Rotor for electric motor

Abstract

An N-pole rotor (1A) for an electric motor according to an embodiment of the present invention includes a plurality of pole regions (2) divided into N equal sections around an axis of rotation (10). The overall shape of the plurality of pole regions (2) is rotationally symmetrical about the axis of rotation (10) and line-symmetrical with respect to a specified line that passes through the axis of rotation (10). The pole regions (2) include at least four asymmetrical pole regions (22), each of the asymmetrical pole regions (22) having an asymmetrical shape with respect to a center line (20) of said asymmetrical pole region (22).

Description

Electric motor rotor

[0001] The present disclosure relates to a rotor for an electric motor.

[0002] N-pole rotors for electric motors have been known for some time. These rotors include permanent magnet rotors and synchronous reluctance rotors. In a permanent magnet rotor, N permanent magnets or groups of permanent magnets are arranged circumferentially and are held on the surface or inside of a rotor core. In a synchronous reluctance rotor, the rotor core includes N salient poles arranged circumferentially.

[0003] It is generally known that in electric motors, increasing the amount of magnetic flux to increase torque increases torque ripple due to magnetic saturation of the rotor core and stator core. For example, Patent Document 1 discloses a rotor for an electric motor that can reduce torque ripple.

[0004] Patent No. 6390506

[0005] Specifically, the rotor in Patent Document 1 is an eight-pole rotor, and the rotor is divided into eight equal pole regions around the rotation axis, and a permanent magnet is held inside the rotor core in each of these eight pole regions. Each permanent magnet extends along the center line of the corresponding pole region, i.e., in a direction perpendicular to the radial direction of the rotor. All eight pole regions have the same shape. In other words, the overall shape of the eight pole regions is rotationally symmetrical around the rotation axis.

[0006] In each pole region, a pair of flux barriers is formed on the rotor core on both sides of the permanent magnet. The rotor in Patent Document 1 rotates in one direction. The flux barrier located on the counter-rotation side of the permanent magnet has a shape in which the outer half of its periphery protrudes in the counter-rotation direction, while the flux barrier located on the rotational side of the permanent magnet has a shape in which the outer half of its periphery is recessed in the counter-rotation direction. In other words, each pole region has an asymmetric shape with respect to the center line of the pole region, which can reduce torque ripple.

[0007] As described above, in the rotor of Patent Document 1, each pole region has an asymmetric shape, and all pole regions have the same shape, so the torque characteristics differ when rotating in a set rotation direction and when rotating in the opposite counter-rotation direction.

[0008] Therefore, an object of the present disclosure is to provide a rotor for an electric motor that can reduce torque ripple and whose torque characteristics do not change regardless of the direction of rotation.

[0009] The present disclosure provides a rotor for an electric motor having N poles (N is an even number greater than or equal to 4), the rotor comprising a plurality of pole regions divided equally into N parts around a rotation axis, the overall shapes of the plurality of pole regions being rotationally symmetric about the rotation axis and line-symmetric with respect to a specific line passing through the rotation axis, the plurality of pole regions including at least four asymmetric pole regions, each of which has an asymmetric shape with respect to the center line of the asymmetric pole region.

[0010] According to the present disclosure, a rotor for an electric motor is provided that can reduce torque ripple and has torque characteristics that do not change regardless of the direction of rotation.

[0011] FIG. 1 is a front view of a rotor according to a first embodiment; FIG. 2 is an enlarged view of one asymmetric pole region; FIG. 3A is a front view of a rotor according to a second embodiment, and FIG. 3B is an enlarged view of one asymmetric pole region; FIG. 4A to FIG. 4D are modified examples of asymmetric pole regions; FIG. 5A is a front view of a rotor according to a third embodiment, and FIG. 5B is an enlarged view of one asymmetric pole region; FIG. 6A is a front view of a rotor according to a fourth embodiment, and FIG. 6B is an enlarged view of one asymmetric pole region; FIG. 7A is a front view of a rotor according to a fifth embodiment, and FIG. 5B is an enlarged view of one asymmetric pole region.

[0012] 1 shows a north pole (N is an even number equal to or greater than 4) rotor 1A for an electric motor according to a first embodiment. In this embodiment, N=6. The rotor 1A, together with a rotating shaft that passes through the rotor 1A and a stator that surrounds the rotor 1A, constitutes an electric motor.

