electric motor

Abstract

This electric motor comprises a rotor having an iron core to which a rotary shaft extending axially is fixed, and a stator disposed to face the rotor, wherein: the stator has a plurality of teeth extending toward the rotor and slots located between adjacent teeth among the plurality of teeth; the iron core has a plurality of magnet insertion holes and a plurality of permanent magnets arranged in the plurality of magnet insertion holes; the plurality of permanent magnets are rare earth magnets; the outermost shape of the iron core corresponding to a magnetic pole of each of the plurality of permanent magnets includes a plurality of circular arcs having different radii; the number of poles of the rotor is 10 or more; and the residual magnetic flux density of the permanent magnet is 1.3 T or more.

Description

Technical Field

[0001] The present disclosure relates to an electric motor, and more particularly to an electric motor including a permanent magnet embedded type rotor in which permanent magnets are embedded in a core.

Background Art

[0002] Electric motors are used in various electrical devices such as household appliances or industrial devices. For example, as an electric motor used in an air conditioner or a vacuum cleaner, a fan motor having a rotary fan attached to a rotating shaft is known. The fan motor in an air conditioner is mounted on, for example, an outdoor unit. As this type of electric motor, Patent Document 1 discloses a brushless motor for driving a fan.

[0003] Conventionally, as an electric motor, an IPM (Interior Permanent Magnet) motor having a permanent magnet embedded type rotor in which a plurality of permanent magnets are embedded in a core is known. The IPM motor can obtain a reluctance torque due to unevenness in the magnitude of magnetic reluctance generated in the core in addition to the magnet torque by the permanent magnets. Therefore, a small and highly efficient motor can be realized.

[0004] Conventionally, a technique using a rare earth magnet having a high energy density as the permanent magnet of an IPM motor is known. In this case, generally, a rare earth magnet made of neodymium-iron-boron (Nd-Fe-B) is used.

[0005] However, in a conventional fan motor equipped with an IPM motor using a rare earth magnet, when trying to suppress vibration and noise while maintaining high output and high efficiency, the number of poles of the rotor has to be limited to 8 poles or less, or a rare earth magnet having a low residual magnetic flux density (Br) (for example, Br < 1.3 T) has to be used.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent No. 5186899 [Overview of the Initiative]

[0007] This disclosure was made to solve these problems and aims to provide an electric motor that can achieve both vibration and noise suppression and high output and high efficiency, even in an IPM motor using rare earth magnets.

[0008] To achieve the above objective, one embodiment of the electric motor according to the present disclosure comprises a rotor having an iron core to which a rotating shaft extending in the axial direction is fixed, and a stator disposed opposite the rotor, wherein the stator has a plurality of teeth extending toward the rotor, and slots located between adjacent teeth of the plurality of teeth, and the iron core has a plurality of magnet insertion holes formed at equal intervals along the circumferential direction so as to surround the rotating shaft with the circumferential direction as the longitudinal direction, a plurality of permanent magnets disposed in each of the plurality of magnet insertion holes, and the outer surface has portions between two adjacent permanent magnets of the plurality of permanent magnets Each of It is formed to be inwardly curved. one The structure has a recess and the plurality of permanent magnets are rare earth magnets, and the outermost shape of the iron core corresponding to each of the magnetic poles of the plurality of permanent magnets is It is composed of one first arc and two second arcs, the first arc and the second arcs having different radii, and the first arc and the two second arcs form a single continuous curve having two inflection points, the first arc is an arc centered on the axis that passes through a first point where a first straight line passing through the centers of the magnetic poles of each of the plurality of permanent magnets and the axis of the rotation axis intersects the outermost circumference of the iron core, the second arc is an arc connecting a second point where a second straight line passing through the centers between the magnetic poles of two adjacent permanent magnets among the plurality of permanent magnets and the axis of the rotation axis intersects the outermost circumference of the iron core and an inflection point, the center of the second arc is a point located on the line segment connecting the inflection point, which is the boundary point between the first arc and the second arc, and the axis of the rotation axis, The rotor includes multiple arcs of different radii, has 10 or more poles, and the residual magnetic flux density of the permanent magnet is 1.3T or more.

[0009] Furthermore, it is preferable that the rotor has 10 poles and the stator has 12 slots.

[0010] Furthermore, it is preferable that the residual magnetic flux density of the permanent magnet is 1.4T or higher.

[0011] Furthermore, the stator may be further covered with a molded resin.

[0012] Furthermore, the molded resin may have a main body portion that covers the stator and a protruding portion that extends outward from the side surface of the main body portion.

[0013] Furthermore, the rare earth magnet does not necessarily have to contain dysprosium.

[0014] Furthermore, the rotating shaft may be further supported by a bearing, and a dielectric material may be provided between the rotating shaft and the outer surface of the iron core.

[0015] According to this disclosure, it is possible to achieve both vibration and noise suppression and high output and high efficiency in an IPM motor using rare earth magnets. [Brief explanation of the drawing]

[0016] [Figure 1] Figure 1 is a semi-cross-sectional view of an electric motor according to an embodiment. [Figure 2] Figure 2 is a plan view of the electric motor according to the embodiment, as seen from the side opposite the output shaft. [Figure 3] Figure 3 is a cross-sectional view taken along the line III-III in Figure 1. [Figure 4A] Figure 4A shows the relationship between the rotor position angle and torque in a comparative example of an electric motor. [Figure 4B] Figure 4B shows the relationship between the rotor position angle and torque in the electric motor of the embodiment. [Modes for carrying out the invention]

[0017] The embodiments of this disclosure will now be described. Note that the embodiments described below are all specific examples of this disclosure. Therefore, the numerical values, components, arrangement and connection configurations of components, as well as the processes and their sequences shown in the following embodiments, are examples only and are not intended to limit this disclosure. Accordingly, any components in the following embodiments that are not described in the independent claims representing the highest-level concepts of this disclosure will be described as arbitrary components.

