Brushless motor

Abstract

To provide a brushless motor capable of further improving motor performance while being flattened.SOLUTION: Long-side flange portions 37 and short-side flange portions 38 are respectively arranged at equal intervals in a circumferential direction, a direction in which a long-side winding trunk portion 35 protrudes from a back yoke 23 intersects with a radial direction, and a direction in which a short-side winding trunk 36 protrudes from the back yoke 23 is along the radial direction. A recess portion 41 is formed on a side surface 35b facing a short-side portion side 38 of a base 35a on a back yoke 23 side of the long-side winding trunk portion 35, and a magnetic path width W1 as viewed from the direction of a rotation axis A at a location where the recess portion 41 of the long-side winding trunk portion 35 is formed is larger than a magnetic path width W2 as viewed from the direction of the rotation axis A at a location other than the recess portion 41 of the long-side winding trunk portion 35.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a brushless motor.

Background Art

[0002] For example, an inner rotor type brushless motor includes an annular stator and a rotor rotatably provided at the radial center of the stator. The stator includes a stator core and a coil wound around the stator core. The stator core includes an annular back yoke and a plurality of teeth protruding radially inward from the inner peripheral surface of the back yoke. A coil is wound around each tooth. The rotor includes a rotor shaft that rotates around the rotation axis, a columnar rotor core fixed to the rotor shaft, and a permanent magnet (magnetic pole) provided on the outer peripheral portion of the rotor core. Under such a configuration, when a current is sequentially supplied to a predetermined coil, a predetermined linked magnetic flux is formed in each tooth. This linked magnetic flux serves as an electromotive force, and a magnetic attractive force or repulsive force is generated between the permanent magnet and the tooth. As a result, the rotor is continuously rotated.

[0003] By the way, when attempting to reduce the size of such a brushless motor, for example, by flattening it, a technique for flattening the stator core has been disclosed (see, for example, Patent Document 1). This device is configured with two linear yokes having a linear shape and two arc-shaped yokes having an arc shape for the back yoke. The linear yokes and the arc-shaped yokes are alternately arranged in the circumferential direction. Teeth protrude from each yoke.

[0004] Since the distances from the rotation axis to the respective yokes are different, among the respective teeth, the lengths of the teeth protruding from the linear yoke and the lengths of the teeth protruding from the arc-shaped yoke are different. For this reason, the sizes of the spaces (hereinafter referred to as winding areas) formed between adjacent teeth in the circumferential direction and capable of accommodating coils vary. In particular, the winding area of the teeth protruding from the linear yoke becomes smaller than the winding area of the teeth protruding from the arc-shaped yoke. In such a case, the balance of the magnetomotive forces of the respective coils deteriorates. For this reason, in Patent Document 1, by inclining the teeth protruding from the linear yoke by a predetermined angle with respect to the radial direction, the variation in the winding area is reduced respectively.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] By the way, in recent years, in addition to the flattening of the brushless motor, further improvement of motor characteristics has been required. However, in the above-mentioned conventional technology, there is a limit to increasing the winding area, and there is a problem that there is a limit to the improvement of motor characteristics.

[0007] Therefore, the present invention provides a brushless motor capable of further improving motor performance while achieving flattening.

Means for Solving the Problems

[0008] In order to solve the above problems, in a first aspect of the present invention, a brushless motor includes an annular stator and a rotor disposed inside the stator in the radial direction and rotatably provided with respect to the stator. The rotor includes a rotor shaft having a rotation axis as its center, a rotor core fixed to the rotor shaft, and a plurality of magnetic poles provided on an outer peripheral portion of the rotor core. The stator includes a stator core and a coil wound around the stator core. The stator core has a flat shape when viewed from the direction of the rotation axis and is an annular back yoke, and a plurality of teeth protruding radially inward from the inner peripheral surface of the back yoke of the back yoke and around which the coil is wound. The back yoke has a pair of long side portions disposed opposite to each other with the rotation axis interposed therebetween, and a pair of short side portions disposed opposite to each other in a direction orthogonal to the opposing direction of the long side portions with the rotation axis interposed therebetween. The length along the circumferential direction of the short side portion is shorter than the length along the circumferential direction of the long side portion. Each of the teeth protrudes from the inner peripheral surface of the back yoke and has a winding cylinder portion around which the coil is wound, and a flange portion provided at an end of the winding cylinder portion opposite to the back yoke and extending in the circumferential direction longer than the circumferential width of the winding cylinder portion. Each of the teeth has two long side teeth provided on each of the pair of long side portions and one short side tooth provided on each of the pair of short side portions. When the winding cylinder portion in the long side tooth is a long side winding cylinder portion, the winding cylinder portion in the short side tooth is a short side winding cylinder portion, the flange portion in the long side tooth is a long side flange portion, and the flange portion in the short side tooth is a short side flange portion, the long side flange portion and the short side flange portion are each arranged at equal intervals in the circumferential direction. The protruding direction of the long side winding cylinder portion from the back yoke intersects the radial direction, and the protruding direction of the short side winding cylinder portion from the back yoke is along the radial direction. A recess is formed on a side surface of the base of the long side winding cylinder portion on the back yoke side facing the short side portion side. The width of the magnetic path when viewed from the direction of the rotation axis at the location where the recess of the long side winding cylinder portion is formed is larger than the width of the magnetic path when viewed from the direction of the rotation axis at locations other than the recess of the long side winding cylinder portion.

