TWI579868B - Coil device - Google Patents

Description

Coil device

The present invention relates to a coil device that constitutes a reactor or a transformer in various AC machines, and more particularly to a coil device in which a coil is wound around a ring core.

In the coil device of this kind, a technique of using a laminated core material is known. The laminated core material is composed of, for example, a pair of C-shaped core pieces, at least two laminated-type rectangular core pieces, and at least four magnetic gap portions, and the pair of C The word core piece is formed by dividing a ring-shaped winding core member obtained by winding a metal strip, and the at least two laminated type of rectangular core sheets are interposed Between the cross-sections of the pair of C-shaped core sheets, and the at least four magnetic gap portions are interposed between the face-to-face of the C-shaped sheet core sheet and the rectangular core sheet (refer to the patent) Document 1).

Further, in the case of the laminated core material, a thin plate-shaped magnetic strip is also punched into a C shape and stacked.

In the coil device described above, the end faces of the C-shaped core piece and the end faces of the rectangular core pieces are opposed to each other with the magnetic gap portion interposed therebetween, so that leakage magnetic flux is generated in the magnetic gap portion and is formed according to the gap. Long and end faces The relative area determines the inductance characteristics.

Therefore, the end faces of the C-shaped core piece and the end faces of the rectangular core piece are formed into the same shape having the same area, and the both end faces are correctly butted against each other.

(previous technical literature)

(Patent Literature)

Patent Document 1: Japanese Laid-Open Patent Publication No. Hei 11-40434.

However, in the coil device in which the C-shaped core piece and the rectangular-shaped core piece are combined, in particular, the C-shaped core piece is obtained by winding a metal strip to produce a ring-shaped roll. After the core member is broken and punched and the strip is laminated, the shape of the C-shaped core sheet will be deviated to some extent, thus causing the two end faces of the C-shaped core sheet. The relative position produces an error.

As a result, when the C-shaped core material piece and the rectangular-shaped core material piece are butted against each other to form a combined coil device, a positional deviation occurs between the end surface of the C-shaped core material piece and the end surface of the rectangular-shaped core material piece. Since it is moved, there is a problem that the relative area of the both end faces is smaller than the area of either end face, and the predetermined inductance characteristics cannot be obtained.

Therefore, an object of the present invention is to provide a coil device in which a C-shaped core piece and a rectangular core piece are combined, and it is possible to obtain a predetermined inductance characteristic irrespective of a deviation of a shape of a C-shaped core piece. Coil Device.

In the coil device of the present invention, a coil is wound around a ring-shaped core material, and the core material has a pair of C-shaped core pieces, which are obtained by winding or laminating a metal strip. a rectangular core piece, interposed between a pair of C-shaped core pieces; and a magnetic gap portion interposed between the end faces of the C-shaped core piece and the rectangular core piece; In the coil device, the rectangular core piece is made of a pressure-molded powder magnetic core, and an end face of the C-shaped core piece facing the magnetic gap portion is opposed to each other. The height of the lamination direction of the strip plate is T1, and when the height of the end surface of the rectangular parallelepiped core piece is T2, it is T2>T1.

When the thickness of the strip provided with the C-shaped core sheet is t, it is preferable that T2-T1>t.

When the number of layers of the C-shaped core sheet is n, the C-shaped core sheet can be T1=n×t.

Further, the width of the strip of the C-shaped core sheet is W1, and the end surface of the rectangular core sheet is orthogonal to the lamination direction of the strip of the end surface of the C-shaped core sheet. When the width is set to W2, it is preferably set to: W2≧W1.

The area (T2 × W2) of the end surface of the rectangular parallelepiped core piece can be formed to be larger than the area (T1 × W1) of the end face of the C-shaped core piece.

The end surface of the rectangular parallelepiped core piece may have a shape that expands in a square shape with the shape of the end surface of the C-shaped core piece.

The coil device has a bobbin case in which a core material is inserted, and the coil is wound around an outer circumferential surface of the bobbin, and a coil body is formed inside the bobbin to accommodate the rectangular core material. a central space of the sheet, and lateral spaces for inserting the front end portion of the C-shaped core sheet, respectively, on both sides of the central space, and the cross-sectional shape of the side space has a C-shaped core sheet The shape of the end surface is enlarged, and the synthetic resin is filled in the front end of the C-shaped core piece in a state where the front end portion of the C-shaped core piece is inserted into the side space of the bobbin. Between the outer peripheral surface and the inner peripheral surface of the bobbin.

