Single-phase DC motor

Abstract

To provide a single-phase DC motor capable of suppressing noise at the time of driving a motor.SOLUTION: A single-phase DC motor includes: a rotor 20 rotatable about a center axis J; a stator 50 facing the rotor through a gap in a radial direction; and an axially extending shaft 40 rotatable about the center axis. The stator is located radially inside of the rotor. The shaft is located radially inside of the stator. The rotor includes: a plurality of magnets 30 arranged radially outside of the stator; a cylindrical unit 22 extending in an axial direction with the center axis being a center and holding the plurality of magnets; and a tabular top panel 23. The top panel has an annular projection 25 whose radially outer end portion is connected to an end portion on one side in the axial direction of the cylindrical unit, whose radially inner end portion is fixed to an outer peripheral surface that is directed to an outside in the radial direction of the shaft, and protrudes in the axial direction more than a position of an end portion on one side in the axial direction of the cylindrical unit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a single-phase DC motor. [Background technology]

[0002] Electric motors having a rotor and a stator are known. For example, Patent Document 1 describes a motor for driving an air compressor. The motor disclosed in Patent Document 1 has a structure with radial ribs to increase the rigidity of the bottom of the rotor frame and eliminate noise. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 208126 Summary of the Invention [Problem to be solved by the invention]

[0004] When a motor with the above configuration is driven by a single-phase DC power supply, the magnetic force between the magnet in the frame and the electromagnet formed by the coil to which voltage is applied fluctuates periodically, causing the frame to deform periodically. This periodic frame deformation can cause noise problems when the motor is driven. In particular, when the motor is driven at low speeds, the driving noise of the motor itself and the driven object connected to the motor becomes quieter, making the noise more noticeable. The rotor vibration mode of a single-phase DC motor differs from that of a three-phase AC motor, etc. Therefore, there is a need to adopt a rotor vibration-resistant structure that is suited to the vibration mode of a single-phase DC motor.

[0005] In view of the above circumstances, one aspect of the present invention has an object to provide a single-phase DC motor that can suppress noise when the motor is driven. [Means for solving the problem]

[0006] One aspect of the single-phase DC motor of the present invention includes a rotor rotatable about a central axis, a stator facing the rotor across a radial gap, and a shaft extending in an axial direction and rotatable about the central axis. The stator is located radially inside the rotor. The shaft is located radially inside the stator. The rotor has a plurality of magnets arranged radially outside the stator, a cylindrical portion centered on the central axis and extending axially to hold the plurality of magnets, and a plate-shaped top surface portion. The top surface portion has a radially outer end connected to one axial end of the cylindrical portion and a radially inner end fixed to an outer peripheral surface facing radially outward of the shaft, and has an annular protrusion that protrudes axially beyond the position of the one axial end of the cylindrical portion. [Effects of the Invention]

[0007] According to one aspect of the present invention, noise caused by vibration of the top surface of the rotor can be suppressed in a single-phase DC motor. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view showing a motor according to an embodiment. [Figure 2] FIG. 2 is a perspective view showing the motor of the embodiment. [Figure 3] FIG. 3 is an external view showing the motor of the embodiment. [Figure 4] FIG. 4 is a schematic diagram illustrating a DC voltage applied to a coil according to an embodiment. [Figure 5] FIG. 5 is a schematic diagram illustrating the magnetic force applied to the case of one embodiment. [Figure 6] FIG. 6 is a schematic diagram illustrating the magnetic force applied to the case of one embodiment. [Figure 7] FIG. 7 is a schematic diagram illustrating the magnetic force applied to the case of one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] In the following description, the figures will appropriately show the X-axis, Y-axis, and Z-axis. The Y-axis indicates the direction in which the central axis J of the motor in the embodiment described below extends. The central axis J shown in each figure is a virtual axis. In the following description, the direction in which the central axis J extends, i.e., the direction parallel to the Y-axis, will be referred to as the "axial direction." The radial direction centered on the central axis J will be simply referred to as the "radial direction." The circumferential direction centered on the central axis J will be simply referred to as the "circumferential direction." The side of the axial direction toward which the Y-axis arrow points (+Y side) will be referred to as the "one axial side." The side of the axial direction opposite to the side toward which the Z-axis arrow points (-Y side) will be referred to as the "other axial side."

[0010] The direction parallel to the Z axis is called the "vertical direction." The side of the vertical direction toward which the Z axis arrow points (+Z side) is called the "one vertical side." The vertical side opposite to the side toward which the Z axis arrow points (-Z side) is called the "other vertical side." The direction parallel to the X axis is called the "width direction." The width direction toward which the X axis arrow points (+X side) is called the "one width side." The width direction opposite to the side toward which the X axis arrow points (-X side) is called the "other width side." The axial direction, vertical direction, and width direction are perpendicular to each other.

[0011] The circumferential direction is indicated by an arrow θ in each drawing. The side of the circumferential direction toward which the arrow θ points is called the "one circumferential side." The opposite side of the circumferential direction to the side toward which the arrow θ points is called the "other circumferential side." The one circumferential side is the side that proceeds clockwise around the central axis J as viewed from one axial side. The other circumferential side is the side that proceeds counterclockwise around the central axis J as viewed from one axial side. Note that the axial direction, vertical direction, and width direction are names that are used simply to explain the positional relationship of each part, and the actual positional relationship may be one other than the positional relationship indicated by these names.

[0012] The motor 10 of this embodiment shown in FIG. 1 is a single-phase DC brushless motor attached to an electric fan. The motor 10 has an outer rotor configuration, with a rotor 20 having multiple magnets 30 radially outside the stator 50. Single-phase DC brushless motors can rotate at lower speeds than AC motors. In the motor 10 of this embodiment, the rotation speed of the rotor 20 is variable. The motor 10 of this embodiment has a low-speed drive mode that allows the rotor 20 to be driven at a low rotation speed of 600 revolutions per minute or less. Electric fans are generally configured to allow the airflow volume to be adjusted according to the user's preference. When a user selects the gentle breeze mode, which provides a low airflow volume, the motor 10 drives the rotor 20 in the low-speed drive mode.

