JP2006120336A - Induction heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an induction heating device that reduces buoyancy exerted on an object to be heated and causes a low loss. <P>SOLUTION: The induction heating device comprises: a heating coil 3 for induction-heating an object to be heated (not shown) that is made of a low permeability material and that has a high electrical conductivity; and an electrical conductor 7 provided between the object to be heated and the heating coil 3. Because of the effect of an induction current induced by the heating coil 3, the electrical conductor 7 has a function of reducing buoyancy exerted on the object to be heated due to a repulsive force between a magnetic field generated by the heating coil 3 and a magnetic field generated by an induction current induced in the object to be heated. The electrical conductor 7 is provided with a slit 9 for limiting the distribution of the induction current that flows circularly in the electrical conductor 7 nearly in parallel with the direction in which the current of the heating coil 3 flows. The slit 9 is formed to extend from an innermost part of the conductor 7 opposed to the heating coil 3 to an outermost part thereof. Since the induction current is thereby limited at a portion of the conductor 7 where a large amount of induction current is induced directly above the coil 3, it is possible to greatly reduce heat generation in the conductor 7 and to increase heating efficiency for the object to be heated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to induction heating devices such as induction heating cookers, induction heating water heaters, induction heating irons used in general homes, offices, restaurants, factories, etc., and in particular, low magnetic permeability such as aluminum and copper. The present invention also relates to an induction heating apparatus for heating an object to be heated made of a material having high electrical conductivity.

  Conventionally, there is an induction heating cooker as an example of this type of induction heating device. The induction heating cooker has a heating coil and a plurality of switching elements, and the cycle is short during the ON period of one of the switching elements. A technology is known that heats an aluminum pan with low noise by generating resonance current in the heating coil and supplying power from the smoothing capacitor to the heating coil, so that no squealing noise occurs due to the pulsating flow of the input voltage. (For example, refer to Patent Document 1).

  In addition, equivalent series resistance in the input impedance of the heating coil (equivalent series resistance in the input impedance of the heating coil measured below using the frequency near the heating coil at the same position as the heated object and the electric conductor in the heated state) By simply providing an electric conductor having the function of increasing the equivalent series resistance of the heating coil) between the heating coil and an object to be heated made of a material having low magnetic permeability and high electrical conductivity such as aluminum. A technique is known in which the current flowing through the coil is reduced to reduce the buoyancy acting on the object to be heated, and even if the input power is large, the deviation or lift of the object to be heated due to buoyancy is reduced (see, for example, Patent Document 2) .

  Hereinafter, the induction heating cooker in the said patent document 2 is demonstrated using FIGS. 5-10 as a conventional induction heating apparatus.

  FIG. 5 is a perspective view showing a configuration of a heating coil built in the induction heating cooker and its surroundings, and FIG. 6 is a cross-sectional view of a main part of the induction heating device.

  5 and 6, the heating coil 21 generates a magnetic field by a high-frequency current of about 70 kHz supplied from an inverter (not shown), and induction-heats an object 29 to be heated placed on the top plate 28. . The electric conductor 27 is formed of an aluminum plate having a thickness of about 1 mm, and is provided between the insulating plate 31 and the top plate 28.

  Since the magnetic field emitted from the upper part of the heating coil 21 is linked to the electric conductor 27, an induced current is induced in the electric conductor 27. Since the thickness of the electric conductor 27 is equal to or greater than the penetration depth of the high-frequency current induced by the current of the heating coil 21 (hereinafter simply referred to as the penetration depth of the induced current), most of the magnetic field linked to the electric conductor 27 is almost electric. It does not pass through the conductor 27 but reaches the object to be heated 29 after detouring to the outer peripheral side or inner peripheral side.

  When there is no electric conductor 27, the inside of the object 29 to be heated is made of aluminum, copper, or an electric conductivity equal to or higher than that of the high frequency magnetic field generated from the heating coil 21 and made of a low magnetic permeability material. An induced current is induced to generate a magnetic field in the repulsive direction. As a result, buoyancy is generated in the heated object 29 due to the interaction between the magnetic field induced from the induced current in the heated object 29 and the magnetic field generated from the heating coil 21.

  However, in the above conventional technique, the electric conductor 27 is provided between the heating coil 21 and the object to be heated 29, and the thickness thereof is larger than the penetration depth of the induced current. The magnetic field generated from the heating coil 21 is linked to the electric conductor 27 and the object to be heated 29 and generates an induced current in both. Thus, the electric conductor is generated so that the superposed magnetic field of the magnetic field generated by the induced current induced in the electric conductor 27 and the magnetic field generated by the current induced in the object to be heated 29 prevents a change in the magnetic field generated by the heating coil 21. An induced current flows through 27 and the object 29 to be heated.

  That is, the current distribution induced in the object to be heated 29 is changed by generating an induced current in the electric conductor 27. With this change in current distribution, the equivalent series resistance of the heating coil 21 is increased, the current flowing through the heating coil 21 when obtaining the same output can be reduced, the buoyancy acting on the object 29 to be heated is reduced, and By sharing a part of the buoyancy that the electric conductor 27 should act on the object 29 to be heated, the buoyancy acting on the object 29 can be reduced.

  FIG. 7 shows the relationship between power consumption and buoyancy when the object to be heated 29 is an aluminum pan. When there is an electric conductor 27 made of aluminum (shown by B) and when there is no electric conductor 27 (shown by A). FIG. 8 shows an example of the measurement result of the relationship between the power consumption and the heating coil current when the electric conductor 27 is present (indicated by B) and when the electric conductor 27 is absent (indicated by A). However, the resonance frequency of the inverter is about 70 kHz.