[0013] The rotor 1A includes six pole regions 2 divided into N equal parts around the rotation axis 10. In other words, the pole regions 2 are regions separated by angle lines 11 at a pitch of 360 / N degrees. In this embodiment, the center line 20 of the pole region 2 is also the center line of the above-mentioned N pole.

[0014] In this embodiment, the rotor 1A is a permanent magnet rotor, and a group of N permanent magnets arranged in the circumferential direction is held inside the rotor core 3. This is known as an interior permanent magnet (IPM). That is, each pole region 2 includes a part of the rotor core 3 and a plurality of permanent magnets 4 that make up one permanent magnet group. The polarity direction of the permanent magnet group in the radial direction of the rotor 1A, i.e., the north pole and south pole, alternates in the circumferential direction.

[0015] In this embodiment, one permanent magnet group is made up of two permanent magnets 4. However, one permanent magnet group may be made up of three or more permanent magnets 4.

[0016] A through hole into which the above-mentioned rotating shaft is inserted is provided at the center of the rotor core 3. The rotor core 3 has a structure in which a plurality of annular electromagnetic steel plates are stacked in the axial direction of the rotor 1A.

[0017] In this embodiment, the polar region 2 includes two symmetrical polar regions 21 and four asymmetrical polar regions 22. The two symmetrical polar regions 21 are located on opposite sides of the rotation axis 10, and two asymmetrical polar regions 22 are arranged between each of the symmetrical polar regions 21.

[0018] The overall shape of the polar region 2 is rotationally symmetric about the rotation axis 10 and is line-symmetric with respect to a specific line passing through the rotation axis 10. In this embodiment, the overall shape of the polar region 2 is line-symmetric with respect to a horizontal line formed by an angle line 11 extending leftward and an angle line 11 extending rightward from the rotation axis 10 in Fig. 1 , and is line-symmetric with respect to a vertical line formed by a center line 20 extending upward and a center line 20 extending downward from the rotation axis 10 in Fig. 1 .

[0019] Each symmetrical pole region 21 has a shape symmetrical with respect to the center line 20 of the symmetrical pole region 21. Specifically, each symmetrical pole region 21 includes two symmetrical permanent magnets 41, 42 that intersect with the center line 20 of the symmetrical pole region 21. The symmetrical permanent magnets 41, 42 are spaced apart from each other in the radial direction of the rotor 1A.

[0020] Each of the symmetrical permanent magnets 41, 42 has a shape symmetrical with respect to the center line 20 of the symmetrical pole region 21. In this embodiment, each of the symmetrical permanent magnets 41, 42 has an arc-like shape that is convex toward the rotation axis 10. In other words, the symmetrical permanent magnets 41, 42 form a double arc.

[0021] Each asymmetric pole region 22 has a shape that is asymmetric with respect to the center line 20 of the asymmetric pole region 22. In this embodiment, the asymmetric pole region 22 includes two asymmetric pole regions 22A and two asymmetric pole regions 22B. The asymmetric pole region 22A and the asymmetric pole region 22B are located on either side of the symmetric pole region 21, and the shapes of the asymmetric pole region 22A and the asymmetric pole region 22B are opposite to each other.

[0022] Specifically, each asymmetric pole region 22A includes two asymmetric permanent magnets 43, 44 that intersect with the center line 20 of the asymmetric pole region 22A. The asymmetric permanent magnets 43, 44 are spaced apart from each other in the radial direction of the rotor 1A. Similarly, each asymmetric pole region 22B includes two asymmetric permanent magnets 45, 46 that intersect with the center line 20 of the asymmetric pole region 22B. The asymmetric permanent magnets 45, 46 are spaced apart from each other in the radial direction of the rotor 1A.

[0023] As described above, the shape of the asymmetric pole region 22A is opposite to the shape of the asymmetric pole region 22B, and therefore, the shape of the asymmetric pole region 22B will be described below as a representative with reference to FIG.

[0024] Each of the asymmetric permanent magnets 45, 46 has an asymmetric shape with respect to the center line 20 of the asymmetric pole region 22B. In this embodiment, each of the asymmetric permanent magnets 45, 46 has an arc-like shape that is convex toward the rotation axis 10. In other words, the asymmetric permanent magnets 45, 46 form a double arc.

[0025] The asymmetric permanent magnet 45 with a small radius of curvature has a shape in which an angle A from the center line 20 of the asymmetric pole region 22B to one end 45a and an angle B from the center line 20 of the asymmetric pole region 22B to the other end 45b and an angle B from the center line 20 of the asymmetric pole region 22B to the rotation axis 10 are different. For example, angle A is 14 degrees or more and 16 degrees or less, and angle B is 16 degrees or more and 18 degrees or less.