[0013] The motor 10 includes a rotor 20, a stator 50, a first bearing 61, a second bearing 62, a control board 70, and a base member 80. The rotor 20 is rotatable about a central axis J. The rotor 20 has a case 21, a plurality of magnets 30, and a shaft 40. The plurality of magnets 30 and the shaft 40 are fixed to the case 21. The rotor 20 is supported rotatably about the central axis J by the first bearing 61 and the second bearing 62, which support the shaft 40.

[0014] The case 21 has a cylindrical shape extending in the axial direction. The case 21 accommodates the plurality of magnets 30, a portion of the shaft 40 on one axial side, the stator 50, the first bearing 61, and a portion of the base member 80 on one axial side. The case 21 has an opening 22a at the other axial end that opens to the other axial side. The opening 22a has a circular shape centered on the central axis J. The case 21 has a cylindrical portion 22 and a top surface portion 23. In this embodiment, the cylindrical portion 22 and the top surface portion 23 are part of the same single member. In this embodiment, the case 21 is manufactured by press working.

[0015] As shown in FIGS. 1 and 2 , the cylindrical portion 22 has a cylindrical shape extending in the axial direction about the central axis J. The cylindrical portion 22 surrounds a portion of the shaft 40, the stator 50, the first bearing 61, and a portion of the base member 80. One axial end of the cylindrical portion 22 is connected to the radially outer end of the top surface portion 23. An opening 22a is provided at the other axial end of the cylindrical portion 22. A plurality of magnets 30 are fixed to the inner circumferential surface of the cylindrical portion 22. In other words, the rotor 20 has a cylindrical cylindrical portion 22 that is centered on the central axis J, extends in the axial direction, and holds a plurality of magnets.

[0016] As shown in Figures 1, 2, and 3, the top surface portion 23 is in the shape of an annular plate centered on the central axis J. In other words, the rotor 20 has a plate-shaped top surface portion 23. The top surface portion 23 is located on one axial side of the stator 50. A radially outer end of the top surface portion 23 is connected to one axial end of the cylindrical portion 22. A radially inner end of the top surface portion 23 is fixed to the outer peripheral surface of the shaft 40. The top surface portion 23 has a first flat portion 24, a convex portion 25, a second flat portion 26, an inclined portion 27, a third flat portion 28, and a retaining portion 29.

[0017] The first flat surface portion 24 has an annular plate shape centered on the central axis J. The plate surface of the first flat surface portion 24 faces the axial direction. In other words, the first flat surface portion 24 has a plane facing one axial side. The radially outer end of the first flat surface portion 24 is connected to the axially one end of the cylindrical portion 22. The radially inner end of the first flat surface portion 24 is connected to the radially outer end of the protrusion 25. In other words, the top surface portion 23 has the first flat surface portion 24 radially outward of the protrusion 25.

[0018] The protrusion 25 has an annular plate shape centered on the central axis J. When viewed in the axial direction, the protrusion 25 is arranged to overlap the coil 52 that protrudes from the stator core to one side in the axial direction. When viewed in the circumferential direction, the shape between the radially outer end of the protrusion 25 and the radially inner end of the protrusion 25 is an arc shape that protrudes to one side in the axial direction. The arc shape of the protrusion 25 is provided around the entire circumferential direction. In the axial direction, the radially outer end of the protrusion 25 and the radially inner end of the protrusion 25 are arranged at the same position. In other words, the top surface portion 23 has an annular protrusion 25 that protrudes to one side in the axial direction further than the one axial end of the cylindrical portion 22.

[0019] In this embodiment, the central angle φ of the arc that forms the protrusion 25 is approximately 70°. The central angle φ of the arc that forms the protrusion 25 is preferably between 45° and 90°. By setting the central angle φ within this range, the protrusion 25 can effectively suppress vibration of the top surface portion 23 in the planar direction.

[0020] It is preferable that the protrusions 25 occupy 50% or more of the axial projected area of ​​the top surface portion 23. If the protrusions 25 are too small compared to the entire top surface portion 23, there is a risk that vibration of the top surface portion 23 will be promoted in areas other than the protrusions 25. If the protrusions 25 occupy 50% or more of the projected area of ​​the top surface portion 23, the protrusions 25 can effectively suppress deformation of the entire top surface portion 23.

[0021] The second flat surface portion 26 has an annular plate shape centered on the central axis J. The plate surface of the second flat surface portion 26 faces the axial direction. That is, the second flat surface portion 26 has a plane facing one axial side. The radially outer end of the second flat surface portion 26 is connected to the radially inner end of the convex portion 25. That is, the top surface portion 23 has the second flat surface portion 26 on the radially inner side of the convex portion 25. In the axial direction, the surface of the second flat surface portion 26 facing one axial side and the surface of the first flat surface portion 24 facing one axial side are arranged at the same position.

[0022] The inclined portion 27 has a cone shape centered on the central axis J. A radially outer end of the inclined portion 27 is connected to a radially inner end of the second flat portion 26. The inclined portion 27 is positioned on the other axial side as it moves radially inward. In other words, the top surface portion 23 has the inclined portion 27 on the radially inner side of the protruding portion 25, and is positioned on the other axial side as it moves radially inward.

[0023] The third flat surface portion 28 has an annular plate shape centered on the central axis J. The plate surface of the third flat surface portion 28 faces the axial direction. The radially outer end of the third flat surface portion 28 is connected to the radially inner end of the inclined portion 27. In the axial direction, the surface of the third flat surface portion 28 facing one axial side is located on the other axial side of the surfaces of the first flat surface portion 24 and the second flat surface portion 26 facing one axial side.

[0024] The retaining portion 29 is cylindrical and extends axially on one side about the central axis J. The other axial end of the retaining portion 29 is connected to the radially inner end of the third flat portion 28. In the axial direction, the one axial end of the retaining portion 29 is located on the other axial side of the faces of the first flat portion 24 and the second flat portion 26 that face the one axial side. The shaft 40 is fixed by press fitting to the inner circumferential surface of the retaining portion 29. As a result, when the case 21, which includes the multiple magnets 30, is rotated, the shaft 40 rotates about the central axis J.

