Electric motor

Abstract

To provide an electric motor the production cost of which can be reduced and in which vibration, noise, and motor characteristics of which can be improved.SOLUTION: A rotor 9 includes a shaft that is cantilever-supported by a first bearing, a rotor core 32 that is fixed to the shaft, a magnet 33 that is disposed on the outer circumferential surface of the rotor core 32, a magnet holder 70 that is disposed only on a first end surface 32a of the rotor core 32, and a magnet cover 71 that surrounds the magnet 33. The position of the first end surface 32a in the rotor core 32 is closer to the first bearing than a first end surface 33a of the magnet 33. The position of a second end surface 32b in the rotor core 32 is closer to the first bearing than a second end surface 33b of the magnet 33.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an electric motor. [Background technology]

[0002] Conventionally, there has been known a motor unit in which an electric motor and a reducer are integrated. The electric motor includes a stator having teeth around which a coil is wound, and a rotor rotatably provided radially inside the stator. The rotor includes a shaft, a cylindrical rotor core fixed to the shaft, and a magnet provided on the rotor core. The shaft may be integrated with an input shaft of the reducer.

[0003] For example, a motor unit using a so-called worm reducer consisting of a worm shaft and a worm wheel meshed with the worm shaft as a reducer has the worm shaft and shaft arranged coaxially and integrated. In this motor unit, both ends of the worm shaft are rotatably supported by bearings, and the motor unit is made smaller by eliminating the bearing on the electric motor side. Therefore, the shaft of the electric motor is supported at one end by the bearing on the reducer side.

[0004] With this configuration, when electricity is applied to the coil, magnetic attraction and repulsion are generated between the interlinked magnetic flux formed in the stator and the magnets provided in the rotor core, causing the rotor to rotate continuously. The rotation of the motor is transmitted to a reducer (e.g., a worm shaft), where it is decelerated and output.

[0005] One way to place magnets on a rotor is the SPM (Surface Permanent Magnet) type, in which the magnets are attached to the outer periphery of the rotor core. In this type of SPM motor, a magnet cover is provided on the rotor core to cover the entire outer surface of the magnet to prevent the magnet from being damaged by foreign objects, etc. The magnet cover has a cylindrical portion that covers the outer peripheral surface of the magnet in the radial direction, and two flanges that are integrally molded on both axial ends of the cylindrical portion. One of the two flanges is formed in a cylindrical shape before being assembled to the rotor core. After the magnet cover is assembled to the rotor core, it is crimped to become a flange.

[0006] In some cases, the magnets are configured to overhang, with both ends of the magnet protruding from both ends of the rotor core in the axial direction. This configuration can reduce magnetic flux leakage from both ends of the magnet to both ends of the rotor core in the axial direction. This increases the effective magnetic flux of the magnet, improving the characteristics of the electric motor.

[0007] When the magnet cover is crimped, if the magnet is configured to overhang, the two flanges of the magnet cover will only contact the magnet. As a result, the stress acting on the magnet by the magnet cover will be large, and there is a possibility that the magnet will be damaged. For this reason, a technology has been disclosed in which magnet holders are provided on both axial sides of the rotor core (see, for example, Patent Document 1).

[0008] In addition, in Patent Document 1, when the shaft is supported at one end, the greater the distance between the bearing and the rotor core or magnet, the greater the dynamic imbalance of the rotor. This results in vibration, noise, and deterioration of the motor characteristics of the electric motor. For this reason, the center positions of the rotor, magnet, and stator are shifted. Specifically, the length between the inner wall surfaces of the magnet holders facing each other in the axial direction, the magnet length in the axial direction of the magnets, and the offset length of the axial center position of the rotor core from the center position of the stator core toward the bearing are specified. By configuring in this way, it is intended to improve the vibration, noise, and motor characteristics of the electric motor. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent Publication No. 2021-35187 Summary of the Invention [Problem to be solved by the invention]

[0010] However, in the above-mentioned conventional technology, the number of parts of the rotor increases due to the provision of two magnet holders, resulting in an increase in manufacturing costs. In addition, the provision of two magnet holders means that the offset length of the rotor core toward the bearing cannot be sufficiently secured, which poses a problem of limitations in reducing vibration and noise in the electric motor and limiting improvements in motor characteristics.