[0009] In this way, by forming a recess in the long-side winding cylinder portion, it is possible to sufficiently secure the winding area of the long-side teeth as compared with the conventional case. Even if a recess is formed, the width of the magnetic path as viewed from the direction of the rotation axis at the location where the recess of the long-side winding cylinder portion is formed is larger than the width of the magnetic path as viewed from the direction of the rotation axis at locations other than the recess of the long-side winding cylinder portion. Therefore, magnetic saturation in the long-side teeth can be avoided. Accordingly, while making the brushless motor flatter, the motor performance can be further improved. Also, to the extent that a recess is formed, the stator core can be lightened. By making the back yoke have a flat shape, while miniaturizing the brushless motor, the winding area of each tooth can be made uniform, so that the balance of the magnetomotive forces of each coil can be improved, and consequently, the operating noise and vibration of the brushless motor can also be reduced.

[0010] In a second aspect of the present invention, in the brushless motor of the first aspect, when looking from the direction of the rotation axis, the intersection of the center line of the width in the direction orthogonal to the protruding direction of the long-side winding cylinder portion and the inner peripheral surface of the flange portion of the long-side flange portion is defined as point Pi, the straight line connecting the rotation axis and point Pi is defined as the first straight line, the straight line connecting the center between two adjacent long-side flange portions in the circumferential direction including the long-side flange portion where point Pi is set and the rotation axis is defined as the second straight line, and when the angle between the first straight line and the second straight line is θ, the angle θ satisfies θ < 25°.

[0011] By configuring in this way, it is possible to sufficiently secure the length of the long-side winding cylinder portion as viewed from the direction of the rotation axis. As a result, the winding area of the long-side teeth can be surely increased.

[0012] In a third aspect of the present invention, in the brushless motor according to the first aspect or the second aspect, the plurality of magnetic poles include a plurality of permanent magnets arranged on the core outer peripheral surface of the rotor core. The permanent magnet has an arcuate magnet inner peripheral surface when viewed from the direction of the rotation axis, and an arcuate magnet outer peripheral surface that is radially outside the magnet inner peripheral surface and faces the magnet inner peripheral surface in the radial direction. The magnetization orientation of the permanent magnet is a parallel orientation in a direction parallel to the radial direction at the center in the circumferential direction of the permanent magnet. When the radius of the circle passing through the outermost side of the magnet outer peripheral surface about the rotation axis is D, the radius of curvature of the magnet outer peripheral surface is R, and the eccentricity of the magnet outer peripheral surface is E, the radius D, the radius of curvature R, and the eccentricity E satisfy E = R / D ≤ 0.81.

[0013] By configuring in this way, the distance between the magnet outer peripheral surface and each flange portion can be gradually increased from the center in the circumferential direction of the magnet outer peripheral surface toward both ends in the circumferential direction. Also, the distance between the magnet outer peripheral surface and each flange portion can be sufficiently ensured toward both ends in the circumferential direction of the magnet outer peripheral surface. As a result, the influence of cogging on the rotor can be reduced. In particular, the fifth harmonic of the induced voltage of the coil can be suppressed. As a result, torque ripple can be reduced.

[0014] In a fourth aspect of the present invention, in the brushless motor according to any one of the first aspect to the third aspect, between the roots in at least two of the long-side teeth with respect to one of the long-side portions, it is formed flat.

[0015] By configuring in this way, the brushless motor can be surely flattened and the brushless motor can be surely miniaturized.

Effects of the Invention

[0016] According to the present invention, while achieving flattening of the brushless motor, the motor performance can be further improved.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0018] Next, embodiments of the present invention will be described with reference to the drawings.

[0019] <Motor with Reducer> FIG. 1 is a sectional view of a motor 1 with a reducer. As shown in FIG. 1, the motor 1 with a reducer includes a motor part 2 and a reduction part 3 that reduces and outputs the rotation of the motor part 2. The motor part 2 and the reduction part 3 are arranged side by side. In the following description, the direction parallel to the rotation axis A of the motor part 2 is referred to as the axial direction.

