicates that the handling stability control is crucial under the extreme driving conditions.Based on the direct yaw-moment control(DYC), a handling stability control strategy with hierachical structure is proposed, where the vehicle motion control with uncertainty and nonlinearity is directly taken into consideration within the superstratum controller, while the torque allocation problem with constraints is taken into consideration within the substratum controller. The superstratum controller, based on the sliding mode control method, calculates the forces and moment generated by lengthways tire forces to control vehicle motion stability. The controlled motion state variables include longitudinal velocity, side slip angle and yaw rate. The simulation results demonstrate that the proposed superstratum controller can significantly improve vehicle handling stability under the extreme conditions.The substratum controller is designed using the optimization-based control allocation method. The issue on the torque allocation based on the objective forces and moment is concluded as a constrained optimization problem. The optimization-based control allocation equation with adjustable weighted coefficients for motor torque allocation is established, where, the weighted coefficients can be adjusted based on the side slip angle and motor fault signal. The control allocation equation is formulated as a quadratic programming problem and solved using the active set algorithm to achieve the optimal torque allocation on motors and brakes. The results demonstrate that the substratum controller efficiently enhances vehicle stability margin. What’s more, the controller can reconstruct the allocation equation to guarantee vehicle stability when some motors fail.A real-time test platform is built based on dSPACE real-time system, and the real-time performance of the proposed control strategy is verified through driver maneuver input. The results show that the proposed handling stability control strategy can efficiently improve vehicle stability on different limit conditions with good real-time performance.