Electric motor and flying object

Abstract

This electric motor has: a shaft that extends in a vertical direction along the central axis; a rotor that is attached to the shaft and rotates about the central axis; a stator that is disposed radially outward of the rotor and has a plurality of teeth; and a housing that accommodates a part of the shaft, the rotor, and the stator. The rotor has: at least one magnet disposed in an annular shape and disposed radially inward of the stator; and a magnet holding portion that holds the magnet and is fixed to the shaft. The stator has: a stator core having a plurality of teeth extending radially inward; and a plurality of coils wound around the teeth. The housing has an upper wall, a side wall connected to the upper wall, and a bottom portion disposed below the side wall. The upper wall has a hole through which the shaft passes and does not have an opening that is in communication with the inside of the housing except for the hole. The bottom portion has a plurality of intake holes into which air can flow from the outside into the inside of the housing. The side wall has a plurality of exhaust holes through which air can flow from the inside to the outside of the housing.

Description

Electric motor and flying vehicle

[0001] The present disclosure relates to an electric motor and a flying vehicle. The present application claims priority based on Japanese Patent Application No. 2025-027631 filed in Japan on February 25, 2025, the content of which is incorporated herein by reference.

[0002] In the electric motor disclosed in Patent Document 1, air is circulated inside a case to cool a coil and a magnet.

[0003] Japanese Unexamined Patent Publication No. 2023-035183

[0004] However, in the electric motor disclosed in Patent Document 1, an air hole is formed in an upper wall of the case. For this reason, there is a risk that rainwater may infiltrate into the case, causing failure of the motor or rusting of components.

[0005] Therefore, an object of the present disclosure is to provide an electric motor and a flying vehicle that cool components inside a housing while reducing infiltration of rainwater into the housing.

[0006] According to one aspect of the present disclosure, an electric motor is provided. The electric motor includes: a shaft extending vertically along a central axis; a rotor attached to the shaft and rotating about the central axis; a stator disposed radially outward of the rotor and having a plurality of teeth; and a housing that accommodates a part of the shaft, the rotor, and the stator. The rotor includes at least one magnet arranged in an annular shape and disposed radially inward of the stator, and a magnet holding portion that holds the magnet and is fixed to the shaft. The stator includes a stator core having the plurality of teeth extending radially inward, and a plurality of coils wound around the teeth. The housing has an upper wall, a side wall connected to the upper wall, and a bottom portion disposed below the side wall. The upper wall does not have an opening communicating with the interior of the housing, except for a hole through which the shaft passes. The bottom portion has a plurality of intake holes that allow air to flow into the interior of the housing from the outside. The side wall has a plurality of exhaust holes that allow air to flow out from the interior of the housing to the outside.

[0007] In embodiments of this disclosure, the top wall of the enclosure is closed, external air flows into the enclosure through an intake vent at the bottom of the enclosure, and internal air flows out through an exhaust vent in the side wall. Therefore, it is possible to cool the components inside the enclosure while reducing the ingress of rainwater into the enclosure.

[0008] Figure 1 is a perspective view showing a drone using an electric motor according to an embodiment of the present disclosure. Figure 2 is a front view showing an electric motor according to an embodiment of the present disclosure. Figure 3 is a top view showing the electric motor. Figure 4 is a bottom view showing the electric motor. Figure 5 is a longitudinal cross-sectional view of the electric motor. Figure 6 is a perspective view of the upper housing of the electric motor seen from diagonally below. Figure 7 is a perspective view of the lower housing of the electric motor seen from diagonally below. Figure 8 is a perspective view of the lower housing of the electric motor seen from diagonally above. Figure 9 is a perspective view of the rotor of the electric motor seen from diagonally above. Figure 10 is a diagram showing the electric motor and the airflow around it. Figure 11 is a bottom view showing the busbar assembly of the electric motor. Figure 12 is a perspective view of the busbar assembly of the electric motor and its vicinity seen from diagonally below. Figure 13 is a perspective view of the insulating member of the busbar assembly seen from diagonally below. Figure 14 is a longitudinal cross-sectional view of an electric motor according to a modified embodiment of the present disclosure.

