Noise filter

Abstract

The purpose of the present invention is to achieve size reduction.　This noise filter (A) comprises: a cylindrical bobbin (11) in which flange parts (22) are formed at both ends in an axis (S) direction; a magnetic body (27) accommodated in the bobbin (11); and a coil (28) wound around the outer periphery of the bobbin (11). The bobbin (11) is made from a synthetic resin. Since the bobbin (11) is made from a synthetic resin having a high degree of freedom in molding, the thickness dimension of each flange part (22) in the axis (S) direction can be kept small. As a result, it is possible to achieve size reduction in the axis (S) direction.

Description

Noise filter

[0001] The present disclosure relates to a noise filter.

[0002] In a communication circuit, a noise filter is used to reduce noise in a transmitted signal. Patent Document 1 discloses a core component that constitutes a noise filter. A noise filter is constituted by winding a coil around the outer periphery of the core component.

[0003] Japanese Patent Application Laid-Open No. 2020-113763

[0004] Flange portions for preventing the coil from detaching from the core component are formed at both axial ends of the core component. As the material of the core component, a ferrite core is widely used. The ferrite core, which is a ceramic mainly composed of iron oxide, is likely to cause brittle fracture. Therefore, when forming a flange portion on a core component made of a ferrite core, it is necessary to ensure a large thickness dimension of the flange portion. Thus, when the core component is made of a ferrite core, there is a problem that the core component becomes larger in the axial direction.

[0005] The noise filter of the present disclosure has been completed based on the above circumstances, and aims to achieve miniaturization.

[0006] The noise filter of the present disclosure includes: a cylindrical bobbin having flange portions formed at both axial ends; a magnetic body accommodated in the bobbin; and a coil wound around the outer periphery of the bobbin, wherein the bobbin is made of a synthetic resin.

[0007] According to the present disclosure, miniaturization can be achieved.

[0008] Figure 1 is a cross-sectional view of the noise filter of Example 1. Figure 2 is a front view of the core of Example 1. Figure 3 is a plan view of the core of Example 1. Figure 4 is a plan view of the bobbin of Example 1 in an expanded and deformed state. Figure 5 is a cross-sectional view of the noise filter of Example 2. Figure 6 is a front view of the core of Example 2. Figure 7 is a plan view of the core of Example 2. Figure 8 is a plan view showing the bobbin separated from the core of Example 2. Figure 9 is a cross-sectional view of the noise filter of Example 3. Figure 10 is a front view of the core of Example 3. Figure 11 is a plan view of the core of Example 3. Figure 12 is a plan view of the core of Example 4. Figure 13 is a cross-sectional view of the noise filter of Example 4 taken along the line X-X in Figure 12. Figure 14 is a cross-sectional view of the noise filter of Example 4 taken along the line Y-Y in Figure 12. Figure 15 is a cross-sectional view of the noise filter of Example 5.

[0009] [Description of Embodiments of the Disclosure] First, embodiments of the Disclosure will be listed and described. Any combination of the following embodiments, as long as it does not cause inconsistencies, is also included as a form for carrying out the invention. The noise filter of the Disclosure comprises (1) a cylindrical bobbin with flange portions formed at both ends in the axial direction, a magnetic material housed in the bobbin, and a coil wound around the outer circumference of the bobbin, wherein the bobbin is made of synthetic resin. According to the configuration of the Disclosure, since the bobbin is made of synthetic resin with a high degree of freedom in molding, the thickness dimension of the flange portion in the axial direction can be kept small. This makes it possible to miniaturize the device in the axial direction.

[0010] (2) In (1), it is preferable that a helical positioning portion for positioning the coil strands in the axial direction is formed on at least a part of the outer surface of the bobbin. This configuration makes it possible to suppress the axial displacement of the coil relative to the bobbin.

[0011] (3) In (1) or (2), it is preferable that the bobbin has a stopper that restricts the magnetic material from detaching from the bobbin. With this configuration, the magnetic material can be kept contained within the bobbin.

[0012] (4) In (3), it is preferable that the stopper is integrally formed on the inner circumferential surface of the bobbin, the bobbin has a slit that connects the inner circumferential surface and the outer circumferential surface of the bobbin, and the bobbin is deformable to open and close the slit. With this configuration, the magnetic material can be attached to the bobbin simply by expanding the slit.

[0013] (5) In (4), it is preferable that the bobbin has a holding portion that holds the slit in a closed state. With this configuration, it is possible to suppress rattling of the magnetic material within the bobbin caused by the deformation of the bobbin so that the slit expands.

[0014] In (6)(3), it is preferable that the bobbin is constructed by combining a plurality of radially separable segments, the stopper is integrally formed on the inner circumferential surface of the segments, and the segments have locking portions capable of holding the plurality of segments in a combined state. With this configuration, the bobbin is constructed by arranging the plurality of segments to surround the magnetic material and combining them, and the magnetic material is held contained within the bobbin.

