JP2024093358A - Axial gap type rotating electric machine and drone - Google Patents

Abstract

To provide an axial gap type rotary electric machine that can improve the heat dissipation of a rotor while reducing a weight of the rotor.SOLUTION: The axial gap type rotary electric machine includes a stator and a rotor axially opposed to the stator. The rotor has a plurality of magnets arranged periodically in a circumferential direction in a Halbach arrangement, and a disc-shaped rotor body part with the plurality of magnets fixed to a first surface opposite to the stator. The rotor body part has a plurality of ribs radially extending in a radial direction formed on a second surface opposite to the first surface. The plurality of ribs are arranged in a position overlapping the magnet with the highest attraction force to the stator among the Halbach arrayed magnets.SELECTED DRAWING: Figure 3

Description

The present invention relates to an axial gap type rotating electric machine and a drone.

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

JP 2019-33578 A

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

In addition, the rotor of a rotating electric machine generates heat due to electromagnetic induction with the interlinked magnetic flux of the stator. Therefore, there is a demand to improve the heat dissipation of the rotor in this type of axial gap type rotating electric machine.

The present invention was made in consideration of the above situation, and aims to provide an axial gap type rotating electric machine that can improve the heat dissipation performance of the rotor while reducing its weight.

An axial gap type rotating electric machine according to one aspect of the present invention includes a stator and a rotor that faces the stator in the axial direction. The rotor has a number of magnets that are periodically arranged in a Halbach array in the circumferential direction, and a disk-shaped rotor body having a first surface that faces the stator and a number of magnets fixed thereto. The rotor body has a number of ribs that extend radially and are formed radially on a second surface opposite the first surface. The number of ribs are arranged at positions that overlap the magnet that has the highest attraction force to the stator among the magnets in the Halbach array.

The magnet may be thermally connected to the second surface of the rotor body.
Moreover, a drone according to another aspect of the present invention includes the above-mentioned axial gap type rotating electric machine.

According to one aspect of the present invention, it is possible to provide an axial gap type rotating electric machine that can improve the heat dissipation performance of the rotor while reducing the rotor weight.

FIG. 1 is a diagram illustrating an example of the configuration of a drone according to an embodiment of the present invention. FIG. 4 is a diagram illustrating a configuration example of a motor of a drive unit. 1A is a view of the rotor as viewed from the outer side, and FIG. 1B is a view of the rotor as viewed from the inner side facing the stator. 3(a) is a cross-sectional view taken along line AA in FIG. FIG. 4 is a diagram showing an example of the arrangement of magnets in a rotor. FIG. 4 is a diagram showing the magnetization direction of each magnet. 1A and 1B are diagrams illustrating examples of electromagnetic forces acting on a magnet. 4 is a graph showing an example of a strength analysis of a rotor body during rotation of the rotor. 4 is a graph showing an example of a strength analysis of a rotor body during rotation of the rotor.

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.

The axial gap type rotating electric machine of this embodiment will be described below. The axial gap type rotating electric machine of this embodiment is a motor that is applied to the drive unit of a drone.

Figure 1 is a diagram showing an example of the configuration of a drone according to this embodiment. The drone 100 shown in Figure 1 is an unmanned aerial vehicle generally known as a multicopter, and can fly by remote control or automatic piloting.

The drone 100 has a main body 10 that incorporates a control unit, a battery, etc., and four sets of drive units 20 that are 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, spaced apart by 90° in a plan view, for example. Since all drive units 20 have the same configuration, the following explanation will describe the configuration of one representative drive unit 20, and will omit any overlapping explanation with the other drive units.

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

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

In addition, legs 24 are attached to the underside of the motor 23. The legs 24 extend vertically perpendicular to the arm 22, and support 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 22 and the legs 24.

Figure 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.

The shaft 31 extends in the vertical direction in FIG. 2 and is rotatably supported by a bearing (not shown) arranged in the casing 34. The rotor 21 is fixed to one side of the shaft 31 (the upper side in FIG. 2).

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

The stator 33 has multiple coil units 35 arranged in a ring shape around the shaft 31 in the circumferential direction of the stator 33, and a cylindrical stator case 36 that houses each coil unit 35. Each coil unit 35 is formed by winding a coil 35b around the outer periphery of a trapezoidal stator core 35a.

