Magnet unit and method of manufacturing the same

Abstract

The present invention relates to a magnet unit including: a tubular holder having a central axis; a magnet formed in an inner region on a side of one end of the tubular holder, wherein the magnet includes a protruding portion at a corner portion at which an end surface of the magnet in a central axis direction intersects with an outer peripheral surface of the magnet, the outer peripheral surface of the magnet is disposed along an inner peripheral surface of the tubular holder, and the protruding portion protrudes in the central axis direction.

Description

Technical Field

[0001] This invention relates to a magnet unit for measuring the rotational position of a rotating body or the like, and a method for manufacturing the same. Background Technology

[0002] Magnetic field detection devices (magnetic sensors) with magnets are widely used to measure the rotational position of rotating bodies. A magnetic field detection device includes a magnet fixed to the rotating body and a magnetic field detector that measures the magnetic field strength from the magnet fixed to the rotating body.

[0003] As a method for fixing a magnet to a rotating body, for example, as described in Patent Document 1 below, a cylindrical, non-magnetic retainer (hereinafter referred to as a cylindrical retainer) is used to fix the magnet to the rotating body. Before assembly, the magnet is placed in the inner region of the cylindrical retainer.

[0004] Patent Document 1: Japanese Patent Application No. 2016-153765 Summary of the Invention

[0005] The relative position between the magnetic field detector and the magnet fixed to the rotating body is crucial for accurately measuring the rotational position of the rotating body. In cases where the rotating body is part of an automotive component, engine vibration or drive vibration can exert long-term external force and stress on both the cylindrical retainer and the magnet. Therefore, sufficient strength is required between the cylindrical retainer and the magnet to prevent deformation or clicking due to long-term stress. On the other hand, in some cases, due to requirements such as size limitations, miniaturization, and cost reduction, ensuring sufficient strength is considered difficult.

[0006] The present invention was made in view of the above circumstances, and the object of the present invention is to provide a magnet unit and a method for manufacturing the same, which can increase the bonding strength between the retainer and the magnet formed in the internal region of the retainer.

[0007] As a result of in-depth research into solving the above problems, the inventor conceived the following invention.

[0008] (1) A magnet unit, comprising:

[0009] A tubular retainer having a central axis; and

[0010] A magnet is formed in the internal region on one end of the tubular retainer.

[0011] The magnet includes a protruding portion at a corner, where the end surface of the magnet in the direction of the central axis intersects with the outer peripheral surface of the magnet. The outer peripheral surface of the magnet is disposed along the inner peripheral surface of the tubular retainer, and the protruding portion protrudes in the direction of the central axis.

[0012] According to the magnet unit in this respect, the contact area between the retainer and the magnet can be increased without significantly changing the shape of the retainer and the magnet constituting the magnet unit, and the bonding strength between the retainer and the magnet can be increased.

[0013] (2) In the magnet unit defined in (1), the protruding portion may include: an outer surface that extends along the central axis and contacts the tubular retainer in a cross-sectional view along the central axis; and a tapered inner surface that separates from the central axis as it advances from the end surface toward the front end of the protruding portion.

[0014] This type of protrusion can be achieved by using a mold with a tapered portion corresponding to the protrusion, the tapered portion being positioned at the tip corner of a portion of the mold inserted into the retainer during injection molding. The tapered portion also functions as a guide when the mold inserts into the retainer and prevents interference between the mold and the retainer, thus improving the manufacturability of the magnet unit during injection molding.

[0015] (3) In the magnet unit defined in (1) or (2), the protruding portion may have an endless ring along the inner circumferential surface of the tubular retainer.

[0016] Based on the magnet unit in this respect, the contact area between the retainer and the magnet can be maximized in the circumferential direction.

[0017] (4) In any of the magnet units defined in (1) to (3), the tubular retainer may include a slot that extends along the central axis and opens on the side where the other end of the tubular retainer is located.

[0018] According to the magnet unit in this respect, when the rotating body is assembled into the retainer, the slot serves as a vent to discharge air from the retainer to the outside.

[0019] (5) In any of the magnet units defined in (1) to (3), the tubular retainer may include a plurality of slots, each slot extending along the central axis and opening on the side where the other end of the tubular retainer is located.

