Field of the Invention
[0001] The present invention relates to a coil device for use in a flyback transformer,
a switching power transformer, a choke coil or the like. And more particularly, it
relates to a coil device employing a magnetic core with a gap starting from the DE-C-31
23 006.
Description of the Prior Art
[0002] In any of the conventional transformers, choke coils and so forth known heretofore,
it is customary to form a gap in a closed magnetic path so that the magnetic core
thereof is not saturated when a desired current is caused to flow. For example, when
a ferrite magnetic core usually having a magnetic permeability µ of 5000 or so is
used in a transformer, a gap (hereinafter referred simply to as gap) is formed therein
to reduce the effective permeability µ within a range of 50 to 300.
[0003] This signifies that a gap having a great magnetic reluctance needs to be existent
in a ferrite magnetic core of which magnetic reluctance is originally small, whereby
a great leakage flux is generated in the periphery of the gap.
[0004] It is generally known that such leakage flux exerts at least two harmful influences
as follows.
(1) Noise is induced in peripheral apparatus (components) which are prone to be affected
by magnetic induction.
(2) In case the coil is so wound as to surround the gap, there occurs abnormal generation
of heat in the coil around the gap due to the leakage flux.
[0005] For the purpose of solving the above problems, a variety of improvements have been
developed.
[0006] In an attempt to settle the problem (1), there is contrived an exemplary method of
forming a gap merely in the coil alone. However, such method brings about another
fault that worsens the problem (2) on the contrary.
[0007] With regard to the problem (2), some prior examples are known as disclosed in Japanese
Patent Laid-open No. 55 (1980)-77115 and Utility Model Laid-open No. 57 (1982)-130402,
wherein a gap positioned in a coil is divided magnetically into a plurality of serial
portions so as to disperse the concentration of leakage flux. In the prior means developed
for solving the problems (1) and (2), there are known examples as disclosed in Japanese
Utility Model Publication Nos. 53 (1978)-53850 and 60 (1985)-7448, wherein a gap filler,
of which relative permeability is greater than that of air (greater than 1), is used
to reduce the magnetic reluctance in the gap portion so as to diminish the leakage
flux.
[0008] When such gap filler of a material having a greater relative permeability than that
of air (greater than 1) is disposed inside of a coil, there exists a possibility that
the problems (1) and (2) can be solved to some extent.
[0009] In the DE-C-31 23 006 a transformer is described in which a variable cross section
of an air gap on the secondary side of the transformer is used to reduce the current
in the transformer. The thickness of this air gap is much larger than that of the
rigid air gap. Such a transformer is especially used for a circuit to produce the
voltage for deflection of the lines of a television apparatus. However, the german
patent DE 31 23 006 does not describe a minimization of the harmful influence of noise
to peripheral apparatus or components and does not diminish any leakage flux generated
in the periphery of a gap to prevent generation of heat in the coil around the gap.
[0010] However, even in such an improved structure, another problem is still left unsettled
that the leakage flux is concentrated on the boundary between the gap and the magnetic
core, and in addition a new problem also arises with regard to difficulty in obtaining
a satisfactory material which has an adequate permeability as a gap filler and still
retains a high saturation flux density and low core loss characteristic equivalent
to that of the magnetic core. Consequently some disadvantages are unavoidable including
that the coil wound on the boundary between the gap and the magnetic core is heated
to an abnormal extent, and the gap portion is also heated excessively due to the core
loss of the gap filler material, and further the B-H curve of the magnetic core with
the gap filler inserted therein is rendered nonlinear to eventually cause wave form
distortion when the coil device is used in a transformer. Thus, in the current technical
stage, completely effective improvements are not available.
OBJECTS AND SUMMARY OF THE INVENTION
[0011] It is therefore an object of the present invention to solve the above problems and
provide an improved coil device which is capable of minimizing the harmful influence
of noise to peripheral apparatus (components) and diminishing any leakage flux generated
in the periphery of a gap to consequently prevent abnormal generation of heat in the
coil around the gap.
