Abstract

This research investigates a new magneto–rheological (MR) damper for washing machines which can effectively replace conventional passive dampers in the field of vibration control. Against traditional MR dampers and self–powered ones, the new damper is extremely cost–effective for commercialization coming from its compact structure and self–adaptive ability to external mechanical vibration for reasonable damping without any equipment or control. By adding a layer of MR fluid (MRF) between the damper shaft and housing, the damping coefficient can be adjusted according to applied magnetic field intensity. Radial ring permanent magnets are installed on the housing and the middle shaft part is made of non–magnetic material for the inactive state of the damper. Under great vibration of washing machines, the magnetic shaft parts move into the region of MRF and magnets, which generates closed magnetic circuits. Subjected to applied magnetic fields, the MRF undergoes a transition from free flowing to semi solid, thereby experiences increases in its rheological characteristics such as yield stress and viscosity. The relative movement between the shearing shaft and the MRF in the gap is then resisted and additional damping force is produced. The higher the oscillatory amplitude is the more magnetic shaft parts contact the MRF, which results in stronger induced magnetic fields and a larger damping force to suppress the oscillation. This displacement–based damping characteristic is especially proper for vibration suppression of washing machines. In order to enhance oscillation isolation efficiency and at the same time meet criteria of assembly space, size and cost, optimization is performed for essential geometrical dimensions of the proposed damper. Then, the advantages in performance characteristics of the proposed damper are figured out from the optimization results with discussions.