[0009] Embodiments relating to this disclosure will be described below with reference to the attached drawings. The scale of the drawings is not necessarily accurate, and some features may be exaggerated or omitted.

[0010] As shown in Figure 1, the electric motor 10 according to the embodiment of this disclosure has a housing 20 and a shaft 30. The electric motor 10 is provided on a multi-rotor drone 11. The housing 20 of the electric motor 10 is attached to the end of the arm 12 of the multi-rotor drone 11. The shaft 30 extends vertically along the central axis Ax and rotates about the central axis Ax. The shaft 30 has a projection 31 that protrudes to the outside of the housing 20, and a propeller 32 that provides thrust to the multi-rotor drone 11 is attached to the projection 31. That is, the multi-rotor drone (flying object) 11 has an electric motor 10 and a propeller 32 that is positioned above the electric motor 10 and attached to the shaft 30. In the illustrated embodiment, the electric motor 10 is provided on a multi-rotor drone 11. However, the electric motor 10 may be provided on other types of eVTOLs (electric vertical take-off and landing aircraft) or other flying objects. Examples of eVTOLs include unmanned aerial vehicles (UAVs) or manned aerial vehicles (MAVs), such as flying cars.

[0011] As shown in Figures 2 to 5, the housing 20 has an upper housing 21 and a lower housing 22. The upper housing 21 has a cylindrical side wall 21a centered on the central axis Ax, an annular flange 21b, and a disc-shaped upper wall 21c. The flange 21b is formed at the lower end of the side wall 21a and extends radially outward. The upper wall 21c is connected to the upper end of the side wall 21a. The lower housing 22 has a cylindrical side wall 22a centered on the central axis Ax, an annular flange 22b, and a bottom portion 22c. The flange 22b is formed at the upper end of the side wall 22a and extends radially outward. The bottom portion 22c is located below the side wall 22a.

[0012] The upper housing 21 and the lower housing 22 are fixed to each other by fastening the flanges 21b and 22b with multiple fasteners 23 and 24 shown in Figure 2. The fasteners 23 and 24 are, for example, bolts and nuts. As the upper housing 21 and the lower housing 22 are fixed to each other, the side walls 21a and 22a are connected. The side walls 21a and 22a can be considered as a single side wall connecting the top wall 21c and the bottom 22c.

[0013] Thus, in this embodiment, the housing 20 has a generally cylindrical shape. In this embodiment, the side walls 21a and 22a can be called peripheral walls. However, the housing 20 may have other shapes, for example, the shape of a regular polygonal cylinder. That is, the side walls 21a and 22a may have the shape of a regular polygonal cylinder, and the top wall 21c may have a regular polygonal shape.

[0014] In the upper housing 21, the upper wall 21c is connected to the side wall 21a without any gaps. As shown in Figures 3 and 6, a through hole 21d is formed in the center of the upper wall 21c, and a shaft 30 extending in the vertical direction passes through the through hole 21d. In other words, the through hole 21d is an axial hole. A sealing member 25 is attached to the through hole 21d. The sealing member 25 seals the gap between the inner circumferential surface of the through hole 21d and the outer circumferential surface of the shaft 30. The upper wall 21c has a through hole 21d through which the shaft 30 passes, but it does not have any openings that communicate with the inside of the housing 20 except for the through hole 21d. In other words, the upper wall 21c is sealed without any gaps. Therefore, the risk of rainwater entering the housing 20 is reduced, and the risk of failure of the electric motor 10 components inside the housing 20 and rusting of those components is reduced.

