JP2022042710A - Rotary electric machine - Google Patents

Abstract

To provide a rotary electric machine using a permanent magnet.SOLUTION: A rotary electric machine 1 comprises: an armature 10; and a field rotator 20 which has a rotary iron core 22 provided with a plurality of spokes 24 in a circumferential direction R2, and a first permanent magnet 30 and a second permanent magnet 32 alternately disposed between the spokes 24. The first permanent magnet 30 has south poles on both ends in the circumferential direction R2 and a north pole on the outer side in a radial direction R1. The second permanent magnet 32 has north poles on both ends in the circumferential direction R2 and a south pole on the outer side in the radial direction R1. The rotary electric machine 1 further comprises: a first magnetic flux 40 which flows between the first permanent magnet 30 and the second permanent magnet 32 adjacent to each other; and a second magnetic flux 44 which flows, when the armature 10 is energized, between the spoke 24 and a tooth 13 of the armature 10 facing the spoke 24.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a rotary electric machine using a permanent magnet.

Increasing the size and output of rotating electric machines using permanent magnets such as motors and generators is a universal need regardless of field or era. For example, in a small rotary electric machine having an outer diameter of 300 mm used in the current automobiles and the like, the generated torque is about 200 Nm.

As such a compact high-output rotary electric machine, Patent Document 1 and Patent Document 2 provide a field rotor, which is a rotor, with an arrangement of special permanent magnets called a Halbach array, which exerts a concentration effect of magnetic flux density. What to adopt is described.

The field rotor described in Patent Document 1 has an annular permanent magnet arranged in a Halbach array with a plurality of parallel magnetized permanent magnets as main magnetic pole magnets and yoke magnets. Further, the field rotor described in Patent Document 2 has an annular permanent magnet in which a polar anisotropic field is applied so as to have the effect of a Halbach array on one permanent magnet. The field rotors using the annular permanent magnets described in Patent Documents 1 and 2 have the effect of having a high magnetic flux concentrated outward in the radial direction due to the Halbach array.

Japanese Unexamined Patent Publication No. 2009-38968 JP-A-2015-33245

However, the field rotor using the annular permanent magnet described in Patent Document 1 and Patent Document 2 does not have an iron core. Therefore, when the armature is energized, there is no torque addition effect due to the magnetic core attraction force (hereinafter referred to as reluctance torque) by the iron core.
Therefore, for example, it is not possible to achieve the torque of 230 Nm, which is the target of 15% improvement, with respect to the torque (about 200 Nm) generated by a small rotary electric machine having an outer diameter of 300 mm used in the current automobiles and the like.

Therefore, the present disclosure has been made to solve the above-mentioned problems, and in addition to the torque due to the high magnetic flux concentrated outward in the radial direction due to the permanent magnets arranged in Halbach, when the armature winding is energized. It has a torque addition effect due to the reluctance torque of the iron core due to the generated magnetic flux. It is an object of the present invention to provide a rotary electric machine that generates high torque.

One embodiment of the present disclosure made to solve the above problems is an armature having a fixed iron core having a plurality of teeth in the circumferential direction and windings wound in three phases between the teeth. , A field rotor having a rotating iron core having a plurality of spokes in the circumferential direction, and first permanent magnets and second permanent magnets alternately arranged between the spokes. In a rotary electric machine in which the outer circumference of the rotor is separated from the inner circumference of the armature with a gap length of a predetermined dimension, the first permanent magnet has S poles at both ends in the circumferential direction and N poles on the outer side in the radial direction. The second permanent magnet is provided with N poles at both ends in the circumferential direction and S poles on the outer side in the radial direction, and has a first magnetic flux flowing between the adjacent first permanent magnet and the second permanent magnet, and the said. It is characterized by having a second magnetic flux flowing between the spoke and the tooth facing the spoke when the armature is energized.

According to this aspect, the first permanent magnet has S poles at both ends in the circumferential direction and N poles on the outside in the radial direction, and the second permanent magnet has N poles on both ends in the circumferential direction and S on the outside in the radial direction. It has poles and has a first magnetic flux flowing between adjacent first and second permanent magnets and a second magnetic flux flowing between the spokes and the teeth facing the spokes when the windings are energized. .. That is, the field rotor has an annular shape provided with spokes, which are iron cores, in addition to the first permanent magnet and the second permanent magnet having a Halbach array.

As a result, the rotating electric machine has a first magnetic flux flowing between the first permanent magnets and the second permanent magnets arranged in Halbach on the field rotor, so that the Lorentz force acts on the field rotor by energizing the armature. And torque is generated. In addition, since the rotary electric machine has a second magnetic flux flowing between the spokes and the teeth facing the spokes due to the energization of the armature, a relaxation torque in which the spokes of the field rotor act as an iron core is generated. That is, the rotary electric machine has a torque generated by the first magnetic flux and a torque generated by the second magnetic flux, and has a torque addition effect. For example, in a small rotary electric machine having an outer diameter of 300 mm used in an automobile or the like, the torque generated by the analysis can be set to 234 Nm. The torque generated by a small rotary electric machine having an outer diameter of 300 mm is usually about 200 Nm. Therefore, according to this aspect, a torque of 17% (234 Nm) that achieves the target 15% (230 Nm) can be generated.

In the above embodiment, the width of the spoke in the circumferential direction is larger than the minimum width of the teeth or 1/2 the width of the tip of the teeth and smaller than the minimum width of the teeth or twice the width of the tip of the teeth. Is preferable.

According to this aspect, the width of the spokes in the circumferential direction is larger than the minimum width of the teeth or 1/2 the width of the tip of the teeth and smaller than the minimum width of the teeth or twice the width of the tip of the teeth. Here, the second magnetic flux generated when the winding is energized flows between the spokes and the teeth facing the spokes and the tip of the teeth. Therefore, the width in the circumferential direction of the spoke is larger than the minimum width of the teeth or 1/2 of the width of the tip of the teeth, and smaller than the minimum width of the teeth or twice the width of the tip of the teeth, so that the second magnetic flux is referred to as the spoke. It can be flowed in a well-balanced manner between the teeth facing the spokes. Further, by making the width of the spokes in the circumferential direction smaller than the minimum width of the teeth or twice the width of the tip of the teeth, the sizes of the first permanent magnet and the second permanent magnet are not made smaller than necessary. Therefore, the magnitude of the first magnetic flux due to the Halbach-arranged first permanent magnets and second permanent magnets can be maintained.

