JPH10106737A - Electromagnetic shield method of electromagnetic induction rice cooker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain radiation noise of electromagnetic waves generated from a magnetic flux generation coil, to increase inductance of the magnetic flux generation coil, and to improve energy efficiency. SOLUTION: A body 12 of an electromagnetic induction rice cooker accommodates an outside iron pot 13 into which an inside iron pot 14 is loosely inserted. A magnetic flux generation coil extends from a bottom face of the outside iron pot 13 to an outer peripheral surface in a lower portion of the outside iron pot 13. Moreover, a ring-shaped shielded material 19 formed out of soft magnetic material is arranged in the body 12 so as to surround a magnetic flux generation coil 16 and a lower portion of the outside iron pot 13. This ring-shaped shielded material 19 is formed either by laminating a band-like soft magnetic thin film wound therearound several times, or by laminating a plurality of soft magnetic thin films.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic induction heating method (hereinafter referred to as induction heating for short).
The present invention relates to a method of shielding an alternating magnetic field and an electric field leaking from a magnetic flux generating coil used in a rice cooker utilizing the method.

[0002]

2. Description of the Related Art Conventionally, as a rice cooker using the IH system, that is, an electromagnetic induction rice cooker, an outer pot is housed in a housing, an inner pot is loosely inserted into the outer pot, and an outer pot is inserted from the bottom of the outer pot. Is known in which a magnetic flux generating coil is disposed over the lower outer peripheral surface of the coil. In this electromagnetic induction rice cooker, when an alternating current having a predetermined frequency is applied to the magnetic flux generating coil, an alternating magnetic field is generated around the coil, and an eddy current is induced inside the magnetic material of the inner pot by the magnetic field lines of the alternating magnetic field. The eddy current generates Joule heat due to the electric resistance of the magnetic material, and the entire inner pot is heated.

However, in the above-mentioned electromagnetic induction rice cooker, since a high-voltage current having a frequency of 20 kHz or more flows through the magnetic flux generating coil, strong electromagnetic waves having a fundamental frequency and a frequency that is an integral multiple of the fundamental frequency (hereinafter referred to as a harmonic) are radiated from the coil. Is done.
Most of this electromagnetic wave is converted into thermal energy and used as eddy current in the inner pot, and a part of the electromagnetic wave is radiated outside the rice cooker as electromagnetic wave noise. As a result, there is a risk that malfunctions may occur in a large number of electronic devices mixed around the rice cooker due to the electromagnetic wave noise.

In order to solve this problem, a method of attaching an electromagnetic shielding core formed of a soft magnetic material to a lower portion of a magnetic flux generating coil to guide a magnetic flux generated from the coil to an inner pot has been proposed. A method of using a shield material in which band-shaped aluminum is formed in a ring shape so as to surround the lower part of the outer pot and utilizing the effect of the shield material as a conductor is used in combination.

[0005]

However, in the above-mentioned conventional electromagnetic induction rice cooker, since the shielding material is formed of aluminum which is a conductor but is a non-magnetic material, the effect as a conductor, that is, the magnetic flux generating coil is used. Thus, when an electromagnetic wave is generated, an electromotive force is induced in the shield material so as to generate a magnetic flux in such a direction as to cancel the magnetic flux linked in the shield material, and only the effect of reducing the magnetic flux is obtained. SUMMARY OF THE INVENTION It is an object of the present invention to provide an electromagnetic induction rice cooker electromagnetic shielding method capable of suppressing radiation noise of electromagnetic waves generated from a magnetic flux generating coil, increasing inductance of the magnetic flux generating coil, and further improving thermal efficiency.

[0006]

The invention according to claim 1 is
As shown in FIG. 1, an outer hook 13 housed in a housing 12,
It is an improvement of the electromagnetic induction rice cooker provided with the inner pot 14 loosely inserted in the outer pot 13 and the magnetic flux generating coil 16 arranged from the bottom surface of the outer pot 13 to the outer peripheral surface of the lower portion of the outer pot 13. The characteristic configuration is that a shield member 19 formed of a soft magnetic material in a ring shape is arranged in the housing 12 so as to surround the magnetic flux generating coil 16 and the lower portion of the outer shuttle 13. The invention according to claim 2 is the invention according to claim 1, wherein the shield member is formed by bending a single band-shaped soft magnetic thin film into a ring shape.

