Permanent magnet synchronous motor
The asymmetrical rotor design with varying void sizes in the embedded holes effectively reduces torque pulsation in permanent magnet synchronous motors, enhancing torque consistency and efficiency.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- MAYEKAWA MFG CO LTD
- Filing Date
- 2024-12-26
- Publication Date
- 2026-07-08
AI Technical Summary
Existing permanent magnet synchronous motors suffer from torque pulsation due to differences in magnetic resistance, leading to increased manufacturing costs and reduced torque efficiency in existing solutions.
A rotor design with asymmetrical embedded holes in the rotor, featuring varying void sizes and orientations to shift the d-axis relative to the q-axis, effectively canceling out harmonic components and reducing torque ripple.
The design significantly reduces torque ripple while maintaining torque, achieving improved torque consistency and efficiency.
Smart Images
Figure 2026114413000001_ABST
Abstract
Description
Technical Field
[0001] The present disclosure relates to a permanent magnet synchronous motor.
Background Art
[0002] As a power source for driving a rotary machine such as an electric compressor used in, for example, an air conditioner or a refrigerator, a permanent magnet synchronous motor is known. The permanent magnet synchronous motor operates by applying an alternating voltage to a coil installed in a stator slot to generate a rotating magnetic field, and causing a rotor provided with permanent magnets to rotate synchronously so that the permanent magnets provided on the rotor are attracted to the rotating magnetic field.
[0003] Among this type of permanent magnet synchronous motor, a permanent magnet embedded type permanent magnet synchronous motor in which permanent magnets are embedded in the rotor is called an IPM (Interior Permanent Magnet) motor, and has the advantage of being able to utilize reluctance torque in addition to magnet torque. In such an IPM motor, the iron core region constituting the stator has a small magnetic resistance because magnetic flux easily passes through it, while in the slot provided for installing the coil in the stator, there is an air portion in the inlet region, so magnetic flux hardly passes through and the magnetic resistance becomes large. Due to such a difference in magnetic resistance, it is known that pulsation (torque ripple) occurs in the magnet torque.
[0004] As a technique for reducing such pulsation in magnet torque, for example, Non-Patent Document 1 describes applying skew to the rotor, and Patent Document 1 describes a method of making the interlinking magnetic flux approach a sine wave by increasing the air gap in the q-axis direction. Further, Patent Document 2 discloses a rotor structure in which a flux barrier on the rear side in the rotation direction of the rotor is enlarged in order to effectively utilize magnet torque and reluctance torque in an IPM motor.
Prior Art Documents
Patent Documents
[0005] [Patent Document 1] Japanese Patent Publication No. 2000-197292 [Patent Document 2] Patent No. 5114963 [Non-patent literature]
[0006] [Non-Patent Document 1] Daido Steel Technical Report, Electrical Steelmaking Vol. 82 No. 1: Optimization of Skew Conditions for Cogging Torque Reduction [Overview of the Initiative] [Problems that the invention aims to solve]
[0007] Non-patent document 1 above attempts to reduce pulsation by adding skew to the rotor, but adding skew increases assembly steps and leads to higher manufacturing costs. In addition, the reduction in flux linkage results in a decrease in torque. In the above-mentioned Patent Document 1, increasing the air gap of the q-axis reduces the salient pole ratio, making it impossible to effectively utilize the reluctance torque. Therefore, in order to obtain sufficient torque, it becomes necessary to increase the amount of magnets embedded in the rotor. Furthermore, in the above-mentioned Patent Document 2, although increasing the flux barrier on the rear side in the rotational direction can increase torque while reducing the amount of magnets embedded in the rotor, it is not possible to reduce pulsation.
