JPH01109688A - Overheat preventive device for heated cooking utensil - Google Patents

Abstract

PURPOSE:To prevent the overheat of a small amount of an object to be heated and prevent the unnecessary action of an overheat preventive device at the time of continuous cooking by switching the overheat preventive action level in two or more stages based on the timer signal counting the heating time. CONSTITUTION:A temperature adjusting means 21 compares the detection temperature information of an object to be heated and the overheat preventive level generated by an overheat preventive level setting means 20 and controls a heating source based on the comparison output. The overheat preventive level setting means 20 switches the set level to the level Tlimit 1 higher than the temperature stable level TA at the equipment ordinary heating from the operation start of the equipment to the branch time t1, to the level Tlimit 2 linearly changing against the elapsed time during the branch time t1-t2, and to the level Tlimit 3 lower than the stable level TA after the branch time t2. An overheat preventive mechanism is operated early at the time of heating a small amount of oil, safety is maintained, and the unnecessary action is prevented in case of the continuous cooking.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to an overheat prevention device for a cooking device that heats a pot or the like for cooking.

BACKGROUND OF THE INVENTION Conventionally, this type of heating cooker has been provided with an overheat prevention device for the purpose of preventing oil from igniting or heating the medium pot.

Hereinafter, an induction heating cooker using a conventional overheating prevention device will be explained with reference to FIG. 4. That is, 1 is a heat-sensitive element such as a thermistor, which is pressed against the lower surface of a top plate 3 made of an insulating material such as ceramic on which the object to be heated 2 is placed, and detects the temperature of the object to be heated 2 via the top plate 3. are doing.

This thermistor 1 and a resistor 4 constitute a temperature detection device 6, and the output of this temperature detection device 5 is input to a level comparison device 6 consisting of a comparator or the like. The other input side of the level comparator 6 receives divided voltage signals from two voltage dividing resistors 8.9 forming the overheat prevention reference level setting device 7. The output voltage of the overheat prevention reference level setting device 7 is set to a voltage level considerably lower than the output voltage of the temperature detection device 5 during normal use of the device. The output of the level comparator 6 is the inverter drive circuit 1o.
The signal is input to the inverter drive circuit 1o, and the inverter drive circuit 1o is configured to perform 0N10FF control of the oscillation of the inverter circuit 12, which includes a heating coil 11 as a component, which heats the object to be heated 2 by causing a high-frequency current to flow in response to this signal. There is.

When the device is in use, if the temperature of the heated object 2 rises due to air conditioning, etc., the thermistor 1 detects the temperature and the output voltage of the temperature detection device 6 is lower than or equal to the output voltage of the overheat prevention setting device. A drive stop signal is output from the comparison device 6 to the inverter drive circuit 12, and upon receiving this signal, the inverter drive circuit 10 outputs an oscillation OFF signal to the inverter circuit 12, and the high frequency current supplied to the heating coil 11 disappears. Heating of the object to be heated 2 is stopped.

Problems to be Solved by the Invention However, in such a configuration, the thermistor 1 detects the temperature of the object to be heated 2 via the top plate 3, so the thermal response is slow, and the temperature of the object to be heated 2 is low. In addition, the thermistor 1 has poor followability when the temperature rises rapidly, and the voltage level set by the overheat prevention level setting device 7 can only be set at one point, and the temperature of the thermistor 1 of the temperature detection device 5 during normal heating is stable. If the voltage level is not set to a lower value than the current voltage level, there will be an inconvenience that the overheating prevention device will operate during normal use, so the overheating prevention voltage level must be set to a very low voltage value. . Then, if the user accidentally heats a small amount of oil, there is a problem that the temperature of the thermistor 1 cannot keep up with the rapidly rising oil temperature, and the overheating prevention device does not operate and the oil ignites.

In view of the above problems, the present invention aims to prevent oil from igniting when a small amount of oil is heated.

Means for Solving the Problems In order to achieve the above object, the temperature control device for a heating cooker of the present invention adjusts the overheat prevention level for a certain period of time from the start of cooking based on a signal from a timer device. The device is provided with an overheating prevention means that switches to at least two stages after that.

Effect With the above configuration, even if a small amount of oil is heated and the oil temperature suddenly rises, the overheating prevention function switches the overheating level in a direction that makes it easier to operate for a certain period of time from the start of heating.
Even if the thermistor temperature does not follow the oil temperature, the overheat prevention function operates quickly, so there is no fear of oil ignition, and the accuracy of overheat prevention detection can be improved, especially when thermal coupling is poor.

