Axial gap type rotary electric machine, and drone

Abstract

To provide an axial gap type rotary electric machine capable of improving a heat dissipation property of a rotor while reducing weight of the rotor.SOLUTION: An axial gap type rotary electric machine comprises a stator, and a rotor opposed to the stator in an axial direction. The rotor comprises a plurality of magnets periodically arranged in a Halbach array in a circumferential direction; a disc-like rotor body in which the plurality of magnets are fixed onto a first face opposed to the stator; and a lattice structure reinforcement part obtained by periodically arranging lattices branched branch-like, that is formed on a second face on an opposite side of the first face of the rotor body.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an axial gap type rotating electric machine and a drone. [Background technology]

[0002] Conventionally, an axial gap type rotating electric machine has been known in which a stator and a rotor are arranged facing each other via an air gap in the axial direction of the rotating electric machine. For this type of axial gap type rotating electric machine, a configuration in which the magnets of the rotor are arranged in a Halbach array has also been proposed (for example, see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-33578 A Summary of the Invention [Problem to be solved by the invention]

[0004] For example, one of the applications of the axial gap type rotating electric motor is being considered as a motor that drives the rotors of unmanned aerial vehicles such as drones. When mounting an axial gap type rotating electric motor on a drone, it is preferable to reduce the weight in order to improve the flight performance of the drone.

[0005] Furthermore, the rotor of the rotating electric machine generates heat due to electromagnetic induction with the interlinkage magnetic flux of the stator, so there is a demand for improving the heat dissipation performance of the rotor in this type of axial gap type rotating electric machine.

[0006] The present invention has been made in consideration of the above circumstances, and has an object to provide an axial gap type rotating electric machine capable of improving the heat dissipation performance of the rotor while reducing the weight of the rotor. [Means for solving the problem]

[0007] An axial gap type rotating electric machine according to one embodiment of the present invention includes a stator and a rotor axially opposed to the stator. The rotor has a plurality of magnets periodically arranged in a Halbach array in the circumferential direction, a disk-shaped rotor body having a first surface facing the stator to which the plurality of magnets are fixed, and a reinforcing portion having a lattice structure formed on a second surface opposite to the first surface of the rotor body and having a periodically arranged lattice that branches out like branches.

[0008] The reinforcing portion may have a lattice structure in which unit cells of a body-centered cubic lattice or a face-centered cubic lattice are periodically arranged. The rotor body may further have an annular mounting portion on the inner peripheral side for connection to the shaft, and the reinforcing portion may be formed in an annular shape on the outer peripheral side of the mounting portion. Moreover, a drone according to another aspect of the present invention includes the above-mentioned axial gap type rotating electric machine. Effect of the Invention

[0009] According to one aspect of the present invention, it is possible to provide an axial gap type rotating electric machine capable of improving the heat dissipation performance of the rotor while reducing the weight of the rotor. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a drone according to an embodiment of the present invention. [Diagram 2] FIG. 4 is a diagram illustrating a configuration example of a motor of a drive unit. [Diagram 3] 3(a) is a view of the rotor as seen from the outer side, and FIG. 3(b) is a cross-sectional view taken along line AA in FIG. 3(a). [Figure 4] 4(a) is a diagram of the rotor as viewed from the inner surface facing the stator, and (b) is a partially enlarged view of FIG. 4(a). [Diagram 5] FIG. 4(a) is a diagram showing the magnetization direction of each magnet in FIG. 4(b), and FIG. 4(b) is a diagram showing an example of the electromagnetic force acting on each magnet. [Figure 6] 4 is a graph showing an example of a strength analysis of a rotor body during rotation of the rotor. [Figure 7] 5A to 5C are schematic diagrams illustrating examples of the configuration of a reinforcing portion. [Figure 8] FIG. 4 is a diagram showing an example of a unit cell of a reinforcing portion. [Figure 9] 13A and 13B are diagrams showing other examples of unit cells of the reinforcing portion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the embodiments, in order to make the description easier to understand, structures and elements other than the main parts of the present invention will be described in a simplified or omitted manner. In addition, in the drawings, the same elements are given the same reference numerals. Note that the shapes, dimensions, etc. of each element shown in the drawings are shown only for illustrative purposes, and do not represent the actual shapes, dimensions, etc.

[0012] The axial gap type rotating electric machine of the present embodiment will be described below. The axial gap type rotating electric machine of the present embodiment is a motor applied to a drive unit of a drone.

