Induction heating cooker

Abstract

To obtain an induction heating cooker capable of suppressing an increase of a temperature of a heating coil.SOLUTION: An induction heating cooker includes: a substrate arranged so as to be opposite to a heated material; a heating coil to which a plurality of conductors is wound to a one flat surface of the substrate, and in which a conductive pattern is formed in a spiral shape; and a driving circuit that flows a high frequency current to the heating coil. The conductive pattern has a part of which a thickness of the conductive pattern is different in a portion of a peripheral direction.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to an induction heating cooker equipped with a heating coil. [Background technology]

[0002] Conventionally, induction heating cookers have been known that are equipped with a heating coil below a top plate on which an object to be heated is placed. The heating coil is made of a coil wire wound in a spiral shape, and generates a high-frequency magnetic field on the surface of the object to be heated by a high-frequency current supplied from an inverter circuit, thereby heating the object to be heated.

[0003] As a coil similar to the heating coil used in an induction heating cooker, a coil for wireless power transmission that prevents an increase in operating temperature is known (see, for example, Patent Document 1). Patent Document 1 discloses a power receiving loop coil in which a thin copper wire is wound multiple times on each of the front and back surfaces of a substrate. The power receiving loop coil disclosed in Patent Document 1 is configured such that in the width direction, which is perpendicular to the winding direction and in the direction within the winding plane, the thickness of the thin copper wire on the inner circumference side, where the current density is relatively high, is made thicker than the thickness of the thin copper wire on the outer circumference side. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2022-071537 Summary of the Invention [Problem to be solved by the invention]

[0005] The power receiving loop coil disclosed in Patent Document 1 is configured such that the thickness of the inner circumference portion is thicker than that of the outer circumference portion in the width direction of the pattern formed by the copper thin film. In other words, when looking at a cross section perpendicular to the winding direction of the coil pattern, the inner circumference portion close to the center of the winding is thicker, while the outer circumference portion far from the center of the winding is thinner. Since the cross-sectional area of ​​the coil is the same at any position in the winding direction, when the frequency of the high-frequency current flowing through the coil increases, the heat dissipation effect is insufficient only by the increase in the thickness of the copper thin film on the inner circumference side of the coil to cover the heat generated by the entire coil, and the temperature of the coil may rise.

[0006] The present disclosure has been made to solve the above-mentioned problems, and provides an induction heating cooker that can suppress an increase in temperature of a heating coil. [Means for solving the problem]

[0007] The induction heating cooker according to the present disclosure comprises a substrate arranged opposite an object to be heated, a heating coil having multiple conductors wound around one flat surface of the substrate to form a spiral conductor pattern, and a drive circuit that passes high-frequency current through the heating coil, wherein the conductor pattern has a portion in which the thickness of the conductor pattern varies depending on the position in the circumferential direction. Effect of the Invention

[0008] According to the present disclosure, the thickness of the conductor pattern of the heating coil varies depending on the circumferential portion, so that when the thickness increases along the radial direction in the width of the conductor pattern, the surface area of ​​the conductor pattern increases, and therefore, even if the frequency of the high-frequency current increases, the heat dissipation effect is large and the temperature rise of the heating coil can be suppressed. [Brief description of the drawings]

[0009] [Figure 1] 1 is an external perspective view showing a configuration example of an induction heating cooker according to a first embodiment. [Diagram 2]1 is a plan view showing one configuration example of a heating coil in an induction heating cooker according to embodiment 1. FIG. [Diagram 3] FIG. 3 is a schematic cross-sectional view taken along line AA in FIG. 2. [Figure 4] 2 is a block diagram showing a configuration example of an electric circuit that controls a heating coil in the induction heating cooker according to the first embodiment. FIG. [Diagram 5] 3 is a diagram showing an example of the configuration of ferrite provided on the back surface side of the substrate shown in FIG. 2. [Figure 6] FIG. 13 is a schematic diagram for explaining the configuration of a heating coil according to Modification 1. [Figure 7] FIG. 11 is a plan view showing a configuration example of a heating coil in an induction heating cooker according to a second embodiment. [Figure 8] FIG. 11 is a block diagram showing a configuration example of an electric circuit that controls a heating coil in an induction heating cooker according to a second embodiment. [Figure 9] FIG. 11 is a plan view showing a configuration example of a heating coil in an induction heating cooker according to embodiment 3. [Figure 10] 10 is a plan view showing a state in which a plurality of substrates constituting the coil assembly shown in FIG. 9 are separated. [Figure 11] FIG. 10 is a schematic cross-sectional view taken along line BB in FIG. [Figure 12] FIG. 11 is a plan view showing a configuration example of a heating coil in an induction heating cooker according to embodiment 4. [Figure 13] FIG. 13 is a schematic cross-sectional view taken along line CC in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] An embodiment of an induction heating cooker according to the present disclosure will be described with reference to the drawings. In some of the drawings, for the sake of convenience in explaining the configuration, three coordinate axes (X-axis, Y-axis, and Z-axis) indicating directions in a three-dimensional space are shown.

[0011] Embodiment 1 The configuration of the induction heating cooker of the present embodiment 1 will be described. Fig. 1 is an external perspective view showing one configuration example of the induction heating cooker according to the embodiment 1. The induction heating cooker 1 has a top plate 7 on which an object to be heated is placed, a housing 10 that supports the top plate 7, an operation input unit 12, and a notification unit 6. The object to be heated is, for example, a cooking pot or a frying pan.

[0012] Heating ports 2a to 2c are provided on top plate 7. Heating ports 2a to 2c are locations on top plate 7 where cooking pots are placed. Top plate 7 is printed with information indicating the positions of heating ports 2a to 2c.

[0013] A heating coil 8a is provided below heating port 2a. A heating coil 8b is provided below heating port 2b. A heating coil 8c is provided below heating port 2c. Since the heating coils 8a to 8c are housed in housing 10 and cannot be seen directly from above top plate 7, the outlines of the heating coils 8a to 8c are shown by dashed lines in FIG.

[0014] The operation input unit 12 has a main power button 3, a heating port power button 4, and a heat setting encoder 5. The main power button 3 is an operation input unit for turning on or off the main power of the induction heating cooker 1. The heating port power button 4 is an operation input unit for inputting instructions to start and stop heating in the heating port 2c. Although symbols and leading lines are not shown in FIG. 1, the operation input unit 12 is provided with heating port power buttons for each of the heating ports 2a and 2b. The heat setting encoder 5 is an operation input unit for setting the heat during heating in the heating ports 2a to 2c.

[0015] The notification unit 6 is a display device formed of, for example, an LED (Light Emitting Diode) or a liquid crystal display. The notification unit 6 displays the output during heating at the heating ports 2a to 2c, setting information, and information to alert the user. The induction heating cooker 1 is an IH (Induction Heating) cooking heater that induction heats cooking pots placed on the heating ports 2a to 2c, respectively, by heating coils 8a to 8c.

[0016] Before describing the configuration of the heating coils 8a to 8c in the present embodiment 1, the configuration of a conventional heating coil will be briefly described.

[0017] A conventional heating coil is formed by winding a copper Litz wire, which is a Litz wire made by twisting together tens to hundreds of copper wires of about φ0.3 mm, in a spiral shape. The twisted copper Litz wire has a thickness of about 6 to 8 mm. The conventional heating coil is fixed to a resin base member. In addition, the resin base member is provided with ferrite, which is a highly magnetic material that converges the interlinkage magnetic flux generated in the copper Litz wire by the high-frequency current supplied to the heating coil from the inverter toward the heated object. As for the ferrite, the material and size related to the magnetic permeability are design matters, so the thickness of the ferrite varies depending on the product, but the ferrite also has a certain thickness. Therefore, a heating coil assembly including a conventional heating coil, ferrite, and a resin base member has a thickness of 10 to 15 mm.

