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       The induction motor system for driving pumps is need to have the variable speed function for the energy saving instead of throttling the discharge control valve. In general, the motor inverters are used to control the induction motor speed, but the inverter system for high-power induction motors to drive large-scale pumps is very expensive. Therefore, the other variable speed control systems substituted for the motor inverter are expected to control the rotational speed of the relatively large-scale pumps.
       In this study, the clutch using a magneto-rheological (MR) fluid is proposed to use as a shaft coupling installed between the induction motor and the pump. The MR fluid clutch generates the magnetic field-dependent transmitting torque under both coupling and sliding modes, because the MR fluid behaves like a Bingham fluid having variable yield stress with magnetic field. Because of this inherent feature, the use of the MR fluid clutch as the shaft coupling device will be suitable for controlling the rotational speed of the pumps. The multi-disk type MR fluid clutch of 400 Nm class has been designed and developed with the help of an electromagnetic field analysis software for the use of the vertical shaft type axial flow pump of 350 mm bore (shaft power: 75 kW). The developed multi-disk type MR fluid clutch has a cylindrical shape of f384 mm in outer diameter and 110 mm in height, and has 2 driving and 3 follower disks of 1.6 mm thickness fixed to the driving and follower rotational parts, respectively. The MR fluid (MRF-132DG, Lord Co.) is filled in the 6 gaps of 1.0 mm between the disks, and a magnetic exciting coil (wire dia.: f1.0 mm, turns: 894) is arranged in the outer casing outside of the multi-disks. The fundamental performances of the developed MR fluid clutch have been investigated, and the clutch has been implemented as the shaft coupling device to a practical vertical shaft type axial pump system and has been practically used and tested. 
        It is found that the developed MR fluid clutch is capable of generating the magnetic-field dependent transmitting torque up to 400 Nm for a coil current of 2.3 A as designed, featuring high controllability of the transmitting torque. In the practical test using the vertical shaft type axial pumping system, the MR fluid clutch worked to control the rotational speed of the pump depending on the applied current under both coupling and sliding modes, resulting in the change of the discharge flow rate and the pumping head.
 

Magneto-Rheological (MR) Fluid, MR Clutch, Shaft Coupling, Axial Pump, Variable Speed