[0020] According to the magnet unit in this respect, when the rotating body is assembled into the retainer, the slot serves to more effectively discharge the air in the retainer to the external vent.

[0021] (6) In any of the magnet units defined in (1) to (5), the tubular retainer may include a protrusion that protrudes radially inward from the inner circumferential surface of the magnet at approximately the middle portion in the direction of the central axis.

[0022] The magnet unit in this aspect prevents the magnet from slipping off the retainer.

[0023] (7) In the magnet unit defined in (6), the protrusion may have an endless ring along the inner circumferential surface of the tubular retainer.

[0024] Based on this aspect of the magnet unit, the magnet is more effectively prevented from slipping off the holder.

[0025] (8) In any of the magnet units defined in (1) to (5), the tubular retainer may include a plurality of protrusions, each protruding radially inward from the inner circumferential surface of the magnet at approximately the middle portion in the direction of the central axis.

[0026] The magnet unit in this aspect effectively prevents the magnet from slipping off the holder and rotating in the circumferential direction.

[0027] (9) A method for manufacturing a magnet unit as described in (2) or (3), comprising:

[0028] The mold is inserted into the tubular retainer to define a cavity within the tubular retainer; and

[0029] The material of the magnet is injected into the cavity to obtain a shaped magnet.

[0030] The mold includes a tapered portion at the tip corner of a portion inserted into the tubular retainer, corresponding to the protruding portion of the magnet.

[0031] According to the manufacturing method in this respect, when the mold is inserted into the retainer, the tapered portion provided at the top corner of the mold for forming the protrusion in the magnet acts as a guide, which can prevent interference between the mold and the retainer and improve the manufacturability of the magnet unit during injection molding. Attached Figure Description

[0032] Figure 1 This is a perspective view of a magnet unit according to an embodiment of the present invention.

[0033] Figure 2A yes Figure 1 A longitudinal cross-sectional view of the magnet unit in the image.

[0034] Figure 2B yes Figure 2A A magnified view of part B in the image.

[0035] Figure 3A yes Figure 1 A plan view of the individual retainer in the design.

[0036] Figure 3B yes Figure 3A The longitudinal cross-sectional view of the retainer in the middle.

[0037] Figure 3C It is along Figure 3B The cross-sectional view taken from line CC in the diagram.

[0038] Figure 4A and Figure 4B This is an explanation Figure 1 A schematic diagram of the manufacturing method of the magnet unit in the diagram.

[0039] Figure 5 It means to follow Figure 4B A schematic diagram of the manufacturing method of the subsequent magnet unit.

[0040] Figure 6A It is a plan view of a variant with an endless ring shape on the protruding part.

[0041] Figure 6B yes Figure 6A A longitudinal cross-sectional view of the deformed protruding portion in the diagram. Detailed Implementation

[0042] Next, the magnet unit according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0043] Figure 1 This is a perspective view of the magnet unit 1 according to an embodiment of the present invention. Figure 2A and Figure 2B This is a longitudinal cross-sectional view of magnet unit 1.

[0044] In this embodiment, the magnet unit 1 is fixed to the rotating body W when measuring its rotational position. The magnet unit 1 includes a cylindrical retainer 2 and a magnet 4 formed in the internal region of the retainer 2. The magnet 4 is magnetized such that the N pole and S pole are present at different positions in the circumferential direction around the central axis P. Alternatively, the magnet 4 may be magnetized such that the N pole and S pole are present at different positions in the thickness direction, depending on various circumstances.

[0045] When the rotating body W rotates, the magnet unit 1 fixed to the rotating body W rotates together with the rotating body W. At this time, the change in magnetic force is detected by a magnetic field detector (not shown) directly arranged above the upper end surface 31 of the magnet 4, thereby measuring the rotational position of the rotating body W.

[0046] Figures 3A to 3C The retaining member 2, which constitutes part of the magnet unit 1, is shown separately. (See example...) Figures 3A to 3CAs shown, the retainer 2 is a cylindrical member open at both ends in the axial direction (central axis direction). The retainer 2 includes a peripheral wall portion 10, which has a straight shape with an outer diameter and an inner diameter that do not change along the axial direction. The retainer 2 (specifically, the peripheral wall portion 10) includes an annular flange portion 12 extending radially outward at one end 11. The flange portion 12 has the effect of increasing the strength of the retainer 2 and is effective in maintaining the cylindrical shape of the retainer 2.

