Reduction of Cogging Torque Caused by Assembly Errors in Flux Modulation Gear

A high-torque-density magnetic flux modulation gear (FMG) employing rare-earth permanent magnets was reported in 2001, triggering extensive research activities. Numerous studies have demonstrated that FMGs achieve substantially higher torque densities than those of conventional magnetic gear systems. FMGs exhibit characteristics that are difficult to realize with mechanical transmissions, including non-contact torque transmission, low backlash, quiet operation, compliance, and inherent torque-limiting capability. However, as in electric machines, manufacturing and assembly imperfections can generate torque ripple. In particular, cogging torque can degrade the quiet operation and controllability of FMGs. This paper presents a study of assembly-error-induced cogging torque using mathematical modeling, finite-element analysis, and experiments, and proposes methods to reduce it. The results demonstrate that the proposed method effectively suppresses the cogging torque and reduces torque ripple.