Rotating Electric Machine

Abstract

To produce a rotary electric machine capable of reducing cogging torque during non-energization and reducing torque ripples during energization.SOLUTION: A stator core 31 has a plurality of teeth 401 having a body part 42 that extends in a direction of the radial inner side from a back yoke 41 which forms the periphery of a circle, and a flange 43 extending to both sides in a circumferential direction from the body part 42 at the tip of the body part 42, in the circumferential direction. The teeth 401 have a plurality of recessed grooves 441, 442 that sink toward the side of the back yoke 41 from one end in a rotation axis side to the other, formed on an apical surface of the body part 42. At a position corresponding to space between the recessed grooves 441, 442 adjoining each other in the circumferential direction, one or more flux reduction parts 45 which are composed of non-magnetic materials or space and reduce a magnetic flux passing through an inflow magnetic path 46 that is a magnetic path between the adjoining recessed grooves 441, 442 are provided.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a rotating electric machine. [Background technology]

[0002] 2. Description of the Related Art Conventionally, in a permanent magnet type rotating electric machine, a technique is known in which the cogging torque during non-energization is reduced by modifying the shape of the teeth of a stator core.

[0003] For example, the permanent magnet motor disclosed in Patent Document 1 has two pseudo slots for each tooth at the tip of the teeth. It is described that providing the pseudo slots has the effect of dispersing the spatial harmonics of the slots and shifting the frequency band of the cogging torque to a higher order. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2002-136001 A Summary of the Invention [Problem to be solved by the invention]

[0005] The motor of Patent Document 1 has a pseudo slot, which can reduce cogging torque when not energized, but has a problem that magnetic flux distortion when energized worsens and torque ripple increases. For example, when applied to a steering assist motor of an electric power steering device, torque ripple increases in the low to medium assist torque range, which may worsen the steering feeling for the driver.

[0006] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a rotating electric machine capable of reducing cogging torque when no current is applied and reducing torque ripple when current is applied. [Means for solving the problem]

[0007] In the rotating electric machine of the present invention, a stator (30) and a rotor (50) are arranged coaxially with respect to a rotating axis (O). The stator is formed by windings (35) wound around an annular stator core (31). The rotor is formed by attaching a plurality of magnets (55) along the outer periphery of a cylindrical rotor core (51), and rotates inside the stator due to a rotating magnetic field generated by passing current through the windings.

[0008] The stator core has a main body portion (42) extending radially inward from a back yoke portion (41) forming the outer edge of the ring, and a plurality of teeth (401-404) arranged circumferentially, the main body portion having flange portions (43) protruding from the main body portion on both circumferential sides at the tip thereof.

[0009] In one aspect of the present invention, The teeth are recessed toward the back yoke portion from one end to the other end in the rotation axis direction on the tip surface of the main body. two The recessed grooves (441, 442) are formed. two The groove may be formed parallel to the rotation axis, or may be inclined with respect to the rotation axis.

[0010] A non-magnetic material or space is formed at a position corresponding to a space between adjacent grooves in the circumferential direction, and a magnetic flux passing through an inflow magnetic path (46), which is a magnetic path between adjacent grooves, is reduced. one A magnetic flux reduction portion (45) is provided. The magnetic flux reduced portion is formed in an elliptical shape whose length in the circumferential direction of the tooth is longer than its length in the radial direction of the tooth. The "non-magnetic material" that constitutes the magnetic flux reduction portion includes non-magnetic metals such as resin and aluminum. The "space" includes holes that penetrate the plate in the thickness direction and depressions where the plate thickness is locally thin.

[0011] In the present invention, as in the conventional technique of Patent Document 1, the cogging torque when no current is applied is reduced by having a recessed groove. Also, the magnetic flux passing through the inflow magnetic path when current is applied is distorted by the recessed groove, but the magnetic flux reducing portion increases the magnetic resistance of the inflow magnetic path and reduces the magnetic flux passing through the inflow magnetic path, thereby reducing the torque ripple when current is applied. Therefore, for example, when applied to a steering assist motor of an electric power steering device, the torque ripple in the low to medium assist torque range can be reduced, improving the steering feeling for the driver. [Brief description of the drawings]

