Electric motors and compressors

Abstract

This reduces the harmonic components superimposed on the magnetic flux density distribution in the air gap between the rotor and stator in the circumferential direction of the rotor. [Solution] The electric motor comprises a rotor having a rotor core in which permanent magnets are embedded in magnet embedding holes and a plurality of magnetic pole portions are provided along the circumferential direction, and a stator having a plurality of teeth portions arranged on the outer circumference of the rotor and an annular yoke portion connecting the plurality of teeth portions. In a plane perpendicular to the rotation centerline of the rotor and passing through the rotor core, the line connecting the center of the magnetic pole portions in the circumferential direction of the rotor core and the rotation center of the rotor is defined as the d-axis, and the line connecting the center between adjacent magnetic pole portions in the circumferential direction of the rotor core and the rotation center of the rotor is defined as the q-axis. In this plane, the magnetic pole portions are provided with a front-side non-magnetic portion at a position on the front side of the rotor's rotation direction with respect to the d-axis, and the front-side non-magnetic portion restricts the short circuit of magnetic flux between a pair of adjacent magnetic pole portions in the circumferential direction of the rotor core and one tooth portion.

Description

Technical Field

[0001] The present invention relates to an electric motor and a compressor.

Background Art

[0002] As an electric motor, one having an embedded magnet type rotor in which permanent magnets are embedded inside a rotor core is known. This type of electric motor includes a rotor provided with a plurality of magnetic pole portions formed on the outer peripheral side of the permanent magnet along the circumferential direction, and a stator having a plurality of teeth portions arranged on the outer peripheral side of the rotor and an annular yoke portion connecting the plurality of teeth portions.

[0003] As a related technique, in the circumferential direction of a rotating rotor, by changing the size of the gap (air gap) between the outer peripheral surface of the rotor core and the inner peripheral surface of the teeth portion, the magnetic flux density distribution in the gap along the circumferential direction is made closer to a sine wave, and there is an electric motor that reduces torque ripple (Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the range between adjacent north pole and south pole portions in the circumferential direction of the rotor during the rotation of such an electric motor, for example, three teeth arranged in the circumferential direction of the rotor may face the outer surface of the rotor. Here, as an example, we focus on the magnetic path generated in the central tooth portion when a magnetic path circulating between the stator and the rotor is formed, and the central tooth portion of the three teeth portion is located on the q-axis, which is a straight line connecting the center between adjacent pole portions and the rotation center of the rotor. At this time, two types of magnetic paths are generated: a magnetic path in which the magnetic flux is short-circuited so that it goes from the north pole portion to the south pole portion via only the inner circumferential end (flange portion) of the tooth portion without passing through the yoke portion of the stator, and a proper magnetic path that goes from the north pole portion, traverses this tooth portion radially in the rotor, passes through the yoke portion, and then through the adjacent tooth portion to the south pole portion. In this way, at the central teeth section, loss occurs due to magnetic flux leaking through the short-circuited magnetic path (hereinafter also referred to as leakage flux) instead of passing through the proper magnetic path. As a result, the magnetic flux density distribution in the air gap between the rotor and stator does not become sinusoidal, and the waveform becomes distorted, generating harmonic magnetic flux containing higher-order components. The fact that the waveform of the magnetic flux density distribution is distorted and not sinusoidal indicates that the magnetic flux density distribution also contains harmonic components.

[0006] As a result, the influence of harmonic flux causes high-frequency components that are integer multiples of the operating frequency to be superimposed on the electromagnetic force acting between the rotor and stator. This high-frequency component of the electromagnetic force resonates with the natural frequency of the stator, leading to increased vibration of the motor. In particular, in electric motors, increasing the magnet torque of the permanent magnets increases the amount of magnetic flux, which in turn increases the amount of leakage flux mentioned above. This makes it difficult to bring the magnetic flux density distribution in the air gap between the rotor and stator closer to a sine wave in the circumferential direction of the rotating rotor, resulting in increased vibration of the motor.

[0007] The disclosed technology has been made in view of the above, and aims to provide an electric motor and a compressor that can reduce harmonic components superimposed on the magnetic flux density distribution in the air gap between the rotor and the stator in the circumferential direction of the rotor. [Means for solving the problem]

[0008] One embodiment of the electric motor disclosed in this application comprises a rotor having a rotor core in which permanent magnets are embedded in magnet embedding holes and a plurality of magnetic pole portions are provided along the circumferential direction, and a stator having a plurality of teeth portions arranged on the outer circumference of the rotor and an annular yoke portion connecting the plurality of teeth portions. In a plane perpendicular to the rotation centerline of the rotor and passing through the rotor core, the line connecting the center of the magnetic pole portions in the circumferential direction of the rotor core and the rotation center of the rotor is defined as the d-axis, and the line connecting the center between adjacent magnetic pole portions in the circumferential direction of the rotor core and the rotation center of the rotor is defined as the q-axis. In this plane, the magnetic pole portions are provided with a front-side non-magnetic portion at a position on the front side of the rotor's rotation direction with respect to the d-axis, and the front-side non-magnetic portion restricts short-circuiting of magnetic flux between a pair of adjacent magnetic pole portions in the circumferential direction of the rotor core and one tooth portion. [Effects of the Invention]

[0009] According to one embodiment of the electric motor disclosed in this application, it is possible to reduce the harmonic components superimposed on the magnetic flux density distribution in the air gap between the rotor and the stator in the circumferential direction of the rotor. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a longitudinal cross-sectional view showing the compressor of Example 1. [Figure 2] Figure 2 is a plan view showing the electric motor of Example 1. [Figure 3] Figure 3 is a plan view showing the rotor in Example 1. [Figure 4] Figure 4 is a plan view illustrating the main components of the rotor core in Example 1. [Figure 5] Figure 5 is a plan view showing the magnetic field lines in Example 1. [Figure 6] Figure 6 shows the circumferential magnetic flux density distribution of the rotor in Example 1. [Figure 7] Figure 7 is a plan view showing the magnetic field lines in the comparative example. [Figure 8]FIG. 8 is a diagram showing the circumferential magnetic flux density distribution of the rotor in the comparative example. [Figure 9] FIG. 9 is a plan view for explaining the main part of the rotor core in Example 2. [Figure 10] FIG. 10 is an enlarged view showing the magnetic pole outer peripheral surfaces of the N - pole and S - pole portions of the rotor core in Example 2. [Figure 11] FIG. 11 is a schematic diagram showing the magnetic pole outer peripheral surfaces of each magnetic pole portion of the rotor core in Example 2. [Figure 12] FIG. 12 is a schematic diagram for explaining the shape of the magnetic pole outer peripheral surface of the rotor core in Example 2. [Figure 13] FIG. 13 is a plan view showing the magnetic lines of force in Example 2. [Figure 14] FIG. 14 is a diagram showing the circumferential magnetic flux density distribution of the rotor in Example 2. [Figure 15] FIG. 15 is a plan view showing the rotor core of Example 3. [Figure 16] FIG. 16 is a plan view showing the magnetic lines of force in Example 3. [Figure 17] FIG. 17 is a diagram showing the circumferential magnetic flux density distribution of the rotor in Example 3. MODE FOR CARRYING OUT THE INVENTION

[0011] Hereinafter, embodiments of the motor and the compressor disclosed in the present application will be described in detail based on the drawings. Note that the motor and the compressor disclosed in the present application are not limited by the following embodiments. EXAMPLE

[0012] (Configuration of Compressor) FIG. 1 is a longitudinal sectional view showing the compressor of Example 1. As shown in FIG. 1, the compressor 101 is a so-called rotary compressor and includes a container 102, a compression section 105, and an electric motor 1. The container 102 is formed of a metal material and forms a sealed internal space 107. The internal space 107 of the container 102 is generally formed in a cylindrical shape. The container 102 is formed such that when it is vertically placed on a horizontal plane, the central axis of the cylinder forming the internal space 107 is parallel to the vertical direction. An oil sump 108 is formed at the lower part of the internal space 107 in the container 102. Refrigeration oil, which is lubricating oil for lubricating the compression section 105, is stored in the oil sump 108. A suction pipe 111 for sucking refrigerant and a discharge pipe 112 for discharging the compressed refrigerant are connected to the container 102. In the internal space 107 of the container 102, a shaft 3 rotated by an electric motor 1 described later is arranged such that one end of this shaft 3 is located in the oil sump 108. The shaft 3 is supported by the container 102 so as to be rotatable about the central axis of the cylinder forming the internal space 107. By rotating, the shaft 3 supplies the refrigeration oil stored in the oil sump 108 to the compression section 105.

[0013] The compression section 105 is arranged at the lower part of the internal space 107 and above the oil sump 108. The compressor 101 further includes an upper muffler cover 114 and a lower muffler cover 115. The upper muffler cover 114 is arranged above the compression section 105 in the internal space 107. The upper muffler cover 114 forms an upper muffler chamber 116 inside. The lower muffler cover 115 is provided at the lower part of the compression section 105 in the internal space 107 and above the oil sump 108. The lower muffler cover 115 forms a lower muffler chamber 117 inside. The lower muffler chamber 117 communicates with the upper muffler chamber 116 through a communication passage (not shown) formed in the compression section 105. A compressed refrigerant discharge hole 118 is formed between the upper muffler cover 114 and the shaft 3, and the upper muffler chamber 116 communicates with the internal space 107 through the compressed refrigerant discharge hole 118.

[0014] The compression unit 105 compresses the refrigerant supplied from the intake pipe 111 as the shaft 3 rotates, and supplies the compressed refrigerant to the upper muffler chamber 116 and the lower muffler chamber 117. The refrigerant is compatible with refrigerant oil. The electric motor 1 is located above the compression unit 105 in the internal space 107.

[0015] (Motor configuration) Figure 2 is a plan view showing the electric motor 1 in Embodiment 1. Figure 3 is a plan view showing the rotor in Embodiment 1. As shown in Figures 2 and 3, the electric motor 1 in Embodiment 1 is a 6-pole, 9-slot concentrated winding 3-phase motor. The electric motor 1 comprises a rotor 21 and a stator 22 arranged on the outer circumference of the rotor 21.

[0016] The rotor 21 has a cylindrical rotor core 23 formed by laminating multiple metal plates made of a soft magnetic material such as silicon steel, and the multiple metal plates are integrated together, for example, by crimping. A shaft 3, which serves as the rotation axis of the rotor core 23, is inserted through the central axis, which is the rotation centerline of the rotor core 23, and the shaft 3 and the rotor 21 are fixed together. Although not shown, the rotor core 23 may be provided with multiple elongated refrigerant gas passages that penetrate through the rotor core 23 in the axial direction (the axial direction of the shaft 3). The multiple refrigerant gas passages are arranged at intervals along the axis of the shaft 3. The main parts of the rotor core 23 in Embodiment 1 will be described later.

[0017] The stator 22 is generally cylindrical in shape and is positioned to surround the outer circumference of the rotor 21. The stator 22 is fixed, for example, inside the container 102 of the compressor 101. As shown in Figures 1 and 2, the stator 22 comprises a stator core 24, an upper insulator 25 and a lower insulator 26, and a plurality of windings 46.

