Magnetorheological fluid damper dynamics: models and measurements

Abstract

Many efforts to understand the response of magnetorheological (MR) fluid dampers have been undertaken in the past several years. Such components are of great interest for use in automotive suspension and safety systems, as well as in aerospace and civil applications. Physically sensible models that contain realistic descriptions of fluid flow would be of great utility in optimizing the performance of these dampers. While simple models based on the familiar Bingham plastic MR fluid constitutive relation capture many of the key features of the steady-state damper response, including the existence of a magnetic-field-dependent 'yield force' and the reduction of the damping coefficient at high velocities, such models do not describe the more complex velocity dependence and dynamic response of the force observed in real dampers. Unfortunately, experimental data on viscometric flows of MR fluids at the high shear rates encountered in MR dampers are scarce. Moreover, a number of sophisticated damper models are available, but many use mathematical constructs that are not easily understood in terms of physical phenomena. Motivated by these challenges, we have measured the response of two automotive MR shock absorbers and developed a lumped-parameter model to describe their dynamic response. Using the parameters provided by this model, we have also compared the measured damper response with that predicted by simple models of magnetic flux and fluid flow in these components.