JP2008311058A - Induction heating cooker - Google Patents

Abstract

In an induction heating cooker capable of performing induction heating and resistance heating, a difference in linear expansion coefficient between a heating element for resistance heating and its substrate is made as small as possible to cause cracks in the heating element. , Prevent peeling as much as possible.
A heating element made of a mixed material of a conductive material having resistance and a filler having a smaller linear expansion coefficient than the conductive material is fired on the lower surface of a top plate made of crystallized glass. Conductive materials generally have a large linear expansion coefficient. If a filler having a low coefficient of linear expansion is mixed with a conductor material having a high coefficient of linear expansion, the coefficient of linear expansion of the heating element 3 made of this mixed material will be low, and the wire of the top plate 3 will be lower than the case of a single conductor material. The expansion rate can be approached.
[Selection] Figure 1

Description

  The present invention relates to an induction heating cooker provided with a heating element that generates heat when energized, in addition to an induction heating coil.

In an induction heating cooker, there has been a problem of how to heat a cooked utensil made of a low permeability material such as aluminum or copper. As a means for solving this problem, Patent Document 1 discloses that by using induction heating by an induction heating coil and resistance heating by a heating element that generates heat when energized, heating can be performed regardless of the material of the cooking utensil. It has been proposed to do. Patent Document 2 discloses a technique for manufacturing the heating element by printing and baking a paste-like resistor on a glass substrate.
Japanese Patent No. 1783680 JP-A-62-21983

  A heat generating body expand | swells by the temperature rise accompanying the heat_generation | fever. At this time, in the structure in which the heating element is fired on the glass substrate as disclosed in Patent Document 2, if there is a large difference in the linear expansion coefficient between the heating element and the glass substrate, thermal stress is applied to the heating element. May occur, causing cracks and peeling.

  The present invention has been made in view of the above circumstances, and an object thereof is an induction heating cooker capable of performing induction heating and resistance heating, a heating element for resistance heating, and a substrate on which the heating element is provided. It is an object of the present invention to provide an induction cooking device capable of minimizing the difference in the linear expansion coefficient of the heat generating element and preventing the heat generating element from cracking or peeling off as much as possible.

  In the present invention, a heating element formed on a substrate made of an inorganic material is formed from a mixed material of a conductive material having a higher linear expansion coefficient and resistance than the substrate and a filler having a lower linear expansion coefficient than the conductive material. It is characterized by that.

  Conductive materials generally have a large linear expansion coefficient. When a filler having a low coefficient of linear expansion is mixed with a conductor material having a large coefficient of linear expansion, the coefficient of linear expansion of the conductor material made of this mixture is reduced, and compared with the case of the conductor material alone, the linear expansion coefficient of the substrate is reduced. The difference becomes smaller.

Hereinafter, the present invention will be specifically described with reference to embodiments.
(First embodiment)
1 to 5 show a first embodiment. FIG. 1 shows an induction heating cooker incorporated in a system kitchen. As shown in FIG. 1, the cooker main body 1 includes a main body case 2 and a top plate 3 disposed above the main body case 2, and the top plate 3 is used for the cooker main body 1. It constitutes the upper surface.

  The top plate 3 has, for example, placement portions 4 and 4 at two places, and the cooked utensils are placed on the placement portions 4 and 4. On the main body case 2, support bases 5 and 5 are provided below the mounting portions 4 and 4 of the top plate 3, and coil bases 6 and 6 are attached on the support bases 5 and 5. It has been. In addition, induction heating coils 8 and 8 are arranged on the coil bases 6 and 6 for induction heating the cooked utensils 7 (see FIG. 2) such as pans placed on the placement parts 4 and 4. It is installed. As shown in FIG. 2, ferrites 9 and 9 for forming magnetic paths of the induction heating coils 8 and 8 are attached to the lower surfaces of the coil bases 6 and 6.

  On the other hand, an operation panel 10 and an oven door 11 that opens and closes the front of an oven chamber (not shown) are provided on the front surface of the main body case 2, and various operations related to cooking are performed by the operation panel 10. Can be done. In the lower surface of the top plate 3, temperature sensors 12, 12 made up of thermistors and the like are provided, particularly at positions immediately below the center portions of the mounting portions 4, 5.

