Electric motor and compressor

Abstract

An electric motor comprises: a rotor that has a rotor core (23) in which permanent magnets (13) are embedded in magnet embedding holes (12) and a plurality of magnetic poles (11) are provided along the circumferential direction; and a stator that has a plurality of teeth that are disposed on the outer peripheral side of the rotor, and an annular yoke that connects the plurality of teeth. In a plane that is orthogonal to the rotation axis of the rotor and passes through the rotor core (23), where the d-axis (D) is a straight line connecting the center of a magnetic pole (11) in the circumferential direction of the rotor core (23) and the rotation center (O) of the rotor and the q-axis (Q) is a straight line connecting the center between magnetic poles (11N, 11S) that are adjacent in the circumferential direction of the rotor core (23) and the rotation center (O) of the rotor, the magnetic poles (11) are provided in said plane with a rear-side non-magnetic portion (30) at a position on the trailing side in the rotation direction (R) of the rotor with respect to the d-axis (D), the rear-side non-magnetic portion (30) limiting short-circuiting of magnetic flux between one of the teeth and a pair of magnetic poles (11N, 11S) that are adjacent in the circumferential direction of the rotor core (23).

Description

Electric motor and compressor

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

[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 tooth portions arranged on the outer peripheral side of the rotor and an annular yoke portion connecting the plurality of tooth portions.

[0003] As a related technique, there is an electric motor that reduces torque ripple 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 tooth portion in the circumferential direction of the rotating rotor, so that the magnetic flux density distribution in the gap along the circumferential direction approaches a sine wave (Patent Documents 1 and 2).

[0004] Japanese Patent No. 5321451 Japanese Unexamined Patent Application Publication No. 2004-260972

[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 by passing only through 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, passes through the adjacent tooth portion, and goes 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 not sinusoidal and is distorted indicates that harmonic components are present in the magnetic flux density distribution.

[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.

[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 rear non-magnetic portion at a position on the rear side of the rotor's rotation direction with respect to the d-axis, and the rear 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.

[0009] According to one embodiment of the rotary compressor 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.

[0010] Figure 1 is a longitudinal cross-sectional view showing the compressor of Example 1. Figure 2 is a plan view showing the electric motor of Example 1. Figure 3 is a plan view showing the rotor of Example 1. Figure 4 is a plan view illustrating the main parts of the rotor core of Example 1. Figure 5 is an enlarged view showing the outer magnetic pole surfaces of the N and S poles of the rotor core of Example 1. Figure 6 is a schematic diagram showing the outer magnetic pole surfaces of each pole of the rotor core of Example 1. Figure 7 is a schematic diagram illustrating the shape of the outer magnetic pole surface of the rotor core of Example 1. Figure 8 is a plan view showing the magnetic field lines of Example 1. Figure 9 is a diagram showing the circumferential magnetic flux density distribution of the rotor of Example 1. Figure 10 is a plan view showing the magnetic field lines in a comparative example. Figure 11 is a diagram showing the circumferential magnetic flux density distribution of the rotor of a comparative example. Figure 12 is a plan view showing the rotor core of Example 2. 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 of Example 2. Figure 15 is a plan view illustrating the main parts of the rotor core in Embodiment 3. Figure 16 is a plan view showing the magnetic field lines in Embodiment 3.

[0011] The following describes in detail embodiments of the electric motor and compressor disclosed in this application with reference to the drawings. However, the following embodiments do not limit the electric motor and compressor disclosed in this application.

[0012] (Compressor Configuration) Figure 1 is a longitudinal cross-sectional view showing the compressor of Embodiment 1. As shown in Figure 1, the compressor 101 is a so-called rotary compressor and comprises a container 102, a compression unit 105, and an electric motor 1. The container 102 is made of a metal material and forms a sealed internal space 107. The internal space 107 of the container 102 is formed in a generally cylindrical shape. When the container 102 is placed vertically on a horizontal plane, the central axis of the cylinder forming the internal space 107 is parallel to the vertical direction. An oil reservoir 108 is formed in the lower part of the internal space 107 of the container 102. Refrigerant oil, which is a lubricating oil for lubricating the compression unit 105, is stored in the oil reservoir 108. The container 102 is connected to an intake pipe 111 for drawing in refrigerant and a discharge pipe 112 for discharging compressed refrigerant. A shaft 3, which is rotated by an electric motor 1 (described later), is positioned in the internal space 107 of the container 102 such that one end of the shaft 3 is located in the oil reservoir 108. The shaft 3 is supported by the container 102 so as to be rotatable about the central axis of the cylinder that makes up the internal space 107. By rotating, the shaft 3 supplies the refrigerant oil stored in the oil reservoir 108 to the compression unit 105.

