Permanent Magnet Synchronous Motor

Abstract

This rotor comprises a rotor core, a shaft disposed inside the rotor core and extending in the axial direction, and a plurality of permanent magnets provided on the rotor core, wherein: the rotor core is provided with lightening holes; and the number of the lightening holes is different from the number of pole pairs of the plurality of permanent magnets.

Description

Technical Field

[0001] The present disclosure relates to a permanent magnet synchronous motor. 、

Background Art

[0002] Conventionally, a permanent magnet synchronous motor is known as a motor used in in-vehicle devices used in electric vehicles and the like, compressors used in air conditioners and the like, and industrial machines and the like. The permanent magnet synchronous motor includes a stator and a rotor rotatably provided with respect to the stator. The rotor has a rotor core and a plurality of permanent magnets provided on the rotor core. In Patent Document 1, in order to reduce the weight of the rotor, a vent hole is provided in the rotor core.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By providing a vent hole in the rotor core, cogging torque and torque ripple may occur. In a permanent magnet synchronous motor, it is required to reduce cogging torque and torque ripple.

[0005] The present disclosure has been made to solve the above problems, and it is possible to reduce cogging torque and torque ripple while achieving weight reduction None with the object of providing a permanent magnet synchronous motor.

Means for Solving the Problems

[0006] ​The rotor according to the present disclosure includes a rotor core, a shaft disposed inside the rotor core and extending in the axial direction, and a plurality of permanent magnets provided on the rotor core. A through hole is provided in the rotor core, and the number of the through holes is different from the number of pole pairs of the plurality of permanent magnets.

[0007] The permanent magnet synchronous motor according to the present disclosure includes the rotor and a stator provided so as to surround the outer periphery of the rotor.

Advantages of the Invention

[0008] According to the present disclosure, it is possible to provide a rotor and a permanent magnet synchronous motor capable of reducing cogging torque and torque ripple while achieving weight reduction.

Brief Description of the Drawings

[0009]

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Embodiments for Carrying Out the Invention

[0010] Embodiment 1. FIG. 1 is a cross-sectional view of the permanent magnet synchronous motor 100 in Embodiment 1, taken perpendicular to the axial direction. The permanent magnet synchronous motor 100 has a stator 10 and a rotor 20 provided inside the stator 10. The rotor 20 is rotatable about the axis O with respect to the stator 10. In this specification, the direction along the axis O of the rotor 20 is referred to as the "axial direction". Also, a cross-section perpendicular to the axial direction is referred to as a "cross-sectional plane". In the cross-sectional plane, the direction intersecting the axis O is referred to as the "radial direction", and the direction circulating around the axis O is referred to as the "circumferential direction".

[0011] The stator 10 is provided so as to surround the outer periphery of the rotor 20. A gap 15 is formed between the inner periphery of the stator 10 and the outer periphery of the rotor 20. The gap 15 is formed over the entire circumference in the circumferential direction.

[0012] The stator 10 has a stator core 11 and a plurality of windings 14. The stator core 11 has an annular core back 12 and a plurality of teeth 13. The core back 12 has a plurality of core blocks 12a formed in an arc shape along the circumferential direction, and is formed in an annular shape by arranging the core blocks 12a in the circumferential direction. The teeth 13 project from the central portion in the circumferential direction of each core block 12a toward the inside in the radial direction. Each winding 14 is wound around a plurality of teeth 13 respectively.

[0013] In the configuration shown in FIG. 1, the core back 12 is formed by a plurality of core blocks 12a. However, the core back 12 may be integrally formed in an annular shape. Also, in the configuration shown in FIG. 1, the core back 12 and the plurality of teeth 13 are integrally formed. However, the core back 12 and the plurality of teeth 13 may be formed separately.

[0014] The rotor 20 has a rotor core 21, a plurality of permanent magnets 22, and a shaft 23. The rotor core 21 has a cylindrical shape extending in the axial direction. The rotor core 21 is formed of a magnetic material. The rotor core 21 is formed, for example, by laminating a plurality of core plates such as electromagnetic steel sheets in the axial direction. The shaft 23 is disposed inside the rotor core 21 and extends in the axial direction. The shaft 23 is fixed to the rotor core 21.

