JPH0421097B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to electric stoves, and particularly to fire prevention and safety devices thereof.

Conventional Structure and Problems Conventionally, electric heaters have been fitted with guards to prevent people's hands, objects, etc. from easily touching the heat generating part.

However, if a flammable object is placed close to the front of the guard, the heat from the heating element will heat the combustible object and reach a high temperature, which may cause a fire to the nearby flammable object or even cause a house fire. Ta.

The conventional electric stove as described above will be explained below with reference to the drawings.

FIG. 1 shows a cross section of a conventional electric stove, and FIG. 2 shows its electric circuit diagram.

1 is a stove casing, 2 is a reflector that reflects heat forward, 3 is a heating element located in front of the reflector 2, 4 is the back of the reflector 2, and the stove casing 1. A thermostat located inside detects the temperature rise inside the stove housing and turns off the electricity to the heating element 3.

The operation of the electric stove configured as above will be explained below.

When a combustible substance or the like falls on the upper part of the stove housing 1 and the temperature inside the housing rises abnormally, the thermostat stops the power supply to the heating element 3.

However, with the above configuration, the thermostat does not operate unless the temperature inside the stove housing 1 rises, so the response is slow when flammable materials, etc. fall onto the electric stove. In such cases, the temperature inside the casing did not rise, so it did not operate as a safety device and was not suitable as a safety device for fire prevention.

OBJECTS OF THE INVENTION The present invention solves the problems of the prior art described above, and aims to prevent fires from occurring due to falling or abnormally approaching flammable materials.

Structure of the Invention In order to achieve the above object, the electric stove of the present invention includes a contact residual type switch, a heating element, a temperature sensor that directly or indirectly detects the temperature rise of an object heated by the heating element, and an electric heater. When the temperature of the object rises abnormally, the heating element is turned off, the OFF state is maintained, and the OFF state is released by turning OFF the switch.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

3 is a front view of one embodiment of the present invention, and FIG. 4 is a sectional view at the center of FIG. 3.

In Figures 3 and 4, 5 is a housing, 6 is a heating element, 7 is a reflector, 8 is a guard, S is a switch,
Rt is a temperature sensor (thermistor) that protrudes from the center of the reflecting plate 7 and is provided close to the guard 8. La is an indicator lamp.

Figure 5 shows the electrical circuit. Ec is a control DC power supply, Bt is a thermistor, Ra is a variable resistor that adjusts the operating temperature, Tr ₁ is a transistor, Tr ₂ is a bidirectional thyristor, and R ₁ to _{R 3} are resistors. Ep indicates AC main power supply, S indicates residual contact type switch,
L ₁ ~ _{L 3} are relay coils, C ₁ is the contact of relay L ₁ ,
C ₂₁ and C ₂₂ are the first and second contacts of relay L ₂ , C ₃₁
and _C32 are the first and second contacts of relay _L3 , La is an indicator lamp, and H is a heater.

The operation of the above configuration will be explained below.

Figure 6 shows the curtain surface temperature T _l when the distance between electric stove ○A and curtain ○B is 50cm and 15cm.
shows the relationship between temperature sensor (thermistor) R _t and temperature T _s . As is clear from the figure, when L = 50 cm, which is the normal state, the curtain surface temperature T _l is saturated at 75°C, and there is no risk of smoke or ignition. At this time, the temperature T _s of the temperature sensor R _t is 60℃.

Next, when the distance L is brought closer to 15 cm, the curtain surface temperature T _l and the temperature T _s of the temperature sensor R _t suddenly rise.
If the heating element 6 continues to be energized, the curtain surface temperature T _l ' will rise to 190°C, and the temperature of the temperature sensor R _t will rise.
T _s ′ increases to 100°C. At this time, the condition of the curtains was only slightly discolored and there was no smoke or fire, but it was in a very dangerous condition.

The electric stove according to one embodiment of the present invention has a temperature sensor
When the temperature of R _t reaches the operating temperature T _s0 , the heating element 6 is turned off.
Turn off. The curtain surface temperature T _l at this time is 120℃
Therefore, there is no need to worry about ignition or smoke generation.

Next, the operation of the electric circuit will be explained. In Figure 5, when the switch (residual contact) S is turned on, the thermistor R _t is lower than the operating temperature, so the bidirectional thyristor T _r2 is in the ON state, and the relay coil L ₁
turns ON, contact C ₁ of the relay switches to NO contact, turns on relay L ₂ , closes contacts C ₂₁ and C ₂₂ , forms a self-holding circuit (referred to as power supply self-holding circuit), and heats the heating element H. Turn on. The temperature of the thermistor R _t gradually rises, but as mentioned above, under normal conditions it is saturated at about 60°C.

