Coaxial Magnetic Gear Research Articles

Comparison of Loss Characteristics of Coaxial Magnetic Gear According to Three Types

Comparison of Loss Characteristics of Coaxial Magnetic Gear According to Three Types

Comparison of Surface Permanent Magnet Axial and Radial Flux Coaxial Magnetic Gears

This paper provides a thorough, parametric comparison of axial and radial flux coaxial magnetic gears with surface-mounted permanent magnets. While both topologies share similar operating principles and can achieve comparable shear stresses, they exhibit different scaling trends with respect to key design parameters. Both topologies’ volumetric torque densities (VTDs) increase with the outer radius, but the axial flux topology's VTD increases with the radius at a much faster rate than the radial flux topology's VTD. Another difference between the topologies involves their cross-sectional scaling parameters. The stack length axially scales radial flux gear cross sections, and, as it increases, the impact of end-effects decreases, which improves the performance. For axial flux gears, the radii ratio scales the cross section's radial width between different radii. This fundamentally changes optimal parameter values and design performance tradeoffs. Finally, axial flux rotors experience significant axial forces, but the radial forces on radial flux rotors can be balanced out. Based on these trends, radial flux gears are superior to axial flux gears for most applications; however, axial flux gears have a significant advantage when a large radius and a small axial length are permissible or when mechanical power needs to be transmitted across a flat barrier.

Optimization and Comparison of Coaxial Magnetic Gears With and Without Back Iron

This paper deals with the analysis and optimization of radial, coaxial magnetic gears. Multi-objective optimizations of the modulator shape of two magnetic gear configurations, one with and one without back iron on the outer rotor, are presented and discussed. The focus of this publication is to show that a magnetic gear with the same total volume and output torque can provide a much higher efficiency when the outer rotor is built with no back iron. To guarantee comparable results, equal start geometries, objectives, and appropriate optimization parameters are considered. After the optimization process, the geometries of the two gear configurations show different optimal modulator shapes and, therefore, different flux distributions. The gear configuration without back iron achieves a comparable torque capability in comparison with the gear configuration with iron yoke. However, 2-D finite elements calculations estimate for the latter design a loss reduction of 70%.

Comparative Analysis of a Coaxial Magnetic Gear With a Flux Concentration Rotor and Consequent Pole Rotor Typology

By utilizing magnetic field space modulation magnetic gearboxes (MGs) are able to create speed amplification without any physical contact [1–3]. An example of a flux-focusing coaxial MG is illustrated in Fig. 1. This coaxial MG consists of an inner rotor 1 that contains $p_{1} = 4$ pole-pairs an outer rotor 3 with $p_{3} = 13$ pole-pairs and a central ferromagnetic segment central rotor 2 that consists of $n_{2} = 17$ pieces. The $n_{2}$ ferromagnetic segments serve to modulate the inner and outer rotor magnetic fields. In order to create the highest level of field coupling between the inner and outer rotors the number of ferromagnetic segments must be chosen to satisfy $n_{2} = p_{1}+p_{3}$. With this condition satisfied the rotor angular velocity relationship between each rotor is $\mathrm{w}_{2} \mathrm{p}_{2} = \mathrm{w}_{3} \mathrm{p}_{3}+ \mathrm{w}_{1} \mathrm{p}_{1}$ where the subscript denotes rotor number. If the outer rotor is fixed $( \omega _{3} = 0)$ the torque will be maximized and the gearing ratio will be $\mathrm{w}1 = $ Gw 2 where $\mathrm{G} = n_{2}/ p_{1}$. For the example MG shown in Fig. 1 the gear ratio is $\mathrm{G} = 4.25$. In order to try to increase the torque density of a MG a range of different coaxial type rotor typologies have recently been investigated [4–14]. Along with the flux focusing MG design two other coaxial radial type MG rotor typologies that have been shown to create high torque density are the flux concentration Halbach rotor typology [15] and the consequent pole triple-PM rotor MG typology [16]. In this paper, these two design typologies are compared for the first time. The objective is to provide an idealized comparative analysis of the two competing typologies and then present the experimental design and testing of the best design.

