JP2013218869A - Induction heating cooker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an induction heating cooker which can more precisely detect a surface temperature of a pot and determine boiling over based on the surface temperature.SOLUTION: An induction heating cooker comprises: a top plate 3 on which a pan P is placed; an induction heating coil 20 arranged below the top plate 3 for inductively heating the pan P; a drive circuit 60 for supplying a high-frequency current to the induction heating coil 20; a temperature sensor 30 for detecting a temperature of the top plate 3; a temperature estimation circuit 40 for calculating a time rate of change of the temperature of the top plate 3 detected by the temperature sensor 30 to estimate a surface temperature of the pot P based on at least the temperature of the top plate 3 and the time rate of change; and a control circuit 50 for controlling the drive circuit 60 by using the surface temperature estimated by the temperature estimation circuit 40. The control circuit 50 determines that boiling over occurs when the estimated surface temperature rapidly changes with respect to a time change.

Description

  The present invention relates to an induction heating cooking device, and more particularly to an induction heating cooking device that accurately estimates the surface temperature of a heated object such as a pan and detects a blow-off.

  In conventional induction cooking appliances, there is a strong market demand for the realization of an optimal cooking method by accurately measuring the surface temperature of the pan and supplying appropriate power to the induction heating coil based on this measurement. It was. And most of the conventional induction cooking devices generally measure the temperature of the top plate using a thermistor or a thermocouple such as a thermocouple (contact temperature sensor) directly in contact with the lower surface of the top plate to achieve thermal equilibrium. The surface temperature of the pan is detected from the temperature of the top plate based on the fact that the temperature of the top plate and the surface temperature of the pan have a certain relationship when in the state.

  On the other hand, for example, by measuring the radiant energy such as infrared rays passing through the top plate using an optical sensor (optical temperature sensor) such as an infrared sensor arranged below the top plate, A device for detecting the surface temperature has also been proposed (see, for example, Patent Document 1).

Japanese Patent Laying-Open No. 2004-227976 (FIG. 1)

  However, the temperature of the top plate measured using a contact-type temperature sensor does not reflect the surface temperature of the pan in real time because of the large thermal resistance and heat capacity of the top plate made of heat-resistant glass, etc. Immediately after the start of heating, the surface temperature of the pan detected from the temperature of the top plate rose with a delay from the actual surface temperature of the pan, so there was an error in the power supply control to the induction heating coil.

  On the other hand, the optical temperature sensor utilizes the fact that the surface temperature is proportional to the fourth power of the radiant energy from a high-temperature object, and in particular, the temperature reached by the surface of the pan during normal practical cooking (about 150 ° C. ) At the following relatively low temperatures, the radiant energy from the surface of the pan was so small that the surface temperature of the pan could not be accurately detected. That is, when the surface temperature of the pan detected using the optical temperature sensor is lower than the practical cooking temperature (immediately after the start of heating), the temperature detection accuracy is low, and induction heating is performed as in the case of using the contact temperature sensor. The power supply to the coil could not be controlled accurately. In addition, detecting the temperature using an optical temperature sensor is likely to impair the detection accuracy due to, for example, the surface condition of the pan (stained, glossy, etc.), and may be affected by other thermal power, contents, and the surrounding environment. It was easy to receive, making accurate detection of the surface temperature of the pan more difficult.

  As described above, there is a limit or limitation in accurately detecting the surface temperature of the pan by the contact temperature sensor and the optical temperature sensor, and it is impossible to accurately determine the spilling that has occurred during conventional cooking. It was. In addition, a method has been proposed in which when the electrostatic capacity type touch panel is blown down, it is determined from the change in the electrostatic capacity.

  This invention was made in order to solve the above problems, and provides the induction heating cooking appliance which can detect the surface temperature of a pan more correctly, and can determine a blow-out based on this. With the goal.

  An induction heating cooker according to the present invention includes a top plate on which a heated body is placed, an induction heating coil that is disposed below the top plate and induction-heats the heated body, and supplies a high-frequency current to the induction heating coil. Driving circuit, a temperature sensor for detecting the temperature of the top plate, and a time change rate of the temperature of the top plate detected by the temperature sensor, and at least the temperature of the object to be heated is calculated based on the temperature of the top plate and the time change rate. A temperature estimation circuit for estimating the surface temperature and a control circuit for controlling the drive circuit using the surface temperature estimated by the temperature estimation circuit are provided. The control circuit rapidly changes the estimated surface temperature with time. It is determined that it has blown out.

  In the present invention, the time change rate of the temperature of the top plate detected by the temperature sensor is calculated, the surface temperature of the heated object is estimated based on at least the temperature of the top plate and the time change rate, and the estimated surface temperature When it suddenly changes with respect to the time change, it is determined that the blown down and the heating power is reduced or the heating is stopped. Therefore, it is possible to accurately detect the blown down and provide a safer induction heating cooker. .

