JPS6030211B2 - Heater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a lid heating element that is attached to the lid of a heat insulator such as a heat insulating jar or jar rice cooker and is used for the purpose of preventing dew droplets from forming on the inner lid. To provide a heat insulator having a lid heating element that can set an optimal heat retention state and always safely generates heat in the case of a heat insulator having a structure in which a lid heating element unit incorporating a lid heating element can be separated from an inner lid. It is something.

Generally, when food, such as rice, is kept warm, the inside of the heat insulator is filled with water vapor, which forms mist droplets on the relatively low-temperature walls of the heat insulator.
If there is a lot of water vapor on the inner lid, it will drip onto the rice, making the surface sticky and making the rice very susceptible to spoilage. In order to prevent these mist droplets from forming, it is necessary to attach a heating element to the lid to heat the inner lid. In addition, in the case of a jar rice cooker, since the rice is kept warm after cooking, sticky rice contained in steam during cooking adheres to the inside of the container, especially to the lid. In order to clean this, the lid needs to be able to be disassembled and washed, and for this purpose a lid heating element unit for heating the inner lid that is detachable from the inner lid and outer lid is used. ′
Hereinafter, a jar rice cooker will be taken as an example, and the present invention will be explained with reference to the drawings, while comparing the related examples and the present invention.

An example of the structure of the jar rice cooker is shown in FIG. 1. Reference numeral 1 denotes a lid heating element unit, which is attached to a handle 2 via a spring. 3 is an outer lid, and 4 is an inner rhombus made of aluminum plate attached to the upper part of the inner pot 5.

The outer cover 3 has a heat insulating structure that covers the inner cover 4, and is configured to detachably engage with a handle 2 whose one end is pivotally supported on the instrument or main body. Reference numeral 6 is a heat-retaining heating element that heats the outer pot 7 attached to the main body of the appliance, and 8 is a heating element for cooking rice, which is connected in series with the heat-retaining heating element 6 when keeping the rice warm, contributing to heat retention. .

FIG. 2 shows the handle 2 and the lid heating element unit 1 in a state where the inner lid 4, the outer lid 3 are separated, and in the figure, 9 is an attachment/detachment lever, and 1 is an attachment/detachment lever. An example of the circuit configuration of a conventional heating element during heat retention is as shown in FIG.

That is, 21 is a power source, 22 is a heating element for cooking rice, 23 is a lid heating element, 24 is a heating element for keeping warm, and the rice cooking switch 25
and the heat retention switch 26 are connected as shown in the figure. 29 is an SCR whose gate is coupled to the output from the temperature detection circuit.

The heating element 24 for keeping warm and the heating element 22 for cooking rice, which are the main heat sources during warming, are connected in series, and when the SCR 29 is conductive, current flows through this circuit.This circuit is shown in Figure 1. It contributes to the heating of the inner pot 5 and keeps the cooked rice at a constant temperature.Also, in the circuit shown in Fig. 6, a current always flows through the lid heating element 23, The inner lid 4 is heated like this.The diode 28 is connected to the SC
It has the role of blowing out the t-current fuse 27 when R29 fails and becomes conductive in the opposite direction.

With the thermal insulation configuration of conventional jar rice cookers, ``If the room temperature fluctuates,'' at low temperatures, not only does the heat from the thermal insulation escape to the outside, but the sensor in the temperature detection circuit is also cooled by the outside air.
The conduction of the SCR 29 becomes longer, and the temperature of the inner steel 5 and rice becomes higher than when kept at a high temperature at room temperature.

On the other hand, when the inner lid 4 cools, dew droplets form and once they are heated, they are difficult to fly off, so continuous heating is required.Also, as shown in Figure 2, the lid is separated from the inner lid mother to the lid. When the heating element unit 1 is removed, the temperature of the lid heating element unit may rise excessively with a heating element such as a general nichrome wire. A heating element has been used.This type of heating element maintains a constant temperature despite voltage fluctuations and room temperature fluctuations, but the
Assuming that both the room temperature is the highest, the comparison shows that the temperature of the inner pot 5 and the rice have the opposite characteristics. Therefore, when the room temperature drops, the temperature of the inner pot 4 becomes lower than that of the inner pot 6. Many mist droplets were seen on the inner lid 4, and these often dripped onto the rice cooker.On the other hand, when the room temperature rose, the inner pot 5 became lower than the inner lid 41, so that the inner periphery of the inner steel There have been cases where dew drops have occurred and dripped onto the rice.This problem in the heat retention structure of the secondary pot is caused by the heating element 22 for heating the inner pot, the heating element 24 for keeping the rice warm, and the inner lid as shown in Fig. 6. According to the present invention, this problem can be solved and the lid heating element has a heat generating element configuration that safely generates heat.