Pseudo direct drive simulation and analysis

PurposeThe purpose of this paper is to simulate a pseudo direct drive (PDD) by using permanent magnet arrays.Design/methodology/approachA 2D finite element model of the PDD was built. The static magnetic torque on air-gaps was obtained by Coulomb’s virtual work method using Ansys Maxwell software. To simulate the relative movement between input rotor and output rotor, two movement bands were applied.FindingsThe PDD’s torque relation was proved. The PDD simulated presents low cogging torque.Practical implicationsThe manufacturing steps and materials applied in a construction of a coaxial magnetic gear, PDD’s main component, are presented.Originality/valueThe value of this paper is to present the numerical techniques applied to simulate a PDD and the manufacturing steps and materials applied in a construction of a coaxial magnetic gear.

A novel bicycle rear hub transmission with a magnetic gear mechanism

This article proposes a new magnetic rear hub transmission for bicycles, which consists of a coaxial magnetic gear mechanism to serve as the speed-changing device and a speed control mechanism to govern the gear stage. A 3-speed magnetic hub transmission, including a low-speed gear, a direct-drive gear, and a high-speed gear, is designed and installed in the rear hub of a bicycle, which allows the rider to select different gears to adjust the pedaling force. For a new kind of rear hub transmission, kinematic analysis and power-flow path analysis are essential to validate the speed ratio and the power-flow path at each gear stage. They are also the fundamentals for the mechanical efficiency analysis. Here, a system’s kinematic equation, which is an analytical approach and analogous to the kinematics of a basic planetary gear train, for the presented coaxial magnetic gear mechanism is derived without considering the complex space harmonics of the magnetic flux density distribution presented in previous studies. Hence, the speed ratio at each gear stage of the magnetic hub transmission can be easily calculated.

A Novel Dual-Flux-Modulator Coaxial Magnetic Gear for High Torque Capability

This paper presents a novel dual-flux-modulator coaxial magnetic gear (DFM-CMG) characterized by high torque capability and high permanent-magnet (PM) utilization efficiency. The DFM-CMG adopts spoke-type outer PM rotor and introduces an auxiliary flux modulator placed in the outermost layer. The harmonic analysis with detailed theoretical derivation is performed to reveal that the ferromagnetic pole shoes on the spoke-type outer PM rotor could modulate the flux density distribution as well and realize a nested magnetic-gearing effect. More effective magnetic harmonics are, thus, led into the air gaps to make contribution to the torque production. The effect of the auxiliary flux modulator on the flux density distribution is also studied by the finite-element (FE) analysis. Due to the presence of the auxiliary flux modulator, the flux leakage is suppressed and the useful harmonics are amplified. A quantitative comparison among the surface-mounted CMG (SM-CMG), spoke-type CMG (ST-CMG), and DFM-CMG is made to verify the performance improvement of the proposed CMG. With the same amount of consumed PMs, the torque capability and PM utilization efficiency of the DFM-CMG shows a 73% growth over the SM-CMG and a 44% growth over the ST-CMG. The ST-CMG and DFM-CMG are finally prototyped and tested to verify the FE analysis.

Comparison of Surface Mounted Permanent Magnet Coaxial Radial Flux Magnetic Gears Independently Optimized for Volume, Cost, and Mass

This study employs a genetic algorithm (GA) to optimize surface mounted permanent magnet coaxial radial flux magnetic gear designs using both 2-D finite element analysis (FEA) and 3-D FEA. Specifically, the GA optimizes different designs, which are all rated for a stall torque of 500 N·m and a gear ratio of approximately 5, to independently maximize volumetric torque density (VTD), torque per dollar (TPD), and gravimetric torque density (GTD). Maximum VTDs of 274 and 210 kN·m/m3 were obtained with 2-D and 3-D simulations, respectively. Including the space required to provide an axial buffer for leakage flux resulted in a maximum leakage adjusted VTD of 162 kN·m/m3. Maximum TPDs of 5.86 and 5.47 N·m/$ were obtained with 2-D and 3-D simulations, respectively. Maximum GTDs of 102.8 and 86.8 N·m/kg were obtained with 2-D and 3-D simulations, respectively. The results demonstrate that independently maximizing these three metrics leads to markedly different designs with widely varying performance characteristics. The most significant differences occur between the maximum VTD and maximum TPD designs, and the analysis includes a thorough discussion of the dominant design parameters driving this phenomenon. Finally, the impacts of end effects on the optimal design parameters are also illustrated to demonstrate that consideration of these 3-D effects leads to significantly different performance predictions and to different optimal design selections.