[0012] [Figure 1] 1 is a radial cross-sectional view of a motor (rotating electric machine) according to each embodiment. [Diagram 2] FIG. 2 is a plan view of a tooth according to the first embodiment. [Diagram 3] 3 is a view of a tip surface of a tooth according to the first embodiment, taken in the direction of an arrow III in FIG. 2. [Figure 4] 4A is a cross-sectional view taken along line IV-IV in FIG. 2 of a tooth according to the first embodiment, and FIG. 4B is a cross-sectional view of a tooth according to a modified example of the first embodiment. [Diagram 5] 6 is an enlarged view of a tip portion of a tooth, illustrating the shape of a magnetic flux reduction portion and an angle between recessed grooves. FIG. [Figure 6] FIG. 4 is an enlarged view of the tip of a tooth for explaining the relationship between the width of a magnetic path. [Figure 7] 1A and 1B are diagrams showing the tips of teeth of comparative example A and comparative example B, respectively. [Figure 8] FIG. 4 is a diagram comparing torque ripple characteristics with respect to line current between the first embodiment and a comparative example. [Figure 9] 8A is a graph comparing the cogging torque when no current is applied (part a in FIG. 8) and the torque ripple when current is applied (part b in FIG. 8) between the first embodiment and a comparative example. [Figure 10] FIG. 11 is a plan view of a tooth according to a second embodiment. [Figure 11] FIG. 11 is an enlarged view of a tip portion of a tooth according to a third embodiment. [Figure 12] FIG. 13 is an enlarged view of a tip portion of a tooth according to a fourth embodiment. [Figure 13]FIG. 13 is a diagram showing a teeth stage skew structure of a stator core according to the fifth embodiment. [Figure 14] FIG. 13 is a diagram showing a teeth linear skew structure of a stator core according to the sixth embodiment. [Figure 15] FIG. 13 is a diagram of a groove-stage skew structure of a stator core according to the seventh embodiment. [Figure 16] FIG. 13 is a diagram showing a groove linear skew structure of a stator core according to the eighth embodiment. [Figure 17] FIG. 13 is a diagram showing a magnet stage skew structure of a rotor core according to the ninth embodiment. [Figure 18] FIG. 23 is a diagram showing the magnet linear skew structure of the rotor core according to the tenth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, multiple embodiments of the rotating electric machine according to the present invention will be described with reference to the drawings. In multiple embodiments, substantially the same configurations are given the same reference numerals and the description will be omitted. The first to tenth embodiments are collectively referred to as "the present embodiment." The rotating electric machine of the present embodiment is a permanent magnet type three-phase brushless motor, and is applied to, for example, a steering assist motor of an electric power steering device. In the steering assist motor, it is required to reduce the pulsation of the output torque (hereinafter referred to as "torque ripple") in order to prevent deterioration of the steering feeling for the driver.

[0014] The radial cross-sectional configuration of motor 10 will be described with reference to FIG. 1. In FIG. 1, cross-sectional hatching is omitted for the stator core and rotor core. In motor 10, stator 30 and rotor 50 are arranged coaxially with respect to rotation axis O. In the following description, rotation axis O serves as the reference for the positional relationship of each part. "Rotation axis direction" refers to the direction perpendicular to the paper surface of FIG. 1. Angles indicating circumferential intervals and offsets are expressed as angles centered on rotation axis O.

[0015] The stator 30 is formed by winding three-phase windings 35 around an annular stator core 31 housed in a cylindrical housing 20. The rotor 50 is formed by attaching a plurality of magnets 55 (eight in this embodiment) along the outer periphery of a cylindrical rotor core 51. The magnets 55 are permanent magnets. Although Fig. 1 shows an IPM structure in which the magnets 55 are embedded in the rotor core 51, an SPM structure in which the magnets 55 are provided on the surface of the rotor core 51 may also be used.

[0016] Rotor 50 rotates inside stator 30 due to a rotating magnetic field generated by energizing windings 35. Shaft 59 is fixed to the center of rotor 50, and both axial ends of shaft 59 are supported by bearings (not shown). Torque of motor 10 is output from one end of shaft 59 to a load via a transmission mechanism.

[0017] The stator core 31 and the rotor core 51 are made of iron. The stator core 31 and the rotor core 51 may be formed by stacking a plurality of thin plates such as electromagnetic steel plates in the axial direction, or may be formed integrally.

[0018] The stator core 31 shown in Fig. 1 is configured as a divided stator core in which a back yoke portion 41 forming the outer edge of a ring is divided into 12 portions in the circumferential direction. However, it may be configured as an annular stator core in which the back yoke portion is integrally formed over the entire circumference. The stator core 31 is provided with a plurality of teeth 401 (12 in this embodiment) in the circumferential direction. Fig. 1 shows the shape of the teeth 401 in the first embodiment as a representative example.

[0019] The teeth 401 have a main body portion 42 and a flange portion 43. The main body portion 42 extends radially inward from the back yoke portion 41. The flange portion 43 protrudes from the main body portion 42 at its tip on both circumferential sides. The tip surface of the main body portion 42 faces the outer circumferential surface of the rotor 50, and magnetic flux of the magnets 55 flows into the main body portion 42. The space between the main body portions 42 of the teeth 401 adjacent in the circumferential direction forms a slot in which the winding 35 is housed. The radial range of the slot is restricted on the outside by the back yoke portion 41 and on the inside by the flange portion 43. The number of slots is equal to the number of teeth 401, which is 12 in this embodiment.

[0020] Here, the number of magnets 55 of the rotor 50 (in other words, the number of magnetic poles) is represented by P, and the number of teeth of the stator 30 (in other words, the number of slots) is represented by S. In this embodiment, the number of magnets P is 8, and the number of teeth S is 12, so it is expressed as "8P12S". If the least common multiple of the number of magnets P and the number of teeth S is k, then the least common multiple k in this configuration is 24. In other words, while the rotor 50 rotates once, there are 24 times when any of the magnets 55 directly faces the center of the tip surface of any of the teeth 401. Therefore, the 24th mechanical angle component of the cogging torque when no current is applied is prominent.

[0021] Conventionally, Patent Document 1 (JP Patent Publication 2002-136001A) discloses a configuration in which pseudo slots are provided on the tip faces of teeth in order to reduce cogging torque. In this conventional technology, the pseudo slots can reduce cogging torque when no current is applied, but there is a problem in that magnetic flux distortion worsens when current is applied, resulting in large torque ripple.

[0022] Therefore, in this embodiment, an object is to provide a rotating electric machine that can reduce the cogging torque when not energized and the torque ripple when energized. To achieve this, a unique configuration is provided mainly for the teeth of the stator core 31. The configuration of the teeth, etc. in each embodiment will be explained in order below. The reference numerals for the teeth in each embodiment are numbered with the embodiment number as the third digit following "40".

