Active Control of Front Wheel Steering Geometry Based on Nonlinear Three-Step Method

With high integration, high efficiency and high flexibility, the front wheel independent Steer-by-Wire system (SbW) is a key link between autonomous vehicles and intelligent chassis technology, and is one of the current focused research in industry and academia. In this paper, a strategy for active control of steering geometry of the Steer-by Wire independent steering system is proposed based on the nonlinear three-step method and Ackermann geometry relationship with the control goal of improving the driving stability and handling performance of the vehicle. The control strategy takes the front wheel steering angle difference and yaw moment as the control variables, and tracks the expected side slip angle and yaw rate as the control objectives. A more accurate vehicle model, and a nonlinear tire model with a reference vehicle model, is used to design the three-step controller to improve the effectiveness of the steady-state control and reduce the system error. When designing the relationship between steering wheel angle and wheel angle, the relationship between vehicle speed and steering wheel angle was considered to improve the vehicle response. After the controller design was completed, a joint simulation of an electric four-wheel drive(4WD) vehicle under multiple operating conditions was conducted based on Simulink and Carsim platforms to verify the effectiveness of the controller. The longitudinal and lateral postures of the vehicle were coordinated and controlled using a transverse moment controller and a front wheel angle controller. The results show that the nonlinear three-step controller can effectively track the desired value of the control target, maintain the stability of the vehicle, and achieve active Ackermann steering geometry control under complex operating conditions.