[0015] As shown in Figure 6, a ring hub 21f projecting downward is formed on the lower surface of the upper wall 21c of the upper housing 21. The ring hub 21f is used as a holder for a bearing 36 (see Figure 5) that rotatably supports the rotating shaft 35. In addition, a plurality of ribs 21g projecting downward are formed on the lower surface of the upper wall 21c. The ribs 21g are arranged at equal angular intervals and extend radially from the ring hub 21f to the side wall 21a. That is, one end of the rib 21g is connected to the ring hub 21f and the other end is connected to the side wall 21a. The ribs 21g reinforce the upper wall 21c. Furthermore, as will be described later, the ribs 21g arrange the airflow near the upper wall 21c inside the housing 20 so that it is directed radially outward. The rib 21g has a thickened portion 21h on its radially inward side. The thickened portion 21h is connected to the ring hub 21f. The thickened portion 21h is thicker than the other parts of the rib 21g. The thickened portion 21h shown in the figure has a tapered shape with a thickness that decreases towards the radially outer side. However, the thickened portion 21h may have a uniform thickness, in which case a step is provided between the other parts of the rib 21g and the thickened portion 21h.

[0016] As shown in Figures 2, 5, and 6, a plurality of first exhaust holes 21e are formed in the side wall 21a of the upper housing 21. The first exhaust holes 21e are arranged at equal intervals. The first exhaust holes 21e are formed at the same height (height position). Air flows out from the inside to the outside of the housing 20 through the first exhaust holes 21e.

[0017] As shown in Figures 2, 5, 7, and 8, the bottom 22c of the lower housing 22 has a plurality of intake holes 22d. Air flows into the housing 20 from the outside through the intake holes 22d, cooling each part of the electric motor 10. A plurality of second exhaust holes 22e are formed in the side wall 22a of the lower housing 22. The second exhaust holes 22e are arranged at equal intervals. The second exhaust holes 22e are formed at the same height. Air flows out from the inside to the outside of the housing 20 through the second exhaust holes 22e. In other words, air from outside the housing 20 flows into the housing 20 through the intake holes 22d, cools each part of the electric motor 10, and flows out to the outside of the housing 20 through the first exhaust hole 21e and the second exhaust hole 22e. Thus, the heat generated from each part of the electric motor 10 can be efficiently diffused into the atmosphere.

[0018] As shown in Figures 4, 5, 7, and 8, the bottom 22c of the lower housing 22 has a hub (second hub) 22f, a number of spokes (second spokes) 22g, and a rim 22h. The hub 22f is used as a holder for a bearing 37 (see Figure 5) that rotatably supports the rotating shaft 35.

[0019] The spokes 22g extend radially outward from the hub 22f. The rim 22h is positioned concentrically with the hub 22f around the spokes 22g. The rim 22h is connected to multiple spokes 22g. The rim 22h is also connected to the side wall 22a. Multiple air intake holes 22d are provided between the hub 22f, the multiple spokes 22g, and the rim 22h.

[0020] As shown in Figure 5, the electric motor 10 has a rotor 40, a stator 60, and a busbar assembly 80. The rotor 40, stator 60, and busbar assembly 80 are housed inside the housing 20. The rotor 40 is mounted on the shaft 30 and rotates about the central axis Ax. The stator 60 is positioned radially outward from the rotor 40.

[0021] In this embodiment, the shaft 30 has a rotating shaft 35. The rotating shaft 35 has the shape of a stepped round bar with a central hole. It is inserted into the central hole of the rotating shaft 35. The rotating shaft 35 rotates about the central axis Ax. The propeller 32 is attached to the rotating shaft 35. However, this embodiment is not limited to this one, and a fixed shaft may be provided separately, which is inserted into the central hole of the rotating shaft 35. As shown in the figure, except for the protruding portion 31, most of the shaft 30 is located inside the housing 20.

[0022] As shown in Figures 5 and 9, the rotor 40 has at least one magnet 41 and a magnet holder 42 that holds the magnet 41. In this embodiment, the rotor 40 has multiple magnets 41. However, if the magnet 41 is a ring magnet, the rotor 40 may have only a single magnet 41. In either case, the magnets 41 are arranged in an annular shape and are positioned radially inward of the stator 60. The magnet holder 42 is fixed to the shaft 30. The magnet holder 42 can be called a rotor yoke.