[0018] As shown in Figures 2 and 3, the stator core 24 is positioned with a predetermined air gap between it and the outer circumferential surface 27 of the rotor core 23. Details of the shape of the outer circumferential surface 27 of the rotor core 23 in the circumferential direction will be described later. The stator core 24 has nine teeth 32 extending radially inward from an annular yoke 31, formed at equal intervals of 40 degrees (mechanical angle) in the circumferential direction of the stator core 24. Each tooth 32 has a flange 33 that protrudes from its tip, located on the inner circumference side of the stator core 24, to both sides in the circumferential direction of the stator core 24. Each tooth 32 is formed to have the same shape. As shown in Figure 2, each tooth 32 has a winding section 45 in which each winding 46 is wound in a concentrated winding manner. The multiple windings 46 include three U-phase windings 46-U1 to 46-U3, three V-phase windings 46-V1 to 46-V3, and three W-phase windings 46-W1 to 46-W3. In the stator 22, the neutral wires drawn from each winding section 45 and bundled together are covered with insulating tubing and inserted into the gaps between adjacent winding sections 45 in the circumferential direction (rotation direction R of the rotor 21) of the stator 22 (see Figure 2). The upper insulator 25 is fixed to the upper end of the stator core 24. The lower insulator 26 is fixed to the lower end of the stator core 24. The upper insulator 25 and the lower insulator 26 are insulating members that insulate the stator core 24 from the windings 46.

[0019] As shown in Figure 3, the rotor core 23 of the electric motor 1 of Embodiment 1 has a plurality of magnet embedding holes 12a, 12b, 12c, 12d, 12e, 12f (hereinafter also referred to as magnet embedding holes 12) into which permanent magnets 13a, 13b, 13c, 13d, 13e, 13f (hereinafter also referred to as permanent magnets 13) are embedded. The rotor core 23 has two slit-shaped magnet embedding holes 12 in each magnetic pole portion 11, which will be described later, and are formed in a substantially V-shape on an orthogonal plane, that is, on the end face of the rotor core 23. The two magnet embedding holes 12 in each magnetic pole portion 11 are adjacent at one end and the other end extends to the outer circumference of the rotor core 23. Plate-shaped permanent magnets 13 are embedded in the magnet embedding holes 12. Although end plates are attached to both axial ends of the rotor core 23 to prevent the permanent magnets 13 from coming loose, the illustration of these end plates is omitted in order to explain the main parts of the rotor core 23. These end plates are fixed to the rotor core 23 by rivets 8 that are passed through the rivet holes 7 of the rotor core 23.

[0020] As described above, the rotor core 23 has six magnetic pole sections 11, namely three north pole sections 11N and three south pole sections 11S, which are arranged alternately along the circumferential direction of the rotor core 23 by embedding permanent magnets 13 in magnet embedding holes 12. Each of the north pole section 11N and south pole section 11S (hereinafter also referred to as magnetic pole section 11) contains two permanent magnets 13 and is the outer peripheral portion of each permanent magnet 13 in the radial direction of the rotor core 23 (the portion between each permanent magnet 13 and the outer peripheral surface 27 of the rotor core 23).

[0021] Furthermore, in the electric motor disclosed in this application, where m is a natural number, the number of pole pairs formed by the magnetic pole portion 11 (N pole portion 11N and S pole portion 11S) is m, and the number of multiple teeth portions 32 is 3m. Also, in the rotor 21, the number of magnetic pole portions 11, i.e., the number of poles, is 2m. In the electric motor 1 of Embodiment 1, as an example, the number of poles is 6, the number of pole pairs is 3, and the number of teeth portions 32 is 9.

[0022] Furthermore, in a plane (hereinafter also referred to as the orthogonal plane) that is perpendicular to the rotation center line passing through the rotation center O of the rotor 21 (the rotation center of the rotor core 23) and passes through the rotor core 23, the line connecting the center of the magnetic pole portion 11 in the circumferential direction of the rotor 21 and the rotation center O is defined as the d-axis D, and the line connecting the center between adjacent magnetic pole portions 11 in the circumferential direction of the rotor 21 and the rotation center O is defined as the q-axis Q. Therefore, in the orthogonal plane, the center between the magnetic pole portions 11 in the circumferential direction of the rotor 21 is a position along the radial direction of the rotor core 23 and refers to a position on a line that coincides with the q-axis Q. The rotation center line passing through the rotation center O of the rotor 21 coincides with the center line of the shaft 3 along the axial direction of the shaft 3. The rotor core 23 has a plurality of d-axis D extending radially from the rotation center O at equal intervals in the circumferential direction of the rotor core 23, and a plurality of q-axis Q extending radially from the rotation center O at equal intervals in the circumferential direction of the rotor core 23.

[0023] Furthermore, in each magnetic pole section 11, two plate-shaped permanent magnets 13 are provided on both sides of the d-axis D, and are arranged to form a roughly V-shape in an orthogonal plane. Note that Embodiment 1 does not limit the number or arrangement of permanent magnets 13 in each magnetic pole section 11.

[0024] Figure 4 is a plan view illustrating the main parts of the rotor core 23 in Embodiment 1. As shown in Figure 4, the rotor core 23 has a plurality of q-axis side non-magnetic parts 14 (14a to 14f), 15 (15a to 15f) formed near the q-axis Q in continuity with the magnet embedding hole 12, a plurality of d-axis side non-magnetic parts 19a to 19f (hereinafter referred to as d-axis side non-magnetic parts 19) formed on the d-axis D in continuity with the magnet embedding hole 12, a plurality of grooves 16, and a plurality of bridge parts 18 formed between the q-axis side non-magnetic parts 14, 15 and the grooves 16.

[0025] Here, of the two q-axis side non-magnetic parts 14 and 15 formed in each magnetic pole part 11, the q-axis side non-magnetic part located on the front side in the rotation direction R of the rotor 21 is referred to as the q-axis side first non-magnetic part 14 (14a to 14f), and the q-axis side non-magnetic part located on the rear side in the rotation direction R is referred to as the q-axis side second non-magnetic part 15 (15a to 15f). In each magnetic pole part 11, the q-axis side non-magnetic parts (q-axis side first non-magnetic part 14, q-axis side second non-magnetic part 15) are formed extending radially outward from each end of the two magnet embedding holes 12 located on the outer circumferential surface 27 side of the rotor core 23, that is, toward the outer circumferential surface 27 of the rotor core 23. In each magnetic pole part 11, the d-axis side non-magnetic part 19 is formed continuously so as to connect adjacent ends in the two magnet embedding holes 12.

[0026] The q-axis non-magnetic portions 14, 15 and the d-axis non-magnetic portion 19 are so-called flux barriers and are formed as spaces continuous with the magnet embedding holes 12. The q-axis non-magnetic portions 14, 15 and the d-axis non-magnetic portion 19 suppress the formation of a magnetic path in which magnetic flux circulates between adjacent magnetic pole portions 11 in the circumferential direction of the rotor core 23, bypassing the yoke portion 31 of the stator 22 and passing through the flange portion 33 of the teeth portion 32. In other words, the rotor core 23 has through holes formed along the rotational centerline of the rotor core 23 which is parallel to the axial direction of the shaft 3. The area of ​​the through hole that is filled by the permanent magnet 13 is the magnet embedding hole 12, and the area of ​​the through hole that is not filled by the permanent magnet 13 is the space, which is the q-axis non-magnetic portion 14, 15 and the d-axis non-magnetic portion 19.

[0027] Furthermore, each magnetic pole portion 11 is provided with a front non-magnetic portion 20, formed separately from the magnet embedding hole 12, at a position on the front side of the rotation direction R of the rotor 21 (the rotation direction R of the rotor core 23) relative to the d-axis D. In other words, each magnetic pole portion 11 is provided with a front non-magnetic portion 20, formed separately from the q-axis non-magnetic portion 14, at a position on the front side of the rotation direction R of the rotor 21 relative to the d-axis D. By forming the front non-magnetic portion 20 separately from the magnet embedding hole 12 in this way, the rotor core 23 can suppress a decrease in the mechanical strength around the magnet embedding hole 12. The front non-magnetic portion 20 is a through hole that penetrates the rotor core 23 along the rotation centerline, and is a space formed in the magnetic pole portion 11. Details of the front non-magnetic portion 20 will be described later.

[0028] On the outer circumferential surface 27 of the rotor core 23, grooves 16 are formed along the rotational centerline of the rotor core 23, where a portion of the outer circumferential surface 27 is cut out and recessed in the radial direction of the rotor core 23, between adjacent magnetic pole portions 11 in the circumferential direction of the rotor core 23. In other words, the grooves 16 are located between adjacent q-axis side non-magnetic portions 14 and q-axis side non-magnetic portions 15 in the circumferential direction of the rotor core 23, and are positioned on the q-axis Q.

[0029] (Characteristic structure of the rotor core) Next, the characteristic structure of the rotor core 23 in Example 1 will be described. The characteristics of Example 1 include the shape of the front non-magnetic portion 20 of each magnetic pole portion 11 and the outer circumferential surface 27 of the rotor core 23.

[0030] (Shape of the non-magnetic part on the front side) As shown in Figure 4, each magnetic pole portion 11 is provided with only a front non-magnetic portion 20, which is a non-magnetic portion provided separately from the magnet embedding hole 12. The front non-magnetic portion 20, like the q-axis non-magnetic portions 14, 15 and d-axis non-magnetic portion 19 described above, restricts the short circuit of magnetic flux between a pair of adjacent magnetic pole portions 11 in the circumferential direction of the rotor core 23 and the flange portion 33 of one tooth portion 32. The total magnetic flux, which is the sum of the magnetic flux passing through the short-circuited magnetic path (leakage flux) and the magnetic flux passing through the proper magnetic path, can be considered constant. Therefore, by reducing the magnetic flux passing through the short-circuited magnetic path (leakage flux) as described above, the front non-magnetic portion 20 can increase the magnetic flux passing through the proper magnetic path that circulates between a pair of adjacent magnetic pole portions 11 in the circumferential direction of the rotor core 23, a pair of adjacent tooth portions 32 in the circumferential direction of the rotor core 23, and the yoke portion 31 connecting these pairs of tooth portions 32.

[0031] Specifically, the front non-magnetic portion 20 suppresses the short circuit of the magnetic flux as described above when the q-axis Q of the rotor 21 coincides with the widthwise center of one of the multiple tooth portions 32 during the rotation of the rotor 21. Here, the widthwise direction of the tooth portion 32 refers to the direction perpendicular to the radial direction of the stator 22 (the radial direction of the rotor 21). The widthwise center of the tooth portion 32 is located on a straight line along the radial direction of the stator 22.

[0032] The front non-magnetic portion 20 is formed over a range of 90 degrees to 150 degrees relative to the magnetic pole portion 11, where the q-axis Q located on the rear side of the rotor 21's rotation direction R is defined as 0 degrees of electrical angle, and the front side of the rotor 21's rotation direction R is defined as positive electrical angle. As a result, the front non-magnetic portion 20 can block the magnetic flux passing through the outer magnetic pole surface 29, which is the outer peripheral side of the magnetic pole portion 11 and will be described later, over a range of electrical angles of 90 degrees to 150 degrees.

[0033] To rephrase the above-mentioned electrical angle in terms of mechanical angle, the front non-magnetic portion 20 is formed in a range of (360 / 2m) × (3 / 6) degrees or more and (360 / 2m) × (5 / 6) degrees or less, when the number of magnetic pole portions 11 is 2m, and the mechanical angle of the circumferential range between adjacent magnetic pole portions 11 (the range of one pole pair described later) is set to 0 degrees, with the q-axis Q located on the rear side relative to the rear magnetic pole portion 11 in the rotational direction R.

[0034] The front non-magnetic portion 20 has a first portion 20a extending from the magnet embedding hole 12 toward the outer magnetic pole surface 29, which will be described later, and a second portion 20b formed continuously with the first portion 20a and extending toward the d-axis D. The front non-magnetic portion 20 is formed such that, for example, the width dimension of the first portion 20a along the short side is equal to the width dimension of the second portion 20b along the short side, and the second portion 20b is formed in an elongated hole shape that is bent relative to the first portion 20a.

