Research On Active Steering Control Strategy Of Steering-by-wire System

The SBW system removes the mechanical connection between steering wheel and steering front wheel,has variable transmission ratio characteristic and capable of activing steering control based on the state of vehicle.SBW system has important research significance for improving vehicles’ maneuverability and stability.In this paper,the active steering control of SBW system is researched.Firstly,using Matlab/Simulink and CarSim software as tools,the SBW vehicle simulation platform was established.The angle step input and double lane change test were selected for simulation verification.Simulation results showed that the established SBW vehicle model has better angular following characteristics and can accurately describe the movement state of the vehicle.Secondly,the influence of vehicle speed and road adhesion coefficient on vehicle transient steering characteristics was analyzed.Based on the constant of steady yaw rate gain,variable angle transmission ratio of SBW system under different adhesion coefficient was designed.The double lane change and steady steer test condition were selected for simulation tests.The results showed that SBW vehicle with variable angle transmission ratio has good handling stability and maneuverability on different adhesion coefficient road.Thirdly,the linear regression relationship between adhesion coefficient and slip rate was established.The regression coefficient K was identified by RLS algorithm,and the estimated value of the road adhesion coefficient was obtained according to the K of identification.In order to verify the accuracy of the estimation model,the linear acceleration test was selected.The results showed that the RLS estimation algorithm has high estimation accuracy for high or low adhesion coefficient road.Based on the 4-DOF vehicle dynamic model,vehicle state observer based on EKF algorithm was designed to estimate the tire lateral force and the side slip angle.In order to verify the accuracy of the observer,continuous sinusoidal steering test conditions was selected and verified by simulation.The results show that the established observer has high estimation accuracy either on high or low adhesion coefficient road surfaces,and has good robustness to the change of vehicle speed.Finally,Considering the nonlinearity and time-varying of vehicle system,a method based on linear time-varying model predictive control was proposed.On the basis of considering the stability of the vehicle yaw,lateral and roll directions,yaw rate,side slip angle and rollover index were selected as control targets.A switching control scheme including 4 control modes was designed for lateral stability.In order to verify the control effect of the switching controller,a simulation experiment on extreme conditions was performed.The results showed that the switching controller can limit the control target to a stable range.By adding the front wheel rotation angle,the vehicle can be prevented from rollover under high speed,sharp-turning conditions.But,the additional rotation angle reduces the front-wheel rotation angle and the turning radius increased,which prevents the vehicle from avoiding obstacles when avoiding obstacles.