Control Bifurcations in a Nonlinear Active Suspension System for System Design

Nonlinear active suspension systems are very popular in the automotive applications. They include nonlinear stiffness and nonlinear damping elements. One of the types of damping element is a magneto-rheological fluid based damper which is receiving increased attention in the applications to the automotive suspension systems. Latest trends in suspension systems also include electronically controlled systems which provide advanced system performance and integration with various processes to improve vehicle ride comfort, handling and stability. A control bifurcation of a nonlinear system typically occurs when its linear approximation loses stabilizability. These control bifurcations are different from the classical bifurcation where qualitative stability of the equilibrium point changes. Any nonlinear control system can also exhibit control bifurcations. In this paper, control bifurcations of the nonlinear active suspension system, modeled as a two degree of freedom system, are analyzed. It is shown that the system looses stability via Hopf bifurcation. Parametric control bifurcation analysis is conducted and results presented to highlight the significance of the design of control system for nonlinear active suspension system. A framework for the design of feedback using the parametric analysis for the control bifurcations is proposed and illustrated for the nonlinear active suspension system.