JP3962757B2 - Electromagnetic cooker - Google Patents

Description

  The present invention relates to an electromagnetic cooker, and more particularly to an electromagnetic cooker including a temperature sensor for detecting the temperature of a load pan.

  Conventionally, in an electromagnetic cooker equipped with a top plate on which a load pan is placed and an electromagnetic induction coil or a heating coil that is arranged on the lower side of the top plate to inductively heat the load pan, the temperature of the load pan is detected, In order to control the heating temperature of the load pan or prevent overheating of the load pan due to emptying or the like, a number of sensors having a temperature sensor attached to the lower surface of the top plate are known.

For example, in the electromagnetic cooker disclosed in Japanese Patent Laid-Open Nos. 4-248290 and 11-87041, the temperature sensor is positioned at or near the winding center of the heating coil when viewed from a direction substantially perpendicular to the top plate. It is arranged.
JP-A-4-248290 JP-A-11-87041

  In such an electromagnetic cooker, the bottom of the load pan may be warped up like an umbrella due to emptying or the like. In the case of a load pan having a warped bottom as described above, a gap (an air layer having a low thermal conductivity) is generated between the bottom portion of the load pan and the top plate, so that it is disposed at or near the winding center of the heating coil. The temperature sensor detects a temperature lower than the actual temperature of the load pan, cannot perform control based on the detected temperature, and there is a risk of overheating of the load pan. In order to solve this, it is conceivable to arrange the temperature sensor at a position other than the winding center of the heating coil or the vicinity thereof.

  By the way, in the conventional electromagnetic cooker, a circle corresponding to the outermost radial position of the heating coil is printed on the upper surface of the top plate as a mark indicating the position where the load pan is placed. However, the load pan may not be placed on the top plate according to the circle, but may be placed in a shifted state. Therefore, even if it is a case where a temperature sensor is arrange | positioned other than the winding center of a heating coil, or its vicinity, there is a possibility that a temperature sensor cannot detect the temperature of a load pan effectively.

  The present inventors have studied various arrangement positions of a temperature sensor capable of effectively detecting the temperature of the load pan even when the bottom of the load pan is warped or when the placement position is shifted. It reached.

One aspect of the electromagnetic cooker according to the present invention is a top plate for placing a load pan, a plurality of heating coils disposed below the top plate and for induction heating the load pan, the electromagnetic cooker and means for applying a current to the heating coil, for each of the plurality of heating coils, the first and second temperature sensors disposed in contact with the top plate lower surface provided, when viewed from a direction substantially perpendicular to said top plate, said first and second temperature sensors, outside the center of the heating coil, and is disposed inside the outermost periphery of the heating coil, the first One temperature sensor is disposed inside a radius of about 50% with respect to the outermost radius of the heating coil, and the second temperature sensor is disposed outside a radius of about 50% with respect to the outermost radius of the heating coil. When done Moni, said first and second temperature sensors, the conjunction is arranged offset about 180 degrees from each other in the circumferential direction of the heating coils, as viewed from a direction substantially perpendicular to said top plate, different radii of said heating coil It is arranged at a position .

  According to the electromagnetic cooker according to the present invention, the temperature of the load pan can be detected effectively even when the bottom of the load pan is warped or shifted from the placement position.

  Embodiments of an electromagnetic cooker according to the present invention will be described below with reference to the accompanying drawings. Note that in this specification, terms indicating directions (for example, “up”, “down”, “right”, “left”, and other terms including these terms) are used as appropriate, but in the drawings used for explanation These terms are only intended to indicate the direction of the present invention, and the present invention should not be construed to be limited to these terms.

Embodiment 1 FIG.
With reference to FIGS. 1-7, Embodiment 1 of the electromagnetic cooker which concerns on this invention is demonstrated. In FIG. 1, an electromagnetic cooker generally indicated by reference numeral 2 includes a box-shaped housing 3 and a top plate 4 formed of glass or the like that covers the top of the housing 3. A temperature adjustment knob 6 and a temperature display unit 8 are provided on the outer surface of the housing 3.

