Stochastic Process Phase-plane Analysis And Control For Vehicle Stability

Frequent vehicle traffic accidents have become one of the major hidden dangers threatening human life safety.Therefore,the research on vehicle stability technology that helps to improve driving safety is one of the key research directions in the field of vehicles.In the past,the vehicle ideal model is often used in vehicle stability research,assuming that the vehicle parameters will not change when the vehicle is driving.However,in the actual driving of vehicles,under the influence of uncertain factors such as complex traffic environment,driving conditions and manufacturing process errors,vehicle parameters will change indefinitely,especially tire parameters.When the tire parameters are uncertain,it will make it difficult to accurately estimate the tire mechanical characteristics,and the vehicle characteristics will be randomly distributed in a certain range.Under extreme working conditions,when there is randomness in tire parameters,the traditional stability controller may cause the vehicle to cross the critical stable state,resulting in instability,which can not ensure the driving safety of the vehicle.In order to solve this problem,a stability control scheme considering the randomness of tire parameters and stability boundary is proposed to improve the safety of vehicles.Firstly,the generalized chaotic polynomial method is used to mathematically express the randomness of tire parameters,establish the random tire model and 14 degree of freedom vehicle model,and analyze the influence of the randomness of vehicle parameters on the driving stability of the whole vehicle;Secondly,the effects of vehicle speed _xV,front wheel angle?,friction coefficient?and the randomness of tire parameters on the stable boundary of?-?phase plane are analyzed,and the stable boundary band considering the randomness of tire parameters is obtained.The stability index is designed according to the position of vehicle state relative to the boundary band on the phase diagram and the motion trend of vehicle state;Then,based on the stability index and model predictive control structure,a stability controller is designed to track the expected state of the two degree of freedom vehicle model and limit the tire slip rate,so as to improve the driving stability of the vehicle under extreme conditions;Finally,the simulation results show that the proposed vehicle stability control algorithm has good robustness to the uncertainty of tire parameters and can enhance the driving stability of vehicles with parameter randomness under extreme conditions.The specific research contents are as follows:（1）The uncertain expression of tire parameters and the establishment of random tire model.The random distribution characteristics of tire parameters are obtained by analyzing the test data of High-speed Tire test-bed and rubber friction test-bed;Based on the generalized chaotic polynomial theory,the mathematical expressions of the uncertainty of friction coefficient and cornering stiffness are obtained,which are introduced into the Uni Tire tire model to establish a random tire model considering the randomness of parameters;The simulation results show that the randomness of tire parameters will lead to the uncertainty of tire mechanical properties,especially when the tire works in the nonlinear region,the distribution range of tire force randomness is wide.（2）Vehicle stability analysis considering parameter randomness.Based on the stochastic Uni Tire tire model,a 14 DOF vehicle model considering the randomness of tire parameters is established to simulate the state randomness of the vehicle under different limit conditions;The simulation results show that the relevant indicators used to characterize vehicle stability are also randomly distributed in a certain range.It can be seen that the randomness of tire mechanical characteristics will eventually appear in the performance of the whole vehicle,and the vehicle in critical stability under extreme conditions may lose stability.（3）Phase plane stability analysis.The?-?phase plane is drawn by using the Uni Tire tire model and the nonlinear two degree of freedom vehicle model.The influence of the randomness of front wheel angle,vehicle speed,friction coefficient and tire parameters on the stability region boundary of?-?phase plane is analyzed,and the stability boundary transition zone of phase plane is proposed.Based on this,the stability margin index of vehicle driving is designed.（4）Vehicle stability control.Based on the phase diagram stability boundary transition zone and model predictive control structure,the stability control algorithm is designed to improve the robustness of vehicle stability to the randomness of tire parameters and improve vehicle driving safety.The simulation results show that the vehicle stability control algorithm considering the randomness of parameters proposed in this paper can enhance the driving stability of vehicles under extreme conditions,while ignoring the randomness of parameters may lead to the vehicle from critical state to unstable state,and the driving safety of vehicles cannot be guaranteed.