[0015] In (7)(3), the bobbin has a housing chamber for housing the magnetic material, and an attachment / detachment opening is formed on the axial end face of the bobbin to allow attachment and detachment of the magnetic material to and from the housing chamber. The stopper is a separate component from the bobbin and can be attached to and detached from the bobbin. When the stopper is attached to the bobbin, it is preferable that the stopper closes at least a part of the attachment / detachment opening. With this configuration, the magnetic material can be attached to and detached from the bobbin when a coil is mounted on the bobbin. This makes it possible to achieve a good noise reduction function in a communication circuit equipped with a noise filter by appropriately replacing the magnetic material according to the frequency of the transmitted signal.

[0016] [Details of Embodiments of the Disclosure] [Example 1] An embodiment of the Disclosure, Noise Filter A of Example 1, will be described with reference to Figures 1 to 4. The present invention is not limited to these examples and is shown in the claims, with all modifications in the meaning and range equivalent to the claims.

[0017] The noise filter A of this embodiment 1 is a component for reducing noise in signals transmitted in a communication circuit (not shown). The noise filter A comprises one core 10 and one coil 28. The core 10 is constructed by assembling a bobbin 11 and a magnetic material 27 made of a ferrite core or the like.

[0018] The bobbin 11 is a single component made of synthetic resin. The bobbin 11 has one cylindrical portion 16, a pair of flange portions 22, and a pair of stoppers 25. The cylindrical portion 16 is a cylindrical part. The pair of flange portions 22 are arc-shaped portions formed on the outer circumferential surfaces of both ends of the cylindrical portion 16 in the axial direction S. The pair of stoppers 25 are annular portions formed on the inner circumferential surfaces of both ends of the cylindrical portion 16 in the axial direction S.

[0019] The bobbin 11 has a single first slit 12 and a pair of second slits 26. The first slit 12 is a narrow space that connects the inner and outer circumferential surfaces of the bobbin 11. The first slit 12 extends linearly along the axial direction S and along the entire length of the bobbin 11 in the axial direction S. In the first slit 12, a pair of opposing surfaces 13, which are the circumferential end faces of the cylindrical portion 16, are positioned close to each other or in contact with each other. On one of the pair of opposing surfaces 13, a plurality of retaining protrusions 14 are formed at intervals in the axial direction S. On the other of the pair of opposing surfaces 13, a plurality of retaining holes 15 are formed at intervals in the axial direction S.

[0020] Inside the cylindrical portion 16, a cylindrical housing chamber 17 is formed, which is concentric with the cylindrical portion 16. The housing chamber 17 is a space that opens to both end faces in the direction of the axial axis S of the bobbin 11. The axial axis S of the bobbin 11 is the same axial axis S as the axial axis S of the noise filter A and the axial axis S of the core 10. A cylindrical magnetic material 27 is housed inside the housing chamber 17. The magnetic material 27 is a component selected according to the frequency of the transmission signal in the communication circuit. The magnetic material 27 is made of ceramics mainly composed of iron oxide.

[0021] A positioning portion 18, consisting of a helical groove, is formed on the outer circumferential surface of the cylindrical portion 16. A notch portion 19 is formed in the cylindrical portion 16, which is a cutout of the outer circumferential portion of the cylindrical portion 16. The portion of the cylindrical portion 16 in which the radial thickness is partially reduced due to the formation of the notch portion 19 is defined as the thin-walled portion 20. The thin-walled portion 20 is formed along the entire length of the cylindrical portion 16 in the axial direction S. In an axial view when viewing the core 10 in the axial direction S, the thin-walled portion 20 is positioned opposite the first slit 12, with the axis S of the bobbin 11 in between.

[0022] The bobbin 11 is formed by joining a pair of split sections 21. The pair of split sections 21 are circumferentially partitioned by a first slit 12, a second slit 26, and a thin-walled section 20. The pair of split sections 21 can be displaced relative to each other, with the thin-walled section 20 as a pivot point, thereby expanding the first slit 12 and the second slit 26. By expanding and deforming the pair of split sections 21, the storage chamber 17 becomes open radially to the bobbin 11. During the process of expanding and deforming the pair of split sections 21, the circumferential dimension of the notch 19 narrows.

[0023] The flange portion 22 is formed coaxially with the cylindrical portion 16. The outer diameter of the flange portion 22 is larger than the outer diameter of the cylindrical portion 16. The thickness dimension of the flange portion 22 in the axial direction S is set to the minimum dimension necessary to prevent the coil 28, which will be described later, from detaching from the bobbin 11 in the axial direction S. The flange portion 22 is composed of a pair of arc-shaped portions 23 that form a sub-arc shape. One end of the pair of arc-shaped portions 23 in the circumferential direction is arranged to face each other via the first slit 12. The other end of the pair of arc-shaped portions 23 faces each other in the circumferential direction with a notch space 24 in the circumferential direction. The notch space 24 is in communication with the notch 19 of the cylindrical portion 16. The notch space 24 prevents the arc-shaped portions 23 from interfering with each other when the pair of half-split portions 21 expand and deform.

