JP2005149976A - Induction heating cooker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an induction heating cooker easy to use for an object to be heated of which the pan bottom like a recessed warpage pan is recessed and high in convenience as well as high in thermal efficiency and reduced in buoyancy even if the object to be heated is one like aluminum having high conductivity and low magnetic permeability. <P>SOLUTION: The cooker is structured to provide a thermal connecting means 23 to increase thermal connection between an electric conductor 17 and a top plate 12, so that the heat generated from the conductor 17 is effectively transferred to an object to be heated 13 and an adverse effect of generated heat onto a heating coil 14 can be reduced, then the thermal efficiency can be enhanced. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an induction heating apparatus that cooks using a pan made of a material having a low magnetic permeability and high electrical conductivity such as aluminum or copper as an object to be heated. In particular, the pot that is an object to be heated is lifted by a high-frequency magnetic flux. It relates to what was prevented.

  An induction heating cooker that generates a high-frequency magnetic field with an induction heating coil and heats an object to be heated such as a pan with eddy current due to electromagnetic induction has been proposed (for example, a patent) Reference 1).

  FIG. 4 is a cross-sectional view of a conventional induction heating cooker. As shown in the figure, a main body 1 constituting the outer shell of the induction heating apparatus, a top plate 2 made of an insulator such as a ceramic material or crystal glass having a thickness of 4 mm provided on the upper portion of the main body 1, and a top plate 2 And an induction heating unit 5 having a heating coil 4 provided in the lower part of the top plate 2. The heating coil 4 is supplied with a high-frequency current from a drive circuit 6 having an inverter to generate a high-frequency magnetic field, and applies a high-frequency magnetic field to the article 3 to be heated to induce heating.

  In such a conventional induction heating cooker, the repulsive force that tries to move away from the heating coil 4 to the bottom of the heated object 3 due to the interaction between the current induced in the bottom of the heated object 3 and the current of the heating coil 4. Occurs. When the object to be heated 3 is made of a high magnetic permeability material such as iron having a certain degree of resistivity, the repulsive force is relatively small because the current value required to obtain a desired heating output may be small. . In addition, since the magnetic flux is absorbed by the object to be heated 3 in iron or the like, there is no possibility that the object to be heated 3 will be lifted or displaced due to the magnetic attraction.

  On the other hand, when the object to be heated 3 is made of a material having a low magnetic permeability and high electrical conductivity such as aluminum or copper, the current to be supplied to the heating coil 4 is increased to obtain a desired heating output. It is necessary to induce a large current in the object 3. As a result, the resilience increases. Further, since the magnetic attraction force does not act on the aluminum heated object 3 as in the case of a high permeability material such as iron, the heated object 3 is heated by the action of the magnetic field of the heating coil 4 and the magnetic field of the induced current. A large force works in the direction away from the coil 4. This force acts as buoyancy on the article 3 to be heated. When the weight of the object to be heated 3 is light, the object to be heated 3 may be lifted and moved from the mounting surface of the top plate 2 due to this buoyancy. This tendency is conspicuous in the case of an object to be heated using aluminum having a specific gravity smaller than that of copper.

  FIG. 5A is a view of the direction of the current flowing through the heating coil 4 as viewed from the heated object 3 side, and FIG. 5B is a diagram illustrating the induction of the heated object 3 based on the current flowing through the heating coil 4. It is the figure which looked at the eddy current which arises and flows from the same direction as Fig.5 (a). As shown in FIG. 5, the eddy current flowing through the article to be heated 3 has a loop shape which is opposite to the current flowing through the heating coil 4 and has substantially the same shape. Therefore, the two annular currents are in the same state as two permanent magnets having substantially the same cross-sectional area as the area of the heating coil 4 placed with the same type of poles, for example, N and N poles facing each other. Become. As a result, a large repulsive force is generated between the object to be heated 3 and the heating coil 4.

  This phenomenon is remarkable when the material of the article to be heated 3 is a substance having high electrical conductivity such as aluminum or copper. On the other hand, even with the same low magnetic permeability material, nonmagnetic SUS is a material having a lower electrical conductivity than aluminum or copper, so that sufficient heat generation can be obtained even with a small current flowing through the heating coil 4. Therefore, the eddy current flowing through the object to be heated 3 is also small, and therefore the magnetic field induced in the object to be heated 3 is small.