Hereinafter, the characteristics when the present invention is used in a rice cooker will be explained with reference to the drawings. The main structure of the heat insulator shown in FIGS. 1 and 2 is the same as that of the conventional example.

FIG. 3 shows an example of a lid heating element unit incorporating the lid heating element 12. In the figure, reference numeral 11 denotes a unit armor body molded from a thermoplastic resin such as polyester or polypropylene mixed with glass fiber or powder, such as FRP. Reference numeral 15 in FIG. 2 denotes a support plate having nut holes for attaching it to the handle 2 and nut holes for assembling the lid heating element unit. An insulating sheet 13 made of rubber or the like and a lid heating element 12 are connected to the support plate 1 via the cliff shell 1.
6 with screws 16.

The lid heating element 12 has the structure shown in FIG. 4, and is formed by printing a silver electrode 18 and a resistor 19 on one side of a ceramic substrate 17 whose main component is alumina. Resistor 19
It has positive resistance-temperature characteristics because it is mainly made of crystalline resin and conductive fine powder such as carbon and metal, and when used in a heating element, it improves the resistance-temperature characteristics of conventional ceramics. A self-temperature control function can be obtained in the same way as a heating element.A number of advantages are created by applying the heat retention circuit configuration shown in Figure 5 to the configuration of the jar rice cooker as described above. , 22 is a heating element for cooking rice, 23 is a lid heating element, 24 is a heating element for keeping warm, and 29 is an SCR that connects the output from the temperature detection circuit to a gate.SC
When R29 is conductive, the heat-retaining heat generating element 24 and the rice-cooking heat generating element 22, which are the main heat generating sources during heat retention, are connected in series, and a current flows through this circuit. Regarding the lid heating element 23, "SCR2
When 9 is conductive, the half-wave current that has passed through the diode 30 passes through the lid heating element 23 and flows through the SCR 29.On the other hand, the half-wave current in the opposite direction always flows through the diode 31, the lid heating element 23, and the diode 28. It flows through the heating element 22 for cooking rice,
Configure a closed circuit. As can be seen from the above, when the SCR 29 is conductive, a half-wave current flows through the heat-retaining heating element 24 that heats the inner pot, and a full-wave current flows through the lid heating element 23 that heats the inner lid. On the other hand, when the SCR 29 is cut off, the heat retention heating element 24
No current flows through the lid heating element 23, and a half-wave current flows through the lid heating element 23. In this way, when the circuit shown in Fig. 5 is used, heating of the inner cover and heating of the inner steel can be controlled by one common SCR, and the heating of the inner cover can be constantly performed by full-wave or half-wave current. Therefore, the imbalance between the heating of the inner lid and the heating of the inner pot, which is seen in conventional heat-retaining devices, can be eliminated, and any possible heat-retaining conditions in actual use can be dealt with, thereby creating an optimal heat-retaining state. However, it has been experimentally confirmed that even with such a configuration, some drawbacks will occur if the lid heating element used in the present invention is not used. Below, when three types of heating elements are used as the lid heating element in the circuit shown in Fig. 5, the characteristics of 1. the lid heating element used in the present invention, 2. the ceramic heating element, and 3. the nichrome heating element, depending on the energization state. A comparison is shown in the table below. [Comparison of characteristics of various lid heating elements depending on the energization state] (The small □ symbol is the 7th
It is the same as that used in FIG.

) Experimentally, the lid heating element requires a power of 8 W or more when kept at a room temperature of -5°C, and 7 W or less when kept at a room temperature of 35 qC.

