Miniature fan motor

Abstract

To realize a high performance miniature fan motor by suppressing eddy current of a rotor.SOLUTION: A miniature fan motor 13 comprises a stator 13c arranged around a rotor 13b via an air gap Ga. The stator 13c comprises: a plurality of teeth 62; and a plurality of coils 65 constituting three-phase coil groups. The miniature fan motor 13 is constituted so that a shaft 13a and the rotor 13b rotate in a fixed direction by energizing each of the coil groups at a predetermined period. The miniature fan motor 13 is constituted so that a rotational side flange 71 and an anti-rotational side flange 72 are provided at tip parts of each of the teeth 62, distance G1 between rotational side gaps is approximately fixed and on the other hand, distance G2 between anti-rotational side gaps becomes larger as going toward the tip of the anti-rotational side flange 72.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The disclosed technology relates to a mini fan motor suitable for a vacuum cleaner.

Background Art

[0002] In recent years, many small and lightweight stick-type vacuum cleaners have been put on the market. Since this type of vacuum cleaner is cordless, it is easy to handle and popular. The same applies to robot-type vacuum cleaners.

[0003] These vacuum cleaners are equipped with a fan (mini fan) having a small impeller with a diameter of about 3 to 5 cm. In order to generate a high suction force with such a mini fan, the motor is also adopted to be small, lightweight, and capable of rotating at a high speed of 50,000 r / min or more while ensuring a certain amount of torque.

[0004] Even in these vacuum cleaners, since a high suction force equal to or higher than that of a conventional canister-type vacuum cleaner is required, the motor speed has been increased, and recently, a motor with an ultra-high rotation speed exceeding 100,000 r / min has also been realized.

[0005] In such a motor (mini fan motor), while being small, lightweight, and having a high output, further higher efficiency and higher strength are required.

[0006] Regarding the disclosed technology, a motor with a devised shape of the tip portion of the teeth is disclosed (Patent Document 1).

[0007] Unlike a three-phase motor in which the rotation direction of the rotor is determined, that motor is a single-phase motor in which the number of magnetic poles of the rotor is the same as the number of teeth of the stator, so the rotation direction of the rotor is not determined.

[0008] In a single-phase motor, generally, the circumferential shape of the flange portions protruding from both the left and right sides of the tip of the teeth is made asymmetric to make the sizes of the air gaps on both sides of the teeth different, thereby determining the rotation direction of the rotor.

[0009] In Patent Document 1, in order to suppress saturation of magnetic flux density and reduce iron loss, the radial size of these flange portions is further increased on the rotation direction side and decreased on the reverse rotation direction side.

Prior Art Documents

Patent Documents

[0010]

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0011] In a mini-fan motor that requires even higher efficiency and strength, it is effective to adopt a rare-earth sintered magnet with a strong magnetic force such as a neodymium magnet as the rotor poles.

[0012] However, since these magnets have a small electrical resistivity, eddy currents are generated and heat is generated. Therefore, when rotating at ultra-high speed, the magnets immediately become hot. For this reason, in a mini-fan motor, it is common to use a bonded magnet with a weak magnetic force but a large electrical resistivity, and there is a problem that it is difficult to adopt a rare-earth sintered magnet with a strong magnetic force.

[0013] Therefore, this specification discloses a technique that can solve such problems.

Means for Solving the Problems

[0014] The disclosed technique relates to a mini-fan motor.

[0015] The mini-fan motor includes a shaft rotatable about a rotation axis, a rotor fixed to the shaft and having a plurality of magnetic poles arranged alternately in the circumferential direction on an outer peripheral surface thereof, and a stator disposed around the rotor with an air gap therebetween.

[0016] The stator has an annular core ring, a plurality of teeth protruding radially inward from the core ring and arranged in a radial pattern, and a plurality of coils each assembled to each of the teeth to form a three-phase coil group. By energizing each of the coil groups at a predetermined period, the shaft and the rotor are configured to rotate in a certain direction.

[0017] At the tip portion of each of the teeth, a rotating-side flange portion protruding in the rotation direction and a reverse-rotating-side flange portion protruding in the reverse-rotation direction are provided. The distance between the rotating-side gaps between the rotating-side flange portion and the rotor is made substantially constant, while the distance between the reverse-rotating-side gaps between the reverse-rotating-side flange portion and the rotor is configured to increase toward the tip of the reverse-rotating-side flange portion.

