Rotating electric machine

Abstract

Rotating electric machine (10) comprising a rotor (12) with a rotor shaft (13) located on a rotor axis and a stator (11) rotatably receiving the rotor (12), wherein the stator (11) comprises several teeth (15) extending in the direction of a circumferential surface of the rotor (12) and terminating at inner circumferential surfaces opposite the circumferential surface of the rotor (12), and several slots (18) located between two adjacent teeth (15) and providing spaces for winding coils around the teeth (15) for the input of the electrical drive power, wherein the rotor (12) has several permanent magnets (16) embedded therein to exert the magnetic force on those surface sections of the teeth (15) which are opposite the permanent magnets (16), wherein the rotor (12) within the stator (11) is driven to rotate by the reluctance torque originating from the magnetic flux flowing through the teeth (15), the rear side of the surface of the teeth (15) and the rotor (12) when current flows through the coils, and the magnetic moment in the form of attraction and repulsion originating from the interference with the permanent magnets (16), wherein an outside diameter ratio of an outside diameter Dr of the rotor (12) to an outside diameter Ds of the stator (11) falls within a range effective for minimizing torque ripple, wherein, where a set of permanent magnets (16) of the multiple permanent magnets (16) corresponds to a set of slots (18) of the multiple slots (18) and forms a magnetic pole, and the set of slots (18) comprises a number of six slots (18), the ratio of the outside diameters Dr / Ds falls within the range expressed as follows: 0.615 ≤ Dr / Ds ≥ 0.63, wherein the rotating electric machine (10) is designed to satisfy a condition which is expressed as follows: L t / D r ≤ 0.04 2 L t ≤ L b 0.35 ≤ d / L s ≤ 0.44 0.32 ≤ L s / L t where: Lt is the thickness of each of the multiple teeth (15), Lb is the thickness of the back side of the surface of each of the multiple teeth (15), d is the diameter of the conductor of the coils, and Ls is the width of the opening of each of the multiple slots (18), wherein the multiple permanent magnets (16) and the multiple slots (18) form an 8-pole 48-slot motor, a 6-pole 36-slot motor, a 4-pole 24-slot motor, or a 10-pole 60-slot motor.

Description

Related registration

[0001] This application claims priority from Japanese Patent Application No. 2011-241408 filed on November 2, 2011, the entire contents of which are incorporated herein by reference. Technical area

[0002] The present invention relates to a rotating electric machine, and more particularly to a permanent magnet electric machine capable of acting as an electric motor providing high quality drive. General state of the art

[0003] Rotating electrical machines must have different characteristics for the different types of equipment with which they are used. For example, an electrical machine is required to function as a motor with variable speed over a wide range, as well as a high-torque motor for low-speed operation, when used as a traction motor, in a hybrid electric vehicle (HEV), with an internal combustion engine, or in an electric vehicle as the power source.

[0004] For an electric machine with such characteristics, the design using an embedded permanent magnet structure (Interior Permanent Magnet - IPM) is proposed, in which multiple pairs of permanent magnets are embedded in a rotor such that the magnets of each pair are arranged in a "V-shaped" arrangement opening toward the rotor circumference, since it is advantageous to use a structure that can effectively utilize the reluctance torque together with the magnetic moment, see, for example, Patent Literature 1.

[0005] In a rotating electrical machine with such an IPM structure, multiple pairs of permanent magnets are embedded in a rotor such that the permanent magnets of each pair are arranged in a "V-shaped" configuration to maintain the magnetic paths along the q-axis to effectively utilize the reluctance torque. This increases the ratio of the reluctance torque to the magnetic moment and also increases the saliency ratio (Ld / Lq), a ratio between the inductance along the d-axis and the inductance along the q-axis, resulting in an increased tendency for higher-order spatial harmonics to overlap with the flux waveform.The d-axis is aligned with a direction of flux generated by magnetic poles and acts as a central axis between each pair of permanent magnets arranged in the "V-shaped" arrangement, while the q-axis is electrically and magnetically at an angle of 90 in electrical degrees from the d-axis and acts as a central axis between the adjacent magnetic poles (i.e., the adjacent pairs of permanent magnets).

[0006] This causes high torque ripple, i.e., the difference between the highest and lowest torque during one revolution, in such a rotating electrical machine. This high torque ripple causes increased machine vibration and electromagnetic noise. It is particularly desirable to reduce electromagnetic noise as much as possible, as it causes unpleasant noise for passengers in a vehicle using the electric machine as an electric drive due to the relatively high frequency of the electromagnetic noise compared to that generated by the drive of an internal combustion engine.

[0007] On the other hand, high efficiency drive by the rotating electric machine is required to effectively generate a desired driving force with less power consumption, but the vibration becomes a loss, causing a reduction in efficiency.

[0008] Not only due to cargo space limitations but also due to new requirements for improving energy conversion efficiency (consumption) in hybrid and electric vehicles, there is a growing demand for lightweight and miniaturized rotating electrical machines capable of delivering high-energy-density output. Reducing torque ripple is effective for controlling shaking, abnormal vibrations, and providing smooth acceleration performance. For example, there is a need to provide high-efficiency propulsion over a range commonly used for driving a car on roads.

[0009] It is very difficult to combine miniaturization as stand-alone units with improved efficiency, reduced electromagnetic noise and low torque ripple, because in rotating electrical machines (motors), due to the occurrence of torque ripple according to an increase in energy density yield per unit volume, there is a tendency for electromagnetic noise to increase and a tendency for efficiency to decrease, but the demand for lightweight and miniaturization is increasing.

[0010] To achieve low electromagnetic noise and low torque ripple, it is proposed to axially divide a rotor to allow one of the adjacent pairs of permanent magnets to assume an angularly wound positional relationship with the other or to yield a deflection angle (see, for example, Patent Literature 2).

[0011] The aforementioned measure of providing a deflection angle in a rotating electrical machine not only causes an increase in assembly costs and thus an increase in manufacturing costs, but also causes a difference in the interfaces between adjacent pairs of permanent magnets and a deterioration in the magnetization rate at the interfaces, which causes the magnetic flux density of the permanent magnets to decrease. As a result, the output torque to be generated by the rotating electrical machine decreases.

