Rotor and motor

Abstract

To provide a rotor which enables a plastic magnet to easily flow thereinto.SOLUTION: A rotor 4 comprises a cylindrical shaft 30 extending in an axial direction and a plastic magnet 40 which covers an outer peripheral surface of the shaft 30 annularly and rotates integrally with the shaft 30. The shaft 30 includes a cylindrical penetration hole 36 which penetrates from a predetermined position on the outer peripheral surface to an opposite position opposed to the predetermined position and in which the plastic magnet 40 is flowed in. The penetration hole 36 includes an inclination part 38 for guiding the plastic magnet 40 from openings 37 in both ends of the penetration hole 36 to the inside of the shaft 30.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a rotor and a motor. [Background technology]

[0002] Rotors for use in brushless DC motors, which have a motor shaft supporting a magnet, are known. For example, Patent Document 1 describes a rotor that includes a cylindrical motor shaft that forms the rotation axis of the motor and a plastic magnet fixed to the shaft. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-043289 Summary of the Invention [Problem to be solved by the invention]

[0004] In the rotor described in Patent Document 1, the plastic magnet and motor shaft are integrated by pouring molten plastic magnet into a mold containing the motor shaft and allowing it to solidify. The motor shaft has a through-hole that penetrates between the two opposing side surfaces, and pouring the molten plastic magnet into the through-hole increases the friction and resistance between them. However, conventional rotors have room for improvement in terms of making it easier for the molten plastic magnet to flow.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a rotor that can make it easier for plastic magnets to flow. [Means for solving the problem]

[0006] To solve the above problems, one aspect of the rotor disclosed herein is a rotor having a cylindrical shaft extending in the axial direction and a plastic magnet that annularly covers the outer circumferential surface of the shaft and rotates integrally with the shaft. The shaft has a cylindrical through-hole that penetrates from a predetermined position on the outer circumferential surface to an opposing position opposite the predetermined position and into which the plastic magnet is poured. The through-hole has inclined portions for guiding the plastic magnet from openings at both ends of the through-hole into the inside of the shaft.

[0007] Any combination of the above components, and conversion of the present disclosure into a method, device, system, recording medium, computer program, etc., are also valid aspects of the present disclosure. [Effects of the Invention]

[0008] According to the present disclosure, a rotor that can facilitate the flow of plastic magnets can be provided. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a side cross-sectional view schematically illustrating a motor according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is an exploded perspective view showing the motor of FIG. 1; [Figure 3] FIG. 2 is a cross-sectional view showing a cross section of the rotor of FIG. [Figure 4] FIG. 10 is a cross-sectional view showing a cross section of a rotor of a comparative example.

[0010] Hereinafter, embodiments for carrying out the present disclosure will be described with reference to the accompanying drawings. Each of the examples described below represents a preferred specific example of the present disclosure. Therefore, the numerical values, shapes, materials, components, the arrangement and connection of the components, steps (processes), and the order of steps shown in the following examples are merely examples and are not intended to limit the present disclosure. Therefore, among the components in the following examples, components that are not recited in the independent claims that represent the highest concept of the present disclosure will be described as optional components. Furthermore, in each figure, substantially identical components are assigned the same reference numerals, and redundant explanations will be omitted or simplified.

[0011] Furthermore, terms including ordinal numbers such as first and second are used to describe various components, but these terms are used only to distinguish one component from another and do not limit the components.

[0012] [Example] The configuration of a motor 10 including a rotor 4 according to an embodiment of the present disclosure will be described with reference to Figures 1 and 2. Figure 1 is a side cross-sectional view that schematically illustrates the motor 10. This figure shows a cross section of the motor 10 cut along a plane that passes through the central axis La of the shaft 30. Figure 2 is an exploded perspective view that illustrates the motor 10. The motor 10 is a brushless DC motor that is suitable for use in, for example, rotating the blades of a ventilation fan.

