Development of a Hitch Force Observer-Based Adaptive Path-Tracking Controller for Sway Suppression in Vehicle-Trailer Systems

This paper presents a novel path-tracking controller for vehicle-trailer systems that adapts to variations in trailer specifications and loading conditions without relying on trailer-side sensors. The proposed controller determines the desired steering angle using a yaw-rate-gain adaptive scheme that estimates the steering-to-yaw dynamics of the towing vehicle in real time. To account for trailer-induced effects, a disturbance observer estimates the lateral hitch force using only the vehicle's yaw rate and speed, while incorporating real-time trailer mass estimation and rear-tire cornering-stiffness scheduling. The estimated hitch force is then used to generate a compensatory steering input that suppresses sway-induced yaw motion, which is selectively activated based on a yaw-rate safety boundary derived from phase-plane analysis and implemented through a finite-state-machine logic. Co-simulation experiments using CarMaker and MATLAB/Simulink demonstrate that the proposed controller achieves accurate and stable path tracking across diverse trailer conditions, including different payloads and driving speeds. The adaptive structure enables robust performance without prior trailer information, while the selective sway suppression strategy effectively mitigates oscillatory yaw responses without degrading path-tracking accuracy.