JP2578759Y2 - Transformer core - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transformer core having a middle leg and a pair of outer legs disposed on both sides of the middle leg.

[0002]

2. Description of the Related Art As shown in FIG. 5, for example, a transformer 22 assembled by a first E-type ferrite core 10 and a second E-type ferrite core 20 is known. Here, for example, the first E-shaped ferrite core 10 on one side has a middle leg portion 12 and a pair of outer leg portions 13 and 14 arranged on both sides of the middle leg portion 12, as shown in FIG. The legs 12, 13, and 14 are arranged in parallel with each other, and are integrally held by the base 15 at each end.

After winding a coil 18 around the center leg 12 via a bobbin, a second E-type ferrite core 20 is attached to the other end of each of the legs 12, 13, and 14. The transformer 22 as shown in FIG. Here, each E-type ferrite core 10, 20
It is manufactured by compression molding into a predetermined shape using a powdery raw material in advance, and then firing this molded body.

FIG. 7 is a sectional view of the E-type ferrite core 10 shown in FIG.
FIG. 5A is a sectional view taken along a line A. In particular, a sectional shape orthogonal to the length direction Z of the middle leg portion 12 on which the coil 18 is to be wound is shown in FIG.
In order to facilitate the bobbin insertion operation when the coil 18 is wound through the bobbin, the coil 18 is composed of a combination of a straight portion 16 and a curved portion 17 as shown in FIG. Here, the straight portion 16 and the curved portion 1 indicated by A in FIG.
The joining portion with 7 has a shape in which both portions are simply joined.

[0005]

An E-shaped ferrite core 10 used as a transformer core has a joint portion in which a straight portion 16 and a curved portion 17 are simply combined in a cross-sectional shape of a middle leg portion 12 thereof. Exists, there is a problem that a molding pressure difference is generated at a joint portion of the E-type ferrite core when the E-type ferrite core is manufactured, so that cracks easily occur.

That is, at the time of raw material compression molding for manufacturing an E-type ferrite core, as shown in FIG.
A crack 19 occurs due to a molding pressure difference centering on a joint A between the shaft and the curved portion 17. Alternatively, even if no cracks occur during the compression molding, similar cracks 19 will occur at the subsequent firing due to the imbalance in the density of the molded body due to the molding pressure difference. The total incidence of these cracks can be as high as 90% in the worst case.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a transformer core that avoids a molding pressure difference at a joint portion to prevent cracks. Things.

[0008]

In order to achieve the above object, the present invention has a middle leg and a pair of outer legs disposed on both sides of the middle leg. A transformer core that is disposed and held together by a base at each end, and a coil is wound around the middle leg,
The profile of the cross-sectional shape perpendicular to the length direction of the middle leg is up and down
Curved portions facing each other and extending to both ends of each curved portion
It is a combination of a straight portion and a round portion provided at each of the joining portions of the curved portion and the straight portion .

[0009]

[Function] The profile of the cross-sectional shape of the middle leg is provided with a rounded portion at the joint between the straight portion and the curved portion. Due to the presence of the rounded portion, the molding pressure difference around the joint at the time of manufacturing is reduced. Can be avoided. Therefore, it is possible to prevent the occurrence of cracks at the joint.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 are a perspective view and a sectional view taken along the line AA of the embodiment of the transformer core according to the present invention. The transformer core 1 of the present embodiment has a middle leg 2 made of, for example, a ferrite core and a pair of outer legs 3 and 4 arranged on both sides of the middle leg 2. 3 and 4 are arranged in parallel with each other and a base 5 at each end 2A, 3A, 4A.
Has a shape integrally held.

Here, the profile of the cross-sectional shape perpendicular to the length direction Z of the middle leg portion 2 around which the coil is wound via the bobbin is particularly a bay which is vertically opposed as shown in FIG. <br/> Curved portions 7 , 7 and straight portions 6, 6 extending at both ends of each curved portion
It consists of a combination of, that of the joint portion of both parts 6, 7
This is provided with a rounded portion 8. The value of the radius of curvature R of the rounded portion 8 is set, for example, in the range of 0.01 to 1 mm.

