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Certain multiply-articulated truck combinations are known to exhibit lightly damped trailer yaw motions in response to rapid inputs of steering. This paper clarifies the yaw response phenomenon and illustrates this characteristic for ten vehicle combinations which are currently in use in the U.S. The phenomenon of interest is described in terms of the “amplification” in lateral acceleration level experienced at the rear-most trailer of the combination with respect to the lateral acceleration level achieved at the truck or tractor. Results from two types of computerized simulation are presented; one representing a linear treatment of the vehicle and producing frequency response characteristics, and the other representing a rather complete nonlinear treatment of the vehicle and producing time history responses in an emergency obstacle-avoidance maneuver.

A class of heavy truck vehicles, characterized primarily by high centers of gravity, was studied using analysis and computer simulation to identify and understand the relationship between directional and roll stability of such vehicles during steady turning maneuvers. Findings of the computer-based study suggest: (1) directional instability (yaw divergence) is possible for such vehicles during steady turning while operating at elevated speeds on horizontal road surfaces, (2) yaw divergence will lead to rollover in the absence of corrective steering action and/or reduced speed, and (3) the primary mechanism responsible for precipitating yaw divergent behavior in such vehicles is the nonlinear sensitivity of truck tire cornering stiffness to vertical load acting in combination with typical heavy truck fore/aft roll stiffness distributions. In addition, the influences of roadway superelevation and driver steering control as contributors to vehicle stabilization are examined and discussed.