[0012] And another object of the present invention resides in providing an improved coil
device which realizes lower production cost and enhanced reliability.
[0013] For the purpose of achieving the objects mentioned, some alterations have been accomplished
in a coil device comprising two magnetic cores each having U-shape in section which
form a closed magnetic path therein with their legs being opposed to each other and
having a gap in such path, and a coil wound so as to cover the gap. And the feature
of the present invention resides in a structure where the mutually opposed portions
of the magnetic cores in the region to form the gap are so shaped that the cross-sectional
area of the fore end becomes smaller than the corss-sectional area of the base end.
[0014] Furthermore, with regard to the magnetic core portions in the region to form the
gap, the rate of the cross-sectional area of the fore end to that of the base end
is defined to be within a range of 1 to 90 percent.
[0015] Other features reside in that fore end is shaped with curves defined by logarithmic
functions, and a planar member is provided on the fore end, or projections are formed
on the face of the fore end.
[0016] Due to the constitution mentioned there occurs no concentration of any leakage flux
between the gap and the core end faces, and since no gap filler is used, any core
loss is not induced to consequently achieve the above objects.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017]
Fig. 1 schematically shows an exemplary embodiment of the coil device according to
the present invention;
Fig. 2 is a schematic diagram illustrating the shape of a gap portion in a magnetic
core used in a conventional coil device;
Figs. 3 through 7 are schematic diagrams illustrating the shapes of gap portions in
magnetic cores which are not inventive;
Fig. 8 graphically represents a B-H curve in the conventional coil device using magnetic
core with the gap shown in Fig. 2;
Figs. 9 through 13 graphically represent B-H curves in coil devices using magnetic
cores with the gaps shown in Figs. 3 through 7;
Fig. 14 illustrates how temperatures are detected in individual portions of the coil
device according to embodiments which are not inventive and
Figs. 15 through 22 are schematic diagrams illustrating modifications of the gap in
the magnetic cores which could be used in the coil devices which are not inventive.
Figs. 23 through 25 are schematic diagrams illustrating modifications of the gap in
the magnetic cores used in the coil devices of the present invention;
Figs. 26 and 27 are perspective views illustrating further modified shapes of the
magnetic core used in the coil device of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] A coil device 1 shown in Fig. 1 comprises two sectionally U-shaped magnetic cores
2, 3 of which fore ends but to each other, wherein a gap 5 is formed between opposed
faces of one-side legs 2a, 3a and a coil 4 is wound thereon.
[0019] Some examples of such sectionally U-shaped magnetic cores are illustrated in Figs.
26 and 27. In the example of Fig. 26, a rectangular core is shaped into U, and its
one-side leg is shaped to be columnar. The text example of Fig. 27 is a magnetic core
33 having four legs, one of which legs is a columnar leg 33a. In the actual coil device,
a pair of such cores are combined with each other and a coil is wound on the columnar
legs thereof, although merely a single core is illustrated in each of the above diagrams.
And such core is composed of ferrite material.
[0020] Referring now to the accompanying drawings, the characteristic and the structure
of an embodiment of the present invention will be described in comparison with that
of a conventional example.
[0021] Fig. 2 illustrates the shape of gap portions in magnetic cores used in a conventional
coil device, wherein the shapes of mutually opposed ends 2b and 3b of the magnetic
cores and the gap width thereof are so determined that the effective permeability
of the magnetic core is rendered uniform in the entirety. The opposed ends 2b₁ and
3b₁ of the magnetic cores in the conventional coil device of Fig. 2 are shaped to
be columnar in a manner that the sectional areas thereof remain unchanged. And the
gap has a width of 3mm.