As described above, when the aluminum object to be heated 3 is heated in the induction heating cooker, buoyancy is exerted on the object to be heated 3, and the object to be heated 3 is lifted, and cooking may not be sufficiently performed. Therefore, a method for detecting floating was considered. For example, the weight sensor is used to detect the floating or movement of the article to be heated 3 (see, for example, Patent Document 2 or 3), or the magnetic sensor is used to detect the position of the article to be heated 3 (for example, , See Patent Document 4). And when buoyancy more than predetermined acts on the to-be-heated object 3, or when it detects that the to-be-heated object floated or moved, heating power is suppressed so that it may not float more or may not move. Alternatively, a method of cooking by stopping the heating operation itself has been performed.
JP 2002-75620 A JP 61-128492 A JP-A-62-276787 JP-A-61-71582

  However, in the conventional configuration, when the object to be cooked is accommodated in the aluminum object to be heated 3 and cooking is performed, it is possible to obtain sufficient thermal power by detecting the floating of the object to be heated and suppressing the heating power. In some cases, the cooking operation is sometimes interrupted.

  For example, when heating an object to be heated with a total weight of 500 g in an aluminum snow pan with a weight of 300 g, according to FIG. 6, the buoyancy of the pot and the cooked item (water) is about 850 W. The total weight exceeds 500g. Therefore, it becomes difficult for the pot to float and to be heated with more input power. In the above prior art, for example, when an aluminum pan is detected, the input power is suppressed to, for example, 800 W, which is equal to or lower than the input power that the pan floats, so that the pan does not float. However, according to experiments by the inventors, it was difficult to bring the above 300 cc of water into a boiling state even when heated with an input power of 800 W. Therefore, the induction heating cooker that can heat the aluminum pan has a problem that the heating performance is extremely low.

  In order to solve the above problem, prior to the present invention, a configuration in which an electrical conductor is provided in close contact with the top plate between the heating coil and the top plate was examined. In this configuration, since the magnetic field generated from the heating coil is linked to the electric conductor and the object to be heated, an induced current is generated in both. The equivalent series resistance of the heating coil is increased by the action of the magnetic field generated by the induced current induced in the electric conductor and the magnetic field generated by the induced current induced in the object to be heated. When the equivalent series resistance is increased, the same power can be supplied to the object to be heated with a small current, and as a result, buoyancy is reduced. The effect of reducing the buoyancy increases as the area or thickness of the electric conductor is increased and the equivalent series resistance of the heating coil is increased. Here, the equivalent series resistance means the input impedance of the heating coil measured using a frequency in the vicinity of the heating frequency in the same arrangement as the heated object and the electric conductor in the heated state.

  As described above, by using an electric conductor, it is practically possible to induction-heat an object to be heated that has a high electrical conductivity such as aluminum and is made of a low magnetic permeability material. .

  However, there is a problem that the heating efficiency, that is, the thermal feeling is slightly inferior to the case of heating an iron object.

  In actual use, the floating of the object to be heated cannot be ignored at all, and the total weight of the pot to be heated and the cooked object is limited to be heavier than a certain weight. In addition, the pan is rarely flat in the bottom surface, and usually has a slight warp (a concave warped pan having a concave bottom, that is, convex toward the inside). Is used). 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.

  Among various configurations having a buoyancy reduction effect, in order to improve the heating efficiency and further relax the weight limit due to buoyancy, the area of the electric conductor is increased, that is, the heat transfer area to the top plate is increased. It was considered practical to increase the heat input to the coil and increase the equivalent series resistance of the heating coil. Therefore, it has been considered that the size of the opening in the central portion of the electric conductor corresponding to the heating coil is limited to the space necessary for the temperature detecting means for contacting the top plate and detecting the temperature. Thereby, the area of the electrical conductor was increased and the buoyancy could be reduced. However, in this configuration, when a warped pan is used, the electric conductor is less likely to enter the pan near the center of the heating coil and preferentially enters the electric conductor. Becomes abnormally fast. In addition, since there is a space between the pan bottom and the top plate in the concave portion, the heat of the electric conductor is not easily transferred to the pan bottom via the top plate, so that the temperature rises quickly. When the temperature of the electric conductor becomes high, the output of the heating coil is reduced to suppress the heat generation of the electric conductor, and the high temperature heat of the electric conductor does not adversely affect the heating coil. Therefore, when the temperature rise rate is fast, the output of the heating coil is controlled from the early stage, and there is a problem that cooking takes too much time or cooking cannot be performed. Therefore, the electric conductor cannot be provided for a predetermined distance from the center of the electric conductor, and there is a problem that the heat transfer area cannot be increased and the buoyancy cannot be reduced accordingly.

