A Computer Simulation Analysis of Safety Critical Maneuvers for Assessing Ground Vehicle Dynamic Stability

Ground vehicle dynamic stability, including spinout and rollover, is highly dependent on maneuvering conditions and the nonlinear force response characteristics of tires. Depending on vehicle configuration, unstable behavior requires high, sustained lateral acceleration, and some maneuver induced excitation of the roll and yaw mode dynamics. Dynamic instability in some vehicles can be induced by a steering reversal maneuver that involves sustained limit performance lateral acceleration. Using a validated vehicle dynamics simulation, analysis is presented to illustrate what constitutes a critical stability sensitive maneuver.

Two example test cases are used to show that a critical stability sensitive maneuver must be more severe than a single lane change. Even reaching tire saturation limits during an aggressive single lane change does not give the sustained lateral acceleration required to provoke instability conditions. One test case involves a utility vehicle that has been shown to be sensitive to rollover conditions. The second example test case involves a small sedan that has been shown to be prone to spinout due to rear biased lateral load transfer distribution. The vehicle shows a stable single lane change response but spins out when an aggressive lateral maneuver of two lane widths is attempted. Some interesting effects of four wheel steer laws applied to this vehicle are also demonstrated. The objective of these examples is to demonstrate how dependent dynamic stability is on maneuvering conditions.