permanent magnet synchronous motor

Abstract

A permanent magnet synchronous electric motor according to the present invention comprises a stator, a rotor, and a plurality of permanent magnets. Each of the plurality of permanent magnets has a first magnet end and a second magnet end in the circumferential direction. A recess in each of the plurality of permanent magnets has a first recess end and a second recess end in the circumferential direction. When L1 is the distance between the first magnet end and the first recess end and L2 is the distance between the second magnet end and the second recess end, L1≠L2.

Description

[Technical Field]

[0001] The present disclosure relates to permanent magnet synchronous motors. [Background technology]

[0002] BACKGROUND ART Permanent magnet synchronous motors have conventionally been used for industrial applications such as machine tools, for in-vehicle applications such as electric vehicles, and for compressors in air conditioners and the like. It is known that in order for a permanent magnet synchronous motor to output torque, the terminal voltage generated by the motor must be equal to or less than the input voltage. For example, the terminal voltage Vt generated by a permanent magnet synchronous motor can be expressed as follows using dq-axis theory:

[0003] Vd=RId+ωLqIq Vq=RIq+ωLdId+ωΦm Vt=√(Vd 2 +Vq 2 )

[0004] Here, Vd is the d-axis voltage, Vq is the q-axis voltage, Ld is the d-axis inductance, Lq is the q-axis inductance, R is the resistance, Id is the d-axis current, Iq is the q-axis current, ω is the angular velocity, φm is the magnetic flux of the magnet, and ωφm is the induced voltage. ωLd, ωLq, and ωφm increase in proportion to the rotation speed or speed. Therefore, when the motor is rotating at high speed or is driven at high speed, the terminal voltage Vt increases.

[0005] Flux-weakening control, which inputs a negative d-axis current Id to the motor, is known as a control technique for keeping the terminal voltage Vt equal to or less than the input voltage Vi. This type of flux-weakening control makes it possible to control the terminal voltage Vt to be equal to or less than the input voltage Vi even when the motor is rotating or driven at high speed. In this type of flux-weakening control, a negative d-axis current Id is passed through the motor to reduce the amount of induced voltage ωφm generated, thereby preventing the terminal voltage Vt from saturating during high-speed rotation.

[0006] However, if the d-axis inductance Ld is small, the function of suppressing the terminal voltage Vt through flux-weakening control cannot be effectively achieved, and therefore it is necessary to pass a d-axis current Id that is greater than necessary through the motor. For example, the following relationship exists between the d-axis current Id, the q-axis current Iq, and the input current Ia.

[0007] Ia=√(Id 2 +Iq 2 )

[0008] Therefore, an increase in the d-axis current Id reduces the q-axis current Iq.

[0009] Generally, the torque T generated by a surface magnet type permanent magnet synchronous motor is expressed as follows, where pn is the number of pole pairs:

[0010] T=pnΦmIq

[0011] To generate torque T, a q-axis current Iq is required. Therefore, a decrease in the q-axis current Iq reduces the torque of the motor. Therefore, to output large torque during high-speed rotation or high-speed driving, effective flux-weakening control must be performed with a small d-axis current Id. In order to perform such flux-weakening control, Patent Document 1 discloses that the d-axis inductance Ld is increased and the flux-weakening control is effective with a small d-axis current Id.

[0012] In Patent Document 1, protrusions are formed radially from the rotor core so as to fit into multiple permanent magnets arranged on the surface of the rotor core, which increases the d-axis inductance Ld, effectively functions as field-weakening control, and improves the torque output of the motor during high-speed rotation. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Japanese Patent Publication No. 2009-131070 Summary of the Invention [Problem to be solved by the invention]

[0014] However, in the above-mentioned prior art document, the protrusions of the rotor core intended to increase the d-axis inductance Ld are located at the magnetic pole centers in the circumferential direction, and the shapes of the protrusions are mirror-symmetric with respect to the magnetic pole centers.

[0015] In a structure with such a protrusion, when a stage-skew structure for reducing torque ripple is applied to the rotor, the d-axis position of each stage will be misaligned, making it difficult to effectively increase the d-axis inductance Ld.

[0016] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a permanent magnet synchronous motor that can increase the d-axis inductance Ld and perform efficient flux-weakening control. [Means for solving the problem]

[0017] A permanent magnet synchronous motor according to the present disclosure includes a stator, a rotor, and a plurality of permanent magnets. The rotor includes a rotor core made of electromagnetic steel sheets and having one or more protrusions protruding radially toward the stator, and a rotating shaft fixed to the rotor core. The rotor is rotatably disposed relative to the stator. Each of the plurality of permanent magnets has an arc-shaped stator-facing surface facing the stator across a gap, a rotor core fixing surface located opposite the stator-facing surface and fixed to the outer circumferential surface of the rotor core, and a recess connected to a portion of the rotor core fixing surface and into which the protrusion fits. The plurality of permanent magnets are arranged in the circumferential direction of the rotor. In the circumferential direction, the polarities of the stator-facing surfaces of two adjacent permanent magnets among the plurality of permanent magnets are opposite to each other. In the circumferential direction, each of the plurality of permanent magnets has a first magnet end connected to the rotor core fixing surface and a second magnet end connected to the rotor core fixing surface and located opposite the first magnet end. In the circumferential direction, the recess of each of the multiple permanent magnets has a first recess end connected to the rotor core fixing surface and a second recess end connected to the rotor core fixing surface and located on the opposite side from the first recess end. The rotor core fixing surface has a first region located between the first magnet end and the first recess end, and a second region located between the second magnet end and the second recess end. The recess is located between the first region and the second region. When the distance between the first magnet end and the first recess end in the first region is L1 and the distance between the second magnet end and the second recess end in the second region is L2, L1 ≠ L2 is satisfied. [Effects of the Invention]

[0018] The permanent magnet synchronous motor according to the present disclosure can increase the d-axis inductance Ld and perform efficient flux-weakening control, thereby improving the torque output of the permanent magnet synchronous motor during high-speed rotation. [Brief explanation of the drawings]

[0019] [Figure 1A] 1 is a cross-sectional view of a permanent magnet synchronous motor according to a first embodiment, as viewed in the axial direction. [Figure 1B] 1 is a cross-sectional view of a permanent magnet synchronous motor according to a first embodiment, as viewed in the axial direction. [Figure 2A] 2 is an enlarged cross-sectional view of a region in the vicinity of a permanent magnet that configures the permanent magnet synchronous motor according to the first embodiment, as viewed in the axial direction. FIG. [Figure 2B] 1B is a partial cross-sectional view of an overlapping state of the permanent magnet shown in FIG. 1A and the permanent magnet shown in FIG. 1B in a two-stage skew structure that constitutes the permanent magnet synchronous motor according to the first embodiment, as viewed in the axial direction. [Figure 3] FIG. 1 is an enlarged cross-sectional view of a region near a permanent magnet constituting a conventional permanent magnet synchronous motor, taken along the axial direction. [Figure 4] FIG. 10 is a diagram showing the results of a comparison of the d-axis inductance Ld between the permanent magnet synchronous motor according to the first embodiment and a conventional permanent magnet synchronous motor. [Figure 5] FIG. 4 is an enlarged cross-sectional view of a region in the vicinity of a permanent magnet that configures a modified example of the permanent magnet synchronous motor according to the first embodiment, as viewed in the axial direction. [Figure 6] FIG. 4 is an enlarged cross-sectional view of a region in the vicinity of a permanent magnet that configures a modified example of the permanent magnet synchronous motor according to the first embodiment, as viewed in the axial direction. [Figure 7A] FIG. 10 is an enlarged cross-sectional view of a region in the vicinity of a permanent magnet that configures a permanent magnet synchronous motor according to a second embodiment, as viewed in the axial direction. [Figure 7B] FIG. 10 is an enlarged cross-sectional view of a region in the vicinity of a permanent magnet that configures a modified example of the permanent magnet synchronous motor according to the second embodiment, as viewed in the axial direction. [Figure 8] FIG. 10 is a diagram showing the results of a comparison between the permanent magnet synchronous motor according to the first embodiment and a conventional permanent magnet synchronous motor with respect to the d-axis inductance Ld and the rate of decrease in induced voltage after demagnetization. [Figure 9A] FIG. 10 is a diagram showing the demagnetization factor distribution of a conventional permanent magnet synchronous motor. [Figure 9B] 4 is a diagram showing a demagnetization factor distribution of the permanent magnet synchronous motor according to the first embodiment. FIG. [Figure 10] FIG. 10 is a diagram showing the results of a comparison of the induced voltage reduction rate after demagnetization between the permanent magnet synchronous motor according to embodiment 1, the permanent magnet synchronous motor according to embodiment 2, and the permanent magnet synchronous motor according to the variation of embodiment 2. [Figure 11A] 4 is a diagram showing a demagnetization factor distribution of the permanent magnet synchronous motor according to the first embodiment. FIG. [Figure 11B] FIG. 10 is a diagram showing a demagnetization factor distribution of the permanent magnet synchronous motor according to the second embodiment. [Figure 11C] FIG. 10 is a diagram showing a demagnetization factor distribution of a permanent magnet synchronous motor according to a modification of the second embodiment. [Figure 12A] FIG. 10 is an enlarged cross-sectional view of a region in the vicinity of a permanent magnet that constitutes a modified example of the permanent magnet synchronous motor according to the second embodiment, as viewed in the axial direction. [Figure 12B] FIG. 10 is an enlarged cross-sectional view of a region in the vicinity of a permanent magnet that configures a modified example of the permanent magnet synchronous motor according to the second embodiment, as viewed in the axial direction. [Figure 13] FIG. 10 is a diagram showing the results of a comparison of the induced voltage reduction rate after demagnetization between the permanent magnet synchronous motor according to the first embodiment and a modified example of the permanent magnet synchronous motor according to the second embodiment. [Figure 14A] FIG. 10 is a diagram showing a demagnetization factor distribution of a modified example of the permanent magnet synchronous motor according to the first embodiment. [Figure 14B] FIG. 10 is a diagram showing a demagnetization factor distribution of a modified example of the permanent magnet synchronous motor according to the second embodiment. [Figure 14C] FIG. 10 is a diagram showing a demagnetization factor distribution of a modified example of the permanent magnet synchronous motor according to the second embodiment. [Figure 15] FIG. 11 is a perspective view showing a rotor that constitutes a permanent magnet synchronous motor according to a third embodiment. [Figure 16] FIG. 11 is a perspective view showing a rotor core that constitutes a permanent magnet synchronous motor according to a third embodiment. [Figure 17]FIG. 10 is a diagram showing the results of a comparison of torque ripple between the permanent magnet synchronous motor according to the third embodiment and a conventional permanent magnet synchronous motor. [Figure 18] FIG. 10 is a perspective view showing a rotor that constitutes a permanent magnet synchronous motor according to a fourth embodiment. [Figure 19] FIG. 10 is a perspective view showing a rotor core that constitutes a permanent magnet synchronous motor according to a fourth embodiment. [Figure 20] FIG. 10 is a diagram showing the results of a comparison of torque ripple between the permanent magnet synchronous motor according to the fourth embodiment and a conventional permanent magnet synchronous motor. [Figure 21] FIG. 10 is a diagram showing the results of a comparison of the d-axis inductance Ld between the permanent magnet synchronous motor according to the fourth embodiment and a conventional permanent magnet synchronous motor. DETAILED DESCRIPTION OF THE INVENTION

