Brushless motor

Abstract

To provide a brushless motor that can reduce demagnetization of permanent magnets even if they are long-pitch wound and that can be improved in motor performance.SOLUTION: The brushless motor includes a stator 12 and a rotor 13. The stator 12 includes an annular back yoke 23 and a plurality of teeth 24 which protrude from the back yoke 23 and around which a coil 22 is wound. The rotor 13 includes a plurality of permanent magnets 18. A ratio of the number of magnetic poles of the permanent magnets 18 to the number of the teeth 24 is 4:3. An orientation of magnetization of the permanent magnets 18 is parallel oriented in a direction parallel to a radial direction at the center of a circumferential direction of the permanent magnets 18. A relation 0.697<Dr / Ds<1 is satisfied where Dr is a diameter of a circle passing through an outermost permanent magnet 18 using a rotation axis A as a center, and Ds is a minimum width of the back yoke 23 as seen in the direction of the rotation axis A.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 becomes the magnetomotive force, and a magnetic attractive force or repulsive force is generated between the permanent magnet. As a result, the rotor is continuously rotated.

[0003] In such a brushless motor, the ratio of the number of magnetic poles of the permanent magnet to the number of teeth (slot number) may be 4:3. That is, in some cases, a so-called long pitch winding is used, where the coil pitch (pitch between teeth) is longer than the pole pitch (for example, see Patent Document 1). By configuring in this way, compared with a short pitch winding where the coil pitch is shorter than the pole pitch, the permanent magnet can be made smaller because the number of magnetic poles is larger. Also, for example, if the number of teeth is six, the outer shape of the stator can be made polygonal to increase the winding area of the coil, and the stator can be easily flattened. The winding area is the size of the space formed between adjacent teeth in the circumferential direction and where the coil is housed.

[0004] In addition, a so-called inset type rotor in which salient poles are formed to protrude between circumferentially adjacent permanent magnets from the outer peripheral surface of the rotor core is known. Since the protruding direction of the salient poles is the outer side in the radial direction, it becomes a direction in which the magnetic flux linked by the stator coil easily flows. Therefore, due to the salient poles, reluctance torque can be generated by rotating the rotor core so as to reduce the magnetic resistance (reluctance) of the magnetic path of the linked magnetic flux.

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 the above-described conventional technology, there is a problem that as the permanent magnet becomes smaller, it becomes easier to demagnetize. In particular, in an inset type rotor, when the magnetic flux linked by the coil flows into the salient pole, as a result of this linked magnetic flux passing through the corner of the permanent magnet, the permanent magnet is likely to be demagnetized. For this reason, there has been a problem that the motor performance deteriorates.

[0007] Therefore, the present invention provides a brushless motor that can suppress demagnetization of a permanent magnet even in a long pitch winding and can improve motor performance.

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 stator includes an annular back yoke and a plurality of teeth protruding radially inward from the inner peripheral surface of the back yoke along the radial direction and around which coils are wound. The rotor includes a rotor shaft having a rotation axis as its axis, a columnar rotor core body fixed to the rotor shaft, a plurality of salient poles protruding radially outward from the outer peripheral surface of the rotor core body, and a plurality of permanent magnets respectively disposed on the outer peripheral surface of the rotor core body and between the adjacent salient poles in the circumferential direction. The ratio of the number of magnetic poles of the permanent magnet to the number of teeth is 4:3. 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 diameter of the circle passing through the outermost side of the permanent magnet centered on the rotation axis is Dr and the minimum width of the back yoke as viewed from the direction of the rotation axis is Ds, 0.697 < Dr / Ds < 1 is satisfied.

[0009] In a second 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 stator includes an annular back yoke and a plurality of teeth protruding radially inward from the inner peripheral surface of the back yoke along the radial direction and around which coils are wound. The rotor includes a rotor shaft having a rotation axis as its axis, a columnar rotor core body fixed to the rotor shaft, a plurality of salient poles protruding radially outward from the outer peripheral surface of the rotor core body, and a plurality of permanent magnets respectively disposed on the outer peripheral surface of the rotor core body and between the adjacent salient poles in the circumferential direction. The ratio of the number of teeth to the number of magnetic poles of the permanent magnet is 4:3. The magnetization orientation of the permanent magnet is a radial orientation along the radial direction as viewed from the direction of the rotation axis. When the diameter of the circle passing through the outermost side of the permanent magnet centered on the rotation axis is Dr and the minimum width of the back yoke as viewed from the direction of the rotation axis is Ds, 0.618 < Dr / Ds < 1 is satisfied.

