Coordinated Steering And Braking Control In High Speed Vehicles For Emergency Collision Avoidance

The automobile brings convenience and quickness to people,and its driving safety has become a global social issue.Automobile emergency avoidance system can save the driver's life in an emergency by actively intervene in vehicles to avoid obstacles.It has a good market prospects.At present,most products are concentrated in the longitudinal collision avoidance of low middle speed.However,when the speed is higher than 45km/h,it is more effective to avoid obstacles with the combination of steering and braking.Under the support of the Jilin Province Science and Technology Found for Young Scholars “redundant drive vehicle dynamics control allocation method”,this paper focuses on the path real time planning and tracking control problem of autonomous avoidance when obstacles suddenly appear at high speed.At first,the required control and simulation models are established.The models are nonlinear two degree of freedom vehicle model,linear two degree of freedom vehicle model,point vehicle model and CarSim vehicle model.They are used to design the nonlinear model predictive path tracking controller,linear time-varying model predictive path tracking controller,path replanning controller and high accuracy simulation model.Path planning is the premise and basis of path tracking.For the path planning problem of high speed emergency avoidance system,this paper adopts a method based on S function to make preliminary planning.On this basis,based on the model prediction theory,combined with the state of vehicle movement and real-time environmental factors to replanning the initial planning path.A high-speed emergency avoidance path planning method based on model predictive control is designed to obtain the desired path of vehicle emergency avoidance control.The lower path tracking controller based on linear model prediction is designed.A multi-objective optimization function is designed to optimize the front wheel angle and additional yaw moment.The linear model based path tracking controller is difficult to track in extreme conditions because it ignores the nonlinear characteristics of the vehicle system.For this reason,based on the model predictive control theory,a path tracking controller considering the nonlinear characteristics of vehicles is designed,and two solutions are proposed:(1)Path tracking control based on linear time-varying model predictive control;(2)Path tracking control based on nonlinear model predictive control.The simulation results show that the nonlinear model predictive controller has better path tracking performance and stronger robustness under extreme conditions.