Rotor and motor

Abstract

Provided is a rotor and an electric motor capable of reducing torque ripple. The rotor comprises: a rotor core (20) having a plurality of magnet placement holes (21); a plurality of permanent magnets (30) respectively placed inside the plurality of magnet placement holes (21); and a rotating shaft (10) fixed to the rotor core (20). The plurality of magnet placement holes (21) are radially provided about the rotating shaft (10), and the permanent magnets (30) are each provided with a projection portion (32) at a corner portion (30a) in a plan view.

Description

Technical Field

[0001] The present disclosure relates to a rotor and a motor used in various devices such as household electric appliances and industrial devices.

Background Art

[0002] Motors are used in various electric appliances such as household appliances or industrial devices. As a motor, an IPM (Interior Permanent Magnet) motor is known. The rotor of an IPM motor includes, for example, a rotor core, permanent magnets disposed in respective ones of a plurality of magnet arrangement holes provided in the rotor core, and a rotating shaft fixed to the center of the rotor core so as to penetrate the rotor core. In an IPM motor, torque for rotating the rotor is generated by passing magnetic flux generated by the permanent magnets of the rotor through the stator.

[0003] Conventionally, as this type of motor, an IPM motor including a rotor in which a plurality of magnet arrangement holes of a rotor core are provided radially is known (Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] In a conventional rotor, in order to improve the insertability of a permanent magnet into a magnet arrangement hole, a predetermined space may be provided between the rotor core and the permanent magnet. In this case, when the permanent magnet is inserted into the magnet arrangement hole, the arrangement position of the permanent magnet in the magnet arrangement hole may vary. As a result, since the difference in the magnetic flux density amount between the magnetic poles of each permanent magnet and other permanent magnets becomes large, there has been a problem that the cogging torque becomes large.

[0006] This disclosure aims to solve the above-mentioned problems and to provide a rotor and motor that can reduce cogging torque.

[0007] A rotor according to a first aspect of the present disclosure comprises a rotor core having a plurality of magnet arrangement holes, a plurality of permanent magnets each disposed inside the plurality of magnet arrangement holes, and a rotating shaft fixed to the rotor core, wherein each of the plurality of permanent magnets has a protrusion at its corner in a plan view.

[0008] In the first embodiment, the rotor according to the second aspect of the present disclosure has an arc-shaped outer surface of the projection.

[0009] In the third aspect of the present disclosure, in the second aspect, the corners of the inner surfaces of each of the plurality of magnet arrangement holes are arc-shaped, and the radius of curvature of the outer surface of the protrusion is greater than the radius of curvature of the corners of the inner surfaces of the magnet arrangement holes.

[0010] In the electric motor according to the fourth aspect of this disclosure, in any of the first to third aspects, the plurality of magnet arrangement holes are arranged radially around the axis of rotation.

[0011] In the fifth aspect of the present disclosure, the electric motor, in any of the first to fourth aspects, has a permanent magnet surface covered with a coating layer made of resin or metal, and a protruding portion is made of the coating layer.

[0012] An electric motor according to the sixth aspect of this disclosure comprises a rotor according to any of the first to fifth aspects and a stator positioned opposite the rotor and generating a magnetic force acting on the rotor.

[0013] According to this disclosure, it is possible to provide a rotor and an electric motor that can reduce cogging torque. [Brief explanation of the drawing]

[0014] [Figure 1] Perspective view of an electric motor according to one embodiment of the present disclosure [Figure 2] Perspective view of the rotor of the electric motor. [Figure 3] Plan view of the main part of the rotor of the electric motor. [Figure 4] Enlarged plan view of the main part of the rotor of the electric motor. [Modes for carrying out the invention]

[0015] 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.

[0016] Furthermore, each figure is a schematic diagram and not necessarily a strictly accurate representation. Note that in each figure, components substantially identical to those in other figures are denoted by the same reference numerals, and redundant explanations are omitted or simplified.

[0017] (Embodiment) First, the general configuration of the electric motor 1 according to the embodiment will be explained using Figure 1. Figure 1 is a perspective view of the electric motor 1 according to the embodiment.

[0018] As shown in Figure 1, the electric motor 1 comprises a rotor 2 and a stator 3. In this embodiment, the electric motor 1 is an inner rotor type motor in which the rotor 2 is positioned inside the stator 3. In other words, the stator 3 is configured to surround the rotor 2.