[0020] <Reduction Part> The reduction part 3 includes a gear case 4 and a worm reduction mechanism 5 housed in the gear case 4. The worm reduction mechanism 5 includes a worm shaft 6 arranged along the axial direction and a worm wheel 7 meshed with the worm shaft 6. Both ends of the worm shaft 6 in the axial direction are rotatably supported by the gear case 4 via bearings 8a and 8b.

[0021] In the gear case 4, an opening 4a for receiving the motor unit 2 is formed on the side surface closer to the bearing 8b among the two bearings 8a and 8b, on the side closer to the motor unit 2. The end of the worm shaft 6 on the motor unit 2 side protrudes toward the motor unit 2 through the bearing 8b and the opening 4a. An end of the worm shaft 6 on the motor unit 2 side is integrally formed with a rotor shaft 16 of the motor unit 2, which will be described later.

[0022] On the worm wheel 7, an output shaft 9 is provided at the center in the radial direction of the worm wheel 7. The output shaft 9 is arranged coaxially with the rotational axis direction of the worm wheel 7 and protrudes outside the gear case 4 through a bearing boss (not shown) of the gear case 4. A spline connectable to an electrical component (not shown) is formed at the protruding tip of the output shaft 9. Examples of the electrical component include a sunroof, a power window, a power seat, etc. However, it is not limited to this, and the output shaft 9 can be connected to various devices other than the electrical component.

[0023] <Motor unit> The motor unit 2 is a so-called brushless motor that does not require a brush when supplying power to the stator 12. The motor unit 2 includes a motor case 11 provided to close the opening 4a of the gear case 4, an annular stator 12 housed in the motor case 11, and a rotor 13 provided on the inner side in the radial direction of the stator 12 and rotatably provided with respect to the stator 12.

[0024] <Motor case> The motor case 11 is formed in a bottomed cylindrical shape. An outer flange portion 11b is formed at the periphery of the opening 11a of the motor case 11. The motor case 11 is fixed to the gear case 4 such that the outer flange portion 11b abuts against the side surface of the gear case 4. A bearing boss 14 protruding to the side opposite to the gear case 4 is formed on the bottom 11c of the motor case 11. A bearing 15 for rotatably supporting the rotor 13 is provided on the bearing boss 14.

[0025] <Rotor> Figure 2 is a cross-sectional view taken along line II-II of Figure 1. As shown in FIGS. 1 and 2, the rotor 13 includes a rotor shaft 16 integrally formed with the worm shaft 6, a cylindrical rotor core 17 fitted and fixed to the rotor shaft 16, and a plurality (for example, four in this embodiment) of permanent magnets 18 provided on the outer peripheral surface of the rotor core 17.

[0026] The rotor shaft 16 is arranged coaxially with the worm shaft 6. The end of the rotor shaft 16 opposite to the worm shaft 6 is rotatably supported by the motor case 11 via a bearing 15. In the following description, the rotation direction of the rotor shaft 16 is referred to as the circumferential direction. The radial direction of the rotor shaft 16, that is, the direction perpendicular to the axial direction and the circumferential direction is simply referred to as the radial direction.

[0027] The rotor core 17 is formed, for example, by laminating a plurality of steel plates in the axial direction. However, it is not limited thereto, and the rotor core 17 may be formed, for example, by pressure molding soft magnetic powder. A through hole 17a is formed at the center of the rotor core 17 in the radial direction. The rotor shaft 16 is inserted or press-fitted into the through hole 17a and fixed. A plurality (for example, four in this embodiment) of salient poles 19 are provided at equal intervals in the circumferential direction on the outer peripheral surface 17b of the rotor core 17. The salient poles 19 project outward in the radial direction and extend over the entire axial direction of the rotor core 17.

[0028] <Permanent Magnet> Figure 3 is a plan view of the permanent magnet 18 viewed from the axial direction. As shown in FIGS. 2 and 3, the permanent magnet 18 is disposed on the outer peripheral surface of the rotor core 17 and between adjacent salient poles 19 in the circumferential direction. The permanent magnet 18 is formed in an arc shape along the outer peripheral surface 17b of the rotor core 17 when viewed from the axial direction. The permanent magnet 18 is formed symmetrically about the center in the circumferential direction when viewed from the axial direction.

[0029] The permanent magnet 18 has a flat magnet side surface 18a facing the salient pole 19 in the circumferential direction, an arcuate inner peripheral surface 18b on the inner side in the radial direction, an arcuate outer peripheral surface 18c on the outer side in the radial direction, parallel surfaces 18d formed at the connection portion between the magnet side surface 18a and the outer peripheral surface 18c and formed in parallel on both sides in the circumferential direction, and a rounded surface portion 18e formed at the connection portion between the magnet side surface 18a and the inner peripheral surface 18b.

