Research On Lateral Stability Control Of Distributed Drive Electric Vehicle Based On STI Tire Model

Distributed drive electric vehicle directly installs the drive motor in or near the drive wheel.It not only has the outstanding advantages of short drive chain,high transmission efficiency and compact structure,but also can independently control the driving and braking torque of each wheel,which brings great advantages and convenience for vehicle lateral stability control.The tire is the only part of the vehicle contacting with the road,and its mechanical characteristics show obvious nonlinear dynamic characteristics in the process of vehicle lateral stability control.The longitudinal force and lateral force of the tire are coupled and restricted each other.How to realize the lateral stability control of distributed drive electric vehicle based on the mathematical model which can accurately reflect the nonlinear mechanical characteristics of the tire Research is of great significance.Based on the STI tire model,this paper accurately describes the coupling relationship between the longitudinal force and lateral force of the tire,and then introduces the nonlinear control and optimal allocation theory to study the lateral stability control of the distributed drive electric vehicle,in order to provide theoretical and technical support for improving the lateral stability control performance of the vehicle.Firstly,the parameter fitting of STI tire model is completed based on the test data.The test data come from the nonlinear tire mechanical properties test,and the test conditions include the compound working conditions of tire longitudinal slip,sideslip and roll,which can completely cover the mechanical properties of tire nonlinear region.Based on the multi-dimensional experimental data,the data preprocessing process is completed.The saturation function parameters in the formula are fitted by Origin software,and the fitting effect analysis and accuracy verification are further completed.Secondly,based on the STI tire model,a 7-DOF vehicle dynamic model is built.The seven degree of freedom model includes vehicle longitudinal,lateral,yaw motion and four-wheel rotation.The longitudinal force of STI tire model is input into the vehicle model through the four-wheel wheel dynamics model,and then affects the vehicle driving attitude.Based on the seven degree of freedom model,CarSim is further used to build a distributed electric vehicle dynamics model,which provides a simulation platform for the design and verification of vehicle stability control system.When building the CarSim vehicle model,the internal tire model is replaced by the self-defined STI tire model,and the input form of wheel torque is modified in the power system to establish a complete distributed driving co-simulation platform.Thirdly,a lateral stability control strategy based on nonsingular fast terminal sliding mode and trust region interior point method is designed.A new type of terminal attractor and sliding surface are designed based on the nonsingular terminal sliding mode algorithm in the upper control strategy.Combined with the tire longitudinal and transverse forces calculated by STI tire model in real time,the direct yaw moment required to maintain vehicle lateral stability is calculated.The trust region interior point method is used as the longitudinal force distribution method in the lower level distribution,which makes the combination of longitudinal forces meet the direct yaw moment and ensure the stability of vehicle driving attitude.Through the design of double line shifting and sinusoidal steering simulation conditions,to verify the accuracy and effectiveness of the control strategy.Finally,in order to further improve the adaptability and robustness of the control system,a distributed lateral stability control system based on adaptive nonsingular fast terminal sliding mode control and robust least square assignment is designed.In the upper control strategy,the parameter adaptive equivalent control law is designed by analyzing the system uncertainty to improve the nonsingular fast terminal sliding mode control law.Aiming at the problem of system uncertainty allocation,the uncertain allocation matrix is introduced based on the least square allocation process,and the same simulation conditions are adopted.The results show that the control effect is further improved.