[0024] The stopper 25 is formed coaxially with the cylindrical portion 16. The inner diameter of the stopper 25 is smaller than the inner diameter of the cylindrical portion 16. The thickness dimension of the stopper 25 in the axial direction S is set to the minimum dimension necessary to prevent the magnetic material 27, described later, from detaching from the bobbin 11 in the axial direction S. The pair of stoppers 25 prevent the magnetic material 27 housed in the housing chamber 17 from detaching from the bobbin 11 (cylindrical portion 16) in the axial direction S. The second slit 26 is a narrow space extending radially from the thin-walled portion 20 to the inner circumferential edge of the stopper 25. One stopper 25 is divided into two in the circumferential direction by the first slit 12 and the second slit 26.

[0025] The coil 28 is composed of a single strand 29 in which a circular cross-section conductor (not shown) is surrounded by an insulating coating (not shown). The strand 29 constitutes the signal transmission path in the communication circuit. The strand 29 is wound spirally around the cylindrical portion 16 along the positioning portion 18. When the coil 28 is wound around the cylindrical portion 16, the radius of the outer edge of the coil 28 in an axial view is smaller than the radius of curvature of the outer edge of the flange portion 22. The pair of flange portions 22 prevent the coil 28 wound around the bobbin 11 from detaching from the core 10 (cylindrical portion 16) in the axial direction S.

[0026] The assembly procedure for noise filter A is described below. First, the bobbin 11 (a pair of split sections 21) is expanded and deformed to open the housing chamber 17 radially, and the magnetic material 27 is housed inside one of the split sections 21. Next, the pair of split sections 21 are displaced relative to each other, using the thin-walled section 20 as a fulcrum. When the pair of opposing surfaces 13 approach each other, the retaining projection 14 comes into contact with the opening edge of the retaining hole 15 on the other opposing surface 13. When a closing pressure is applied to the pair of split sections 21 from this state, the retaining projection 14 is fitted into the retaining hole 15. As a result, the pair of split sections 21 are assembled to form the bobbin 11, and the magnetic material 27 is housed inside the bobbin 11 to form the core 10. After the core 10 is assembled, the wires 29 are wound spirally around the outer circumference of the bobbin 11 (cylindrical section 16) to form the coil 28. With the above steps, the assembly of noise filter A is complete.

[0027] The noise filter A of this embodiment 1 comprises a bobbin 11, a magnetic material 27, and a coil 28. The bobbin 11 is a cylindrical member with flange portions 22 integrally formed at both ends in the axial direction S. The magnetic material 27 constitutes the core 10 by being housed inside the bobbin 11. The coil 28 is wound around the outer circumference of the bobbin 11. The material of the bobbin 11 is not ceramics mainly composed of iron oxide, but rather a synthetic resin with a high degree of freedom in molding.

[0028] Ferrite cores, which are ceramics primarily composed of iron oxide, are prone to brittle fracture. Therefore, if the bobbin 11 is made of a ferrite core, it is necessary to ensure a large thickness for the flange portion 22. In contrast, in this embodiment 1, the material of the bobbin 11 is a synthetic resin with a high degree of molding freedom, so the thickness of the flange portion 22 in the axial S direction can be kept small. As a result, the noise filter A (core 10) can be miniaturized in the axial S direction.

[0029] A helical positioning portion 18 is formed on the outer circumferential surface of the bobbin 11 to position the strands 29 of the coil 28 in the axial direction S. This configuration prevents the coil 28 from shifting position relative to the bobbin 11 in the axial direction S. The bobbin 11 also has a stopper 25 that restricts the magnetic material 27 from detaching from the bobbin 11 in the axial direction S. This configuration allows the magnetic material 27 to be held in a state where it is housed within the bobbin 11.

[0030] The stopper 25 is integrally formed on the inner circumferential surface of the bobbin 11. The bobbin 11 has a first slit 12 and a second slit 26 that connect the inner circumferential surface and the outer circumferential surface of the bobbin 11. The bobbin 11 can be deformed to expand the first slit 12 and the second slit 26. With this configuration, the magnetic material 27 can be attached to the bobbin 11 simply by deforming the bobbin 11 to expand the first slit 12 and the second slit 26. The bobbin 11 has a holding projection 14 and a holding hole 15 that hold the first slit 12 and the second slit 26 in a closed state. With this configuration, it is possible to prevent the magnetic material 27 from becoming loose inside the bobbin 11 due to the deformation of the bobbin 11 to expand the first slit 12 and the second slit 26.

[0031] [Example 2] An example of the noise filter B of Example 2, which embodies the present disclosure, will be described with reference to Figures 5 to 8. The noise filter B of Example 2 has a different configuration for the bobbin 31 than that of Example 1. The other components are the same as those of Example 1, so the same components are denoted by the same reference numerals, and the explanation of the structure, operation and effect is omitted.

