# Development of a Magnetorheological Damper with Self-Powered Ability for Washing Machines
## 2 Configuration and Operating Principles  
MR dampers typically operate in three modes: shear, flow, and mixed modes (the combination of the first two modes). The flow and mixed modes of MR dampers can provide high damping because of the pressure generated in the lower and upper chambers. However, they are more complicated and have higher cost than the shear-mode due to a large amount of MR fluid used in the chambers. It is noteworthy that washing machines do not require a so high damping force, but the zero-field friction force needs to be as small as possible to suppress the force transmissibility at high frequencies. Consequently, the shear-mode is implemented in our study. The schematic of the proposed self-powered MR damper in shear-mode is shown in Figure 2. As shown in the figure, the shaft of damper moves reciprocally due to the vibration of washing machines, developing damping force via direct shearing of the MR fluid. With this configuration, the interaction of the magnetic field between the damping and energy-harvesting parts could be diminished.  
Compared with conventional MR dampers, the self-powered shear-mode MR damper is able to adapt itself based on the mechanical energy produced from its working process via an energy-harvesting  
Figure 2: Schematic of the proposed self-powered shear-mode magnetorheological (MR) damper.  
vibration absorber. In general, the self-powered MR damper consists of two main components: the MR damping part and the energy-harvesting one. The MR damping part is composed of an inner housing with a thin wall, on which the exciting coils are wound directly, and an outer housing for covering and creating a closed magnetic circuit of the damper. The MR fluid is fully injected into the gap between the shaft and inner housing. The cross-section area of the thin wall is built to be as small as possible for a quick magnetic saturation of the flux lines. As a result, the magnetic flux is compelled to move across the MR fluid gap. In addition, appropriate chamfers are added to the cross-section of the coils to maximize this magnetic flux. When a magnetic field is applied, the solidification of the MR fluid occurs, and the damping force is produced from the friction between the housing and the shaft. In some researches, the MR damper could be designed with more exciting coils to improve the damping effectiveness. However, this lengthens the damper, which may not satisfy the installation space in washing machines. Furthermore, the more coils are used, the more exciting powers are demanded, which leads to high heat emission and more maintenance cost. Considering the above problems, the design with two exciting coils is proposed for the MR damping part.  
The energy-harvesting (EH) part consists of magnetized permanent magnets and pole spacers alternately fastened together on the moving shaft and a slotted stator core covered by an outer housing. In this paper, the linear multipole type is proposed for the configuration of the EH part. One magnet and one adjacent pole spacer are grouped into one pole pair. The magnets are ring-shaped and possess axial magnetization; thus, they are placed in cross-pole positions to force the flux going through the spacers and across the air gap. The inducing coils are wound directly on the slots of the stator core and connected to the exciting coils of the damping part. Under linear excitations caused by the vibration of washing machines, the relative movement between the magnets mounted on the shaft end and the stator core appears. This results in an induced electric power supplied to the MR damping part.