[0030] The position of the arc center Ci of the inner peripheral surface 18b of the permanent magnet 18 coincides with the position of the rotation axis A. In contrast, the position of the arc center Co of the outer peripheral surface 18c of the permanent magnet 18 is offset radially outward from the rotation axis A and is eccentric. Thereby, the permanent magnet 18 is formed such that the center in the circumferential direction bulges out most radially outward. Here, when the radius of the circle passing through the outermost side of the outer peripheral surface 18c of the permanent magnet 18 (the radius of the rotor 13) centered on the rotation axis A is D, the radius of curvature (the radius of curvature in the claims) of the outer peripheral surface 18c is Ro, and the eccentricity of the outer peripheral surface 18c is E, the radius D, the radius of curvature Ro, and the eccentricity E satisfy E = R / D ≦ 0.81 ···(1) and satisfy.

[0031] The radius of curvature Ri of the inner peripheral surface 18b of the permanent magnet 18 is, for example, the same as the radius of curvature of the outer peripheral surface 17b of the rotor core 17. The magnetization orientation of the permanent magnet 18 (see the arrow J in FIG. 3) is a parallel orientation in a direction parallel to the radial direction at the center in the circumferential direction of the permanent magnet 18. The permanent magnets 18 are arranged such that the magnetic poles are alternately arranged in the circumferential direction. Examples of the permanent magnet 18 include a ferrite magnet, a neodymium bonded magnet, and a neodymium sintered magnet.

[0032] Thus, the rotor 13 is a surface magnet (SPM: Surface Permanent Magnet) type rotor having the permanent magnet 18 for field excitation on the outer peripheral surface 17b of the rotor core 17, and is an inset type rotor provided with the salient poles 19 protruding radially outward of the rotor core 17 between the permanent magnets 18 arranged in the circumferential direction.

[0033] <Stator> As shown in FIG. 2, the stator 12 includes a stator core 21 formed in an annular shape so as to surround the rotor 13, and a plurality of coils 22 wound around the stator core 21. In FIG. 2, the illustration of the coil 22 is simplified for easy understanding. The stator core 21 is formed, for example, by axially laminating a plurality of steel plates. However, it is not limited thereto, and the stator core 21 may be formed, for example, by pressure-molding soft magnetic powder.

[0034] The stator core 21 includes an annular back yoke 23 and six teeth 24 protruding radially inward from the inner peripheral surface of the back yoke 23. Between two adjacent teeth 24 in the circumferential direction, sawtooth-shaped slots 25 are respectively formed. Since the number of teeth 24 is six, the number of slots 25 is also six. In this embodiment, for example, since the number of permanent magnets 18 is four, the number of magnetic poles is four poles. That is, the motor unit 2 is a four-pole six-slot brushless motor.

[0035] The back yoke 23 is formed in a flat shape when viewed from the axial direction. That is, the back yoke 23 has a pair of long side portions 26 disposed opposite to each other with the rotation axis A interposed therebetween, and a pair of short side portions 27 disposed opposite to each other in a direction orthogonal to the opposing direction of the long side portions 26 with the rotation axis A interposed therebetween. Each long side portion 26 linearly extends in a direction orthogonal to the opposing direction when viewed from the axial direction. In other words, each long side portion 26 extends flatly along a direction orthogonal to the opposing direction. The short side portion 27 has a short straight portion 28 extending in a direction orthogonal to the extending direction of the long side portion 26 when viewed from the axial direction, and a connecting portion 29 connecting the short straight portion 28 and the long side portion 26. The short straight portion 28 and the connecting portion 29 are each formed linearly when viewed from the axial direction. In other words, each short side portion 27 extends flatly along a direction orthogonal to the opposing direction.

[0036] The connecting part 29 is formed as if the corner of the long side part 26 and the short side part 27 is planed. The connecting part 29 extends by bending from both circumferential ends of the short straight part 28. The length along the circumferential direction of the short side part 27, that is, the length LS1 of the short straight part 28 as viewed from the axial direction plus the length LS2 of the two connecting parts 29 is shorter than the length LL of the long side part 26 as viewed from the axial direction.

[0037] The teeth 24 are integrally formed with a winding part 31 that protrudes radially inward from the inner peripheral surface of the back yoke 23, and a flange part 32 that extends circumferentially from the radially inner end of the winding part 31. Each flange part 32 is formed to have the same circumferential length and is arranged at equal intervals in the circumferential direction. The flange part 32 is a part that generates a magnetic attractive force or repulsive force with respect to the permanent magnet 18 of the rotor 13 (details will be described later).

