JP7293859B2 - Embedded magnet rotor and method for manufacturing embedded magnet rotor - Google Patents

Description

The present invention relates to an embedded magnet rotor and a method for manufacturing an embedded magnet rotor.

Conventionally, there is an embedded magnet type rotor in which permanent magnets serving as a magnetic field source are embedded. For example, as described in Patent Literature 1, a cylindrical rotor is provided with a plurality of U-shaped magnet holes that open toward the outer periphery and are arranged in the circumferential direction. U-shaped magnets corresponding to the inner shape are embedded in these magnet holes. A curved surface having a predetermined radius is provided at the corner of the U-shaped tip of the magnet. The smoother flow of magnetic flux from the rotor to the stator suppresses torque fluctuations of the motor.

JP-A-2005-57951

According to the rotor disclosed in Patent Document 1, it may be possible to suppress torque fluctuations by providing curved surfaces at the corners of the U-shaped tips of the magnets. However, in the rotor of Patent Document 1, the amount of magnets is reduced by the amount of the curved surface provided, compared to the rotor in which the curved surface is not provided at the corner of the U-shaped tip of the magnet. Therefore, the motor torque may decrease as the amount of magnets decreases.

SUMMARY OF THE INVENTION An object of the present invention is to provide an embedded magnet rotor capable of reducing torque fluctuations while ensuring motor torque. Another object of the present invention is to provide a method for manufacturing an interior magnet rotor that can reduce torque fluctuation while ensuring motor torque.

An embedded magnet type rotor capable of achieving the above object comprises a cylindrical core inserted rotatably relative to a cylindrical stator, and permanent magnets respectively embedded in a plurality of magnet holes provided in the core. , and when viewed from the axial direction of the core, the magnet hole has an extension portion extending from the center side of the core toward the peripheral surface side. When viewed from the axial direction of the core, the width of the extension portion is set so as not to narrow toward the peripheral surface of the core. The thickness of the wall, which is the portion between the peripheral surface, is set so as to gradually decrease toward other magnet holes that are closest to each other in the peripheral direction of the core.

According to this configuration, the magnetic resistance of the wall gradually increases toward the other magnet holes that are closest to each other in the circumferential direction of the core. Therefore, the magnetic flux emitted from the permanent magnet can easily pass through the portion of the wall on the side opposite to the other magnet holes. Therefore, the high-order components of the magnetic flux density distribution in the gap between the core and stator are reduced, and cogging torque and torque fluctuation are suppressed. In addition, since the magnetic resistance of the wall gradually increases toward the other magnet hole that is closest in the circumferential direction of the core, the magnetic flux emitted from the permanent magnet passes through the wall and is embedded in the other magnet hole. Leakage magnetic flux, which is useless magnetic flux reaching the permanent magnets, is reduced. Thereby, motor torque can be ensured. In addition, since the width of the extending portion is set so as not to narrow toward the peripheral surface side of the core when viewed from the axial direction of the core, the thickness of the portion corresponding to the extending portion of the permanent magnet embedded in the magnet hole is also becomes constant. Since the permeance coefficient of the permanent magnet is ensured, the permanent magnet is difficult to demagnetize.

In the above-described embedded magnet rotor, the inner surface corresponding to the peripheral surface of the core in the extended portion is provided so as to gradually approach the peripheral surface of the core toward the other magnet holes. is preferred.

According to this configuration, when viewed from the axial direction of the core, the thickness of the wall can be gradually reduced toward the other magnet holes that are closest to each other in the circumferential direction of the core. Also, the amount of permanent magnets can be increased compared to, for example, the case where the wall thickness is constant. As the amount of permanent magnets increases, the motor torque can be increased.

In the above-described embedded magnet rotor, the inner surface corresponding to the peripheral surface of the core in the extended portion is a pole extending along the radial direction of the core through the middle of the boundary portion with the other magnet hole. It is preferably an arcuate surface centered on a center point set on the interval line.

With this arrangement, the thickness of the wall can be effectively and simply varied. Also, the amount of permanent magnets can be increased compared to, for example, the case where the wall thickness is constant. As the amount of permanent magnets increases, the motor torque can be increased.

A method of manufacturing an embedded magnet rotor that can achieve the above object includes: a cylindrical core inserted to be relatively rotatable with respect to a cylindrical stator; and a permanent magnet, and the magnet hole has an extension portion extending from the center side of the core toward the peripheral surface side when viewed from the axial direction of the core. When viewed from the axial direction of the core, the width of the extended portion is set so as not to narrow toward the peripheral surface of the core. In addition, the thickness of the wall, which is the portion between the extending portion of the magnet hole in the core and the peripheral surface of the core when viewed from the axial direction of the core, is the above-described thickness in consideration of motor torque and torque fluctuations. It is set so that it becomes thinner toward the other magnet holes that are closest to each other in the circumferential direction of the core.