[0012] For this reason, various concepts other than the measure of providing a deflection angle are proposed to achieve low electromagnetic noise and low torque ripple. These include an approach of changing an air gap between a rotor and a stator surrounding the rotor such that an air gap length at a position where each p-axis crosses the air gap is larger than the air gap lengths at other positions, for example, by changing the shape of the rotor circumference such that the rotor circumference has a bulbous shape, such as a "petal shape" at each magnetic pole (see, for example, Patent Literatures 1, 3, and 4).

[0013] In the rotating electric machines described in Patent Literatures 1, 3, and 4, an inductance at each p-axis increases because an air gap is wide, which causes not only a decrease in saliency ratio and a decrease in torque, but also a reduction in efficiency of the machine. State-of-the-art documentsPatent literature Patent Literature 1: Japanese Patent Laid-Open No. JP 2008-99418A Patent Literature 2: Japanese Patent Laid-Open No. JP 2006-304546 A Patent Literature 3: Japanese Patent Laid-Open No. JP 2000-197 292 A Patent Literature 4: Japanese Patent Laid-Open No. JP 2007- 312 591 A

[0014] The study regulations for the electrical engineering degree program without practical semester with the study areas of electrical power engineering, environmental engineering and building systems technology and for the electrical engineering degree program with integrated practical semester with the study areas of electrical power engineering and environmental engineering and building systems technology at the Dortmund University of Applied Sciences dated 9 July 1999 list the subjects “Numerical Calculation of Electrical Machines” and “Finite Element Theory and Application”.

[0015] The article "Small motor drives expand their technology horizons," written by Jim Miller and published in the "Power Engineering Journal," September 1987, pages 283-290, refers to numerical analysis in the design of electric motors. Materials selection and geometry optimization are performed through electromagnetic field analysis. The finite element method is often used for this purpose. A limitation of the finite element method is that it is only accurate if parasitic effects are removed. Furthermore, this method is based on currents and cannot be easily applied to voltage-based problems.

[0016] The article "Finite Elements applied to synchronous and switched reluctance motors," written by TJ E. Miller et al. from the SPEED Laboratory at the University of Glasgow and published in the IEE Seminar "Current trends in the use of finite elements (FE) in electromechanical analysis and design," IEE Savoy Place, 2000 IEEE, refers to calculation methods in which the geometry of the electric motor is defined in a motor design program editor. During the calculation, the rotor automatically moves through a series of positions.

[0017] The article "Electrical machines and electromagnetics - computer aids to design," written by ABJ Reece and published in the November 1988 issue of Power Engineering Journal, pages 315 to 321, addresses factors enabling new technologies in electrical machines. These include materials, improved cooling systems, manufacturing processes, improvements in semiconductors, and design and analysis techniques. The difficulties in calculating the electromagnetic field lie in the complex geometry, saturation effects, induced currents in coupled circuits, particularly eddy currents, and the excitation of permanent magnets. These difficulties limit analytical approaches.

[0018] The article "Ampere-Containing X-Ray Vision," written by Bernd Aschendorf and published in KEM 2001, February issue, pages 56ff., refers to the fact that the design and optimization of electrical machines in drive technology are among the most important activities of an electrical engineer. A finite element mesh is generated, including the coil interconnection. The material properties of the stator and rotor laminations, the conductor material, the permanent magnets, and the shaft are then defined linearly or nonlinearly. The calculation of the generated electrical machines is possible using a variety of static, quasi-stationary, harmonic, and transient approaches.

[0019] The article "First Calculate, Then Build," written by Bernd Aschendorf and published in Konstruktionspraxis No. 6, June 1996, pages 16 to 19, refers to the use of the finite element method for magnetic problems of electrical machines. Squirrel-cage synchronous machines are modeled and calculated fully automatically using simple specifications such as slot numbers, geometric parameters, and magnetic quantities.

[0020] Document GB 388 100 A relates to a squirrel-cage rotor for induction motors, particularly for electric percussion instruments, where the squirrel-cage rotor is subjected to vibrations in the axial direction. Some of the rotor bars are made of a material with high tensile strength, while others are made of a different material with high electrical conductivity. The bars of different materials alternate.

[0021] Document DE 11 78 143 A relates to press plate segments for laminated cores of electrical machines. To ensure that the stator core is sufficiently tightly compressed, solid plates are attached to the end faces of the laminated cores and clamped against each other. At both ends, these plates are clamped together by means of a press bolt.

[0022] Document US 3,826,940 A relates to a squirrel-cage rotor for an electric motor, comprising a slotted laminate and a pair of end plates at each end of the laminate stack. Conductor bars are arranged in each of the slots and extend to the ends of the end plates. Each lamination layer and each of the end plates have aligned openings. A bolt extends through the openings.

[0023] Document US 4,697,114 A relates to a rotor with permanent magnets. The rotor has a rotor shaft and four yokes extending axially from the rotor shaft and arranged circumferentially spaced from each other around the rotor. Each of the yokes consists of a plurality of magnetic sheets laminated together along the axial direction.

[0024] Document JP 2005-102460 A relates to a rotor of a rotating electrical machine. The core of the rotor is formed by stacking a plurality of magnetic steel sheets of different sizes and providing a fixing structure so that the rotor is stable during high-speed rotation. The core comprises two different types of magnetic steel plates stacked on top of each other. A bolt extends through a through hole formed in the core.

[0025] Document US 2009 / 0 026 867 A1 relates to a rotor having a rotor core rigidly connected to a rotating shaft and a plurality of holes arranged circumferentially. A magnet is arranged in each of the holes. An epoxy resin is provided in the holes to secure the magnets.

[0026] Document US 2007 / 0 063 607 A1 relates to a rotor core in which a plurality of slots are provided, extending in the direction of the rotor shaft. First slots are arranged at a center of the magnetic pole of the rotor core to accommodate a load acting on an inner circumferential surface of each opening in a direction normal to a main surface of the permanent magnet. Second slots are arranged between the magnetic poles of the rotor core to accommodate the load acting parallel to the main surface of the permanent magnet. This prevents deformation of the rotor in a radially outward direction.

[0027] Document JP 2005-184968 A relates to a rotor of a dynamoelectric machine. A structure is provided that prevents adhesive leakage when mounting a permanent magnet in a rotor of the dynamoelectric machine. The magnet is arranged in the core, which is formed from a stack of steel plates. The core has two types of magnetic steel plates, which differ in the shape of magnetic holes provided for the arrangement of magnets. The magnet is inserted into the holes and secured with an adhesive.