It is a perspective view which shows the induction heating cooking appliance 1 which concerns on Embodiment 1. FIG. It is the expanded sectional view which looked at the induction heating cooking appliance of FIG. 1 from the II-II line. It is a fragmentary sectional view which expands and shows the area | region shown with the broken line of FIG. It is a graph which shows the time transition of the estimated temperature of the pan estimated based on the measured temperature of the top plate with respect to the measured temperature of the empty pan. It is a graph which shows the time transition of the estimated temperature of the pan estimated based on the measured temperature of the top plate with respect to the measured temperature of the pan containing water. 3 is a circuit block diagram of the induction heating cooker according to Embodiment 1. FIG. It is a graph which shows the time transition of the estimated temperature of the pan estimated based on the measured temperature of the top plate when the blow-off occurs. 3 is a flowchart showing the operation of the control circuit in the first embodiment. It is a graph which shows the time transition of the estimated temperature of the pan estimated based on the measured temperature of the top plate when the blow-off occurs, and the estimated temperature weighted with time.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of an induction heating cooker according to the present invention will be described with reference to the accompanying drawings. In the description of the embodiments, terms indicating directions (for example, “upward”, “downward”, etc.) are used as appropriate for easy understanding. Is not limited. Moreover, in the following attached drawings, the same component is demonstrated using the same code | symbol.

Embodiment 1 FIG.
The induction heating cooker of the present embodiment will be described in detail below with reference to FIGS.
1 is a perspective view showing an induction heating cooker 1 according to Embodiment 1. FIG.
An induction heating cooker 1 shown in FIG. 1 covers a housing 2 and substantially the entire upper portion of the housing 2, and a top plate 3 on which heating portions 4a, 4b, and 5 indicating a heating position of a heated object are displayed. An operation panel 7 and a liquid crystal display unit 9 provided in the front part of the top plate 3, an intake hole 10 and an exhaust hole 11 provided in the rear part of the top plate 3, and a grill part 6 having a heating chamber in the housing 2. Heating power adjustment dials 8a, 8b, and 8c provided adjacent to the grill portion 6, an induction heating coil disposed in the housing 2 facing the heating portions 4a and 4b, and facing the heating portion 5 in the housing 2 Equipped with a heater. The top plate 3 is formed of heat-resistant glass, and printing is performed on the back surface so that the inside cannot be seen. The induction heating coil is formed by spirally winding a copper wire, and a radiant type radial heater is used as the heater.

  In addition, in the following embodiment, although the induction heating cooking appliance 1 which has what is called a side grill structure where the grill part 6 is biased and arrange | positioned on the left side of the housing | casing 2 is demonstrated exemplarily, it is limited to this. For example, the present invention can be equally applied to an induction heating cooker having a center grill structure in which the grill portion 6 is disposed at substantially the center of the housing 2 or an induction heating cooker that does not include the grill portion 6. . In addition, although it has been described that the heater 5 is a radiant heater, an induction heating coil may be used.

FIG. 2 is an enlarged cross-sectional view of the induction heating cooker of FIG. 1 as seen from the line II-II, and a heated object P (hereinafter simply referred to as “pan P”) is placed on the top plate 3. It shows the state.
The induction heating cooker 1 according to the present embodiment includes a temperature sensor 30 such as a thermistor disposed so as to contact the lower surface of the top plate 3 and measures the temperature (Tg) of the top plate 3.

  As will be described later, the induction heating cooker 1 includes a drive circuit (inverter circuit) for supplying a high-frequency current to the induction heating coil 20 of each heating unit 4a, 4b, and the top plate 3 measured by the temperature sensor 30. Appropriate for the induction heating coil 20 based on the surface temperature of the pan P estimated from the temperature (Tg) and the “heating power” (load heating value of the induction heating coil 20) set by the user with the heating power adjustment dial 8 or the like. A control circuit for controlling the drive circuit to supply a high-frequency current is provided.

Next, a method (estimation principle) for estimating the surface temperature of the pan P from the temperature (Tg) of the top plate 3 measured by the temperature sensor 30 will be described with reference to FIG.
FIG. 3 is an enlarged partial sectional view showing a region indicated by a broken line in FIG.
When a high frequency current corresponding to a desired heating power set by the user using the operation panel 7 and the heating power adjustment dial 8 is supplied to the induction heating coil 20 provided below the pan P, the pan P around the induction heating coil 20 is supplied. An alternating magnetic field (closed magnetic path) including the bottom plate B of is formed. At this time, an eddy current is generated near the surface of the bottom plate B of the pan P, and the bottom plate B of the pan P is heated by the Joule heat. That is, the pot P is directly heated by induction.