[0011] Therefore, the present invention provides an electric motor that can reduce manufacturing costs and improve vibration, noise, and motor characteristics. [Means for solving the problem]

[0012] In order to solve the above problems, an electric motor according to the present invention includes a stator having a coil and a stator core around which the coil is wound, and a rotor arranged radially inside the stator and supported by a bearing so as to be rotatable about a rotation axis relative to the stator, the rotor including a shaft that is cantilevered by the bearing and has a tip end side in the direction of the rotation axis disposed radially inside the stator relative to the bearing, a rotor core that is fixed to the shaft and disposed radially inside the stator, a magnet arranged on an outer circumferential surface of the rotor core, and a magnet provided only at the end of the rotor core opposite the bearing and in contact with the rotor core. the rotor core has a rotor holder that covers the end of the magnet opposite the bearing, and a magnet cover that covers the periphery of the magnet, and the positions of both ends of the magnet in the direction of the rotation axis are located on the same plane as the ends of the stator core in the direction of the rotation axis or outside the ends in the direction of the rotation axis, the position of the end of the rotor core opposite the bearing is located closer to the bearing than the end of the magnet opposite the bearing, and the position of the end of the rotor core on the bearing side is located closer to the bearing than the end of the magnet on the bearing side. Effect of the Invention

[0013] According to the present invention, the number of magnet holders can be reduced, and manufacturing costs can be reduced, compared to when magnet holders are provided on both axial ends of the rotor core. Also, the rotor core can be offset sufficiently toward the bearing side by the amount that the magnet holder on the bearing side can be eliminated. This improves dynamic balance, and improves vibration, noise, and motor characteristics of the electric motor. [Brief description of the drawings]

[0014] [Figure 1] FIG. 2 is a perspective view of a motor unit according to the embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Diagram 3]1 is a cross-sectional view taken along an axial direction of a rotor according to an embodiment of the present invention. [Figure 4] FIG. 2 is an exploded perspective view of a rotor according to an embodiment of the present invention. [Diagram 5] 5A to 5C are explanatory diagrams showing an assembly process of the magnet cover in the embodiment of the present invention. [Figure 6] 5A to 5C are explanatory diagrams showing an assembly process of the magnet cover in the embodiment of the present invention. [Figure 7] 5A to 5C are explanatory diagrams showing an assembly process of the magnet cover in the embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Next, an embodiment of the present invention will be described with reference to the drawings.

[0016] <Motor unit> Fig. 1 is a perspective view of a motor unit 1 using an electric motor 2 according to the present invention. Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1. The motor unit 1 is used, for example, as a drive source for a wiper device of a vehicle. As shown in FIGS. 1 and 2, the motor unit 1 includes an electric motor 2, a speed reducer 3 that reduces the rotation speed of the electric motor 2 and outputs the reduced speed, and a controller 4 that controls the drive of the electric motor 2.

[0017] In the following description, the term "axial direction" refers to the direction along the rotation axis C of the shaft 31 of the electric motor 2. The term "circumferential direction" refers to the circumferential direction of the shaft 31. The term "radial direction" refers to the radial direction of the shaft 31.

[0018] <Electric motor> The electric motor 2 is a so-called brushless motor that does not require brushes to supply power to the stator 8. The electric motor 2 includes a motor case 5, a cylindrical stator 8 housed in the motor case 5, and a rotor 9 disposed radially inside the stator 8 and rotatably provided relative to the stator 8.

[0019] <Motor case> The motor case 5 is made of a material with excellent heat dissipation properties, such as an aluminum alloy. The motor case 5 is made up of a first motor case 6 and a second motor case 7, which are configured to be separable in the axial direction. The first motor case 6 and the second motor case 7 are each formed in a cylindrical shape with a bottom. The first motor case 6 has a bottom portion 10 integrally formed with a gear case 40 of the reduction gear unit 3. A through hole 10a is formed in the approximate center in the radial direction of the bottom portion 10, through which the shaft 31 of the electric motor 2 can be inserted.

[0020] Outer flange portions 16, 17 that protrude radially outward are formed at the openings 6a, 7a of the first motor case 6 and the second motor case 7. In the motor case 5, the outer flange portions 16, 17 are butted against each other to form an internal space. The stator 8 and the rotor 9 are disposed in this internal space.

[0021] <Stator> The stator 8 is fixed to the inner peripheral surface of the motor case 5. The stator 8 includes a stator core 20 made of laminated electromagnetic steel sheets or the like, and a plurality of coils 24 wound around the stator core 20. The stator core 20 includes an annular core body 21 and a plurality of (for example, six) teeth 22 protruding radially inward from the inner peripheral portion of the core body 21. The inner peripheral surface of the core body 21 and each of the teeth 22 are covered with a resin insulator 23. The coils 24 are wound around corresponding predetermined teeth 22 from above the insulator 23. When power is supplied from the controller 4, each coil 24 forms a linkage magnetic flux that contributes to the rotation of the rotor 9.