[0013] Hereinafter, for convenience, the direction along the central axis La of the shaft 30 will be referred to as the "axial direction," and the circumferential direction and radial direction of a circle centered on the central axis La on a plane perpendicular to the central axis La will be referred to as the "circumferential direction" and the "radial direction," respectively. Also, a plane perpendicular to the axial direction will be referred to as the "axially perpendicular plane."

[0014] The motor 10 mainly includes a stator 2, a rotor 4, a shaft 30, a first bearing 31, a second bearing 32, and a substrate 50. The stator 2 and the substrate 50 form a stationary body, and the rotor 4 and the shaft 30 form a rotating body.

[0015] The rotor 4 is rotatably supported relative to the stator 2 via a first bearing 31 and a second bearing 32. The rotor 4 mainly includes a shaft 30 and a cup-shaped plastic magnet 40. The shaft 30 extends cylindrically in the axial direction along the central axis La. The plastic magnet 40 has a hollow cylindrical portion 41 that surrounds the stator core 21 and a fixed end portion 42 that extends from one end of the cylindrical portion 41 to the outer circumferential surface of the shaft 30, and an open end portion 43 is provided at the end of the cylindrical portion 41 opposite the fixed end portion 42.

[0016] The plastic magnet 40 is formed by resin molding such as injection molding using a plastic such as polyamide resin mixed with magnetic powder (hereinafter referred to as "magnetic resin"). The rotor 4 of this embodiment is manufactured by insert molding, in which molten magnetic resin (hereinafter referred to as "molten resin") is poured into a molding die containing the shaft 30. The shaft 30 and the plastic magnet 40 are integrated by insert molding.

[0017] The plastic magnet 40 is a polar anisotropic plastic magnet with a high residual magnetic flux density. The plastic magnet 40 is insert molded while a polar anisotropic magnetic field is applied. A predetermined number of driving magnetic poles are provided on the inner circumferential surface of the cylindrical portion 41 of the plastic magnet 40 by a magnetization process. Due to the characteristics of polar anisotropic magnets, no magnetic poles are formed on the outer circumferential surface of the cylindrical portion 41. For this reason, a back yoke is not provided in this embodiment.

[0018] In the axial direction, the side where the open end 43 is provided relative to the fixed end 42 is referred to as the first direction. In each drawing, the first direction is indicated by the direction of arrow Z1. The first direction side may also be referred to as the lower side, and the opposite side as the upper side. These directional notations do not limit the orientation of the motor 10, and the motor 10 may be used in any orientation.

[0019] The stator 2 mainly includes a stator core 21, a pair of insulators 22, 23 that sandwich the stator core 21 from both sides in the axial direction, a winding 24 wound around the stator core 21 via the insulators 22, 23, a stator base 26, and shaft supports 28, 29. The insulators 22, 23 are resin members formed by molding. The insulators 22, 23 include a first insulator 22 arranged above the stator core 21 and a second insulator 23 arranged below the stator core 21. The stator core 21, the insulators 22, 23, the winding 24, and the substrate 50 are integrated to form a stator unit 25. In this embodiment, four windings 24 are provided at 90° intervals in the circumferential direction.

[0020] The stator base 26 is a disk-shaped member that supports the stator unit 25. The shaft supports 28, 29 are members that rotatably support the base end side of the shaft 30, and include a first shaft support 28 provided on the upper side of the stator base 26 and a second shaft support 29 provided on the lower side of the stator base 26 and engaged with the first shaft support 28.

[0021] The first shaft support portion 28 is formed integrally with the stator base 26. The second shaft support portion 29 is inserted into a central hole 262 of the stator base 26 from below, thereby engaging with the first shaft support portion 28. The washer 34 is fitted into a circumferential groove 35 formed in the shaft 30. The washer 34 functions as a retainer that regulates the axial position of the shaft 30 between the second bearing 32 and the first shaft support portion 28.

[0022] The substrate 50 is a substantially semicircular printed circuit board extending along a plane perpendicular to the axial direction. A Hall element 52 and a drive circuit 53 are mounted on the substrate 50. When magnetic flux from the drive magnetic pole of the cylindrical portion 41 passes through the Hall element 52, the Hall element 52 outputs a detection signal that is substantially proportional to the magnetic flux density of the magnetic flux. The drive circuit 53 supplies a drive current to the winding 24 based on the detection signal from the Hall element 52. The lower part of the second insulator 23 is fixed to the substrate 50.