[0035] In the orthogonal plane, the front non-magnetic portion 20 is positioned such that the center line 20c of the first portion 20a, which is aligned with the direction in which the first portion 20a extends, intersects with the permanent magnet 13. Here, the center line 20c of the first portion 20a is a straight line that passes through the center of the width direction, which is the short side of the first portion 20a, and extends along the longitudinal direction of the first portion 20a. By positioning the front non-magnetic portion 20 in this way, it becomes easier to block the path of magnetic flux that would otherwise pass through the front non-magnetic portion 20. As a result, it is possible to suppress the occurrence of a magnetic path in which magnetic flux passing through the permanent magnet 13 returns to the permanent magnet 13 via the inner end (flange portion 33) of the teeth portion 32 without passing through the yoke portion 31, thereby enhancing the effect of restricting the short circuit of magnetic flux as described above. In addition, because the center line 20c of the first portion 20a is positioned to intersect with the permanent magnet 13, the thickness between the front non-magnetic portion 20 and the outer magnetic pole surface 29 can be increased compared to the case where the center line 20c of the first portion 20a does not intersect with the permanent magnet 13 (for example, when the center line 20c of the first portion 20a extends in a direction along the center line 20d of the second portion 20b), thereby suppressing a decrease in the mechanical strength around the front non-magnetic portion 20 and the q-axis non-magnetic portion 14 in the rotor core 23.

[0036] In the front non-magnetic portion 20, the length J2 of the second portion 20b extending toward the d-axis D is longer than the length J1 of the first portion 20a extending toward the outer magnetic pole surface 29. This ensures that the length of the front non-magnetic portion 20 extending in the circumferential direction of the rotor core 23 is sufficiently secured, thereby enhancing the effect of restricting the occurrence of the aforementioned short circuit of magnetic flux. Here, the length J1 of the first portion 20a is, for example, the length along the center line 20c of the first portion 20a along the direction in which the first portion 20a extends. Similarly, the length J2 of the second portion 20b is, for example, the length along the center line 20d of the second portion 20b along the direction in which the second portion 20b extends.

[0037] The front non-magnetic portion 20 is positioned radially inward from the q-axis side first non-magnetic portion 14 in the radial direction of the rotor core 23. This prevents the front non-magnetic portion 20 from being too close to the q-axis side first non-magnetic portion 14. As a result, the wall thickness between the front non-magnetic portion 20 and the q-axis side first non-magnetic portion 14 can be increased, thus suppressing a decrease in the mechanical strength around the front non-magnetic portion 20 and the q-axis side non-magnetic portion 14 in the rotor core 23.

[0038] Furthermore, in Embodiment 1, the front non-magnetic portion 20 is positioned only on the front side of the magnetic pole portion 11 in the rotation direction R of the rotor 21 with respect to the d-axis D. This makes it easy to realize a cross-sectional shape of the magnetic pole portion 11 in an orthogonal plane that is asymmetrical with respect to the d-axis D.

[0039] (Outer surface of the rotor core) Next, the shape of the outer circumferential surface 27 of the rotor core 23 will be described. As shown in Figure 4, in the orthogonal plane of the rotor core 23, the area of ​​the outer circumferential surface 27 of the rotor core 23 that forms one pole pair is defined as the pole pair outer circumferential surface 28. Also, in the orthogonal plane, the number of pole pairs formed by the magnetic pole portion 11 (a pair of N pole portion 11N and S pole portion 11S) is m (m is a natural number). In this case, the overall shape of the outer circumferential surface 27 of the rotor core 23 in the orthogonal plane is formed by repeating the shape of one pole pair outer circumferential surface 28 m times in the circumferential direction of the rotor core 23. In other words, in the orthogonal plane, each of the m pole pair outer circumferential surfaces 28 is formed to be rotationally symmetric with respect to the rotation center O of the rotor 21. In other words, in an orthogonal plane, the outer surface 27 of the rotor core 23 is divided into m equal parts in the circumferential direction with respect to the q-axis Q described later, and each of the m single-pole pair outer surface 28 is the same shape as the others. As a result, the path of the magnetic flux formed by the rotor core 23 and the stator core 24 radially opposite to the rotor core 23 is also repeated periodically m times. Consequently, the same magnetic flux density distribution is repeated periodically every 360 degrees in mechanical angle and every 360 degrees in electrical angle, thus suppressing the increase in vibration caused by irregular fluctuations in the magnetic flux density distribution during one rotation of the rotor core 23. For example, in Embodiment 1, the outer surface 27 of the rotor core 23 is formed by repeating single-pole pair outer surface 28 three times around the entire circumference of the rotor core 23.

[0040] Here, on the orthogonal plane described above, the angles C1 and C2 on the d-axis D side of the ends of the two permanent magnets 13 of the magnetic pole portion 11, which are located on the outer peripheral surface 27 side of the rotor core 23, are defined as the points located furthest outward in the radial direction of the rotor core 23. The first boundary line B1 is defined as the straight line passing through the rotation center O of the rotor 21 and the angle C1 at the end of the permanent magnet 13 located on the front side in the rotation direction R of the rotor 21. The second boundary line B2 is defined as the straight line passing through the rotation center O of the rotor 21 and the angle C2 at the end of the permanent magnet 13 located on the rear side in the rotation direction R of the rotor 21. At this time, the outer peripheral surface 27 of each magnetic pole portion 11 of the rotor core 23 has a magnetic pole outer peripheral surface 29 formed in the range between the two boundary lines (first boundary line B1 and second boundary line B2) that pass through one magnetic pole portion 11.

[0041] Therefore, the single pole pair outer surface 28 is a single pole pair that includes, in the circumferential direction of the outer surface 27 of the rotor core 23, as shown in Figure 4, the outer pole surface 29 of the N pole portion 11N (hereinafter also referred to as the N pole outer surface 29N) and the outer pole surface 29 of the S pole portion 11S (hereinafter also referred to as the S pole outer surface 29S), the inner surface of the groove portion 16 located between the N pole outer surface 29N and the S pole outer surface 29S, the inner surface of the groove portion 16 located on the rear side in the rotation direction R with respect to the N pole portion 11N and on the front side in the rotation direction R with respect to the q axis Q, and the inner surface of the groove portion 16 located on the front side in the rotation direction R with respect to the S pole portion 11S and on the rear side in the rotation direction R with respect to the q axis Q. Each magnetic pole outer surface 29 (N pole outer surface 29N or S pole outer surface 29S) is the area of ​​the outer surface 27 of the rotor core 23 that is located between two adjacent q-axis Qs in the circumferential direction, and does not include the groove portion 16, but is on the outer side of the magnetic pole portion 11. In other words, each magnetic pole outer surface 29 (N pole outer surface 29N and S pole outer surface 29S) is a portion formed in the circumferential direction of the outer surface 27 between two boundary lines (first boundary line B1 and second boundary line B2) that pass through one magnetic pole portion 11.

[0042] (Shape of the outer surface of the magnetic pole) In the orthogonal plane described above, the outer magnetic pole surface 29, which is the outer peripheral side of the magnetic pole portion 11, is formed such that the distance between the outer magnetic pole surface 29 and the rotation center O gradually decreases as you move from the d-axis D towards the q-axis Q. Therefore, in the orthogonal plane, the outer diameter L of the outer magnetic pole surface 29 of each magnetic pole portion 11 is largest at a position on the d-axis D, i.e., the distance from the rotation center O of the rotor 21, i.e., the radius of the rotor core 23. In Embodiment 1, the outer magnetic pole surface 29 of each magnetic pole portion 11 is formed in a shape symmetrical with respect to the d-axis D.

[0043] (Comparison between Example 1 and the Comparative Example) Figure 5 is a plan view showing the magnetic field lines in Example 1. Figure 6 is a diagram showing the circumferential magnetic flux density distribution of the rotor 21 in Example 1. Figure 7 is a plan view showing the magnetic field lines in the Comparative Example. In the Comparative Example, the same members and parts as in Example 1 are denoted by the same reference numerals. Figure 8 is a diagram showing the circumferential magnetic flux density distribution of the rotor in the Comparative Example. In Figures 6 and 8, the vertical axis represents magnetic flux density [T], and the horizontal axis represents electrical angle [degrees (deg)]. In Figure 6, the solid line represents a sine wave, and the dashed line represents Example 1. In Figure 8, the solid line represents a sine wave, and the dashed line represents the Comparative Example. The Comparative Example has the same structure as Example 1, except that it does not have a front non-magnetic part 20.

[0044] Comparing Figure 5 and Figure 7, in each magnetic pole section 11 of Embodiment 1, the path of the magnetic flux on the front side of the rotor 21 in the rotation direction R relative to the d-axis D is changed by the front non-magnetic section 20 to pass through the d-axis D side. Therefore, the front non-magnetic section 20 plays a role in reducing the magnetic flux passing through the q-axis Q side in front of the magnetic pole section 11 and increasing the amount of magnetic flux passing through the d-axis D side in front of the magnetic pole section 11 by the same amount. In other words, the front non-magnetic section 20 has the function of concentrating the path of the magnetic flux on the front side of the rotor 21 in the rotation direction R relative to the d-axis D side. Therefore, in Example 1, compared to the comparative example, the occurrence of a short-circuit magnetic path where the magnetic flux passing through the permanent magnet 13 returns to the permanent magnet 13 via the inner circumferential end (flange) of the tooth portion 32 without passing through the yoke portion 31 is suppressed, and the amount of magnetic flux passing through the proper magnetic path that returns to the permanent magnet 13 after traversing the tooth portion 32 radially in the rotor 21, passing through the yoke portion 31, and passing through adjacent tooth portions 32 is increased. Accordingly, in Example 1, in each magnetic pole portion 11, the front non-magnetic portion 20 prevents the magnetic flux passing through the front side of the magnetic pole portion 11 from short-circuiting between a pair of adjacent magnetic pole portions 11 in the circumferential direction of the rotor core 23 and the flange portion 33 of one tooth portion 32.

[0045] As shown in Figures 6 and 8, in the range of electrical angles from approximately 270 to 330 degrees starting from the q-axis Q on the north pole side (and from approximately 90 to 150 degrees starting from the q-axis Q on the south pole side), the magnetic flux density distribution at the air gap between the rotor 21 and the stator 22 in the circumferential direction of the rotor 21 is closer to a sine wave in Example 1 compared to the comparative example. The fact that the magnetic flux density distribution is closer to a sine wave indicates that the harmonic components superimposed on the magnetic flux density distribution at the air gap between the rotor 21 and the stator 22 have been reduced. In other words, in Example 1, the harmonic components superimposed on the magnetic flux density distribution at the air gap between the rotor 21 and the stator 22 have been reduced compared to the comparative example.

[0046] Here, the harmonic components superimposed on the magnetic flux density distribution at the location of the air gap between the rotor 21 and the stator 22 are thought to be due to the short circuit of the magnetic flux passing in front of the magnetic pole portion 11 as described above. Therefore, since the magnetic flux density distribution at the location of the air gap between the rotor 21 and the stator 22 in the circumferential direction of the rotor 21 approaches a sine wave, it can be said that in Example 1, the short circuit of the magnetic flux passing in front of the magnetic pole portion 11 is suppressed compared to the comparative example.