[0020] A permanent magnet synchronous motor according to an embodiment will be described with reference to FIGS. 1A to 21. FIG. In the description of the embodiments, the permanent magnet synchronous motor may be simply referred to as a motor. 1 to 21, identical or similar components are denoted by the same reference numerals. The drawings are intended to illustrate the embodiments in a schematic or conceptual manner, and the relationship between the thickness and width of each part shown in the drawings, the size ratio between parts, etc. may not necessarily be the same as those of the actual members. Configurations that are not related to the features of the present disclosure may be omitted from the illustration.

[0021] In the drawings used to explain the embodiments, X, Y, and Z directions corresponding to a three-dimensional Cartesian coordinate system are shown (symbols X, Y, and Z). The Z direction coincides with the axial direction of the permanent magnet synchronous motor. In other words, the Z direction coincides with the axial direction in which the rotation axis located at the axial center of the rotor extends. The Z direction can also be referred to as the up-down direction in the two-stage skew structure. The X and Y directions intersect (e.g., are perpendicular to) the Z direction. The X and Y directions intersect (e.g., are perpendicular to) each other.

[0022] The terms "circumferential direction" and "radial direction" used in the following description correspond to the "circumferential direction" and "radial direction", respectively, of a stator or rotor that constitutes a permanent magnet synchronous motor. The term "circumferential direction" corresponds to the direction of rotation of the rotor. In other words, the circumferential direction is the direction around the rotation axis of the rotor in a cross section viewed in the axial direction. The term "radial" refers to the direction of the radius of the rotor. For example, the term "radially outer" refers to the direction from the center of the rotor toward the outer periphery. The term "radially inner" refers to the direction from the outer periphery toward the center of the rotor.

[0023] Embodiment 1 An electric motor according to the first embodiment will be described. 1A and 1B are cross-sectional views showing a permanent magnet synchronous motor 100 according to a first embodiment. The permanent magnet synchronous motor 100 has a two-stage skew structure. FIG. 1A shows a cross-section of one stage structure of the two-stage skew structure. FIG. 1B shows a cross-section of the other stage structure of the two-stage skew structure. For example, FIG. 1A shows the structure of the upper stage of the two-stage skew structure. Also, FIG. 1B shows the structure of the lower stage of the two-stage skew structure.

[0024] 1A and 1B, the symbol CL indicates the center line of the permanent magnet synchronous motor 100. The symbol O indicates the axial center of a rotating shaft 23, which will be described later. The positions of the center line CL and the axial center O are the same in both FIGS. 1A and 1B. In other words, the center line CL corresponds to the d-axis of the permanent magnet synchronous motor 100. In the following description, the position of the d-axis may be referred to as the d-axis position d1. The symbol S indicates a magnet center line that extends radially outward from the axial center O and passes through the circumferential center point of a permanent magnet 22, which will be described later. In other words, the magnet center line S passes through the circumferential center point C of a stator opposing surface 26, which will be described later.

[0025] In the structure of permanent magnet synchronous motor 100 according to embodiment 1, the skew structure on the upper side and the skew structure on the lower side are circumferentially offset by a skew angle θ. The shape of the skew structure shown in FIG. 1A is the same as the shape of the skew structure shown in FIG. 1B. Therefore, the structure of permanent magnet synchronous motor 100 will be described using FIG. 1A. The skew angle θ will be described later.

[0026] <Permanent magnet synchronous motor> As shown in FIG. 1A, the permanent magnet synchronous motor 100 includes a stator 10 and a rotor 20. In the two-stage skew structure, the circumferential centers of the magnets in stages aligned in the Z direction are shifted circumferentially by a skew angle θ from the center of the rotation axis 23 of the rotor 20. This gives the permanent magnet synchronous motor 100 a so-called stage-skew structure. Each of the multiple stages constituting the stage-skew structure may be referred to as a "stage." In a structure with two stages, that is, in a description of a two-stage skew structure, the skew structure on the upper stage may be simply referred to as the "upper stage," and the skew structure on the lower stage may be simply referred to as the "lower stage."

[0027] In this specification, the terms "upper stage" and "lower stage" are used for ease of explanation and do not define the up-down direction of the permanent magnet synchronous motor 100. For example, the skew structure on the upper stage side may be referred to as the first skew structure, and the skew structure on the lower stage side may be referred to as the second skew structure. In this case, the first skew structure and the second skew structure are aligned in the Z direction.

[0028] <Stator> The stator 10 is disposed so as to surround the outer periphery of the rotor 20 via an air gap 15, which serves as a magnetic gap. The stator 10 has a stator core 11 and a winding 14. The stator core 11 has a core back 12 formed in an annular shape in the circumferential direction, and a plurality of teeth 13 protruding radially inward from the core back 12. The winding 14 is wound around each of the plurality of teeth 13. In the following description, the winding 14 wound around the teeth 13 may be referred to as a coil portion. In the example shown in FIG. 1A, one coil portion is provided for one tooth 13.

[0029] 1A, the number of teeth 13 is 12. The number of teeth 13 is not limited to 12 and may be determined appropriately depending on the design of permanent magnet synchronous motor 100. In the first embodiment, the core back 12 is configured by connecting a plurality of core blocks, each formed in an arc shape, in an annular shape. The structure of the core back 12 is not limited to the structure shown in Fig. 1A. The core back 12 may be configured by integrally forming a plurality of core blocks. Furthermore, the core back 12 and the teeth 13 may be separated.

[0030] <Rotor> The rotor 20 includes a rotor core 21 , a rotating shaft 23 , and a plurality of permanent magnets 22 . Rotor core 21 is formed by stacking multiple electromagnetic steel plates in the Z direction. The electromagnetic steel plates may also be referred to as core plates, for example. Rotating shaft 23 is fixed to rotor core 21 so as to penetrate rotor core 21 in the Z direction. Rotating shaft 23 may also be referred to as a shaft. Such rotor 20 is disposed inside permanent magnet synchronous motor 100 so as to be rotatable relative to stator 10.

[0031] The rotor core 21 has protrusions 24 that protrude in the radial direction. The protrusions 24 protrude radially outward toward the stator 10. In the first embodiment, the shape of the protrusions 24 is rectangular. In the first embodiment, the number of the protrusions 24 is eight, corresponding to the number of the permanent magnets 22. The number of the protrusions 24 may be one or more.

[0032] <Permanent magnet> The plurality of permanent magnets 22 are arranged in the circumferential direction on the outer peripheral surface 28 of the rotor core 21. The permanent magnet synchronous motor 100 including such a plurality of permanent magnets 22 is an example of a surface permanent magnet motor (SPM).

[0033] Each of the multiple permanent magnets 22 has a stator-facing surface 26 and a rotor core fixing surface 27. The stator-facing surface 26 faces the stator 10 across a gap 15. The stator-facing surface 26 has an arc-shaped configuration. The rotor core fixing surface 27 is located on the opposite side of the stator-facing surface 26. The rotor core fixing surface 27 is fixed to the outer peripheral surface 28 of the rotor core 21. The recess 25 is provided in a portion of the rotor core fixing surface 27. In other words, the recess 25 is connected to a portion of the rotor core fixing surface 27. The recess 25 fits into the protrusion 24. In the first embodiment, the shape of the recess 25 is rectangular, just like the protrusion 24.