  The present invention solves the above-mentioned conventional problems, and even in the case of a heated object having a high electrical conductivity and a low magnetic permeability such as aluminum, the thermal efficiency is further increased, the buoyancy is further reduced, and the concave warpage pan An object of the present invention is to provide a highly convenient induction heating cooker that is easy to use even for a heated object having a concave pot bottom.

  In order to solve the above-described conventional problems, an induction heating apparatus according to the present invention includes a main body constituting an outer shell, a top plate provided on an upper portion of the main body on which an object to be heated is placed, and high electrical conductivity such as aluminum. And a heating coil for induction heating the object to be heated made of a low magnetic permeability material from below the top plate, and the object to be heated by a magnetic field generated between the heating coil and the top plate. And an electrical conductor that reduces the buoyancy that is generated, and includes a thermal connection means that facilitates the heat of the electrical conductor to be transmitted to the top plate.

  Thereby, the heat generated in the electric conductor is effectively transmitted to the object to be heated, and the adverse effect of the generated heat on the heating coil can be reduced, and the thermal efficiency can be improved.

  In addition, the induction heating device of the present invention is provided with a plurality of electric conductors stacked so that the projected area of the thermal connection means is larger than the projected area of the electric conductors on the top plate side of the plurality of electric conductors, It is configured to contact directly or indirectly.

  This makes it easier for the electric conductor to act on the magnetic field, so that even if the thermal connecting means is made of a conductor, the effect of the magnetic field on the thermal connecting means is reduced. In addition to preventing heat generation, the heat generated by the electric conductor due to the increase in the heat transfer area is effectively transmitted to the object to be heated, and the adverse effect of the generated heat on the heating coil can be reduced, and the thermal efficiency can be improved. Further, the effective area and thickness of the thermal connection means and the electric conductor are increased, that is, the equivalent series resistance is increased, so that buoyancy can be further reduced.

  The induction heating device of the present invention can further improve thermal efficiency and reduce buoyancy.

  1st invention is the said to-be-heated object which consists of the main body which comprises an outer shell, the top plate provided in the upper part of the said main body which mounts to-be-heated material, and high electrical conductivity and low magnetic permeability materials, such as aluminum A heating coil for induction heating from below the top plate, and an electric conductor provided between the heating coil and the top plate for reducing buoyancy generated in the heated object by a magnetic field generated by the heating coil. By providing a thermal connection means that makes it easy for the heat of the electric conductor to be transferred to the top plate, the heat generated by the electric conductor is effectively transferred to the object to be heated and the adverse effect of the generated heat on the heating coil is also reduced. And thermal efficiency can be improved.

  In the second invention, in particular, the thermal connection means of the first invention is provided on the top plate side of the electrical conductor, and the projected area of the electrical conductor is made larger than the projected area of the thermal connection means. Due to the configuration in which the top plate is in direct or indirect contact with each other, the magnetic field easily acts on the electric conductor and the magnetic field on the thermal connecting means is reduced, so that the thermal connecting means has conductivity. However, while preventing the temperature from rising suddenly, the heat generated by the electrical conductor is effectively transferred to the object to be heated by increasing the heat transfer area by the thermal connection means, and the adverse effect of the generated heat on the heating coil can be reduced, Thermal efficiency can be improved. Further, the total effective area and effective thickness of the thermal connecting means and the electric conductor are increased, that is, the equivalent series resistance is increased, so that buoyancy can be further reduced.