[0010] By configuring as described above, even in the case of a long-core brushless motor, demagnetization of the permanent magnet can be suppressed and motor performance can be improved.

[0011] In a third aspect of the present invention, in the brushless motor according to the first aspect or the second aspect, the back yoke may be polygonal when viewed from the direction of the rotation axis.

[0012] Thus, it can be suitably used for a polygonal back yoke. That is, by making the back yoke polygonal, the winding area of the coil can be increased. As a result, the electric loading can be increased, while the permanent magnet is likely to be demagnetized. However, with the above configuration, demagnetization of the permanent magnet can be effectively suppressed.

[0013] In a fourth aspect of the present invention, in the brushless motor according to any one of the first aspect to the third aspect, the rotor core body may have a plurality of holes provided so as to face each of the permanent magnets separately in the radial direction.

[0014] By configuring as described above, the weight of the rotor core body can be reduced, so that the motor performance can be further improved. The holes are arranged inside the permanent magnet in the radial direction. Among the rotor core body, the positions corresponding to both sides in the circumferential direction of the permanent magnet function as magnetic paths. The holes are formed avoiding the portions functioning as the magnetic paths. Therefore, even if the holes are formed, the magnetic paths of the rotor core body can be sufficiently ensured. Thus, a decrease in motor performance due to magnetic saturation can be suppressed.

[0015] In a fifth aspect of the present invention, in the brushless motor according to the fourth aspect, the rotor core body is formed by laminating a plurality of steel plates, and in the rotor core body, the bridge portions formed between the holes adjacent to each other in the circumferential direction face the salient poles in the radial direction, respectively, and the bridge portions may be provided with lamination bosses for connecting the plurality of steel plates.

[0016] By forming the laminated boss in the bridge portion in this way, it is possible to prevent the periphery of the laminated boss from becoming thin in the rotor core body. As a result, for example, it becomes possible to suppress damage and wear to the mold for performing press working on the steel plate.

[0017] In the sixth aspect of the present invention, in the brushless motor of the fifth aspect, the hole portion includes a wide hole portion disposed on the inner side in the radial direction, and is disposed on the outer side in the radial direction of the wide hole portion and communicated with the wide hole portion, and has a narrow hole portion whose width along the circumferential direction is shorter than the width along the circumferential direction of the wide hole portion, and the laminated boss may be disposed between the narrow hole portions adjacent to each other in the circumferential direction.

[0018] By configuring in this way, a large area of the portion where the laminated boss is formed can be ensured in the bridge portion. Therefore, it is possible to surely prevent the periphery of the laminated boss from becoming thin in the rotor core body. Even if the laminated boss is formed, a sufficient magnetic path can be ensured around the laminated boss. Therefore, while surely suppressing damage and wear of the mold, it is possible to suppress a decrease in motor performance due to magnetic saturation.

Effect of the Invention

[0019] According to the present invention, even in a brushless motor with a long pitch winding, demagnetization of the permanent magnet can be suppressed and motor performance can be improved.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

[0021] Next, embodiments of the present invention will be described with reference to the drawings.

[0022] <Motor with Reducer> FIG. 1 is a cross-sectional view of a motor 1 with a reducer. As shown in FIG. 1, the motor 1 with a reducer includes a motor unit 2 and a reduction unit 3 that reduces the rotation of the motor unit 2 and outputs it. The motor unit 2 and the reduction unit 3 are arranged side by side.

[0023] <Reduction Unit> The reduction unit 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 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. In the following description, the direction parallel to the rotation axis A of the worm shaft 6 is referred to as the axial direction. The rotation direction of the worm shaft 6 is referred to as the circumferential direction. The radial direction of the worm shaft 6, that is, the direction perpendicular to the axial direction and the circumferential direction is simply referred to as the radial direction.

[0024] 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 side through the bearing 8b and the opening 4a. An aforementioned rotor shaft 16 of the motor unit 2 is integrally formed at the end of the worm shaft 6 on the motor unit 2 side.

[0025] In the worm wheel 7, an output shaft 9 is provided at the radial center 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.

