Research On Coordinated Control Of Electro-Hydraulic ESC And Active Front Steering For Distributed-Electric-Driven Vehicles

The distributed electric vehicles are regarded as an important direction in the future with the rapid development of vehicles.Moreover,powered by the electrification of vehicles,By-wire technologies have also made great progress.This paper,taking the distributed electric vehicles as the research object and realizing the lateral stability control as the research purpose,has explored the vehicle stability control with coordinations of electro-hydraulic ESC and active front steering.First of all,based on the expressions of 6 DOF dynamics deduced,the nonlinear7 DOF model of the distributed electric vehicle is established,including the vehicle body model,the motor model and the estimations of wheel vertical loads,slip rates and side-slip angles.In addition,the nonlinear magic formula tire model is introduced and analyzed in detail on single and combined working conditions.In order to verify the model accuracy,the model built on Simulink is compared to the Carsim model on the conditions of wheel steering step and sinusoidal inputs,the results show that the model built is precise relatively and meet the requirements.Then,Based on the hierarchical control structure designed,the upper related theories of vehicle stability control are introduced,including the design of nominal control variables,identification of vehicle stability,judgment of vehicle steering status and so on,in which the estimations of vehicle state and road adhesion coefficient have been studied deeply.The integral method,linear Kalman state observer and extended Kalman state observer for the estimation of side-slip angle are introduced,in which a novel variable structure method is proposed based on extended Kalman filter.A damping term and a feedback term are added to the lateral vehicle dynamics,fully balancing the reliability between the sensor data and the model.The simulation results show that the variable structure extended Kalman filter proposed in this paper has the highest estimation accuracy compared to the other two methods.Finally,the coordinated control strategy of electro-hydraulic ESC and active front steering is lucubrated roundly.According to the fact that each motor of the vehicle is controllable independently,the optimal distribution of longitudinal force on each wheel is carried out using the quadratic optimization principle.After comparing the influence of hydraulic and motor intervention on vehicle stability,a reasonable electro-hydraulic ESC strategy is established.Besides,the paper,pays close attention on the coordinated control algorithm between additional yaw moment and active front steering angle,and designs the corresponding controllers on the basis of Linear Quadratic Regulator and Optimal Guaranteed Cost Control theory,where a novel algorithm including not only a feedback part but also a feedforward part is proposed which compensates the control delay properly caused by the phase difference between the nominal and actual control variables.Then,a Hardware-In-the-Loop platfrom is built based on NI-PXI equipment,The test results show that the novel coordinated algorithm proposed is proved to be superior to Linear Quadratic Regulator while the proposed strategy of electro-hydraulic ESC and active front steering can ensure the vehicle stability,which has applicable prospects in the future.