[0022] In the exemplary magnetic cores which are not inventive shown in Figs. 3,4 and 5,
opposed ends 2b₂, 3b₂ are so shaped that the sectional areas thereof are reduced by
tapered portions 2d, 3d toward opposed faces 2c, 3c, and the gap 5 is formed to have
a width of 2.5 mm in Fig. 3, 2.0 mm in Fig. 4, and 1.8 mm in Fig. 5 respectively so
that the effective permeability µ becomes uniform. In further examples, opposed ends
2b₃, 3b₃ of Fig. 6 are so formed that the sectional areas thereof are reduced by stepped
projections 2e, 3e; and opposed ends 2b₄, 3b₄ of Fig. 7 are so formed that the sectional
areas thereof are reduced, and a core member 5a identical in material with the magnetic
cores is inserted there between while being held in a gap filler (not shown) which
exerts no harmful influence on the magnetic permeability µ.
[0023] Fig. 8 graphically represents a B-H curve obtained in a conventional coil device
using magnetic cores of the shape shown in Fig. 2, and Figs. 9 through 13 graphically
represent B-H curves in coil devices using magnetic cores of the shapes shown in Figs.
3 through 7, respectively. Comparing such curves with one another, the saturation
magnetic flux density Bm in the conventional coil device with opposed ends of the
known shape shown in Fig. 8 is 5510 Gs; whereas in the coil devices which are not
inventive using magnetic cores of the shapes shown in Figs. 9, 10, 11, 12 and 13,
the saturation magnetic flux densities are 5480, 5400, 5200, 5330 and 5400 Gs, respectively.
It is also found that the linearity in the latter is not changed, although each desity
thereof is slightly lower than that in Fig. 8.
[0024] Table 1 shown below is a list of experimental results obtained by using a tester
6 of Fig. 14 and detecting the temperatures in coil centers X, coil ends Y, cores
Z and peripheries W of coil devices 1 having the opposed ends of the aforementioned
shapes (under the testing conditions including a frequency of 100 kHz, a current of
0.8 A, sine wave and ambient temperature of 40 °C ). (In this table, the shapes (a)
through (f) correspond respectively to the shapes of magnetic cores shown in Figs.
2 through 7.)
[0025] In comparison with the known shape of Fig. 2, the shapes in the embodiments shown
in Figs. 3 through 7, being not inventive, are so improved that, as listed in Table
1, the temperature in the coil center X is lower by 5 to 20 °C ;the temperature in
the coil end Y is lower by 3 to 12°C the temperature in the core Z is lower by 1.5
to 10°C ; and the temperature in the periphery W is lower by 2.5 to 5.5 °C . In the
shape of Fig. 7, the saturation magnetic flux density is retained at a relatively
high value, and the temperatures in the individual portions are lower due to the insertion
of a core member 5a which is composed of the same material as that of the magnetic
core.
[0026] A variety of modifications to the present invention may be contrived. For example,
a gap filler of a suitable material free from exerting any harmful influence on the
magnetic permeability µ may be inserted in the gap, and the gap may be formed between
some other legs than the center legs. As for the shape of the opposed ends, similar
effects can be achieved in modified ones as well as in the exemplary shapes of the
aforementioned embodiments on condition that the sectional area is reduced toward
the opposed faces. The present invention is applicable also to any device with one,
three or more closed magnetic paths. It is a matter of course that the invention can
be carried into effect in any other coil device than the aforementioned embodiments.
[0027] In each of the embodiments described, equivalent effects are attainable if, with
regard to the mutually opposed core portions in the region to form a gap, the rate
of the cross-sectional area of the fore end to that of the base end is within a range
of 1 to 90 percent.
[0028] In addition, if the fore ends of the magnetic cores 10a, 10b are so curved as defined
by logarithmic functions, as illustrated in Fig. 23, then the characteristics can
further be enhanced when such magnetic cores are employed in the coil device. The
curves of such fore end shape are expressed by the following logarithmic functions:
When the fore ends of magnetic cores 11a, 11b are furnished with planar members
12, 12 as illustrated in Fig. 24, remarkable convenience is achieved since the areas
of the fore end faces remain unchanged in adjusting the gap there between by partially
grinding the planar faces of such members in parallel with each other.