  According to these measurement results, by inserting the electric conductor 27, the equivalent series resistance of the heating coil 21 is increased, the buoyancy acting on the object to be heated 29 is reduced, and the current of the heating coil 21 is also reduced.

  FIG. 9 shows the tendency regarding the thickness and buoyancy of the electric conductor 27. By making the thickness of the electrical conductor 27 equal to or greater than the penetration depth, it is possible to obtain a buoyancy reduction effect.

  Further, in the above conventional technique, the electric conductor 27 is provided with the circulating current limiting means 27a for limiting the distribution of the induced current flowing around the heating coil 21 in a direction substantially parallel to the current flowing direction of the heating coil 21. However, the amount of heat generated by induction heating by the current flowing through the heating coil 21 is suppressed, and the equivalent series resistance of the electric conductor 27 is increased, which acts on the heating coil 21 and the object 29 to be heated. The buoyancy reduction effect is obtained.

  FIG. 10 is a diagram showing the shape of the electric conductor 27. The electric conductor 27 is based on a substantially disk-shaped aluminum plate having a thickness of about 1 mm, and is further provided with four radial cutouts 40a. In FIG. 10, when a high-frequency current is supplied to the heating coil 21 so as to flow in the direction of the broken line arrow A, a large current flow induced in the electric conductor 27 is schematically illustrated in the direction of the solid line arrow B. Become.

  Thereby, the magnetic field of the heating coil 21 is directly irradiated through the notch 40a, and a part of the magnetic field is bypassed and linked to the object 29 to be heated. It is possible to suppress the occurrence of current distribution and increase the equivalent series resistance, and also to prevent heat generation in the electrical conductor 27 by providing the notch 40a.

As described above, by using the electric conductor 27, it is practically possible to inductively heat the heated object 29 having a high electric conductivity such as aluminum and made of a low magnetic permeability material.
Japanese Patent Laid-Open No. 2003-257609 JP 2003-264054 A

  However, according to the configuration of the above-described conventional induction heating apparatus, in actual use, the buoyancy acting on the heated object 29 cannot be ignored at all, and the total weight of the pot that is the heated object 29 and the cooked food is It was limited to be heavier than a certain weight. In addition, the pan is rare in the case where the bottom surface is actually flat, and usually has a slight warp (the use of a concave warp pan in which the bottom of the pan is concave, that is, convex on the inside is used. Is). When the warpage becomes large, the thermal efficiency is lowered and the cooking performance is not good, so it is common to limit the degree of warpage.

  In order to alleviate the weight limitation due to the buoyancy and make it easier to use, the area of the electric conductor 27 is increased, that is, the equivalent series resistance of the heating coil 21 is increased, among various configurations having a buoyancy reduction effect. It is considered practical.

  In other words, the size of the opening in the central portion of the electric conductor 27 corresponding to the heating coil 21 is limited to a space necessary for placing the temperature detecting means 35 that abuts the top plate 28 and detects its temperature. It is considered that buoyancy can be further reduced by designing the area of the electric conductor 27 as large as possible.

  However, in this configuration, when a pan with a warp is used, the object 29 to be heated is far from the heating coil 21, so that the magnetic flux hardly reaches the object 29 near the center of the heating coil 21. Thus, the magnetic flux reaches the inner peripheral portion of the electric conductor 27 that is close to the distance, and as a result, the heat generation in the inner peripheral portion of the electric conductor 27 is abnormally accelerated.

  Furthermore, since there is a space between the bottom of the pan and the top plate 28 in the portion with the concave warp, the temperature rises faster because the heat of the electric conductor 27 is not easily transferred to the bottom of the pan through the top plate 28.

  When the temperature of the electric conductor 27 becomes high, control is performed to reduce the output of the heating coil 21 so that the heat generation of the electric conductor 27 is suppressed and the heat of the electric conductor 27 does not adversely affect the heating coil 21 and the like. Therefore, if the temperature rise rate of the electric conductor 27 is fast, control is performed so that the output of the heating coil 21 is lowered from an early point in time, and there is a problem that cooking takes too much time or cooking cannot be performed. It was.

  For the above reasons, there is a problem that the electric conductor 27 cannot be provided for a predetermined distance from the inner peripheral portion of the electric conductor 27, and buoyancy cannot be reduced accordingly.

  The present invention solves the above-mentioned conventional problems, further reducing the buoyancy acting on the heated object having high electrical conductivity and low permeability such as aluminum, and the bottom of the pan like a concave warp pan is concave. An object of the present invention is to provide a highly convenient induction heating apparatus that can be easily used even with an object 29 to be heated.

  In order to solve the above-described conventional problems, an induction heating apparatus according to the present invention includes a top plate on which an object to be heated made of aluminum, copper, or a low-permeability material having an electric conductivity substantially equal to or higher than these is placed. A heating coil provided below the top plate for induction heating the object to be heated, and an electric conductor provided between the heating coil and the object to be heated, wherein the electric conductor is the heating coil. Due to the action of the induced current induced inside the electric conductor, the magnetic field generated by the heating coil and the repulsive force of the magnetic field generated from the induced current induced in the heated object Has a buoyancy reduction function that reduces the buoyancy that works, and restricts the distribution of the induced current that flows around and parallel to the current flow direction of the heating coil in the electric conductor. A current limiting means, wherein the circulating current limiting means is formed from the innermost part of the electric conductor facing the heating coil to the outermost part, and induces a large amount of induced current immediately above the heating coil of the electric conductor. Since the induced current in the portion to be applied is limited, heat generation in the electric conductor is greatly reduced, and the heating efficiency of the object to be heated can be improved. In addition, since the area of the electric conductor can be expanded within a range where the heat generation of the electric conductor can be allowed, the equivalent series resistance of the heating coil can be increased and the buoyancy acting on the object to be heated can be further reduced.

