Design And Air-gap Magnetic Field Analysis For High Efficiency Eccentric Magnetic Harmonic Gears

Magnetic gears offer several advantages compared to mechanical gears in terms of low noise,no lubrication,reduced maintenance,high reliability and inherent overload protection and so on.A high torque density can be obtained by the modulated air gap magnetic field through the steel pole-pieces in the concentric magnetic gear;but the gear ratios should not be too high.The eccentric magnetic harmonic gear utilizes the change of the magnetic permeability caused by eccentric structure to achieve speed change and torque transmission with high gear ratios and high torque density.Therefore,eccentric magnetic harmonic gear has a good prospect in low-speed and high-torque drive field.This dissertation devotes to the fundamental researches on the eccentric magnetic harmonic gear.The specific researches are as follows:First of all,the boundary perturbation method is used to establish a two-dimensional analytical model in the magnetic field for the harmonic gear with small eccentricity using magnetic vector potential.The eccentric air gap magnetic field is calculated.Air-gap flux density,electromagnetic torque and unbalanced magnetic force of the analytical results are in good agreement with those calculated by Ansoft finite element software,which verifies the correctness of the analytical model.Secondly,a two-dimensional analytical model of the magnetic scalar potential in the magnetic field for the harmonic gear with large eccentricity is established by hyperbolic cotangent transformation.The analytical expressions of the eccentric air-gap magnetic field are derived.The air-gap magnetic flux density and electromagnetic torque of a dual-stag harmonic gear are calculated.Comparing the analytical results with the finite element analysis results,the analytical model is proved to be correct.This analytical model provides an effective method for optimization and design of the harmonic gear.It has important theoretical significance and application value for the further study on the electromagnetic performance of the eccentric harmonic magnetic gear.Thirdly,the genetic algorithm based on the analytical method is used to optimize and design the harmonic gear.The optimization algorithm has strong robustness and applicability.The computational speed is fast;the optimization process can be completed automatically.It is more convenient and effective than the traditional finite element optimization process.The electromagnetic torque of the harmonic gear has been improved after optimization,which verifies the correctness and effectiveness of the optimization algorithm.Finally,a dual-stag eccentric magnetic harmonic gear prototype is designed and fabricated for the first time in China.The prototype testing platform is built.The prototype load test is carried out.The dual-stage structure realizes the concentric rotation output.The eccentric movement of the eccentric harmonic gear is changed into concentric rotation.The experimental results demonstrate that,the transmission ratio is basically consistent with the theoretical value-18.29:1 and the transmission efficiency is over 91%.The torque density of the single-stage and dual-stag prototype are 86 kN·m/m~3 and 43kN·m/m~3,respectively.The prototype has the characteristics of high transmission efficiency and stable output torque,which has the value of promotion and application.The researches in this dissertation will provide a good foundation on the practicality of the magnetic harmonic gear in low-speed and high-torque drive field.It is of great significance to realize the industrialization of the magnetic harmonic gear.