ON THE EXTENSION OF THE GRATZMULLER CRITICAL VELOCITY FOR LOCKED STEERING ROAD VEHICLE TO THE CASE OF PILOTED VEHICLE

SUMMARY

This study deals with the stability of a vehicle/pilot system in which the pilot mathematical model is derived from a single-loop general model and is characterized by a set of four parameters involving a loop gain constant K, a phase-lead time Ta, a pure time delay τ, and a neuromuscular lag-time constant Tr. The vehicle model consist of a two degrees of freedom model in yaw ψ and lateral displacement y. The properties of the coupled system are then studied and the existence of a maximum control velocity u as a function of the pilot longitudinal visibility L is demonstrated. This velocity is seen to be independant of the pilot interaction parameter and may serve as a safety criterion for a given vehicle.

Finally, the effect of the stiffness of the rear and front tires upon the critical velocity is evaluated and it is shown that as the visibility L becomes infinite, this velocity expression coincides with the one proposed by Gratzmuller in the context of a fixed steering road vehicle.