A third aspect of the present invention is the invention according to the first aspect, wherein the shielding material is formed by winding and laminating a band-shaped soft magnetic thin film a plurality of times or laminating a plurality of soft magnetic thin films. And is formed by bending into a ring shape. The invention according to claim 4 is the invention according to claim 1, wherein the shielding material is formed of an alloy containing one or more metals selected from the group consisting of iron, nickel and cobalt. It is characterized by. The invention according to claim 5 is the invention according to claim 1, further comprising: a ring-shaped shield main body in which the shield material is formed of a non-magnetic metal or resin; and a soft magnetic plating layer attached to a surface of the shield main body. And characterized in that:

In the electromagnetic shielding method for an electromagnetic induction rice cooker according to the first to fifth aspects, the magnetic flux generating coil 16 and the outer pot 13
When an electromagnetic wave is generated from the magnetic flux generating coil 16 in a state where the ring-shaped shield member 19 is arranged so as to surround the lower part,
The magnetic flux that changes in the shield member 19 interlinks, and an electromotive force is induced in the shield member 19 so as to generate a magnetic flux in a direction to cancel the interlinking magnetic flux, so that the magnetic flux decreases. Although the reduced magnetic flux passes through the shield member 19, since the shield member 19 is formed of a soft magnetic material, leakage of the magnetic flux to the outside can be suppressed. As a result, radiation noise of electromagnetic waves can be suppressed. Further, since the shield member 19 also functions as a core of the magnetic flux generating coil 16, the inductance of the magnetic flux generating coil 16 can be increased.

The invention according to claim 6 is the invention according to claim 3, wherein a shielding material is formed by interposing an insulating layer between the laminated soft magnetic thin films. . According to the electromagnetic shielding method for an electromagnetic induction rice cooker according to the sixth aspect, an eddy current is not generated in the soft magnetic thin film when the electromagnetic induction rice cooker is operated, and heat generation of the soft magnetic thin film can be suppressed.

[0010]

Embodiments of the present invention will now be described in detail with reference to the drawings. As shown in FIGS. 1 and 2,
The electromagnetic induction rice cooker 11 includes an outer pot 13 housed in a housing 12.
And an inner hook 14 loosely inserted into the outer hook 13, and a magnetic flux generating coil 16 disposed from a bottom surface of the outer hook 13 to a lower outer peripheral surface of the outer hook 13. The casing 12 is formed of an insulating material such as plastics into a tubular shape having a bottom wall 12a, and the outer pot 13 is mainly made of polyethylene terephthalate (hereinafter, PE).
T) to form a cylinder having a bottom wall 13a. The inner pot 14 is formed in a cylindrical shape having a bottom wall 14a mainly by a cladding material of stainless steel, which is a magnetic material, and aluminum having high thermal conductivity, and a coating of a fluorine resin or the like (not shown) is provided on the inner side. You. On the upper surface of the bottom wall 12a of the housing 12, a plurality of pedestals 12b are provided at equal intervals on the same circumference around the central axis of the housing 12,
A plurality of legs 13b projecting toward the plurality of pedestals 12b, respectively, are protruded from a lower outer peripheral surface of the base. The lower ends of these legs 13b are fixed by screws (not shown) while being placed on the upper surfaces of the plurality of pedestals 12b, respectively. Coil 1
Reference numeral 6 denotes a spirally wound conductive wire covered with an insulating material, which is attached to the bottom surface of the outer pot 13 and the outer peripheral surface of the lower part of the outer pot by an adhesive, and terminals 16a at both ends of the coil 16 have a predetermined frequency (not shown). Is connected to an AC generation element of an AC generation device that generates a current of

A plurality of substantially L-shaped portions extend from the outside of the coil 16, that is, from the lower surface of the coil 16 disposed on the bottom surface of the outer hook 13 to the outer surface of the coil 16 disposed on the outer peripheral surface of the lower portion of the outer hook 13. Of the electromagnetic shielding cores 17 are radially arranged. These cores 17 are formed by sintered ferrite, by dispersing soft magnetic powder in resin or rubber, or by alternately laminating soft magnetic thin films and insulating thin films. On one side of the core 17, the core 17 is provided.
A mounting portion 17a is integrally formed with the mounting portion 17a.
Are formed with through holes (not shown). A plurality of bosses 13c project from the lower surface of the bottom wall 13a of the outer hook 13 at predetermined intervals on the same circumference around the center axis of the outer hook 13, and these bosses 13c are provided with female screws (not shown). Is formed respectively. The screw 18 is screwed into the screw hole through the screw hole of the boss 13c with the through hole of the mounting portion 17a aligned with the screw hole of the boss 13c.
3 is fixed to the lower surface with the magnetic flux generating coil 16 sandwiched therebetween. The through hole is directly formed in the electromagnetic shield core without projecting the mounting portion on the electromagnetic shield core, and the screw is screwed into the screw hole of the boss through the through hole to remove the core. You may attach to a shuttle. Instead of screwing the electromagnetic shielding core to the bottom of the outer hook, the core may be adhered to the lower surface of the magnetic flux generating coil via an adhesive or directly fused.