[0018] That is, according to this mini-fan motor, the distance between the rotating-side flange portion of one adjacent tooth and the reverse-rotating-side flange portion of the other tooth is larger than that of the symmetrically arranged flange portions. As a result, the leakage magnetic flux is reduced, so the performance of the motor can be improved.

[0019] And since the distance between the reverse-rotating-side gaps gradually increases as it moves away from the center line of the teeth, on the reverse-rotating side of each tooth, the magnetic flux gradually weakens. Thereby, the eddy current generated in the rotor is reduced, and the heat generation of the rotor can be effectively suppressed. As a result, it becomes possible to employ a rare-earth sintered magnet having a low electrical resistivity for the rotor, and the magnetic force of the magnetic poles of the rotor can be strengthened.

[0020] On the other hand, the larger the distance between the reverse-rotating-side gaps, the lower the torque of the motor. In contrast, since the distance between the rotating-side gaps is made substantially constant, on the rotating side of each tooth, a decrease in torque can be suppressed. Thereby, eddy current can be reduced while suppressing a decrease in torque, so the performance of the motor can be improved in a well-balanced manner.

[0021] The magnetic poles may be configured by a permanent magnet having an electrical resistivity of 10 Ω·cm or less.

[0022] It is preferable that the poles of the rotor are made of rare earth sintered magnets with strong magnetic force. However, rare earth sintered magnets have an electrical resistivity of 10 Ω·cm or less and are very conductive. Therefore, if such permanent magnets are used to form the poles, eddy currents are likely to be generated. In contrast, in the disclosed technology, since the generation of eddy currents can be suppressed, it becomes possible to adopt rare earth sintered magnets for the poles of the rotor. Therefore, the performance of the motor can be improved.

[0023] Also, it may be provided with a cylindrical metal cover covering the outer peripheral surface of the rotor.

[0024] Eddy currents are generated in the metal cover. Therefore, the disclosed technology is suitable for such a form of mini-fan motor.

[0025] The rotating-side facing surface of the rotating-side flange portion facing the air gap has an arcuate cross section concentric with the outer peripheral surface of the rotor, and the non-rotating-side facing surface of the non-rotating-side flange portion facing the air gap has a linear cross section perpendicular to the center line of the teeth. It may be such that the distance from the center line of the teeth to the tip of the rotating-side facing surface is longer than the distance from the center line of the teeth to the tip of the non-rotating-side facing surface.

[0026] According to the results of the inventors' study on the influence of these distances, by setting the distances in this way, while maintaining the lamination thickness of the stator core, iron loss and eddy current loss can be reduced in a well-balanced manner, and both weight reduction and efficiency improvement can be achieved.

[0027] The mini-fan motor may be capable of inputting 500 W or more of power and outputting at 100,000 revolutions per minute or more.

[0028] That is, the disclosed technology is suitable for a mini-fan motor that can input a large amount of power and rotate at a super-high speed. When the rotor rotates at a super-high speed, particularly the eddy current generated in the magnetic poles becomes a problem. However, if the disclosed technology is applied, the eddy current can be effectively suppressed. Thereby, it becomes possible to adopt a high-magnetic-force magnet with a small electrical resistivity for the magnetic poles, and a high-performance mini-fan motor can be realized.

Advantages of the Invention

[0029] According to the disclosed technology, since the eddy current generated in the magnetic poles of the rotor can be suppressed, it becomes possible to adopt a high-magnetic-force magnet with a small electrical resistivity. Therefore, a high-performance mini-fan motor can be realized.

Brief Description of the Drawings

[0030]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0031] Hereinafter, the disclosed technology will be described. However, the following description is merely illustrative in nature. In the following description, the direction in which the rotation axis extends is referred to as the axial direction, the direction around the rotation axis is referred to as the circumferential direction, and the direction of its radius is also referred to as the radial direction.

[0032] <Vacuum cleaner> Figure 1 shows a stick-type vacuum cleaner (hereinafter also simply referred to as vacuum cleaner 1) as a preferred application example of the disclosed technology. This vacuum cleaner 1 is a cordless type.