[0013] The compression section 105 is located in the lower part of the internal space 107 and above the oil reservoir 108. The compressor 101 further comprises an upper muffler cover 114 and a lower muffler cover 115. The upper muffler cover 114 is located 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 located below the compression section 105 in the internal space 107 and above the oil reservoir 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 via a connecting 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 via the compressed refrigerant discharge hole 118.

[0014] The compression unit 105 compresses the refrigerant supplied from the intake pipe 111 by the rotation of the shaft 3, 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 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 motor 1 of Embodiment 1 is a 6-pole, 9-slot concentrated winding type 3-phase motor. The 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 in the figures, 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 roughly V-shape on the orthogonal plane, i.e., 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 out, the illustration of the end plates is omitted in order to explain the main part of the rotor core 23. These end plates are fixed to the rotor core 23 by rivets 8 that are passed through 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) includes 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, the two plate-shaped permanent magnets 13 are provided on both sides of the d-axis D, and are arranged to form a substantially 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, 17, and a plurality of bridge parts 18 formed between the q-axis side non-magnetic parts 14, 15 and the grooves 16, 17.

[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 the rotor core 23, that is, toward the outer circumferential surface 27 of the rotor core 23, from each end of the two magnet embedding holes 12 located on the outer circumferential surface 27 side 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 that penetrate along the rotational centerline of the rotor core 23 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 portions 14, 15 and the d-axis non-magnetic portion 19.

[0027] Furthermore, each magnetic pole portion 11 is provided with a rear non-magnetic portion 30, 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 rear non-magnetic portion 30, formed separately from the q-axis non-magnetic portion 15, 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 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. 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. Details of the rear non-magnetic portion 30 will be described later.

[0028] On the outer circumferential surface 27 of the rotor core 23, grooves 16 and 17 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 and 17 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 Embodiment 1 will be described. The characteristics of Embodiment 1 include the rear non-magnetic portion 30 of each magnetic pole portion 11 and the shape of the outer peripheral surface 27 of the rotor core 23.

[0030] (Shape of the rear non-magnetic section) As shown in Figure 4, each magnetic pole section 11 is provided with only a rear non-magnetic section 30, which is a non-magnetic section provided separately from the magnet embedding hole 12. The rear non-magnetic section 30, like the q-axis non-magnetic sections 14, 15 and the d-axis non-magnetic section 19 described above, restricts the short circuit of magnetic flux between a pair of adjacent magnetic pole sections 11 in the circumferential direction of the rotor core 23 and the flange section 33 of one tooth section 32. Note that 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, the rear non-magnetic section 30 reduces the magnetic flux (leakage flux) passing through the short-circuited magnetic path described above, thereby increasing the magnetic flux passing through the appropriate magnetic path circulating between the pair of adjacent magnetic pole sections 11 in the circumferential direction of the rotor core 23, the pair of adjacent tooth sections 32 in the circumferential direction of the rotor core 23, and the yoke section 31 connecting these pairs of tooth sections 32.

[0031] Specifically, the rear non-magnetic portion 30 restricts 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 rear non-magnetic portion 30 is formed over a range of 30 degrees to 90 degrees, 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 rear non-magnetic portion 30 can block the magnetic flux passing through the outer magnetic pole surface 29, which is the outer peripheral surface of the magnetic pole portion 11 and will be described later, over a range of electrical angles of 30 degrees to 90 degrees.

[0033] To rephrase the above-mentioned 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 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 rear non-magnetic portion 30 has a first portion 30a extending from the magnet embedding hole 12 toward the outer magnetic pole surface 29, which will be described later, 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.

[0035] In a perpendicular 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 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 30c of the first portion 30a is positioned to intersect with the permanent magnet 13, the thickness between the rear non-magnetic portion 30 and the outer magnetic pole surface 29 can be increased compared to the case where the center line 30a of the first portion 30a does not intersect with the permanent magnet 13 (for example, when the center line 30c of the first portion 30a extends in a direction along the center line 30d of the second portion 30b), 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.

[0036] 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 surface 29 of the magnetic pole. This ensures that the rear non-magnetic portion 30 extends sufficiently in the circumferential direction of the rotor 21, 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.

[0037] The rear non-magnetic portion 30 is positioned radially inward from the q-axis side second non-magnetic portion 15 in the radial direction of the rotor core 23. This prevents the rear non-magnetic portion 30 from being too close to the q-axis side second non-magnetic portion 15. As a result, a larger wall thickness can be secured between the rear non-magnetic portion 30 and the q-axis side second non-magnetic portion 15, thereby suppressing a decrease in the mechanical strength around the rear non-magnetic portion 30 and the q-axis side non-magnetic portion 15 in the rotor core 23.