[0032] The noise filter B of this embodiment 2, like that of embodiment 1, comprises one core 30 and one coil 28. The core 30 is constructed by assembling a bobbin 31 made of synthetic resin and a magnetic material 27 made of a ferrite core or the like. The coil 28 and the magnetic material 27 are the same parts as in embodiment 1.

[0033] The bobbin 31 is a cylindrical member formed by combining a pair of divided parts 32 that have the same shape. The divided parts 32 form a semi-circular arc shape when viewed along the axis S of the bobbin 31. The axis S of the bobbin 31 coincides with the axis S of the noise filter B and the axis S of the core 30. The bobbin 31 in the combined state of the pair of divided parts 32 has a cylindrical portion 33, a pair of flange portions 34, and a pair of stoppers 35.

[0034] Each divided body 32 has a semi-cylindrical portion 36 that constitutes a cylindrical portion 33. The circumferential end faces of the semi-cylindrical portion 36 are defined as a pair of mating surfaces 37. One of the pair of mating surfaces 37 has a plurality of locking protrusions 38 formed at intervals in the axial direction S. The other of the pair of mating surfaces 37 has a plurality of locking holes 39 formed at intervals in the axial direction S. When the pair of divided bodies 32 are joined together, the locking protrusions 38 of one divided body 32 fit into the locking holes 39 of the other divided body 32, thereby holding the pair of divided bodies 32 in the joined state.

[0035] The following describes the configuration of the bobbin 31 when the pair of divided bodies 32 are joined together. A positioning portion 40, consisting of a spiral groove, is formed on the outer circumferential surface of the cylindrical portion 33. Inside the cylindrical portion 33, a cylindrical housing chamber 41 is formed, which is concentric with the cylindrical portion 33. The housing chamber 41 is a space that opens to both end faces in the axial direction S of the bobbin 31. A cylindrical magnetic body 27 is housed inside the housing chamber 41. The magnetic body 27 is a component selected according to the frequency of the transmission signal in the communication circuit. The magnetic body 27 is made of ceramics mainly composed of iron oxide.

[0036] The pair of flange portions 34 are arc-shaped parts formed on the outer circumferential surfaces of both ends of the cylindrical portion 33 in the axial direction S. The outer diameter of the flange portions 34 is larger than the outer diameter of the cylindrical portion 33. The flange portions 34 are formed coaxially with the cylindrical portion 33. The thickness dimension of the flange portions 34 in the axial direction S is set to the minimum dimension necessary to prevent the coil 28, which will be described later, from detaching from the bobbin 31 in the axial direction S.

[0037] The pair of stoppers 35 are annular portions formed on the inner circumferential surfaces of both ends of the cylindrical portion 33 in the axial direction S. The inner diameter of the stoppers 35 is smaller than the inner diameter of the cylindrical portion 33 and is formed coaxially with the cylindrical portion 33. The thickness dimension of the stoppers 35 in the axial direction S is set to the minimum dimension necessary to prevent the magnetic material 27, which will be described later, from detaching from the bobbin 31 in the axial direction S. The pair of stoppers 35 prevent the magnetic material 27 housed in the housing chamber 41 from detaching from the bobbin 31 (cylindrical portion 33) in the axial direction S.

[0038] Next, the assembly procedure for noise filter B will be described. First, the pair of divided bodies 32 are separated, and the magnetic material 27 is housed inside one of the divided bodies 32. Next, the other divided body 32 is joined with the first divided body 32. When both divided bodies 32 are joined, the mating surface 37 of one divided body 32 and the mating surface 37 of the other divided body 32 come close together, and the locking projection 38 comes into contact with the opening edge of the locking hole 39 in the mating surface 37 of the other divided body 32. When a radially inward pressing force is applied to the pair of divided bodies 32 from this state, the locking projection 38 is fitted into the locking hole 39. As a result, the pair of divided bodies 32 are assembled to form a bobbin 31, and the magnetic material 27 is housed inside the bobbin 31 to form a core 30. Once the core 30 is assembled, the wires 29 are wound spirally around the outer circumference of the bobbin 31 (cylindrical body) to form the coil 28. This completes the assembly of the noise filter B.

[0039] The bobbin 31 constituting the noise filter B of this embodiment 2 is formed by combining a plurality of radially separable segments 32. The stopper 35 is integrally formed on the inner circumferential surface of the segments 32. The segments 32 have a locking projection 38 and a locking hole 39 as locking parts that can hold the plurality of segments 32 in a combined state. With this configuration, the bobbin 31 is formed by arranging the plurality of segments 32 so as to surround the magnetic material 27 and combining them, and the magnetic material 27 is held in a state where it is housed inside the bobbin 31.