[0018] In contrast to the conventional heating coils described above, the heating coils 8a to 8c of the present embodiment 1 have a configuration in which a conductor pattern is formed by a printing technique using copper foil as a conductor, like the wiring of a printed circuit board. The configuration of the heating coils 8a to 8c in the induction heating cooker 1 of the present embodiment 1 will be described with reference to Fig. 2. Since the heating coils 8a to 8c have the same configuration, they will be described below as heating coil 8. Fig. 2 is a plan view showing one configuration example of the heating coils in the induction heating cooker according to embodiment 1.

[0019] As shown in Fig. 2, the heating coil 8 is formed on one plane (a plane parallel to the XY plane) of a rectangular substrate 15. The material of the substrate 15 is, for example, an insulator such as a paper phenolic material, a composite substrate epoxy resin, or a glass cloth substrate epoxy resin. The thickness of the substrate 15 is, for example, about 1.6 mm. When the heating coil 8 is housed in the induction heating cooker 1 shown in Fig. 1, the surface of the substrate 15 on which the heating coil 8 is formed faces the object to be heated via the top plate 7. The heating coil 8 is configured such that a plurality of copper foils are wound to form a spirally shaped conductive pattern.

[0020] The heating coil 8 shown in Fig. 2 has an inner coil 18a disposed near the center of the winding, and an outer coil 18b disposed farther from the center than the inner coil 18a. The outer coil 18b shares the center of the winding with the inner coil 18a, and has a configuration in which a conductor pattern is formed in a spiral shape. The inner coil 18a and the outer coil 18b are formed of a single conductor pattern. In other words, the heating coil 8 is configured in a spiral shape in a single stroke from one end 14a to the other end 14b.

[0021] The surface of the heating coil 8 is covered with an insulator 13. The insulator 13 maintains the insulation of the heating coil 8 and acts as a resist to prevent corrosion of copper, which is a conductive material of the heating coil 8. In the substrate 15 shown in FIG. 2, the surface on which the heating coil 8 is formed is taken as the front surface, and the wiring portion 17 is formed on the back surface of the substrate 15. The wiring portion 17 is also covered with an insulator 13. The wiring portion 17 also has a wiring pattern formed of copper foil. One end of the wiring portion 17 is electrically connected to the end portion 14a through a conductive via (not shown) such as solder. The surface of the other end of the wiring portion 17 is exposed by an opening 16a formed in the insulator 13 covering the wiring portion 17. In addition, the surface of the end portion 14b is exposed by an opening 16b formed in the insulator 13 and the substrate 15 covering the wiring portion 17. The openings 16a and 16b serve as electrode pads for electrically connecting the driving circuit to be described later and the heating coil 8.

[0022] In the heating coil 8 shown in FIG. 2, the inner coil 18a has three turns and the outer coil 18b has about 3.5 turns, but the number of turns of each coil is not limited to the configuration shown in FIG. 2. FIG. 2 shows a configuration in which an electrode pad is provided on the back surface of the substrate 15, but the position of the electrode pad for connecting the heating coil 8 to the drive circuit is not limited to the back surface of the substrate 15. The electrode pad for connecting the heating coil 8 to the drive circuit may be provided on the front surface of the substrate 15. Furthermore, although the wiring portion 17 is provided on the back surface of the substrate 15 in the above description, a lead wire may be used instead of the wiring portion 17. Although the inner coil 18a and the outer coil 18b have a concentric circular shape in the above description, they may be a concentric rectangular shape or a concentric elliptical shape.

[0023] FIG. 3 is a schematic cross-sectional view taken along line AA in FIG. 2. As shown in FIG. 3, the inner coil 18a and the outer coil 18b are formed on the surface of the substrate 15. As described above, the insulator 13 that covers the wiring portion 17 is provided on the back surface of the substrate 15. The thickness of the conductor pattern of the inner coil 18a is t1, and the thickness of the conductor pattern of the outer coil 18b is t2. The width of the conductor pattern of the inner coil 18a is w1, and the width of the conductor pattern of the outer coil 18b is w2. The width of the conductor pattern is the radial length of the conductor pattern when the center of the winding is assumed to be the center of the circle. In the configuration example shown in FIG. 3, the relationship is w1=w2, t2>t1. As will be described later, w1>w2 may also be satisfied.

[0024] Heating coil 8 in the present embodiment 1 is configured such that the thickness of the conductive pattern varies depending on the portion around which it is wound. A configuration in which thickness t1 of the conductive pattern of inner coil 18a is greater than thickness t2 of the conductive pattern of outer coil 18b is one example of the present embodiment 1. For example, the thickness of the conductive pattern of heating coil 8 may vary depending on the shape of a filament (not shown) provided on the back side of substrate 15. This will be described later.

[0025] Here, a manufacturing method of the heating coil 8 will be briefly described. First, a typical printed circuit board used in a circuit board will be described. The printed circuit board has a C-side on which electrical components are attached and an S-side on which solder is applied. In the printed circuit board, wiring for connecting the terminals of multiple electrical components is provided not only on the S-side but also inside the board. The wiring provided inside the board and the wiring provided on the S-side are electrically insulated even when crossing three-dimensionally due to the insulating properties of the board material. The material of the printed circuit board is, for example, a composite substrate epoxy resin or a glass cloth substrate epoxy resin. The wiring of the printed circuit board is formed by a printing technique using copper foil instead of ink.

[0026] The conductor pattern of the heating coil 8 in the present embodiment 1 is formed by a printing technique, similar to the wiring pattern on a printed circuit board. When forming the conductor pattern with copper foil, the conductor patterns of the inner coil 18a and the outer coil 18b are formed by making the thickness of the copper foil different between an inner portion close to the center of the substrate 15 and a portion outside the inner portion in the heating coil 8 shown in Fig. 2 and Fig. 3 .

[0027] The wiring pattern formed on the printed circuit board usually has a constant thickness of copper foil. For example, the thickness of the wiring pattern of the printed circuit board used for the circuit board is 35 to 70 μm in the case of standard specifications, and about 200 μm in the case of thick film specifications. In this way, the thickness of the wiring pattern can be adjusted depending on the specifications selected. Therefore, the heating coil 8 in the present embodiment 1 is formed so that the thickness of the copper foil differs depending on the part where it is wound. Specifically, as described with reference to FIG. 2 and FIG. 3, the thickness of the copper foil of the unicursal conductive pattern is different between the inner part close to the center of the substrate 15 and the part outside the inner part. The heating coil 8 formed on the substrate 15 by printing technology as in the present embodiment 1 is called a sheet coil.

[0028] Next, the control of the heating coil 8 will be described. FIG. 4 is a block diagram showing an example of the configuration of an electric circuit that controls the heating coil in the induction heating cooker according to the first embodiment. The induction heating cooker 1 has a drive circuit 23 that supplies a high-frequency current to the heating coil 8, and a control unit 20 that controls the drive circuit 23. The drive circuit 23 is, for example, an inverter circuit. The control unit 20 is, for example, a microcomputer. The control unit 20 is connected to the drive circuit 23, the operation input unit 12, and the notification unit 6 via signal lines (not shown). The control unit 20 controls the drive circuit 23 that supplies a high-frequency current to the heating coil 8 according to an instruction input via the operation input unit 12.