  According to a third aspect of the invention, in particular, the thermal connecting means and the electrical conductor have an opening at the center, and the thermal connecting means has a portion protruding inward from the opening of the electrical conductor. The thermal connection means can improve the thermal efficiency and reduce the buoyancy most efficiently by increasing the area at the central opening.

  According to the fourth aspect of the invention, in particular, the thermal connection means is made thinner than the thickness dimension of the electric conductor, so that the thermal connection means is more difficult to be induction-heated than the electric conductor, and the thermal connection means is abrupt. It is possible to effectively prevent the temperature from rising.

  The fifth aspect of the invention is particularly any one of the second to fourth aspects of the invention, wherein the thermal connection means is made of a material having a high thermal conductivity equal to or higher than that of aluminum, so that the heat transfer from the electric conductor to the object to be heated. Efficiency can be improved and thermal efficiency can be further improved.

  According to a sixth aspect of the present invention, the thermal connection means is made of an electric conductor and has a function of reducing buoyancy generated in an object to be heated, so that the total effective area and effective thickness of the thermal connection means and the electric conductor are reduced. The buoyancy can be further reduced since the equivalent series resistance is increased.

  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, FIG. 2 (a) (b) shows sectional drawing and a top view of the induction heating apparatus in the 1st Embodiment of this invention. As shown in FIG. 1, a main body 11 that forms an outline of the induction heating device, a top plate 12 made of an insulator such as a ceramic material or crystal glass having a thickness of 4 mm, for example, provided on the top of the main body 11, and the top plate 12 includes an object to be heated 13 such as a pan placed on 12 and an induction heating unit 15 having a heating coil 14 provided below the top plate 12. The heating coil 14 is supplied with a high-frequency current from a drive circuit 16 having an inverter to generate a high-frequency magnetic field, and applies a high-frequency magnetic field to the article 13 to be heated to induce heating. This object to be heated is a material having high electrical conductivity and low magnetic permeability such as aluminum, aluminum alloy, copper, and copper alloy. The electric conductor 17 is fixed on the support 18, and the support 18 is fixed to the induction heating unit 15. The electric conductor 17 has an annular shape having an opening 19 at the center, and is disposed on the lower surface of the top plate 12 so as to face the heating coil 14. Similarly to the object to be heated 13, the electric conductor 17 is made of a material having high electrical conductivity and low magnetic permeability such as aluminum, aluminum alloy, copper, copper alloy or carbon. In this embodiment, aluminum having a thickness of 1 mm is used. This is for the following reason. That is, the thickness necessary for shielding the magnetic flux from the heating coil 14 is required to be greater than the penetration depth. In this embodiment, the frequency of the current flowing through the heating coil 14 is 70 kHz, and the material is aluminum. The penetration depth is about δ = 0.3 mm. Therefore, the effect of reducing buoyancy can be increased by making the thickness of the electric conductor 17 equal to or greater than the penetration depth. This is because the present inventors have confirmed through experiments that a sufficient buoyancy reduction effect can be obtained when the depth is slightly larger than the penetration depth and about 1 mm.

  FIG. 2A shows an opening 19 of an annular electric conductor 17, that is, a case where two slits 22 extending symmetrically between the inner periphery 20 of the ring and the outer periphery 21 of the ring are provided symmetrically. The case where the electric conductors 17a and 17b divided into two are opposed to each other to form one annular electric conductor is shown. And it arrange | positions so that the center O of this annular ring and the center of a heating coil may correspond substantially.

  Further, a thermal connection means 23 is provided above the support 18 and at the position of the opening 19 of the electric conductor 17 and above the electric conductor 17. The thermal connection means 23 is a heat-resistant thermal diffusion compound, and particularly between the top plate 12 and the electrical conductor 17, it is applied thinly at a level that can fill each unevenness or improve the contact state (FIG. 1, FIG. 2 (b)).

  About the induction heating apparatus comprised as mentioned above, the operation | movement and an effect | action are demonstrated below.

  When the object to be heated 13 is placed on the top plate 12 and the power is turned on, the object to be heated 13 is induction-heated by the magnetic flux from the heating coil 14. At this time, the magnetic flux from the heating coil 14 is linked to the electric conductor 17, and an induced current is also generated in the electric conductor 17.

