JP2007236130A - Rotary electric machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rotary electric machine in which motor loss is reduced by shortening the length of magnetic path, as much as possible, and compound effect is not reduced, when independent driving is performed with a composite current. <P>SOLUTION: In the rotary electric machine where a rotor to which a permanent magnet is attached and a stator to which an armature winding is applied are opposing in the axial direction, magnetic path r formed via the rotor and the stator is constituted of a flux along the rotating shaft direction, and flux along the radial direction of an end face perpendicularly intersecting the rotating shaft and passes in the radial direction of the end face perpendicularly intersecting the rotating shaft. The rotor consists of a pair, arranged opposite so as to hold the stator in between. The stator consists of a pair arranged opposite so as to hold the rotor in between. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a rotating electrical machine, and more particularly to an axial gap type rotating electrical machine.

2. Description of the Related Art Conventionally, an axial gap type motor that is a rotating field type motor in which a rotor including a permanent magnet and a stator including an armature winding face each other in the axial (axial) direction is known.
8A and 8B show a schematic structure of a conventional axial gap motor, where FIG. 8A is a plan view seen from the stator side of the rotor core, and FIG. 8B is a cross-sectional view taken along line BB in FIG. . As shown in FIG. 8, the axial gap type motor 1 includes a stator 2 and a pair of rotors 3 a and 3 b disposed on both sides of the stator 2 via an air gap (gap) a. Each of the rotors 3a and 3b formed in a disk shape is connected by a rotating shaft 4 that is rotatably supported (see (b)).

  The stator 2 is formed by arranging a plurality of stator cores 6 wound with a stator winding 5 in an annular shape (in this example, only four and two are shown) with substantially equal intervals. (See (b)). The rotors 3a and 3b correspond to the rotor cores 7a and 7b and the stator core 6 in which the stator winding 5 is wound on the stator 2 side of the rotor yokes 7a and 7b. It has the permanent magnet 8 arrange | positioned, and each permanent magnet 8 is arrange | positioned so that adjacent mutually may become a different polarity while facing the stator 2 (refer (a), (b)). ).

  In this conventional motor 1, for example, the permanent magnet 8 of the rotor 3 b goes through the stator 2 to the permanent magnet 8 of the rotor 3 a (see (b)), and then along the outer peripheral edge of the rotor 3 a. Toward the adjacent permanent magnet 8 (see (a)), from the permanent magnet 8 through the stator 2 to the permanent magnet 8 of the rotor 3b (see (b)), and further to the outside of the rotor 3b. A magnetic path r toward the adjacent permanent magnet 8 along the periphery is formed. Similarly, the permanent magnet 8 of the rotor 3a, the permanent magnet 8 of the stator 2, the rotor 3b, and the permanent magnet 8, the stator 2, and the permanent magnet 8 of the rotor 3a that are adjacent along the outer peripheral edge of the rotor 3b. A magnetic path r is formed in the order of description to the adjacent permanent magnet 8 along the outer peripheral edge of the rotor 3a.

That is, for each permanent magnet 8, 8, two magnetic paths r having opposite directions are formed between the adjacent permanent magnets 8, 8. In the figure, ◯ indicates that the traveling direction is from the back side to the front side, and x indicates that the traveling direction is from the front side to the back side, and the traveling direction is shown for only one magnetic path r.
As described above, the magnetic path r formed in the conventional axial gap type motor 1 includes the magnetic path r1 from the rotor 3a through the stator 2 to the rotor 3b, and each of the rotor 3a and the rotor 3b. A magnetic path along the outer peripheral edge of the rotor between the adjacent permanent magnets 8, that is, a magnetic path r <b> 2 passing through the outer peripheral edge of the end surface of the motor 1 is formed.

In addition, as such an axial gap type motor, there is a “disk type non-bearing motor” (see Patent Document 1).
Japanese Patent Laid-Open No. 10-080113

However, if the length of the magnetic path r is increased, the iron loss is increased, and thus it is inevitable that the motor loss is increased. In addition, when the motor is independently driven with a composite current, there is a concern that the magnetic resistance becomes high and the composite effect is reduced. Therefore, it is desirable to make the length of the magnetic path r as short as possible.
An object of the present invention is to provide a rotating electrical machine in which the length of a magnetic path is shortened as much as possible to reduce motor loss and the combined effect is not reduced when driven independently by a combined current.

