JP2000287394A - Permanent magnet electric motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase reluctance torque and to obtain higher torque and higher efficiency of a motor in a permanent magnet electric motor. SOLUTION: In a permanent magnet electric motor having a rotor core 10 inside a stator core 1 which generates rotating magnetic field, magnets 11 of a quonset shape in cross section are embedded into the rotor core 10 in the proximity of a d-axis along the outside circumference of the rotor core 10 at an equal interval for the corresponding number of poles, in such a manner that a given magnetic path width from one q-axis to the other q-axis is secured for the magnetic path from the stator core 1, and grain-oriented magnetic steel sheets 12 of a given thickness are embedded at a fixed interval in such a way as to surround the center hole side of these magnets 11. The neighboring magnets 11 generate magnet torque by reversing its magnetizing direction. The steel sheets 12 increase the q-axis inductance by letting the magnetic flux from the stator core 1 pass easily, thereby enlarging the difference of inductance between d- and q-axis so that a reluctance torque is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a permanent magnet motor of an IPM motor used for an air conditioner, an automobile, and the like.
More particularly, the present invention relates to a permanent magnet motor that makes effective use of magnet torque and reluctance torque.

[0002]

2. Description of the Related Art As shown in FIG. 9, for example, this permanent magnet motor has a rotor core 2 in a 24-slot stator core 1 for generating a rotating magnetic field, and the rotor core 2 has poles of the permanent magnet motor. As many as three (four poles) magnets 3 are arranged in the circumferential direction along the outer diameter. 4 is a center hole for the shaft, 5 is the rotor core 2
Rivets.

In the permanent magnet motor, the magnet 3 has a cross-sectional shape of an arc curve and a bathtub shape along the outer periphery of the rotor core 2 so that a magnetic flux path from the stator core 1 (from one q-axis to the other q-axis). Magnetic path) (see the dashed arrow in FIG. 9). Therefore, not only the magnet torque but also the reluctance torque is generated, so that both torques can be utilized, so that a low-cost, high-torque, high-efficiency motor can be realized.

[0004]

However, the rotor core 2 of the permanent magnet electric motor is formed by laminating core sheets of magnetic steel sheets. However, non-directional electromagnetic steel sheets must be used. Therefore, there is a limit in facilitating passage of the magnetic flux from stator core 1. Therefore,
Even if a magnetic path from one q-axis to the other q-axis could be secured, the generation of reluctance torque is small, and the effective use of torque is limited.

The present invention has been made in view of the above problems, and has as its object to increase the generation of reluctance torque, and to obtain a high torque and high efficiency motor in combination with a magnet torque. It is to provide an electric motor.

[0006]

In order to achieve the above object, the present invention relates to a permanent magnet electric motor having a rotor core inside a stator core for generating a rotating magnetic field, wherein the rotor core has one of a magnetic path from the stator core. In order to secure a predetermined magnetic path width from the q-axis to the other q-axis, a magnet having a predetermined cross-sectional shape is embedded in the vicinity of the d-axis at equal intervals along the outer circumference of the rotor core by the number of poles. A directional electromagnetic steel sheet of a predetermined thickness is embedded at regular intervals so as to surround the center hole side of the magnet,
A magnet torque is generated by reversing the magnetization direction of the adjacent magnet, and a reluctance torque is generated by increasing a difference between d-axis and q-axis inductances by the grain-oriented magnetic steel sheet. .

According to the present invention, in a permanent magnet motor having a rotor core inside a stator core for generating a rotating magnetic field, the rotor core has a predetermined magnetic path width from one q axis to the other q axis with respect to a magnetic path from the stator core. In order to ensure that the outer peripheral side of the rotor core is an arc curve, and the center hole side is a cross-section bathtub curve, a magnet having a cross section of a semicircular shape is provided in the vicinity of the d axis along the outer periphery of the rotor core by the number of poles. Embedded at equal intervals only, cut a directional electromagnetic steel sheet of a predetermined thickness so as to surround the center hole side of the magnet, bend the directional electromagnetic steel sheet into the cross-section bathtub curve shape, and maintain a constant interval with the magnet. Placed adjacent to each other, to generate a magnet torque with the direction of magnetization of the adjacent magnet being reversed, and More d-axis, a permanent magnet motor, characterized in that to increase the difference between the q-axis inductance to generate a reluctance torque.

[0008] It is preferable that the grain-oriented electrical steel sheet is formed by stacking a plurality of grain-oriented electrical steel sheets.