[0025] As shown in FIGS. 1 and 5 , the multiple magnets 30 are plate-shaped and extend in the axial direction. When viewed in the axial direction, the radially outer surface of each magnet 30 is arc-shaped and extends along the inner circumferential surface of the cylindrical portion 22. When viewed in the axial direction, the radially inner surface of each magnet 30 is also arc-shaped. Each magnet 30 is fixed to the inner circumferential surface of the cylindrical portion 22 by adhesive. Each magnet 30 is disposed radially outward from the stator 50 and faces the stator 50 across a gap. That is, the rotor 20 has multiple magnets 30 disposed radially outward from the stator 50. The magnets 30 are disposed at equal intervals along the circumferential direction. In this embodiment, eight magnets 30 are provided. That is, the magnets 30 are disposed at 45° intervals along the circumferential direction. The magnetic poles of each magnet 30 are opposite to the magnetic poles of the magnets 30 adjacent to each other in the circumferential direction. That is, the rotor 20 has four magnets with their north poles facing radially inward and four magnets with their south poles facing radially inward.

[0026] The number of magnets 30 provided on the rotor 20 is not limited to eight, and may be any number between six and ten. In a single-phase DC motor, all magnets 30 on the rotor 20 are subjected to in-phase vibration from the stator 50. In a single-phase DC motor, a small number of magnets 30 provided on the rotor 20 tends to resonate in a low-order vibration mode, which increases the radial amplitude of the rotor during low-speed operation with a low drive frequency. More specifically, when the number of magnets 30 is four or less, the order of the vibration mode generated in the rotor 20 becomes low, and the magnetic force generated by the electromagnets formed by the coils 52 and each magnet 30 is concentrated at four (or two) locations on the cylindrical portion 22 in the circumferential direction. Therefore, when the motor 10 is driven, noise may be generated due to circumferential deformation of the cylindrical portion 22. When the number of magnets 30 is four or less, this noise becomes more noticeable during low-speed operation to blow a gentle breeze, which is essentially required for quiet operation. Therefore, the number of magnets 30 is preferably six or more. Furthermore, if the number of magnets 30 is twelve or more, the cost of the magnets 30 increases, so the number of magnets 30 is preferably ten or less. The number of magnets 30 is always an even number. Therefore, the preferred number of magnets 30 provided in the rotor 20 is six, eight, or ten.

[0027] As shown in FIG. 5, in this embodiment, the north poles of magnets 30N1, 30N2, 30N3, and 30N4 face radially inward. Magnet 30N2 is located 90° circumferentially on one side from magnet 30N1. Magnet 30N3 is located 90° circumferentially on one side from magnet 30N2. Magnet 30N4 is located 90° circumferentially on one side from magnet 30N3. In this embodiment, the south poles of magnets 30S1, 30S2, 30S3, and 30S4 face radially inward. Magnet 30S1 is located between magnets 30N1 and 30N4. Magnet 30S2 is located 90° circumferentially on one side from magnet 30S1. Magnet 30S3 is located 90° circumferentially on one side from magnet 30S2. Magnet 30S4 is located 90° to one side in the circumferential direction from magnet 30S3.

[0028] As shown in FIG. 1 , the shaft 40 has a cylindrical shape extending in the axial direction about the central axis J. As described above, the shaft 40 is fixed to the case 21 by press-fitting. More specifically, the shaft 40 is fixed to the inner circumferential surface of the retaining portion 29 by press-fitting. A portion of the shaft 40 is located inside the case 21. A portion of the shaft 40 is located radially inside the stator 50. One axial end of the shaft 40 protrudes axially toward the one side beyond the retaining portion 29. The one axial end of the shaft 40 is located on the other axial side beyond the one axial end of the protrusion 25. The other axial end of the shaft 40 protrudes axially toward the other side from the case 21 through the opening 22 a. Inside the case 21, the outer circumferential surface of the shaft 40 is supported by a first bearing 61. On the other axial side beyond the case 21, the outer circumferential surface of the shaft 40 is supported by a second bearing 62. As a result, the shaft 40 is supported by the first bearing 61 and the second bearing 62 so as to be rotatable about the central axis J. In other words, the rotor 20 is supported by the first bearing 61 and the second bearing 62 so as to be rotatable about the central axis J. The shaft 40 has a through hole 41 and a threaded portion 42.

[0029] The through hole 41 is provided on the other axial side of the second bearing. The through hole 41 is a circular hole that passes through the shaft 40 in the radial direction. A pin (not shown) is inserted into the through hole 41 and fixed therein. The pin is fitted into a recess in the blade member of the electric fan (not shown). This connects the rotor 20 and the blade member, and when the rotor 20 rotates, the blade member also rotates.

[0030] The threaded portion 42 is provided at the other axial end of the shaft 40. The threaded portion 42 is a male screw provided on the outer peripheral surface of the shaft 40. After the shaft 40 is inserted into the central hole of the blade members of an electric fan (not shown), a female screw provided on a spinner of the electric fan (not shown) is tightened into the threaded portion 42, and the spinner is fixed to the shaft 40. At this time, the surface of the spinner facing one axial side comes into contact with the surface of the blade member facing the other axial side. This determines the position of the blade member in the axial direction, and the blade member is fixed to the shaft 40.

[0031] The base member 80 holds the stator 50, the first bearing 61, the second bearing 62, and the control board 70. The base member 80 is fixed to a motor housing of the fan (not shown). One axial side of the base member 80 is disposed inside the case 21. The other axial side of the base member 80 protrudes axially beyond the case 21 through the opening 22a. One axial side of the base member 80 is surrounded by the stator 50. The base member 80 surrounds the shaft 40, the first bearing 61, and the second bearing 62. The base member 80 has a base 81, a connecting portion 81a, a coupling portion 82, and legs 83. In this embodiment, the base 81, the connecting portion 81a, the coupling portion 82, and the legs 83 are part of the same single member.

[0032] The base 81 is the portion on the other axial side of the base member 80. The base 81 is cylindrical and extends in the axial direction with the central axis J as its center. The base 81 surrounds the shaft 40 and the second bearing. The base 81 is disposed on the other axial side of the case 21. When viewed in the axial direction, the base 81 overlaps with the stator 50. The second bearing 62 is fixed to the inner circumferential surface of the base 81 by press fitting.