  In order to achieve the above object, a rotating electrical machine according to the present invention is the rotating electrical machine in which the rotor on which a permanent magnet is mounted and the stator on which an armature winding is mounted face each other in the axial direction. A magnetic path formed through the child is composed of a magnetic flux in the rotation axis direction along the rotation axis direction and a magnetic flux in a radial direction along the radial direction of the end surface orthogonal to the rotation axis, and passes through the radial direction of the end surface orthogonal to the rotation axis. It is characterized by that.

  According to the present invention, the rotating electrical machine in which the rotor mounted with the permanent magnet and the stator mounted with the armature winding face each other in the axial direction has a magnetic path formed through the rotor and the stator rotating. The rotation direction magnetic flux along the axial direction and the radial direction magnetic flux along the radial direction of the end surface orthogonal to the rotation axis, and the end surface orthogonal to the rotation axis passes through the end surface radial direction. As a result, the length of the magnetic path is made as short as possible to reduce the motor loss, and the composite effect is not reduced when the composite current is independently driven.

The best mode for carrying out the present invention will be described below with reference to the drawings.
(First embodiment)
FIG. 1 shows a schematic structure of a motor according to a first embodiment of the present invention, where (a) is an explanatory plan view seen from the stator side of the rotor, and (b) is along the BB line of (a). FIG. As shown in FIG. 1, an axial gap type motor (rotating electric machine) 10 includes a stator (stator) 11 and a pair of rotors arranged with air gaps (gap) a provided on both sides of the stator 11. (Rotor) 12a, 12b is provided, and each rotor 12a, 12b formed in the shape of a disk is connected by a rotating shaft 13 that is rotatably supported (see (b)).

  The stator 11 has a plurality of outer stator cores 15 wound with a stator winding 14 arranged in an annular shape (in this example, only four and two are shown) with substantially equal intervals, and is fixed outside. By arranging a plurality of inner stator cores 16 around which the stator windings 14 are wound in an annular shape (four in this example, only two are shown in this example) with a substantially equal interval inside the child core 15. It is formed (see (b)). That is, the outer stator core 15 and the inner stator core 16 around which the stator windings 14 are wound, respectively, approach the concentric circles on the outer side of the rotating shaft 13 and the electrical angles differ by 180 degrees (U, U-).

  Each of the rotors 12a and 12b has a plurality of rotor yokes 17a and 17b and a plurality of rotor yokes 17a and 17b protruding from the stator 11 side (only four and two are shown in this example). The outer permanent magnet 18a and the inner permanent magnet 18b are provided. Each of the rotor yokes 17a and 17b is divided into substantially four equal parts by a partition wall portion 19 (which may be a groove-like space) made of a nonmagnetic member, and has four sections that are magnetically isolated from each other. (See (a)). The outer permanent magnet 18 a is arranged corresponding to the outer stator core 15 wound with the stator winding 14, and the inner permanent magnet 18 b corresponds to the inner stator core 16 wound with the stator winding 14. Are arranged. The outer permanent magnet 18a and the inner permanent magnet 18b are arranged so as to face the stator 11 and have different polarities in the rotor circumferential direction and the rotor radial direction adjacent to each other ((a). (See (b)).

That is, the outer permanent magnets 18a and the inner permanent magnets 18b are arranged on the stator 11 side of each of the rotor yokes 17a and 17b so as to be close to the stator radial direction every four sections (see (a)). ).
In the motor 10, for example, the inner permanent magnet 18 b of the rotor 12 b passes through the rotor yoke 18 b toward the outer permanent magnet 18 a, passes through the outer stator core 15, and then passes from the outer permanent magnet 18 a of the rotor 12 a to the rotor yoke. A magnetic path r (see (b)) is formed through the inner permanent magnet 18b through the inner stator core 16 and then toward the inner permanent magnet 18b of the rotor 12b.

  At this time, the magnetic path r is formed by the rotation direction magnetic flux in the outer stator core 15 and the inner stator core 16 and the rotor radial direction magnetic flux in each of the rotors 12a and 12b. Then, in each rotor 12a, 12b, a magnetic path r2 between the inner permanent magnet 18b and the outer permanent magnet 18a (see (a). Shown from the stator 11 side, and some magnets are not shown) In this case, since the inner permanent magnet 18b and the outer permanent magnet 18a are arranged close to each other in the rotor radial direction, they become a part of the rotor radius and can pass through the shortest distance.

