Design, analysis and application of magnetic variable gears

Abstract

As symbolized in many logos, mechanical gears have significant impact on daily life and industrial modern society. By fully utilizing the mechanical gears and gearboxes, torque and speed can be properly varied for various applications. However, they inevitably suffer from the demerits of annoying noise, contact friction and regular maintenance. Magnetic gears are considered as one of the most promising candidate for the traditional mechanical gears because they offer the advantages of physical isolation, maintenance free, silent operation and inherent overload protection. However, a direct replacement of mechanical gears by magnetic gears cannot solve the problems aroused by the mechanical gearboxes. Namely, the gear ratio of magnetic gears cannot be adjusted whereas the gear ratio of mechanical gears can be flexibly varied via the gearboxes for different load requirements.

It is well known that the renaissance of magnetic gears mainly attributes to the invention of rare-earth permanent magnet (PM) materials which take the definite advantages of high energy and flux density. Although the rare-earth PM materials such as neodymium-iron-born (NdFeB) and samarium-cobalt (SmCo) are widely adopted for magnetic gears, there is an increasing concern on the price and supply of the rare-earth elements. Particularly, the use of non-rare-earth aluminum- nickel-cobalt (Alnico) PM material takes the merit of high Curie temperature which is very acceptable for industrial application. Also, by purposely employing the low coercivity of the Alnico PM material, the memory machines perform controllable magnetization to flexibly vary the air-gap flux density, hence achieving the wide constant-power speed range.

The purpose of this thesis is to design a new type of magnetic variable gear by combining the concept of magnetic gear and the concept of memory machine. Firstly, the background information and the development of flux-controllable PMs are introduced. Secondly, the previous research worked on magnetic gears is presented. Next, the cost-effectiveness comparison between rare-earth PMs and non-rare-earth PMs is sufficiently conducted. After that, a new magnetic gear with multiple controllable gear ratios is proposed, with emphasis on mathematical deduction of the design principle and operation principle. By using finite element analysis, the electromagnetic performances of proposed magnetic variable gear at different gear ratios are investigated. Then design optimization of coaxial magnetic variable gear is conducted and analyzed. Two kinds of methods aiming to increase the torque capability and reduce the torque ripple are discussed. Furthermore, the concept of coaxial magnetic variable gear is extended to the axial-field counterpart. The electromagnetic performances of proposed axial-field MVG is investigated by finite element method. Furthermore, two kinds of industrial applications of coaxial magnetic gears, including wind power system and hybrid propulsion system, are investigated. Finally, a prototype is built up for the verification of the gear ratio changing concept. Hence the corresponding validities are further verified by experimental results.