According to the manufacturing method described above, the thickness of the wall can be set to an appropriate thickness in consideration of the motor torque and torque fluctuation. According to the embedded magnet type rotor obtained by the above manufacturing method, the following effects can be obtained. That is, the magnetic resistance of the wall gradually increases toward other magnet holes that are closest to each other in the circumferential direction of the core. Therefore, the magnetic flux emitted from the permanent magnet can easily pass through the portion of the wall on the side opposite to the other magnet holes. Therefore, the high-order components of the magnetic flux density distribution in the gap between the core and stator are reduced, and cogging torque and torque fluctuation are suppressed. In addition, since the magnetic resistance of the wall gradually increases toward the other magnet hole that is closest in the circumferential direction of the core, the magnetic flux emitted from the permanent magnet passes through the wall and is embedded in the other magnet hole. Leakage magnetic flux, which is useless magnetic flux reaching the permanent magnets, is reduced. Thereby, motor torque can be ensured. In addition, since the width of the extending portion is set so as not to narrow toward the peripheral surface side of the core when viewed from the axial direction of the core, the thickness of the portion corresponding to the extending portion of the permanent magnet embedded in the magnet hole is also becomes constant. Since the permeance coefficient of the permanent magnet is ensured, the permanent magnet is difficult to demagnetize.

In the above-described method for manufacturing an embedded magnet rotor, the core is formed by laminating electromagnetic steel sheets, and the thickness of the thinnest portion, which is the thinnest portion of the wall, is obtained by punching the electromagnetic steel sheets. It is preferable to set based on the minimum thickness that can be achieved and the manufacturing tolerance of the electromagnetic steel sheet.

According to this manufacturing method, the thickness of the wall can be set to an appropriate thickness in consideration of the manufacturing process of the core.

According to the embedded magnet rotor of the present invention, it is possible to reduce torque fluctuation while ensuring motor torque. Further, according to the method for manufacturing an interior magnet rotor of the present invention, an interior magnet rotor that can reduce torque fluctuation while ensuring motor torque is obtained.

1 is a partially cutaway front view of a motor in which an embodiment of an embedded magnet rotor is used; FIG. 1 is a perspective view showing an embodiment of an embedded magnet rotor; FIG. FIG. 2 is a plan view showing a main part of the rotor of the embodiment as seen from its axial direction; (a) is a graph showing the rated torque of the motors using the rotors of the embodiment and the comparative example, and (b) is a graph showing the cogging torque ratio of the motors using the rotors of the embodiment and the comparative example. , (c) is a plan view showing a main part of a rotor of one embodiment and a comparative example; 5 is a graph showing the distribution of magnetic flux density in the air gap in motors using the rotors of the embodiment and the comparative example; 4 is a graph showing changes in motor torque in motors using the rotors of the embodiment and the comparative example; 4 is a graph showing changes in cogging torque in motors using the rotors of the embodiment and the comparative example; 4 is a graph showing changes in magnetic flux density in the air gap in a motor using the rotor of one embodiment; FIG. 10 is a plan view showing a main part of a rotor according to another embodiment as seen from its axial direction; 4(a) and 4(b) are plan views showing essential parts of a rotor of another embodiment as seen from the axial direction; FIG.

An embodiment of the embedded magnet rotor will be described below. First, the structure of an IPM motor (Interior Permanent Magnet Motor) in which an embedded magnet type rotor is used will be described.
As shown in FIG. 1 , the IPM motor 10 has a cylindrical case 11 , a cylindrical stator 12 , an output shaft 13 and a cylindrical rotor 14 . The stator 12 is fixed while being press-fitted into the inner peripheral surface of the case 11 . A plurality of teeth (not shown) are formed on the inner peripheral surface of the stator 12 . These teeth are provided with coils 12a corresponding to three phases (U-phase, V-phase, W-phase) by winding conductive wires respectively. The output shaft 13 is rotatably supported with respect to the case 11 via a bearing (not shown). The rotor 14 is fixed to the outer circumference of the output shaft 13 . An air gap Gp (clearance) is formed over the entire circumference between the outer peripheral surface of the rotor 14 and the inner peripheral surface of the stator 12 .