[0023] The magnet holder 42 has a hub (first hub) 42a, a plurality of spokes (first spokes) 42b, an annular portion 42c, a flange 42d, and a plurality of fins 43. The hub 42a is fixed to the rotating shaft 35 and rotates about the central axis Ax. Therefore, the entire magnet holder 42 is rotatable about the central axis Ax. The spokes 42b extend radially outward from the hub 42a.

[0024] The annular portion 42c is positioned radially outward of the spokes 42b and concentrically with the hub 42a. The annular portion 42c is connected to multiple spokes 42b. A magnet 41 is positioned radially outward of the annular portion 42c, and the annular portion 42c holds the magnet 41. In Figure 9, the magnet 41 is shown by a dashed line. A flange 42d extends radially outward from the upper end of the annular portion 42c.

[0025] Multiple fins 43 protrude radially inward from the inner surface of the annular portion 42c. The multiple fins 43, including the annular portion 42c, are made of magnesium alloy and absorb heat from the magnet 41 and dissipate it into the atmosphere. In addition, when the magnet holder 42 fixed to the rotating shaft 35 rotates, the fins 43 create airflow inside the housing 20, allowing the fins 43 to dissipate heat through forced convection, further improving the cooling effect of each part of the electric motor 10.

[0026] Furthermore, the multiple fins 43 are shaped to extend linearly along the direction of the central axis Ax. In this case, the fins 43 create an airflow radially outward through rotation. The air flowing radially outward strikes the radially inner wall surface of the annular portion 42c, then splits into upper and lower streams, flowing radially outward from the upper and lower ends of the annular portion 42c. That is, the multiple fins 43 function as an impeller that directs airflow to the upper and lower ends in the direction of the central axis Ax. However, the shape of the multiple fins 43 is not limited to this embodiment, and may be any shape that creates a similar airflow. For example, the fins 43 may have a shape in which the central part in the direction of the central axis Ax protrudes circumferentially.

[0027] The stator 60 has a stator core 61 and a plurality of coils 63. The stator core 61 is annular. The stator core 61 has a plurality of teeth 62 that extend radially inward. The plurality of coils 63 are wound around each of the teeth 62. The teeth 62 and coils 63 are spaced apart from the rotor 40 and the magnet 41. The vertical position, i.e., height, of the teeth 62 is approximately the same as the vertical position, i.e., height, of the magnet 41.

[0028] The coil 63 and magnet 41 generate heat while the electric motor 10 is in operation. The first exhaust port 21e is formed at a position between the upper wall 21c and the coil 63 in the vertical direction. That is, the height of the first exhaust port 21e is between the height of the upper wall 21c and the height of the coil 63. Therefore, the air that flows into the housing 20 through the intake port 22d passes around the coil 63 and magnet 41, cooling the coil 63 and magnet 41, and is then discharged to the outside of the housing 20 through the first exhaust port 21e.

[0029] Figure 10 shows the airflow around the electric motor 10 when the rotating shaft 35 is rotated (i.e., when the propeller 32 (see Figure 1) is rotated). Figure 10 shows the results of a simulation. The arrows in Figure 10 indicate the airflow. Figure 10 does not show the reference numerals for the parts. The airflow in each part will be explained with reference to Figures 5 and 10. Due to the rotation of the propeller 32, a downdraft is generated around the electric motor 10. However, as described above, the upper wall 21c of the housing 20 is closed without any gaps, so the downdraft does not flow into the inside of the housing 20 through the upper wall 21c. On the other hand, the fins 43 that rotate with the rotating shaft 35 create an airflow inside the housing 20. More specifically, the fins 43 create an airflow radially outward, so the air below the electric motor 10 flows towards the fins 43 and into the inside of the housing 20 through the intake holes 22d in the bottom 22c. The air that flows into the housing 20 through the intake hole 22d initially flows radially inward along the fins 43, and then flows radially outward from the upper and lower ends of the annular portion 42c, respectively, due to the fins 43. The air then passes around the upper and lower ends of the coil 63 and the magnet 41, cooling the coil 63 and the magnet 41, and is discharged to the outside of the housing 20 through the first exhaust hole 21e.

