Optimization of Stack Length in Magnetic-Geared Motor with Magnetically Suspended High-Speed Rotor

Magnetic geared motors have many advantages over mechanical gearboxes, including the absence of lubrication, and intrinsic overload protection. However, in terms of durability, the limited lifetime of mechanical bearings holding the high-speed rotor is a critical issue. To solve this problem, a magnetic gear with an integrated bearingless high speed motor has been proposed. Suspension force is generated upon the high-speed rotor with a three-phase winding system added to the conventional motor winding. In previous papers, the stack length was designed to be thinner than the rotor diameter. This configuration enhances passive tilting stiffness of the magnetic suspension, but as a trade-off, torque density is reduced due to leakage flux caused by the edge effect. Therefore, this paper evaluates the effect of stack length on torque and passive tilting stiffness.