On The Steering Condition Torque Optimal Allocation Of Four Wheel Independent Drive Electric Vehicles

With the rapid development of auto industry and the vehicle ownership increased,the traffic safety problem is increasingly serious.The electric vehicle's research and the vehicle safety of stability control become the focus of attention all over the world.Electric vehicle has high efficiency and lower energy,low noise,zero emissions and other outstanding advantages.Meanwhile electric vehicle uses hub motor driver,which can realize each wheel independent control,precise measurement generated torque and obtain fast torque response.These advantages make the vehicle motion control method is more flexible,help to enhance the vehicle active safety performance.The four-wheel independent drive electric vehicle steering conditions of vehicle stability control and torque allocation problem is studied in this thesis,mainly research on the following several aspects:1.Based on the four-wheel independent drive electric vehicle as the research object,we establish the vehicle dynamics model.The vehicle body dynamics model,wheel dynamics model,tire model and motor model are set up respectively.On the lateral movement,the classic 2-d model has been used and established the corresponding state equation.These works provide a theoretical basis for the controller design of the rest of the article.2.The sideslip angle is not convenient to directly measure by sensor,so this paper adopts the square-root unscented kalman filter algorithm to estimate it.Meanwhile the least square method is adopted to estimate the tire cornering stiffness by using the estimated sideslip angle.By building the Car Sim associated with Simulink simulation model,the experimental results verify the validity of the estimation algorithm.3.In this thesis,the lateral stability of the controller adopts the hierarchical control structure.The upper controller calculates the yawing moment which maintain the vehicle stability.The tire longitudinal force control is used in the lower controller to optimize the torque allocation,guarantee the desired vehicle yawing moment and the vehicle's safety and stability.Among them,the upper controller select yawing angular velocity and sideslip angle as control variable.Then a sliding mode controller is designed to get the vehicle yaw moment demand.4.The lower controller is designed to optimize the vehicle torque allocation in this thesis.According to the desired yawing moment,the weighted least squares method is adopted to get each wheel's optimized allocation torque under the actuators and the friction oval constraint conditions.The Car Sim associated with Simulink simulation experiments verify that the proposed control strategy and the optimized torque allocation algorithm are effective.