According to the coil device of the present invention, the end face of the C-shaped core piece obtained by winding or laminating the metal strip, and the end face of the rectangular core piece composed of the powder magnetic core are The end face formed as a rectangular core piece is larger than the end face of the C-shaped core piece in the lamination direction of the C-shaped core piece, and therefore, even if the shape of the C-shaped core piece has a slight deviation, It is also possible to adjust the relative relationship between the two core materials while the end faces of the C-shaped core piece and the end faces of the rectangular core pieces are mutually abutted. The position of the C-shaped core piece is converged in the contour shape of the end surface of the rectangular core piece. Therefore, even if the end surface of the C-shaped core piece is slightly offset, it can be made to face the end face of the rectangular core piece, and the desired inductance characteristics can be obtained.

In particular, the C-shaped core sheet is liable to vary in the lamination direction due to the number of layers n of the strip or the bonding strength between the strips, etc., but the press forming of the magnetic core of the rectangular core-shaped powder core Since the rectangular core piece is formed to have a larger end surface than the C-shaped core piece, the C-shaped core piece has a variation in the shape of the end face in the lamination direction, It is also possible to make the C-shaped core piece positively face the end face of the rectangular-shaped core piece.

1‧‧‧ core material

2‧‧‧C-shaped core piece

3‧‧‧Rectangle core piece

5‧‧‧ coil group

7‧‧‧ coil

8‧‧‧ coil holder

9‧‧‧Binder

21‧‧‧Rolling core member

71‧‧‧ winding start end

72‧‧‧Connecting line

73‧‧‧ winding end

80‧‧‧ side space

81‧‧‧Molded resin wall

82‧‧‧锷

83,84‧‧‧Card groove

85,86‧‧‧ ribs

87‧‧‧Resin cover

88‧‧‧ openings

G‧‧‧magnetic gap

Thickness of the strip of t‧‧‧C-shaped core sheets

Height of the laminated direction of the T1‧‧‧C-shaped core piece

Height of T2‧‧‧ rectangular core piece

W1‧‧‧C-shaped core sheet width in strip direction

W2‧‧‧Width of the rectangular core piece

Fig. 1 is a perspective view of a coil device of the present invention.

Figure 2 is a partially cutaway plan view of the coil assembly.

Fig. 3 (a) and Fig. 3 (b) are plan views showing an example of a manufacturing procedure of a C-shaped core piece.

Fig. 4 is a perspective view of a rectangular core piece.

Fig. 5 (a) and Fig. 5 (b) are explanatory views for comparing the height and width of the laminated direction of the C-shaped core piece and the rectangular core piece.

Fig. 6 (a) and Fig. 6 (b) are views for explaining the overlapping of the end faces of the C-shaped core piece and the rectangular core piece.

Fig. 7 is a perspective view of a bobbin in which a rectangular core piece is built.

Figure 8 is a cross-sectional view of the bobbin of Figure 7 extending along the line B-B and viewed in the direction of the arrow.

Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.

In the coil device of the present invention, as shown in Fig. 1, a pair of coil assemblies (5, 5) are attached to the annular core member (1), and each coil group (5) includes A cylindrical bobbin (8) and a coil (7) wound around the outer circumference of the bobbin (8). The core material (1) extends through the two bobbins (8, 8) and extends in a ring shape.

The two coils (7, 7) constituting the two coil groups (5, 5) are formed by one lead wire, and the two coils (7, 7) are connected to each other via the dielectric connecting wire (72). Further, the winding start end portion (71) and the winding end portion (73) of the lead wire are pulled out from the two coils (7, 7).

The core material (1) includes a pair of C-shaped core sheets (2, 2) and two sheets sandwiched between two C-shaped core sheets (2, 2) as shown in Fig. 2; It is composed of a rectangular parallelepiped core piece (3, 3).

Further, although the shape of the core material sheets (2, 2) is assumed to be C-shaped for ease of explanation, it may be U-shaped or U-shaped, and the shapes are also included in the generalized C-shape.

