Analysis of Hopf Bifurcation of Steering Wheel Shimmy of Automobile

It proves that steering wheel shimmy is a vibration of stable limit cycle occurring after Hopf bifurcation, which is elaborated by nonlinear dynamics theory, and the control objectives of shimmy are proposed according to its bifurcation properties. Numerical analysis of bifurcation characteristics has been conducted with a nonlinear shimmy model whose parameters come from a domestic automobile with independent suspension. The results indicate that when the speed reaches 49.98Km/h, supercritical Hopf bifurcation occurs to the system and stable limit cycle appears, i.e. wheels oscillate around the kingpin at the same amplitude; when the speed comes to 76.30 Km/h, Hopf bifurcation occurs again and limit cycle disappears. The bifurcation speed and amplitude of limit cycle match the shimmy speed and amplitude measured from road experiments very well, which confirms the conclusions that shimmy is a vibration of stable limit cycle occurring after Hopf bifurcation at critical speed.

THE COHERENCE RESONANCE IN VAN DER POL SYSTEM INDUCED BY NOISE RECYCLING

The phenomenon of coherence resonance (CR) in a delayed noisy Van der Pol system with supercritical Hopf bifurcation, which is influenced by a recycled noise, is numerically studied. Different from the traditional CR theory, in this paper, the characteristics of CR is affected by the time delay in the input noise. Namely, the CR is weakened or enhanced by the time delay feedback. Moreover, we find that several characteristics of this particular system vary periodically and its period has some certain relation with the natural frequency. By using the results given by the paper, we can control the noise-induced motion by modulating the time delay in noise.