[0008] At least one embodiment of this disclosure has been made in view of the above circumstances and aims to provide a permanent magnet synchronous motor that can reduce pulsation occurring in the magnet torque while maintaining torque. [Means for solving the problem]
[0009] A permanent magnet synchronous motor according to at least one embodiment of this disclosure solves the above problem, A rotor that can rotate around the axis of rotation, Multiple embedded holes are provided in the rotor along the circumferential direction with respect to the rotation axis, Multiple permanent magnets are embedded in each of the aforementioned multiple buried holes, Equipped with, Each of the aforementioned plurality of buried holes is The main body in which the aforementioned permanent magnet is embedded, A first gap portion is provided upstream of the main body portion in the rotational direction, A second gap is provided downstream of the main body in the rotational direction, Includes, The plurality of buried holes include a first buried hole and a second buried hole adjacent to the first buried hole on the downstream side in the rotational direction, The first buried hole has a second void that is larger than the first void, The second buried hole has the first void portion which is larger than the second void portion. [Effects of the Invention]
[0010] According to at least one embodiment of the present disclosure, a permanent magnet synchronous motor is provided that can suitably reduce torque ripple while maintaining torque. [Brief explanation of the drawing]
[0011] [Figure 1] This is a cross-sectional view of a permanent magnet synchronous motor according to one embodiment. [Figure 2] This is a cross-sectional diagram of a permanent magnet synchronous motor related to reference technology. [Figure 3A] This figure shows the rotor magnetic flux generated by the permanent magnets embedded in the rotor shown in Figure 2. [Figure 3B] This figure shows the stator magnetic flux generated by the coils installed in the slots of the stator in Figure 2. [Figure 4A] Figure 1 shows an example of the measurement results of cogging torque as a function of electrical angle for a permanent magnet synchronous motor. [Figure 4B] Figure 4A shows the FFT analysis results of the cogging torque. [Figure 5] Figure 1 shows an example of the measured load torque with respect to electrical angle at the same current for a permanent magnet synchronous motor, compared with reference technology. [Figure 6] Verification results of the relationship between the normalized deviation amount and the harmonic components included in the cogging torque in the permanent magnet synchronous motor of FIG. 1.
Embodiments for Carrying Out the Invention
[0012] Hereinafter, some embodiments of the present disclosure will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the configurations described as embodiments or shown in the drawings are not intended to limit the scope of the present disclosure, but are merely illustrative examples.
[0013] FIG. 1 is a cross-sectional configuration diagram of a permanent magnet synchronous motor 1 according to an embodiment. The permanent magnet synchronous motor 1 includes a rotor 2 and a stator 4.
[0014] The rotor 2 is a rotating body (rotor) that can rotate around the rotation axis L, and is rotatably supported by bearings (not shown) in the front and rear in the axial direction of the rotation axis L. Although the detailed structure of the rotor 2 will be omitted, for example, the rotor 2 is configured by laminating a plurality of laminated plates made of a magnetic material along the axial direction. A pair of fixing plates are disposed at both axial ends of these plurality of laminated plates, and a shaft member provided between the pair of fixing plates may be inserted through the plurality of laminated plates, and the pair of fixing plates may be fastened to fix the plurality of laminated plates.
[0015] The rotor 2 is provided with a plurality of embedding holes 8 for embedding a plurality of permanent magnets 6 respectively. The plurality of embedding holes 8 are provided along the circumferential direction with respect to the rotation axis L. Each of the plurality of embedding holes 8 includes a main body portion 8a, a first gap portion 8b, and a second gap portion 8c. A permanent magnet 6 is embedded in the main body portion 8a. The first gap portion 8b is provided on the upstream side in the rotation direction from the main body portion 8a in which the permanent magnet 6 is embedded. The second gap portion 8c is provided on the downstream side in the rotation direction from the main body portion 8a in which the permanent magnet 6 is embedded. No permanent magnet 6 is embedded in the first gap portion 8b and the second gap portion 8c, and they are, for example, air gaps occupied by air.
[0016] The stator 4 is a stator disposed on the outer circumference side of the rotor 2 with a predetermined gap between them. On the inner circumferential surface of the stator 4 facing the rotor 2, a plurality of slots 10 are provided at predetermined pitch intervals along the circumferential direction of the rotation axis L. Coils for generating a rotating magnetic field are installed in each of the plurality of slots 10.
[0017] In the permanent magnet synchronous motor 1 having the above configuration, a rotating magnetic field is generated by applying an AC voltage to a coil installed in the slot 10 of the stator 4, and the rotor 2 rotates synchronously along the rotation direction A so that the permanent magnets 6 embedded in the embedded holes 8 of the rotor 2 are attracted to the rotating magnetic field, thereby enabling operation.
[0018] In the following explanation, we will focus on the first buried hole 8-1 and the second buried hole 8-2, which is adjacent to the first buried hole 8-1 on the downstream side in the rotational direction, among the multiple buried holes 8 provided in the rotor 2.