[0040] [Example 3] An example 3 of the noise filter C embodying the present disclosure will be described with reference to Figures 9 to 11. The noise filter C of this example 3 has a different configuration for the bobbin 51 than that of Example 1. The other components are the same as those of Example 1, so the same components are denoted by the same reference numerals, and the explanation of the structure, operation and effect is omitted. The noise filter C of this example 3 includes one core 50 and one coil 28, similar to Example 1. The core 50 is constructed by assembling the bobbin 51 with magnetic materials 65 and 66 made of ferrite cores or the like. The coil 28 is the same component as in Example 1.

[0041] The bobbin 51 is constructed by assembling a main body member 52 and a stopper 70, which is a separate part from the main body member 52. Both the main body member 52 and the stopper 70 are made of synthetic resin. The main body member 52 is a single part having a cylindrical tubular portion 53, a bottom wall portion 57, and a pair of flange portions 58. For convenience, the following description of the bobbin 51 will be given with the axis S of the bobbin 51 oriented in the vertical direction. The axis S of the bobbin 51 is the same axis as the axis S of the noise filter C and the axis S of the core 50.

[0042] A positioning portion 54, consisting of a spiral groove, is formed on the outer circumferential surface of the cylindrical portion 53. The strands 29 of the coil 28 are fitted into the positioning portion 54. Inside the cylindrical portion 53, a housing chamber 55 is formed, which is cylindrical and concentric with the cylindrical portion 53. The housing chamber 55 is a space that opens only on the upper end surface of the bobbin 51 (main body member 52). The opening of the housing chamber 55 on the upper surface of the bobbin 51 functions as an attachment / detachment port 56 for attaching and detaching magnetic materials 65 and 66 to and from the housing chamber 55. The lower end of the housing chamber 55 is closed by a bottom wall portion 57.

[0043] Inside the containment chamber 55, two cylindrical magnetic bodies 65 and 66 are housed stacked vertically. The two magnetic bodies 65 and 66 are components selected according to the frequency of the transmission signal in the communication circuit. The frequency bands of the noise to be removed by the two magnetic bodies 65 and 66 are different from each other. The magnetic bodies 65 and 66 are made of ceramics with iron oxide as the main component.

[0044] The pair of flange portions 58 are formed on the outer peripheral surfaces of both ends in the axial direction S of the cylindrical portion 53. Each flange portion 58 is composed of four arc portions 59. One arc portion 59 generally forms a substantially semi - circular arc shape in the axial direction view when the bobbin 51 is viewed in the axial direction S. The four arc portions 59 are formed at equal intervals in the circumferential direction and coaxially with the cylindrical portion 53. The outer diameter of the outer peripheral edge of the flange portion 58 is larger than the maximum outer diameter of the cylindrical portion 53. The thickness dimension of the flange portion 58 in the axial direction S is set to the minimum dimension necessary to prevent the coil 28 described later from detaching from the bobbin 51 in the axial direction S.

[0045] On the upper end surface of the main body member 52, four communication grooves 60 that communicate the inner peripheral surface and the outer peripheral surface of the main body member 52 are formed. Each communication groove 60 is a space extending in the radial direction orthogonal to the axis S. One communication groove 60 is composed of a space between adjacent arc portions 59 in the circumferential direction and a notch groove formed by notching the upper end portion of the cylindrical portion 53. On the lower end surface of the main body member 52, four locking grooves 61 are formed. The four locking grooves 61 are arranged at the same positions as the four communication grooves 60 in the axial direction view. One locking groove 61 is composed of a space between adjacent arc portions 59 in the circumferential direction and a notch groove formed by notching the upper end portion of the cylindrical portion 53. Each locking groove 61 is a space extending in the radial direction. At the innermost peripheral end of each locking groove 61, a recess 62 in the form of recessing the lower end surface of the cylindrical portion 53 is formed.

[0046] The stopper 70 is a single component having a disk-shaped closing portion 71 that closes the insertion / removal opening 56 and four elastic arm portions 72. The four elastic arm portions 72 are arranged at equal angular pitches in the circumferential direction and extend in a cantilevered manner from the outer peripheral edge of the closing portion 71. Each elastic arm portion 72 has a first arm portion 73, a second arm portion 74, a third arm portion 75, and a locking projection 76. The first arm portion 73 is an elongated portion extending radially outward from the outer peripheral edge of the closing portion 71. The second arm portion 74 is a portion extending in a cantilevered manner downward (in the direction of the axis S) from the extending end of the first arm portion 73. The third arm portion 75 is a portion extending in a cantilevered manner radially inward from the extending end (lower end portion) of the second arm portion 74. The locking projection 76 is a portion protruding upward from the extending end of the third arm portion 75. The elastic arm portion 72 can be elastically deformed in a direction intersecting the extending directions of the respective arm portions 73, 74, 75.

[0047] Next, the assembly procedure of the noise filter C will be described. First, with the stopper 70 removed from the main body member 52, the wire element 29 is wound spirally around the outer periphery of the cylindrical portion 53 while being fitted into the positioning portion 54 to form the coil 28. Next, the magnetic bodies 65, 66 are accommodated into the accommodation chamber 55 from the insertion / removal opening 56. Incidentally, the forming of the coil 28 may be performed after the magnetic bodies 65, 66 are accommodated in the accommodation chamber 55.