[0033] The vacuum cleaner 1 is composed of a tube portion 2, a main body portion 3, a dust case 4, a handle portion 5, etc. The handle portion 5 is the part that the user grips. The vacuum cleaner 1 is configured to be operable with the user holding the handle portion 5 with one hand.

[0034] The tube portion 2 is composed of an elongated cylindrical member, and a head 2a of the vacuum cleaner 1 for sucking dust is attached to the tip portion thereof. The main body portion 3 and the handle portion 5 are provided integrally with the base end portion of the tube portion 2. A mini-fan 10 is housed in the main body portion 3. A battery 6 is housed in the handle portion 5.

[0035] The battery 6 is a rechargeable secondary battery and supplies power to the mini-fan 10. Thereby, a motor 13 (mini-fan motor) installed in the mini-fan 10 is driven, and the impeller 20 rotates.

[0036] A dust case 4 is installed below the main body portion 3. The dust case 4 is configured to be detachable from the main body portion 3. When the mini-fan is driven, a strong suction force is generated at the head 2a. Thereby, the dust sucked from the head 2a is accumulated in the dust case 4 through the tube portion 2.

[0037] (Inside the main body) The internal structure of the main body portion 3 is shown enlarged below Figure 1.

[0038] Inside the main body portion 3, an exhaust chamber 30, a filtration chamber 31, etc. are provided. The exhaust chamber 30 consists of a cylindrical space with one end sealed, and a plurality of inner exhaust holes 30a are formed on its outer peripheral surface. The filtration chamber 31 is provided so as to surround the exhaust chamber 30. A cylindrical filter 32 for capturing dust is mounted over its entire circumference in the filtration chamber 31.

[0039] A case of the main body 3 partitioning the outer peripheral side of the filtration chamber 31 is formed with a plurality of outer exhaust holes 33. The mini-fan 10 is housed inside the main body 3 in a state where a part of it enters the exhaust chamber 30.

[0040] (Mini-fan) Fig. 2 shows an enlarged view of the internal structure of the mini-fan 10. The mini-fan 10 is composed of a shroud 11 (cover), a motor 13, an impeller 20, a diffuser 15, etc. Regarding the diffuser 15, in Fig. 2, both its cross-sectional shape and outer shape are illustrated left and right.

[0041] (Shroud) The shroud 11 is composed of a cylindrical member with a constricted middle part, and has an upstream large-diameter part 11a with a large inner diameter, a reduced-diameter part 11c with the smallest inner diameter, and a downstream large-diameter part 11b with a large inner diameter. A reduced-diameter part 11c exists between the upstream large-diameter part 11a and the downstream large-diameter part 11b, and relay regions 11d are provided in each of the downstream part of the upstream large-diameter part 11a and the upstream part of the downstream large-diameter part 11b. Each relay region 11d is formed such that the inner diameter gradually decreases from each of the upstream large-diameter part 11a and the downstream large-diameter part 11b toward the reduced-diameter part 11c.

[0042] As shown in Fig. 1, the downstream large-diameter part 11b is arranged inside the exhaust chamber 30. The upstream large-diameter part 11a is arranged so as to face the inside of the dust case 4 in a state where its periphery is covered with a filter case 4a capable of removing dust in the air.

[0043] An air flow path (air duct 40) is formed inside the shroud 11. The shroud 11 covers the outside of the air duct 40. When the impeller 20 rotates, the air in the air duct 40 flows as shown by the arrow Y1 in Fig. 2. In the description, the terms "upstream side" and "downstream side" are also used for this air flow.

[0044] The shroud 11 also has a moving blade part 11P, a suction part 11V connected to the upstream side thereof, a stationary blade part 11E connected to the downstream side thereof, etc. from the functional viewpoint of the air passage 40. The moving blade part 11P is constituted by a part from the reduced-diameter part 11c to the relay region 11d of the downstream-side large-diameter part 11b, and the impeller 20 is accommodated therein.

[0045] The suction part 11V is constituted by the upstream-side large-diameter part 11a, and the motor 13 is accommodated therein. The stationary blade part 11E is constituted by the downstream-side large-diameter part 11b, and the diffuser 15 is accommodated therein.

