JPS6139045B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pressure type cooking device using a positive temperature coefficient thermistor as a heat source.

Conventionally, a pressure cooker using a positive temperature coefficient thermistor as a heat source has been invented, and this is because the input of the positive temperature coefficient thermistor automatically decreases as the temperature rises, thereby reducing heat release loss during operation of the pressure regulating valve. Although it had excellent potential, it was difficult to put it into practical use for the following reasons. Figure 1 shows the structure of a conventional heat source. In FIG. 1, reference numeral 1 denotes a positive temperature coefficient thermistor sandwiched between electrodes 2 and 3. This positive coefficient thermistor 1 is in contact with a pot bottom 4 via the electrode 3 and an insulating plate 5. According to the structure, it is experimentally known that the total thermal resistance between the heat generation center of the PTC thermistor 1 and the surface of the pot bottom 4 is extremely large, and the thermal resistance is 5 to 10°C/W per PTC thermistor. It is being This is due to the thermal resistance of the PTC thermistor 1 in the thickness direction, the contact resistance between the PTC thermistor 1 and the electrode 3, and the thermal resistance of the insulating plate 5 in the thickness direction. The total thermal resistance as a heat source is inversely proportional to the number of PTC thermistors 1 arranged, but in the case of a pressure cooker, the maximum number of such thermistors arranged is about five, so the thermal resistance should be about 1°C/W. That is the limit. on the other hand,
The thermal output P of a positive temperature coefficient thermistor is approximately expressed by the following equation.

P=C _p -T _p /P _th ...(1) Here, C _p is the Curie point temperature of the PTC thermistor, T _p is the temperature of the load, and P _th is the time from the PTC thermistor to the load such as the bottom of the pot. is the thermal resistance of FIG. 5 shows the relationship between the input P in a pressure cooker using a positive temperature coefficient thermistor as a heat source and the temperature T of the load (contents), for example, water. In FIG. 5, a curve 6 shows the temperature characteristics of the load with respect to the input. In particular, the one-dot chain line 7 of the curve 6 shows the temperature characteristics after the pressure regulating valve starts operating, and the two-dot chain line 8 shows the temperature characteristic when the pressure regulating valve malfunctions. The dotted line 9 shows the temperature characteristics when the pressure cooker is used in an abnormal manner, such as when the pressure cooker is wrapped in cloth or the like, with very low heat dissipation, and when the pressure regulating valve breaks down. Indicates temperature characteristics. Straight line 10 has C _p =230°C and R _th
1 shows the thermal characteristics of the positive temperature coefficient thermistor 1 of =1°C/W. This straight line 10 is obtained by the above equation (1). In the positive temperature coefficient thermistor 1 under the above conditions, the outputs P ₅₀ and P ₁₀₀ when the load temperature is 50° C. and 100° C. are respectively obtained by the following equations based on equation (1).

P ₅₀ =230-50(℃)/1(℃/W)=180(W
) P ₁₀₀ =230-100(℃)/1(℃/W)=130
(W) The point corresponding to these P ₅₀ and P ₁₀₀ is A ₁ on the straight line 10
Point and A ₂ points. The internal pressure of the pressure cooker becomes stable near the intersection A5 of straight line 10 and dashed line ₇ , and the load is approximately
Experimentally, the average output of the positive temperature coefficient thermistor 1 when the temperature is about 120℃ is about 140 (W) ( ₄ points in the figure A), which makes the load temperature about 90℃. Not suitable for To prevent this, as understood from equation (1), it is possible to use a positive temperature coefficient thermistor with a high Curie point temperature, but at present it is extremely difficult to obtain one with a Curie point of about 230° C. or higher. On the other hand, straight line 1
If the pressure regulating valve fails in a device using a positive temperature thermistor 1 with characteristics such as 0, the internal pressure of the pressure cooker will stabilize at point _A5 or point _A6 , but the Curie point temperature will be extremely low at 230℃. It is possible for the temperature to rise to this temperature, posing an extremely high risk of explosion. Mainly as described above, it has been extremely difficult to use a PTC thermistor as a heat source in a pressure cooker due to the high thermal resistance of the PTC thermistor.