[0029] As shown in FIG. 4, the driving circuit 23 is connected to one end 14a of the heating coil 8 via the wiring portion 17 and the opening 16a, and is connected to the other end 14b of the heating coil 8 via the opening 16b. In the present embodiment 1, the heating coil 8 and the driving circuit 23 correspond one-to-one, and the heating coil 8 is configured to be connected to a pair of input and output lines. The driving circuit 23 supplies a high-frequency current having a frequency of 20 kHz to 100 kHz to the heating coil 8 according to the control by the control unit 20. When the high-frequency current flows through the conductor pattern of the heating coil 8, an eddy current is induced in the object to be heated placed on the top plate 7 shown in FIG. 1, and the bottom surface of the object to be heated is induction-heated.

[0030] FIG. 5 is a diagram showing an example of a configuration of ferrite provided on the back side of the substrate shown in FIG. 2. FIG. 5 shows a configuration in which eight ferrites 19 are arranged on the back side of the substrate 15. Each of the eight ferrites 19 has a rectangular parallelepiped shape. The eight ferrites 19 are arranged radially with the center of the winding of the heating coil 8 as the axis, so that the longitudinal direction of each ferrite 19 is in the radial direction. FIG. 5 shows a configuration in which eight ferrites 19 are provided, but the number of ferrites 19 is not limited to eight. Note that in FIG. 5, the wiring portion 17 shown in FIG. 2 is omitted from the drawing.

[0031] The ferrite serves to converge the interlinkage magnetic flux generated by the high-frequency current flowing through the heating coil to the object to be heated. The amount of interlinkage magnetic flux varies depending on the shape of the ferrite. In addition, the conductor pattern of the heating coil also undergoes a physical phenomenon in which it is induced heated by the interlinkage magnetic flux of other conductor patterns in the vicinity, for example, a conductor pattern wound next to itself. This physical phenomenon is called the proximity effect. Not only does the amount of interlinkage magnetic flux generated on the inner periphery side of the spiral conductor pattern differ from the amount of interlinkage magnetic flux generated on the outer periphery side, but the degree to which the conductor pattern itself is induced heated by the amount of interlinkage magnetic flux also differs depending on the shape of the ferrite. Due to the nature of the ferrite and the proximity effect, the amount of induction heating increases in the portion of the conductor pattern where the amount of interlinkage magnetic flux is large, so in the present embodiment 1, the thickness of the copper foil in the portion of the conductor pattern where the amount of interlinkage magnetic flux is large is made thicker in the heating coil 8.

[0032] This will be described with reference to FIG. 5. The ferrite 19 arranged on the back side of the substrate 15 generates a magnetic flux linkage in the conductor pattern of the heating coil 8, inducing an eddy current on the bottom surface of the heated object. Since the magnetic flux is concentrated on the end surface of the ferrite 19, the induction heating of the conductor pattern of the heating coil 8 itself is also strong near the end surface of the ferrite 19. In the configuration example shown in FIG. 5, the ends of the eight ferrites 19 are concentrated near the center of the winding of the heating coil 8. Therefore, the amount of magnetic flux linkage generated on the inner periphery side of the conductor pattern of the heating coil 8 is larger than the amount of magnetic flux linkage generated on the outer periphery side. The film thickness t1 of the conductor pattern of the inner coil 18a is made thicker than the film thickness t2 of the conductor pattern of the outer coil 18b. For example, the film thickness t1 of the conductor pattern of the inner coil 18a is 500 μm, and the film thickness t2 of the conductor pattern of the outer coil 18b is 200 μm.

[0033] In the first embodiment, in the heating coil 8, the copper foil thickness of the inner coil 18a having a large amount of interlinkage magnetic flux is made thicker and the copper foil thickness of the portion of the outer coil 18b is made thinner, but the setting of the copper foil thickness is not limited to the configuration shown in FIG. 3. Consider a case where a spiral conductor pattern is divided into three portions in the radial direction. The first portion is the inner peripheral portion closest to the center of the winding and having a large amount of interlinkage magnetic flux. The second portion is a middle portion located radially outward from the inner peripheral portion and wound around the same center as the inner peripheral portion. The third portion is a middle portion located radially outward from the middle portion and wound around the same center as the inner peripheral portion.

[0034] In this case, the thickness of the copper foil in the intermediate portion and the thickness of the copper foil in the portion on the outer periphery side may be made equal, and the thickness of the copper foil in the portion on the inner periphery side may be made thicker than those portions. Also, when the amount of magnetic flux linkage increases in the order of the outer periphery side, the intermediate portion, and the inner periphery side, the thickness of the copper foil may be made thicker in the order of the outer periphery side, the intermediate portion, and the inner periphery side. Thus, in the first embodiment, since the amount of magnetic flux linkage differs between the inner periphery side, the intermediate portion, and the outer periphery side depending on the shape of the ferrite, the thickness of the copper foil is configured to differ depending on the shape of the ferrite.

[0035] As described above, the heating coil 8 is configured such that the thickness of the copper foil of the conductor pattern varies depending on the location. When the conductor pattern itself is induction heated due to the proximity effect or the like, causing the temperature at a particular location to rise excessively, the thickness of the copper foil at that particular location is increased to increase the surface area of ​​the conductor pattern. This increases the heat dissipation area at that particular location, making it possible to suppress the temperature rise of the conductor pattern. This improves the reliability of the heating coil 8.

[0036] It should be noted that the width of the conductor pattern of the heating coil 8 may be changed in addition to the thickness of the copper foil. Specifically, with reference to FIG. 3, the width w1 of the conductor pattern of the inner coil 18a and the width w2 of the conductor pattern of the outer coil 18b are equal to each other, but w1>w2 may be satisfied. By increasing the width of the conductor pattern in the area where the temperature is likely to rise, the surface area of ​​the conductor pattern can be further increased. As a result, the heat dissipation area of ​​the area where the temperature is likely to rise in the heating coil 8 can be increased, and the temperature rise of the heating coil 8 can be suppressed.

[0037] In the first embodiment, the thickness of the conductor pattern of the inner coil 18a near the center of the winding of the heating coil 8 is made relatively thicker than the thickness of the conductor pattern of the outer coil 18b located on the outside in the circumferential direction of the inner coil 18a, but the configuration in which the thickness of the conductor pattern varies depending on the part in the circumferential direction is not limited to the case in which the thickness is divided into two types. The thickness of the conductor pattern may vary along the circumferential direction.

[0038] (Variation 1) In this modified example 1, the thickness of a part of the heating coil 8 shown in FIG. 2 changes along the radial direction. In the heating coil 8 shown in FIG. 2, a conductor pattern for one turn with the center of the winding as the center of the spiral conductor pattern is called a "turn". FIG. 6 is a schematic diagram for explaining the configuration of the heating coil of modified example 1. The upper diagram of FIG. 6 is a plan view of a turn TRC for one turn extracted from the inner coil 18a shown in FIG. 2. The lower diagram of FIG. 6 is a perspective view showing a state in which the turn TRC shown in the upper diagram of FIG. 6 is linearly extended so that the conductor pattern of the turn TRC is parallel to one direction (X-axis) in order to explain this modified example 1. Hereinafter, the conductor pattern in the state in which the turn TRC is linearly extended is called a linear pattern TRL.

[0039] The turn TRC is formed by winding a copper foil with a pattern width of w3 one turn counterclockwise from point PA to point PB with the center Oab as the axis. The distance between point PA and center Oab and the distance between point PB and center Oab are called radii r. The radius r connecting point PA and center Oab is called ra, and the radius r connecting point PB and center Oab is called rb. It is assumed that when the central angle θ of the turn TRC changes from 0 to 2π, the distance from center Oab to the copper foil pattern changes linearly from ra in the case of point PA to rb in the case of point PB. As shown in the upper diagram of FIG. 6, ra and rb have the relationship rb>ra.