[0015] The plurality of permanent magnets 22 are provided at intervals in the circumferential direction on the outer peripheral surface of the rotor core 21. The plurality of permanent magnets 22 are arranged at equal intervals in the circumferential direction. Each permanent magnet 22 is magnetized so that an S pole or an N pole appears on its outer peripheral surface (the surface facing the stator 10). The permanent magnets 22 adjacent to each other in the circumferential direction are magnetized so that the poles appearing on their outer peripheral surfaces are different from each other. That is, when one outer peripheral surface of the permanent magnets 22 adjacent to each other in the circumferential direction is an N pole, the other outer peripheral surface is an S pole. The permanent magnet synchronous motor 100 in the present embodiment is a surface magnet type (Surface Permanent Magnetic, SPM) motor in which a plurality of permanent magnets 22 are arranged on the outer peripheral surface of the rotor core 21.

[0016] In the configuration shown in FIG. 1, the number of teeth 13 is 12. The number of windings 14 is 12. The number of permanent magnets 22 (i.e., the number of magnetic poles) Nm is 8. Also, the number of pole pairs Pm of the permanent magnets 22 with N poles and S poles as a pair is 4. That is, the permanent magnet synchronous motor 100 in the present embodiment is a so-called 8-pole 12-slot motor. Note that the numbers of the teeth 13, the windings 14, and the permanent magnets 22 are not limited to these. The number of teeth 13 and the number of windings 14 may be different.

[0017] The rotor core 21 is provided with a plurality of through holes 31. By providing the through holes 31, the weight of the rotor 20 can be reduced, and the moment of inertia of the rotor 20 can be reduced. The punching holes 31 are formed to penetrate the rotor core 21 in the axial direction. The punching holes 31 are formed in an arc shape along the circumferential direction. The plurality of punching holes 31 are arranged at equal intervals in the circumferential direction. The plurality of punching holes 31 have the same shape. The punching holes 31 are arranged radially inside the permanent magnets 22. The punching holes 31 are arranged such that the circumferential center of the punching holes 31 coincides with the circumferential center of the permanent magnets 22 in the circumferential direction. The punching holes 31 are formed symmetrically with respect to a straight line connecting the axis O of the shaft 23 and the circumferential center of the punching holes 31.

[0018] In the present embodiment, the number Nl of the punching holes 31 is 2. That is, the number Nl of the punching holes 31 is different from the number Pm of the pole pairs of the permanent magnets 22. The number Nl of the punching holes 31 is smaller than the number Pm of the pole pairs of the permanent magnets 22. Also, the number Nl of the punching holes 31 is different from the number Nm of the permanent magnets 22.

[0019] The operation of the permanent magnet synchronous motor 100 will be described. When power is supplied to the winding 14, a rotating magnetic field is generated in the stator 10. The permanent magnets 22 rotate following this rotating magnetic field. Thereby, the rotor 20 rotates around the axis O with respect to the stator 10.

[0020] As shown in the following mathematical formula (1), the torque T of the permanent magnet synchronous motor 100 is obtained by differentiating the magnetic energy Wm in the air gap 15 between the stator 10 and the rotor 20 with respect to the rotation angle θ. T = ∂Wm / ∂θ …(1) Also, as shown in the following mathematical formula (2), the magnetic energy Wm is obtained by the magnetic flux density Bg in the air gap 15 and the permeability μ0. Wm = ∫(Bg 2 / 2μ0)dφ …(2)

[0021] The magnetic flux density Bg in the air gap 15 is determined by the magnetomotive force generated by the winding 14, the shape of the stator 10, the magnetic flux generated by the permanent magnet 22, etc. Further, when there are manufacturing variations in the rotor 20 (for example, variations in dimensions, arrangement, magnetization, etc. among a plurality of permanent magnets 22), distortion occurs in the magnetic flux density Bg in the air gap 15, which causes cogging torque and torque ripple.