[0046] A motor case 12 is fitted into the upstream-side large-diameter part 11a. At the center of the motor case 12, a shaft 13a is rotatably supported about the rotation axis A via a bearing 12a. A rotor 13b is fixed to an intermediate part of the shaft 13a. A stator 13c is assembled to the motor case 12 such that the stator 13c is positioned around the rotor 13b with an air gap Ga therebetween.

[0047] Thereby, a motor 13 including the shaft 13a, the rotor 13b, and the stator 13c is constituted at the central part of the suction part 11V. The motor 13 is integrated with the motor case 12. The rotation axis A of the motor 13 coincides with the centers of the motor case 12 and the shroud 11. Details of the motor 13 will be described later.

[0048] The motor case 12 is fitted into the shroud 11 with the end on the side where the shaft 13a protrudes facing downstream. Thereby, the above-described air passage 40 is formed between the motor 13 and the inner surface of the suction part 11V of the shroud 11.

[0049] On the upstream side of the motor case 12, a control unit 14 for a mini-fan composed of electronic components, a printed circuit board, etc. is installed. Specifically, the control unit 14 is arranged on the upstream side of the motor 13 in a state where it overlaps with the motor 13 in the axial direction and its plate surface faces the air passage 40. The control unit 14 controls the driving of the motor 13 according to the operation of the vacuum cleaner 1.

[0050] The motor 13 is very small. For example, in the case of this embodiment, the outer diameter of the stator 13c is approximately 40 mm, and the overall height is approximately 70 mm (so-called palm size) (outer diameter is 50 mm or less, overall height is 80 mm or less). Therefore, its weight is also extremely light.

[0051] However, the motor 13 is configured to obtain high efficiency and high output so that sufficient performance as a vacuum cleaner 1 can be obtained using the power of the battery 6. Specifically, in the case of this motor 13, power of 500 W or more can be input. Thereby, it is configured to be able to output at an ultra-high rotation speed of 100,000 revolutions per minute or more.

[0052] (Diffuser, impeller) As described above, the diffuser 15 is housed in the stationary blade portion 11E. The illustrated diffuser 15 is composed of two parts, an upper diffuser 15U and a lower diffuser 15D. Depending on the specifications of the mini-fan, the diffuser 15 may be one or three.

[0053] Each of the upper diffuser 15U and the lower diffuser 15D is composed of a cylindrical member, and a plurality of vanes 15a extending obliquely with respect to the axial direction are formed on its outer peripheral surface. The lower diffuser 15D has a smaller inclination angle of the vanes 15a than the upper diffuser 15U. Each of the upper diffuser 15U and the lower diffuser 15D is fixed to the inner peripheral surface of the downstream large-diameter portion 11b.

[0054] As described above, the impeller 20 is disposed on the rotor blade portion 11P of the shroud 11 that constitutes the air passage 40. The impeller 20 includes a boss portion 21 that is fixed in a state where the rotation axis A coincides with the shaft 13a of the motor 13, and an annular base portion 22 that extends from the boss portion 21 to the periphery. The base portion 22 has a plurality of blades 23.

[0055] (Operation of vacuum cleaner, mini fan) During the operation of the vacuum cleaner 1, the shaft 13a of the motor 13 rotates at high speed in a certain direction (in the case of this embodiment, counterclockwise as viewed from the upstream side, see FIG. 3). As a result, the impeller 20 rotates at an extremely high speed, so that as shown by the arrow Y1 in FIG. 2, air flows from the dust case 4 through the motor case 12 into the shroud 11, and a suction force is generated on the upstream side of the rotor blade portion 11P, that is, the suction portion 11V and the like.

[0056] The air flowing toward the shroud 11 is sucked into the rotor blade portion 11P while air-cooling the control unit 14 and the motor 13. Since the heat generation amount of the control unit 14 and the motor 13 increases with an increase in speed and suction force, cooling of these is important. On the other hand, in this mini fan 10, since the motor 13 is disposed on the upstream side of the rotor blade portion 11P, it can exchange heat with air having a relatively low temperature, similar to the outside air. Therefore, these have excellent cooling properties.

