| With the continuous development of the automobile industry,the traffic situation is becoming more and more severe,and people have higher and higher requirements for the safety performance of vehicles.The adhesion coefficients on both sides of the spilt-μ roads are different,and the adhesion coefficients on both sides of the road surface are quite different in rain and snow weather.When the vehicle is driving on the road surface with small adhesion coefficient,such as snow and ice,locking phenomenon will occur.When the front wheel is locked,the car will lose steering ability,and the driver cannot control the direction of the car,that is,the car loses steering controllability.When the rear wheel is locked,the vehicle slips or throws the tail,which will deviate from the direction of travel.In serious cases,the vehicle will turn around and lose stability,resulting in serious traffic accidents.When the vehicle is under emergency braking on the opposite road,the adhesion coefficient on both sides of the road is different,and the braking force on both sides of the wheel is different,and then the larger yaw moment will be generated.The body will be biased to the track with large braking force,and the tail swing phenomenon may occur in serious cases.Therefore,it is a practical topic to study the transverse and longitudinal stability of the vehicle under emergency braking on the opposite road.This paper will take the electric vehicle as the research object to analyze the horizontal and longitudinal stability control problem of the vehicle under emergency braking on the opposite road.Firstly,in order to enhance the adaptability and safety of the control strategy to dynamic road conditions,a spilt-μ roads adhesion coefficient estimation scheme based on vehicle dynamic response was proposed.In this paper,a seven-degree-of-freedom dynamic model and a Burkhardt tire model are established for the vehicle driving on the spilt-μ roads.The traceless Kalman filter(UKF)is used to estimate the adhesion coefficient on both sides of the road surface.Car Sim vehicle dynamics simulation software was used to provide vehicle and road surface information input,and the road surface adhesion coefficient estimation system was built on the MATLAB/Simulink simulation platform.The effectiveness of the estimation algorithm was verified by simulation experiments under different simulation conditions.Secondly,the control requirements of emergency braking on the spilt-μ roads surface are analyzed,and the reference model of vehicle stability controller is designed to meet the actual road conditions When the vehicle is under differential braking on the spilt-μ roads,the influence of the direct yaw moment and the different adhesion coefficients on both sides of the vehicle on the reference signal is analyzed,and the reference model conforming to the actual road conditions is designed to determine the ideal state of the vehicle side and yaw.According to the classification of braking intensity and the constraint of braking force on the ground,a reasonable expected value of acceleration is designed,and the expected value of longitudinal velocity is obtained from the relationship between acceleration and velocity.According to the adhesion coefficient of the road surface,the optimal slip rate can be obtained,and thus the desired wheel speed can be obtained.Finally,in order to prevent sideslip or tail spin of the vehicle during emergency braking on the spilt-μ roads,a horizontal and longitudinal cooperative controller based on Nonlinear Model Predictive Control(NMPC)was designed,and a seven-degree-offreedom vehicle dynamics model based on the Dugoff tire model was built.The requirements of suppressing side yaw Angle of the center of mass,tracking yaw speed,reducing slip rate and tracking expected longitudinal speed were integrated into the objective function.At the same time,considering the control constraints and state constraints of the system,the optimization problem is solved,and the optimal control law is obtained to improve the safety and maneuverability of emergency braking on the spilt-μ roads.Simulation software is used to verify the proposed horizontal and longitudinal cooperative control scheme.The experimental results show that the controller can improve the horizontal and longitudinal stability of the vehicle when braking on the spilt-μ roads,and can effectively reduce the braking distance of the vehicle. |