[0022] The operation of the permanent magnet synchronous motor 100 according to the present embodiment will be described by comparison with a comparative example shown in FIG. 3. FIG. 3 is a cross-sectional view of a permanent magnet synchronous motor 200 according to the comparative example. In the permanent magnet synchronous motor 200, four cutout holes 31 are provided in the rotor core 21. That is, in the comparative example, the number Nl of the cutout holes 31 is equal to the number of pole pairs Pm of the permanent magnets 22.

[0023] FIG. 2 is a diagram showing the magnetic flux density distribution of a 1 / 2 model of the permanent magnet synchronous motor 100 according to Example 1 as an example of the present embodiment. FIG. 4 is a diagram showing the magnetic flux density distribution of a 1 / 2 model of the permanent magnet synchronous motor 200 according to the comparative example. Note that the 1 / 2 model is a model diagram showing one of the permanent magnet synchronous motors 100 and 200 bisected in the circumferential direction. Since the permanent magnet synchronous motors 100 and 200 are rotationally symmetric about the axis O, analysis is performed using the 1 / 2 model. In FIGS. 2 and 4, the darker the color, the higher the magnetic flux density, and the lighter the color, the lower the magnetic flux density. As shown in FIG. 2, in Example 1, when the first separation angle around the axis O at both ends in the circumferential direction of the cutout hole 31 is α, and the second separation angle around the axis O at the center of the circumferentially adjacent permanent magnets 22 is β, the first separation angle α and the second separation angle β are equal. When the number of permanent magnets 22 is Nm, the second separation angle β is 360° / Nm.

[0024] As shown in FIGS. 2 and 4, among the outer peripheral portions of the rotor core 21, the magnetic flux density of the portion 21a located between the vent hole 31 and the permanent magnet 22 becomes higher than that of the other portions 21b. At this time, the relative permeability of the portion 21a located between the vent hole 31 and the permanent magnet 22 becomes smaller than that of the other portions 21b. The magnetic resistance of the portion 21a located between the vent hole 31 and the permanent magnet 22 becomes larger than that of the other portions 21b. Therefore, the permeance coefficient of the permanent magnet 22 facing the vent hole 31 becomes smaller than that of the other permanent magnets 22. The magnetic flux generated by the permanent magnet 22 facing the vent hole 31 becomes less than the magnetic flux generated by the other permanent magnets 22. That is, even when there is no manufacturing variation in the rotor 20, the provision of the vent hole 31 causes variations in characteristics among the plurality of permanent magnets 22. As a result, distortion occurs in the magnetic flux density in the air gap 15, and cogging torque and torque ripple are generated. The cogging torque and torque ripple thus generated include harmonic components (for example, when the number of teeth 13 is 12, the 12th harmonic component) that match the number of teeth 13 per one rotation of the mechanical angle.

[0025] In the permanent magnet synchronous motor 200 according to the comparative example, the number Nl of vent holes 31 is equal to the number of pole pairs Pm of the permanent magnets 22. Therefore, as shown in FIG. 4, in the outer peripheral portion of the rotor core 21, a portion (portion 21a located between the vent hole 31 and the permanent magnet 22) where the magnetic flux density becomes relatively high and a portion (other portion 21b) where the magnetic flux density becomes relatively low appear alternately for each pole. Further, the change in the magnetic flux density over the entire outer peripheral portion of the rotor core 21 becomes large. That is, the magnetic flux generated by the permanent magnet 22 periodically increases and decreases for each pole. Further, the change in the magnetic flux generated by the permanent magnet 22 becomes large. As a result, the distortion of the magnetic flux density in the air gap 15 becomes large, and the cogging torque and torque ripple increase. Note that the permanent magnet synchronous motor with 8 poles and 12 slots is formed with two adjacent permanent magnets 22 and three teeth 13 (2 poles and 3 slots) in the circumferential direction as a basic unit. Therefore, the difference in the characteristics of two adjacent permanent magnets 22 in the circumferential direction has a great influence on the generation of cogging torque and torque ripple. In the permanent magnet synchronous motor 200 according to the comparative example, the magnetic flux generated by the permanent magnet 22 periodically increases and decreases for each pole. Therefore, since the difference in the characteristics of two adjacent permanent magnets 22 in the circumferential direction becomes large, the cogging torque and torque ripple further increase.