Preferably, the grain-oriented electrical steel sheet has a slit that is long in the same direction as the magnetic flux from the rotor core.

It is preferable that one or more slits long in the same direction as the magnetic flux from the rotor core are formed on each side of the grain-oriented electrical steel sheet bent into the bathtub curve section.

It is preferable that the grain-oriented electrical steel sheet is constituted by a plurality of grain-oriented electrical steel sheets divided into two or more in the axial direction of the center hole.

The rotor core is a core obtained by punching out an electromagnetic steel sheet by an automatic press and automatically laminating the magnetic steel sheet in a mold. At the time of the automatic press, the rotor core is simultaneously punched out of the buried holes of the magnet and the directional electromagnetic steel sheet. A rivet through hole is punched on the q-axis between the buried hole of the grain-oriented magnetic steel sheet and the center hole, and at least the interval between the holes is set to be equal to or greater than the thickness of the magnetic steel sheet, and the magnet is attached to the automatically laminated core. It is preferable to embed a grain-oriented electrical steel sheet and to caulk through a rivet of a magnetic material.

Preferably, the magnet is a ferrite magnet.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to FIGS. In the figure,
The same parts as those in FIG. 9 are denoted by the same reference numerals, and redundant description will be omitted.

In the permanent magnet motor of the present invention, a magnet is embedded in the d-axis direction by the IPM method, and a directional magnetic steel sheet is embedded so as to surround the center hole side of the magnet. The focus is on the fact that if the magnetic flux is easily transmitted to the shaft, the difference between the d-axis inductance and the q-axis inductance is further increased, that is, the reluctance torque can be improved.

Therefore, as shown in FIGS. 1 to 3,
The rotor core 10 of this permanent magnet motor has a semi-cylindrical cross section so as to secure one magnetic path (a path of magnetic flux from one q-axis to the other q-axis) from the stator core 1 (see the wavy arrow in FIG. 2). The magnets 11 are embedded at equal intervals along the outer circumference of the rotor core 10 by the number of poles, and a directional magnetic steel sheet 12 having a bathtub-shaped cross section is embedded so as to surround the center hole 4 side of the magnet 11 in order to easily pass the magnetic flux. Do it.

The magnet 11 is magnetized in the same manner as the magnet 3 shown in FIG. 9, and the adjacent magnet 11 has a different polarity. The cross-sectional outer shape of the magnet 11 is a combination of an arc curve and a cross-section bathtub curve, and the bending angle of the cross-section bathtub curve is obtuse so that the side of the cross-section bathtub curve is parallel to the q-axis.

The arc-shaped curve of the kamaboko shape corresponds to the rotor core 1
0 at predetermined intervals along the outer circumference of 0, the cross-section bathtub curve,
It is arranged toward the center hole 4 side. Therefore, the amount of the magnet 11 used is at least the same as the conventional amount.

On the other hand, as shown in FIGS. 3 and 4, the grain-oriented electrical steel sheet 12 determines one piece of grain-oriented electrical steel sheet having a predetermined thickness in accordance with the size of the rotor core 10 and has a predetermined shape. After cutting and bending, the magnet 11
Is bent along a magnetic path (a path of magnetic flux from one q-axis to the other q-axis) sufficiently secured by the cross-sectional shape (cross-section bathtub curve shape). In this case, the direction of the grain-oriented electrical steel sheet 12 is the direction from one q-axis to the other q-axis in a state of being embedded in the rotor core 10. The shape is formed along the bathtub curve, and the distance between the magnet 11 and the grain-oriented electromagnetic steel sheet 12 is constant.

As described above, the grain-oriented electrical steel sheet 12
Since the magnetic flux from the stator core 1 (magnetic flux from one q-axis to the other q-axis) easily passes, the q-axis inductance can be further increased. On the other hand, the magnet 11 made of a low magnetic permeability material has an IP along the outer periphery of the rotor core 10.
Since the magnetic flux is embedded in the M type, the magnetic flux from the stator core 1 (magnetic flux from one d-axis to the other d-axis) does not easily pass, so that the d-axis inductance is reduced.

Therefore, the difference between the d-axis inductance and the q-axis inductance increases, and as a result, the reluctance torque can be increased. Therefore, a high torque and high efficiency motor can be realized by combining the large reluctance and the magnet torque. Can be.