EXAMPLE Hereinafter, an example of the present invention will be explained in the case of an induction heating cooker with reference to FIGS. 1, 2, and 3. Reference numeral 13 denotes a heat-sensitive element such as a thermistor, which is pressed against the lower surface of a top plate 16 made of an insulating material such as ceramic on which the object to be heated 14 is placed, and is connected to the object to be heated 14 via the top plate 16.
is detecting the temperature. The thermistor 13 and the resistor 16 constitute a temperature detection device 17, and the output of this temperature detection device 17 is input to an A/D converter 18. 19 is a timer device, which starts operating when the device starts heating. The output of the timer device 19 is input to the overheating prevention level setting means 2o, and the overheating prevention level setting means 2o maintains the temperature of the thermistor 13 at a stable level T during normal heating of the equipment, and a higher level Tl1m1t from equipment oscillation until branch time t. The level is set to 1, and from branch time t to branch time t2, the above
The overheating prevention level Tl1m1t2, which changes linearly from 11m1t1 to the oscillation elapsed time t, is calculated and set, and after the branch time t2, the level T, which is lower than T, is set constant. The level setting is being changed. Then, the overheating prevention level T1゜7 set by this overheating prevention level setting means 20
1 and the output of the human/D converter 18 are input to the temperature control means 21. This temperature control means 21 compares the thermistor temperature Tth outputted from the A/D converter 18 and the overheating prevention level T1°7.1 outputted from the overheating prevention level setting means 2o, and adjusts the amplitude during temperature regulation. TILL half of it! I (medium 1°C
), “th-Tl.Oscillates when 7゜1≧Tam” F
, a duty signal is output to the inverter drive circuit 22 in accordance with the processing command to turn on oscillation at TLevel "th≧"am, and the inverter drive circuit 22 drives the object to be heated by the inverter circuit 23 and the high-frequency current supplied from the inverter circuit 23. Duty control is applied to the heating coil 24 for heating.

Note that 18 to 19 above are devices built into a one-chip microcomputer. Therefore, when a user performs normal cooking, the thermistor temperature "th" rises slowly with the temperature of the object to be heated, so that the overheating prevention level "lev" is reached. Since the value does not reach 1, no inconvenience occurs in cooking. When cooking with a small amount of oil, even if the temperature of the oil rises rapidly and the thermistor temperature Tth cannot follow it and rises slowly, the oil will not ignite because Tl1m1t1 prevents overheating. .

In addition, in this embodiment, the overadjustment prevention level is the Tl1m1
t' + Said Tl1m1t 2・ Said "11m1t s
Although we have explained the case where the overheating prevention level is set in three stages, the above Tl1m at a predetermined branch temperature depends on the equipment.
It goes without saying that a two-stage setting in which switching is directly performed from 1t' to Tl1m1t3 may also be used.

Effects of the Invention As is clear from the embodiments, according to the present invention, the overheating prevention level of the device is changed depending on the heating time, so when the user performs normal cooking, the overheating prevention level of the device is changed according to the rise in the thermistor temperature. The overheating prevention level of the device also changes from a fast-acting level to a slow-acting level, so there is no inconvenience that the overheating prevention function activates during cooking and you cannot cook, and if the user accidentally heats a small amount of oil, the thermistor temperature will change. Even if it is difficult to follow the sudden rise in oil temperature, the overheat prevention level at the start of heating is set to the level set in the fast-acting direction, so the overheat prevention function will always operate, preventing unsafe operation of equipment such as oil ignition. It can be prevented.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an overheat prevention device for an induction heating cooker according to an embodiment of the present invention, Fig. 2 is a flowchart showing the operation of the same microcomputer, and Fig. 3 is a diagram showing the overheat prevention level and thermistor temperature in the same device. Characteristic diagram showing the relationship,
FIG. 4 is a configuration diagram of a conventional overheating prevention device for an induction heating cooker. 13... Thermistor, 14... Heated object, 17... Temperature detection device, 19...
Timer device, 20... Overheat prevention level setting means, 21... Temperature control means. Name of agent: Patent attorney Toshio Nakao and 1 other person/3
-Ichijo-S Star t4-J17J] Netmari Figure 3 Figure 4

Claims (1)

[Claims] a temperature detection device for detecting the temperature of the object to be heated; a temperature control means for controlling the temperature of the object to be heated to a predetermined stable temperature; The apparatus includes an overheat prevention means that stops heating or switches to duty control, and a timer device that counts the heating time of the device, and the overheat prevention means is set within the overheat prevention means based on a signal from the timer device. An overheat prevention device for a heating cooker, comprising means for switching an overheat prevention operation level into at least two stages.