Inductor devices – With closed core interrupted by an air gap
Reexamination Certificate
1997-11-03
2001-05-15
Mai, Anh (Department: 2832)
Inductor devices
With closed core interrupted by an air gap
C336S165000
Reexamination Certificate
active
06232864
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a gap-providing ferrite core half and a method for producing it.
One example of conventional gap-providing ferrite core halves is shown in FIG.
21
. An E-type ferrite core half
63
comprising two outside leg portions
61
and one center leg portion
62
which is shorter than each outside leg portion
61
by a distance called a gap “G.” The gap is provided for the purpose of controlling direct-current superposition properties of the ferrite core.
A conventional ferrite core
220
with a gap for transformers, choke coils, etc. as shown in
FIG. 22
is formed by combining a gap-providing E-type ferrite core half
63
as shown in FIG.
21
and an E-type ferrite core half
64
with no gap-providing recess such that legs of both core halves abut each other, with a coil disposed around the aligned center leg portions. Such a combination of core halves is called “EE-type core assembly” or simply “EE-type core.”
In addition to an EE-type ferrite core, there is an EI-type ferrite core comprising a gap-providing E-type ferrite core half as shown in
FIG. 21 and a
flat I-type ferrite core half. Though the gap-providing E-type ferrite core half shown in
FIG. 21
has three legs, there may be ferrite core halves having two or four or more legs.
The provision of a gap-providing recess to a ferrite core half has been achieved by forming a ferrite core half
230
having outside leg portions
65
a,
65
a
and a center leg portion
65
b
of the same length (shown in FIG.
23
), sintering it, grinding flat an end surface
66
of each leg
65
, and further grinding an end surface
66
of a center leg portion
65
b
only. Also, as shown in
FIG. 24
, with an integral diamond grinder
67
rotatable around an axis
69
and having a grinding layer
68
disposed on a stepwise surface of the grinder
67
such that the grinding layer
68
is complementary with the legs of a ferrite core half to be ground, abutting surfaces of the legs of the E-type ferrite core half can be ground.
FIG. 25
is a perspective view showing another example of the conventional gap-providing ferrite core half, and
FIG. 26
is a front view showing the gap-providing ferrite core half of FIG.
25
. This gap-providing ferrite core half is a U-type ferrite core half
101
with two legs
102
,
103
, one leg
103
being shorter than another leg
102
by a distance called a gap “G” for the purpose of controlling direct-current superposition properties of the ferrite core. This gap-providing ferrite core half
101
is combined with a U-type ferrite core half
104
of the same shape without a gap-providing portion to form a transformer with a coil wound around one leg.
In this conventional gap-providing U-type ferrite core half, only one leg thereof is provided with a gap-providing recess as shown in the drawings. In this case, end surfaces of two legs are ground flat to a high precision, and an end surface of only one leg is further ground to a predetermined depth to provide a gap-providing recess.
Since a gap dimension greatly affects the properties of these ferrite core assemblies with gaps, it is important to provide the gap dimension with a high precision. However, since a particular leg end is ground after all leg ends are ground flat in the conventional gap-providing method, two grinding steps are needed, making the production cost high. Further, since the grinding of the center leg portion is conducted at a different work position from the previous one at which the outside leg portions are ground, it is difficult to provide a gap-providing recess with a high grinding precision.
Though it is possible to grind both outside leg portions and a center leg portion simultaneously with an integral grinder as shown in
FIG. 24
, grinders having different grinding surfaces should be prepared for ferrite core halves with different gap-providing recesses, making the types of the grinders stocked extremely many. For this reason, the conventional methods suffer from high production cost due to large numbers of grinding steps and difficulty in fine control of gap dimension.
If a sufficient number of steps are used with an expensive grinding machine, a gap dimension with a high precision may be obtained. However, this would be low in productivity and high in cost.
As shown in
FIG. 27
, a ferrite core assembly with a gap may be constituted by two ferrite core halves
105
,
105
each having no gap-providing recess, with one or two spacers
106
,
106
inserted between the ends of aligned legs.
In case where a spacer is inserted between the abutting ends of legs to provide a gap-providing recess, there are the following disadvantages:
(1) The step of inserting a spacer is necessary;
(2) Varieties of spacers should be prepared depending on the gap dimensions;
(3) Particularly in the case of a small gap dimension, an extremely thin spacer is needed, making its handling difficult.
As mentioned above, there have not been gap-providing ferrite core halves which can be produced precisely at a high productivity and low cost.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a ferrite core half with a high-precision gap-providing recess which can be produced at a high productivity and low cost.
Another object of the present invention is to provide a method for producing such a gap-providing ferrite core half at a high productivity and low cost.
As a result of research in view of the above objects, the inventors have found that by grinding an abutting end surface of a leg of a ferrite core half along a concavely curved plane, a high-precision gap dimension can be achieved, and that such a concavely curved surface of the abutting end of a leg can be formed by grinding with a rotating grinder whose rotation shaft is slightly inclined in a plane vertical to a core surface to be ground and parallel to a core width direction.
Thus, the gap-providing ferrite core half according to the present invention comprises at least one abutting end surface whose envelope extends along a concavely curved plane, and a distance between the highest point and the lowest point in the abutting end surface being 1 &mgr;m or more.
The ferrite core assembly with a gap according to the present invention is constituted by two ferrite core halves with their end surfaces abutting each other, at least one ferrite core half having an abutting surface whose envelope extends along a concavely curved plane, and the gap being 1 &mgr;m or more at a deepest point.
The method for producing a gap-providing ferrite core half according to the present invention comprises the step of grinding an abutting surface of a ferrite core half by a rotating grinder with a rotation shaft inclined by 0.01-90° relative to a line vertical to a surface of the ferrite core half to be ground in a plane parallel to a core width direction, such that a distance between the highest point and the lowest point in the abutting surface is 1 &mgr;m or more. The gap-providing recess is preferably constituted by a concave elliptical plane expressed by the following formula:
A
2
4
R
2
+
(
R
sin
θ
-
G
)
2
R
2
sin
2
θ
=
1
,
wherein A is a width of the ferrite core half, R is an effective radius of the grinder, &thgr; is an inclination angle of the rotation shaft of the grinder relative to a line vertical to a surface of the ferrite core half to be ground in a plane parallel to a core width direction, and G is a gap depth.
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Hosozawa Takashi
Umezane Kazuhiro
Hitachi Metals Ltd.
Mai Anh
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