[0026] The asymmetric permanent magnet 46 with a large radius of curvature has a shape in which the angle C from the center line 20 of the asymmetric pole region 22B to one end 46a about the rotation axis 10 is different from the angle D from the center line 20 of the asymmetric pole region 22B to the other end 46b about the rotation axis 10. For example, the angle C is 25 degrees or more and 27 degrees or less, and the angle D is 27 degrees or more and 29 degrees or less.

[0027] Returning to FIG. 1 , the six pole regions 2 are configured so that the total amount of magnetic flux on the rotor surface of each pole region 2 is equal to one another. In this embodiment, the permanent magnets 4 are held inside the rotor core 3, so the rotor surface is the surface of the rotor core 3. The total amount of magnetic flux on the rotor surface of each pole region 2 is found by integrating the magnetic flux density on the rotor surface for each pole region 2. Here, "the total amount of magnetic flux on the rotor surface of each pole region 2 is equal to one another" means that the difference between the maximum and minimum values ​​of the total magnetic flux on the rotor surface in all pole regions 2 is 10% or less of the maximum value.

[0028] As described above, in the rotor 1A of this embodiment, the pole region 2 includes four asymmetric pole regions 22, so that torque ripple can be reduced by overlapping the torque waveforms. Moreover, because the overall shape of the pole region 2 is rotationally symmetric and axisymmetric, the torque characteristics do not change regardless of the direction in which the rotor 1A is rotated, and the occurrence of torque imbalance can also be suppressed.

[0029] Furthermore, in this embodiment, the shape of the permanent magnet 4 is made asymmetric by varying the angle from the center line 20 to both ends of the permanent magnet 4 in the asymmetric pole region 22. The shape of the portion close to the air gap has a large effect on the phase of the torque waveform. For this reason, the configuration of this embodiment is more effective in reducing torque ripple than when the shape of the permanent magnet 4 is made asymmetric while the angle from the center line 20 to both ends of the asymmetric pole region 22 remains the same.

[0030] Furthermore, in this embodiment, since the total amount of magnetic flux on the rotor surface of each pole area 2 is equal to each other, the difference in the attractive force acting between the stator core and each pole area 2 is reduced, thereby reducing vibration noise and torque imbalance.

[0031] <Modifications> In each asymmetric pole region 22, it is not necessary for all of the multiple permanent magnets 4 constituting one permanent magnet group to be asymmetric, as long as at least one permanent magnet 4 is asymmetric. In other words, a mixture of symmetric and asymmetric permanent magnets may be present in each asymmetric pole region 22. Furthermore, it is not necessary for a permanent magnet group made up of multiple permanent magnets to be disposed in each pole region 2, and a single permanent magnet may be disposed therein.

[0032] Furthermore, the asymmetric shape of the asymmetric pole region 22 does not necessarily have to be realized by an asymmetric permanent magnet. For example, when flux barriers are formed on both sides of the permanent magnet 4, the asymmetric shape of the asymmetric pole region 22 may be realized by making the shapes of the flux barriers different.

[0033] 3A shows a north pole rotor 1B for an electric motor according to a second embodiment. In this embodiment and in the third to fifth embodiments described below, the same components as those in the first embodiment are designated by the same reference numerals, and redundant description will be omitted.

[0034] In this embodiment, N=4, and the rotor 1B includes four pole regions 2. Each pole region 2 includes a part of the rotor core 3 and a permanent magnet 51 held inside the rotor core 3. In this embodiment, all of the pole regions 2 are asymmetric pole regions 23.

[0035] As in the first embodiment, the overall shape of the polar region 2 is rotationally symmetric about the rotation axis 10 and is line-symmetric with respect to a specific line passing through the rotation axis 10. In this embodiment, the overall shape of the polar region 2 is line-symmetric with respect to an oblique line formed by an angle line 11 extending diagonally downward to the left and an angle line 11 extending diagonally upward to the right from the rotation axis 10 in Fig. 3A , and is line-symmetric with respect to an oblique line formed by an angle line 11 extending diagonally upward to the left and an angle line 11 extending diagonally downward to the right from the rotation axis 10 in Fig. 3A .

