ABSTRACT
The paper deals with the bifurcation analysis of a validated simple model describing a vehicle+driver running straight ahead. The mechanical model of the car has two degrees of freedom and the related equations of motion contain the nonlinear tyre characteristics. The driver is described by a non linear model. Bifurcation analysis is adopted for characterizing straight ahead motion at different speeds for different drivers. A non linear sensitivity analysis is performed as function of driver’s parameters. A wealth of unreferenced bifurcations is discovered both for the understeering and for the oversteering vehicle. For the understeering vehicle, a supercritical Hopf bifurcation may occur as forward speed is increased. Also tangent (fold) bifurcations occur as the speed (or disturbance) are further increased. For the oversteering vehicle a subcritical Hopf bifurcation occurs as the speed reaches a critical value. The prevision distance (a driver’s control parameter) plays a fundamental role in straight ahead driving. Bot too short or too long prevision distances are negative for straight ahead running. Overtaking maneuvers, when the prevision distance is forced to be too short, may cause a stable limit cycle which is related with the driver stress during such manoeuvers.