[0018] The figures are schematic diagrams and are not necessarily drawn precisely. In each figure, substantially identical components are denoted by the same reference numerals, and duplicate descriptions are omitted or simplified.

[0019] In the present embodiment, the radial direction of the stator 10 and the rotor 20 is referred to as the "radial direction", and the rotational direction of the rotor 20 is referred to as the "circumferential direction". That is, the direction extending from the axis C of the rotary shaft 21 centered on the axis C is the "radial direction", and the direction orbiting around the axis C centered on the axis C of the rotary shaft 21 is the "circumferential direction". Therefore, the "radial direction" is perpendicular to the direction of the axis C of the rotary shaft 21. The rotor 20 rotates about the axis C of the rotary shaft 21 as the center of rotation.

[0020] (Embodiment) First, the configuration of the motor 1 according to the embodiment will be described with reference to FIGS. 1 to 3. FIG. 1 is a half-sectional view of the motor 1 according to the embodiment. FIG. 2 is a plan view of the motor 1 as viewed from the reverse output shaft side. FIG. 3 is a cross-sectional view taken along line III-III of FIG. 1.

[0021] As shown in FIGS. 1 to 3, the motor 1 includes a stator 10, a rotor 20 disposed opposite to the stator 10, and a molded resin 30 covering the stator 10. In the present embodiment, the number of poles (magnetic poles) of the rotor 20 is 10. The number of slots 14 of the stator 10 is 12. Note that the same effects can be expected if the number of poles (magnetic poles) of the rotor 20 is 10 or more.

[0022] The motor 1 further includes a first bearing 41 and a second bearing 42, a heat sink 50, and a first bracket 61 and a second bracket 62.

[0023] Note that the motor 1 in the present embodiment is a molded motor in which the stator 10 is covered with the molded resin 30. Also, the motor 1 is a brushless motor that does not use motor brushes.

[0024] As shown in Figures 1 and 3, the stator 10 is positioned opposite the rotor 20 with a small air gap between them. Specifically, the stator 10 is positioned to surround the iron core 22 of the rotor 20. In other words, the electric motor 1 is an inner rotor type motor in which the rotor 20 is positioned inside the stator 10.

[0025] The stator 10 generates a magnetic force that acts on the rotor 20. Specifically, the stator 10 is configured to have multiple alternating north and south poles so as to generate a magnetic flux at the air gap surface between the rotor 20 and the iron core 22. The stator 10, together with the rotor 20, constitutes a magnetic circuit.

[0026] The stator 10 includes an iron core 11, windings 12, and an insulator 13.

[0027] The iron core 11 of the stator 10 is an annular stator core that forms the core of the stator 10 and generates the magnetic force necessary to rotate the rotor 20. As shown in Figure 1, the iron core 11 is, for example, a laminate in which multiple steel plates are stacked in the direction of the axis C of the rotation shaft 21 of the rotor 20. Each of the multiple steel plates is, for example, a punched electrical steel sheet formed into a predetermined shape. The iron core 11 is not limited to a laminate of multiple steel plates, but may also be a bulk body made of a magnetic material.

[0028] As shown in Figure 3, the iron core 11 has a yoke 11a formed in an annular shape to surround the iron core 22 of the rotor 20, and a plurality of teeth 11b extending toward the rotor 20.

[0029] The yoke 11a is a back yoke formed on the outside of each tooth 11b. The yoke 11a is formed in an annular shape with axis C as the center.

[0030] Multiple teeth 11b protrude from the yoke 11a toward the rotation shaft 21. Specifically, the multiple teeth 11b extend radially in a direction perpendicular to the axis C of the rotation shaft 21 (radial direction). The multiple teeth 11b are arranged at equal intervals in the circumferential direction, forming slots 14 between any two adjacent teeth 11b. In other words, a slot 14 is located between each of the multiple teeth 11b. The iron core 11 is provided with 12 teeth 11b, and the number of slots 14 is 12. In other words, the number of slots in the electric motor 1 (stator 10) is 12.

[0031] Each tooth 11b is provided with an extended portion that extends from the inner circumferential tip of the tooth 11b to both sides in the circumferential direction. This extended portion is formed to protrude from the inner circumferential tip of the tooth 11b. The inner circumferential surface located at the tip of the tooth 11b, including this extended portion, becomes the magnetic pole surface facing the outer circumferential surface of the rotor 20. In two adjacent teeth 11b, a gap (slot opening) exists between the extended portion of one tooth 11b and the extended portion of the other tooth 11b.

[0032] Winding 12 is the armature winding of the stator 10. Winding 12 is a winding coil wound around the iron core 11 as a stator coil.

[0033] The windings 12 are wound around each of the multiple teeth 11b of the iron core 11. Specifically, the windings 12 are wound around each of the multiple teeth 11b via the insulator 13. In other words, multiple windings 12 are wound around the stator 10. Each winding 12 is a concentrated winding coil wound around a corresponding tooth 11b and is housed in a slot 14 of the iron core 11.

