Axial Flux Magnetic Gear Research Articles

Performance Investigation and Experimental Testing of a Stator-PM-Excitation Axial-Flux Magnetic Gear

This paper proposes a stator-excitation axial-flux magnetic gear (SEAMG) based on innovative improvement from rotor excitation to stator excitation for the magnetic gear. The key design of the proposed SEAMG is to place the permanent magnets (PMs) on the stator, aiming at only retaining iron on rotors to enhance its mechanical robustness, and the PMs located on the stator can be avoided falling off to further improve operation reliability. An axial-flux pattern is adopted so as to make that the stator can be easily fixed to the housing and the high- and low-speed rotor shafts can be conveniently led out from axial side. Hence, compared with the existing coaxial rotor-excitation MGs, the proposed SEAMG has improved mechanical reliability and low processing difficulty. Its operation principle is explained and the general optimization design considerations are illustrated to achieve expected torque transmission performance. A prototype is built and performance evaluation using the 3-D finite element analysis (FEA) and the experiments is conducted to verify its validity.

Design Optimization of an Axial Flux Magnetic Gear by Using Reluctance Network Modeling and Genetic Algorithm

The use of a suitable modeling technique for the optimized design of a magnetic gear is essential to simulate its electromagnetic behavior and to predict its satisfactory performance. This paper presents the design optimization of an axial flux magnetic gear (AFMG) using a two-dimensional (2D) magnetic equivalent circuit model (MEC) and a Multi-objective Genetic Algorithm (MOGA). The proposed MEC model is configured as a meshed reluctance network (RN) with permanent magnet magnetomotive force sources. The non-linearity in the ferromagnetic materials is accounted for by the MEC. The MEC model based on reluctance networks (RN) is considered to be a good compromise between accuracy and computational effort. This new model will allow a faster analysis and design for the AFMG. A multi-objective optimization is carried out to achieve an optimal volume-focused design of the AFMG for future practical applications. The performance of the optimized model is then verified by establishing flux density comparisons with finite element simulations. This study shows that with the combination of an MEC-RN model and a GA for its optimization, a satisfactory accuracy can be achieved compared to that of the finite element analysis (FEA), but with only a fraction of the computational time.

Cogging Torque Reduction of Integer Gear Ratio Axial-Flux Magnetic Gear for Wind-Power Generation Application by Using Two New Types of Pole Pieces

Flux-modulated-type magnetic gears are expected to be applied as a step-up gear for wind-power generation because of their advantages, including high torque density and maintenance-free operation. Furthermore, the flux-modulated-type magnetic gears with an axial-flux structure have attracted great attention recently since they have a smaller axial length and are relatively easy to assemble. In some cases, magnetic gears are required to have an integer gear ratio based on the design requirements of the entire system, which results in larger cogging torque in the high-speed (H-speed) rotor that causes vibration, acoustic noise, and startup error. A skewed rotor structure is well known to be capable of reducing the cogging torque; however, it is complicated and poor in assembling, especially in a large-scale axial-flux magnetic gear (AFMG) used for the wind-power generation. To resolve the above problem, this article presents two new types of pole pieces for reducing the cogging torque: one is an unequal-space type, and the other is an unequal-width type. The validity of the two newly proposed types of pole pieces is proved by both a 3-D finite-element method (3D-FEM) and experiment.

Cogging Torque Reduction of Axial-flux Magnetic Gear with Integer Gear Ratio by Unequal-width Pole-pieces

Cogging Torque Reduction of Axial-flux Magnetic Gear with Integer Gear Ratio by Unequal-width Pole-pieces

A HTS Stator-Excited Axial-Flux Magnetic Gear With Static Seal

This paper proposes a novel high-temperature superconducting stator-excited axial-flux magnetic gear (HTS-SEAFMG) for the high-torque transmitting system. The proposed magnetic gear combines the merits of both HTS-excitation and stator-excitation. By using the HTS-excitation, a high air-gap flux density can be easily obtained, thus achieving the high torque density. The HTS-excitation windings are placed on the stator with a static seal of cooling Dewar which greatly reduces the manufacturing difficulty and the cost of refrigeration system compared with the dynamic seal. Thanks to the stator-excitation pattern, both the high-speed rotor and the low-speed rotor comprise only iron, thus contributing to the high mechanical reliability. The axially sandwich structure can also simplify its assembly in the high torque transmission applications. The dimensional parameter optimization and the electromagnetic performance evaluation are conducted by using the finite element method, respectively. The results show that the torque density of the proposed HTS-SEAFMG can reach 123 kNm/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . Theoretical analysis and results are both given to verify the feasibility of the proposed HTS magnetic gear design.