[0030] As described above, the fins 43 that rotate with the rotating shaft 35 create airflow inside the housing 20, improving the cooling effect of the coil 63 and magnet 41. The ribs 21g formed on the lower surface of the upper wall 21c of the housing 20 do not rotate. However, the radially extending ribs 21g direct the airflow near the upper wall 21c inside the housing 20 radially outward. In other words, the ribs 21g restrict the airflow in the circumferential direction around the central axis Ax, guiding the air to flow radially outward. The thickened portion 21h of each rib 21g is positioned to overlap with the rotor 40, particularly the magnet holding portion 42, when viewed along the central axis Ax. As shown in Figures 5, 6, and 10, the thickened portion 21h reduces the volume of the radially inward space near the upper wall 21c, reducing the amount of air flowing into that space from inside the housing 20. Therefore, the airflow to the coil 63 and magnet 41, which are the main heat sources, is promoted, and the cooling effect of the coil 63 and magnet 41 is improved.

[0031] As shown in Figure 5, a busbar assembly 80 that supplies power to the coil 63 is housed inside the housing 20. The busbar assembly 80 can also be called a bus ring unit. The busbar assembly 80 is positioned between the bottom 22c of the housing 20 and the coil 63 in the vertical direction. That is, the height of the busbar assembly 80 is positioned between the height of the bottom 22c and the height of the coil 63.

[0032] As shown in Figure 11, the busbar assembly 80 has a plurality of busbars 81u, 81v, 81w, 81n, a plurality of connection terminals 82u, 82v, 82w, a plurality of power supply terminals 83u, 83v, 83w, and an insulating member 84. The plurality of busbars 81u, 81v, 81w, 81n extend in the circumferential direction and are electrically connected to the coil 63. The electric motor 10 in this embodiment is a three-phase motor and has three busbars 81u, 81v, 81w and a neutral busbar 81n. Busbar 81u is powered to power supply terminal 83u and connected to the coil end 64u of the U-phase coil 63 (see Figure 5) via connection terminal 82u. Busbar 81v is powered to power supply terminal 83v and connected to the coil end 64v of the V-phase coil 63 via connection terminal 82v. The busbar 81w is powered at the power supply terminal 83w and connected to the coil end 64w of the W-phase coil 63 via the connection terminal 82w. The neutral busbar 81n is connected to any of the U-phase, V-phase, or W-phase coils 63.

[0033] The power supply terminals 83u, 83v, and 83w are connected to the power supply units 90u, 90v, and 90w shown in Figure 12, respectively. The power supply units 90u, 90v, and 90w are supported by the support member 91. Although the housing 20 is not shown in Figure 12, as shown in Figure 4, the support member 91 is fixed to the rim 22h of the bottom 22c of the lower housing 22.

[0034] As shown in Figures 11 and 13, the insulating member 84 has an insulating ring 85, an insulating annular wall 86, and a plurality of connecting pieces 87. The insulating ring 85 holds a plurality of busbars 81u, 81v, 81w, and 81n formed from a conductive material. As shown in Figure 13, the insulating ring 85 has an inner circumferential wall 85a, an outer circumferential wall 85b, and a plurality of intermediate spacing walls 85c. The inner circumferential wall 85a, the outer circumferential wall 85b, and the intermediate spacing walls 85c are concentric cylindrical. Figure 13 is a perspective view of the insulating member 84 viewed from diagonally below, where the upper ends of the inner circumferential wall 85a, the outer circumferential wall 85b, and the plurality of intermediate spacing walls 85c are connected by an annular plate. The busbars 81u, 81v, 81w, and 81n are fitted into the plurality of grooves defined by the inner circumferential wall 85a, the outer circumferential wall 85b, and the plurality of intermediate spacing walls 85c. Therefore, the busbars 81u, 81v, 81w, and 81n are insulated from each other. Figure 5 shows that the busbars 81u, 81v, 81w, and 81n are fitted into the insulating ring 85.