[0057] And the air in the suction portion 11V is configured to flow from the outer peripheral side, curve, concentrate on the center side, and then flow to the rotor blade portion 11P. Specifically, after flowing axially along the inner surface of the upstream large-diameter portion 11a and the side portion of the motor 13, it flows from the outer peripheral side (radially outward) to the center side (radially inward) along the inner surface of the relay region 11d of the upstream large-diameter portion 11a and the end portion of the motor 13, and is configured to flow toward the rotor blade portion 11P.

[0058] Thereby, the air efficiently contacts and flows through the control unit 14 and the motor 13, so that it is easy to exchange heat with these. Therefore, it has more excellent cooling properties.

[0059] The air that has flowed into the moving blade part 11P passes through the space between the inner surface of the moving blade part 11P and the base part 22 of the impeller 20 (specifically, between each blade 23) and flows into the stationary blade part 11E. The air that has flowed into the stationary blade part 11E passes through the space between its inner surface and the outer peripheral surface of the diffuser 15 (specifically, between each vane 15a) and flows into the exhaust chamber 30.

[0060] By passing through the diffuser 15, the air flows into the exhaust chamber 30 in an axially rectified state. The air that has flowed into the exhaust chamber 30 flows out into the filtration chamber 31 through the inner exhaust holes 30a and is exhausted outside the main body part 3 through the outer exhaust holes 33.

[0061] <Motor> Fig. 3 shows a schematic cross-sectional view of the motor 13. The main parts of the motor 13, namely the shaft 13a, the rotor 13b, and the stator 13c, are shown in a simplified manner.

[0062] The rotor 13b is formed in a cylindrical shape by permanent magnets 50. On the outer peripheral surface of the rotor 13b, N poles and S poles are magnetized alternately at equal intervals in the circumferential direction, forming four magnetic poles. Note that the rotor 13b may have a rotor core formed by laminating steel plates in the axial direction, and the rotor 13b may be constituted by attaching the permanent magnets 50 to the surface of the rotor core.

[0063] The stator 13c has a stator core 60 formed by laminating steel plates in the axial direction. The stator core 60 of this motor 13 is constituted by alternately connecting two types of parts (the first part 60a and the second part 60b), each consisting of six, in the circumferential direction.

[0064] Thereby, the stator core 60 has an annular core ring 61 and six teeth 62 protruding radially inward from the core ring 61 and arranged at equal intervals. Although not shown, the inside of the stator core 60 is covered with an insulating insulator except for the side facing the air gap Ga.

[0065] By winding an electric wire around the teeth 62 through the slots 64 between two adjacent teeth 62, 62, coils 65 are assembled on each of the teeth 62. These coils 65 constitute a three-phase coil group consisting of U, V, and W. Specifically, in the case of this motor 13, since there are six teeth 62, two coils 65, 65 facing each other are composed of electrically connected wires and constitute the coil group of each phase.

[0066] That is, the slot combination of this motor 13 is 4 poles and 6 slots. In addition, the slot combination may also be 2 poles and 3 slots, or 6 poles and 9 slots. That is, since this motor 13 is very small, its slot combination is preferably 2n poles and 3n slots (n = 1, 2, 3).

[0067] Since this motor 13 is a so-called three-phase motor, by energizing the coil groups of each phase with currents of different phases at a predetermined cycle, it can be started to rotate in a certain direction. As described above, it is configured to rotate counterclockwise when viewed from the upstream side.

[0068] In this motor 13, a rare earth sintered magnet with strong magnetic force is adopted for the permanent magnet 50 constituting the rotor 13b. Particularly, a neodymium magnet is preferable.

[0069] Examples of rare earth sintered magnets that can be adopted for the rotor 13b include samarium cobalt magnets and alnico magnets in addition to neodymium magnets. There are also bonded magnets and rubber magnets formed by mixing fine powders of these rare earth sintered magnets with synthetic resins or rubbers. Rare earth sintered magnets have high purity and stronger magnetic force than bonded magnets, etc., so they are preferable for the magnetic poles of the rotor 13b.

[0070] On the other hand, while it is difficult for electricity to flow through bonded magnets, etc., electricity flows very easily through rare earth sintered magnets. Specifically, the electrical resistivity of bonded magnets, etc. is generally 10000 Ω·cm or more, while the electrical resistivity of rare earth sintered magnets is 10 Ω·cm or less.

