JP7850892B2 - Rotor and motor - Google Patents

Description

This disclosure relates to rotors and electric motors used in various devices, including household electrical appliances and industrial equipment.

Electric motors are used in a variety of electrical equipment, such as household appliances and industrial equipment. One well-known type of electric motor is the IPM (Internal Permanent Magnet) motor. The rotor of an IPM motor comprises, for example, a rotor core, permanent magnets positioned in multiple magnet arrangement holes provided in the rotor core, and a rotating shaft fixed to the center of the rotor core, penetrating the core. In an IPM motor, torque is generated to rotate the rotor by passing the magnetic flux generated by the rotor's permanent magnets through the stator.

Conventionally, an IPM motor is known as a type of motor that has a rotor in which multiple magnet arrangement holes are radially arranged on the rotor core (Patent Document 1).

Japanese Patent Publication No. 2017-46386

In conventional rotors, a predetermined space is sometimes provided between the rotor core and the permanent magnets to improve the ease of inserting the permanent magnets into the magnet placement holes. In this case, when inserting the permanent magnets into the magnet placement holes, there was a possibility of variations in the placement of the permanent magnets within the holes. As a result, the difference in magnetic flux density between the magnetic poles of each permanent magnet became large, leading to the problem of increased cogging torque.

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

A rotor according to a first aspect of this disclosure comprises a rotor core having a plurality of magnet arrangement holes, a plurality of permanent magnets each disposed within 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.

In the second aspect of this disclosure, the rotor has an arc-shaped outer surface of the projection in the first aspect.

In the third aspect of this disclosure, the electric motor, in the second aspect, has arc-shaped corners on the inner surfaces of each of the multiple magnet placement holes, and the radius of curvature of the outer surface of the protrusion is greater than the radius of curvature of the inner surface corners of the magnet placement holes.

In the fourth aspect of this disclosure, the electric motor, in any of the first to third aspects, has a plurality of magnet arrangement holes arranged radially around the axis of rotation.

In the fifth aspect of this 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 formed from the coating layer.

The 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.

According to this disclosure, it is possible to provide a rotor and motor that can reduce cogging torque.

Perspective view of an electric motor according to one embodiment of the present disclosure Perspective view of the rotor of the electric motor. Plan view of the main part of the rotor of the electric motor. Enlarged plan view of the main part of the rotor of the electric motor.

The embodiments of this disclosure will be described below. Note that the embodiments described below are all specific examples of this disclosure. Therefore, the numerical values, components, arrangement and connection configurations of components, and processes and their sequences shown in the following embodiments are examples and are not intended to limit this disclosure. Accordingly, 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 optional components.

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.

(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.

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, where the rotor 2 is positioned inside the stator 3. In other words, the stator 3 is configured to surround the rotor 2.

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

The rotor 2 generates a magnetic force acting on the stator 3. The rotor 2 has a configuration in which multiple N-poles and S-poles, which constitute the main magnetic flux, are repeated along the circumferential direction. In this embodiment, the direction of the main magnetic flux generated by the rotor 2 is perpendicular to the direction of the axis C of the rotation axis 10 (the direction of the rotation axis). In other words, the direction of the main magnetic flux generated by the rotor 2 is the radial direction.

The rotor 2 is positioned relative to the stator 3 via an air gap. Specifically, a small air gap exists between the surface of the rotor 2 and the surface of the stator 3. As will be described in detail later, the rotor 2 is a permanent magnet-embedded rotor (IPM rotor) with permanent magnets embedded in an iron core. Therefore, the electric motor 1 in this embodiment is an IPM motor.

The stator 3 is positioned opposite the rotor 2 via an air gap and generates the magnetic force acting on the rotor 2. Specifically, the stator 3 is positioned to surround the rotor core 20 of the rotor 2. Together with the rotor 2, the stator 3 constitutes a magnetic circuit.

The stator 3 is configured such that north and south poles are alternately generated in the circumferential direction as the main magnetic flux on the air gap surface. In this embodiment, the stator 3 has a stator core 3a and a winding coil 3b (stator coil).

The stator core 3a is provided with multiple teeth 3a1 that protrude toward the rotor core 20 of the rotor 2. Specifically, the multiple teeth 3a1 are arranged to protrude toward the axis C of the rotation axis 10. Furthermore, the multiple teeth 3a1 are arranged at equal intervals in the circumferential direction. Therefore, the multiple teeth 3a1 extend radially in a direction perpendicular to the axis C of the rotation axis 10 (radial direction).

The stator core 3a is composed of 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 composed of a magnetic material.