[0034] As will be described later, the rotor core fixing surface 27 has a first region 27F and a second region 27S. Each of the first region 27F and the second region 27S is fixed to the outer peripheral surface 28 of the rotor core 21. The recessed portion 25 is located between the first region 27F and the second region 27S.

[0035] The multiple permanent magnets 22 are aligned in the circumferential direction of the rotor 20. The polarities of the stator-facing surfaces 26 of two adjacent permanent magnets 22 in the circumferential direction are opposite to each other. For example, the multiple permanent magnets 22 are arranged with their magnetization directions set to be different such that if the polarity of the stator-facing surface 26 of one of two circumferentially adjacent permanent magnets 22 is an N pole, the polarity of the stator-facing surface 26 of the other is an S pole.

[0036] The permanent magnet synchronous motor 100 shown in FIG. 1A has 12 teeth 13, 12 coil sections formed by windings 14, and 8 permanent magnets. In other words, FIG. 1A shows a so-called 8-pole, 12-slot permanent magnet synchronous motor. The combination of the number of multiple permanent magnets 22, teeth 13, and coil sections is not limited to this. Also, although the number of teeth 13 and the number of coil sections are the same in the example shown in FIG. 1A, the number of teeth 13 and the number of coil sections may be different.

[0037] 1A, the circumferential center positions of the multiple permanent magnets 22 are shifted in the circumferential direction as they progress in the axial direction. When the skew angle between the upper and lower permanent magnets 22 in the step-wise skew structure is θ, the recesses 25 are shifted in different directions by the amount of shift θ of the permanent magnets 22 shown in the same cross-sectional view.

[0038] In the step-to-step skew structure, the multiple permanent magnets 22 include a first magnet group 41 and a second magnet group 42 adjacent to each other in the Z direction. Fig. 1A shows the first magnet group 41. Fig. 1B shows the second magnet group 42. Between the first magnet group 41 and the second magnet group 42, the rotor 20 has a step-to-step skew structure. In the following description, each of the multiple permanent magnets 22 constituting the first magnet group 41 may be referred to as a first permanent magnet 22A. Each of the multiple permanent magnets 22 constituting the second magnet group 42 may be referred to as a second permanent magnet 22B.

[0039] In other words, the first permanent magnets 22A constituting the first magnet group 41 are arranged so as to be offset from the center line CL by an offset amount of θ / 2 in the counterclockwise direction of the circumferential direction. That is, in the counterclockwise direction, the magnet center line S shown in FIG. 1A is offset from the center line CL by an offset amount of θ / 2. That is, the first permanent magnets 22A constituting the first magnet group 41 are offset by θ / 2 with respect to the d-axis of the permanent magnet synchronous motor 100 in the counterclockwise direction of the circumferential direction.

[0040] The second permanent magnets 22B constituting the second magnet group 42 are arranged so as to be offset from the center line CL by an offset amount of θ / 2 in the clockwise direction of the circumferential direction. That is, in the clockwise direction, the magnet center line S shown in FIG. 1B is offset from the center line CL by an offset amount of θ / 2. That is, the second permanent magnets 22B constituting the second magnet group 42 are offset by θ / 2 with respect to the d-axis of the permanent magnet synchronous motor 100 in the clockwise direction of the circumferential direction. Focusing on the second magnet group 42 and the first magnet group 41, the second permanent magnet 22B constituting the second magnet group 42 is circumferentially shifted by an amount of shift θ (skew angle θ) relative to the first permanent magnet 22A constituting the first magnet group 41.

[0041] With reference to Figures 1A, 1B, 2A, and 2B, the multiple first permanent magnets 22A that make up the first magnet group 41 and the multiple second permanent magnets 22B that make up the second magnet group 42 will be described in detail. The permanent magnet 22 shown in Fig. 2A corresponds to the first permanent magnet 22A shown in Fig. 1. However, if the permanent magnet shown in Fig. 2A is flipped left and right, the permanent magnet 22 shown in Fig. 2A becomes the second permanent magnet 22B. For this reason, a description of the second permanent magnet 22B will be omitted in Fig. 2A.

[0042] Referring to FIG. 2A, the recessed portion 25 that engages with the protruding portion 24 will be described in detail. Fig. 2A is an enlarged cross-sectional view taken along the axial direction of the area near the permanent magnet 22. Fig. 2A is an enlarged view of the area surrounded by the dashed line A in Fig. 1A. As shown in FIG. 2A , the magnet center line S, which extends radially outward from the axial center O of the rotating shaft 23 and passes through the circumferential center point C of the permanent magnet 22, is defined as the circumferential center position CP of the permanent magnet 22. Here, the center point C is located at the circumferential center of the stator-facing surface 26 of the permanent magnet 22. The center point C is located at the portion of the arc-shaped stator-facing surface 26 closest to the teeth 13. A line passing through the center of the protrusion 24 and parallel to the magnet center line S is defined as the protrusion center position TP. The protrusion center position TP can also be referred to as the center of the protrusion 24. The protrusion center position TP is located at the center between the first recess end 35 and the second recess end 36.

[0043] Each of the multiple permanent magnets 22 has a first magnet end 31 connected to the rotor core fixing surface 27 in the circumferential direction, and a second magnet end 32 connected to the rotor core fixing surface 27. The second magnet end 32 is located on the opposite side of the first magnet end 31 with respect to the circumferential center position CP. The permanent magnet 22 has a first side surface 33 and a second side surface 34 located on opposite sides of the circumferential direction. The first magnet end 31 corresponds to the portion where the first side surface 33 and the rotor core fixing surface 27 are connected. The second magnet end 32 corresponds to the portion where the second side surface 34 and the rotor core fixing surface 27 are connected.

[0044] Each recess 25 of the multiple permanent magnets 22 has, in the circumferential direction, a first recess end 35 that connects to the rotor core fixing surface 27, and a second recess end 36 that connects to the rotor core fixing surface 27 and is located on the opposite side of the first recess end 35. The first region 27F of the rotor core fixing surface 27 is located between the first magnet end 31 and the first recessed portion end 35. The second region 27S of the rotor core fixing surface 27 is located between the second magnet end 32 and the second recessed portion end 36.

[0045] In other words, first region 27F is a surface formed between first magnet end 31 and first recess end 35. Second region 27S is a surface formed between second magnet end 32 and second recess end 36. In other words, first region 27F and second region 27S are located on either side of recess 25. When the distance between the first magnet end 31 and the first recessed portion end 35 in the first region 27F is L1 and the distance between the second magnet end 32 and the second recessed portion end 36 in the second region 27S is L2, L1 ≠ L2 is satisfied. In the step-skew structure, each of the multiple permanent magnets 22 satisfies L1 ≠ L2 and also satisfies L1 > L2.

[0046] Furthermore, the magnet center line S intersects with the first region 27F. In other words, the magnet center line S intersects with the line connecting the first magnet end 31 and the first recess end 35. Specifically, in the skewed structure on the upper side shown in FIG. 1A, the magnet center line S, which is offset from the center line CL in the counterclockwise direction by an amount of offset of θ / 2, intersects with the first region 27F of the permanent magnet 22. In the skew structure on the lower side shown in FIG. 1B, the magnet center line S, which is shifted clockwise from the center line CL by an amount of shift of θ / 2, intersects with the first region 27F of the permanent magnet 22.

[0047] Next, the arrangement of the first permanent magnet 22A and the second permanent magnet 22B in the two-stage skew structure that constitutes a permanent magnet synchronous motor will be described with reference to Fig. 2B. Fig. 2B is a partial cross-sectional view showing the state in which the first permanent magnet 22A and the second permanent magnet 22B overlap when viewed in the Z direction. In FIG. 2B, the first permanent magnet 22A is shown by a solid line, and the second permanent magnet 22B is shown by a dotted line.

[0048] The first permanent magnet 22A has a first rotor core fixing surface 27A fixed to the outer peripheral surface 28 of the rotor core 21. The first rotor core fixing surface 27A is a surface corresponding to the rotor core fixing surface 27. Therefore, as shown in FIG. 2A , the first rotor core fixing surface 27A has a first region 27F having a distance L1 and a first recessed end 35, and a second region 27S having a distance L2 and a second recessed end 36.

[0049] The second permanent magnet 22B has a second rotor core fixing surface 27B fixed to the outer peripheral surface 28 of the rotor core 21. The second rotor core fixing surface 27B is a surface that corresponds to the rotor core fixing surface 27. Therefore, as shown in FIG. 2A , the second rotor core fixing surface 27B has a first region 27F having a distance L1 and a first recessed end 35, and a second region 27S having a distance L2 and a second recessed end 36.

[0050] The central point of the first permanent magnet 22A in the circumferential direction is defined as a first central point C1. In other words, the first central point C1 corresponds to the central point of the stator-facing surface 26 of the first permanent magnet 22A in the circumferential direction. The circumferential center point of the second permanent magnet 22B is defined as a second center point C2. In other words, the second center point C2 corresponds to the circumferential center point of the stator-facing surface 26 of the second permanent magnet 22B. A line extending radially outward from the axial center O of the rotation shaft 23, passing through the first center point C1, and intersecting the first region 27F of the first permanent magnet 22A is defined as the first magnet center line S1. A line extending radially outward from the axial center O of the rotation shaft 23, passing through the second center point C2, and intersecting the first region 27F of the second permanent magnet 22B is defined as the second magnet center line S2. The midpoint between the first recess end 35 and the second recess end 36 of the first permanent magnet 22A in a direction 27AD parallel to the first rotor core fixing surface 27A is defined as a first midpoint 37A. The midpoint between the first recess end 35 and the second recess end 36 of the second permanent magnet 22B in the direction 27BD parallel to the second rotor core fixing surface 27B is defined as a second midpoint 37B. A line extending radially outward from the axial center O of the rotary shaft 23 and passing through the first midpoint 37A is defined as a first recess center line N1. A line extending radially outward from the axial center O of the rotary shaft 23 and passing through the second midpoint 37B is defined as a second recess center line N2.

