Research On Vehicle Emergency Collision Avoidance Control Based On Estimation Of Road Adhesion Coefficient

With the birth of the world's first vehicle,traffic safety has become an eternal topic.In order to further improve road traffic safety and help drivers to reduce erroneous operations,intelligent vehicle safety technology as Advanced Driver Assistance Systems(ADAS)has gradually been paid attention and developed in recent years.The existing vehicle active collision avoidance control system mainly adopts collision avoidance control by means of braking,which can effectively improve the driving safety of vehicle.Studies have shown that collision avoidance by steering control is more advantageous than using braking system in high-speed emergency conditions.To solve the problem of collision avoidance control based on steering system,a hierarchical control scheme is mainly adopted at present.The reference trajectory is dynamically planned on the basis of a high level path planning module according to external environment and vehicle states information.The lower path tracking moduleis used to track the planned trajectory.In the design of the high-level controller,a simple vehicle model(such as point-mass vehicle model)is usually used for path planning,and a longer prediction horizon is always set.In the lower layer,a higher fidelity vehicle model and a shorter prediction horizon are used for path tracking.However,due to the neglect of the non-linear characteristics of vehicle dynamics and the variation of road parameters(road adhesion coefficient,etc.)in the high level path planning,the collision avoidance control effect may be unsatisfactory under emergency conditions.To solve the above problems,in this paper an emergency collision avoidance control system is designed based on model predictive control.In order to reduce the computational burden of the algorithm,the trajectory of collision avoidance is optimized based on vehicle model in spatial domain.In addition,obstacles and road boundaries are translated into spatial constraints on system states.In order to enhance the driving safety of vehicle,an objective function considering tire adhesion margin is introduced in the path tracking controller.Meanwhile,the dynamic constraints of vehicle lateral acceleration,sideslip angle,and tire slip angle are designed according to tire-road adhesion coefficient.In addition,considering the obvious difference of pneumatic trail under different road conditions,adhesion coefficient,in order to accurately obtain tire-road adhesion coefficient,an estimator of tireroad adhesion coefficient is designedbased on the relationship between pneumatic trail and road adhesion coefficient.Finally,in order to verify the control effect of collision avoidance control system,simulation experiments are conducted based on the joint simulation platform of MATLAB/Simulink and CarSim.Simulation results show that the hierarchical vehicle emergency collision avoidance control system designed in this paper has good collision avoidance performance and robustness.