圆筒式磁流变离合器的设计分析

磁流变离合器是通过磁流变液的剪切应力传递转矩的器件.本文建立了圆筒式磁流变离合器的几何设计方法,得到了磁流变液传递的转矩和两圆筒间能产生磁流变效应的最小间隙的设计计算公式,为离合器的几何设计奠定了理论基础.研究结果表明:转矩可由外加磁场连续控制;选择磁饱和时高屈服应力和零磁场时低粘度的磁流变液材料,能使设计的离合器的尺寸小而紧凑.     

基于圆筒剪切模式的磁流变脂流变学特性检测方法与装置

针对现有测试装置剪切率低且难以使磁流变脂达到磁饱和的问题,提出了一种基于同心圆筒双边剪切模式的磁流变脂流变学特性检测方法,分析了剪切通道中磁流变脂在转子作用下的剪切流动特性与剪切应力分布,建立了磁流变脂传递力矩与剪切应力的理论关系,得出了由传递力矩导出标称剪切应力的近似算法;通过建立剪切率与剪切应力之间的函数关系,利用剪切通道中磁流变脂的平衡微分方程和流动边界条件,得出了由转子角速度导出磁流变脂标称剪切率近似算法;通过实验方法研究了剪切通道平均磁通密度与励磁电流的关系;设计与制作了磁流变脂检测装置,并利用磁流变脂检测装置完成了某典型磁流变脂检测,使磁流变脂的剪切率达到2000s~(-1)、磁通密度超过0.6T,测试结果与其它检测装置检测结果能较好吻合.     

High Field Magnetoresistance and Magnetic Torque in One-Dimensional Organic Conductor TPP[Fe(Pc)(CN)2]2

Magnetoresistance (MR) and magnetic torque measurements are performed for a magnetic organic conductor TPP[Fe(Pc)(CN)₂]₂. The results suggest that the large negative MR is associated with a magnetic transition. This magnetic transition is considered as a metamagnetic transition of the localized Fe moments, and the MR effect is qualitatively explained by an analogy with the double exchange interaction system.     

近邻软磁层偏置磁阻磁头结构参数设计的数学模型

概述了软磁层偏置磁阻磁头的工作原理和特点 ,采用传输线模型对其工作点的选取和结构参数进行了初步设计 ,与实验结果符合较好     

An indirect test method for the characterization of variablereluctance motors

The determination of the characteristics of the variable reluctance motors (both in static and dynamic conditions) represents a quite critical point, due to the heavy nonlinearity of the motor magnetic paths, to the high distortion of the supply voltage from the converter, and to the high level of saturation of the magnetic paths in normal working conditions. This creates a great difficulty in the accurate measurement of the motor magnetic characteristics (saturation curves or flux linkage versus current curves) and consequently in the determination of the mechanical characteristics (static torque versus current and static torque versus rotor position) which are directly related to the saturation curves. The paper proposes an original digital method that, starting from the measurement of the flux linkage in the motor magnetic paths, determines the saturation curves, evaluates the coenergy versus current curves and then the motor torque characteristics in static conditions. It is then shown how the availability of a fast and accurate method for the measurement of the flux linkage allows the determination of the electromagnetic torque in dynamic conditions, too     

基于多级磁流变阻尼器的操纵面振动半主动抑制--数值仿真与风洞试验

推出了一种旋转式多级磁流阻尼器,将阻尼器的输出力分为7个等级,并基于试验数据建立了该阻尼器的简化模型。为了将磁阻尼器应用于机翼操纵面的振动抑制,建立了包含阻尼器的机翼-操纵面三自由度气动弹性方程,并设计了基于输出反馈的次最优控制。风洞试验结果表明,多级磁流变阻尼器能够较好地抑制操纵面的振动,并将系统的颤振临界速度提高了26．2％。     