[0048] After that, the stopper 70 is assembled so as to cover the main body member 52 from above. At the time of assembly, the closing portion 71 is fitted into the insertion / removal opening 56, and the first arm portion 73 is fitted into the communication groove 60. Then, while elastically deforming the elastic arm portion 72, the third arm portion 75 is fitted into the locking groove 61, and the locking projection 76 is fitted into the recess 62. As described above, the assembly of the stopper 70 to the main body member 52 is completed, and at the same time, the bobbin 51 and the core 50 are formed, and the assembly of the noise filter C is completed.

[0049] When the stopper 70 is assembled, the fitting of the closing portion 71 with the attachment / detachment opening 56 restricts the radial displacement of the closing portion 71 relative to the main body member 52. The fitting of the locking projection 76 with the recess 62 restricts the radial outward displacement of the third arm portion 75. The first arm portion 73 and the third arm portion 75 sandwich the cylindrical portion 53 in the axial direction S, thereby restricting the axial displacement of the stopper 70 relative to the main body member 52 in the axial direction S. As a result, the stopper 70 is held in the assembled state relative to the main body member 52.

[0050] The magnetic materials 65 and 66 housed in the bobbin 51 can be replaced by removing the stopper 70 from the main body member 52. When removing the stopper 70 from the main body member 52, the elastic arm portion 72 is elastically deformed while the third arm portion 75 is displaced downward to disengage the locking projection 76 from the recess 62 and detach the third arm portion 75 radially outward from the locking groove 61. Next, the stopper 70 is moved upward and the third arm portion 75 is again displaced radially outward to remove the stopper 70 from the main body member 52. Once the stopper 70 is removed, the attachment / detachment opening 56 is opened, so the magnetic materials 65 and 66 in the housing chamber 55 are taken out and other magnetic materials 65 and 66 are placed in the housing chamber 55. After this, the stopper 70 is attached to the main body member 52. In this way, the magnetic materials 65 and 66 can be replaced while the coil 28 remains attached to the bobbin 51.

[0051] The bobbin 51 constituting the noise filter C of this embodiment 3 has a housing chamber 55 for housing magnetic materials 65 and 66. An attachment / detachment opening 56 is formed on the end face of the bobbin 51 in the axial direction S, which allows the magnetic materials 65 and 66 to be attached to and detached from the housing chamber 55. The stopper 70 is a separate component from the bobbin 51 and can be attached to and detached from the bobbin 51. When the stopper 70 is attached to the bobbin 51, the stopper 70 closes at least a part of the attachment / detachment opening 56. With this configuration, the magnetic materials 65 and 66 can be attached to and detached from the bobbin 51 even when the coil 28 is mounted on the bobbin 51. As a result, in a communication circuit to which the noise filter C is attached, a good noise reduction function can be achieved by appropriately replacing the magnetic materials 65 and 66 according to the frequency of the transmitted signal.

[0052] [Example 4] An example 4 of the noise filter D embodying the present disclosure will be described with reference to Figures 12 to 14. The noise filter D of this example 4 has a different configuration for the bobbin 81 than that of Example 2. The other components are the same as those of Example 2, so the same components are denoted by the same reference numerals, and the explanation of the structure, operation and effect is omitted.

[0053] The noise filter D of this embodiment 4, like that of embodiment 2, comprises one core 80 and one coil 28. The core 80 is constructed by assembling a bobbin 81 with a magnetic material 27 made of a ferrite core 80 or the like. The coil 28 and magnetic material 27 are the same parts as in embodiment 2. The basic structure of the bobbin 81 of this embodiment 4 is the same as that of the bobbin 31 of embodiment 2. That is, the bobbin 81 is a cylindrical member constructed by combining a pair of divided parts 82 of the same shape. The bobbin 81 in the state in which the pair of divided parts 82 are combined has a cylindrical part 83, a pair of flange parts 84, and a pair of stoppers 85.

[0054] Multiple locking protrusions 86 are formed on the mating surface of one of the divided parts 82 at intervals in the axial direction. Multiple locking holes 87 are formed on the mating surface of the other divided part 82 at intervals in the axial direction. The pair of divided parts 82 are held together by the fitting of the locking protrusions 86 and the locking holes 87. A magnetic material 27 is housed in a housing chamber 88 formed inside the cylindrical part 83. The pair of flange parts 84 are formed on the outer circumferential surfaces of both ends of the cylindrical part 83 in the axial direction. The pair of stoppers 85 are annular parts formed on the inner circumferential surfaces of both ends of the cylindrical part 83 in the axial direction.