The present invention has been made in order to eliminate the above-mentioned drawbacks, and its purpose is to form a positive temperature coefficient thermistor with a low thermal resistance and use this as a heat source to provide a positive coefficient thermistor with a relatively low Curie temperature. It is also possible to use a positive temperature coefficient thermistor as a heat source for pressure heating cooking. To provide a pressure type heating cooker which reduces the risk of explosion even if it generates a lot of heat, and which facilitates the formation of a heat-resistant and pressure-resistant structure.

An embodiment of the present invention will be described below with reference to FIGS. 2 to 6. In the pressure cooker 20 shown in FIG. 2, 21 is the pot body, 22 is a lid, 23 is a pressure regulating valve provided on the lid, 24 is a safety valve, 25 and 26
27 is a handle on the lid 22 side, 28 is a leg of the pot body 21, 29 is a power supply plug, 30 is a bottom cover of the pot body 21, 3
1 is a heating device. Next, this heating device 31 will be specifically explained with reference to FIGS. 3 and 4.
That is, 32 is a rectangular positive temperature coefficient thermistor with a thickness of 1 mm, and on one side surface of this thermistor 32 is provided with first and second electrodes 3 in the form of comb teeth corresponding to each of the two poles.
Terminal plates 35 and 34 are formed by screen printing, for example, to a thickness of about 20 μm so that the electrodes 3 and 34 are inserted into each other.
36 are connected. An insulating plate 38 made of alumina porcelain or the like having good thermal conductivity is fixed to the one side surface of the positive temperature coefficient thermistor 32 on which the electrodes 33 and 34 are formed through a thin layer 37 of thermosetting silicone rubber. A positive temperature coefficient thermistor 32 with such an insulating plate 38 integrated therein is molded and installed inside the case 39 using silicone rubber 40 having high thermal conductivity, and its terminal plates 35 and 36 are attached to the case 39.
The case 39 is then fixed to the bottom wall 21a of the pot body 21 with screws 41. In this fixing process, one side surface of the PTC thermistor 32 is brought into close contact with the outer surface of the bottom wall 21a via the electrodes 33, 34, the insulating plate 38, and the grease.
According to such a configuration, voltage is applied to the thermistor 32 by both electrodes 33 and 34 provided on one surface thereof, so that current flows through the positive temperature coefficient thermistor 3.
It flows on one side surface of 2 and generates heat on that one side surface. Therefore, since the heat generation center is extremely close to one surface, the thermal resistance in the thickness direction of the PTC thermistor 32 is extremely low, and in particular, in this embodiment, each electrode 33, 34 is extremely thin and the insulation is extremely low. Coupled with the high thermal conductivity of the plate 38, the thermal resistance R _th from the PTC thermistor 32 to the load is extremely low, and R _th is 0.4 with one PTC thermistor.
It was experimentally confirmed that ℃/W. In this embodiment, two positive temperature coefficient thermistors 32 are used, and both have a Curie point temperature of approximately 160°C. Therefore, the thermal resistance R _th is 0.2°C/W, and the characteristics of the positive temperature coefficient thermistor 32 using this method are expressed as
It is indicated by a straight line 42 in the figure. This straight line 42 is R
_th = 0.2℃/W, C _p = 160℃, T _p is 90℃,
The above formula (1) is calculated assuming that the temperature is 120℃, and the resulting points A ₇ and A ₈ are connected with a straight line, and the slope of the straight line 42 is the same as the conventional R _th of 1℃/W. On the other hand, it can be understood from equation (1) that the slope of _the straight line 10 is larger than that of the straight line 10, as shown in FIG. As is clear from this FIG.
In the vicinity, as shown at point _A7 , the output is as high as 350 (W), which is sufficiently useful as a cooking source. At around the set temperature of 120° C. where the pressure regulating valve 23 is operating, the output of the positive temperature coefficient thermistor 32 is 200 (W) as shown at point _A8 , and the internal pressure of the pressure cooker 20 is stabilized at this point. If the pressure regulating valve 23 fails during heating by the PTC thermistor 32, the temperature will rise to the temperature shown at point _A9 or _A10 , but the PTC thermistor 32 will reach the Curie point temperature in the worst case. Even if it's summer,
Its Curie point temperature is 160°C, which is much lower than before, and the internal pressure does not increase at all.
In FIG. 6, a curve 43 shows the relationship between the temperature T inside the pressure cooker 20 and the saturated steam pressure _Ps .
In this Figure 6, point B ₉ corresponds to point A ₉ in Figure 5, and is approximately 3.4 atmospheres. In addition, point B ₁₁ is the fifth point where the positive temperature coefficient thermistor 32 has reached the Curie point temperature of 160°C.
Figure A corresponds to ₁₁ points and is approximately 6 atmospheres. Note that point A ₁₂ in Figure 5 indicates the point where the supplied heat and heat loss become equal when using a 350 (W) nichrome wire heater, and B ₁₂ in Figure 6 corresponds to A ₁₂ above. and
The pressure is 16 atmospheres. Therefore, when the pressure regulating valve fails, the internal pressure of the pressure cooker becomes 16°C when the positive temperature coefficient thermistor 1 in the conventional example reaches the Curie point temperature of 23°C.
You can see that it far exceeds the atmospheric pressure. On the other hand, in the case of the above-mentioned embodiment of the present invention, even in the worst case, the pressure resistance is extremely low at about 6 atmospheres as shown at point _B11 in Figure 6, which is lower than the pressure resistance of existing pressure cookers of 7 to 8 atmospheres.
Since the pressure is below the atmospheric pressure, there is little risk of explosion, and the Curie point temperature is naturally low, it is generally easier to form a pressure-resistant and heat-resistant structure for the pressure cooker 20. In the above example, the number of PTC thermistors installed was two, but this is not necessarily limited to this, and the Curie point temperature was set to 160°C, and the number of PTC thermistors installed at the bottom of the pot was Setting the thermal resistance to 0.2℃/W is just an example;
If it is below ℃/W, there is no problem in terms of performance.