When the value of R is 0.01 mm or less, many cracks are likely to occur during molding of the core 1. On the other hand, the maximum value of R is set in consideration of the ease of insertion of the bobbin for winding the coil around the center leg portion 2 and the rattling generated between the bobbin and the rounded portion 8. It is. That is, as shown in FIG. 4, when the center P is provided on an extended line L extending outward from the corner 9 of the straight portion 6 of the middle leg 2 in the thickness direction, as shown in FIG. It is set by the distance between the corners 9.

According to the transformer core 1 of the present embodiment, the contour of the cross section perpendicular to the length direction Z of the middle leg 2 around which the coil is wound is formed by the straight portion 6 and the curved portion 7. Because the rounded part 8 was provided at the joint part of
When the core 1 is manufactured, the pressure generated during the compression molding of the raw material can be dispersed due to the presence of the rounded portion 8. Therefore, it is possible to prevent the occurrence of a molding pressure difference centering on the joining portion, thereby preventing the occurrence of cracks.

In addition, since the pressure at the time of molding can be dispersed as described above, the unevenness of the density balance of the molded body is reduced, so that the occurrence of cracks can be prevented even at the time of firing performed after molding.

Table 1 is a graph showing the cracking rate during molding and the cracking rate during firing when the value of R of the rounded portion 8 of the middle leg 2 is variously changed in this embodiment. Note that each N
In o, 1,000 samples were prepared.

[0017]

[Table 1]

As is apparent from Table 1, according to the present embodiment, by selecting the value of R of the rounded portion 8 in the range of, for example, 0.01 to 1 mm as described above, the crack occurrence rate during molding and firing The crack occurrence rate at the time can be suppressed to 10% or less, respectively, and the total thereof is 10% or less. The crack generation rate tends to decrease as the value of R is increased within the above range. Then, the maximum value of R is set as described above.

The material of the core shown in the embodiment is not limited to a specific composition, and any material commonly used as a core material can be used.

[0020]

As described above, according to the present invention, the contour of the cross-sectional shape of the middle leg constituting the core is vertically arranged to face each other.
Of curved sections and straight sections extending to both ends of each curved section
Setoko, since the shape of providing a rounded portion on each of the joint portion between the curved portion and a straight portion, the occurrence of cracking order to be able to avoid the molding pressure difference around the joint portion at the time of core production occurs Can be prevented.

[0021]

[Brief description of the drawings]

[0022]

FIG. 1 is a perspective view showing an embodiment of a transformer core according to the present invention.

[0023]

FIG. 2 is a sectional view taken along line AA of FIG.

[0024]

FIG. 3 is an enlarged view of a main part of the embodiment.

[0025]

FIG. 4 is an explanatory diagram for setting a maximum value of R of a round portion in the embodiment.

[0026]

FIG. 5 is a plan view of a transformer to which the transformer core according to the embodiment is applied;

[0027]

FIG. 6 is a perspective view showing a conventional transformer core.

[0028]

FIG. 7 is a sectional view taken along line AA of FIG. 5;

[0029]

FIG. 8 is an enlarged view of a main part of FIG. 5;

[0030]

FIG. 9 is an explanatory view of a conventional defect.

[0031]

[Explanation of symbols]

 2 Middle leg part 3, 4 Outer leg part 6 Straight part 7 Curved part 8 Round part 9 Corner part

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Claims (3)

(57) [Scope of request for utility model registration] A first leg having a middle leg and a pair of outer legs disposed on both sides of the middle leg, wherein each leg is arranged in parallel with each other and held integrally by a base at each end; A transformer core around which a coil is wound around a middle leg portion, wherein a contour of a cross-sectional shape orthogonal to a length direction of the middle leg portion is formed.
Curved portions arranged vertically opposite each other and extended to both ends of each curved portion
A transformer core comprising a combination of a curved portion and a straight portion , wherein a rounded portion is provided at each of the joining portions of the curved portion and the straight portion . 2. The maximum value of the radius of curvature of the rounded portion is set by the distance between the center and the corner when the center is provided on an extension line extending outward from the corner in the thickness direction from the corner of the straight portion. The transformer core according to claim 1. 3. The transformer core according to claim 1, wherein the radius of curvature of the rounded portion is set in a range of 0.01 to 1 mm.