Forces in Axial Flux Magnetic Gears with Integer and Fractional Gear Ratios

This paper presents a comparison of two variants of an axial flux magnetic gear (AFMG), namely, with integer and fractional gear ratios. Based on calculations derived with the use of three-dimensional numerical models, the torque characteristics of the analyzed AFMGs are computed and verified on a physical model. The greatest emphasis is put on the detailed decomposition and analysis of local forces in modulator pole pieces (also used in the structural analysis) within the no-load and maximal load conditions. The authors also describe the unbalanced magnetic forces (UMF) in the axial and radial directions resulting from the construction of the considered AFMGs variants, and their possible effects in the context of the use of additive manufacturing (AM) in prototypes. The paper also proposes an effective method for limiting the axial strain by using the asymmetry of the air gaps, which slightly reduces the torque transmitted by AFMGs. Finally, a static strength analysis was presented that allows us to assess the effects of local forces in the form of modulator disc deformation for selected cases of air gap asymmetry.

Optimal Design and Analysis of a Novel Reluctance Axial Flux Magnetic Gear

This paper proposes modelling and optimization of a new reluctance axial flux magnetic gear (RAMG) with stationary outer rotor and advantages of lower permanent magnet usage. Due to the less use of the PMs, this structure has a higher economic interest, more reliability, and very simple and robust structure than its conventional ones. Gear ratio and operating principles are extracted and verificated using 3-D finite element method (FEM) simulations. Finally, a parametric optimization is done based on effective dimensions in design procedure with maximum torque density objective function. The magnetic flux distributions of optimized RAMG are calculated by 3-D FEM, as well as static and dynamic magnetic torques are derived correspondingly.

An Axial Flux Focusing Magnetically Geared Generator for Low Input Speed Applications

An axial-flux magnetic gear (MG) is integrated into a radial field stator to construct a unique magnetically geared generator for low input speed applications. The high-speed rotor of the axial-flux MG uses a flux-focusing typology. This article presents the stator design and experimental testing of this unique proof-of-principle axial-flux focusing MG generator. The peak torque and active region torque density were measured to be 473 N m and 94.4 N m/L, respectively. The stator of the proposed machine shares the high-speed rotor with the axial-flux MG. Therefore, there is no need for a separate rotor. It is shown that the stator can also be used to provide additional flux into the MG in order to boost torque during transient overshoots.

Designing and experimentally testing a flux‐focusing axial flux magnetic gear for an ocean generator application

The torque density characteristics for an axial flux magnetic gear using a flux-focusing topology is experimentally studied when using neodymium iron boron (NdFeB) rare-earth magnets. A geometric parameter sweep analysis was utilised in order to maximise both the calculated volumetric and mass torque density. The calculated torque and torque density was 628.6 N·m and 173.02 N·m/L while the experimentally measured torque and resultant torque density was 553.2 N·m and 152.3 N·m/L.

Design of an Axial-Type Magnetic Gear for the Contact-Less Recharging of a Heavy-Duty Bus Flywheel Storage System

This paper presents the electromagnetic design and performance assessment of an axial flux magnetic gear (AMG) for the contact-less energy transfer to an on-board flywheel energy storage system (FESS) to supply heavy-duty electric buses. The AMG electromagnetic configuration is designed to cope with the system torque/speed requirements according to the FESS specifications for a typical driving cycle of an urban bus. Starting from a preliminary sizing by analytical formulations, the torque performance is improved by more accurate finite element analyses based on simplified models. Different parameters also affecting the AMG size are considered to identify an optimized feasible configuration. Finally, the evaluation of the core losses for a full recharge operation enables one to choose the more convenient ferromagnetic material.

Design and Analysis of an Axial Flux Magnetically Geared Generator

Axial flux magnetically geared machines offer the potential to achieve exceptional torque densities at high diameters. This paper proposes a topology for an axial flux magnetically geared machine, in which the electric machine is placed in the bore of the axial flux magnetic gear. This new topology offers the advantage of correctly matching the size of the electric machine to its required torque without increasing the volume of the system beyond that of the magnetic gear. A proof-of-concept prototype with a torque density of $\text{7.8 kN}\cdot\text{m/m}^{3}$ was designed, fabricated, and tested to evaluate the novel topology. A less conservative alternate design capable of achieving $\text{60.6 kN}\cdot\text{m/m}^{3}$ was also simulated to demonstrate the topology's potential for high torque densities, and even higher torque densities can be reached at larger scale designs.

Viable Arcuate Double-sided Magnetic Gear for Competitive Torque Density Transmission Capability

Magnetic gears (MGs) offer significant potential advantages relative to conventional mechanical gears, such as: no contact, no friction, no lubrication, inherent overload protection and free from noise and vibration. Despite of these superior features they have received little attention due to complexity of operation and relatively low torque density transmission. This paper introduces a new magnetic gear topology with a highly competitive torque density transmission capability. This configuration is inspired of combination of the traditional radial and axial flux MGs. The assurance of accuracy based on a basic design of axial flux magnetic gear dimensions leading to Proof-of-Concept “Arcuate Double-Sided MG”. The Proof-of-Concept seeks to provide a better solution to the problems of flux maldistribution and concentration compared to what has been proposed previously. Thus, torque density performance of this MG is intensively augmented. The cogging torque is also computed in further simulations. However, the above requires advanced numerical techniques and hence 3-Dimensional simulations for calculating localized flux density and the corresponding torque density. Completion of this development will mark an important milestone in magnetic gear technology, and significant performance improvement will be realized.