[0023] The operation of motor 10 will now be described. When a drive current is supplied from drive circuit 53 to windings 24 based on the detection signal from Hall element 52, a magnetic field corresponding to the drive current is generated around stator core 21. Interaction between this magnetic field and the drive magnetic poles of plastic magnet 40 generates a rotational torque in rotor 4, and in response to this torque, rotor 4 and shaft 30 rotate around central axis La. As shaft 30 rotates, the driven body connected to shaft 30 rotates.

[0024] The shaft 30 and the plastic magnet 40 will be further described with reference to Figures 3 and 4. Figure 3 is a cross-sectional view showing a cross section of the rotor 4 of the embodiment. Figure 4 is a cross-sectional view showing a cross section of the rotor 4B of the comparative example. Figure 3(A) shows a cross section of the rotor 4, Figure 3(B) shows an enlarged cross section of a portion of the rotor 4, Figure 3(C) shows a cross section of the shaft 30, and Figure 3(D) shows an enlarged cross section of a portion of the shaft 30. Figure 4(A) shows a cross section of the rotor 4B, Figure 4(B) shows an enlarged cross section of a portion of the rotor 4B, Figure 4(C) shows a cross section of the shaft 30B, and Figure 4(D) shows an enlarged cross section of a portion of the shaft 30B.

[0025] 3 and 4, a downward-pointing triangle marked with the symbol G indicates the position of the gate G during resin molding. The comparative rotor 4B was prototyped for comparison purposes during the development of the rotor 4 of the embodiment. To distinguish between the elements of the comparative rotor 4B, the letter "B" is added to the symbol of each element.

[0026] The rotor 4B of the comparative example differs from the rotor 4 of the embodiment in that it includes a shaft 30B that has a different shape from the shaft 30, but otherwise has the same configuration. The shaft 30B is a cylindrical member that extends in the axial direction and has the same external shape as the shaft 30.

[0027] As described above, the rotor 4 of the embodiment and the rotor 4B of the comparative example have cylindrical shafts 30, 30B extending in the axial direction and plastic magnets 40 that annularly cover the outer circumferential surfaces of the shafts 30, 30B and rotate integrally with the shafts 30, 30B. The shafts 30, 30B have cylindrical through-holes 36, 36B that penetrate from a predetermined position on the outer circumferential surface to an opposing position opposite the predetermined position and into which the plastic magnets 40 are poured. The portion of the plastic magnet 40 that is poured into the through-holes 36, 36B is referred to as the hole interior 46. As an example, the through-holes 36, 36B are holes with a circular cross section.

[0028] By providing through holes 36, 36B in shafts 30, 30B, hole interiors 46 are formed, and the action of through holes 36, 36B and hole interiors 46 increases the strength of plastic magnet 40 against removal from shafts 30, 30B, thereby increasing the rotational strength between plastic magnet 40 and shafts 30, 30B.

[0029] First, a rotor 4B of a comparative example will be described. The through-hole 36B of the shaft 30B penetrates in a direction perpendicular to the axial direction from one opening 37 at a predetermined position on the outer peripheral surface and the other opening 37 at an opposing position. An edge portion 39 exists at each opening 37 of the through-hole 36B.

[0030] The arrows indicate the flow direction of the molten resin injected from gate G. The flow of the molten resin injected from gate G is hindered at edge portion 39, and due to the difference in linear expansion coefficient between the metal shaft and the plastic magnet, distortion that can become the starting point for cracks may occur at that portion when the molten resin thermally contracts. When an external twisting force acts between shaft 30B and plastic magnet 40, stress concentrates at edge portion 39, which may cause cracks in plastic magnet 40 around edge portion 39.

[0031] A rotor 4 according to an embodiment will now be described based on the description of the comparative example. As shown in Fig. 3, the through hole 36 of the shaft 30 according to the embodiment has inclined portions 38 for guiding the plastic magnet 40 from openings 37 at both ends of the through hole 36 to the inside of the shaft 30. By providing the inclined portions 38, there are no sharp edges 39, and the molten resin is guided into the through hole 36 along the inclined portions 38.