[0036] Each asymmetric pole region 23 has a shape that is asymmetric with respect to the center line 20 of the asymmetric pole region 23. In this embodiment, the asymmetric pole region 23 includes two asymmetric pole regions 23A and two asymmetric pole regions 23B. The asymmetric pole regions 23A and the asymmetric pole regions 23B are alternately arranged, and the shapes of the asymmetric pole regions 23A and the asymmetric pole regions 23B are opposite to each other. For this reason, the shape of the asymmetric pole region 23A will be described below as a representative with reference to FIG. 3B.

[0037] The permanent magnet 51 intersects with the center line 20 of the asymmetric pole region 23 A. The permanent magnet 51 has a shape that is symmetrical with respect to the center line 20 of the asymmetric pole region 23 A. In this embodiment, the permanent magnet 51 extends in a direction perpendicular to the center line 20.

[0038] In this embodiment, flux barriers 31 are provided on both sides of the permanent magnets 51 in the rotor core 3. The flux barriers 31 may be air gaps or may be made of a non-magnetic material such as resin. Both flux barriers 31 have shapes symmetrical with respect to the center line 20 of the asymmetric pole region 23A.

[0039] Furthermore, in this embodiment, two holes 32 are provided outside the permanent magnets 51 in the rotor core 3. The two holes 32 are located on both sides of the center line 20 of the asymmetric pole region 23A. The two holes 32 have the same shape, but the distance from the center line 20 of the asymmetric pole region 23A to the center of one hole 32 is different from the distance from the center line 20 of the asymmetric pole region 23A to the center of the other hole 32. The difference in the positions of the holes 32 makes the shape of the asymmetric pole region 23A asymmetric.

[0040] As in the first embodiment, the four pole regions 2 are configured so that the total amount of magnetic flux on the rotor surface of each pole region 2 is equal to one another.

[0041] In this embodiment, as in the first embodiment, the pole region 2 includes four asymmetric pole regions 23, so that torque ripple can be reduced by overlapping the torque waveforms. Moreover, because the overall shape of the pole region 2 is rotationally symmetric and axisymmetric, the torque characteristics do not change regardless of the direction in which the rotor 1B is rotated, and the occurrence of torque imbalance can also be suppressed.

[0042] Furthermore, in this embodiment, since the total amount of magnetic flux on the rotor surface of each pole area 2 is equal to each other, the difference in the attractive force acting between the stator core and each pole area 2 is reduced, thereby reducing vibration noise and torque imbalance.

[0043] <Modifications> The configuration for making the shape of the asymmetric pole region 23 asymmetric can be modified as appropriate. For example, the distances from the center line 20 of the asymmetric pole region 23 to the centers of the two holes 32 may be the same, but the shapes of the holes 32 may be different. Furthermore, the number of holes 32 does not necessarily have to be two, and may be one, three, or more.

[0044] Alternatively, as shown in Fig. 4A, instead of the holes 32, two notches 33 may be provided on the surface of the rotor core 3, and the positions or shapes of the notches 33 may be different. Alternatively, as shown in Fig. 4B, neither the holes 32 nor the notches 33 may be provided, and the shape of the flux barrier 31 may be asymmetric.

[0045] 4C, each pole region 2 may include a plurality of permanent magnets 52 that form a permanent magnet group. In the example shown in FIG. 4C, the shape of the asymmetric pole region 23 is asymmetric due to the difference in the shape of the hole 32.

[0046] 4D, the shape of the asymmetric pole region 23 may be asymmetric by making the shapes of the multiple permanent magnets 53, 54 that make up the permanent magnet group asymmetric. Alternatively, when one permanent magnet 4 is arranged in each pole region 2, the shape of the permanent magnet 4 may be asymmetric.

[0047] Furthermore, in each pole region 2, the permanent magnets may extend along the center line 20 of the pole region 2 so that the permanent magnets are arranged in a spoke shape. In this case, to make the shape of the asymmetric pole region 23 asymmetric, the positions or shapes of the holes or cutouts provided in the rotor core 3 may be made different, the shape of the flux barriers provided outside the permanent magnets in the radial direction of the rotor may be made asymmetric, or the shape of the permanent magnets themselves may be made asymmetric.

[0048] 5A shows an N-pole rotor 1C for an electric motor according to a third embodiment. In this embodiment, N=8, and the rotor 1C includes eight pole regions 2. In this embodiment, N permanent magnets 6 are arranged in the circumferential direction and held on the surface of the rotor core 3. These are so-called SPMs (Surface Permanent Magnets).