In the manufacture of a pair of C-shaped core material sheets (2, 2), as shown in Fig. 3(a), a ring is formed by laminating a steel sheet or an amorphous crucible, and a loop is formed. After winding the core member (21), the winding core is broken by a cutting line AA shown by a broken line in the drawing. The member (21) is obtained as a pair of left and right C-shaped core sheets (2, 2) as shown in Fig. (b).

The C-shaped core material sheet (2) has a variation in winding strength when the belt is wound, a deviation between the winding start end and the winding end, and the like, and thus it is difficult to suppress variations in the dimension of the belt sheet in the lamination direction. Further, there is a case where the size of the strip is shifted in the width direction of the strip when the strip is wound.

Further, the C-shaped core material sheets (2, 2) can also be obtained by punching a thin-plate-shaped magnetic strip sheet into a C-shape and then stacking them.

Even in this case, it is difficult to suppress variations in the size of the lamination direction due to the bending of the respective strips or the joint strength between the strips and the number of layers.

Regardless of the C-shaped core sheet obtained by any of the above-described methods, it is difficult to suppress variations in the lamination direction of the strip and variations in the width direction of the strip. In particular, when the deviation in the lamination direction of the strip is compared with the deviation in the width direction of the strip, it is difficult to suppress the variation in the lamination direction.

On the other hand, the rectangular core material sheet (3) can be made of iron, iron-lanthanum, iron-aluminum-lanthanum, iron-nickel powder, or iron-based or Co-based amorphous germanium. Powder or the like is obtained by compacting powder into a rectangular parallelepiped shape as shown in Fig. 4.

Since the rectangular core piece (3) is a press-molded body belonging to the powder magnetic core, the dimensional accuracy is higher than that of the C-shaped core piece (2), and the variation in the size of the product can be reduced.

As shown in Fig. 5 and Fig. 6, for the above-mentioned C-shaped core material sheet (2), the thickness of the strip plate is t, and the product of the strip at the end surface of the breaking end is obtained. The height in the layer direction is T1, and the width in the direction orthogonal to the lamination direction in the end surface is W1.

Further, as shown in Figs. 4 to 6, the above-described rectangular parallelepiped core piece (3) is oriented on the end face opposed to the end face of the C-shaped core piece (2). The stacking direction of the strip is parallel to the height T2, and the width in the direction orthogonal to the lamination direction is W2.

At this time, as shown in FIGS. 5 and 6, the height T2 of the rectangular core piece (3) is formed to be larger than the height T1 of the winding direction of the C-shaped core piece (2). That is, T2>T1 is satisfied.

Here, T1 and T2 are defined in the above-described manner because the C-shaped core material sheet (2) has a large variation in the size of the lamination direction in the lamination direction and the width direction.

When the C-shaped core material piece (2) has a deviation in the width direction, W2>W1 can be made, and the deviation in the width direction is small, and the width W1 and the width W2 of the rectangular-shaped core material piece (3) can be Let W1=W2.

Thereby, the rectangular core piece (3) can make the sum of the height and the width orthogonal to the magnetic path (preferably the height) larger than the C shape in the lamination direction of the C-shaped core piece (2). The sum (higher height) of the height and width of the core sheet (2) orthogonal to the magnetic path. Therefore, even if the C-shaped core material piece (2) has a variation in the lamination direction, the end faces of the C-shaped core material piece (2) and the end faces of the rectangular-shaped core material piece (3) are mutually abutted. In the state, the relative positions of the two core sheets (2, 3) can be adjusted, and the end faces of the C-shaped core sheets (2) converge in the contour shape of the end faces of the rectangular core sheets (3). Therefore, the end face and the rectangular body of the C-shaped core material piece (2) The opposing area of the end face of the core piece (3) is correctly matched with the area (T1 × W1) of the end face of the C-shaped core piece (2).

Further, it is preferable that when the thickness of the strip of the C-shaped core sheet (2) is t, T2-T1>t. Thereby, when the core member (21) is wound, even if the winding start end or the winding end of the strip is shifted, the C-shaped core sheet (2) can be converged in the rectangular core. Inside the contour shape of the end face of the material piece (3).

When considering the deviation of the winding strength of the strip, it is more preferable to set it as T2-T1 ≧ 2 × t to 10 × t.

Further, the T2-T1 system is preferably 0.5 mm or more.