[0033] The connection portions 81a extend radially outward from a portion of the outer peripheral surface of the base portion 81. The connection portions 81a are provided at equal intervals along the outer peripheral surface of the base portion 81. In this embodiment, three connection portions 81a are provided. A fastening hole 81b is provided on the surface on the other axial side of each connection portion 81a. When screws (not shown) are fastened into the fastening holes 81b with the motor housing of the fan sandwiched between them, the base member 80 is fixed to the motor housing. In this way, the motor 10 is fixed to the motor housing via the base member 80.

[0034] The connecting portion 82 is annular and surrounds the shaft 40. The other axial end of the connecting portion 82 is connected to the one axial end of the base portion 81. The connecting portion 82 is positioned radially inward as it approaches the one axial side. A board holding surface 82a facing radially outward is provided on the radially outer surface of the connecting portion 82. A board support surface 82b extending radially from the other axial end of the board holding surface 82a is provided on the radially outer surface of the connecting portion 82. The board support surface 82b faces the one axial side. The control board 70 is fixed to the board holding surface 82a by press-fitting. The board support surface 82b supports the surface of the control board 70 facing the other axial side.

[0035] The leg portion 83 has a cylindrical shape extending in the axial direction around the central axis J. One axial side portion of the leg portion 83 is disposed radially inside the stator 50. The leg portion 83 surrounds the shaft 40 and the first bearing 61. The other axial side end of the leg portion 83 is connected to the one axial side end of the connecting portion 82. The one axial side end of the leg portion 83 is disposed on the other axial side of the one axial side end of the stator 50. The one axial side end of the leg portion 83 is the one axial side end of the base member 80. The stator 50 is fixed to the outer peripheral surface of the leg portion 83 by press fitting. A first bearing retaining surface 83a facing radially inward is provided on the inner peripheral surface of the leg portion 83. The one axial side end of the first bearing retaining surface 83a is the one axial side end of the base member 80. A first bearing support surface 83b is provided on the inner peripheral surface of the leg portion 83, extending radially inward from the other axial end of the first bearing retaining surface 83a. The first bearing 61 is fixed to the first bearing retaining surface 83a by press fitting. The first bearing support surface 83b supports the other axial end of the first bearing 61.

[0036] The stator 50 is disposed radially inside the rotor 20. The stator 50 is annular and surrounds the shaft 40, the first bearing 61, and the base member 80. As described above, the stator 50 is fixed to the outer peripheral surface of the base member 80 by press-fitting. More specifically, the inner peripheral surface of the stator core 51 is fixed to the outer peripheral surface of the base member 80 by press-fitting. The stator 50 faces the rotor 20 across a gap in the radial direction. More specifically, the outer peripheral surface of the stator core 51 faces the multiple magnets 30 across a gap. The stator 50 has a stator core 51 and multiple coils 52 wound around the stator core 51.

[0037] As shown in FIGS. 1 and 5, the stator core 51 is disposed radially inside the rotor 20 and has an annular shape surrounding the shaft 40, the first bearing 61, and the base member 80. The stator core 51 is formed by stacking and fixing a plurality of plate-shaped plate members in the axial direction. In this embodiment, the stator core 51 is made of electromagnetic steel plates. The stator core 51 has a substantially annular core back 54 and a plurality of teeth 53 extending radially outward from the core back 54.

[0038] Each of the teeth 53 protrudes radially from the outer peripheral surface of the core back 54. The radially outer portion of each tooth 53 extends to one circumferential side and the other circumferential side. When viewed in the axial direction, the radially outer shape of each tooth 53 is arc-shaped. The radially outer surfaces of each of the teeth 53 face the magnet 30 with a radial gap therebetween. The teeth 53 are arranged at equal intervals along the circumferential direction. In this embodiment, eight teeth 53 are provided. That is, the teeth 53 are arranged at 45° intervals along the circumferential direction. In other words, in this embodiment, the number of slots is eight. Note that in this embodiment, each tooth 53 has an axially extending notch (not shown) on the radially outer side of the tooth 53, on the circumferential side opposite the rotation direction R of the rotor 20. As a result, when the driving of the motor 10 stops, the circumferential center of each magnet 30 is shifted in the rotational direction from the circumferential center of each tooth 53, thereby stopping the rotor 20. Therefore, when the motor 10 starts, the rotor 20 can rotate in the rotational direction.

[0039] The number of slots is not limited to eight, and can be anywhere from six to ten. In a single-phase DC motor, the number of slots matches the number of magnetic poles of the rotor 20 (the number of magnets 30 in this embodiment). As described above, the number of magnets 30 in the rotor 20 in this embodiment is preferably six to ten. Therefore, the number of slots is also preferably six to ten. Furthermore, if the number of slots is twelve or more, winding the coils 52 around the stator core 51 becomes complicated. This poses a problem of increased manufacturing steps and costs for the motor 10. Therefore, the number of slots is preferably ten or less.

[0040] The coils 52 are wound around the stator core 51. More specifically, the coils 52 are wound around teeth 53 of the stator core 51. Each coil 52 is connected to a control board 70, which will be described later. Each coil 52 is connected to an external power supply (not shown) via the control board 70, and a DC voltage is applied to the coils 52.

[0041] When a voltage is applied to the coil 52, the coil 52 forms an electromagnet, and a magnetic pole is formed on the radially outer side of each tooth 53. In this embodiment, the magnetic poles formed on adjacent teeth 53 in the circumferential direction are opposite. More specifically, when a positive voltage is applied to the coil 52, the teeth 53a1, 53a2, 53a3, and 53a4 form N-pole electromagnets, and the teeth 53b1, 53b2, 53b3, and 53b4 form S-pole electromagnets. On the other hand, when a negative voltage is applied to the coil 52, the teeth 53a1, 53a2, 53a3, and 53a4 form S-pole electromagnets, and the teeth 53b1, 53b2, 53b3, and 53b4 form N-pole electromagnets.

