A cycloidal magnetic gear with a novel flux shield (“moon”) achieving higher torque density and lower unbalanced electromagnetic forces

Abstract

Magnetic gears’ numerous potential advantages, such as contactless operation, reduced maintenance requirements, lack of lubrication, and inherent overload protection, have led to significant interest in the technology. The cycloidal magnetic gear (CyMG) is an enticing option for applications requiring high gear ratios. CyMGs do not require the modulators used in coaxial magnetic gears, but CyMGs have disadvantages, including counterproductive torque developed in the larger air gap region and unbalanced magnetic forces, which must be supported by the bearings. This paper introduces a novel “moon” structure, which serves as a flux shield, for CyMGs. The moon is made out of ferromagnetic material and is located in the larger region of the air gap. The moon increases torque density by providing a leakage path for the flux that would otherwise create counterproductive torque. The moon also reduces the unbalanced magnetic forces. This structure’s benefits are investigated using finite element analysis. The results show that, within the evaluated design space, the proposed moon can increase the maximum achievable active volumetric torque density (VTD) by 7.6% to 8.6% for each of the considered gear ratios or it can reduce the no-load eccentric force of the maximum VTD moon-free 20:1 CyMG by as much as ∼86% without decreasing the VTD.