[0019] The rotor 2 rotates due to the magnetic force generated on the stator 3. Specifically, the rotor 2 has a rotation shaft 10, and rotates around the axis C of the rotation shaft 10 as the center of rotation.

[0020] The rotor 2 generates a magnetic force acting on the stator 3. The rotor 2 is configured such that a plurality of N poles and S poles that become main magnetic fluxes repeatedly exist over the circumferential direction. In the present embodiment, the direction of the main magnetic flux generated by the rotor 2 is a direction orthogonal to the direction of the axis C of the rotation axis 10 (rotation axis direction). That is, the direction of the main magnetic flux generated by the rotor 2 is the radial direction (diameter direction).

[0021] The rotor 2 is arranged via an air gap with respect to the stator 3. Specifically, a minute air gap exists between the surface of the rotor 2 and the surface of the stator 3. Although details will be described later, the rotor 2 is a permanent magnet embedded type rotor (IPM rotor) in which a permanent magnet is embedded in an iron core. Therefore, the motor 1 in the present embodiment is an IPM motor.

[0022] The stator 3 (stator) is arranged to face the rotor 2 via an air gap and generates a magnetic force acting on the rotor 2. Specifically, the stator 3 is arranged so as to surround the rotor core 20 of the rotor 2. The stator 3 constitutes a magnetic circuit together with the rotor 2.

[0023] The stator 3 is configured such that N poles and S poles are alternately generated as main magnetic fluxes in the circumferential direction on the air gap surface. In the present embodiment, the stator 3 has a stator core 3a (stator core) and a winding coil 3b (stator coil).

[0024] A plurality of teeth 3a1 protruding toward the rotor core 20 of the rotor 2 are provided on the stator core 3a. Specifically, the plurality of teeth 3a1 are provided so as to protrude toward the axis C of the rotation axis 10. Also, the plurality of teeth 3a1 are provided at equal intervals in the circumferential direction. Therefore, the plurality of teeth 3a1 extend radially in a direction orthogonal to the axis C of the rotation axis 10 (radial direction).

[0025] The stator core 3a is composed of, for example, multiple steel plates stacked in the direction of the axis C of the rotation shaft 10. Each of the multiple steel plates is, for example, an electromagnetic steel plate punched into a predetermined shape. Note that the stator core 3a is not limited to a stack of multiple steel plates, but may also be a bulk body made of magnetic material.

[0026] The winding coils 3b are wound around each of the multiple teeth 3a1 of the stator core 3a. Specifically, the winding coils 3b are wound around each tooth 3a1 via an insulator. Each winding coil 3b consists of three unit coils for the U, V, and W phases, which are electrically 120 degrees out of phase with respect to each other. In other words, the winding coils 3b wound around each tooth 3a1 are driven by three-phase alternating currents, which are energized separately for the U, V, and W phases. This generates the main magnetic flux of the stator 3 at each tooth 3a1.

[0027] The winding coil 3b is composed of a circular or rectangular winding made of a metal material such as copper, with an insulating coating on its surface.

[0028] In the electric motor 1 configured in this way, when current is supplied to the winding coil 3b of the stator 3, a field current flows through the winding coil 3b, generating a magnetic field. This generates a magnetic flux from the stator 3 toward the rotor 2. On the other hand, the rotor 2 generates a magnetic flux toward the stator 3. In other words, the permanent magnets of the rotor 2 generate a magnetic flux passing through the stator 3. The magnetic force generated by the interaction between the magnetic flux generated in the stator 3 and the magnetic flux generated in the rotor 2 becomes the torque that rotates the rotor 2, causing the rotor 2 to rotate around the rotation axis 10.

[0029] Next, the detailed configuration of the rotor 2 according to this embodiment will be described with reference to Figure 1, and using Figures 2 and 3. Figure 2 is a perspective view of the rotor 2 according to this embodiment. Figure 3 is a plan view of the main part of the rotor 2 according to this embodiment. The rotating shaft 10 is omitted in Figures 2 and 3.

[0030] As shown in Figures 1 to 3, the rotor 2 comprises a rotating shaft 10, a rotor core 20, and a plurality of permanent magnets 30.