Next, the configuration of the rotor 14 will be explained in detail.
As shown in FIG. 2, the rotor 14 has a cylindrical rotor core 21 formed by laminating a plurality of electromagnetic steel plates 20 and ten permanent magnets 22 embedded inside the rotor core 21 .

An insertion hole 23 into which the output shaft 13 is inserted is provided in the center of the rotor core 21 . The insertion hole 23 extends through the rotor core 21 along the axial direction. Ten magnet holes 24, which are the same number as the permanent magnets 22, are provided around the insertion holes 23 in the rotor core 21. As shown in FIG. Each magnet hole 24 extends through the rotor core 21 along the axial direction. When the rotor core 21 is viewed from the axial direction, the magnet holes 24 are provided at regular intervals along the circumferential direction of the rotor core 21 . When viewed from the axial direction of the rotor core 21, each magnet hole 24 has a U-shape that opens from the inner peripheral surface of the rotor core 21 toward the outer peripheral surface thereof.

A permanent magnet 22 is embedded in each magnet hole 24 . Permanent magnets 22 are, for example, resin-bonded magnets. A bonded magnet is manufactured by molding a mixture of magnetic powder and a synthetic resin as a binder (binding agent) into a predetermined shape (here, a U-shaped column) and magnetizing it. The permanent magnet 22 is magnetized such that the inner portion of the U-shape has an N pole and the outer portion of the U-shape has an S pole.

As shown in FIG. 3, the magnet hole 24 is formed by connecting a first hole portion 31, a second hole portion 32 and a third hole portion 33 to each other. The first hole portion 31 and the second hole portion 32 are portions corresponding to the two arms of the U shape, and are arranged in the circumferential direction of the rotor core 21 toward the outer peripheral side along the radial direction of the rotor core 21 . It is provided so that the facing distance becomes gradually longer. The third hole portion 33 is a portion corresponding to the bottom portion of the U shape, and connects the ends of the first hole portion 31 and the second hole portion 32 on the inner peripheral side in the radial direction of the rotor core 21 . is provided in The first hole portion 31 and the second hole portion 32 correspond to extension portions of the magnet hole 24 that extend from the center side of the rotor core 21 toward the peripheral surface side.

When viewed from the axial direction of the rotor core 21, the thickness of the wall 34, which is the portion between the outer peripheral side inner surface 31a of the first hole 31 and the outer peripheral surface 21a of the rotor core 21, is the closest in the circumferential direction of the rotor core 21. It is set so that it becomes gradually thinner toward another adjacent magnet hole 24 (the right adjacent magnet hole 24 in FIG. 3). In other words, when viewed from the axial direction of the rotor core 21, the thickness of the wall 34 extends from the pole center line L1 side inside the U-shape of the magnet hole 24 to the pole outside the U-shape of the magnet hole 24 in the circumferential direction of the rotor core 21. It is set so that it becomes gradually thinner toward the interval line L2 side.

The pole center line L1 is a straight line extending along the radial direction of the rotor core 21 and passing through the center of the rotor core 21 when viewed from the axial direction of the rotor core 21, and coincides with the axis of symmetry of the magnet hole 24 or the permanent magnet 22. say a straight line. Further, the line L2 between poles is a straight line extending along the radial direction of the rotor core 21 and passing through the center of the rotor core 21 when viewed from the axial direction of the rotor core 21. A straight line passing through the middle of the boundary between the magnet holes 24 , 24 .

When viewed from the axial direction of the rotor core 21, the inner surface 31a on the outer peripheral side of the first hole 31, which is also the inner surface of the wall 34, is an arcuate surface centered on the center point P01 set on the line L2 between poles. be. In the circumferential direction of the rotor core 21, the inner side surface 31a on the outer peripheral side of the first hole portion 31 extends from the pole center line L1 side to the inter-polar line L2 side, in other words, from the inside of the magnet hole 24 to the U shape. It gradually approaches the outer peripheral surface of the rotor core 21 toward the outer side of the letter.

The center point P01 is set as follows. First, the thickness t1 of the thickest portion 34a, which is the thickest portion of the wall 34, and the thickness t2 of the thinnest portion 34b, which is the thinnest portion of the wall 34, are set. Next, the center point P01 is the center of an arc passing through two points P1 and P2 where the inner side surface 31a on the outer peripheral side of the first hole portion 31 and two inner side surfaces facing each other in the circumferential direction of the rotor core 21 intersect. It is set on the gap line L2.

