A new high-torque retarder based on combined effects of magnetorheological fluid and eddy current

In this article, a new high-torque retarder combining the effects of magnetorheological fluid and eddy current is researched. The new retarder provides a part of the braking torque generated by the shear stress of the magnetorheological fluid and an additional braking torque generated by the effect of the eddy current on the rotors. This operating concept is realized by a common magnetic excitation circuit generated by a new structure with several separated coils. The configurations and design details of the new retarder, including the structure, material selection, and magnetic circuit, are discussed. The mathematical models of braking torque caused by the magnetorheological fluid and eddy current are also derived. Then, a finite element analysis is performed to verify the magnetic field design of the new retarder. Finally, a prototype is fabricated, and the relevant parameters are tested. The experimental result shows that the new retarder provides not only a stable braking torque at low speed but also a great increment of braking torque varied with rotation speed, which effectively improves the total braking torque compared with conventional magnetorheological retarders.