Mechanical Strength Enhancement of a Speed Multiplier Magnetic Gear Using an Aluminium Bridge Modulator Rotor Structure

Abstract

Operating electrical machines (EMs) at high speeds induces severe rotor stress and efficiency losses. A coaxial speed multiplier magnetic gear (SMMG) enables low-speed EMs to operate efficiently while achieving high output rotational velocities, thus avoiding the associated EM design penalties. In the SMMG topology, the ferromagnetic pole piece (FMP) rotor, also known as the modulator rotor, is the high-speed output component receiving input from EM, making its structural integrity critical. While prior studies have focused on electromagnetic performance, the mechanical strength of the modulator rotor under extreme operational loads remains unexplored. This study employs 3D finite element analysis (FEA) to evaluate the structural performance of three modulator rotor designs: an unreinforced baseline, a polymer-filled variant, and a novel aluminium bridge-reinforced structure. Simulations performed at rotational speeds up to 10,800 rpm under a constant torque load of ~83 Nm demonstrate that the aluminium bridge reinforcement reduces the von Mises stress from 458 MPa (unreinforced) to 161 MPa, a 64.85% reduction. It also maintains a safety factor above 1.6 across all speeds and ensures operation within the yield strength (250 MPa) of the NSSMC 35H210 pole material. In contrast, the unreinforced and polymer-filled designs experienced catastrophic stress levels, exceeding the material's yield limit. This work provides essential design guidelines and validates the aluminium bridge modulator as a robust candidate for high-speed applications.