[0022] <Deceleration section> The reduction unit 3 includes a gear case 40 integrated with the motor case 5, and a worm reduction mechanism 41 housed in the gear case 40. The gear case 40 is made of a metal material with excellent heat dissipation properties, such as an aluminum alloy. The gear case 40 is formed in a box shape with an opening 40a on one side. The gear case 40 has a gear housing portion 42 that houses the worm reduction mechanism 41 therein. An opening 43 that communicates with the through hole 10a of the first motor case 6 and the gear housing portion 42 is formed in a portion of the side wall 40b of the gear case 40 where the first motor case 6 is integrally formed.

[0023] A cylindrical bearing boss 49 is formed to protrude from the bottom wall 40c of the gear case 40. The bearing boss 49 is for rotatably supporting the output shaft 48 of the worm reduction mechanism 41, and a plain bearing (not shown) is disposed on the inner periphery side. An O-ring (not shown) is attached to the inner periphery of the tip of the bearing boss 49. A plurality of ribs 52 are provided on the outer periphery of the bearing boss 49 to ensure rigidity.

[0024] The worm reduction mechanism 41 housed in the gear housing portion 42 is made up of a worm shaft 44 formed integrally with the shaft 31 of the rotor 9, and a worm wheel 45 meshed with the worm shaft 44. Both axial ends of the worm shaft 44 are supported by the gear case 40 via bearings 46, 47 (a first bearing 46 and a second bearing 47) so as to be rotatable about a rotation axis (shaft center) C. An output shaft 48 of the electric motor 2 is provided coaxially and integrally with the worm wheel 45.

[0025] The worm wheel 45 and the output shaft 48 are arranged so that their rotation axes are perpendicular to the rotation axis C of the worm shaft 44 (shaft 31 of the electric motor 2). The output shaft 48 protrudes to the outside via a bearing boss 49 of the gear case 40. A spline 48a is formed at the protruding tip of the output shaft 48, which can be connected to an object to be driven by the motor.

[0026] In addition, a sensor magnet (not shown) is provided on the worm wheel 45. The rotational position of this sensor magnet is detected by a magnetic detection element 61 (described later) provided in the controller 4. In other words, the rotational position of the worm wheel 45 is detected by the magnetic detection element 61 of the controller 4.

[0027] <Controller> The controller 4 has a controller board 62 on which a magnetic detection element 61 is mounted. The controller board 62 is disposed in the opening 40a of the gear case 40. The magnetic detection element 61 mounted on the controller board 62 faces the sensor magnet of the worm wheel 45. The opening 40a of the gear case 40 is closed by a cover 63.

[0028] Terminal portions of the multiple coils 24 drawn out from the stator core 20 are connected to the controller board 62. Terminals of a connector 11 (see FIG. 1) provided on a cover 63 are electrically connected to the controller board 62. In addition to the magnetic detection element 61, the controller board 62 also has mounted thereon a power module made up of switching elements such as a FET (Field Effect Transistor) that controls the drive voltage supplied to the coils 24, a capacitor that smooths the voltage (neither of which is shown), and the like.

[0029] <Rotor> Fig. 3 is a cross-sectional view taken along the axial direction of the rotor 9. Fig. 4 is an exploded perspective view of the rotor 9. 2 to 4, the rotor 9 is rotatably disposed radially inside the stator 8 via a small gap. The rotor 9 includes a rotor core 32 fixed to the shaft 31, four magnets 33 attached to the outer circumferential surface of the rotor core 32, a magnet holder 70 disposed on a first end face 32a of the rotor core 32 opposite to the reduction gear unit 3, and a metallic magnet cover 71 that covers the rotor core 32 and the magnets 33 together with the magnet holder 70 from the axial and radial outside.

[0030] <Shaft> The shaft 31 is formed integrally with the worm shaft 44 of the speed reducer portion 3. That is, the shaft 31 is coaxially disposed on the end of the worm shaft 44 on the electric motor 2 side. Here, the electric motor 2 does not have a bearing for rotatably supporting the shaft 31 inside the motor case 5. The shaft 31 is formed integrally with the worm shaft 44, and is supported by two bearings 46, 47 that rotatably support the worm shaft 44. That is, the shaft 31 is cantilevered by a first bearing (an example of a bearing in the claims) 46, which is one of the two bearings 46, 47 and is disposed on the electric motor 2 side. The rotor core 32 is fixed to a tip 31a side of the shaft 31 that extends from the first bearing 46 radially inward of the stator 8 (stator core 20).

[0031] <Rotor core> The rotor core 32 has a cylindrical core body 34 and four salient poles 35 protruding in the radial direction from the outer circumferential surface of the core body 34. The rotor core 32 is formed, for example, by pressure molding soft magnetic powder or by stacking a plurality of electromagnetic steel plates in the axial direction. The axial length L1 of the rotor core 32 is approximately the same as the axial length L2 of the stator core 20. A shaft holding hole 72 centered on the rotation axis C of the rotor 9 is formed in the rotor core 32. The shaft 31 is press-fitted and fixed into the shaft holding hole 72. This allows the rotor core 32 to rotate around the rotation axis C together with the shaft 31.