[0049] The polar region 2 includes four symmetrical polar regions 24 and four asymmetrical polar regions 25. The symmetrical polar regions 24 and the asymmetrical polar regions 25 are arranged alternately.

[0050] As in the first embodiment, the overall shape of the polar region 2 is rotationally symmetric about the rotation axis 10 and is line-symmetric with respect to a specific line passing through the rotation axis 10. In this embodiment, the overall shape of the polar region 2 is line-symmetric with respect to a horizontal line formed by a center line 20 extending leftward and a center line 20 extending rightward from the rotation axis 10 in Fig. 5A , and is line-symmetric with respect to a vertical line formed by a center line 20 extending upward and a center line 20 extending downward from the rotation axis 10 in Fig. 5A .

[0051] Each symmetrical pole region 24 has a shape symmetrical with respect to the center line 20 of the symmetrical pole region 24. Specifically, each symmetrical pole region 24 includes an arc-shaped symmetrical permanent magnet 61. The outer surface of the symmetrical permanent magnet 61 is smooth, and the symmetrical permanent magnet 61 has a shape symmetrical with respect to the center line 20 of the symmetrical pole region 24.

[0052] Each asymmetric pole region 25 has a shape that is asymmetric with respect to the center line 20 of the asymmetric pole region 25. In this embodiment, the asymmetric pole region 25 includes two asymmetric pole regions 25A and two asymmetric pole regions 25B. The asymmetric pole regions 25A and the asymmetric pole regions 25B are arranged alternately with the symmetric pole region 24 therebetween, and the shapes of the asymmetric pole regions 25A and 25B are opposite to each other.

[0053] Specifically, each asymmetric pole region 25A includes an arc-shaped asymmetric permanent magnet 62, and each asymmetric pole region 23B includes an arc-shaped asymmetric permanent magnet 63. As described above, the shape of the asymmetric pole region 25A is opposite to the shape of the asymmetric pole region 25B, and therefore, the shape of the asymmetric pole region 25B will be described below as a representative with reference to FIG.

[0054] The asymmetric permanent magnet 63 has a shape that is asymmetric with respect to the center line 20 of the asymmetric pole region 25B. In this embodiment, three notches 63a are provided on the outer surface of the asymmetric permanent magnet 63. One of the three notches 63a is located on one side of the center line 20 of the asymmetric pole region 25B, and the remaining two are located on the other side of the center line 20 of the asymmetric pole region 25B. The arrangement of the notches 63a makes the shape of the asymmetric pole region 25B asymmetric.

[0055] In this embodiment, as in the first embodiment, the eight pole regions 2 are configured so that the total amount of magnetic flux on the rotor surface of each pole region 2 is equal to one another. In this embodiment, since the permanent magnets 6 are held on the surface of the rotor core 3, the rotor surface is the surface of the permanent magnets 6.

[0056] In this embodiment, as in the first embodiment, the pole region 2 includes four asymmetric pole regions 25, so that torque ripple can be reduced by overlapping the torque waveforms. Moreover, because the overall shape of the pole region 2 is rotationally symmetric and axisymmetric, the torque characteristics do not change regardless of the direction in which the rotor 1C is rotated, and the occurrence of torque imbalance can also be suppressed.

[0057] Furthermore, in this embodiment, since the total amount of magnetic flux on the rotor surface of each pole area 2 is equal to each other, the difference in the attractive force acting between the stator core and each pole area 2 is reduced, thereby reducing vibration noise and torque imbalance.

[0058] <Modifications> The configuration for making the shape of the asymmetric pole region 25 asymmetric can be modified as appropriate. For example, only one notch may be provided on the outer surface of the asymmetric permanent magnet 62 or 63, positioned on one side or the other side of the center line 20 of the asymmetric pole region 25.

[0059] Alternatively, two notches may be provided on the outer surface of the asymmetric permanent magnet 62 or 63 so as to be the same distance from the center line 20 of the asymmetric polar region 25, and the shapes of these notches may be different.

[0060] 6A shows an N-pole rotor 1D for an electric motor according to a fourth embodiment. In this embodiment, the rotor 1D is a synchronous reluctance rotor, and the rotor core 3 includes N salient poles 7 arranged in the circumferential direction.

[0061] In this embodiment, N=4, and the rotor 1D includes four pole regions 2. In this embodiment, the angle lines 11 that separate the pole regions 2 are also the center lines of the salient poles 7. In other words, the four pole regions 2 are obtained by dividing the rotor core 3 into N equal parts by the center lines of the salient poles 7.