  The amount of heat generated when the bottom plate B of the pan P is heated cooks and heats the food F such as moisture contained in the pan P and is also transmitted to the top plate 3 below the bottom plate B. At this time, in particular, the bottom plate B (and the top plate 3) of the pan P cannot be formed to be completely flat (the flatness is zero) and has a minute curved shape. Is formed with an air layer A having a predetermined interval or gap (δa).

Here, the amount of heat Q1 conducted from the bottom surface of the bottom plate B of the pan P to the top plate 3 (that is, the amount of heat Q1 conducted through the air layer A formed between the bottom surface of the bottom plate B of the pan P and the top plate 3) is considered. . In general, the amount of heat Q1 is such that the larger the temperature difference (Tp-Ta) between the temperature (Tp) of the bottom plate B of the pan P and the temperature (Ta) of the surface of the top plate 3 is, the larger the area (S) where the two are opposed to each other. The larger it is and the smaller the gap (δa) is, the larger it is. The amount of heat Q1 also depends on the thermal conductivity (λa) of the air layer A. Therefore, the amount of heat Q1 conducted per unit time from the lower surface of the bottom plate B of the pan P to the top plate 3 is expressed by the following equation (1).
Q1 = λa × (Tp−Ta) × S / δa (1)

Further, the amount of heat Q2 conducted to the top plate 3 is transmitted from the upper surface to the lower surface of the top plate 3. At this time, when the top plate 3 formed of heat-resistant glass or the like is viewed as a sensible heat storage material, the amount of stored heat Q2 varies with time in the mass (M), specific heat (cg), and temperature (Tg) of the top plate 3. Using the rate (ΔTg / Δt), it is expressed by the following equation (2).
Q2 = M × cg × (ΔTg / Δt) (2)

Here, it is assumed that the thermal conductivity (λg) of the top plate 3 is infinite (that is, Ta and Tg are equal. Ta = Tg), and the amount of heat on the left side of the equations (1) and (2) Since Q1 and Q2 (Q1 = Q2) are equal, Equation (3) can be obtained by arranging them together.
Tp = Tg + C × δa × (ΔTg / Δt) (3)
C = ρg × cg × δg / λa
Tp: estimated temperature of the pan P Tg: temperature δa of the top plate 3 measured by the temperature sensor 30: interval ρg between the pan P and the top plate 3: density cg of the top plate 3: specific heat δg of the top plate 3: Thickness λa of top plate 3: thermal conductivity t of air: time from start of heating

  That is, since the coefficient C is a constant uniquely determined by the top plate 3, the temperature Tp of the bottom plate B of the pan P is an air layer formed between the lower surface of the bottom plate B of the pan P and the top plate 3. It can be expressed by using the interval A (δa), the temperature (Tg) of the top plate 3 measured by the temperature sensor 30 and the time change rate (ΔTg / Δt).

As described above, the following evaluation experiment was performed in order to verify that the relationship represented by the above formula (3) holds even if the thermal conductivity (λg) of the top plate 3 is assumed to be infinite.
That is, when the pot P is induction heated by the induction heating coil 20,
i) the measured temperature (Tg) of the top plate 3 measured by the temperature sensor 30;
ii) the actual temperature of the pan P measured by another temperature sensor (not shown),
iii) The estimated temperature of the pan P determined by the above formula (3) was compared.

FIG. 4 is a graph showing the temporal transition of the estimated temperature of the pan estimated based on the measured temperature of the top plate with respect to the measured temperature of the empty pan. That is, FIG. 4 is a graph obtained by plotting the temporal transition of the above i) to iii).
At this time, a spacer (thickness δa≈0.5 mm) is arranged between the pan P and the top plate 3 so that the interval (δa) of the air layer A is defined as δa≈0.5 mm, and the induction heating coil A high frequency current was supplied to 20 for 250 seconds to heat the pan P, and then the power supply to the induction heating coil 20 was stopped.

As is apparent from the graph of FIG. 4, the measured temperature of the top plate 3 measured by the temperature sensor 30 (Tg) while the measured temperature of the pan P reached 200 ° C. or more when 250 seconds had elapsed since the start of heating. Is about 70 ° C., there is a temperature difference of about 130 ° C. or more between the two, and the response is very poor.
On the other hand, the estimated temperature of the pan P obtained by the above formula (3) is generally approximated (estimated) with good follow-up to the measured temperature of the pan P immediately after the start of heating. Therefore, according to the method for estimating the temperature of the object to be heated defined by the above formula (3), it is possible to estimate the surface temperature of the pan P from the measured temperature (Tg) of the top plate 3 very precisely with good followability. It was confirmed from the graph.

Thus, although the actual thermal conductivity (λg) of the heat-resistant glass that is the constituent material of the top plate 3 is about 1 W / (m · K), it is assumed that it is infinite. The above formula (3) was derived, and it was confirmed that the estimated temperature of the pan P obtained based on the formula (3) accurately approximates the actually measured temperature of the pan P.
In other words, the density, specific heat, and thickness of the heat-resistant glass constituting the top plate 3 are design matters and known (the coefficient C is uniquely determined). Based on the interval (δa), the measured temperature (Tg) of the top plate 3 and the rate of change with time (ΔTg / Δt), the temperature of the pan P is accurately determined in real time with the above formula (3). Can be estimated.