The distance between the magnet 11 and the outer periphery of the rotor core 10 is equal to one-thickness of a core sheet 10a described later.
More than twice (about 1 to 3 times) and a magnet 1
1 and the grain-oriented electrical steel sheet 12 are spaced from the core sheet 10a.
And a rivet 13 for caulking the rotor core 10 is formed between the center hole 4 and each directional magnetic steel sheet 12 on the q-axis. The distance may be equal to or greater than the thickness of the core sheet 10a.

As a result, the core can be manufactured with high precision without the occurrence of burrs and the like at the time of manufacturing the core, which will be described later, and the leakage and short circuit of the magnetic flux of the magnet 11 can be prevented. Contribute.

Considering the cost of the motor, the cost depends on the size of the magnet 11, but since the amount used is the same as that of the conventional magnet, the cost is increased by the cost of the grain-oriented electromagnetic steel sheet 12. Become. However, since the grain-oriented electrical steel sheet 12 can be formed by simple processing such as bending, the cost can be reduced and the motor cost can be prevented from being significantly affected.

As the magnet 11, a ferrite magnet can be used in consideration of improvement in reluctance torque. However, since the ferrite magnet itself is low in cost, the cost of the motor can be reduced.

In manufacturing the rotor core 10, a core laminating method (automatic laminating method) in which an electromagnetic steel sheet is punched out by an automatic press using a core press die and integrally formed in the die is adopted.

As shown in FIGS. 2 and 3, in this press working step, the core of the rotor core 10 is punched, but the center hole 4 for the shaft and the hole 11 for burying the magnet 11 are formed.
a and a core sheet 10a punched out of a hole 12a having a bathtub-shaped cross section in which the grain-oriented electromagnetic steel sheet 12 is embedded. This caulking is performed by covering both ends of the laminated cores and passing rivets 13 for caulking through the holes 13a. Therefore, when the core sheet 10a is pressed, the holes 13a through which the rivets 13 pass are also punched.

Then, the magnet 11 is formed by IPM in the hole of the core of the rotor core 10 obtained by automatically pressing and laminating.
And the magnet 11 is magnetized and magnetized. The magnet 11 is magnetized and magnetized in the d-axis direction, and the direction of magnetization and magnetization of the adjacent magnet 11 is reversed.

The hole 13a for passing the rivet 13 is provided between the center hole 4 and the hole 12a of the grain-oriented electromagnetic steel plate 12 on the q axis. Therefore, as the material of the rivet 13, a magnetic material having good magnetic permeability is used. That is, the magnetic path from the stator core 1 (the magnetic path from one q-axis to the other q-axis) is not only the directional electromagnetic steel sheet 12 but also the magnet 11
And the center hole 4 to contribute to the q-axis inductance.

Further, the rotor core 1 formed as described above
If the DC motor is used as a DC brushless motor, for example, as a compressor motor of an air conditioner, the performance of the air conditioner can be improved (increased operation efficiency, reduced vibration and noise) without increasing cost. be able to.

FIGS. 5 and 6 show the grain-oriented electrical steel sheet 12.
It is a schematic perspective view which shows the modification of.

Incidentally, the grain-oriented electrical steel sheet 12 shown in FIG.
Is made of one magnetic steel sheet, and when a magnetic flux passes through it, eddy current is generated, so-called eddy current loss is generated, which hinders improvement of reluctance torque. Therefore, as shown in FIG. 5, in the grain-oriented electrical steel sheet 20, slits (long holes) 21, 22, and 23 are formed on each of the bent sides so that the flow of magnetic flux from one q-axis to the other q-axis is reduced. It is formed in a direction that does not hinder (the direction of magnetic flux), and is formed in a plurality in the axial direction of the center hole 4.

In this case, slits 21, 22, 23 are formed in one directional magnetic steel sheet, and then the directional magnetic steel sheet is bent into a bathtub shape in cross section.
What is necessary is just to embed in the hole 12a of the rotor core 10 as 0.

As described above, since the shape of the grain-oriented electrical steel sheet 20 is divided into a plurality of parts by the slits 21, the eddy current loss can be reduced, and the decrease in reluctance torque can be suppressed.

As shown in FIG. 6, the grain-oriented electrical steel sheet 30 is divided into a plurality of pieces in a direction that does not impede the flow of magnetic flux from one q-axis to the other q-axis (magnetic flux direction). .
In this case, the grain-oriented electrical steel sheet may be bent into a bathtub shape in cross section to form a plurality of grain-oriented electrical steel sheets 30a, and these grain-oriented electrical steel sheets 30a may be sequentially embedded in the holes 12a of the rotor core 10.