[0023] (First embodiment) The configuration and effects of the first embodiment will be described with reference to Fig. 2 to Fig. 9. As shown in Fig. 2, the stator core 31 is divided into 12 parts, and the central angle between both ends of the back yoke portion 41 in the circumferential direction is 30°. In each cross section perpendicular to the rotation axis O, the teeth 401 are formed symmetrically with respect to an axis of symmetry V passing through the rotation axis O. Expressed three-dimensionally, the teeth 401 are formed symmetrically with respect to an imaginary plane including the rotation axis O. Fig. 3 shows the tip surface of the teeth 401 formed of a thin plate laminated structure.

[0024] Two grooves 441, 442 recessed toward the back yoke 41 are formed in the tip surface of the main body 42. The grooves 441, 442 correspond to the pseudo slots of Patent Document 1. In the first embodiment, the two grooves 441, 442 are arranged symmetrically with respect to the symmetry axis V of the tooth 401 and formed parallel to each other. Therefore, the two grooves 441, 442 are arranged on either side of the symmetry axis V. As shown in FIG. 3, the grooves 441, 442 in the first embodiment are formed parallel to the rotation axis O from one end to the other end in the rotation axis direction. It is self-evident that the two grooves 441, 442 are adjacent to each other in the circumferential direction.

[0025] A magnetic path formed between the two grooves 441, 442 along the tip end surface of the main body 42 is defined as an inflow magnetic path 46. When the magnet 55 of the rotor 50 faces the center of the tip end surface of the tooth 401, the magnetic flux of the magnet 55 flows into the main body 42 mainly through the inflow magnetic path 46. In addition, a magnetic path between the corner of the grooves 441, 442 on the side away from the axis of symmetry V and the circumferential end of the flange 43 is defined as an outer inflow magnetic path 49. The magnetic flux of the magnet 55 flows into the main body 42 through the outer inflow magnetic path 49 at a position where the magnet 55 of the rotor 50 faces the center of the tip end surface of the tooth 401, that is, at a position slightly away from the position where the cogging torque peaks.

[0026] One magnetic flux reduction portion 45 that reduces the magnetic flux passing through the inflow magnetic path 46 is provided at a position corresponding to the gap between the recessed grooves 441, 442. In this example, the "position corresponding to the gap between the recessed grooves 441, 442" refers to a circumferential position between the portions of the recessed grooves 441, 442 extended toward the back yoke portion 41. In the first embodiment, one magnetic flux reduction portion 45 is disposed symmetrically with respect to the axis of symmetry V of the tooth 401. Therefore, one magnetic flux reduction portion 45 is disposed such that its center is located on the axis of symmetry V.

[0027] As shown in FIG. 4(a), the magnetic flux reduction portion 45 of the first embodiment is formed of a "hole" penetrating in the plate thickness direction. Alternatively, as shown in a modified example in FIG. 4(b), the magnetic flux reduction portion 45 may be formed of a "recess" in which the plate thickness is locally thinned by a method such as crimping or crushing. The holes and recesses are collectively referred to as "space." A space filled with air, which has a low magnetic permeability, functions as the magnetic flux reduction portion 45. In addition, as described later in the "Other embodiments" section, the magnetic flux reduction portion 45 may be formed by filling the holes and recesses with a non-magnetic material such as resin or aluminum.

[0028] In this way, the motor 10 of this embodiment reduces the cogging torque when no current is applied by having the recessed grooves 441, 442, as in the conventional technology of Patent Document 1. Also, although the magnetic flux passing through the inflow magnetic path 46 when current is applied is distorted by the recessed grooves 441, 442, the magnetic flux reducer 45 increases the magnetic resistance of the inflow magnetic path 46 and reduces the magnetic flux passing through the inflow magnetic path 46, thereby reducing the torque ripple when current is applied.

[0029] The tooth 401 of the first embodiment can achieve a simple configuration by having two grooves 441, 442 and one magnetic flux reduction portion 45. Moreover, the grooves 441, 442 and the magnetic flux reduction portion 45 are arranged symmetrically with respect to the axis of symmetry V of the tooth 401, eliminating differences in characteristics such as torque ripple depending on the direction of rotation. Furthermore, the grooves 441, 442 are formed parallel to the axis of symmetry V of the tooth 401, making manufacturing easy.

[0030] 5 and 6, more preferable shapes of the recessed grooves 441, 442 and the magnetic flux reducing portion 45 will be described. As shown in Fig. 5, the magnetic flux reducing portion 45 is formed in an elliptical shape in which the length Da in the circumferential direction of the tooth 401 is longer than the length Db in the radial direction of the tooth 401. From the viewpoint of making the teeth 401 less susceptible to magnetic saturation, it is preferable to minimize the area of ​​the magnetic flux reducing portion 45 and ensure that the iron main body portion 42 is as large as possible.

[0031] Furthermore, the longer the circumferential length Da of the teeth 401, the more the magnetic flux from the inflow magnetic path 46 toward the back yoke portion 41 will detour from the front of the magnetic flux reduction portion 45 to both sides, increasing the magnetic resistance. Therefore, by making the circumferential length Da of the teeth 401 longer than the radial length Db, the magnetic flux passing through the inflow magnetic path 46 can be further restricted while minimizing the reduction in the total magnetic flux amount, and the torque ripple when current is applied can be further reduced.