[0026] <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 is arranged coaxially with the worm shaft 6. 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.

[0027] <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. On the bottom 11c of the motor case 11, a bearing boss 14 protruding to the side opposite to the gear case 4 is formed. A bearing 15 for rotatably supporting the rotor 13 is provided on the bearing boss 14.

[0028] <Stator> FIG. 2 is a plan view of the stator 12 and the rotor 13 as viewed from the axial direction. As shown in FIGS. 1 and 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 of the explanation. The stator core 21 is formed, for example, by axially laminating a plurality of steel plates. However, it is not limited to this, and the stator core 21 may be formed, for example, by pressure molding soft magnetic powder.

[0029] 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.

[0030] The back yoke 23 is formed in a cylindrical shape that is hexagonal when viewed from the axial direction. That is, the back yoke 23 has six flat long side portions 26 arranged at equal intervals in the circumferential direction, and six flat connecting portions 27 connecting the adjacent long side portions 26 in the circumferential direction. Among the long side portions 26, two long side portions 26 face each other with the rotation axis A interposed therebetween. The same applies to the connecting portions 27. Among the connecting portions 27, two connecting portions 27 face each other with the rotation axis A interposed therebetween. The length of the connecting portion 27 along the circumferential direction is sufficiently shorter than the length of the long side portion 26 along the circumferential direction, and forms the corner portion of the back yoke 23 when viewed from the axial direction.

[0031] The teeth 24 are integrally formed with a winding drum portion 31 that protrudes radially along the inner circumferential surface of each long side portion 26 from the circumferential center, and a flange portion 32 that extends circumferentially from the radially inner end of the winding drum portion 31. The flange portion 32 is a portion 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). Each coil 22 is wound around each tooth 24 in a concentrated winding method. Each coil 22 is connected, for example, by a △ (delta) connection method.

[0032] <Rotor> Figure 3 is an enlarged view of part III of Figure 2. As shown in FIGS. 1 to 3, the rotor 13 includes a rotor shaft 16 disposed coaxially with the worm shaft 6 and integrally formed with the worm shaft 6, a rotor core 17 fitted and fixed to the rotor shaft 16, and eight permanent magnets 18 provided on the rotor core 17. Thus, the motor unit 2 is a brushless motor with 8 poles of permanent magnets 18 and 6 slots (the number of teeth 24) of 8 poles and 6 slots.

[0033] The rotor shaft 16 is disposed 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.

[0034] The rotor core 17 is formed, for example, by laminating a plurality of steel plates 40 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. The rotor core 17 includes a cylindrical rotor core body 41 and eight salient poles 19 protruding radially outward from the outer peripheral surface 41a of the rotor core body 41. A through hole 41b is formed at the radial center of the rotor core body 41. The rotor core body 41 is fitted and fixed to the rotor shaft 16 by inserting or press-fitting the rotor shaft 16 into the through hole 41b.

[0035] In the rotor core body 41, eight holes 42 penetrating in the axial direction are formed between the through hole 41b and the outer peripheral surface 41a. Each hole 42 is arranged at equal intervals in the circumferential direction. The hole 42 has a wide hole 43 arranged on the inner side in the radial direction and a narrow hole 44 arranged on the outer side in the radial direction in the wide hole 43. The wide hole 43 and the narrow hole 44 are in communication. The width W1 along the circumferential direction of the narrow hole 44 is shorter than the width W2 along the circumferential direction of the wide hole 43.

[0036] A bridge portion 45 is formed between the holes 42 adjacent to each other in the circumferential direction. The bridge portion 45 is formed to extend in the radial direction as viewed from the axial direction. The bridge portion 45 is formed to correspond to the shape of the hole 42. That is, the bridge portion 45 has a narrow bridge portion 46 formed between the wide holes 43 adjacent to each other in the circumferential direction and a wide bridge portion 47 formed between the narrow holes 44 adjacent to each other in the circumferential direction.

[0037] Laminated bosses 48 are formed on the bridge portions 45 of the respective steel plates 40. The laminated bosses 48 are arranged at the center of a region R from the wide bridge portion 47 to the outer peripheral surface 41a of the rotor core body 41. That is, as viewed from the axial direction, the center C1 of the laminated boss 48 and the circumferential center C2 of the bridge portion 45 coincide with each other. The laminated boss 48 is a convex portion formed by bending by performing press working on each steel plate 40. When laminating the respective steel plates 40, the convex side of one laminated boss 48 is press-fitted into the concave side of the other laminated boss 48 among the two overlapping steel plates 40. Thereby, the laminated state of the steel plates 40 is maintained.