[0051] In the above definition, the angle between the first magnet center line S1 and the second magnet center line S2 is the skew angle θ. Also, the angle between the first recess center line N1 and the second recess center line N2 is the recess center-to-center angle M. In this case, the recess center-to-center angle M is smaller than the skew angle θ. Also, L1 ≠ L2 is satisfied, and L1 > L2 is satisfied. The value obtained by dividing L1 by L2, that is, the value of L1 / L2, is within the range of 1.0 < L1 / L2 < 1.6.

[0052] <Effect> Next, while comparing a conventional permanent magnet synchronous motor and the permanent magnet synchronous motor 100 according to Embodiment 1, the effects obtained by Embodiment 1 will be described.

[0053] <Conventional Permanent Magnet Synchronous Motor> First, a conventional permanent magnet synchronous motor will be described. FIG. 3 is a diagram showing an enlarged view of a region near a permanent magnet constituting a conventional permanent magnet synchronous motor, and is a cross-sectional view taken axially. In FIG. 3, the illustration of the stator is omitted. In FIG. 3, the configurations not described are the same as those in FIG. 1A.

[0054] As shown in FIG. 3, a conventional permanent magnet synchronous motor has a permanent magnet 122 fixed to a stator. The convex portion of the stator of the conventional permanent magnet synchronous motor engages with the recess 125 of the permanent magnet 122. The shape of the recess 125 has a shape that is mirror-symmetric with respect to the circumferential center of the permanent magnet 122. That is, in the permanent magnet 122, when the distance between the first magnet end 31 and the first recess end 35 is L1, and the distance between the second magnet end 32 and the second recess end 36 is L2, L1 = L2 is satisfied. Further, the magnet center line S intersects the recess 125 but does not intersect the first region 27F.

[0055] Next, the effects of Embodiment 1 will be described. In a permanent magnet synchronous motor, it is not possible to generate a terminal voltage Vt that exceeds the input voltage Vi and output torque T. Generally, when the rotation speed of the motor increases, the terminal voltage Vt increases according to the following equation:

[0056] Vt=√(Vd 2 +Vq 2 )···(1) Vd = RId + ωLqIq (2) Vq=RIq+ωΦm+ωdLdId (3) ω=2πf=2π(N / 60)pn (4)

[0057] Here, Vd is the d-axis voltage, Vq is the q-axis voltage, R is the phase resistance, Id is the d-axis current, Iq is the q-axis current, Φm is the magnet magnetic flux, Ld is the d-axis inductance, Lq is the q-axis inductance, ω is the angular velocity, f is the frequency, N is the number of rotations per minute, and pn is the number of pole pairs.

[0058] As a control method for a permanent magnet synchronous motor, a control system for increasing torque output at high speed rotation, known as flux-weakening control, which suppresses an increase in terminal voltage, is known. This flux-weakening control is a control method that passes a d-axis current Id in a direction that weakens the magnetic flux Φm of the magnet. With this control method, if the d-axis inductance Ld is small, it is necessary to pass a large d-axis current Id through the motor. However, there is an upper limit to the current that can be passed through the motor. If the current supplied from the inverter to the motor is Iinv, then the following equation is obtained:

[0059] √3×Iinv=√(Id 2 +Iq 2 )···(5)

[0060] The torque T output by an SPM type permanent magnet synchronous motor is generally expressed by the following equation:

[0061] T=PnΦmIq (6)

[0062] For this reason, when the d-axis current Id increases, the q-axis current Iq required to output the torque T decreases, resulting in a drop in torque output. Therefore, to increase the torque T at high speeds, it is necessary to effectively obtain flux-weakening control with a small d-axis current Id, and the d-axis inductance Ld must be increased. Therefore, by adopting the structure shown in FIG. 3, the d-axis inductance Ld can be increased.

[0063] Furthermore, if the permanent magnet magnetic flux contains harmonic components, the torque T generated according to equation (6) will contain harmonic pulsations, and this torque pulsation is called torque ripple. Torque ripple can cause vibration or noise, so measures to reduce it are generally taken.

[0064] One known method for addressing this issue is to use a rotor structure known as stage skew. This structure is made up of two or more stages of rotors, and there is an angular difference when comparing the circumferential center positions of the permanent magnets in each stage. This angular difference is called the skew angle. Adjusting this angular difference makes it possible to reduce torque ripple throughout the entire motor.

[0065] However, as shown in FIG. 2A, an electrical angle deviation (angular difference) of Pn×θ / 2 occurs between the d-axis position d1 and the circumferential center position CP of the permanent magnets 22 in each stage of the rotor 20 throughout the entire motor.

[0066] In contrast, the structure shown in Fig. 3 can effectively increase the d-axis inductance Ld when the d-axis position d1 and the circumferential center position CP are aligned. However, when a step-skew structure with a skew angle θ is applied, there is an angular difference between the circumferential center position CP of the protrusions 124 of each step and the d-axis position d1 in the structure shown in Fig. 3. As a result, the d-axis inductance Ld cannot be increased efficiently.

[0067] The first embodiment solves the problems of conventional permanent magnet synchronous motors. Specifically, as shown in FIG. 2A, by shifting the convex portion 24 from the circumferential center position CP of the magnet in the direction opposite to the skew direction, a structure satisfying L1≠L2 is obtained. FIG. 4 is a diagram showing a comparison result of the d-axis inductance Ld between the case of the condition L1 = L2 of the conventional motor and the case of the condition L1≠L2 of the first embodiment.

[0068] In FIG. 4, the vertical axis represents the d-axis inductance Ld, and the horizontal axis represents the shape of the recess. "Rectangle" refers to the shape of the recess shown in FIGS. 2A and 3. "Sawtooth" indicates the shape of one tooth constituting a saw having a plurality of teeth. "Arc" indicates a substantially U-shaped or substantially C-shaped. In FIG. 4, the d-axis inductance Ld in the case of L1 = L2 is normalized to 1.0. Note that "sawtooth" corresponds to the shape shown in Modification 1A described later. Also, "arc" corresponds to the shape shown in Modification 1B described later.

[0069] As shown in FIG. 4, as in the first embodiment, by setting L1≠L2, the d-axis inductance Ld can be increased more than that of the conventional permanent magnet synchronous motor. Furthermore, the permanent magnet synchronous motor 100 includes a first magnet group 41 and a second magnet group 42 adjacent to each other in the Z direction, and between the first magnet group 41 and the second magnet group 42, the rotor 20 has a stepped skew structure. Thereby, the d-axis inductance Ld can be efficiently improved.

[0070] Furthermore, unlike the conventional permanent magnet synchronous motor, in the first embodiment, the recess center-to-center angle M is smaller than the skew angle θ. Also, L1≠L2 is satisfied, and L1>L2 is satisfied. Furthermore, the value of L1 / L2 is within the range of 1.0 < L1 / L2 < 1.6. Therefore, the d-axis inductance Ld can be more efficiently improved.

[0071] <Modifications of the First Embodiment> Next, Modifications 1A and 1B of the permanent magnet synchronous motor according to the first embodiment will be described. In the description of Modification Examples 1A and 1B, descriptions of parts common to the above-described Embodiment 1 are omitted.

[0072] <Modification Example 1A> FIG. 5 is a diagram showing an enlarged view of a region near a permanent magnet constituting Modification Example 1A, and is a cross-sectional view taken in the axial direction. As shown in FIG. 5, the recess 25 has a first bottom end 51 and a second bottom end 52. Each of the first bottom end 51 and the second bottom end 52 forms the bottom 50 of the recess 25. The second bottom end 52 is separated from the first bottom end 51. When the distance between the first recess end 35 and the first bottom end 51 in the radial direction is H1, and the distance between the second recess end 36 and the second bottom end 52 in the radial direction is H2, H1≠H2 is satisfied. In this modification, H1<H2 is satisfied. Further, this modification satisfies L1≠L2.

[0073] According to Modification Example 1A, as shown in the results of "L1≠L2" and "sawtooth type" in FIG. 4, the d-axis inductance Ld can be increased more than that of a conventional permanent magnet synchronous motor.

[0074] <Modification Example 1B> FIG. 6 is a diagram showing an enlarged view of a region near a permanent magnet constituting Modification Example 1B, and is a cross-sectional view taken in the axial direction. As shown in FIG. 6, the surface 53 forming the bottom 50 of the recess 25 has an arc shape. Further, this modification satisfies L1≠L2.

[0075] According to Modification Example 1B, as shown in the results of "L1≠L2" and "arc" in FIG. 4, the d-axis inductance Ld can be increased more than that of a conventional permanent magnet synchronous motor.

[0076] Embodiment 2. A permanent magnet synchronous motor according to Embodiment 2 will be described. In Embodiment 2, the same members as those in the above-described embodiments and modification examples are denoted by the same reference numerals, and the description thereof is omitted or simplified.