[0032] The angle between the circumferential centers of the two grooves 441, 442, centered on the rotation axis O, is referred to as the groove-to-groove angle θg. In a configuration in which the number of teeth 401 is 12 and the central angle of each tooth 401 is 30°, the groove-to-groove angle θg is set to be "7°<θg<9°". This maximizes the torque ripple reduction effect.

[0033] 6, two magnetic paths extending from the inflow magnetic path 46 toward the back yoke portion 41 via both sides of the magnetic flux reduced portion 45 are designated as a first outflow magnetic path 471 and a second outflow magnetic path 472. The sum (G1+G2) of the width G1 of the first outflow magnetic path 471 and the width G2 of the first outflow magnetic path 471 is configured to be smaller than the width F of the inflow magnetic path 46. This limits the magnetic flux passing through the inflow magnetic path 46 to less than the sum of the magnetic flux passing through the first outflow magnetic path 471 and the second outflow magnetic path 472. Therefore, the torque ripple during current flow can be further reduced.

[0034] Moreover, the width F of the inflow magnetic path 46 is formed shorter than the width E of the outer inflow magnetic path 49. Here, since the teeth 401 are symmetrical with respect to the symmetry axis V, the widths E of both outer inflow magnetic paths 49 are equal. The presence of the magnetic flux reduction portion 45 reduces the total amount of magnetic flux from the magnet 55 of the rotor 50 to the stator 30, and the motor output decreases. If the width F of the inflow magnetic path 46 is made longer than the width E of the outer inflow magnetic path 49, the magnetic flux reduction portion 45 needs to be made larger in order to reduce the magnetic flux passing through the inflow magnetic path 46, and the motor output decreases significantly. However, by making the width F of the inflow magnetic path 46 shorter than the width E of the outer inflow magnetic path 49, the effect of the magnetic flux reduction portion 45 is concentrated only on the inflow magnetic path 46. This makes it possible to reduce torque ripple during energization while suppressing a decrease in motor output.

[0035] Next, with reference to Figs. 7 to 9, the verification results of the effects of the first embodiment will be described in comparison with teeth of two comparative examples. Tooth 409a of comparative example A shown in Fig. 7(a) has no groove at the tip of main body portion 42. Tooth 409b of comparative example B shown in Fig. 7(b) has two grooves 441, 442 at the tip of main body portion 42, but has no magnetic flux reduction portion. Comparative example B corresponds to the prior art disclosed in Patent Document 1.

[0036] FIG. 8 shows torque ripple characteristics versus line current (effective value) of motor 10. Numerical values ​​other than 0 are omitted on the horizontal and vertical axes. In the steering assist motor of an electric power steering device, the region where the line current is less than the boundary value Ix corresponds to the low to medium assist torque region, and the region where the line current is equal to or greater than the boundary value Ix corresponds to the high assist torque region. In the first embodiment and comparative example A, the torque ripple increases almost monotonically as the line current increases, and is maximum in the high assist torque region. On the other hand, in comparative example B, the torque ripple is maximum in the low to medium assist torque region. The maximum torque ripple value of comparative example B is greater than the maximum torque ripple value of the first embodiment and comparative example A in the high assist torque region.

[0037] FIG. 9(a) shows the cogging torque when no current is applied (part a in FIG. 8). FIG. 9(b) shows the torque ripple when current is applied in the low to medium assist torque region (part b in FIG. 8). Numerical values ​​other than 0 on the vertical axis are omitted. The difference from the positive peak to the negative peak of each waveform is the cogging torque and torque ripple. In a 12-slot three-phase motor, an electrical angle of 360° corresponds to a mechanical angle of 90°. Therefore, one scale mark on the horizontal axis, which is a period of 60° of the 6th electrical angle component, corresponds to a period of 15° of the 24th mechanical angle component.

[0038] 9(a), the 24th-order cogging torque is large in Comparative Example A having no grooves, whereas the 24th-order cogging torque is reduced in Comparative Example B having grooves 441 and 442. Furthermore, in the first embodiment, the 24th-order cogging torque is smaller than that in Comparative Example B. Thus, in the first embodiment, it was verified that the effect of grooves 441 and 442 reduces the cogging torque when no current is applied.

[0039] As shown in FIG. 9(b), in Comparative Example B, the magnetic flux distortion is aggravated by the grooves 441 and 442 when current is applied, so that the 24th-order torque ripple becomes large. In contrast, in the first embodiment, the 24th-order cogging torque is small, similar to that of Comparative Example A. In this way, in the first embodiment, it was verified that the torque ripple when current is applied is reduced due to the effect of the magnetic flux reducer 45. Therefore, when the configuration of the first embodiment is applied to a steering assist motor of an electric power steering device, the torque ripple in the low to medium assist torque range can be reduced, and the steering feeling for the driver can be improved.

[0040] Incidentally, the brushless motor disclosed in JP 2015-192592 A has holes formed at the inner periphery of the teeth and notches formed at the inner periphery of the teeth. It is described that this can simultaneously achieve high assist torque, low cogging torque and torque pulsation, and low vibration of the motor in a wide range of rotation speeds including the field-weakening region. However, this configuration has a problem in that the notches are on both sides of the teeth main body, so that the repeated fatigue strength against the radial electromagnetic attraction force acting on the tip flange is low. In contrast, in the first embodiment, the grooves 441 and 442 are formed on the wire end surface of the main body 42, so that the repeated fatigue strength is high.