On the other hand, when T2-T1 is too large, the coil device is increased in size or material loss, so that the T2-T1 system is preferably 2 mm or less.

Here, when it is difficult to measure the actual size T1 of the C-shaped core piece (2) when determining the T2 of the rectangular core piece (3), when the C-shaped core piece (2) When the number of layers of the strip is set to n, the above T1 can be replaced by n × t, and T2 is determined as T1 = n × t.

The rectangular parallelepiped core piece (3) has a cross section (T2 × W2) orthogonal to the magnetic path and a shape larger than a cross section (T1 × W1) of the C-shaped core piece (2) orthogonal to the magnetic path, Therefore, the end surface of the rectangular core piece (3) is preferably formed to have a shape larger than the end surface of the C-shaped core piece (2).

The end surface of the rectangular parallelepiped core piece (3) can be expanded from the center of the shape of the end surface of the C-shaped core material piece (2) toward the square. That is, as shown in Figs. 5(b) and 6(b), the end faces of the rectangular core piece (3) have the following shapes: C The shape of the end surface of the front end portion of the word core piece (2) is expanded toward the laminated direction of the C-shaped core material piece (2) by T2-T1, and is expanded to a predetermined distance in the width direction orthogonal to the lamination direction. W2-W1 shape.

As shown in Fig. 7 and Fig. 8, the rectangular core piece (3) having the above configuration is housed in a cylindrical bobbin (8) formed by inserting an insert mold or the like.

The bobbin (8) can be molded as an integral member as shown in the figure, and two or more molded bodies can be joined in advance as an integral member. Further, although not shown, two or more formed bodies may be prepared, and the formed bodies are combined and joined in a state in which a rectangular core piece (3) is inserted in advance.

When the coil bobbin (8) is inserted into the rectangular core material piece (3), the center of the one side of the one side, that is, the substantially center of the outer side of the upper side of the seventh figure and the eighth figure, can be inserted. The opening (88) of the rectangular core piece (3).

Further, as shown in Fig. 8, on the inner circumferential surface of the bobbin (8), ribs (85, 86) for holding the rectangular core piece (3) from both sides are provided inwardly, and are molded. Both ends of the mold resin wall (81) are provided with a flange portion (82) protruding outward. Here, the thickness of the ribs (85, 86) is formed as a gap between the C-shaped core sheet (2) and the rectangular core sheet (3) as shown in Fig. 2 The same size as the long G.

As shown in Fig. 7, in the crotch portion (82) on one side of the bobbin (8), in one of the four end faces which are formed in a quadrangular shape, one end face is recessed with a winding for locking a coil as will be described later. 2 locking grooves (83, 84).

In the aforementioned bobbin (8), a pair of side spaces (80, 80) are formed on both sides of the central space facing the opening (88). Here, the central space and the side space (80) have the same shape as the rectangular core piece (3) in the cross section orthogonal to the magnetic path of the core material (1), and are surrounded by the central space. A rectangular parallelepiped core piece (3) is accommodated without forming a gap. In other words, both the central space and the side space (80) can be formed such that the inner dimension in the direction parallel to the strip-shaped lamination direction of the C-shaped core material piece (2) is a rectangular core piece ( 3) The same T2, and the internal dimension in the direction orthogonal thereto is W2.

Further, it is preferable that the central space is inserted into the rectangular core piece (3), and the opening (88) is sealed with a rectangular resin cover (87) or by winding an insulating tape or the like to cause a rectangular core piece ( 3) Does not fall off from the central space and does not shake in the central space.

As shown in Figs. 1 and 2, a coil (7) is wound around the outer peripheral surface of the bobbin (8).

As shown in Fig. 2, the pair of side walls (80, 80) of one of the bobbins (8) are inserted with the ends of a pair of C-shaped core sheets (2, 2) to form a ring-shaped core. Material (1).

The side space (80, 80) has the same shape as the cross section of the central space in which the rectangular core piece (3) is accommodated, so that the end surface is smaller than the C-shaped core material of the rectangular core piece (3). The slice (2) is capable of having a margin and is embedded in the side space (80, 80). Therefore, even in the C-shaped core material sheet (2), there is a deviation in the lamination direction or a deviation in the width direction orthogonal to the lamination direction. It is also possible to easily insert the C-shaped core material piece (2) from the end surface.