[0038] Furthermore, in Embodiment 1, the rear non-magnetic portion 30 is positioned only on the rear 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 rotor core) Next, the shape of the outer 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 surface 27 of the rotor core 23 that forms one pole pair is defined as the pole pair outer surface 28. Also, in the orthogonal plane, the number of pole pairs formed by the magnetic pole portion 11 (a set of N pole portion 11N and S pole portion 11S) is m (m is a natural number). At this time, the overall shape of the outer surface 27 of the rotor core 23 in the orthogonal plane is formed by repeating the shape of one pole pair outer surface 28 m times with respect to the circumferential direction of the rotor core 23. In other words, in the orthogonal plane, each of the m pole pair outer 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 the 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 points on the radially outermost side of the rotor core 23 among the ends of the two permanent magnets 13 of the magnetic pole portion 11 located on the outer peripheral surface 27 side of the rotor core 23 are defined as angles C1 and C2 on the d-axis D side at the ends. 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 17 located on the rear side in the rotation direction R with respect to the q axis Q in the groove portion 17 located on the front side in the rotation direction R with respect to the q axis Q in the groove portion 17 located on the front side in the rotation direction R with respect to the S pole portion 11S in the groove portion 17 located on the rear side in the rotation direction R with respect to the q axis Q in the groove portion 17. 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 grooves 16 and 17, but is the outer surface 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] FIG. 5 is an enlarged view showing the magnetic pole outer peripheral surfaces 29 of the N - pole magnetic pole portion 11N and the S - pole magnetic pole portion 11S of the rotor core 23 in Example 1. As shown in FIGS. 4 and 5, in the orthogonal plane, the N - pole outer peripheral surface 29N of the N - pole magnetic pole portion 11N and the S - pole outer peripheral surface 29S of the S - pole magnetic pole portion 11S in Example 2 are formed in shapes that do not match each other when one of the magnetic pole portions of the N - pole magnetic pole portion 11N and the S - pole magnetic pole portion 11S is virtually rotated 60 [degrees] around the rotation center O of the rotor 21 and overlapped with the other magnetic pole portion of the N - pole magnetic pole portion 11N and the S - pole magnetic pole portion 11S. Note that the magnetic pole portion to be virtually rotated may be either the N - pole magnetic pole portion 11N or the S - pole magnetic pole portion 11S. Also, the direction of rotation around the rotation center O may be either clockwise or counterclockwise. Here, it will be described assuming that the N - pole magnetic pole portion 11N is virtually rotated 60 [degrees] counterclockwise and overlapped with the S - pole magnetic pole portion 11S.

[0043] When focusing on one pair of pole outer peripheral surfaces 28 of the rotor core 23 in Example 1, since the one pair of pole outer peripheral surfaces 28 are formed in different shapes with respect to the q - axis Q, in the N - pole permanent magnet 13 and the S - pole permanent magnet 13 forming one pole pair, the magnetic flux density distribution passing between the N - pole permanent magnet 13 and the tooth portion 32 adjacent to this 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 this S - pole permanent magnet 13 can be made to approach symmetry with respect to the q - axis Q. Therefore, the magnetic flux density distribution (the radial magnetic flux density [T] at the gap position measured or analyzed over the circumferential direction) at the position of the air gap (air gap) formed between the rotor core 23 and the tooth portion 32 within the range of the one pair of pole outer peripheral surfaces 28 can be made to approach a sine wave more closely.

[0044] For example, in Example 1, 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 between 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. Thereby, it is possible to easily realize that the one pair of pole outer peripheral surfaces 28 have different shapes with respect to the q - axis Q.

[0045] Note that when one of the magnetic pole parts 11 of the N - pole magnetic pole part 11N and the S - pole magnetic pole part 11S is overlapped with the other magnetic pole part 11, the rotation angle around the rotation center O for virtually rotating one of the magnetic pole parts 11 is 360 / (2m) [degrees]. (Let the number of pole pairs be m.) Also, in the following description, the rotation angle in the case of virtually rotating around the rotation center O of the rotor 21 is also 360 / (2m) [degrees]. For example, in Example 2, since the number of pole pairs is m = 3, when the N - pole magnetic pole part 11N is virtually rotated around the rotation center O of the rotor 21 and overlapped with the S - pole magnetic pole part 11S, the rotation angle is 360 / 6 = 60 [degrees].

