Research On Steering Stability Control Of Four-wheel Independent Drive Electric Vehicle

In order to cope with the impact of the rapid increase in car ownership on environmental pollution,energy crisis and traffic congestion,the state actively promotes the rapid development of the new energy automobile industry.Four-wheel independent driving of electric vehicles will be a hot spot in the future development of automobiles.The powertrain of the four-wheel independent drive electric vehicle is based on the design of the hub motor,which is different from the new electric vehicle power actuator of the traditional automobile;it is a driving method that integrates components such as power and transmission into an electric wheel,and removes a large number of mechanical components.The vehicle structure is simplified,which is conducive to the development of lightweight vehicles,while reducing the mechanical transmission to improve energy efficiency and thus save energy to a certain extent.However,it also brings many technical problems to the four-wheel independent driving electric vehicle,especially the control of vehicle handling stability,which has a significant impact on the safe driving of the vehicle.Because this article mainly studies the stability of four-wheeled single-drive electric vehicles under the steering conditions,it needs to analyze not only its system dynamics,but also some key operating state parameters.Accurate model building and analysis,as well as the use of low-cost,high-precision soft-measurement methods to observe vehicle driving state parameters.When the vehicle is driving under the steering condition,the slip or slip phenomenon will inevitably occur.Therefore,the adhesion coefficient of the road surface cannot be approximated by the adhesion rate of the wheel,which is not conducive to the distribution of the wheel torque.The road surface adhesion coefficient under the condition of optimal slip ratio is used as the standard parameter of the road surface adhesion constraint in the torque distribution.At the same time,the vehicle is subjected to lateral excitation from the road surface during the vehicle's steering.It is easy to produce unstable yaw moment.Therefore,according to the four-wheeled single-drive electric vehicle,the torque of each wheel is independently controllable,and the torque distribution optimization control of the vehicle's direct yaw moment is performed to suppress the vehicle side deviation.Wait for an unstable state.This article,the state and stability control characteristics of the four-wheel independent drive electric vehicle during the steering process are studied.The following research work is mainly carried out:(1)Taking the four-wheel independent driving electric vehicle as the research object,the vehicle model is set up in the Carsim software by means of parametric modeling,and the theoretical analysis of the body dynamics and wheel dynamics is carried out separately,and in MATLAB/Simulink.In the tire and motor model,the accuracy and effectiveness of the model are demonstrated,and the corresponding state equation is established.(2)In the process of driving,in order to cope with the negative impact of different road surface attachment conditions on the stability of the vehicle,it is necessary to estimate the adhesion coefficient of the wheel on the road,mainly to make the wheel at the optimal slip rate.The fuzzy control is used to estimate the road surface adhesion coefficient under the condition that the wheel is at the optimal slip rate,and this is used as the constraint condition for the optimal distribution of the vehicle yaw moment,and the established vehicle stability control strategy can achieve the best effect.(3)Extended Kalman Filter(EKF)can be used to linearize the nonlinear system,and the vehicle's centroid angle and horizontal and vertical vehicle speed are observed and estimated.(4)In order to control the direct yaw moment of the vehicle and formulate the corresponding control strategy,the upper and lower layers are used,and the upper controller uses the fuzzy sliding mode control strategy to solve the additional yaw moment required to control the stability of the vehicle.In the lower controller,the minimum longitudinal force utilization of the vehicle is taken as the objective function,and under the constraint conditions of the wheel drive motor and the road surface adhesion,the wheel torque is optimally distributed by the weighted least squares method.(5)Using Carsim software to carry out parametric modeling of the four-wheel independent drive electric vehicle,and build a control model in MATLAB/Simulink to realize the joint vehicle control model by Casim and MATLAB/Simulink.Finally,in order to verify the effectiveness of the wheel torque optimization distribution control,the NI/PXI platform is combined with the software and hardware for testing.The test results prove that the control strategy proposed in this paper has a good control effect on the stability of the vehicle.