[0028] The article "The Permanent Magnet Synchronous Machine," published in the journal "Electrical Machines and Drives" 1-2 / 2011, pp. 4 to 9, by Prof. Dr.-Ing. Andreas Baral, Electrical Machines and Drive Technology, FHWT - Private University of Applied Sciences for Business and Technology in Vechta and Diepholz, refers to the structure and fields of a permanent magnet synchronous machine. Unlike with a separately excited synchronous machine, the magnetization of the machine cannot be influenced by the excitation current, but is determined by the machine's design. The main materials for the permanent magnets are (ceramic) ferrites, AlNiCo (aluminum-nickel-cobalt), and rare earth (RE) compounds, such as samarium-cobalt (SmCo) and neodymium-iron-boron (NdFeB). The document WO 2011 / 118062 A1 shows a permanent magnet rotor with V-magnets. Brief description of the invention

[0029] Therefore, it is an object of the present invention to provide a rotating electrical machine capable of providing high quality and high efficiency machine operation with reduced vibration and noise by reducing torque ripple.

[0030] According to a first aspect of the present invention, there is provided a rotating electrical machine comprising a rotor having a rotor shaft located on a rotor axis and a stator rotatably supporting the rotor, wherein the stator comprises a plurality of teeth extending toward a circumferential surface of the rotor and terminating at inner circumferential surfaces facing the circumferential surface of the rotor, and a plurality of grooves each located between two adjacent ones of the teeth and providing spaces for winding coils around the teeth for the input of the electric drive power, wherein the rotor has a plurality of permanent magnets embedded therein to allow the magnetic force to act on those surface portions of the teeth which are opposite to the permanent magnets, wherein the rotor within the stator is driven to rotate by the reluctance torque resulting from the magnetic flux flowing through the teeth, the back surface of the teeth and the rotor when current flows through the coils, and the magnetic moment in the form of attraction and repulsion resulting from the interference with the permanent magnets, wherein an outer diameter ratio of an outer diameter Dr of the rotor to an outer diameter Ds of the stator falls within a range effective to minimize torque ripple.

[0031] According to a second aspect of the present invention, in addition to the feature specified in the first aspect, when a set of permanent magnets of the plurality of permanent magnets corresponds to a set of slots of the plurality of slots and forms a magnetic pole and the set of slots comprises a number of six slots, the ratio of the outer diameters Dr / Ds in the range which is expressed as follows: 0.61≤Dr / Ds≤0.645.

[0032] According to a third aspect of the present invention, the rotating electrical machine is designed, in addition to the feature specified in the first and second aspects, to satisfy the condition expressed as follows: Lt / Dr≤0.04 2Lt≤Lb 0.35≤d / Ls≤0.44 0.32≤Ls / Lt where: Lt is the thickness of each of the plurality of teeth, Lb is the thickness of the back side of the surface of each of the plurality of teeth, d is the diameter of the conductor of the coils, and Ls is the width of the opening of each of the plurality of slots.

[0033] The magnetic pole can be formed by permanent magnets of each pair embedded in the rotor and arranged in a “V-shaped” arrangement opening towards the rotor circumference.

[0034] According to the first aspect of the present invention, the rotor and stator satisfy the condition that the ratio of the rotor outer diameter Dr to the stator outer diameter Ds falls within a range effective for minimizing torque ripple. As a result, high-quality machine operation with reduced vibration and noise, and simultaneously high-efficiency machine operation with reduced losses, is provided because torque ripple is reduced.

[0035] According to the second aspect of the present invention, the outer diameter ratio falls within the range of 0.61 to 0.645 when one magnetic pole for the permanent magnets of each set or pair in the rotor corresponds to a set with a number of six slots. This results in high-quality machine operation with reduced losses, in addition to reduced vibration and noise.

[0036] According to the third aspect of the present invention, coils can be formed by automatically binding windings using an automatic binding machine in each slot between the adjacent teeth, in addition to reducing iron loss due to the condition of (the thickness of each stator tooth Lt) / (the outer diameter of the rotor Dr) ≤0.04, (2Lt) ≤ (the thickness of the rear side of the surface of each stator tooth Lb), 0.35 ≤ (the diameter of the coil conductor d) / (the width of the opening of each slot Ls) ≤0.44, and 0.32 ≤ (the width of the opening of each slot Ls) / (the thickness of each stator tooth Lt). Short description of the drawings Fig. 1 is a plan view showing an embodiment of a rotating electrical machine according to the present invention, showing the plan of its overall structure. Fig. 2 is a fragmentary plan view showing an effective magnetic pole opening angle for a magnetic pole in the machine. Fig. 3 is a plan view showing a flux pattern of magnetic flux generated by a stator of the machine when a rotor of the machine has no magnetic poles. Fig. Figure 4 is a graphical representation of an approximate waveform of the magnetic flux (the first harmonic). Fig. Figure 5 is a schematic diagram showing the relationship between the approximate magnetic flux waveform, the effective magnetic pole opening angle, and a magnet opening angle. Fig. 6A and Fig. 6B are schematic diagrams illustrating an oscillation or vibration mode generated in the stator. Fig. 7A and Fig. 7B are schematic diagrams illustrating another oscillation or vibration mode in the stator, which is different from the vibration mode of Fig. 6A and Fig. 6B differs. Fig. Figure 8 is a graph showing electromagnetic analysis results versus the ratio of the rotor outer diameter to that of the stator as a parameter. Fig. Figure 9 is a graph showing results of electromagnetic analysis against the ratio of the outer diameter of the rotor to that of the stator as parameters, which are different from those of Fig. 8 distinguish. Fig. Figure 10 is a graph showing results of electromagnetic analysis against the ratio of the outer diameter of the rotor to that of the stator as parameters, which are different from those of Fig. 8 and Fig. 9 differ. Description of versions

[0037] Hereinafter, embodiments of the present invention will be specifically explained with reference to the accompanying drawings. Fig. 1 to 10 show an embodiment of a rotating electrical machine according to the present invention.

[0038] With reference to Fig. 1 and Fig. 2, a rotating electrical machine (motor) 10 has good performance for use in, for example, a hybrid electric car or electric car as a drive source in a similar manner to an internal combustion engine or as an in-wheel drive unit, and comprises a stator 11 formed in a cylindrical configuration and a rotor 12 rotatably received in the stator 11 with a rotor shaft 13 such that the rotor 12 is located on a rotor axis common to an axis for the stator 11.