[0040] Also, the thickness of the copper foil at point PA is ta, and the thickness of the copper foil at point PB is tb. As shown in the lower diagram of FIG. 6, ta and tb have a relationship of ta>tb. The thickness difference tc is tc=ta-tb. In this modified example 1, the copper foil pattern of the turn TRC is configured such that the thickness gradually decreases from point PA to point PB along the circumferential direction. As shown in the lower diagram of FIG. 6, the upper surface of the linear pattern TRL is an inclined surface. Note that, for convenience of explanation, the lower diagram of FIG. 6 exaggerates the change in the thickness of the copper foil.

[0041] Here, referring to Fig. 6, the difference between the surface area Sm of the turn TRC when the thickness t of the copper foil changes from ta to tb along the circumferential direction and the surface area Sref of the turn TRC when the thickness t of the copper foil is constant at t = tb as a comparative example will be described. The area of ​​the top surface of the turn TRC of the comparative example is taken as Sp.

[0042] In the diagram shown at the bottom of FIG. 6, the area of ​​the slope of the linear pattern TRL is Sd. The area of ​​the right triangle with the side of length tc as the base is Sws. In the linear pattern TRL, the area of ​​a rectangle formed by two sides of length w3 and two sides of length tc, which is a surface parallel to the XZ plane, is Swr. However, since this rectangle is the connection surface with the next turn TRC, the area Swr is not considered to be the surface area of ​​the turn TRC here. If the area difference, which is the value obtained by subtracting the surface area Sref of the turn TRC of the comparative example from the surface area Sm of the turn TRC of this modified example 1, is Sdf, the area difference Sdf is expressed by Equation (1). Sdf = 2 × Sws + (Sd - Sp) (1)

[0043] The area Sws shown on the right side of formula (1) is calculated. The area Sws is the area of ​​a triangle, so it is expressed by the formula Sws = L1 × tc × 1 / 2. L1 is the length in the X-axis direction of the linear pattern TRL shown in the lower part of FIG. 6. Since it is assumed that the distance from the center Oab to the copper foil pattern changes linearly from ra in the case of point PA to rb in the case of point PB, the circumferential length of the conductor pattern from point PA to point PB is expressed by π(ra + rb). In other words, L1 = π(ra + rb). The area Sws is expressed by the formula Sws = π(ra + rb) × tc × 1 / 2 = π(ra + rb) × (ta-tb) × 1 / 2. The area Sp shown on the right side of formula (1) is expressed by the formula Sp = L1 × w3 = π(ra + rb) × w3.

[0044] Find the area Sd on the right side of equation (1). If the length of the slope of the linear pattern TRL in the direction parallel to the XZ plane is L2, then by Pythagoras' theorem, L2 = (tc 2 +L1 2 ) -2 = {(ta-tb) 2 +π 2 (ra+rb) 2} -2 The area Sd is expressed as Sd=L2×w3={(ta-tb) 2 +π 2 (ra+rb) 2} -2 ×w3. Now, for L2, rewrite it as an equation that takes the square root of (ra+rb) outside, as shown in equation (2). L2 = [(ra + rb) 2 ×{(ta-tb) 2 / (ra+rb) 2 +π 2}] -2 =(ra+rb){(ta-tb) 2 / (ra+rb) 2 +π 2} -2 (2)

[0045] In Equation (2), for example, if the film thickness difference tc of the turn TRC is several hundred μm and the distances ra and rb are several cm, then (ta - tb) 2 <<(ra + rb) 2 is obtained. That is, (ta - tb) 2 / (ra + rb) 2 ≈ 0. Therefore, L2 = π(ra + rb), and the area Sd is Sd = π(ra + rb)×w3.

[0046] The area Sp of the upper surface of the turn TRC in the comparative example is Sp = π(ra + rb) = Sd. So, the right side (Sd - Sp) of Equation (1) is (Sd - Sp) = 0. Substituting this result and the above area Sws into Equation (1), the area difference Sdf is expressed as in Equation (3). Sdf = π(ra + rb)×(ta - tb) ···(3)

[0047] In addition, in this Modification Example 1, it has been described for the case where the number of turns of the heating coil 8 is 1. However, the number of turns may be 2 or more, or less than 1. The central angle θ at which the film thickness of the conductor pattern changes may be, for example, (1 / 4)π. Also, in this Modification Example 1, regarding the surface area of the conductor pattern of the heating coil 8, the increase in the area of the upper surface of the conductor pattern has been approximated to zero compared with the case where the film thickness is constant. However, when the number of turns of the turn is large, the increase in the area of the upper surface of the conductor pattern may be considered. Further, in this Modification Example 1, it has been described for the case where the film thickness of the conductor pattern becomes thinner as it moves away from the center of the turn. However, the film thickness of the conductor pattern may become thicker as it moves away from the center of the turn.

[0048] According to this Modification Example 1, when the radius r of the turn increases from ra to rb in one turn and the film thickness t of the conductor pattern changes from tb to ta along the circumferential direction (assuming tb < ta), the surface area increases by {π(ra + rb)×|ta - tb|} or more compared with the case where the film thickness t is constant at tb. In the heating coil 8 shown in FIG. 2, the part connecting the inner coil 18a and the outer coil 18b may have the configuration described in this Modification Example 1.

[0049] The induction heating cooker 1 of the present embodiment 1 includes a substrate 15 arranged opposite an object to be heated, a heating coil 8 having a conductor pattern formed on the substrate in which a plurality of conductors are wound in a spiral shape on one plane of the substrate 15, and a drive circuit 23 that applies a high-frequency current to the heating coil 8. The conductor pattern has a portion in which the thickness of the conductor pattern varies depending on the portion in the circumferential direction.

[0050] According to the first embodiment, the thickness of the conductor pattern of the heating coil 8 varies depending on the circumferential portion, so that when the thickness increases along the radial direction in the width of the conductor pattern, the surface area of ​​the conductor pattern increases. Therefore, even if the frequency of the high-frequency current increases, the heat dissipation effect is large, and the temperature rise of the heating coil 8 can be suppressed.

[0051] In addition, in the heating coil 8 of the present embodiment 1, when the amount of induction heating of the conductor pattern by the generated interlinkage magnetic flux varies depending on the location of the conductor pattern, the thickness of the copper foil of the conductor pattern may be changed according to the amount of induction heating so that the greater the amount of induction heating, the thicker the copper foil becomes. By increasing the thickness of the copper foil in the conductor pattern part with a large amount of induction heating, the surface area of ​​the conductor pattern of the heating coil 8 can be increased. By increasing the surface area of ​​the conductor pattern of the heating coil 8, the heat dissipation efficiency can be improved. As a result, the temperature rise of the heating coil 8 can be suppressed, and the reliability of the heating coil 8 is improved.

[0052] Embodiment 2 While the first embodiment has a heating coil to which one set of input and output wires is connected, the second embodiment has a heating coil that is composed of multiple split coils and to which multiple sets of input and output wires are connected. The induction heating cooker 1 of the second embodiment has the same overall configuration as that described in the first embodiment, except for the heating coil 8. Therefore, in the second embodiment, the heating coil 8 will be mainly described in terms of differences from the first embodiment, and a detailed description of the same configuration as that described in the first embodiment will be omitted.

[0053] The configuration of the heating coil 8 in the induction heating cooker 1 of the present embodiment 2 will be described. Fig. 7 is a plan view showing one configuration example of the heating coil in the induction heating cooker according to the embodiment 2. In the present embodiment 2, the heating coil 8 has two divided coils, an inner coil 28a and an outer coil 28b. The heating coil 8 shown in Fig. 7 has a configuration in which the inner coil 18a and the outer coil 18b described in the embodiment 1 are electrically separated.