[0062] In this embodiment, each pole region 2 is provided with an arc-shaped flux barrier 71 that is convex toward the rotation axis 10. The flux barrier 71 may be an air gap or may be made of a non-magnetic material such as resin. The space between the ends of adjacent flux barriers 71 forms a salient pole 7. Each pole region 2 may be provided with a flux barrier group made up of a plurality of flux barriers 71 arranged concentrically.

[0063] In this embodiment, all of the polar regions 2 are asymmetric polar regions 26. As in the first embodiment, the overall shape of the polar regions 2 is rotationally symmetric about the rotation axis 10 and is line-symmetric with respect to a specific line passing through the rotation axis 10. In this embodiment, the overall shape of the polar regions 2 is line-symmetric with respect to a horizontal line formed by an angle line 11 extending leftward and an angle line 11 extending rightward from the rotation axis 10 in Fig. 6A , and is line-symmetric with respect to a vertical line formed by an angle line 11 extending upward and an angle line 11 extending downward from the rotation axis 10 in Fig. 6A .

[0064] Each asymmetric pole region 26 has a shape that is asymmetric with respect to the center line 20 of the asymmetric pole region 26. In this embodiment, the asymmetric pole region 26 includes two asymmetric pole regions 26A and two asymmetric pole regions 26B. The asymmetric pole regions 26A and the asymmetric pole regions 26B are arranged alternately, and the shapes of the asymmetric pole regions 26A and the asymmetric pole regions 26B are opposites. For this reason, the shape of the asymmetric pole region 26B will be described below as a representative with reference to FIG. 6B.

[0065] Two holes 72, 73 are provided in the rotor core 3 outside the flux barrier 71. The holes 72, 73 are located on both sides of the center line 20 of the asymmetric pole region 26B. The distance from the center line 20 of the asymmetric pole region 26B to the center of one hole 72 is the same as the distance from the center line 20 of the asymmetric pole region 26B to the center of the other hole 73, but the shapes of the holes 72, 73 are different from each other. The difference in the shapes of the holes 72, 73 makes the shape of the asymmetric pole region 26B asymmetric.

[0066] As in the first embodiment, the four pole regions 2 are configured so that the total amount of magnetic flux on the rotor surface of each pole region 2 is equal to one another.

[0067] In this embodiment, as in the first embodiment, the polar region 2 includes four asymmetric polar regions 26, so that torque ripple can be reduced by overlapping the torque waveforms. Moreover, because the overall shape of the polar region 2 is rotationally symmetric and axisymmetric, the torque characteristics do not change regardless of the direction in which the rotor 1D is rotated, and the occurrence of torque imbalance can also be suppressed.

[0068] Furthermore, in this embodiment, since the total amount of magnetic flux on the rotor surface of each pole area 2 is equal to each other, the difference in the attractive force acting between the stator core and each pole area 2 is reduced, thereby reducing vibration noise and torque imbalance.

[0069] <Modifications> The configuration for making the shape of the asymmetric pole region 26 asymmetric can be modified as appropriate. For example, the holes 72 and 73 may have the same shape, but the distances from the center line 20 of the asymmetric pole region 26 to the centers of the holes 72 and 73 may be different. Alternatively, one of the holes 72 and 73 may be omitted.

[0070] Alternatively, instead of the holes 72 and 73, two notches may be provided on the surface of the rotor core 3, and the positions or shapes of the notches may be different. Alternatively, neither the holes 72 and 73 nor the notches may be provided, and the shape of the flux barrier 71 may be asymmetric.

[0071] 7A shows an N-pole rotor 1E for an electric motor according to a fifth embodiment. In this embodiment, as in the fourth embodiment, the rotor 1E is a synchronous reluctance rotor, and the rotor core 3 includes N salient poles 7 arranged in the circumferential direction.

[0072] In this embodiment, N=4, and the rotor 1E includes four pole regions 2. In this embodiment, the angle lines 11 separating the pole regions 2 are also the center lines of the salient poles 7. In other words, the four pole regions 2 are obtained by dividing the rotor core 3 into N equal parts by the center lines of the salient poles 7.

[0073] In this embodiment, four grooves 74 are provided at equal angular intervals on the outer peripheral surface of the rotor core 3, and salient poles 7 are formed between these grooves 74.