In the above aspect, it is preferable that the spoke has an intermediate polarity between the N magnetic pole and the S magnetic pole.

According to this aspect, the spokes have an intermediate polarity between the N pole and the S pole. Normally, when a magnetic material is in close proximity to a permanent magnet, it is magnetized to the N or S magnetic poles of the adjacent permanent magnets. However, in this embodiment, the spokes, which are magnetic materials, are arranged between the S magnetic pole of the first permanent magnet and the N magnetic pole of the second permanent magnet. Therefore, on the outer periphery of the spoke, the magnetic flux from the S magnetic pole of the first permanent magnet and the magnetic flux of the N magnetic pole from the second permanent magnet cancel each other out, and the polarity of the magnetic pole seen from the armature of the spoke is neither the N magnetic pole nor the S magnetic pole. It has an intermediate polarity. On the other hand, when energized, the polarity of the pole of the tip of the armature facing the spoke is N pole or S pole. Therefore, the second magnetic flux can act on the spokes, that is, the iron cores having intermediate polarities to generate reluctance torque.

In the above aspect, both ends of the outer periphery of the field rotor corresponding to the first permanent magnet and the second permanent magnet on the spoke side correspond to the first permanent magnet and the second permanent magnet. It is preferable that the field rotor is offset radially inward with respect to the central portion of the outer periphery.

According to this aspect, both ends of the outer periphery of the field rotor corresponding to the first permanent magnet and the second permanent magnet on the spoke side are the outer periphery of the field rotor corresponding to the first permanent magnet and the second permanent magnet. It is offset inward in the radial direction with respect to the central part of the magnet.
That is, the gap length between the field rotor and the armature is wider at both ends of the first permanent magnet and the second permanent magnet on the spoke side than at the central portion. If the gap length between the field rotor and the armature is narrow and wide, the first magnetic flux and the second magnetic flux are concentrated in the narrow space. Therefore, the magnetic flux flowing around the outer periphery of the field rotor corresponding to the first permanent magnet and the second permanent magnet can be concentrated in the central portion without offset, and the amplitude of the generated torque can be reduced.
For example, in the case where the outer circumference of the field rotor corresponding to the first permanent magnet and the second permanent magnet is a bridge covering the first permanent magnet and the second permanent magnet, the offset ratio of both ends on the spoke side of the bridge is set. The generated torque was analyzed by offsetting both ends of the bridge on the spoke side by 16% and setting the central portion without offset to 68%. As a result, the average torque is the same as 234 Nm as compared with the case without offset, but the torque amplitude can be reduced from 68 Nm (200 Nm to 268 Nm) to 28 Nm (220 Nm to 248 Nm) by about 59%.

In the above embodiment, the first permanent magnet is a permanent magnet having two yoke magnets and a first magnetic pole magnet between the yoke magnets, and the second permanent magnet has two yoke magnets. It is preferable that the magnet is a permanent magnet having a yoke magnet and a second magnetic pole magnet between the yoke magnets.

According to this aspect, the first permanent magnet is a permanent magnet having two yoke magnets and a first magnetic pole magnet between the yoke magnets. The second permanent magnet is a permanent magnet having two yoke magnets and a second magnetic pole magnet between the yoke magnets. That is, since the permanent magnet of this embodiment is divided into three parts and reduced in size, magnetization is easy and the cost is low. The rotating core of this embodiment has an opening for fitting a first permanent magnet and a second permanent magnet with a plurality of spokes in the radial direction. Therefore, the permanent magnet divided into three can be easily assembled to each opening.
Further, when the three permanent magnets are arranged in a Halbach array, the repulsive force due to the magnetic force of the permanent magnets acts. The rotating core of this embodiment may have a plurality of spokes radially, a hub connecting the inner ends of the spokes, and a bridge connecting the outer ends of the spokes. Therefore, the permanent magnet divided into three can be firmly fixed by the opening portion fitted with the first permanent magnet and the second permanent magnet.

According to the present disclosure, in addition to the torque due to the high magnetic flux concentrated outward in the radial direction due to the Halbach array of permanent magnets, there is a torque addition effect due to the reluctance torque of the iron core due to the magnetic flux generated when the armature winding is energized. Therefore, it is possible to provide a rotary electric machine that generates a high torque.

Magnetic circuit structure of the rotary electric machine of the first embodiment Schematic diagram of the flow of the first magnetic flux and the second magnetic flux Partial structure of the rotary electric machine of the first embodiment Flow of magnetic flux by analysis of the first embodiment Torque by analysis of the first embodiment The structure of the teeth portion of the second embodiment. Figure (a) 48 teeth, Figure (b) 96 teeth Partial structure of the rotary electric machine of the third embodiment Offset structure of the bridge Torque by analysis of the third embodiment The schematic diagram which shows the flow of the 1st magnetic flux by the presence or absence of an offset. Fig. (A) With offset, Fig. (B) Without offset Permanent magnet of the 4th embodiment. Fig. (A) Permanent magnet corresponding to the first permanent magnet, Fig. (B) Permanent magnet corresponding to the second permanent magnet Magnetic circuit structure of rotary electric machine in comparative example (Halbach array) Magnetic flux flow by analysis of rotary electric machine of comparative example

Hereinafter, the rotary electric machine 1 according to the embodiment of the present disclosure will be shown with reference to the drawings. It should be noted that the embodiment is merely a disclosure and does not limit the present disclosure in any way, and it goes without saying that various improvements and modifications can be made without departing from the gist thereof.

<Applications and configurations of rotary electric machines>
The field rotor 20 of the rotary electric machine 1 of the present disclosure has an annular shape having spokes 24 which are iron cores in addition to the first permanent magnets 30 and the second permanent magnets 32 arranged in Halbach. Therefore, in the rotary electric machine 1, in addition to the torque generated by the first magnetic flux 42 generated in the first permanent magnets 30 and the second permanent magnets 32 arranged in Halbach, the iron core is generated by the second magnetic flux 44 generated when the armature 10 is energized. It has a torque addition effect due to the relaxation torque. Therefore, the rotary electric machine 1 has a high output and can be miniaturized. It has high applicability to automobiles, drones, etc., which are strongly desired to be lightweight and have high output.

