A Study of the Closed-Loop Directional Stability of Various Commercial Vehicle Configurations

Abstract

Computer analysis of the closed-loop directional stability of four common commercial vehicle configurations was performed using 1) a disturbance input technique to study low lateral acceleration driving conditions, and 2) a lane-change maneuver for studying system response at elevated lateral acceleration conditions. The results of the disturbance input calculations indicated, that under low lateral acceleration conditions, drivers of different commercial vehicle configurations should be capable of providing adequate control compensation to achieve more or less equal stability margins for most systems. Evaluation of directional stability, based upon the transient lane-change maneuver, indicated systematic reduction in system damping for all vehicles with increased levels of lateral acceleration. The 5-axle tractor-semitrailer system exhibited the greatest level of directional damping and rollover immunity during the lane-change maneuver. The truck full-trailer was the least damped system while also producing rollover occurrences for the least lateral lane-change displacement. Use of the disturbance input test, as employed here, is not applicable for examining the total system stability of vehicle configurations employing single pintle-hook (or "A—dolly") hitching arrangements and which also exhibit rearward amplification tendancies. Train units rearward of such hitching mechanisms lie outside the closed-loop control structure of the driver. Recommendations for improving the closed-loop control structure of these systems are offered.