[0038] The salient pole 19 extends over the entire axial direction of the rotor core 17. The circumferential width W3 of the salient pole 19 is the same as the circumferential width W4 of the narrow bridge portion 46. The circumferential center C3 of the salient pole 19 coincides with the circumferential center C2 of the bridge portion 45 and the center C1 of the laminated boss 48. In other words, the salient pole 19 faces the bridge portion 45 in the radial direction. The magnet housing recesses 51 are respectively formed by the salient poles 19 adjacent in the circumferential direction and the outer peripheral surface 41a of the rotor core body 41. Permanent magnets 18 are respectively arranged in these magnet housing recesses 51. For this reason, the respective hole portions 42 forming the bridge portion 45 face the respective permanent magnets 18 separately in the radial direction.

[0039] <Permanent magnet> FIGS. 4 and 5 are plan views of the permanent magnet 18 viewed from the axial direction. The permanent magnet 18 shown in FIG. 4 and the permanent magnet 18 shown in FIG. 5 have the same shape. For this reason, in the description of the shape of the permanent magnet 18, both permanent magnets 18 in FIGS. 4 and 5 are denoted by the same reference numerals for description. The difference between FIGS. 4 and 5 is the difference in the magnetization orientation described later. In the present embodiment, it is possible to adopt either the permanent magnet 18 shown in FIG. 4 or the permanent magnet 18 shown in FIG. 5.

[0040] As shown in FIGS. 2 to 4, the permanent magnet 18 is formed in an arc shape so as to follow the outer peripheral surface 41a of the rotor core body 41 when viewed from the axial direction. The permanent magnet 18 is formed symmetrically with respect to the center in the circumferential direction when viewed from the axial direction. 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.

[0041] 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 line A. On the other hand, the position of the arc center Co of the outer peripheral surface 18c of the permanent magnet 18 is displaced radially outward from the rotation axis line A and is eccentric. Thereby, the permanent magnet 18 is formed such that the center in the circumferential direction bulges most radially outward. 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 41a of the rotor core body 41. The radius of curvature Ro of the outer peripheral surface 18c of the permanent magnet 18 is smaller than the radius of curvature Ri of the inner peripheral surface 18b, for example.

[0042] As shown in detail in FIG. 4, the magnetization orientation (see arrow J1 in FIG. 4) in the permanent magnet 18 can be a parallel orientation in a direction parallel to the radial direction at the center in the circumferential direction in the permanent magnet 18. Further, as shown in detail in FIG. 5, the magnetization orientation (see arrow J2 in FIG. 5) in the permanent magnet 18 can also be a radial orientation along the radial direction when viewed from the axial direction. 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.

[0043] Thus, the rotor 13 is a surface magnet (SPM: Surface Permanent Magnet) type rotor having the field permanent magnets 18 on the outer peripheral surface 41a of the rotor core body 41, and is also an inset type rotor including the salient poles 19 protruding radially outward of the rotor core body 41 between the permanent magnets 18 arranged in the circumferential direction.

[0044] <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 magnetic flux linkage is formed in the predetermined teeth 24. The magnetic flux linkage flows from the flange portion 32 of each tooth 24 toward the rotor 13, and generates a magnetic attractive force or repulsive force (magnet torque) with the effective magnetic flux formed by the permanent magnets 18 of the rotor 13. Further, the salient poles 19 of the rotor core 17 generate a reluctance torque that rotates the rotor core 17 so that the protruding direction is a direction in which the magnetic flux linkage from each flange portion 32 easily flows and the magnetic reluctance of the magnetic path of the magnetic flux linkage is reduced.

[0045] These magnetic torques and reluctance torques continuously rotate the rotor 13. The rotation of the rotor 13 is transmitted to a worm shaft 6 integrated with a rotor shaft 16. Further, it is transmitted to a worm wheel 7 meshed with the worm shaft 6. The rotation of the worm wheel 7 is transmitted to an output shaft 9 connected to the worm wheel 7. The rotation of the output shaft 9 drives a desired electrical component.