[0054] The conductor pattern is wound three times between one end 14a and the other end 14c of the inner coil 28a. The conductor pattern is wound four or more times between one end 14d and the other end 14b of the outer coil 28b. In the second embodiment, the thickness of the conductor pattern of the inner coil 28a is t1 and the thickness of the conductor pattern of the outer coil 28b is t2, so that t2>t1.

[0055] In the substrate 15 shown in FIG. 7, the surface on which the heating coil 8 is formed is defined as the front surface, and the wiring portions 17a, 17c, and 17d are formed on the back surface of the substrate 15. The wiring portions 17a, 17c, and 17d are also formed with a wiring pattern using copper foil. One end of the wiring portion 17a is electrically connected to the end portion 14a through a conductive via (not shown). The surface of the other end portion of the wiring portion 17a is exposed through an opening 16a formed in the insulator 13 on the back surface side of the substrate 15. One end of the wiring portion 17c is electrically connected to the end portion 14c through a via (not shown). The surface of the other end portion of the wiring portion 17c is exposed through an opening 16c formed in the insulator 13 on the back surface side of the substrate 15. One end of the wiring portion 17d is electrically connected to the end portion 14d through a via (not shown). The surface of the other end portion of the wiring portion 17d is exposed through an opening 16d formed in the insulator 13 on the back surface side of the substrate 15. The surface of end 14b is exposed through insulator 13 on the rear side of substrate 15 and opening 16b formed in substrate 15. Openings 16a to 16d serve as electrode pads for electrically connecting heating coil 8 to a drive circuit described later.

[0056] 8 is a block diagram showing an example of the configuration of an electric circuit that controls a heating coil in an induction heating cooker according to embodiment 2. Induction heating cooker 1 of embodiment 2 has drive circuits 23a and 23b.

[0057] The driving circuit 23a is connected to one end 14a of the inner coil 28a via the wiring portion 17a and the opening 16a, and is connected to the other end 14c of the inner coil 28a via the wiring portion 17c and the opening 16d. The driving circuit 23b is connected to one end 14d of the outer coil 28b via the wiring portion 17d and the opening 16d, and is connected to the other end 14b of the outer coil 28b via the opening 16b. In the second embodiment, the heating coil 8 and the driving circuits 23a and 23b correspond to each other in a one-to-two manner. The heating coil 8 has two pairs of input lines and output lines. The control unit 20 controls the driving circuits 23a and 23b according to an instruction inputted via the operation input unit 12. For example, the control unit 20 outputs a PWM (Pulse Width Modulation) signal as a control signal to the driving circuits 23a and 23b.

[0058] The induction heating cooker 1 is permitted by the Radio Law to operate the inverter circuit at a frequency in the 20 kHz to 100 kHz frequency band and output a high-frequency current from the inverter circuit to the heating coil 8. The driving circuit 23a supplies the inner coil 28a with a high-frequency current of 20 kHz to about 40 kHz, which is a low frequency in the high frequency band of 20 kHz to 100 kHz. The driving circuit 23b supplies the outer coil 28b with a high-frequency current of about 50 kHz to 100 kHz, which is a high frequency in the high frequency band of 20 kHz to 100 kHz. Each of the split coils of the inner coil 28a and the outer coil 28b inductively heats an object to be heated placed on the top plate 7 shown in FIG. 1. Hereinafter, the frequency band of 20 kHz to about 40 kHz is referred to as the "high-frequency-low frequency region", and the frequency band of about 50 kHz to 100 kHz is referred to as the "high-frequency-high frequency region".

[0059] The heating coil 8 of the present embodiment 2 is configured such that the thickness of the conductor pattern of the inner coil 28a, through which a high-frequency current in the high-frequency to low-frequency region flows, is thin, and the thickness of the conductor pattern of the outer coil 28b, through which a high-frequency current in the high-frequency to high-frequency region flows, is thick. Thus, the heating coil 8 of the present embodiment 2 is configured such that the thicknesses of the copper foil of the multiple split coils differ depending on the frequency band of the high-frequency current supplied to the split coils.

[0060] In the second embodiment, the number of turns of the inner coil 28a and the outer coil 28b are not limited to those shown in FIG. 7. FIG. 8 shows a configuration in which electrode pads are provided on the back surface of the substrate 15, but the position of the electrode pads for connecting the heating coil 8 to the drive circuits 23a and 23b is not limited to the back surface of the substrate 15. The electrode pads for connecting the heating coil 8 to the drive circuits 23a and 23b may be provided on the front surface of the substrate 15. Furthermore, although the wiring parts 17a, 17c, and 17d are provided on the back surface of the substrate 15, lead wires may be used instead of these wiring parts. FIG. 7 shows a case in which the inner coil 28a and the outer coil 28b have a concentric circular shape, but they may have a concentric rectangular shape or a concentric elliptical shape.

[0061] Next, the operation of the heating coil 8 in the present embodiment 2 will be described. As one of the objects to be heated, a frying pan made of aluminum material with a magnetic material attached to the bottom of the pan so that it can be used with an IH cooking heater is widely used. Hereinafter, such a frying pan will be referred to as an IH compatible aluminum frying pan. A case will be described where the object to be heated is an IH compatible aluminum frying pan.

[0062] Since a high impedance magnetic material is attached to the bottom surface of an IH compatible aluminum frying pan, if the frequency of the high frequency current of the inner coil 28a is about 20 kHz, eddy currents sufficient to generate Joule heat are generated in the magnetic material. On the other hand, in an IH compatible aluminum frying pan, the aluminum part of the bottom of the pan and the aluminum part of the outer side wall forming the pan skin have extremely low impedance characteristics. In order to reduce the penetration depth of the eddy current generated in the aluminum part, the frequency of the high frequency current passed through the outer coil 28b is increased to about 50 kHz or more. This increases the current density on the surface of the aluminum part with extremely low impedance characteristics, increases the impedance of the path through which the eddy current flows, generates Joule heat, and can inductively heat the aluminum part.

[0063] However, even if the frequency of the high-frequency current is increased to inductively heat the aluminum portion, the aluminum portion has extremely low impedance, so an overcurrent flows as a secondary current into outer coil 28b and drive circuit 23b, which are the secondary side of the circuit. Because the overcurrent flows into outer coil 28b, the temperature of the conductor pattern of outer coil 28b rises.

[0064] Therefore, the heating coil 8 of the present embodiment 2 is configured such that the thickness of the copper foil of the conductor pattern of the inner coil 28a close to the center of the winding is thinner than the thickness of the copper foil of the conductor pattern of the outer coil 28b far from the center of the winding. By increasing the thickness of the copper foil of the conductor pattern of the outer coil 28b, the surface area is increased, the heat dissipation area is increased, and the heat dissipation of the conductor pattern can be promoted. As a result, the temperature rise of the conductor pattern of the outer coil 28b is suppressed, and the reliability of the heating coil 8 is improved. In addition, it is possible to efficiently inductively heat an object to be heated having different characteristics in which high impedance characteristics and low impedance characteristics are mixed, such as an IH-compatible aluminum frying pan.

[0065] The heating coil 8 of the second embodiment is configured such that the thickness of the copper foil of the conductor pattern of the outer coil 28b, which is the split coil through which a high-frequency current flows, is relatively thicker than the thickness of the copper foil of the conductor pattern of the inner coil 28a, which is the split coil through which a low-frequency current flows, among the multiple split coils sharing the center of winding. Since the thickness of the copper foil of the conductor pattern of the outer coil 28b is thicker than the thickness of the copper foil of the inner coil 28a, the surface area of ​​the conductor pattern of the outer coil 28b is larger than the surface area of ​​the inner coil 28a. Therefore, it is possible to promote the heat dissipation of the conductor pattern of the outer coil 28b against the large current generated when inductively heating the low-impedance part of the heated object. As a result, the reliability of the heating coil 8 is improved.