[0042] As shown in FIG. 5, in this embodiment, the teeth 53a2 are located 90° circumferentially on one side from the teeth 53a1. The teeth 53a3 are located 90° circumferentially on one side from the teeth 53a2. The teeth 53a4 are located 90° circumferentially on one side from the teeth 53a3. The teeth 53b1 are located between the teeth 53a1 and 53a2. The teeth 53b2 are located 90° circumferentially on one side from the teeth 53b1. The teeth 53b3 are located 90° circumferentially on one side from the teeth 53b2. The teeth 53b4 are located 90° circumferentially on one side from the teeth 53b3.

[0043] 1, as described above, the first bearing 61 is fixed by press-fitting to the first bearing holding surface 83a of the leg portion 83 of the base member 80. The first bearing 61 is housed inside the case 21. The first bearing 61 is disposed radially inside the stator 50. The shaft 40 is inserted into the inner circumferential surface of the first bearing 61. In this way, the first bearing 61 rotatably supports the shaft 40.

[0044] As described above, the second bearing 62 is fixed by press fitting to the inner circumferential surface of the base portion 81 of the base member 80. The second bearing 62 is disposed on the other axial side of the case 21 and the control board 70. The shaft 40 is inserted into the inner circumferential surface of the second bearing 62. In this way, the second bearing 62 rotatably supports the shaft 40. In this embodiment, the first bearing 61 and the second bearing 62 are ball bearings.

[0045] The control board 70 is in the shape of an annular plate that surrounds the shaft 40 and the connecting portion 82 of the base member 80. The plate surface of the control board 70 faces the axial direction. As described above, the control board 70 is fixed to the board holding surface 82a of the base member 80 by press-fitting. In the axial direction, the control board 70 is disposed on the other axial side of the case 21 and the stator 50. The outer peripheral surface of the control board 70 protrudes radially outward beyond the case 21.

[0046] A plurality of electronic components (not shown), such as a sensor that detects the rotation of the rotor 20, are attached to one axial surface of the control board 70. The sensor is, for example, a Hall sensor that faces the magnet 30 in the axial direction and detects the magnetic flux of the magnet 30. In a single-phase DC motor, the rotation of the rotor 20 can be controlled based on the detection result of a single sensor, and therefore can be manufactured more inexpensively than a three-phase AC motor, which requires multiple sensors.

[0047] An external power supply (not shown) and the plurality of coils 52 are connected to the control board 70. Therefore, power from the external power supply is supplied to the coils 52 via the control board 70. More specifically, the voltage of the external power supply is converted into a DC voltage in the control board 70 and applied to the plurality of coils 52.

[0048] As shown in FIG. 4, this embodiment uses a half-wave control method in which positive and negative DC voltages are alternately applied to the multiple coils 52. The horizontal axis of FIG. 4 represents time T, and the vertical axis represents the applied voltage Vc to the multiple coils 52. In this embodiment, for example, the applied voltage Vc is a positive voltage +V1 when time T is between 0 and t2. The applied voltage Vc is switched from the positive voltage +V1 to a negative voltage −V1 when time T is t2. The applied voltage Vc is a negative voltage −V1 when time T is between t2 and t4. The applied voltage Vc is switched from the negative voltage −V1 to the positive voltage +V1 when time T is t4. After time T is t4, the applied voltage Vc is switched from the positive voltage +V1 to the negative voltage −V1 or from the negative voltage −V1 to the positive voltage +V1 at a predetermined timing, as described above. More specifically, the applied voltage Vc is switched at the timing when the center position of each magnet 30 (described later) faces the center position of a tooth 53 (described later). In other words, the applied voltage Vc is switched at a period when the rotor 20 rotates 45°. The timing for switching the applied voltage Vc is determined by the detection result of a sensor mounted on the control board 70.

[0049] 5 to 7 are schematic diagrams showing the magnetic force acting on the cylindrical portion 22 of the case 21 when the motor 10 is running. In FIGS. 5 to 7, the rotation direction R of the rotor 20 is the same as the direction of one circumferential side. That is, the rotor 20 rotates clockwise around the central axis J when viewed from one axial side. Hereinafter, the reference line Z1 is a straight line extending vertically from the central axis J to one side when viewed from one axial side. The angle from the reference line Z1 toward one circumferential side is referred to as the position angle α. The value of the position angle α increases as one moves from the reference line Z1 toward one circumferential side. The central position of the magnet 30 in the circumferential direction is referred to as the "center position of the magnet." The central position of the tooth 53 in the circumferential direction is referred to as the "center position of the tooth." Furthermore, the direction in which the center position of the magnet moves when the rotor 20 rotates is referred to as the "direction of travel." When viewed from one axial side, the direction of travel is a direction perpendicular to a line passing through the central axis J and the center position of the magnet, and faces the rotation direction R.

[0050] For simplicity of explanation, the magnetic force applied to magnet 30 below will be described as the magnetic force applied to the center of magnet 30. Also, for simplicity of explanation, a detailed explanation of the magnetic force applied to magnet 30 will be provided only for magnets 30N1 and 30S1. The magnitude of the magnetic force applied to magnets 30N1, 30N2, 30N3, and 30N4 is the same. The direction of the magnetic force applied to magnets 30N1, 30N2, 30N3, and 30N4 is the same relative to the direction of travel of each magnet. The magnitude of the magnetic force applied to magnets 30S1, 30S2, 30S3, and 30S4 is the same. The direction of the magnetic force applied to magnets 30S1, 30S2, 30S3, and 30S4 is the same relative to the direction of travel of each magnet.

[0051] 5 to 7, the position angles of the centers of the teeth 53a1, 53a2, 53a3, and 53a4 are 67.5°, 157.5°, 247.5°, and 337.5°, respectively. The position angles of the centers of the teeth 53b1, 53b2, 53b3, and 53b4 are 112.5°, 202.5°, 292.5°, and 22.5°, respectively.