[0047] The side of the retainer 2 with the flange portion 12 located at one end 11 is the side where the magnet 4 is formed, and the space for forming and retaining the magnet 4 is defined inside the side where the end 11 is located. A plurality of (in this case, four) protrusions 15 are provided at intervals along the circumferential direction. The protrusions 15 protrude radially inward (i.e., toward the central axis P) from the inner circumferential surface 10a of the peripheral wall portion 10 on the side where the end 11 is located. The protrusions 15 are configured to prevent the magnet 4 from slipping. The protrusions 15 are located approximately at the center position in the axial direction of the space where the magnet 4 is formed.

[0048] On the other hand, the side where the other end 22 of the retainer 2 is located is the side to which the rotating body W is assembled, and the space for accommodating the rotating body W is defined inside the side where the other end 22 is located. In the inner circumferential surface 10a of the peripheral wall portion 10 located on the side where the other end 22 is located, a plurality of slots 23 are provided at intervals along the circumferential direction (here, three). The slots 23 extend in the axial direction toward the opening edge located on the side where the other end 22 is located and open on the side where the other end 22 is located. When the rotating body W is assembled into the retainer 2, the slots 23 serve as vents to expel air from the retainer 2 to the outside. The retainer 2 may have only one slot 23, or it may have multiple slots 23.

[0049] The retainer 2 having the above-described structure is preferably made of a non-magnetic material. Examples of non-magnetic materials include aluminum, copper, brass, and stainless steel. Alternatively, when a magnetic circuit is intended, steel such as SPCC (cold-pressed commercial steel sheet) or SUS420 can be used as the retainer 2.

[0050] The length and number of the protrusions 15 formed on the retainer 2 can be appropriately changed. Figure 6A and Figure 6B A variation of the protruding portion of the retainer 2 is shown. In this variation, a protruding portion 15B is provided in an endless ring shape on the entire circumference of the inner circumferential surface 10a of the retainer 2. The protruding shape of the protruding portion 15 can also be appropriately changed, and the number of protruding portions can be increased or decreased as needed. The protruding portion may be omitted as long as the strength and fixation between the retainer 2 and the magnet 4 can be ensured.

[0051] Next, magnet 4 will be described. Magnet 4 according to this embodiment is a bonded magnet obtained by mixing a magnetic material and resin and injection molding the mixture inside the retainer 2. Examples of magnetic materials include magnetic materials containing one or more rare earth elements, such as Sm, Nd, and Pr, and for example, SmFeN rare earth magnetic powder, NdFeB rare earth magnetic powder, ferrite magnetic powder, or mixtures thereof can be used.

[0052] Examples of resins used for mixing with magnetic materials include thermoplastic polyamide 12, polyamide 6, polyphenylene sulfide (PPS), polybutylene terephthalate (PBT), ethylene-vinyl alcohol (EVA), polypropylene, etc.

[0053] Magnet 4 has a roughly disk-shaped form, and as... Figure 2A and Figure 2B As shown, it has a first end surface 31 and a second end surface 32 spaced apart along the axial direction. The first end surface 31 and the second end surface 32 are in the direction intersecting the central axis P ( Figure 2A It extends in the left-right direction. Here, the first end surface 31 is an axially outer end surface and is disposed near the end opening on the side where one end 11 is located, and the second end surface 32 is an axially inner end surface and is disposed on the side where the other end 22 is located relative to the first end surface 31. The outer peripheral surface 34, which contacts the inner peripheral surface 10a of the retainer 2, is disposed between the first end surface 31 and the second end surface 32.

[0054] In the magnet 4, the protrusion 15 of the retainer 2 is approximately embedded in the middle of the outer peripheral surface 34 in the axial direction. In this embodiment, the assembly between the protrusion 15 and the magnet 4 prevents the magnet 4 from slipping in the axial direction and prevents the magnet 4 from rotating in the circumferential direction.

[0055] Furthermore, at the corner where the second end surface 32, located on the inner side in the axial direction, intersects with the outer peripheral surface 34, a protruding portion 40 is provided in an endless annular shape along the inner peripheral surface 10a of the retainer 2. The protruding portion 40 protrudes in the axial direction and expands the contact portion between the magnet 4 and the retainer 2.