  The induction heating device of the present invention is provided with a top plate on which an object to be heated made of aluminum, copper, or a low permeability material having an electric conductivity substantially equal to or higher than these is placed, and below the top plate. A heating coil for induction heating the object to be heated; and an electric conductor provided between the heating coil and the object to be heated, the electric conductor facing the heating coil to The equivalent series resistance of the heating coil when arranged is larger than that when the electric conductor is not provided, and flows around the electric conductor in a direction substantially parallel to the current flow direction of the heating coil. Circulating current limiting means for limiting the distribution of the induced current is provided, and the circulating current limiting means is formed from the innermost part facing the heating coil of the electric conductor to the outermost part. Because the induced current is limited in the part of the electrical conductor where the induced current is induced directly above the heating coil, heat generation in the electrical conductor is greatly reduced, and the heating efficiency of the object to be heated is improved. Can do. In addition, since the area of the electric conductor can be expanded within a range where the heat generation of the electric conductor can be allowed, the equivalent series resistance of the heating coil can be increased and the buoyancy acting on the object to be heated can be further reduced.

  The induction heating apparatus of the present invention can heat an object to be heated formed of a material having low magnetic permeability and high electrical conductivity, reduces buoyancy acting on the object to be heated, and has little loss. Can be provided.

  According to a first aspect of the present invention, there is provided a top plate on which a heated object made of aluminum, copper, or a low magnetic permeability material having an electric conductivity substantially equal to or higher than these is placed, and the heated object provided below the top plate. A heating coil for inductively heating an object, and an electric conductor provided between the heating coil and the object to be heated, the electric conductor having an induced current induced inside the electric conductor by the heating coil. And a buoyancy reduction function for reducing buoyancy acting on the heated object due to the repulsive force of the magnetic field generated from the magnetic field generated by the heating coil and the induced current induced in the heated object. A circulating current limiting means for limiting the distribution of the induced current flowing around and in parallel with the current flow direction of the heating coil in the electric conductor; The electric conductor is formed from the innermost part facing the heating coil to the outermost part, and the induced current is limited in the part of the electric conductor where the induced current is induced directly above the heating coil. The heat generation in the electric conductor is greatly reduced, and the heating efficiency of the object to be heated can be improved. In addition, since the area of the electric conductor can be expanded within a range where the heat generation of the electric conductor can be allowed, the equivalent series resistance of the heating coil can be increased and the buoyancy acting on the object to be heated can be further reduced.

  According to a second aspect of the present invention, there is provided a top plate on which a heated object made of aluminum, copper, or a low permeability material having an electric conductivity substantially equal to or higher than these is placed, and the heated object provided below the top plate. A heating coil for inductively heating an object, and an electric conductor provided between the heating coil and the object to be heated, and the electric conductor is disposed when the object to be heated is disposed opposite the heating coil. The equivalent series resistance of the heating coil is made larger than that when the electric conductor is not provided, and the induction current flowing around the parallel to the current flow direction of the heating coil in the electric conductor A circulation current limiting means for limiting the distribution, wherein the circulation current limiting means is formed from the innermost part facing the heating coil of the electric conductor to the outermost part, Since the induced current in a portion where the induction current is often induced directly above the heating coil is limited, heat generated in the electric conductor is greatly reduced, thereby improving the heating efficiency of the object to be heated. In addition, since the area of the electric conductor can be expanded within a range where the heat generation of the electric conductor can be allowed, the equivalent series resistance of the heating coil can be increased and the buoyancy acting on the object to be heated can be further reduced.

  In the third invention, in particular, the outermost part of the electric conductor of the first or second invention is positioned outward from the outer diameter of the heating coil so that the outermost part of the electric conductor covers the heating coil. It has a substantially ring shape, and an induction current flows in the direction of canceling out the magnetic field that does not contribute to induction heating of the object to be heated, and a canceling magnetic field is generated, so that it does not contribute to induction heating of the object to be heated. The leakage magnetic field that affects other devices can be reduced.

  In the fourth invention, in particular, the circulating current limiting means of any one of the first to third inventions is provided radially from the center of the electric conductor, and the induced current is drawn in a concentric circle with the heating coil in the electric conductor. However, since the circulating current limiting means is provided radially from the center of the electric conductor, it is arranged in a direction substantially perpendicular to the large flow of induced current induced by the heating coil. Thus, the flow of the induced current can be hindered and easily restricted, and the heat generation of the electric conductor can be reduced.

  In the fifth aspect of the invention, in particular, the circulating current limiting means of the fourth aspect of the invention is provided in at least 12 directions, and the heat generation of the electric conductor can be greatly reduced.

  In the sixth invention, the circulating current limiting means according to any one of the first to fifth inventions is formed by a notch, an opening, a slit, or any combination thereof, and is generated from a heating coil. The direction and magnitude of the induced current induced in the electrical conductor by the magnetic field is forcibly changed, and the induced current flowing around the parallel to the heating coil current in the electrical conductor can be limited with a simple configuration. Thereby, the heat generated in the electric conductor can be reduced.

  In the seventh invention, in particular, a magnetic material having a high magnetic permeability is arranged in the vicinity of the heating coil according to any one of the first to sixth inventions, and the distribution of the induced current in the vicinity of the portion of the electric conductor facing the magnetic material. The local induction current limiting means for locally limiting is arranged, and the high magnetic permeability magnetic material causes the high-frequency magnetic field to concentrate locally in the vicinity or above the local electric conductor and the object to be heated. However, the induced current flowing locally can be effectively suppressed by the locally induced current limiting means, and the heat generation of the electric conductor can be suppressed.