[0013] Fig. 1 is a diagram showing an example of the configuration of a drone according to the present embodiment. The drone 100 shown in Fig. 1 is an unmanned aerial vehicle generally called a multicopter, and can fly by remote control or automatic piloting.

[0014] The drone 100 has a main body 10 incorporating a control unit, a battery, etc., and four sets of drive units 20 each attached to the main body 10. The main body 10 may incorporate a camera 11, for example. The drive units 20 are arranged on all four sides of the main body 10 at intervals of 90° in a plan view, for example. Since all the drive units 20 have the same configuration, the following description will describe the configuration of one representative drive unit 20, and will omit any overlapping description with the other drive units.

[0015] The driving unit 20 includes a rotor 21, an arm unit 22, a motor 23, a leg unit 24, and a rib unit 25. The rotor 21 is a fixed pitch propeller, and rotates when driven by the motor 23 to generate lift (vertical upward thrust). The rotor 21 can adjust the lift by controlling the rotation speed of the motor 23.

[0016] The arm portion 22 extends horizontally from the main body portion 10. One end of the arm portion 22 is connected to the main body portion 10, and a motor 23 is attached to the other end of the arm portion 22.

[0017] In addition, a leg portion 24 is attached to the underside of the motor 23. The leg portion 24 extends in the vertical direction perpendicular to the arm portion 22, and supports the drone 100 by contacting the ground when the drone 100 is on the ground. In addition, a rib portion 25 extending in an oblique direction is connected to the arm portion 22 and the leg portion 24.

[0018] 2 is a diagram showing an example of the configuration of the motor 23 of the drive unit 20. The motor 23 is a so-called axial gap motor, and has a shaft 31, a rotor 32, a stator 33, and a casing 34 that houses the elements of the motor 23.

[0019] 2, and is rotatably supported by a bearing (not shown) disposed in a casing 34. The rotor 21 is fixed to one side of the shaft 31 (the upper side in FIG. 2).

[0020] The stator 33 is a cylindrical body that is concentrically disposed on the outer periphery of the shaft 31 and located between the pair of rotors 32 in the axial direction of the shaft 31. The stator 33 is disposed with a small gap between the shaft 31 and the rotors 32.

[0021] The stator 33 has a plurality of coil units 35 arranged annularly in the circumferential direction of the stator 33 centered on the shaft 31, and a cylindrical stator case 36 that houses each of the coil units 35. Each of the coil units 35 is configured by winding a coil 35b around the outer periphery of a trapezoidal stator core 35a.

[0022] The stator core 35a is formed, for example, by stacking a plurality of electromagnetic steel plates in the axial direction, and is arranged in the stator 33 so that the radially outer side is wider than the radially inner side. The winding direction of the coil 35b is a direction intersecting the axial direction (horizontal direction). By sequentially switching the magnetic field of the stator 33 by controlling the current of the coil 35b, an attractive force or a repulsive force against the magnetic field of the rotor 32, which will be described later, is generated in the stator 33. This causes the shaft 31 and the rotor 32 to rotate.

[0023] The stator case 36 is hollow, and a flow path for cooling oil (coolant) is formed inside the stator case 36 around the coil unit 35. An oil inlet 37 and an oil outlet 38 are formed on the side surface of the stator case 36. The inlet 37 and the outlet 38 are formed at positions facing each other (positions at 180° with respect to the axial center), but are not limited to this.

[0024] Oil is introduced into the stator 33 of the motor 23 from the inlet 37. The oil flows inside the stator case 36, removes heat from the coil unit 35, and is discharged from the outlet 38 to the outside of the motor 23. This allows the coil unit 35 of the stator 33 to be cooled by the flow of oil. Note that the oil discharged from the outlet 38 is cooled outside the motor 23, and then introduced from the inlet 37 to circulate inside the motor 23.

[0025] The rotors 32 are composed of a pair of disks arranged facing each other at a predetermined interval, and the shaft 31 is inserted and fixed at the center of each rotor 32. This causes the rotors 32 to rotate together with the shaft 31.

[0026] Fig. 3(a) is a view of rotor 32 as viewed from the outer side, and Fig. 3(b) is a cross-sectional view taken along line AA in Fig. 3(a). Fig. 4(a) is a view of rotor 32 as viewed from the inner side facing stator 33, and Fig. 4(b) is a partially enlarged view of Fig. 4(a). Note that the outer side of rotor 32 is an example of the second surface, and the inner side of rotor 32 is an example of the first surface.