[0026] On the other hand, in the permanent magnet synchronous motor 100 according to the first embodiment, the number Nl of the through holes 31 and the number of pole pairs Pm of the permanent magnets 22 are different. Therefore, as shown in FIG. 2, at the outer peripheral portion of the rotor core 21, there are a portion 21a where the magnetic flux density becomes relatively high (the portion located between the through hole 31 and the permanent magnet 22) and a portion 21b where the magnetic flux density becomes relatively low (the other portion). However, the change in the magnetic flux density over the entire outer peripheral portion of the rotor core 21 is smaller than that in the comparative example. Further, at the outer peripheral portion of the rotor core 21, it is prevented that a portion where the magnetic flux density becomes relatively high and a portion where the magnetic flux density becomes relatively low alternately appear for each pole. Therefore, the change in the magnetic flux generated by the permanent magnet 22 is smaller than that in the comparative example. Also, the magnetic flux generated by the permanent magnet 22 does not periodically increase and decrease for each pole. As a result, the distortion of the magnetic flux density in the air gap 15 can be reduced, and the cogging torque and torque ripple can be reduced.

[0027] FIG. 5 is a graph showing the variation component of the torque waveform obtained by the permanent magnet synchronous motor 100 according to Example 1 and the variation component of the torque waveform obtained by the permanent magnet synchronous motor 200 according to the comparative example. Note that the vertical axis of the graph in FIG. 5 represents the variation component [p.u.] of the torque waveform normalized with respect to the variation component of the torque waveform obtained by the permanent magnet synchronous motor 200 according to the comparative example. The variation component of the torque waveform in the present disclosure is a harmonic component generated in the torque waveform due to the variation in characteristics among a plurality of permanent magnets 22. The variation component of the torque waveform in FIG. 5 is calculated by separating the torque waveform obtained from electromagnetic field analysis into a plurality of harmonic components by Fourier series expansion and extracting the value of the 12th harmonic component from these plurality of harmonic components. The larger the variation component of the torque waveform, the more the cogging torque and torque ripple increase. As shown in FIG. 5, it can be confirmed that the permanent magnet synchronous motor 100 according to Example 1 has a reduction of about 50% in the variation component of the torque waveform compared to the permanent magnet synchronous motor 200 according to the comparative example. That is, it can be seen that the permanent magnet synchronous motor 100 according to Example 1 can reduce the cogging torque and torque ripple.

[0028] FIG. 6 is a diagram showing the magnetic flux density distribution of a 1 / 2 model of the permanent magnet synchronous motor 100 according to Example 2 as an example of the present embodiment. FIG. 7 is a diagram showing the magnetic flux density distribution of a 1 / 2 model of the permanent magnet synchronous motor 100 according to Example 3 as an example of the present embodiment. FIG. 8 is a graph showing the variation components of the torque waveforms obtained by the permanent magnet synchronous motors 100 according to Examples 1 to 3. Note that the vertical axis of the graph in FIG. 8 represents the variation component [p.u.] of the torque waveform normalized with respect to the variation component of the torque waveform obtained by the permanent magnet synchronous motor 200 according to the comparative example. As shown in FIG. 6, in Example 2, the first separation angle α is twice the second separation angle β. As shown in FIG. 7, in Example 3, the first separation angle α is three times the second separation angle β. In Examples 2 and 3, the relief hole 31 is arranged across three permanent magnets 22.

[0029] As shown in FIGS. 6 and 7, also in the permanent magnet synchronous motor 100 according to Embodiments 2 and 3, the change in the magnetic flux density over the entire outer peripheral portion of the rotor core 21 is smaller compared to the comparative example. Further, as shown in FIG. 8, in the permanent magnet synchronous motor 100 according to Embodiment 2, it can be confirmed that the variation component of the torque waveform is reduced by about 75% compared to the permanent magnet synchronous motor 200 according to the comparative example. In the permanent magnet synchronous motor 100 according to Embodiment 3, it can be confirmed that the variation component of the torque waveform is reduced by about 55% compared to the permanent magnet synchronous motor 200 according to the comparative example. Therefore, it can be understood that also in the permanent magnet synchronous motors 100 according to Embodiments 2 and 3, the cogging torque and torque ripple can be reduced. From the above, it can be understood that by forming the vent holes 31 so that the first separation angle α satisfies β ≦ α ≦ 3β, the cogging torque and torque ripple can be more effectively reduced.