[0031] The rotating shaft 10 is a long shaft that serves as the center when the rotor 2 rotates. The rotating shaft 10 is, for example, a metal rod and is fixed to the center of the rotor 2. Specifically, the rotating shaft 10 is fixed to the rotor core 20. In this embodiment, the rotating shaft 10 is fixed to the rotor core 20 in such a way that it protrudes from both sides of the rotor 2 and passes through the center of the rotor core 20. The rotating shaft 10 is fixed to the rotor core 20 by press-fitting or shrink-fitting into a through hole 20a formed in the center of the rotor core 20.

[0032] Although not shown in the diagram, the first portion of the rotating shaft 10 protruding from one side of the rotor 2 is supported by a first bearing, and the second portion of the rotating shaft 10 protruding from the other side of the rotor 2 is supported by a second bearing. A load driven by the electric motor 1 is attached to either the first or second portion of the rotating shaft 10.

[0033] The rotor core 20 is composed of, for example, multiple steel plates stacked in the direction of the axis C of the rotating shaft 10. Each of the multiple steel plates is, for example, an electromagnetic steel plate punched into a predetermined shape, and they are fixed to each other by crimping or the like. Note that the rotor core 20 is not limited to a stack of multiple steel plates, but may also be a bulk body made of magnetic material.

[0034] The rotor core 20 is a core having multiple magnet placement holes 21. The multiple magnet placement holes 21 are holes for magnet arrangement where permanent magnets 30 are placed. Specifically, permanent magnets 30 are inserted into the magnet placement holes 21. In other words, the magnet placement holes 21 are magnet insertion holes into which permanent magnets 30 are inserted. One permanent magnet 30 is inserted into each magnet placement hole 21. As an example, the rotor 2 is a 10-pole rotor with 10 magnetic poles. Therefore, the rotor core 20 is provided with 10 magnet placement holes 21 and 10 permanent magnets 30. However, this is not limited to this, and it can be applied to other numbers of magnetic poles as well.

[0035] Furthermore, in this embodiment, the magnet placement holes 21 are through holes that penetrate the rotor core 20 along the direction of the axis C of the rotation axis 10. Therefore, in any cross-section when cut with a plane perpendicular to the rotation axis 10, the cross-sectional shape of the magnet placement holes 21 is the same in the direction of the axis C of the rotation axis 10. In other words, all the steel plates constituting the rotor core 20 have magnet placement holes 21 of the same shape formed therein. Note that the magnet placement holes 21 do not have to be through holes, as long as permanent magnets 30 can be placed in them.

[0036] As shown in Figures 1 and 2, the multiple magnet placement holes 21 are arranged radially around the rotation axis 10. Furthermore, the multiple magnet placement holes 21 are arranged at equal intervals along the circumferential direction of the rotor core 20 (the rotation direction of the rotation axis 10). Each of the multiple magnet placement holes 21 extends in the radial direction of the rotor core 20 (the direction perpendicular to the axis C of the rotation axis 10) in a plan view. In other words, the magnet placement holes 21 are elongated in the radial direction of the rotor core 20, with their radial length being longer than their rotational (circumferential) length. Alternatively, the magnet placement holes 21 could be elongated in the rotational (circumferential) direction of the rotor core 20, with their rotational (circumferential) length being longer than their radial length.

[0037] Multiple elongated magnet placement holes 21 are formed in a spoke-like manner around the rotation axis 10. In other words, the rotor 2 is a spoke-type IPM rotor, and the electric motor 1 is a spoke-type IPM motor. In this embodiment, the plan view shape of each magnet placement hole 21 is approximately rectangular, with the radial direction of the rotor core 20 as the longitudinal direction. Furthermore, the plan view shapes of the multiple magnet placement holes 21 are the same as those of each other.

[0038] As shown in Figure 2, a permanent magnet 30 is inserted into each of the magnet placement holes 21 of the rotor 2 along the direction of the axis C of the rotation shaft 10, so that a permanent magnet 30 is placed in each of the multiple magnet placement holes 21. In this embodiment, the permanent magnet 30 is inserted from above (above the plane of the paper) the axis C of the rotation shaft 10, but the permanent magnet 30 may also be inserted from below (below the plane of the paper).