[0027] Each rotor 32 has a disk-shaped rotor body 40 and a plurality of magnets 41 fixed to the rotor body 40. Each magnet 41 is composed of a permanent magnet such as a ferrite magnet or a rare earth magnet. The rotor body 40 is attached from the outside in the axial direction to a cylindrical mounting base 39 fixed to the shaft 31. Specifically, a mounting portion 40a formed in an annular shape on the inner peripheral side of the rotor body 40 is fixed to the mounting base 39 with bolts 46.

[0028] The magnets 41 are fixed to the inner surface of the rotor body 40 that faces the stator 33. Each magnet 41 is fixed in a state in which it is thermally connected to the rotor body 40 by a heat-conductive adhesive or the like.

[0029] Fig. 5(a) is a diagram showing the magnetization direction of each magnet 41 in Fig. 4(b). In Fig. 5(a), the magnetization direction of magnet 41 is indicated by an arrow, with the upper side in the figure corresponding to the stator 33 side and the lower side in the figure corresponding to the surface facing the rotor body 40. Also, Figs. 4(b) and 5(a) partially show magnets 41a to 41k, which are a part of the magnets 41 of rotor 32.

[0030] In this embodiment, the magnets 41 of the rotor 32 are periodically arranged in a Halbach array along the circumferential direction of the rotor 32. Specifically, as shown in FIG. 5(a), the magnets 41 are fixed in the order of magnets 41a to 41k in the circumferential direction of the rotor body 40 so that the magnetic pole orientation (magnetization direction) of each magnet 41 rotates in sequence by 90° in a plane perpendicular to the radial direction. As described above, by arranging the magnets 41 in a Halbach array, the rotor body 40 of this embodiment is not required to function as an iron core that forms a magnetic circuit through magnetic flux. In addition, since the magnets 41a to 41k each have a different magnetization direction, the electromagnetic force generated on the stator 33 side in the circumferential direction of the rotor 32 is different for each magnet 41.

[0031] Fig. 5(b) is a diagram showing an example of electromagnetic forces acting on magnets 41a to 41k. The magnetization direction of magnet 41 shown in Fig. 5(b) is the same as that in Fig. 5(a). Moreover, the electromagnetic forces in Fig. 5(b) are expressed as positive in the direction from the stator 33 side to the magnet 41 side. As shown in Fig. 5(b), in this embodiment, among magnets 41a to 41k, magnet 41h has the greatest magnetic attraction force toward the stator 33 side.

[0032] On the other hand, when the rotor 32 rotates, a resultant force of the centrifugal force due to the rotation and the magnetic attraction force toward the stator 33 acts on the rotor body 40. For this reason, the specifications of the rotor body 40 require that it is not plastically deformed when the magnets 41 are magnetically attracted to the stator 33 at the rated rotation speed, and that it is strong enough to maintain a predetermined gap between the stator 33 and the rotor 32.

[0033] 6(a) and (b) are graphs showing an example of strength analysis of the rotor body 40 when the rotor 32 rotates. FIG. 6(a) shows an example of the correspondence relationship between the thickness of the rotor body 40 and the maximum displacement of the magnet 41 in the gap direction. The horizontal axis of FIG. 6(a) shows the thickness [mm] of the rotor body 40, and the vertical axis of FIG. 6(a) shows the maximum displacement [%] of the rotor body 40 and the magnet 41 in the gap direction. The maximum displacement shows a value normalized by the gap between the stator 33 and the rotor 32. From FIG. 6(a), it can be seen that when the thickness of the rotor body 40 is 1 mm, the maximum displacement in the gap direction is below 200%, and when the thickness of the rotor body 40 is 2 mm, the maximum displacement in the gap direction is below 100%.

[0034] Moreover, Fig. 6(b) shows an example of the correspondence relationship between the thickness of the rotor body 40 and the maximum von Mises stress value. The horizontal axis of Fig. 6(b) shows the thickness [mm] of the rotor body 40, and the vertical axis of Fig. 6(b) shows the maximum von Mises stress value, which is a scalar quantity. Fig. 6(b) shows that when the thickness of the rotor body 40 is 1 mm, the maximum von Mises stress value exceeds 50.0, but when the thickness of the rotor body 40 is 2 mm, the von Mises stress value approaches 50.0.