[0046] (Shape of the magnetic - pole outer peripheral surface) Fig. 6 is a schematic view showing the magnetic - pole outer peripheral surface 29 of each magnetic - pole part 11 of the rotor core 23 in Example 1. Fig. 7 is a schematic view for explaining the shape of the magnetic - pole outer peripheral surface 29 of the rotor core 23 in Example 1.

[0047] As shown in Figs. 6 and 7, in the orthogonal plane, the N - pole outer peripheral surface 29N of the N - pole magnetic - pole part 11N is formed in a shape asymmetric with respect to the N - pole d - axis DN which is the d - axis D in this N - pole magnetic - pole part 11N, and the S - pole outer peripheral surface 29S of the S - pole magnetic - pole part 11S is formed in a shape asymmetric with respect to the S - pole d - axis DS which is the d - axis in this S - pole magnetic - pole part 11S.

[0048] Thus, by devising the shape of the magnetic - pole outer peripheral surface 29 formed within the range of each magnetic - pole part 11, in the N - pole permanent magnet 13 and the S - pole permanent magnet 13 forming one pole pair, the magnetic - flux density distribution passing between the N - pole permanent magnet 13 and the tooth part 32 close to this N - pole permanent magnet 13 and the magnetic - flux density distribution passing between the S - pole permanent magnet 13 and the tooth part 32 close to this S - pole permanent magnet 13 can be made closer to symmetry with respect to the q - axis Q. Therefore, in addition to the effect obtained by devising the shape of the outer peripheral surface 28 of one pole pair described above, the magnetic - flux density distribution in the air gap formed between the rotor core 23 and the tooth part 32 within the range of the outer peripheral surface 28 of one pole pair can be made closer to a sine wave.

[0049] (Shape of the outer surface of the north pole) Specifically, as shown in Figure 6, the outer surface 29N of the north pole magnetic pole portion 11N has a front outer surface 29N-F of the north pole located on the front side of the rotation direction R of the rotor 21 with respect to the north pole d axis DN, and a rear outer surface 29N-R of the north pole located on the rear side of the rotation direction R with respect to the north pole d axis DN.

[0050] Figure 7 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 7, 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).

[0051] (Shape of the outer surface of the south pole) Also, similar to the outer surface of the north pole 29N described above, as shown in Figure 6, the outer surface of the south pole 29S of the south pole magnetic pole portion 11S has a front outer surface of the south pole 29S-F located on the front side of the rotation direction R of the rotor 21 with respect to the south pole d axis DS, and a rear outer surface of the south pole 29S-R located on the rear side of the rotation direction R with respect to the south pole d axis DS.

[0052] The case where the S-pole magnetic pole portion 11S is virtually folded back will be explained. As shown in Figure 7, 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 overlapped, 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). Furthermore, 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).

[0053] (Relationship between the outer surface of the north pole and the outer surface of the south pole) Furthermore, as shown in Figures 4 and 5, in an orthogonal plane, the outer surface 29N-R on the rear side of the north pole and the outer 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.

[0054] 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 4 and 5) 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).

[0055] 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).

[0056] For example, in Embodiment 1, 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.

[0057] 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 5).

[0058] 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 4 and 5) located inside 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 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 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).

[0059] 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 inside 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 inside 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).

[0060] For example, in Embodiment 1, 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.

[0061] 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 4. 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.

[0062] Furthermore, in Embodiment 1, 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 1, 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.

[0063] Furthermore, in Embodiment 1, in the magnetic pole portion 11, the rear non-magnetic portion 30 is arranged only on the rear side in the rotation direction R of the rotor 21 with respect to the d axis D, the shapes of the q-axis non-magnetic portion 14 on the front side and the q-axis non-magnetic portion 15 on the rear side in the rotation direction R of the rotor 21 are different in an orthogonal plane, and the outer circumferential surface 29 of the magnetic pole is formed in an asymmetric shape with respect to the d axis D, so that the cross-sectional shape of the magnetic pole portion 11 in an orthogonal plane is asymmetric with respect to the d axis D.

[0064] 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.

[0065] As shown in Figures 4 and 6, the outer surface of the magnetic pole 29 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 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 by a radius of curvature that is the maximum radius of curvature rm from the rotation center O. The diameter-changing region A3 is formed by a plurality of radii of curvature smaller than the maximum radius of curvature rm from the rotation center O in the constant diameter region A2.

[0066] In Figure 4, 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.

[0067] 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 1, 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.

