An Electrodynamic/Magnetorheological Clutch Powered by Permanent Magnets

This paper presents an electrodynamic/magnetorheological fluid-based clutch activated using permanent magnets attached to one shaft. During the electromechanical transient phase, when the two clutch shafts rotate at different speed, the Permanent Magnets (PMs) induce eddy currents on some conductive materials strategically placed in the system. The interaction between these currents and the magnetic induction produces an electromagnetic torque which is added to that of the Magneto-Rheological Fluid (MRF), helping the clutch engagement in the start up phase when an extra torque is necessary to overcome possible static frictions. Once the two shafts have reached the same speed, the eddy currents (and consequently the electromagnetic torque) vanish and the torque transmission is assured by the MRF only. The conductive material is arranged as a copper sheet and the performance of the device is investigated. The proposed clutch is analyzed using a 3-D finite-element code which takes into account the B-H curve of the nonlinear materials (e.g. MRF, Permanent Magnets and ferromagnetic materials) and the movement of the different parts. Finally, in order to verify the FEM model, some experimental measurements are performed on a prototype.