[0047] As described above, in Example 1, since the magnetic pole portion 11 has a front non-magnetic portion 20, short-circuiting of magnetic flux through the flange portion 33 of the teeth portion 32 between adjacent magnetic pole portions 11 is restricted, so the amount of magnetic flux from the teeth portion 32 to the rotor core 23 through the yoke portion 31 of the stator 22 can be increased. In addition, compared to the comparative example, in Example 1, the harmonic components superimposed on the magnetic flux density distribution at the location of the air gap between the rotor 21 and the stator 22 can be reduced.

[0048] (Effects of Example 1) As described above, in the electric motor 1 of Embodiment 1, the magnetic pole portion 11 of the rotor core 23 is provided with a front non-magnetic portion 20 at a position on the front side of the rotation direction R of the rotor 21 with respect to the d axis D in a plane perpendicular to the rotation centerline of the rotor 21 and passing through the rotor core 23. The front non-magnetic portion 20 restricts the short circuit of magnetic flux between a pair of adjacent magnetic pole portions 11 in the circumferential direction of the rotor core 23 and one tooth portion 32. Here, a short circuit of magnetic flux means that the magnetic flux passing through the permanent magnet 13 circulates so that it returns to the permanent magnet 13 via the inner circumferential end (flange portion 33) of the tooth portion 32 without passing through the yoke portion 31. As a result, the path of the magnetic flux on the front side of the rotation direction R of the rotor 21 with respect to the d axis D of each magnetic pole portion 11 is changed by the front non-magnetic portion 20 to pass through the d axis D side. Therefore, the front non-magnetic portion 20 reduces the magnetic flux passing through the q-axis Q side in front of the magnetic pole portion 11 and increases the amount of magnetic flux passing through the d-axis D side in front of the magnetic pole portion 11. As a result, with the electric motor 1, the magnetic flux density distribution at the location of the air gap between the rotor 21 and the stator 22 in the circumferential direction of the rotor 21 is made closer to a sine wave, so that the harmonic components superimposed on the magnetic flux density distribution in the air gap between the rotor 21 and the stator 22 can be reduced. Accordingly, with the embodiment 1, the vibration of the rotor 21 of the electric motor 1 can be reduced and the noise around the electric motor 1 can be reduced.

[0049] Furthermore, in the electric motor 1 of Embodiment 1, the front non-magnetic portion 20 of the rotor core 23 is formed separately from the magnet embedding hole 12. This prevents a decrease in the mechanical strength around the magnet embedding hole 12 in the rotor core 23.

[0050] Furthermore, in the electric motor 1 of Embodiment 1, the front non-magnetic portion 20 of the rotor core 23 is formed over a range of 90 degrees to 150 degrees, where the q-axis Q located on the rear side of the rotation direction R of the rotor 21 relative to the magnetic pole portion 11 is defined as 0 degrees of electrical angle, and the front side of the rotation direction R is defined as positive electrical angle. As a result, the front non-magnetic portion 20 can block the magnetic flux passing through the outer circumferential surface 29 of the magnetic pole portion 11 over a range of electrical angles of 90 degrees to 150 degrees.

[0051] Furthermore, in the electric motor 1 of Embodiment 1, the front non-magnetic portion 20 of the rotor core 23 has a center line 20c of the first portion 20a that extends in the direction in which the first portion 20a extends, which intersects with the permanent magnet 13. As a result, the front non-magnetic portion 20 makes it easier to block the path of magnetic flux that is trying to pass through it, thereby enhancing the effect of restricting the short circuit of magnetic flux as described above. In addition, since a large thickness can be secured between the front non-magnetic portion 20 arranged as described above and the outer surface 29 of the magnetic pole, a decrease in the mechanical strength around the front non-magnetic portion 20 and the q-axis side non-magnetic portion 14 of the rotor core 23 is suppressed.

[0052] Furthermore, in the electric motor 1 of Embodiment 1, the front non-magnetic portion 20 of the rotor core 23 is positioned radially inward of the rotor core 23 compared to the q-axis non-magnetic portion 14. This allows for a larger wall thickness between the front non-magnetic portion 20 and the outer magnetic pole surface 29, thereby suppressing a decrease in the mechanical strength around the front non-magnetic portion 20 and the q-axis non-magnetic portion 14 of the rotor core 23.

[0053] Other embodiments will be described below with reference to the drawings. In other embodiments, the same components and parts as in Embodiment 1 are denoted by the same reference numerals as in Embodiment 1, and their descriptions are omitted. [Examples]

[0054] Figure 9 is a plan view illustrating the main parts of the rotor core 23 in Embodiment 2. Figure 10 is an enlarged view showing the outer magnetic pole surfaces 29 of the N pole portion 11N and the S pole portion 11S of the rotor core 23 in Embodiment 2. Embodiment 2 has a front non-magnetic portion 20, similar to Embodiment 1, but differs from Embodiment 1 in that the outer magnetic pole surfaces 29 of the rotor core 23 in the circumferential direction have an asymmetric shape with respect to the d axis D.

[0055] As shown in Figures 9 and 10, in the orthogonal plane, the outer surface 29N of the north pole of the north pole portion 11N and the outer surface 29S of the south pole of the south pole portion 11S in Embodiment 2 are formed in such a shape that they do not coincide when one of the pole portions, the north pole portion 11N or the south pole portion 11S, is virtually rotated 60 degrees around the rotation center O of the rotor 21 and superimposed on the other pole portion of the north pole portion 11N or the south pole portion 11S. Note that the pole portion to be virtually rotated can be either the north pole portion 11N or the south pole portion 11S. Also, the direction of rotation around the rotation center O can be either clockwise or counterclockwise. Here, we will explain assuming that the north pole portion 11N is virtually rotated 60 degrees counterclockwise and superimposed on the south pole portion 11S.

[0056] In Example 2, when focusing on one pole pair outer peripheral surface 28 of the rotor core 23, the fact that this pole pair outer peripheral surface 28 is formed in a shape different from that of the q axis Q makes it possible to bring the magnetic flux density distribution passing between the N pole permanent magnet 13 and the tooth portion 32 adjacent to the N pole permanent magnet 13, and the magnetic flux density distribution passing between the S pole permanent magnet 13 and the tooth portion 32 adjacent to the S pole permanent magnet 13, closer to a symmetrical relationship with respect to the q axis Q. Therefore, the magnetic flux density distribution at the location of the air gap formed between the rotor core 23 and the tooth portion 32 within the range of the pole pair outer peripheral surface 28 (the radial magnetic flux density [T] at the air gap location measured or analyzed over the circumferential direction) can be brought even closer to a sine wave.

[0057] For example, in Embodiment 2, the radius of curvature r of the diameter change region A3 (described later), where the distance from the rotation center O of the rotor 21 to the outer peripheral surface 27 of the rotor core 23 changes, is different for the diameter change region A3 of the N pole outer peripheral surface 29N and the diameter change region A3 of the S pole outer peripheral surface 29S. This makes it easy to realize that the outer peripheral surfaces 28 of each pole have different shapes with respect to the q axis Q.

[0058] Furthermore, when one of the pole portions 11 of the north pole portion 11N and the south pole portion 11S is superimposed on the other pole portion 11, the rotation angle around the rotation center O that virtually rotates one of the pole portions 11 is 360 / (2m) [degrees]. (Let the number of pole pairs be m.) Also, in the following explanation, the rotation angle when virtually rotating the rotor 21 around the rotation center O is also 360 / (2m) [degrees]. For example, in Embodiment 2, since the number of pole pairs is m=3, when the north pole portion 11N is virtually rotated around the rotation center O of the rotor 21 and superimposed on the south pole portion 11S, the rotation angle is 360 / 6 = 60 [degrees].

[0059] (Shape of the outer surface of the magnetic pole) Figure 11 is a schematic diagram showing the outer magnetic pole surfaces 29 of each magnetic pole portion 11 of the rotor core 23 in Example 2. Figure 12 is a schematic diagram illustrating the shape of the outer magnetic pole surfaces 29 of the rotor core 23 in Example 2.

[0060] As shown in Figures 11 and 12, in the orthogonal plane, the outer surface 29N of the north pole of the north pole portion 11N is formed in a shape asymmetric with respect to the north pole d-axis DN, which is the d-axis D in the north pole portion 11N, and the outer surface 29S of the south pole of the south pole portion 11S is formed in a shape asymmetric with respect to the south pole d-axis DS, which is the d-axis in the south pole portion 11S.

[0061] In this way, by devising the shape of the outer magnetic pole surface 29 formed within the range of each magnetic pole portion 11, it becomes possible to make the magnetic flux density distribution passing between the N-pole permanent magnet 13 and the tooth portion 32 adjacent to it, and the magnetic flux density distribution passing between the S-pole permanent magnet 13 and the tooth portion 32 adjacent to it, more symmetrical with respect to the q-axis Q, for a single pole pair consisting of an N-pole permanent magnet 13 and a S-pole permanent magnet 13. Therefore, in addition to the effect obtained by devising the shape of the outer magnetic pole surface 28 described above, the magnetic flux density distribution in the air gap formed between the rotor core 23 and the tooth portion 32 within the range of the outer magnetic pole surface 28 can be made even closer to a sine wave.

[0062] (Shape of the outer surface of the north pole) Specifically, as shown in Figure 11, the outer peripheral surface 29N of the N pole magnetic pole portion 11N has an outer peripheral surface 29N-F of the N pole located on the front side of the rotation direction R of the rotor 21 with respect to the N pole d axis DN, and an outer peripheral surface 29N-R of the N pole located on the rear side of the rotation direction R with respect to the N pole d axis DN.

[0063] Figure 12 shows the rotor core 23 with the magnetic pole portion 11 virtually folded along the d-axis D in the orthogonal plane, and the front outer peripheral surface 29-F virtually superimposed on the rear outer peripheral surface 29-R. Here, we will explain the case where the N pole magnetic pole portion 11N is virtually folded. As shown in Figure 12, when the N pole magnetic pole portion 11N is virtually folded along the N pole d-axis DN in the orthogonal plane of the rotor core 23 and superimposed, the N pole front outer peripheral surface 29N-F has a small diameter outer peripheral surface 34 that is located inside the N pole rear outer peripheral surface 29N-R in the radial direction of the rotor core 23. On the other hand, the N pole rear outer peripheral surface 29N-R does not have a portion that is located inside the N pole front outer peripheral surface 29N-F in the radial direction of the rotor core 23. In other words, the outer peripheral surface 29N-F on the front side of the north pole has only a portion that overlaps with the outer peripheral surface 29N-R on the rear side of the north pole (overlapping outer peripheral surface 35) and a portion that is located on the inner side of the outer peripheral surface 29N-R on the rear side of the north pole (small diameter outer peripheral surface 34). And, when viewed from the side of the outer peripheral surface 29N-R on the rear side of the north pole, the outer peripheral surface 29N-R on the rear side of the north pole has only a portion that overlaps with the outer peripheral surface 29N-F on the front side of the north pole (overlapping outer peripheral surface 35) and a portion that is located on the outer side of the outer peripheral surface 29N-F on the rear side of the north pole (large diameter outer peripheral surface 36).

[0064] (Shape of the outer surface of the south pole) Furthermore, similar to the N pole outer peripheral surface 29N described above, as shown in Figure 11, the S pole outer peripheral surface 29S of the S pole magnetic pole portion 11S has an S pole front outer peripheral surface 29S-F located on the front side of the rotation direction R of the rotor 21 with respect to the S pole d axis DS, and an S pole rear outer peripheral surface 29S-R located on the rear side of the rotation direction R with respect to the S pole d axis DS.

