Note: Descriptions are shown in the official language in which they were submitted.
;8
l BACKGROUND OF THE INVENTION
This invention relates to heating coil assemblies
for electromagnetic lnduction cooking heater, and methods for manu-
facturing the heating coil assemblies, more particularly,
to heating coil assemblies having larger coil winding
pitch at the middle part between the outer and inner circum-
ferential parts thereof and methods for manufacturing the
same.
The nature, utility and principle of the invention
will become more apparent from the following detailed de-
scription and the appended claims when read in conjunctionwith the accompanying drawings.
B~IEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 2 are a sectional view and a perspec-
tive view, respectively, showing a first example of a heating
coil assembly for electromagnetic induction cooking heater which ismanufactured according to one example of a heating coil
assembly manufacturing method of the invention;
FIGS. 3 and 4 are a sectional view and a perspec-
tive view, respectively, showing another example of the
heating coil assembly which is manufactured according toanother example of the heating coil assembly manufacturing
method of the invention in such a manner that the coil has
a gap at the middle part which is located between the
outer-and inner peripheral parts of the coil;
~2~
1 FIGS. 5 and 6 are a sectional view and a perspec-
tive view, respectively/ showing the same heating coil
assembly as that shown in FIGS. 3 and 4 which is now manu-
factured according to another example of the heating coil
assembly manufacturing method of the invention in which
spacers are used.to form the gap in the coil;
FIG. 7 is a perspective view for a description
of the difficulty that, where the coil supporting base
has no protrusions, the coil is deformed.
FIG. 8 is a graphical representation for a de-
scription of the temperature distribution of the heating
coil assembly of the invention in comparison with that of
a conventional heating coil assembly;
FIG. 9 is a sectional view showing another example
of the heating coil assembly manuacturing method of the
invention in which the coil winding frame has the pro-
trusions;
FIG. 10 is a sectional view showing another
example of the heating coil assembly manufacturing method
of the invention in which the protrusions are formed both
on the coil supporting base and on the coil winding frame;
FIGS. 11 and 12 are a sectional view and a
perspective view, respectively, showing a conventional
heating coil assembly for electromagnetic induction cooking heater;
and
FIG. 13 is a plan view for a description of a
method of preventing the permeation of impregnating
varnish into the lead wires of the coil.
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6~
1 An electromagnetic induction ox~ing heater compri~s a
heating coil assembly. The coil assembly is generally
manufactured as follows: As shown in FIGS. 11 and 12, a
Litz wire 3 consisting of a number of separately insulated
strands of enameled wires is wound spirally and
secured to a coil supporting base2 with varnish. More
specifically, as shown in FIG. 5, the coil supporting
base ~ and a coil winding frame 1 are fixedly mounted on
the shaft of a coil winding machine in such a manner that
a space for receiving the Litz wire 3 is formed therebetween,
and then the Litz wire 3 is spirally wound in the space.
The coil manufacturing method is advantageous in that the
number of manufacturing steps is relatively small and the
productivity is high.
However, in the heating coil assembly manufactured
according to the above-described conventional coil manufac-
turing method, the Litz wire is uniformly and closely
wounded as is apparent from FIG. 11, thus providing the
following difficulty: When the heating coil is energized,
the middle part of the heating coil, located between the
inner and outer parts thereof, becomes higher in magnetic
flux density than any other parts. Therefore, when a
cooking utensil to be heated, such as a pan, is placed
over the heating coil, its part confronting the middle
part of the heating coil is heated more than the other
76~
1 parts. This phenomenon may result in the difficulty that,
especially in preparing food by baking, the food is non-
uniformly baked.
In order to eliminate the difficulty, a method
has been proposed in the art in which the coil winding
pitch is made smaller towards the outer periphexy of the
coil (cf. Japanese Patent Application Laid-Open No.
