An Electrodynamic/Magnetorheological Clutch Powered by Permanent Magnets

This paper presents an electrodynamic/magnetorheological fluid (MRF)-based clutch activated using permanent magnets (PMs) attached to one shaft. During the electro-mechanical transient phase, when the two clutch shafts rotate at different speed, the 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 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 considers the B-H curve of the nonlinear materials (e.g., MRF, PMs, and ferromagnetic materials) and the movement of the different parts. Finally, in order to verify the finite element method model, some experimental measurements are performed on a prototype.