Investigation on magnetorheological elastomers based on natural rubber

Magnetorheological Elastomers (MR Elastomers or MREs) are a kind of novel smart material, whose mechanical, electrical, magnetic properties are controllable under applied magnetic fields. They have attracted increasing attentions and broad application prospects. But conventional MREs are limited to wide applications because their MR effects and mechanical performances are not high enough. This paper aims to optimize the fabrication method and to fabricate good natural rubber based MREs with high modulus by investigating the influences of a variety of fabrication conditions on the MREs performances, such as matrix type, external magnetic flux density, and temperature, plasticizer and iron particles. Among these factors, the content of iron particles plays a most important contribution in shear modulus. When the iron particle weight fraction is 80% and the external magnetic flux density is 1 T, the field-induced increment of shear modulus reaches 3.6 MPa, and the relative MR effect is 133%. If the iron weight fraction increases to 90%, the field-induced increment of shear modulus is 4.5 MPa. This result has exceeded the best report in the literatures researching the MREs on the same kind of matrix. The dynamic performances of MREs were also experimentally characterized by using a modified Dynamic Mechanical Analyzer (DMA) system. The effects of strain amplitude and driving frequency on viscoelastic properties of MREs were analyzed.     

Three-Dimensional Magnetic Effects in Permanent-Magnet Magnet Synchronous Machines

This paper presents the results of an investigation of the three-dimensional (3-D) magnetic effects in permanent-magnet synchronous machines (PMSMs). Using 3-D finite-element analysis, effects of geometry and also a high-frequency excitation on the magnetic parameters of the machine have been studied. According to our findings, high-frequency phenomena come into effect at excitation frequencies of the order of a few kilohertz, which is not uncommon when the machine is operated at super high speeds. Our results show that normalized torque productivity is a function of stack length and an increase in stack length results in an increased torque density. It is also observed that an increase in excitation frequency decreases the self inductance of the stator windings while the phase difference between the flux linkage and magnetomotive force increases. This is a significant finding, especially the shift in the phase of the air gap flux, as it has a direct impact on the accuracy of the controller that drives the PMSM under field-oriented control. Another significant observation was the reduction in the induced voltage (back electromotive force) in a search coil located in the stator slots at high frequencies. Such observations mandate the use of 3-D analysis of machine geometry to optimize performance throughout the machine's speed range.     

Energy calculation of a permanent magnet system by surface and fluxintegrals (the flux-mmf method)

Formulas are derived for the total magnetic energy of a system with no currents, linear soft magnetic materials, and linear permanent magnets that satisfy a zero curl condition involving their magnetization vector (zero equivalent volume current density). This class of magnets includes common parallel and radially magnetized NdFeB and ferrite magnets above the knee in their demagnetization curves. The formulas express the energy as a constant plus either an integral over the magnet surface of the magnetic vector potential or an integral through the magnet of the magnetic flux. The formulas provide theoretical foundation for the flux-magnetomotive force (mmf) method for calculating cogging torque of permanent magnet motors     

Design of a new magnetic refrigeration field source running with rotating bar-shaped magnets

Magnetic refrigeration (MR) based on the magnetocaloric effect (MCE) is a prime candidate for the next generation of cooling systems. The essential components of magnetic refrigeration are the magnetic field generator and the magnetocaloric material. Although, several permanent magnet systems (magnetic field sources) for MR have been developed, recent development in magnetic refrigeration technology has encouraged researchers all over the world to think about new and original systems. This paper aims to describe a new and original magnetic refrigeration system based on a simple principle of magnetism called the Halbach effect. The proposed system is running with rotating bar-shaped magnets. This structure provides the desired varying magnetic field to the magnetocaloric material. Several configurations for the proposed systems have been investigated and presented in this paper. The design and modeling have been accomplished by using the finite elements method.     

Development of a Magnetic Planetary Gearbox

In this paper, we describe a new design for a magnetic planetary gearbox. We discuss the theory of operation and a simulated design. We constructed and verified the simulation by measuring the transmitted torque and cogging torque. A magnetic planetary gearbox operates like a mechanical planetary gearbox, except that it is contact-free and needs no gear lubrication. Hence, it has the same characteristics of three transmission modes, a high-speed-reduction ratio, and high durability. The starting point for the design procedure is to avoid possible sliding (i.e., pole-slipping), and we propose three steps to obtain the maximum number of magnetic planet gears. We show that using more planetary gears is a way to increase the transmission torque. Cogging torque can be high in this design. We assessed this potential by using finite-element analysis and then measuring performance of the fabricated gearbox. While the simulation overestimates the cogging torque (for various reasons), we propose a method to reduce the cogging torque to a very low value. We present a literature review to illustrate the development of magnetic gearing and highlight the innovation of this design.     