  Now, the top plate 3 is formed of an inorganic material such as crystallized glass. In the present embodiment, the heating elements 13 are provided on the lower surface side of the top plate 3 and corresponding to the placement portions 4 and 4. These heating elements 13, 13 are formed by directly baking the top plate 3 using the top plate 3 as a substrate. When energized, Joule heat is generated and the cooked utensil 7 is heated by resistance (heater heating). )

Here, a method of forming the heating element 13 will be described. First, the material constituting the heating element 13 is made of a mixed material of a conductive material having resistance and a filler having a smaller linear expansion coefficient than the conductive material. The linear expansion coefficient of the top plate 3 as the substrate is −4 to ⁻⁷ × 10 ⁻⁷ / ° C., and the conductor material has a larger linear expansion coefficient than the top plate 3. Furthermore, the conductor material should just be a material whose linear expansion coefficient is larger than a top plate, and larger than a filler. The conductive material having resistance is preferably a non-magnetic material so as not to generate an electromotive force due to a high-frequency magnetic field during induction heating by the dielectric heating coil 8, for example, ruthenium oxide (70 to 90). Using.

As the filler, β-eucryptite (−40), dry silica (5), aluminum titanate (14), β-spodumene (19), cordierite (25), celsian (34), zircon (41), Zirconyl phosphate (8-13), zirconium tungstate phosphate (-26), etc. are used. In addition, the numerical value in () is a linear expansion coefficient (unit; 10 ^<-7 > / degreeC) in normal use temperature.

In this embodiment, in order to make the linear expansion coefficient of the heating element 13 as close as possible to the linear expansion coefficient of the crystallized glass, and to prevent the heating element 13 from generating an electromotive force due to the high frequency magnetic field by the induction heating coil, the filler In this case, β-eucryptite and zirconium tungstate phosphate having a negative linear expansion coefficient were used. Thereby, even if the linear expansion coefficient of ruthenium oxide which is a conductor material is 70 to 90 × 10 ⁻⁷ / ° C., the linear expansion coefficient of the heating element 13 is made as close as possible to that of the top plate 3 by mixing the filler. be able to. Among these, it is preferable to use a nonmagnetic filler.

  In order to form the heating element 13 on the lower surface of the top plate 3, first, ruthenium oxide powder as a conductor material and β-eucryptite powder and / or zirconium tungstate phosphate powder as a filler are mixed, Glass frit, organic solvent, etc. are added to the mixed powder and mixed homogeneously to prepare a paste. And this paste-form mixed material is apply | coated to two places of the lower surface of the top plate 3 by screen printing, and it bakes. As a result, the heating elements 13 are formed in an integrated state on the lower surface of the top plate 3.

  As shown in FIG. 3, when the heating element 13 in this embodiment draws an arc in a counterclockwise direction, it is folded back at the end of the arc, this time it is drawn in a clockwise arc, and is folded back at the end of the arc again. Moreover, it is formed so as to form a concentric circle by repeating a procedure of drawing an arc counterclockwise several times. And when this heat generating body 13 applies a voltage across both ends, it generates Joule heat and resistance-heats the to-be-heated cooking utensil 7. Note that lands (not shown) are formed at both ends of the heating element 13 by a nonmagnetic material such as tungsten, copper, and nonmagnetic stainless steel in order to connect lead wires (not shown).

  Here, FIG. 5 shows a plan view of a state in which the induction current ie flows through the bottom P of the cooking utensil 7 when induction heating is performed on the pan that is the cooking utensil 7. Since the induction current ie flows in a large amount where the magnetic flux density generated by the induction heating coil 8 is high, it flows in a concentrated manner around the center of the coil bundle of the induction heating coil 8 (intermediate portion between the inner diameter and the outer shape). Such an induced current tends to flow slightly in the heating element 13 made of a non-magnetic material, but is induced to flow in the opposite direction between adjacent conductors by forming a folded shape. The direction of the applied voltage is also reversed. Therefore, the heating element 13 is not easily heated by induction.