[0065] The case where the S-pole magnetic pole portion 11S is virtually folded back will be explained. As shown in Figure 12, when the S-pole magnetic pole portion 11S is virtually folded back along the S-pole d-axis DS in the orthogonal plane of the rotor core 23 and superimposed, the S-pole front outer peripheral surface 29S-F has a small-diameter outer peripheral surface 34 that is located inside the S-pole rear outer peripheral surface 29S-R in the radial direction of the rotor core 23. On the other hand, the S-pole rear outer peripheral surface 29S-R does not have a portion that is located inside the S-pole front outer peripheral surface 29S-F in the radial direction of the rotor core 23. In other words, the S-pole front outer peripheral surface 29S-F has only a portion that overlaps with the S-pole rear outer peripheral surface 29S-R (overlapping outer peripheral surface 35) and a portion that is located on the inner circumference side of the S-pole rear outer peripheral surface 29S-R (small-diameter outer peripheral surface 34). When viewed from the rear outer peripheral surface 29S-R of the south pole, the rear outer peripheral surface 29S-R of the south pole has only a portion that overlaps with the front outer peripheral surface 29S-F of the south pole (overlapping outer peripheral surface 35) and a portion that is located further outward than the front outer peripheral surface 29S-F of the south pole (large diameter outer peripheral surface 36).

[0066] (Relationship between the outer surface of the north pole and the outer surface of the south pole) Furthermore, as shown in Figures 9 and 10, in an orthogonal plane, the outer peripheral surface 29N-R on the rear side of the north pole and the outer peripheral surface 29S-R on the rear side of the south pole are formed in such a shape that they do not coincide with each other when the north pole magnetic portion 11N and the south pole magnetic portion 11S are superimposed by virtually rotating them around the rotation center O of the rotor 21.

[0067] Specifically, in the orthogonal plane of the rotor core 23, when the outer peripheral surface 29N-R on the rear side of the north pole is virtually rotated 360 / (2m) [degrees] around the rotation center O of the rotor 21 and superimposed on the outer peripheral surface 29S-R on the rear side of the south pole, the outer peripheral surface 29S-R on the rear side of the south pole has a small-diameter outer peripheral surface 34 (see Figures 9 and 10) located inside the outer peripheral surface 29N-R on the rear side of the north pole in the radial direction of the rotor core 23, and the outer peripheral surface 29N-R on the rear side of the north pole does not have a portion located inside the outer peripheral surface 29S-R on the rear side of the south pole in the radial direction of the rotor core 23. In other words, the outer peripheral surface 29S-R on the rear side of the south pole has only a portion that overlaps with the outer peripheral surface 29N-R on the rear side of the north pole (overlapping outer peripheral surface 35) and a portion located on the inner circumference side of the outer peripheral surface 29N-R on the rear side of the north pole (small-diameter outer peripheral surface 34). The outer peripheral surface 29N-R on the rear side of the north pole has only a portion that overlaps with the outer peripheral surface 29S-R on the rear side of the south pole (overlapping outer peripheral surface 35) and a portion that is located further outward than the outer peripheral surface 29S-R on the rear side of the south pole (large diameter outer peripheral surface 36).

[0068] Alternatively, conversely, when the outer peripheral surface 29N-R on the rear side of the north pole is virtually rotated 360 / (2m) [degrees] around the rotation center O of the rotor 21 in the orthogonal plane of the rotor core 23 and superimposed on the outer peripheral surface 29S-R on the rear side of the south pole, the outer peripheral surface 29N-R on the rear side of the north pole has a small diameter outer peripheral surface (not shown) located inside the outer peripheral surface 29S-R on the rear side of the south pole in the radial direction of the rotor core 23, and the outer peripheral surface 29S-R on the rear side of the south pole does not have to have a portion located inside the outer peripheral surface 29N-R on the rear side of the north pole in the radial direction of the rotor core 23. In other words, the outer peripheral surface 29N-R on the rear side of the north pole may be formed to have a portion that overlaps with the outer peripheral surface 29S-R on the rear side of the south pole (overlapping outer peripheral surface 35) and a portion located on the inner circumference side of the outer peripheral surface 29S-R on the rear side of the south pole (small diameter outer peripheral surface 34). The rear outer peripheral surface 29S-R of the south pole may be formed to have only a portion that overlaps with the rear outer peripheral surface 29N-R of the north pole (overlapping outer peripheral surface 35) and a portion that is located further outward than the rear outer peripheral surface 29N-R of the north pole (large diameter outer peripheral surface 36).

[0069] For example, in Embodiment 2, the radius of curvature r of the diameter change region A3, where the distance from the rotation center O of the rotor 21 to the outer magnetic pole surface 29 of the rotor core 23 changes, is different for the diameter change region A3 of the N pole outer surface 29N and the diameter change region A3 of the S pole outer surface 29S. This makes it easy to realize shapes that do not coincide when either the N pole portion 11N or the S pole portion 11S is virtually rotated 360 / (2m) [degrees] around the rotation center O of the rotor 21 and superimposed on the other pole portion of the N pole portion 11N or the S pole portion 11S.

[0070] Similarly, in the orthogonal plane of the rotor core 23, the outer peripheral surface 29N-F on the front side of the north pole and the outer peripheral surface 29S-F on the front side of the south pole are formed in such a shape that they do not coincide with each other when the north pole portion 11N and the south pole portion 11S are superimposed by virtually rotating them 360 / (2m) [degrees] around the rotation center O of the rotor 21 (see Figure 10).

[0071] Specifically, in the orthogonal plane of the rotor core 23, when the N-pole front outer peripheral surface 29N-F is virtually rotated 360 / (2m) [degrees] around the rotation center O of the rotor 21 and superimposed on the S-pole front outer peripheral surface 29S-F, the S-pole front outer peripheral surface 29S-F has a small-diameter outer peripheral surface 34 (see Figures 9 and 10) located inward from the N-pole front outer peripheral surface 29N-F in the radial direction of the rotor core 23, and the N-pole front outer peripheral surface 29N-F does not have a portion located inward from the S-pole front outer peripheral surface 29S-F in the radial direction of the rotor core 23. In other words, the S-pole front outer peripheral surface 29S-F has only a portion that overlaps with the N-pole front outer peripheral surface 29N-F (overlapping outer peripheral surface 35) and a portion located on the inner circumference side of the N-pole front outer peripheral surface 29N-F (small-diameter outer peripheral surface 34). The outer peripheral surface 29N-F on the front side of the north pole has only a portion that overlaps with the outer peripheral surface 29S-F on the front side of the south pole (overlapping outer peripheral surface 35) and a portion that is located further outward than the outer peripheral surface 29S-F on the front side of the south pole (large diameter outer peripheral surface 36).

[0072] Alternatively, conversely, when the N-pole front outer peripheral surface 29N-F is virtually rotated 360 / (2m) [degrees] around the rotation center O of the rotor 21 in the orthogonal plane of the rotor core 23 and superimposed on the S-pole front outer peripheral surface 29S-F, the N-pole front outer peripheral surface 29N-F has a small-diameter outer peripheral surface (not shown) located inward of the S-pole front outer peripheral surface 29S-F in the radial direction of the rotor core 23, and the S-pole front outer peripheral surface 29S-F does not have to have a portion located inward of the N-pole front outer peripheral surface 29N-F in the radial direction of the rotor core 23. In other words, the N-pole front outer peripheral surface 29N-F may be formed to have a portion that overlaps with the S-pole front outer peripheral surface 29S-F (overlapping outer peripheral surface 35) and a portion located on the inner circumference side of the S-pole front outer peripheral surface 29S-F (small-diameter outer peripheral surface 34). The outer peripheral surface 29S-F on the front side of the south pole may be formed to have only a portion that overlaps with the outer peripheral surface 29N-F on the front side of the north pole (overlapping outer peripheral surface 35) and a portion that is located further outward than the outer peripheral surface 29N-F on the front side of the north pole (large diameter outer peripheral surface 36).

[0073] For example, in Embodiment 2, the radius of curvature r of the diameter change region A3, where the distance from the rotation center O of the rotor 21 to the outer circumferential surface of the rotor core 23 changes, is different for the diameter change region A3 of the N pole outer circumferential surface 29N and the diameter change region A3 of the S pole outer circumferential surface 29S. This makes it easy to realize shapes that do not coincide when either the N pole portion 11N or the S pole portion 11S is virtually rotated 360 / (2m) [degrees] around the rotation center O of the rotor 21 and superimposed on the other pole portion of the N pole portion 11N or the S pole portion 11S.

[0074] In the orthogonal plane described above, the outer magnetic pole surface 29, which is the outer peripheral side of the magnetic pole portion 11, is formed such that the distance between the outer magnetic pole surface 29 and the rotation center O gradually decreases as you move from the d-axis D towards the q-axis Q. Therefore, in the orthogonal plane of the rotor core 23, each of the outer magnetic pole surfaces 29 of the rotor core 23 has its maximum outer diameter L at a position on the d-axis D where it is at the distance (radius) from the rotation center O of the rotor 21, as shown in Figure 9. Also, in the orthogonal plane, the outer magnetic pole surface 29N of the N-pole magnetic pole portion 11N and the outer magnetic pole surface 29S of the S-pole magnetic pole portion 11S have the same distance from the rotation center O, i.e., the same outer diameter L, at a position on the d-axis D.

[0075] Furthermore, in Embodiment 2, since the outer magnetic pole surfaces 29 of each magnetic pole portion 11 are formed in an asymmetric shape with respect to the d-axis D in an orthogonal plane, grooves 16 and 17 with different recess shapes are alternately arranged in the circumferential direction of the rotor core 23. Similarly, in Embodiment 2, since the outer magnetic pole surfaces 29 of each magnetic pole portion 11 are formed in an asymmetric shape with respect to the d-axis D in an orthogonal plane, the shapes of the q-axis side non-magnetic portion 14 on the front side and the q-axis side non-magnetic portion 15 on the rear side of the rotor 21 in the rotation direction R are different from each other.

[0076] Furthermore, Embodiment 2 includes the following features: in the magnetic pole portion 11, the front non-magnetic portion 20 is positioned only on the front side in the rotation direction R of the rotor 21 with respect to the d-axis D; in the orthogonal plane, the shapes of the q-axis non-magnetic portion 14 on the front side in the rotation direction R of the rotor 21 and the q-axis non-magnetic portion 15 on the rear side are different from each other; and the outer circumferential surface 29 of the magnetic pole is formed in an asymmetric shape with respect to the d-axis D. This makes it easy to realize a cross-sectional shape of the magnetic pole portion 11 in an orthogonal plane that is asymmetric with respect to the d-axis D.

[0077] Furthermore, the outer circumferential surface 27 of the rotor core 23 has a groove region A1 in which the inner surface 16a of the groove 16 is formed so that the q axis Q passes through the groove 16, and a groove region A1 in which the inner surface 17a of the groove 17 is formed so that the q axis Q passes through the groove 17.

[0078] As shown in Figures 9 and 11, the outer surface of the magnetic pole 29 has a constant diameter region A2 formed at the position through which the d-axis D passes and at a constant distance from the rotation center O of the rotor 21, and a diameter-changing region A3 formed between the groove region A1 and the constant diameter region A2, at which the distance from the rotation center O of the rotor 21 changes. The constant diameter region A2 is a maximum radius of curvature region formed with a radius of curvature that is the maximum radius of curvature rm from the rotation center O. The diameter-changing region A3 is formed with multiple radii of curvature smaller than the maximum radius of curvature rm from the rotation center O in the constant diameter region A2.

