Research On Direct-yaw-moment Control Method For Four-wheel-independent-driven Electric Vehicles

China’s total number of motor vehicles and drivers has ranked first in the world,and car travel has become the main mode of travel for residents.With the rising car ownership,it also brings a series of challenges such as environmental pollution,energy shortage and traffic problems,and people are increasingly concerned about the environmental protection and safety of vehicle travel.This paper focuses on the direct-yaw-moment control method according to the characteristics of four-wheel independent drive electric vehicles,and the main research work of this paper is divided into four aspects as follows:1.In this paper,we design a seven-degree-of-freedom vehicle model including an electric vehicle body dynamics model,a wheel dynamics model,a tire model,an electric motor model and a driver model for the dynamics of four-wheel independent drive electric vehicles during steering,and provide a basic model for vehicle state estimation and environment sensing as well as direct-yaw-moment controller design.2.Tire lateral deflection stiffness,longitudinal vehicle speed,yaw rate,and vehicle cg sideslip angle are important parameters to ensure lateral maneuvering stability of a vehicle.In this paper,a recursive least squares method with forgetting factor is applied to estimate the front tire lateral deflection stiffness and rear tire lateral deflection stiffness,and an extended Kalman filter-based vehicle state observer is designed to estimate the longitudinal vehicle speed,yaw rate,and vehicle cg sideslip angle.3.The vehicle direct-yaw-moment control system can effectively improve the maneuvering stability during extreme speed cornering and emergency avoidance.In this paper,a direct-yaw-moment control system including a reference model,a DYC(Direct Yaw Moment Control)controller and a torque distribution is built.The reference model is designed by applying the two-degree-of-freedom vehicle model,and the torque distribution is carried out by using the optimal distribution strategy,focusing on the design of the DYC controller with different control algorithms.In this paper,four different direct-yaw-moment control systems are built using PID control,fuzzy control,sliding mode control based on the angular velocity of the transverse pendulum,and sliding mode control based on the vehicle cg sideslip angle for DYC controller design.Simulation tests are conducted to simulate the serpentine working condition,and the simulation results show that the designed control system effectively improves the lateral stability of the vehicle.4.In order to verify the effectiveness of the control strategy more comprehensively,this paper applies Carsim and Matlab/Simulink to build a joint simulation platform for simulation verification.The double-shift line working conditions with different vehicle speeds and low friction coefficients are selected to simulate and verify the direct-yaw-moment control strategy proposed in this paper through comprehensive comparative analysis,i.e.,the vehicle direct-yaw-moment control system based on the design of sliding mode controller for the vehicle cg sideslip angle,and the simulation experimental results show that the control strategy designed in this paper can effectively ensure the lateral safety stability of the vehicle.