[0056] like Figure 2B As shown, the protrusion 40 includes: an outer surface 42 extending along the axial direction and contacting the retainer 2 in a cross-sectional view along the central axis P; and a tapered inner surface 44 that separates from the central axis P as it advances from the second end surface 32 toward the front end of the protrusion 40. The protrusion 40 has a generally triangular cross-section, and the thickness of the protrusion 40 gradually decreases from its base end toward its front end.

[0057] In the magnet unit 1 according to this embodiment, which includes a magnet 4 having a protruding portion 40, compared to the virtual case where the protruding portion 40 is not provided, the contact portion between the magnet 4 and the retainer 2 is... Figure 2B The length δ is extended in the axial direction shown. Therefore, the bonding strength between the retainer 2 and the magnet 4 can be increased. For example, in the case where the magnet 4 has a diameter D of 7 mm to 10 mm and a thickness t of 2 mm to 4 mm, in this embodiment, the axial length δ of the protruding portion 40 can be set in the range of 0.3 mm to 2.0 mm, and more preferably in the range of 0.5 mm to 1.0 mm.

[0058] Reference Figure 4A , Figure 4B and Figure 5 The manufacturing method of the magnet unit 1 according to this embodiment will be described. Figure 4A , Figure 4B and Figure 5 In the figure, reference numeral 50 indicates a mold. The mold 50 is divided into a first mold opening 50A and a second mold opening 50B, which are separated along the axial direction of the magnet unit 1.

[0059] The first mold opening 50A is a mold located below and supporting the retainer 2. The first mold opening 50A includes an annular groove 52 for positioning and a bottom portion 53 located inside the first mold opening 50A and projecting upward from the groove 52. The second mold opening 50B includes a columnar forming portion 55, which is inserted into the retainer 2 from above (from the side where the other end 22 is located). The columnar forming portion 55 includes a tapered portion 57 at its apex corner corresponding to a protrusion 40 provided on the magnet 4.

[0060] First, such as Figure 4A As shown, the retainer 2, which has been machined into a predetermined shape, is placed with the flange portion 12 facing downwards, and the flange portion 12 is fitted into the groove 52 provided in the first mold opening 50A. At this time, the end opening of the retainer 2 located on the side where one end 11 is located is blocked by the bottom surface portion 53 of the first mold opening 50A.

[0061] Subsequently, the columnar forming portion 55 of the second mold 50B is inserted into the retainer 2 through the upward-opening end opening located on the side where the other end 22 is located. Then, with the first mold 50A and the second mold 50B closed, as... Figure 4B As shown, the cavity 58 is defined by the retainer 2, the bottom portion 53 of the first mold opening 50A, and the forming portion 55 of the second mold opening 50B.

[0062] The molding portion 55 of the second mold 50B has a channel 56 in its middle section for injecting magnetic material (material for bonding magnets). When the magnetic material is injected into the cavity 58 through the channel 56, as... Figure 5 As shown, a magnet molded body 4A is obtained inside the retainer 2. A raised portion (not shown) due to the remaining gate can be formed at the connection between the second end surface 32 of the formed magnet molded body 4A and the channel 56.

[0063] Subsequently, the obtained magnet molded body 4A is magnetized to obtain magnet 4, thereby obtaining magnet unit 1 according to this embodiment.

[0064] As described above, in the magnet unit 1 according to this embodiment, a protruding portion 40 that extends and expands the contact portion between the retainer 2 and the magnet 4 along the axial direction is provided at the corner portion of the magnet 4. At this corner portion, a second end surface 32 extending in a direction intersecting the central axis P intersects with an outer peripheral surface 34 provided along the inner peripheral surface 10a of the retainer 2. Therefore, the contact area between the retainer 2 and the magnet 4 can be increased without significantly changing the shape of the retainer 2 and the magnet 4 constituting the magnet unit 1, and the bonding strength between the retainer 2 and the magnet 4 can be increased.

