Driver oriented path following in ITS: wide speed-range steering control by multiple look-ahead distances

This paper presents a method for realizing a driver compatible steering system for ITS. The method aims to maintain smoothness of the steering system in path following tasks, at not only high speeds but also at mid to low speeds where tighter turns become involved. Generally large corrections by the steering becomes necessary at low speeds, which is due to the natural characteristic that the vehicle´s lateral response to the steering decreases at lower speeds. To solve such issues, multiple look-ahead points, one for recognizing the deviation from the path for feedback control and the other for predicting the future steering angle for feed-forward control, is introduced. They are varied in a manner that the look-ahead distance for feed-forward is initially further than the look-ahead distance for feedback at low speed, and shortens as the speed increases. The look-ahead distance for the feedback acts the vice-versa. The method was implemented on an experimental vehicle and path following experiments involving various turns, in a wide spread-range were conducted. Results show steering smoothness is maintained whilst minimizing the influence on path following error.