# Patent

## Title
Electric current detector and core component used therefor

## Abstract

In an electric current detector according to the present invention, an annular core 2 having a magnetic gap G and a Hall element 41 which is located in the magnetic gap of the core 2 and detects a magnitude of an electric current passing through the core 2 are arranged in an outer case 1. Here, in the core 2, a mold resin portion 3 which covers a surface of the core 2 over part of an overall length along a magnetic path thereof is molded at one or a plurality of portions along the magnetic path to configure an integral core component, the core component being fixed into the outer case 1 in a state where a surface of the mold resin portion 3 makes contact with an inner surface of the outer case 1.

## Background
TECHNICAL FIELD
The present invention relates to an electric current detector which detects a magnitude of an electric current by using an electromagnetic conversion element such as a Hall element, and a core component used for the electric current detector.
BACKGROUND ART
As shown in FIG. 9, there has been known such an electric current detector in which a core (7) having a magnetic gap G and a printed circuit board (4) to which a Hall element (41) is attached are accommodated in an outer case (6), the Hall element (41) being interposed in the magnetic gap G of the core (7).
When an electric current passes through the hollow portion of the core (7), the magnitude of the electric current is detected by the Hall element (41).
Typically, the electric current detector in which the outer case is previously resin molded is adopted. After the core is accommodated in a core accommodating chamber formed in the outer case, a synthetic resin (e.g., an epoxy resin) is filled into the core accommodating chamber to fix the core into the outer case (see Patent Document 1).
In the assembling process of the electric current detector in which the synthetic resin is filled into the outer case, first, the core is accommodated in the core accommodating chamber in the outer case to temporarily fix the core into the outer case, and the synthetic resin is filled into the outer case to fix the core into the outer case, thereby performing electric insulation with respect to the core.
In this connection, in the electric current detector, the Hall element is required to be precisely positioned in the magnetic gap of the core.
However, in the electric current detector in which the synthetic resin is filled into the outer case, a large space (clearance) is necessary for filling the synthetic resin into the outer case, resulting in increase in size of the outer case. In addition, to ensure positioning accuracy for temporarily fixing the core into the outer case, a complicate configuration for forming a positioning projection on the inner surface of the case, or the like is necessary. The positioning operation of the core is troublesome.
PRIOR ART DOCUMENT
Patent Document