[0030] As described above, the rotor 20 according to the present embodiment includes a rotor core 21, a shaft 23 disposed inside the rotor core 21 and extending in the axial direction, and a plurality of permanent magnets 22 provided on the rotor core 21. The rotor core 21 is provided with vent holes 31. The number Nl of the vent holes 31 is different from the number of pole pairs Pm of the plurality of permanent magnets 22. With this configuration, while reducing the weight of the rotor 20, the cogging torque and torque ripple can be reduced.

[0031] Further, when the first separation angle around the axis O at both ends in the circumferential direction of the vent hole 31 is α, and the second separation angle around the axis O at the center of the circumferentially adjacent permanent magnets 22 is β, the vent hole 31 is provided so as to satisfy β ≦ α ≦ 3β. With this configuration, the cogging torque and torque ripple can be more effectively reduced. Also, the vent hole 31 can be enlarged, and the weight of the rotor 20 can be more reliably reduced.

[0032] Embodiment 2. FIG. 9 is a cross-sectional view showing the rotor 20A according to the second embodiment. Although not shown, a stator 10 is provided on the outer peripheral side of the rotor 20A with a gap 15 therebetween (see FIG. 1). Note that components having the same functions and operations as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted.

[0033] As shown in FIG. 9, in the second embodiment, the hollow hole 31 is arranged such that the center in the circumferential direction of the hollow hole 31 and the intermediate position of the permanent magnet 22 adjacent in the circumferential direction coincide with each other in the circumferential direction. The hollow hole 31 is formed symmetrically with respect to a straight line connecting the axial center O and the center in the circumferential direction of the hollow hole 31 (that is, a straight line connecting the axial center O and the intermediate position of the permanent magnet 22 adjacent in the circumferential direction). Also in this embodiment, similar to the first embodiment, two hollow holes 31 are provided in the rotor core 21, and the number Nl of the hollow holes 31 is different from the number of pole pairs Pm of the permanent magnets 22.

[0034] FIG. 10 is a diagram showing the magnetic flux density distribution of a 1 / 2 model of the permanent magnet synchronous motor 100A according to Example 4 as an example of this embodiment. FIG. 11 is a diagram showing the magnetic flux density distribution of a 1 / 2 model of the permanent magnet synchronous motor 100A according to Example 5 as an example of this embodiment. FIG. 12 is a diagram showing the magnetic flux density distribution of a 1 / 2 model of the permanent magnet synchronous motor 100A according to Example 6 as an example of this embodiment. FIG. 13 is a graph showing the variation component of the torque waveform obtained by the permanent magnet synchronous motor 100A according to Examples 4 to 6. Note that the vertical axis of the graph in FIG. 13 represents the variation component [p.u.] of the torque waveform normalized with respect to the variation component of the torque waveform obtained by the permanent magnet synchronous motor 200 according to the comparative example. As shown in FIG. 10, in Example 4, the first separation angle α is equal to the second separation angle β. As shown in FIG. 11, in Example 5, the first separation angle α is twice the second separation angle β. In Examples 4 and 5, the relief hole 31 is arranged across two permanent magnets 22. As shown in FIG. 12, in Example 6, the first separation angle α is three times the second separation angle β. In Example 6, the relief hole 31 is arranged across four permanent magnets 22.

[0035] As shown in FIGS. 10 to 12, also in the permanent magnet synchronous motor 100A according to Examples 4 to 6, the change in the magnetic flux density at the outer peripheral portion of the rotor core 21 is smaller than that in the comparative example. Further, as shown in FIG. 13, in the permanent magnet synchronous motor 100A according to Examples 4 to 6, it can be confirmed that the variation component of the torque waveform is reduced by about 90% compared to the permanent magnet synchronous motor 200 according to the comparative example. Therefore, it can be seen that in Examples 4 to 6 as well, the cogging torque and torque ripple can be reduced.

