This paper addresses the interpretation of data obtained from transient response tests currently used to evaluate the response to steering of highway vehicles. For the random input test, calculated results from a computerized model of a passenger car are used to demonstrate that (1) coulomb friction in the steering system tends to reduce the values of yaw rate and lateral acceleration coherence functions at frequencies less than 0.5 Hz and (2) the sideslip angle “transfer function” has interesting properties related to the amplitude of the steering input.
Two phase planes, called the “angle plane” and the “curvature plane,” present results for step/ramp and sinusoidal input tests. The angle plane provides information concerning the slip angles occurring at the vehicle’s front and rear tires. The curvature plane displays both the curvature of the path of the vehicle’s center of gravity and the reciprocal of the distance from the center of gravity to the instantaneous center of rotation. Curvature plane results are used to provide a detailed summary of the response information fed back to a driver during an obstacle-avoidance maneuver.