  As shown in FIG. 2, in the housing 3, an electromagnetic induction coil or heating coil 10 that is generally disposed on the lower side of the top plate 4, a power source 12 for supplying high-frequency current to the heating coil 10, and a power source And a control device 14 for controlling 12. On the top surface of the top plate 4, a circle 18 (FIG. 1) having a radius that substantially matches the outermost radius of the heating coil 10 is printed in order to place the load pan 16 (not shown in FIG. 1). Yes. Two temperature sensors (for example, thermistors) 20a and 20b are installed on the lower surface of the top plate 4 at predetermined positions on a virtual line extending outward from the center of the heating coil 10 when viewed from a direction substantially perpendicular to the top plate 4. The temperature of the load pan 16 is detected via the plate 4. The installation positions of the temperature sensors 20a and 20b will be described in detail later. Detection signals from the temperature sensors 20a and 20b are sent to the control device 14, and the current supplied to the heating coil 10 is adjusted as necessary.

  With reference to FIG. 3 (a), (b), the peripheral part of the heating coil 10 is demonstrated in more detail. A central ferrite 24 is disposed at the center of the heating coil 10, and rod-shaped ferrites 26 are disposed radially below the heating coil 10. These ferrites 24 and 26 are for guiding the magnetic flux generated by the heating coil 10 to the load pan 16 with high efficiency. When the shape and arrangement position of the ferrites 24 and 26 are changed, the heat generation distribution of the load pan 16 is also changed.

  A heating coil 10a as shown in FIG. 4, a load pan 16 having a flat bottom, a central ferrite 24 (see FIG. 3), and a bar cooker 26 (see FIG. 3) are used. Three-dimensional electromagnetic field analysis of how the heat distribution of the load pan 16 changes when the arrangement and shape of the central ferrite 24 and the bar ferrite 26 are changed when the center axis of the load pan 16 coincides. Determined by That is, by performing an electromagnetic field analysis, the Joule loss due to the induced current flowing through the load pan 16 in an attempt to cancel the magnetic flux generated by the heating coil 10a was obtained. The distribution of Joule loss in the radial direction is the heat generation distribution of the load pan 16. The heating coil 10a used for the analysis has a shape in which a coil is wound at a constant ratio on the center side and the outer diameter side, and a gap is provided between the coil portion on the center side and the coil portion on the outer diameter side. (See FIG. 4).

  FIG. 5 collectively shows representative examples of the heat generation density (heat generation amount per unit volume) of the load pan 16 that is obtained by electromagnetic field analysis and is induction-heated by the heating coil 10a. FIG. 5 shows the results of electromagnetic field analysis using a heating coil having an outermost diameter of 200 mm and an outer diameter of the load pan 5 of 200 mm. In FIG. 5, the horizontal axis represents the ratio of the diameter of the heating position of the load pan 16 to the outermost radius of the heating coil 10. For example, 50% of the horizontal axis represents the ratio of the diameters of the 50 mm radius portions of the pan. The vertical axis represents the heat generation density ratio of the load pan 16, and the portion where the heat generation density shows a predetermined high value is shown as 100%.

  In the following, based on the distribution of the heat generation density ratio obtained from the electromagnetic field analysis, the optimum arrangement position of the temperature sensor will be considered.

As is clear from FIG. 5, the heat generation density at the center portion and the outermost peripheral portion of the load pan 16 is substantially zero. If the temperature sensor is installed at a radial position where the heat generation density is substantially zero, the temperature after the heat has moved in the pan is measured by the temperature sensor, so the responsiveness of the temperature sensor is not good.

  It can be considered that the heat generation density ratio is high, and therefore, the region where the temperature sensor can be arranged so that the temperature of the load pan can be detected effectively is practically considered as a region larger than about 50% of the maximum heat generation density. When the temperature sensor is arranged in an area smaller than about 50%, the difference between the temperature detected by the temperature sensor and the maximum temperature of the load pan 16 is large, so that the temperature control by the control device 14 is not accurately performed, and the load pan Experiments have confirmed that there is a risk of 16 overheating. When the ratio of the radius of the heat generation position of the load pan 16 to the outermost radius of the heating coil 10 at which the heat generation density ratio is 50% is determined from FIG. 5, it is about 15% to about 90%.

  From the above, for the load pan 16 whose bottom is not warped, at least one temperature sensor is disposed in a region having a radius of about 15 to about 90% with respect to the outermost radius of the heating coil 10. Can be detected effectively.