[0039] With an air gap G between the stator 11 and the rotor 12, the stator 11 includes slots 18 extending over an entire circular inner periphery toward the rotor axis, and a plurality of stator teeth 15 defined by the slots 18. The stator teeth 15 extend in radial directions toward the rotor axis, with their ends facing an outer circular peripheral surface 12a of the rotor 12 with the air gap G therebetween. The stator teeth 15 are wound to provide a distributed three-phase winding (not shown) to form coil windings designed to induce flux patterns for generating rotor torque transmitted to the rotor 12.

[0040] The rotor 12 is an embedded permanent magnet (IPM) rotor in which multiple sets (pairs in this example) of permanent magnets 16 are embedded such that magnets from each set comprise a pair of permanent magnets 16 arranged in a "V-shaped" configuration opening toward its outer circular peripheral surface 12a. The rotor 12 is formed with multiple pairs of holes 17 arranged in a "V-shaped" configuration opening toward the outer circular peripheral surface 12a and extending axially through the rotor 12.The holes 17 of each pair include a pair of hole sections 17a in which the permanent magnets 16 of each pair, which are plate-shaped magnets (flat magnets), are housed and are inserted with their corner sections 16a into the adjacent two angled inner walls defining the corresponding hole section 17a and held immovably in a facing relationship. Each of the holes 17 includes two space sections 17b located on the opposite sides of the corresponding plate-shaped magnet 16 and spaced apart in a width direction from the magnet 16 to act as flux barriers for restricting spurious flux (hereinafter referred to as "flux barriers").The bores 17 of each pair are provided with a central web 20 which connects the permanent magnets 16 of the associated pair to each other in order to hold the permanent magnets 16 in a suitable position against the centrifugal force at high speeds of the rotor 12.

[0041] In this rotating electrical machine 10, the stator teeth 15 are angularly spaced to provide spaces, such as the slots 18, to accommodate the coil windings, such that six stator teeth 15 cooperate with the corresponding one of eight sets of permanent magnets 16, in other words, six (6) slots 18 face one of eight sets of permanent magnets 16. For this reason, the rotating electrical machine 10 is designed to act as an 8-pole 48-slot three-phase IPM motor comprising eight (8) magnetic poles (four magnetic pole pairs) for eight (8) sets of permanent magnets 16, in which the N poles and S poles of the permanent magnets 16 of each set are rotated 180 in mechanical degrees with respect to those of the adjacent set, and forty-eight (48) slots 18 accommodate coil windings formed by a distributed single-phase winding using six (6) slots 18 defining five (5) stator teeth 15.The illustrated markings N and S are used in this declaration for the purpose of simplicity, but these are not located on the surfaces of the components.

[0042] This structure causes the rotating electrical machine 10 to drive the rotor 12 and the rotor shaft 13 when the coil windings in the slots 18 are energized such that the magnetic flux patterns from the stator teeth 15 flow inwardly into the rotor 12 from the outer circular peripheral surface 12a, since a rotor torque is generated by a reluctance torque tending to minimize the magnetic flux paths for the magnetic flux patterns from the stator 11 in addition to the magnetic moment resulting from the attraction and repulsion by the interaction of the magnetic flux patterns with magnetic pole flux patterns for the permanent magnets 16 of each set.

[0043] As in Fig. As shown in Figure 3, the coil windings of the rotating electrical machine 10, formed by the distributed winding, are housed in the slots 18 to provide a flux pattern of the flux from the stator 11 into the rotor 12 that includes distributed magnetic paths for each of a plurality of sets of stator teeth 15 corresponding to one of the magnetic poles for the plurality of pairs of permanent magnets 16. The V-shaped holes 17 of each pair for the permanent magnets 16 extend along the magnetic paths, or in other words, in a manner that does not interfere with the formation of such magnetic paths.It should be noted that thin sheets of magnetic steel such as silicon steel or the like are arranged in a layered axial relationship to a suitable thickness for a desired output torque and are fastened with fastening screws using driver holes 19 in a process for manufacturing the stator 11 and the rotor 12.

[0044] Considering the rotating electrical machine 10 which uses the IPM structure in which the permanent magnets 16 are embedded in the rotor 12, the change of the magnetic flux in one tooth of the stator teeth 15 of the stator 11 can be determined by a Fig. 4. The superposition of these first harmonics of the magnetic flux and the lower-order spatial harmonics, the fifth (5th) and seventh (7th) harmonics, is a factor that affects not only the vibration and noise experienced by vehicle occupants, but also iron losses and a reduction in the efficiency of machine operation due to a loss as heat energy generated by high torque ripple (i.e., the difference between the maximum and minimum torque during one revolution). Suppressing the spatial harmonics reduces the iron losses to improve the efficiency of machine operation in terms of electrical energy supply because the hysteresis loss is the product of frequency and magnetic flux density, and the eddy current loss is the product of the square of frequency and magnetic flux density. With reference to Fig. 4, in which the vertical axis represents magnetic flux and the horizontal axis represents time, the illustrated square waveform approximates the change in magnetic flux in a tooth of the stator teeth 15 over a cycle T (4L1 + 2L2) in electrical degrees, in which no magnetic flux flows through the tooth during a period L1 and magnetic flux flows forward through the tooth with an amplitude during a period L2 of the first half of the cycle T and flows in the reverse direction through the tooth during the period L2 of the second half of the cycle T.

[0045] Electromagnetic noise from the motor (rotating electrical machine) is generated by stator vibration caused by an electromagnetic force acting on the stator. When the electromagnetic force acts on the stator, a radial electromagnetic force originating from the magnetic coupling between the rotor and the stator and an angular electromagnetic force originating from the torque are present. Considering the radial electromagnetic force acting on each of the stator teeth 15 when a linear magnetic circuit approaches the motor, the radial electromagnetic force fr and the magnetic energy W can be expressed in the following formulas (1) and (2): W=12ϕ2Rg=12(B⋅S)2⋅xμS=12μB2⋅x⋅S fr=∂W∂x=12μB2S∂∂x(x)=12μB2S where ϕ is the magnetic flux, W is the magnetic energy, fr is the radial electromagnetic force, Rg is the reluctance, B is the magnetic flux density, S is a region through which the magnetic flux flows, x is the length of the air gap (G) and ε is the permeability in the magnetic path.

