Electromagnetic induction heating cooker

Abstract

To provide an electromagnetic induction heating cooker capable of reliably supporting a relatively thick and heavy magnetic shield even when it is used.SOLUTION: A top plate 2 on which an object to be heated is placed includes: a top frame 41 having a rectangular frame shape; a top plate 42 having a rectangular plate shape fitted inside the top frame 41; and a magnetic shield plate 43 made of a conductive material and in close contact with a lower surface of the top plate 42. A support flange 44 that supports the top plate 42 and the magnetic shield plate 43 overlapping each other in a vertical direction from below is formed on an inner peripheral edge of the top frame 41. The magnetic shield plate 43 is formed in a rectangular plate shape having the same outline as that of the top plate 42 in a plan view, and a circular coil opening 45 that allows a heating coil 8 to face the top plate 42 is opened in the center of the magnetic shield plate 43.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electromagnetic induction cooking appliance in which a magnetic shield is provided on a top plate on which a cooking vessel such as a pot is placed in order to suppress magnetic leakage around the cooking vessel. [Background technology]

[0002] This type of electromagnetic induction cooking appliance (hereinafter referred to as "cooker") is disclosed, for example, in Patent Document 1. In this appliance, a magnetic shield portion for suppressing magnetic leakage from the heating coil is formed on the heating coil side, i.e., the backside, of a ceramic top plate. This magnetic shield portion is made of a conductive material and is directly fixed to the backside of the top plate, and is formed as a strip-like loop with an inner diameter larger than the outer diameter of the heating coil.

[0003] When a magnetic field is generated from the heating coil, an induced current is generated in the magnetic shield. This induced current acts to strengthen the magnetic field inside the magnetic shield and weaken the magnetic field outside the magnetic shield. Strengthening the magnetic field inside the magnetic shield allows for rapid heating of a cooking vessel such as a pot placed on the top plate, while weakening the magnetic field outside the magnetic shield prevents magnetic leakage around the cooking vessel. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-45631 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, in the cooker of Patent Document 1, the magnetic shield is directly attached to the back surface of the top plate. In other words, the magnetic shield is not supported from below, and if its thickness is too large, there is a risk that the magnetic shield will peel off from the top plate due to its own weight. Some cookers are high-output models with heating coils with an outer diameter of approximately 30 cm. In such models, the magnetic shield must be relatively thick. Therefore, directly attaching a thick and heavy magnetic shield to the back surface of the top plate is undesirable from the perspective of preventing the magnetic shield from peeling off.

[0006] An object of the present invention is to provide an electromagnetic induction cooking appliance that can reliably support a relatively thick and heavy magnetic shield even when such a shield is used. [Means for solving the problem]

[0007] The present invention is directed to an electromagnetic induction heating cooker including a top plate 2 on which an object to be heated is placed, and a heating coil 8 that generates an induction magnetic field above the top plate 2. The top plate 2 includes a rectangular top frame 41, a rectangular top plate 42 fitted inside the top frame 41, and a magnetic shield plate 43 made of a conductive material that is in close contact with the underside of the top plate 42. The top frame 41 is characterized by having a support flange 44 that projects from below and supports the top plate 42 and magnetic shield plate 43, which are stacked one on top of the other, from the inner peripheral edge.

[0008] The magnetic shield plate 43 is formed as a square plate having the same outer shape as the top plate 42 when viewed in a plane, and a circular coil opening 45 is opened in the center of the magnetic shield plate 43 so that the heating coil 8 faces the top plate 42.

[0009] The heating coil 8 is housed in a housing 13 having an opening on the top surface, and the top plate 2 is supported at the upper end of the housing 13.

[0010] The housing 13 has a pair of side walls 55 that face each other with the heating coil 8 therebetween. At the upper end of each side wall 55, an outer support piece 56 that protrudes outward to support the top frame 41 from below, and an inner support piece 57 that protrudes inward to support the support flange 44 from below are formed.

[0011] A magnetically permeable sheet 61 having a higher magnetic permeability than the magnetic shield plate 43 is attached to the lower surface of the magnetic shield plate 43 .