  On the other hand, when the load pan 16 is warped, particularly when it is warped in an umbrella shape as shown in FIG. 6, the air having a low thermal conductivity except for the portion where the load pan 16 and the top plate 4 are in contact with each other. Since heat is transferred to the top plate 4 through the layer, the responsiveness is deteriorated particularly when a temperature sensor is installed on the lower surface of the top plate 4 corresponding to a portion where the air layer is thick. Therefore, it is necessary to install a temperature sensor on the lower surface of the top plate 4 corresponding to the portion where the air layer is as thin as possible.

  For example, when the load pan 16 is warped in an umbrella shape, the outermost periphery (end portion) is in contact with the top plate 4. The air layer at the center of the load pan 16 is thicker and becomes thinner toward the end. Since the end of the load pan 16 is in contact with the top plate 4, when the temperature is detected as close as possible to the end of the load pan 16, a position close to the center of the load pan 16 (for example, a load pan having an outer diameter of 200 mm). Compared to the case of detection at a radius of about 20 mm), the temperature sensor has much better responsiveness.

  As described above, the temperature sensor is disposed in a region having a radius of about 15 to about 90% with respect to the outermost radius of the heating coil 10, particularly in a region close to the outermost radius position of the heating coil 10, so that the bottom portion is warped. The temperature can be detected effectively for both the load pan 16 and the flat load pan 16.

  In the above considerations, it is assumed that the load pan 16 is arranged right above the heating coil 10, but in the following, the load pan 16 is displaced from the position directly above the heating coil 10 as shown in FIG. Of the temperature sensor that can effectively detect the temperature of the load pan 16 even when the center of the load pan 16 is shifted from the center of the mounting circle 18 (FIG. 1). Consider the optimal location.

  In the example of FIG. 7, the temperature sensors 20a and 20b are respectively installed at the radial positions of about 30 mm and about 80 mm of the heating coil 10 having an outer diameter of 200 mm. FIG. 7 is a view in which the heating coil 10, the load pan 16, and the temperature sensors 20 a and 20 b are seen from above, and shows the load pan 16 placed at various positions at the same time. As is apparent from the figure, by installing one temperature sensor 20a in the region where the radius of the heating coil 10 is small and installing the other temperature sensor 20b in the region where the radius of the heating coil 10 is large, the load pan 16 is somewhat. Even when the position of is shifted, the temperature sensor 20 b can detect the temperature in the vicinity of the end of the load pan 16. When the position of the load pan 16 is greatly shifted, the temperature sensor 20a provided in a region having a small radius of the heating coil 10 may be able to detect the temperature in the vicinity of the end portion of the load pan 16.

  In addition, when the outer diameter of the load pan 16 is smaller than the maximum diameter of the heating coil 10, for example, the outer diameter of the heating coil 10 is 200 mm, and the outer diameter of the load pan 16 is 100 mm, the heating coil 10 and the load pan Even if the load pan 16 is placed on the top plate so that the center axes of the 16 are substantially coincident with each other, the temperature sensor 20 b provided on the outer diameter side of the heating coil 10 is detached from the bottom of the pan 16. The temperature sensor 20a is always required in a region having a small radius.

  As described above, the temperature sensor has a region with a small radius of the heating coil 10, that is, a region with a radius of about 15 to about 50% with respect to the outermost radius of the heating coil 10, and a region with a large radius of the heating coil 10, that is, the heating coil 10. By disposing at least one each in a region having a radius of about 50 to about 90% with respect to the outermost radius, even when the load pan 16 is displaced or when the load pan 16 is warped, the temperature of the load pan 16 is effectively detected. it can.

Embodiment 2. FIG.
With reference to FIGS. 8-10, Embodiment 2 of the electromagnetic cooker which concerns on this invention is demonstrated. Since the electromagnetic cooker according to the present embodiment has the same configuration as that of the first embodiment except that the position of the temperature sensor is different, the description of the overlapping contents is omitted. In the first embodiment, as shown in FIG. 9, the two temperature sensors 20 a and 20 b have the same position in the circumferential direction of the heating coil 10 (in other words, a radius from the coil center when viewed from a direction substantially perpendicular to the top plate). On one imaginary line extending outward in the direction). On the other hand, as shown in FIG. 10, the electromagnetic cooker according to the present embodiment heats the temperature sensor 20 b in a region having a radius of about 15 to about 50% with respect to the outermost radius of the heating coil 10. The temperature sensors 20 a and 20 b are arranged at positions shifted by about 180 degrees with respect to the circumferential direction of the heating coil 10 while being arranged in a region having a radius of about 50 to about 90% with respect to the outermost radius of the coil 10.