[0079] In Figure 9, within the constant diameter region A2, the N pole side of the magnetic pole portion 11N is designated as constant diameter region An2. Within this constant diameter region An2, the front side in the rotation direction R is designated as constant diameter region An2-F, and the rear side in the rotation direction R is designated as constant diameter region An2-R. Similarly, within the constant diameter region A2, the S pole side of the magnetic pole portion 11S is designated as constant diameter region As2. Within this constant diameter region As2, the front side in the rotation direction R is designated as constant diameter region As2-F, and the rear side in the rotation direction R is designated as constant diameter region As2-R.

[0080] The multiple radii of curvature that form the diameter change region A3 gradually decrease in radius r as they approach the grooves 16 and 17. For the sake of simplicity, we will assume that the combination of radii of curvature that forms the diameter change region A3 on the outer peripheral surface 29N-F on the front side of the N pole and the combination of radii of curvature that forms the diameter change region A3 on the outer peripheral surface 29N-R on the rear side of the N pole are equal. That is, the first radius of curvature r1-F of the front side diameter change region A3-F and the first radius of curvature r1-R of the rear side diameter change region A3-R are set to r1-F=r1-R=r1, and the second radius of curvature r2-F of the front side diameter change region A3-F and the second radius of curvature r2-R of the rear side diameter change region A3-R are set to r2-F=r2-R=r2. As an example, the diameter-changing region A3 has a first region A3-1 formed with a first radius of curvature r1 smaller than the maximum radius of curvature rm, and a second region A3-2 formed with a second radius of curvature r2 smaller than the first radius of curvature r1. The diameter-changing region A3 is formed continuously from the constant diameter region A2 toward the groove region A1, in the order of the first region A3-1 and the second region A3-2. In Example 2, since the difference in size between the first radius of curvature r1 and the second radius of curvature r2 is relatively small, the first region A3-1 and the second region A3-2 are smoothly continuous. The centers Or(Or1, Or2) of each radius of curvature r(r1, r2) are arranged to approach the outer circumferential surface 27 of the rotor core 23 as the radius of curvature decreases. Note that the number of types of radii of curvature is not limited to two.

[0081] In Figure 9, within the second radius of curvature r2-F of the forward diameter change region A3-F, the N pole side 11N is defined as the second radius of curvature rn2-F, and the S pole side 11S is defined as the second radius of curvature rs2-F. Similarly, within the second radius of curvature r2-R of the rear diameter change region A3-R, the N pole side 11N is defined as the second radius of curvature rn2-R, and the S pole side 11S is defined as the second radius of curvature rs2-R. Note that the first radius of curvature r1 is not shown in Figure 9.

[0082] Furthermore, as shown in Figure 11, the constant diameter region A2 has a front constant region A2-F located on the front side of the rotation direction R of the rotor 21 with respect to the d axis D, and a rear constant region A2-R located on the rear side of the rotation direction R with respect to the d axis D. The circumferential length of the front constant region A2-F is smaller than the circumferential length of the rear constant region A2-R. This makes it easy to obtain a shape in which, at each magnetic pole outer surface 29, the air gap formed in the front outer surface 29-F gradually increases toward the q axis Q, and the ratio of the air gap formed in the rear outer surface 29-R gradually increasing toward the q axis Q is smaller than the ratio of the air gap formed in the front outer surface 29-F gradually increasing toward the q axis Q. In other words, because the constant front region A2-F is smaller than the constant rear region A2-R, when the N pole magnetic portion 11N is virtually folded back along the N pole d axis DN in each orthogonal plane, and the front outer peripheral surface 29N-F of the N pole is superimposed on the rear outer peripheral surface 29N-R of the N pole, the front outer peripheral surface 29N-F of the N pole has a small-diameter outer peripheral surface 34 located inside the rear outer peripheral surface 29N-R of the N pole in the radial direction of the rotor core 23, and the rear outer peripheral surface 29N-R of the N pole does not have a portion located inside the front outer peripheral surface 29N-F of the N pole in the radial direction of the rotor core 23.

[0083] Furthermore, in Example 2, as shown in Figure 11, the front diameter change region A3-F, located on the front side of the rotation direction R of the rotor 21 with respect to the d-axis D, is larger than the rear diameter change region A3-R, located on the rear side of the rotation direction R with respect to the d-axis D. This makes it easy to obtain a shape in which the gap formed in the area of ​​the front outer surface 29-F of each magnetic pole outer surface 29 gradually increases, while the ratio of the gap formed in the area of ​​the rear outer surface 29-R gradually increasing is smaller than that of the front outer surface 29-F.

[0084] For the sake of simplicity, the explanation has been given assuming that the combinations of multiple radii of curvature forming the front diameter change region A3-F of the front outer peripheral surface 29N-F of the N pole and the combinations of multiple radii of curvature forming the rear diameter change region A3-R of the rear outer peripheral surface 29N-R of the N pole are equal. However, the combinations of multiple radii of curvature in the front diameter change region A3-F and the rear diameter change region A3-R may be different from each other. For example, the first radius of curvature r1-F of the front diameter change region A3-F (As3-F) and the first radius of curvature r1-R of the rear diameter change region A3-R (As3-R) may be different from each other. Similarly, the second radius of curvature r2-F (rs2-F) of the front diameter change region A3-F (As3-F) and the second radius of curvature r2-R (rs2-R) of the rear diameter change region A3-R (As3-R) may be different from each other.

[0085] (Inner surface shape of the groove) As shown in Figure 9, in the orthogonal plane of the rotor core 23, the shape of the inner surface 16a of the groove 16 is formed asymmetrically with respect to the q-axis Q. Similarly, the shape of the inner surface 17a of the groove 17 is formed asymmetrically with respect to the q-axis Q. Furthermore, on the outer circumferential surface 27 of the rotor core 23, grooves 16 and grooves 17 are arranged alternately along the circumferential direction of the rotor core 23. In the orthogonal plane, the shapes of the inner surfaces 16a of adjacent grooves 16 and 17a of adjacent grooves 17 in the circumferential direction of the rotor core 23 are different from each other. The shapes of the inner surfaces 16a and 17a of the grooves 16 and 17 are formed as a result of smoothly continuing the inner surfaces 16a and 17a with the diameter change region A3 of each magnetic pole outer circumferential surface 29.

[0086] Figure 13 is a plan view showing the magnetic field lines in Example 2. Figure 14 is a diagram showing the circumferential magnetic flux density distribution of the rotor 21 in Example 2. In Figure 14, the vertical axis represents magnetic flux density [T] and the horizontal axis represents electrical angle [degrees (deg)]. In Figure 14, the solid line represents a sine wave, and the dashed line represents Example 2.

[0087] As shown in Figure 13, in Embodiment 2, similar to Embodiment 1, the path of the magnetic flux on the front side of the rotor 21 in the rotation direction R relative to the d-axis D is changed by the front non-magnetic part 20 to pass through the d-axis D side. Therefore, the front non-magnetic part 20 plays a role in reducing the magnetic flux passing through the q-axis Q side in front of the magnetic pole part 11 and increasing the amount of magnetic flux passing through the d-axis D side in front of the magnetic pole part 11 by the same amount. Accordingly, in Embodiment 2, in each magnetic pole part 11, the front non-magnetic part 20 prevents the magnetic flux passing through the front side of the magnetic pole part 11 from short-circuiting between a pair of adjacent magnetic pole parts 11 in the circumferential direction of the rotor core 23 and the flange 33 of one tooth part 32.

[0088] In Example 2, in the range of electrical angles from approximately 270 to 330 degrees, the magnetic flux density distribution at the air gap between the rotor 21 and the stator 22 in the circumferential direction of the rotor 21 is closer to a sine wave in Example 2, shown in Figure 14, compared to Example 1, shown in Figure 6, which also shows the magnetic flux density distribution. By bringing the magnetic flux density distribution closer to a sine wave in this way, Example 2 can reduce the harmonic components superimposed on the magnetic flux density distribution at the air gap between the rotor 21 and the stator 22 compared to Example 1.

[0089] Therefore, in Embodiment 2, since the magnetic pole portion 11 has a front non-magnetic portion 20 and the outer magnetic pole surface 29 is formed in an asymmetric shape with respect to the d-axis D, short-circuiting of magnetic flux through the flange portion 33 of the teeth portion 32 between adjacent magnetic pole portions 11 is restricted, so that the amount of magnetic flux that goes from the teeth portion 32 to the rotor core 23 through the yoke portion 31 of the stator 22 can be further increased.

[0090] (Effects of Example 2) As described above, in the motor of Embodiment 2, similar to Embodiment 1, the magnetic pole portion 11 has a front non-magnetic portion 20, which brings the magnetic flux density distribution at the location of the air gap between the rotor 21 and the stator 22 in the circumferential direction of the rotor 21 closer to a sine wave. This reduces the harmonic components superimposed on the magnetic flux density distribution in the air gap between the rotor 21 and the stator 22.

[0091] In addition, in the motor of Embodiment 2, the magnetic pole outer surface 29 of the rotor core 23 has a front outer surface 29-F located on the front side of the rotation direction R of the rotor 21 with respect to the d axis D, and a rear outer surface 29-R located on the rear side of the rotation direction R with respect to the d axis D. When the magnetic pole portion 11 is virtually folded back along the d axis D in an orthogonal plane and the front outer surface 29-F is superimposed on the rear outer surface 29-R, the front outer surface 29-F has a small-diameter outer surface 34 located inward from the rear outer surface 29-R in the radial direction of the rotor core 23. As a result, for example, when considering a magnetic path in the central tooth portion 32 of the three tooth portions 32 arranged in the circumferential direction of the rotor core 23, where the magnetic flux from the N pole portion 11N passing through the tooth portion 32 short-circuits to the adjacent S pole portion 11S via the flange portion 33 without passing through the yoke portion 31, the asymmetry of the magnetic flux distribution with respect to the q axis Q is suppressed. This is because, in an electric motor where the ratio of the number of poles to the number of teeth is 2:3, when the magnetic pole portion 11 is virtually folded back along the d-axis D in an orthogonal plane and the front outer peripheral surface 29-F is superimposed on the rear outer peripheral surface 29-R, if the front outer peripheral surface 29-F and the rear outer peripheral surface 29-R coincide, then the magnetic flux density distribution passing between the N-pole permanent magnet and the teeth portion adjacent to it, and the magnetic flux density distribution passing between the S-pole permanent magnet and the teeth portion adjacent to it, cannot be symmetrical with respect to the q-axis. Rather, by making the front outer peripheral surface 29-F and the rear outer peripheral surface 29-R not coincide when the magnetic pole portion 11 is virtually folded back along the d-axis D in an orthogonal plane and the front outer peripheral surface 29-F is superimposed on the rear outer peripheral surface 29-R, the distribution of magnetic flux can be made closer to symmetrical with respect to the q-axis Q. Therefore, the magnetic flux density distribution when the central teeth portion 32 described above is located on the q-axis Q can be brought closer to an ideal sine wave. Thus, the magnetic flux density distribution at the location of the air gap between the rotor 21 and the stator 22 in the circumferential direction of the rotor 21 can be brought closer to a sine wave.