  FIG. 4 is a functional block diagram showing the configuration of the control system. A thermal power control device (heating control means, material judgment means, repulsion movement state detection means) 14 is provided inside the main body case 2 and is constituted by a microcomputer. The thermal power control device 14 receives an operation signal from an operation unit (operation means) 15 disposed on the operation panel 10 and a temperature detection signal from the temperature sensor 12. The thermal power control device 14 controls the operation of the display unit 16 arranged on the operation panel 10 and the inverter (high-frequency current supply means) 17 based on these inputs and a previously stored control program. The induction heating coil 8 is controlled by supplying a high frequency current via the inverter 17.

  A resonance capacitor 18 is connected to the induction heating coil 8 in series. Since the coil 8 or the capacitor 18 adjusts the output according to the material of the cooked utensil 7 as will be described later, the number of high-frequency current supply turns of the coil 8 is variable (for example, a multistage coil configuration). Or it is preferable to comprise so that the capacity | capacitance of the capacitor | condenser 18 may be variable.

  The inverter 17 is supplied with a commercial AC power source 19 converted into a DC voltage via a rectifier circuit 20 as a driving power source. The commercial AC power supply 19 is also supplied to a heating element energization control unit (energization means) 21. The heating element energization control unit 21 is connected to both ends of the heating element 13 through a lead wire (not shown) and energizes the heating element 13 with an AC power supply. It is controlled by the thermal power control device 14 through 21.

  Further, current transformers 22 and 23 are arranged on the input side of the rectifier circuit 20 and the output side of the inverter 17, respectively, and these detection signals are given to the thermal power control device 14. And the thermal-power control apparatus 14 detects the input electric current to a heating cooker, and the output electric current (coil electric current) of the inverter 17. FIG. In the above description, the induction heating coils 8 and 8, the inverter 17, the heating elements 13 and 13, and the heating element energization control unit 21 constitute the heating means 24.

  The material determination means in the thermal power control device 14 determines whether or not the cooked utensil 7 is a high resistance metal material. Although not described in detail, for example, a constant high frequency current is supplied to the induction heating coil 8 and input. The determination is made based on the relationship between the current and the coil current that is the output current of the inverter 17. For example, in the case of a magnetic material such as iron, the magnetic flux generated by the induction heating coil 8 is likely to flow through the cooking utensil 7, and the skin effect (the eddy current on the induction heating coil 8 side at the bottom of the cooking utensil 7 (The effect of concentrating) is also large, and the equivalent resistance of the induction heating coil 8 is also large.

  On the other hand, in the case of a non-magnetic and low resistance material such as aluminum or copper, the magnetic flux generated by the induction heating coil 8 becomes difficult to reach the cooked appliance 7 and the leakage magnetic flux increases. Since the specific resistance is small and the skin effect is small, the equivalent resistance is also small. As a result, the material is determined based on the change in magnitude between the input current and the output current, and induction heating by the induction heating coil 8 and resistance heating by the heating element 13 (heater heating) are performed based on a preset input power setting value. Can be executed.

Next, the operation of the induction heating cooker having the above configuration will be described.
The cooked utensil 7 containing the food to be cooked is placed on, for example, the placement unit 4 of the top plate 3, and a necessary input operation is performed from the operation unit 15 to start cooking. At this time, when it is determined that the material of the cooked utensil 7 is a high-resistance metal material based on the material determination means of the thermal power control device 14, cooking by the induction heating coil 8 is performed.

  On the other hand, when the material of the cooked utensil 7 is not a high resistance metal material, the thermal power control device 14 is made of a low resistance nonmagnetic metal material such as aluminum, copper or nonmagnetic SUS, or a non-magnetic material such as a clay pot. Judge whether it is a metal material (or no load). And if it is a low-resistance metal material, the thermal-power control apparatus 14 is based on the preset thermal-power adjustment so that the "pan floating" phenomenon where the bottom of the to-be-heated cooking utensil 7 moves repulsively from the top plate 3 may not arise. Induction heating cooking is performed.

