Optimal Stability Control Of Electric Vehicle Considering Uncertainty Of Cornering Stiffness

In daily life,with the widespread use of the automobile,its pollution effect on the environment and its stability performance has been the focus of many scholars,and the research on the optimal control of vehicle stability with electric vehicle as the research object has attracted much attention.The electric vehicle with four in-wheel motors can be operated independently without transmission device,which improves the vehicle power performance and driving safety performance.Therefore,according to the above analysis,this paper chooses the electric vehicle with four in-wheel motors as the control target.In the process of driving,the change of driving state make the vehicle structure parameters change accordingly.The tire cornering stiffness is the key parameter used to describe the tire lateral force,it changes according to a series of factors such as current tire sideslip angle,tire pressure,vertical load and road friction coefficient,so it has uncertainty.When the tire cornering stiffness is set as a constant value,there is a error with the actual engineering phenomenon.The force between the tire and the ground is the key factor affecting the handling stability of the vehicle.According to the driving dynamics analysis,with the increase of the sideslip angle,the side force of the tire increases to a certain extent and then reaches saturation,this is easy to lead to traffic accidents.Therefore,in this paper,the following research is carried out in the stability optimization control of electric vehicle considering the uncertainty of cornering stiffness:Firstly,the overall structure of the electric vehicle with four in-wheel motors selected in this paper is described.The two degree of freedom vehicle model is selected as the reference model.Considering the road adhesion coefficient,the state reference value is calculated according to the driving dynamics reference model.At the same time,the motor torque tracking model considering the maximum output torque of the motor and the wheel dynamics model are built.Secondly,in the process of building tire cornering stiffness fitting model,the low adhesion road conditions are selected,and the tire pressure is ignored.The tire sideslip angle change and vertical load transfer are selected as the main influencing factors.The least square method and moving least square method are used to establish the fitting model of cornering stiffness,and the fitting effect is compared.In the design of the stability control system,the layered structure is adopted.The model predictive control algorithm is selected in the high-level controller,and the time-varying tire cornering stiffness is added to the control model.In order to avoid sideslip,the constraints of tire sideslip angle of the front and rear axles are derived by vehicle dynamics,and controlled it in a small range to improve the handling performance.The lower controller is the torque optimal distribution controller,which is to optimize the distribution of the desired yaw moment to the four wheels,select the quadratic programming algorithm,and the tire utilization is selected as the optimization objective to solve the four wheel torques under the constraints.Finally,a joint simulation platform is built by using CarSim and MATLAB / Simulink,and simulation experiments are carried out under different working conditions.The accuracy of the tire cornering stiffness fitting model proposed in this paper is verified,as well as the restraint effect of sideslip angle and the tracking effect of state reference value in the design process of electric vehicle stability controller considering the uncertainty of tire cornering stiffness.