[0032] Furthermore, in the rotor 4 of the embodiment, the inclined portions 38 are provided around the entire circumference of the openings 37 at both ends of the through holes 36. In this case, by providing the inclined portions 38 around the entire circumference of the openings 37, the molten resin can flow more easily into the through holes 36 compared to when the inclined portions 38 are provided only partially, thereby reducing damage during cooling.

[0033] The shape of the inclined portion 38 is not particularly limited as long as it can improve the fluidity of the molten resin. In the rotor 4 of this embodiment, the through hole 36 passes through the central axis La of the shaft 30, and the inclined portion 38 has a conical shape whose diameter increases toward the openings 37 at both ends. In other words, the inclined portion 38 has a tapered portion whose diameter increases toward the openings 37 at both ends. The shape of the inclined portion 38 can be determined through experiments or simulations to ensure a desired level of fluidity of the molten resin around the openings 37. The inclination angle of the inclined portion 38 may be set, for example, in the range of 20° to 70° with respect to the extension direction of the through hole 36, and the depth of the inclined portion 38 from the openings 37 may be set in the range of 0.5 mm to 3.0 mm. In this embodiment, the chamfer is C1 (45°, depth 1 mm). In other words, the inclination angle of the inclined portion 38 is 45°, and the depth of the inclined portion 38 from the openings 37 is 1 mm.

[0034] As described above, the plastic magnet 40 has a hollow cylindrical portion 41 that surrounds the stator core 21 and a fixed end portion 42 that extends from one end of the cylindrical portion 41 to the outer circumferential surface of the shaft 30, and the through hole 36 in the embodiment overlaps with the fixed end portion 42 in the radial direction. In other words, the axial range of the through hole 36 overlaps with the axial range of the fixed end portion 42. In the embodiment, molten resin is injected from a gate G provided on the upper surface of the fixed end portion 42, so the molten resin flows radially through the fixed end portion 42. When the axial ranges of the through hole 36 and the fixed end portion 42 overlap, the molten resin flowing radially from the fixed end portion 42 tends to flow smoothly into the through hole 36.

[0035] The axial thickness of the fixed end 42 is larger than the diameter of the openings 37 at both ends. In this case, the large thickness of the fixed end 42 allows the molten resin to flow smoothly inside the fixed end 42 and more easily into the through-hole 36. In this embodiment, the portion of the fixed end 42 that contacts the shaft 30 covers the entire opening 37 in the axial direction.

[0036] The features of the rotor 4 configured as described above will be explained. The rotor 4 is a rotor having a cylindrical shaft 30 extending in the axial direction, and a plastic magnet 40 that annularly covers the outer circumferential surface of the shaft 30 and rotates integrally with the shaft 30. The shaft 30 has a cylindrical through-hole 36 that penetrates from a predetermined position on the outer circumferential surface to an opposing position opposite the predetermined position, and into which the plastic magnet 40 is poured. The through-hole 36 has inclined portions 38 for guiding the plastic magnet 40 from openings 37 at both ends of the through-hole 36 into the inside of the shaft 30.

[0037] According to this configuration, the presence of the inclined portion 38 eliminates sharp edges, and the molten resin is guided into the through-hole 36 along the inclined portion 38. This makes it easier for the molten resin to flow into the through-hole 36, making distortion less likely to occur. In addition, stress concentration when a twisting external force acts between the shaft 30 and the plastic magnet 40 is also alleviated. As a result, cracks are less likely to occur, and the pull-out strength and rotation strength between the plastic magnet 40 and the shaft 30 can be easily ensured.