(First Embodiment)
The rotary electric machine 1 according to the first embodiment of the present disclosure will be described with reference to FIGS. 1 to 5. FIG. 1 shows the magnetic circuit structure of the rotary electric machine 1 of the first embodiment. The armature 10 has a winding 18 wound around a fixed iron core 12. The fixed iron core 12 has a plurality of teeth 13 in the radial direction R1. A slot 16 is opened and a winding 18 is wound between the adjacent teeth 13. At the tip of the teeth 13, there is a teeth tip 14.
The field rotor 20 has a rotating iron core 22, a first permanent magnet 30, and a second permanent magnet 32. The rotating core 22 includes a plurality of spokes 24 in the radial direction R1, a hub 28 connecting the inner ends of the spokes 24, and a plurality of bridges 26 connecting the outer ends of the spokes 24. Here, the hub 28 has an integral cylindrical shape. On the other hand, the bridge 26 is connected to the end of the spoke 24 in the radial direction R1.
The armature 10 and the field rotor 20 have a tooth tip 14 which is the inner circumference of the armature 10 and a gap length 5 having a predetermined dimension on the outer circumferences of the bridge 26 and the spoke 24 which are the outer circumferences of the field rotor 20. It is separated.
The inside of the hub 28 of the field rotor 20 is connected to a rotation shaft (not shown). The rotation axis rotates in the circumferential direction R2 in the rotation axis direction Z.

The rotary core 22 has a plurality of openings by the spokes 24 in the radial direction R1, a hub 28 connecting the inner ends of the spokes 24, and a bridge 26 connecting the outer ends of the spokes 24. The first permanent magnets 30 and the second permanent magnets 32 are alternately arranged in the openings, that is, between the spokes 24. The first permanent magnet 30 and the second permanent magnet 32 are fitted to the spokes 24, the hub 28, and the bridge 26 of the arranged openings.
The bridge 26 connects the tips of the spokes 24 to cover the entire first permanent magnet 30 and the second permanent magnet 32, but may be separated. For example, two protrusions facing each other from the spokes 24 may be provided so that the first permanent magnet 30 and the second permanent magnet 32 are fitted and fixed. In this case, the outer circumference of the field rotor 20 is composed of spokes 24, protrusions, a first permanent magnet 30 and a second permanent magnet 32.
The first permanent magnet 30 is provided with S poles at both ends in the circumferential direction R2 and N poles outside the radial direction R1. The second permanent magnet 32 is provided with N poles at both ends in the circumferential direction R2 and S poles outside the radial direction R1. Therefore, since the adjacent first permanent magnets 30 and second permanent magnets 32 are arranged in a Halbach array, the rotary electric machine 1 has a first magnetic flux circulating between them.
The field rotor 20 has an annular shape provided with spokes 24, which are iron cores, in addition to the first permanent magnet 30 and the second permanent magnet 32 having a Halbach array. Therefore, the rotary electric machine 1 has a second magnetic flux 44 generated when the armature 10 is energized.
Further, the rotary electric machine 1 shown in FIG. 1 is a 16-pole machine having a total of 16 first permanent magnets 30 and second permanent magnets 32.

<Flow of first magnetic flux and second magnetic flux>
FIG. 2 shows a schematic diagram of the flow of the first magnetic flux and the second magnetic flux. In FIG. 2, the teeth 13 and the winding 18 of the fixed iron core 12 show only the parts required for the following description.
The first permanent magnet 30 is magnetized in a substantially arc shape in which the magnetic field 30a in the magnet is directed from the S poles at both ends of the circumferential direction R2 to the outside of the radial direction R1 toward the N pole. On the other hand, the second permanent magnet 32 is magnetized in a substantially arc shape in which the magnetic field 32a in the magnet is directed from the outer S pole in the radial direction R1 to the N poles at both ends in the circumferential direction R2. The directions of the magnetic field in the magnet 30a and the magnetic field in the magnet 32a are from the S pole to the N pole. That is, the first permanent magnet 30 is magnetized with an in-magnet magnetic field 30a, and the second permanent magnet 32 is magnetized with an in-magnet magnetic field 32a, respectively. The polar anisotropic magnetized first permanent magnet 30 and the second permanent magnet 32 have the effect of concentrating the magnetic flux outward in the radial direction R1 due to the Halbach array. Therefore, between the adjacent first permanent magnet 30 and the second permanent magnet 32, a first magnetic flux 42 that circulates outside the radial direction R1 in the same direction as the magnet internal magnetic field 30a and the magnet internal magnetic field 32a flows.

On the other hand, the second magnetic flux 44 flowing through the spokes 24, which is the iron core, is generated when the winding 18 of the armature 10 is energized. FIG. 2 shows the position of the winding 18 to be energized. The position of the winding 18 to be energized is set to the rear of the rotation direction R2 from the center of the first permanent magnet 30, and the energizing direction is from the upper side to the lower side of the paper surface. The magnetic field is generated in the same direction as the first magnetic flux 42 including the energized winding 18. Therefore, the second magnetic flux 44 due to this magnetic field is in the first magnetic flux 42, and the circulation direction is the same as that of the first magnetic flux 42 (clockwise toward the paper surface).
Similarly, the position of the winding 18 to be energized is set to the rear of the rotation direction R2 from the center of the second permanent magnet 32, and the energizing direction is set from the lower side to the upper side of the paper surface. The magnetic field is generated in the same direction as the first magnetic flux 42 including the energized winding 18. Therefore, the second magnetic flux 44 due to this magnetic field is in the first magnetic flux 42, and the circulation direction is the same as that of the first magnetic flux 42 (counterclockwise toward the paper surface).
In addition, the second magnetic flux 44 flows between the spokes 24 of the rotating core 22 and the teeth 13 facing the spokes 24 of the fixed core 12. Further, the second magnetic flux 44 flows in the direction of the magnetic field facing the generation when the winding 18 is energized, that is, in the same direction as the first magnetic flux 42. Therefore, the circulation of the second magnetic flux 44 in the rotary electric machine 1 is considered with the spoke 24 as the starting point.