[0092] Furthermore, in the electric motor of Embodiment 2, the outer circumferential surface 27 of the rotor core 23 has a grooved region A1 in which a groove 16 is formed so that the q-axis Q passes through the groove 16, and a grooved region A1 in which a groove 17 is formed so that the q-axis Q passes through the groove 17. The outer circumferential surface 29 of the magnetic pole has a constant diameter region A2 formed at a position through which the d-axis D passes and at a constant distance from the rotation center O, and a diameter-changing region A3 formed between the grooved region A1 and the constant diameter region A2 and at a constant distance from the rotation center O. The constant diameter region A2 has a front-side constant region A2-F located on the front side of the rotation direction R of the rotor 21 with respect to the d-axis D, and a rear-side constant region A2-R located on the rear side of the rotation direction R with respect to the d-axis D. The circumferential size of the front-side constant region A2-F is smaller than the circumferential size of the rear-side constant region A2-R. This makes it easy to obtain a shape in which, at each magnetic pole outer surface 29, the gap formed in the area of ​​the front outer surface 29-F gradually increases, while the ratio of the rate at which the gap formed in the area of ​​the rear outer surface 29-R gradually increases is smaller than that of the front outer surface 29-F. In other words, when the magnetic pole portion 11 is virtually folded along the d-axis D in an orthogonal plane and the front outer surface 29-F is superimposed on the rear outer surface 29-R, the front outer surface 29-F can easily be made to have a shape in which a small-diameter outer surface 34 is located inside the rear outer surface 29-R in the radial direction of the rotor core 23. [Examples]

[0093] Figure 15 is a plan view showing the rotor core 23 of Example 3. Example 3 differs from Example 2 in that a non-magnetic portion is added to each magnetic pole portion 11.

[0094] As shown in Figure 15, the magnetic pole portion 11 in Embodiment 3 has a front non-magnetic portion 20, similar to Embodiments 1 and 2, and the outer magnetic pole surface 29 is formed in an asymmetric shape with respect to the d-axis D, similar to Embodiment 2. In addition, the magnetic pole portion 11 in Embodiment 3 is provided with a rear non-magnetic portion 30, which is formed separately from the magnet embedding hole 12, at a position on the rear side of the rotation direction R of the rotor 21. In other words, each magnetic pole portion 11 is provided with a rear non-magnetic portion 30, which is formed separately from the q-axis non-magnetic portion 15, at a position on the rear side of the rotation direction R of the rotor 21 with respect to the d-axis D. The rear non-magnetic portion 30 is a through hole that penetrates the rotor core 23 along the rotation centerline, and is a space formed in the magnetic pole portion 11. By forming the rear non-magnetic portion 30 separately from the magnet embedding hole 12 in this way, the rotor core 23 can suppress a decrease in the mechanical strength around the magnet embedding hole 12.

[0095] (Shape of the non-magnetic part on the rear side) As shown in Figure 15, one magnetic pole portion 11 is provided with a rear non-magnetic portion 30, which is a non-magnetic portion provided separately from the magnet embedding hole 12. In an orthogonal plane, the rear non-magnetic portion 30 has a different shape from the front non-magnetic portion 20. For example, the opening area of ​​the rear non-magnetic portion 30 in an orthogonal plane is formed to be smaller than that of the front non-magnetic portion 20. The rear non-magnetic portion 30, like the q-axis non-magnetic portions 14, 15, d-axis non-magnetic portion 19 and front non-magnetic portion 20 described above, restricts the short circuit of magnetic flux between a pair of adjacent magnetic pole portions 11 in the circumferential direction of the rotor core 23 and the flange portion 33 of one tooth portion 32. Therefore, the rear non-magnetic section 30 increases the magnetic flux circulating between a pair of adjacent magnetic pole sections 11 in the circumferential direction of the rotor core 23, a pair of adjacent tooth sections 32 in the circumferential direction of the rotor core 23, and a yoke section 31 connecting these pairs of tooth sections 32.

[0096] Specifically, the rear non-magnetic portion 30 restricts the short-circuiting of the magnetic flux as described above when the q-axis Q of the rotor 21 coincides with the widthwise center of one of the multiple tooth portions 32 during the rotation of the rotor 21.

[0097] The rear non-magnetic portion 30 is formed over a range of 30 degrees to 90 degrees relative to the magnetic pole portion 11, where the q-axis Q located on the rear side of the rotor 21's rotation direction R is defined as 0 degrees of electrical angle, and the front side of the rotor 21's rotation direction R is defined as the positive electrical angle. As a result, the rear non-magnetic portion 30 can block the magnetic flux passing through the outer circumferential surface 29 of the magnetic pole portion 11 over a range of electrical angles of 30 degrees to 90 degrees.

[0098] To rephrase the above electrical angle in terms of mechanical angle, the rear non-magnetic portion 30 is formed in a range of (360 / 2m) × (1 / 6) degrees or more and (360 / 2m) × (3 / 6) degrees or less, when the number of magnetic pole portions 11 is 2m, and the mechanical angle of the circumferential range (range of one pole pair) between adjacent magnetic pole portions 11 is set to 0 degrees, with the q-axis Q located on the rear side relative to the rear magnetic pole portion 11 in the rotational direction R.

[0099] The rear non-magnetic portion 30 has a first portion 30a extending from the magnet embedding hole 12 toward the outer surface 29 of the magnetic pole, and a second portion 30b formed continuously with the first portion 30a and extending toward the d-axis D. The rear non-magnetic portion 30 is formed such that, for example, the width dimension of the first portion 30a along the short direction is equal to the width dimension of the second portion 30b along the short direction, and the second portion 30b is formed in an elongated hole shape that is bent relative to the first portion 30a.

[0100] In the orthogonal plane, the rear non-magnetic portion 30 is positioned such that the center line 30c of the first portion 30a, which is aligned with the direction in which the first portion 30a extends, intersects with the permanent magnet 13. Here, the center line 30c of the first portion 30a is a straight line that passes through the center of the width direction, which is the short side of the first portion 30a, and extends along the longitudinal direction of the first portion 30a. By positioning the rear non-magnetic portion 30 in this way, it becomes easier to block the path of magnetic flux that would otherwise pass through the rear non-magnetic portion 30. As a result, it is possible to suppress the occurrence of a magnetic path in which magnetic flux passing through the permanent magnet 13 returns to the permanent magnet 13 via the inner circumference side (flange portion 33) of the teeth portion 32 without passing through the yoke portion 31, thereby enhancing the effect of restricting the short circuit of magnetic flux as described above. In addition, since a large wall thickness can be secured between the rear non-magnetic portion 30, which is arranged as described above, and the outer surface 29 of the magnetic pole, a decrease in the mechanical strength around the rear non-magnetic portion 30 and the q-axis non-magnetic portion 15 of the rotor core 23 can be suppressed.

[0101] Furthermore, in the rear non-magnetic portion 30, the length K2 of the second portion 30b extending toward the d-axis D is shorter than the length K1 of the first portion 30a extending toward the outer magnetic pole surface 29. This ensures that the rear non-magnetic portion 30 has sufficient length extending in the circumferential direction of the rotor core 23, thereby enhancing the effect of restricting the occurrence of the aforementioned short circuit of magnetic flux. Here, the length K1 of the first portion 30a is, for example, the length along the center line 30c of the first portion 30a along the direction in which the first portion 30a extends. Similarly, the length K2 of the second portion 30b is, for example, the length along the center line 30d of the second portion 30b along the direction in which the second portion 30b extends.

[0102] Furthermore, the rear non-magnetic portion 30 is positioned radially inward from the q-axis non-magnetic portion 15 in the radial direction of the rotor core 23. This allows for a larger wall thickness between the rear non-magnetic portion 30 and the outer magnetic pole surface 29, thereby suppressing a decrease in the mechanical strength around the rear non-magnetic portion 30 and the q-axis non-magnetic portion 15 in the rotor core 23.

[0103] Furthermore, in an orthogonal plane, the total length of the front non-magnetic portion 20 extending in the circumferential direction of the rotor core 23 is longer than the total length of the rear non-magnetic portion 30 extending in the circumferential direction of the rotor core 23. As a result, the range over which the front non-magnetic portion 20 changes the path of the magnetic flux in the magnetic pole portion 11 is larger than that of the rear non-magnetic portion 30. The total length of the front non-magnetic portion 20 here refers to the sum of the longitudinal dimensions of the first portion 20a and the second portion 20b, for example, the length of a straight line passing through the centers of the width directions of the first portion 20a and the second portion 20b. Similarly, the total length of the rear non-magnetic portion 30 refers to the sum of the longitudinal dimensions of the first portion 30a and the second portion 30b, for example, the length of a straight line passing through the centers of the width directions of the first portion 30a and the second portion 30b.

[0104] Furthermore, in the orthogonal plane, the distance M1 between the front non-magnetic part 20 and the d-axis D is smaller than the distance M2 between the d-axis D and the rear non-magnetic part 30. Distances M1 and M2 refer to the shortest distance relative to the d-axis D. As a result, the front non-magnetic part 20 has a greater effect than the rear non-magnetic part 30 in changing the path of the magnetic flux in the magnetic pole part 11 toward the d-axis D side.

[0105] Furthermore, in Embodiment 3, the shapes of the front non-magnetic portion 20 and the rear non-magnetic portion 30 in the orthogonal plane of the magnetic pole portion 11 are different from each other, the shapes of the front q-axis side non-magnetic portion 14 and the rear q-axis side non-magnetic portion 15 in the rotation direction R in the orthogonal plane are different from each other, and the outer circumferential surface 29 of the magnetic pole is formed in an asymmetric shape with respect to the d-axis D. This makes it easy to realize a cross-sectional shape of the magnetic pole portion 11 in the orthogonal plane that is asymmetric with respect to the d-axis D.

[0106] Figure 16 is a plan view showing the magnetic field lines in Example 3. Figure 17 is a diagram showing the circumferential magnetic flux density distribution of the rotor 21 in Example 3. In Figure 17, the vertical axis represents magnetic flux density [T] and the horizontal axis represents electrical angle [degrees (deg)]. In Figure 17, the solid line represents a sine wave, and the dashed line represents Example 3.

[0107] As shown in Figure 16, in Embodiment 3, similar to Embodiments 1 and 2, the path of the magnetic flux on the front side of the rotor 21 in the rotation direction R relative to the d-axis D is changed by the front non-magnetic part 20 to pass through the d-axis D side. Therefore, the front non-magnetic part 20 plays a role in reducing the magnetic flux passing through the q-axis Q side in front of the magnetic pole part 11 and increasing the amount of magnetic flux passing through the d-axis D side in front of the magnetic pole part 11 by the same amount. Accordingly, in Embodiment 3, in each magnetic pole part 11, the front non-magnetic part 20 prevents the magnetic flux passing through the front side of the magnetic pole part 11 from short-circuiting between a pair of adjacent magnetic pole parts 11 in the circumferential direction of the rotor core 23 and the flange 33 of one tooth part 32.

[0108] In addition, in Embodiment 3, the path of the magnetic flux on the rear side of the rotor 21 in the rotation direction R relative to the d-axis D is changed by the rear non-magnetic part 30 to pass through the d-axis D side. Therefore, the rear non-magnetic part 30 plays a role in reducing the magnetic flux passing through the q-axis Q side behind the magnetic pole part 11 and increasing the amount of magnetic flux passing through the d-axis D side behind the magnetic pole part 11 by the same amount. Accordingly, in Embodiment 3, in each magnetic pole part 11, the rear non-magnetic part 30 prevents the magnetic flux passing through the front side of the magnetic pole part 11 from short-circuiting between a pair of adjacent magnetic pole parts 11 in the circumferential direction of the rotor core 23 and the flange 33 of one tooth part 32.

[0109] Comparing Figure 17 with Figure 14, which shows the magnetic flux density distribution in Example 2, in Example 3, similar to Example 2, the magnetic flux density distribution at the location of the air gap between the rotor 21 and the stator 22 in the circumferential direction of the rotor 21 can be made closer to a sine wave in the range of electrical angles of approximately 270 to 330 degrees. By making the magnetic flux density distribution closer to a sine wave in this way, in Example 3, the harmonic components superimposed on the magnetic flux density distribution at the location of the air gap between the rotor 21 and the stator 22 can be reduced.