[0041] Second embodiment The configuration of the tooth 402 of the second embodiment will be described with reference to Fig. 10. In the second embodiment, the two grooves 441, 442 are not parallel to the symmetrical axis V of the tooth 402, but are formed radially around the rotation axis O. For ease of understanding, the grooves 441, 442 are shown deep in Fig. 10. This makes it possible to reduce the width F of the inflow magnetic path 46 while maintaining the dimensions of the magnetic flux reduction portion 45 and the outflow magnetic paths 471, 472 in Fig. 6. This makes it possible to further restrict the magnetic flux passing through the inflow magnetic path 46, and further reduce the torque ripple when current is applied.

[0042] Third embodiment The configuration of teeth 403 in the third embodiment will be described with reference to Fig. 11. In the third embodiment, the length Da of magnetic flux reduced portion 45 in the circumferential direction of teeth 403 is formed to be longer than the width F of inflow magnetic path 46. As a result, magnetic flux from inflow magnetic path 46 toward back yoke portion 41 largely detours from the front of magnetic flux reduced portion 45 to both sides as indicated by dashed arrow Φ, resulting in increased magnetic resistance. Therefore, the magnetic flux passing through inflow magnetic path 46 can be further restricted, and torque ripple during current flow can be further reduced.

[0043] (Fourth embodiment) The number of grooves formed in the teeth and the number of magnetic flux reduction portions provided are not limited to those in the first to third embodiments. In other words, the teeth may have two or more grooves and a total of two or more magnetic flux reduction portions, each of which is provided corresponding to an inflow magnetic path between circumferentially adjacent grooves. The configuration of the teeth 404 of the fourth embodiment, which has a different number of grooves and magnetic flux reduction portions, will be described with reference to Fig. 12. The teeth 404 of the fourth embodiment have four grooves 445-448 and four magnetic flux reduction portions 455-458.

[0044] At the tip end of the tooth 404, a first groove 445, a second groove 446, a third groove 447, and a fourth groove 448 are formed symmetrically with respect to an axis of symmetry V, in that order from one side in the circumferential direction (the left side in FIG. 12) to the other side (the right side in the same figure). The second groove 446 and the third groove 447 closer to the axis of symmetry V are relatively deep, and the first groove 445 and the fourth groove 448 farther from the axis of symmetry V are relatively shallow.

[0045] The first magnetic flux reduced portion 455 is provided in correspondence with the first inflow magnetic path 461 between the first groove 445 and the second groove 446. The second magnetic flux reduced portion 456 and the third magnetic flux reduced portion 457 are provided in correspondence with the second inflow magnetic path 462 between the second groove 446 and the third groove 447. The fourth magnetic flux reduced portion 458 is provided in correspondence with the third inflow magnetic path 463 between the third groove 447 and the fourth groove 448. The second magnetic flux reduced portion 456 and the third magnetic flux reduced portion 457 are relatively large circular shapes. The first magnetic flux reduced portion 455 and the fourth magnetic flux reduced portion 458 are relatively small circular shapes.

[0046] The magnetic paths from the first inflow magnetic path 461 toward the back yoke part 41 via both sides of the first magnetic flux reduced part 455 are defined as a first outflow magnetic path 481 and a second outflow magnetic path 482. The magnetic paths from the second inflow magnetic path 462 toward the back yoke part 41 via the second groove 446 side of the second magnetic flux reduced part 456, between the second magnetic flux reduced part 456 and the third magnetic flux reduced part 457, and the third groove 447 side of the third magnetic flux reduced part 457 are defined as a third outflow magnetic path 483, a fourth outflow magnetic path 484, and a fifth outflow magnetic path 485, respectively. The magnetic paths from the third inflow magnetic path 463 toward the back yoke part 41 via both sides of the fourth magnetic flux reduced part 458 are defined as a sixth outflow magnetic path 486 and a second outflow magnetic path 487.

[0047] The widths of the first, second, and third inflow magnetic paths 461, 462, and 463 are F1, F2, and F3, respectively. The widths of the first, second, third, fourth, fifth, sixth, and seventh outflow magnetic paths 481, 482, 483, 484, 485, 486, and 487 are H1, H2, H3, H4, H5, H6, and H7, respectively. The total width (H1+H2+H3+H4+H5+H6+H7) of the seven outflow magnetic paths 481-487 is smaller than the total width (F1+F2+F3) of the three inflow magnetic paths 461-463. The effect is the same as that of the first embodiment.

[0048] In the fourth embodiment, as in the second embodiment, the four grooves 445-448 may be formed radially. Furthermore, the number and arrangement of the grooves and magnetic flux reduction portions may be appropriately set according to required characteristics, ease of manufacture, and the like.

[0049] [Skew structure] 13 to 18 show fifth to tenth embodiments in which a skewed structure is adopted for the purpose of reducing cogging torque. In general, a skewed structure is a twisted structure in which the magnetic resistance between the stator 30 and the rotor 50 is shifted in sequence according to the position in the direction of the rotation axis. In each of the fifth to tenth embodiments, the entire teeth, only the grooves in the teeth, or the magnets of the rotor are skewed. Note that the reference symbols for the stator core, teeth, or rotor core used only in the embodiments of the skewed structure will not be described as reference symbols in the claims.