[0071] Therefore, when a rare earth sintered magnet is used for the magnetic pole, eddy currents are likely to be generated and heat is easily generated. Therefore, when the rotor 13b employing a rare earth sintered magnet rotates at an ultra-high speed, it immediately becomes hot, so there is a disadvantage that temperature control is extremely difficult. As a result, in this type of rotor 13b, it is common to use a bonded magnet with weak magnetic force.

[0072] However, in order to achieve even higher efficiency and strength, it is inevitable to configure the magnetic pole with a permanent magnet 50 having a strong magnetic force. Therefore, in this motor 13, even for a permanent magnet 50 having a very small electrical resistivity that allows electricity to flow very easily, the shape of the tip portion of the teeth 62 is devised so that the generation of eddy currents can be effectively suppressed and heat generation can be reduced.

[0073] (Detailed shape of teeth) The teeth 62 are prismatic portions extending radially inward from the core ring 61. As shown enlarged in FIG. 4, when viewed from the axial direction, the center line CL of each tooth 62 is configured to intersect the rotation axis A. The teeth 62 have a pair of side surfaces 70, 70 that are located at an equal distance from the center line CL and extend substantially parallel. These side surfaces 70, 70 face the slots 64 on both sides of the teeth 62.

[0074] And at the tip portion of the teeth 62, a pair of flange portions 71, 72 are formed so as to project from the side surfaces 70 on both sides thereof. In the case of a three-phase motor, from the viewpoint of ripple suppression and the like, these flange portions are generally provided symmetrically. On the other hand, in this motor 13, on the premise that it is a fan motor that rotates in a certain direction, the flange portions are formed in an asymmetrical shape so as to effectively suppress the generation of eddy currents while reducing leakage magnetic flux and improving performance.

[0075] Specifically, at the tip portion of each of the teeth 62, a flange portion (rotating side flange portion 71) that projects in the rotation direction (CCW direction in this motor 13) and a flange portion (counter-rotating side flange portion 72) that projects in the counter-rotation direction (CW direction in this motor 13) are provided.

[0076] These flange portions 71 and 72 are formed so as to project more greatly in the circumferential direction as they go radially inward from the side surfaces 70 of the teeth 62. Therefore, at the boundary portion thereof, there is an inflection point 73 where the surface shape changes greatly. The distance D1 from the rotation axis A to the inflection point 73 of the rotation-side flange portion 71 and the distance D2 from the rotation axis A to the inflection point 73 of the counter-rotation-side flange portion 72 are configured to be the same.

[0077] That is, on the rotation side and the counter-rotation side, the radial lengths of both side surfaces 70 and 70 of the teeth 62 excluding the flange portions 71 and 72 are the same. Thereby, even if the shapes of the rotation-side flange portion 71 and the counter-rotation-side flange portion 72 are asymmetric, it is possible to prevent adverse effects of the flange portions such as a decrease in the occupation ratio and winding collapse on the coil 65 wound around the teeth 62.

[0078] And, the opposing surface of the rotation-side flange portion 71 facing the air gap Ga (rotation-side opposing surface 75), that is, the surface of the tip of the tooth 62 extending from the center line CL toward the rotation direction side, has a cross section in an arc shape concentric with the outer peripheral surface of the rotor 13b. Thereby, the distance (rotation-side gap distance G1) between the rotation-side opposing surface 75 of the rotation-side flange portion 71 and the outer peripheral surface of the rotor 13b is made substantially constant over the entire area.

[0079] On the other hand, the opposing surface of the counter-rotation-side flange portion 72 facing the air gap Ga (counter-rotation-side opposing surface 76), that is, the surface of the tip of the tooth 62 extending from the center line CL toward the counter-rotation direction side, has a cross section in a linear shape orthogonal to the center line CL of the tooth 62. Thereby, the distance (counter-rotation-side gap distance G2) between the counter-rotation-side opposing surface 76 of the counter-rotation-side flange portion 72 and the outer peripheral surface of the rotor 13b is configured to increase toward the tip of the counter-rotation-side flange portion 72.

[0080] By doing so, the distance TD between the rotation-side flange portion 71 of one adjacent tooth 62 and the counter-rotation-side flange portion 72 of the other tooth 62 expands more than that of the symmetrically shaped flange portions. As a result, the leakage magnetic flux decreases, so that the performance of the motor 13 can be improved.