[0077] Referring to FIG. 7A, the concave portion 25 that engages with the convex portion 24 will be described in detail. FIG. 7A is a diagram showing an enlarged view of the region near the permanent magnet 22, and is a cross-sectional view taken axially. FIG. 7A corresponds to FIG. 2A and is an enlarged view showing the portion surrounded by the broken line portion A in FIG. 1A. Although not shown in FIG. 7A, the permanent magnet synchronous motor according to Embodiment 2 is composed of a stator 10 and a rotor 20, similar to FIG. 1.

[0078] As shown in FIG. 7A, the permanent magnet synchronous motor according to Embodiment 2 is different from the permanent magnet synchronous motor according to Embodiment 1 in that an inclined surface connected to the second bottom end 52 is formed inside the concave portion 25.

[0079] Specifically, the concave portion 25 has a first bottom end 51 and a second bottom end 52. Each of the first bottom end 51 and the second bottom end 52 forms the bottom 50 of the concave portion 25. The second bottom end 52 is spaced apart from the first bottom end 51. The concave portion 25 has a first inner wall 61 and a second inner wall 62. The first inner wall 61 is formed between the first concave end 35 and the first bottom end 51 and extends in the radial direction. The second inner wall 62 is formed between the second concave end 36 and the second bottom end 52. The second inner wall 62 has a vertical surface 63 and an inclined surface 64. The vertical surface 63 is connected to the second concave end 36 and extends in the radial direction. The inclined surface 64 is connected to the vertical surface 63 and the second bottom end 52, is inclined with respect to the vertical surface 63, and extends linearly.

[0080] Furthermore, in Embodiment 2, L1≠L2 is satisfied, and L1>L2 is satisfied. The value obtained by dividing L1 by L2, that is, the value of L1 / L2, is within the range of 1.0 < L1 / L2 < 1.6.

[0081] <Modification 2A of Embodiment 2> Next, a modification 2A of the permanent magnet synchronous motor according to Embodiment 2 will be described. In the description of Modification 2A, the description of the parts common to the above-described Embodiment 1 and Embodiment 2 will be omitted.

[0082] Referring to FIG. 7B, the concave portion 25 that engages with the convex portion 24 will be described in detail. FIG. 7B is a view showing an enlarged area near the permanent magnet 22 and is a cross-sectional view taken axially. FIG. 7B corresponds to FIG. 2A and is an enlarged view showing the portion surrounded by the broken line portion A in FIG. 1A. Although not shown in FIG. 7B, the permanent magnet synchronous motor according to the modified example 2A is composed of a stator 10 and a rotor 20, similar to FIG. 1.

[0083] As shown in FIG. 7B, the permanent magnet synchronous motor according to the modified example 2A is different from the permanent magnet synchronous motor according to the first embodiment in that a curved surface connected to the second bottom end 52 is formed inside the concave portion 25.

[0084] Specifically, the concave portion 25 has a first bottom end 51 and a second bottom end 52. Each of the first bottom end 51 and the second bottom end 52 forms the bottom 50 of the concave portion 25. The second bottom end 52 is spaced apart from the first bottom end 51. The concave portion 25 has a first inner wall 61 and a second inner wall 62. The first inner wall 61 is formed between the first concave end 35 and the first bottom end 51 and extends in the radial direction. The second inner wall 62 is formed between the second concave end 36 and the second bottom end 52. The second inner wall 62 has a curved surface 65 connected to the second bottom end 52.

[0085] Furthermore, in the modified example 2A, L1≠L2 is satisfied, and L1>L2 is satisfied. The value obtained by dividing L1 by L2, that is, the value of L1 / L2, is within the range of 1.0 < L1 / L2 < 1.6.

[0086] <Effect> Next, after explaining the irreversible demagnetization phenomenon related to the magnetic force change and the decrease in the magnet magnetic flux due to demagnetization, the effects obtained by the second embodiment will be described.

[0087] For example, in the structure described in the first embodiment, the shape of the protrusions 24 of the rotor core 21 is rectangular, and the protrusion center position TP of the protrusions 24 is offset from the circumferential center of the permanent magnet 22. Furthermore, in this structure, the outer shape of the stator-facing surface 26 is an arc. In this case, at the positions of the corners of the protrusions 24, in other words, at the second bottom ends 52 of the recesses 25, the distance between the stator-facing surface 26 and the second bottom ends 52 is extremely short.

[0088] In permanent magnets, a phenomenon called irreversible demagnetization occurs, in which the residual magnetic flux density Br of the permanent magnet decreases due to the effect of a temperature rise in the permanent magnet or the effect of a demagnetizing field, in which the magnetic field from the stator is applied to the permanent magnet in the direction opposite to the magnetization direction. The likelihood of this type of irreversible demagnetization occurring is related to the coercive force of the permanent magnet and the permeance coefficient Pc, which is determined by the magnetic circuit. The permeance coefficient Pc depends on the thickness of the magnet in the magnetization direction and the magnetic resistance. In a magnetic circuit with a narrow magnetic gap between the stator and rotor, such as a permanent magnet synchronous motor, the permeance coefficient Pc can be approximately calculated using the following formula.

[0089] Pc≒Hm / gm (7)

[0090] Here, Hm is the thickness of the permanent magnet in the magnetization direction, and gm is the magnetic gap between the stator and rotor. From equation (7), Pc decreases as the thickness of the permanent magnet in the magnetization direction, Hm, decreases. This decrease in Pc affects the likelihood of irreversible demagnetization occurring.

[0091] Fig. 8 is a diagram showing the results of a comparison between the permanent magnet synchronous motor according to embodiment 1 and a conventional permanent magnet synchronous motor with respect to the d-axis inductance Ld and the rate of decrease in induced voltage after demagnetization. Fig. 8 shows the d-axis inductance Ld and the rate of decrease in induced voltage due to demagnetization relative to L1 / L2 when the condition for permanent magnet 22 is L1>L2. Note that the d-axis inductance Ld and the rate of decrease in induced voltage when L1=L2 are normalized to 1.0.

[0092] As is clear from FIG. 8, as L1 / L2 increases, the d-axis inductance Ld increases, but the rate of decrease in the induced voltage also increases.

[0093] Furthermore, focusing on the increasing trend of the d-axis inductance Ld, the increase amount of the d-axis inductance Ld is saturated. On the other hand, focusing on the increasing trend of the rate of decrease in the induced voltage, it can be seen that the increase amount of the rate of decrease in the induced voltage is not saturated.

[0094] Therefore, it is possible to effectively increase the d-axis inductance Ld within the range where 1.0 < L1 / L2 < 1.6 is satisfied. However, in the range where L1 / L2 > 1.6 is satisfied, demagnetization progresses significantly.

[0095] FIGS. 9A and 9B are the results obtained by calculating the demagnetization rate distribution by magnetic field analysis in the demagnetized state. FIG. 9A is a diagram showing the demagnetization rate distribution of a conventional permanent magnet synchronous motor. In FIG. 9A, L1 = L2 is satisfied as the condition of the permanent magnet. FIG. 9B is a diagram showing the demagnetization rate distribution of the permanent magnet synchronous motor according to Embodiment 1. In FIG. 9B, L1 ≠ L2 and L1 / L2 > 1.6 are satisfied as the conditions of the permanent magnet.

[0096] In FIGS. 9A and 9B, the regions indicated by reference numerals 70, 71, and 72 show the progress state of demagnetization. The region indicated by reference numeral 70 shows that the progress amount of demagnetization is the least. The region indicated by reference numeral 72 shows that the progress amount of demagnetization is the most. The region indicated by reference numeral 71 shows that the progress amount of demagnetization is larger than that of the region 70 and smaller than that of the region 72. Comparing the results shown in FIGS. 9A and 9B, the region 72 occurs in the portion where the distance between the second bottom end 52 of the concave portion 25 and the stator facing surface 26 is short. In other words, it can be seen that the range in which demagnetization progresses expands as the distance between the corner of the convex portion 24 and the stator facing surface 26 becomes shorter.

[0097] The progress of demagnetization leads to a decrease in the residual magnetic flux density Br, which leads to a decrease in the magnet magnetic flux Φm. As a result, the torque T calculated based on equation (6) decreases. Therefore, the output of the permanent magnet synchronous motor decreases.

[0098] The second embodiment solves the above problem. FIG. 10 is a diagram showing the results of a comparison of the induced voltage reduction rate after demagnetization between the permanent magnet synchronous motor according to embodiment 1, the permanent magnet synchronous motor according to embodiment 2, and the permanent magnet synchronous motor according to modification 2A. In FIG. 10, the induced voltage reduction rate of permanent magnet 22 according to embodiment 1 is normalized to 1.0. Specifically, "no inclined surface, no curved surface" corresponds to embodiment 1. Furthermore, "with inclined surface" corresponds to embodiment 2. Furthermore, "with curved surface" corresponds to modification 2A.

[0099] 10, it can be seen that the induced voltage drop rate is lower in the second embodiment, which uses the permanent magnet 22 having the inclined surface 64, than in the first embodiment. Similarly, it can be seen that the induced voltage drop rate is lower in the modified example 2A, which uses the permanent magnet 22 having the curved surface 65, than in the first embodiment.

[0100] 11A to 11C show the results obtained by calculating the demagnetization factor distribution by magnetic field analysis of the demagnetized state. FIG. 11A is a diagram showing the demagnetization factor distribution of permanent magnet 22 according to embodiment 1. As shown in FIG. FIG. 11B is a diagram showing the demagnetization factor distribution of permanent magnet 22 according to embodiment 2. FIG. 11C is a diagram showing the demagnetization factor distribution of the permanent magnet 22 according to Modification 2A.