[0034] Each of the multiple teeth 11b is a magnetic pole tooth, and generates a magnetic force when energized in the winding 12. In this embodiment, the multiple windings 12 in the stator 10 are electrically connected as three-phase windings so that the rotor 20 rotates as a three-phase synchronous motor. Specifically, the multiple windings 12 are composed of three unit coils, U-phase, V-phase, and W-phase, each electrically 120 degrees out of phase with respect to the others. In other words, the windings 12 attached to each tooth 11b are energized and driven by three-phase alternating currents, each energized in its respective U-phase, V-phase, and W-phase units. This generates the main magnetic flux of the stator 10 in each tooth 11b.

[0035] The 12 windings 12, each wound around a 12 tooth 11b, are divided into four U-phase coils, four V-phase coils, and four W-phase coils, according to the phase of the current flowing through each winding 12, and arranged in predetermined slots 14. The four U-phase coils are electrically connected in series. Similarly, the four V-phase coils and the four W-phase coils are also electrically connected in series.

[0036] The insulator 13 is a coil bobbin and has a frame-shaped body around which the winding 12 is wound. Specifically, the frame of the insulator 13 is formed to surround the body of the teeth 11b. An insulator 13 is provided for each of the multiple teeth 11b. Each insulator 13 is a resin molded product integrally formed from, for example, an insulating resin material.

[0037] The rotor 20 rotates due to the magnetic force generated on the stator 10. The rotor 20 also generates magnetic force. Specifically, the rotor 20 has a configuration in which multiple N poles and S poles that generate magnetic flux are alternately repeated along the circumferential direction. As a result, the rotor 20 generates a magnetic force that acts on the stator 10. In this embodiment, the direction of the magnetic flux generated from the rotor 20 is perpendicular to the direction of the axis C of the rotation axis 21 (axial direction). In other words, the direction of the magnetic flux generated by the rotor 20 is radial.

[0038] The rotor 20 has a rotating shaft 21, an iron core 22, a plurality of permanent magnets 23, and a dielectric 24. The rotor 20 rotates around the axis C of the rotating shaft 21 as the center of rotation. In other words, the rotating shaft 21 is the center of rotation of the rotor 20.

[0039] The rotor 20 is a permanent magnet embedded rotor (IPM rotor) in which permanent magnets 23 are embedded in an iron core 22. Therefore, the electric motor 1 in this embodiment is an IPM motor.

[0040] The rotating shaft 21 has an axis C that is the center of rotation of the rotor 20. The rotating shaft 21 extends in the direction of axis C. The rotating shaft 21 is a long shaft, for example, a metal rod. The rotating shaft 21 is fixed to the iron core 22. Specifically, the rotating shaft 21 is inserted into a through hole provided in the center of the iron core 22 and fixed to the iron core 22 so as to extend on both sides of the iron core 22 along the direction of axis C. The rotating shaft 21 is fixed to the iron core 22 by, for example, press-fitting or shrink-fitting into the through hole of the iron core 22.

[0041] One portion 21a of the rotating shaft 21, which protrudes from one side of the iron core 22, is supported by the first bearing 41. On the other hand, the other portion 21b of the rotating shaft 21, which protrudes from the other side of the iron core 22, is supported by the second bearing 42. In other words, the first bearing 41 and the second bearing 42, as a pair of bearings, rotatably support the rotating shaft 21. In this way, the rotating shaft 21 is held in a rotatable state by the first bearing 41 and the second bearing 42. As a result, the rotor 20 is rotatable relative to the stator 10.

[0042] The first bearing 41 and the second bearing 42 are bearings. For example, the first bearing 41 and the second bearing 42 are ball bearings, but they may be other types of bearings such as thrust bearings.

[0043] In this embodiment, the end of the first portion 21a of the rotating shaft 21 is the output end and protrudes from the first bracket 61 and the first bearing 41. In other words, the first portion 21a of the rotating shaft 21 is the output shaft, and a load such as a rotating fan is attached to the end of the first portion 21a. The end of the rotating shaft 21 on the second portion 21b side is the non-output end and does not protrude from the second bracket 62 and the second bearing 42. The second portion 21b of the rotating shaft 21 is the non-output shaft.

[0044] The rotor core 22 of the rotor 20 is positioned with respect to the stator core 11 via an air gap. The core 22 is the rotor core, which is the core of the rotor 20. The core 22 is a laminate in which multiple steel plates are stacked in the direction of the axis C of the rotation shaft 21. Each of the multiple steel plates is, for example, a punched electrical steel sheet formed into a predetermined shape. The multiple steel plates are fixed to each other, for example, by crimping. Note that the core 22 is not limited to a laminate of multiple steel plates, but may also be a bulk body made of a magnetic material.

[0045] The iron core 22 has a plurality of magnet insertion holes 22a. Each of the plurality of magnet insertion holes 22a is a magnet embedding hole into which a permanent magnet 23 is embedded. The plurality of magnet insertion holes 22a are formed in the iron core 22 at equal intervals along the circumferential direction so as to surround the rotation axis 21. Each of the plurality of magnet insertion holes 22a extends in the direction of the axis C of the rotation axis 21.

[0046] Each of the multiple magnet insertion holes 22a has a permanent magnet 23 placed inside it. Specifically, one permanent magnet 23 is inserted into each magnet insertion hole 22a. The multiple permanent magnets 23 are arranged at equal intervals along the circumference surrounding the rotation axis 21, similar to the multiple magnet insertion holes 22a. Each permanent magnet 23 is a magnetized permanent magnet. The multiple permanent magnets 23 are arranged such that the magnetic poles, S and N, alternate in the circumferential direction of the rotor 20. In other words, two adjacent permanent magnets 23 have their S and N magnetic poles facing opposite directions.

