Analysis and control for ideal variable transmission ratio characteristics of active front wheel steering

The change law of ideal transmission ratio with vehicle speed and hand-wheel angle is studied based on constant gain of steady-state vehicle system. It is used to resolve the conflict between steering sensitivity at the low-speed segment and steering stability at the high-speed segment for the traditional vehicle. For preventing the sudden change of hand-wheel torque caused by the transmission ratio change, the ideal variable transmission ratio (VTR) law is fitted by the improved S-type function and optimised by particle swarm optimisation (PSO) algorithm. For improving driving stability of vehicle, the stability control strategy based on linear quadratic regulator (LQR) is studied based on the optimised ideal variable transmission ratio control law. The front wheel angle is decided by the vehicle stability control strategy, and then the active front wheel steering (AFS) motor angle is obtained by the AFS calculation module to realise the AFS control. The closed-loop driver-vehicle system is established. This system includes driver model, the vehicle dynamic model, AFS model and so on. The results indicate that the performance of the proposed controller is good in the front wheel steering angle control for the better tracking to desired vehicle state.