[0032] The rotor core 32 press-fitted and fixed to the shaft 31 is disposed offset toward the first bearing 46 (reduction section 3) from the stator core 20 of the stator 8. That is, the position of the first end face 32a of the rotor core 32 is located closer to the first bearing 46 than the first end face 20a of the stator core 20 opposite the reduction section 3. The position of the second end face 32b on the reduction section 3 side of the rotor core 32 is located closer to the first bearing 46 than the position of the second end face 20b of the stator core 20 on the reduction section 3 side.

[0033] Four escape grooves 73 extending radially outward are formed on the inner circumferential surface of the shaft holding hole 72. The escape grooves 73 are arranged at equal intervals in the circumferential direction. Each escape groove 73 is connected to the radial inside of the shaft holding hole 72. Each escape groove 73 is formed over the entire axial direction of the rotor core 32. The radially outer end of each escape groove 73 is formed as an arc-shaped engagement portion 73a. A locking claw 74 (core restriction portion) of the magnet holder 70, which will be described later, is fitted into the engagement portion 73a.

[0034] The four salient poles 35 protrude at equal intervals on the outer periphery of the core body 34 and extend in the axial direction. The outer periphery of the core body 34 is formed in a circular shape centered on the rotation axis C of the rotor 9. The circumferential side of each salient pole 35 is formed flat. A magnet 33 is assembled between two salient poles 35 adjacent to each other in the circumferential direction of the rotor core 32.

[0035] <Magnet> For example, a ferrite magnet is used as the magnet 33. However, the magnet 33 is not limited to this, and a neodymium bonded magnet, a neodymium sintered magnet, or the like can also be used.

[0036] The magnet 33 is formed in an arc shape when viewed from the axial direction. Specifically, the inner surface of the magnet 33 is formed in an arc shape (an arc shape that approximately matches the outer circumferential surface of the core body 34) centered on the rotation axis C of the rotor 9. The inner surface of the magnet 33 abuts against the outer circumferential surface of the core body 34.

[0037] The outer surface of the magnet 33 is formed in an arc shape with a smaller radius of curvature than the inner surface. The distance from the rotation axis C of the rotor 9 to the maximum bulge 33c (the circumferential center of the magnet 33, see FIG. 5) of the outer surface of the magnet 33 is approximately the same as the distance from the rotation axis C of the rotor 9 to the radially outer end of each salient pole 35. The circumferential length of the magnet 33 is approximately equal to or slightly shorter than the length between two circumferentially adjacent salient poles 35 .

[0038] The axial length L3 of the magnet 33 is longer than the axial length L2 of the stator core 20 (the axial length L1 of the rotor core 32). When the magnet 33 is assembled to the rotor core 32, the magnet 33 is disposed offset from the rotor core 32 to the opposite side to the first bearing 46 (reduction section 3). Moreover, the rotor core 32 protrudes from the magnet 33 towards the first bearing 46 (reduction section 3).

[0039] That is, the position of the first end face 32a of the rotor core 32 is located closer to the first bearing 46 than the first end face 33a of the magnet 33 on the side opposite the speed reducer 3. The position of the second end face 32b of the rotor core 32 is located closer to the first bearing 46 than the second end face 33b of the magnet 33 on the speed reducer 3 side. Further, each end face 33a, 33b of the magnet 33 protrudes axially outward beyond the stator core 20. That is, each end face 33a, 33b of the magnet 33 is positioned axially outward beyond each end face 20a, 20b of the corresponding stator core 20. In other words, the magnet 33 is configured to overhang the stator core 20.

[0040] <Magnetic cover> The magnet cover 71 is formed by deep drawing a non-magnetic metal plate such as stainless steel, etc. The magnet cover 71 includes a cylindrical portion 71a that covers the outer peripheral surfaces of the rotor core 32 and the magnet 33, a protruding portion 71b integrally molded at the end of the cylindrical portion 71a on the side of the reduction unit 3 (the end on the side of the second end face 33b of the magnet 33), an inner flange portion 71c integrally molded at the radially inner end of the protruding portion 71b, and a crimping portion 71d integrally molded at the end of the cylindrical portion 71a opposite to the reduction unit 3.

[0041] The protruding portion 71b is formed so as to be convex from the end of the cylindrical portion 71a toward the speed reducer portion 3 side (the outer side in the axial direction) and bent back toward the inner side in the radial direction. The protruding portion 71b is formed around the entire circumference of the cylindrical portion 71a. An inner flange portion 71c extends from the folded-back radially inner end of the protruding portion 71b so as to protrude radially inward.