[0047] In this embodiment, the iron core 22 is provided with 10 magnet insertion holes 22a, so 10 permanent magnets 23 are inserted into the iron core 22. Therefore, the rotor 20 has 10 poles (5 pole pairs). Regarding the magnetization of the permanent magnets 23, the permanent magnets 23 may be magnetized after being placed in the magnet insertion holes 22a, or they may be magnetized before being inserted into the magnet insertion holes 22a. However, considering the ease of inserting the permanent magnets 23 into the magnet insertion holes 22a, it is preferable to magnetize the permanent magnets 23 after they have been inserted into the magnet insertion holes 22a.

[0048] Each permanent magnet 23 is plate-shaped. Each permanent magnet 23 is a plate-shaped rectangular parallelepiped, and its shape in plan view is rectangular. Therefore, when the permanent magnet 23 is cut by a plane perpendicular to the axis C of the rotation axis 21, the cross-sectional shape of the permanent magnet 23 is rectangular. Each permanent magnet 23 is placed in the magnet insertion hole 22a such that its thickness direction is the radial direction of the iron core 22.

[0049] Each permanent magnet 23 is positioned within its corresponding magnet insertion hole 22a, closer to the radially outer (outer circumference) side of the iron core 22. The permanent magnets 23 inserted into the magnet insertion holes 22a may be fixed to the iron core 22 by adhesive, or they may be fixed to the iron core 22 by providing a separate fixing member having a projection that fills the gap between the permanent magnet 23 and the magnet insertion hole 22a.

[0050] The permanent magnet 23 is a rare-earth magnet. For example, the permanent magnet 23 is a neodymium rare-earth magnet whose main component is neodymium-iron-boron (Nd-Fe-B). Although the permanent magnet 23 is a sintered magnet, it may also be a bonded magnet.

[0051] The permanent magnet 23, which is a rare-earth magnet, is a high-density magnet, and the residual magnetic flux density (Br) of the permanent magnet 23 is 1.3T (Tesla) or higher. The residual magnetic flux density of the permanent magnet 23 is more preferably 1.33T or higher, and more preferably 1.4T or higher.

[0052] Furthermore, when the electric motor 1 is used in a high-temperature atmosphere such as a compressor, the coercivity (Hcj) of the permanent magnet decreases as the temperature rises. The coercivity of the permanent magnet 23 may be improved by adding dysprosium (Dy) to the rare-earth permanent magnet 23. However, while adding dysprosium to a rare-earth magnet improves its coercivity, it also reduces the residual magnetic flux density (Br) of the rare-earth magnet. For this reason, when adding dysprosium to the permanent magnet 23, it is preferable to add only a small amount of dysprosium. In this embodiment, the permanent magnet 23 does not contain dysprosium.

[0053] As shown in Figure 3, the outer circumferential surface of the iron core 22 of the rotor 20 has recesses 22b formed such that the portion between two adjacent permanent magnets 23 drops inward (i.e., toward the axis C). As a result, when viewed from the direction of the axis C of the rotation shaft 21, the iron core 22 has a shape in which each corresponding position of the multiple permanent magnets 23 at the outermost periphery bulges outward. In other words, when viewed from the direction of the axis C of the rotation shaft 21, the iron core 22 has a shape in which each bulge 22c resembles a flower petal. In this embodiment, since 10 permanent magnets 23 are provided on the iron core 22, 10 recesses 22b are formed on the outermost periphery of the iron core 22. On the outermost periphery of the iron core 22, bulges 22c are formed in which the portion corresponding to the magnetic pole center of each of the 10 permanent magnets 23 bulges outward. In other words, the rotor 20 is a petal rotor formed such that the iron core 22 has 10 petals.

[0054] Specifically, on a plane intersecting the axis C of the rotation axis 21, the outermost shape of the core 22 corresponding to each magnetic pole of the multiple permanent magnets 23 includes multiple arcs of different radii. In other words, in the bulge 22c (petal portion) corresponding to each permanent magnet 23, the outermost shape of the core 22 includes multiple arcs of different radii. The outermost shape of the core 22 in each bulge 22c includes a first arc and a second arc that are continuous via an inflection point. This inflection point is the connection point (boundary point) between the first arc and the second arc, and the first arc and the second arc form a single curve that is continuous via the inflection point.

[0055] The first arc is an arc that passes through a first point where a first straight line (i.e., the d-axis) passing through the center of the magnetic pole of the permanent magnet 23 and the axis C of the rotation axis 21 intersects the outermost circumference of the iron core 22. Specifically, the first arc is an arc that passes through the first point and connects two adjacent inflection points.

[0056] The second arc is an arc connecting the second point where a second straight line (i.e., the q-axis), which passes through the inter-pole centers of two adjacent permanent magnets 23 among the multiple permanent magnets 23 and the axis C of the rotation axis 21, intersects the outermost circumference of the iron core 22, and the inflection point.

[0057] The outermost shape of the core 22 at each bulge 22c is composed of one first arc and two second arcs. In other words, the outermost shape of the core 22 corresponding to one magnetic pole of each permanent magnet 23 is composed of one first arc and two second arcs. Specifically, the outermost shape of the core 22 at each bulge 22c (one magnetic pole of each permanent magnet 23) has two inflection points, and is configured such that one first arc is sandwiched between two second arcs.