  As a result, the magnetic path r2 passing through the end face of the motor 10, which is the end face orthogonal to the rotating shaft 13, is surely made shorter than the magnetic path r2 along the outer peripheral edge of the conventional rotor (see FIG. 8A). Therefore, the length of the magnetic path r is made as short as possible to reduce the motor loss, and the composite effect is not reduced when the composite current is independently driven.

(Second Embodiment)
2A and 2B show a schematic structure of a motor according to a second embodiment of the present invention, in which FIG. 2A is an explanatory plan view viewed from the rotor side of the stator, and FIG. 2B is taken along line BB in FIG. FIG. As shown in FIG. 2, the motor 20 includes a rotor 21 and stators 22 a and 22 b arranged to face each other with air gaps (gap) a provided on both sides of the rotor 21. The rotor 21 is attached to the case 23 via a rotating shaft 21a. The case 23 is formed by a cylindrical part 23a and a disk-like part 23b that covers both openings of the cylindrical part 23a, and the rotating shaft 21a is rotatably supported by the disk-like part 23b.

  The stator 22a is formed by arranging a plurality of stator cores 24a around which the stator windings 14 are wound in an annular shape (in this example, only four and two are shown) at substantially equal intervals. 22b is formed by arranging a plurality of stator cores 24b around which the stator windings 14 are wound in an annular shape (in this example, only four and two are shown) with substantially equal intervals. (See (b)). The stator cores 24 a and 24 b are fixed to the disk-like portion 23 a of the case 23. That is, a plurality of stator cores 24a and stator cores 24b each wound around the stator winding 14 are opposed to each other on the inner surface of the case 23, and are arranged in an annular shape outside the rotating shaft 21a. .

In addition, the rotor 21 includes a plurality of permanent magnets 26 that are embedded in the rotor core 25 corresponding to the rotor core 25 and the stator core 24 a (24 b) around which the stator winding 14 is wound. have. In addition, each permanent magnet 26 is arrange | positioned so that adjacent may become a different polarity (refer (a), (b)).
In this motor 20, for example, from the permanent magnet 26 of the rotor 21 through the stator core 24a of the stator 22a, the disk-shaped portion 23b, which is a stator fixing location, moves from the disk-shaped portion 23a to the cylindrical portion 23a. A magnetic path r (see (b)) is formed from the circular portion 23a to the disk-shaped portion 23b and further to the permanent magnet 26 through the stator core 24b of the stator 22b.

  At this time, the magnetic path r is formed by the rotation axis direction magnetic flux in the stator core 24a, the cylindrical portion 23a and the stator core 24a, and the case radial direction magnetic flux in the disk-like portion 23b. Then, from the stator core 24a in the stator 22a to the cylindrical portion 23a through the disk-shaped portion 23b, and from the cylindrical portion 23a in the stator 22b to the stator core 24a through the disk-shaped portion 23b. In the magnetic path r2 (see (a), showing a state viewed from the stator 11 side, and some magnets are not shown), the permanent magnet 26 and the cylindrical portion 23a approach each other along the rotor radial direction. So you can take the shortest distance.

  As a result, in the case where the two stators 22a and 22b are provided and the stators 22a and 22b are fixed to the stator fixing place, the magnetic path r2 passing through the end face side of the motor 20 is replaced with the conventional outer periphery of the rotor. Therefore, the length of the magnetic path r can be made as short as possible to reduce the motor loss, and the composite current can be independently driven. The combined effect is not reduced.

(Third embodiment)
3A and 3B show a schematic structure of a motor according to a third embodiment of the present invention, in which FIG. 3A is an explanatory plan view seen from the stator side of the rotor, and FIG. 3B is taken along line BB in FIG. FIG. As shown in FIG. 3, the motor 30 is replaced with a rotor 31 in which permanent magnets are arranged in two rows adjacent to the rotor radial direction and the two stators 22 a and 22 b instead of the rotor 21. , And two stators 32a and 32b in which the stators are arranged in two rows on the outer side and the inner side, respectively. The two stators 32a and 32b are fixed to a stator fixing place 33 (corresponding to the disk-shaped portion 23b of the case 23). Other configurations and operations are the same as those of the motor 20.