A characteristic configuration of this embodiment is that a shield member 19 formed of a soft magnetic material in a ring shape is disposed in the housing 12 so as to surround the magnetic flux generating coil 16 and the lower portion of the outer shuttle 13. It is in. The legs 13b protruding from the lower outer peripheral surface of the outer hook 13 are composed of a horizontal portion 13d extending horizontally from the lower outer peripheral surface of the outer hook 13, a vertical portion 13e hanging down from the tip of the horizontal portion 13d, and a vertical portion 13e. A rib 13f suspended from the horizontal portion 13d at a predetermined interval in the direction of the outer shuttle 13; The lower end of the shielding material 19 is the pedestal 1
2b is fixed to rice cooker 11 by abutting on the upper surface and inserting the upper end between vertical portion 13e and rib 13f. In this embodiment, the shield member 19 is formed in a circular ring shape. The shield material may be formed not in a circular ring shape but in a rectangular or other polygonal ring shape.

The shielding material 19 has a thickness of, for example, 0.1 mm.
It is formed by bending a single band-shaped soft magnetic thin film into a ring shape. When the shield member 19 is thin and has a problem in strength, the shield member 19 is attached or attached to a ring made of a resin such as PET. Further, the shield member 19 may be formed by winding and laminating a band-shaped soft magnetic thin film a plurality of times, or by laminating a plurality of soft magnetic thin films and bending them into a ring shape.
The soft magnetic thin film is formed of iron-based amorphous, cobalt-based amorphous or silicon steel to a thickness of 5 to 50 μm. Further, a shielding material may be formed by interposing an insulating layer between the laminated soft magnetic thin films. In this case, no eddy current is generated in the soft magnetic thin film during operation of the electromagnetic induction rice cooker, and heat generation of the soft magnetic thin film can be suppressed.

The shield member 19 may be formed of an alloy containing one or more metals selected from the group consisting of iron, nickel and cobalt. As this alloy,
For example, there are silicon steel containing 0.5 to 8% by weight of silicon and permalloy, all of which are soft magnetic materials. Further, the shield member 19 may be formed by attaching a soft magnetic plating layer to the surface of a ring-shaped shield body made of a non-magnetic metal or resin. Aluminum is mainly used as the non-magnetic metal, and permalloy, Co-B, or the like is used as the soft magnetic plating layer.

In the electromagnetic induction rice cooker configured as described above, when power is supplied to the electromagnetic rice cooker 11, an AC current of a predetermined frequency is supplied to the magnetic flux generating coil 16 by a switching operation of an AC generator of an AC generator (not shown). Flows.
When an alternating current flows through the magnetic flux generating coil 16, the coil 16
, An eddy current is induced inside the magnetic material of the inner pot 14 by the magnetic lines of force of the alternating magnetic field, as shown by arrows in FIG. As a result, the eddy current generates Joule heat due to the electric resistance of the magnetic material, and the entire inner pot 14 is heated.

On the other hand, the magnetic flux generating coil 16 generates an electromagnetic wave. Due to the generation of the electromagnetic waves, the magnetic flux that changes in the shield member 19 is linked, and an electromotive force is induced in the shield member 19 so as to generate a magnetic flux in a direction to cancel the linked magnetic flux. As a result, the magnetic flux decreases, so that the magnetic field of the electromagnetic wave weakens and, at the same time, the electric field weakens. Although the reduced magnetic flux passes through the shield member 19, since the shield member 19 is formed of a soft magnetic material, leakage of the magnetic flux to the outside can be suppressed. As a result, radiation noise of electromagnetic waves can be suppressed. Further, since the shield member 19 is formed of a soft magnetic material, the shield member 19 is
6 also functions as a core. As a result, the inductance of the magnetic flux generating coil 16 increases, so that the eddy current generated in the inner pot 14 increases, and the thermal efficiency of the rice cooker 11 can be improved. Also, since the inductance of the magnetic flux generating coil 16 increases, the switching loss of the AC generating element can be reduced, and the heat generation of this element can be suppressed. That is, the shield member 19 also has a function as an inductor.