First, the second magnetic flux 44 that circulates counterclockwise toward the paper surface will be described with the spoke 24 located behind the rotation direction R2 of the second permanent magnet 32 as a starting point. First, the second magnetic flux 44 flows toward the teeth 13 facing the spokes 24.
Next, the second magnetic flux 44 flows in the same direction as the first magnetic flux 42 in the arc portion 19 of the fixed iron core 12. At this time, the second magnetic flux 44 merges with the first magnetic flux 42 to become a magnetic flux 40. Next, the first magnetic flux 42 and the second magnetic flux 44 flow through the teeth 13 facing the S pole of the second permanent magnet 32. Next, the first magnetic flux 42 and the second magnetic flux 44 flow from the teeth 13 toward the S pole of the opposite second permanent magnet 32. Next, the first magnetic flux 42 and the second magnetic flux 44 flow from the S pole of the second permanent magnet 32 toward the N pole, that is, the spoke 24 which is the starting point, inside the second permanent magnet 32.
Therefore, the second magnetic flux 44 flows and circulates inside the spoke 24 to the outside in the radial direction R1. On the other hand, the first magnetic flux 42 penetrates the inside of the spoke 24, flows to the S pole of the adjacent first permanent magnet 30, and flows inside the first permanent magnet 30 toward the N pole. Next, the teeth 13 of the fixed core 12 facing the north pole of the first permanent magnet 30 flow, and at the arc portion 19 of the fixed core 12, merge with the second magnetic flux 44 and circulate. Therefore, the second magnetic flux 44 circulates inside the first magnetic flux 42 in the same direction as the first magnetic flux 42.

Secondly, the second magnetic flux 44 that circulates clockwise toward the paper surface will be described. First, starting from the spoke 24 located behind the rotation direction R2 of the first permanent magnet 30, the first magnetic flux 42 and the second magnetic flux 44 move the inside of the adjacent first permanent magnet 30 from the S pole to the N pole. It flows.
Next, the first magnetic flux 42 and the second magnetic flux 44 flow from the N pole inside the first permanent magnet 30 to the teeth 13 of the opposite fixed iron core 12. Next, in the arc portion 19 of the fixed iron core 12, the first magnetic flux 42 and the second magnetic flux 44 are separated.
The divided second magnetic flux 44 flows to the teeth 13 facing the spokes 24 at the starting point, and returns to the spokes 24 at the starting point to circulate. The separated first magnetic flux 42 flows to the teeth 13 facing the S pole of the second permanent magnet adjacent to the rear of the rotation direction R2, flows from the S pole to the N pole inside the second permanent magnet, and the spoke 24 at the starting point. Return to and circulate. Therefore, as in the first case, the second magnetic flux 44 circulates inside the first magnetic flux 42 in the same direction as the first magnetic flux 42.
As described above, the magnetic flux 40 when the rotary electric machine 1 is energized (during rotation) circulates in a mixture of the second magnetic flux 44 inside the first magnetic flux 42.

<Permanent magnet>
As the first permanent magnet 30 and the second permanent magnet 32, sintered metal magnets or plastic magnets are used.
As the sintered metal magnet, for example, N36Z manufactured by Shin-Etsu Chemical Co., Ltd. is used. This is a sintered neodymium magnet, which has a residual magnetic flux density of 1.1 [T] and a coercive force of 875 [kA / m]. The resistivity (resistivity ratio) that influences the eddy current of the sintered metal magnet is 1.4 [μΩ · m]. It is more expensive than plastic magnets.
As the plastic magnet, for example, NEOMAX-P6 (NEOMAX Co., Ltd.) is used. It is a plastic mag-bonded magnet with a residual magnetic flux density of 0.5 [T] and a coercive force of 630 [kA / m]. The electrical resistivity (resistance ratio) that influences the eddy current is 50 [μΩ · m]. The plastic magnet uses a plastic material as a base material and mixes a magnetic material (for example, a rare earth magnet material). Rubber materials are also included in plastic materials.
Needless to say, even if the material is other than the above, a material having similar characteristics can be used.

<Laminated iron core>
As the fixed core 12 and the rotating core 22, a steel plate material based on iron, which is a magnetic material, is used as the laminated core.
For the fixed iron core 12, for example, VACOFLUX 50 (VAC, Germany), which is a 49% cobalt steel plate, is used. The main specifications are a plate thickness of 0.2 mm, a magnetic saturation density of 2.35 [T], and a tensile strength of 720 [MPa].
For the rotating iron core 22, a metal having an amorphous mother phase, for example, 2605HB1M (Hitachi Metals, Ltd.), which is an amorphous steel plate, is used. The main specifications are an iron loss of 0.17 W / kg (1.3 [T], [50 Hz]), a tensile strength of 2100 MPa, and a magnetic saturation density of 1.5 [T]. For example, the rotating iron core 22, which is a kind of amorphous metal, is used by NANOMET (R) (Tohoku Magnet Institute Co., Ltd.), which is a nanocrystal alloy in which nanocrystals of iron are dispersed at high density in its matrix. Will be. The iron loss is about 0.3 W / kg (1.5 [T], [50 Hz]), and the magnetic saturation density is 1.8 [T]. Further, for example, 35H300 (Nippon Steel Co., Ltd.), which is an ordinary silicon steel plate, is used for the rotary iron core 22. The main specifications are iron loss of 3 W / kg (1.3 [T], [50 Hz]), tensile strength of 509 MPa, and magnetic saturation density of 2 [T]. Further, for the rotor core 22, 35HXT780T (Nippon Steel Co., Ltd.), which is a high-strength silicon steel plate, is used. The main feature of the specifications is that the tensile strength is as strong as 822 MPa, and it is possible to design with durability suitable for supporting the above-mentioned magnetic pole group and magnet group.
Needless to say, even if the material is other than the above, a material having similar characteristics can be used.
The fixed core 12 and the rotary core 22 are usually manufactured by processing the above-mentioned steel plates into their respective shapes by pressing and laminating them. Therefore, the mechanical strength of the opening portion into which the first permanent magnet 30 and the second permanent magnet 32 of the rotating iron core 22 are inserted can be increased.

<Analysis means>
The analysis conditions used in this disclosure are as follows. The Finite Element Analysis analysis (hereinafter referred to as FEA analysis) used for the transient magnetic field analysis is Femtet manufactured by Murata Software Co., Ltd. In the FEA analysis model of the rotating machine 1, the field rotor 20 is installed with the diameter of the fixed iron core 12 of the armature 10 being 300 mm and the void length 5 having a length of 1 mm inside. The number of poles of the field rotor 20 is 16 poles. In the armature 20, the winding 18 of the slot 16 of the fixed iron core 12 is a three-phase winding. The number of slots 16 is 96, and the three-phase winding is a distributed winding having two slots 16 per phase and one pole. The winding 18 is a flat conductor, and a plurality of windings 18 are wound in the slot 16. The fixed iron core 12 of the armature 20 is a 49% cobalt steel plate VACOFLUX 50. The rotating core of the field rotor 20 is an amorphous steel plate 2605HB1M. Permanent magnets are sintered neodymium magnets. The rotation speed is 3000 rpm and the input current is 240 [A].