[0052] As shown in FIGS. 4 and 5, when time T is t1, the applied voltage Vc applied to each coil 52 is set to a positive DC voltage +V1. In this embodiment, for simplicity, the waveform of the applied voltage Vc applied to each coil 52 is described as a rectangular wave. However, the waveform of the applied voltage Vc applied to each coil 52 is not limited to this. For example, a trapezoidal waveform with shortened periods of maximum positive and negative voltages, a waveform close to a sine wave, or the like can be used. In this case, as described above, the teeth 53a1, 53a2, 53a3, and 53a4 are configured as N-pole electromagnets. Meanwhile, the teeth 53b1, 53b2, 53b3, and 53b4 are configured as S-pole electromagnets. The position angles of the centers of the magnets 30N1, 30N2, 30N3, and 30N4 are 90°, 180°, 270°, and 0°, respectively. The position angles of the centers of the magnets 30S1, 30S2, 30S3, and 30S4 are 45°, 135°, 225°, and 315°.

[0053] The magnet 30N1 is subjected to a repulsive force Fna with the magnetic pole of the tooth 53a1 and an attractive force Fnb with the magnetic pole of the tooth 53b1. The magnitudes of the repulsive force Fna and the attractive force Fnb are the same. The directions of the repulsive force Fna and the attractive force Fnb are symmetrical with respect to the direction of travel Pn1. Therefore, the resultant force Fn of the repulsive force Fna and the attractive force Fnb faces the direction of travel Pn1. In other words, the force Fn that faces the direction of travel Pn1 is applied to the magnet 30N1, and no force that faces in the radial direction is applied.

[0054] The magnet 30S1 is subjected to a repulsive force Fsb with the magnetic pole of the tooth 53b4 and an attractive force Fsa with the magnetic pole of the tooth 53a1. The magnitude of the repulsive force Fsb is the same as the attractive force Fsa. The directions of the attractive force Fsa and the repulsive force Fsb are symmetrical with respect to the direction of travel Ps1. Therefore, the resultant force Fs of the repulsive force Fsb and the attractive force Fsa faces the direction of rotation. In other words, the magnet 30S1 is subjected to a force Fs that faces the direction of travel, but not a force that faces in the radial direction. Therefore, at time T=t1, no force that faces in the radial direction is applied to the cylindrical portion 22. Therefore, no radial deformation of the cylindrical portion 22 occurs. Furthermore, the case 21 is rotated in the direction of rotation R by the forces Fn and Fs that face the direction of rotation.

[0055] 4 and 6, when time T reaches t2, the applied voltage Vc applied to coil 52 is switched from a positive DC voltage +V1 to a negative DC voltage -V1. Therefore, teeth 53a1, 53a2, 53a3, and 53a4 form an electromagnet with an S pole. Meanwhile, teeth 53b1, 53b2, 53b3, and 53b4 form an electromagnet with an N pole.

[0056] The magnet 30N1 is subjected to an attractive force Fna1 with the magnetic pole of the tooth 53a1, an attractive force Fna2 with the magnetic pole of the tooth 53a2, and a repulsive force Fnb with the tooth 53b1 that faces radially outward. The attractive forces Fna1 and Fna2 have the same magnitude. The directions of the attractive forces Fna1 and Fna2 are symmetrical with respect to each other in the radial direction. Therefore, the resultant force Fna of the attractive forces Fna1 and Fna2 faces radially inward. Furthermore, the repulsive force Fnb is greater than the resultant force Fna. In other words, the magnet 30N1 is subjected to a resultant force Fn that faces radially outward, and no force that faces in the traveling direction Pn1. Similarly, the magnet 30S1 is subjected to a force Fs that faces radially inward, and no force that faces in the traveling direction Ps1. Therefore, when time T becomes t2, the cylindrical portion 22 is deformed radially outward. Furthermore, although no force is applied to the case 21 in the direction of travel, the rotor 20 rotates in the direction of rotation R due to the moment of inertia of the rotor 20.

[0057] As described above, when the applied voltage Vc applied to the coil 52 is switched from +V1 to −V1 when the time T is t2, the magnetic force applied to each magnet 30 is directed radially outward. That is, the direction of the force applied to the cylindrical portion 22 of the case 21 suddenly changes to the radially outward direction, causing the cylindrical portion 22 to suddenly deform radially outward. As described above, in this embodiment, the cylindrical portion 22 and the top surface portion 23 of the case 21 are part of the same single member, and therefore, the sudden radially outward deformation of the cylindrical portion 22 causes the top surface portion 23 to suddenly deform in the axial direction. When the top surface portion 23 is suddenly deformed in the axial direction, sound is generated.

[0058] As shown in FIGS. 4 and 7, when time T is t3, the applied voltage Vc applied to the coil 52 is continuously set to a negative DC voltage −V1. The rotor 20 is rotated 45° between time T t1 and time T t3. At this time, the magnet 30N1 is subjected to a repulsive force Fnb with the tooth 53b1 and an attractive force Fna with the tooth 53a2. The magnitude of the repulsive force Fnb is equal to the magnitude of the attractive force Fna. The directions of the repulsive force Fnb and the attractive force Fna are symmetrical with respect to the direction of travel Pn1. Therefore, the resultant force Fn of the repulsive force Fnb and the attractive force Fna is directed in the direction of travel Pn1. In other words, the force Fn directed in the direction of travel Pn1 is applied to the magnet 30N1, and no force directed in the radial direction is applied. Similarly, the force Fs directed in the direction of travel Ps1 is applied to the magnet 30S1, and no force directed in the radial direction is applied. Therefore, when time T is t3, no radial deformation of cylindrical portion 22 occurs. In other words, between time T t2 and t3, the radially outward deformation of cylindrical portion 22 is gradually eliminated as rotor 20 rotates. Therefore, between time T t2 and t3, the axial deformation of top surface portion 23 is also gradually eliminated, and no sound is generated. Furthermore, case 21 is rotated in rotation direction R by forces Fn and Fs that are directed in the rotation direction.

[0059] After time T reaches t3, the applied voltage Vc applied to the coils 52 is switched from +V1 to −V1 or from −V1 to +V1 each time the center position of each magnet 30 coincides with the center position of a tooth 53. In other words, the applied voltage Vc is switched every time the rotor 20 rotates 45°. Therefore, the top surface 23 is suddenly deformed in the axial direction every time the rotor 20 rotates 45°, generating sound. Therefore, high-frequency noise is generated when the motor 10 is driven.