  When the heating power adjusted with the heating power becomes smaller than the normal input power setting value, the heating power control device 14 controls the heating element energization control unit 21 so that the difference power is supplied to the heating element 13. To do. That is, the heating element energization control unit 21 supplies power from the commercial AC power supply 19 to the heating element 13 to cause the heating element 13 to generate heat. The Joule heat generated in the heating element 13 is transmitted to the cooked utensil 7 via the top plate 3 to heat the cooked utensil 7.

  Further, when the material is a non-metallic material or no load, induction heating by the induction heating coil 8 is not performed. When the material is a non-metallic material, electric power equal to a normal input power set value is supplied. 2 1 is supplied and heating is performed only by the heating element 13.

  In this case, it is necessary to determine whether it is a non-metallic material or no load. Therefore, the temperature sensor 12 detects the degree of temperature rise from the start of heating of the heating element 13, and for example, if the temperature rises moderately, it is determined that a clay pot or the like is installed. If there is no load, the power supply to the heating element 13 is stopped. In this way, cooking by the induction heating coil 8 or the heating element 13 and further cooking by both are performed according to the material of the cooked utensil 7.

According to the present embodiment as described above, the heating element 13 is formed of a mixed material obtained by adding a filler having a smaller linear expansion coefficient to the conductive material. The linear expansion coefficient can be reduced as compared with the case where the conductive material is formed alone, and the linear expansion coefficient of the top plate 3 can be approached. For this reason, even when a heat stress is generated in the heat generating element 13 due to the difference in expansion amount from the top plate 3 when the heat generating element 13 generates heat, the heat stress can be minimized, and the heat generating element 13 is cracked. It is possible to prevent the occurrence or peeling as much as possible.
Moreover, since the heating element 13 has a shape having portions where the directions of the currents flowing adjacent to each other are opposite to each other, the heating element 13 is less likely to be induction-heated.

(Second embodiment)
FIG. 6 shows a second embodiment of the present invention. The same parts as those of the first embodiment are denoted by the same reference numerals and the description thereof is omitted. Only different parts will be described below. The second embodiment is different from the first embodiment in the shape of a heating element 25 that replaces the heating element 13, and the other configuration is the same as that of the first embodiment.

  As shown in FIG. 6, the heating element 25 is configured by connecting divided heating elements 26 and 27 having the same shape by wiring 28. Thereby, the heat generating body 25 becomes the form arrange | positioned with respect to the circumferential direction of the induction heating coil 3, for example, dividing into two or more. Each of the divided heating elements 26 and 27 has a shape in which a linear conductor is reciprocated in the radial direction while being folded back on the inner peripheral side and the outer peripheral side. The start ends 26S, 27S of the divided heat generating elements 26, 27 and the end points 26E, 27E are arranged adjacent to each other. The starting end 26S of the divided heating element 26 and the end 27E of the divided heating element 27 are connected to the heating element energization control unit 21 by lead wires (not shown).

  By configuring the heating element 25 as described above, the portions of the divided heating elements 26 and 27 that reciprocate in the radial direction have a positional relationship that is orthogonal to the conductors that constitute the induction heating coil 8. The generated magnetic flux is less likely to be linked to the divided heating elements 26 and 27, so that an induced current is less likely to be generated. In addition, although induced currents are generated in the outer and inner peripheral portions of the divided heating elements 26 and 27, since the respective induced currents flow in opposite directions in the divided heating elements 26 and 27, generation of an induced voltage is generated. Can be canceled.

(Third embodiment)
FIG. 7 shows a third embodiment of the present invention. This embodiment differs from the first embodiment in that the heating element 29 is formed not on the lower surface of the top plate 13 but on a circular flat plate 30 as a substrate.

  As the flat plate 30, a thin ceramic plate made of an inorganic material such as aluminum nitride or silicon nitride is used. In order to form the heating element 29 on the flat plate 30, a mixed material of a conductive material and a filler made into a paste is applied to one surface of the flat plate 30 before firing, for example, the lower surface, by screen printing in a predetermined shape. The flat plate 30 is cured and the heating element 29 is integrated with the flat plate 30.