However, it is not easy to define the interval (δa) between the pan P and the top plate 3. The pan P and the top plate 3 each have some warping or unevenness, and the distance (δa) between the pan P and the top plate 3 varies greatly even in the proximity plane.
Therefore, in the formula (3), when the temperature (Tp) of the bottom plate B of the pan P is assumed to be the specified surface temperature (Tsh) of the pan P at a predetermined time (τ) (Tp = Tsh), The distance (δa) between the bottom plate B and the top plate 3 can be expressed by the following equation.
δa = (Tsh−Tg, t = τ) / (ΔTg / Δt) t = τ × λa / (ρg × cg × δg) (4)
Tsh: Specified surface temperature of pan P at a predetermined time τ: Predetermined time That is, the interval (δa) between pan P and top plate 3 is the temperature (Tg) of top plate 3 measured by temperature sensor 30 And its time change rate (ΔTg / Δt). The estimated interval (δa) is an interval directly above the temperature sensor 30 and is not affected by the position in the proximity plane.

The results measured in the configuration of this embodiment are shown in FIG.
FIG. 5 is a graph showing the temporal transition of the estimated temperature of the pot estimated based on the measured temperature of the top plate with respect to the measured temperature of the pot containing water. In the drawing, the temperature of the food F, the output of the temperature sensor 30, the temperature of the bottom plate B of the pan P, and the estimated temperature of the bottom plate B are shown.

In FIG. 5, from the start of heating to 20 seconds, the food F and the bottom plate B of the pan P are hardly heat-exchanged, and the temperature of the bottom plate B of the pan P rises rapidly. From 20 seconds to 80 seconds, natural convection occurs in the food F, and heat exchange occurs between the food F and the bottom plate B of the pan P due to natural convection, but the heat exchange characteristics (natural convection heat transfer) are poor, and the pot P The temperature of the bottom plate B rises gently. In 80 seconds to 130 seconds, the temperature of the food F in contact with the bottom plate B of the pan P becomes equal to or higher than the saturation temperature (100 ° C. in the case of water) (the temperature of the food F away from the bottom plate B is lower than the saturation temperature). Since subcooled boiling occurs at, the temperature rises more gradually, and conversely, as the boiling becomes active, the temperature starts to decrease. If it is 130 seconds or more, it will be in a stable saturated boiling state, and will be stabilized at a temperature higher by the degree of superheat than the saturation temperature (about 140 ° C. in FIG. 5).
The predicted temperature is also shown in FIG. The output of the temperature sensor 30 increases in temperature as a gentle convex curve, and does not agree qualitatively and quantitatively even at 800 seconds from the start of heating. The predicted temperature rises with a delay of about 30 seconds with respect to the temperature (Tp) of the bottom plate B of the pan P until 130 seconds of boiling, but after that, it shows a constant temperature and shows a relatively good qualitative quantitative agreement.

In the subcooled boiling heat transfer, the heat transfer coefficient (an index indicating heat exchange characteristics) changes from moment to moment, but in the case of saturated boiling heat transfer, the surface properties of the bottom plate B of the pan P, the physical property values of the food F, and The heat transfer depends mainly on the heat flux, and the natural convection heat transfer depends mainly on the temperature difference between the bottom plate B of the pan P and the food F and the physical properties of the food F.
The heat transfer is related to the temperature difference between the bottom plate B of the pan P and the food F, and in addition, a temperature difference related to heat conduction in the bottom plate B of the pan P is generated.

Therefore, the change in the heat transfer coefficient during natural convection or boiling is small, and it is desirable to determine the predetermined time (τ) and the specified surface temperature (Tsh) of the pan P in these states.
On the other hand, the faster the prediction of the temperature of the bottom plate B of the pan P, the better. Therefore, 20 to 80 seconds at which natural convection occurs is preferable, but the effect of the temperature of the pan P is about 10 seconds until the temperature sensor 30 is affected. Since a delay occurs, the predetermined time (τ) is preferably from 30 seconds to 90 seconds. More preferably, 40 seconds to 60 seconds or less is desirable. In addition, when the mass of the pan P and the mass of the foodstuff F become large, the temperature at which subcooled boiling starts will be further delayed.

