Abstract

The suspension springs and dampers, employed in road vehicles, typically exhibit nonlinear and asymmetric force-deflection and force-velocity characteristics. The asymmetric characteristics of the suspension components are characterized to investigate the phenomenon of drift in dynamic equilibrium, also known as the 'ride height drift'. A quarter-vehicle model, incorporating nonlinear and asymmetric suspension components, is mathematically modeled and simulated using 'simulink'. Suspension damper is represented by multistage nonlinear asymmetric characteristics, while the stiffness is treated as a nonlinear cubical spring, asymmetric in compression and rebound. The model results are validated by comparing the responses over a wide frequency range with the published data. A comprehensive parametric study is performed to establish the influence of variation in design and operating parameters of suspension components on 'ride height drifting' phenomenon. The study clearly reveals that the 'ride height drifting' phenomenon is a direct result of asymmetric properties of the suspension damper. The magnitude of the drift increases with an increase in asymmetry as well as amplitude of excitation, and it approaches maximum corresponding to the wheel hop natural frequency. Reduced damping with a fixed asymmetry also tends to increase the magnitude of drift over the entire frequency range. The results further suggest that, the suspension spring with hardening and softening characteristics in compression and extension, respectively, yields the sprung mass drift in the opposite direction. Suspension springs with asymmetric characteristics may thus reduce the magnitude of the sprung mass drift.