  In an eighth aspect of the invention, in particular, a plurality of circulating current limiting means are provided so as to divide the inside of the electrical conductor of any one of the first to seventh aspects, and the width of the electrical conductor divided by the circulating current limiting means 0.5 to 10 mm, the induced current induced in the electric conductor is sufficiently suppressed, the heat generation of the electric conductor is sufficiently reduced, and the electric conductor is easy to process and can be manufactured stably. Can do.

  In the ninth aspect of the invention, in particular, the width of the circulating current limiting means in the vicinity of the center of the electric conductor of any one of the first to eighth aspects is 0.2 to 3 mm. If it becomes larger, the area of the electric conductor becomes smaller, the equivalent series resistance of the heating coil decreases, and the buoyancy acting on the object to be heated increases, but by setting the width of the circulating current limiting means to 0.2 to 3 mm, It is possible to stably manufacture an electric conductor that suppresses an induced current while suppressing an increase in buoyancy acting on an object to be heated.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a schematic cross-sectional view of a main part of the induction heating apparatus according to the first embodiment of the present invention, and FIG. 2 is a shape diagram of an electric conductor provided in the induction heating apparatus.

  In FIG. 1, a top plate 2 made of a heat-resistant ceramic, which is an insulator, is provided on an upper portion of a main body 1 constituting an outline of the induction heating device. Below the top plate 2, there is provided a heating coil 3 that is formed by winding a plurality of strands of bundled strands on a flat plate. The approximate dimensions of the heating coil 3 are an inner diameter of φ80 mm and an outer diameter of φ170 mm.

  In the vicinity of the heating coil 3, twelve rod-like ferrites 4 made of a highly magnetic material are provided radially. The ferrite 4 is disposed substantially in parallel with the surface of the heating coil 3, and in particular, both ends thereof are bent vertically upward toward the top plate 2 as shown in FIG.

  Reference numeral 5 denotes an object to be heated, which is made of aluminum, copper, or a low magnetic permeability material having a high electric conductivity substantially equal to or higher than these, and is induction-heated by the heating coil 3. The heating coil 3 sandwiches the top plate 2 in use. Is placed on the top plate 2 so as to oppose.

  6 is a thermistor serving as a temperature detecting means for detecting the temperature of the top plate 2, is in contact with the surface of the top plate 2 on the side of the heating coil 3, and is provided so as to be positioned substantially at the center of the heating coil 3. . The back surface of the top plate 2 with which the thermistor 6 abuts faces an opening 8 provided in an electric conductor 7 described later.

  The electric conductor 7 is formed of an aluminum coating film having a thickness of about 15 μm, and is joined to the surface of the top plate 2 on the heating coil 3 side by transfer. FIG. 2 is a diagram of the shape of the electric conductor 7 viewed from the heating coil 3 side. The electric conductor 7 is formed in a substantially donut shape, and the outermost part is larger than the outer diameter of the heating coil 3, that is, located outside. Further, the innermost part is also set smaller than the inner diameter of the heating coil 3, and specifically, it is about φ220 mm and about φ50 mm, respectively. Further, at least twelve slits 9 having a width of 1 mm, which serve as a circulating current limiting means, are provided radially from the center of the electric conductor 7 and 24 in the present embodiment.

  The slit 9 is smaller than φ80 mm, which is the innermost portion where the electric conductor 7 faces the heating coil 3, and has one end at the innermost φ50 mm of the electric conductor 7. That is, the slit 9 has a shape in which the innermost part of the electric conductor 7 is divided.

  The slit 9 has the other end at φ200 mm, which is larger than φ170 mm, which is the outermost portion where the electric conductor 7 faces the heating coil 3. That is, the slit 9 is configured from the innermost side where the electric conductor 7 faces the heating coil 3 to the outermost side.

  The electric conductor 7 is provided with an opening 8 at the center, and the opening edge is located inward from the inner end of the ferrite 4.

  The width of the electric conductor 7 divided by the slit 9 serving as the circulating current limiting means in the vicinity of the center of the electric conductor 7 is about 7 mm in the innermost part of the electric conductor 7. Further, the width of the slit 9 serving as the circulating current limiting means near the center of the electric conductor 7 is 1 mm as described above.

  In the electric conductor 7, a slit 10 serving as a local induction current limiting means is disposed in the vicinity of a portion facing the high permeability ferrite 4 provided in the vicinity of the heating coil 3 when viewed from the electric conductor 7. The slit 10 is located at φ150 mm-φ190 mm from the center of the heating coil 3 and has a length of 20 mm and a width of 1 mm.

  A part 11 of the electric conductor 7 is as thin as about 2 mm in width and has a portion 11 having a larger thermal resistance than the other parts, and is electrically connected to the lead wire 12 by a conductive seal or the like. Furthermore, the lead wire 12 is connected to a commercial power source potential or a potential obtained by rectifying a commercial power source input by an inverter (not shown) that supplies a high-frequency current to the heating coil 3 via the capacitor 13 or the ground.

  The operation of the induction heating apparatus having the above configuration will be described.

  The heating coil 3 is supplied with a high-frequency current of about 70 kHz. The heating coil 3 generates a magnetic field when a high-frequency current is supplied, but there is a ferrite 4 which is a high permeability material below the heating coil 3, and the magnetic field concentrates on the ferrite 4, so that the magnetic field is heated. 5 can be prevented from bulging to the opposite side. Even if the ferrite 4 is constituted by combining a plurality of ferrite cores, the same effect can be obtained.