[0068] In Figure 4, within the second radius of curvature r2-F of the front diameter change region A3-F, the N pole side of the magnetic pole 11N is defined as the second radius of curvature rn2-F, and the S pole side of the magnetic pole 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 of the magnetic pole 11N is defined as the second radius of curvature rn2-R, and the S pole side of the magnetic pole 11S is defined as the second radius of curvature rs2-R. Note that the first radius of curvature r1 is not shown in Figure 4.

[0069] Furthermore, as shown in Figure 6, 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 area of ​​the front outer surface 29-F gradually increases toward the q axis Q, and the ratio of the air gap formed in the area of ​​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 area of ​​the front outer surface 29-F gradually increasing toward the q axis Q. In other words, because the forward constant region A2-F is smaller than the rear constant region A2-R, when the N pole magnetic pole portion 11N is virtually folded back along the N pole d axis DN in each orthogonal plane, and the N pole forward outer peripheral surface 29N-F is superimposed on the N pole rear outer peripheral surface 29N-R, the N pole forward outer peripheral surface 29N-F has a small diameter outer peripheral surface 34 located inside the N pole rear outer peripheral surface 29N-R in the radial direction of the rotor core 23, and the N pole rear outer peripheral surface 29N-R does not have a portion located inside the N pole forward outer peripheral surface 29N-F in the radial direction of the rotor core 23.

[0070] Furthermore, in Embodiment 1, as shown in Figure 6, 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.

[0071] 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 side diameter change region A3-F (As3-F) and the second radius of curvature r2-R (rs2-R) of the rear side diameter change region A3-R (As3-R) may be different from each other.

[0072] (Inner surface shape of grooves) As shown in Figure 4, in the orthogonal plane of the rotor core 23, the shape of the inner surface 16a of groove 16 is formed asymmetrically with respect to the q-axis Q. Similarly, the shape of the inner surface 17a of groove 17 is formed asymmetrically with respect to the q-axis Q. In addition, grooves 16 and groove 17 are arranged alternately along the circumferential direction of the rotor core 23 on the outer circumferential surface 27 of the rotor core 23. In the orthogonal plane, the shapes of the inner surfaces 16a of groove 16 and the inner surfaces 17a of groove 17 adjacent to each other in the circumferential direction of the rotor core 23 are different from each other. The shapes of the inner surfaces 16a and 17a of 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.

[0073] (Shape of the q-axis side non-magnetic parts) The two q-axis side non-magnetic parts 14 and 15 of the S-pole magnetic part 11S are formed in a shape that is asymmetrical with respect to the S-pole d-axis DS, which is the d-axis of the S-pole magnetic part 11S. The two q-axis side non-magnetic parts 14 and 15 of the N-pole magnetic part 11N are formed in a shape that is asymmetrical with respect to the N-pole d-axis DN, which is the d-axis of the N-pole magnetic part 11N. Furthermore, the two q-axis side non-magnetic parts 14 and 15 of the N-pole magnetic part 11N and the two q-axis side non-magnetic parts 14 and 15 of the S-pole magnetic part 11S are formed in a shape that does not coincide with each other when the N-pole magnetic part 11N and the S-pole magnetic part 11S are superimposed by virtually rotating them 360 / (2m) [degrees] around the rotation center O of the rotor 21.

[0074] (Comparison of Example 1 and Comparative Example) Figure 8 is a plan view showing the magnetic field lines in Example 1. Figure 9 is a diagram showing the circumferential magnetic flux density distribution of the rotor 21 in Example 1. Figure 10 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 indicated with the same reference numerals as in Example 1. Figure 11 is a diagram showing the circumferential magnetic flux density distribution of the rotor in the Comparative Example. In Figures 9 and 11, the vertical axis shows magnetic flux density [T], and the horizontal axis shows electrical angle [degrees (deg)]. In Figure 9, the solid line shows a sine wave, and the dashed line shows Example 1. In Figure 11, the solid line shows a sine wave, and the dashed line shows the Comparative Example. The Comparative Example has the same structure as Example 1, except that it does not have a rear non-magnetic part 30.

[0075] Comparing Figure 8 and Figure 10, in each magnetic pole section 11 of Embodiment 1, 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 section 30 to pass through the d-axis D side. Therefore, the rear non-magnetic section 30 plays a role in reducing the magnetic flux passing through the q-axis Q side behind the magnetic pole section 11 and increasing the amount of magnetic flux passing through the d-axis D side behind the magnetic pole section 11 by the same amount. In other words, the rear non-magnetic section 30 has the function of concentrating 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 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 portion 33) 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 via the yoke portion 31, after traversing the tooth portion 32 radially in the rotor 21, and then passing through adjacent tooth portions 32 is increased. Accordingly, in Example 1, in each magnetic pole portion 11, the rear non-magnetic portion 30 prevents the magnetic flux passing through the rear 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.