FIG. 3 shows a partial structure of the rotary electric machine 1 of the first embodiment. Three teeth 13 and three windings 18 are arranged on the armature 10 with respect to the first permanent magnet 30. Similarly, with respect to the second permanent magnet 32, the armature 10 is provided with three teeth 13 and three windings 18. Therefore, in the rotary electric machine 1, 48 teeth 13 and 48 windings 18 are arranged.

<Results of FEA analysis>
FIG. 4 shows the result of FEA analysis of the flow of the magnetic flux 40 in the range of 1/4 of the rotary electric machine 1. In FIG. 4A, two first permanent magnets 30 (30-1, 30-2), three second permanent magnets 32 (32-1, 32-2, 32-3), and five Represents the arrangement of spokes 24 (24-1, ..., 24-5) and 14 teeth 13 (13-1, ..., 13-14).
The flow of the magnetic flux 40 in the second permanent magnet 32-2.30-3 adjacent to the first permanent magnet 30-2 will be described. The starting point is the north pole of the first permanent magnet 30-2. The magnetic flux 40 flowing from the circumferential arc of the N pole of the first permanent magnet 30-2 to the armature 10 flows to the two teeth 13-9 and 13-10.
The magnetic flux 40 from the teeth 13-9 flows through the arc portion 19 of the fixed iron core 12 and flows to the teeth 13-6, 13-11, and 13-12.
The flow in the counterclockwise direction (rotational direction R2) to the teeth 13-6 flows to the S pole of the second permanent magnet 32-2. Next, it circulates from the S pole of the second permanent magnet 32-2 through the spokes 24-3 and returns to the N pole of the first permanent magnet 30-2 as an adjacent starting point. This is the first magnetic flux 42.
The flow to the teeth 13-11 in the clockwise direction flows to the spokes 24-4 facing the teeth 13-11, and returns to the north pole of the first permanent magnet 30-2 as the starting point and circulates. This is the second magnetic flux 44.
The flow to the teeth 13-12 in the clockwise direction flows to the S pole of the second permanent magnet 32-3. Next, it circulates from the S pole of the second permanent magnet 32-3 through the spokes 24-4 and returns to the N pole of the first permanent magnet 30-2 as an adjacent starting point. This is the first magnetic flux 42.
The magnetic flux 40 from the teeth 13-10 flows through the arc portion 19 of the fixed iron core 12, flows to the teeth 13-11, flows to the spokes 24-4 facing the teeth 13-11, and flows to the first permanent magnet 30-2 as the starting point. Return to and circulate. This is the second magnetic flux.
From the above, the magnetic flux 40 during rotation (when energized) of the rotary electric machine 1 circulates in a mixture of the second magnetic flux 44 inside the first magnetic flux 42.

FIG. 4B is a diagram of FEA analysis in which the display of the magnetic flux 40 is increased. In the first permanent magnet 30-2, the spokes 24-4, and the second permanent magnet 32-3, there is a first magnetic flux 42 circulating in the first permanent magnet 30-2 and the second permanent magnet 32-3. Further, the first permanent magnet 30-2 and the spokes 24-4 have a second magnetic flux 44 circulating in the same direction as the first magnetic flux 42. The second magnetic flux 44 is inside the first magnetic flux 42. This is the same as in FIG. 4 (a). Further, the rotary electric machine 1 shown in FIG. 1 has 16 first magnetic fluxes and 16 second magnetic fluxes.
From the above, the flows of the first magnetic flux 42 and the second magnetic flux 42 described with reference to FIG. 2 are almost the same as the results of the FEA analysis.

Since the rotary electric machine 1 of the first embodiment has a first magnetic flux 42 flowing between the first permanent magnets 30 and the second permanent magnets 32 arranged in the field rotor 20, the field is energized by the armature 10. Lorentz force acts on the magnetic rotor 20 to generate torque. In addition, since the rotary electric machine 1 has a second magnetic flux 44 that flows between the spokes 24 and the teeth 13 facing the spokes 24 due to the energization of the armature 10, the reluctance torque in which the spokes 24 act as an iron core on the field rotor 20. Occurs. That is, the rotary electric machine has a torque generated by the first magnetic flux 42 and a torque generated by the second magnetic flux 42, and has a torque addition effect.
For example, in a small rotary electric machine 1 having an outer diameter of 300 mm used in an automobile or the like, the torque generated as shown in FIG. 5 can be set to 234 Nm by FEA analysis. That is, FIG. 5 shows an average torque of 234 Nm with respect to the rotation angle. The torque amplitude is 68 Nm (minimum value 200 Nm to maximum value 268 Nm).
The torque of a small rotary electric machine having an outer diameter of 300 mm used in an automobile or the like is usually about 200 Nm. Therefore, according to the rotary electric machine 1 of the first embodiment, the torque can be increased to 17% (torque 234 Nm), which achieves the target torque of 15% (torque 230 Nm).

<Comparison example>
As a comparative example, FIG. 12 shows, for example, the magnetic circuit structure of a rotary electric machine 101 having a field rotor 120 of a permanent magnet in a Halbach array shown in Patent Document 1. The fixed iron core 112 of the armature 110 has 48 teeth 113. The field rotor 120 is composed of a first magnetic pole magnet 137, a second magnetic pole magnet 138, and a yoke magnet 139. The first magnetic pole magnet 137 is magnetized in parallel and has a magnetic field inside the magnet outward in the radial direction R1. The second magnetic pole magnet 138 is magnetized in parallel and has a magnetic field inside the magnet inward in the radial direction R1. The yoke magnet 139 is magnetized in parallel and has a magnetic field inside the magnet in the circumferential direction R2. The first magnetic pole magnet 137 and the second magnetic pole magnet 138 are alternately arranged via the yoke magnet 139. Further, the yoke magnet 139 is arranged so that its field direction faces the first magnetic pole magnet 137. The field rotor 120 is a 16-pole rotary electric machine 101 in which a total of 16 first magnetic pole magnets 137 and second magnetic pole magnets 138 are arranged. The rotary electric machine 101 has a first magnetic flux 142 outside the field rotor 120, which exits from the first magnetic pole magnet 137 and returns to the second magnetic pole magnet 138.