[0074] In this embodiment, all of the polar regions 2 are asymmetric polar regions 27. As in the first embodiment, the overall shape of the polar regions 2 is rotationally symmetric about the rotation axis 10 and is line-symmetric with respect to a specific line passing through the rotation axis 10. In this embodiment, the overall shape of the polar regions 2 is line-symmetric with respect to a horizontal line formed by an angle line 11 extending leftward and an angle line 11 extending rightward from the rotation axis 10 in Fig. 7A , and is line-symmetric with respect to a vertical line formed by an angle line 11 extending upward and an angle line 11 extending downward from the rotation axis 10 in Fig. 7A .

[0075] Each asymmetric pole region 27 has a shape that is asymmetric with respect to the center line 20 of the asymmetric pole region 27. In this embodiment, the asymmetric pole region 27 includes two asymmetric pole regions 27A and two asymmetric pole regions 27B. The asymmetric pole regions 27A and the asymmetric pole regions 27B are alternately arranged, and the shapes of the asymmetric pole regions 27A and the asymmetric pole regions 27B are opposite to each other. For this reason, the shape of the asymmetric pole region 27B will be described below as a representative with reference to FIG. 7B.

[0076] The asymmetric pole region 27B has salient pole halves 7h, which are half of the salient pole 7, on both sides of the groove 74. Holes 75 and 76 are provided in both salient pole halves 7h. The distance from the center line 20 of the asymmetric pole region 27B to the center of one hole 75 is the same as the distance from the center line 20 of the asymmetric pole region 27B to the center of the other hole 76, but the shapes of the holes 75 and 76 are different. The difference in the shapes of the holes 75 and 76 makes the asymmetric pole region 27B asymmetric in shape.

[0077] As in the first embodiment, the four pole regions 2 are configured so that the total amount of magnetic flux on the rotor surface of each pole region 2 is equal to one another.

[0078] In this embodiment, as in the first embodiment, the pole region 2 includes four asymmetric pole regions 27, so that torque ripple can be reduced by overlapping the torque waveforms. Moreover, because the overall shape of the pole region 2 is rotationally symmetric and axisymmetric, the torque characteristics do not change regardless of the direction in which the rotor 1E is rotated, and the occurrence of torque imbalance can also be suppressed.

[0079] Furthermore, in this embodiment, since the total amount of magnetic flux on the rotor surface of each pole area 2 is equal to each other, the difference in the attractive force acting between the stator core and each pole area 2 is reduced, thereby reducing vibration noise and torque imbalance.

[0080] <Modifications> The configuration for making the shape of the asymmetric pole region 27 asymmetric can be modified as appropriate. For example, the holes 75 and 76 may have the same shape, but the distances from the center line 20 of the asymmetric pole region 26 to the centers of the holes 75 and 76 may be different. Alternatively, one of the holes 75 and 76 may be omitted.

[0081] Alternatively, notches may be provided in the tip surfaces of both salient pole halves 7h, with the positions or shapes of the notches being different, instead of the holes 75, 76. Alternatively, neither the holes 75, 76 nor the notches may be provided, and the shape of the bottom surface of the groove 74 or the salient pole halves 7h may be asymmetric.

[0082] Other Embodiments The present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the gist of the present disclosure.

[0083] For example, N is not limited to 4, 6, or 8 as described above, but may be 10 or more. In this case, the polar region 2 includes at least four asymmetric polar regions. Alternatively, the polar region 2 may include at least two symmetric polar regions.

[0084] Furthermore, if N is 6 or more, it is possible to provide three or more types of shapes for the polar regions 2, as in the first and third embodiments, thereby effectively reducing torque ripple. This is because torque waveforms have pulsations (ripples), and superimposing torque waveforms with different phases makes it possible to reduce the ripples.

[0085] <Summary> In a first aspect, the present disclosure provides a rotor for an electric motor having N poles (N is an even number greater than or equal to 3), the rotor comprising a plurality of pole regions divided into N equal parts around a rotation axis, the overall shapes of the plurality of pole regions being rotationally symmetric about the rotation axis and line-symmetric with respect to a specific line passing through the rotation axis, the plurality of pole regions including at least four asymmetric pole regions, each of which has an asymmetric shape with respect to a center line of the asymmetric pole region.

[0086] With the above configuration, the polar regions include at least four asymmetric polar regions, which allows torque waveforms to be overlapped to reduce torque ripple. Moreover, because the overall shape of the polar regions is rotationally symmetric and axisymmetric, the torque characteristics do not change regardless of the direction of rotor rotation, and torque imbalance can also be suppressed.

