Optimal Design Of The Axial Magnetic Gear

The gear is a wide range of transmissions.The active rotor and driven rotor of the magnetic gear use the magnetic field coupling to change speed and transmit torque.The magnetic gear has the advantages that the mechanical gear couldn't match,such as easy maintenance,no lubrication,high reliability,long life,low noise and inherent overload protection.The axial force of the axial magnetic gear is relatively large,which may make its assembly more difficult than the radial magnetic gear.However,the axial magnetic gear is more advantageous when sealing isolation is required.In this paper,optimal design of the axial magnetic gear is taken as the main researching object.The research of this paper as follow:Firstly,taking the axial flux magnetic gear as an example,working principle of the axial magnetic gear is analyzed.Then the Maxwell software is used to build the 3D finite element model of the axial flux magnetic gear and obtain its flux density distribution map.Based on the air-gap flux density distribution of the axial magnetic gear,two simplified formulas for calculating the torque and axial force are proposed.Second,according to the magnetization direction and arrangement of permanent magnets,axial magnetic gears could be divided into the axial flux magnetic gear,the axial flux focusing magnetic gear and the axial magnetic gear with Halbach permanent magnet arrays.3D finite element method is used to compare the air-gap flux density distribution,torque characteristics and axial force of the three axial magnetic gears,respectively.Based on the harmonic analysis of the air-gap flux density of the axial magnetic gear,the torque and axial force generated by harmonics are calculated by the two simplified formulas mentioned above,and the effects of harmonics on the torque transmission and the axial force are clarified.The comparison demonstrates that the maximum static torque and permanent magnet utilization efficiency of the axial flux focusing magnetic gear is largest,which shows a 17.5% and 32.6% growth over the axial flux magnetic gear,and a 2% and 15.1% growth over the axial magnetic gear with Halbach permanent magnet arrays.The torque ripple of the axial magnetic gear with Halbach permanent magnet arrays is smaller than the other two axial magnetic gears.The low-speed rotor of the axial flux magnetic gear has the lowest axial force,38.3% smaller than that of the axial flux focusing magnetic gear,and 32.7% smaller than that of the axial magnetic gear with Halbach permanent magnet arrays.Besides,to improve the torque transmission capability of the axial magnetic gear with Halbach permanent magnet arrays,parametric analysis of eight dimensional parameters such as axial thickness of permanent magnets on the high-speed rotor,length of rectangular shape modulation pieces and inner radius of the axial magnetic gear with Halbach permanent magnet arrays is conducted based on the 3D finite element method.By parametric analysis,six parameters such as axial thickness of permanent magnets on the high-speed rotor and the inner radius have been found to have obvious impact on the output torque and output torque density.Then based on the air-gap flux density distribution,it is analyzed how the above six key parameters affect the output torque of the low-speed rotor of the axial magnetic gear with Halbach permanent magnet arrays.Optimization of the axial magnetic gear with Halbach permanent magnet arrays is carried out by Maxwell software,and the optimization goal is to maximize the output torque density.By optimization,the output torque of the axial magnetic gear with Halbach permanent magnet arrays increases from 54.7Nm to 82.61 Nm with an increase of 51.02%.Based on the optimization,the drawing of the axial magnetic gear with Halbach permanent magnet arrays is drawn according to the optimized dimensional parameters.