In other words, even if the shape of the C-shaped core material piece (2) has a slight deviation, the end faces of the C-shaped core material piece (2) and the end faces of the rectangular-shaped core material piece (3) can be mutually butted. In the state, the relative positions of the two core sheets (2, 3) are adjusted, and the end faces of the C-shaped core sheets (2) are converged in the contour shape of the end faces of the rectangular core sheets (3), Therefore, as shown in Fig. 6, the opposing area of the end surface of the C-shaped core material piece (2) and the end surface of the rectangular-shaped core material piece (3) is correctly matched with the C-shaped core material piece (2). The area of the end faces is the same.

More specifically, the variation of the C-shaped core material sheet (2) is allowed to be T2-T1 in the lamination direction of the strip, and is allowed to be W2-W1 in the width direction.

Moreover, the height of the end surface of the rectangular parallelepiped core piece (3) with respect to the laminated direction of the C-shaped core material piece (2) is formed by expanding only T2-T1, and the width direction is equal (W1=W2). The cross-sectional shape of the side space (80) of the bobbin (8) is formed so as to have a margin T2-T2 only in the lamination direction of the C-shaped core material piece (2).

In the obtained core material (1), since the ribs (85, 86) are interposed between the end surface of the C-shaped core material piece (2) and the end surface of the rectangular core material piece (3), In the magnetic circuit of the core material (1), a predetermined gap G is formed at four locations.

Further, as shown in Fig. 2, in the two lateral spaces of each bobbin (8), the end portions of the C-shaped core material sheets (2) can be surrounded and filled with the adhesive (9), and The following agent (9) can take the C-shaped core The material piece (2) is fixed to the bobbin (8).

Further, the adhesive (9) can also be filled in a gap formed between the end surface formed on the rectangular core sheet (3) and the end surface of the C-shaped core sheet (2), whereby the rectangular parallelepiped can be connected to each other. Core piece (3) and C-shaped core piece (2).

In an embodiment of the combination of the coil devices, as shown in FIG. 1, the bobbins (8, 8) having one pair of the rectangular core pieces (3) are arranged in a series positional relationship, and Winding is applied to the outer circumferential surfaces of the two bobbins (8, 8). In the winding step, first, in a state where the winding start end portion (71) of the wire is locked to one of the locking grooves (83) of one of the bobbins (8), the bobbin is sequentially oriented in one direction. After the winding is applied, the winding is sequentially fed in the opposite direction, and the wire is locked to the other locking groove (84) of the bobbin.

Next, the connecting line (72) passing through the locking groove (84) is locked to the locking groove (83) of one of the other bobbins (8), and in this state, the bobbin is applied in one direction. After the sequential winding, the winding is reversed and the sequential winding is applied in the opposite direction, and the wire is locked to the locking groove (84) of the other side of the bobbin, and the winding end end is pulled out by the locking groove. (73).

Next, one of the bobbins (8) is rotated 180 degrees with respect to the other bobbin (8), and as shown in Fig. 1, the two bobbins (8, 8) are arranged to each other so that the crotch portions are in contact with each other. The positional relationship of the juxtaposition. Accordingly, the connecting line (72) extending from one coil (7) to the other coil (7) is curved in an arc shape, and is formed to be adjacent to the two bobbins (8, 8) at the shortest distance. Between the locking grooves (84, 83).

After the winding step of the coils (7, 7) of the two bobbins (8, 8), the leading ends of the pair of C-shaped core sheets (2, 2) are inserted into the two bobbins (8, 8), Further, a pair of C-shaped core pieces (2, 2) are fixed to the two bobbins (8, 8). Here, the cross-sectional shape of the side space (80) of the bobbin (8) has a cross-sectional shape at the front end portion of the C-shaped core material piece (2) in the lamination direction T2-T2, and in the width direction W2- Since there is a margin of W1, the insertion work can be easily performed even when the C-shaped core material piece (2) has a deviation in winding or lamination of the strip.

Further, before the insertion of the C-shaped core material sheet (2), an appropriate amount of the adhesive is pre-filled in the lateral space of the bobbin (8), and the C-shaped core material sheet can also be used by the adhesive (2). The end of the ) is fixed to the bobbin (8). The adhesive filled in the side space of the bobbin (8) is reversed from the inside of the side space toward the opening side as the C-shaped core piece (2) is inserted, forming a large area as shown in Fig. 2 The end portion of the C-shaped core piece (2) is covered, and as a result, the C-shaped core piece (2) and the bobbin (8) are followed by a large area, and a larger adhesion can be obtained.