[0046] When considering the space harmonics, the flux density B can be expressed as shown in the following formula (3), and it follows that the superposition of the first harmonic and the space harmonic is a factor that increases the radial electromagnetic force fr, since the radial electromagnetic force fr comprises the square of the flux density B. Careful study and observation by the inventor has shown that reducing the space harmonics reduces the torque ripple, resulting in not only the implementation of reducing the electromagnetic noise of the motor but also improving the efficiency of the machine operation. B=∑t=1tBt sin t(θ+δt)

[0047] The inventor's careful study and observation has also proved that the torque ripple in an IPM three-phase motor results from the 6f-th (where f = 1, 2, 3, ... are natural numbers) harmonic components at θ in electrical degrees, which results from the combination, with respect to one phase for one magnetic pole, of the space harmonics with the time harmonics contained in the input-phase power supply.

[0048] More specifically, the three-phase output P(t) and the torque τ(t) can be given by the expressions in the following formulas (4) and (5). P(t)=Eu(t)Iu(t)+Ev(t)Iv(t)+Ew(t)Iw(t)=ωm⋅τ(t) τ(t)=[Eu(t)Iu(t)+Ev(t)Iv(t)+Ew(t)Iw(t)] / ωm where ω m is the angular velocity; E u (t), E v (t) and E w (t) are the voltages induced in the U-phase, V-phase and W-phase, respectively; and I u (t), I v (t) and I w(t) are the U-phase, V-phase and W-phase currents respectively.

[0049] The three-phase torque is the sum of the torques of the U-phase, V-phase, and W-phase. Assuming that m is the order of the harmonic component in the current and n is the order of the harmonic component in the voltage, the voltage induced in the U-phase can be u (t) can be written as in the following formula (6) and the U-phase current I u (t) can be written as in the following formula (7), and the torque in the U-phase τ u (t) can be given by the expression shown in the following formula (8). Eu(t)=∑n=1nEn⋅sin n⋅(θ+αn) Iu(t)=∑m=1mImsin m⋅(θ+βm) τu(t)=1ωm[∑n=1n∑m=1mEm Im{−12(cos((n+m)θ+n αn+mβm)−cos((n−m)θ+n αn−mβm)}]

[0050] It is well known that the phase voltage E(t) and the phase current I(t) are symmetrical waves and thus n and m are only odd numbers. It is also known that the voltage E induced in the V-phase v (t) and current I v (t) for the torque in the V-phase and the voltage induced in the W-phase E w (t) and current I w (t) for the torque in the W-phase by + 2π / 3 radians and - 2π / 3 radians from the voltage E induced in the U-phase u (t) or current I u (t) for the torque in the U-phase are shifted. It can be seen that in the three-phase torque expression, only terms with the coefficient 6 remain, and all other terms cancel each other out. It follows that the three-phase torque τ(t) can be written as the following formula (9). τ(t)=1ωm[∑n=1n∑m=1mEm Im{−12{3 cos(6 f θ+s)−3 cos(6 f θ+t)}}] where 6f = n±m (f is the natural number), s = nαn + mβ m , t = nα n - mβ.

[0051] From the previous formula, it is clear that when the order n of the space harmonics contained in the flux (induced voltage) and the order m of the time harmonics contained in the phase supply current are combined to give the number 6f, torque ripples of the 6fth order are generated in the three-phase AC motor because, since an induced voltage is known as the time derivative of a magnetic flux, the harmonics contained in the induced voltage for each phase are of the same order as the harmonics contained in a single-phase magnetic pole flux with the same phase.

[0052] Now, torque ripples in the three-phase motor are generated when the first harmonic and the space harmonic of order n = 5, 7, 11, 13 are superimposed in a sine approximation method with, for example, only the time harmonic of order m = 1 contained in the phase current, because the torque ripples are generated when the order m of the space harmonic in the waveform of the magnetic flux of one phase for one magnetic pole and the order n of the time harmonic in the phase current of the same phase are combined to satisfy the condition that n±m=6f (f is the natural number).

[0053] For a three-phase IPM motor such as the rotating electrical machine 10, which has six (6) slots 18 for each magnetic pole and twelve (12) slots 18 corresponding to each pair of magnetic poles, the reluctance in some of all the slots 18 at circumferentially spaced twelve (12) positions during a cycle becomes high in electrical degrees, causing a superposition of the first harmonic of the flux waveform and the eleventh (11th) and thirteenth (13th) space harmonics (n = 11, 13).

[0054] However, it is difficult to reduce torque ripple components caused by the fifth (5th) and seventh (7th) spatial harmonics (n = 5, 7), ie harmonics of the 6th order, since 6f = 6, since, as in Fig. 4, the flux waveform resulting from the flux linkage of the magnetic field on one of the stator teeth 15 approaches the square waveform and the 5th and 7th harmonics can thus easily overlap with the first harmonic of the flux waveform.

[0055] The Fourier transform equation f(t) when the flux waveform in one of the stator teeth 15 for the three-phase IPM structure approaches a rectangular waveform can be given by the expression in the following formula (10) and the Fig. The flux waveform F(t) shown in Figure 4 can be given by the expression in the following formula (11). This flux waveform F(t) can be written as the following formula (12), an approximate formula that includes space harmonics not higher than the 7th harmonic, which in turn can be converted into the following formula (13) by the arrangement of terms obtained after expansion using the sum-product formula in trigonometry. From this formula (13), it is clear that the satisfaction of the following condition 1 or 2 is required to reduce the 5th or 7th harmonic. cos 5ω⋅L1=0 cos 7ω⋅L1=0 f(t)=4π∑k=1∞sin{(2k−1)ωt}2k−1 F(t)=12[f(t−α)+f(t+α)]=12[4π∑k=1∞sin{(2k−1)ω(t−α)}2k−1+4π∑k=1∞sin{(2k−1)ω(t+α)}2k−1] F(t)=12[4π{sinω(t−α)+13sin3ω(t−α)+15sin5ω(t−α)+17sin7ω(t−α)} +4π{sinω(t+α)+13sin3ω(t+α)+15sin5ω(t+α)+17sin7ω(t+α)}] F(t)=4π[sinω t⋅cosω α+13sin3ω t⋅cosω α +15sin5ω t⋅cos5ω α+17sin7ω t⋅cos7ω α]