[0050] The skew structure includes a step-skew structure and a linear skew structure. In the step-skew structure, multiple steps are stacked so that the circumferential distribution of magnetic resistance is shifted stepwise in a predetermined direction. The number of steps in the step-skew structure is represented by n (n≧2). An example of three steps (n=3) is shown in FIG. 13, FIG. 15, and FIG. 17. In this specification, a unit of one step that constitutes a stator core of the step-skew structure is called a "sub-stator core". Similarly, a unit of one step that constitutes a rotor core of the step-skew structure is called a "sub-rotor core". In the linear skew structure, the circumferential distribution of magnetic resistance is configured to be continuously shifted from one end to the other end in the rotation axis direction. Note that in FIG. 13 to FIG. 18, illustration of the thin plate stacking structure as shown in FIG. 3 and FIG. 4 is omitted.

[0051] In each embodiment, an 8P12S configuration is assumed in which the number of magnets P of the rotor 50 is 8 and the number of teeth S is 12, and the aim is to reduce at least the 24th order component of the cogging torque, which corresponds to the least common multiple k of 8 and 12. Note that in addition to the 24th order component, it is also possible to aim to reduce the 8th order component and the 12th order component as well. In general, each embodiment aims to reduce at least the kth order component of the cogging torque, which corresponds to the least common multiple of the number of magnets P and the number of teeth S of the rotor 50. The theoretical angle that minimizes the kth order component of the cogging torque is calculated using the formula described below.

[0052] However, there is a trade-off in that the larger the skew angle, the lower the output torque when current is applied. Therefore, it is preferable that the skew angle in each embodiment is configured to be in the range of "greater than 0 and equal to or less than the theoretical angle" so as not to exceed the theoretical angle that minimizes the cogging torque of the kth order component. Note that the "greater than 0" part is self-explanatory and will be omitted as appropriate. In each embodiment, the cogging torque is appropriately reduced by combining with the effect of the recessed grooves 441 and 442.

[0053] (Fifth and Sixth Embodiments) The fifth and sixth embodiments will be described with reference to Figs. 13 and 14. In the fifth and sixth embodiments, the teeth of the stator core are all configured in a skew structure. The fifth embodiment shown in Fig. 13 has a multi-stage (three stages in this example) stage skew structure. The sixth embodiment shown in Fig. 14 has a linear skew structure.

[0054] A stator core 315 of the fifth embodiment has three stacked sub-stator cores 3151, 3152, 3153, each having grooves 441, 442 extending parallel to the rotation axis O. The teeth 405 of each stage are formed symmetrically with respect to the axis of symmetry V, and are similar to the configuration of the teeth 401 of the first embodiment. The positions of the grooves 441, 442 in the teeth 405 of each stage are constant, and the circumferential positions of the grooves 441, 442 are shifted in a predetermined direction depending on the position of each stage.

[0055] A groove-stage skew angle θsd between adjacent grooves 441, 442 about the rotation axis O is set to be within the range of the following formula. In FIG. 13, an angle indication line is drawn at the midpoint between the two grooves 441, 442. 0<θsd≦360°÷k÷n

[0056] When the cogging torque of the 24th order component is to be reduced, the groove step skew angle θsd is 5° or less in a three-step skew structure. Note that in a two-step skew structure, the groove step skew angle θsd is 7.5° or less.

[0057] The stator core 315 of the sixth embodiment has a linear skew structure in which the grooves 441, 442 of the teeth 406 are inclined at a certain angle with respect to the rotation axis O. The shape of the tip end surface of the teeth 406 when viewed from the rotation axis O side is a parallelogram.

[0058] In this case, as a three-dimensional shape, the teeth 406 are not symmetrical with respect to a certain plane. However, in each cross section perpendicular to the rotation axis O, the teeth 406 are formed symmetrical with respect to an axis of symmetry V passing through the rotation axis O. Also, the grooves 441, 442 and the magnetic flux reduction portions 45 are arranged symmetrical with respect to the axis of symmetry V of the teeth 406 in each cross section perpendicular to the rotation axis O. In each cross section perpendicular to the rotation axis O, the width F of the inflow magnetic path 46 is formed shorter than the width E of the outer inflow magnetic path 49, similarly to the first embodiment.

[0059] A linear skew angle θsL between one end and the other end of the grooves 441, 442 about the rotation axis O is set to be within the range of the following formula. In FIG. 14, an angle indication line is drawn at the midpoint between the two grooves 441, 442. 0<θsL≦360°÷k

[0060] When the cogging torque of the 24th order component is to be reduced, the groove linear skew angle θsL is 15° or less.

[0061] (Seventh and Eighth Embodiments) The seventh and eighth embodiments will be described with reference to Fig. 15 and Fig. 16. In the seventh and eighth embodiments, only the recessed grooves 441, 442 at the tips of the teeth of the stator core are configured with a skew structure. The seventh embodiment shown in Fig. 15 has a multi-stage (three stages in this example) stage skew structure. The eighth embodiment shown in Fig. 16 has a linear skew structure.

[0062] In the stator core 317 of the seventh embodiment, sub-stator cores 3171, 3172, 3173, each having grooves 441, 442 extending parallel to the rotation axis O, are stacked in three stages. The teeth 4071, 4072, 4073 of each stage are all disposed at the same circumferential position, and only the positions of the grooves 441, 442 in each tooth 4071, 4072, 4073 are shifted. Therefore, the circumferential positions of the grooves 441, 442 are shifted in a predetermined direction depending on the position of each stage.