[0019] Here, we will explain the permanent magnet synchronous motor 1' related to the reference technology. Figure 2 is a cross-sectional view of the permanent magnet synchronous motor 1' related to the reference technology, Figure 3A shows the rotor magnetic flux B1 generated by the permanent magnet 6 embedded in the rotor 2 of Figure 2, and Figure 3B shows the stator magnetic flux B2 generated by the coil provided in the slot 10 of the stator 4 of Figure 2.
[0020] The permanent magnet synchronous motor 1' relating to this reference technology differs in that each of the multiple embedded holes 8 provided in the rotor 2 has a symmetrical configuration with respect to a reference line M passing through the rotation axis L and the center of the main body 8a (the midpoint between the two ends along the rotation direction A of the main body 8a). Specifically, in both the first embedded hole 8-1 and the second embedded hole 8-2, the first void 8b and the second void 8c are formed to have equal circumferential widths along the radial direction of the rotation axis L and are configured to have the same shape as each other.
[0021] Furthermore, unless otherwise specified, the other configurations of the permanent magnet synchronous motor 1' relating to the reference technology are the same as those of the permanent magnet synchronous motor 1 according to this embodiment, so redundant explanations will be omitted as appropriate.
[0022] Figure 3A shows the rotor magnetic flux B1 generated by the permanent magnets 6 embedded in the embedded holes 8 provided in the rotor 2. The dm axis is the direction through which the rotor magnetic flux B1 easily passes, and the qm axis is the direction through which the rotor magnetic flux B1 difficult to pass. As mentioned above, in the permanent magnet synchronous motor 1' relating to the reference technology, each embedded hole 8 has a symmetrical configuration with respect to the reference line M, so the dm axis coincides with the reference line M. The qm axis is located between the dm axes corresponding to adjacent embedded holes 8. That is, the dm axis corresponding to the first embedded hole 8-1 is located 45 degrees upstream in the rotational direction relative to the qm axis, and the dm axis corresponding to the second embedded hole 8-2 is located 45 degrees downstream in the rotational direction relative to the qm axis.
[0023] Figure 3B also shows the stator magnetic flux B2 generated by the coils provided in the slots 10 of the stator 4. The dr axis is the direction through which the stator magnetic flux B2 easily passes, and the qr axis is the direction through which the stator magnetic flux B2 difficult to pass. As mentioned above, in the permanent magnet synchronous motor 1' relating to the reference technology, each buried hole 8 has a symmetrical configuration with respect to the reference line M, so the qr axis coincides with the reference line M. The dr axis is located between the qr axes corresponding to adjacent buried holes 8. That is, the qr axis corresponding to the first buried hole 8-1 is located 45 degrees upstream in the rotational direction relative to the dr axis, and the qr axis corresponding to the second buried hole 8-2 is located 45 degrees downstream in the rotational direction relative to the dr axis.
[0024] As a result, in the permanent magnet synchronous motor 1' relating to the reference technology, as shown in Figure 2, the dm axis and the qr axis coincide, and the qm axis and the dr axis coincide. In a permanent magnet synchronous motor 1' having such a configuration, a certain amount of pulsation occurs in the magnet torque, but this pulsation can be suitably reduced by the permanent magnet synchronous motor 1 according to this embodiment while maintaining the load torque, as will be explained below.
[0025] As shown in Figure 1, in the permanent magnet synchronous motor 1 according to this embodiment, the multiple embedded holes 8 provided in the rotor 2 each have an asymmetrical configuration with respect to the reference line M. In particular, in this embodiment, the first embedded hole 8-1 has a second void 8c that is larger than the first void 8b, while the second embedded hole 8-2 has a first void 8b that is larger than the second void 8c.
[0026] The specific configurations of the first void 8b and the second void 8c are not limited, but to describe one example, in the first buried hole 8-1, the first void 8b is configured to have a uniform circumferential width along the radial direction of the rotation axis L, while the second void 8c is configured to have a circumferential width that widens from the radially inner side to the radially outer side of the rotation axis L. Similarly, in the second buried hole 8-2, the first void 8b is configured to have a circumferential width that widens from the radially inner side to the radially outer side of the rotation axis L, while the second void 8c is configured to have a uniform circumferential width along the radial direction of the rotation axis L. In other words, in a pair of adjacent buried holes 8 (first buried hole 8-1 and second buried hole 8-2), the voids that are back-to-back with each other are configured to be larger than the other void.