[0101] In FIGS. 11A to 11C, the regions indicated by reference numerals 70, 71, and 72 show the progress of demagnetization. The region indicated by reference numeral 70 shows that the progress amount of demagnetization is the least. The region indicated by reference numeral 72 shows that the progress amount of demagnetization is the largest. The region indicated by reference numeral 71 shows that the progress amount of demagnetization is larger than that of the region of reference numeral 70 and smaller than that of the region of reference numeral 72.

[0102] Comparing the results shown in FIGS. 11A to 11C, it can be seen that in the case of Embodiment 2 having an inclined surface and the case of Modified Example 2A having a curved surface, the total area where regions 71 and 2 occur is smaller than that in Embodiment 1 having no inclined surface and no curved surface. In other words, by forming an inclined surface or a curved surface, it becomes possible to increase the distance between the point on the stator facing surface 26 closest to the second bottom end 52 and the second bottom end 52. Thus, it can be seen that in Embodiment 2 and Modified Example 2A, the progress of demagnetization can be suppressed as compared with Embodiment 1.

[0103] Therefore, according to Embodiment 2 and Modified Example 2A, even when weak magnetic flux control is performed, it is possible to increase the output of the motor. Further, since L1 / L2 is within the range satisfying 1.0 < L1 / L2 < 1.6, the demagnetization resistance can be improved. That is, it is possible to achieve both an increase in the output of the motor and an improvement in the demagnetization resistance.

[0104] <Modified Examples 2B and 2C of Embodiment 2> Next, Modified Examples 2B and 2C of the permanent magnet synchronous motor according to Embodiment 2 will be described. In the description of Modified Examples 2B and 2C, the description of the parts common to Embodiment 1 and Embodiment 2 described above will be omitted.

[0105] <Modified Example 2B> FIG. 12A is a view showing an enlarged region near the permanent magnet constituting Modified Example 2B, and is a cross-sectional view taken axially. As shown in FIG. 12A, the recess 25 has a first bottom end 51 and a second bottom end 52. Each of the first bottom end 51 and the second bottom end 52 forms the bottom 50 of the recess 25. The second bottom end 52 is spaced apart from the first bottom end 51. When the distance between the first recess end 35 and the first bottom end 51 in the radial direction is H1, and the distance between the second recess end 36 and the second bottom end 52 in the radial direction is H2, H1≠H2 is satisfied. In this modification, H1<H2 is satisfied. Further, this modification satisfies L1≠L2. The value of L1 / L2 is within the range of 1.0<L1 / L2<1.6.

[0106] Furthermore, in this modification, the recess 25 has a first inner wall 61 and a second inner wall 62. The first inner wall 61 is formed between the first recess end 35 and the first bottom end 51 and extends in the radial direction. The second inner wall 62 is formed between the second recess end 36 and the second bottom end 52. The second inner wall 62 has a vertical surface 63 and an inclined surface 64. The vertical surface 63 is connected to the second recess end 36 and extends in the radial direction. The inclined surface 64 is connected to the vertical surface 63 and the second bottom end 52, is inclined with respect to the vertical surface 63, and extends linearly.

[0107] <Modification 2C> FIG. 12B is a diagram showing an enlarged view of a region near the permanent magnet constituting Modification 2C, and is a cross-sectional view taken axially. Similar to FIG. 12A, FIG. 12B satisfies H1≠H2, satisfies H1<H2, and satisfies L1≠L2. The value of L1 / L2 is within the range of 1.0<L1 / L2<1.6.

[0108] Furthermore, in this modification, the recess 25 has a first inner wall 61 and a second inner wall 62. The first inner wall 61 is formed between the first recess end 35 and the first bottom end 51 and extends in the radial direction. The second inner wall 62 is formed between the second recess end 36 and the second bottom end 52. The second inner wall 62 has a curved surface 65 connected to the second bottom end 52.

[0109] <Effect> FIG. 13 is a diagram showing a comparison result of the induced voltage reduction rate after demagnetization, comparing a permanent magnet synchronous motor according to Modification 1A, a permanent magnet synchronous motor according to Modification 2B, and a permanent magnet synchronous motor according to Modification 2C. In FIG. 13, the induced voltage reduction rate of the permanent magnet 22 of Modification 1A is normalized to 1.0. Specifically, "no inclined surface, no curved surface" corresponds to Modification 1A. In other words, in Modification 1A, although H1 < H2 is satisfied as described above, no inclined surface or curved surface is formed in the recess 25. Further, "with inclined surface" corresponds to Modification 2B. Furthermore, "with curved surface" corresponds to Modification 2C.

[0110] As shown in FIG. 13, it can be seen that in Modification 2B using the permanent magnet 22 having the inclined surface 64, the induced voltage reduction rate is lower than that of Modification 1A. Similarly, it can be seen that in Modification 2C using the permanent magnet 22 having the curved surface 65, the induced voltage reduction rate is lower than that of Modification 1A.

[0111] FIGS. 14A to 14C are results obtained by calculating the demagnetization rate distribution by magnetic field analysis in the demagnetized state. FIG. 14A is a diagram showing the demagnetization rate distribution of the permanent magnet 22 according to Modification 1A. FIG. 14B is a diagram showing the demagnetization rate distribution of the permanent magnet 22 according to Modification 2B. FIG. 14C is a diagram showing the demagnetization rate distribution of the permanent magnet 22 according to Modification 2C.

[0112] In FIGS. 14A to 14C, the regions indicated by reference numerals 70, 71, and 72 indicate the progress state of demagnetization. The region indicated by reference numeral 70 indicates that the progress amount of demagnetization is the least. The region indicated by reference numeral 72 indicates that the progress amount of demagnetization is the most. The region indicated by reference numeral 71 indicates that the progress amount of demagnetization is larger than that of the region of reference numeral 70 and smaller than that of the region of reference numeral 72.

[0113] Comparing the results shown in FIGS. 14A to 14C, it can be seen that in the case of Modified Example 2B having an inclined surface and the case of Modified Example 2C having a curved surface, the total area where regions 71 and 2 occur is smaller than that of Modified Example 1A having no inclined surface and no curved surface. In other words, by forming an inclined surface or a curved surface, it becomes possible to increase the distance between the point on the stator facing surface 26 closest to the second bottom end 52 and the second bottom end 52. From this, it can be understood that in Modified Examples 2B and 2C, the progress of demagnetization can be suppressed as compared with Modified Example 1A.

[0114] Therefore, according to Modified Example 2B and Modified Example 2C, even when performing weak magnetic flux control, it is possible to increase the output of the motor. Also, since L1 / L2 is within the range satisfying 1.0 < L1 / L2 < 1.6, the demagnetization resistance can be improved. That is, it is possible to achieve both an increase in the output of the motor and an improvement in the demagnetization resistance.

[0115] Embodiment 3. A permanent magnet synchronous motor according to Embodiment 3 will be described. In Embodiment 3, the same members as those in the above-described embodiments and modified examples are denoted by the same reference numerals, and the description thereof is omitted or simplified.

[0116] FIG. 15 is a perspective view showing a permanent magnet synchronous motor according to Embodiment 3. FIG. 16 is a perspective view showing only the rotor core 21 including the convex portion 24. In other words, FIG. 16 shows a state in which a plurality of permanent magnets 22 are removed from the permanent magnet synchronous motor.

[0117] As shown in FIGS. 15 and 16, the permanent magnet synchronous motor according to Embodiment 3 is different from the permanent magnet synchronous motor according to Embodiment 1 in that the circumferential center position CP of the permanent magnet 22 is the same in the upper and lower stages.

[0118] Specifically, of the multiple permanent magnets 22, the stator-facing surfaces 26 of the permanent magnets 22 aligned in the Z direction in which the rotation shaft 23 extends are aligned with each other in the Z direction. There is no skew between the permanent magnets 22 aligned in the Z direction. Only the recesses 25 of the multiple permanent magnets 22 and the protrusions of the rotor core 21 are skewed.

[0119] The permanent magnet synchronous motor according to the third embodiment will now be described more specifically. The permanent magnet synchronous motor according to the third embodiment has an upper stage portion 100U and a lower stage portion 100L adjacent to the upper stage portion 100U in the Z direction. The upper stage portion 100U is an example of a first rotor portion. The lower stage portion 100L is an example of a second rotor portion.

[0120] The plurality of permanent magnets 22 includes a first magnet group 41 arranged in the upper stage portion 100U and a second magnet group 42 arranged in the upper stage portion 100U. Each of the plurality of permanent magnets 22 constituting the first magnet group 41 is the above-mentioned first permanent magnet. Each of the plurality of permanent magnets 22 constituting the second magnet group 42 is the above-mentioned second permanent magnet. The stator-facing surfaces 26 of the first permanent magnets constituting the first magnet group 41 coincide with the stator-facing surfaces 26 of the second permanent magnets constituting the second magnet group 42 in the Z direction. In other words, the position of the circumferential center point C of the stator-facing surfaces 26 of the first permanent magnets coincides with the position of the circumferential center point C of the stator-facing surfaces 26 of the second permanent magnets in the axial direction. The circumferential center point C of the stator-facing surfaces 26 has been described with reference to FIG. 2A.