[0042] In a state where the magnet cover 71 is attached to the rotor core 32 (hereinafter simply referred to as a state where the magnet cover 71 is attached), the inner flange portion 71c abuts against a first end face 32a of the salient pole 35 of the rotor core 32. The first end face 32a of the rotor core 32 protrudes toward the first bearing 46 beyond the first end face 33a of the magnet 33. For this reason, in the attached state of the magnet cover 71, a minute gap S is formed between the inner flange portion 71c and the first end face 33a of the magnet 33.

[0043] The crimped portion 71d is formed by plastically deforming the end of the cylindrical portion 71a opposite to the protruding portion 71b by crimping, with the rotor core 32 and the magnet 33 disposed inside the cylindrical portion 71a together with the magnet holder 70. The method of assembling the magnet cover 71 will be described in detail later. Except for the description of this assembling method, the crimped portion 71d of the magnet cover 71 will be described as being crimped.

[0044] It is desirable to make the thickness of the magnet cover 71 as thin as possible. This is because the thickness of the magnet cover 71 is proportional to the size of the clearance (gap) between the rotor 9 and the stator 8. If this clearance becomes large, the magnetic attractive and repulsive forces between the rotor 9 and the stator 8 decrease, and the torque characteristics of the electric motor 2 deteriorate.

[0045] <Magnet holder> The magnet holder 70 is formed of, for example, a hard resin. The magnet holder 70 is formed in a shape that overlaps substantially the rotor core 32 when viewed in the axial direction. That is, the magnet holder 70 has an annular portion 81 that is arranged to overlap the first end face 32a of the core body portion 34 of the rotor core 32, four leg portions 82 that radially protrude from the outer circumferential surface of the annular portion 81, and an end wall 83 that is integrally connected to the axial outer sides of the annular portion 81 and the leg portions 82.

[0046] Four locking claws 74 are integrally formed at equal intervals in the circumferential direction on the inner peripheral edge of the annular portion 81. The locking claws 74 protrude toward the rotor core 32 along the axial direction. The locking claws 74 are formed in a semicircular cross section. When the magnet holder 70 is assembled to the first end face 32a of the rotor core 32, the locking claws 74 are fitted into escape grooves 73 (engagement portions 73a) on the inner circumference of the rotor core 32. By fitting each locking claw 74 into the corresponding escape grooves 73 (engagement portions 73a), the relative radial displacement of the magnet holder 70 with the rotor core 32 is restricted. Further, at the end of the annular portion 81 overlapping with the core body portion 34, a recess 59 is formed between two locking claws 74 adjacent to each other in the circumferential direction.

[0047] The four legs 82 are formed to protrude radially outward from positions on the outer periphery of the annular portion 81 corresponding to the locking claws 74. The four legs 82 are arranged to overlap with the axial end faces of the respective salient poles 35 of the rotor core 32. The positions of the radial outer ends of the four legs 82 are substantially the same as the radial outer ends of the corresponding salient poles 35 when viewed from the axial direction. The axial length H of each leg 82 is slightly longer than the distance L4 between the first end face 32 a of the rotor core 32 and the first end face 33 a of the magnet 33 .

[0048] A pair of press-fit protrusions 76 are formed on both circumferential side surfaces of each leg portion 82, near the annular portion 81. Each press-fit protrusion 76 extends along the axial direction and is formed so that its protruding height gradually decreases toward the rotor core 32. When the magnets 33 are arranged on the outer peripheral surface of the rotor core 32 and the magnet holder 70 is further assembled to the rotor core 32, the ends of the magnets 33 are inserted between two circumferentially adjacent legs 82 of the magnet holder 70. At this time, the circumferential side surface of the magnets 33 comes into contact with the press-in protrusions 76. This restricts the circumferential displacement of the magnets 33.

[0049] The end wall 83 is formed to protrude radially outward from the annular portion 81. The end wall 83 is in the shape of a disk (a disk with a hole) with a radius substantially equal to the length from the axis C of the rotor core 32 to the tip of the leg portion 82. The end wall 83 closes the space between two circumferentially adjacent leg portions 82 at the axially outer positions of the leg portions 82. The end wall 83 also covers the first end face 33a of the magnet 33 via a small gap.

[0050] A circular confirmation hole 57 is formed in the end wall 83 between two circumferentially adjacent leg portions 82. The confirmation hole 57 is formed in a position facing the axial end face of each magnet 33. This allows the position of each magnet 33 to be visually confirmed from outside the rotor core 32 when the magnet holder 70 is assembled in the magnet cover 71 together with the rotor core 32 holding the magnets 33 (hereinafter referred to as the assembled state of the magnet holder 70). Four confirmation holes 57 are provided so as to correspond one-to-one with each magnet 33.