[0029] In another example where projections 14, 14 are formed on the faces of fore ends
of magnetic cores 12a, 12b as illustrated in Fig. 25, there is attainable an advantage
of rendering the flux density uniform in the gap and reducing the leakage flux that
interlinks with the coil.
1. A coil device comprising:
two magnetic cores each being U-shaped in section and having first and second legs,
the first leg being longer than the second leg, said two magnetic cores being positioned
so as to form a magnetic path therein with the first and second legs of one of said
two magnetic cores being mutually opposed to the first and second legs, respectively,
of the other said two magnetic cores, the mutually opposed second legs forming a gap
in the magnetic path,
characterized in that each of the second legs being formed such that a fore end of each of the
second legs is tapered from a base end to a center of the fore end to become narrow
according to a logarithmic curve represented by the equation:
where X
g is a distance from a center of the gap to a surface of the fore end of one of the
second legs, X
s is a distance from the center of the gap to the base end of the one second leg, X
is a distance from an origin of coordinates of an X-axis along a longitudinal centerline
of the second legs wherein the origin is the center of the gap, r
s is a radius of the base end of the one second leg, and r is a radius of the one second
leg relative to X along the X-axis; and
a coil wound so as to cover the gap, wherein mutually opposed portions of the mutually
opposed second legs of said magnetic cores to form the gap are completely enclosed
by said coil.
2. A coil device according to claim 1, wherein the mutually opposed portions of the second
legs forming the gap are formed such that a ratio of the cross-sectional area of the
fore end to that of the base end is within a range of 1 to 90 percent.
3. A coil device according to claim 1, wherein a member having a planar surface is provided
on said fore end.
4. A coil device according to claim 1, wherein projections are formed on the face of
said fore end.
5. A coil device having first and second magnetic cores each having a first leg formed
longer than a second leg, the first legs of said first and second cores being positioned
with each other and the second legs being positioned with each other, respectively,
in opposing relationship so as to form a gap between opposing surfaces of the second
legs, a coil being wound so as to enclose the gap completely,
characterized in that each of the second legs forming the gap and opposed from each other being
formed such that a fore end of each of the second legs is tapered from the base end
to a center of the fore end to become narrow according to a logarithmic curve represented
by the equation:
where X
g is a distance from a center of the gap to a surface of the fore end of one of the
second legs, X
s is a distance from the center of the gap to the base end of the one second leg, X
is a distance from an origin of coordinates of an X-axis along a longitudinal centerline
of the second legs wherein the origin is the center of the gap, r
s is a radius of the base end of the one second leg, and r is a radius of the one second
leg relative to X along the X-axis.
6. A coil device according to claim 5, wherein the second legs forming such that a ratio
of the cross-sectional area of the fore end to that of the base end within a range
of 1 to 90 percent.
7. A coil device according to claim 5, wherein a member having a planar surface is provided
on the fore end.
8. A coil device according to claim 5, wherein projections are formed on a face of the
fore end.
1. Spulenelement, welches folgendes aufweist:
zwei Magnetkerne mit jeweils U-förmigem Querschnitt und mit einem ersten und zweiten
Schenkel, wobei der erste Schenkel länger als der zweite ist und wobei die beiden
Magnetkerne so angeordnet sind, daß sie zwischen sich einen Magnetweg bilden, während
der erste und zweite Schenkel eines der beiden Magnetkerne jeweils dem ersten bzw.
