Research On Vehicle Lateral Stability Control Under Extreme Conditions

The extreme conditions of a car mainly refer to the driving conditions in which the car’s motion is close to or reaches the dynamic limit due to unexpected situations,harsh environments and extreme road conditions,and it is mostly related to the lateral movement of the car.In the study of vehicle lateral stability control,it is generally believed that when the tire appears sideslip,the tire lateral force will be in the nonlinear zone,and the vehicle’s maneuverability will be greatly reduced.Therefore,in this paper,it is considered that the condition that makes the tire lateral force enter the nonlinear zone is the extreme conditions.This paper studies the lateral stability control of vehicles under extreme conditions,and designs a lateral stability control system based on Linear Time Invariant-Model Predictive Control(LTI-MPC)by using model predictive control theory.Stability controller,linear time varying model predictive controller(Linear Time Varying-Model Predictive Control,abbreviated as LTV-MPC)based on steady state prediction,and vehicle lateral stability controller considering wheel speed longitudinal disturbance.Simulation results show that the proposed control strategy can better improve the lateral stability of the vehicle.The main content specifically includes:(1)Vehicle lateral stability control based on LTI-MPCFirstly,a vehicle lateral stability controller based on LTI-MPC is designed.The controller is based on a linear two-degree-of-freedom vehicle model,ignoring the longitudinal dynamics and vertical dynamics factors,adopting a linear lateral force tire model,ignoring the nonlinear factors of the tire lateral force,so as to achieve better real-time performance.At the same time,a nonlinear model predictive controller(Nonlinear Model Predictive Control,abbreviated as NMPC)using the magic formula tire model is designed.The simulation experiment results show that the designed LTI-MPC controller has poor control effect under the conditions of high speed and low road adhesion coefficient,while the NMPC controller has better control effect.(2)Vehicle lateral stability control based on steady state predictionTo enhance the lateral stability of vehicles during extreme conditions,we propose a stability control approach that takes into account both the vehicle’s yaw and lateral stability steady-state trend.The tire model curve of the magic formula is simplified to two straight lines,which replaces the nonlinear characteristics of the tire and reduces the solution time of the controller on the premise of ensuring a good tracking effect.Tire cornering stiffness is selected based on vehicle state prediction trends.The results show that,compared with the aforementioned LTI-MPC-based controller,this method can effectively improve the tracking performance of the reference vehicle center of mass side slip angle and yaw rate,especially during extreme conditions.Additionally,the controller exhibits superior real-time performance compared to the one based on NMPC.(3)Vehicle lateral stability control considering wheel speed longitudinal disturbanceIn order to improve the accuracy of stability control of autonomous vehicles,a stability control method based on LTV-MPC considering wheel longitudinal dynamic disturbance is proposed.The controller adopts a four-wheel three-degree-of-freedom vehicle model,considers the four-wheel dynamic disturbance in the prediction model,and performs discretization and linearization on the nonlinear vehicle dynamics control system.The experimental results of variable-frequency sinusoidal conditions and double-lane-changing conditions show that the proposed vehicle lateral stability control method considering the longitudinal disturbance of wheel speed can effectively improve the lateral stability of the vehicle.