[0051] The end wall 83 has a flat surface on the axially outer side. In contrast, a plurality of radially extending reinforcing ribs 58 are formed to protrude from an inner surface 83a of the end wall 83 facing the magnet 33. Two reinforcing ribs 58 are disposed between each pair of legs 82 adjacent to each other in the circumferential direction of the inner surface 83a of the end wall 83.

[0052] The reinforcing rib 58 has a function of suppressing the occurrence of deformation such as dents and waves in the circumferential area of ​​the end wall 83 when the magnet holder 70 is, for example, injection molded from resin. The reinforcing rib 58 also has a function of increasing the mechanical strength of the end wall 83. Furthermore, the reinforcing rib 58 abuts against the first end face 33a of the magnet 33 when the magnet holder 70 is in an assembled state. This restricts the axial displacement of the magnet 33 when an excessive load is applied to the magnet 33 in the axial direction.

[0053] With this configuration, a crimped portion 71d is formed on the outer periphery of the end wall 83 of the magnet holder 70. That is, the crimped portion 71d of the magnet cover 71 is positioned axially outward of the first end face 33a of the magnet 33.

[0054] <How to attach the magnet cover> Next, a method for assembling the magnet cover 71 will be described with reference to FIGS. 5 to 7 are explanatory diagrams showing the process of assembling the magnet cover 71. FIG. First, before assembling the magnet cover 71, the magnet 33 is arranged in advance on the outer peripheral surface of the rotor core 32. In this state, the magnet holder 70 is temporarily assembled to the first end surface 32a of the rotor core 32. In the following description, this temporarily assembled state is referred to as a preliminary assembly 79.

[0055] In this state of the preliminary assembly 79, as shown in Fig. 5, the magnet cover 71 is placed on the second end surface 32b side of the rotor core 32. At this time, the magnet cover 71 is placed with the crimped portion 71d facing the rotor core 32 side. Also, at this time, the crimped portion 71d is not crimped, and is formed in a fan-shaped manner so that the opening area gradually increases toward the opposite side to the protruding portion 71b (the rotor core 32 side). The opening 77 of the magnet cover 71 formed in this manner is placed facing the rotor core 32 side.

[0056] In this state, as shown in Fig. 6, the protruding portion 71b is pressed from above by a press-fitting jig 91. The protruding portion 71b is formed so as to be convex from the end of the cylindrical portion 71a toward the speed reducer portion 3 side (the outer side in the axial direction) and bent back toward the inside in the radial direction. Therefore, the press-fitting jig 91 presses the protruding portion 71b and does not come into contact with the inner flange portion 71c. Moreover, the protruding portion 71b formed as described above has high mechanical strength against forces applied in the axial direction, and can reliably bear the pressing load of the press-fitting jig 91.

[0057] 6, the cylindrical portion 71a of the magnet cover 71 is press-fitted onto the outer surface of the magnet 33 while the magnet cover 71 is pressed toward the spare assembly 79 by a press-fitting jig 91. The magnet cover 71 is then attached to the spare assembly 79. At this time, since the crimping portion 71d is formed in a fan-shaped shape, the magnet cover 71 can be easily fitted to the spare assembly 79. The pressing of the magnet cover 71 by the press-fitting jig 91 is continued until the inner flange portion 71c of the magnet cover 71 abuts against the second end face 32b of the rotor core 32 (salient pole 35). When the inner flange portion 71c abuts against the second end face 32b, the magnet cover 71 is completely pressed into the preliminary assembly 79.

[0058] As shown in FIG. 7, after magnet cover 71 is completely pushed into preliminary assembly 79, crimping tool 92 is used to crimp crimped portion 71d by folding it radially inward (see arrow Y in FIG. 7). Here, the magnet holder 70 arranged on the crimped portion 71d side is arranged to overlap the first end face 32a of the rotor core 32 and the first end face 33a of the magnet 33. Therefore, the crimped portion 71d is formed on the outer periphery of the end wall 83 of the magnet holder 70.

[0059] That is, the crimped portion 71d of the magnet cover 71 is positioned axially outward of the first end face 33a of the magnet 33. Furthermore, the outer periphery of the end wall 83 is disposed between the first end face 32a of the rotor core 32 and the first end face 33a of the magnet 33 and the crimped portion 71d. Therefore, the end wall 83 bears the crimping load during the crimping operation of the crimped portion 71d. As a result, the crimping load from the crimping jig 92 is not applied to the magnet 33. Furthermore, the reinforcing rib 58 of the magnet holder 70 suppresses deformation of the outer periphery of the end wall 83 of the magnet holder 70 due to the crimping load when the end of the magnet cover 71 is crimped.

