Nonlinear Behaviors of a Half-Car Magneto- Rheological Suspension System Under Harmonic Road Excitation

Magneto-rheological (MR) suspension systems offer meritorious potential for realizing an effective compromise between driving comfort and handling performance. The inherent hysteresis nonlinearity of a magneto-rheological damper (MRD), however, may lead to unpredictable and complex dynamic behavior of the vehicle system. In this study, a pitch-plane half-car model comprising MR suspension with hysteresis nonlinearities was formulated to investigate its dynamic responses as a function of the driving speed. The dynamic stability of the vehicle model was investigated under harmonic excitations through Lyapunov exponents to globally illustrate strong dependencies on the excitation frequency and amplitude. The influences of driving speed, and excitation amplitude and frequency on the nonlinear response characteristics were analyzed through bifurcation diagrams, phase portraits and Poincaré maps. The dynamic evolution of periodic motion to chaotic motion was illustrated through Hopf, saddle node and period-doubling bifurcations, respectively, under low-, mid- and high-speeds. Moreover, the hyperchaotic oscillation of the system was observed for the first time. The results show that the nonlinear response behavior of the half-car MR suspension is mostly concentrated in the medium frequency range for low- as well mid-speeds, which is concerned with ride comfort performance of the vehicle. The results obtained in the study provide essential basis for further investigations on effective controller synthesis and stability analyses of more practical higher order models of vehicles with MR suspension.