[0012] On the lower surface of the magnetic shield plate 43, strip-shaped magnetic shielding portions 62 containing ferrite are formed radially. [Effects of the Invention]

[0013] The top plate 2 of the electromagnetic induction cooking device according to the present invention includes a rectangular top frame 41, a rectangular cooking plate 42 fitted inside the top frame 41, and a magnetic shield plate 43 made of a conductive material that is in close contact with the underside of the cooking plate 42, and a support flange 44 that protrudes from the inner peripheral edge of the top frame 41 and supports the top plate 42 and magnetic shield plate 43, which are stacked one on top of the other, from below. The support structure in which the support flange 44 supports the top plate 42 and the magnetic shield plate 43 ensures that even when a relatively thick and heavy magnetic shield plate 43 is used, it can be firmly supported and the top plate 42 and the magnetic shield plate 43 can be kept in close contact with each other.

[0014] If the magnetic shield plate 43 is formed in the shape of a square plate having the same outer contour as the top plate 42 when viewed in a plane, the magnetic shield plate 43 can be easily and accurately positioned relative to the top frame 41 by utilizing the inner peripheral edge of the top frame 41 into which the top plate 42 is fitted, thereby preventing misalignment of the coil opening 45 of the magnetic shield plate 43 relative to the heating coil 8.

[0015] By supporting the top plate 2 at the upper end of the housing 13 that houses the heating coil 8, the vertical distance between the heating coil 8 and the top plate 2, and therefore the vertical distance between the heating coil 8 and the cooking container P on the top plate 2, can always be kept constant, allowing the cooking container P to be always heated stably by the heating coil 8.

[0016] If outer support pieces 56 that protrude outward to support the top frame 41 from below and inner support pieces 57 that protrude inward to support the support flange 44 from below are formed at the upper end of each side wall 55 of the housing 13, the load of the top plate 2 can be distributed to the outer support pieces 56 and inner support pieces 57, reducing the pressure acting on each support piece 56, 57. In addition, the inner support pieces 57 reinforce the support flange 44 from below, allowing this support flange 44 to more firmly support the top plate 42 and magnetic shield plate 43.

[0017] By attaching a magnetically permeable sheet 61 with high magnetic permeability to the underside of the magnetic shield plate 43, the magnetically permeable sheet 61 can absorb part of the magnetic field generated from the heating coil 8, thereby further suppressing leakage of magnetic field around the cooking container P on the top plate 2.

[0018] By forming a radial strip-shaped magnetic shielding portion 62 made of ferrite on the underside of the magnetic shield plate 43, part of the magnetic field generated from the heating coil 8 can be shielded by the magnetic shielding portion 62, thereby further suppressing leakage of magnetic field around the cooking container P on the top plate 2. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a longitudinal sectional front view of a main part of an electromagnetic induction heating cooker according to an embodiment of the present invention. [Figure 2] FIG. 1 is a perspective view of an electromagnetic induction heating cooker. [Figure 3] FIG. 2 is a vertical cross-sectional side view of the upper part of the electromagnetic induction cooking appliance. [Figure 4] FIG. 1 is a plan view of an electromagnetic induction cooking appliance. [Figure 5] FIG. 2 is a plan view of a top frame of a top plate of the electromagnetic induction cooking appliance. [Figure 6] 10A and 10B are diagrams showing modified examples of the magnetic shield plate of the top plate. [Figure 7] 10A and 10B are diagrams showing another modified example of the magnetic shield plate of the top plate. DETAILED DESCRIPTION OF THE INVENTION

[0020] (Embodiment) Figures 1 to 5 show an embodiment of an electromagnetic induction heating cooker (hereinafter referred to as "cooker" where appropriate) according to the present invention. In this embodiment, front, back, left, right, and top and bottom refer to the crossed arrows shown in Figure 2 and the indications of front, back, left, right, and top and bottom written near each arrow. As shown in Figures 2 and 3, the cooker has a square box-shaped casing 1 with an opening on the top surface, and a top plate 2 arranged to close the opening from above, and a cooking container P such as a pot containing an object to be heated is placed on the top plate 2.

[0021] The casing 1 contains, from top to bottom, a heating unit 3 that heats the object to be heated (the object to be heated contained in the cooking container P) placed on the top plate 2, a weighing unit 4 that measures the weight of the object to be heated, and a control unit 5 that controls the entire cooker. The heating unit 3 and the weighing unit 4 are each electrically connected to the control unit 5 via a power cable not shown. The top of the casing 1 surrounds the sides of the weighing unit 4 and the heating unit 3 on all four sides. In addition, the casing 1 is not in contact with the top plate 2, the heating unit 3, or the weighing unit 4. The casing 1 is made of a metal such as stainless steel to prevent leakage of magnetic fields and electromagnetic waves generated by the heating unit 3.