[0046] By the way, as described above, in the inset type rotor 13, the magnetic flux linked from each flange portion 32 flows into the salient pole 19. At this time, as a result of this linked magnetic flux passing through the corners (around the parallel planes 18d and 18d) of the permanent magnet 18, the permanent magnet 18 is likely to be demagnetized.

[0047] Therefore, as shown in FIG. 2, when the diameter of the circle passing through the outermost side of the permanent magnet 18 around the rotation axis A is Dr and the minimum width of the back yoke 23 viewed from the axial direction is Ds, for the permanent magnet 18 with the magnetization orientation being the parallel orientation, the diameter Dr and the minimum width Ds satisfy 0.697 < Dr / Ds < 1 ···(1) This was made to satisfy. On the other hand, for the permanent magnet 18 with the magnetization orientation being the parallel orientation, the diameter Dr and the minimum width Ds satisfy 0.618 < Dr / Ds < 1 ···(2) This was made to satisfy. The reasons for these will be described in detail below.

[0048] FIG. 6 is a graph showing the change in the current value when the vertical axis is the current value [A] supplied to the coil 22 and the horizontal axis is the torque [N·m], and is compared for each demagnetization rate [%] of the permanent magnet 18. As shown in FIG. 6, it can be confirmed that when trying to obtain the same torque, when the demagnetization rate of the permanent magnet 18 exceeds 5%, a larger current needs to be supplied to the coil 22 compared to the case where the demagnetization rate is 5% or less. For this reason, first, it was determined that the demagnetization rate of the permanent magnet 18 should be 5% or less.

[0049] FIG. 7 shows the change in the demagnetization rate when the vertical axis is the demagnetization rate [%] and the horizontal axis is the value obtained by dividing the diameter Dr by the minimum width Ds (hereinafter referred to as the Dr / Ds value), and is a graph comparing the magnetization orientation in the permanent magnet 18 in the case of parallel orientation and the case of radial orientation. As shown in FIG. 7, it can be confirmed that in the parallel orientation, when the Dr / Ds value is less than 0.697, the demagnetization rate exceeds 5 [%]. In the radial orientation, it can be confirmed that when the Dr / Ds value is less than 0.618, the demagnetization rate exceeds 5 [%].

[0050] Therefore, according to the above-described embodiment, in the long-pitch-wound motor unit 2 in which the number of magnetic poles of the permanent magnet 18 is 8 poles and the number of slots 25 (the number of teeth 24) is 6, i.e., 8 poles 6 slots, when the magnetization orientation in the permanent magnet 18 is parallel orientation, by satisfying the Dr / Ds value with the above formula (1), demagnetization of the permanent magnet 18 can be suppressed and motor performance can be improved. On the other hand, when the magnetization orientation in the permanent magnet 18 is parallel orientation, by satisfying the Dr / Ds value with the above formula (2), demagnetization of the permanent magnet 18 can be suppressed and motor performance can be improved.

[0051] In particular, when the shape of the back yoke 23 is hexagonal as viewed from the axial direction as in the present embodiment, a configuration that satisfies the above formula (1) or the above formula (2) can be preferably used. That is, when the shape of the back yoke 23 is polygonal as viewed from the axial direction, the winding area of the coil 22 can be increased as compared with the case where the shape of the back yoke 23 is circular as viewed from the axial direction. As a result, the electric loading can be increased, but the permanent magnet 18 is likely to be demagnetized. However, by the configuration that satisfies the above formula (1) or the above formula (2), demagnetization of the permanent magnet 18 can be effectively suppressed.

[0052] By forming the hole portion 42 in the rotor core main body 41, the rotor core main body 41 can be lightened. Therefore, the motor performance of the motor unit 2 can be further improved.

[0053] Each hole portion 42 faces each permanent magnet 18 separately in the radial direction. That is, each hole portion 42 is separately arranged inside the permanent magnet 18 in the radial direction. Here, as shown in detail in FIG. 3, on the inner peripheral surface 18b side of the permanent magnet 18, in the rotor core body 41, the positions corresponding to both sides in the circumferential direction of the permanent magnet 18 become the magnetic path M through which the magnetic flux J3 passes. For this reason, each hole portion 42 is formed avoiding the portion that becomes the magnetic path M in the rotor core body 41. Therefore, even if the hole portion 42 is formed, the magnetic path M of the rotor core body 41 can be sufficiently secured. Thus, a decrease in the motor performance of the motor unit 2 due to magnetic saturation can be suppressed.