Design of a wound-field flux switching machine with dual-stator to reduce unbalanced shaft magnetic force

Abstract

This paper presents the design and experimental verification of an outer-rotor, wound-field flux switching machine for in-wheel traction applications. The 12-stator slot, 7-rotor pole topology was selected because it produces higher torque and fewer back-electromotive force voltage harmonics than the other topologies. The machine was designed on the basis of the physical dimension limitations for in-wheel traction in a lightweight electric scooter. Because this machine exhibits shaft radial magnetic force caused by the odd rotor poles, a novel dual-stator motor structure is proposed to reduce this force. The finite element analysis calculation results demonstrated that the shaft radial force can be reduced to nearly 0 with this design, whereas the generated torque reduced only by 3%. The effectiveness of the design was also verified through the experiments that compared the vibrations of the original and the dual-stator motors. The vibration of the dual-stator motor was substantially lower than that of the original motor.     

Analytical Solution of Air-Gap Field in Permanent-Magnet Motors Taking Into Account the Effect of Pole Transition Over Slots

We present an analytical method to study magnetic fields in permanent-magnet brushless motors, taking into consideration the effect of stator slotting. Our attention concentrates particularly on the instantaneous field distribution in the slot regions where the magnet pole transition passes over the slot opening. The accuracy in the flux density vector distribution in such regions plays a critical role in the prediction of the magnetic forces, i.e., the cogging torque and unbalanced magnetic pull. However, the currently available analytical solutions for calculating air-gap fields in permanent magnet motors can estimate only the distribution of the flux density component in the radial direction. Magnetic field and forces computed by the new analytical method agree well with those obtained by the finite-element method. The analytical method provides a useful tool for design and optimization of permanent-magnet motors.     

Fast Analytical Determination of Aligned and Unaligned Flux Linkage in Switched Reluctance Motors Based on a Magnetic Circuit Model

The main advantages of the switched reluctance motor are high torque, wide speed range, simple structure and fault tolerance. Because a switched reluctance motor has inherently nonlinear magnetic characteristics and a doubly salient pole structure, a finite-element analysis approach (FEA) is often adopted to obtain accurate magnetic representation. However, the solution time can be large for a FEA simulation if the mesh is detailed and/or many simulations are required. We propose a rapid analytical solution for determining the aligned and unaligned flux linkage using a magnetic circuit model. We present a simple method for obtaining the air-gap permeance for unaligned linkage. The results of our method agree well with FEA solutions.      

Magnetically induced vibration in a permanent-magnet brushless DC motor with symmetric pole-slot configuration

The paper reports a numerical and experimental study of magnetically induced vibration associated with rotor/stator eccentricity and imperfect magnetization for 8-pole 6-slot symmetric brushless dc (BLDC) motors. Magnetic forces and cogging torque are calculated for various slot angles by using the finite-element method (FEM). The results show that there is an optimal slot angle for minimum cogging torque, but this slot angle is not optimal for reducing magnetic forces. In the idle acoustics test, the motors with reduced magnetic forces show clear reduction at the expected frequencies while the motors with minimum cogging torque show no change at the cogging torque frequency, which implies unbalanced magnetic forces have greater effect on actual vibration of the spindle motor than cogging torque. The results show that the proper direction in motor design is to reduce unbalanced magnetic forces when both cogging torque and unbalanced magnetic forces are not achievable simultaneously.     