[0022] The measuring unit 4 supports the entire heating unit 3 from below. The heating unit 3 also supports the entire top plate 2 from below. In addition, as described above, the casing 1 is not in contact with the top plate 2, heating unit 3, and measuring unit 4, so the weight of the top plate 2 and the like does not act on the casing 1. Therefore, the weights of the heating unit 3 and top plate 2 and the weight of the object to be heated (including the cooking container P) on the top plate 2 act on the measuring unit 4. Because the former weight (the weight of the heating unit 3 and top plate 2) is constant, the latter weight, i.e., the weight of the object to be heated, can be measured by subtracting the former weight in advance from the measurement value of the measuring unit 4.

[0023] As shown in FIG. 1 , the heating unit 3 comprises a horizontal, disk-shaped heating coil 8 facing the inner surface of the top plate 2, an inverter board 9 supplying high-frequency current to the heating coil 8, a partition wall 10 separating the heating coil 8 from the inverter board 9, two temperature sensors 11 and 12 detecting the temperature of the cooking container P through the top plate 2, and a housing 13 accommodating these components. The heating coil 8 is mounted on the upper surface of the partition wall 10 via a plurality of spacers 16 spaced equally spaced around its circumference. The inverter board 9 comprises a rectangular plate-shaped substrate 17 mounted on the bottom surface of the housing 13 and a heat sink 18 for heat dissipation attached to the right half of the substrate 17. When high-frequency current is supplied from the inverter board 9 to the heating coil 8, an induced magnetic field is generated above the top plate 2, eddy currents flow in the cooking container P on the top plate 2, and Joule heat generated by the electrical resistance heats the cooking container P and the food contained therein.

[0024] Of the two temperature sensors 11 and 12 that make up the heating unit 3, the first temperature sensor 11 is a thermistor that is in close contact with the center of the underside of the top plate 2 and detects its temperature, and is supported by a sensor bracket 19 that stands upright from the upper surface of the partition wall 10 toward the central hole of the heating coil 8. The second temperature sensor 12 is a radiation thermometer that detects the temperature of infrared rays emitted from the top plate 2 and is disposed in a recumbent position on the underside of the partition wall 10. A triangular prism 20 with a 45-degree reflective surface is disposed in front of the second temperature sensor 12, and a detection hole 21 is formed in the center of the partition wall 10 that faces the reflective surface of the prism 20 and the central hole of the heating coil 8. In other words, infrared rays radiated downward from the center of the underside of the top plate 2 pass through the central hole of the heating coil 8 and the detection hole 21 to reach the prism 20, where they are reflected horizontally by the reflective surface toward the second temperature sensor 12, whose temperature is detected by the second temperature sensor 12.

[0025] The housing 13 of the heating unit 3 is made of a metal such as stainless steel and is shaped like a square box with an opening on the top. As shown in FIG. 3 , an air intake 24 is provided on the front surface of the housing 13, and an exhaust 25 is provided on the rear surface of the housing 13. A cooling mechanism 27 for cooling the heating unit 3 is disposed on the inner surface of the front wall 26 of the casing 1. The cooling mechanism 27 includes a supply duct 28 extending vertically along the inner surface of the front wall 26 and an axial cooling fan 29 housed inside the supply duct 28. When the cooling fan 29 is driven, an upward airflow is generated within the supply duct 28. An intake 30 for taking in outside air is formed at the lower end of the supply duct 28, and an outlet 31 for blowing out air is formed at the upper end of the supply duct 28. The outlet 31 opens rearward and faces closely to the air intake 24 of the heating unit 3 (through a gap). The air blown out from the air outlet 31 toward the air intake 24 flows inside the housing 13 from the front (air intake 24) to the rear (air exhaust 25), cooling the heating coil 8, inverter board 9, and other components that generate heat inside the housing 13.