[0054] The lamination boss 48 for maintaining the laminated state of the plurality of steel plates 40 is formed in the bridge portion 45. For this reason, it is possible to prevent the periphery of the lamination boss 48 from becoming thin compared to the case where the lamination boss 48 is formed outside the bridge portion 45. Thus, it is possible to suppress breakage or wear of a die (not shown) for performing press working on the steel plate 40.

[0055] The hole portion 42 has a wide hole portion 43 and a narrow hole portion 44. A wide bridge portion 47 is formed between the narrow hole portions 44 adjacent in the circumferential direction. The lamination boss 48 is arranged in this wide bridge portion 47. For this reason, it is possible to surely prevent the periphery of the lamination boss 48 from becoming thin in the rotor core body 41. Even if the lamination boss 48 is formed, a sufficient magnetic path M can be secured around the lamination boss 48. Thus, it is possible to suppress breakage and wear of the die for forming the steel plate 40 (not shown) surely, and to suppress a decrease in the motor performance of the motor unit 2 due to magnetic saturation.

[0056] It is possible to suppress demagnetization of the permanent magnet 18 in the motor unit 2 and improve the motor performance. Therefore, 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, "Build resilient infrastructure, promote inclusive and sustainable industrialization, and foster innovation."

[0057] [Modification Example] The present invention is not limited to the above-described embodiments, and includes those obtained by making various modifications to the above-described embodiments without departing from the spirit of the present invention.

[0058] For example, in the above-described embodiment, the case where the motor unit 2 is provided in the motor 1 with a speed reducer has been described. However, the present invention is not limited to this, and the motor unit 2 can be used alone, or the motor unit 2 can be adopted in various devices.

[0059] In the above-described embodiment, the case where the motor unit 2 is a brushless motor with 8 poles of the permanent magnet 18 and 6 slots (number of teeth 24) has been described. However, the present invention is not limited to this, and it is sufficient that the ratio of the number of poles of the permanent magnet 18 to the number of slots 25 (number of teeth 24) is 4:3. The number of salient poles 19 may be the same as the number of permanent magnets 18.

[0060] In the above-described embodiment, the case where the back yoke 23 is formed in a cylindrical shape having a hexagonal shape when viewed from the axial direction has been described. However, the present invention is not limited to this, and the back yoke 23 may be circular when viewed from the axial direction. In this case, the minimum width Ds of the back yoke 23 as viewed from the direction of the rotation axis line A coincides with the outer diameter of the back yoke 23. When the back yoke 23 is polygonal when viewed from the axial direction, it may be changed according to the number of teeth 24.

[0061] In the above-described embodiment, the case where the rotor core 17 is formed by laminating a plurality of steel plates 40 in the axial direction, for example, has been described. However, the present invention is not limited to this, and the rotor core 17 may be formed by, for example, pressure-molding soft magnetic powder. In this case, it is not necessary to form the laminated boss 48 on the rotor core 17.

[0062] In the above-described embodiment, the hole portion 42 has been described as having the wide hole portion 43 and the narrow hole portion 44. However, the present invention is not limited to this, and various shapes can be adopted as the hole portion 42. For example, it may be configured as follows. FIG. 8 shows a modified example of the rotor 13 and is a plan view seen from the axial direction. FIG. 8 corresponds to the rotor 13 of FIG. 2 described above. That is, as shown in FIG. 8, for example, an arc-shaped hole portion 61 may be formed in the rotor core body 41 instead of the hole portion 42. The arc-shaped hole portion 61 is formed in an oval shape along the circumferential direction when seen from the axial direction.

[0063] When configured in this way, in order to dispose the laminated boss 48 on the bridge portion 62 formed between the adjacent arc-shaped hole portions 61 in the circumferential direction, it is desirable to make the circumferential interval of the arc-shaped hole portions 61 slightly larger than the circumferential interval of the hole portion 42 in the above-described embodiment. Thereby, the width W5 along the circumferential direction of the bridge portion 62 can be made larger than the width W3 in the circumferential direction of the salient pole 19. For this reason, the same effects as those of the above-described embodiment can be obtained.