Multi-criteria-based design approach of multi-phase permanent magnet low-speed synchronous machines

A design methodology dedicated to multi-phase permanent magnet synchronous machines (PMSMs) supplied by pulse width modulation voltage source inverters (PWM VSIs) is presented. First, opportunities for increasing torque density using the harmonics are considered. The specific constraints caused by the PWM supply of multi-phase machines are also taken into account during the design phase. All the defined constraints are expressed in a simple manner by using a multi-machine modelling of the multi-phase machines. This multi-machine design is then applied to meet the specifications of a marine propeller: verifying simultaneously four design constraints, an initial 60-pole three-phase machine is converted into a 58-pole five-phase machine without changing the geometry and the active volume (iron, copper and magnet). First, a specific fractional-slot winding, which yields to good characteristics for PWM supply and winding factors, is chosen. Then, using this winding, the magnet layer is designed to improve the flux focussing. According to analytical and numerical calculations, the five-phase machine provides a higher torque (about 15%) and less pulsating torque (71% lower) than the initial three-phase machine with the same copper losses.     

结构参数对磁力平衡头自锁和启动力矩的影响研究

为了简化平衡头的自锁结构,提出了一种磁路自锁型电磁—永磁混合式平衡头。当线圈不通电时,依靠相邻两个永磁体与磁性内齿盘之间的磁阻最小,平衡头锁定在稳定位置。当线圈通电后,在电磁场和永磁体作用下,平衡头启动并向下一稳定位置运动。讨论了影响平衡头自锁力矩和启动力矩的结构参数,并对各个参数的取值范围进行了初步设计。通过有限元电磁分析,得到了其与自锁力矩、启动力矩之间的量化关系。基于此,设计并开发了一套电磁平衡头样机,完成了其自锁可靠性计算和启动能力试验。对比计算和试验结果,平衡头结构设计和参数选取正确。研究工作为该平衡头的工程应用提供了重要的参考价值。     

基于Herschel-Bulkley模型的火炮磁流变后坐阻尼器设计与分析

针对枪炮冲击型MR阻尼器的特点，以某单管25mm火炮为研究对象，基于Herschel-Bulkley本构模型，建立了该25mm火炮磁流变后坐阻尼器的轴对称一维层流模型。同时运用ANSYS软件，建立了该阻尼器MR阀的电磁有限元模型，求得了环状流口间MR流体的磁通密度。将MR流体流动模型和MR阀有限元结果相结合，求得了不同MR流体行为指数和不同磁场作用下阻尼力随活塞速度的变化规律。建立了火炮后坐运动方程，评价了MR流体行为指数对后坐阻尼器性能的影响。     

Detections of secondary current and torque of induction motors using amorphous microcore field sensors

New secondary-current sensors for squirrel-cage induction motors are presented using a multivibrator with two group amorphous microcores. The 8-pair micro cores are set near the both endrings of a rotor for cancellation of the influence of unstable rotor motion on sensing of the secondary current. Electromagnetic torque was detected as an output voltage of a multiplier for the secondary current and the main flux. The main flux was detected using a multivibrator-type flux sensor utilizing two stator teeth as two cores. A possible new control system for variable speed induction motors with a torque feedback loop is discussed, which stably works independently of variations of motor parameters.     

全通道有效磁流变阻尼器的性能测试与滞回模型

传统剪切阀式磁流变阻尼器在活塞上缠绕励磁线圈,导致1/2以上长度阻尼通道无效,影响阻尼器的最大出力。为了克服上述缺陷,在前期概念设计和理论分析的基础上,制作了2个全通道有效的磁流变阻尼器模型,测试了其在不同电流输入状态下阻尼通道处的磁场分布以及力-位移、力-速度等力学性能曲线,并通过对改进型Sigmoid模型的参数识别建立了模型阻尼器的动力滞回模型。研究表明,模型阻尼器阻尼通道处的磁场分布与有限元分析结果基本符合,其磁路结构可较好地实现全通道有效;全通道有效磁流变阻尼器的最大阻尼力比传统剪切阀式磁流变阻尼器的最大阻尼力提高一倍以上,阻尼力调节系数提高70%以上;改进型Sigmoid模型结构形式简单,识别精度高,可作为全通道有效磁流变阻尼器的动力滞回模型。