  The flat plate 30 to which the heating element 29 is fixed is placed on a non-magnetic support board 32 made of plastic, for example, as a support via a heat insulating material 31. Then, the coil base 6 provided with the induction heating coil 8 is supported by a compression coil spring 33 as an elastic member, and the support plate 32 is mounted on the coil base 6, whereby the flat plate 30 is elasticized by the compression coil spring 33. It is configured to be pressed against the lower surface of the top plate 3 by force.

Even in this configuration, the linear expansion coefficient of aluminum nitride is 44 to 50 × 10 ⁻⁷ / ° C., the linear expansion coefficient of silicon nitride is about 35 × 10 ⁻⁷ / ° C., and the ruthenium oxide wire that is a conductive material is used. Even if it is smaller than the expansion coefficient, the linear expansion coefficient of the heating element 29 is made closer to the flat plate 30 by mixing β-eucryptite or zirconium tungstate phosphate having a lower linear expansion coefficient into this conductive material. be able to.

(Other embodiments)
The present invention is not limited to the embodiments described above and illustrated in the drawings, and the following modifications are possible.
The shape of the heating element is not limited to that disclosed in the above embodiments, and may be changed as appropriate according to the individual design.
The material of the cooked utensil is not limited to the one automatically determined by the cooking device, but may be set by the user inputting the material, for example.
The linear expansion coefficient may be configured such that the heating element 13 is fired on the lower surface of the intermediate substrate having an intermediate value between the top plate 3 and the heating element 13, and this intermediate substrate is bonded to the lower surface of the top plate 3.

In the second embodiment, similar heating elements may be arranged concentrically so as to fill the inner peripheral portions of the heating elements 26 and 27. If comprised in this way, the heating density by the radiant heat of a heat generating body can be raised, and efficiency can be improved by heating a to-be-heated cooking utensil in the state nearer to a surface.
In the second embodiment, the heating element 25 may be divided into three or more with respect to the circumferential direction of the induction heating coil 3.

The longitudinal front view of the induction heating cooking appliance which shows the 1st Embodiment of this invention FIG. 1 is an enlarged view of one mounting portion side. Plan view showing shape of heating element Functional block diagram showing the configuration of the control system The figure which shows in plan the state where the induction current ie flows through the bottom of the pan when induction heating the pan FIG. 3 equivalent view showing the second embodiment of the present invention FIG. 2 equivalent view showing the third embodiment of the present invention

Explanation of symbols

  In the drawings, 1 is a cooker body, 3 is a top plate (substrate), 7 is a cooking device to be heated, 8 is an induction heating coil, 13 is a heating element, 17 is an inverter, 21 is a heating element energization control unit, 25 and 29 Denotes a heating element, and 30 denotes a flat plate (substrate).

Claims (7)

A top plate made of an inorganic material that constitutes the upper surface of the cooker body and on which the cooked utensil can be placed;
An induction heating coil that is arranged below the top plate and induction-heats the cooked utensil placed on the top plate by supplying a high-frequency current;
The top plate or a flat plate made of an inorganic material provided between the top plate and the induction heating coil is formed on the substrate as a substrate and is heated and placed on the top plate when energized. A heating element for heating the cooked utensil;
The heating element is formed of a mixed material of a conductive material having a higher linear expansion coefficient and resistance than the substrate and a filler having a lower linear expansion coefficient than the conductive material. Induction heating cooker.   The induction heating cooker according to claim 1, wherein the filler has a negative linear expansion coefficient.   The induction heating cooker according to claim 1 or 2, wherein the conductive material is a non-magnetic material.   The induction heating cooker according to any one of claims 1 to 3, wherein the filler is a non-magnetic material.   The induction heating cooker according to any one of claims 1 to 4, wherein the heating element has portions in which directions of currents flowing adjacent to each other are opposite to each other.   The induction heating cooker according to any one of claims 1 to 5, wherein a part of the heating element is arranged so as to be orthogonal to a conductor constituting the induction heating coil.   7. The heating elements are arranged so as to be divided into a plurality of parts in the circumferential direction of the induction heating coil, and are connected so that energization directions of adjacent portions are opposite to each other. The induction heating cooking appliance in any one of.

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