In FIG. 5, when time is 50 seconds, the temperature of the bottom plate B of the pan P is 125 degreeC. The specified surface temperature (Tsh) of the pan P varies depending on the temperature and heating power of the food F, but when normal temperature water is heated at a heating power of 3000 W, it is preferably from 100 ° C to 140 ° C, and preferably from 110 ° C to 120 ° C.
In addition, the temperature of the top plate 3 detected by the temperature sensor 30 when any of the top plate 3, the pan P and the food F or all of the temperatures are high, such as when performing another cooking or reheating after cooking. When (Tg) is high, it is preferable to provide a lower limit for the difference between the specified surface temperature (Tsh) of the pan P and the temperature (Tg) of the top plate 3 detected by the temperature sensor 30 at a predetermined time (τ). . By doing in this way, it can suppress that the said temperature difference is too small or takes a negative value, and worsens the prediction accuracy of the estimated temperature of the pan P.

  In addition, the space | interval (delta a) between the baseplate B of the pan P and the topplate 3 assumed is 0.1 mm (0 mm is also considered)-3 mm, and the upper limit with respect to this lower limit is 30 times (change of 30 times) On the other hand, the amount of change based on the specified surface temperature (Tsh) of the pan P is Tsh-Tg at 3000 W, t = τ is from 70K to 110K, assuming that the output of the temperature sensor 30 is 30 ° C. The upper limit for the value is about 1.57 times, and the variation with respect to the assumed value (δa or Tsh) is significantly small, and the prediction accuracy is improved.

In addition, the formula which estimates the temperature (Tp) of the baseplate B of the pan P by Formula (3), and the formula which estimates the space | interval (δa) between the pan P and the top plate 3 were shown by Formula (4). Is an equation that is derived by combining both equations,
Tp = Tg + (Tsh−Tg, t = τ) / (ΔTg / Δt) t = τ × (ΔTg / Δt) (5)
Thus, the temperature (Tp) of the bottom plate B of the pan P may be estimated.
In addition, the temperature (Tg) of the top plate 3 measured by the temperature sensor 30 and its time change rate (ΔTg / Δt) use an average value of a plurality of transient measurement values in order to improve the accuracy of each value. Is preferred.
Further, the use of the plurality of temperature sensors 30 can improve the temperature prediction accuracy of the bottom plate B of the pan P, and the temperature is locally high in the plane where the bottom plate B of the pan P and the top plate 3 are close to each other. The part can be detected, and the accuracy of the abnormality determination is improved.

FIG. 6 is a circuit block diagram of the induction heating cooker according to the first embodiment.
As described above, the induction heating cooker 1 includes a drive circuit (inverter circuit) 60 for supplying a high-frequency current to the induction heating coil 20 and a temperature sensor 30 such as a thermistor for measuring the temperature (Tg) of the top plate 3. And a temperature estimation circuit 40 that estimates the surface temperature of the pan P from the measured temperature (Tg) of the top plate 3. Further, the induction heating cooker 1 is configured so that an appropriate high-frequency current is supplied to the induction heating coil 20 based on the “heating power” (load heat generation amount) set by the user with the setting device 70 such as the heating power adjustment dial 8. A control circuit 50 that controls the drive circuit 60 is included. The control circuit 50 according to the present embodiment receives information about the temperature (Tp) of the pan P, which is precisely estimated with good followability as described above, from the temperature estimation circuit 40 so that a more accurate high-frequency current is supplied. The drive circuit 60 is controlled.
Note that the induction heating cooker 1 preferably warns from the control circuit 50 when it detects an abnormal use state exceeding the reference value, such as when the estimated temperature of the pan P reaches an abnormally high temperature. A warning device 80 such as a liquid crystal display unit 9 for displaying a “beeper” that receives a signal and emits a warning sound for giving a warning to a user or a warning display is provided.

The operation of the induction heating cooker 1 according to the present embodiment will be described with reference to FIG.
When the user places a pan P such as a frying pan on the top plate 3 and sets the heating power by the setting device 70 such as the operation panel 7 and the heating power adjustment dial 8, the control circuit 50 causes the drive circuit 60 to be changed accordingly. The induction heating coil 20 is controlled to supply a high frequency current. When a high frequency current is supplied to the induction heating coil 20, a high frequency magnetic field is generated around the induction heating coil 20, an eddy current is generated in the bottom plate B of the pan P, and the pan P is heated by the Joule heat. The heat generated in the bottom plate B of the pan P by induction heating is transmitted from the pan P to the food F, and the food F is cooked.

  On the other hand, the heat generated in the bottom plate B of the pan P is transmitted to the top plate 3 through the air layer A formed therebelow to raise the temperature of the top plate 3. The temperature sensor 30 provided below the top plate 3 continuously measures the temperature (Tg) of the top plate 3 and inputs the measurement signal to the temperature estimation circuit 40. The temperature estimation circuit 40 calculates the time change rate of the temperature (Tg) based on the measurement signal from the temperature sensor 30 as described above, and calculates the calculated interval (δa) between the pan P and the top plate 3. ) Is used to estimate the surface temperature of the pan P, and the signal is input to the control circuit 50.