[0055] A positioning portion 89, consisting of a spiral groove similar to that in Embodiment 2, is formed on the outer circumferential surface of the cylindrical portion 83. The cross-sectional shape of the positioning portion 89 (spiral groove) is triangular. Multiple retaining grooves 90 are formed in the cylindrical portion 83, with the groove bottoms of the positioning portion 89 recessed. As shown in Figure 12, the multiple retaining grooves 90 are formed at multiple positions spaced apart in the circumferential direction. One retaining groove 90 is a spiral groove along the positioning portion 89. The cross-sectional shape of the retaining groove 90 is a rounded arc. The radius of curvature in the cross-section of the retaining groove 90 is the same as the radius of the strands 29 of the coil 28.

[0056] The strands 29 of the coil 28 are alternately fitted into the positioning portion 89 and the retaining groove 90 in the helical direction (the longitudinal direction of the strands 29), surrounding the magnetic body 27 and the cylindrical portion 83. The minimum radial thickness dimension Ta (see Figure 14) of the cylindrical portion 83 where the retaining groove 90 is formed is smaller than the minimum radial thickness dimension Tb (see Figure 13) of the cylindrical portion 83 where the retaining groove 90 is not formed. The minimum radial thickness dimension Ta of the cylindrical portion 83 where the retaining groove 90 is formed is, for example, about 1 mm.

[0057] The noise filter D of this embodiment 4 has excellent noise removal and noise shielding performance because it provides a region where the magnetic material 27 and the strands 29 (coil 28) are close together by forming retaining grooves 90. Furthermore, the retaining grooves 90 are not continuous around the entire circumference of the cylindrical portion 83, but are dispersed in the circumferential direction, so the reduction in strength of the cylindrical portion 83 caused by the formation of the retaining grooves 90 is suppressed.

[0058] [Example 5] An example 5 of the noise filter E embodying the present disclosure will be described with reference to Figure 15. The noise filter E of this example 5 has a different configuration for the bobbin 93 than that of Example 2. The other components are the same as those of Example 2, so the same components are denoted by the same reference numerals, and the explanation of the structure, operation and effect is omitted.

[0059] The noise filter E of this embodiment 5, like that of embodiment 2, comprises one core 92 and one coil 28. The core 92 is constructed by assembling a bobbin 93 and a magnetic material 27 made of a ferrite core 92 or the like. The coil 28 and magnetic material 27 are the same parts as in embodiment 2. The basic structure of the bobbin 93 of this embodiment 5 is the same as that of the bobbin 31 of embodiment 2. That is, the bobbin 93 is a cylindrical member constructed by combining a pair of divided parts 94 of the same shape. The bobbin 93 in the state in which the pair of divided parts 94 are combined has a cylindrical part 95 and a pair of flange parts 96.

[0060] Multiple locking protrusions 98 are formed on the mating surface of one divided body 94, and multiple locking holes 99 are formed on the mating surface of the other divided body 94. The pair of divided bodies 94 are held in a joined state by the fitting of the locking protrusions 98 and the locking holes 99. A magnetic material 27 is housed in a housing chamber 100 formed inside the cylindrical portion 95. A pair of flange portions 96 are formed on the outer circumferential surfaces of both ends of the cylindrical portion 95 in the axial direction. A pair of stoppers 97 are formed on the inner circumferential surfaces of both ends of the cylindrical portion 95 in the axial direction.

[0061] A single spiral-shaped positioning portion 101 is formed on the outer circumferential surface of the cylindrical portion 95. The positioning portion 101 is a rib-like projection that extends radially outward from the outer circumferential surface of the cylindrical portion 95. The formation of the positioning portion 101 creates a spiral-shaped groove portion 102. The cross-sectional shape of the groove portion 102 is rectangular. The axial dimension of the groove portion 102 is the same as the radius of the strands 29 of the coil 28. The minimum radial thickness dimension of the cylindrical portion 95 (the radial thickness dimension between the outer circumferential surface of the housing chamber 100 and the groove bottom surface of the groove portion 102) is set to, for example, about 1 mm.

[0062] The noise filter E of this embodiment 5 has excellent noise removal and noise shielding performance because the minimum thickness dimension of the cylindrical portion 95 is set small, allowing the strands 29 (coil 28) to be positioned in close proximity to the magnetic material 27. Furthermore, the positioning portion 101 that constitutes the groove portion 102 protrudes perpendicular to the outer surface of the cylindrical portion 95, and thus functions as a reinforcing rib. Therefore, the reduction in strength of the cylindrical portion 95 caused by the reduction in the minimum thickness dimension of the cylindrical portion 95 is suppressed by the positioning portion 101.