Thickness t1 of thickest portion 34a is set to a thickness approximately equal to the thickness of electromagnetic steel sheet 20, for example. The thickness t2 of the thinnest portion 34b is set based on the minimum thickness with which hole portions corresponding to the magnet holes 24 of the electromagnetic steel plate 20 can be punched.

The thickness t2 of the thinnest portion 34b is represented by the following formula (A).
t2=t _min ±ε (A)
where “t _min ” is the minimum possible thickness of wall 34 . The minimum thickness t _min is a theoretical value of the minimum thickness with which hole portions corresponding to the magnet holes 24 of the electromagnetic steel sheet 20 can be punched, and is determined by the thickness of the electromagnetic steel sheet 20 . Minimum thickness t _min is set, for example, to a value obtained by subtracting a value of about 30% to 50% from the thickness of electromagnetic steel sheet 20 . “ε” is a manufacturing tolerance, and is a value determined by the precision of a die used when stamping the electromagnetic steel sheet 20 by a press, for example.

For example, when the thickness of the electromagnetic steel sheet 20 is "0.5 mm", the minimum thickness t _min is "0.35 mm" and the manufacturing tolerance ε is "0.14 mm". In this case, the possible range of the thickness t2 of the thinnest portion 34b is "0.21 mm to 0.49 mm", the desirable range is "0.28 mm to 0.42 mm", and the optimum range is "0.32 mm to 0.38 mm." ”.

The thickness of the wall 35, which is a portion between the outer peripheral inner surface 32a of the second hole 32 and the outer peripheral surface 21a of the rotor core 21 when viewed from the axial direction of the rotor core 21, is the same as the thickness of the wall 34. It is set based on the viewpoint of That is, the wall 35 is set so as to gradually become thinner toward the other magnet hole 24 (the magnet hole 24 on the left in FIG. 3) that is closest in the circumferential direction of the rotor core 21 . When viewed from the axial direction of the rotor core 21, the inner side surface 32a on the outer peripheral side of the second hole portion 32 faces the other magnet hole 24 that is closest in the circumferential direction of the rotor core 21 (the left magnet hole 24 in FIG. 3). ) is an arc surface centered on the center point P02 set on the line L3 between poles. In addition, the inner side surface 32a on the outer peripheral side of the second hole portion 32 extends from the pole center line L1 side toward the inter-polar line L3 side in the circumferential direction of the rotor core 21. It gradually approaches the outer peripheral surface of the rotor core 21 as it goes to the U-shaped outer side from . Wall 35 also has a thickest portion 35a, which is its thickest portion, and a thinnest portion 35b, which is its thinnest portion.

<Action of Embodiment>
Next, the operation of the present embodiment will be described through comparison between an example of the rotor 14 and comparative examples 1 to 4. FIG. In Examples and Comparative Examples 1 to 4, the thickness of the magnetic steel sheet 20 is the same, and is set to "0.5 mm" here. Further, since the walls 34 and 35 of the rotor core 21 have similar functions, the function of the wall 34 of the rotor core 21 will be mainly described here, and the detailed description of the function of the wall 35 will be omitted.

As shown in FIG. 4(c), in the embodiment, the thickness of the wall 34 of the rotor core 21 gradually decreases from the inner side of the magnet hole 24 to the outer side of the U shape in the circumferential direction of the rotor core 21. is set to In the embodiment, the thickness t1 of the thickest portion 34a of the wall 34 is set to "0.5 mm", and the thickness t2 of the thinnest portion 34b is set to "0.35 mm".

In Comparative Example 1, the thickness of the wall 34 in the rotor core 21 is set to a constant value over the entire length in the circumferential direction. The thickness of the wall 34 is constant at 0.5 mm, which is the same as the thickest portion 34a of the embodiment.

In Comparative Examples 2 to 4, curved surfaces S2, S3, and S4 were formed at the corners (upper left corners in FIG. 4(c)) on the outer peripheral side of the first hole portion 31 in the magnet hole 24 and inside the U-shape. is provided. The magnitude relationship between the radii R2, R3 and R4 of these curved surfaces S2 to S4 is as shown in the following equation (B).

R2<R3<R4 (B)
Here, the radius R2 of the curved surface S2 is set to "1.0 mm", the radius R3 of the curved surface S3 is set to "2.0 mm", and the radius R4 of the curved surface S4 is set to "2.9 mm".