[0056] With reference to the Fig. 4, its behavior can be expressed by the following formula (14). Substituting this formula for the relationship (i.e., 5ω·L1=±π / 2) derived from Condition 1 yields the expression in the following formula (15), which is called "Condition 1 as modified." This expression is rewritten using the fact that L1, L2 > 0 can yield the expression in the following Condition 1A. It should be noted that Condition 1A, when satisfied, provides a reduction in torque ripple by lowering the 5th spatial harmonic to zero. Angular frequency (angular velocity) ω = 2π / T = 2π / (4L1 + 2L2) Condition 1 as changed: 5ω⋅L1=5⋅2πL1 / (4L1+2L2)=±π / 2Condition 1A: L1=L2 / 8

[0057] Similarly, Condition 2, as modified, can be written as the following formula (16). This expression is rewritten using the fact that L1, L2 > 0 can yield the expression in Condition 2A below. It should be noted that Condition 2A, when satisfied, provides a reduction in torque ripple by lowering the 7th spatial harmonic to zero. Condition 2 as changed: 7ω⋅L1=7⋅2πL1 / (4L1+2L2)=±π / 2Condition 2A: L1=L2 / 12

[0058] For the 8-pole 48-slot rotating electric machine 10, the peripheral speed V of the rotor 12 is expressed in the following formula (17) using the following relationship maintained in the machine 10, which is rewritten as the following formula (18), where r is the radius of the rotor 12. 45 in mechanical degrees = T / 2 revolution in electrical degrees V(m / sec)=2πr⋅(45° / 360°) / (T / 2)=2πr⋅(45° / 360°) / {(4L1+2L2) / 2}=r(m)⋅ω(rad / sec) 2L1+L2=π / 4ω

[0059] Substituting condition 1A and condition 2A in the previous formula (18) yields the following conditions. The 5th spatial harmonic=0→(L2,L1)=(π / 5ω,π / 40ω) The 7th spatial harmonic=0→(L2,L1)=(3π / 14ω,π / 56ω)

[0060] This increases the tendency to reduce the 5th and 7th space harmonics in the rotating electrical machine 10 to limit the increase of the torque ripple by providing an arrangement that satisfies the following concatenated representation of inequalities (19). π / 5ω≤L2≤3π / 14ω(sec)

[0061] Here, the term L2 in the concatenated representation of inequalities (19) represents the area on the side of the rotor 12 facing the stator teeth 15, which is a magnetic path for the magnetic flux that carries the magnetic fields shown in Fig. 4, and therefore it can be interpreted as an arc in the air gap G connecting these two lines diverging from the rotor axis (the apex) and passing through the flux barriers 17b from both sides of a given pair of permanent magnets 16 forming a divergence angle θ1, which is called the “effective magnetic pole opening angle θ1”.

[0062] With reference to the Fig. 4, the effective magnetic pole opening angle θ1 can be written as θ1=ωL2, since the relationship θ=ωt is maintained, and thus the concatenated representation of inequalities (19) can be written as various expressions as follows. In the case of an 8-pole, 48-slot rotating electric machine 10 (the arrangement in which six (6) slots consecutively correspond to or oppose eight (8) magnetic poles), for example, one revolution of the rotor 12 through 360 in mechanical degrees corresponds to four revolutions in electrical degrees, since each of four pairs of eight (8) magnetic poles undergoes one revolution. The various expressions are: π / 5(rad)≤θ1(in mechanical degrees)≤3π / 14(rad), and 36(deg rees)≤θ1(in mechanical degrees)≤270 / 7(deg rees). Since θ1(in mechanical degrees)=(8poles / 2poles)⋅θ1(in electrical degrees), 144(degrees)≤θ1(in electrical degrees)≤154.3(degrees).

[0063] As in Fig. As shown in Figure 5, this results, per magnetic pole in the rotating electrical machine.10, in an arrangement of the permanent magnets 16 with their flux barriers 17b at one and the opposite edges within a range defined by these two lines diverging from the rotor axis (the apex) and forming the effective magnetic pole opening angle θ1, which falls within a range expressed as follows: 36°≤θ1(in mechanical degrees)≤38.6° or 144°≤θ1(in electrical degrees)≤154.3°

[0064] In the IPM structure in which the permanent magnets 16 of each pair embedded in the rotor 12 are arranged in a "V-shaped" configuration, a d-axis represents a direction of the magnetic flux generated by the magnetic poles, that is, a central axis between each pair of permanent magnets 16 arranged in the "V-shape," while a g-axis represents an axis that is electrically and magnetically at an angle of 90 in electrical degrees from the d-axis and acts as a central axis between the permanent magnets 16 of the adjacent magnetic poles. In this situation, the effective magnetic pole opening angle θ1 per magnetic pole in the rotor 12 corresponds to the duration L2 during which the magnetic flux flowing through the stator teeth 15 continues, as can be seen from the waveform adapted to the Fig. 4, is easily seen. As shown in Fig. 5, the duration L2 of the magnetic flux waveform is located at the midpoint between the q-axes of each pair, forming an angle θ2 such that the d-axis passes through the midpoint of the duration L2. The illustrated angle θ2 of Fig. 2 is an angle formed by the q-axes of each pair, equal to 45° in mechanical degrees, and an angle in electrical degrees equal to half the cycle in the magnetic flux waveform.

[0065] Accordingly, the rotating electrical machine 10 with the effective magnetic pole opening angle θ1 covering not only the permanent magnets 16 of each pair but also their flux barriers 17b in the rotor 12 and falling within the range {144° ≤ θ1 (in electrical degrees) ≤ 154.3°}, which is effective for reducing the torque ripple by suppressing the 5th and 7th space harmonics, n = 5, 7, in the phase voltage, each of which cooperates with the time harmonic of the phase current of order m = 1 to satisfy the specific order of the 6f-th (n = 5, 7), is enabled to drive its rotor shaft 13 with high-quality rotation with reduced torque ripple, vibration, and noise.In addition, it enables it to drive the rotor shaft 13 with the highly efficient rotation through reduced losses, since the reduced torque ripple reduces the vibration to suppress not only the heat loss but also hysteresis and iron loss.