    Patent Document 1: Japanese Patent Laid-open Publication No. 2006-78255


SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
Accordingly, the applicant has developed the electric current detector in which, as shown in FIG. 9, the core (7) is covered with mold resins (61), (62) to form the outer case (6) with the mold resins (61),(62).
In such an electric current detector, the complicate configuration and the troublesome operation for temporarily fixing the core into the outer case are not necessary, thereby improving assembling accuracy.
However, in the electric current detector in which, as shown in FIG. 9, the core (7) is covered with the mold resins (61), (62), and the core (7) receives an external force from the surrounding resins at the time of resin molding, thereby causing large hysteresis in a relation (BH curve) between a coercive force (Hc) and a residual magnetic flux density (Br).
In addition, fine dust can enter into the resins at the time of resin molding, with the result that the dust is exposed on the surface of the outer case (6) to lower the yield due to poor appearance.
Accordingly, an object of the present invention intend to provide an electric current detector which can reduce hysteresis without being increased in size, can precisely and easily position a core into an outer case, and can prevent the yield from being lowered, and a core component used therefor.
Means for Solving the Problems
In an electric current detector according to the present invention, an annular core (2) having a magnetic gap G and an electromagnetic conversion element which is located in the magnetic gap of the core (2) and detects a magnitude of an electric current passing through the core (2) are arranged in an outer case (1).
Here, in the core (2), a mold resin portion (3) which covers a surface of the core (2) over part of an overall length along a magnetic path thereof is molded at one or a plurality of portions along the magnetic path to configure an integral core component (20), the core component (20) being fixed into the outer case (1) in a state where a surface of the mold resin portion (3) makes contact with an inner surface of the outer case (1).
In the electric current detector of the present invention, after the outer case (1) and the core component (20) are previously manufactured in individual processes, the core component (20) is fixed into the outer case (1).
In the core component (20), part of the overall length along the magnetic path of the core (2) is only covered with the mold resin portion (3). Therefore, a force that the core (2) receives from the surroundings thereof at the time of molding the mold resin portion (3) is relatively small, thereby preventing hysteresis in the core (2) from being increased.
The outer case (1) and the core component (20) can obtain high accuracy in outer shape dimensions thereof by quality control in individual resin molding processes. Therefore, in the process for fixing the core component (20) into the outer case (1), the surface of the mold resin portion (3) is made in contact with the inner surface of the outer case (1), so that the core (2) can be precisely positioned into the outer case (1). In this state, the mold resin portion (3) is engaged into the outer case (1), so that the core component (20) is fixed into the outer case (1).
In addition, the outer case (1) is manufactured in the resin molding process different from that of the core component (20), so that any foreign particles such as dust can be prevented from entering into the resin which is the material of the outer case (1), thereby improving the manufacturing yield.
In a specific form, the core (2) has a polygonal shape having a plurality of corners, and the mold resin portion (3) is formed to cover at least one of the corners.
According to the specific form, the mold resin portion (3) is formed at a corner of the core (2), and the mold resin portion (3) makes contact with the inner surface of the outer case (1) to position the core component (20). Two surfaces of the mold resin portion (3) make close contact with the inner surface of the outer case (1), thereby improving positioning accuracy.
A core component for an electric current detector according to the present invention includes an annular core (2) having a magnetic gap G and a mold resin portion (3) which covers a surface of the core (2) over part of an overall length along a magnetic path of the core (2), and a manufacturing method of the core component includes:
manufacturing an annular core member (21);
molding a mold resin portion (32) which covers a surface of the core member (21) over part of an overall length along a magnetic path of the manufactured annular core member (21); and
cutting the core member (21) and the mold resin portion (32) in a region in which the mold resin portion (32) is formed and forming the magnetic gap G and two mold resin portions (3a), (3b).
In the manufacturing method of the core component according to the present invention, after the mold resin portion (32) is molded on the core member (21), the core member (21) and the mold resin portion (32) are cut to form the magnetic gap G. Therefore, when the core member (21) is a stacked type core member in which a plurality of electromagnetic steel plates are stacked, in the cutting process, the plurality of electromagnetic steel plates are constrained by the surroundings thereof by the mold resin portion (32), and are cut. This can avoid the separation of some electromagnetic steel plates and the entering of any cutting pieces and metal burrs, which are caused by the cutting, into the mold resin portion (32).
Effects of the Invention
The electric current detector according to the present invention and the core component used therefor can reduce hysteresis without being increased in size, can precisely and easily position the core into the outer case, and can prevent the yield from being lowered.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an electric current detector according to the present invention.
FIG. 2 is a perspective view, partially broken away, of the electric current detector.
FIG. 3 is a cross-sectional view taken along line A-A of FIG. 1.
FIG. 4 is a cross-sectional view taken along line B-B of FIG. 1.
FIG. 5 is a cross-sectional view taken along line C-C of FIG. 1.
FIG. 6 is an exploded perspective view of the electric current detector according to the present invention.
FIG. 7 is a process diagram showing a manufacturing method of a core component according to the present invention.
FIG. 8 is a diagram showing a plurality of arrangement forms of one or a plurality of mold resin portions with respect to a core member.
FIG. 9 is a cross-sectional view of a conventional electric current detector.