The stator core 35a is formed, for example, by stacking multiple 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 that intersects with 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.

The stator case 36 is hollow, and inside the stator case 36, a flow path for cooling oil (coolant) is formed around the coil unit 35. In addition, an oil inlet 37 and an oil outlet 38 are formed on the side of the stator case 36. Note that the inlet 37 and the outlet 38 are formed in positions facing each other (positions 180° from the axial center), but are not limited to this.

Oil is introduced into the stator 33 of the motor 23 from the inlet 37. The oil flows through 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. The oil discharged from the outlet 38 is cooled outside the motor 23, and then introduced from the inlet 37 to circulate within the motor 23.

The rotors 32 are composed of a pair of disks arranged facing each other at a specified distance, and the shaft 31 is inserted and fixed at the center of each rotor 32. This allows the rotors 32 to rotate together with the shaft 31.

Figure 3(a) is a view of the rotor 32 from the outer side, and Figure 3(b) is a view of the rotor 32 from the inner side facing the stator 33. Figure 4 is a cross-sectional view taken along line A-A in Figure 3(a). Note that the outer side of the rotor 32 is an example of the second surface, and the inner side of the rotor 32 is an example of the first surface.

Each rotor 32 has a disk-shaped rotor body 40 and a number 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, and is fixed to the mounting base 39 with bolts 46.

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 where it is thermally connected to the rotor body 40 by a heat-conductive adhesive or the like.

Figure 5 is a diagram showing an example of the arrangement of magnets 41 of rotor 32. Figure 6 is a diagram showing the magnetization direction of each magnet 41. In Figure 6, the magnetization direction of magnet 41 is indicated by an arrow. In Figure 6, the upper side corresponds to the stator 33 side, and the lower side corresponds to the surface facing the rotor body 40. Figures 5 and 6 also partially show magnets 41a to 41k, which are a part of the magnets 41 of rotor 32.

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. 6, the magnets 41a to 41k are fixed in the order of the circumferential direction of the rotor body 40 so that the magnetic pole orientation (magnetization direction) of each magnet 41 rotates 90° in sequence 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.

Figure 7 is a diagram showing an example of the electromagnetic forces acting on magnets 41a to 41k. The magnetization direction of magnet 41 shown in Figure 7 is the same as that in Figure 6. Furthermore, the electromagnetic forces in Figure 7 are expressed as positive in the direction from the stator 33 side to the magnet 41 side. As shown in Figure 7, in this embodiment, of magnets 41a to 41k, magnet 41h has the greatest magnetic attraction force toward the stator 33 side.

On the other hand, when the rotor 32 rotates, the combined force of the centrifugal force due to the rotation and the magnetic attraction force toward the stator 33 acts on the rotor body 40. Therefore, the specifications of the rotor body 40 require that it does not undergo plastic deformation when the magnets 41 are magnetically attracted to the stator 33 at the rated rotation speed, and that it has the strength to maintain a specified gap between the stator 33 and the rotor 32.

8 and 9 are graphs showing an example of strength analysis of the rotor body 40 when the rotor 32 rotates. FIG. 8 shows an example of the correspondence 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. 8 shows the thickness [mm] of the rotor body 40, and the vertical axis of FIG. 8 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. 8, 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%.

Figure 9 also shows an example of the correspondence between the thickness of the rotor body 40 and the maximum von Mises stress value. The horizontal axis of Figure 9 indicates the thickness [mm] of the rotor body 40, and the vertical axis of Figure 6 indicates the maximum von Mises stress value, which is a scalar quantity. It can be seen from Figure 9 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.

8 and 9 show that a thickness of 2 mm or more is required in the portion of the rotor body 40 where the magnetic attraction force toward the stator 33 is the strongest in order to satisfy the criteria for maximum allowable displacement and maximum von Mises stress value. However, as described above, the magnetic attraction force toward the stator 33 in the circumferential direction of the rotor 32 varies among the magnets 41a to 41k. Therefore, the thickness of the rotor body 40 does not need to be uniform in the circumferential direction, and it is sufficient to satisfy the above conditions at the portion where the magnetic attraction force toward the stator 33 is the strongest (the position of magnet 41h). From this perspective, in this embodiment, ribs 42 are formed on the outer surface (the surface opposite the inner surface) of the rotor body 40 to reinforce the rotor body 40.