[0036] Further, comparing FIGS. 5 and 13, it can be confirmed that in the permanent magnet synchronous motor 100A according to Examples 4 to 6, the variation component of the torque waveform is further reduced. As described above, in the 8 - pole 12 - slot permanent magnet synchronous motor, the influence of the difference in characteristics between two adjacent permanent magnets 22 in the circumferential direction on the generation of cogging torque and torque ripple is large. In the present embodiment, the center in the circumferential direction of the relief hole 31 and the intermediate position of the two adjacent permanent magnets 22 in the circumferential direction coincide in the circumferential direction, and the relief hole 31 is formed symmetrically with respect to the straight line connecting the axial center O and the intermediate position of the two adjacent permanent magnets 22 in the circumferential direction. Therefore, for the two permanent magnets 22 adjacent in the circumferential direction across the center in the circumferential direction of the relief hole 31, since the change in the magnetic flux density at the outer peripheral portion of the rotor core 21 is symmetric with respect to the above - mentioned straight line, the difference in characteristics between these two permanent magnets 22 becomes small. As a result, the cogging torque and torque ripple can be more effectively reduced.

[0037] As described above, in the rotor 20A according to the present embodiment, the hollow hole 31 is arranged such that the center of the hollow hole 31 in the circumferential direction coincides with the intermediate position of the circumferentially adjacent permanent magnets 22 among the plurality of permanent magnets 22 in the circumferential direction. With this configuration, cogging torque and torque ripple can be more effectively reduced.

[0038] Embodiment 3. FIG. 14 is a cross-sectional view showing a rotor 20B according to Embodiment 3. Although not shown, a stator 10 is provided on the outer peripheral side of the rotor 20B with a gap 15 therebetween (see FIG. 1). Note that components having the same functions and operations as those in Embodiment 1 are denoted by the same reference numerals and their descriptions are omitted.

[0039] As shown in FIG. 14, in Embodiment 3, three hollow holes 31 are provided in the rotor core 21. The three hollow holes 31 are arranged at equal intervals in the circumferential direction. In the present embodiment, the number Nl of the hollow holes 31 is 3. The number Nl of the hollow holes 31 is different from the number of pole pairs Pm of the permanent magnets 22. The number Nl of the hollow holes 31 is smaller than the number of pole pairs Pm of the permanent magnets 22. Also, the number Nl of the hollow holes 31 is different from the number Nm of the permanent magnets 22.

[0040] FIG. 15 is a diagram showing the magnetic flux density distribution of a permanent magnet synchronous motor 100B according to Example 7 as an example of the present embodiment. FIG. 17 is a graph showing the variation component of the torque waveform obtained by the permanent magnet synchronous motor 100B according to Example 7. Note that the vertical axis of the graph in FIG. 17 represents the variation component [p.u.] of the torque waveform normalized with respect to the variation component of the torque waveform obtained by the permanent magnet synchronous motor 200 according to the comparative example.

[0041] As shown in FIG. 15, also in the permanent magnet synchronous motor 100B according to the seventh embodiment, the change in the magnetic flux density at the outer peripheral portion of the rotor core 21 is smaller than that in the comparative example. Further, as shown in FIG. 17, in the permanent magnet synchronous motor 100B according to the seventh embodiment, it can be confirmed that the variation component of the torque waveform is reduced by about 70% compared to the permanent magnet synchronous motor 200 according to the comparative example. Therefore, it can be seen that also in the seventh embodiment, the cogging torque and the torque ripple can be reduced.

[0042] Further, comparing FIG. 5 and FIG. 17, it can be confirmed that in the permanent magnet synchronous motor 100B according to the seventh embodiment, the variation component of the torque waveform is further reduced. In the permanent magnet synchronous motor 100B, by increasing the number Nl of the vent holes 31, the variation in the magnetic flux density at the outer peripheral portion of the rotor core 21 is further suppressed, and the change in the magnetic flux generated by the permanent magnet 22 becomes smaller. As a result, the distortion of the magnetic flux density in the air gap 15 can be further reduced, and the cogging torque and the torque ripple can be further reduced.

