Flux Angle Mapping Coaxial Magnetic Gears for High Gear Ratios

Abstract

Magnetic gears use noncontact operation to achieve the same function as mechanical gears but benefit from a variety of potential advantages due to their noncontact power transfer. This paper proposes a new topology of coaxial magnetic gear that utilizes flux angle mapping (FAM). The ferromagnetic pieces (FPs) in the FAM magnetic gear are designed to map flux from any given electromagnetic angle in the inner airgap to the same electromagnetic angle in the outer airgap. The gear ratio is derived based on this mapping function. Using finite element analysis (FEA), the performance of the new topology is investigated by changing the shape, size and number of FPs. Additionally, the performance of the new topology is compared against a conventional coaxial magnetic gear at high gear ratios (≥ 40:1). Based on the FEA results, the proposed FAM CMG can obtain higher gravimetric torque densities (GTDs) than the conventional gear at high gear ratios. For example, at a gear ratio of 80, the FAM gear achieves about 250% as much GTD as the conventional gear. The FAM gear can be designed with symmetry to balance the magnetic forces on each rotor; however, this comes at the cost of reduced gear ratio.