As described above, since the grain-oriented electrical steel sheet 30 is composed of a plurality of grain-oriented electrical steel sheets 30a, eddy current loss can be reduced, and reduction in reluctance torque can be suppressed.

FIGS. 7 and 8 are a schematic plan view and a schematic perspective view for explaining another embodiment of the present invention. In the drawing, the same parts as those in FIG. 1 are denoted by the same reference numerals, and the description thereof will not be repeated. For the configuration of the stator core, see FIG.

The rotor core 40 shown in FIG. 7 has a directional electromagnetic steel plate portion 41 in which a plurality of directional electromagnetic steel plates 41a and 41b are stacked in place of the directional electromagnetic steel plate 12 shown in FIG. Note that the distance between the directional electromagnetic steel plate portion 41 and the magnet 11 is equal to or greater than the thickness of the core sheet 10a as in the previous embodiment.

In this case, each of the grain-oriented electrical steel sheets 41a, 41
Since b is manufactured in the same manner as the grain-oriented electromagnetic steel sheet 12 and is buried by overlapping, the width of the region where the magnetic flux from one q-axis to the other q-axis can easily pass is widened. Accordingly, the q-axis inductance is larger than that of the previous embodiment, that is, the difference between the d-axis inductance and the q-axis inductance is larger, and the reluctance torque is increased.

The directional electromagnetic steel plate portion 41 is composed of two directional electromagnetic steel plates 41a and 41b, but the number thereof may be increased to improve the reluctance torque. In this case, since the rivet 13 is passed between the central hole 4 and the grain-oriented magnetic steel sheet part 41, the number of grain-oriented magnetic steel sheets may be determined in consideration of this.

In order to reduce the eddy current loss, as shown in FIG. 8, instead of the grain-oriented magnetic steel sheet part 41, the grain-oriented magnetic steel sheets 50a, 50a, 5
Slits 51 and 5 are formed in the grain-oriented electromagnetic steel sheet 50 on which
2 and 53 are preferably formed. The grain-oriented electrical steel sheet 50
The slits 51, 52, 53 provided in a may not coincide with the slits provided in the grain-oriented electrical steel sheet 51b.

Further, although not shown, for the same reason, each of the grain-oriented electromagnetic steel sheets 41 constituting
It is good to divide a and 41b into a plurality like the grain-oriented electrical steel sheet 30 shown in FIG. In this case, the grain-oriented electrical steel sheet 41
The division position of a and the division position of the grain-oriented electrical steel sheet 41b do not need to match.

The manufacturing of the rotor core using the above-described modified example of the grain-oriented magnetic steel sheet, the grain-oriented magnetic steel sheet part used in the other embodiment or the grain-oriented magnetic steel sheet part is performed in the same manner as in FIG. In order to embed the steel sheet or the directional electromagnetic steel sheet portion, holes having a width of two sheets of the directional electromagnetic steel sheet are formed in the core sheet 10a during automatic pressing.

The stator core 1 will be additionally described. In the stator core 1, for example, the outer-diameter winding is a U-phase, the inner-diameter winding is a W-phase, and an intermediate winding is a V-phase. The 24-slot stator core 1 has:
Although three-phase (U-phase, V-phase, and W-phase) armature windings are provided, the number of slots and the armature windings may be different.

[0045]

As described above, according to the first aspect of the present invention, in a permanent magnet motor having a rotor core inside a stator core for generating a rotating magnetic field, the rotor core is connected to the stator core. In order to secure a predetermined magnetic path width from one q-axis to the other q-axis for the magnetic path, magnets having a predetermined cross-sectional shape are arranged at equal intervals along the outer circumference of the rotor core by the number of poles in the vicinity of the d-axis. Along with the embedding, a directional electromagnetic steel sheet having a predetermined thickness is embedded at a constant interval so as to surround the center hole side of the magnet, and a magnet torque is generated with the magnetization direction of the adjacent magnet being reversed, and Since the difference between the d-axis and q-axis inductances is increased by the grain-oriented electrical steel sheet to generate reluctance torque, Since the easily as flux to the other q axis from one of the q-axis from the stator core by steel sheets, q-axis inductance increases. Therefore,
The reluctance torque can be increased, and the magnet torque can be maintained. By combining the reluctance torque and the magnet torque, high torque,
There is an effect that a highly efficient motor can be obtained.