[0035] 6(a) and (b) show that the part of the rotor body 40 that has the greatest magnetic attraction force toward the stator 33 requires a thickness of 2 mm or more to satisfy the criteria for the maximum allowable displacement and the maximum von Mises stress value. As an example, if the thickness of the rotor body 40 is 2 mm, the weight of the rotor body 40 is 71.7 g.

[0036] In order to reduce the weight of the rotor 32, it is necessary to make the thickness of the rotor body 40 as thin as possible while still satisfying the strength specifications required of the rotor 32. From this perspective, in this embodiment, a reinforcing portion 42 having a lattice structure is formed on the outer surface (the surface opposite to the inner surface) of the rotor body 40 to reinforce the rotor body 40.

[0037] The reinforcing portion 42 has an overall shape of a flat plate, and is disposed in an annular shape on the outer peripheral side of the mounting portion 40a on the outer surface of the rotor body 40 as shown in Fig. 3(a). The reinforcing portion 42 is fixed to the outer surface of the rotor body 40 in a stacked state on the rotor body 40 as shown in Fig. 3(b).

[0038] FIG. 7 is a schematic diagram showing a configuration example of the reinforcing part 42. The reinforcing part 42 is configured by arranging a plurality of square unit cells 43 in the planar direction and the height direction. The unit cells 43 of the reinforcing part 42 are lattices branched into branches, and are arranged so as to share one face and a plurality of sides forming that face with each of the adjacent unit cells 43. As a result, the reinforcing part 42 forms a lattice structure in which the lattices formed by the unit cells 43 are periodically arranged in a predetermined direction. Note that FIG. 7 shows an example in which a plurality of unit cells 43 of the reinforcing part 42 are arranged in the planar direction and the height direction, but the unit cells 43 may be arranged only in the planar direction, and the reinforcing part 42 may be a single layer in the height direction.

[0039] Fig. 8 is a diagram showing an example of a unit cell 43 of the reinforcing portion 42. Fig. 8(a) is a perspective view of the unit cell 43, Fig. 8(b) is a front view of the unit cell 43 of Fig. 8(a), and Fig. 8(c) is a cross-sectional view taken along line BB of Fig. 8(b).

[0040] The unit cell 43 shown in Fig. 8 has a lattice structure called a body-centered cubic lattice. The unit cell 43 shown in Fig. 8 has a structure in which cylindrical beams 44 extend from the center of the unit cell 43 forming a cube toward each vertex of the cube. That is, in the unit cell 43 of Fig. 8, the cylindrical beam 44 is connected from a certain vertex of the cube through the center of the cube to a diagonal vertex. Although not particularly limited, the unit cell 43 of Fig. 8 may be, for example, 2.5 mm cubed, and the diameter of the beam 44 may be 1 mm.

[0041] Fig. 9 is a diagram showing another example of a unit cell 43 of the reinforcing portion 42. Fig. 9(a) is a perspective view of the unit cell 43, Fig. 9(b) is a front view of the unit cell 43 of Fig. 9(a), and Fig. 9(c) is a cross-sectional view taken along line CC of Fig. 9(b).

[0042] The unit cell 43 shown in Fig. 9 has a lattice structure called a face-centered cubic lattice. The unit cell 43 shown in Fig. 9 has a structure in which, on each face of the unit cell 43 forming a cube, two cylindrical beams 44 are arranged so as to be connected diagonally through the center of the face. That is, in the unit cell 43 in Fig. 9, the cylindrical beams 44 are arranged along any face of the unit cell 43, and no beam 44 passes through the center of the cube. Although not particularly limited, the unit cell 43 in Fig. 9 may be, for example, 2.5 mm cubed, and the diameter of the beams 44 may be 1 mm.

[0043] The reinforcing portion 42 is formed by, for example, selecting one of the unit cells 43 shown in FIG. 8 and FIG. 9 and arranging the selected unit cells 43 periodically in the planar direction and the height direction. Even if the unit cells 43 cannot be completely generated, it is possible to generate partial cells if there is a loss in one axis direction while the cube is aligned with each axis of the XYZ coordinate system. In addition, considering the cell structure of a body-centered cubic lattice or a face-centered cubic lattice, it is also possible to generate partial cells cut at an inclination of 45° along the extension direction of the beam 44. Therefore, when designing the reinforcing portion 42, the strength of the lattice structure at the outer edge of the reinforcing portion 42 can be ensured by arranging the partial cells as described above at the outer edge of the reinforcing portion 42.