[0043] Embodiment 4. FIG. 16 is a diagram showing the magnetic flux density distribution of the permanent magnet synchronous motor 100C according to the eighth embodiment as an example of the present embodiment. FIG. 17 is a graph showing the variation component of the torque waveform obtained by the permanent magnet synchronous motor 100C according to the eighth embodiment. Note that components having the same functions and operations as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

[0044] As shown in FIG. 16, in the fourth embodiment, five vent holes 31 are provided in the rotor core 21 of the rotor 20C. The five vent holes 31 are arranged at equal intervals in the circumferential direction. In the present embodiment, the number Nl of the vent holes 31 is 5. The number Nl of the vent holes 31 is different from the number of pole pairs Pm of the permanent magnet 22. The number Nl of the vent holes 31 is larger than the number of pole pairs Pm of the permanent magnet 22. Further, the number Nl of the vent holes 31 is also different from the number Nm of the permanent magnets 22.

[0045] As shown in Fig. 16, also in the permanent magnet synchronous motor 100C according to the eighth embodiment, the change in the magnetic flux density at the outer peripheral portion of the rotor core 21 is smaller than that in the comparative example. Further, as shown in Fig. 17, in the permanent magnet synchronous motor 100C according to the eighth embodiment, it can be confirmed that the variation component of the torque waveform is significantly reduced as compared with the permanent magnet synchronous motor 200 according to the comparative example. Therefore, it can be understood that also in the eighth embodiment, the cogging torque and the torque ripple can be reduced.

[0046] Further, comparing Fig. 5 and Fig. 17, it can be confirmed that in the permanent magnet synchronous motor 100C according to the eighth embodiment, the variation component of the torque waveform is further reduced. In the permanent magnet synchronous motor 100C, the number Nl of the vent holes 31 is larger than the number of pole pairs Pm of the permanent magnets 22. Thereby, the variation in the magnetic flux density at the outer peripheral portion of the rotor core 21 is further suppressed, and the change in the magnetic flux generated by the permanent magnets 22 becomes smaller. As a result, the distortion of the magnetic flux density in the air gap 15 can be further reduced, and the cogging torque and the torque ripple can be further reduced.

[0047] Embodiment 5. Fig. 18 is a cross-sectional view showing the rotor 20D according to the fifth embodiment. Although not shown, a stator 10 is provided on the outer peripheral side of the rotor 20D with an air gap 15 therebetween (see Fig. 1). Note that components having the same functions and operations as those in the first embodiment are denoted by the same reference numerals and their description is omitted.

[0048] As shown in Fig. 18, in the fifth embodiment, a plurality of positioning holes 32 are provided in the rotor core 21 in addition to the vent holes 31. The rotor core 21 has a plurality of core plates laminated in the axial direction. In order to ensure the circumferential uniformity of the rotor core 21, the plurality of core plates are laminated while shifting the angles of the respective core plates (that is, cross-laminated). By providing the positioning holes 32, the relative positions of the core plates during cross-lamination can be easily adjusted.

[0049] In the configuration shown in FIG. 18, the rotor core 21 is provided with two relief holes 31 and six positioning holes 32. The relief holes 31 and the positioning holes 32 are arranged at equal intervals (at 45° intervals) in the circumferential direction. However, the number of relief holes 31, the number of positioning holes 32, and the arrangement of the relief holes 31 and the positioning holes 32 are not limited to this. For example, as shown as a modification example in FIG. 20, the rotor core 21 may be provided with two positioning holes 32. In this case, the relief holes 31 and the positioning holes 32 may be arranged at equal intervals (at 90° intervals) in the circumferential direction. Also, the shape of the positioning holes 32 is not limited to a circular shape, and may be a square shape, a trapezoidal shape, a fan shape, or the like.