[0063] [Other Embodiments] The present invention is not limited to the embodiments described above and in the drawings, but is shown in the claims. The present invention includes the meaning of equivalences to the claims and all modifications within the claims, and also includes the following embodiments: - In embodiments 1 to 3, the positioning portion is not limited to a helical groove, but may be in the form of a rib protruding from the object, as in embodiment 5. - In embodiments 1 to 3, the cross-sectional shape of the helical groove constituting the positioning portion is not limited to a triangle, but may be a semicircular arc, a trapezoid, etc. - In embodiments 1 to 5, the positioning portion may be formed only on a part of the circumferential direction of the cylindrical portion. - In embodiments 1 to 3, the bobbin may be in a form without a positioning portion. - In embodiments 1 to 5, the magnetic material may be fixed to the bobbin with adhesive. - In embodiments 1 to 5, the stopper is not limited to a form that extends rib-like in the circumferential direction, but may be in a form that is scattered at multiple locations with circumferential spacing. - In embodiments 1 to 5, the stopper may be in a form that completely blocks both ends of the housing chamber in the axial direction. - In Example 1, the bobbin may be elastically deformable to widen the slit and elastically return to narrow the slit spacing. In this case, the holding part can be omitted. - In Examples 1, 2, 4, and 5, only one magnetic material is housed in the bobbin, but multiple types of magnetic materials may be housed in one bobbin depending on the frequency of the transmission signal. - In Example 2, the number of divided parts constituting one bobbin may be three or more. - In Example 3, the number of magnetic materials housed in the bobbin may be just one or three or more. - In Example 3, the stopper may be configured to close only a part of the attachment / detachment opening. - In Example 4, the number of holding grooves in a plan view is not limited to four, but may be one to three or five or more. - In Example 4, the arrangement of the holding grooves in the circumferential direction is not limited to a constant pitch, but may be an irregular pitch. - In Example 4, the holding grooves may be continuous around the entire circumference of the positioning part (bobbin). - In Example 4, the retaining groove may be in a form that penetrates into the housing chamber. - The configuration of forming an arc-shaped retaining groove in the positioning portion of Example 4 can also be applied to Examples 1 to 3.

[0064] A...Noise filter B...Noise filter C...Noise filter D...Noise filter E...Noise filter S...Axis 10...Core 11...Bobbin 12...First slit 13...Opposite surface 14...Retaining projection (retaining part) 15...Retaining hole (retaining part) 16...Cylindrical part 17...Housing chamber 18...Positioning part 19...Notch 20...Thin-walled part 21...Half-split part 22...Flange part 23...Arch-shaped part 24...Notch space 25...Stopper 26...Second slit 27...Magnetic material 28...Coil 29...Strand wire 30...Core 31...Bobbin 32...Divided body 33...Cylindrical part 34...Flange part 35...Stopper 36...Semi-cylindrical part 37...Mating surface 38...Locking projection (locking part) 39...Locking hole (locking part) 40...Positioning part 41...Housing chamber 50...Core 51...Bobbin 52...Main body member 53...Cylindrical part 54...Positioning part 55...Housing chamber 56...Attachment / detachment opening 57...Bottom wall part 58...Flange part 59...Arc part 60...Communication groove 61...Locking groove 62...Recess 65...Magnetic material 66...Magnetic material 70...Stopper 71...Closing part 72...Elastic arm part 73...First arm part 74...Second arm part 75...Third arm part 76...Lock projection 80...Core 81...Bobbin 82...Divided body 83...Cylindrical part 84...Flange part 85...Stopper 86...Locking projection 87...Locking hole 88...Housing chamber 89...Positioning part 90...Retaining groove 92...Core 93...Bobbin 94...Divided body 95...Cylindrical part 96...Flange section 97...Stopper 98...Locking projection 99...Locking hole 100...Housing chamber 101...Positioning section 102...Groove section

Claims

1. A noise filter comprising: a cylindrical bobbin with flanges formed at both ends in the axial direction; a magnetic material housed within the bobbin; and a coil wound around the outer circumference of the bobbin, wherein the bobbin is made of synthetic resin.

2. The noise filter according to claim 1, wherein a helical positioning portion for positioning the wires of the coil in the axial direction is formed on at least a part of the outer surface of the bobbin.

3. The noise filter according to claim 1 or claim 2, wherein the bobbin has a stopper that restricts the magnetic material from detaching from the bobbin.

4. The noise filter according to claim 3, wherein the stopper is integrally formed on the inner circumferential surface of the bobbin, the bobbin has a slit that connects the inner circumferential surface and the outer circumferential surface of the bobbin, and the bobbin is capable of being deformed to open and close the slit.

5. The noise filter according to claim 4, wherein the bobbin has a holding portion that holds the slit in a closed state.

6. The noise filter according to claim 3, wherein the bobbin is formed by combining a plurality of radially separable segments, the stopper is integrally formed on the inner circumferential surface of the segments, and the segments have locking portions capable of holding the plurality of segments in a combined state.

7. The noise filter according to claim 3, wherein the bobbin has a housing chamber for housing the magnetic material, the end face of the bobbin in the axial direction has an attachment / detachment opening that allows the magnetic material to be attached to and detached from the housing chamber, the stopper is a separate component from the bobbin and can be attached to and detached from the bobbin, and when the stopper is attached to the bobbin, the stopper closes at least a part of the attachment / detachment opening.

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