[0039] In this embodiment, the permanent magnet 30 is, for example, a sintered magnet. The multiple permanent magnets 30 are arranged so that the direction of their magnetic poles is in the circumferential direction of the rotor core 20 (the rotation direction of the rotation axis 10). In other words, the permanent magnets 30 are magnetized so that the direction of their magnetic poles is in the circumferential direction of the rotor core 20. Note that two adjacent permanent magnets 30 have their S pole and N pole directions opposite.

[0040] The plan view shape and size of the permanent magnet 30 are approximately the same as the plan view shape and size of the magnet placement hole 21, and the permanent magnet 30 is fitted into the magnet placement hole 21. Therefore, the plan view shape of the permanent magnet 30 is a long, roughly rectangular shape. As an example, the permanent magnet 30 is a plate-shaped rectangular parallelepiped with thickness in the direction perpendicular to the radial direction of the rotor core 20. Note that the permanent magnet 30 in each magnet placement hole 21 may be divided into multiple parts.

[0041] In each magnet placement hole 21, a gap (space, clearance) of a certain size exists between the outer surface of the permanent magnet 30 and the inner surface of the magnet placement hole 21. Adhesive may be provided in this gap to bond and fix the permanent magnet 30 to the magnet placement hole 21. On the other hand, adhesive may not be provided in this gap.

[0042] The permanent magnet 30 is composed of, for example, an Nd-Fe-B sintered magnet or a ferrite sintered magnet. Alternatively, it may be a bonded magnet formed from magnet powder such as Nd-Fe-B magnet powder or ferrite magnet powder, a resin material, and a small amount of additives.

[0043] Regarding the magnetization of the permanent magnet 30, it is possible to magnetize the permanent magnet 30 after placing it in the magnet placement hole 21, or to magnetize it before inserting it into the magnet placement hole 21. However, considering the ease of inserting the permanent magnet 30 into the magnet placement hole 21, it is preferable to magnetize the permanent magnet 30 after inserting it into the magnet placement hole 21.

[0044] Furthermore, the permanent magnet 30 is covered with a resin coating material to form a coating layer 31, which covers the periphery of the permanent magnet 30.

[0045] As shown in Figure 3, each permanent magnet 30 has a projection 32 at each of its four corners 30a in a plan view (viewed from the direction of the axis C of the rotation axis 10). The outer surface of each projection 32 is arc-shaped. The projections 32 protrude from the permanent magnet 30 along a line connecting the center of the permanent magnet 30 and the corners 30a in a plan view. The four projections 32 fix the permanent magnet 30 to the inner surface of the magnet placement hole 21.

[0046] The protrusion 32 is formed along the entire axis C of the rotation axis 10. That is, the protrusion 32 is provided along the entire length of the permanent magnet 30 in the vertical direction (rotation axis direction). Alternatively, the protrusion 32 may be formed only on the upper and lower parts of the permanent magnet 30 in the vertical direction (rotation axis direction).

[0047] The protrusions 32 are formed by shaping a portion of the coating layer 31 to protrude. While a portion of the permanent magnet 30 itself could also protrude, forming them in the coating layer 31 is preferable from the viewpoint of ease of production. The four protrusions 32 are substantially identical in shape and size.

[0048] The protrusion 32 is in contact with the corner 21a of the inner surface of the magnet placement hole 21. Specifically, the protrusion 32 is in contact with two inner surfaces connected via the corner 21a of the magnet placement hole 21. Because the outer surface of the protrusion 32 is arc-shaped, the area of ​​contact between the inner surface of the magnet placement hole 21 and the protrusion 32 in a plan view can be reduced. This reduces friction when inserting the permanent magnet 30 into the magnet placement hole 21, making it less likely for problems such as damage to the coating layer 31 covering the permanent magnet 30 or deformation of the rotor core 20 to occur. Furthermore, since the protrusion 32 is made of a resin coating layer 31, damage to the rotor core 20 during insertion can also be prevented.

[0049] Figure 4 is an enlarged plan view of a part of the main section of the rotor 2, showing another example of this embodiment. As shown in Figure 4, the inner circumferential surface of the corner 21a on the inner surface of the magnet placement hole 21 is arc-shaped. Furthermore, as shown in Figure 4, the radius of curvature of the outer circumferential surface of the protrusion 32 is larger than the radius of curvature of the corner 21a on the inner surface of the magnet placement hole 21. The radius of curvature represents the radius of the arc. This fixes the position of the protrusion 32 (permanent magnet 30).