[0050] FIG. 19 is a diagram showing the magnetic flux density distribution of a 1 / 2 model of a permanent magnet synchronous motor 100D according to Example 9 as an example of the present embodiment. FIG. 21 is a diagram showing the magnetic flux density distribution of a 1 / 2 model of a permanent magnet synchronous motor 100D according to Example 10 as an example of the present embodiment. FIG. 22 is a graph showing the variation component of the torque waveform obtained by the permanent magnet synchronous motors 100D according to Examples 9 and 10. Note that the vertical axis of the graph in FIG. 22 represents the variation component [p.u.] of the torque waveform normalized with respect to the variation component of the torque waveform obtained by the permanent magnet synchronous motor 200 according to the comparative example. The permanent magnet synchronous motor 100D according to Example 9 is formed by providing six positioning holes 32 in the rotor core 21 of the permanent magnet synchronous motor 100 according to Example 1. The permanent magnet synchronous motor 100D according to Example 10 is formed by providing two positioning holes 32 in the rotor core 21 of the permanent magnet synchronous motor 100 according to Example 1.

[0051] As shown in FIGS. 19 and 21, also in the permanent magnet synchronous motor 100D according to Embodiments 9 and 10, the change in the magnetic flux density at the outer peripheral portion of the rotor core 21 is smaller than that in the comparative example. Further, as shown in FIG. 22, also in the permanent magnet synchronous motor 100D according to Embodiments 9 and 10, it can be confirmed that the variation component of the torque waveform is reduced by about 60% as compared with the permanent magnet synchronous motor 200 according to the comparative example. That is, it can be seen that the variation component of the torque waveform does not increase due to the formation of the positioning holes 32, and the cogging torque and torque ripple can be reduced even in the permanent magnet synchronous motor 100D provided with the positioning holes 32.

[0052] It should be noted that it is possible to combine each embodiment, or to appropriately modify or omit each embodiment. For example, as the permanent magnet synchronous motor 100, an interior permanent magnetic (IPM) motor in which a plurality of permanent magnets 22 are embedded in the rotor core 21 may be employed. The positioning holes 32 shown in FIGS. 19 and 21 may be provided in the rotor core 21 according to other embodiments.

Description of Reference Numerals

[0053] 10... stator 20, 20A, 20B, 20C, 20D... rotor 21... rotor core 22... permanent magnet 23... shaft 31... relief hole 32... positioning hole 100, 100A, 100B, 100C, 100D... permanent magnet synchronous motor O... axis

Claims

1. A rotor having a rotor core, a shaft disposed inside the rotor core and extending in the axial direction, and a plurality of permanent magnets provided on the rotor core; A stator provided so as to surround the outer periphery of the rotor, having a core back, and a plurality of teeth protruding radially inward from the core back; Comprising: The number of the plurality of permanent magnets and the number of the plurality of teeth are set with two adjacent permanent magnets and three teeth in the circumferential direction as a basic unit; A through-hole is provided in the rotor core; The number of the through-holes is different from the number of pole pairs of the plurality of permanent magnets; The plurality of permanent magnets are arranged at equal intervals in the circumferential direction; The through-holes extend along the circumferential direction; In a cross section perpendicular to the axial direction, when the separation angle between both ends in the circumferential direction of the through-hole around the axis of the shaft is α, and the separation angle between the centers of adjacent permanent magnets in the circumferential direction among the plurality of permanent magnets around the axis of the shaft is β, the through-hole is provided so as to satisfy β≦α≦3β; A permanent magnet synchronous motor in which the number of the through-holes is different from the number of magnetic poles of the plurality of permanent magnets.

2. The permanent magnet synchronous motor according to claim 1, wherein the circumferential center of the through-hole and the circumferential center of the permanent magnet are arranged to coincide in the circumferential direction.

3. The permanent magnet synchronous motor according to claim 1, wherein the circumferential center of the through-hole and the intermediate position between adjacent permanent magnets in the circumferential direction among the plurality of permanent magnets are arranged to coincide in the circumferential direction.

4. The permanent magnet synchronous motor according to any one of claims 1 to 3, wherein the through-hole is formed symmetrically with respect to a straight line connecting the axis of the shaft and the circumferential center of the through-hole.

5. The rotor core has a plurality of core plates laminated in the axial direction; The permanent magnet synchronous motor according to any one of claims 1 to 4, wherein positioning holes for adjusting the positions of the plurality of core plates are provided in the rotor core.

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