[0027] As a result, in the region corresponding to the first buried hole 8-1, the second void 8c, which is located downstream of the first void 8b in the rotational direction, is larger, so the dm axis is shifted upstream of the qr axis in the rotational direction. On the other hand, in the region corresponding to the second buried hole 8-2, the first void 8b, which is located upstream of the second void 8c in the rotational direction, is larger, so the dm axis is shifted downstream of the qr axis in the rotational direction. In other words, the direction of the shift of the dm axis relative to the qr axis is reversed between the region corresponding to the first buried hole 8-1 and the region corresponding to the second buried hole 8-2.
[0028] Furthermore, in the permanent magnet synchronous motor 1 according to this embodiment, the qm axis and the dr axis remain aligned with each other, similar to the permanent magnet synchronous motor 1' in the reference technology described above.
[0029] Next, we will explain the verification results of the performance of the permanent magnet synchronous motor 1 having the above configuration, compared with the permanent magnet synchronous motor 1' related to the reference technology mentioned above. Figure 4A is an example of the measurement results of the cogging torque with respect to the electrical angle of the permanent magnet synchronous motor 1 in Figure 1, and Figure 4B is the FFT analysis result of the cogging torque shown in Figure 4A.
[0030] As shown in Figures 4A and 4B, it was confirmed that the permanent magnet synchronous motor 1 according to this embodiment significantly reduced the harmonic components (especially the 12th harmonic component) of the cogging torque compared to the permanent magnet synchronous motor 1' according to the reference technology. This indicates that in the permanent magnet synchronous motor 1, the phase of the magnet torque in the harmonic frequency band is reversed in the first buried hole 8-1 and the second buried hole 8-2 because the direction of displacement of the dm axis with respect to the qr axis is opposite to that of the first buried hole 8-1 and the second buried hole 8-2, thereby canceling out the harmonic components of the magnet torque and reducing pulsation.
[0031] Figure 5 shows an example of the measured load torque with respect to electrical angle at the same current for the permanent magnet synchronous motor 1 in Figure 1, compared with the reference technology. As shown in Figure 5, in the permanent magnet synchronous motor 1 according to this embodiment, a reduction in torque ripple was observed in the load torque compared to the permanent magnet synchronous motor 1' according to the reference technology.
[0032] As described above, in the permanent magnet synchronous motor 1 according to this embodiment, the effect of reducing magnet torque pulsation can be obtained by shifting the dm axis relative to the qr axis in the region corresponding to each embedded hole 8. Here, we will describe the results of our verification of the relationship between the amount of displacement of the dm axis relative to the qr axis and the harmonic components of the pulsation. Here, the amount of displacement of the dm axis relative to the qr axis is defined as the actual amount of displacement θ1 of the dm axis relative to the qr axis, normalized with respect to the width size θ of the slot 10 along the circumferential direction of the rotation axis L (hereinafter referred to as "normalized displacement θ1 / θ" as appropriate).
[0033] Figure 6 shows the results of verifying the relationship between the normalized deviation θ1 / θ and the harmonic components included in the cogging torque in the permanent magnet synchronous motor 1 shown in Figure 1. The vertical axis of Figure 6 shows the ratio based on the value of the harmonic components in the permanent magnet synchronous motor 1' related to the reference technology, as an index of the harmonic components.
[0034] As the normalized deviation θ1 / θ is gradually increased, the harmonic components of the cogging torque gradually decrease, and at a normalized deviation θ1 / θ of 0.25, the harmonic components reach their minimum value. If the normalized deviation θ1 / θ is further increased, the harmonic components of the cogging torque begin to increase. From these verification results, it was confirmed that in the numerical range of normalized deviation θ1 / θ from 0.22 to 0.28, the harmonic components of the cogging torque can be suppressed to 50% or less compared to the permanent magnet synchronous motor 1' related to the reference technology. Furthermore, when the normalized deviation θ1 / θ is 0.25, the harmonic components of the cogging torque reach their minimum value of approximately zero, confirming that the harmonic components of the cogging torque can be suppressed in the best possible way.
[0035] As described above, according to the above embodiment, the pulsation of the magnet torque can be suitably reduced while maintaining torque.
[0036] This disclosure is not limited to the embodiments described above, but also includes modified forms of the embodiments described above, as well as forms that combine these forms as appropriate.