According to the second aspect of the present invention, in the permanent magnet motor having the rotor core inside the stator core for generating the rotating magnetic field, the rotor core has a magnetic path from one of the q axes to the other q axis of the magnetic path from the stator core. In order to secure a predetermined magnetic path width, the outer peripheral side of the rotor core is formed into an arc curve, and the center hole side is formed into a bathtub curve, and a magnet having a cross section of a semicircular shape is provided along the outer periphery of the rotor core in the vicinity of the d axis. And embedded at equal intervals by the number of poles to surround the center hole side of this magnet,
The grain-oriented electrical steel sheet is cut to a predetermined thickness, and the grain-oriented electrical steel sheet is bent into the bathtub curve shape in cross section, and is embedded at a predetermined interval from the magnet. A torque is generated, and d-axis, q
Since the reluctance torque is generated by increasing the difference in shaft inductance, a low cost directional electromagnetic steel sheet is used to move one q-axis from the stator core to the other q-axis.
The magnetic flux to the axis can be easily passed, that is, the q-axis inductance can be increased to increase the difference between the d-axis and the q-axis inductance. Accordingly, the reluctance torque can be increased, and at least the magnet torque can be maintained by the magnet having a cross section of a semi-cylindrical shape, and a high torque, high efficiency motor can be obtained by combining the reluctance torque and the magnet torque. There is.

According to the third aspect of the present invention, the grain-oriented electrical steel sheet according to the first or second aspect is obtained by laminating a plurality of grain-oriented electrical steel sheets. Since the path width through which the magnetic flux from one q-axis to the other q-axis easily passes becomes wider, the difference between the d-axis and the q-axis inductances becomes larger, and the reluctance torque can be made larger. ,
There is an effect that a highly efficient motor can be obtained.

According to the invention of claim 4, according to claim 1,
Since the grain-oriented electrical steel sheet in 2 or 3 has a long slit in the same direction as the magnetic flux from the rotor core,
In addition to the effects of the first, second, and third aspects, there is an effect that the eddy current loss due to the grain-oriented electrical steel sheet can be reduced and the reduction of the reluctant torque can be suppressed.

According to the fifth aspect of the present invention, in each of the second and third aspects, a slit long in the same direction as the magnetic flux from the rotor core is provided on each side of the grain-oriented electrical steel sheet bent into the bathtub curve shape. Since at least one is formed, in addition to the effect of the second or third aspect, there is an effect that the eddy current loss due to the grain-oriented electrical steel sheet can be more appropriately reduced.

According to the invention of claim 6, according to claim 1,
The grain-oriented magnetic steel sheet in 2 or 3 is constituted by a plurality of grain-oriented magnetic steel sheets divided into two or more in the axial direction of the center hole. There is an effect that the eddy current loss due to the steel plate can be reduced and the reduction of the reluctant torque can be suppressed.

According to the invention of claim 7, according to claim 1,
In 2, 3, 4, 5 or 6, the rotor core is a core formed by automatically laminating an electromagnetic steel sheet in a mold while punching out the electromagnetic steel sheet by an automatic press. Simultaneously punching the buried holes, punching rivet through holes on the q axis between the buried hole of the grain-oriented electrical steel sheet and the center hole, and at least the interval between the holes is equal to or greater than the thickness of the electromagnetic steel sheet, 7. The effect of claim 1, 2, 3, 4, 5 or 6, wherein the magnet and the grain-oriented electrical steel sheet are embedded in the automatically laminated core, and caulked through a rivet of a magnetic material. When producing a core, it is possible to eliminate the occurrence of burrs and the like, and to produce a core of good quality. Therefore, the yield of the core can be improved, and the cost of the motor can be reduced. Further, by using a rivet made of a magnetic material having a high magnetic permeability, the reluctance torque can be increased, and as a result, higher torque and higher efficiency can be achieved. There is an effect that you can expect.

According to the invention of claim 8, according to claim 1,
In 2, 3, 4, 5 or 6, since the magnet is a ferrite magnet, in addition to the effects of claims 1, 2, 3, 4, 5 and 6, a low-cost motor is obtained by using an inexpensive ferrite magnet. Is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of a permanent magnet motor showing one embodiment of the present invention.

FIG. 2 is a schematic side sectional view of a rotor core for explaining the permanent magnet electric motor shown in FIG.