  On the other hand, since the magnetic field emitted upward from the heating coil 3 is linked to the electric conductor 7, an induced current is induced in the electric conductor 7. At this time, the frequency of the induced current is about 70 kHz, and the penetration depth δ of the induced current when the electric conductor 7 is made of aluminum is about 300 μm. In the present embodiment, since the electric conductor 7 is about 15 μm, which is sufficiently thinner than the penetration depth of the induced current, the magnetic field from the heating coil 3 cannot be shielded, and the magnetic field penetrates and passes through the electric conductor 7. And it is guide | induced to the to-be-heated material 5 direction. Since both end portions of the ferrite 4 are bent vertically upward, the ferrite 4 has an effect of efficiently inducing a magnetic field in the direction of the object 5 to be heated.

  The magnetic field emitted upward from the heating coil 3 reaches the object to be heated 5 as a combined magnetic field of the magnetic field that has permeated and passed through the electric conductor 7 and the magnetic field that has passed through the slits 9, 10 and the opening 8. The induced current induced in the object to be heated 5 is generated by this combined magnetic field. Therefore, the presence of the electric conductor 7 changes the induced current distribution as compared with the case where the electric conductor 7 is not provided.

  Further, the total heating area to be induction-heated as viewed from the heating coil 3 is the area to be heated on the slits 9 and 10 and the opening 8 that are not covered by the electric conductor 7 as viewed from the heating coil 3. The area to be heated 5 of the portion covered with the electric conductor 7 when viewed from the heating coil 3 is further added to the five areas. The electric conductor 7 has an action of strengthening the magnetic coupling between the heating coil 3 and the article 5 to be heated. By increasing the total heating area viewed from the heating coil 3, the equivalent series resistance of the heating coil 3 is increased, and the current flowing through the heating coil 3 when obtaining the same output can be reduced. The acting buoyancy is reduced.

  FIG. 3 shows the relationship between the thickness of the electrical conductor 7 and the equivalent series resistance of the heating coil 3 when the aluminum pan is the object to be heated 5 and measured in the same position arrangement as in the heated state (shown in FIG. 3A). ) And the case where there is no object to be heated 5 (shown in FIG. 3B), an example of the measurement result is shown. However, the high frequency current frequency of the heating coil 3 is about 70 kHz.

  As shown in FIG. 3B, when there is no object to be heated 5, the equivalent series resistance increases monotonously from 0 (no state) to 10 μm in the thickness of the electric conductor 7 and monotonous when the thickness of the electric conductor 7 is 10 μm or more. is decreasing. In the region where the penetration depth δ of the induced current in aluminum exceeds about 300 μm, the equivalent series resistance has a substantially constant value.

  This is presumably because the electric conductor 7 is the object to be heated instead of the article 5 to be heated. When the electrical conductivity of the electrical conductor 7 made of aluminum is σ, the thickness is t, and the penetration depth of the induced current in the electrical conductor 7 is δ, when the thickness of the electrical conductor 7 is smaller than δ, the electrical conductor 7 The high-frequency resistance Rs (hereinafter simply referred to as skin resistance) viewed from the induced current flowing through the skin is defined as Rs = 1 / (t · σ). That is, the skin resistance is inversely proportional to the thickness t. When the thickness of the electric conductor 7 is larger than δ, it is defined by Rs = 1 / (δ · σ), and the skin resistance is a constant value.

  When the thickness of the electric conductor 7 is 0 (no state) to 10 μm, the thickness of the electric conductor 7 is sufficiently small, and the skin resistance is theoretically very large. That is, it becomes a state close to an insulator, and the magnetic field generated from the heating coil 3 easily passes through, so that the state is almost the same as when there is no electric conductor 7. The equivalent series resistance of the heating coil 3 is substantially the same as the high-frequency resistance of the heating coil 3 without the object to be heated 5 and the electric conductor 7 and the combined resistance such as the high-frequency resistance of the nearby ferrite 4 and is a small value. However, it increases monotonically as the thickness of the electrical conductor 7 increases. In the region where the thickness of the electric conductor 7 is not less than 10 μm and not more than 300 μm, the equivalent series resistance of the heating coil 3 also monotonously decreases in an inversely proportional relationship with the thickness of the electric conductor 7 due to the influence of the skin resistance reduction of the electric conductor 7. In the region where the thickness of the electric conductor 7 is 300 μm or more, the skin resistance of the electric conductor 7 is constant, so that the equivalent series resistance of the heating coil 3 is also substantially constant.

  On the other hand, when the object to be heated 5 is present as shown in FIG. 3A, the equivalent series resistance increases monotonously and has a peak when the thickness of the electric conductor 7 is 0 to 15 μm. The equivalent series resistance monotonously decreases and becomes the minimum until the thickness of the electric conductor 7 reaches 200 μm. The equivalent series resistance again monotonously increases until the thickness of the electric conductor 7 is 1200 μm.

  The peak of the equivalent series resistance of the heating coil 3 when the thickness of the electric conductor 7 is 15 μm is the same as in FIG. 3B when the object to be heated 5 is not present, and the thickness of the electric conductor 7 is sufficiently small. This is considered to be caused by a balance between a region in which the skin resistance is high and the region regarded as an insulator, and a region in which the thickness increases to some extent and the electrical resistance skin resistance decreases.

  From another viewpoint, as described above, the effect of increasing the apparent total induction heating area due to the magnetic field penetrating and passing through the electric conductor 7 is maximized when the thickness of the electric conductor 7 is 15 μm. I can say that.

  Further, in the region where the thickness of the electric conductor 7 is 15 μm or more, the thickness of the electric conductor 7 increases, so that the skin resistance of the electric conductor 7 decreases monotonously. Furthermore, since the induced current easily flows inside the electric conductor 7, the magnetic field generated from the heating coil 3 is shielded to some extent, and the total heating area viewed from the heating coil 3 is reduced. That is, the equivalent series resistance of the heating coil 3 is reduced.