[0035] The insulating annular wall 86 is arranged around the insulating ring 85. The insulating annular wall 86 is cylindrical and concentric with the insulating ring 85. The outer peripheral wall 85b of the insulating ring 85 is connected to the insulating annular wall 86 by a plurality of connecting pieces 87. The connecting pieces 87 are arranged intermittently in the circumferential direction, and a gap 88 is formed between the insulating ring 85 and the insulating annular wall 86. In the illustrated embodiment, three connecting pieces 87 are provided, but the number of connecting pieces 87 may be two or four or more.

[0036] As shown in Figures 5 and 12, the insulating annular wall 86 is fitted into the insulating protective ring 89 and held by the side wall 22a of the lower housing 22. As shown in Figure 5, the internal space of the insulating ring 85 is where the hub 22f of the bottom 22c of the housing 20 holds the bearing 37. In this embodiment, the protective ring 89 is part of an insulator that insulates the stator core 61 and the coil 63.

[0037] The busbars 81u, 81v, 81w, and 81n generate heat during operation of the electric motor 10. Referring again to Figures 5 and 10, the airflow in each part, particularly its cooling effect on the busbar assembly 80, will be explained. As previously mentioned, some of the air that flows into the housing 20 through the intake hole 22d at the bottom 22c of the housing 20 flows radially outward from the lower end of the annular portion 42c. The air flowing radially outward passes around the rotor 40 and the coil 63, and over the upper surface of the insulating ring 85 of the busbar assembly 80. Therefore, the busbars 81u, 81v, 81w, and 81n of the busbar assembly 80 are cooled by the air passing around the insulating ring 85.

[0038] The second exhaust port 22e is formed at a position between the busbar assembly 80 and the bottom 22c in the vertical direction. That is, the height of the second exhaust port 22e is between the height of the busbar assembly 80 and the height of the bottom 22c. Therefore, the air passing around the rotor 40 and coil 63, and over the top surface of the insulating ring 85 of the busbar assembly 80, passes through the gap 88 and moves downward. Thus, the busbars 81u, 81v, 81w, and 81n of the busbar assembly 80 are further cooled by the air passing around them. The air is then discharged to the outside of the housing 20 through the second exhaust port 22e.

[0039] In this embodiment, the height of the second exhaust port 22e is between the height of the busbar assembly 80 and the height of the bottom 22c. However, the second exhaust port 22e may be formed at the same height as the busbar assembly 80 or at a height higher than the busbar assembly 80. In this case, through holes communicating with the second exhaust port 22e are formed in the protective ring 89 and the insulating annular wall 86 of the busbar assembly 80. It is sufficient that air passing around the rotor 40 and coil 63, and over the upper surface of the insulating ring 85 of the busbar assembly 80, can pass through the second exhaust port 22e. That is, the second exhaust port 22e may be formed at a position between the first exhaust port 21e and the bottom 22c in the vertical direction. In this case as well, since air passes over the upper surface of the insulating ring 85 of the busbar assembly 80, the busbars 81u, 81v, 81w, and 81n are cooled.

[0040] Figure 14 shows an electric motor 100 according to a modified embodiment of the present disclosure. The electric motor 100 has the same basic configuration as the electric motor 10 and further includes a flow rectifier 101. The flow rectifier 101 is an annular thin plate and is positioned between the upper wall 21c of the housing 20 and the rotor 40 in the vertical direction. That is, the height of the flow rectifier 101 is between the height of the upper wall 21c and the height of the rotor 40. The flow rectifier 101 is fixed to the ring hub 21f of the upper housing 21.