FIG. 3 is a schematic plan view of a rotor core for explaining the permanent magnet electric motor shown in FIG. 1;

FIG. 4 is a schematic perspective view of a grain-oriented electrical steel sheet embedded in the rotor core shown in FIG. 3;

FIG. 5 is a schematic perspective view of a grain-oriented electrical steel sheet showing a modification of the present invention.

FIG. 6 is a schematic perspective view of a grain-oriented electrical steel sheet showing another modification of the present invention.

FIG. 7 is a schematic plan view of a rotor core for illustrating a permanent magnet motor according to another embodiment of the present invention.

8 is a schematic perspective view of a grain-oriented electrical steel sheet embedded in a rotor core of the permanent magnet motor shown in FIG.

FIG. 9 is a schematic plan view of a conventional permanent magnet motor.

[Explanation of symbols]

Reference Signs List 1 stator core 4 center hole (for shaft) 10, 40 rotor core 10a core sheet 11 magnet (semi-cylindrical section) 11a hole (magnet buried hole) 12, 20, 30, 30a, 41a, 41b, 50a,
50b Grain-oriented magnetic steel sheet 12a Hole (buried hole for grain-oriented magnetic steel sheet) 13 Rivet 13a Hole (rivet through hole) 21, 22, 23, 51, 52, 53 Slit 41, 50 Grain-oriented magnetic steel sheet part

Claims (8)

[Claims] 1. A permanent magnet motor having a rotor core inside a stator core for generating a rotating magnetic field, wherein the rotor core has a predetermined magnetic path width from one q-axis to the other q-axis for a magnetic path from the stator core. As
A magnet having a predetermined cross-sectional shape is buried in the vicinity of the d-axis along the outer periphery of the rotor core at equal intervals by the number of poles, and a directional electromagnetic member having a predetermined thickness is provided at a constant interval so as to surround the center hole side of the magnet. By embedding a steel plate, generating magnet torque by reversing the magnetization direction of the adjacent magnet, and generating a reluctance torque by increasing the difference in d-axis and q-axis inductances by the directional magnetic steel plate. A permanent magnet electric motor characterized in that: 2. A permanent magnet motor having a rotor core inside a stator core that generates a rotating magnetic field, wherein the rotor core has a predetermined magnetic path width from one q axis to the other q axis with respect to a magnetic path from the stator core. As
While the outer peripheral side of the rotor core is an arc curve, the center hole side is a bathtub curve and a magnet having a cross section in the shape of a cross section is buried in the vicinity of the d axis at equal intervals along the outer circumference of the rotor core by the number of poles, In order to surround the center hole side of the magnet, a directional electromagnetic steel sheet having a predetermined thickness is cut, the directional electromagnetic steel sheet is bent into the cross-section bathtub curve shape, and embedded at a constant interval from the magnet, A magnet torque is generated by reversing the magnetization direction of the adjacent magnet, and a difference in d-axis and q-axis inductances is increased by the grain-oriented magnetic steel sheet to generate reluctance torque. Permanent magnet motor. 3. The permanent magnet motor according to claim 1, wherein the grain-oriented electrical steel sheet is formed by stacking a plurality of grain-oriented electrical steel sheets. 4. The permanent magnet electric motor according to claim 1, wherein the grain-oriented electrical steel sheet has a slit elongated in the same direction as the magnetic flux from the rotor core. 5. The slit according to claim 2, wherein one or more slits are formed on each side of the grain-oriented electrical steel sheet bent into the bathtub curve shape in cross section, the slit being long in the same direction as the magnetic flux from the rotor core. Permanent magnet motor. 6. The permanent magnet electric motor according to claim 1, wherein the directional magnetic steel sheet is constituted by a plurality of directional magnetic steel sheets divided into two or more in an axial direction of the center hole. 7. The rotor core is a core formed by punching out an electromagnetic steel sheet by an automatic press and automatically laminating the magnetic steel sheet in a mold. Along with punching, a rivet through hole was punched on the q axis between the buried hole of the grain-oriented electrical steel sheet and the center hole, and at least the interval between the holes was set to be equal to or greater than the thickness of the electromagnetic steel sheet, and the automatic lamination was performed. 7. The permanent magnet motor according to claim 1, wherein the magnet and the grain-oriented electrical steel sheet are embedded in a core and swaged through a rivet of a magnetic material. 8. A permanent magnet motor according to claim 1, wherein said magnet is a ferrite magnet.