[0060] According to this embodiment, the top surface portion 23 of the case 21 has an annular protrusion 25 that protrudes axially beyond the position of one axial end of the cylindrical portion. This increases the axial rigidity of the top surface portion 23. This reduces axial deformation of the top surface portion 23 caused by switching the polarity of the DC voltage applied to the multiple coils 52. More specifically, switching the polarity of the DC voltage applied to the multiple coils 52 causes the direction of the magnetic force applied to each magnet 30 to suddenly change radially outward. This reduces sudden axial deformation of the top surface portion 23 even if the cylindrical portion 22 suddenly deforms radially outward. This reduces high-frequency noise when the single-phase DC motor 10 is driven.

[0061] According to this embodiment, the top surface 23 is provided with a protrusion 25 that protrudes in the axial direction, thereby increasing the rigidity of the top surface 23. Therefore, the case 21 including the top surface 23 can be easily formed by press working. Another configuration for increasing the rigidity of the top surface 23 is to increase the plate thickness of the top surface 23, but this configuration makes it difficult to form the case 21 by press working. Another configuration for increasing the rigidity of the top surface 23 is to provide a rib member that protrudes in the axial direction on the surface of the top surface 23, but this configuration increases the manufacturing steps and manufacturing costs of providing the rib member on the top surface 23. Therefore, in this embodiment, the rigidity of the top surface 23 can be easily increased while suppressing an increase in the manufacturing steps and manufacturing costs of the case 21.

[0062] According to this embodiment, the protrusion 25 protrudes axially further toward one axial side than the position of the end portion on that side of the cylindrical portion 22. Therefore, by utilizing the shape of the protrusion 25 that protrudes toward one axial side, interference between the top surface portion 23 and the coil 52 can be prevented. In other words, interference between the coil 52 and the top surface portion 23 can be prevented while preventing an increase in the axial dimension of the cylindrical portion 22. Therefore, interference between the top surface portion 23 and the coil 52 can be prevented while preventing an increase in the size of the motor 10.

[0063] According to this embodiment, the shape of the protrusion 25, as viewed in the circumferential direction, is an arc shape that protrudes to one side in the axial direction, thereby increasing the rigidity of the top surface portion 23 in the axial direction. This makes it possible to suppress axial deformation of the top surface portion 23 caused by switching the polarity of the DC voltage applied to the multiple coils 52. This also makes it possible to suppress high-frequency noise when the single-phase DC motor 10 is driven. In addition, compared to when the protrusion 25 protrudes to the other side in the axial direction, a larger internal space can be secured in the case 21, allowing for a more compact motor 10.

[0064] In particular, in a single-phase DC motor, all of the magnets 30 of the rotor 20 are subjected to vibrations from the stator 50 that are in phase with each other. As a result, a radially vibrating force is applied to the outer edge of the top surface portion 23 from the cylindrical portion 22. In the motor 10 of this embodiment, the top surface portion 23 is provided with an arc-shaped protrusion 25. This allows the protrusion 25 to receive the radial force applied to the top surface portion 23 through its arc structure, thereby suppressing deformation of the top surface portion 23. As a result, vibration of the cylindrical portion 22 can be effectively suppressed.

[0065] The protrusions 25 of this embodiment are continuous in the circumferential direction around the central axis J. Therefore, the protrusions 25 can uniformly increase the rigidity of the top surface portion 23 at any position in the circumferential direction. As described above, the outer edge of the top surface portion 23 is subjected to a vibrating force inward and outward in the radial direction from the cylindrical portion 22. By making the rigidity of the top surface portion 23 uniform in the circumferential direction, localized large vibrations do not occur in parts of the top surface portion 23 and the cylindrical portion 22 in the circumferential direction, and as a result, vibration of the entire rotor 20 can be suppressed. Furthermore, according to this embodiment, the protrusions 25 extend uniformly in the circumferential direction, which facilitates press working of the case 21. Furthermore, the case 21 of this embodiment has a rotationally symmetric shape, which has the same cross-sectional shape in any cross section passing through the central axis J. Therefore, there is no need to consider the orientation of the case 21 during assembly, and the manufacturing process can be reduced.

[0066] According to this embodiment, the top surface 23 has a first flat surface 24 and a second flat surface 26, and the first flat surface 24 and the second flat surface 26 have flat surfaces facing the axial direction. Therefore, during manufacturing of the motor 10, the first flat surface 24 and the second flat surface 26 can be used as a reference for positioning the case 21. More specifically, for example, during manufacturing of the motor 10, when the case 21 is held in an assembly jig, the flat surfaces of the assembly jig can be brought into contact with the flat surfaces of the first flat surface 24 and the second flat surface 26 facing one axial side, thereby stabilizing the axial position of the case 21 relative to the assembly jig. Furthermore, tilt of the central axis of the case 21 relative to the assembly jig can be suppressed. This allows components such as the shaft 40 and the base member 80 to be easily and accurately assembled to the case 21. This reduces the number of steps and costs required to manufacture the motor 10.

[0067] According to this embodiment, the top surface 23 has a first flat surface 24 on the radially outer side of the protrusion 25 and a second flat surface 26 on the radially inner side of the protrusion 25. That is, the top surface 23 has flat surfaces facing one axial direction on the radially outer and inner sides of the protrusion 25. Therefore, when the case 21 is held in an assembly jig during manufacturing of the motor 10, the radially outer and inner flat surfaces of the top surface 23 can contact the flat surfaces of the assembly jig. This further stabilizes the axial position of the case 21 relative to the assembly jig. Furthermore, this further reduces tilt of the central axis of the case 21 relative to the assembly jig. This allows components such as the shaft 40 and the base member 80 to be assembled to the case 21 more easily and accurately. This further reduces the number of steps and costs required to manufacture the motor 10.

[0068] According to this embodiment, the top surface portion 23 has an inclined portion 27 located radially inward of the protrusion 25, which is positioned toward the other axial side as it moves radially inward. This further increases the rigidity of the top surface portion 23 in the axial direction. This further reduces axial deformation of the top surface portion 23 due to switching of the polarity of the DC voltage applied to the multiple coils 52. This further reduces high-frequency noise when the single-phase DC motor 10 is driven.