As described above, the present invention has a configuration in which a PTC thermistor is provided as a heat source in a cooking appliance, with an electrode formed on one surface and the PTC thermistor mainly generating heat on this one surface, thereby reducing the load on the PTC thermistor. The thermal resistance is reduced and the output is increased, and as a result, even a positive temperature coefficient thermistor with a low Curie point temperature can fully serve as a heat source for heating adjustment. , a pressure-type heating cooker that reduces the risk of explosion even if it generates heat up to the Curie point temperature, makes it easy to form a heat-resistant and pressure-resistant structure, and generally ensures that a positive temperature coefficient thermistor is used as the heat source for pressure cooking. can be provided.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal sectional view showing a conventional heat source structure using a positive temperature coefficient thermistor, Fig. 2 is a longitudinal sectional view of a pressure cooker showing an embodiment of the present invention, and Figs. 3 and 4 are the same. A longitudinal sectional view of the heating device, a perspective view of the PTC thermistor, and FIGS. 5 and 6 are characteristic curve diagrams for explaining the operation. In the figure, 21 is a pot body, 22 is a lid, 23 is a pressure regulating valve, 31 is a heating device, 32 is a positive temperature coefficient thermistor, 33 and 34 are electrodes, and 38 is an insulating plate.

Claims (1)

[Claims] 1. A pressure type cooking device characterized in that both poles of an electrode are formed on one side surface of a positive temperature coefficient thermistor arranged as a heat source so that the main heat generation is performed on this one side surface.