[0066] To study a three-phase IPM motor, which uses the rotating electric machine 10 as its basic structure, a vibration analysis of the stator 11 (stator iron core) was performed. This analysis clarified that the vibration mode shape of a rotating octagon (mode number k = 8) is generated by the 2nd, 4th, 8th, and 10th orders of the radial electromagnetic force fr, see formula (2), which are generated due to the superposition of the first harmonic (t = 1), 3rd spatial component (t = 3), and 5th spatial component (t = 5), as expressed in the previous formula (3), and the vibration mode shape of a perfect circle exhibiting cyclic expansion and contraction (mode number k = 0) is generated by the 6th and 12th orders of the radial electromagnetic force fr. For example, the octagon converted by the vibration of the stator 11 rotates in the vibration mode determined by the 2nd harmonic (or the 2ndorder of the radial electromagnetic force fr) which is generated in . Fig. 6A and Fig. 6B at two different times T1 and T2, and in the oscillation mode generated by the 6th harmonic (or the 6th order of the radial electromagnetic force fr) present in Fig. 7A and Fig. 7B, a cyclic expansion and contraction of the stator 11 takes place. Furthermore, in the vibration mode generated by the 10th order of the radial electromagnetic force fr, which is not illustrated, the oval shape of the vibration mode is combined with the octagonal shape of the vibration mode (mode number k = 8).

[0067] In the rotating electrical machine 10 in the form of an 8-pole, 48-slot motor, the magnetic flux density is distributed such that eight (8) magnetic fluxes are arranged angularly one after another with respect to one revolution of 360 in mechanical degrees, and the eight (8) radial electromagnetic forces fr are arranged angularly one after another such that the eight angularly arranged radial electromagnetic forces fr induce the vibration mode with its mode number k=8. In addition, the stator 11 vibrates in the vibration mode generated by the 6th and 12th order radial electromotive force fr by a composite electromagnetic force vector, which is the sum of an electromagnetic force vector due to the torque ripple and a radial electromagnetic force vector due to the magnetic coupling with the stator 11.Therefore, during the vibration mode k = 0, in which expansion and contraction alternately occur, the vibration caused by the 6f-th order accompanied by torque ripple—that is, the 6th and 12th orders in this example—propagates through the circumferential clearance of the stator 11, causing an increase in the level of electromagnetic noise of the motor of the rotating electrical machine 10 compared to the other orders. In the other orders except the aforementioned 6f-th order, no torque ripple, vibration, or noise, which can cause problems, occur.

[0068] Accordingly, it is clarified that the suppression of the 6th order harmonics (m = 1, n = 5, 7) in the magnetic flux waveform, which is considered to be a cause of problems, provides a reduction in torque ripple and shaking in the rotating electrical machine 10, thereby suppressing not only abnormal vibrations in its car-mounted state called "judder" but also electromagnetic noise.

[0069] In addition to reducing torque ripple, not only the structure per magnetic pole on the rotor 12 but also the ratio of the outer diameter of the rotor 12 to that of the stator 11 in the rotating electrical machine 10 are adjusted such that the ratio of the outer diameters falls within a range effective for minimizing torque ripple.

[0070] Like the Fig. As the data shown in Figures 8 to 10 clearly show, not only the torque ripple but also the THD of the line voltage is reduced when a ratio of the outer diameter Δ (= Dr / Ds), where: Dr is the outer diameter of the rotor 12 of the rotating electrical machine 10, and Ds is the outer diameter of the stator 11, falls within a range expressed as follows: 0.61≤Δ≤0.645 or preferably 0.615≤Δ≤0.63 or even more preferable 0.62≤Δ≤0.625.

[0071] The data in Fig. Figures 8 to 10 result from the analysis of the electromagnetic field using the finite element method and show the torque and torque ripple generated by 6th and 12th (6f.) order harmonics versus the outer diameter ratio Δ as a parameter.

[0072] Fig. 8 shows not only a torque ripple ratio or a torque change amplitude, that is, a torque ripple to average torque ratio {(maximum - minimum) / average torque} against the outer diameter ratio Dr / Ds (Δ) as a parameter, but also a change rate of torque with harmonics when superimposed on the first harmonic flux waveform, a change rate of a 6th order high harmonic torque, and a change rate of a 12th order high harmonic torque with values ​​determined with the outer diameter ratio Δ as a basis thereof set to 0.61.

[0073] As in Fig. As shown in Figure 8, the torque ripple ratio when the outer diameter ratio Δ=0.61 is equal to that when the outer diameter ratio Δ=0.635, and the torque ripple ratio is lower within a section when the outer diameter ratio Δ is in a range of 0.61 to 0.635 than within the other sections. In addition to the lower torque ripple ratio levels, a change rate of the torque ripple ratio is kept low within a section when the outer diameter ratio Δ is in a range of 0.615 to 0.63, and it is further kept low within a section when the outer diameter ratio Δ is in a range of 0.62 to 0.625.A suitable range within which the outer diameter ratio Δ should fall can be determined by considering the torque ripple ratio and the change rates of high harmonic torques, although there is a tendency to increase until the outer diameter ratio Δ reaches 0.65, the torque change rate has an upper limit of about 0.03 and is not so high.

[0074] Fig. Figure 9 shows high levels of spatial harmonics (spatial harmonic content or components) of the line voltage, including the levels of high spatial harmonics of order n = 5, 7 (caused by the torque of the 6th harmonic) and high spatial harmonics of order n = 11, 13 (caused by the torque of the 12th harmonic) and the THD (Total Harmonic Distortion) of the line voltage versus the ratio of the outer diameters Δ as a parameter.

[0075] As in Fig. As shown in Figure 9, the content of the high 11th-order spatial harmonics changes more significantly than the contents of the other high spatial harmonics. The harmonic content is the same when the outer diameter ratio Δ=0.61 and the other when the outer diameter ratio Δ=0.645, and it is lower in one section than in the other sections when the outer diameter ratio Δ is in the range of 0.61 to 0.645. Furthermore, the high content of the 11th-order spatial harmonics is further kept low in a section when the outer diameter ratio Δ is in the range of 0.61 to 0.63.

[0076] Fig. 10 shows a change rate of the 6th harmonic content (the 6th harmonic content) of the electromagnetic force and a change rate of the 12th harmonic content (the 12th harmonic content) of the electromagnetic force with values ​​determined when the ratio of the outer diameters Δ is set to 0.61 as their base.

[0077] As in Fig. As shown in Figure 10, each of the contents of the harmonics of the electromagnetic force does not change significantly and shows a tendency to decrease within a section when the ratio of the outer diameters Δ is in a range of 0.61 to 0.66, but the content of the 6th harmonic shows a tendency to increase rapidly when the ratio of the outer diameters Δ exceeds 0.66.