[0017]

Next, examples of the present invention will be described in detail together with comparative examples. <Embodiment 1> As shown in FIGS. 1 and 2, an electromagnetic induction rice cooker 11 is a PET housed in a plastic housing 12.
And an inner pot 14 which is loosely inserted into the outer pot 13 and is formed of a clad material of stainless steel and aluminum.
And a magnetic flux generating coil 16 disposed from the bottom surface of the outer hook 13 to the outer peripheral surface of the lower portion of the outer hook 13. The inside of the inner pot 14 is coated with a fluorine resin or the like (not shown), and the terminals 16a at both ends of the coil 16 are connected to an AC generating element of an AC generator (not shown) for generating a current of a predetermined frequency. Eight electromagnetic shielding cores 17 formed of sintered ferrite in a substantially L-shape are radially arranged outside the coil 16. The core 17 was fixed to the outer hook 13 by forming a mounting portion 17a on the core 17 and screwing a screw 18 into a screw hole (not shown) of a boss 13b of the outer hook 13 via the mounting portion 17a. .

The shield member 19 is formed in a ring shape from a soft magnetic material, and the shield member 19 is arranged in the housing 12 so as to surround the magnetic flux generating coil 16 and the lower portion of the outer pot 13. The lower end of the shield member 19 is attached to the pedestal 12b of the housing 12.
The shield member 19 was fixed to the rice cooker 11 by making contact with the upper surface and inserting the upper end of the shield member 19 between the vertical portion 13e of the leg portion 13b protruding from the outer hook 13 and the rib 13f. The shield material 19 was manufactured by the following method.
First, 88% by weight of iron, 4% by weight of boron, 8% by weight of silicon
Was rapidly cooled from a molten state to obtain iron-based amorphous ribbons having a thickness and a width of 25 μm and 35 μm.
Next, this iron-based amorphous ribbon was wound three times on a cylindrical winding die having an outer diameter of 260 mm to produce a shield material. The electromagnetic induction rice cooker 11 configured as described above was used as Example 1.

<Embodiment 2> An electromagnetic induction rice cooker having the same configuration as that of Embodiment 1 except that the shield material is different from the shield material of Embodiment 1 is used as Embodiment 2. Although not shown, the shield material of Example 2 was produced by the following method. First, a non-oriented silicon steel sheet was rolled to a thickness of 0.1 mm. Next, a shield material was produced by bending the rolled non-oriented silicon steel sheet into a ring shape having the same shape as the shield material of Example 1. <Example 3> An electromagnetic induction rice cooker having the same configuration as that of Example 1 except that the shield material was different from that of Example 1 was used as Example 3. Although not shown, the shield material of Example 3 was produced by the following method. First, permalloy (50% by weight of Ni and 50% by weight of Fe) is adhered to one surface of a shield body made of a nonmagnetic metal aluminum strip having a thickness and width of 0.5 mm and 40 mm by electrolytic plating. Thereby, a soft magnetic plating layer having a thickness of 20 μm was formed on one surface of the shield body. Next, a shield material was produced by bending the shield body into a ring shape having the same shape as the shield material of Example 1 so that this plating layer was located on the outer peripheral surface of the shield body.

<Comparative Example 1> An electromagnetic induction rice cooker having the same configuration as that of Example 1 except that the shield material was different from the shield material of Example 1 was used as Comparative Example 1. Although not shown, the shield material of Comparative Example 1 was formed by bending an aluminum strip having a thickness and a width of 0.5 mm and 40 mm into the same shape as the shield material of Example 1. <Comparative Example 2> An electromagnetic induction rice cooker having the same configuration as in Example 1 except that no shield material was used was used as Comparative Example 2.

<Comparative Test and Evaluation> The power was supplied to each of the electromagnetic induction cookers of Examples 1 to 3, and Comparative Examples 1 and 2, and the intensity of the radiated electric field during operation of each cooker was measured. The radiated electric field strength is measured using a radiated electric field strength meter in an anechoic chamber, and each frequency is about 1 time, about 2 times, about 3 times and about 4 times the frequency of the alternating current flowing through the magnetic flux generating coil of each rice cooker. The measurement was performed at a frequency where the discharge electric field intensity near the frequency peaked. At this time, each electromagnetic rice cooker was placed on a wooden table having a height of 40 cm from the floor, and the antenna of the radiation electric field strength meter was set at a distance of 3 m from the rice cooker and at a height of 1 m from the floor. Table 1 shows the test results.