[0110] Therefore, in Embodiment 3, since the magnetic pole portion 11 has a front non-magnetic portion 20 and the outer magnetic pole surface 29 is formed in an asymmetric shape with respect to the d-axis D, short-circuiting of magnetic flux through the flange portion 33 of the teeth portion 32 between adjacent magnetic pole portions 11 is restricted, thereby increasing the amount of magnetic flux that travels from the teeth portion 32 to the rotor core 23 through the yoke portion 31 of the stator 22.

[0111] Furthermore, comparing Figure 17 with Figure 14, which shows the magnetic flux density distribution in Example 2, in Example 3, at an electrical angle of approximately 50 degrees, the magnetic flux density distribution at the location of the air gap in the circumferential direction of the rotor 21 can be made closer to a sine wave. By making the magnetic flux density distribution closer to a sine wave in this way, in Example 3, the harmonic components superimposed on the magnetic flux density distribution at the location of the air gap between the rotor 21 and the stator 22 can be reduced.

[0112] Therefore, in Embodiment 3, since the magnetic pole portion 11 has a rear non-magnetic portion 30, short-circuiting of magnetic flux through the flange portion 33 of the teeth portion 32 between adjacent magnetic pole portions 11 is restricted, and thus the amount of magnetic flux in the path from the rotor core 23 through the teeth portion 32 to the yoke portion 31 can be increased.

[0113] (Effects of Example 3) As described above, in the motor of Example 3, similar to Examples 1 and 2, the magnetic pole portion 11 has a front non-magnetic portion 20, which brings the magnetic flux density distribution at the location of the air gap between the rotor 21 and the stator 22 in the circumferential direction of the rotor 21 closer to a sine wave. This reduces the harmonic components superimposed on the magnetic flux density distribution in the air gap between the rotor 21 and the stator 22.

[0114] In addition, according to the motor of Embodiment 3, in an orthogonal plane, the magnetic pole portion 11 of the rotor core 23 is provided with a rear non-magnetic portion 30 at a position on the rear side of the rotation direction R of the rotor 21 with respect to the d-axis D. The rear non-magnetic portion 30 restricts the short circuit of magnetic flux between a pair of adjacent magnetic pole portions 11 and one tooth portion 32 in the circumferential direction of the rotor core 23. In an orthogonal plane, the front non-magnetic portion 20 and the rear non-magnetic portion 30 have different shapes. In Embodiment 3, the front non-magnetic portion 20 increases the amount of magnetic flux from the tooth portion 32 to the rotor core 23 through the yoke portion 31 of the stator 22, and the rear non-magnetic portion 30 increases the amount of magnetic flux in the path from the rotor core 23 through the tooth portion 32 to the yoke portion 31. As a result, in Example 3, the magnetic flux density distribution at the location of the air gap between the rotor 21 and the stator 22 in the circumferential direction of the rotor 21 is brought even closer to a sine wave, so that the harmonic components superimposed on the magnetic flux density distribution in the air gap between the rotor 21 and the stator 22 can be further reduced.

[0115] Furthermore, in the rotor core 23 of the motor in Embodiment 3, the distance M1 between the front non-magnetic portion 20 and the d-axis D in the orthogonal plane is smaller than the distance M2 between the d-axis D and the rear non-magnetic portion 30. As a result, the front non-magnetic portion 20 has a greater effect of changing the path of the magnetic flux in the magnetic pole portion 11 toward the d-axis D side compared to the rear non-magnetic portion 30.

[0116] Furthermore, in the electric motor of Embodiment 3, the rear non-magnetic portion 30 of the rotor core 23 is positioned radially inward of the rotor core 23 than the q-axis side non-magnetic portion 15 in the circumferential direction of the rotor core 23. This allows for a larger wall thickness between the rear non-magnetic portion 30 and the outer magnetic pole surface 29, thereby suppressing a decrease in the mechanical strength around the rear non-magnetic portion 30 and the q-axis side non-magnetic portion 15 of the rotor core 23.

[0117] Although not shown in the figures, the rear non-magnetic portion 30 in Embodiment 3 may be provided on a rotor core 23 in which the outer magnetic pole surface 29 is formed in a shape symmetrical with respect to the d-axis D, as in Embodiment 1, and the same effects as in Embodiment 3 can be obtained. [Explanation of symbols]

[0118] 1 electric motor 3 shafts 11 Magnetic pole part 11N N pole magnetic pole part 11S S pole magnetic pole part 12 (12a~12f) Magnet embedding holes 13 Permanent Magnets 14(14a~14f), 15(15a~15f) q-axis side non-magnetic part 16, 17 Groove 19 d-axis side non-magnetic part 20 Front non-magnetic part 20a Part 1 20b 2nd part 20c center line 21 Rotors 22 stata 23 Rotor Core 24 stator cores 27 Outer surface 29 Magnetic pole outer surface 29-F Front outer circumferential surface 29-R Rear outer peripheral surface 30 Rear non-magnetic part 31 York section 32 Teeth section 101 Compressor 102 Container 105 Compression section A1 Groove area A2 constant diameter area A2-F Front fixed area A2-R Rear certain area A3 Diameter change region C1, C2 corner D d axis O Center of rotation Q (q-axis) R rotation direction M1, M2 distance

Claims

1. A rotor having a rotor core in which permanent magnets are embedded in magnet embedding holes and multiple magnetic pole portions are provided along the circumferential direction, The stator comprises a plurality of teeth arranged on the outer circumference of the rotor and an annular yoke connecting the plurality of teeth, In a plane perpendicular to the rotor's rotational centerline and passing through the rotor core, when the line connecting the center of the magnetic pole portion in the circumferential direction and the rotor's rotational center is defined as the d-axis, and the line connecting the center between adjacent magnetic pole portions in the circumferential direction and the rotational center is defined as the q-axis, In the aforementioned plane, the magnetic pole portion is provided with a front non-magnetic portion at a position on the front side of the rotor's rotation direction relative to the d-axis. The aforementioned front non-magnetic portion restricts a short circuit of magnetic flux between a pair of circumferentially adjacent magnetic pole portions and one of the teeth portions, in the electric motor.

2. The aforementioned front non-magnetic portion is formed separately from the magnet embedding hole. The electric motor according to claim 1.

3. The magnetic pole portion is provided with only the front non-magnetic portion, which is a non-magnetic portion provided separately from the magnet embedding hole. The electric motor according to claim 2.

4. The aforementioned front non-magnetic portion is formed over a range of 90 degrees or more and 150 degrees or less, where the q-axis located on the rear side in the rotational direction relative to the magnetic pole portion is defined as 0 degrees of electrical angle, and the front side in the rotational direction is defined as the positive electrical angle. The electric motor according to claim 1.

5. The front non-magnetic portion increases the magnetic flux circulating between the pair of circumferentially adjacent magnetic pole portions, the pair of circumferentially adjacent tooth portions, and the yoke portion connecting the pair of tooth portions. The electric motor according to claim 1.

6. The forward non-magnetic portion restricts the short circuit of the magnetic flux when the q-axis of the rotor coincides with the widthwise center of one of the multiple tooth portions during the rotation of the rotor. The electric motor according to claim 5.

7. The cross-sectional shape of the magnetic pole portion in the plane is asymmetrical with respect to the d-axis. The electric motor according to claim 1.

8. The front non-magnetic portion has a first portion that extends from the magnet embedding hole side toward the outer surface of the magnetic pole, which is the outer surface of the magnetic pole portion. The electric motor according to claim 1.

9. In the aforementioned plane, the front non-magnetic portion is such that the center line of the first portion, along the direction in which the first portion extends, intersects with the permanent magnet. The electric motor according to claim 8.

10. The aforementioned front non-magnetic portion has a second portion that is formed continuously with the first portion and extends toward the d-axis. The electric motor according to claim 8.

11. In the magnet embedding hole, a q-axis side non-magnetic portion is formed continuously with the magnet embedding hole, extending toward the outer peripheral surface of the magnetic pole, which is the outer peripheral side of the magnetic pole portion, near the q-axis. The aforementioned front non-magnetic portion is positioned radially inward of the rotor core than the aforementioned q-axis non-magnetic portion. The electric motor according to claim 1.

12. In the aforementioned plane, the magnetic pole portion is provided with a rear non-magnetic portion at a position on the rear side in the rotational direction with respect to the d-axis. The rear non-magnetic portion restricts the short circuit of magnetic flux between a pair of adjacent magnetic pole portions in the circumferential direction and one of the teeth portions. In the aforementioned plane, the front non-magnetic portion and the rear non-magnetic portion have different shapes from each other. The electric motor according to claim 1.

13. In the aforementioned plane, the total length of the front non-magnetic portion extending in the circumferential direction is longer than the total length of the rear non-magnetic portion extending in the circumferential direction. The electric motor according to claim 12.

14. In the aforementioned plane, the distance between the front non-magnetic portion and the d-axis is smaller than the distance between the d-axis and the rear non-magnetic portion. The electric motor according to claim 13.

15. In the magnet embedding hole, a q-axis side non-magnetic portion is formed continuously with the magnet embedding hole, extending from the magnet embedding hole toward the outer peripheral surface of the magnetic pole, which is the outer peripheral side surface of the magnetic pole portion, near the q-axis. The rear non-magnetic portion is positioned radially inward of the rotor core than the q-axis non-magnetic portion. The electric motor according to claim 12.

16. The outer surface of the magnetic pole, which is the outer side surface of the magnetic pole portion, has a distance between the outer surface of the magnetic pole and the center of rotation that gradually decreases as you move from the d-axis towards the q-axis. The electric motor according to claim 1.

17. The magnetic pole outer surface has a front outer surface located on the front side in the rotational direction with respect to the d axis, and a rear outer surface located on the rear side in the rotational direction with respect to the d axis. When the magnetic pole portion is virtually folded back along the d-axis in the aforementioned plane, and the front outer peripheral surface is superimposed on the rear outer peripheral surface, The front outer peripheral surface has a smaller diameter outer peripheral surface located inward from the rear outer peripheral surface in the radial direction of the rotor core. The electric motor according to claim 16.

18. On the outer circumferential surface of the rotor core, grooves are formed between adjacent magnetic pole portions in the circumferential direction, with the outer circumferential surface recessed in the radial direction of the rotor core, along the rotational centerline. The outer circumferential surface of the rotor core has a groove region in which the groove is formed such that the q-axis passes through the groove, The outer surface of the magnetic pole has a constant diameter region formed at a position through which the d-axis passes and at a constant distance from the center of rotation, and a diameter-changing region formed between the groove region and the constant diameter region, at which the distance from the center of rotation changes. The electric motor according to claim 16.

19. The constant diameter region comprises a forward constant region located on the forward side in the rotational direction with respect to the d-axis, and a rear constant region located on the rear side in the rotational direction with respect to the d-axis. The aforementioned forward fixed region is smaller in size in the circumferential direction than the aforementioned rear fixed region. The electric motor according to claim 18.

20. The aforementioned front non-magnetic portion is a through-hole that penetrates the rotor core along the rotational centerline. The electric motor according to claim 1.

21. The magnetic pole portion is provided with the permanent magnets on both sides of the d-axis. The electric motor according to claim 1.

22. When m is a natural number, the number of the multiple magnetic pole parts is 2m, and the number of the multiple teeth parts is 3m. The electric motor according to claim 1.

23. An electric motor according to any one of claims 1 to 22, A compression section driven by the aforementioned electric motor, A container housing the electric motor and the compression unit inside, A compressor equipped with the following features.

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