[0076] As shown in Figures 9 and 11, in Example 1, compared to the comparative example, 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 the range of electrical angles from approximately 20 to 60 degrees. 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, compared to the comparative example, 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.

[0077] 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 behind 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 behind the magnetic pole portion 11 is suppressed compared to the comparative example.

[0078] As described above, in Example 1, 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, so 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. In addition, in Example 1, compared with the comparative example, 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.

[0079] (Effects of Example 1) As described above, in the electric motor 1 of Example 1, 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 in a plane perpendicular to the rotation centerline of the rotor 21 and passing through the rotor core 23. The rear non-magnetic portion 30 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 rear 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 rear non-magnetic portion 30 to pass through the d axis D side. Therefore, the rear non-magnetic portion 30 reduces the magnetic flux passing through the q-axis Q side behind the magnetic pole portion 11 and increases the amount of magnetic flux passing through the d-axis D side behind 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.

[0080] Furthermore, in the electric motor 1 of Embodiment 1, the rear non-magnetic portion 30 of the rotor core 23 is formed separately from the magnet embedding hole 12. This makes it possible to suppress a decrease in the mechanical strength around the magnet embedding hole 12 in the rotor core 23.

[0081] Furthermore, in the electric motor 1 of Embodiment 1, the rear non-magnetic portion 30 of the rotor core 23 is formed over a range of 30 degrees to 90 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 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.

[0082] Furthermore, the magnetic pole portion 11 of the rotor core 23 of the electric motor 1 of Embodiment 1 has a rear non-magnetic portion 30, and the outer magnetic pole surface 29 has an asymmetric shape with respect to the d-axis D, so that the cross-sectional shape of the magnetic pole portion 11 in the orthogonal plane is asymmetric with respect to the d-axis D. The rotor core 23, by having a rear non-magnetic portion 30 in the magnetic pole portion 11, can obtain the effect of bringing the magnetic flux density distribution at the location of the air gap between the rotor 21 and the stator 22 closer to a sine wave in the circumferential direction of the rotor 21, and the asymmetric shape of the outer magnetic pole surface 29 of the magnetic pole portion 11 can bring the magnetic flux density distribution even closer to a sine wave.

[0083] Furthermore, in the electric motor 1 of Embodiment 1, 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.

[0084] Furthermore, in the electric motor 1 of Embodiment 1, 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 change in distance from the rotation center O. The constant diameter region A2 has a front constant region A2-F located on the front side in 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 in the rotation direction R with respect to the d axis D. The circumferential size of the front constant region A2-F is smaller than the circumferential size 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 gap formed in the area of ​​the front outer surface 29-F gradually increases, while the ratio of rear outer surface 29-R to the ratio of the front outer surface 29-F. In other words, 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, it is easy to realize a shape in which the front outer surface 29-F has a small diameter outer surface 34 that is located inside the rear outer surface 29-R in the radial direction of the rotor core 23.

[0085] Furthermore, in the electric motor 1 of Embodiment 1, the rear non-magnetic portion 30 of the rotor core 23 has a center line 30c of the first portion 30a that runs in the direction in which the first portion 30a extends, which intersects with the permanent magnet 13. As a result, the rear non-magnetic portion 30 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 rear non-magnetic portion 30 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 side non-magnetic portion 15 of the rotor core 23 is suppressed.

[0086] Furthermore, in the electric motor 1 of Embodiment 1, the rear non-magnetic portion 30 of the rotor core 23 is positioned radially inward of the rotor core 23 compared to the q-axis side 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 side non-magnetic portion 15 of the rotor core 23.

[0087] 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.

[0088] Figure 12 is a plan view showing the rotor core 23 of Embodiment 2. Embodiment 2 differs from Embodiment 1 in the shape of the rear non-magnetic portion provided on each magnetic pole portion 11.

[0089] (Shape of the rear non-magnetic portion) As shown in Figure 12, in Embodiment 2, the magnetic pole portion 11 is formed in the same way as in Embodiment 1, with the outer magnetic pole surface 29 having an asymmetric shape with respect to the d-axis D. In Embodiment 2, the magnetic pole portion 11 is provided with only a rear non-magnetic portion 40 as a non-magnetic portion that is provided separately from the magnet embedding hole 12. The rear non-magnetic portion 40, like the rear non-magnetic portion 30 in Embodiment 1, 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.