56743/1981). However, the method is low in productivity
and h~gh in manufacturing cost, because it is necessary
to prepare a plastic spacer for manufacture of each coil
and the wire is wound on the spacer.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of this
invention is to provide a heating coil assembly in which
the coil wound spirally has a gap at its middle part which
is located between the outer and inner parts of the coil,
thereby to eliminate the above-described difficulties ac-
companying a conventional heating coil assembly.
Another object of the invention is to provide a
method of manufacturing the above-described heating coil
assembly with high productivity.
The foregoing objects and other objects of the
invention have been achieved by the provision of a coil
assembly which, according to the invention, comprises: a
flat shaped coil support base; and a coil formed on the
~25~
1 coil base by spirally winding a stranded wire in such
a manner that a gap is formed in the coil at the mlddle
part thereof, and by the provision of a coil assembly manu-
facturing method in which a flat shaped coil support
base and a flat shaped coil winding frame are fixedly
mounted on the output shaft of a coil winding machine in
such a manner that the coil base and the coil windinq
frame define a coil receiving space, and a stranded wire
is wound spirally in the space to form a coil therein, in
which, according to the invention, the coil base and/or
coil winding frame has a plurality of protrusions which
extend in the space at the middle part, which is located
between the outer and inner peripheries of the space,
thereby to change the coil winding pitch.
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of this invention will be
described with reference to the accompanying drawings.
_ 5 _
~57~
A first example of a heating coil assembly for
electromagnetic induction cooking hea-ter according to ~he in~ention,
as shown in FIGS. 1 and 2, comprises a coil supporting
base 2 having pro-trusions 8 at the middle part thereof;
and a spiral coil 3 formed on the coil supporting base 2.
The coil is generally formed as follows: A coil
winding frame 1 is placed on the coil supporting base 2,
and a stranded wire is spirally wound in the space 7 formed
between the coil winding frame 1 a~d the coil supporting
base 2. In this case, the gap between the frame 1 and the
base 2 at each of the protrusions 8 of the base 2 is smaller
than that at any other part, and therefore, at the pro-
trusions 8, the stranded wire is flattened and its winding
pitch is increased as much.
Thus, the winding pitch of the spiral coil can
be readily changed according to the method of the in~ention.
In the present invention, the stranded wire
preferably has a stranding pitch which is more than twenty
times as large as the outside diameter of the stranded wire.
Alternatively, the stranded wire may be a plurality oE
enameled wires boundled together~
FIGS. 3 and 4 show a second example of the
heating coil assembly manufactured according to a-second
example of the coil manufacturing method of the invention.
In the heating coil assembly, a gap G is provided a-t the
middle part of a coil 3, between the outer and inner parts.
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~,2~76~8
In the coil manufacturing method, forming the
coil 3 is started after, on the wire supplying side, the
backward tension given to the wire has been set relatively
high.
As a winding machine (not shown) is rotated, a
coil supporting base 2 and a coil winding frame 1 mounted
or:. the output shaft of the winding machine are turned so
that the stranded wire is wound in the space 7 between the
coil supporting base 2 and the coil winding frame le
In this operation, since the coil supporting base
2 has protrusions 8 on its uppèr surface as is shown best
in FIG. 3 and the space 7 is made narrower at the protrusions
8, while the backward tension is maintained high the wire
is deformed while passing over the protrusions 8, thus
being wound along the inner circumference of the space 7.
After the output shaft of the coil winding machine
has made a predetermined number of revolutions, the backward
tension is decreased so that the wire is prevented from
passing over the protrusions 8 and it is wound along the
latter 8.
Accordingly, the aforementioned gap G can be
readily formed at the middle part of the coil.
In the above~described method, the heating coil
assembly is manufactured by changing the backward tension
given to the wire. However, the same heat coil assembly
can be manufactured according to a third example of the
heating coil assembly manufacturing method accordin~ to
the invention in which spacers turning in synchronization
with the output shaft of a coil winding machine are em-
ployed as shown in FIGS. 5 and 6.