A Novel Magnetic Gear: Toward a Higher Torque Density

Magnetic gears (MGs) are potential alternatives to conventional mechanical gear boxes. With high performance permanent magnets (PMs) and new topologies, today MGs are capable to transmit a torque that is competitive with mechanical gear boxes in a totally contact-free way. MGs can be categorized by their flux orientations, namely, radial flux magnetic gear (RFMG), axial flux magnetic gear (AFMG) and transverse flux magnetic gear (TFMG). Their torque densities found in the literature are summarized in Fig. 1. The ratio between axial length and outer diameter of the active parts is defined in order to describe the geometrical characteristics of MGs. Fig. 1 shows that torque densities of RFMGs range from 50 Nm/L to 160 Nm/L. A very high torque density was achieved by a flux focusing AFMG [1]. To make a clear comparison in Section III, an AFMG model is simulated by 3D finite element method (FEM) using the same dimensions as those in [1] and the resultant torque density is about 260 Nm/L (design 1 in Fig.1).

3-D Printing-Based Design of Axial Flux Magnetic Gear for High Torque Density

It is known that the magnetic gears have been widely developed due to its contactless property and its potential benefits such as low acoustic noise, low vibration and overload protection. For the application of contactless coupling, the axial flux type of magnetic gear (AFMG) is more applicable than the radial flux type of magnetic gear (RFMG) because of the assembly difficulty [1][2]. However, design of the AFMG faces the challenges of the high cost resulting from the magnetic material and the complications in assembling process of the 3D pole-piece shapes. In this paper, a novel design of AFMG adopting a L-type ferromagnetic pole pieces and spoke type ferrite magnet arrangement is proposed. This design not only decreases the flux leakage, but also improves the torque density. Moreover, a newly developed 3D printing process is employed to overcome the fabrication difficulty. A prototype is given to verify the computed torque characteristics designed by 3D FEA and the feasibility of the proposed 3D printing approach.

Cogging Torque Mitigation in Axial Flux Magnetic Gear System Based on Skew Effects Using an Improved Quasi 3-D Analytical Method

Since the flux leakage phenomenon is dominant in the inner and outer radii of axial flux magnetic gears (AFMGs), a prominent overestimation of torque prediction is obtained by the 2-D analytical method (AM) in comparison with the 3-D finite-element method (FEM) simulations. The main motivation of this paper is to present an improved quasi-3-D AM (IQAM), which is an improvement and amendment of the 2-D AM by a simple and effective radial dependence modeling of the axial and tangential magnetic field distribution in AFMGs. This IQAM plays an important role in a reliable and accurate prediction of static and transient behavior of AFMGs. The cogging torque of the AFMG is predicted using the obtained IQAM and Maxwell’s stress tensor. However, the proposed IQAM will become more prominent by focusing on the effects of single- and dual-skews’ designs for ferromagnetic pole-pieces and permanent magnets through suitable step changes in a combined skewed-MG model, as an effective passive method, in order to mitigate the cogging torque and thereby intensively augmenting torque quality in an exemplary AFMG. The accuracy of the developed skewing method is verified using 3-D FEM simulations.

A Novel Hybrid-Flux Magnetic Gear and Its Performance Analysis Using the 3-D Finite Element Method

This paper presents a novel hybrid-flux magnetic gear, which integrates a transverse-flux magnetic gear and an axial-flux magnetic gear into a single unit. Compared to its conventional counterparts, the proposed magnetic gear transmits a relatively high torque density. When compared to the transverse-flux magnetic gear, this new structure employs an extra iron segment between the low-speed rotor and high-speed rotor to modulate the magnetic field and contribute to the transmission of additional torque. A three-dimensional (3-D) finite element method (FEM) is used for the analysis of the magnetic field. In the paper a variables-decoupling method based on the sensitivity analysis of the design parameters is also presented to accelerate the optimization process of the proposed machine.

A Novel Triple-Permanent-Magnet-Excited Hybrid-Flux Magnetic Gear and Its Design Method Using 3-D Finite Element Method

This paper presents a novel triple-permanent-magnet-excited (TPME) hybrid-flux magnetic gear (MG) that integrates a transverse-flux MG and an axial-flux MG into a single unit. Compared with its conventional counterparts, the proposed MG transmits a relatively high-torque density. When compared with the transverse-flux MG, this new structure employs a new configuration on the high-speed rotor, an extra iron segment between the low-speed rotor and the high-speed rotor to modulate the magnetic field, and hence contributing to the transmission of additional output torque. It also employs permanent magnets on the iron segments to produce additional torque. The proposed TPME hybrid-flux MG can offer a much higher torque transmission capacity than its conventional counterparts, making it more competitive for low-speed high-torque applications. A 3-D finite-element method is used for the analysis of the magnetic field and evaluation of the output torque.