[0058] In this embodiment, the center of the first arc is the axis C of the rotation axis 21. That is, if the radius of the first arc is R1, then the first arc is an arc with radius R1 and rotation centered at axis C. Therefore, the first arc is a part of the circle that forms the maximum diameter of the iron core 22.

[0059] On the other hand, the center of the second arc is located not at the axis C of the rotation axis 21, but between the axis C and the outermost edge (outer part) of the core 22. The second arc is an arc that forms a recess 22b by recessing a part of the circle that makes up the maximum diameter of the core 22 toward the axis C. In other words, by providing the second arc, a part of the outermost part of the core 22 can be recessed.

[0060] In this embodiment, the center of the second arc is a point located on the line segment connecting the inflection point, which is the boundary point between the first and second arcs, and the axis C of the axis of rotation 21. In other words, if the radius of the second arc is R2, then the second arc is an arc with radius R2 and this point as its center of rotation.

[0061] As shown in Figures 1 and 3, the dielectric 24 is provided between the rotating shaft 21 and the outer surface of the iron core 22. As shown in Figure 3, when viewed from the direction of the axis C of the rotating shaft 21, the dielectric 24 is an annular shape surrounding the rotating shaft 21. Also, as shown in Figure 1, the dielectric 24 extends in the direction of the axis C of the rotating shaft 21. The dielectric 24 is formed of an insulating material such as an insulating resin material. Therefore, the dielectric 24 insulates and separates the iron core 22 in series into an outer core and an inner core, with the dielectric 24 as the boundary. As the material of the dielectric 24, for example, thermosetting resins such as unsaturated polyester resin or epoxy resin, thermoplastic resins such as polybutylene terephthalate or polyamide, and elastic materials such as elastomers or vulcanized rubber can be used.

[0062] In this way, by providing a dielectric 24 on the rotor 20, the equivalent circuit on the rotor 20 side is configured with the capacitance of the dielectric 24 connected in series, which increases the impedance on the rotor 20 side. As a result, the potential difference between the inner ring and the outer ring of the first bearing 41 and the second bearing 42, i.e., the shaft voltage, can be lowered, and thus the occurrence of electrolytic corrosion in the first bearing 41 and the second bearing 42 can be suppressed.

[0063] As shown in Figure 3, the dielectric 24 is a polygonal ring shape centered on the rotation axis 21 when viewed from the direction of the axis C of the rotation axis 21. By making the dielectric 24 polygonal in this way, it is possible to prevent the inner core and outer core of the iron core 22, which are separated by the dielectric 24, from free-spinning due to the rotation of the rotor 20.

[0064] In this embodiment, the number of angles and sides of the polygon of the dielectric 24 is preferably the same as the number of permanent magnets 23, so the dielectric 24 is a regular decagonal ring. By making the number of angles of the polygon of the dielectric 24 the same as the number of magnetized poles of the permanent magnets 23 held in the rotor 20, the imbalance caused by the rotation of the rotor 20 can be minimized.

[0065] The vertices of the polygonal corners of the dielectric 24 are located at the centers of the magnetized poles of the permanent magnets 23 held by the rotor 20, with respect to the rotation axis 21. This allows the dielectric 24 to be positioned without obstructing the flow of magnetic flux generated from the permanent magnets 23. Furthermore, rounding (R) the vertices of the polygonal corners of the dielectric 24 improves the machinability of the iron core 22.

[0066] As shown in Figure 1, the stator 10 is covered with molded resin 30. The molded resin 30 covers the outer portion of the stator 10 around its entire circumference. Specifically, the molded resin 30 covers the outer portions of the iron core 11, the windings 12, and the insulator 13. In this embodiment, the molded resin 30 is in contact with the outer surfaces of the windings 12 and the insulator 13, respectively.

[0067] The mold resin 30 is formed from an insulating resin material with excellent thermal conductivity, such as polyester resin or epoxy resin. Alternatively, the mold resin 30 can be formed from a thermosetting resin. In this embodiment, the mold resin 30 is formed from an unsaturated polyester, which is a thermosetting resin. Specifically, the mold resin 30 is formed from a white BMC (Bulk Molding Compound) unsaturated polyester resin.

[0068] The molded resin 30 constitutes the outer casing of the electric motor 1, and the outer surface of the molded resin 30 includes exposed surfaces. Specifically, the outer circumferential surface, which is the side surface of the molded resin 30, and the upper surface on the first bracket 61 side are exposed. Furthermore, the molded resin 30 covering the stator 10 constitutes a housing that encloses the rotor 20. A printed circuit board to which the windings 12 of the stator 10 are connected may be arranged inside this housing.

[0069] As shown in Figures 1 and 2, the molded resin 30 has a main body 31 that forms the body of the electric motor 1 and protrusions 32 provided on the main body 31. Multiple protrusions 32 are provided on the main body 31. Specifically, as shown in Figure 2, four protrusions 32 are provided at equal intervals along the circumferential direction. The main body 31 and the protrusions 32 are integrated into a single molded resin 30 by molding.

[0070] As shown in Figure 1, the main body 31 covers the stator 10. Specifically, the main body 31 covers the iron core 11, the windings 12, and the insulator 13.

[0071] The protruding portion 32 projects outward in the radial direction. Specifically, the protruding portion 32 projects outward from the side surface of the main body portion 31. The protruding portion 32 is a leg portion of the electric motor 1 and functions as a mounting portion for attaching the electric motor 1 to an external device or the like. The protruding portion 32 is provided with a through hole for inserting a screw or the like.