[0044] The reinforcing portion 42 is formed by integrally molding the rotor body 40 and the reinforcing portion 42 using, for example, a 3D metal printer. Note that the reinforcing portion 42 may be formed later using a 3D metal printer on a rotor body 40 that has been prepared in advance, and the reinforcing portion 42 may be fixed to the rotor body 40.

[0045] The reinforcing part 42 has a lattice structure in which branching lattices are periodically arranged, and therefore has a large hollow portion in its volume and is lighter than a solid material. The periodically arranged lattices of the reinforcing part 42 ensure high strength. Furthermore, the reinforcing part 42 has an increased surface area due to its lattice structure, which enhances the cooling effect due to heat exchange with the air.

[0046] Therefore, in this embodiment, by forming the reinforcing portion 42 with a lattice structure on the outer surface of the rotor body 40, it is possible to reduce the thickness of the rotor body 40 and reduce the weight of the rotor 32 while ensuring the strength required of the rotor 32. As an example, when the reinforcing portion 42 with a lattice structure is provided on the rotor body 40 as in this embodiment, the weight of the rotor body 40 can be reduced to 48.1 g while ensuring the strength of the rotor body 40, which is a weight reduction of approximately 32.9% compared to a case where the reinforcing portion 42 is not provided.

[0047] Furthermore, in this embodiment, heat from the magnets 41 generated by electromagnetic induction with the interlinkage magnetic flux of the stator 33 can be efficiently dissipated from the reinforcing portion 42 on the outer surface of the rotor body 40 that is thermally connected to the magnets 41, thereby improving the heat dissipation performance of the rotor 32. As an example, a rotor body that does not have the reinforcing portion 42 was used as a comparative example, and a simulation of temperature analysis of the rotor body 40 of this embodiment was performed. While the maximum temperature in the comparative example was 105.14°C, the maximum temperature in the configuration of this embodiment was 98.5°C, and the cooling effect in the configuration of this embodiment was improved compared to the comparative example.

[0048] The present invention is not limited to the above-described embodiment, and various improvements and design changes may be made without departing from the spirit of the present invention.

[0049] Furthermore, the configuration of the axial gap type rotating electric machine of this embodiment is not limited to being applied to the drone 100, but may also be applied, for example, as a power source for electric vehicles such as EVs, HEVs, PHEVs, and FCVs.

[0050] For example, in the above embodiment, the drone 100 including four sets of drive units 20 has been described as an example, but the number of drive units 20 included in the drone 100 may be other than four.

[0051] Furthermore, the lattice structure of the reinforcing portion 42 in this embodiment is not limited to the body-centered cubic lattice in Fig. 8 or the face-centered cubic lattice in Fig. 9, and may be another structure. For example, the reinforcing portion 42 may be configured with a lattice structure suitable for a cylinder by arranging unit cells into which beams are introduced in the R, θ, and Z directions.

[0052] Also, in this embodiment, a rotor formed by laminating the lattice-structured reinforcing portion 42 on the outer surface of the plate-shaped rotor body 40 has been described. However, the area between the mounting portion 40a of the rotor body 40 and the area where the magnets 41 are arranged may be configured with only the lattice-structured reinforcing portion 42, and air may be allowed to flow in the thickness direction of the rotor body 40 at the position of the reinforcing portion 42.

[0053] In addition, the embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0054] 10...main body, 20...driver, 21...rotor, 23...motor, 31...shaft, 32...rotor, 33...stator, 40...rotor body, 41...magnet, 42...reinforcement, 43...unit cell, 100...drone

Claims

1. A stator; a rotor facing the stator in the axial direction, The rotor is A plurality of magnets arranged periodically in a circumferential direction in a Halbach array; a rotor body having a disk shape and a plurality of magnets fixed to a first surface facing the stator; a reinforcing portion having a lattice structure formed on a second surface of the rotor body opposite to the first surface, the reinforcing portion having a lattice structure in which branched lattices are periodically arranged. Axial gap type rotating electric motor.

2. The reinforcing portion has a lattice structure in which unit cells of a body-centered cubic lattice or a face-centered cubic lattice are periodically arranged.

2. The axial gap type rotating electric machine according to claim 1.

3. The rotor body further has an annular mounting portion on an inner peripheral side for connection to a shaft, The reinforcing portion is formed in an annular shape on the outer circumferential side of the mounting portion.

3. The axial gap type rotating electric machine according to claim 2.

4. A drone comprising the axial gap type rotating electric machine according to any one of claims 1 to 3.

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