  The control circuit 50 calls a drive program (default value) stored in a memory (not shown) built in the control circuit 50 in accordance with the input signal set by the setting device 70, and based on this drive program A driving signal is transmitted to the driving circuit 60 and, if necessary, a warning signal is supplied to the warning device 80 to give a warning to the user.

  The drive circuit 60 drives a semiconductor switching element such as an IGBT by a drive signal from the control circuit 50, supplies an appropriate high frequency current to the induction heating coil 20, and according to an input signal set by the setting device 70. Adjust the heating power to the pan P. The warning device 80 gives a warning to the user based on a warning signal from the control circuit 50.

  As described above, the control circuit 50 according to the present embodiment repeatedly monitors the setting signal from the setting device 70 and the measurement signal from the temperature sensor 30 in the above-described series of operations, so that the cooking desired by the user can be performed. The drive circuit 60 can be controlled to maintain the state.

  According to the prior art, as shown in the graph of FIG. 4, since the measured temperature (Tg) of the top plate does not change responsively to the measured temperature of the pan P, the accurate temperature of the pan P can be detected in real time. It was not possible to achieve the cooking state desired by the user. For example, although the actual temperature of the pan P is sufficiently high and the food F is boiling, the pan P may be heated excessively to cause spillage.

  However, in the present embodiment, by using the time change rate (ΔTg / Δt) of the actually measured temperature (Tg) of the top plate as a new parameter, the responsiveness of the estimated temperature of the pan P is improved and the actual pan is used. Since it can be approximated and estimated by the temperature of P, the user can grasp the desired cooking state with good followability.

  Here, the foodstuff accommodated in the pan P means foods, such as water, dashi soup, oil, vegetables, meat, and fish. Moreover, the pan P means what accommodates the said foodstuffs, such as a pan, a frying pan, a kettle which can be heated by induction heating.

  The setting device 70 refers to the operation state of the induction heating cooker 1 such as an ON / OFF switch of a power source, a cooking mode, a thermal power mode, or a pan temperature selection switch in addition to the operation panel 7 and the thermal power adjustment dial 8 described above. This means that a signal for setting is input to the control circuit 50.

  The warning device 80 is a warning when the safety standard is deviated by using sounds such as synthesized voice, beeper sound, melody, etc., or light such as lighting / flashing of light in addition to the liquid crystal display unit 9 described above. Or something that informs the user of the cooking situation. Moreover, you may make it display the temperature of the actual pan P in the liquid crystal display part 9 in real time so that it can compare with the temperature of the pan P set with the setting apparatus 70 by the user. Further, the progress of cooking may be displayed on the liquid crystal display unit 9.

  As the temperature sensor 30 in the present embodiment, any thermistor (which estimates the temperature using the characteristic that the electrical resistance of the semiconductor changes with temperature) can be used as long as it can measure the temperature of the top plate 3. (Contact temperature sensor and optical temperature sensor) can be used. A contact-type temperature sensor uses, for example, a thermocouple (a weak thermoelectromotive force generated according to a temperature difference between both ends when a temperature is applied to the joint portion by joining one end of two types of metal wires having different properties). Temperature sensor), resistance thermometer (if the material is metal, the temperature is estimated using the property that the electrical resistance increases in proportion to the temperature), radiation thermometer (the object radiates) Infrared energy received by an infrared sensor, and a reference temperature correction, emissivity correction, etc. are applied to estimate the temperature). Moreover, when measuring the temperature of the pan P using the radiation thermometer of an optical temperature sensor, you may form the film | membrane (painting etc.) which suppresses permeation | transmission of infrared light on the lower surface of the top plate 3. FIG.

  FIG. 7 is a graph showing a temporal transition of the estimated temperature of the pan estimated based on the measured temperature of the top plate when the blow-off occurs. This graph shows the temperature of the bottom plate B of the pan P when the pot P containing water as the food F is induction-heated and blown down at 200 seconds and 350 seconds from the start of heating, predicted by the above estimation method. It shows the transient temperature change of the measured temperature, the output of the temperature sensor 30, and the temperature of the food F.

  In FIG. 7, from the start of heating to 20 seconds, the food F and the bottom plate B of the pan P are hardly heat-exchanged, and the temperature of the bottom plate B of the pan P rises rapidly. From 20 seconds to 100 seconds, natural convection occurs in the food F, and heat exchange occurs between the food F and the bottom plate B of the pan P due to natural convection, but the heat exchange characteristics (natural convection heat transfer) are poor, and the pot P The temperature of the bottom plate B rises gently. From 100 seconds to 150 seconds, the temperature of the food F in contact with the bottom plate B of the pan P exceeds the saturation temperature (100 ° C. in the case of water) (the temperature of the food F away from the bottom plate B is equal to or lower than the saturation temperature), and the bottom plate B surface Since subcooled boiling occurs at, the temperature rises more gradually, and conversely, as the boiling becomes active, the temperature starts to decrease. If it is 150 seconds or more, it will be in a stable saturated boiling state, and will be stabilized at a temperature higher by the degree of superheat than the saturation temperature (about 135 ° C. in FIG. 7).