[0081] And since the counter-rotating side gap distance G2 gradually increases as it moves away from the center line CL of the teeth 62, on the counter-rotating side of each tooth 62, the magnetic flux gradually weakens. Thereby, the eddy current generated by the permanent magnet 50 of the rotor 13b is reduced, and the heat generation of the permanent magnet 50 can be effectively suppressed. As a result, it becomes possible to employ a rare earth sintered magnet with a low electrical resistivity for the rotor 13b, and the magnetic force of the magnetic poles of the rotor 13b can be strengthened.

[0082] On the other hand, the larger the counter-rotating side gap distance G2 becomes, the lower the torque of the motor 13. In contrast, since the rotating side gap distance G1 is made substantially constant, on the rotating side of each tooth 62, a decrease in torque can be suppressed. Thereby, eddy current can be reduced while suppressing a decrease in torque, so that the motor performance can be improved well in balance.

[0083] Furthermore, it is preferable that the distance W1 from the center line CL of the tooth 62 to the tip of the rotating side facing surface 75 is longer than the distance W2 from the center line CL of the tooth 62 to the tip of the counter-rotating side facing surface 76.

[0084] The inventors examined the influence on the main characteristics by the protruding amounts of the rotating side flange portion 71 and the counter-rotating side flange portion 72 through simulation. Specifically, using a motor model, the distances to the tips of the rotating side facing surface 75 and the counter-rotating side facing surface 76 were changed in size between 1.8 mm and 2.6 mm, and the resulting losses (total iron loss) due to the cores of the rotor 13b and the stator 13c, the losses due to the eddy current of the rotor 13b (eddy current loss), and the influence on the lamination thickness of the stator core 60 were investigated.

[0085] The total iron loss and the eddy current loss are preferably small from the viewpoint of efficiency improvement. The lamination thickness is preferably small from the viewpoint of weight reduction. If the lamination thickness increases, accordingly, the coil 65 also increases and the thickness of the rotor 13b also increases, so the influence on the weight is large.

[0086] As shown in FIG. 5, as an example, a motor model obtained by simplifying the above-described motor 13 was used. That is, the slot combination, the shape of the teeth, etc. of the motor model are the same as those of the above-described motor 13. As a comparative example, a motor model in which the flange portions of the teeth are symmetric (both having the shape of the rotating-side flange portion 71) as in the prior art was used. For convenience, the distance W1 on the rotating side was designated as L, and the distance W2 on the reverse-rotating side was designated as R.

[0087] The results for an air gap Ga of 0.5 mm are shown in FIG. 6. Each figure is a contour diagram of each performance. The arrows generally represent the direction of the change in their magnitudes, and the broken lines represent the image of the contour lines. The total iron loss is relatively larger in terms of the loss amount than the eddy current loss, and its influence is significant.

[0088] As shown in FIG. 6, in the comparative example, the total iron loss decreases as L increases and R decreases, and the total iron loss increases as L decreases and R increases. On the other hand, in the example, the total iron loss decreases as L increases, and the total iron loss increases as L decreases, but the magnitude of R does not significantly affect the total iron loss.

[0089] Therefore, in the example, the magnitude of R can be selected while minimizing the total iron loss. On the other hand, in the comparative example, the total iron loss can be minimized only under specific conditions (L = 2.6 mm, R = 1.8 mm). And the smallest value of the total iron loss in that comparative example is 16.7 W, whereas in the example it is 15.1 W, and the example can reduce the total iron loss by about 10%.

[0090] No significant difference is recognized between the example and the comparative example in terms of the influence on the eddy current loss and the lamination thickness. However, in the example, since the magnitude of R can be selected, the optimum value can be selected in consideration of the influence of both the eddy current loss and the lamination thickness.

[0091] Specifically, as described above, the distance W1 from the center line CL of the tooth 62 to the tip of the rotation-side facing surface 75 may be made longer than the distance W2 from the center line CL of the tooth 62 to the tip of the counter-rotation-side facing surface 76. In the case of this motor 13, for example, L = 2.6 mm and R = 2.2 mm can be selected as its optimal conditions.

