On the Lateral Stability and Control of the Automobile as Influenced by the Dynamics of the Steering System

Measurements of the directional response of an automobile to torque inputs applied at the steering wheel are compared with predictions yielded by a five-degree-of-freedom model of a four-wheeled, pneumatic-tired vehicle. This comparison demonstrates that the directional control and stability of the “free-control” automobile is satisfactorily characterized by the addition of a quasilinear representation of a steering system (i.e., a mechanism having two degrees of freedom with Coulomb friction introduced as the single nonlinear element) to a linear three-degree-of-freedom representation of the “fixed-control” automobile. Use is made of the experimentally substantiated five-degree-of-freedom mathematical model to study the relationship between automotive design parameters and the response and stability in each of the four natural modes of motion that exist for the free-control vehicle.