[0072] As shown in Figure 1, a heat sink 50 is positioned on one side of the molded resin 30 in the direction of the axis C of the rotating shaft 21. As shown in Figure 2, the heat sink 50 has a plurality of fins 51. The heat sink 50 is made of, for example, aluminum, but may be made of a metal material other than aluminum.

[0073] A first bracket 61 is fixed to one side of the molded resin 30 in the direction of the axis C of the rotating shaft 21. A second bracket 62 is fixed to the other end of the molded resin 30 in the direction of the axis C of the rotating shaft 21. The first bracket 61 holds the first bearing 41. The first bearing 41 is fixed to a recess in the first bracket 61. The second bracket 62 holds the second bearing 42. The second bearing 42 is fixed to the second bracket 62.

[0074] The first bracket 61 and the second bracket 62 are made of a metal material such as iron. For example, the first bracket 61 and the second bracket 62 are made of a metal plate of a constant thickness. The first bracket 61 and the second bracket 62 are fixed to the molded resin 30.

[0075] In the electric motor 1 configured in this way, when current is supplied to the windings 12 of the stator 10, a field current flows through the windings 12, generating a magnetic field. This generates a magnetic flux from the stator 10 toward the rotor 20. Specifically, a magnetic flux is generated from each of the teeth 11b of the iron core 11 of the stator 10 toward the iron core 22 of the rotor 20. Meanwhile, in the rotor 20, a magnetic flux is generated passing through the stator 10 by the permanent magnets 23 embedded in the iron core 22. The magnetic force generated by the interaction between the magnetic flux generated in the stator 10 and the magnetic flux generated from the permanent magnets 23 of the rotor 20 becomes a torque that rotates the rotor 20, causing the rotor 20 to rotate.

[0076] The electric motor 1 in this embodiment is used, for example, in an air conditioner or other air conditioning unit. Specifically, the electric motor 1 is mounted on the compressor of the outdoor unit of the air conditioner as a fan motor with a rotating fan attached to a rotating shaft 21.

[0077] Next, the effects and advantages of the electric motor 1 according to this embodiment will be explained, including the background leading to the technology disclosed herein.

[0078] Conventionally, a technique using high-energy-density rare-earth magnets as permanent magnets in IPM motors is known. This can improve the output and efficiency of IPM motors.

[0079] On the other hand, in IPM motors, the magnetic attractive force differs depending on the rotor's rotational position due to the magnetic flux generated from the permanent magnets held in the rotor's core. As a result, a torque pulsation called cogging torque occurs when the rotor rotates. Therefore, when an IPM motor is used as a fan motor, the cogging torque can cause vibrations and noise, as well as a decrease in output and efficiency.

[0080] In this case, increasing the number of rotor poles to suppress cogging torque increases the harmonic components of the IPM motor's drive current. For example, in conventional IPM motors using rare-earth magnets, increasing the number of rotor poles to 10 or more significantly increases the harmonic components. Therefore, conventional IPM motors using rare-earth magnets had to limit the number of rotor poles to 8 or less. Consequently, there were limitations to suppressing vibrations due to cogging torque and preventing a decrease in output and efficiency by increasing the number of rotor poles.

[0081] Therefore, in order to increase output and efficiency, it is conceivable to use rare earth magnets with high residual magnetic flux density (Br). However, in IPM motors, using rare earth magnets with high residual magnetic flux density (e.g., Br≧1.3T) increases vibration and noise. For this reason, conventional fan motors equipped with IPM motors using rare earth magnets had no choice but to use rare earth magnets with low residual magnetic flux density (e.g., Br<1.3T).

[0082] Thus, in conventional IPM motors using rare-earth magnets, various factors are intricately intertwined, making it difficult to achieve both vibration and noise suppression and high output and high efficiency.

[0083] Therefore, the inventors of the present invention diligently studied this problem and were able to arrive at a configuration for an electric motor 1 that can achieve both vibration and noise suppression and high output and high efficiency, even with an IPM motor using rare earth magnets.

[0084] Specifically, in the electric motor 1 according to this embodiment, first, a rare earth magnet with a residual magnetic flux density of 1.3T or more (Br≧1.3T) is used as the permanent magnet 23 placed in the magnet insertion hole 22a of the iron core 22 of the rotor 20. This makes it possible to improve the output and efficiency of the electric motor 1.

[0085] On the other hand, when using rare-earth magnets with a residual magnetic flux density of 1.3T or higher, vibration and noise increase when the electric motor 1 is used as a fan motor.

[0086] Therefore, in the electric motor 1 according to this embodiment, the number of poles of the rotor 20 is set to 10 or more. This suppresses cogging torque, and thus suppresses vibration and noise caused by cogging torque. In other words, the increase in vibration and noise caused by using rare earth magnets with a residual magnetic flux density of 1.3T or more as permanent magnets 23 can be offset by setting the number of poles of the rotor 20 to 10 or more.

[0087] Furthermore, the output and efficiency can be improved by increasing the number of poles of the rotor 20 to 10 or more. In other words, in addition to the fact that the output and efficiency can be improved by using a rare earth magnet with a residual magnetic flux density of 1.3T or more as the permanent magnet 23, the output and efficiency can be further improved.

[0088] On the other hand, if the number of poles of the rotor 20 is increased to 10 or more, the harmonic components of the drive current of the motor 1 increase. Therefore, in the motor 1 according to this embodiment, the outermost shape of the iron core 22 corresponding to each magnetic pole of the plurality of permanent magnets 23 is configured to include a plurality of circular arcs with different radii. In other words, when viewed from the direction of the axis C of the rotating shaft 21, the iron core 22 is configured to have a plurality of bulging portions 22c like petals.