[0038] The six teeth 24 are composed of long side teeth 33 provided two by two on a pair of long side parts 26 and short side teeth 34 provided one by one on a pair of short side parts 27. In the following description, among the winding parts 31, the winding part 31 that constitutes the long side teeth 33 is referred to as the long side winding part 35. Among the winding parts 31, the winding part 31 that constitutes the short side teeth 34 is referred to as the short side winding part 36. Among the flange parts 32, the flange part 32 of the long side teeth 33 is referred to as the long side flange part 37. Among the flange parts 32, the flange part 32 of the short side teeth 34 is referred to as the short side flange part 38.

[0039] The short side winding part 36 protrudes in a direction orthogonal to the short straight part 28, that is, along the radial direction. In contrast, the protruding direction of the long side winding part 35 intersects the radial direction with respect to the long side part 26. Specifically, first, let the intersection point of the center line LC of the width in the direction orthogonal to the protruding direction of the long side winding part 35 as viewed from the direction of the rotation axis and the inner peripheral surface 37a of the long side flange part 37 be the point Pi. The center line LC is parallel to the protruding direction of the long side winding part 35. Since the long side winding part 35 is formed long in the protruding direction, the center line LC can also be said to be the central line in the short side direction of the long side winding part 35 as viewed from the axial direction.

[0040] Next, let the straight line connecting the rotation axis line A and the point Pi be the first straight line L1. Let the straight line connecting the center Pc between two adjacent long-side flange portions 37 in the circumferential direction including the long-side flange portion 37 where the point Pi is set and the rotation axis line A be the second straight line L2. In FIG. 2, the long-side flange portion 37 where the point Pi is set is the upper-left long-side flange portion 37L. The long-side flange portion adjacent to this long-side flange portion 37L in the circumferential direction is the upper-right long-side flange portion 37R in FIG. 2. The center Pc is between these long-side flange portions 37L and 37R.

[0041] Next, let the angle between the first straight line L1 and the second straight line L2 be θ. At this time, the angle θ satisfies θ < 25° ···(2) is satisfied.

[0042] The base 35a on the side opposite to the long-side flange portion 37 of the long-side winding cylinder portion 35 formed so as to satisfy the above formula (2) is connected to both longitudinal ends of the long-side portion 26 as viewed from the axial direction. That is, between the bases 35a of the two long-side teeth 33 with respect to one long-side portion 26, it is formed flat.

[0043] A recess 41 is formed in the side surface 35b of the base 35a of the long-side winding cylinder portion 35 facing the short-side portion 27 side. The recess 41 is formed over the entire axial direction of the long-side winding cylinder portion 35. The recess 41 is formed to taper so that the width as viewed from the axial direction gradually decreases from the side surface 35b toward the long-side portion 26. As viewed from the axial direction, the minimum width W1 of the portion of the long-side winding cylinder portion 35 where the recess 41 is formed is larger than the short-side width W2 of the portion of the long-side winding cylinder portion 35 other than the recess 41.

[0044] <Regarding the winding area> Next, based on FIG. 4, the winding area will be described. FIG. 4 is a plan view of the stator core 21 as viewed from the axial direction. FIG. 4 corresponds to FIG. 2 described above. As shown in FIG. 4, coils 22 are wound around each tooth 24 in a concentrated winding method. Each coil 22 is connected by, for example, a △ (delta) connection method. Here, the back yoke 23 is formed in a flat shape when viewed from the axial direction. Therefore, the distance LK1 from the rotation axis line A to the long side portion 26 is shorter than the distance LK2 from the rotation axis line A to the short side portion 27. Accordingly, the winding areas MA1, MA2 (the first long side winding area MA1, the second long side winding area MA2) of the long side teeth 33 are likely to be smaller than the short side winding area MA3 of the short side teeth 34 (each winding area MA1 to MA3 refers to the shaded portion in FIG. 4).

[0045] However, the protruding direction of the long side winding cylinder portion 35 from the long side portion 26 intersects the radial direction so as to satisfy the above formula (2). For this reason, compared with the case where the long side winding cylinder portion 35 protrudes along the radial direction from the long side portion 26, the depth of the long side teeth 33 becomes deeper. Accordingly, the first long side winding area MA1 on the long side portion 26 side of the long side teeth 33 can be increased. Further, a concave portion 41 is formed in a side surface 35b facing the short side portion 27 at the base 35a of the long side winding cylinder portion 35. The second long side winding area MA2 on the short side portion 27 side of the long side teeth 33 can be increased compared with the case where the concave portion 41 is not formed, due to the formation of the concave portion 41.

