Research On Active Collision Avoidance Control Strategy Of Vehicle Based On Electronically Controlled Power-Assisted Braking System

Automobile intelligent technology has driven the development of autonomous vehicles and provides effective and feasible solutions for traffic safety.Autonomous vehicles have put forward new requirements for the chassis braking system,which requires active braking functions and high dynamic pressure building ability,thereby shortening the braking distance and improving safety performance.The electronically controlled power-assisted braking system can meet this demand due to its stable active braking function,and can better realize the collision avoidance function,so it can be used as an active braking actuator for active collision avoidance.Active collision avoidance is an integral part of the intelligent technology of autonomous vehicles,including longitudinal active collision avoidance and transverse active collision avoidance.Compared with longitudinal active collision avoidance,it has greater advantages in collision avoidance under the conditions of high speed,low adhesion road surface and low overlap rate.Therefore,from the perspective of improving vehicle safety performance,it is of great significance to study the vehicle’s active collision avoidance control strategy on the basis of the electronically controlled power-assisted braking system.This paper relies on the national key research and development plan “Multi-System Efficient Integration of In-wheel Motor Action Module and Vehicle Torque Vector Distribution Technology”(Project Number:2021YFB2500703)and Jilin Province Science and Technology Development Plan Projects “Research on decision-making and control of automatic lane change of electric vehicle with X-by-Wire chassis”(No.:20230101121JC).On the basis of the domestic and foreign research status of active braking actuators,collision risk assessment and decision-making,longitudinal active collision avoidance control and transverse active collision avoidance,this paper develops the vehicle active collision avoidance control strategy based on electronically controlled power-assisted braking system.Research specifically includes active pressure multi-level control of electronically controlled power-assisted braking system,active collision avoidance decision algorithm,and longitudinal and transverse active collision avoidance control.The following aspects are mainly included.(1)Modeling and control of electronically controlled power-assisted braking system.Firstly,the principle analysis of the electronically controlled power-assisted braking system is carried out;then,the mathematical modeling of the electronically controlled power-assisted braking system is carried out,including the model of permanent magnet synchronous motor,the model of deceleration and torque increasing and force coupling mechanism,and the model of hydraulic system,and simultaneously the model is simulated and verified;finally,design an active pressure multi-level control strategy based on the electronically controlled power-assisted braking system,including: feedforward decoupling current control strategy,first-order nonlinear active disturbance rejection control speed control strategy,and position control strategy based on speed compensation and active pressure control strategy.And test and verify the control strategy.Therefore,it lays the foundation for the design of the longitudinal active collision avoidance control algorithm,and makes the electronically controlled power-assisted braking system cooperate with the longitudinal active collision avoidance control.(2)Research and establishment of active collision avoidance decision algorithm.Firstly,the longitudinal collision avoidance safety distance model is established to determine the expected safety distance for car following collision avoidance and the minimum safety distance for longitudinal emergency braking collision avoidance;Then,the trajectory planning of emergency steering collision avoidance is combined with the transverse collision avoidance constraints including vehicle dynamics and road surface adhesion characteristics,and the five polynomial trajectories of emergency steering collision avoidance and the critical longitudinal safety distance of steering collision avoidance under different states of the target obstacle ahead are obtained.Finally,the decision mechanism between following vehicle collision avoidance and emergency collision avoidance and between longitudinal emergency braking collision avoidance and transverse emergency steering collision avoidance is analyzed by considering the front vehicle motion state,front vehicle width,road surface adhesion coefficient and selfvehicle speed to make decisions on longitudinal and transverse active collision avoidance.(3)Design of longitudinal active collision avoidance control strategy.Using the idea of layered control,firstly,a longitudinal acceleration control strategy of feedforward and feedback is designed as the lower layer controller for longitudinal active collision avoidance;Secondly,aiming at the car-following collision avoidance mode,a discrete car-following kinematics model considering the acceleration disturbance of the preceding vehicle is established,and the followability,safety,comfort and economic indicators of the vehicle are constrained and optimized based on the model predictive control theory.Based on fuzzy control,the variable weight coefficients are used to adaptively adjust the weights of inter-vehicle distance error,relative speed,and self-vehicle acceleration in the objective function,and the desired acceleration for collision avoidance is obtained;Then,for the emergency braking collision avoidance mode,in order to match the electronically controlled power-assisted braking system pressure limit response characteristics,the transition processing process is designed using the tracking differentiator for the expected step deceleration;Finally,Car Sim and MATLAB/Simulink co-simulation test platform is built to test and verify the longitudinal acceleration control strategy,while typical carfollowing collision avoidance and emergency braking collision avoidance test conditions are selected to test and verify the longitudinal following collision avoidance control strategy and emergency braking collision avoidance algorithm by combining with active collision avoidance decision mechanism.(4)Design of transverse active collision avoidance control strategy.Aiming at the situation that the longitudinal emergency braking cannot avoid the collision in the active collision avoidance and the planned transverse collision avoidance trajectory,combined with the active collision avoidance decision algorithm,a model predictive control trajectory tracking controller is designed.First,a simplified three-degree-freedom vehicle transverse dynamics model is established and linearized using the state trajectory method;Then,considering the requirements of transverse collision avoidance control,design an objective function that considers the accuracy of collision avoidance trajectory tracking control,the smooth transition characteristics of actuators,and the size of energy consumption,and takes the boundary limit of collision avoidance output and the execution ability of actuators as constraints;finally,select The vehicle in front is stationary and at a constant speed.In each state,three groups of working conditions with different road adhesion coefficients and widths of the vehicle in front are selected to verify the designed trajectory tracking controller for emergency steering collision avoidance.