[0066] Conventionally, when induction heating an aluminum object to be heated, there is a problem that the temperature of the power element and the heating coil rises due to an overcurrent. In order to address this problem, there is an induction heating cooker that is provided with a boost circuit that boosts the bus voltage of the inverter circuit, and raises the voltage to maintain the output power and suppresses the secondary current. The boost circuit is, for example, a circuit that boosts 280V to 400V. In contrast, in the second embodiment, the temperature rise of the heating coil 8 is suppressed by the above-mentioned configuration, so there is no need to provide a boost circuit for the power (about 500W) that supplementarily heats the aluminum part of an IH-compatible aluminum frying pan.

[0067] Embodiment 3 In the second embodiment, the two split coils are provided on the same substrate, whereas in the third embodiment, the two split coils are provided on separate substrates. The induction heating cooker 1 of the third embodiment has the same overall configuration as that described in the first embodiment, except for the heating coil 8. In the third embodiment, based on the second embodiment, the heating coil 8 will be mainly described with reference to the differences from the second embodiment, and a detailed description of the configuration similar to that described in the second embodiment will be omitted.

[0068] The configuration of the heating coil 8 in the induction heating cooker 1 of the present embodiment 3 will be described. Fig. 9 is a plan view showing one configuration example of a heating coil in the induction heating cooker according to the embodiment 3. Fig. 10 is a plan view showing a state in which the multiple boards constituting the coil assembly shown in Fig. 9 are separated. The induction heating cooker 1 of the present embodiment 3 has the coil assembly 30 shown in Fig. 9 including the heating coil 8. The coil assembly 30 shown in Fig. 9 is a board formed by integrating the multiple boards shown in Fig. 10.

[0069] As shown in FIG. 10, the coil assembly 30 has a substrate 15a, a substrate 15b, and a fixing member 31. The substrate 15b is stacked on the fixing member 31, and the substrate 15a is stacked on the substrate 15b. The three substrates, substrate 15a, substrate 15b, and fixing member 31, are positioned on the XY plane so that the positions of the screw holes 33a and 33b shown in FIG. 10 match on the three substrates, and then are integrally configured by screws 34a and 34b shown in FIG. 9. Specifically, the screw 34a is inserted into the screw hole 33a of the three substrates, and the screw 34b is inserted into the screw hole 33b of the three substrates, thereby fixing the substrate 15a and substrate 15b to the fixing member 31 that serves as the base. FIG. 9 shows the coil assembly 30 in which the substrate 15a, substrate 15b, and fixing member 31 are integrally configured, as viewed from above.

[0070] An outer coil 28b is provided on the front surface of the substrate 15a. Although not shown in FIG. 10, an opening is formed at the position of the end 14b of the outer coil 28b on the rear side of the substrate 15a, so that the end 14b is exposed on the rear side of the substrate 15a. An inner coil 28a is provided on the front surface of the substrate 15b. Wiring portions 17a, 17c, and 17d are provided on the rear side of the substrate 15b. An opening 16b is formed in the substrate 15b to expose the rear side of the end 14b of the outer coil 28b. Although not shown in FIG. 10, an opening is formed at the electrode pad portion of each of the wiring portions 17a, 17c, and 17d on the rear side of the substrate 15b, so that the electrode pad portion of each wiring portion is exposed. Openings 16a to 16d are formed in the fixing member 31. The inner coil 28a is electrically connected to the driving circuit 23a shown in FIG. 8 through the openings 16a and 16c. The outer coil 28b is electrically connected to the drive circuit 23b shown in FIG. 8 through the openings 16b and 16d.

[0071] FIG. 11 is a schematic cross-sectional view taken along the line BB in FIG. 9. The materials of the substrate 15a, the substrate 15b, and the fixing member 31 are, for example, a paper phenol material, a composite substrate epoxy resin, or a glass cloth substrate epoxy resin. As shown in FIG. 11, the conductor pattern of the outer coil 28b is disposed closer to the object to be heated (not shown) disposed opposite the surface of the substrate 15a than the conductor pattern of the inner coil 28a. This is to facilitate the generation of eddy currents in the object to be heated (not shown) due to the high-frequency current flowing through the outer coil 28b. In addition, the thickness of the copper foil of the conductor pattern of the outer coil 28b is greater than the thickness of the copper foil of the conductor pattern of the inner coil 28a. If the thickness of the conductor pattern of the inner coil 28a is t1 and the thickness of the conductor pattern of the outer coil 28b is t2, then the relationship t2>t1 holds.

[0072] Although not shown in Fig. 11, end 14d of outer coil 28b and end of wiring portion 17d are electrically connected by a via made of a conductive material such as solder. The via (not shown) may be a solid body as long as it has conductivity, and may be an elastic body whose volume shrinks when pressed. Also in this third embodiment, inner coil 28a is connected to drive circuit 23a shown in Fig. 8, and outer coil 28b is connected to drive circuit 23b shown in Fig. 8, but in this third embodiment, the configuration is not shown in the figure and detailed description thereof is omitted.

[0073] Also in the third embodiment, the number of turns of the inner coil 28a and the outer coil 28b are not limited to those shown in FIG. 9. FIG. 10 shows a configuration in which electrode pads are provided on the fixing member 31 on the back side of the coil assembly 30, but the position of the electrode pads for connecting the heating coil 8 to the driving circuits 23a and 23b is not limited to the fixing member 31. The electrode pads for connecting the heating coil 8 to the driving circuits 23a and 23b may be provided on the front surface of the substrate 15a. Furthermore, FIG. 10 shows a case in which the wiring parts 17a, 17c, and 17d are provided on the back surface of the substrate 15b, but lead wires may be used instead of these wiring parts. FIGS. 9 and 10 show a case in which the inner coil 28a and the outer coil 28b have concentric circular shapes, but they may have concentric rectangular shapes or concentric elliptical shapes.

[0074] In this manner, in the third embodiment, heating coil 8 described in the second embodiment is configured by two substrates, substrate 15a and substrate 15b shown in FIG.

[0075] Next, the operation of the heating coil 8 in the present embodiment 3 will be described. In the present embodiment 3, as in the embodiment 2, the case where the object to be heated is an IH compatible aluminum frying pan will be described, and the description of the contents that overlap with the contents described in the embodiment 2 will be omitted.

[0076] Drive circuit 23a supplies a current in the high-frequency to low-frequency range of 20 kHz to approximately 40 kHz to inner coil 28a. Drive circuit 23b supplies a current in the high-frequency to high-frequency range of approximately 50 kHz to 100 kHz to outer coil 28b. Because a high-impedance magnetic material is attached to the bottom surface of the IH-compatible aluminum frying pan, when a current in the high-frequency to low-frequency range flows through inner coil 28a, an eddy current sufficient to generate Joule heat is generated in the magnetic material.

[0077] On the other hand, in an IH-compatible aluminum frying pan, the aluminum portion of the outer side wall that forms the surface of the pot has extremely low impedance characteristics, but by passing a current in the high-frequency to high-frequency range through the outer coil 28b, the current density on the surface of the aluminum portion is increased, generating Joule heat and inductively heating the aluminum portion.

[0078] Since the aluminum portion has extremely low impedance, an overcurrent flows into the outer coil 28b and the driving circuit 23b as a secondary current, but the thickness t2 of the conductive pattern of the outer coil 28b is thicker than the thickness t1 of the conductive pattern of the inner coil 28a. By increasing the thickness of the copper foil of the conductive pattern of the outer coil 28b, the surface area is increased, and the heat dissipation area is increased, thereby promoting heat dissipation of the conductive pattern. As a result, the temperature rise of the conductive pattern of the outer coil 28b is suppressed, and the reliability of the heating coil 8 is improved.