[0046] <Operation of the motor with a speed reducer> Next, the operation of the motor 1 with a speed reducer will be described. The motor 1 with a speed reducer includes a controller (not shown) that selectively supplies current to each coil 22. When current is selectively supplied to each coil 22 via this controller, a linked magnetic flux is formed in a predetermined tooth 24. The linked magnetic flux flows through the winding cylinder portion 31 and the flange portion 32 of each tooth 24, and further flows from the flange portion 32 toward the rotor 13. That is, the winding cylinder portion 31 and the flange portion 32 serve as magnetic paths of the linked magnetic flux. The minimum width W1 of the portion where the concave portion 41 is formed in the long side winding cylinder portion 35 when viewed from the axial direction, and the width W2 in the short direction of the portion other than the concave portion 41 of the long side winding cylinder portion 35 can be regarded as the widths of the magnetic paths, respectively. In the following description, the minimum width W1 of the portion where the concave portion 41 is formed in the long side winding cylinder portion 35 is referred to as the magnetic path width W1 of the concave portion 41. The width W2 in the short direction of the portion other than the concave portion 41 of the long side winding cylinder portion 35 is referred to as the magnetic path width W2 of the long side winding cylinder portion 35.

[0047] The interlinking magnetic flux formed in each tooth 24 generates a magnetic attractive force or repulsive force (magnet torque) with the effective magnetic flux formed by the permanent magnet 18 of the rotor 13. In addition, the salient pole 19 of the rotor core 17 generates a reluctance torque that rotates the rotor core 17 so that the protruding direction is the direction in which the interlinking magnetic flux from each flange portion 32 easily flows and the magnetic reluctance of the magnetic path of the interlinking magnetic flux is reduced.

[0048] Due to these magnet torques and reluctance torques, the rotor 13 is continuously rotated. The rotation of the rotor 13 is transmitted to the worm shaft 6 integrated with the rotor shaft 16. Further, it is transmitted to the worm wheel 7 meshed with the worm shaft 6. The rotation of the worm wheel 7 is transmitted to the output shaft 9 connected to the worm wheel 7. By the rotation of the output shaft 9, a desired electrical component is driven.

[0049] <Actions and effects of each component> Next, the actions and effects of each component will be described. The above-described motor unit 2 is formed in a flat shape when viewed from the axial direction of the back yoke 23, and the teeth 24 are composed of a long-side tooth 33 and a short-side tooth 34. The long-side winding cylinder portion 35 has a protruding direction from the long-side portion 26 intersecting the radial direction. The short-side winding cylinder portion 36 has a protruding direction from the short straight portion 28 along the radial direction. A recess 41 is formed in the side surface 35b facing the short-side portion 27 at the root 35a of the long-side winding cylinder portion 35. Therefore, the first long-side winding area MA1 and the second long-side winding area MA2 can be sufficiently ensured as compared with the conventional case. Even when the recess 41 is formed in the long-side winding cylinder portion 35, the width W1 of the magnetic path of the recess 41 is larger than the width W2 of the magnetic path of the long-side winding cylinder portion 35. Therefore, magnetic saturation in the long-side tooth 33 can be avoided. In this way, while achieving the flattening of the motor unit 2, the motor performance can be improved.

[0050] In addition, the stator core 21 can be lightened by the amount corresponding to the formation of the recess 41. By making the back yoke 23 have a flat shape, the motor unit 2 can be downsized while making the winding areas of the respective teeth 24 uniform. Therefore, the balance of the magnetomotive forces of the respective coils 22 can be improved, and it is also possible to reduce the operating noise and vibration of the motor unit 2.

[0051] In addition to this, the long-side winding cylinder part 35 is formed so as to satisfy the above formula (2). For this reason, it is possible to sufficiently secure the length of the long-side winding cylinder part 35 as viewed in the axial direction. For this reason, the first long-side winding area MA1 and the second long-side winding area MA2 can be surely increased. The permanent magnet 18 of the rotor 13 is formed so as to satisfy the above formula (1). In addition to this, the magnetization orientation of the permanent magnet 18 is a parallel orientation. For this reason, the distance between the outer peripheral surface 18c of the permanent magnet 18 and each flange part 32 can be gradually increased from the center in the circumferential direction of the outer peripheral surface 18c toward both ends in the circumferential direction. Also, the distance between the outer peripheral surface 18c and each flange part 32 can be sufficiently secured toward both ends in the circumferential direction of the outer peripheral surface 18c. As a result, the influence of cogging on the rotor 13 can be reduced. In particular, the fifth harmonic of the induced voltage of the coil 22 can be suppressed. As a result, the torque ripple of the rotor 13 can be reduced.