[0090] The rear non-magnetic portion 40 is formed in the shape of an elongated hole extending from the magnet embedding hole 12 toward the outer magnetic pole surface 29, which will be described later. In a perpendicular plane, the rear non-magnetic portion 40 is positioned such that its center line 40c, which runs along its longitudinal direction, intersects with the permanent magnet 13. Here, the center line 40c is a straight line that passes through the center of the rear non-magnetic portion 40 in the width direction, which is the short direction of the rear non-magnetic portion 40, and extends along the longitudinal direction of the rear non-magnetic portion 40. By positioning the rear non-magnetic portion 40 in this way, it becomes easier to block the path of magnetic flux that would otherwise pass through the rear non-magnetic portion 40. 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 circumferential end (flange portion 33) of the teeth portion 32 without passing through the yoke portion 31, thereby obtaining the effect of restricting the short circuit of magnetic flux as described above.

[0091] The rear non-magnetic portion 40 is positioned radially inward of the rotor core 23 compared to the q-axis non-magnetic portion 15. This allows for a larger wall thickness between the rear non-magnetic portion 40 and the outer magnetic pole surface 29, thereby preventing a decrease in the mechanical strength around the rear non-magnetic portion 40 and the q-axis non-magnetic portion 15 in the rotor core 23.

[0092] Furthermore, in Embodiment 2, the rear non-magnetic portion 40 is positioned only on the rear 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.

[0093] 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 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.

[0094] As shown in Figure 13, in Embodiment 2, similar to Embodiment 1, 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 the role of 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 2, 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.

[0095] In the range of electrical angles from approximately 20 to 60 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 the comparative example shown in Figure 11. By making the magnetic flux density distribution closer to a sine wave in this way, in Example 2, compared to the comparative example, the harmonic components superimposed on the magnetic flux density distribution at the air gap between the rotor 21 and the stator 22 can be reduced.

[0096] Therefore, in Embodiment 2, since the magnetic pole portion 11 has a rear non-magnetic portion 40, 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.

[0097] (Effects of Example 2) As described above, in the electric motor of Example 2, the magnetic pole portion 11 also has a rear non-magnetic portion 40, so, similar to Example 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 to approach a sine wave, and 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.

[0098] Figure 15 is a plan view illustrating the main parts of the rotor core in Embodiment 3. Embodiment 3 has a rear non-magnetic portion 30, similar to Embodiment 1, but differs from Embodiment 1 in that the outer magnetic pole surface 29 in the circumferential direction of the rotor core 23 has a symmetrical shape.

[0099] (Shape of the outer surface of the magnetic pole) As shown in Figure 15, in Embodiment 3, the outer surface 29 of each magnetic pole portion 11 is formed in a shape symmetrical with respect to the d axis D. In Embodiment 3, in the orthogonal plane described above, the outer surface 29 of the magnetic pole portion 11, which is the outer peripheral side, is formed such that the distance between the outer surface 29 and the rotation center O gradually decreases as you move from the d axis D toward the q axis Q. Therefore, in the orthogonal plane, the outer diameter L of the outer surface 29 of each magnetic pole portion 11 is greatest at a position on the d axis D, which is the distance from the rotation center O of the rotor 21, i.e., the radius of the rotor core 23.

[0100] Figure 16 is a plan view showing the magnetic field lines in Embodiment 3. As shown in Figure 16, in Embodiment 3, similar to Embodiment 1, 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 the role of 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. As a result, 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.

[0101] (Effects of Example 3) As described above, in the electric motor of Example 3, even when the outer magnetic pole surface 29 of the magnetic pole portion 11 is formed in a shape symmetrical with respect to the d axis D, by appropriately setting the size, shape, and arrangement of the rear non-magnetic portion 30 of the magnetic pole portion 11, it is possible to make the magnetic flux density distribution at the position of the air gap between the rotor 21 and the stator 22 in the circumferential direction of the rotor 21 approach a sine wave, similar to Example 1, and it is possible to reduce the harmonic components superimposed on the magnetic flux density distribution in the air gap between the rotor 21 and the stator 22.