[0050] Conversely, if the radius of curvature of the outer surface of the protrusion 32 is smaller, the corner 21a on the inner surface of the arc-shaped magnet arrangement hole 21 and the outer surface of the arc-shaped protrusion 32 may come into contact, causing the protrusion 32 to rotate along the corner 21a and potentially become fixed in a rotated state. In this case, the rotation state of each permanent magnet 30 becomes uneven. As a result, the difference in magnetic flux density between the magnetic poles of each permanent magnet 30 and the other permanent magnets 30 becomes large, leading to a higher cogging torque.

[0051] By using the above configuration, each permanent magnet 30 inserted into each magnet placement hole 21 is securely fixed approximately in the center of the magnet placement hole 21.

[0052] Therefore, variations in the placement of the permanent magnets 30 in each magnet placement hole 21 can be suppressed. As a result, the difference in magnetic flux density between each permanent magnet 30 and other permanent magnets 30 can be reduced, which has the advantage of preventing increased torque ripple and cogging torque.

[0053] Furthermore, in areas where the protruding portion 32 of the permanent magnet 30 is not formed, there is a space between it and the inner surface of the magnet placement hole 21. By forming adhesive in this space, the permanent magnet 30 can be securely held within the magnet placement hole 21.

[0054] On the other hand, if the protrusion 32 is not formed and there is no space, there will be no adhesive surface, and it may not be possible to hold the permanent magnet 30.

[0055] In the above embodiment, the surface of the permanent magnet 30 is covered with a coating layer 31 made of resin, but the coating layer 31 is not limited to resin and may be made of metal or may contain metal. That is, the surface of the permanent magnet 30 may be covered with a coating layer 31 made of metal, or with a coating layer 31 made of resin containing metal. Examples of metals used here include copper, nickel, or aluminum.

[0056] The above embodiment is merely an example, and this disclosure is not limited thereto; it can be modified as appropriate. For example, some of the configurations of the above embodiment may be replaced with other known configurations. Furthermore, configurations not mentioned in the above embodiment are optional, and for example, known configurations can be appropriately selected and combined with this disclosure. [Industrial applicability]

[0057] The rotor and motor described herein can be widely used in electric motors and other components used in various devices, including household electrical appliances and industrial equipment. [Explanation of Symbols]

[0058] 1 electric motor 2 rotors 3 Stator 3a Stator core 3a1 Teeth 3b Winding coil 10 Rotation axis 20 Rotor core 21 Magnet placement holes 21a Corner 30 permanent magnets 30a Corner 31 Covering layer 32 Protrusion

Claims

1. A rotor core having multiple magnet placement holes, Each of the above-mentioned multiple permanent magnets is placed inside the multiple magnet placement holes, The rotor core comprises a rotating shaft fixed to the rotor core, A rotor in which each of the aforementioned plurality of permanent magnets has a protrusion at each of its four corners when viewed from above.

2. The rotor according to claim 1, wherein the outer circumferential surface of the protruding portion is arc-shaped.

3. The rotor according to claim 2, wherein the corners of the inner surface of the magnet arrangement hole are arc-shaped, and the radius of curvature of the outer surface of the protrusion is greater than the radius of curvature of the corners of the inner surface of the magnet arrangement hole.

4. The rotor according to any one of claims 1 to 3, wherein the plurality of magnet arrangement holes are arranged radially with respect to the rotation axis.

5. The rotor according to any one of claims 1 to 4, wherein the surface of the permanent magnet is covered with a coating layer made of resin or metal, and the protruding portion is made of the coating layer.

6. The rotor according to claim 1, wherein in a location where no protrusions are formed on the permanent magnet, a gap of a certain dimension exists between the outer surface of the permanent magnet and the inner surface of the magnet placement hole.

7. The rotor according to claim 1, wherein the protruding portion protrudes from the permanent magnet along a line connecting the center and corner of the permanent magnet in a plan view.

8. The rotor according to claim 1, wherein the protruding portion is in contact with the corner of the inner surface of the magnet arrangement hole.

9. An electric motor comprising a rotor according to any one of claims 1 to 8, and a stator disposed opposite the rotor and generating a magnetic force acting on the rotor.

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