MR grease application to a controllable clutch system

Magneto-Rheological (MR) grease has been applied to a controllable clutch system, and its performance was investigated experimentally. MR fluid is known as a functional fluid whose yield shear stress can be controlled reversibly by the applied magnetic field strength. But its peculiar characteristics may change as time passes because of sedimentation of dispersed iron particles. To overcome this defect, grease has been adopted as a carrier fluid of particles. Three-dimensional structure of thickener developed in grease is expected to prevent iron particles from settling out. In this paper, a controllable clutch system was designed and constructed to investigate the performance of MR grease clutch system. It was shown experimentally that the transmitted torque could be controlled quite smoothly by the applied electric current to the coil equipped inside of clutch system, and the response time was estimated about 0.12 s at the fastest. However, the transmit torque decreases as time passes because of the effect of temperature rise. To stabilize the output torque, the electric current to coil was controlled by a simple feedback control system.