Nonlinear Dynamic Analysis of a Skyhook-Based Semi-Active Suspension System With Magneto-Rheological Damper

Response characteristics of a magneto-rheological suspension with a modified skyhook control scheme, focusing directly on the command current, were analyzed considering hysteresis nonlinearities. Suspension performance and its dynamic stability were investigated under harmonic excitation at frequencies up to 50 Hz to illustrate highly nonlinear influences of the excitation frequency and magnitude. The nonlinear response characteristics of the system, attributed to damper hysteresis and on-off control, were thoroughly analyzed considering the bifurcation diagrams, Lyapunov exponent spectra, phase portraits, and the Poincare maps. These, invariably, showed the presence of quasi-periodic, multiperiodic, and chaotic responses of the system under mid- as well as high-frequency excitations. The conducted electromagnetic interference (EMI) due to high frequency variations in the drive current, caused by the nonlinear system responses, was further evaluated using the method described in EN 55022 for the first time. The assessments using the GB9254 guidelines showed that the EMI levels exceed the recommended limits. The chaos-induced EMI may thus be detrimental to the electronic control systems of the automobile and cannot be ignored. This work is considered to serve as a theoretical foundation for future studies on EMI reduction and nonlinear control of intelligent semi-active suspensions.