[0037] The contents described in each of the above embodiments can be understood, for example, as follows:
[0038] (1) A permanent magnet synchronous motor according to one embodiment is: A rotor that can rotate around the axis of rotation, Multiple embedded holes are provided in the rotor along the circumferential direction with respect to the rotation axis, Multiple permanent magnets are embedded in each of the aforementioned multiple buried holes, Equipped with, Each of the aforementioned plurality of buried holes is The main body in which the aforementioned permanent magnet is embedded, A first gap portion is provided upstream of the main body portion in the rotational direction, A second gap is provided downstream of the main body in the rotational direction, Includes, The plurality of buried holes include a first buried hole and a second buried hole adjacent to the first buried hole on the downstream side in the rotational direction, The first buried hole has a second void that is larger than the first void, The second buried hole has the first void portion which is larger than the second void portion.
[0039] According to the embodiment of (1) above, each of the plurality of embedding holes provided for embedding permanent magnets in the rotor includes a main body in which the permanent magnets are embedded, a first void provided upstream of the main body in the rotational direction, and a second void provided downstream of the main body in the rotational direction. In the first embedding hole, the second void is larger than the first void, while in the second embedding hole adjacent to the first embedding hole downstream in the rotational direction, the first void is larger than the second void. This allows for a suitable reduction in magnet torque pulsation while maintaining torque.
[0040] (2) In other embodiments, in the embodiment of (1) above, In the region corresponding to the first buried hole, the d-axis corresponding to the permanent magnet is shifted upstream in the rotational direction relative to the q-axis corresponding to the rotating magnetic field provided on the outer circumference of the rotor, In the region corresponding to the second buried hole, the d-axis corresponding to the permanent magnet is shifted downstream in the rotational direction relative to the q-axis corresponding to the rotating magnetic field.
[0041] According to the embodiment of (2) above, in the region corresponding to the first buried hole, the second void located downstream of the first void in the rotational direction is larger, so the d-axis (i.e., dm-axis) corresponding to the permanent magnet is shifted upstream in the rotational direction with respect to the q-axis (i.e., qr-axis) corresponding to the rotating magnetic field provided by the stator on the outer circumference of the rotor core. On the other hand, in the region corresponding to the second buried hole, the first void located upstream of the second void in the rotational direction is larger, so the d-axis (i.e., dm-axis) corresponding to the permanent magnet is shifted downstream in the rotational direction with respect to the q-axis (i.e., qr-axis) corresponding to the rotating magnetic field provided by the stator on the outer circumference of the rotor core. In this way, in the first and second buried holes, the direction of the shift of the dm-axis relative to the qr-axis is opposite to that of the qr-axis, which inverts the phase of the magnet torque in the harmonic frequency band, thereby canceling out the harmonic components of the magnet torque and effectively reducing pulsation.
[0042] (3) In other embodiments, in the embodiment of (2) above, The amount of displacement of the d-axis corresponding to the permanent magnet relative to the q-axis corresponding to the rotating magnetic field is 22-28% of the slot width into which the coil provided in the stator for generating the rotating magnetic field is inserted.
[0043] According to the embodiment of (3) above, the amount of displacement of the QR axis with respect to the dm axis in the first or second buried hole may be within a numerical range of 22-28% of the slot width into which the coil provided in the stator for generating a rotating magnetic field is inserted. This allows for effective suppression of magnet torque pulsation while maintaining torque.
[0044] (4) In other embodiments, in the embodiment of (3) above, The aforementioned displacement is 25% of the slot width.
[0045] According to the embodiment of (4) above, the amount of displacement of the qr axis with respect to the dm axis in the first or second buried hole may be 25% of the slot width into which the coil provided in the stator for generating a rotating magnetic field is inserted. In this case, the pulsation of the magnet torque can be more preferably suppressed while maintaining the torque.
[0046] (5) In other embodiments, in any one embodiment of (2) to (4) above, The q-axis corresponding to the permanent magnet and the d-axis corresponding to the rotating magnetic field are configured to coincide.
[0047] According to the embodiment of (5) above, in the first and second buried holes, the qm axis and the dr axis coincide, while the qr axis is offset relative to the dm axis, thereby effectively suppressing the pulsation of the magnet torque while maintaining the torque.
[0048] (6) In other embodiments, in any one embodiment of (1) to (5) above, The first void portion of the first buried hole has a circumferential width that is equal along the radial direction of the rotation axis. The second void portion of the first buried hole is configured such that its circumferential width increases from the radially inner side to the radially outer side of the rotation axis.