[0102] 1. Electric motor 3. Shaft 11. Magnetic pole section 11N. N-pole magnetic pole section 11S. S-pole magnetic pole section 12. (12a-12f) Magnet mounting holes 13. (13a-13f) Permanent magnets 14. (14a-14f), 15. (15a-15f) q-axis side non-magnetic section 16, 17. Groove section 19. d-axis side non-magnetic section 21. Rotor 22. Stator 23. Rotor core 24. Stator core 27. Outer surface 29. Magnetic pole outer surface 29-F. Front outer surface 29-R. Rear outer surface 30. Rear side non-magnetic section 30a. First section 30b. Second section 30c. Centerline 31. Yoke section 32. Teeth section 40. Rear side non-magnetic section 101. Compressor 102. Container 105 Compression part A1 Groove area A2 Constant diameter area A2-F Front constant area A2-R Rear constant area A3 Diameter changing area C1, C2 Angle D d-axis O Center of rotation Q Q-axis R Rotation direction

Claims

1. An electric motor comprising: 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; a stator having a plurality of teeth portions arranged on the outer circumference side of the rotor and an annular yoke portion connecting the plurality of teeth portions, wherein, in a plane perpendicular to the rotational centerline of the rotor and passing through the rotor core, the line connecting the center of the magnetic pole portions in the circumferential direction and the rotational 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 and the rotational center is defined as the q-axis, in the plane, the magnetic pole portions are provided with a rear non-magnetic portion at a position on the rear side of the rotational direction of the rotor with respect to the d-axis, and the rear non-magnetic portion restricts short-circuiting of magnetic flux between a pair of adjacent magnetic pole portions in the circumferential direction and one of the teeth portions.

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

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

4. The electric motor according to claim 1, wherein the rear non-magnetic portion is formed over a range of 30 degrees or more and 90 degrees or less, with respect to the magnetic pole portion, the q-axis located on the rear side in the direction of rotation being defined as 0 degrees of electrical angle, and the front side in the direction of rotation being defined as positive electrical angle.

5. The electric motor according to claim 1, wherein, when the number of magnetic poles is 2 m, the rear non-magnetic portion is formed in a range of (360 / 2m) × (1 / 6) degrees or more and (360 / 2m) × (3 / 6) degrees or less in the mechanical angle of the circumferential range between adjacent magnetic poles, with respect to the rear magnetic pole in the rotational direction, the q-axis located on the rear side is defined as 0 degrees.

6. The electric motor according to claim 1, wherein the rear 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.

7. The electric motor according to claim 6, wherein the rear non-magnetic portion restricts short-circuiting of the magnetic flux when the q-axis of the rotor coincides with the widthwise center of one of the plurality of teeth portions during the rotation of the rotor.

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

9. The electric motor according to claim 1, wherein the rear non-magnetic portion has a first portion extending from the magnet embedding hole side toward the outer magnetic pole surface, which is the outer peripheral side of the magnetic pole portion.

10. The electric motor according to claim 9, wherein in the plane, the rear non-magnetic portion has a center line of the first portion that extends in the direction in which the first portion extends, and intersects with the permanent magnet.

11. The electric motor according to claim 9, wherein the rear non-magnetic portion has a second portion formed in continuity with the first portion and extending toward the d-axis.

12. The electric motor according to claim 1, wherein a q-axis side non-magnetic portion is formed in the magnet embedding hole, in the vicinity of the q-axis, and extends toward the outer peripheral surface of the magnetic pole, which is the outer peripheral side of the magnetic pole portion, and the rear side non-magnetic portion is positioned radially inward of the rotor core than the q-axis side non-magnetic portion.

13. The electric motor according to claim 1, wherein the outer surface of the magnetic pole, which is the outer 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 it moves from the d-axis toward the q-axis.

14. The electric motor according to claim 13, wherein 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, and when the magnetic pole portion is virtually folded back along the d axis in the plane and the front outer surface is superimposed on the rear outer surface, the front outer surface has a smaller diameter outer surface located inward from the rear outer surface in the radial direction of the rotor core.

15. The electric motor according to claim 13, wherein the outer circumferential surface of the rotor core has grooves formed between adjacent magnetic pole portions in the circumferential direction, the grooves being recessed in the radial direction of the rotor core along the rotational centerline, and the outer circumferential surface of the rotor core has groove regions in which the grooves are formed such that the q-axis passes through the grooves.

16. The electric motor according to claim 15, wherein 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 and at a change in distance from the center of rotation.

17. The constant diameter region comprises a front constant region located on the front 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, wherein the front constant region is smaller in the circumferential direction than the rear constant region, as described in claim 16.

18. The electric motor according to claim 1, wherein the rear non-magnetic portion is a through hole that penetrates the rotor core along the rotational centerline.

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

20. The electric motor according to claim 1, wherein, when m is a natural number, the number of the plurality of magnetic poles is 2m and the number of the plurality of teeth is 3m.

21. A compressor comprising: an electric motor according to any one of claims 1 to 20; a compression unit driven by the electric motor; and a container housing the electric motor and the compression unit.

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