[0026] As shown in FIG. 2, an operation unit 34 operated by a cook is provided on the outer surface of the front wall 26 of the casing 1. The operation unit 34 is composed of a touch panel 35, a rotary dial 36, and a push button 37. The operation unit 34 is located at the top of the front wall 26, and the top of the operation unit 34 slopes downward toward the front. A transparent, rectangular operation cover 38 is detachably attached to the upper end of the front wall 26. As shown in FIG. 4, the operation cover 38 covers the operation unit 34 from above to protect it from water spilling over from the cooking container P on the top plate 2. A cook standing in front of the cooker can adjust the output of the heating coil 8 by operating the operation unit 34 while viewing the entire operation unit 34 through the operation cover 38.

[0027] As shown in FIG. 1, the top plate 2 on which the cooking container P is placed is composed of a rectangular top frame 41, a rectangular cooking table 42 fitted inside the top frame 41, and a magnetic shield plate 43. The cooking table 42 and the magnetic shield plate 43 are stacked one on top of the other in the order shown, and are supported from below by a support flange 44 with an L-shaped cross section that protrudes from the inner peripheral edge of the top frame 41. The cooking table 42 is made of heat-resistant glass, and its upper surface is approximately flush with the upper surface of the top frame 41. The support flanges 44 are provided on each of the front, rear, left, and right sides that make up the inner peripheral edge of the top frame 41 (see FIG. 5).

[0028] The magnetic shield plate 43 is made of a nonmagnetic, conductive material such as aluminum or copper, and has a circular coil opening 45 at its center, allowing the heating coil 8 to face the top plate 42. When a magnetic field is generated from the heating coil 8, an induced current is generated in the magnetic shield plate 43. This induced current acts to strengthen the magnetic field inside the magnetic shield plate 43 and weaken the magnetic field outside the magnetic shield plate 43. Strengthening the magnetic field inside the magnetic shield plate 43 allows for rapid heating of the cooking container P on the top plate 2 and the food therein. Weakening the magnetic field outside the magnetic shield plate 43 prevents magnetic leakage to the surroundings of the cooking container P. The diameter of the coil opening 45 is set slightly larger than the outer diameter of the heating coil 8, specifically, by 5 to 30 mm. The first temperature sensor 11 of the heating unit 3 is located at the center of the coil opening 45 and is in close contact with the center of the underside of the top plate 42.

[0029] Covering walls 48 extend downward from the left and right ends and rear end of the top frame 41, covering the upper end of the casing 1 from the outside, and a gutter 49 running left and right is provided at the front end of the top frame 41, as shown in Figure 5. The gutter 49 is located above the operation cover 38 and catches water that spills forward from the cooking container P before the operation cover 38 reaches it. Liquid holes 50 are opened at both left and right ends of the bottom wall of the gutter 49 to allow water that has flowed into the gutter 49 to flow down. Therefore, water that has flowed into the gutter 49 flows down from the liquid holes 50 before overflowing from the gutter 49.

[0030] As shown in FIG. 1 , the top plate 2 is supported at the upper end of a housing 13 of the heating unit 3. Specifically, the housing 13 is composed of a center case 53 that forms the left-right center portion thereof and a pair of side cases 54 that form both left and right ends thereof. Each side case 54 has a side wall 55 that forms the left or right surface of the housing 13, and the side walls 55 face each other laterally with the heating coil 8 and inverter board 9 between them. An outer support piece 56 that protrudes outward and supports the top frame 41 from below, and an inner support piece 57 that protrudes inward and supports the support flange 44 from below are formed at the upper end of each of these side walls 55.

[0031] As described above, the top plate 2 of the cooker of this embodiment includes a rectangular top frame 41, a rectangular top plate 42 fitted inside the top frame 41, and a magnetic shield plate 43 made of a conductive material that is in close contact with the underside of the top plate 42, and a support flange 44 that protrudes from the inner peripheral edge of the top frame 41 and supports the top plate 42 and magnetic shield plate 43, which are stacked one on top of the other, from below. The support structure in which this support flange 44 supports the top plate 42 and the magnetic shield plate 43 ensures that even when a relatively thick and heavy magnetic shield plate 43 is used, it can be firmly supported and the top plate 42 and the magnetic shield plate 43 can be kept in close contact with each other.