[0049] According to the embodiment of (6) above, in the first buried hole, a second void portion is provided that is larger than the first void portion in a suitable layout, by configuring the second void portion to have a wider circumferential width from the radially inner side to the radially outer side of the rotation axis, in addition to the first void portion which has a uniform circumferential width along the radial direction of the rotation axis.
[0050] (7) In other embodiments, in any one embodiment of (1) to (6) above, The first void portion of the second buried hole is configured such that its circumferential width increases from the radially inner side to the radially outer side of the rotation axis. The second void in the second buried hole has a circumferential width that is equal along the radial direction of the rotation axis.
[0051] According to the above embodiment (7), in the second buried hole, a first void portion larger than the second void portion can be provided in a suitable layout by configuring the first void portion to have a wider circumferential width from the radially inner side to the radially outer side of the rotation axis, in contrast to the second void portion which has an equal circumferential width along the radial direction of the rotation axis.
[0052] (8) In other embodiments, in any one embodiment of (1) to (7) above, This is a hermetic motor that operates in an environment containing corrosive gases.
[0053] According to the embodiment of (8) above, in the permanent magnet synchronous motor according to each of the embodiments described above, the harmonic components of the magnet torque can be suppressed by the structural features of the void portion, without filling the void portion of the embedding hole in which the permanent magnet is embedded with a non-magnetic material that has low resistance to corrosive gases such as ammonia, chlorine, or hydrocarbons. For this reason, it can be suitably used as a hermetic motor used in an atmosphere of corrosive gases such as ammonia, chlorine, or hydrocarbons. [Explanation of Symbols]
[0054] 1. Permanent magnet synchronous motor 2 rotors 4 Stator 6 Permanent Magnets 8. Burial hole 8-1 First buried hole 8-2 Second buried hole 8a Main body 8b 1st cavity 8c 2nd cavity 10 slots L rotation axis A Rotation direction M reference line B1 Rotor magnetic flux B2 Stator flux
Claims
1. A rotor that can rotate around the axis of rotation, Multiple embedded holes are provided in the rotor along the circumferential direction with respect to the rotation axis, Multiple permanent magnets are embedded in each of the aforementioned multiple buried holes, Equipped with, Each of the aforementioned plurality of buried holes is The main body in which the aforementioned permanent magnet is embedded, A first gap portion is provided upstream of the main body portion in the rotational direction, A second gap is provided downstream of the main body in the rotational direction, Includes, The plurality of buried holes include a first buried hole and a second buried hole adjacent to the first buried hole on the downstream side in the rotational direction, The first buried hole has a second void that is larger than the first void, A permanent magnet synchronous motor wherein the second buried hole has the first void portion larger than the second void portion.
2. In the region corresponding to the first buried hole, the d-axis corresponding to the permanent magnet is shifted upstream in the rotational direction relative to the q-axis corresponding to the rotating magnetic field provided on the outer circumference of the rotor, In the region corresponding to the second buried hole, the d-axis corresponding to the permanent magnet is shifted downstream in the rotational direction with respect to the q-axis corresponding to the rotating magnetic field, as described in claim 1.
3. The permanent magnet synchronous motor according to claim 2, wherein the amount of displacement of the d-axis corresponding to the permanent magnet with respect to the q-axis corresponding to the rotating magnetic field is 22 to 28% of the slot width into which the coil provided in the stator for generating the rotating magnetic field is inserted.
4. The permanent magnet synchronous motor according to claim 3, wherein the displacement is 25% of the slot width.
5. The permanent magnet synchronous motor according to claim 2, wherein the q-axis corresponding to the permanent magnet and the d-axis corresponding to the rotating magnetic field coincide.
6. The first void portion of the first buried hole has a circumferential width that is equal along the radial direction of the rotation axis. The permanent magnet synchronous motor according to claim 1 or 2, wherein the second void portion of the first embedded hole is configured such that its circumferential width increases from the radially inner side to the radially outer side of the rotating shaft.
7. The first void portion of the second buried hole is configured such that its circumferential width increases from the radially inner side to the radially outer side of the rotation axis. The permanent magnet synchronous motor according to claim 1 or 2, wherein the second void portion of the second buried hole has a circumferential width equal to that along the radial direction of the rotation axis.
8. A permanent magnet synchronous motor according to claim 1 or 2, which is a hermetic motor operated in an environment containing corrosive gases.