  That is, the outer stator cores 34a and 34b and the inner stator cores 35a and 35b, which form the two stators 32a and 32b and are wound with the stator winding 14, respectively, are connected to the rotating shaft 31a of the rotor 31. They are arranged on the outside so as to be concentrically spaced apart from each other and so that their electrical angles differ by 180 degrees (U, U−) (see (b)). Further, the rotor 31 includes a rotor core 36, an outer permanent magnet 37a disposed in an embedded state in the rotor core 36 corresponding to the outer stator cores 34a and 34b around which the stator winding 14 is wound, Corresponding to the inner stator cores 35a and 35b around which the stator winding 14 is wound, there is an inner permanent magnet 37b disposed in an embedded state in the rotor core 36.

The rotor 31 is substantially divided into four equal parts by a partition wall portion 19 (which may be a groove-like space) made of a nonmagnetic member, and has four sections that are magnetically isolated from each other ((a)). reference). An outer permanent magnet 37a and an inner permanent magnet 37b are arranged in proximity to the stator radial direction for each of the four sections (see (a)).
In this motor 30, for example, the inner permanent magnet 37b of the rotor 31 is passed through the inner stator core 35b, the stator fixing place 33, and the outer stator core 34b in the order of description, toward the outer permanent magnet 37a. A magnetic path r (see (b)) toward the inner permanent magnet 37b is formed through the stator core 34a, the stator fixing place 33, and the inner stator core 35a in the order described.

  At this time, the magnetic path r is formed by the rotation axis direction magnetic flux in the outer stator cores 34 a and 34 b and the inner stator cores 35 a and 35 b and the stator radial magnetic flux in each stator fixing location 33. Become. Then, the magnetic path r2 between the outer permanent magnet 37a and the inner permanent magnet 37b (see (a) in each stator fixing location 33. The state seen from the stator 32b side is shown, and some of the magnets are not shown. Can be passed through the shortest distance because the outer permanent magnet 37a and the inner permanent magnet 37b are arranged close to each other along the rotor radial direction.

  As a result, the magnetic path r2 passing through the end face side of the motor 30 can be reliably shortened compared to the magnetic path r2 (see FIG. 8A) along the outer periphery of the conventional rotor. The length is shortened as much as possible to reduce the motor loss, and the composite effect is not reduced when independently driven by the composite current.

(Fourth embodiment)
FIG. 4 is a cross-sectional explanatory view similar to FIG. 1B, showing the schematic structure of a motor according to a fourth embodiment of the present invention. As shown in FIG. 4, the motor 40 includes an inner stator core 16 around which the stator winding 14 is wound, and inner permanent cores disposed on the rotor yokes 17 a and 17 b corresponding to the inner stator core 16. Instead of the magnet 18b, a connecting member 41 for connecting both the rotor yokes 17a and 17b is provided. Other configurations and operations are the same as those of the motor 10.

  In the motor 40, a magnetic path r that passes through the connecting member 41 is formed instead of the inner stator core 16 and the inner permanent magnet 18b. As a result, the magnetic path r2 passing through the end face side of the motor 40 can be reliably shortened compared to the magnetic path r2 (see FIG. 8A) along the outer periphery of the conventional rotor. The length is made as short as possible to reduce the motor loss, and the composite effect is not reduced when independently driven by the composite current. In addition, since the number of coils formed on the inner stator core can be reduced, the number of parts can be reduced and the cost can be reduced.

  An air gap may be provided in place of the connecting member 41 to form a magnetic path r passing through the air gap. The connecting member 41 is not limited to the inner stator core 16 and may be replaced with the outer stator core 15. Further, the present invention is not limited to the case where the two rotor yokes 17a and 17b are connected, and the present invention can be applied to the case where the stator is connected in a two-stator structure (see FIG. 3).

(Fifth embodiment)
5A and 5B show a schematic structure of a motor according to a fifth embodiment of the present invention, in which FIG. 5A is an explanatory plan view viewed from the stator side of the rotor, and FIG. 5B is along the BB line of FIG. FIG. As shown in FIG. 5, the motor 45 is fixed by replacing the stator 46 with an outer stator core 15 around which the stator winding 14 is wound and an inner stator core 16 around which the stator winding 14 is wound. It is formed by one stator core 47 in which the child winding 14 is vertically wound. Other configurations and operations are the same as those of the motor 10.