  The predicted temperature is also shown in FIG. The output of the temperature sensor 30 rises as a gentle convex curve, and does not match qualitatively and quantitatively even at the start of heating for 600 seconds. The predicted temperature rises with a delay of about 30 seconds with respect to the temperature (Tp) of the bottom plate B of the pan P until 150 seconds of boiling, but then shows a constant temperature and relatively good qualitative quantitative agreement.

  As can be seen from the transient temperature change in FIG. 7, when the blow-off occurs, the temperature of the bottom plate B of the pan P changes slightly, but does not change greatly, and it is difficult to determine the blow-down. On the other hand, when the thermistor output is 200 seconds, the temperature rise gradient is clearly large, and when it is 350 seconds, the temperature gradient is small, but the temperature gradient is small. It can be seen that the temperature estimated using these temperature gradients rises significantly at 200 seconds and conversely falls at 350 seconds.

When the blow-off occurs, the food (F) flows out from the pan P and spills around the pan P. The spilled liquid (foodstuff (F)) is sucked by the capillary action generated at the interval between the bottom plate B and the top plate 3 of the pan P, and the interval is filled with the liquid. At 200 seconds, as can be seen from the output of the temperature sensor 30, the temperature of the top plate 3 is lower than the temperature of the food (F) (approximately 100 ° C. at the time of boiling). Since the high-conductivity and higher-temperature food (F) is filled instead, the food (F) and the top plate 3 exchange heat, and the temperature of the top plate 3 rises rapidly. Therefore, the temperature of the top plate 3 rises as described above.
In the present embodiment, the temperature estimation method for the bottom plate B of the pan P is an estimation method that takes into consideration the thickness of the gap and the thermal conductivity, and therefore, when blown down, the thermal conductivity is higher as described above. Since the food (F) is replaced, the estimated temperature of the bottom plate B of the pan P rapidly increases.

  On the other hand, at 350 seconds, as can be seen from the output of the temperature sensor 30, the temperature of the top plate 3 is slightly higher than the temperature of the food (F) (approximately 100 ° C. at the time of boiling). Since it fills instead, foodstuff (F) and the top plate 3 exchange heat, and the temperature increase rate of the top plate 3 decreases. Therefore, the temperature of the bottom plate B of the pan P estimated according to the above-described temperature estimation method suddenly drops.

Next, the blow-out determination operation by the control circuit 50 will be described with reference to FIG.
FIG. 8 is a flowchart showing the operation of the control circuit in the first embodiment.
The control circuit 50 starts acquiring the measured temperature of the temperature sensor 30 below the top plate 3 as data from the start of heating (S81). Then, the control circuit 50 calculates the coefficient (C) by the expression (3) at a certain time from the start of heating (S82), and thereafter sets the coefficient as a fixed value and then calculates the temperature (Tp) of the bottom plate B of the pan P by the expression (3). ) Is calculated (S83). The control circuit 50 always determines whether the temperature (Tp) of the bottom plate B of the pan P has changed abruptly (S84), and when the temperature (Tp) of the bottom plate B of the pan P has not changed rapidly, the pan The temperature of the bottom plate B of P (Tp) is calculated and the above operation is repeated (S85). In addition, when the temperature (Tp) of the bottom plate B of the pan P changes abruptly, the control circuit 50 determines that the blowing is zero and stops heating (S86).

Therefore, it is possible to cook safely by determining that the temperature predicted by the estimation method of the bottom plate B of the pan P has changed abruptly as being blown down and controlling the thermal power.
In this embodiment, in order to clarify the estimation method, it is limited to the estimation method, but is not limited to this, the temperature predicted by the estimation method of the bottom plate B of any pan P, A case where it changes suddenly may be determined to be blown down.

Embodiment 2. FIG.
Next, Embodiment 2 of the induction heating cooker according to the present invention will be described in detail below.
The predicted value of the temperature of the bottom plate B of the pan P actually changes the pan bottom temperature in the initial stage of heating or with a change in heating power. Therefore, it is determined that this temperature change is a case where the predicted temperature is suddenly changed, and there is a possibility that it is erroneously determined that the blown down is zero.
Therefore, as shown in FIG. 9, a predicted value calculated from the average value of the output values (temperature of the top plate 3) of the temperature sensor 30 within a long time (first time) and a short time (second time) By using as an index the difference from the predicted value calculated from the average value of the output value of the temperature sensor 30 (the temperature of the top plate 3) within the time), the temperature change that occurs in normal cooking is removed, and the blow-off is related to Only a component of a rapid temperature change can be extracted, and more accurate blow-off detection can be performed.