[0052] FIG. 5 is a graph showing the change in the cogging of the rotor 13 when the vertical axis represents the cogging [mNm] of the rotor 13 and the horizontal axis represents the eccentricity E (hereinafter simply referred to as the eccentricity E) of the outer peripheral surface 18c in the permanent magnet 18. As shown in FIG. 5, it can be confirmed that the cogging can be reduced when the eccentricity E is 0.81 or less.

[0053] FIG. 6 is a graph comparing the ratios of the harmonic components of the induced voltage of the coil 22 while changing the eccentricity E. The eccentricity E in FIG. 6(a) is 0.9. The eccentricity E in FIG. 6(b) is 0.87. The eccentricity E in FIG. 6(c) is 0.81. The eccentricity E in FIG. 6(d) is 0.75. The eccentricity E in FIG. 6(e) is 0.69. As shown in FIGS. 6(a) to 6(e), it can be confirmed that when the eccentricity E exceeds 0.81, the fifth harmonic of the induced voltage of the coil 22 becomes particularly large. When the eccentricity E is 0.81 or less, it can be confirmed that each harmonic component including the fifth harmonic of the induced voltage of the coil 22 can be suppressed. Therefore, the torque ripple of the rotor 13 can be reduced.

[0054] Further, with respect to one long side portion 26 of the stator core 21, a flat portion is formed between the roots 35a of the two long side teeth 33. For this reason, the motor portion 2 can be surely flattened and the motor portion 2 can be surely miniaturized.

[0055] While flattening the motor portion 2, the motor performance can be improved, so that it is possible to contribute to Goal 7 of the Sustainable Development Goals (SDGs) led by the United Nations, "Ensure access for all people to affordable, reliable and sustainable modern energy", and Goal 9, "Promote the construction of resilient infrastructure, inclusive and sustainable industrialization, and innovation".

[0056] [Modification Example] The present invention is not limited to the above-described embodiments, and includes those obtained by making various changes to the above-described embodiments without departing from the gist of the present invention.

[0057] For example, in the above-described embodiment, the case where each long side portion 26 linearly extends in a direction orthogonal to the facing direction when viewed from the axial direction has been described. The short side portion 27 has been described as having a short straight line portion 28 that extends in a direction orthogonal to the extending direction of the long side portion 26 when viewed from the axial direction, and a connecting portion 29 that connects the short straight line portion 28 and the long side portion 26. The case where the short straight line portion 28 and the connecting portion 29 are each linearly formed when viewed from the axial direction has been described. The case where the connecting portion 29 extends from both circumferential ends of the short straight line portion 28 by bending has been described.

[0058] However, it is not limited to this. The back yoke 23 is formed in a flat shape when viewed from the axial direction, and it is only necessary that the length along the circumferential direction of the short side portion 27 is shorter than the length along the circumferential direction of the long side portion 26. For example, the long side portion 26 may be formed in a bent shape. It is sufficient if the six teeth 24 are constituted by long side teeth 33 provided two by two on a pair of long side portions 26 and short side teeth 34 provided one by one on a pair of short side portions 27, respectively.

[0059] In the above-described embodiment, the motor unit 2 has been described for the case where it is provided in the motor 1 with a speed reducer. However, it is not limited to this, and it is also possible to use the motor unit 2 alone, and it is possible to adopt the motor unit 2 in various devices.

Explanation of Reference Numerals

[0060] 1... Motor with speed reducer, 2... Motor part (brushless motor), 3... Speed reduction part, 4... Gear case, 4a... Opening, 5... Worm speed reduction mechanism, 6... Worm shaft, 7... Worm wheel, 8a... Bearing, 8b... Bearing, 9... Output shaft, 11... Motor case, 11a... Opening, 11b... Outer flange part, 11c... Bottom, 12... Stator, 13... Rotor, 14... Bearing boss, 15... Bearing, 16... Rotor shaft, 17... Rotor core, 17a... Through hole, 17b... Outer peripheral surface (core outer peripheral surface), 18... Permanent magnet (magnetic pole), 18a... Magnet side surface, 18b... Inner peripheral surface (magnet inner peripheral surface), 18c... Outer peripheral surface (magnet outer peripheral surface), 18d... Parallel surface, 18e... Chamfered part, 19... Salient pole, 21... Stator core, 22... Coil, 23... Back yoke, 24... Teeth, 25... Slots, 26... Long side part, 27... Short side part, 28... Short straight line part, 29... Connecting part, 31... Winding cylinder part, 32... Flange part, 33... Long side teeth, 34... Short side teeth, 35... Long side winding cylinder part, 35a... Root, 35b... Side surface, 36... Short side winding cylinder part, 37... Long side flange part, 37a... Inner peripheral surface, 37L... Long side flange part, 37R... Long side flange part, 38... Short side flange part, 41... Concave part, A... Axis of rotation, Ci... Center of arc, Co... Center of arc, D... Radius, E... Eccentricity, J... Arrow, L1... First straight line, L2... Second straight line, LC... Center line, LK1... Distance, LK2... Distance, LL... Length, LS1... Length, LS2... Length, MA1... First long side winding area, MA2... Second long side winding area, MA3... Short side winding area, Pc... Center, Pi... Point, Ri... Radius of curvature, Ro... Radius of curvature, W1... Minimum width, width of magnetic path, W2... Width in the short side direction, width of magnetic path, θ... Angle

