Lane-keeping benefits of practical rear axle steer

Abstract

The classic two-degree-of-freedom yaw-plane or 'bicycle' vehicle model is augmented with two additional states to describe lane-keeping behaviour and further augmented with an additional control input to steer the rear axle. A simple driver model is hypothesised where the driver closes a loop on a projected lateral lane position. The driver can select the preview distance to compensate driver/vehicle dynamics, consistent with the 'cross-over' model found in the literature. A rear axle steer control law is found to be a function of the front axle steering input and vehicle speed that exhibits stability similar to a positive-real system, while at the same time improving the ability of the driver/vehicle system to track a complex curved lane and improving steady-state manoeuvrability. The theoretically derived control law bears similarity to practical embodiments allowing a deeper understanding of the functional value of steering a rear axle.

Directional Dynamics of Steering the Third Axle

“…(4) (5) In the lane maintenance mode the longitudinal velocity is the same constant value in both the body fixed and inertially fixed reference frames as seen in (4). Lateral velocity in the inertially fixed frame is a function of the constant forward velocity and state variables, and is the derivative of lateral displacement Y with respect to time.…”

“…Currently electronically controlled rear axle steering systems are offered on European production commercial vehicles that fully counter-steer at low speeds, and remain at their nominal center positions at higher vehicle speeds [4]. It has also been shown that steering the rear axle of a vehicle can improve high-speed lanekeeping [5], although for a three-axle vehicle this high speed benefit would come at the expense of increased tire wear. Qu and Zu describe theoretical opportunities to improve the handling of three-axle vehicles [6].…”

Automated steering controller design for vehicle lane keeping combining linear active disturbance rejection control and quantitative feedback theory

“…A steering controller was developed to control the steering of both front and rear axles simultaneously. 3 Rear axle steering is beneficial to lane keeping but is not a practical solution in most vehicles. A steering control approach based on linear matrix inequality and bilinear matrix inequality was proposed to constrain the vehicle states within the prescribed limits.…”