  On the other hand, since the electric conductor 7 that is in a state in which the induced current easily flows with a small skin resistance is disposed at a position close to the heating coil 3, the magnetic coupling between the heating coil 3 and the electric conductor 7 is strong, An effect of increasing the equivalent series resistance of the coil 3 also occurs.

  The sufficiently thick electric conductor 7 shields the magnetic field generated from the heating coil 3, but a part of the magnetic field bypasses the electric conductor 7 and induction heats the side opposite to the heating coil 3 of the electric conductor 7. Even if the skin depth of 7 exceeds about 300 μm, the equivalent series resistance of the heating coil 3 increases. Therefore, it is estimated that the thickness of the electric conductor 7 is 200 μm and the equivalent series resistance of the heating coil 3 has a minimum point. However, if the thickness of the electric conductor 7 is equal to or greater than a certain value, the equivalent series resistance of the heating coil 3 becomes a substantially constant value.

  As a result of detailed studies, the inventors have found a point where the thickness of the electric conductor 7 is about 15 μm and the equivalent series resistance of the heating coil 3 is maximized. Therefore, the current flowing through the heating coil 3 when obtaining the same output can be reduced, and the buoyancy acting on the article to be heated 5 is also reduced. According to the experiments by the inventors, if the equivalent series resistance of the heating coil 3 is the same regardless of whether the electric conductor 7 is thinner or thicker than the penetration depth of the induction current, It was confirmed that a buoyancy reduction effect was obtained.

  Moreover, since the equivalent series resistance of the heating coil 3 is almost uniquely determined with respect to the target buoyancy as the induction heating device, the thickness of the electric conductor 7 is changed to obtain a predetermined heating coil 3 equivalent series resistance. It is possible. Accordingly, when buoyancy acting on the object to be heated 5 is accepted to some extent, in the heating configuration of the present embodiment, a predetermined buoyancy is obtained by setting the thickness of the electric conductor 7 to be smaller or larger than 15 μm. An induction heating device is obtained.

  Conventionally, there has been no idea of providing a very thin electric conductor 7 through which an induction current can flow between the object to be heated 5 and the heating coil 3 when performing induction heating.

  In the conventional idea, there is an example in which a very thin electric conductor 7 is provided and connected to a constant potential in order to suppress a leakage current. However, in such a case, since it has been known that heat is generated when an induced current is passed through the electric conductor 7, the equivalent series resistance of the heating coil 3 is not changed so as to suppress the induced current and the heat generated in the electric conductor 7. The material and shape of the electric conductor 7 were designed. Accordingly, in the extension of the conventional idea, an effect of inducing an induced current in the very thin electric conductor 7 to change the distribution of the induced current flowing in the object to be heated 5, or an effect of increasing the equivalent series resistance of the heating coil 3, Or the effect of reducing the buoyancy acting on the article 5 to be heated was not obtained.

  Furthermore, since the electric conductor 7 is thin, the high-frequency magnetic field generated from the heating coil 3 penetrates and passes through the electric conductor 7. That is, a large energy that generates a repulsive magnetic field that does not allow the magnetic field from the heating coil 3 to pass through, that is, a large induced current is not generated inside the electric conductor 7, compared with a case where the thickness of the electric conductor 7 is large. Thus, loss due to heat generation of the electric conductor 7 can be reduced, and cooling in the vicinity of the heating coil 3 can be facilitated. Moreover, it is possible to increase the electric power transmitted to the article to be heated 5 and improve the heating efficiency.

  The slit 9 provided in the electric conductor 7 is a circulating current limiting unit that suppresses an induced current in the electric conductor 7 that is induced by the magnetic field generated from the heating coil 3 and flows in the rotating direction of the heating coil 3. FIG. 4 is a diagram showing the induced current flowing inside the electric conductor 7, when there is no slit 9 (shown in FIG. 4 (a)), when there is one slit 9 (shown in FIG. 4 (b)), the slit When 9 is configured at only one location from the innermost side to the outermost side of the electrical conductor 7 (shown in FIG. 4C), the slit 9 is configured at 24 locations from φ90 mm to φ160 mm of the electrical conductor 7. In the case where the slit 9 is composed of 24 locations extending from the innermost part of the electric conductor 7 to φ130 mm (shown in FIG. 4 (e)), the slit 9 is formed in the present embodiment. As in the embodiment, the case where 24 locations are formed from the innermost part of the electric conductor 7 over φ200 mm (shown in FIG. 4 (f)) is shown.

  In FIG. 4, in order to simplify the description, the electric conductor 7 is shown in a shape without the slit 10. In the figure, the dotted line indicates the position of the heating coil 3.

  As shown in FIG. 4A, when there is no slit 9, the magnetic field generated from the heating coil 3 generates a concentric induction current in a large loop inside the electric conductor 7. This induced current is distributed so as to flow largely in an intermediate portion between the inner peripheral portion and the outer peripheral portion of the heating coil 3, and generates large heat.

  In the case of FIG. 4B, the electric conductor 7 is partially narrowed by the slit 9 that exists only at one place. As in FIG. 4A, a large induced current is induced in the direction of the thin line arrow in the portion facing the heating coil 3 directly above the electric conductor 7. The induced current that is about to flow directly above the heating coil 3 is limited by the slit 9, but the direction of flow is changed and flows in the outer circumferential direction along the slit 9. The induced current whose direction of flow is changed is concentrated on a part of the electric conductor 7 narrowed by the slit 9. Accordingly, heat generation in the portion narrowed by the slit 9 of the electric conductor 7 increases, and the temperature rise locally increases.

  In the case of FIG. 4C, the large induced current induced immediately above the heating coil 3 changes its direction along the slit 9 and flows in the direction of the thin line arrow along the inner and outer peripheral portions of the electric conductor 7. As a result, the induced current flows in a concentrated manner on the inner and outer peripheral portions of the electric conductor 7, so that heat generation increases.