Further, an adhesive (9) filled in a side space of the bobbin (8) is also filled in a magnetic gap portion between the C-shaped core sheet (2) and the rectangular core sheet (3). Further, the C-shaped core piece (2) and the rectangular core piece (3) can be fixed to each other.

In the coil device combined as described above, the opposing area of the end face of the C-shaped core piece (2) and the end face of the rectangular core piece (3) is correctly aligned with the C-shaped core piece. Since the area (T1 × W1) of the end faces of (2) is identical, predetermined inductance characteristics can be obtained.

In addition, by pressing the rectangular core piece (3) into a pressure The shaped powder core and the C-shaped core sheet (2) are laminated bodies of the strip, so that the combined characteristics due to the combination of the different characteristics can be obtained.

In the coil device of the present invention, even if there is a variation in the lamination direction or a shift in the width direction of the C-shaped core material piece (2), the offset can be released when the coil device is combined, and the coil device can be obtained. Homogenization of properties.

Further, the configuration of each unit of the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the technical features described in the claims. For example, the rectangular parallelepiped core piece (3) is disposed between the C-shaped core pieces (2) in the above embodiment, but may be disposed between the C-shaped core pieces (2). One. In this case, the size of the rectangular core piece (3) forming the both ends of the C-shaped core piece (2) may be adjusted at least along the above-described manner. Further, the winding method or the locking method for the wires of the lead frame (8) is not limited to the aforementioned method.

1‧‧‧ core material

2‧‧‧C-shaped core piece

3‧‧‧Rectangle core piece

Height of the laminated direction of the T1‧‧‧C-shaped core piece

Height of T2‧‧‧ rectangular core piece

W1‧‧‧C-shaped core sheet width in strip direction

W2‧‧‧Width of the rectangular core piece

Claims (6)

A coil device comprising a coil package wound around an annular core material, the core material having: a pair of C-shaped core material sheets, which are obtained by winding or laminating a metal strip; a rectangular parallelepiped core piece disposed between the pair of C-shaped core pieces; and a magnetic gap portion interposed between the C-shaped core piece and the end face of the rectangular core piece; In the coil device, the rectangular core piece is made of a pressure-molded powder magnetic core, and an end face of the C-shaped core piece facing the magnetic gap portion is opposed to each other. The height of the lamination direction of the strip plate is T1, the height of the end surface of the rectangular core piece is T2, and when the thickness of the strip of the C-shaped core piece is t, it is: T2>T1 And, T2-T1>t. The coil device according to claim 1, wherein the C-shaped core piece has a number of layers of the tape plate: n is T1 = n × t. The coil device according to claim 1, wherein the width of the strip of the C-shaped core sheet is W1, and the end surface of the rectangular core sheet is C-shaped. When the width direction of the strips of the end plates of the core sheet is orthogonal to W2, it is W2 ≧ W1. The coil device of claim 1, wherein The width of the strip of the C-shaped core sheet is W1, and the end surface of the rectangular core sheet is perpendicular to the lamination direction of the strip of the end surface of the C-shaped core sheet. When W2 is set, the area (T2 × W2) of the end surface of the rectangular parallelepiped core piece is formed to be larger than the area (T1 × W1) of the end face of the C-shaped core piece. The coil device according to the first aspect of the invention, wherein the end surface of the rectangular core piece has a shape that expands in a square shape with a shape of an end surface of the C-shaped core piece. The coil device according to claim 1, comprising a bobbin case in which the core material is inserted, and the coil is wound around an outer circumferential surface of the bobbin, and is formed inside the bobbin a central space for accommodating the rectangular parallelepiped core piece, and a side space for inserting the end portion of the C-shaped core piece before the side space is formed on both sides of the central space, and a profile of the side space The shape has a shape in which the end surface shape of the C-shaped core piece is enlarged, and the synthetic resin is filled in the C-shaped state in a state where the front end portion of the C-shaped core piece is inserted into the side space of the bobbin. The outer peripheral surface of the front end portion of the core piece is between the inner peripheral surface of the bobbin.