[0092] On the other hand, in the comparative example, even under the condition (L = 2.6, R = 1.8) with the smallest total iron loss, the eddy current loss is 3.25 W, which is larger than 2.1 W under the optimal conditions of the example. Similarly, its lamination thickness is 15.3 mm, while the lamination thickness under the optimal conditions of the example is 15.6 mm, and there is almost no difference.

[0093] Therefore, by adopting the example, that is, a predetermined asymmetric flange portion, it is possible to reduce the total iron loss and the eddy current loss without causing an increase in weight as compared with the comparative example, that is, adopting a conventional symmetric flange portion.

[0094] Note that the disclosed technology is not limited to the above-described embodiments, and includes various other configurations.

[0095] For example, in the above-described embodiment, the motor 13 in which the permanent magnet 50 is disposed on the outer surface of the rotor 13b is exemplified. However, in the motor 13 that rotates at high speed, the permanent magnet 50 may come off and scatter due to centrifugal force. Therefore, in order to prevent the permanent magnet 50 from scattering, as shown in FIG. 7, the outer peripheral surface of the rotor 13b may be covered with a cylindrical metal cover 80.

[0096] In the case of such a motor 13, eddy currents are generated in the metal cover 80 and heat is generated. Therefore, even if a permanent magnet 50 (a permanent magnet 50 with a large electrical resistivity) through which electricity hardly flows, such as a ferrite magnet or a bonded magnet, is adopted for the magnetic poles of the rotor 13b, eddy current loss occurs in the same manner as in the above-described motor 13. Therefore, the disclosed technology is also effective for a motor 13 in such a form.

Explanation of Reference Numerals

[0097] 1 Vacuum cleaner 10 Mini fan 12 Motor case 12a Bearing 13 Motor (mini fan motor) 13a Shaft 13b Rotor 13c Stator 20 Impeller 40 Air passage 50 Permanent magnet 60 Stator core 60a First part 60b Second part 61 Core ring 62 Teeth 64 Slots 65 Coil 70 Side surface 71 Rotating side flange part 72 Reverse rotating side flange part 73 Inflection point 75 Rotating side opposing surface 76 Reverse rotating side opposing surface 80 Metal cover A Rotation axis Ga Air gap CL Center line of teeth G1 Rotating side gap distance G2 Reverse rotating side gap distance

Claims

1. A mini fan motor, comprising: a shaft rotatable about a rotation axis; a rotor fixed to the shaft and having a plurality of magnetic poles arranged alternately in the circumferential direction on an outer peripheral surface thereof; a stator disposed around the rotor with an air gap therebetween; wherein the stator includes an annular core ring; a plurality of teeth protruding radially inward from the core ring and arranged radially; a plurality of coils each assembled to each of the teeth and constituting a three-phase coil group; and by energizing each of the coil groups at a predetermined period, the shaft and the rotor are configured to rotate in a certain direction; at a tip portion of each of the teeth, a rotation-side flange portion protruding in the rotation direction and a reverse-rotation-side flange portion protruding in the reverse-rotation direction are provided, wherein a rotation-side gap distance between the rotation-side flange portion and the rotor is made substantially constant, while a reverse-rotation-side gap distance between the reverse-rotation-side flange portion and the rotor is configured to increase toward a tip of the reverse-rotation-side flange portion.

2. The mini fan motor according to claim 1, wherein the magnetic poles are formed of a permanent magnet having an electric resistivity of 10 Ω·cm or less.

3. The mini fan motor according to claim 1, further comprising a cylindrical metal cover covering an outer peripheral surface of the rotor.

4. The mini fan motor according to claim 2 or 3, wherein a rotation-side facing surface of the rotation-side flange portion facing the air gap has an arcuate cross section concentric with an outer peripheral surface of the rotor, and a reverse-rotation-side facing surface of the reverse-rotation-side flange portion facing the air gap has a linear cross section perpendicular to a center line of the teeth, and a distance from the center line of the teeth to a tip of the rotation-side facing surface is longer than a distance from the center line of the teeth to a tip of the reverse-rotation-side facing surface.

5. The mini fan motor according to claim 2 or 3, which is capable of inputting power of 500 W or more and outputting at 100,000 revolutions per minute or more.

Images