[0041] The rectifier member 101 overlaps the rotor 40 in the axial direction. Therefore, the rectifier member 101 restricts or prevents air flowing between the hub 42a and the annular portion 42c of the rotor 40 from moving towards the upper wall 21c. Consequently, air flowing into the housing 20 does not flow much into the space between the upper wall 21c and the rectifier member 101, but instead flows concentratedly towards the coil 63 and the magnet 41. This improves the cooling effect on the coil 63 and the magnet 41.

[0042] While the present disclosure has been illustrated and described above with reference to preferred embodiments thereof, those skilled in the art will understand that modifications to form and detail are possible without departing from the scope of the invention as described in the claims. Such modifications, alterations, and changes should be included within the scope of the present disclosure.

[0043] The technology of the present disclosure can be configured as follows. [1] An electric motor comprising: a shaft extending vertically along a central axis; a rotor attached to the shaft and rotating about the central axis; a stator disposed radially outward of the rotor and having a plurality of teeth; and a housing that accommodates a part of the shaft, the rotor, and the stator, wherein the rotor includes at least one magnet annularly disposed and radially inward of the stator, and a magnet holding portion that holds the magnet and is fixed to the shaft, the stator includes a stator core having the plurality of teeth extending radially inward, and a plurality of coils wound around the teeth, the housing has an upper wall, a side wall connected to the upper wall, and a bottom portion disposed below the side wall, the upper wall has a hole through which the shaft passes, and has no opening communicating with the interior of the housing except for the hole, the bottom portion has a plurality of intake holes through which air can flow into the interior of the housing from the outside, and the side wall has a plurality of exhaust holes through which air can flow out of the interior of the housing to the outside.

[0044] [2] The electric motor according to [1], wherein the magnet holding portion includes: a first hub rotating about the central axis; a plurality of first spokes extending radially outward from the first hub; an annular portion connected to the plurality of first spokes and holding the magnet; and a plurality of fins protruding radially inward from an inner side surface of the annular portion.

[0045] [3] The electric motor according to [1] or [2], wherein the plurality of exhaust holes include a plurality of first exhaust holes formed at a position between the upper wall and the coil in the vertical direction.

[0046] [4] The electric motor according to [3], further comprising a bus bar assembly accommodated in the housing, disposed at a position between the bottom portion of the housing and the coil in the vertical direction, and configured to supply power to the coil, wherein the plurality of exhaust holes include a plurality of second exhaust holes formed at a position between the first exhaust holes and the bottom portion in the vertical direction.

[0047] [5] The electric motor according to [4], wherein the plurality of second exhaust holes are formed at a position between the bus bar assembly and the bottom portion in the vertical direction.

[0048] [6] The electric motor according to [4] or [5], wherein the bus bar assembly comprises: a plurality of bus bars extending in a circumferential direction and electrically connected to the coils; an insulating ring that holds the plurality of bus bars; an insulating annular wall disposed around the insulating ring and held by the housing; and a plurality of connecting pieces that connect the insulating ring and the insulating annular wall, wherein the connecting pieces are intermittently arranged in the circumferential direction.

[0049] [7] The electric motor according to any one of [1] to [6], further comprising a rectifying member disposed at a position between the upper wall of the housing and the rotor in the vertical direction, the rectifying member axially overlapping the rotor.

[0050] [8] The electric motor according to any one of [1] to [7], wherein a plurality of ribs protruding downward and extending in a radial direction are formed on a lower surface of the upper wall of the housing, and the rib has a thickened portion with a larger thickness than other portions at a position overlapping the rotor when viewed along the central axis.

[0051] [9] The electric motor according to any one of [1] to [8], wherein the bottom portion of the housing comprises: a second hub that rotatably supports the shaft; a plurality of second spokes extending radially outward from the second hub; and a rim disposed around the plurality of second spokes and connected to the second spokes, wherein the plurality of air intake holes are provided between the plurality of second spokes.

[0052]

[10] A flying object comprising: the electric motor according to any one of [1] to [9]; and a propeller disposed above the electric motor and attached to the shaft.

