In this paper, a disc type, radial flow-mode magneto-rheological (MR) fluid damper comprising a permanent magnet and an electromagnet is designed, built and tested. The proposed MR fluid damper has an MR valve with which two-way controllability through cancellation or enhancement of the magnetic field is obtained. This added feature provides damping forces less than or greater than that of a passive viscous original equipment manufacturer damper. A three-dimensional electromagnetic finite element analysis has been performed to realize this unique function in the proposed design. Experimental and theoretical studies have been conducted in order to demonstrate that this new design can provide softer damping properties by cancelling the effect of the permanent magnet, while at the same time enhancing the field effect, resulting in a harder damping device. Softer and harder damping refer to decrease and increase in the damping, respectively.
This study focuses on the theoretical analysis, design, fabrication and characterization of a small Magneto-Rheological (MR) fluid damper. It can be potentially applied to a horizontal axis, front-loading washing machine. In such washing machines, although washing cycle is slow, spin cycle is much faster. During acceleration from washing cycle to spin cycle, the tub passes through its resonant speed requiring relatively high damping. On the other hand, high damping results in increased force transmission to the housing and noise at high-speed spin cycle. Controllability of the MR fluid damper allows adjustment of damping requirements for different cycles and helps to reduce the noise at high speed spin cycle while limiting the tub motion at resonance. A patented geometry of an MR valve developed by Composite and Intelligent Materials Laboratory at the University of Nevada, Reno is used as the basis of this new design to satisfy the requirements of the application. Fabricated prototype damper is characterized using harmonic displacement input. Test results are in good agreement with the theoretical predictions and design values.
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