[0089] This configuration allows the deviation of the magnetic flux density distribution from an ideal sinusoidal shape to be reduced, thereby reducing the amplitude of induced voltage harmonics at almost all orders. Therefore, the increase in harmonic components due to having 10 or more poles in the rotor 20 can be offset by shaping the iron core 22 of the rotor 20 into a petal shape.

[0090] Thus, according to this embodiment, the electric motor 1, while being an IPM motor using rare earth magnets, can achieve high output and high efficiency while suppressing the increase in harmonic components of the electric drive current, suppressing cogging torque, and thus suppressing vibration and noise. Therefore, even with an IPM motor using rare earth magnets, it is possible to realize an electric motor 1 that can achieve both vibration and noise suppression and high output and high efficiency.

[0091] Furthermore, in the electric motor 1 according to this embodiment, the residual magnetic flux density of the permanent magnet 23, which is a rare earth magnet, is preferably 1.4T or higher.

[0092] This makes it possible to further increase the output and efficiency of the electric motor 1 while maintaining the suppression of vibration and noise.

[0093] Furthermore, in the electric motor 1 according to this embodiment, the permanent magnet 23, which is a rare earth magnet, does not contain dysprosium.

[0094] This configuration allows for an improvement in the residual magnetic flux density of the permanent magnet 23 compared to the case where dysprosium is added to the permanent magnet 23, thereby further improving the output and efficiency of the electric motor 1. Moreover, since dysprosium is expensive and difficult to obtain, by not using dysprosium, an electric motor 1 that can achieve both vibration and noise suppression and high output and high efficiency can be manufactured at low cost and easily.

[0095] Furthermore, the electric motor 1 according to this embodiment includes a molded resin 30 that covers the stator 10.

[0096] This configuration further suppresses vibration and noise. Therefore, it is possible to realize an electric motor 1 with even lower vibration and noise, as well as higher output and higher efficiency.

[0097] In this case, the molded resin 30 may have a protruding portion 32 that protrudes outward from the side surface of the main body portion 31 that covers the stator 10.

[0098] This configuration allows for an increase in the natural frequency of the electric motor 1, thereby suppressing vibration and noise from the electric motor 1.

[0099] Furthermore, in the rotor 20 of the electric motor 1 according to this embodiment, a dielectric 24 is provided between the rotating shaft 21 and the outer circumferential surface of the iron core 22.

[0100] This configuration allows the rotor 20 to have a double-insulated structure, thereby increasing the impedance on the rotor side. This reduces the potential difference (shaft voltage) between the inner and outer rings of the first bearing 41 and the second bearing 42, thus suppressing the occurrence of electrolytic corrosion in the first bearing 41 and the second bearing 42.

[0101] Here, we conducted an experiment to actually measure the cogging torque of the comparative motor and the example motor, and the measurement results will be explained using Figures 4A and 4B. Figure 4A is a diagram showing the relationship between the rotor position angle and torque in the comparative motor. Figure 4B is a diagram showing the relationship between the rotor position angle and torque in the example motor. In Figures 4A and 4B, the horizontal axis shows the mechanical angle A (deg) of the rotor, and the vertical axis shows the torque (unit: mN·m).

[0102] In this experiment, the motor 1 according to this embodiment, shown in Figures 1 to 3, was used as the motor for the embodiment. Specifically, the motor in the embodiment is a 10-pole, 12-slot (10P12S) IPM motor, with 10 poles on the rotor 20 and 12 slots on the stator 10. A neodymium rare-earth magnet with a residual magnetic flux density (Br) of 1.41T was used as the permanent magnet 23. It should be noted that when using a 10-pole, 12-slot IPM motor, suppression of cogging torque can be expected even when using a neodymium rare-earth magnet with a residual magnetic flux density of 1.5T.

[0103] On the other hand, the comparative example motor used an 8-pole, 12-slot (8P12S) IPM motor, which is the same as the motor 1 according to this embodiment shown in Figures 1 to 3, but with the number of poles of the rotor 20 changed to 8 poles. In the comparative example motor, a neodymium rare-earth magnet with a residual magnetic flux density of 1.28 was used as the permanent magnet 23. Except for the number of poles of the rotor 20 and the residual magnetic flux density of the permanent magnet 23, the comparative example motor and the motor of the embodiment are the same.

[0104] Furthermore, the torque of the electric motor was measured by rotating the rotor 20 with an external rotation speed of 1 r / min. The results are shown in Figures 4A and 4B.

[0105] As shown in Figure 4A, the comparative example motor (8P12S) had a maximum cogging torque range of 40.9 mN·m. On the other hand, as shown in Figure 4B, the example motor (10P12S) had a maximum cogging torque range of 20.9 mN·m. Thus, it was confirmed that the example motor could significantly reduce cogging torque compared to the comparative example motor.

[0106] As described above, the electric motor 1 according to this embodiment comprises a rotor 20 having an iron core 22 to which a rotating shaft 21 extending in the axial direction is fixed, and a stator 10 arranged opposite the rotor 20. The stator 10 has a plurality of teeth 11b extending toward the rotor 20, and slots 14 located between adjacent teeth 11b. The iron core 22 has a plurality of magnet insertion holes 22a and a plurality of permanent magnets 23 arranged in each of the magnet insertion holes 22a. The plurality of permanent magnets 23 are rare earth magnets, and the outermost shape of the iron core 22 corresponding to each magnetic pole of the plurality of permanent magnets 23 includes a plurality of arcs with different radii. The rotor 20 has 10 or more poles, and the residual magnetic flux density of the permanent magnets 23 is 1.3T or more.