DETAILED DESCRIPTION OF EMBODIMENTS
Hereinafter, an embodiment of the present invention will be specifically described with reference to the drawings.
As shown in FIGS. 1 and 2, in an electric current detector according to the present invention, the electric current detector accommodate a core component (20) having a magnetic gap G, and a printed circuit board (4) having a Hall element (41) in an outer case (1) made of a synthetic resin.
As shown in FIG. 6, in the outer case (1), an inner peripheral wall (12) in a square tubular shape and a planar partitioning wall (13) are integrally molded in an inner space surrounded by an outer peripheral wall 11 in a square tubular shape, the inner space being partitioned into a core accommodating chamber (16) and a board accommodating chamber (17) by the partitioning wall (13). The partitioning wall (13) can be omitted.
A cutaway (14) is formed in the partitioning wall (13). In addition, one or more slits (15), (15) (two slits in the embodiment) are formed in each of the right and left wall surfaces of the outer peripheral wall (11).
The core component (20) has a core (2) having a substantially square annular shape and the magnetic gap G, and four mold resin portions (3a), (3b), (3c), (3d), which cover four corners of the core (2). A projection (31) is integrally formed on the side surface of a mold resin portion (3) so as to be engageable into the corresponding slit (15) in the outer case (1).
The Hall element (41) is formed to be planar, and is erected vertically on the surface of the printed circuit board (4). In addition, two screw holes (42), (42) are formed in both ends of the printed circuit board (4). The Hall element (41) can also be surface mounted on the printed circuit board (4).
The core component (20) is accommodated in the core accommodating chamber (16) in the outer case (1), and the printed circuit board (4) is accommodated in the board accommodating chamber (17) in the outer case (1). In this state, the Hall element (41) passes through the cutaway (14) in the outer case (1), and is interposed in the magnetic gap G of the core component (20) (see FIGS. 3 to 5).
In the state where the core component (20) is accommodated in the core accommodating chamber (16) in the outer case (1), as shown in FIG. 3, four mold resin portions (3a), (3b), (3c), (3d) of the core component (20) are provided at four corners of the core accommodating chamber (16) in the outer case (1), respectively, and two surfaces of the mold resin portion (3) orthogonal to each other make contact with the inner surface of the outer case (1). Thereby, the core component (20) is precisely positioned into the outer case (1).
As shown in FIG. 5, the projection (31) of the mold resin portion (3) is engaged into the slit (15) in the outer case (1), thereby fixing the core component (20) into the outer case (1).
As shown in FIG. 2, the printed circuit board (4) is fixed into the outer case (1) by screwing two screws (5), (5) from the screw holes (42), (42) shown in FIG. 6 into the partitioning wall (13) in the outer case (1). Other fixing methods different from the fastening method using the screw (5) can also be adopted.
Thereby, the Hall element (41) is held in the precise position in the magnetic gap G of the core component (20).
FIG. 7 shows the manufacturing process of the core component (20) according to the present invention.
First, as shown in FIG. 7(a), a core member (21) which has a substantially square annular shape and four corners (21a), (21b), (21c), (21d) is manufactured. The core member (21) is manufactured, for example, by helically winding a belt-shaped electromagnetic plate.
Next, as shown in FIG. 7(b), a first mold resin portion (32) which has a long rectangular parallelepiped shape and covers two corners (21a), (21b) on the upper side of the core member (21), a second mold resin portion (33) which has a short rectangular parallelepiped shape and covers one corner (21c) on the lower side thereof, and a third mold resin portion (34) which has a short rectangular parallelepiped shape and covers the other corner (21d) on the lower side thereof are molded. Here, the projection (31) is integrally molded on the side surface of each of the mold resin portions.
Finally, the core member (21) and the first mold resin portion (32) are cut by a cutter (not shown) in the range of the first mold resin portion (32). Therefore, as shown in FIG. 7(c), the core component (20) which has the magnetic gap G and four mold resin portions (3a), (3b), (3c), (3d) is obtained.
The core component (20) and the printed circuit board (4), which have been obtained in such a manner are fixed into the separately manufactured outer case (1). Therefore, the electric current detector of the present invention shown in FIGS. 1 to 5 is completed.
Here, the resin for fixing the core component (20) is not filled into the outer case (1).
FIG. 8 shows a plurality of arrangement forms of one or a plurality of mold resin portions to be formed on the core member (21) before the magnetic gap is formed in the manufacturing process of the core component according to the present invention. In these forms, a mold resin portion (35) which has a long rectangular parallelepiped shape is cut for forming the gap.
In the form of FIG. 8(a), three mold resin portions (35), (36), (37) are formed on the core member (21), and the two mold resin portions (36), (37) on the lower side each cover the corners of the core member (21). In addition, in the form of FIG. 8(b), the three mold resin portions (35), (36), (37) are formed on the core member (21), and each of the mold resin portions (35), (36), (37) cover the corners of the core member (21).
In the form of FIG. 8(c), three mold resin portions (35), (36), (37) are formed on the core member (21), and any mold resin portions (35), (36), (37) do not cover the corners of the core member (21). In addition, in the form of FIG. 8(d), the three mold resin portions (35), (36), (37) are formed on the core member (21), and the mold resin portion (35) on the upper side covers two corners of the core member (21).
In the form of FIG. 8(e), one mold resin portion (35) is formed on the core member (21), and the mold resin portion (35) does not cover the corners of the core member (21). In addition, in the form of FIG. 8(f), one mold resin portion (35) is formed on the core member (21), and the mold resin portion (35) covers two corners of the core member (21).
Even when any of the forms is adopted, in the electric current detector according to the present invention, the surface of the mold resin portion (3) makes close contact with the inner surface of the outer case (1). Thereby, the core component (20) is precisely positioned into the outer case (1).
Table 1 below shows the results obtained by measuring the coercive forces (Hc) and the residual magnetic flux densities (Br) in the unmolded electric current detector in which after the core is accommodated in the previously manufactured outer case, the resin is filled into the outer case, the currently-used electric current detector in which the core is covered with the mold resin to form the outer case, and the partially-molded electric current detector according to the present invention.