  A plurality of stator cores 47 are arranged in an annular shape (in this example, only four and two are shown) with substantially equal intervals, and fixed to the center of each stator core 47 in the radial direction of the stator. A groove 47a for vertically winding the child winding 14 along the direction of the rotary shaft 13 is formed. The stator winding 14 is wound around the groove 47a by vertical (rotating axis direction) winding. The end portions 47b of the stator cores 47 other than the grooves 47a forming portions face the outer permanent magnets 18a and the inner permanent magnets 18b, respectively, and between the end portions 47b and the permanent magnets 18a and 18b An air gap a (gap) is provided. The permanent magnets 18a and 18b having the same polarity are arranged at the same position in the stator radial direction, that is, facing each other.

  In this motor 45, in each stator core 47, the rotor 12b passes from the inner permanent magnet 18b of the rotor 12b to the outer permanent magnet 18a of the rotor 12b through the stator core 47 and passes through the rotor yoke 17b. From the inner permanent magnet 18b of the rotor 12a to the outer permanent magnet 18a of the rotor 12a through the stator core 47 and through the rotor yoke 17a. A magnetic path r (see (b)) toward the inner permanent magnet 18b is formed.

  As a result, the magnetic path r2 passing through the end face side of the motor 45 can be surely shortened than the magnetic path r2 (see FIG. 8A) along the outer periphery of the conventional rotor. The length is made as short as possible to reduce the motor loss, and the composite effect is not reduced when independently driven by the composite current. In addition, since the stator winding 14 can be wound even in a small space, the size can be reduced.

(Sixth embodiment)
FIG. 6 shows a schematic structure of a motor according to a sixth embodiment of the present invention, in which (a) is an explanatory plan view seen from the stator side of the rotor, and (b) is taken along line BB in (a). FIG. As shown in FIG. 6, the motor 50 is driven by flowing a composite current so that a plurality of rotating magnetic fields are generated in the coil. Other configurations and operations are the same as those of the motor 45.

  By passing a composite current, one of the two rotors (A pole pair) rotates from the inner permanent magnet 18b of the rotor 12b through the stator core 47 to the outer permanent magnet 18a of the rotor 12b. A magnetic path r3 (see (b)) is formed through the child yoke 17b toward the inner permanent magnet 18b of the rotor 12b. A magnetic path r4 (see (b)) is formed through the core 47 toward the outer permanent magnet 18a of the rotor 12a and toward the inner permanent magnet 18b of the rotor 12a through the rotor yoke 17a.

  As a result, the magnetic path r2 passing through the end face side of the motor 50 can be reliably shortened compared to the magnetic path r2 (see FIG. 8A) along the conventional outer periphery of the rotor. The length is made as short as possible to reduce the motor loss, and the composite effect is not reduced when independently driven by the composite current. In addition, by driving the motor with a composite current, the magnetic resistance is reduced, so that the composite effect is easily exhibited.

(Seventh embodiment)
7A and 7B show a schematic structure of a motor according to a seventh embodiment of the present invention, in which FIG. 7A is an explanatory plan view viewed from the stator side of the rotor, and FIG. 7B is taken along line BB in FIG. FIG. As shown in FIG. 7, the motor 55 has an outer permanent magnet 18a and an inner permanent magnet 18b arranged in a Halbach array. Other configurations and operations are the same as those of the motor 10.

  As a result, the magnetic path r2 passing through the end face side of the motor 55 can be reliably shortened compared to the magnetic path r2 (see FIG. 8A) along the outer periphery of the conventional rotor. The length is made as short as possible to reduce the motor loss, and the composite effect is not reduced when independently driven by the composite current. In addition, by arranging the permanent magnets in the Halbach array, the thickness of each of the rotor yokes 17a and 17b can be reduced, so that the motor can be reduced in size.