Comparison of Radial Force at Modulating Pieces in Coaxial Magnetic Gear and Magnetic Geared Machine

Unlike the coaxial magnetic gear (CMG), the magnetic geared machine (MGM) has the ac armature winding on the inner part or the outer part. Besides, the PM excitation field of the CMG and the ac armature field of the MGM have different space harmonic components of magnetic field from one other. Hence, the flux modulation characteristics in the CMG and the MGM are different, and the resultant magnetic radial forces at the modulating pieces are also occurred differently from one another. Thus, in this paper, first, the flux modulation characteristics of the PM excitation field in the CMG and the ac armature field in the MGM are presented. Second, the characteristics of the magnetic radial forces at the modulating pieces are analyzed, and the causes of the radial force according to the space harmonic components of the magnetic field are compared in the CMG and the MGM.

Design Comparison of NdFeB and Ferrite Radial Flux Surface Permanent Magnet Coaxial Magnetic Gears

Magnetic gears promise the benefits of mechanical gears with added advantages from contactless power transfer. Although most of the literature focuses on minimizing the size of magnetic gears, their material costs must also be reduced to achieve economic feasibility. This paper compares the active material costs of NdFeB and ferrite radial flux coaxial magnetic gears with surface permanent magnets through a parametric two-dimensional (2-D) and 3-D finite element analysis study. Differences in optimal design trends such as pole counts and magnet thicknesses are illustrated for the two materials. The results demonstrate that, for most historical price rate scenarios, NdFeB gear designs are capable of achieving lower active material costs than ferrite gear designs, and they are always capable of achieving much higher torque densities. Based on the selected design constraints, relative to a nominal ferrite cost of $10/kg, NdFeB must cost more than $90/kg before ferrite is cost competitive. However, ferrite gears can achieve higher efficiencies than NdFeB gears, especially at high speeds, and generally emit less axial leakage flux. Additionally, contour plots are provided to show the impact of material price rate variation on the cost break points.

Multi-objective optimization of coaxial magnetic gears

Multi-objective optimization of coaxial magnetic gears

Towards Miniaturization of Magnetic Gears: Torque Performance Assessment.

Magnetomechanical components can be a good solution in order to reduce, or even completely avoid, friction phenomena in micro-electro-mechanical systems (MEMS) since they can transmit forces through magnetic fields without contacts. In this communication, electromagnetic simulations of the expected specific torque of a coaxial magnetic gear are given. The results show that micromagnetic gears (3 mm of diameter) could provide a specific torque up to 8.98 Nm/kg, several times larger than the specific torque that microgears (<9 mm of diameter) can provide. This implies that micromagnetic gears could provide speed conversion without contact in the teeth, avoiding corresponding friction, but also that it would even improve the specific torque transmission with respect to contact microgears.

Performance Analysis and Parametric Study of a Co-axial Magnetic Gear

Performance Analysis and Parametric Study of a Co-axial Magnetic Gear

Coaxial Magnetic Gear Design and Optimization

The main aim of this paper is the imposition of constraints for the multiobjective optimizations of magnetic gears. In order to reduce the computational effort, a semianalytic design procedure is adopted, providing a fast simulation tool that can be embedded within an optimization loop. Magnetic, thermal, and mechanical constraints are discussed and embedded into a stochastic algorithm, in order to identify immediately infeasible geometries. The algorithm that has been developed provides a useful initial design tool that can be adopted to locate the optimal solutions in the search space. This paper also presents the multistage magnetic gear topology as the counterpart of the multistage mechanical gearboxes.

Analysis, design and experimental verification of a coaxial magnetic gear using stationary permanent‐magnet ring

This study presents the analysis and experimental verification of a coaxial magnetic gear (CMG) for speed-change transmission. The key design of this CMG is to adopt a stationary permanent-magnet (PM) ring between the inner and outer rotors, aiming at removing the PMs and only retaining the salient-pole-iron on the outer rotor to improve its mechanical reliability. Meanwhile, due to a large equivalent magnetic clearance promoting low torque ripples, the proposed CMG can offer the advantages of achieving a consistent speed ratio and stable transmission within the entire pull-out torque range. By using the two-dimensional finite element method, the detailed parametric analysis and static characteristics of the proposed CMG are performed to set up its design criteria. Moreover, a quantitative comparison with a conventional CMG is conducted, and a prototype is also fabricated for experimentation to verify the validity of the proposed CMG.