TABLE 1









Coercive force (Hc)
Residual magnetic flux density (Br)














Unmolded
Currently-used
Partially-molded
Unmolded
Currently-used
Partially-molded



electric
electric
electric
electric
electric
electric



current detector
current detector
current detector
current detector
current detector
current detector


















237.1
310.1
224
41.8
62.2
42.0



226.9
282.1
231
41.5
61.9
41.8



246.3
311.3
237
43.0
60.9
44.9



225.0
291.7
226
40.5
62.3
42.0



225.8
277.4
225
40.3
58.2
41.8



228.0
293.4
226
39.7
63.2
42.3



227.6
304.8
238
40.8
59.8
43.6



222.2
296.2
211
39.2
63.7
39.4


(Average
229.9
295.9
227.1
40.8
61.5
42.2


values)


(Comparison)
100%
128.7%
98.8%
100%
150.6%
103.4%









As is apparent from Table 1, in the partially-molded electric current detector according to the present invention, the same magnetic characteristic as the conventional unmolded electric current detector is maintained, and hysteresis caused by the action of an external force at the time of resin molding is not increased.
On the contrary, the coercive force (Hc) and the residual magnetic flux density (Br) in the currently-used electric current detector are about 30% to 50% higher than those in the unmolded electric current detector, resulting in increasing hysteresis.
In this way, in the partially-molded electric current detector according to the present invention, part of the overall length along the magnetic path of the core (2) is only covered with the mold resin portion (3). Therefore, a force that the core (2) receives from the surroundings thereof at the time of molding the mold resin portion (3) is relatively smaller than that in the currently-used electric current detector, thereby preventing hysteresis from being increased.
In addition, in the electric current detector according to the present invention, the outer case (1) and the core component (20) can obtain a high accuracy in the outer shape dimensions thereof by the quality control in individual resin molding processes. Therefore, in the process for fixing the core component (20) into the outer case (1), the surface of the mold resin portion (3) is made in contact with the inner surface of the outer case (1), so that the core (2) can be precisely positioned into the outer case (1).
In addition, the outer case (1) is manufactured in the resin molding process different from that of the core component (20), so that any foreign particles such as dust can be prevented from entering into the resin which is the material of the outer case (1), thereby improving the manufacturing yield.
Further, in the manufacturing method of the core component according to the present invention, after the mold resin portion (32) is molded on the core member (21), the core member (21) and the mold resin portion (32) are cut to form the magnetic gap G. Therefore, when the core member (21) is a stacked type core member in which a plurality of electromagnetic steel plates are stacked, in the cutting process, the plurality of electromagnetic steel plates are constrained by the surroundings thereof by the mold resin portion (32), and are cut. This can avoid the separation of some electromagnetic steel plates and the entering of any magnetic particles, which are caused by the cutting, into the mold resin portion (32).
The configurations of the respective portions of the present invention are not limited to the above embodiment, and various modifications can be made within the technical range of the claims. For example, various configurations in which the core component (20) is fixed into the outer case (1), other than the configuration manufactured by adhesion with resin filling can be adopted without being limited to the engaging configuration of the slit (15) in the outer case (1) and the projection (31) on the core component (20).
DESCRIPTION OF REFERENCE CHARACTERS


    (1) Outer case
    (16) Core accommodating chamber
    (17) Board accommodating chamber
    (20) Core component
    (G) Magnetic gap
    (2) Core
    (3) Mold resin portion
    (4) Printed circuit board
    (41) Hall element

## Claims

1. An electric current detector, comprising:
an outer case;
an annular core having a magnetic gap G;
an electromagnetic conversion element which is located in the magnetic gap of the core and detects a magnitude of an electric current passing through the core, the annular core and the electromagnetic conversion element arranged in the outer case; and
a mold resin portion configured to cover an outer peripheral surface of the core over a part of an overall length along a magnetic path thereof and be molded at one or a plurality of portions along the magnetic path to configure an integral core component in the core, the core component being fixed into the outer case, wherein
the core has a polygonal shape having a plurality of corners, and the mold resin portion is formed to cover at least one of the corners, and
wherein the mold resin portion covering the corner of the core is provided at a corner of the outer case, and two surfaces of the mold resin portion make contact with the inner surface of the outer case.

2. The electric current detector according to claim 1, wherein the core component is fixed into the outer case by engaging the mold resin portion into the outer case via an engaging configuration.

3. A manufacturing method of a core component for an electric current detector which has an annular core having a magnetic gap G and a mold resin portion which covers a surface of the core over part of an overall length along a magnetic path of the core, the method comprising:
manufacturing an annular core member having a polygonal shape having a plurality of corners along a magnetic path;
molding a mold resin portion which covers an outer peripheral surface of the core member over part of an overall length along a magnetic path of the manufactured annular core member and which straddles two adjacent corners of the core to cover both corners; and
cutting the core member and the mold resin portion in a region in which the mold resin portion is formed, thereby forming the magnetic gap G and two mold resin portions covering the two corners.

4. The manufacturing method of the core component according to claim 3, wherein the step of molding a mold resin portion provides three surfaces perpendicular to a surface which is parallel to the magnetic path of the core member with the mold resin portion.