FIG. 13 shows an FEA analysis of the flow of the first magnetic flux 142 of the rotary electric machine 101 shown in FIG. The calculation conditions are the same as in FIG. 4 (a). For example, we see the first magnetic flux 142 circulating from the first magnetic pole magnet 137-2 to the yoke magnets 139-2 and 139-3 on both sides and the second magnetic pole magnets 138-1 and 138-2. First, the first magnetic flux 142 flows through the teeth 113-6 and 113-7 facing the north pole of the first magnetic pole magnet 137-2.
The first magnetic flux 142 from the teeth 113-6 is divided into two directions, a counterclockwise direction (rotational direction R2) and a clockwise direction opposite to the counterclockwise direction (rotational direction R2). The first magnetic flux 142 in the counterclockwise direction flows through the arc portion 119 of the fixed iron core 112, passes through the teeth 113-3, then the second magnetic pole magnet 138-1, and then the yoke magnet 139-2, and then the first magnetic pole magnet 137. Return to -2. The first magnetic flux 142 in the clockwise direction flows through the arc portion 119 of the fixed iron core 112, passes through the teeth 113-9, then the second magnetic pole magnet 138-2, and then the yoke magnet 139-3, and then the first magnetic pole magnet 137-. It returns to 2 and circulates.
The first magnetic flux 142 in the clockwise direction from the teeth 113-7 flows through the arc portion 119 of the fixed iron core 112, passes through the teeth 113-8, then the second magnetic pole magnet 138-2, and then the yoke magnet 139-3. It returns to the first magnetic flux magnet 137-2 and circulates.

The FEA analysis of the torque of the rotary electric machine 101 having the field rotor 120 of the permanent magnets of the Halbach array, which is a comparative example, is 220 Nm, for example, the torque of a small rotary electric machine having an outer diameter of 300 mm used in an automobile or the like. The analysis conditions are the same as in FIG. This is about 10% higher than the torque of about 200 Nm of a small rotary electric machine having an outer diameter of 300 mm used in a normal automobile or the like that does not use a Halbach array.
However, the torque of the rotary electric machine 1 of the first embodiment is 234 Nm, which is about 6.4% larger than the torque of 220 Nm of the rotary electric machine 101 of the comparative example. This is because, in the first embodiment, the permanent magnet is relatively small and the first magnetic flux 42 is small as compared with the comparative example, but the spoke 24 which is the iron core causes the torque addition by the reluctance torque by the second magnetic flux 44. This is because it has an effect.

(Second Embodiment)
The second embodiment relates to the width 24w of the spoke 24, which is an iron core, and the polarity of the magnetic poles of the spoke 24. FIG. 6 shows the structure of the teeth portion of the second embodiment. FIG. 6A shows a case where the number of teeth 13 is 48, and FIG. 6B shows a case where the number of teeth 13 is 96.
As shown in FIG. 6, the inner circumference of the armature 10 and the outer circumference of the field rotor 20 are separated from each other with a gap length 5 having a predetermined dimension. The outer circumference of the field rotor 20 is composed of the outer circumferences of the bridge 26 and the spokes 24. The inner circumference of the armature 10 is composed of a tooth tip 14 arranged with a certain gap. The width 14a of the tooth tip 14 on the inner circumference of the armature 10 is large so that the magnetic flux 40 (first magnetic flux 42 and second magnetic flux 44) can easily flow. On the other hand, since the winding 18 is arranged in the slot 16 of the teeth 13, the width of the teeth 13 is narrowed inside the radial direction R1. Therefore, the connection portion between the teeth 13 and the tip 14 of the teeth has the minimum width 13a of the teeth 13.

First, the width 24w of the spoke 24, which is an iron core, will be described. When the number of teeth 13 shown in FIG. 6A is 48, the width 24w of the spokes 24 is smaller than the minimum width 13a of the teeth 13 or the width 14a of the tip 14 of the teeth. In FIG. 6B, when the number of teeth 13 is 96, the width 24w of the spokes 24 is larger than the minimum width 13a of the teeth 13 or the width 14a of the tip 14 of the teeth.
Here, the second magnetic flux 44 generated when the winding 18 is energized flows between the spokes 24 and the teeth 13 and the teeth tips 14 facing the spokes 24. Therefore, the width 24w in the circumferential direction of the spokes 24 is larger than the minimum width 13a of the teeth 13 or 1/2 of the width 14a of the teeth tip 14, and smaller than twice the minimum width 13a of the teeth 13 or the width 14a of the teeth tip 14. By doing so, the second magnetic flux 44 can be flowed between the spokes 24 and the teeth 13 facing the spokes 24 in a well-balanced manner.
Further, by making the width 24w of the spoke 24 in the circumferential direction smaller than the minimum width 13a of the teeth 13 or the width 14a of the tip 14 of the teeth, the sizes of the first permanent magnet 30 and the second permanent magnet 32 are made larger than necessary. There is no need to make it smaller. Therefore, the magnitude of the first magnetic flux 42 by the first permanent magnets and the second permanent magnets arranged in Halbach can be maintained.

Next, the polarity of the spokes 24, which is the iron core, is an intermediate polarity between the N pole and the S pole.
Normally, when a magnetic material is in close proximity to a permanent magnet, it is magnetized to the N or S magnetic poles of the adjacent permanent magnets. However, in the second embodiment, the spoke 24, which is a magnetic material, is arranged between the S magnetic pole of the first permanent magnet 30 and the N magnetic pole of the second permanent magnet 32. Therefore, on the outer periphery of the spoke 24, the magnetic flux from the S magnetic pole of the first permanent magnet 30 and the magnetic flux of the N magnetic pole from the second permanent magnet 32 cancel each other out, and the polarities of the magnetic poles seen from the armature of the spoke 24 are N magnetic poles. It has an intermediate polarity that is not an S magnetic flux. On the other hand, when energized, the polarity of the tooth tip 14 of the armature 10 facing the spoke 24 is N pole or S pole. Therefore, the second magnetic flux 44 can act on the spokes 24, that is, the iron core having an intermediate polarity to generate reluctance torque.

