| dc.description.abstract | Like mechanical gears, magnetic gears convert power between low-speed, hightorque rotation and high-speed, low-torque rotation. This work compares various magnetic gear designs and topologies, introduces an approach for evaluating their dynamic behavior, and describes a prototype’s design, fabrication, and test results. Significant differences are illustrated between the designs minimizing cost and those minimizing volume, especially regarding the usage of permanent magnet material. Axial flux coaxial magnetic gears can outperform their radial flux counterparts at form factors with outer radii much larger than the axial length, but axial flux gears suffer from large forces on the rotors. Cycloidal magnetic gears achieve higher torque densities at high gear ratios than coaxial magnetic gears, but cycloidal magnetic gears perform worse at low gear ratios and suffer from increased mechanical complexity and large forces on the bearings. For coaxial magnetic gears, the torque density and efficiency of a single-stage reduce significantly as the gear ratio increases; however, a high gear ratio can be achieved with less reduction in torque density if magnetic gears are connected in series to form a multistage magnetic gearbox. Alternatively, a compound differential coaxial magnetic gear can be formed from two single-stage coaxial magnetic gears and can achieve a very high gear ratio, but it suffers from circulating power, which results in poor efficiencies. The gear ratio significantly impacts the dynamic behavior of magnetically geared systems.
This dynamic behavior can be evaluated by separating the system’s motion into rigid body motion and fixed center motion and by applying the conservation of energy principle to the torque angle reference frame. Halbach arrays and air cores can significantly increase a magnetic gear’s torque density with respect to mass, when used together. To further explore this concept, a prototype magnetic gear with Halbach arrays and air cores was designed, fabricated, and tested. The prototype showed good agreement with simulation regarding slip torque and gear ratio. The prototype achieved a mass competitive with some similarly rated commercially available mechanical gears and also achieved a favorable projected efficiency compared to these mechanical gears. | |
