Research On Steering Control Method Of Wheel-side-driven Electric Vehicle

In recent years, electric vehicle is considered to be the inevitable developmenttrend of the future automobile due to their high energy efficiency, low environmentalpollution and other advantages. The wheel-side-driven electric vehicle is designed bythe characteristics of the car itself, which is composed of separate driving motor andsteering motor beside each active wheel. Through steering-by-wire (SBW), wire signalsfrom upper controller directly manipulate the wheels’ turning. Because the driving andsteering control method of wheel-side-driven system is different from the traditionalfuel vehicle, harmonious relationship between the two front wheels can not directlyimplement, and therefore most traditional vehicle’s steering control strategies are notsuited. So there is a certain significance and value to do research on the steering controlmethod of the wheel-side-driven electric vehicles.First, for the steering system used in wheel-side-driven electric vehicle, thesteering actuator model and wheel model are set up based on dynamic analysis in thispaper. Simplify the steering actuator model on the principle of SBW, and based on theAckermann-Jeantand ideal steering model, the steering angles and rotate speeds needmeet the geometry constraint equations, corresponding to the two control objectives ofthis article, corner coordinate control and electronic differential control.The constraint problem of two wheel angles is a class of multi-object coordinationcontrol. Considering the mutual influence between the two wheels, put the control goalson the contouring error between the two control objectives, a cross-coupled controller isdesigned. First, design a lower controller to make a single wheel to achieve the desiredinstruction steering location, using the PD control strategy and in order to compensatethe nonlinear disturbance, using BP neural networks to estimate two wheels’ self-aligning torque, and finally got a good tracking performance. The higher controller isbased on the analysis of system contouring error and designed in use of cross-coupledcontrol strategy and PID control. The simulation under different conditions is based on veDYNA, a comprehensive software for the efficient simulation of vehicle dynamics.The results show that the cross-coupled controller has an excellent control performance.In order to smooth steering, the inner and outer wheel should have a differentrotate speed, but only consider the speed control will ignore the traffic impact of thevehicle steering, and may lead to a sliding instability phenomena.Based on the differential principle, the constraint relationship of the wheel slipratio on each side is planned out according to the wheel kinematics and trafficinformation, what’s more, an electronic differential controller which use sliding modevariable structure method is designed. Through the simulation analysis in the veDYNAsoftware environment, the electronic differential controller has played a significant role.Chattering problem in sliding mode variable structure controller makes the controlleroutput torque shocked. Set a boundary layer according to quasi-sliding mode methodsuccessfully weaken the chattering, and finally we reach a satisfactory control effect.