Description of Reference Numerals

[0064] 1... Motor with speed reducer, 2... Motor part, 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, 18... Permanent magnet, 18a... Magnet side surface, 18b... Inner peripheral surface, 18c... Outer peripheral surface, 18d... Parallel surface, 18e... Chamfered part, 19... Pole projection, 21... Stator core, 22... Coil, 23... Back yoke, 24... Teeth, 25... Slot, 26... Long side part, 27... Connecting part, 31... Winding drum part, 32... Flange part, 40... Steel plate, 41... Rotor core body, 41a... Outer peripheral surface, 41b... Through hole, 42... Hole part, 43... Wide hole part, 44... Narrow hole part, 45... Bridge part, 46... Narrow bridge part, 47... Wide bridge part, 48... Stacked boss, 51... Magnet housing recess, 61... Arc hole part, 62... Bridge part, A... Axis of rotation, C1... Center, C2... Center in circumferential direction, C3... Center in circumferential direction, Ci... Arc center, Co... Arc center, Dr... Diameter, Ds... Minimum width, J3... Magnetic flux, M... Magnetic circuit, R... Region, Ri... Radius of curvature, Ro... Radius of curvature, W1... Width, W2... Width, W3... Width, W4... Width, W5... Width

Claims

1. An annular stator, a rotor disposed inside the stator in the radial direction and rotatably provided with respect to the stator, comprising: The stator includes: an annular back yoke, a plurality of teeth protruding radially inward from the inner peripheral surface of the back yoke along the radial direction and around which coils are wound, comprising: The rotor includes: a rotor shaft centered on the rotation axis, a columnar rotor core body fixed to the rotor shaft, a plurality of salient poles protruding radially outward from the outer peripheral surface of the rotor core body, a plurality of permanent magnets respectively disposed on the outer peripheral surface of the rotor core body and between the adjacent salient poles in the circumferential direction, comprising: The ratio of the number of magnetic poles of the permanent magnet to the number of teeth is 4:3, 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, Let the diameter of the circle passing through the outermost side of the permanent magnet centered on the rotation axis be Dr, When the minimum width of the back yoke as viewed from the direction of the rotation axis is Ds, 0.697 < Dr / Ds < 1 is satisfied, A brushless motor characterized by this.

2. An annular stator, a rotor disposed inside the stator in the radial direction and rotatably provided with respect to the stator, comprising: The stator includes: an annular back yoke, a plurality of teeth protruding radially inward from the inner peripheral surface of the back yoke along the radial direction and around which coils are wound, comprising: The rotor includes: a rotor shaft centered on the rotation axis, a columnar rotor core body fixed to the rotor shaft, a plurality of salient poles protruding radially outward from the outer peripheral surface of the rotor core body, a plurality of permanent magnets respectively disposed on the outer peripheral surface of the rotor core body and between the adjacent salient poles in the circumferential direction, comprising: The ratio of the number of teeth to the number of magnetic poles of the permanent magnet is 4:3, The magnetization orientation of the permanent magnet is a radial orientation along the radial direction as viewed from the direction of the rotation axis, Let the diameter of the circle passing through the outermost side of the permanent magnet centered on the rotation axis be Dr, When the minimum width of the back yoke as viewed from the direction of the rotation axis is Ds, 0.618 < Dr / Ds < 1 is satisfied, A brushless motor characterized by this.

3. The back yoke is polygonal as viewed from the direction of the rotation axis. The brushless motor according to claim 1 or claim 2, characterized in that.

4. The rotor core body has a plurality of holes provided so as to face each of the permanent magnets separately in the radial direction. The brushless motor according to claim 1 or claim 2, characterized in that.

5. The rotor core body is formed by laminating a plurality of steel plates. In the rotor core body, the bridge portions formed between the holes adjacent in the circumferential direction face the salient poles in the radial direction, respectively. The bridge portions are provided with lamination bosses for connecting the plurality of steel plates. The brushless motor according to claim 4, characterized in that.

6. The holes are a wide hole portion disposed on the inner side in the radial direction, and a narrow hole portion disposed on the outer side in the radial direction of the wide hole portion and communicating with the wide hole portion, and having a shorter width along the circumferential direction than the width along the circumferential direction of the wide hole portion. and have the lamination bosses are disposed between the narrow hole portions adjacent in the circumferential direction. The brushless motor according to claim 5, characterized in that.

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