[0079] According to the third embodiment, the same effect as that of the second embodiment can be obtained. Moreover, according to the third embodiment, since a plurality of heating coils having different copper foil thicknesses are formed on different substrates, the thickness of the copper foil can be changed for each substrate. Therefore, the design freedom of the copper foil thickness is improved. Moreover, it becomes easy to manufacture the coil assembly 30 in which two or more substrates are combined from a plurality of types of substrates on which heating coils having different copper foil thicknesses are formed. As a result, the manufacturing cost of various heating coils can be suppressed, and a more inexpensive induction heating cooker 1 can be provided.

[0080] In addition, by configuring multiple heating coils with different copper foil thicknesses on separate substrates, it is possible to prevent heat generated in substrate 15a through which high-frequency current flows from being transferred to substrate 15b, thereby improving the reliability of substrate 15b on which a conductive pattern with a thin copper foil thickness is formed.

[0081] Embodiment 4 In the first to third embodiments, a heating coil is formed on one plane of a single substrate, but in the fourth embodiment, a heating coil is formed on an inner layer of a multi-layer substrate. The induction heating cooker 1 of the fourth embodiment has the same overall configuration as that described in the first embodiment, except for the heating coil 8. In the fourth embodiment, based on the second embodiment, the heating coil 8 will be mainly described in terms of differences from the second embodiment, and a detailed description of the same configuration as that described in the second embodiment will be omitted.

[0082] The configuration of the heating coil 8 in the induction heating cooker 1 of the present embodiment 4 will be described. Fig. 12 is a plan view showing one configuration example of the heating coil in the induction heating cooker according to embodiment 4. Fig. 13 is a schematic cross-sectional view taken along line CC in Fig. 12.

[0083] The induction heating cooker 1 of the present embodiment 4 has a multilayer substrate 40 shown in FIG. 12, which includes a heating coil 8. The multilayer substrate is a substrate having an inner layer in addition to a C-face and an S-face. When the multilayer substrate has a five-layer structure, it has three inner layers in addition to the C-face and the S-face. There are types of multilayer substrates having a four-layer structure, a five-layer structure, or a six-layer structure, as well as those having even more layers. In the present embodiment 4, a case in which the multilayer substrate 40 has a five-layer structure will be described.

[0084] As shown in FIG. 13, the multilayer substrate 40 has a first layer 41, a second layer 42, a third layer 43, a fourth layer 44, and a fifth layer 45. The material of the first layer 41 is the same as that of the substrate 15 described in the first embodiment. The first layer 41 is a layer that serves as a C surface, and is the uppermost layer of the five layers. The first layer 41 is the layer closest to the bottom surface of the object to be heated (not shown) that is placed opposite the multilayer substrate 40 via the top plate 7 shown in FIG. 1. A temperature detection sensor (not shown) that detects the temperature of the object to be heated (not shown) may be provided in the first layer 41.

[0085] The second layer 42 is a layer where the outer coil 28b made of a conductor pattern with a thick copper foil is formed. In the second layer 42, the spaces between the conductor patterns are filled with insulators 13. The third layer 43 is a layer where the inner coil 28a made of a conductor pattern with a thin copper foil is formed. In the third layer 43, the spaces between the conductor patterns are filled with insulators 13. The outer coil 28b, which has a thicker copper foil than the inner coil 28a, is formed on the second layer 42 near the object to be heated (not shown). This is to make it easier for eddy currents caused by the high-frequency current flowing through the outer coil 28b to be generated in the object to be heated (not shown).

[0086] The fourth layer 44 is a layer on which the wiring portions 17a, 17c, and 17d are formed. In the fourth layer 44, the spaces between the conductor patterns of the wiring portions 17a, 17c, and 17d are filled with the insulator 13. The upper surfaces of the wiring portions 17a, 17c, and 17d are covered with the insulator 13 except for the portions connected to the ends of the inner coil 28a and the outer coil 28b. This is to prevent the wiring portions 17a, 17c, and 17d from contacting each other at places other than the ends of the inner coil 28a and the outer coil 28b.

[0087] The fifth layer 45 is a layer that serves as an S-plane and is the bottom layer of the five layers. The fifth layer 45 is the layer farthest from the bottom surface of the object to be heated (not shown) among the five layers. The material of the fifth layer 45 is the same as that of the substrate 15 described in the first embodiment. The fifth layer 45 has openings 16a to 16d shown in FIG. 12 that serve as electrode pads for connecting to the drive circuits 23a and 23b shown in FIG. 8. The fifth layer 45 may be a layer in which no conductive pattern is formed as shown in FIG. 13, or may have wiring parts 17a, 17c, and 17d formed instead of the fourth layer 44. The heating coil 8 may have another coil (not shown) in addition to the inner coil 28a and the outer coil 28b, and in this case, the other coil may be formed on the fifth layer 45. In this case, a drive circuit (not shown) that supplies a high-frequency current to the other coil (not shown) is separately provided in the induction heating cooker 1.

[0088] In the fourth embodiment, the heating coil 8 described in the second embodiment is also configured on the multilayer substrate 40. As a configuration for efficiently and effectively inductively heating the object to be heated (not shown) placed directly above the first layer 41 via the top plate 7 shown in FIG. 1, it is desirable to arrange the divided coils so that they do not overlap each other when looking down on the divided coils with the object to be heated as a reference. The object to be heated (not shown) is, for example, an IH-compatible aluminum frying pan. In the fourth embodiment, as in the first to third embodiments, the inner coil 28a is arranged on the inner periphery side close to the center of the winding of the heating coil 8, and the outer coil 28b is arranged on the outer periphery side away from the center of the winding, thereby preventing the divided coils from overlapping each other.

[0089] Next, the operation of the heating coil 8 in the present embodiment 4 will be described. In the present embodiment 4, as in the embodiment 2, the case where the object to be heated is an IH compatible aluminum frying pan will be described, and the description of the contents that overlap with the contents described in the embodiment 2 will be omitted.

[0090] The driving circuit 23a supplies a current in the high-frequency to low-frequency range of 20 kHz to about 40 kHz to the inner coil 28a. The driving circuit 23b supplies a current in the high-frequency to high-frequency range of about 50 kHz to 100 kHz to the outer coil 28b. The second layer 42 has a shorter physical distance to the bottom surface of the IH-compatible aluminum frying pan by one layer compared to the third layer 43. Therefore, by forming the outer coil 28b, to which a current in the high-frequency to high-frequency range of about 50 kHz to 100 kHz is supplied, on the second layer 42, the aluminum part of the outer peripheral side wall of the IH-compatible aluminum frying pan is induction-heated by the outer coil 28b. This improves the power transmission efficiency and heating efficiency from the heating coil 8 to the bottom surface of the IH-compatible aluminum frying pan, and suppresses overcurrent on the secondary side of the circuit. Furthermore, by forming the copper foil of the outer coil 28b to be thick, the surface area of ​​the conductor pattern of the outer coil 28b into which the overcurrent flows is increased. Therefore, the heat dissipation effect of the conductive pattern of the outer coil 28b is promoted, the temperature rise of the conductive pattern can be suppressed, and the reliability of the heating coil 8 is improved.

[0091] On the other hand, inner coil 28a of third layer 43, to which current in the high-frequency to low-frequency range of 20 kHz to about 40 kHz is supplied, induction heats the magnetic material attached to the bottom surface of the IH-compatible aluminum frying pan. Therefore, the large current generated when heating the aluminum part does not flow to the secondary side of the circuit. In inner coil 28a, it is possible to prevent the conductor pattern of inner coil 28a from overheating without improving the heating efficiency, and it is possible to prevent the reliability of heating coil 8 from decreasing.