As shown in the graph of FIG. 4(a), when the rated torque of the IPM motors having the rotors of the example and comparative examples 1 to 4 was analyzed, the rated torque of the IPM motor using the rotor of the example was the highest. became. The rated torque of the IPM motors having the rotors of Comparative Examples 1 to 4 decreased in the order of Comparative Examples 1 and 2, Comparative Example 3, and Comparative Example 4. That is, the larger the radii R2, R3, R4 of the curved surfaces S2, S3, S4, the smaller the value of the rated torque of the IPM motor.

This is for the following reason. That is, in the embodiment, the inner side surface 31a on the outer peripheral side of the first hole portion 31 has an arcuate shape that gradually approaches the outer peripheral surface of the rotor core 21 as it goes from the inner side of the U shape to the outer side of the U shape of the magnet hole 24. be provided. Therefore, the thickness of the wall 34 is not constant, and gradually decreases from the inner side of the magnet hole 24 to the outer side of the U shape in the circumferential direction of the rotor core 21 . Moreover, the thickness t2 of the thinnest portion 34b of the wall 34 is set based on the minimum thickness _tmin , which is the minimum thickness that can be punched. Therefore, the volume of the magnet hole 24 increases by the amount that the thickness of the wall 34 is gradually reduced from the thickness t1 of the thickest portion 34a to the thickness t2 of the thinnest portion 34b. That is, according to the rotor of the example, it is possible to increase the amount of the permanent magnets 22 embedded in the magnet holes 24 compared to the rotors of the first to fourth comparative examples. As the amount of permanent magnets 22 increases, the rated torque of the IPM motor also increases. Further, when the thickness of the wall 34 is gradually reduced from the thickness t1 of the thickest portion 34a to the thickness t2 of the thinnest portion 34b, the magnetic resistance increases as the thickness of the wall 34 decreases. For this reason, leakage magnetic flux, which is wasted magnetic flux that reaches the adjacent permanent magnet 22 through the wall 34 among the magnetic flux emitted from a specific permanent magnet 22, is reduced. The rated torque of the IPM motor can be ensured by the amount of reduction in this leakage magnetic flux.

On the other hand, in the rotors of Comparative Examples 2 to 4, the larger the radius of the curved surfaces S2, S3, and S4 of the first hole portion 31, the larger the volume of the magnet hole 24, and thus the more permanent magnets embedded in the magnet hole 24. 22 is reduced, and the rated torque of the IPM motor is reduced by the amount that the permanent magnet 22 is reduced. Incidentally, the rated torques of the IPM motors using the rotors of Comparative Examples 1 and 2 are substantially the same. That is, since the radius R2 of the curved surface S2 of Comparative Example 2 is set to a very small value, it is considered that the curved surface S2 hardly affects the magnet amount.

As shown in the graph of FIG. 4(b), when the ratio of cogging torque to the rated torque of the IPM motors having the rotors of Example and Comparative Examples 1 to 4 was analyzed, the rotors of Example and Comparative Example 4 were used. The cogging torque ratio of the IPM motor was particularly small compared to the IPM motors using the rotors of Comparative Examples 1 to 3.

This is for the following reason. In the IPM motor using the rotor of Comparative Example 4, a curved surface S4 is provided at the outer corner of the first hole 31 in the magnet hole 24 and inside the U shape. This curved surface S4 has the largest radius R4 among Comparative Examples 1 to 4, and is It is provided so as to reach the inner surface of the outer side of the U-shape (right inner surface in FIG. 4(c)). With this configuration, the distribution of the magnetic flux density in the air gap Gp of the IPM motor, more specifically, the flow of the magnetic flux from the rotor to the stator becomes smoother, thereby reducing the cogging torque.

In the IPM motor using the rotor of the embodiment, the thickness of the wall 34 between the inner surface 31a on the outer peripheral side of the first hole 31 and the outer peripheral surface 21a of the rotor core 21 is equal to the U of the magnet hole 24. It gradually becomes thinner as it goes from the inner side of the character to the outer side of the U character. In other words, the inner side surface 31a on the outer peripheral side of the first hole portion 31 has an arcuate shape that gradually approaches the outer peripheral surface of the rotor core 21 as it goes from the inner side of the U shape to the outer side of the U shape of the magnet hole 24. ing. With this configuration, the same effect as the curved surface S4 of Comparative Example 4 can be obtained, so it is considered that the cogging torque is reduced.

