Active four-wheel steering control of steer-by-wire vehicle for lateral stability control with uncertainty and tire saturation nonlinearity

The four-wheel steer-by-wire system can improve the high-speed lateral stability of vehicles and is the inevitable trend in the development of steer-by-wire systems. However, tire nonlinearity and system uncertainty constrain the improvement of stability performance in four-wheel steer-by-wire systems. This work proposes a segmented control method for the four-wheel steer-by-wire vehicle system. Firstly, a basic controller is designed to solve the multiple perturbations and multi-input multi-output problems. Secondly, a nonlinear controller is designed to expand the stable bandwidth under extreme conditions. Then, combining the experimental design with the response surface method, multi-objective optimisation of the parameters, such as the switching time of the segmented controller, is conducted based on an improved non-dominated sorting genetic algorithm. Finally, hardware-in-the-loop tests and real vehicle tests are carried out to verify the effect of the controller. The test results illustrate that the designed controller can ensure the vehicle effectively tracks the yaw rate and sideslip angle under nonlinear conditions.