Fatigue Life Prediction of a Coaxial Multi-Stage Magnetic Gear

Abstract

Magnetic gearing is an emerging approach to avoid contact failures from the gear teeth interface of mechanical gearboxes through a non-contact torque transmission concept. In this concept, magnetic flux between the inner and outer rotors is modulated through an array of magnetic pieces called the cage rotor. Despite the non-contact nature of magnetic gears in torque transmission, a minimal air-gap between the three rotors is required to achieve the best performance, which leads to more prerequisites in the design process, including bending analysis, thermal stress analysis, dynamic analysis, etc. Due to the fact that there are segmented magnets in a circumferential direction in the inner and outer rotors, as well as segmented pole pieces in the cage rotor, rotation of the gears causes oscillating forces in the active region. On the other hand, in order to increase the performance of the magnetic gearing system, steel bars in the active region are substituted with laminated stacks to gain stronger flow of magnetic flux throughout the system. The presence of the laminated parts is a potential candidate for failure under static and dynamic loads in the system, especially in long term system operation. Due to the lack of contact failure modes in magnetic gears, they are originally designed to be utilized in remote access applications, e.g. offshore, marine hydro-kinetic, and wind turbines, which require the longest operational life time. This demands fatigue analysis in all the critical parts under dynamic loads, specifically the laminated parts and rods holding magnetic components still. In this study, dynamic and fatigue analysis of a flux focusing multi stage magnetic gearbox is investigated through a multi-body dynamics and Finite Element Method, respectively.