In the IPM motor using the rotor of the embodiment, the relationship between the rotation angle of the rotor and the magnetic flux density in the air gap in the IPM motor is as follows.
As shown in the graph of FIG. 8, when the rotor 14 rotates through an angle corresponding to one permanent magnet 22, the magnetic flux density in the air gap Gp of the IPM motor 10 peaks with respect to changes in the rotation angle of the rotor. It changes to a concave smooth trapezoid. That is, the magnetic flux density rapidly increases as the rotation angle of the rotor increases from 0°. After that, as the rotation angle of the rotor increases, the magnetic flux density changes from a decrease to an increase in the form of a smooth concave curve that is convex downward, and then decreases sharply. From the graph of FIG. 8, it can be seen that the distribution of the magnetic flux density within the air gap Gp of the IPM motor 10 changes smoothly with the rotation of the rotor 14 .

Here, the magnetic flux density distribution within the air gap Gp in the IPM motor 10 contains many distortions (harmonic components). The distortion of the magnetic flux density distribution is also a factor that increases the cogging torque of the IPM motor and, in turn, torque fluctuations.

As shown in the graph of FIG. 5, when the magnetic flux density distribution in the air gap of the IPM motor using the rotors of Example and Comparative Example 1 was analyzed, the general trend of the IPM motor using the rotor of Example was Higher-order components in the magnetic flux density distribution in the air gap have smaller values than in the IPM motor using the rotor of Comparative Example 1. In particular, the quintic component in the magnetic flux density distribution in the air gap of the IPM motor using the rotor of the example is greatly reduced compared to the IPM motor using the rotor of comparative example 1. Therefore, the cogging torque of the IPM motor using the rotor of the example is smaller than the cogging torque of the IPM motor using the rotor of the first comparative example.

As shown in the graph of FIG. 6, when the change in torque with respect to the rotation angle of the rotor in the IPM motors using the rotors of Example and Comparative Example 1 was measured, the torque generated by the IPM motor using the rotors of Example was The average value T0 was larger than the average value T1 of the torque generated by the IPM motor using the rotor of Comparative Example 1. As for the generated torque of the IPM motor, actual measurement results similar to the analysis results shown in FIG. 4(a) were obtained.

As shown in the graph of FIG. 7, when the change in cogging torque with respect to the rotation angle of the rotor in the IPM motors using the rotors of the example and comparative example 1 was actually measured, the cogging torque A0 of the IPM motor using the rotors of the example was measured. was smaller than the cogging torque A1 of the IPM motor using the rotor of Comparative Example 1. Incidentally, the cogging torque fluctuates depending on the positional relationship between the rotor and stator, and is evaluated as the amplitude of that fluctuation. As for the cogging torque of the IPM motor, actual measurement results corresponding to the analysis results shown in FIG. 4(b) were obtained.

As shown in FIG. 4B, the cogging torque ratio of the IPM motor using the rotor of Comparative Example 4 is slightly smaller than the cogging torque ratio of the IPM motor using the rotor of the example. However, as shown in the graph of FIG. 4A, in terms of the rated torque of the IPM motor, the IPM motor using the rotor of Comparative Example 4 is significantly inferior to the IPM motor using the rotor of Example. Therefore, according to the IPM motor using the rotor of the embodiment, it is possible to reduce the torque fluctuation while ensuring the rated torque.

<Effect of Embodiment>
Therefore, according to this embodiment, the following effects can be obtained.
(1) When viewed from the axial direction of the rotor core 21, the thickness of the wall 34, which is the portion between the outer peripheral side inner surface 31a of the first hole portion 31 of the magnet hole 24 and the outer peripheral surface 21a of the rotor core 21, is equal to the thickness of the magnet hole. It is set so that it becomes gradually thinner from the inner side of the U-shape of 24 to the outer side of the U-shape. Therefore, the magnetic resistance of the wall 34 gradually increases from the inside of the magnet hole 24 to the outside of the U shape. Since the magnetic flux emitted from the permanent magnet 22 can easily pass through the U-shaped inner portion of the wall 34, the higher-order component, particularly the fifth-order component, of the magnetic flux density distribution within the air gap Gp in the IPM motor 10 is reduced. Therefore, the cogging torque of the IPM motor 10 and, by extension, torque fluctuations are suppressed. Wall 35 also provides the same function and effect as wall 34.

(2) The magnetic resistance of the wall 34 gradually increases from the inner side of the magnet hole 24 to the outer side of the U-shape, so that the magnetic flux emitted from the specific permanent magnet 22 passes through the wall 34 to the nearest magnetic flux. Leakage magnetic flux, which is useless magnetic flux reaching the adjacent permanent magnets 22, is reduced. The amount of torque generated by the IPM motor can be ensured by the reduction in this leakage magnetic flux. That is, the torque fluctuation can be reduced while ensuring the torque of the IPM motor 10 . Wall 35 also provides the same function and effect as wall 34.

