Research On Direct Yaw Moment Control Strategy Of Vehicle With In-Wheel Motors

Increasing attention is paid to the research and application of electric vehicle（EV）due to its advantages of energy conservation and environmental protection.With simple structure and flexible control mode,vehicle with electric motored wheels（EMW）lays foundation for advanced control algorithms aiming at improving vehicle performance.Because of the differences on structure,vehicle stability control modes vary from traditional vehicles to EMW vehicle,it is necessary to study the stability control issue of EMW vehicles.8 degrees of freedom（DOFs）EMW vehicle model and nonlinear tire model are built.Hierarchical structure of Direct Yaw Moment Control（DYC）system is discussed,and a control framework consisting of upper and lower levels is applied: the upper is motion track level,calculating the required generlized control with Model Predictive Control（MPC）theory;the lower is torque distribution level,distributing the generalized control to each wheel using the strategy of optimal allocation.Upper controller of DYC system is designed based on MPC theory through the description of the control problem: the maximum additional yawing moment which can be generated by the driving system severs as the input constraint of the controller.Considering the road adhesion coefficient,the maximum safe side slip angel β_max and ideal yaw velocity γ_d are calculated.β_max is the output constraint,the additional yaw moment required to make the predicted value of yaw velocity in the predicted horizon as close as possible to the given expected value is calculated in real time.The different effect caused by driving/braking force applied to each wheel is analyzed.Different yawing moment distribution methods are formulated according to different working conditions such as oversteer and understeer.Combined with the wheel slip rate PID control,the strategy aiming at reducing the motor output torque by the means of controling the wheels with high control efficiency preferentially is put forword.The upper and lower control algorithms are simulated and verified.Based on the equal distribution,the effectiveness of the upper motion tracking control algorithm is verified by the simulation experiment of front wheel step and sinusoidal input in different road conditions.On that basis,a joint simulation of motion track level and the distribution level aiming at reducing the energy consumption is conducted.Compared with equal and proportional distribution between front and rear axles,the distribution strategy formulated in the paper can reduce the energy consumption of driving motors in the control process effectively,improving the vehicle handling stability and path tracking ability significantly,the effectiveness of the DYC strategy proposed in this paper is verified.