  As described above, according to the present invention, the rotating electrical machine in which the rotor mounted with the permanent magnet and the stator mounted with the armature winding are opposed in the axial direction is a magnetic field formed through the rotor and the stator. Since the path is constituted by the rotation axis direction magnetic flux along the rotation axis direction and the radial direction magnetic flux along the radial direction of the end surface orthogonal to the rotation axis, the end surface orthogonal to the rotation axis passes through the end surface radial direction. The length of the magnetic path is made as short as possible to reduce the motor loss, and the composite effect is not reduced when independently driven by the composite current.

The schematic structure of the motor which concerns on 1st Embodiment of this invention is shown, (a) is plane explanatory drawing seen from the stator side of the rotor, (b) is sectional explanatory drawing in alignment with the BB line of (a). is there. The schematic structure of the motor which concerns on 2nd Embodiment of this invention is shown, (a) is plane explanatory drawing seen from the rotor side of the stator, (b) is sectional explanatory drawing in alignment with the BB line of (a). is there. The schematic structure of the motor which concerns on 3rd Embodiment of this invention is shown, (a) is plane explanatory drawing seen from the stator side of the rotor, (b) is sectional explanatory drawing in alignment with the BB line of (a). is there. It is a cross-sectional explanatory drawing similar to FIG.1 (b) which shows schematic structure of the motor which concerns on 4th Embodiment of this invention. The schematic structure of the motor which concerns on 5th Embodiment of this invention is shown, (a) is plane explanatory drawing seen from the stator side of the rotor, (b) is sectional explanatory drawing in alignment with the BB line of (a). is there. The schematic structure of the motor which concerns on 6th Embodiment of this invention is shown, (a) is plane explanatory drawing seen from the stator side of the rotor, (b) is sectional explanatory drawing in alignment with the BB line of (a). is there. The schematic structure of the motor which concerns on 7th Embodiment of this invention is shown, (a) is plane explanatory drawing seen from the stator side of the rotor, (b) is sectional explanatory drawing in alignment with the BB line of (a). is there. The schematic structure of the conventional axial gap type | mold motor is shown, (a) is plane explanatory drawing seen from the stator side of the rotor core, (b) is sectional explanatory drawing in alignment with the BB line of (a).

Explanation of symbols

10, 20, 30, 40, 45, 50, 55 Motor 11, 22a, 22b, 32a, 32b, 46 Stator 12a, 12b, 21, 31 Rotor 13, 21a Rotating shaft 14 Stator winding 15, 34a, 34b Outer stator core 16, 35a, 35b Inner stator core 17a, 17b Rotor yoke 18a, 37a Outer permanent magnet 18b, 37b Inner permanent magnet 19 Partition part 23 Case 23a Cylindrical part 23b Disc-like part 24a, 24b, 47 Stator core 25, 36 Rotor core 26 Permanent magnet 33 Stator fixing place 41 Connecting member 47a Groove 47b End a Air gap r, r2 Magnetic path

Claims (8)

In a rotating electrical machine in which a rotor mounted with a permanent magnet and a stator mounted with an armature winding are opposed in the axial direction,
A magnetic path formed through the rotor and the stator is composed of a rotation axis direction magnetic flux along the rotation axis direction and a radial direction magnetic flux along the radial direction of the end surface orthogonal to the rotation axis, and is orthogonal to the rotation axis. A rotating electrical machine characterized by passing through a radial direction of an end face.   The rotating electrical machine according to claim 1, wherein the rotor is composed of a pair arranged to face each other so as to sandwich the stator.   The rotating electrical machine according to claim 1, wherein the stator is composed of a pair arranged to face each other so as to sandwich the rotor.   4. The rotating electrical machine according to claim 2, wherein the stator core around which the armature winding is wound is arranged in two rows in the stator radial direction.   One of the stator cores arranged in two rows by providing a connecting member or an air gap for connecting the rotor cores of a pair of opposed rotors or a pair of stator cores of a pair of opposed stators. The rotating electrical machine according to claim 4, wherein a magnetic path passing through the connecting member or the air gap is formed.   The armature winding is wound around the stator core of the stator by vertical winding along the rotation axis direction, and the permanent magnets at the same position in the rotor radial direction have the same polarity. The rotating electrical machine described.   The rotating electrical machine according to any one of claims 1 to 6, wherein the rotating electrical machine is driven by flowing a composite current so that a plurality of rotating magnetic fields are generated in the coil.   The rotating electric machine according to claim 1, wherein the permanent magnets are arranged in a Halbach array.

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