(3) The inner side surface 31a on the outer peripheral side of the first hole portion 31 gradually approaches the outer peripheral surface 21a of the rotor core 21 as it goes from the inner side of the U shape to the outer side of the U shape of the magnet hole 24 . For this reason, the amount of permanent magnets 22 can be increased compared to, for example, the case where wall 34 has a constant thickness. The torque generated by the IPM motor 10 can be further increased by the amount of the permanent magnets 22 increased. The inner side surface 32 a on the outer peripheral side of the second hole portion 32 also provides the same function and effect as the inner side surface 31 a on the outer peripheral side of the first hole portion 31 .

(4) Moreover, the inner side surface 31a on the outer peripheral side of the first hole portion 31 is an arcuate surface centered on the center point P01 set on the interpolar line L2. An inner side surface 32a on the outer peripheral side of the second hole portion 32 is an arcuate surface centered on a central point P02 set on the interpolar line L3. Therefore, the thickness of the wall 34 can be changed effectively and easily.

(5) The widths of the first hole portion 31, the second hole portion 32 and the third hole portion 33 in the magnet hole 24 are all set to the same value. That is, the thickness of the permanent magnet 22 (that is, the length of the permanent magnet 22 in the magnetization direction) is constant over the entire length of the U shape. Since the value of the permeance coefficient of the permanent magnet 22 is the same over the entire length of the U shape, the permanent magnet 22 is difficult to demagnetize. On the other hand, in Comparative Examples 2 to 4 shown in FIG. 4(c), the thickness of the U-shaped tip of the permanent magnet is thinner than the thickness of the other portion, so the permeance coefficient is lowered. Therefore, the permanent magnets used in the rotors of Comparative Examples 2 to 4 are more easily demagnetized than the permanent magnets used in the rotors of the Examples.

Incidentally, the permeance coefficient is the ratio of the demagnetizing field (magnetic field intensity) to the magnetic flux density. The permeance coefficient is also a value representing the effect of self-demagnetization and depends on the shape of the permanent magnet 22 . A demagnetizing field is a magnetic field generated on the surface of a magnetized permanent magnet, which is directed from the N pole to the S pole, and which is opposite to the direction of magnetization acting inside the permanent magnet. This demagnetizing field varies depending on the dimensional ratio of the permanent magnet, and becomes smaller as the permanent magnet elongates in the magnetization direction. The effect of the demagnetizing field is practically represented by the slope of the ratio of the demagnetizing field to the magnetic flux density.

(6) The thickness of the walls 34 and 35 when viewed from the axial direction of the rotor core 21 is set in consideration of motor torque and torque fluctuations. Therefore, the thickness of the walls 34 and 35 can be set to an appropriate thickness in consideration of the motor torque and torque fluctuation.

(7) The thickness of the thinnest portions 34b and 35b, which are the thinnest portions of the walls 34 and 35, is set based on the minimum thickness with which the electromagnetic steel sheet 20 can be stamped and the manufacturing tolerance of the electromagnetic steel sheet 20. . Therefore, the thickness of walls 34 and 35 can be set to an appropriate thickness in consideration of the manufacturing process of rotor core 21 .

<Other embodiments>
It should be noted that this embodiment may be implemented with the following modifications.
- As the permanent magnet 22, a sintered magnet may be employed instead of a bonded magnet. A sintered magnet is made by sintering magnetic powder at a high temperature.

- As the rotor core 21, instead of a laminated core formed by laminating a plurality of electromagnetic steel sheets 20, a dust core formed by compressing magnetic powder may be employed. In this case, depending on the strength of the dust core, the thickness t2 of the thinnest portion 34b based on the minimum possible thickness _tmin of the wall 34 can be set to a smaller value than in the above embodiment.

- In the present embodiment, the rotor 14 having a ten-pole structure having ten permanent magnets 22 is used as an example, but the number of magnetic poles of the rotor 14 is not particularly limited and may be changed as appropriate.
- As shown in FIG. 10( a ), rectangular parallelepiped permanent magnets 22 may be embedded in the rotor core 21 so as to form a V shape when viewed from the axial direction of the rotor 14 . In this case, the magnet holes 24 in which the permanent magnets 22 are embedded may be provided independently. In this case, the magnet hole 24 corresponds to an extended portion extending from the center side of the rotor core 21 toward the peripheral surface side. Further, as shown in FIG. 10(b), the permanent magnet 22 may have a rectangular U-shaped cross section orthogonal to the axial direction of the rotor core 21. As shown in FIG. Although not shown, the permanent magnet 22 may have a V-shaped cross-section perpendicular to the axial direction of the rotor core 21 .

