A 2-D Hybrid FE Model With Double Air Gap Elements for Eccentric Magnetic Harmonic Gears

Abstract

Eccentric magnetic harmonic gears with high gear ratios exhibit high torque densities. However, the revolution and rotation of the eccentric rotor increase the magnetic field analysis complexity. This paper presents a hybrid finite element approach of magnetic field analysis for magnetic harmonic gears. The eccentric air gap region has been divided into three parts: two uniform layers, adjoining the stator and the rotor respectively, are treated as air gap elements; one non-uniform middle layer, as a variable air gap permeance, is discretized by FE meshes similar to the stator and the rotor. Mesh reconstruction can be avoided because the annular cylindrical rings of the two air gap elements are introduced. The mixed eccentric motion of the rotor can be easily treated. In order to save the computational time an equivalent motion mode is introduced and the sliding surface technique is applied by which the coefficient calculation of the air gap elements only needs to be done once wherever the rotor moves. The torques are calculated from the flux densities of the air gap elements. A prototype test confirms the validity of the prediction, and the accuracy of the obtained results is evaluated with FEM.

Keywords

• Hybrid finite element method
• double air-gap element
• eccentric magnetic harmonic gear