  In the first embodiment, as shown in FIG. 9, when the load pan 16 is largely deviated from the placement position, the temperature sensors 20 a and 20 b may be detached from the load pan 16, but in the second embodiment, As shown in FIG. 10, even when the load pan 16 is largely deviated from the placement position, the temperature sensor 20 a located on the center side of the heating coil 10 is highly likely to detect the temperature of the load pan 16.

Reference Example 1
In the reference example 1 , for example, as shown in FIGS. 11A and 11B, the three temperature sensors 20c, 20d, and 20e extend from the center of the heating coil 10 to the outside in the radial direction and have substantially the same angle. They are arranged on three imaginary lines 30c, 30d, 30e of 120 degrees (in other words, at substantially equal pitches with respect to the circumferential direction of the heating coil 10). The temperature sensors 20 c, 20 d, and 20 e are also disposed in a region having a radius of about 15 to about 90% with respect to the outermost radius of the heating coil 10. In this case, the temperature of the load pan 16 can be detected effectively regardless of the direction in which the load pan deviates from the placement position. FIG. 11A shows an example in which a load pan 16 having an outer diameter equal to the outermost diameter of the heating coil 10 is shifted, and FIG. 11B is compared with the outermost diameter of the heating coil 10. An example in which the load pan 16 having a small or large outer diameter is shifted is shown.

  In the example of FIG. 11, the three temperature sensors 20 c, 20 d, and 20 e are arranged at positions where the distance from the center of the heating coil 10 is equal, but the same effect can be obtained even if arranged at different positions.

  Four or more temperature sensors may be arranged. In this case, each temperature sensor is arranged on an imaginary line that is the same number as the number of temperature sensors and the angles formed by each other are substantially equal.

Reference Example 2
The position of the temperature sensor in Reference Example 1 can effectively detect the temperature of the pan when the load pan is flat at the bottom, but when the load pan with the warped bottom is placed on the top plate, There is a possibility that the air layer between the bottom of the pan and the top plate has a relatively thick part. In this case, the temperature of the load pan cannot be detected effectively. Therefore, in the present embodiment, as shown in FIG. 12, for example, as in Reference Example 1 , the temperature sensors 20 c, 20 d, and 20 e are placed around the coil periphery in a region having a radius of about 15 to about 90% with respect to the outermost radius of the heating coil 10. The temperature sensor 20a is arranged in a region having a radius of about 15 to about 50% with respect to the outermost radius of the heating coil 10 and the temperature sensor 20b is arranged in the heating coil 10 as in the first and second embodiments. It is arranged in a region having a radius of about 50 to about 90% with respect to the outermost radius. FIG. 12A shows an example in which the load pan 16 having an outer diameter equal to the outermost diameter of the heating coil 10 is shifted and FIG. 12B is compared with the outermost diameter of the heating coil 10. An example in which the load pan 16 having a small or large outer diameter is shifted is shown.

  In such a configuration, the temperature of the load pan can be effectively detected even when the load pan with the warped bottom portion is displaced in any direction from the placement position.

  In the example of the figure, the temperature sensors 20a and 20b are arranged on the virtual line 30c on which the temperature sensor 20c is arranged. However, the temperature sensors 20a and 20b are not necessarily arranged on the virtual line, and the temperature sensors 20a, 20b It is not necessary to arrange 20b at the same position in the circumferential direction of the heating coil 10.

Reference Example 3.
The electromagnetic cooker generally includes a cooling fan for cooling the top plate and the heating coil. Since the cold air from the cooling fan is supplied through the gap between the top plate and the heating coil, an error may occur in the detected temperature when the cold air hits a temperature sensor (eg, a thermistor) attached to the lower surface of the top plate. .

  Thus, in this embodiment, the cooling air is prevented from directly hitting the temperature sensor by surrounding the temperature sensor with a heat insulating material.

  More specifically, with reference to FIGS. 13 to 15, the temperature sensor (for example, thermistor) 20 is disposed on a heat insulating member 32 that is soft and somewhat cushioned, such as heat insulating wool. The heat insulating member 32 is fixed on a support stand 34 installed on the heating coil 10, for example. In this configuration, since the temperature sensor 20 is covered with the heat insulating member 32 except for the portion in contact with the lower surface of the top plate 4, the cold air 36 from the cooling fan does not hit the temperature sensor 20. Further, since the heat insulating member 32 and the support base 34 occupy only a part of the gap between the top plate 4 and the heating coil 10, the cold air 36 cools substantially the entire top plate 4 and the heating coil 10. be able to.