  Even if the shape of the electric conductor 7 is smaller than that of the heating coil 3, that is, the inner diameter of the electric conductor 7 is larger than the inner diameter of the heating coil 3, or the outer diameter of the electric conductor 7 is smaller than the outer diameter of the heating coil 3. Due to the difference between the induced currents induced at the inner periphery and the outer periphery, heat flows from the larger induced current to the smaller induced current. In addition, the area of the electric conductor 7 is reduced, the equivalent series resistance of the heating coil 3 is reduced, and the buoyancy acting on the article to be heated 5 is increased.

  In the case of FIG. 4 (d), since the plurality of slits 9 are arranged, the induced current induced is small, but the electric conductor 7 has a partially continuous ring shape directly above the heating coil 3, The induced current flows through the ring part. Accordingly, the heat generation is also large in this case.

  The case of FIG. 4E is the same as that of FIG.

  However, in the case of the present embodiment of FIG. 4F, the electrical conductor 7 immediately above the heating coil 3 is divided into a plurality of parts, and the induced current amount is small. Therefore, even if the induced current whose direction is changed by the slit 9 tries to flow to the outer peripheral portion of the electric conductor 7 as shown in FIG. Further, since no continuous ring is formed immediately above the heating coil 3, the concentration of induced current does not occur.

  A slit 9 serving as a plurality of circulating current limiting means is formed over the opposing electrical conductors 7 immediately above the heating coil 3 where a large induced current is induced, and a large heat generation reduction effect is achieved by suppressing the induced current. can get.

  In addition, since the slits 9 are provided radially from the center of the electric conductor 7 so as to be substantially perpendicular to the circulating induced current, the flow of the induced current is obstructed and easily restricted, and the electric conductor 7 generates heat. It becomes possible to reduce.

  In the present embodiment, the width formed by the slit 9 near the center of the electric conductor 7 and the width of the slit 9 itself are about 7 mm and 1 mm, respectively. If the width of the electric conductor 7 is increased, the amount of induced current induced in the circumferential direction is increased and heat generation is increased. Further, if the width of the slit 9 itself is increased, the area of the electric conductor 7 is reduced, the heating coil 3 equivalent series resistance is lowered, and the buoyancy acting on the object to be heated 5 is increased.

  Inventors have practically determined that the width of the electric conductor 7 and the width of the slit 9 are practically limited to a predetermined value to balance heat generation and buoyancy, and to realize stable manufacturing. .

  In the present embodiment, the slit 9 extending from the opening 8 in the central portion of the electric conductor 7 to φ200 mm is provided, but the slit 9 is not provided on the outermost part of the electric conductor 7, and a large substantially ring shape is provided. It has become.

  The magnetic field generated from the heating coil 3 includes a component directed to the object to be heated 5 and a component that does not contribute to induction heating of the object to be heated 5 and is radiated to the other air. A magnetic field of a component that does not contribute to induction heating of the object to be heated 5 has an influence on other devices, and its radiation level is limited by the radio wave method or the like.

  In the present embodiment, the induced current flows in the direction of canceling out the magnetic field that does not contribute to induction heating of the object to be heated 5 in the substantially ring-shaped portion at the outermost part of the electric conductor 7, and generates a canceling magnetic field. Can be reduced.

  Further, when the electric conductor 7 has a continuous ring shape and the ring-shaped portion faces the heating coil 3, the characteristics greatly change depending on the size of the object to be heated 5. For example, since the inductance of the heating coil 3 including the object to be heated 5 is affected by the ring-shaped electric conductor 7, the inductance varies greatly depending on the size of the object to be heated 5, making inverter design difficult.

  However, in the present embodiment, the outermost substantially ring-shaped portion of the electric conductor 7 is outside the outer diameter of the heating coil 3 due to the slit 9, so that the inductance of the heating coil 3 including the article to be heated 5 and the like The characteristics are not greatly affected, the magnetic-shielding effect is almost, the influence on the inverter design is small, and the design becomes easy.

  The portion corresponding to the portion directly above the ferrite 4 is a portion that is particularly easily locally heated by the magnetic field concentration effect of the ferrite 4. However, as shown in FIG. 2, since the slit 10 serving as the local induced current limiting means is provided on the outer peripheral portion of the electric conductor 7, the induced current is effectively suppressed, and the heat generation of the electric conductor 7 is suppressed. It will be. As a result, it is possible to increase the heating efficiency with less loss.

  Further, since the slit 10 serving as the local induction current limiting means is provided in a limited portion of the electric conductor 7, the change in the equivalent series resistance of the heating coil 3 and the increase in buoyancy acting on the object to be heated 5 are suppressed. Can do.

  Further, a part 11 of the electric conductor 7 is as thin as about 2 mm in width, and a part 11 having a larger thermal resistance than the other part extends, and is electrically connected to the lead wire 12 with a conductive seal or the like. Further, since the lead wire 12 is connected to the commercial power supply potential or the ground obtained by rectifying the commercial power supply input to the commercial power supply potential or an inverter (not shown) for supplying a high frequency current to the heating coil 3 via the capacitor 13, the heating coil The leakage current leaking from 3 to the user can be reduced.

  Since the electric conductor 7 having a role of suppressing buoyancy is electrically connected to a constant potential, it is possible to suppress leakage current at the same time. In addition, since it is not necessary to separately provide a leakage current suppressing configuration between the heating coil 3 and the object to be heated 5, the distance between the heating coil 3 and the object to be heated 5 can be reduced, and heating efficiency can be improved. become. Furthermore, since the connection between the electric conductor 7 and the constant potential portion is performed through the portion 11 having a large thermal resistance, the influence of the heat generated by the electric conductor 7 on other portions can be suppressed.