[0078] Based on the previously mentioned trend in Fig. 9 and Fig.10, the outer diameter Ds of the stator 11 and that Dr of the rotor 12 are preferably set such that, as mentioned in the foregoing description, the outer diameter ratio Δ (Dr / Ds) falls within a range of 0.61 to 0.645, preferably within a range of 0.615 to 0.63, and more preferably within a range of 0.62 to 0.625. Without arranging the stator 11 and the rotor 12 such that their positions assume an angularly wound relationship to each other or a so-called deflection angle, adjusting the outer diameter ratio Δ of the stator 11 and the rotor 12 to a value falling within the foregoing range can reduce not only the torque ripple but also the THD of the line voltage even in a range commonly used for running a car on a road after starting.

[0079] The teeth 15 of the stator 11 are wound using the slots 18 by winding using an insert-type winding machine to provide a distributed three-phase winding. By setting the coil occupancy of each stator slot 18 to fall within a range of 75% to 90%, which is derived from a calculation based on the assumption that a rectangular wire is used, under the condition that a ratio d / Ls falls within a range of 0.35 to 0.44 when a parallel winding is inserted into each stator slot 18, where d is the diameter of the coil conductor and Ls is the width of the opening of each stator slot 18 facing the rotor 12, the aim is to reduce copper loss. In addition to reducing copper loss, the dimensions of various sections of the stator 11 are determined to meet the conditions expressed as follows: Lt / Dr≤0.04, 2Lt≤Lb, 0.32≤Ls / Lt where Lt is the thickness of each stator tooth 15; and Lb is the thickness of the side behind each stator tooth 15 (Back York).

[0080] When two parallel windings are introduced into each stator tooth 18, the dimensions are determined to satisfy the condition that the ratio d / Ls falls within a range of 0.29 to 0.32.

[0081] According to the present embodiment, the torque ripple is reduced to the minimum range because the outer diameter ratio Δ (Dr / Ds) of the outer diameter Dr of the rotor 12 to the outer diameter Ds of the stator 11 falls within the range of 0.61 to 0.645. With the automatic bonding applied to form coils and the reductions in copper and iron loss, efficient operation of the rotating electrical machine 10 is achieved because the thickness Lt of each stator tooth 15, the thickness Lb of the back York behind each stator tooth 15, and the like in the stator 11 are designed to meet the aforementioned optimal conditions. As a result, in addition to high-quality operation of the rotating electrical machine 10 with reduced vibration and noise, high-efficiency operation of the rotating electrical machine 10 with reduced loss is achieved.

[0082] In the foregoing description of the present embodiment, the structure in which multiple pairs of permanent magnets 16 are embedded in a rotor 12 such that the magnets of each pair are arranged in a "V-shaped" configuration is described as an example. This present embodiment is not limited to this example, but can be applied, for example, to the configuration in which permanent magnets are embedded in a rotor 12 such that they face the peripheral surface 12a in a manner to provide the same effects.

[0083] In the foregoing description of the present embodiment, a rotating electrical machine 10 in the form of an 8-pole, 48-slot motor is used as an example, but it is not limited to this structure. The present invention can be applied to motors that include six (6) slots for each magnetic pole, such as a 6-pole, 36-slot, 4-pole, 24-slot, or 10-pole, 60-slot motor, by utilizing only θ1 in electrical degrees within the range of the effective magnetic pole opening angle θ1.

[0084] It is not intended to limit the scope of the present invention to the illustrated and described embodiment. It is understood that all variations that achieve similar effects to those aimed at by the present invention are within the scope of the present invention. It is understood that various changes may be made to the function and arrangement of elements without departing from the scope of the present invention as set forth in the appended claims and their legal equivalents. [Industrial applicability]

[0085] It will be understood that although one embodiment of the present invention has been described, this is merely an example and is not intended to limit the scope of the present invention. It will also be understood that a large number of variations exist without departing from the spirit of the present invention. [Explanation of reference symbols] 10 rotating electrical machine 11 Stator 12 Rotor 13 Rotor shaft 15 stator teeth 16 permanent magnet 16a corner section 17 holes arranged in a “V-shape” 17b River barrier 18 grooves 20 central bridge Dr rotor diameter Ds stator diameter Lt Thickness of the stator tooth Lb Thickness of Back York Ls slot opening width θ1 Effective magnetic pole opening angle

Claims

[1] Rotating electrical machine (10) comprising a rotor (12) with a rotor shaft (13) located on a rotor axis, and a stator (11) rotatably supporting the rotor (12), wherein the stator (11) comprises a plurality of teeth (15) extending toward a circumferential surface of the rotor (12) and terminating at inner circumferential surfaces facing the circumferential surface of the rotor (12), and a plurality of grooves (18) each located between two adjacent ones of the teeth (15) and providing spaces for winding coils around the teeth (15) for the input of the electric drive power, wherein the rotor (12) has a plurality of permanent magnets (16) embedded therein to allow the magnetic force to act on those surface portions of the teeth (15) which are opposite the permanent magnets (16), wherein the rotor (12) within the stator (11) is driven to rotate by the reluctance torque resulting from the magnetic flux flowing through the teeth (15), the rear side of the surface of the teeth (15) and the rotor (12) when current flows through the coils, and the magnetic moment in the form of attraction and repulsion resulting from the interference with the permanent magnets (16), wherein an outer diameter ratio of an outer diameter Dr of the rotor (12) to an outer diameter Ds of the stator (11) falls within a range effective to minimize torque ripple, wherein when a set of permanent magnets (16) of the plurality of permanent magnets (16) corresponds to a set of slots (18) of the plurality of slots (18) and forms one magnetic pole and the set of slots (18) comprises six slots (18), the ratio of the outer diameters Dr / Ds falls within the range expressed as follows: 0.615≤Dr / Ds≥0.63, wherein the rotating electrical machine (10) is designed to satisfy a condition expressed as follows: Lt / Dr≤0.04 2Lt≤Lb 0.35≤d / Ls≤0.44 0.32≤Ls / Lt where: Lt is the thickness of each of the plurality of teeth (15), Lb is the thickness of the back side of the surface of each of the plurality of teeth (15), d is the diameter of the conductor of the coils and Ls is the width of the opening of each of the plurality of slots (18), wherein the plurality of permanent magnets (16) and the plurality of slots (18) form an 8-pole 48-slot motor, a 6-pole 36-slot motor, a 4-pole 24-slot motor or a 10-pole 60-slot motor.

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