Electromagnetic Design and Analysis of a Novel Transmission System Supporting Multi-Path Power Flows for Electric Vehicles

This paper proposes a novel transmission system supporting multi-path power flows for electric vehicles (EVs). It mainly consists of a coaxial magnetic gear (CMG), a lock, a clutch, and two electric machines (EMs). The key feature of the CMG is that its modulating ring can rotate freely. One of the EMs is integrated with the CMG, which constitutes an integrated magnetic gear permanent magnet machine. And the other is connected to the inner rotor of the CMG through a clutch and a shaft with a lock. By toggling the clutch, controlling the states of the lock and the two EMs, the proposed transmission system can achieve flexible power splits. It is very interesting that one of the EM can play the role of a flywheel storage device when necessary, which is capable of buffering the energy from regenerative braking, so as to protect the battery. In this paper, the configuration of the transmission system is illustrated; its operating principle is elaborated. Then, the electromagnetic design is conducted to meet the demands arising from EVs. Finally, the electromagnetic performances are analyzed by using finite-element method, which verifies the rationality of the electromagnetic design.

Optimization of the pole piece in coaxial magnetic gears for transfer torque ripple improvement

Optimization of the pole piece in coaxial magnetic gears for transfer torque ripple improvement

An optimization tool for coaxial magnetic gears

PurposeThis paper aims to show a complete optimization tool that can be used for the design of coaxial magnetic gears. In the first part, the paper deals with the semi-analytic modelling of these machines and also discusses how to reduce the computational efforts. In the second part, an optimization algorithm is adopted for finding the Pareto optimal geometries.Design/methodology/approachThe machine is subdivided into a set of domains according to their physical and geometrical properties, and the potential distribution is found semi-analytically in them under some simplifying hypothesis. A loss estimation is performed for both ferromagnetic and permanent magnet regions. A stochastic differential evolution (DE) algorithm for multi-objective constrained problems is then applied.FindingsIt is shown that the presented design tool gives results in accordance to finite element method (FEM)-based analysis keeping the advantages of robustness and simplicity of the analytical methods. The DE-based strategy performs well on the magnetic gear optimization problem.Practical implicationsThe proposed tool appears to be a good starting point when designing coaxial magnetic gears. The optimal Pareto points can be used as initial seeds of FEM-based optimizations, resulting in a cheaper computational method with respect to a full FEM optimization.Originality/valueThis paper takes inspiration from recent works on magnetic gear modelling and completes the design procedure with a suitable efficiency estimation. The paper also shows how to use mature optimization strategies to solve the constrained multi-objective magnetic gear design problem.

A Design Approach for Coaxial Magnetic Gear and Determination of Torque Capability

This paper presents a time saving methodology for design and sizing the magnetic gear sets. Some new design parameters similar to mechanical gears are defined to calculate the torque capacity based on these. Finite element analysis is extensively used to calculate the variation of gear set torque capacity due to changes in different geometric parameters of a set. Different design curves are obtained by which the design and sizing of the gears can routinely be accomplished. Optimal performance of magnetic gear wasn’t the main target of this research and just this method helps gear designers to decide on parameters such as scale of gears, magnet thickness, stack length and pole pair numbers and come up with a close to optimum geometry design

Topologies and performance study of a variety of coaxial magnetic gears

This study aims to provide a comprehensive study of various magnetic gears (MGs) with simple coaxial radial flux structure. A total of 15 topologies are first introduced, by either using various rotor structures or adding extra permanent magnets (PMs) on the magnetic modulation ring. Then, all topologies with ferrite magnets are parametrically optimised, aiming to compare and evaluate the performance of these MGs. The results show that the proposed MGs with dual consequent-pole PM rotors exhibit a higher torque density than the conventional coaxial MG. Therefore, magnetic field distribution, torque-angle characteristic and on-load torque performance of these promising MGs are analysed in detail, revealing their inherent superiorities. In addition, influence of magnet material on the MG performance are investigated with emphasis on the torque density and cost effectiveness. Finally, two MG prototypes are fabricated and tested to validate the analysis.