[0087] As a second aspect, in the first aspect, N may be 6 or more. With this configuration, it is possible to provide three or more types of polar region shapes, which makes it possible to effectively reduce torque ripple. This is because torque waveforms have pulsations (ripples), and superimposing torque waveforms with different phases makes it possible to reduce the ripples.

[0088] As a third aspect, in the second aspect, for example, the plurality of polar regions may include at least two symmetrical polar regions, each of which may have a shape symmetrical with respect to a center line of the symmetrical polar region.

[0089] As a fourth aspect, in any of the first to third aspects, for example, each of the plurality of pole regions may include a portion of a rotor core and at least one permanent magnet held on the surface or inside of the rotor core.

[0090] As a fifth aspect, in the fourth aspect, the at least one permanent magnet may be held inside the rotor core, and each of the at least four asymmetric polar regions may include at least one asymmetric permanent magnet that intersects with the center line of the asymmetric polar region, and the asymmetric permanent magnet may have a shape such that the angle from the center line of the asymmetric polar region to one end thereof about the rotation axis is different from the angle from the center line of the asymmetric polar region to the other end thereof about the rotation axis. The shape of the portion near the air gap has a significant impact on the phase of the torque waveform. Therefore, if the shape of the permanent magnet is made asymmetric by making the angle from the center line of the asymmetric polar region to both ends of the permanent magnet different, the torque ripple reduction effect is greater than if the shape of the permanent magnet is made asymmetric while the angle from the center line of the asymmetric polar region to both ends of the permanent magnet remains the same.

[0091] As a sixth aspect, in the fourth or fifth aspect, the plurality of pole regions may be configured so that the total amount of magnetic flux on the rotor surface of each pole region is equal to one another. With this configuration, it is possible to reduce the difference in attractive force acting between the stator core and each pole region, thereby reducing vibration noise and torque imbalance.

[0092] As a seventh aspect, in any of the first to third aspects, for example, the plurality of pole regions may be formed by dividing a rotor core including N salient poles arranged circumferentially into N equal parts along the center lines of the salient poles.

[0093] 1A, 1B, 1C, 1D, 1E Rotor 10 Rotating shaft 2 Pole area 21 Symmetrical pole area 22 Asymmetrical pole area 20 Center line 3 Rotor core 4 Permanent magnet 41 Symmetrical permanent magnet 42, 43, 44, 45, 46 Asymmetrical permanent magnet 45a, 46a One end 45b, 46b Other end 51, 52, 53, 54 Permanent magnet 6 Permanent magnet 61 Symmetrical permanent magnet 62, 63 Asymmetrical permanent magnet 7 Salient pole

Claims

1. A rotor for an electric motor with N poles (N is an even number greater than or equal to 4), comprising a plurality of pole regions divided into N equal parts around a rotation axis, the overall shapes of the plurality of pole regions being rotationally symmetric around the rotation axis and line symmetric with respect to a specific line passing through the rotation axis, the plurality of pole regions including at least four asymmetric pole regions, each of which has an asymmetric shape with respect to the center line of the asymmetric pole region.

2. A rotor for an electric motor as set forth in claim 1, wherein said N is 6 or more.

3. A rotor for an electric motor according to claim 2, wherein said plurality of pole areas includes at least two symmetrical pole areas, each of said symmetrical pole areas having a shape symmetrical with respect to a center line of said symmetrical pole area.

4. A rotor for an electric motor as claimed in any one of claims 1 to 3, wherein each of the plurality of pole regions includes a portion of a rotor core and at least one permanent magnet held on a surface of or inside the rotor core.

5. A rotor for an electric motor as described in claim 4, wherein the at least one permanent magnet is held inside the rotor core, each of the at least four asymmetric pole regions includes at least one asymmetric permanent magnet intersecting a center line of the asymmetric pole region, and the asymmetric permanent magnet has a shape such that an angle from the center line of the asymmetric pole region to one end thereof about the rotation axis is different from an angle from the center line of the asymmetric pole region to the other end thereof about the rotation axis.

6. A rotor for an electric motor according to claim 4, wherein said plurality of pole regions are configured so that the total amount of magnetic flux on the rotor surface of each pole region is equal to each other.

7. A rotor for an electric motor according to any one of claims 1 to 3, wherein the plurality of pole regions are defined by dividing a rotor core, which includes N salient poles arranged in the circumferential direction, into N equal parts by center lines of the salient poles.

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