Next, if a flammable object approaches abnormally, the thermistor will
The temperature of R _t rises rapidly, and when it reaches the operating temperature T _s0 (Fig. 6) set by the variable resistor R _a , the bidirectional thyristor T _r2 is turned off and the relay coil L ₁ is turned off. , contact _C1 switches to the NC side,
Relay L ₃ turns ON, its contact C ₃₁ switches to NO side, relay L ₃ is self-holding (referred to as heating element OFF self-holding circuit), and at the same time heating element H is turned off.
It is turned OFF and the OFF state is maintained. Also C ₃₂
is also turned on, and the indicator lamp L _a lights up, indicating that the safety device has been activated due to an abnormal temperature rise.

When the heating element H turns off and the temperature of the thermistor _Rt falls, the bidirectional thyristor _Tr2 turns on again.
Contact C ₁ switches to the NC side, but relays L ₂ and L ₃ are self-held, and heating element H is OFF.
The status is maintained and the indicator lamp L _a remains lit.

When removing combustible materials, etc., and reusing in normal conditions, turn off switch S and then turn on switch S again.

When switch S is turned OFF, relays L ₂ and L ₃ that were self-holding are released from self-holding, and their respective contacts return to their original states, as shown in Figure 5. When switch S is turned ON again, the above-mentioned state is restored. The heater H turns on and can be used normally.

As described above, according to this embodiment, (1) the temperature sensor _Rt installed near the guard of the electric stove sensitively detects the temperature rise of the object heated by the electric stove, and abnormal temperature rise is detected. If so, the heating element H is turned off, thereby preventing fires from falling or abnormally approaching flammable materials.

(2) Since this is an abnormal temperature detection method using the temperature sensor _Rt , it does not malfunction, unlike the abnormal approach detection method of an object using ultrasonic waves, for example.

(3) In the event of an abnormality, the self-holding circuit shuts down the heating element H.
Since it is a method that keeps it in the OFF state, once
Once it is turned off, it will not turn on automatically again, making it safe.

(4) Reuse is possible by turning off the switch once, and there is no need to separately provide a reset switch, start switch, etc.

It has this effect.

In addition, by replacing the indicator lamp L _a with an alarm buzzer in FIG. 5, there is an effect that an abnormality can be detected even at a distance from the electric stove.

Effects of the Invention As described above, according to the present invention, the following effects can be obtained.

(1) Prevents discoloration, scorching, and burnout due to abnormal temperature rises of all objects heated by electric stoves.

(2) Abnormalities are detected by temperature sensors, so there are no malfunctions.

(3) In the event of an abnormality, the self-holding circuit shuts down the heating element.
It is highly safe because it is configured to remain in the OFF state.

(4) When reusing after the abnormal condition has been removed,
This can be done by turning off the switch once, and the configuration and operation are simple.

(5) If an indicator lamp or alarm buzzer is installed, it will be possible to know that an abnormal temperature rise has occurred and that a safety device has been activated.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a conventional electric stove, Fig. 2 is an electric circuit diagram of Fig. 1, Fig. 3 is a front view of an electric stove according to an embodiment of the present invention, and Fig. 4 is the center of Fig. 3. The cross-sectional view, Figure 5 is the electric circuit diagram of Figure 3, and Figure 6 is the electrical circuit diagram of Figure 3.
The figure is an explanatory diagram of temperature rise depending on the distance between the electric stove and the curtain. H...heating element, 7...reflector, 8...guard,
S...Switch, _Rt ...Temperature sensor, La...Indication lamp (or alarm buzzer), _L2 , _C21 ...Power self-holding circuit, _L3 , _C31 ...Heating element OFF self-holding circuit.

Claims (1)

[Scope of Claims] 1. A contact residual type switch, a heating element, a temperature sensor that directly or indirectly detects a temperature rise of an object heated by the heating element, and an electric circuit; When the temperature rises abnormally, the electric heater is configured to turn off the heating element, maintain the OFF state, and release the OFF state by turning off the switch. 2. The electric stove according to claim 1, wherein a guard is provided in front of the heating element, and the temperature sensor is located near the guard. 3 Turn off the heating element by the signal from the temperature sensor
2. The electric stove according to claim 1, further comprising an indicator lamp or an alarm buzzer that indicates when the electric stove is activated. 4. There is a circuit in the electrical circuit that self-holds when the switch is turned on when the temperature sensor is below the operating temperature, and continues to hold itself even when the temperature sensor exceeds the operating temperature.
The electric stove according to claim 1, further comprising a power supply self-holding circuit that releases self-holding when the switch is turned off. 5 In the electric circuit, when the switch is turned on and the temperature sensor reaches the operating temperature or higher, it will self-hold and turn on the heating element.
The electric stove according to claim 1, further comprising a heating element OFF self-holding circuit that continues self-holding and holds the heating element in the OFF state even when the temperature sensor becomes OFF and the temperature sensor becomes lower than the operating temperature.