  The induced current induced in the object to be heated 13 is linked to the object to be heated 13 by the magnetic field distribution generated by superimposing the magnetic field distribution generated by the heating coil 14 and the magnetic field distribution generated by the current induced in the electric conductor 17. It is what happens. As described above, the current distribution induced in the object to be heated 13 is changed by the presence of the electric conductor 17 and the current distribution generated in the electric conductor 17 is further added. Therefore, the equivalent DC resistance of the heating coil 14 is reduced. growing.

  When the equivalent series resistance is increased, the amount of heat generated in the article to be heated 13 is increased even with the same heating coil current, so that the heating coil current can be reduced when the same power consumption is to be obtained, and the buoyancy is also reduced accordingly. be able to.

  As described above, in the present embodiment, by providing the thermal connection means 23 by the thermal diffusion compound, the expansion of the heat radiation path from the electric conductor 17 to the top plate 12 to the object to be heated 13, The effect of improving the contact between the conductor 17 and the top plate 12 is exhibited, the heat input to the object to be heated 13 is improved, the adverse effect of the heat generated by the electric conductor 17 on the heating coil 14 is reduced, and the loss wattage of the heating coil 14 can also be reduced. . As a result, the thermal efficiency can be improved.

  Note that the application position of the thermal diffusion compound is not limited to this, and it is arbitrary to increase or decrease the application position in balance of workability, cost, performance, and the like. It goes without saying that even if it is not a thermal diffusion compound, it is the same as long as it is similar to this.

  Further, the thermal connection means 23 may be made of, for example, mica, ceramic, heat-resistant resin, metal, etc. in the sense of increasing the heat transfer area especially to the side of the electric conductor 17. At least, if the heat transfer property is improved over air, the effect is obtained. Furthermore, it is not limited to solid, For example, a liquid metal may be sufficient. In this case, however, a heat-resistant container for storing the liquid metal is required.

(Embodiment 2)
FIG. 3 shows a cross-sectional view of the induction heating apparatus in the second embodiment of the present invention. As shown in FIG. 3, the thermal connecting means 23 having the opening 19 and the electric conductor 17 are provided so as to overlap each other, and the thermal connecting means 23 is used as an electric conductor (upper) 24 made of a conductive material, The conductor 17 is composed of an electric conductor (lower) 25 (in the claims, the electric conductor (upper) 24 is the electric conductor on the most top plate side, and the electric conductor (lower) 25 is the electric other than the most on the top plate side. It will be a conductor, but for the sake of convenience, it will be expressed as an electrical conductor (upper) and (lower)). In the opening 19, the electric conductor (upper) 24 has a larger projected area than the electric conductor (lower) 25, and is sandwiched between the top plate 12 and the electric conductor (lower) 25, and serves as a thermal connecting means 23. I'm in charge.

  As in the first embodiment, the electric conductor (lower) 25 is aluminum having a thickness of about 1 mm. The electric conductor (top) 24 is a carbon sheet having a high thermal conductivity equal to or higher than that of aluminum and a thickness of about 0.1 mm. Since the penetration depth is about 0.4 mm in calculation, the thickness is sufficiently smaller than that, and the distance from the heating coil 14 is further away from the electric conductor (lower) 25. First, the electric conductor (lower) 25 is preferentially used. The electric conductor (upper) 24 is hardly induction-heated. In terms of design, the electric conductor (lower) 25 has a thickness greater than or equal to the penetration depth (about 1 mm in this embodiment), but the electric conductor (upper) 24 is preferably set to a thickness less than or equal to the penetration depth. A support body 26 is provided between the electrical conductor (upper) 24 and the support body 18 in order to prevent the electrical conductor (upper) 24 from drooping and to positively bias the top plate 12. If the electrical conductor (top) 24 is sufficiently rigid, the support 26 is not necessary.

