An analytical design method of thin, isotropic press-fit retention sleeve for surface-mounted permanent magnet drives

Abstract

Electric drives with surface-mounted permanent magnets feature magnet retention sleeves found in the air gap between the rotor and the stator. The design of these components, whose thickness affects the size of the magnetic air gap, has thus significant implications for the overall drive performance. The present work proposes a systematic analytical method for the mechanical design of press-fit retention sleeves for surface-mounted permanent magnet drives. The model relies on the premise that the sleeve is thin and mounted on a much stiffer rotor-magnet assembly. This leads to the assumption of constant thickness before and after the interference fit, as well as the only significant deformation being the hoop extension of the sleeve induced by the press fit. The proposed design method allows for rapid estimations of such sleeve parameters as the thickness and effective overlap, providing critical design points to be verified by subsequent high fidelity approaches. Accordingly, finite-element analysis results are provided as verification of the analytical approach, demonstrating very good agreement between the two approaches.

Keywords:

• Analytical method
• bandage
• dimensioning
• FEM
• interference fit
• magnet retention sleeve
• NX Nastran
• PM drive
• rotor

Acknowledgments

The author is grateful to Mr. Heintje Wyczisk the Head of Design and Engineering/Head of Airworthiness Department of Electric Aircraft at Siemens AG Corporate Research and Technology for helpful assistance during the work on this method. The author is grateful to his teammate Dr. Izabela Kuder for the internal review of the work.