Analysis and experiment both demonstrate that, in respons to a sinusoidal displacement of the handwheel, the steerable roadwheels lead the motion of the handwheel at frequencies below 2 hz. In addition, the roadwheel displacement, relative to its steady- state (i.E., Zero- frequency) value is amplified at frequencies below 2 hz. By carefully examining the transfer function which relates the roadwheel response to handwheel displacement, it can be shown, that the indicated phase lead and amplification phenomenon derives from two causes: (1) both the inertia and the damping of the roadwheel mass are essentially negligible with respect to the mass of the vehicle and other sources of damping moments.; (2) The zeros of the applicable transfer function reflectthe undamped natural frequency and damping ratio associated with the directional response to roadwheel displacement, whereas the poles reflect the higher undamped natural frequency and smaller damping ratio associated with the directional response of a motor car whose und ersteer gradient reflects the compliance of the steering mechanism.
Samenvatting