[0038] An outline of one aspect of the present disclosure is as follows. [Item 1] A rotor having a cylindrical shaft (30) extending in the axial direction and a plastic magnet (40) annularly covering the outer circumferential surface of the shaft (30) and rotating integrally with the shaft (30), The shaft (30) has a cylindrical through-hole (36) that penetrates from a predetermined position on the outer circumferential surface to a position opposite the predetermined position and into which a plastic magnet (40) is poured, The through hole (36) has an inclined portion (38) for guiding the plastic magnet (40) from openings (37) at both ends of the through hole (36) to the inside of the shaft (30).

[0039] [Item 2] Item 1. The rotor (4) according to item 1, wherein the inclined portion (38) is provided around the entire circumference of the opening (37) at both ends of the through hole (36).

[0040] [Item 3] The through hole (36) passes through the central axis of the shaft (30), Item 3. The rotor (4) according to item 2, wherein the inclined portion (38) has a conical shape whose diameter increases as it approaches the openings (37) at both ends.

[0041] [Item 4] The plastic magnet (40) has a hollow cylindrical portion (41) for surrounding the stator core (21) and a fixed end portion (42) extending from one end of the cylindrical portion (41) to the outer circumferential surface of the shaft (30), 2. The rotor (4) according to item 1, wherein the through-hole (36) overlaps with the fixed end (42) when viewed in the radial direction.

[0042] [Item 5] Item 4. The rotor (4) according to item 4, wherein the axial thickness of the fixed end (42) is greater than the diameter of the openings (37) at both ends.

[0043] [Item 6] A motor (10) comprising the rotor (4) according to any one of items 1 to 5.

[0044] The present disclosure has been described above based on examples. These examples are merely illustrative, and it will be understood by those skilled in the art that various modifications are possible in the combination of each component or each treatment process, and that such modifications are also within the scope of the present disclosure.

[0045] In the description of the embodiment, an example was shown in which the rotor 4 does not have a back yoke, but this is not limiting. For example, the rotor may be provided with a member that surrounds the outer circumferential surface of the cylindrical portion of the plastic magnet.

[0046] Although the inclined portion 38 has a conical surface in the description of the embodiment, the inclined portion 38 is not limited to this. For example, the inclined portion may include a curved surface.

[0047] In the description of the embodiment, an example in which the injection gate G is provided on the upper surface of the fixed end portion 42 has been shown, but the invention is not limited to this. For example, the injection gate may be provided on the cylindrical portion, the open end portion, or the like. [Explanation of symbols]

[0048] 2 Stator, 4, 4B Rotor, 10 Motor, 21 Stator core, 22 First insulator, 23 Second insulator, 24 Winding, 25 Stator unit, 26 Stator base, 28 First shaft support portion, 29 Second shaft support portion, 30, 30B Shaft, 31 First bearing, 32 Second bearing, 34 Washer, 35 Circumferential groove, 36, 36B Through hole, 37 Opening, 39 Edge portion, 38 Inclined portion, 40 Plastic magnet, 41 Cylindrical portion, 42 Fixed end, 43 Open end, 50 Circuit board, 51 Board body, 52 Hall element, 53 Drive circuit.

Claims

1. A rotor having a cylindrical shaft extending in an axial direction and a plastic magnet annularly covering the outer circumferential surface of the shaft and rotating integrally with the shaft, the shaft has a cylindrical through-hole that penetrates from a predetermined position on the outer circumferential surface to a position opposite the predetermined position and into which the plastic magnet is poured, The through hole has an inclined portion for guiding the plastic magnet from the openings at both ends of the through hole to the inside of the shaft.

2. The rotor according to claim 1 , wherein the inclined portion is provided over the entire circumference of the opening at both ends of the through hole.

3. The through hole passes through a central axis of the shaft, The rotor according to claim 2 , wherein the inclined portion has a conical shape whose diameter increases as it approaches the openings at both ends.

4. the plastic magnet has a hollow cylindrical portion for surrounding the stator core and a fixed end portion extending from one end of the cylindrical portion to the outer circumferential surface of the shaft, The rotor according to claim 1 , wherein the through hole overlaps with the fixed end portion in a radial direction.

5. The rotor according to claim 4 , wherein the axial thickness of the fixed end is greater than the diameter of the openings at both ends.

6. A motor comprising the rotor according to any one of claims 1 to 5.

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