More specifically, the spacers 6 are pins whichar.e embedded in a disc 5 in such a manner that they are
arranged on a circumference coaxal with the disc 5. The
di.sc 5 is mounted on the output s~aft`of the coil winding
10 machine.
Forming a coil 3 is started in the same manner
as that in the second example of the heating coil assembly
manufacturing method shown in FIGS. 3 and 4.
After the coil 3 has had predetermined turns the
.5 spacers 6 are pushed towards the coil 3 together with the
d sc. Under this condition, the coil winding machine is
rotated again. Therefore, the wire ~s now wound along the
spacers 6 to form the outer part of the coil.
Thus, the coil 3 having the gap G at its middle
part can be manufactured according to thP third example of
the heating coil assembly manufacturing method of the
invention.
The coil 3 thus formed the coil supporting base
2 and the coil winding frame 1 are fixedly combined together
with screws or the like, and then are removed from the
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output shaft of the coil winding machine. Thereafter,
the coil is bonded to the coil supporting base with
adhesive such as impregnating varnish.
In the above-described operation, when the coll
3, the base 2 and frame 1 are removed from the coil winding
machine, simultaneously the spacers 6 for forming the gap
G are disengaged from the coil 3. Therefore, the part B
o the wire which crosses over the gap (hereinafter referred
tc "a crossover part or wire ~", when applicable) is dis~
placed by the elasticity of the wire itself as shown in
FIG. 7; that is, it is difficult to maintain the configura-
tion of th~ coil unchanged.
The above-described difficulty a~companying the~
third example of the heating coll assembly manufacturing
method can be eliminated by providing protrusions 8 as shown
in FIGS. 1 and 2 in such a manner that the protrusions 8
are arranged along the outer periphery of the gap G. That
is, the protrusions 8 thus provided prevents the displace-
ment of the crossover wire which otherwise may be caused
by the elasticity of the wire. Thus, the heating coil
assembly whose coil has a predetermined gap at the middle
part can be readily mass-produced.
When the coil is secured to the coil base with
impregnating varnish, both end portions C and D (shown in
FIG. 13) of the coil are preferably applied with varnish
~2~;7~
which, at high temperature, is low in fluidity or hardened
. quickly, whereby permea-tion oE the impregnating varnish
into the lead wires connected to the two end portions of
the coil is prevented and flexible lead wires are formed.
In the heating coil assembly of FIG. 1, the coil-
supporting base 2 has a plurality of protrusions 8 at the
middle part. However, it should be noted that the invention
is not limited thereto or thereby. That is, the coil sup-
porting base 2 may have only one protrusion 80 In this
.10 c.~se also, the protrusion can effectively prevent the
: d:isplacement of the crossover wire, although the plural
p;:otrusisns 8 can prevent the displacement of the crossover
w:ire more effectively than the one protrusion.
In the above-described heating coil manuEacturing
methods of the invention, the coil supporting base has the
protrusions 8. However, the same effect can be obtained
b~ a method in which protrusions 8' are formed on the coil
wi.nding frame as shown in FIG. 9, or protrusions 8 and 8'
are formed both on the coil supporting base 2 and on the
coil winding frame 1.as.:shcwn in FIG;10. In FIGS. 9 and 10, reference
numeral 3 designates the coil formed on the coil supporting
base 2.
FIG. 8 is a graphical representation indicating
the temperature distribution P of the conventional heating
coil assembly and that Q of the heating coil assembly of
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~L%5766~3
the invention, It is apparent from FIG. 8 that the heating
eo~l assembly of the invention in whieh the coil has the
gap at the middle part is mueh uniform in temperature
distribution than the eonventional heati.ng eoil assembly.
As was described above, according to the invention,
the protrusions are formed on the eoil supporting base
and/or the coil winding frame, whereby the coil winding
pitch can be readily ehanged at the middle part of the
eoil, between the outer and inner parts. Aceordingly, the
heating coil assembly for eleetromagnetic induction eooking heater
a-eording to the invention is uniform in heating charaeter~
istie.:
