Vehicle Stability Analysis And Control Considering Tire Parameter Uncertainty

Considering the dynamic characteristics of the vehicle,it is likely for the vehicle to lose its stability under the limit conditions of low friction coefficient,high speed,large angle,side slip and longitudinal slip.As the only part of the vehicle that is in contact with the ground,the mechanical characteristics of the tire play an important role in the performance of the vehicle.However,under the influence of environmental changes,manufacturing errors and the limitations of measurement technology,all kinds of tire parameters are uncertain,and some dynamic performance of tire is difficult to be accurately estimated,which is not good for the stability analysis of vehicles under extreme conditions.The purpose of this paper is to consider the uncertainty of tire parameters,establish a stochastic tire mechanics model for vehicle dynamics research,analyze the vehicle stability performance under the influence of uncertain factors,and propose a yaw moment control method to maintain the vehicle stability under the critical condition with probability of instability.In the aspect of the random expression of tire parameters,polynomial chaos is used to express the random distribution of tire friction coefficient and sideslip stiffness.In the aspect of vehicle stability analysis,the stochastic phase plane is established to obtain vehicle stability performance through region division.In the aspect of vehicle control,the concept of instability degree is put forward,which is used for the weight distribution of two LQR controllers to make the vehicle with probability instability return to stable state.The main research contents and conclusions are as follows:(1)Expression of stochastic tire parameter: with imitating the uncertain factors in tire test,and analyzing the random distribution of friction coefficient and tire cornering stiffness,the results show that the randomness of friction coefficient is normal distribution,and the randomness of cornering stiffness is uniform distribution;the randomness expression of two parameters based on polynomial chaos principle is done.(2)Tire stochastic mechanical characteristics modeling and vehicle performance simulation: Based on the Uni Tire tire model and polynomial chaos method,tire stochastic mechanical model is established.Simulation shows that tire stochastic mechanical characteristics are in band distribution in a certain range,and the distribution band of linear area is narrower than that of nonlinear area,which is closer to the performance under certain conditions;The 14 DOF model of vehicle is established,and the simulation results show that the vehicle stability index is also in band distribution,and the vehicle in critical stable condition has a certain probability of instability.(3)Stability analysis in phase plane: With randomness considered into phase plane analysis,a stochastic phase plane method is proposed to analyze the vehicle stability under the influence of uncertainty.The stable region is divided,and the vehicle stability boundary becomes a stable boundary band.The vehicle is unstable after it across the boundary band external line,the vehicle is stable after it across boundary belt internal line,and the vehicle has a probability of instability when it is in the area of the boundary band.(4)Vehicle stability control: Based on the stochastic phase plane stability boundary band,the concept of instability degree is proposed to express the probability of vehicle instability with uncertainness.Two LQR controllers based on stability region and instability region are designed,and the weight is distributed through the instability degree.Simulation results show that the stability of critical stable vehicle is guaranteed under the influence of uncertainty.