[0032] The magnetic shield plate 43 is formed in the shape of a square plate having the same outer contour as the top plate 42 when viewed in a plane, so that the magnetic shield plate 43 can be easily and accurately positioned relative to the top frame 41 by utilizing the inner peripheral edge of the top frame 41 into which the top plate 42 is fitted, thereby preventing misalignment of the coil opening 45 of the magnetic shield plate 43 relative to the heating coil 8.

[0033] Since the top plate 2 is supported at the upper end of the housing 13 that houses the heating coil 8, the vertical distance between the heating coil 8 and the top plate 2, and therefore the vertical distance between the heating coil 8 and the cooking container P on the top plate 2, can always be kept constant, allowing the cooking container P to be always stably heated by the heating coil 8.

[0034] The upper end of each side wall 55 of the housing 13 is formed with outer support pieces 56 that protrude outward to support the top frame 41 from below, and inner support pieces 57 that protrude inward to support the support flange 44 from below, so that the load of the top plate 2 can be distributed to the outer support pieces 56 and the inner support pieces 57, reducing the pressure acting on each of the support pieces 56, 57. The inner support pieces 57 also reinforce the support flange 44 from below, allowing this support flange 44 to more firmly support the top plate 42 and the magnetic shield plate 43.

[0035] 6 shows a modified example of magnetic shield plate 43, in which a magnetic permeable sheet 61 having a higher magnetic permeability than magnetic shield plate 43 is attached to the underside of magnetic shield plate 43. According to this modified example, a portion of the magnetic field generated by heating coil 8 is absorbed by magnetic permeable sheet 61, thereby further suppressing leakage of magnetic field to the periphery of cooking container P on top plate 2.

[0036] 7 shows another modified example of the magnetic shield plate 43, in which a shielding sheet 63 having a magnetic shielding portion 62 is attached to the underside of the magnetic shield plate 43. The magnetic shielding portion 62 contains ferrite and is formed in a band shape extending radially from the coil opening 45 of the magnetic shield plate 43. According to this modified example, the magnetic shielding portion 62 can shield a portion of the magnetic field generated by the heating coil 8, thereby further suppressing leakage of the magnetic field to the periphery of the cooking container P on the top plate 2. [Explanation of symbols]

[0037] 1 casing 2 top plate 8 heating coils 13. Cabinet 41 Top Frame 42 Top plate 43 Magnetic shield plate 44 Support flange 45 Coil opening 55 Side wall 56 Outer support piece 57 Inner support piece 61 Magnetic permeability sheet 62 Magnetic shielding section

Claims

1. The heating device includes a top plate (2) on which an object to be heated is placed, and a heating coil (8) that generates an induction magnetic field above the top plate (2), The top plate (2) includes a rectangular top frame (41), a rectangular top plate (42) fitted inside the top frame (41), and a magnetic shield plate (43) made of a conductive material and in close contact with the underside of the top plate (42); This electromagnetic induction cooking device is characterized in that a support flange (44) is formed on the inner peripheral edge of the top frame (41) to protrude and support from below a top plate (42) and a magnetic shield plate (43) that are stacked one on top of the other.

2. The magnetic shield plate (43) is formed in a rectangular plate shape having the same outer contour as the top plate (42) in a plan view, 2. The electromagnetic induction cooking appliance according to claim 1, wherein a circular coil opening (45) is formed in the center of the magnetic shield plate (43) to allow the heating coil (8) to face the top plate (42).

3. The heating coil (8) is housed in a housing (13) having an opening on the top surface, 3. The electromagnetic induction cooking appliance according to claim 1, wherein the top plate (2) is supported at an upper end of the housing (13).

4. The housing (13) has a pair of side walls (55) facing each other with the heating coil (8) interposed therebetween, 4. An electromagnetic induction heating cooker as claimed in claim 3, wherein an outer support piece (56) that protrudes outward and supports the top frame (41) from below, and an inner support piece (57) that protrudes inward and supports the support flange (44) from below, are formed at the upper end of each side wall (55).

5. 3. The electromagnetic induction cooking appliance according to claim 1, wherein a magnetically permeable sheet (61) having a higher magnetic permeability than the magnetic shield plate (43) is attached to the underside of the magnetic shield plate (43).

6. 3. The electromagnetic induction cooking appliance according to claim 1, wherein a strip-shaped magnetic shielding portion (62) made of ferrite is radially formed on the underside of the magnetic shield plate (43).

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