- As shown in FIG. 9, when viewed from the axial direction of the rotor core 21, the inner side surface 31a on the outer peripheral side of the first hole portion 31 of the magnet hole 24 may be provided in a planar shape instead of an arcuate shape. The same applies to the inner side surface 32a of the second hole portion 32 of the magnet hole 24 on the outer peripheral side. Even in this way, the thickness of the walls 34 and 35 gradually decreases from the inner side of the U-shape of the magnet hole 24 to the outer side of the U-shape. Therefore, the same effects as (1) to (5) of the above embodiment can be obtained.

In the present embodiment, the widths of the first hole portion 31, the second hole portion 32, and the third hole portion 33 in the magnet hole 24 are all set to the same value (constant width). The width of at least the first hole portion 31 and the second hole portion 32 should be set so as not to narrow toward the outer peripheral surface side of the rotor core 21 when viewed from the direction. For example, when viewed from the axial direction of rotor core 21 , the widths of first hole portion 31 and second hole portion 32 may be set so as to gradually widen toward the outer peripheral surface side of rotor core 21 .

The IPM motor 10 is, for example, a source of steering assist force in an electric power steering device, a source of steering reaction force in a steer-by-wire steering device, or a source of steering force for steering the steerable wheels of a vehicle. Alternatively, it may be used as a drive source for running an electric vehicle or a hybrid vehicle. Also, the IPM motor 10 may be used as a drive source for an electric oil pump (EOP).

DESCRIPTION OF SYMBOLS 12... Stator 14... Embedded magnet type rotor 20... Electromagnetic steel plate 21... Rotor core 21a... Outer peripheral surface of rotor core 22... Permanent magnet 24... Magnet hole 31... First hole (extending part ), 31a... inner side surface, 32... second hole portion (extended portion), 32a... inner side surface, 33... third hole portion, 34, 35... wall, 34a, 35a... thickest portion, 34b, 35b ... Thinnest part, L2 ... Interpolar line, P01, P02 ... Center point.

Claims (4)

A cylindrical core inserted to be relatively rotatable with respect to a cylindrical stator, and permanent magnets respectively embedded in a plurality of magnet holes provided in the core. The embedded magnet rotor, wherein the hole has an extended portion extending from the center side of the core toward the peripheral surface side,
When viewed from the axial direction of the core, the width of the extension portion is set so as not to narrow toward the peripheral surface of the core. The thickness of the wall, which is the portion between the peripheral surface and the peripheral surface, is set so as to become thinner toward other magnet holes that are closest to each other in the peripheral direction of the core ,
The embedded magnet rotor, wherein the inner surface corresponding to the peripheral surface of the core in the extended portion is provided so as to gradually approach the peripheral surface of the core toward the other magnet holes. The inner surface of the extending portion corresponding to the peripheral surface of the core has a center point set on a line between poles extending along the radial direction of the core through the middle of the boundary portion with the other magnet hole. 2. The embedded magnet rotor according to claim 1, which is a centered circular arc surface. A cylindrical core inserted to be relatively rotatable with respect to a cylindrical stator, and permanent magnets respectively embedded in a plurality of magnet holes provided in the core. A method for manufacturing an embedded magnet rotor, wherein the hole has an extended portion extending from the center side of the core toward the peripheral surface side,
When viewed from the axial direction of the core, the width of the extension portion is set so as not to narrow toward the peripheral surface side of the core, while the width of the extension portion of the magnet hole in the core and the peripheral surface of the core is set so as not to narrow toward the peripheral surface side of the core. The thickness of the wall, which is the portion between them, is set so that it becomes thinner toward the other magnet holes that are closest to each other in the circumferential direction of the core, taking into account motor torque and torque fluctuations ,
A method of manufacturing an embedded magnet rotor, wherein the inner side surface corresponding to the peripheral surface of the core in the extended portion is provided so as to gradually approach the peripheral surface of the core toward the other magnet holes. The core is formed by laminating electromagnetic steel sheets,
4. The embedded magnet according to claim 3, wherein the thickness of the thinnest portion, which is the thinnest portion of the wall, is set based on the minimum thickness with which the electromagnetic steel sheet can be punched and manufacturing tolerances of the electromagnetic steel sheet. A method of manufacturing a mold rotor.

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