Comparing the lid heating element used in the present invention in No. 1 and the ceramic heating element No. 2, No. 1 shows much better characteristics. Furthermore, when the lid heating element unit is removed from the inner lid, the load becomes smaller, so the temperature of the lid heating element unit tends to rise. Comparing the lid heating element used in the present invention in No. 1 and the nichrome heating element No. 3, No. 1 is much safer.

In the case of No. 3, the heating element becomes overheated and the resin molded product around the heating element melts, which is extremely dangerous.

The resistance-temperature characteristics of the lid heating element 1 according to the present invention are as shown in FIG. 7, and the resistance-temperature characteristics of the other lid heating elements 2 and 3 are as shown in FIG. 8. In the figure, the characteristic 1 is a curve indicated by 41 in the figure, which has a large positive temperature coefficient of resistance from around 13,000. In the figure, A is the heat radiation curve when kept at room temperature of -5℃, B is the heat radiation curve when kept at room temperature of 35qC, and C is the heat radiation when the lid heating element unit is removed from the inner lid at -5℃. It is a curve. The intersection points AI, B1, and CI of these curves A, B, and C and the characteristic curve 41 are the heating element temperatures that are saturated in each of the energization states A, B, and C. AI~BI
does not have a positive resistance-temperature characteristic and is easily subject to power control, so AI
~CI has a large slope and is safe. 8th
In the figure, 42 is the resistance temperature characteristic of 2, and 43 is the resistance temperature characteristic of 3, and the same can be said as in FIG. The temperature change rate of resistance is called the X value for this type of heating element, where

−1]. The × value of lid heat generation 1 according to the present invention is 1
050-13500 is around 0.01/00, 13
If it is 0.04/°C or more at 500 to 150 dC, the temperature of the heating element will not exceed 14,700 and is safe.
As explained above, according to the present invention, it is possible to create a heat insulator that can always create an optimal heat retention state even if the room temperature or power supply voltage fluctuates, and a jar with a system in which the lid heating element unit can be detached from the inner lid. To provide an innovative heat insulator that always safely generates heat even when the heat load on the lid heating element changes in a rice cooker or the like.

The lid heating element according to the present invention may be made of a ceramic material, but the slope of the curve showing the positive resistance temperature characteristic and the resistance value can be set arbitrarily by changing the material composition and formulation.Crystalline resin, carbon, or metal It is more advantageous to use a heating element having a positive temperature coefficient of resistance made of a resin composition whose main material is a conductive fine powder such as .

For the material exhibiting characteristic 41 as the example shown in FIG. 7, for example, a copolymer of polyvinylidene fluoride and polytetrafluoroethylene is used as the resin, furnace-based carbon black and artificial graphite are used as the conductive layer, Compositions using fluororubber as a binder are preferred.

[Brief explanation of drawings]

Figure 1 is a diagram showing an example of the configuration of a jar rice cooker, Figure 2 is a perspective view of the handle of the jar rice cooker with the lid removed, and Figure 3 is a lid heating element incorporating the lid heating element used in the invention. FIG. 4 is a cross-sectional view showing an example of the body unit, FIG. 4 is a diagram showing an example of the lid heating element used in the present invention, FIG. 5 is a circuit diagram when the present invention is applied to a jar rice cooker, and FIG. A circuit diagram of a conventional jar rice cooker, FIG. 7 is a diagram showing the resistance-temperature characteristics of the lid heating element of the present invention, and FIG. 8 is a diagram showing the resistance-temperature characteristics of the conventional heating element. 1... Lid heating element unit, 3... Outer lid, 4
...Inner lid, 6...Heating element for heat retention, 8.
...Heating element for cooking rice. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] 1. It has an inner lid, a lid heating element unit for heating the inner lid that is detachably attached to the inner lid, a heating element for heating the inner pot and a heating element for cooking rice, and the inner pot is heated by the three heating sources. In a heat insulator that keeps the food inside warm, a heating element having a positive resistance temperature characteristic made of a crystalline resin mixed with conductive fine powder is incorporated in the lid heating element unit, and this heating element is equipped with a temperature detection circuit. A heat insulator configured to flow a full-wave current when the thyristor whose output is supplied to the gate is conductive, and to flow a half-wave current when the thyristor is non-conductive.