(Third Embodiment)
The third embodiment relates to reducing the amplitude of the generated torque shown in FIG. 5 of the first embodiment. As shown in FIG. 4, the circumferential arc (N magnetic pole) of the first permanent magnet 30 and the circumferential arc (S magnetic flux) of the second permanent magnet 32 are the armature 10 and the magnetic flux 40 (the first magnetic flux 42 and the second magnetic flux 44). Is flowing in the entire circumference of the arc. Here, the magnetic flux 40 flowing through the circumferential arcs at both ends on the spoke 24 side shortcuts to the spoke 24, which is a nearby iron core, so that the reluctance torque, that is, the amplitude of the torque is increased.

In the third embodiment, both ends of the outer periphery of the field rotor 20 corresponding to the first permanent magnet 30 and the second permanent magnet 32 on the spoke 24 side correspond to the first permanent magnet 30 and the second permanent magnet 32. It is offset inward in the radial direction R1 with respect to the central portion of the outer periphery of the field rotor 20.
That is, the gap length 5 between the field rotor 29 and the armature 10 has wider ends on the spoke 24 side of the first permanent magnet 30 and the second permanent magnet 32 than the central portion. If the gap length 5 between the field rotor 20 and the armature 10 has a narrow space and a wide space, the magnetic flux 40 (first magnetic flux 42 and second magnetic flux 44) is concentrated in the narrow space. Therefore, the magnetic flux 40 flowing through the outer periphery of the field rotor 20 corresponding to the first permanent magnet 30 and the second permanent magnet 32 can be concentrated in the central portion without offset, and the amplitude of the generated torque can be reduced. can.
For example, when the outer periphery of the field rotor corresponding to the first permanent magnet and the second permanent magnet is the bridge 26 covering the first permanent magnet and the second permanent magnet, both ends of the bridge 26 on the spoke 24 side are It has an offset portion 26a which is a gap inside the radial direction R1. Therefore, both ends of the bridge 26 on the spoke 24 side have a wider gap length 5 between the field rotor 20 and the armature 10 than the central portion without the offset portion 26a. If the gap length 5 between the field rotor 20 and the armature 10 has a narrow space and a wide space, the magnetic flux 40 (first magnetic flux 42 and second magnetic flux 44) is concentrated in the narrow space. Therefore, the magnetic flux 40 flowing through the bridge 26 covering the first permanent magnet 30 and the second permanent magnet 32 can be concentrated in the central portion without the offset portion 26a, and the amplitude of the generated torque can be reduced.

FIG. 7 shows a partial structure of the rotary electric machine 1 having the bridge 26 of the third embodiment. Six teeth 13 and six windings 18 are arranged on the armature 10 with respect to the first permanent magnet 30. Similarly, with respect to the second permanent magnet 32, six teeth 13 and six windings 18 are arranged on the armature 10. Therefore, in the rotary electric machine 1, 96 teeth 13 and windings 18 are arranged.

FIG. 8 shows the structure of the offset portion 26a of the bridge 26 used in the FEA analysis as an example. The ratio of the offset portion 26a per pole is calculated. Since the rotary electric machine 1 has 16 poles, one pole is 22.5 ° (machine angle, the same applies hereinafter). The spokes 24 are 4 °. Therefore, the width of the bridge covering the first permanent magnet 30 is 18.5 °.
The width of the offset portions 26a at both ends of the bridge is 3 °, and the central portion without the offset 26a is 12.5 °. Therefore, the ratio of the offset portion 26a is (3 ° × 2)) /18.5 ° = 32% (16% per offset portion 26a). The shape of the offset portion 26a is substantially triangular. The height of the offset portion 26a in the radial direction R1 was gradually increased from the central portion of the bridge 26 without the offset portion 26a toward the spokes 24 to be 2 mm at the end face with the spokes 24.
For example, when the diameter of the fixed iron core 12 is 300 mm, the width of the offset portion 26a is 7 mm. Therefore, the size of the offset portion 26a is a substantially right triangle having a base of 7 mm and a height of 2 mm. The width 24 of the spoke 24 is 9.6 mm.

The result of FEA analysis of the torque of the third embodiment corresponding to FIG. 5 is shown in FIG. The average torque is the same, 234 Nm, but the torque amplitude can be reduced by about 59% from 68 Nm (200 Nm to 268 Nm) to 28 Nm (220 Nm to 248 Nm).

FIG. 10 shows a schematic diagram of the flow of the first magnetic flux 42 from the second permanent magnet 32 to the first permanent magnet 30 in the vicinity of the spoke 24 facing the teeth 13. FIG. 10A shows a case where there is an offset, and FIG. 10B shows a case where there is no offset. In both figures, the flow of the first magnetic flux 42 from the central portion of the S pole of the second permanent magnet 32 to the central portion of the N pole of the first permanent magnet 30, and the first permanent magnet from the teeth 13 via the opposite spokes 24. The flow to the north pole of 30 is the same. However, the flow of the first magnetic flux 42 from the second permanent magnet 32 in the vicinity of the spoke 24 facing the teeth 13 to the first permanent magnet 30 differs depending on the presence or absence of offset.
In the case of no offset in FIG. 10B, the first magnetic flux 42 flowing into the second permanent magnet 32 in the vicinity of the spoke 24 passes through the spoke 24 and flows to the first permanent magnet 30. Therefore, the first magnetic flux 42 flows from the entire circumferential arc of the S pole of the second permanent magnet 32 to the entire circumferential arc of the N pole of the first permanent magnet 32.
On the other hand, in the case of the offset in FIG. 10A, the first magnetic flux 42 in the vicinity of the spoke 24 has a large gap length 5 due to the offset portion 26a, so that the second permanent magnet having a narrow gap length 5 is present. It flows into the central portion of the 32 S pole without the offset portion 26a. The first magnetic flux 42 that has flowed into the central portion of the S pole of the second permanent magnet 32 penetrates the spokes 24 and flows into the central portion of the first permanent magnet 30 that does not have the offset portion 26a of the N pole. Therefore, the first magnetic flux 42 flows from the central portion of the second permanent magnet 32 without the offset portion 26a of the S pole to the central portion of the first permanent magnet 32 without the offset portion 26a of the N pole. That is, the width in which the first magnetic flux 42 flows is reduced by the offset portion 26a. It is presumed that this reduced the torque amplitude.
As described above, the rotary electric machine 1 of the third embodiment, which can reduce the torque amplitude, can be used not only in the transportation equipment but also in the measuring device. The rotary electric machine 1 of the measuring device needs to have a certain torque stability. Therefore, the torque stability can be ensured and the measurement system of the measuring device can be improved by the rotary electric machine 1 having a small torque amplitude.