[0069] In this embodiment, the rotor 20 has eight magnets 30 on the inner circumferential surface of the cylindrical portion 22. That is, the rotor 20 has six to ten magnets 30 on the inner circumferential surface of the cylindrical portion. As described above, if the number of magnets 30 is four or less, the magnetic force generated by the electromagnets formed by the coils 52 and the magnets 30 is concentrated at four locations on the cylindrical portion 22 in the circumferential direction. This increases the circumferential deformation of the cylindrical portion 22 and may generate noise. Therefore, the number of magnets 30 is preferably six or more. Furthermore, if the number of magnets 30 is twelve or more, the cost of the magnets 30 increases, so the number of magnets 30 is preferably ten or less. This allows the manufacturing cost of the motor 10 to be reduced while suppressing noise during operation.

[0070] In this embodiment, the stator 50 has eight teeth 53. That is, the stator 50 has eight slots. That is, the stator 50 has any number between six and ten slots. As described above, if the number of slots is four or less, the circumferential spacing between the electromagnets formed by the coils 52 to which voltage is applied becomes large. As a result, the magnetic force generated between the magnets 30 may fluctuate in the circumferential direction. This may cause the rotation of the rotor 20 to become unstable. Therefore, the number of slots is preferably six or more. Furthermore, if the number of slots is twelve or more, winding the coils 52 around the stator core 51 becomes complicated. This increases the number of manufacturing steps and costs of the motor 10. Therefore, the number of slots is preferably ten or less. This allows the rotation of the rotor 20 to be stabilized while reducing the number of manufacturing steps and costs of the motor 10.

[0071] In this embodiment, the motor 10 has a low-speed drive mode in which the rotor 20 is driven to rotate at a rotational speed of 600 revolutions per minute or less. As described above, when a user selects the gentle breeze mode, which produces a low airflow volume, the motor 10 drives the rotor 20 in the low-speed drive mode. When the fan is operated in the gentle breeze mode, the rotation speed of the fan's blades is low, reducing the wind noise generated by the rotation of the blades. As a result, the noise generated by the motor 10 becomes relatively noticeable. However, in the motor of this embodiment, the top surface 23 of the case 21 has an annular protrusion 25 that protrudes axially to one side. This reduces axial deformation of the top surface 23, thereby reducing high-frequency noise generated when the single-phase DC motor 10 is driven. Therefore, the noise generated by the motor 10 can be reduced when the fan is operated in the gentle breeze mode.

[0072] The present invention is not limited to the above-described embodiments, and other configurations and methods may be adopted within the scope of the technical concept of the present invention. For example, the shape of the top surface portion may be any shape as long as it can suppress axial deformation of the top surface portion. For example, the convex portion may have a shape that protrudes to the other axial side. Furthermore, the shape of the convex portion may be a quadratic curve shape or a triangular shape that protrudes in the axial direction. Furthermore, the top surface portion may not have at least one of the first flat surface portion or the second flat surface portion. The top surface portion may not have an inclined surface.

[0073] The number of poles on the magnet in the case and the number of slots in the stator can be any number as long as it stabilizes rotor rotation, suppresses noise when the motor is driven, and reduces the number of steps and manufacturing costs for the motor. As mentioned above, taking into account the stability of rotor rotation, noise when the motor is driven, and the number of steps and manufacturing costs for the motor, the number of poles and slots on the magnet is preferably 6 to 10. However, if the case is thick and the cylindrical portion and top surface are highly rigid, the number of poles and slots may be 4. The number of poles and the number of slots may also be different from each other.

[0074] The use of the single-phase DC motor to which the present invention is applied is not particularly limited. The single-phase DC motor may be installed in devices other than electric fans. Note that the configurations and methods described in this specification can be combined as appropriate within the scope of not mutually contradicting each other. [Explanation of symbols]

[0075] 10... Single-phase DC motor, 20... Rotor, 30... Magnet, 40... Shaft, 22... Cylindrical portion, 23... Top surface portion, 24... First flat portion, 25... Convex portion, 26... Second flat portion, 27... Inclined portion, 30... Magnet, 50... Stator, J... Central axis

Claims

1. a rotor rotatable about a central axis; a stator facing the rotor with a gap in the radial direction; an axially extending shaft rotatable about a central axis; Equipped with the stator is located radially inside the rotor, the shaft is located radially inside the stator, The rotor is a plurality of magnets arranged radially outward of the stator; a cylindrical portion having a cylindrical shape centered on the central axis and extending in the axial direction to hold the plurality of magnets; A plate-shaped top surface, and The top portion is a radially outer end portion connected to one axial end portion of the cylindrical portion; The radially inner end is fixed to the outer peripheral surface of the shaft facing radially outward, a ring-shaped protrusion that protrudes in the axial direction beyond the position of one axial end of the cylindrical portion, A single-phase DC motor, wherein, when viewed in the circumferential direction, the shape between the radially outer end of the convex portion and the radially inner end of the convex portion is an arc shape that protrudes to one side in the axial direction.

2. 2. The single-phase DC motor according to claim 1, wherein the protrusion protrudes axially further to one axial side than the position of one axial end of the cylindrical portion.

3. A single-phase DC motor as described in claim 1 or 2, wherein the convex portions are connected seamlessly in a circumferential direction around the central axis.

4. The top portion is A first flat portion is provided on the radially outer side of the protrusion, A second flat portion is formed on the radially inner side of the protrusion, Has, The single-phase DC motor according to claim 1 , wherein the first flat portion and the second flat portion have a flat surface facing one side in the axial direction.

5. The single-phase DC motor according to claim 4 , wherein the top surface portion has an inclined portion located radially inward of the protrusion and positioned toward the other axial side as it extends radially inward.

6. the rotor has six to ten of the magnets on the inner circumferential surface of the cylindrical portion, 6. The single-phase DC motor according to claim 1, wherein the stator has any number of slots between six and ten.

7. 7. The single-phase DC motor according to claim 1, further comprising a low-speed drive mode in which the rotor is driven to rotate at a rotational speed of 600 revolutions per minute or less.

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