[0063] The groove-stage skew angle θsd between the grooves 441, 442 of adjacent stages about the rotation axis O is configured to be within the range of the following formula, as in the fifth embodiment. In FIG. 15, an angle indication line is drawn at the midpoint between the two grooves 441, 442. 0<θsd≦360°÷k÷n

[0064] A stator core 318 of the eighth embodiment has a linear skew structure in which recessed grooves 441, 442 of teeth 408 are inclined at a certain angle with respect to the rotation axis O. The teeth 408 themselves are not skewed, but are rectangular when viewed from the rotation axis O side.

[0065] The linear skew angle θsL between one end and the other end of the grooves 441, 442 about the rotation axis O is set to be within the range of the following formula, as in the sixth embodiment. In FIG. 16, an angle indication line is drawn at the midpoint between the two grooves 441, 442. 0<θsL≦360°÷k

[0066] (Ninth and Tenth Embodiments) The ninth and tenth embodiments will be described with reference to Figs. 17 and 18, which are partial developments of the outer circumferential surface of rotor 50 as viewed from the radially outer side. In the ninth and tenth embodiments, the magnets of the rotor core are configured in a skewed structure. The ninth embodiment shown in Fig. 17 has a multi-stage (three stages in this example) stage skewed structure. The tenth embodiment shown in Fig. 18 has a linear skewed structure.

[0067] A rotor core 519 of the ninth embodiment has three stacked sub-rotor cores 5191, 5192, 5193, in which magnets 55 extend parallel to the rotation axis O. The circumferential positions of the magnets 55 are shifted in a predetermined direction depending on the position of each stage. The magnet stage skew angle ψsd between magnets 55 of adjacent stages about the rotation axis O is configured to be within the range of the following formula. Examples of the stage skew angle are the same as those of the fifth and seventh embodiments. 0<ψsd≦360°÷k÷n

[0068] The rotor core 520 of the tenth embodiment has a linear skew structure in which the magnets 55 are inclined at a certain angle with respect to the rotation axis O. The magnet linear skew angle ψsL between one end and the other end of the magnet 55 with the rotation axis O as the center is configured to be within the range of the following formula. Examples of the linear skew angle are the same as those of the sixth and eighth embodiments. 0<ψsL≦360°÷k

[0069] (Other embodiments) (a) The number P of magnets in the rotor 50 and the number S of teeth in the stator 30 may be a "2:3" combination such as 4P6S, 6P9S, etc., other than 8P12S in the above embodiment. Also, combinations other than "2:3" such as 10P12S may be used.

[0070] (b) The shape of the magnetic flux reduction portion 45 is not limited to an oval or a circle, and may be any shape. Furthermore, the magnetic flux reduction portion 45 is not limited to a space such as a hole or a depression, and may be made of a non-magnetic material having a smaller magnetic permeability than iron. Non-magnetic materials include non-magnetic metals such as resin and aluminum. For example, by making the magnetic flux reduction portion 45 out of a non-magnetic material filled in the hole or depression, the effect of reducing the magnetic flux passing through the inflow magnetic path 46 is further enhanced.

[0071] (c) The rotating electric machine of the present invention is not limited to being used as a steering assist motor in an electric power steering device, and may be used as a motor or generator for any application in which reduction of cogging torque or torque ripple is required.

[0072] The present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit of the present invention. [Explanation of symbols]

[0073] 10 Motor (rotating electric machine), 30 stator, 31 stator core, 35 winding, 401-404... Teeth, 41 back yoke portion, 42 main body portion, 43 flange portion, 441, 442, 445-448... groove, 45, 455-458 ···Magnetic flux reduction section, 46, 461-463...inflow magnetic path, 50 rotor, 51 rotor core, 55 magnet.

Claims

1. A rotating electric machine in which a stator (30) formed by windings (35) wound around an annular stator core (31) and a rotor (50) formed by attaching a plurality of magnets (55) along the outer periphery of a cylindrical rotor core (51) and rotating inside the stator by a rotating magnetic field generated by passing current through the windings are arranged coaxially with a rotation axis (O), The stator core is provided with a plurality of teeth (401-403) in a circumferential direction, the teeth (401-403) having a main body portion (42) extending radially inward from a back yoke portion (41) forming an outer edge of a ring, and flange portions (43) protruding from the main body portion on both sides in the circumferential direction at the tip of the main body portion, The teeth are Two grooves (441, 442) are formed on the tip surface of the main body, the grooves being recessed toward the back yoke portion from one end to the other end in the rotation axis direction, a magnetic flux reducing portion (45) is provided at a position corresponding to a space between adjacent grooves in the circumferential direction, the magnetic flux reducing portion (45) being made of a non-magnetic material or space and reducing a magnetic flux passing through an inflow magnetic path (46) which is a magnetic path between the adjacent grooves; The magnetic flux reduction portion is formed in an elliptical shape whose length in a circumferential direction of the teeth is longer than the length in a radial direction of the teeth.

2. The rotating electric machine according to claim 1 , wherein a length of the magnetic flux reduced portion in a circumferential direction of the tooth is longer than a width of the inflow magnetic path (46).

3. 3. The rotating electric machine according to claim 1, wherein the sum of the widths of two outflow magnetic paths (471, 472), which are magnetic paths that run from the inflow magnetic path through both sides of the magnetic flux reduction section toward the back yoke section, is configured to be smaller than the width of the inflow magnetic path.