Claims

1. An annular stator and, A rotor disposed inside the stator in the radial direction and rotatably provided with respect to the stator, Comprising, The rotor is, A rotor shaft having a rotation axis as its axis, A rotor core fixed to the rotor shaft, A plurality of magnetic poles provided on the outer peripheral portion of the rotor core, Comprising, The stator is, A stator core and, A coil wound around the stator core, Comprising, The stator core is, Flat and annular back yoke when viewed from the direction of the rotation axis, and A plurality of teeth protruding radially inward from the inner peripheral surface of the back yoke of the back yoke and around which the coil is wound, Comprising, The back yoke is, A pair of long side portions disposed opposite each other across the rotation axis, and A pair of short side portions disposed opposite each other in a direction orthogonal to the opposing direction of the long side portions across the rotation axis, Having, the length along the circumferential direction of the short side portion is shorter than the length along the circumferential direction of the long side portion, Each of the teeth is, A winding cylinder portion protruding from the inner peripheral surface of the back yoke and around which the coil is wound, and A flange portion provided at the end of the winding cylinder portion on the side opposite to the back yoke and extending in the circumferential direction longer than the circumferential width of the winding cylinder portion, Having, and Each of the teeth is, Long side teeth provided two by two on each of the pair of long side portions, and Short side teeth provided one by one on each of the pair of short side portions, Having, When the winding cylinder portion in the long side teeth is the long side winding cylinder portion, the winding cylinder portion in the short side teeth is the short side winding cylinder portion, the flange portion in the long side teeth is the long side flange portion, and the flange portion in the short side teeth is the short side flange portion, The long side flange portion and the short side flange portion are each arranged at equal intervals in the circumferential direction, The protruding direction of the long side winding cylinder portion from the back yoke intersects the radial direction, The protruding direction of the short side winding cylinder portion from the back yoke is along the radial direction, At the base of the long side winding cylinder portion on the back yoke side, a recess is formed on the side surface facing the short side portion side, The width of the magnetic path when viewed from the direction of the rotation axis at the location where the recess of the long side winding cylinder portion is formed is larger than the width of the magnetic path when viewed from the direction of the rotation axis at locations other than the recess of the long side winding cylinder portion, A brushless motor characterized by this.

2. When looking from the direction of the rotation axis, taking the intersection point of the center line of the width in the direction orthogonal to the protruding direction of the long-side winding drum portion and the inner peripheral surface of the flange portion of the long-side flange portion as point Pi, and taking the straight line connecting the rotation axis and point Pi as the first straight line, and taking the straight line connecting the center between two adjacent long-side flange portions in the circumferential direction including the long-side flange portion where point Pi is set and the rotation axis as the second straight line, when the angle between the first straight line and the second straight line is θ, the angle θ satisfies θ < 25° which is satisfied by the brushless motor according to claim 1, characterized in that.

3. The plurality of magnetic poles include a plurality of permanent magnets arranged on the outer peripheral surface of the core of the rotor core, The permanent magnet has an arcuate inner peripheral surface of the magnet when looking from the direction of the rotation axis, and an arcuate outer peripheral surface of the magnet that is radially outside the inner peripheral surface of the magnet and faces the inner peripheral surface of the magnet in the radial direction, and has the magnetization orientation of the permanent magnet is a parallel orientation in a direction parallel to the radial direction at the center in the circumferential direction of the permanent magnet, When taking the radius of the circle passing through the outermost side of the outer peripheral surface of the magnet around the rotation axis as D, the radius of curvature of the outer peripheral surface of the magnet as R, and the eccentricity of the outer peripheral surface of the magnet as E, the radius D, the radius of curvature R, and the eccentricity E satisfy E = R / D ≤ 0.81 which is satisfied by the brushless motor according to claim 1 or claim 2, characterized in that.

4. For one of the long sides, between the roots of at least two of the long-side teeth are formed flat, the brushless motor according to claim 1 or claim 2, characterized in that.

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