Straight running stability of automobiles: experiments with a driving simulator

The stability of the straight ahead running motion of automobiles is studied with proper theoretical tools pertaining to bifurcation theory. The study is both theoretical and experimental. Four theoretical models have been employed. They refer, respectively, to one simple car model, one simple driver model, one complex car model and one complex driver model. The existence of bifurcations, namely Hopf bifurcations, is found for both the simple car/simple driver model combination and for the complex car/complex driver model combination. The experimental study refers to the employment of a driving simulator in which a human driver controls the complex car model. At the driving simulator, bifurcations are found which correspond to the ones predicted either with the simple car/simple driver model combination or the complex car/complex driver model combination. At the driving simulator a chaotic motion is found, after a subcritical Hopf bifurcation has occurred. Apparently, for the first time in the sector of vehicle system dynamics, the actual existence of bifurcations and chaos has been shown for a real system with a human driver in-the-loop. The driving simulator does not seem introducing factors affecting sensibly bifurcations, so the bifurcations that have been found appear to be real, i.e. bifurcations could be found in an actual car running straight ahead.