[0107] This makes it possible to achieve both vibration and noise suppression and high output and high efficiency in IPM motors using rare earth magnets.

[0108] Furthermore, it is preferable that the rotor has 10 poles and the stator 10 has 12 slots 14.

[0109] Furthermore, the residual magnetic flux density of the permanent magnet 23 is preferably 1.4T or higher.

[0110] Furthermore, the stator 10 may also be covered with a molded resin 30.

[0111] Furthermore, the molded resin 30 may have a main body portion 31 that covers the stator 10 and a protruding portion 32 that protrudes outward from the side surface of the main body portion 31.

[0112] Furthermore, rare earth magnets do not necessarily need to contain dysprosium.

[0113] Furthermore, the rotating shaft 21 may be rotatably supported by a bearing, and a dielectric material may be provided between the rotating shaft 21 and the outer surface of the iron core.

[0114] (modified version) Although the electric motor 1 relating to this disclosure has been described above based on embodiments, this disclosure is not limited to the above embodiments.

[0115] For example, in the above embodiment, the number of poles of the rotor 20 is set to 10 (i.e., the number of permanent magnets 23 is 10), but this is not the only option. Any number of poles of 10 or more can be applied to the rotor 20.

[0116] Furthermore, although the number of slots in the stator 10 was 12 in the above embodiment, it is not limited to this. Any number of slots can be applied to the stator 10.

[0117] Furthermore, in the above embodiment, the windings 12 of the stator 10 were wound around the iron core 11 in a concentrated winding manner, but this is not the only possible configuration. For example, the windings 12 of the stator 10 may be wound around the iron core 11 in a distributed winding manner.

[0118] Furthermore, although the above embodiment describes the case in which the electric motor 1 is applied to the fan motor of an air conditioner, it is not limited to this. For example, the electric motor 1 in the above embodiment can be used in various electrical devices such as household electrical appliances such as vacuum cleaners or refrigerators, or industrial electrical appliances such as automotive equipment or robots.

[0119] Furthermore, this disclosure also includes forms that can be obtained by applying various modifications to the above embodiments that a person skilled in the art could conceive, as well as forms that can be realized by arbitrarily combining the components and functions of the above embodiments without departing from the spirit of this disclosure. [Industrial applicability]

[0120] The electric motor described herein can be widely used in various fields, including fan motors used in air conditioners and the like, and in equipment equipped with electric motors. [Explanation of Symbols]

[0121] 1 electric motor 10 Stator 11 Iron Heart 11a York 11b Teeth 12 windings 13 Insulators 14 slots 20 rotors 21 Rotation axis 21a Part 1 21b 2nd part 22 Iron Heart 22a Magnet insertion hole 22b Recess 22c bulge 23 Permanent Magnets 24 Dielectrics 30 mold resin 31 Main body 32 Protrusion 41 First bearing 42 Second bearing 50 Heatsink 51 Fins 61 First bracket 62 Second bracket

Claims

1. The system comprises a rotor having an iron core to which a rotating shaft extending in the axial direction is fixed, and a stator positioned opposite the rotor, The stator has a plurality of teeth extending toward the rotor, and slots located between adjacent teeth among the plurality of teeth, The iron core has a plurality of magnet insertion holes formed at equal intervals along the circumferential direction so as to surround the rotation axis with the circumferential direction as the longitudinal direction, a plurality of permanent magnets arranged in each of the plurality of magnet insertion holes, and a single recess formed on the outer circumferential surface such that the portion between each of the plurality of permanent magnets falls inward. The aforementioned multiple permanent magnets are rare-earth magnets, The outermost shape of the core corresponding to each magnetic pole of the plurality of permanent magnets is composed of one first arc and two second arcs, the first arc and the second arcs having different radii, and the first arc and the two second arcs form a single continuous curve having two inflection points. The first arc is an arc centered on the axis, passing through a first point where a first straight line passing through the center of each of the magnetic poles of the plurality of permanent magnets and the axis of the rotation axis intersects the outermost circumference of the iron core. The second arc is an arc connecting a second point where a second straight line passing through the inter-pole centers of two adjacent permanent magnets among the plurality of permanent magnets and the axis of the rotation axis intersects the outermost circumference of the iron core, and an inflection point, with the center of the second arc being a point located on the line segment connecting the inflection point, which is the boundary point between the first arc and the second arc, and the axis of the rotation axis. The rotor has 10 or more poles. An electric motor in which the residual magnetic flux density of the permanent magnet is 1.3 T or more.

2. The electric motor according to claim 1, wherein the rotor has 10 poles and the stator has 12 slots.

3. The electric motor according to claim 1 or 2, wherein the residual magnetic flux density of the permanent magnet is 1.4 T or more.

4. Furthermore, the electric motor according to any one of claims 1 to 3, comprising a molded resin covering the stator.

5. The electric motor according to claim 4, wherein the molded resin has a main body portion that covers the stator and a protruding portion that protrudes outward from the side surface of the main body portion.

6. The electric motor according to any one of claims 1 to 5, wherein the rare earth magnet does not contain dysprosium.

7. Furthermore, the electric motor according to any one of claims 1 to 6, further comprising a bearing that rotatably supports the rotating shaft, and a dielectric material provided between the rotating shaft and the outer circumferential surface of the iron core.

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