[0022]

[Table 1]

As is clear from Table 1, the electromagnetic induction rice cookers of Examples 1 to 3 were found to have a lower radiated electric field intensity than the electromagnetic induction rice cookers of Comparative Examples 1 and 2. In addition, the electromagnetic induction rice cookers of Examples 1 to 3 have the peak frequency of the discharge electric field intensity shifted to a lower frequency side as compared with the electromagnetic induction rice cookers of Comparative Examples 1 and 2, and It was found that the shielding material also had a function as an inductor.

[0024]

As described above, according to the present invention, the outer pot is housed in the casing of the electromagnetic induction rice cooker, the inner pot is loosely inserted into the outer pot, and the lower portion of the outer pot is inserted from the bottom of the outer pot. A magnetic flux generating coil is arranged over the outer peripheral surface, and a ring-shaped shield material made of a soft magnetic material is arranged in the housing so as to surround the magnetic flux generating coil and the lower part of the outer hook. When an electromagnetic wave is generated from the electromagnetic wave, an electromotive force is induced in the shield material so as to generate a magnetic flux in such a direction as to cancel the magnetic flux linked in the shield material, and the magnetic flux is reduced. Since the reduced magnetic flux passes through the shield material formed of the soft magnetic material, the leakage of the magnetic flux to the outside is suppressed, and the radiation noise of the electromagnetic wave can be suppressed. Also, since the shielding material made of soft magnetic material also functions as the core of the magnetic flux generating coil,
The inductance of the magnetic flux generating coil can be increased. As a result, the eddy current generated in the inner pot increases, so that the thermal efficiency of the rice cooker can be improved.

The shield material is formed by bending a single band-shaped soft magnetic thin film in a ring shape, winding the band-shaped soft magnetic thin film a plurality of times and laminating the same, or laminating a plurality of soft magnetic thin films. The shield material is made of an alloy containing one or more metals selected from the group consisting of iron, nickel and cobalt, or the shield material is made of a non-magnetic metal. Alternatively, when the soft magnetic plating layer is formed on the surface of the ring-shaped shield main body made of a resin, the above-described effect is remarkably exhibited. Furthermore, if a shielding material is formed by interposing an insulating layer between the laminated soft magnetic thin films, no eddy current is generated in the soft magnetic thin film when the electromagnetic induction rice cooker operates,
Heat generation of the soft magnetic thin film can be suppressed.

[Brief description of the drawings]

FIG. 1 is a sectional view taken along the line AA of FIG. 2, showing an electromagnetic induction rice cooker shielded by an electromagnetic shielding method according to one embodiment of the present invention.

FIG. 2 is a sectional view taken along line BB of FIG. 1;

[Explanation of symbols]

 11 electromagnetic induction rice cooker 12 housing 13 outer pot 14 inner pot 16 magnetic flux generating coil 19 shield material

Claims (6)

[Claims] An outer pot (13) housed in a housing (12), an inner pot (14) loosely inserted into the outer pot (13), and an outer pot (13) from the bottom of the outer pot (13). An electromagnetic induction rice cooker having a magnetic flux generating coil (16) disposed over the lower outer peripheral surface of the shuttle (13), wherein a shield material (19) formed of a soft magnetic material in a ring shape
Is inside the housing (12) and the magnetic flux generating coil (16) and the outer hook
(13) An electromagnetic shielding method for an electromagnetic induction rice cooker, wherein the electromagnetic shielding rice cooker is arranged so as to surround a lower part. 2. The electromagnetic shielding method for an electromagnetic induction rice cooker according to claim 1, wherein the shielding material is formed by bending a single band-shaped soft magnetic thin film into a ring shape. 3. The electromagnetic material according to claim 1, wherein the shielding material is formed by winding and laminating a band-shaped soft magnetic thin film a plurality of times or by laminating a plurality of soft magnetic thin films and bending the ring into a ring shape. Electromagnetic shield method for induction cookers. 4. The electromagnetic shielding method for an electromagnetic induction cooker according to claim 1, wherein the shielding material is formed of an alloy containing one or more metals selected from the group consisting of iron, nickel and cobalt. 5. The electromagnetic induction rice cooker according to claim 1, wherein the shield member has a ring-shaped shield main body formed of a non-magnetic metal or resin, and a soft magnetic plating layer attached to a surface of the shield main body. Electromagnetic shielding method. 6. The electromagnetic shielding method for an electromagnetic induction rice cooker according to claim 3, wherein a shielding material is formed by interposing an insulating layer between the laminated soft magnetic thin films.