zweiten Schenkel des jeweils anderen der beiden Magnetkerne gegenüberstehen, und wobei
die sich gegenüberstehenden zweiten Schenkel einen Spalt im Magnetweg bilden,
dadurch gekennzeichnet, daß jeder der zweiten Schenkel, die so geformt sind, daß jedes ihrer Vorderenden
von einem Sockelende zu einer Mitte des Vorderendes hin konisch zuläuft und sich dabei
gemäß einer logarithmischen Kurve verjüngt, die durch folgende Gleichung darstellbar
ist:
wobei X
g den Abstand von einem Mittelpunkt des Spalts bis zu einer Oberfläche des Vorderendes
eines der zweiten Schenkel angibt, X
s für einen Abstand von der Mitte des Spalts bis zum Sockelende des einen zweiten Schenkels
steht, X einen Abstand von einem Koordinatenursprung einer X-Achse entlang einer Mittellängslinie
der zweiten Schenkel bezeichnet, wobei der Ursprung die Mitte des Spalts ist, r
s einen Radius des Sockelendes des einen zweiten Schenkels angibt, und r einem Radius
des einen zweiten Schenkels relativ zu X entlang der X-Achse entspricht; und
daß eine Spule so gewickelt ist, daß sie den Spalt überdeckt, wobei sich jeweils gegenüberliegende
Abschnitte der den Spalt bildenden und sich gegenüberstehenden zweiten Schenkel der
Magnetkerne von der Spule vollständig umschlossen sind.
2. Spulenelement nach Anspruch 1,
bei welchem die sich gegenüberstehenden Abschnitte der den Spalt bildenden zweiten
Schenkel so geformt sind, daß ein prozentualer Anteil der Querschnittsfläche des Vorderendes
zu der des Sockelendes in einem Bereich zwischen 1 und 90 Prozent liegt.
3. Spulenelement nach Anspruch 2,
bei welchem auf dem Vorderende ein Teil mit ebener Fläche vorgesehen ist.
4. Spulenelement nach Anspruch 1,
bei welchem auf der Fläche des Vorderendes Vorsprünge ausgebildet sind.
5. Spulenelement mit einem ersten und einem zweiten Magnetkern, wobei an den Kernen jeweils
ein erster Schenkel länger als ein zweiter Schenkel ausgebildet ist, und wobei die
ersten Schenkel der ersten und zweiten Kerne jeweils gegenüber einander positioniert
sind und die zweiten Schenkel jeweils gegenüberliegend so angeordnet sind, daß zwischen
sich gegenüberliegenden Flächen der zweiten Schenkel ein Spalt gebildet wird, während
eine Spule so aufgewickelt ist, daß sie den Spalt vollständig umschließt,
dadurch gekennzeichnet, daß jeder der den Spalt bildenden und sich gegenüberliegenden zweiten Schenkel so
geformt ist, daß ein Vorderende jedes der zweiten Schenkel von einem Sockelende zu
einer Mitte des Vorderendes hin sich konisch gemäß einer logarithmischen Kurve verjüngt,
die durch folgende Gleichung darstellbar ist:
wobei X
g den Abstand von einem Mittelpunkt des Spalts bis zu einer Oberfläche des Vorderendes
eines der zweiten Schenkel angibt, X
s für einen Abstand von der Mitte des Spalts bis zum Sockelende des einen zweiten Schenkels
steht, X einen Abstand von einem Koordinatenursprung einer X-Achse entlang einer Mittellängslinie
der zweiten Schenkel bezeichnet, wobei der Ursprung die Mitte des Spalts ist, r
s einen Radius des Sockelendes des einen zweiten Schenkels angibt, und r einem Radius
des einen zweiten Schenkels relativ zu X entlang der X-Achse entspricht.
6. Spulenelement nach Anspruch 5,
bei welchem die zweiten Schenkel so geformt sind, daß ein Verhältnis der Querschnittsfläche
des Vorderendes zu der des Sockelendes in einem Bereich zwischen 1 und 90 Prozent
liegt.
7. Spulenelement nach Anspruch 5,
bei welchem auf dem Vorderende ein Teil mit ebener Fläche vorgesehen ist.
8. Spulenelement nach Anspruch 5,
bei welchem auf der Fläche des Vorderendes Vorsprünge ausgebildet sind.