[0053] Ax: central axis, 10, 100: electric motor, 20: housing, 11: drone (flying object), 21: upper housing, 21a: side wall, 21c: top wall, 21e: first exhaust port, 21g: rib, 21h: thick section, 22: lower housing, 22a: side wall, 22c: bottom, 22d: intake port, 22e: second exhaust port, 22f: hub (second hub), 22g: spoke (second spoke), 22h: rim, 30: shaft, 32: propeller, 35: rotation 40: Rotor, 41: Magnet, 42: Magnet holder, 42a: Hub (first hub), 42b: Spoke (first spoke), 42c: Annular section, 43: Fin, 60: Stator, 61: Stator core, 62: Teeth, 63: Coil, 80: Busbar assembly, 81u, 81v, 81w, 81n: Busbars, 84: Insulating member, 85: Insulating ring, 86: Insulating annular wall, 87: Connecting piece, 88: Gap, 101: Rectifying member

Claims

1. An electric motor comprising: a shaft extending vertically along a central axis; a rotor attached to the shaft and rotating about the central axis; a stator positioned radially outward from the rotor and having a plurality of teeth; and a housing that accommodates a part of the shaft, the rotor, and the stator, wherein the rotor has at least one magnet arranged in an annular manner and positioned radially inward from the stator; and a magnet holder that holds the magnet and is fixed to the shaft; the stator has a stator core having a plurality of teeth extending radially inward; and a plurality of coils wound around the teeth; the housing has an upper wall, a side wall connected to the upper wall, and a bottom positioned below the side wall; the upper wall has a hole through which the shaft passes, and has no openings communicating with the inside of the housing except for the hole; the bottom has a plurality of intake holes through which air can flow into the inside of the housing from the outside; and the side wall has a plurality of exhaust holes through which air can flow out from the inside of the housing to the outside.

2. The electric motor according to claim 1, wherein the magnet holding portion comprises: a first hub that rotates about the central axis; a plurality of first spokes extending radially outward from the first hub; an annular portion connected to the plurality of first spokes and holding the magnet; and a plurality of fins protruding radially inward from the inner surface of the annular portion.

3. The electric motor according to claim 1 or 2, wherein the plurality of exhaust holes have a plurality of first exhaust holes formed at positions between the upper wall and the coil in the vertical direction.

4. The electric motor according to claim 3, further comprising a busbar assembly housed inside the housing and positioned between the bottom of the housing and the coil in the vertical direction, for supplying power to the coil, wherein the plurality of exhaust holes have a plurality of second exhaust holes formed between the first exhaust hole and the bottom in the vertical direction.

5. The electric motor according to claim 4, wherein the plurality of second exhaust ports are formed in the vertical direction between the busbar assembly and the bottom.

6. The electric motor according to claim 4, wherein the busbar assembly comprises: a plurality of busbars extending circumferentially and electrically connected to the coil; an insulating ring holding the plurality of busbars; an insulating annular wall disposed around the insulating ring and held by the housing; and a plurality of connecting pieces connecting the insulating ring and the insulating annular wall, the connecting pieces being intermittently arranged in the circumferential direction.

7. The electric motor according to claim 1 or 2, further comprising a flow straightening member positioned between the upper wall of the housing and the rotor in the vertical direction, and overlapping the rotor in the axial direction.

8. The electric motor according to claim 1 or 2, wherein a plurality of ribs projecting downward and extending radially are formed on the lower surface of the upper wall of the housing, and each rib has a thicker portion than other portions at a position that overlaps with the rotor when viewed along the central axis.

9. The electric motor according to claim 1 or 2, wherein the bottom of the housing has a second hub that rotatably supports the shaft, a plurality of second spokes extending radially outward from the second hub, and a rim arranged around the plurality of second spokes and connected to the second spokes, and the plurality of intake holes are provided between the plurality of second spokes.

10. A flying object comprising an electric motor according to claim 1 or 2, and a propeller positioned above the electric motor and attached to the shaft.

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