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 is composed of three unit coils for the U, V, and W phases, each electrically 120 degrees out of phase with respect to the others. In other words, the winding coils 3b wound around each tooth 3a1 are driven by three-phase alternating current, with the U, V, and W phases being energized separately. This generates the main magnetic flux of the stator 3 at each tooth 3a1.

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.

In the 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 directed from the stator 3 towards the rotor 2. Conversely, the rotor 2 generates a magnetic flux directed towards 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.

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.

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.

The rotating shaft 10 is a long shaft that serves as the center of rotation for the rotor 2. 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 a manner that it passes through the center of the rotor core 20, protruding from both sides of the rotor 2. 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.

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.

The rotor core 20 is composed of 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; it may also be a bulk body made of magnetic material.

The rotor core 20 is a core having multiple magnet placement holes 21. These 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 the 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. Note that this is not limited to this, and it can be applied to other numbers of magnetic poles as well.

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 steel plates constituting the rotor core 20 have magnet placement holes 21 of the same shape. Note that the magnet placement holes 21 do not necessarily have to be through-holes, as long as permanent magnets 30 can be placed within them.

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, and their radial length is longer than their rotational (circumferential) length. Alternatively, the magnet placement holes 21 may be elongated in the rotational (circumferential) direction of the rotor core 20, with their rotational (circumferential) length being longer than their radial length.

The elongated magnet placement holes 21 are formed in a spoke-like pattern 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 identical to each other.

As shown in Figure 2, permanent magnets 30 are 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 each of the multiple magnet placement holes 21 is filled with permanent magnets 30. In this embodiment, the permanent magnets 30 are inserted from above (above the plane of the paper) the axis C of the rotation shaft 10, but they may also be inserted from below (below the plane of the paper).

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 and N poles facing opposite directions.

The plan view shape and size of the permanent magnet 30 are approximately the same as those of the magnet placement holes 21, and the permanent magnet 30 is fitted into the magnet placement holes 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-like rectangular parallelepiped with thickness in the direction perpendicular to the radial direction of the rotor core 20. Note that the permanent magnet 30 within each magnet placement hole 21 may be divided into multiple sections.

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 for bonding and fixing the permanent magnet 30 to the magnet placement hole 21. Alternatively, adhesive may not be provided in this gap.

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 magnetic powder such as Nd-Fe-B magnetic powder or ferrite magnetic powder, a resin material, and a small amount of additives.

Regarding the magnetization of the permanent magnet 30, it may be magnetized after placing it in the magnet placement hole 21, or it may be magnetized 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 it after inserting it into the magnet placement hole 21.

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

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 to the corner 30a in a plan view. The four projections 32 fix the permanent magnet 30 to the inner surface of the magnet placement hole 21.

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 vertical direction (rotation axis direction) of the permanent magnet 30. 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).

The protrusions 32 are formed by molding a portion of the coating layer 31 to protrude. While it is also possible to have a portion of the permanent magnet 30 itself 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.

The protruding portion 32 is in contact with the corner 21a of the inner surface of the magnet placement hole 21. Specifically, the protruding portion 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 protruding portion 32 is arc-shaped, the area of contact between the inner surface of the magnet placement hole 21 and the protruding portion 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 and deformation of the rotor core 20 to occur. Furthermore, since the protruding portion 32 is made of a resin coating layer 31, damage to the rotor core 20 during insertion can also be prevented.

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).

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 rotational state of each permanent magnet 30 becomes uneven. This leads to a larger difference in magnetic flux density between the magnetic poles of each permanent magnet 30 compared to the other permanent magnets 30, resulting in increased cogging torque.

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.

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.

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 within this space, the permanent magnet 30 can be securely held within the magnet placement hole 21.

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.

In the above embodiment, the surface of the permanent magnet 30 is covered with a coating layer 31 made of resin. However, the coating layer 31 is not limited to resin; it 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 a resin containing metal. Examples of metals used here include copper, nickel, or aluminum.

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.

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

1. Electric motor 2. Rotor 3. Stator 3a. Stator core 3a1. Teeth 3b. Winding coil 10. Rotating shaft 20. Rotor core 21. Magnet placement hole 21a. Corner 30. Permanent magnet 30a. Corner 31. Coating layer 32. Protrusion

Claims (9)

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. The rotor according to claim 1, wherein the outer circumferential surface of the protruding portion is arc-shaped. The rotor according to claim 2, wherein the corners of the inner surface of the magnet placement 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 surface of the magnet placement holes. The rotor according to any one of claims 1 to 3, wherein the plurality of magnet arrangement holes are arranged radially around the rotation axis. 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. 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. 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. 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. 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.