  As shown in FIG. 4, the heating coil is wound around the center side and the outer diameter side at a constant rate, and a gap is provided between the center side coil portion and the outer diameter side coil portion. When using a thing, you may arrange | position the support stand for supporting a heat insulation member in this clearance gap.

  An experiment was conducted in which a current was applied to the heating coil to heat the load pan, and then the cooling fan was activated for each of the cases where the heat insulating member was provided around the temperature sensor. The magnitude of the applied current was varied depending on whether the heat insulating member was provided or not. FIG. 16 is a graph showing the indicated temperature of the temperature sensor with respect to the elapsed time from the start of current application. When the heat insulation member is not provided, an inflection point is observed in the temperature indicated by the temperature sensor when the cooling fan is activated. However, when the heat insulation member is provided, the inflection point is observed even when the cooling fan is activated. I couldn't. This is because when the cooling fan is activated when the heat insulation member is not provided, the cold air hits the temperature sensor and the detected temperature error increases, but when the heat insulation member is provided, the temperature indicated by the temperature sensor is not affected by the cold air, It shows that the temperature of the load pan is detected effectively.

The schematic perspective view which shows Embodiment 1 of the electromagnetic cooker which concerns on this invention. FIG. 2 is a schematic sectional view taken along line II-II in FIG. 1. (A) Detailed sectional drawing of the peripheral part of the heating coil of FIG. (B) Top view of the heating coil of FIG. The schematic sectional drawing which shows the electromagnetic cooker model for calculating | requiring the heat_generation | fever distribution of a load pan. The graph which shows the heat distribution of the load pan calculated | required using the electromagnetic cooker model of FIG. The figure which shows the load pan with which the bottom part curved. FIG. 3 shows a positional relationship between a heating coil and two temperature sensors in the first embodiment. The schematic sectional drawing similar to FIG. 2 which shows Embodiment 2 of the electromagnetic cooker which concerns on this invention. The electromagnetic cooker which concerns on Embodiment 1 WHEREIN: The figure which shows the state by which the load pan was shifted | deviated from the mounting position. The electromagnetic cooker which concerns on Embodiment 2 WHEREIN: The figure which shows the state by which the load pan was shifted | deviated from the mounting position. The figure which shows the state by which the load pan was shifted | deviated from the mounting position in the electromagnetic cooker of the reference example 1. FIG. The figure which shows the state in which the load pan was shifted | deviated from the mounting position in the electromagnetic cooker of the reference example 2. FIG. Sectional drawing which shows the peripheral part of a temperature sensor in detail in the reference example 3. FIG. In the reference example 3 , the perspective view which shows the heat insulation member for covering a temperature sensor, and the support stand for supporting this member. In the reference example 3, it is a top view which shows the positional relationship of a temperature sensor and a heating coil, Comprising: A temperature sensor and a heat insulation member are shown through. The graph which showed the instruction | indication temperature of the temperature sensor when an electric current is applied to a heating coil about the case where a heat insulating member is provided around a temperature sensor, and the case where it does not provide, respectively.

Explanation of symbols

2: electromagnetic cooker, 4: top plate, 10: heating coil, 12: power supply, 14: control device, 16: load pan, 20a: temperature sensor, 20b: temperature sensor.

Claims (2)

A top plate for placing the load pan;
A plurality of heating coils disposed under the top plate for inductively heating the load pan;
Means for applying an electric current to the heating coil ;
For each of the plurality of heating coils, there are provided first and second temperature sensors disposed in contact with the bottom surface of the top plate ,
When viewed from a direction substantially perpendicular to the top plate, the first and second temperature sensors are disposed outside the center of the heating coil and inside the outermost periphery of the heating coil, and The temperature sensor is disposed inside a radius of about 50% with respect to the outermost radius of the heating coil, and the second temperature sensor is disposed outside of a radius of about 50% with respect to the outermost radius of the heating coil. In addition, the first and second temperature sensors are arranged to be shifted from each other by about 180 degrees with respect to the circumferential direction of the heating coil, and different radial positions of the heating coil as viewed from a direction substantially perpendicular to the top plate. An electromagnetic cooker characterized by being arranged in   The electromagnetic cooking device according to claim 1, wherein the heating coil is divided in a radial direction.

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