[0060] By plastically deforming the crimped portion 71d, the rotor core 32 and the magnet 33 are fixed inside the magnet cover 71 together with the magnet holder 70. This completes the assembly of the magnet cover 71.

[0061] <Motor unit operation> Next, the operation of the motor unit 1 will be described. In the motor unit 1, when power is supplied from the controller 4 to each coil 24 of the electric motor 2, a predetermined magnetic field is formed in the stator 8. In response to this magnetic field, magnetic attraction and repulsion are generated between the magnetic field and the magnet 33 of the rotor 9. This causes the rotor 9 to rotate continuously.

[0062] Here, the shaft 31 of the rotor 9 is cantilevered by the first bearing 46. Therefore, the further the center of gravity of the rotor 9 is from the first bearing 46, the greater the dynamic unbalance becomes, and the greater the rotation of the rotor 9 becomes. However, in the rotor 9, even though the magnet 33 is configured to overhang with respect to the stator core 20, the position of the first end face 32a of the rotor core 32 is offset so as to be located closer to the first bearing 46 than the first end face 33a of the magnet 33 on the opposite side to the speed reducer 3. Therefore, the center of gravity of the rotor 9 is as close to the first bearing 46 as possible. Therefore, the dynamic unbalance of the rotor 9 becomes as small as possible, and the rotation of the rotor 9 becomes smaller.

[0063] When the rotor 9 rotates, the worm shaft 44 integrated with the shaft 31 is rotated, which in turn rotates the worm wheel 45 meshed with the worm shaft 44. Then, the output shaft 48 integrally provided with the worm wheel 45 is rotated, and for example, a wiper device of a vehicle (not shown) is driven.

[0064] In this manner, the end faces 33a, 33b of the magnet 33 in the rotor 9 described above are positioned axially outward of the corresponding end faces 20a, 20b of the stator core 20. The first end face 32a of the rotor core 32 is positioned closer to the first bearing 46 than the first end face 33a of the magnet 33. The second end face 32b of the rotor core 32 is positioned closer to the first bearing 46 than the second end face 33b of the magnet 33.

[0065] Therefore, in the electric motor 2 in which the shaft 31 is cantilevered by the first bearing 46, the effective magnetic flux of the magnet 33 can be sufficiently ensured, and the characteristics of the electric motor 2 can be improved. Also, the rotor core 32 can be sufficiently offset toward the first bearing 46. Moreover, the second end face 32b of the rotor core 32 protrudes toward the first bearing 46 further than the second end face 33b of the magnet 33. In such a case, the inner flange portion 71c of the magnet cover 71 abuts only against the second end face 32b of the rotor core 32. Therefore, without providing a magnet holder 70, the stress acting on the magnet 33 due to the provision of the magnet cover 71 can be minimized on the second end face 32b side of the rotor core 32, and damage to the magnet 33 can be prevented.

[0066] In this way, the number of magnet holders can be reduced, and manufacturing costs can be reduced, compared to when magnet holders are provided on both end faces 32a, 32b of rotor core 32. Also, since the magnet holder on the first bearing 46 side can be eliminated, rotor core 32 can be offset sufficiently toward first bearing 46. This improves the dynamic balance of rotor 9, and reduces vibration and noise of electric motor 2. Furthermore, the motor characteristics of electric motor 2 can be improved more reliably.

[0067] However, by arranging the end faces 33a, 33b of the magnet 33 axially outwardly of the end faces 20a, 20b of the stator core 20, there is a concern that the magnetic flux of the magnets 33 flowing in from the axially outer side may affect the stator core 20 in terms of iron loss. However, by using a ferrite magnet as the magnet 33, for example, the magnetic flux density of the magnet 33 inside the stator core 20 can be reduced compared to when a neodymium magnet is used. As a result, the iron loss of the stator core 20 can be suppressed.

[0068] Because it is possible to improve the motor characteristics of electric motor 2 and provide a small, inexpensive electric motor 2, it will be possible to contribute to Goal 7 of the Sustainable Development Goals (SDGs) led by the United Nations, "Ensure access to affordable, reliable, sustainable and modern energy for all," and Goal 9, "Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation."

[0069] The present invention is not limited to the above-described embodiment, and includes various modifications to the above-described embodiment without departing from the spirit of the present invention. For example, in the above embodiment, the motor unit 1 is described as being used as a drive source for a wiper device of a vehicle. However, the present invention is not limited to this, and the motor unit 1 can be used as a drive source for various electrical components.

