Design of Steering Controller of Automated Driving Bus

In this paper, steering control methods of automated driving bus using Real-time kinematic GPS for localization are proposed. Firstly, root locus method indicates considering transfer lag from a steering motor to front tires is needed to explain unstable movement of the actual vehicle. Experimental results show that the transfer lag from the tire angle to the handle angle is approximately expressed as the second-order delay system. Secondly, the method and experimental results show that yaw angle and lateral position feedback with look-ahead model is more stable than that without it or single lateral position feedback control. Thirdly, the root locus method explains that feedback gains tuned through vehicle experiments are reasonable because using those gains make a vehicle's motion more stable and highly responsive. Finally, it is necessary to consider nonlinearity near zero point of steering angle when the vehicle velocity is high since steering angle needed for lane keeping becomes lower.