4. If an inter-groove angle, which is an angle between the circumferential centers of the two grooves with the rotation axis as the center, is θg, when the number of teeth is 12, the inter-groove angle is expressed as follows: 7°<θg<9° 4. The rotating electric machine according to claim 1, wherein the rotating electric machine is configured as follows:

5. A rotating electric machine in which a stator (30) formed by windings (35) wound around an annular stator core (31) and a rotor (50) formed by attaching a plurality of magnets (55) along the outer periphery of a cylindrical rotor core (51) and rotating inside the stator by a rotating magnetic field generated by passing current through the windings are arranged coaxially with a rotation axis (O), The stator core is provided with a plurality of teeth (404) in a circumferential direction, the teeth (404) having a main body portion (42) extending radially inward from a back yoke portion (41) forming an outer edge of a ring, and flange portions (43) protruding from the main body portion on both sides in the circumferential direction at the tip of the main body portion, The teeth are A plurality of grooves (445-448) recessed toward the back yoke portion from one end to the other end in the rotation axis direction are formed on the tip surface of the main body, At positions corresponding to the spaces between the circumferentially adjacent grooves, a total of two or more magnetic flux reducing portions (455-458) are provided corresponding to the inflow magnetic paths (461-463) that are made of a non-magnetic material or space and reduce the magnetic flux passing through the inflow magnetic paths (461-463) that are magnetic paths between the adjacent grooves, and one or more magnetic flux reducing portions are provided corresponding to the inflow magnetic paths, The magnetic flux reduction portion of the rotating electric machine is formed in a circular shape.

6. The teeth are Four grooves, namely, a first groove (445), a second groove (446), a third groove (447) and a fourth groove (448), arranged in order in the circumferential direction; the magnetic flux reducing portion including four magnetic flux reducing portions, the first magnetic flux reducing portion (455) being provided corresponding to the inflow magnetic path (461) between the first groove and the second groove, the second magnetic flux reducing portion (456) and the third magnetic flux reducing portion (457) being provided corresponding to the inflow magnetic path (462) between the second groove and the third groove, and the fourth magnetic flux reducing portion (458) being provided corresponding to the inflow magnetic path (463) between the third groove and the fourth groove, 6. The rotating electric machine according to claim 5, wherein the total width of a plurality of outflow magnetic paths (481-487), which are magnetic paths extending from each of the inflow magnetic paths toward the back yoke portion via both sides of the corresponding magnetic flux reduction portion, is configured to be smaller than the total width of the plurality of inflow magnetic paths.

7. The teeth are formed symmetrically with respect to an axis of symmetry (V) passing through the rotation axis in each cross section perpendicular to the rotation axis, A rotating electric machine as described in any one of claims 1 to 6, wherein the plurality of grooves and one or more of the magnetic flux reduction portions are arranged symmetrically with respect to the axis of symmetry of the teeth in each cross section perpendicular to the rotation axis.

8. The teeth have two of the grooves (441, 442), A rotating electric machine as described in claim 7, wherein in each cross section perpendicular to the rotation axis, the width of the inflow magnetic path (46) between the two grooves is formed shorter than the width of the magnetic path (49) between the corner of the groove away from the axis of symmetry and the circumferential end of the flange portion.

9. the stator core has a plurality of sub-stator cores, each sub-stator core having a groove extending parallel to the rotation shaft, stacked in a plurality of stages, and has an n-stage (n≧2) stage skew structure in which the circumferential positions of the grooves are shifted in a predetermined direction depending on the position of each stage, Let k be the least common multiple of the number of magnets and the number of teeth of the rotor, and θ be the groove-stage skew angle between the grooves of adjacent stages about the rotation axis, 0<θsd≦360°÷k÷n 9. The rotating electric machine according to claim 1, wherein the rotating electric machine is configured as follows:

10. The stator core has a linear skew structure in which the groove is inclined at a certain angle with respect to the rotation axis, Let k be the least common multiple of the number of the magnets and the number of the teeth of the rotor, and θsL be the linear skew angle of the groove between one end and the other end of the groove about the rotation axis, 0<θsL≦360°÷k 9. The rotating electric machine according to claim 1, wherein the rotating electric machine is configured as follows:

11. the rotor core has a plurality of sub-rotor cores, each sub-rotor core having a magnet extending parallel to the rotation shaft, stacked in a plurality of stages, and has an n-stage (n≧2) stage skew structure in which the circumferential positions of the magnets are shifted in a predetermined direction depending on the position of each stage, Let k be the least common multiple of the number of magnets and the number of teeth of the rotor, and ψ be the magnet stage skew angle between the magnets of adjacent stages about the rotation axis. 0<ψsd≦360°÷k÷n 9. The rotating electric machine according to claim 1, wherein the rotating electric machine is configured as follows:

12. The rotor core has a linear skew structure in which the magnets are inclined at a certain angle with respect to the rotation axis, Let k be the least common multiple of the number of magnets and the number of teeth of the rotor, and ψsL be the magnet linear skew angle between one end and the other end of the magnet about the rotation axis. 0<ψsL≦360°÷k 9. The rotating electric machine according to claim 1, wherein the rotating electric machine is configured as follows:

13. The rotating electric machine according to any one of claims 1 to 12, wherein the plurality of grooves are formed radially around the rotation shaft.

14. The teeth are formed symmetrically with respect to an axis of symmetry (V) passing through the rotation axis in each cross section perpendicular to the rotation axis, The rotating electric machine according to any one of claims 1 to 12, wherein the plurality of grooves are formed parallel to an axis of symmetry of the teeth.

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