[0065] In the magnet unit 1 of this embodiment, in a cross-sectional view along the central axis P, the protruding portion 40 includes an outer surface 42 that extends along the axial direction and contacts the retainer 2, and a tapered inner surface 44 that separates from the central axis P as it moves from the second end surface 32 toward the front end of the protruding portion 40.

[0066] This type of protrusion 40 can be achieved by providing a tapered portion 57 corresponding to the protrusion 40 at the tip corner of the molding portion 55 of the second mold opening 50B inserted into the retainer 2 during injection molding. When the second mold opening 50B is inserted into the retainer 2, the tapered portion 57 also functions as a guide and can prevent interference between the second mold opening 50B and the retainer 2, thus improving manufacturability during injection molding.

[0067] In the magnet unit 1 of this embodiment, the contact area between the retainer 2 and the magnet 4 can be maximized in the circumferential direction by providing an endless annular protrusion 40 along the inner circumferential surface 10a of the retainer 2.

[0068] Although embodiments of the invention have been described in detail above, the invention is not limited thereto, and various modifications can be made without departing from the spirit of the invention. For example, although a cylindrical retainer is used in the above embodiments, a tubular member with a polygonal cross-section or an elliptical cylindrical member can be used as the retainer. When the tubular member has a cross-section other than circular, the magnet has a cross-section corresponding to that of the tubular member. Furthermore, the invention includes various other modifications without departing from the scope of the claims, and for example, the retainer may have a shape with a diameter that decreases or increases relative to the diameter of one end on the side to be fitted to the rotating body.

[0069] This application is based on Japanese Patent Application No. 2021-084460, filed on May 19, 2021, the contents of which are incorporated herein by reference.

[0070] List of reference numerals

[0071] 1 Magnet Unit

[0072] 2. Retaining components

[0073] 4. Magnet (bonded magnet)

[0074] 4A Magnet Molding Body

[0075] 10a inner peripheral surface

[0076] 15. Protruding part

[0077] 32 Second end surface

[0078] 34 Peripheral surface

[0079] 40 Highlighted parts

[0080] 42 Outer surface

[0081] 44 Inner surface

[0082] 50A and 50B mold making

[0083] 57. Conical section

[0084] 58 cavities

[0085] P Central axis

Claims

1. A magnet unit, comprising: A tubular retainer having a central axis; as well as A magnet is formed in the internal region on one end side of the tubular retainer. The magnet includes a protruding portion at a corner, where an end surface of the magnet in the direction of its central axis intersects with the outer peripheral surface of the magnet. The outer peripheral surface of the magnet is disposed along the inner peripheral surface of the tubular retainer, and the protruding portion protrudes along the direction of the central axis. The protruding portion, in a cross-sectional view along the central axis, includes an outer surface extending along the central axis and facing outward in a direction perpendicular to the central axis, and the protruding portion contacts the tubular retainer only on the outer surface. The protruding portion further includes a tapered inner surface that separates from the central axis as it advances from the end surface toward the front end of the protruding portion.

2. The magnet unit according to claim 1, wherein, The protruding portion has an endless ring shape along the inner circumferential surface of the tubular retainer.

3. The magnet unit according to claim 1, wherein, The tubular retainer includes a groove that extends along the central axis and opens at the other end of the tubular retainer.

4. The magnet unit according to claim 1, wherein, The tubular retainer includes a plurality of grooves, each groove extending along the central axis and opening at the other end of the tubular retainer.

5. The magnet unit according to any one of claims 1 to 4, wherein, The tubular retainer includes a protrusion that protrudes radially inward from the inner circumferential surface of the magnet at approximately the middle portion in the direction of the central axis.

6. The magnet unit according to claim 5, wherein, The protruding portion has an endless ring shape along the inner circumferential surface of the tubular retainer.

7. The magnet unit according to any one of claims 1 to 4, wherein, The tubular retainer includes a plurality of protrusions, each protruding radially inward from the inner circumferential surface of the magnet at approximately the middle portion in the direction of the central axis.

8. A method for manufacturing the magnet unit according to claim 1 or 2, the method comprising: The mold is inserted into the tubular retainer to define a cavity within the tubular retainer; as well as The material of the magnet is injected into the cavity to obtain a shaped magnet body. The mold includes a tapered portion at the tip corner of a portion inserted into the tubular retainer, corresponding to the protruding portion of the magnet.

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