[0092] Incidentally, the five-layered multilayer substrate 40 is merely an example, and the multilayer substrate 40 may be three or four layers, or may be five or more layers. Furthermore, when the multilayer substrate 40 is five layers, the above-mentioned allocation of the multiple split coils to the five layers is merely an example, and is not limited to the above-mentioned configuration example. The heating coil 8 similar to that of the second embodiment is formed by allocating the multiple split coils through which high-frequency current flows to any of the first layer 41 to the fifth layer 45. The multiple split coils may be formed in any of the first layer 41 to the fifth layer 45, but are formed in different layers.

[0093] For example, the inner coil 28a with a thin copper foil may be formed on the second layer 42, and the outer coil 28b with a thick copper foil may be formed on the third layer 43. In this case, the distance from the outer coil 28b on the third layer 43 to the IH-compatible aluminum frying pan is closer by the thickness difference (t2-t1) than the distance from the inner coil 28a to the IH-compatible aluminum frying pan when the inner coil 28a is formed on the third layer 43. Also in this case, when looking down on the inner coil 28a and the outer coil 28b with the IH-compatible aluminum frying pan as a reference, these split coils are arranged so that they do not overlap each other. When a current in the high-frequency-high-frequency range is supplied to the outer coil 28b formed on the third layer 43, the outer coil 28b inductively heats the aluminum part of the outer peripheral side wall of the IH-compatible aluminum frying pan. On the other hand, when a current in the high-frequency-low-frequency range is supplied to the inner coil 28a formed on the second layer 42, the inner coil 28a inductively heats the magnetic material part attached to the bottom surface of the IH-compatible aluminum frying pan with high efficiency.

[0094] According to the fourth embodiment, multiple split coils are formed on multiple layers of the multilayer substrate 40 so that each split coil is formed on a different layer, and the thickness of the copper foil of the split coil that supplies current in the high-frequency to high-frequency range is increased to increase the surface area. This promotes the heat dissipation effect of the conductor pattern formed by printing technology, and realizes induction heating of the aluminum part while ensuring the heat resistance of the conductor pattern. This suppresses the temperature rise of the conductor pattern to improve the reliability of the heating coil 8, and also allows the bottom surface of the IH-compatible aluminum frying pan to be heated to an even temperature.

[0095] According to the fourth embodiment, the heating coil 8 is formed by the multi-layer substrate 40, which eliminates the need for members for constructing a coil assembly and allows a plurality of split coils to be formed compactly. As a result, the manufacturing cost of the heating coil 8 can be reduced, and a cheaper induction heating cooker 1 can be provided.

[0096] Various aspects of the induction heating cooker of the present disclosure will be described below as an appendix.

[0097] (Appendix 1) A substrate disposed opposite the object to be heated; A heating coil in which a conductor is wound around one surface of the substrate to form a spiral conductor pattern; A drive circuit that applies a high-frequency current to the heating coil; having The conductor pattern has a portion in which a thickness of the conductor pattern varies depending on a portion in a circumferential direction. Induction heating cooker. (Appendix 2) The heating coil is an inner coil in which the conductor pattern is formed at a position close to the center of the winding; an outer coil in which the conductor pattern is formed, the outer coil being located farther from the center than the inner coil and sharing a center of winding with the inner coil; a thickness of the conductor pattern of one of the inner coil and the outer coil is greater than a thickness of the conductor pattern of the other coil; 2. An induction heating cooker as described in appendix 1. (Appendix 3) a width of the conductor pattern of the one coil is greater than a width of the conductor pattern of the other coil; 5. An induction heating cooker as described in appended claim 2. (Appendix 4) The inner coil and the outer coil are electrically isolated, The drive circuit includes: a first drive circuit that causes the high-frequency current to flow through the one coil; A second drive circuit that causes the high-frequency current to flow through the other coil. 4. An induction heating cooker according to claim 2 or 3. (Appendix 5) The frequency of the high frequency current supplied to the one coil by the first drive circuit is higher than the frequency of the high frequency current supplied to the other coil by the second drive circuit. 5. An induction heating cooker as described in appendix 4. (Appendix 6) The one coil is the outer coil and the other coil is the inner coil. 6. An induction heating cooker as described in appendix 5. (Appendix 7) The substrate is a first substrate on which the conductor pattern of the one coil is formed on the one plane; a second substrate on which the conductor pattern of the other coil is formed on the one plane, The first substrate is disposed closer to the object to be heated than the second substrate. 7. The induction heating cooker according to any one of claims 2 to 6. (Appendix 8) The substrate is A first layer having an upper surface facing the object to be heated and made of an insulating material; a second layer provided under the first layer, the second layer having the conductor pattern of the one coil formed on the one plane; a third layer provided under the second layer, the third layer having the conductor pattern of the other coil formed on the one plane; a fourth layer provided below the third layer and made of the insulator; 7. The induction heating cooker according to any one of claims 2 to 6. [Explanation of symbols]

[0098] 1 induction heating cooker, 2a to 2c heating port, 3 main power button, 4 heating port power button, 5 heat setting encoder, 6 notification unit, 7 top plate, 8, 8a to 8c heating coil, 10 housing, 12 operation input unit, 13 insulator, 14a to 14d end, 15, 15a, 15b board, 16a to 16d opening, 17, 17a, 17c, 17d wiring unit, 18a inner coil, 18b outer coil, 19 ferrite, 20 control unit, 23, 23a, 23b drive circuit, 28a inner coil, 28b outer coil, 30 coil assembly, 31 fixing member, 33a, 33b screw hole, 34a, 34b screw, 40 multi-layer board, 41 first layer, 42 second layer, 43 third layer, 44 fourth layer, 45 5th layer.

Claims

1. A substrate disposed opposite the object to be heated; A heating coil in which a conductor is wound around one surface of the substrate to form a spiral conductor pattern; A drive circuit that applies a high-frequency current to the heating coil; having The conductor pattern has a portion in which a thickness of the conductor pattern varies depending on a portion in a circumferential direction. Induction heating cooker.

2. The heating coil is an inner coil in which the conductor pattern is formed at a position close to the center of the winding; an outer coil in which the conductor pattern is formed, the outer coil being located farther from the center than the inner coil and sharing a center of winding with the inner coil; a thickness of the conductor pattern of one of the inner coil and the outer coil is greater than a thickness of the conductor pattern of the other coil; 2. The induction heating cooker according to claim 1.

3. a width of the conductor pattern of the one coil is greater than a width of the conductor pattern of the other coil; 3. The induction heating cooker according to claim 2.

4. The inner coil and the outer coil are electrically isolated, The drive circuit includes: a first drive circuit for causing the high frequency current to flow through the one coil; a second drive circuit for causing the high frequency current to flow through the other coil; 4. The induction heating cooker according to claim 2 or 3.

5. the frequency of the high frequency current supplied to the one coil by the first drive circuit is higher than the frequency of the high frequency current supplied to the other coil by the second drive circuit; 5. The induction heating cooker according to claim 4.

6. The one coil is the outer coil and the other coil is the inner coil.

6. The induction heating cooker according to claim 5.

7. The substrate is a first substrate on which the conductor pattern of the one coil is formed on the one plane; a second substrate on which the conductor pattern of the other coil is formed on the one plane, The first substrate is disposed closer to the object to be heated than the second substrate.

4. The induction heating cooker according to claim 2 or 3.

8. The substrate is A first layer having an upper surface facing the object to be heated and made of an insulating material; a second layer provided below the first layer, the second layer having the conductor pattern of the one coil formed on the one plane; a third layer provided below the second layer, the third layer having the conductor pattern of the other coil formed on the one plane; a fourth layer provided below the third layer and made of the insulator; 4. The induction heating cooker according to claim 2 or 3.

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