Effective Test Procedures for Evaluating Force Characteristics of Magneto-Rheological Dampers

Abstract

This paper will provide a new test procedure for determining the force characteristics of magneto rheological (MR) dampers that are commonly used for vehicle suspensions. Force characteristics of a damper, in this case, refers to establishing the amount of force that the damper can provide at different relative velocities across the two ends of the damper, Force characteristics of a damper, which are commonly presented as a plot of force versus relative velocity—commonly known as force-velocity curve—are established in a shock (or damper) dynamometer in which one end of the damper is kept fixed and the other end is moved in a cyclical manner at a prescribed displacement and frequency. The peak damper force at each velocity is measured and plotted as discrete data points versus relative velocity across the damper. This is a well-understood and commonly used procedure for passive shock absorbers or dampers. For magneto rheological dampers, however, our study shows that such procedures do not necessarily provide an accurate assessment of the force characteristics of MR dampers in all damping conditions. The damping condition of MR dampers can be changed by a small amount of electrical current that can be provided to the damper. The inaccuracies are mainly due to the changing dynamics of the MR fluid inside the damper at different damping conditions. This paper will provide the test results for a MR damper, using the new and the conventional test procedures. The test results indicate that the use of the new test procedure will procedure will allow for an accurate representation of the MR damper force at all velocities, within the range of the currents that the damper is designed for.