1. Élément de bobine comprenant:
deux noyaux d'aimant, chacun à section en U, ainsi qu'une première branche et une
deuxième branche, dont la première branche est plus longue que la deuxième, les deux
noyaux d'aimant étant disposés de façon qu'il forment une voie magnétique y entre,
pendant que les première et deuxième branches d'un des deux noyaux d'aimant faisant
face respectivement à la première ou respectivement la deuxième branche du respectivement
autre desdits deux noyaux d'aimant, et lesdites deuxièmes branches opposées formant
un entrefer dans ladite voie magnétique,
caractérisé en ce que chacune desdites deuxièmes branches, qui sont formées de façon que chacune de
ses extrémités avant s'étendent en cône, partant d'une extrémité de base vers un centre
de l'extrémité avant, et étant réduit selon la loi d'une courbe logarithmique laquelle
on peut représenter par l'équation suivante:
où X
g corresponde à la distance entre un centre de l'entrefer et une surface de l'extrémité
avant d'une desdites deux branches, X
s représente la distance entre le centre dudit entrefer et l'extrémité de base de ladite
une deuxième branche, X corresponde à une distance entre un point d'origine de coordonnées
d'un axe X le long d'une ligne médiane longitudinale de ladite deuxième branche, ledit
point d'origine étant le centre de l'entrefer, et où r
s corresponde à un rayon de l'extrémité de base de ladite une deuxième branche, et
r représente un rayon de ladite une deuxième branche relativement à X le long de l'axe
X; et
en ce qu'une bobine est enroulée de façon qu'elle couvre ledit entrefer, des partes
respectivement opposées desdites deuxièmes branches opposées, qui forment ledit entrefer,
desdits noyaux d'aimant étant renfermées complètement par ladite bobine.
2. Élément de bobine selon la revendication 1,
dans lequel les parties opposées desdites branches, qui forment ledit entrefer, sont
formées de façon qu'un taux de l'aire de section de l'extrémité avant relativement
à celle de ladite extrémité de base soit dans une gamme entre 1 et 90 pour cent.
3. Élément de bobine selon la revendication 2,
dans lequel un élément à face plane est disposé sur ladite extrémité avant.
4. Élément de bobine selon la revendication 1,
dans lequel des parties en saillie sont formées sur l'aire de ladite extrémité avant.
5. Élément de bobine à un premier et un deuxième noyaux d'aimant, lesdits noyaux présentant
chacun une première branche plus longue qu'une deuxième branche, dans lequel lesdites
premières branches desdits premier et deuxièmes noyaux sont positionnées l'une enface
de l'autre, et lesdites deuxièmes branches étant disposées chacune en face, de façon
à former un entrefer entre les faces opposées desdites deuxièmes branches, pendant
qu'une bobine est enroulée de façon à entourer ledit entrefer complètement,
caractérisé en ce que chacune desdites branches, qui forment ledit entrefer et font face l'une à l'autre,
est formée de façon qu'une extrémité avant de chacune desdites deuxièmes branches
est réduite en cône, partant d'une extrémité de base vers un centre de l'extrémité
avant, suivant la loi d'une courbe logarithmique laquelle on peut représenter par
l'équation suivante:
où X
g corresponde à la distance entre un centre de l'entrefer et une surface de l'extrémité
avant d'une desdites deux branches, X
s représente la distance entre le centre dudit entrefer et l'extrémité de base de ladite
une deuxième branche, X corresponde à une distance entre un point d'origine de coordonnées
d'un axe X le long d'une ligne médiane longitudinale de ladite deuxième branche, ledit
point d'origine étant le centre de l'entrefer, et où r
s corresponde à un rayon de l'extrémité de base de ladite une deuxième branche, et
r représente un rayon de ladite une deuxième branche relativement à X le long de l'axe
X.
6. Élément de bobine selon la revendication 5,
dans lequel lesdites deuxièmes branches sont formées de façon qu'un taux de l'aire
de section à l'extrémité avant relativement à celle de ladite extrémité de base soit
dans une gamme entre 1 et 90 pour cent.
7. Élément de bobine selon la revendication 5,
dans lequel un élément à face plane est disposé sur ladite extrémité avant.
8. Élément de bobine selon la revendication 5,
dans lequel des parties en saillie sont formées sur l'aire de ladite extrémité avant.