| The research of vehicle active safety has become an important research direction of vehicle engineering.yaw stability control in active safety control can maintain the vehicle’s driving stability under the extreme conditions such as driving in high speed,emergency lane change and steering,driving in low adhesion road,etc.In the actual driving process,whether the vehicle state such as slip angle,yaw rate and road surface adhesion coefficient can be accurately estimated will affect the effect of the yaw stability control system.The selection of a suitable yaw stability control strategy is very important to the control effect.Therefore,the vehicle yaw state estimation and yaw stability control strategy have important research significance.First,based on the Newton-Euler method,the 4-DOF vehicle model based on longitudinal,lateral,yaw,and roll directions is established,and the tire slip angle,tire vertical load and other parameters are converted into tire longitudinal force,lateral force and aligning torque through the Magic Formula of tire to complete the overall construction of the vehicle model.Further build the Carsim verification model,keep the parameters in Carsim and in vehicle model consistent;construct the double-shift,fish hook and snake-shaped driving conditions;set the output port of Carsim to Matlab&Simulink,output the front wheel angle,slip angle and yaw rate.They are used as model verification comparisons to verify the accuracy of 4-DOF vehicle model,and provide a model basis for the next step of yaw state estimation and yaw stability control strategy research.Secondly,briefly describe the ideas and characteristics of Kalman filter,analyze the causes of Kalman filter divergence,and propose solutions in this article.The extended Kalman filter(EKF)and iterative extended Kalman filter(IEKF)are designed based on the nonlinear model,and the simulation estimation is carried out under the double-shift,fish hook and snake-shaped driving conditions.The simulation results show that the effect of IEKF on vehicle yaw state estimation is better than EKF.IEKF can effectively track the actual value of the state and filter noise,which can be used as an effective input for the yaw stability control system;The recursive least squares method is designed to simulate the road surface with adhesion coefficient 0.8 and 0.4.The simulation result can be used for the calculation of the proportional coefficient of weighted additional yaw moment in the research of vehicle yaw stability control strategy and the road reference for simulation verification.Finally,the structure and principle of the yaw stability control system are summarized,and the reasons for choosing slip angle and yaw rate as the control variables are put forward.Based on the linear 2-DOF vehicle model,the state expected values of slip angle and yaw rate are calculated.By analyzing the characteristics of various control strategies,fuzzy control is used as the yaw stability control strategy.Through the four parts of fuzzification,establishment of rule base,fuzzy inference and defuzzification,the fuzzy control module of mass slip angle and yaw rate is established on Matlab.The IEKF estimated value of slip angle and the yaw rate and its rate of change are used as the input of the fuzzy control module and the additional yaw moment is output through the fuzzy control module,and the proportional coefficient is established considering the influence of the road adhesion coefficient and slip angle,The weighted additional yaw moment is calculated and processed into weighted additional braking force,and the weighted additional braking force is fed back to the established vehicle model to complete the overall process of yaw stability control.Complete simulations on different road adhesion coefficients and driving conditions,and compare the effects of PID control.The simulation results show that the system that uses fuzzy control as a yaw stability control strategy is better than PID control,and fuzzy control can realize vehicle stability control. |
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