  The determination method is based on a change in the output value of the temperature sensor 30 due to the intrusion of liquid that has blown between the bottom plate B and the top plate 3 of the pan P. By providing a plurality of temperature sensors 30, the determination method is as follows. Since the temperature change when it spills to a part in the circumferential direction can be detected earlier, the temperature sensor 30 that detects at least two blown spills under the top plate 3 in the region of the heating part 4a or 4b. It is desirable to provide

  Further, a structure in which a gap is formed between the bottom plate B of the pan P and the top plate 3 is desirable. For example, protrusions may be provided on the surfaces of the heating portions 4a and 4b of the top plate 3, and conversely the bottom plate of the pan P A protrusion may be provided on the surface of B. Further, during cooking, a spacer may be formed between the bottom plate B and the top plate 3 of the pan P to form a gap. By doing so, the intrusion of the spilled liquid is facilitated, and the temperature sensor 30 Can be detected quickly and reliably, and the blow-off detection can be performed more accurately.

  Blowing at the time of cooking is a phenomenon in which the food (F) flows out from the pan P, and the outer peripheral portions of the heating portions 4a and 4b of the top plate 3 get wet. Therefore, by providing the temperature sensor 30 under the top plate 3 on the outer periphery of the heating units 4a and 4b, it is possible to detect the blow-off quickly and surely even if the liquid blown between the pan and the top plate 3 does not enter. This is preferable.

  Moreover, according to the induction heating cooking appliance 1 of this Embodiment, when the said abnormal mode is detected, a warning can be given to a user using the said warning device 80. FIG. This is particularly useful when the user leaves the induction heating cooker 1.

  For example, when detecting the abnormal mode, the control circuit 50 controls various warning devices 80 to emit a beeper sound, output a synthesized voice, turn on or blink a warning lamp, or display the liquid crystal display unit 9. Can be displayed as a warning. Thereby, when the abnormal mode is detected, the control circuit 50 promptly notifies the user to call attention, and stops or suppresses the power supply to the induction heating coil 20 to realize higher safety. can do.

  In addition, when putting a foodstuff (F) in the pan P and cooking it, the water | moisture content in a foodstuff (F) may evaporate and it may be in an empty cooking state. In this case as well, since the estimated temperature of the bottom plate B of the pan P changes abruptly, it is possible to provide safer cooking by detecting and controlling the thermal power in the same manner as in the case of zero blowing. it can.

  DESCRIPTION OF SYMBOLS 1 Induction cooking device, 2 housing | casing, 3 top plate, 4 and 5 heating part, 6 grill part, 7 operation panel, 8 thermal power adjustment dial, 9 liquid crystal display part, 10 inlet hole, 11 exhaust hole, 20 induction heating coil , 30 temperature sensor, 40 temperature estimation circuit, 50 control circuit, 60 drive circuit, 70 setting device, 80 warning device, 94 protective tube (disturbance suppression container or magnetic shield pipe), P pan (heated object), B heated object Bottom plate, A air layer.

Claims (6)

A top plate on which the object to be heated is placed;
An induction heating coil that is disposed below the top plate and induction-heats the object to be heated;
A drive circuit for supplying a high-frequency current to the induction heating coil;
A temperature sensor for detecting the temperature of the top plate;
A temperature estimation circuit that calculates a time change rate of the temperature of the top plate detected by the temperature sensor, and estimates a surface temperature of the object to be heated based on at least the temperature of the top plate and the time change rate;
A control circuit for controlling the drive circuit using the surface temperature estimated by the temperature estimation circuit,
An induction heating cooker characterized in that the control circuit determines that the blown down has occurred when the estimated surface temperature changes rapidly with respect to time, and stops heating power reduction or heating.   The temperature estimation circuit calculates a time change rate of the temperature of the top plate detected by the temperature sensor, and calculates a distance between the heated body and the top plate from the temperature of the top plate and the time change rate at a predetermined time. The induction heating cooker according to claim 1, wherein the surface temperature of the object to be heated is estimated based on the temperature, the time change rate, and the interval.   The control circuit calculates a predicted value from an average value of the temperature of the top plate within a first time, and further, from an average value of the temperature of the top plate within a second time shorter than the first time. 3. The induction according to claim 1, wherein a difference is obtained by calculating a predicted value, and when the difference between the predicted values is equal to or greater than a specified temperature difference, it is determined that the surface temperature has changed abruptly. Cooking cooker. A heating unit indicating the placement position of the object to be heated is displayed on the upper surface of the top plate,
The induction heating cooker according to any one of claims 1 to 3, wherein at least two temperature sensors are provided in a region of the heating unit.   The induction heating cooker according to claim 4, wherein a gap is formed between the object to be heated and the top plate. A heating unit indicating the placement position of the object to be heated is displayed on the upper surface of the top plate,
The induction heating cooker according to any one of claims 1 to 3, wherein the temperature sensor is provided under a top plate on an outer periphery of the heating unit.

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