The width 26a of the radial R1 of the bridge 26 covering the first permanent magnet and the second permanent magnet is 1.5 mm to 2 mm. Therefore, both ends of the first permanent magnet 30 and the second permanent magnet 32 are chamfered corresponding to the offset.

(Fourth Embodiment)
In the fourth embodiment, the first permanent magnet 30 is a permanent magnet having two yoke magnets 39 and a first magnetic pole magnet 37 between the yoke magnets 39. Further, the second permanent magnet 32 is a permanent magnet having two yoke magnets 39 and a second magnetic pole magnet 38 between the yoke magnets 39.

FIG. 11 shows a permanent magnet according to a fourth embodiment. FIG. 11A shows a permanent magnet corresponding to the first permanent magnet 30. The first magnetic pole magnet 37 and the yoke magnet 39 are magnetized in parallel. The first magnetic pole magnet 37 has an in-magnet magnetic field 37a outward in the radial direction R1. The yoke magnet 39 has a magnetic field in the magnetic pole 39a in the circumferential direction R2. In the first permanent magnet 30, the first magnetic pole magnet 37 is arranged between the two left and right yoke magnets 39, and the magnetic field 37a in the magnet of the yoke magnet 39 faces each other toward the first magnetic pole magnet 37. Is placed in. Further, FIG. 11B shows a permanent magnet corresponding to the second permanent magnet 32. The second magnetic pole magnet 38 and the yoke magnet 39 are magnetized in parallel. The second magnetic pole magnet 38 has an inward magnetic field 38a in the radial direction R1. In the second permanent magnet 32, the second magnetic pole magnet 38 is arranged between the two left and right yoke magnets 39, so that the magnetic field 37a in the magnet of the yoke magnet 39 does not face each other toward the first magnetic pole magnet 37. Is placed in.

In the fourth embodiment, the first permanent magnet and the second permanent magnet are each composed of three permanent magnets magnetized in parallel. That is, since it is divided into three parts, the permanent magnet is small. By using a small permanent magnet, magnetization is easy and the cost can be reduced. Further, the rotating iron core 22 has an opening portion for fitting the first permanent magnet and the second permanent magnet by a plurality of spokes in the radial direction. Therefore, the permanent magnet divided into three can be easily assembled to each opening.
Further, when the three permanent magnets are arranged in a Halbach array, the repulsive force due to the magnetic force of the permanent magnets acts. The rotary core 22 of the fourth embodiment may have a plurality of spokes 24 in the radial direction, a hub 28 connecting the inner ends of the spokes 24, and a bridge 26 connecting the outer ends of the spokes 24. .. Therefore, the permanent magnet divided into three can be firmly fixed by the opening portion fitted with the first permanent magnet 30 and the second permanent magnet 32.

The first magnetic pole magnet 37 and the second magnetic pole magnet 38 have the same size. On the other hand, the size of the yoke magnet 39 in the circumferential direction R2 was set to 1/2 the size of the first magnetic pole magnet 37 or the second magnetic pole magnet 38 in the circumferential direction R2. The magnetic field 39a in the magnet of the yoke magnet 39 can be doubled by adjoining the first permanent magnet 30 and the second permanent magnet 32. By making the double magnetic field 39a in the magnet equal to the magnetic field 37a in the magnet of the first magnetic pole magnet 37 or the magnetic field 38a in the magnet of the second magnetic pole magnet 38, the balance of the magnetic field in the magnet is improved. The effect of concentrating the magnetic field due to the Halbach array to the outside of the radial direction R1 can be enhanced. The yoke magnet 39 can change the direction of the magnetic field 39a in the magnet by reversing the insertion direction into the opening.

1 Rotor 5 Air gap length (between armature and field rotor)
10 Armature 12 Fixed iron core 13 Teeth 13a Minimum width of teeth 14 Teeth tip 14a Width of teeth tip 16 Slot 18 Winding 19 Arc part 20 Field rotor 22 Rotor core 24 Spoke 24a Width (spoke circumferential direction) 26 Bridge 26a Offset part 28 Hub 30 First permanent magnet 30a Magnetic field inside magnet (first permanent magnet)
32 Second permanent magnet 32a Magnetic field inside the magnet (second permanent magnet)
37 1st magnetic pole magnet 38 2nd magnetic pole magnet 39 York magnet 40 Magnetic flux 42 1st magnetic flux 44 2nd magnetic flux Z Rotation axis direction R1 radial direction R2 circumferential direction (rotation direction)

Claims (5)

An armature having a fixed iron core with a plurality of teeth in the circumferential direction, and windings wound in three phases between the teeth.
A rotating iron core with multiple spokes in the circumferential direction,
It has a field rotor having first permanent magnets and second permanent magnets arranged alternately between the spokes.
In a rotary electric machine in which the outer circumference of the field rotor is separated from the inner circumference of the armature with a gap length of a predetermined dimension.
The first permanent magnet has S poles at both ends in the circumferential direction and N poles on the outside in the radial direction.
The second permanent magnet has N poles at both ends in the circumferential direction and S poles on the outside in the radial direction.
The first magnetic flux flowing between the adjacent first permanent magnet and the second permanent magnet,
A rotary electric machine characterized by having a second magnetic flux flowing between the spokes and the teeth facing the spokes when the armature is energized. In the rotary electric machine of claim 1,
A rotary electric machine characterized in that the width of the spokes in the circumferential direction is larger than the minimum width of the teeth or 1/2 the width of the tip of the teeth and smaller than the minimum width of the teeth or twice the width of the tip of the teeth. In the rotary electric machine of claim 1 or claim 2.
The spoke is a rotary electric machine characterized by having an intermediate polarity between an N magnetic pole and an S magnetic pole. In the rotary electric machine according to any one of claims 1 to 3.
Both ends of the outer periphery of the outer periphery of the field rotor corresponding to the first permanent magnet and the second permanent magnet on the spoke side are of the field rotor corresponding to the first permanent magnet and the second permanent magnet. A rotating electric machine characterized by being offset inward in the radial direction with respect to the central part of the outer circumference. In the rotary electric machine according to any one of claims 1 to 4.
The first permanent magnet is a permanent magnet having two yoke magnets and a first magnetic pole magnet between the yoke magnets.
The second permanent magnet is a permanent magnet having two yoke magnets and a second magnetic pole magnet between the yoke magnets.

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