[0070] In the above embodiment, the position of the radial outer ends of the four legs 82 of the magnet holder 70 is approximately the same as the radial outer ends of the corresponding salient poles 35 when viewed from the axial direction. However, this is not limited to this, and the position of the radial outer ends of the legs 82 does not necessarily have to be the same as the radial outer ends of the corresponding salient poles 35 when viewed from the axial direction. It is sufficient that the legs 82 protrude from the annular portion 81 of the magnet holder 70 so that the crimping load does not act on the magnet 33 when forming the crimping portion 71d of the magnet cover 71.

[0071] In the above embodiment, the position of each end face 33a, 33b of the magnet 33 is described as being located axially outward of each end face 20a, 20b of the corresponding stator core 20. However, this is not limited thereto, and each end face 33a, 33b of the magnet 33 may be located on the same plane as each end face 20a, 20b of the corresponding stator core 20. [Explanation of symbols]

[0072] Reference Signs List 1...motor unit, 2...electric motor, 3...reduction section, 4...controller, 5...motor case, 6...first motor case, 6a...opening, 7...second motor case, 7a...opening, 8...stator, 9...rotor, 10...bottom, 10a...through hole, 11...connector, 16...outer flange portion, 17...outer flange portion, 20...stator core, 20a...first end surface, 20b...second end surface, 21...core main body portion, 22...teeth, 23...interconnector Insulator, 24... coil, 31... shaft, 31a... tip, 32... rotor core, 32a... first end face (end of rotor core opposite bearing), 32b... second end face (end of rotor core on bearing side), 33... magnet, 33a... first end face (end of magnet opposite bearing), 33b... second end face (end of magnet on bearing side), 33c... maximum bulge, 34... core body, 35... salient pole, 40... gear Case, 40a...opening, 40b...side wall, 40c...bottom wall, 41...worm reduction mechanism, 42...gear housing, 43...opening, 44...worm shaft, 45...worm wheel, 46...first bearing (bearing), 47...second bearing, 48...output shaft, 48a...spline, 49...bearing boss, 52...rib, 57...check hole, 58...reinforcing rib, 59...recess, 61...magnetic detection element, 62...controller board, 63...cover, 70...magnet holder, 71...magnet cover, 71a...cylindrical portion, 71b...projection portion, 71c...inner flange portion, 71d...crimping portion, 72...shaft holding hole, 73...groove, 73a...engagement portion, 74...locking claw, 76...press-fit projection, 77...opening, 79...spare assembly, 81...annular portion, 82...leg portion, 83...end wall, 83a...inner surface, 91...press-fit jig, 92...crimping jig, C...rotation axis, H...length, L1 to L4...distance, S...minor gap

Claims

1. a stator having a coil and a stator core around which the coil is wound; a rotor disposed radially inside the stator and supported by a bearing so as to be rotatable about a rotation axis relative to the stator; Equipped with The rotor is a shaft that is cantilevered by the bearing and has a tip end side in the rotation axis direction disposed radially inward of the stator relative to the bearing; A rotor core fixed to the shaft and disposed radially inside the stator; A magnet disposed on an outer peripheral surface of the rotor core; a magnet holder provided only on an end of the rotor core opposite to the bearing, the magnet holder being in contact with the rotor core and covering an end of the magnet opposite to the bearing; A magnet cover that covers the periphery of the magnet; Equipped with The rotor core and the stator core are formed by laminating a plurality of steel plates in the direction of the rotation axis, The magnet cover is a cylindrical portion covering an outer circumferential surface of the rotor core and the magnet; a flange portion extending from an end portion of the cylindrical portion on the bearing side toward a radially inner side of the cylindrical portion; a crimping portion extending radially inward from an end of the cylindrical portion opposite the bearing and crimped to the magnet holder; Equipped with the magnet has opposite ends in the direction of the rotation axis that are flush with the opposite ends of the stator core in the direction of the rotation axis or are positioned outward of the opposite ends in the direction of the rotation axis; a position of an end portion of the rotor core opposite to the bearing is located closer to the bearing than a position of an end portion of the magnet opposite to the bearing, a position of the end of the rotor core on the bearing side is located closer to the bearing than a position of the end of the magnet on the bearing side, an end portion of the rotor core on the bearing side abuts against the flange portion; a position of an end portion of the rotor core opposite to the bearing is located closer to the bearing than a position of an end portion of the stator core opposite to the bearing, a position of the end portion of the rotor core on the bearing side is located closer to the bearing than a position of the end portion of the stator core on the bearing side, The amount of deviation of the rotor core from the stator core in the bearing direction is equivalent to 5 to 7 pieces of the steel plates.

1. An electric motor comprising:

2. 2. The electric motor according to claim 1, wherein both ends of the magnet in the direction of the rotation axis are positioned outward in the direction of the rotation axis with respect to both ends of the stator core in the direction of the rotation axis.

Images