[0121] The protrusions 24 of the rotor core 21 have a first protrusion 24U arranged in the upper stage 100U and a second protrusion 24L arranged in the lower stage 100L. The first protrusion 24U fits into the recessed portion 25 of the first permanent magnet that constitutes the first magnet group 41. The second protrusion 24L fits into the recessed portion 25 of the second permanent magnet that constitutes the second magnet group 42. In the circumferential direction, the second protrusions 24L are offset at a skew angle from the first protrusions 24U.

[0122] 16, the positions of the first protrusions 24U(24) in the circumferential direction of the upper stage 100U and the second protrusions 24L(24) in the circumferential direction of the lower stage 100L are shifted from the circumferential center position CP of the permanent magnet 22 as shown in FIG. 2A. The positions of the first protrusions 24U in the circumferential direction of the upper stage 100U and the second protrusions 24L in the circumferential direction of the lower stage 100L are mirror-symmetrical with respect to the circumferential center position CP of the permanent magnet 22.

[0123] <Effects> Next, the effects obtained by the third embodiment will be described while explaining the rotor manufacturing process for a permanent magnet synchronous motor. The rotor manufacturing process for a permanent magnet synchronous motor includes a magnetization process for attaching permanent magnets 22 to rotor core 21.

[0124] In the magnetization process of the permanent magnets, a widely used method is to use a magnetizer to magnetize the permanent magnets 22 after they are attached to the rotor core 21. However, when a stage-skew structure is applied to the rotor 20, the magnetization directions of the upper and lower stage permanent magnets differ by the skew angle θ, making it difficult to magnetize the permanent magnets of each stage simultaneously, and magnetization is performed on each stage. Therefore, an increase in the number of magnetizations leads to a shortened life of the magnetizer or a worsening of the tact time in rotor manufacturing.

[0125] The third embodiment solves the above problem. 16, the positions of the first protrusions 24U(24) in the circumferential direction of the upper stage portion 100U and the positions of the second protrusions 24L(24) in the circumferential direction of the lower stage portion 100L are mirror-symmetrical with respect to the circumferential center position CP. Due to the influence of the positions of the protrusions 24, a phase difference occurs between the harmonic components of the magnetic flux of the permanent magnet in the upper stage portion 100U and the lower stage portion 100L.

[0126] Therefore, by appropriately positioning the protrusions 24 in the circumferential direction and canceling out the harmonic components of the magnetic flux of the permanent magnets at each stage, it is possible to reduce the torque ripple of the entire motor.

[0127] Fig. 17 is a diagram showing the results of a comparison of torque ripple between the conventional motor when the condition L1 = L2 and the condition L1 ≠ L2 of embodiment 3. In Fig. 17, the torque ripple when L1 = L2 is normalized to 1.0.

[0128] As shown in FIG. 17, it can be seen that the torque ripple is reduced when the condition L1≠L2 in the third embodiment is met.

[0129] Therefore, according to the third embodiment, it is possible to reduce the number of steps required for the magnetization process. Furthermore, even when performing flux-weakening control as in the conventional case, it is possible to increase the output of the electric motor or reduce torque ripple.

[0130] Embodiment 4 A permanent magnet synchronous motor according to the fourth embodiment will be described. In the fourth embodiment, the same members as those in the above-described embodiments and modifications are given the same reference numerals, and their description will be omitted or simplified.

[0131] FIG. 18 is a perspective view showing a permanent magnet synchronous motor according to the fourth embodiment. Fig. 19 is a perspective view showing only the rotor core 21 including the protrusions 24. In other words, Fig. 19 shows a state in which the plurality of permanent magnets 22 have been removed from the permanent magnet synchronous motor.

[0132] As shown in Figures 18 and 19, the permanent magnet synchronous motor according to embodiment 4 differs from the permanent magnet synchronous motor according to embodiment 1 in that the circumferential positions of the protrusions 24 of the rotor core are the same on the upper and lower rows.

[0133] Specifically, the positions of the protrusions 24 in the rotor core 21 are consistent in the Z direction, and only the recesses 25 of the permanent magnets 22 are skewed. Also, as shown in Fig. 18, in each of the upper and lower stages, the positions of the recesses 25 of the permanent magnets 22 in the circumferential direction are shifted from the circumferential center position CP of the permanent magnets 22, and L1 ≠ L2 is satisfied.

[0134] The permanent magnet synchronous motor according to the fourth embodiment will now be described more specifically. The permanent magnet synchronous motor according to the fourth embodiment has an upper stage portion 100U and a lower stage portion 100L adjacent to the upper stage portion 100U in the Z direction. The plurality of permanent magnets 22 includes a first magnet group 41 arranged in the upper stage portion 100U and a second magnet group 42 arranged in the upper stage portion 100U. Each of the plurality of permanent magnets 22 constituting the first magnet group 41 is a first permanent magnet. Each of the plurality of permanent magnets 22 constituting the second magnet group 42 is a second permanent magnet.

[0135] The stator-facing surfaces 26 of the first permanent magnets constituting the first magnet group 41 are offset in the Z direction from the stator-facing surfaces 26 of the second permanent magnets constituting the second magnet group 42. In other words, the position of the circumferential center point C of the stator-facing surfaces 26 of the first permanent magnets and the position of the circumferential center point C of the stator-facing surfaces 26 of the second permanent magnets do not coincide in the axial direction. The circumferential center point C of the stator-facing surfaces 26 has been described with reference to FIG. 2A. The protrusions 24 of the rotor core 21 extend continuously from the upper stage 100U to the lower stage 100L. The protrusions 24 fit into the recesses 25 of the first permanent magnets that make up the first magnet group 41 and the recesses 25 of the second permanent magnets that make up the second magnet group 42.

[0136] In the circumferential direction, the stator-facing surfaces 26 of the first permanent magnets constituting the first magnet group 41 are offset at a skew angle from the stator-facing surfaces 26 of the second permanent magnets constituting the second magnet group 42.

[0137] The positions of the convex portions 24 in the circumferential direction of the upper stage portion 100U and the positions of the convex portions 24 in the circumferential direction of the lower stage portion 100L are mirror symmetrical with respect to the circumferential center position CP of the permanent magnet 22.

[0138] <Effects> Next, the effects obtained by the fourth embodiment will be described while explaining the rotor manufacturing process for a permanent magnet synchronous motor.

[0139] When a stage skew is applied to a rotor, in the rotor core manufacturing process for a permanent magnet synchronous motor, after forming the rotor core for each stage, the rotor core is fitted onto a rotating shaft so that a skew angle is generated.

[0140] Therefore, man-hours and processing are required to achieve a precise skew angle, and the manufacturing cost of the rotor is higher than in a rotor manufacturing process that does not use step-to-step skew.

[0141] The fourth embodiment solves the above problem. 19, the protrusions 24 are the same in the circumferential direction in the upper stage portion 100U and the lower stage portion 100L of the rotor core 21. Therefore, it is not necessary to manufacture the rotor core 21 so as to have separate protrusions 24 for each of the upper stage portion 100U and the lower stage portion 100L.

[0142] Furthermore, the positions of the recesses 25 of the permanent magnets 22 satisfy L1≠L2, and the circumferential center positions CP of the permanent magnets 22 in the upper and lower stages are mirror symmetrical with respect to the positions of the recesses 25, resulting in an angular difference.

[0143] Due to this angular difference in the circumferential center positions CP of the permanent magnets 22, a phase difference occurs between the harmonic components of the magnetic flux of the permanent magnets in the upper and lower stages.

[0144] Therefore, by appropriately positioning the recesses 25 and canceling out the harmonic components of the permanent magnet magnetic flux at each stage, it is possible to reduce the overall torque ripple of the motor. Furthermore, because the rotor core 21 can be molded as a single unit, the number of steps required to manufacture the rotor core 21 can be reduced.

[0145] Fig. 20 is a diagram showing the results of a comparison of torque ripple between the conventional motor when the condition L1 = L2 is satisfied and the motor according to embodiment 4 when the condition L1 ≠ L2 is satisfied. In Fig. 20, the torque ripple when L1 = L2 is normalized to 1.0.

[0146] As shown in FIG. 20, it can be seen that the torque ripple is reduced when the condition L1≠L2 in the fourth embodiment is met.

[0147] Fig. 21 is a diagram showing the results of a comparison of the d-axis inductance Ld when the condition L1 = L2 of a conventional motor is met and when the condition L1 ≠ L2 of embodiment 4 is met. In Fig. 21, the d-axis inductance Ld when L1 = L2 is normalized to 1.0.