  As described above, in the present embodiment, the two electric conductors 17 are provided so as to overlap each other so as to be larger than the projected area of the electric conductor (lower) 25 of the electric conductor (upper) 24 and the top from the heating coil 14 side. Because of the configuration in contact with the plate 12, the action of the magnetic field is likely to act on the electric conductor (lower) 25 close to the heating coil 14, and therefore the action of the magnetic field on the electric conductor (upper) 24 is reduced. Even if a warp pan is used, the temperature of the electric conductor (upper) 24 is prevented from rising rapidly, and the heat generated in the electric conductor 17 due to the increase in the heat transfer area is effectively transmitted to the object 13 to be heated. The adverse effect on the heating coil 14 can also be reduced, and the thermal efficiency can be improved. Further, the area and thickness of all electrical conductors are increased, that is, the equivalent series resistance is increased, so that buoyancy can be further reduced.

  However, although the electric conductor 17 is divided into two parts, if the area and thickness of all the electric conductors are too large, the electric conductor 17 itself generates more heat, increasing the heat loss inside the device and increasing the heating efficiency. In some cases, the design may need to be considered so that the overall balance is improved.

  In addition, since the area of the electric conductor (upper) 24 is increased at the central opening 19, there is little waste of heat transfer to the article 13 to be heated, so that the most efficient improvement in thermal efficiency and reduction in buoyancy can be achieved. it can.

  Further, since the electric conductor (upper) 24 is thinner than the electric conductor (lower) 25, it is more difficult to be induction-heated than the electric conductor (lower) 25, and it is effective that the temperature of the electric conductor (upper) 24 rapidly increases. Can be prevented.

  Moreover, the electric conductor (upper) 24 is made of a material having a high thermal conductivity equal to or higher than that of aluminum, so that the efficiency of heat transfer from the electric conductor 17 to the object to be heated 13 is improved, and the thermal efficiency can be further improved.

  The number of electrical conductors (upper) 24 and electrical conductors (lower) 25 is not limited to one each, and may be plural. The electric conductor (upper) 24 is not limited to the material / thickness of the embodiment, but the material is aluminum or copper, and the thickness is an appropriate thickness depending on the shape and thickness of the electric conductor (lower) 25. Needless to say, it should be set to.

  As described above, since the induction heating device according to the present invention can improve thermal efficiency and reduce buoyancy, all induction heating is performed on an object to be heated made of a material having high electrical conductivity and low permeability such as aluminum. It can be applied to any use.

Sectional drawing of the induction heating apparatus in Embodiment 1 of this invention (A) Plan view of electric conductor in embodiment 1 of the present invention (b) Plan view of electric conductor and thermal connection means in embodiment 1 of the present invention Sectional drawing of the induction heating apparatus in Embodiment 2 of this invention Sectional view of a conventional induction heating device (A) The figure which shows the direction of the electric current which flows into a heating coil (b) The figure which shows the direction of the electric current which flows into a to-be-heated material Graph showing the relationship between current and buoyancy

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Main body 12 Top plate 13 Object to be heated 14 Heating coil 17 Electrical conductor 23 Thermal connection means 24 Electrical conductor (top)
25 Electrical conductor (bottom)

Claims (6)

A main body constituting an outer shell, a top plate provided on an upper portion of the main body on which the object to be heated is placed, and the object to be heated made of a material having a high electric conductivity and a low magnetic permeability such as aluminum is disposed below the top plate. A heating coil for further induction heating, and an electric conductor provided between the heating coil and the top plate for reducing buoyancy generated in the object to be heated by a magnetic field generated by the heating coil. An induction heating device provided with a thermal connection means that facilitates transmission to the top plate. The thermal connection means is provided so as to overlap the top plate side of the electrical conductor, and the projected area of the electrical conductor is made larger than the projected area of the thermal connection means, and is brought into direct or indirect contact with the top plate. Item 2. The induction heating device according to Item 1. The induction heating device according to claim 2, wherein the thermal connection means and the electrical conductor have an opening at a central portion, and the thermal connection means has a portion protruding inward from the opening of the electrical conductor. The induction heating device according to claim 2 or 3, wherein the thermal connecting means has a thickness smaller than a thickness dimension of the electric conductor. The induction heating device according to any one of claims 2 to 4, wherein the thermal connection means is made of a material having a high thermal conductivity equal to or higher than that of aluminum. The induction heating device according to any one of claims 1 to 5, wherein the thermal connection means is made of an electrical conductor and has a function of reducing buoyancy generated in an object to be heated.

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