  Further, since the electric conductor 7 is joined to the surface of the top plate 2 on the heating coil 3 side by transfer, it is easy to transmit the heat generated by the electric conductor 7 to the top plate 2 by heat conduction. The same applies to the object to be heated 5 placed on the upper part. Thus, an increase in loss due to heat generation of the electric conductor 7 is transmitted to the object to be heated 5 as a result, and the temperature of the electric conductor 7 can be suppressed and the heating efficiency of the object to be heated 5 can be increased.

  In the present embodiment, the electric conductor 7 is formed by transferring it to the top plate 2, but the present invention is not limited to this, and the electric conductor 7 may be formed of a thin nonmagnetic plate having a thickness of about 1 mm. Moreover, you may join the electrical conductor 7 and the top plate 2 by spraying or vapor deposition, for example. Further, the electric conductor 7 may be made of copper instead of aluminum, and the top plate 2 may be plated. Further, fine irregularities may be formed by surface processing of the top plate 2 to enhance the bonding property between the electric conductor 7 and the top plate 2. What is necessary is just to select the suitable joining means so that it may become the required thickness while employ | adopting the material which becomes easy to make a thing and becomes low cost for the electrical conductor 7. FIG.

  Moreover, the electrical conductor 7 is easily joined to the top plate 2 in advance, so that it can be easily handled at the time of assembly in a factory or the like.

  As described above, the induction heating device according to the present invention can heat an object to be heated formed of a material having low magnetic permeability and high electrical conductivity, reduce buoyancy acting on the object to be heated, and It can be applied to various induction heating devices such as induction heating water heaters and induction heating irons that heat high electrical conductivity and low magnetic permeability materials such as aluminum and copper, as well as induction heating cookers.

Main part schematic sectional drawing of the induction heating apparatus in Embodiment 1 of this invention Shape of electrical conductor as seen from the heating coil side of the induction heating device (A) The figure which shows the correlation of the electrical conductor thickness when the to-be-heated object of the same induction heating apparatus exists, and the equivalent series resistance of a heating coil (b) The electrical conductor thickness when there is no to-be-heated object, and the equivalent series of a heating coil Diagram showing resistance correlation (A)-(f) The figure which shows the induction electric current which flows through the inside of various electric conductors including the electric conductor used for the induction heating apparatus. The perspective view which shows the structure of the heating coil of the conventional induction heating apparatus, and its periphery Cross section of the main part of the induction heating device The figure which shows the correlation of the equivalent series resistance and buoyancy of the heating coil of the same induction heating device The figure which shows the correlation of the equivalent series resistance of the heating coil of the same induction heating apparatus, and a heating coil electric current value The figure which shows the correlation of the thickness of the electric conductor of the same induction heating apparatus, and the buoyancy which acts on a to-be-heated material Plan view of the electrical conductor of the induction heating device

Explanation of symbols

1 Body 2 Top plate 3 Heating coil 4 Ferrite (magnetic material)
5 Object to be heated 6 Thermistor (temperature detection means)
7 Electrical conductor 8 Opening 9 Slit (Circular current limiting means)
10 Slit (Locally induced current limiting means)

Claims (9)

A top plate on which an object to be heated made of aluminum, copper, or a low magnetic permeability material having an electric conductivity substantially equal to or higher than these is placed, and heating for inductively heating the object to be heated provided below the top plate A coil, and an electric conductor provided between the heating coil and the object to be heated, and the electric conductor is caused by the action of an induced current induced in the electric conductor by the heating coil. And a buoyancy reduction function for reducing the buoyancy acting on the heated object due to the repulsive force of the magnetic field generated from the magnetic field generated by the induced current induced in the heated object, and in the electric conductor Circulating current limiting means for limiting the distribution of induced current flowing around and parallel to the current flow direction of the heating coil is provided, and the circulating current limiting means is Induction heating apparatus from the most inner facing of the heating coil is formed over the outermost portion. A top plate on which an object to be heated made of aluminum, copper, or a low magnetic permeability material having an electric conductivity substantially equal to or higher than these is placed, and heating for inductively heating the object to be heated provided below the top plate A coil, and an electric conductor provided between the heating coil and the object to be heated, and the electric conductor is equivalent to the heating coil when the object to be heated is disposed facing the heating coil. A series resistance is made larger than that when the electric conductor is not provided, and a circulating current that restricts the distribution of the induced current flowing around the parallel direction of the electric current flowing through the heating coil in the electric conductor. An induction heating apparatus comprising a limiting means, wherein the circulating current limiting means is formed from the innermost portion facing the heating coil of the electric conductor to the outermost portion. The induction heating apparatus according to claim 1 or 2, wherein the outermost part of the electric conductor is positioned outward from the outer diameter of the heating coil. The induction heating device according to any one of claims 1 to 3, wherein the circulating current limiting means is provided radially from the center of the electric conductor. The induction heating apparatus according to claim 4, wherein the circulating current limiting means is provided in at least 12 directions. The induction heating device according to any one of claims 1 to 5, wherein the circulating current limiting means is formed by a notch, an opening, a slit, or any combination thereof. 7. A magnetic material having high permeability is arranged in the vicinity of the heating coil, and local induction current limiting means for locally limiting the distribution of induced current is arranged in the vicinity of the portion of the electric conductor facing the magnetic material. The induction heating device according to any one of the above. A plurality of circulating current limiting means is provided so as to divide the inside of the electric conductor, and the width of the electric conductor divided by the circulating current limiting means is 0.5 to 10 mm. The induction heating apparatus described. The induction heating apparatus according to any one of claims 1 to 8, wherein a width of the circulating current limiting means in the vicinity of the center of the electric conductor is 0.2 to 3 mm.

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