[0148] As shown in FIG. 21, when the condition L1≠L2 in the fourth embodiment is satisfied, the d-axis inductance Ld can be increased more effectively. Therefore, according to the fourth embodiment, it is possible to reduce the number of steps required to manufacture rotor core 21. Furthermore, even when performing flux-weakening control as in the conventional case, it is possible to achieve higher output of the electric motor or reduce torque ripple compared to the conventional structure. [Explanation of symbols]

[0149] 10... Stator, 11... Stator core, 12... Core back, 13... Teeth, 14... Winding (coil portion), 15... Air gap, 20... Rotor, 21... Rotor core, 22... Permanent magnet, 22A... First permanent magnet (permanent magnet), 22B... Second permanent magnet (permanent magnet), 23... Rotating shaft, 24... Convex portion, 24L... Second convex portion (convex portion), 24U... First convex portion (convex portion), 25... Concave portion, 26...stator facing surface, 27...rotor core fixing surface, 27A...first rotor core fixing surface (rotor core fixing surface), 27B...second rotor core fixing surface (rotor core fixing surface), 27F...first region, 27S...second region, 28...outer circumferential surface, 31...first magnet end, 32...second magnet end, 33...first side surface, 34...second side surface, 35...first recess end, 36...second recess end, 37 A...first midpoint, 37B...second midpoint, 41...first magnet group, 42...second magnet group, 50...bottom, 51...first bottom end, 52...second bottom end, 53...surface, 61...first inner wall, 62...second inner wall, 63...vertical surface, 64...inclined surface, 65...curved surface, 100...permanent magnet synchronous motor, 100L...lower section (second rotor section), 100U...upper section (first rotor section), 122... Permanent magnet, 124...convex portion, 125...concave portion, C...center point, C1...first center point, C2...second center point, CL...center line, CP...circumferential center position, L1, L2...distance, M...angle between recess centers, N1...first recess center line, N2...second recess center line, O...axial center, S...magnet center line, S1...first magnet center line, S2...second magnet center line, TP...convex portion center position, θ...skew angle

Claims

1. a stator; a rotor comprising: a rotor core made of electromagnetic steel plates and having one or more protrusions protruding in a radial direction toward the stator; and a rotating shaft fixed to the rotor core, the rotor being rotatably disposed relative to the stator; a plurality of permanent magnets arranged in the circumferential direction of the rotor, each permanent magnet having an arc-shaped stator-facing surface facing the stator across a gap, a rotor core fixing surface located on the opposite side of the stator-facing surface and fixed to the outer circumferential surface of the rotor core, and a recess connected to a part of the rotor core fixing surface and into which the protrusion is fitted; and In the circumferential direction, the polarities of the stator-facing surfaces of two adjacent permanent magnets among the plurality of permanent magnets are different from each other, In the circumferential direction, each of the plurality of permanent magnets has a first magnet end connected to the rotor core fixing surface and a second magnet end connected to the rotor core fixing surface and located on the opposite side to the first magnet end, In the circumferential direction, the recessed portion of each of the plurality of permanent magnets has a first recessed portion end connected to the rotor core fixing surface and a second recessed portion end connected to the rotor core fixing surface and located on the opposite side to the first recessed portion end, the rotor core fixing surface has a first region located between the first magnet end and the first recessed portion end, and a second region located between the second magnet end and the second recessed portion end, the recess is located between the first region and the second region, When the distance between the first magnet end and the first recess end in the first region is L1, and the distance between the second magnet end and the second recess end in the second region is L2, L1≠L2 is satisfied. Permanent magnet synchronous motor.

2. the plurality of permanent magnets include a first magnet group and a second magnet group adjacent to each other in an axial direction in which the rotation shaft extends, each of the plurality of permanent magnets constituting the first magnet group is a first permanent magnet; each of the plurality of permanent magnets constituting the second magnet group is a second permanent magnet, The skew angle is called θ. the first permanent magnet is offset by θ / 2 with respect to a d-axis of the permanent magnet synchronous motor in a counterclockwise direction of the circumferential direction, the second permanent magnet is offset by θ / 2 with respect to the d-axis of the permanent magnet synchronous motor in a clockwise direction of the circumferential direction, a magnet center line extending radially outward from the axial center of the rotation shaft and passing through a circumferential center point of each of the plurality of permanent magnets intersects with the first region; L1≠L2 is satisfied and L1>L2 is satisfied.

2. The permanent magnet synchronous motor according to claim 1.

3. The recessed portion is a first bottom edge forming a bottom of the recess; a second bottom end forming a bottom of the recess and spaced from the first bottom end; and When the distance between the first recess end and the first bottom end in the radial direction is H1 and the distance between the second recess end and the second bottom end in the radial direction is H2, H1≠H2 is satisfied.

3. The permanent magnet synchronous motor according to claim 1 or 2.

4. The surface forming the bottom of the recess has an arc shape.

3. The permanent magnet synchronous motor according to claim 1 or 2.

5. the first permanent magnet has a first rotor core fixing surface fixed to an outer peripheral surface of the rotor core, the first rotor core fixing surface is a surface corresponding to the rotor core fixing surface, and includes the first region having the distance L1 and the first recessed portion end, and the second region having the distance L2 and the second recessed portion end, the second permanent magnet has a second rotor core fixing surface fixed to an outer peripheral surface of the rotor core, the second rotor core fixing surface is a surface corresponding to the rotor core fixing surface, and includes the first region having the distance L1 and the first recessed portion end, and the second region having the distance L2 and the second recessed portion end, A central point in the circumferential direction of the first permanent magnet is defined as a first central point, A center point in the circumferential direction of the second permanent magnet is defined as a second center point, A line extending radially outward from the axial center of the rotation shaft, passing through the first center point, and intersecting the first region of the first permanent magnet is defined as a first magnet center line; A line extending radially outward from the axial center of the rotation shaft, passing through the second center point, and intersecting the first region of the second permanent magnet is defined as a second magnet center line; a midpoint between the first recessed end and the second recessed end of the first permanent magnet in a direction parallel to the first rotor core fixing surface is defined as a first midpoint; a midpoint between the first recessed end and the second recessed end of the second permanent magnet in a direction parallel to the second rotor core fixing surface is defined as a second midpoint; A line extending radially outward from the axial center of the rotation shaft and passing through the first midpoint is defined as a first recess center line, A line extending radially outward from the axial center of the rotation shaft and passing through the second midpoint is defined as a second recess center line, the angle between the first magnet center line and the second magnet center line is the skew angle θ; the angle between the first recess centerline and the second recess centerline is a recess center-to-recess center angle; the recess center-to-center angle is smaller than the skew angle θ; When L1>L2 is satisfied, The value of L1 / L2 is in the range of 1.0<L1 / L2<1.

6.

3. The permanent magnet synchronous motor according to claim 2.

6. The recessed portion is a first bottom edge forming a bottom of the recess; a second bottom end forming a bottom of the recess and spaced from the first bottom end; a first inner wall formed between the first recess end and the first bottom end and extending in the radial direction; a second inner wall formed between the second recess end and the second bottom end; and The second inner wall is a vertical surface that is connected to the second recess end and extends in the radial direction; an inclined surface that is connected to the vertical surface and the second bottom end and is inclined relative to the vertical surface and extends linearly; having 3. The permanent magnet synchronous motor according to claim 2.

7. The recessed portion is a first bottom edge forming a bottom of the recess; a second bottom end forming a bottom of the recess and spaced from the first bottom end; a first inner wall formed between the first recess end and the first bottom end and extending in the radial direction; a second inner wall formed between the second recess end and the second bottom end; and The second inner wall has a curved surface that is connected to the second bottom end.

3. The permanent magnet synchronous motor according to claim 2.

8. The recessed portion is a first inner wall formed between the first recess end and the first bottom end and extending in the radial direction; a second inner wall formed between the second recess end and the second bottom end; and The second inner wall is a vertical surface that is connected to the second recess end and extends in the radial direction; an inclined surface that is connected to the vertical surface and the second bottom end and is inclined relative to the vertical surface and extends linearly; having 4. The permanent magnet synchronous motor according to claim 3.

9. The recessed portion is a first inner wall formed between the first recess end and the first bottom end and extending in the radial direction; a second inner wall formed between the second recess end and the second bottom end; and The second inner wall has a curved surface that is connected to the second bottom end.

4. The permanent magnet synchronous motor according to claim 3.

10. the rotor has a first rotor portion and a second rotor portion adjacent to the first rotor portion in an axial direction in which the rotation shaft extends, the plurality of permanent magnets includes a first magnet group disposed in the first rotor portion and a second magnet group disposed in the second rotor portion; each of the plurality of permanent magnets constituting the first magnet group is a first permanent magnet; each of the plurality of permanent magnets constituting the second magnet group is a second permanent magnet, a center position of the stator-facing surface of the first permanent magnet in the circumferential direction and a center position of the stator-facing surface of the second permanent magnet in the circumferential direction coincide with each other in the axial direction, the protruding portion of the rotor core includes a first protruding portion disposed in the first rotor portion and a second protruding portion disposed in the second rotor portion, the first protrusion fits into the recess of the first permanent magnet, the second protrusion is fitted into the recess of the second permanent magnet, The second convex portion is shifted at a skew angle with respect to the first convex portion in the circumferential direction.

2. The permanent magnet synchronous motor according to claim 1.

11. the rotor has a first rotor portion and a second rotor portion adjacent to the first rotor portion in an axial direction in which the rotation shaft extends, the plurality of permanent magnets includes a first magnet group disposed in the first rotor portion and a second magnet group disposed in the second rotor portion; each of the plurality of permanent magnets constituting the first magnet group is a first permanent magnet; each of the plurality of permanent magnets constituting the second magnet group is a second permanent magnet, a center position of the stator-facing surface of the first permanent magnet in the circumferential direction and a center position of the stator-facing surface of the second permanent magnet in the circumferential direction do not coincide with each other in the axial direction, the protruding portion of the rotor core extends continuously from the first rotor portion to the second rotor portion, the protrusion fits into the recess of the first permanent magnet and the recess of the second permanent magnet, In the circumferential direction, a center position of the stator-facing surface of the first permanent magnet is shifted by a skew angle with respect to a center position of the stator-facing surface of the second permanent magnet.

2. The permanent magnet synchronous motor according to claim 1.

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