In this embodiment, multiple ribs 42 extending radially from the inner diameter end to the outer diameter end are formed radially on the outer surface of the rotor body 40. The ribs 42 of the rotor body 40 are formed integrally with the rotor body 40. In addition, each rib 42 is arranged so that its phase overlaps circumferentially with the position of the magnet 41h that has the largest magnetic attractive force in the Halbach arrangement. The width of each rib 42 is preferably set to a dimension that makes the rib 42 wider than the range of the magnet 41h, but may be narrower than the range of the magnet 41h as long as the strength of the rotor body 40 can be ensured.

The thickness t1 of the first portion of the rotor body 40 where the ribs 42 are formed is greater than the thickness t2 of the second portion of the rotor body where the ribs 42 are not formed. For example, the thickness t1 of the first portion is 2 mm or more, which satisfies the criteria for the maximum allowable displacement and the maximum von Mises stress value. The thickness t2 of the second portion can be, for example, 1/4 or less of the thickness of the first portion (e.g., 0.5 mm).

The above configuration reduces the weight of the rotor body 40 by the amount that the second portion of the rotor body 40 is thinner than the first portion. Therefore, when there is an imbalance in the magnetic attraction forces between the magnets 41 in the circumferential direction, the rotor 32 can be made lighter while still satisfying the strength required of the rotor 32.

In addition, because ribs 42 are formed on the outer surface of the rotor body 40, the outer surface of the rotor body 40 in this embodiment has a larger surface area than when the rotor body 40 is flat. Therefore, in this embodiment, the heat of the magnet 41 generated by electromagnetic induction with the interlinkage magnetic flux of the stator 33 can be efficiently dissipated from the outer surface of the rotor body 40 that is thermally connected to the magnet 41. This can further improve the performance of the motor 23.

As described above, the motor 23 of this embodiment includes the stator 33 and the rotor 32 that faces the stator 33 in the axial direction. The rotor 32 has a plurality of magnets 41 that are periodically arranged in a Halbach array in the circumferential direction, and a disk-shaped rotor body 40 having a first surface that faces the stator 33 and a plurality of magnets fixed thereto. The rotor body 40 has a plurality of ribs 42 that extend radially and are formed radially on a second surface opposite to the first surface. The plurality of ribs 42 are arranged at positions that overlap the magnets 41h that have the highest attraction force to the stator 33 among the magnets 41 arranged in the Halbach array.
In the rotor 32 of this embodiment, the rib 42 is disposed at a position overlapping with the magnet 41h that has the highest attraction force to the stator 33, thereby ensuring strength that satisfies the standards for maximum allowable displacement and maximum von Mises stress value. Also, in this embodiment, the thickness t2 of the second portion of the rotor body 40 where the rib 42 is not formed is reduced, thereby making it possible to reduce the weight of the rotor 32. Furthermore, the formation of the rib 42 increases the surface area of the outer surface of the rotor body 40, thereby improving the heat dissipation from the magnet 41 in the rotor 32.

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.

In this embodiment, an example has been described in which ribs 42 are periodically formed on the outer surface of the rotor body 40 at positions that overlap with the magnets 41h that have the highest attractive force to the stator 33. However, the ribs 42 of the rotor body 40 may be added to positions other than the above-mentioned magnets 41h.

In addition, 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.

For example, in the above embodiment, a drone 100 having four sets of drive units 20 is described as an example, but the number of drive units 20 provided on the drone 100 may be other than four.

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 indicated by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

10: Main body, 20: Drive unit, 21: Rotor, 23: Motor, 31: Shaft, 32: Rotor, 33: Stator, 40: Rotor body, 41: Magnet, 42: Rib, 100: Drone

Claims (3)

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 disk-shaped rotor body having a first surface facing the stator and a plurality of the magnets fixed to the first surface,
The rotor body has a second surface opposite to the first surface, and a plurality of ribs extending in a radial direction are formed radially on the second surface,
The axial gap type rotating electric machine, wherein the plurality of ribs are arranged at positions overlapping with a magnet having the highest attraction force to the stator among the magnets arranged in a Halbach array. 2. The axial gap type rotating electric machine according to claim 1, wherein the magnet is fixed in a state of being thermally connected to the second surface of the rotor body. A drone comprising the axial gap type rotating electric machine according to claim 1 or 2.

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