Oscillatory Behavior of Understeering Vehicles

Oscillations in understeering vehicles are occasionally described in the literature, primarily in terms of the poles of the yaw rate response, but perhaps not completely appreciated in their complexity. This work shows that as speeds of the understeering vehicle increase, the increasingly underdamped poles of the yaw rate transfer function combine with the effects of a low frequency zero and a reduced steady-state response to result in oscillations greater than would be expected from eigenvalues alone. A speed range for acceptable yaw rate response is suggested, and it is shown that a typical understeering passenger car operates within this range. As the understeering vehicle’s speed increases beyond this range, the high speed limit of the oscillation frequency is found.