JPH0590879U - Heating cooker using negative heating element - Google Patents

Abstract

(57) [Summary] [Purpose] To make the temperature control of a cooking device extremely simple. [Structure] Two negative characteristic ceramic heaters (2) and (3) are provided, and connection of these heaters (2) and (3) can be switched between series and parallel.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a heating cooker using a negative heating element.

In this specification, the negative-characteristic heating element refers to a heating element that has a large electric resistance value in the initial stage of energization and has a small electric resistance value due to a temperature rise accompanying the passage of electricity. A positive-characteristic heating element is a heating element that has a small electrical resistance value at the beginning of energization, immediately increases the electrical resistance value, and rapidly increases the electrical resistance value when the temperature rises above a predetermined temperature as the energization progresses. ..

[0003]

[Prior Art]

 It is well known that household heating cookers that use heating elements are those that use metal resistance wire heating elements such as nichrome wire, and those that use positive temperature heating elements such as positive temperature ceramic heaters. Has been.

The metal resistance wire heating element has the most stable electric characteristics and is low in cost, and is therefore used in a wide range of applications. This is because the stability of the electric power immediately after energization is fast and the electric resistance value after energization changes slightly in the increasing direction, but it is not so much as changing the electric power significantly. Further, it has high heat resistance and can be used at a high temperature of about 1000 ° C.

The positive-characteristic ceramic heater has a small electric resistance value at the beginning of energization, and an overcurrent of about twice as much as that at the rated time momentarily flows immediately after energization to exceed the rated output, but the rated output is instantaneously output. Stabilize. Then, when the temperature of the heater exceeds a predetermined temperature of around 200 ° C, the electric resistance value suddenly increases and the current is reduced to adjust the output, so that the output is stabilized at the rated output. Is instantly close. In addition, since it is controlled by its own temperature regardless of the ambient temperature, it does not exceed the rated output and is safe.

[0006]

[Problems to be Solved by the Invention] In the case of a metal resistance wire heating element, the metal oxidation may be prematurely disconnected depending on the place of use, so caution is required in its application. Also, since the metal resistance wire itself is an electric conductor, it is necessary to take care not to contact it from the outside.

In the case of a positive-characteristic heating element such as a positive-characteristic ceramic heater, as described above, an overcurrent about twice the rated current flows immediately after energization, and depending on the case, other electric appliances such as a breaker are adversely affected. May be given.

In the heating cooker, it is necessary to adjust the temperature according to the type of cooking, which is relatively difficult in the conventional heating cooker as described above.

An object of the present invention is to solve the above problems and to provide a heating cooker whose temperature can be controlled very easily.

[0010]

[Means for Solving the Problems]

 The heating cooker according to the present invention comprises a plurality of negative-characteristic heating elements, and the connection of these heating elements can be switched between series and parallel.

As the negative characteristic heating element, for example, a negative characteristic ceramic heater or the like is used.

[0012] Preferably, a relay for switching the connection of the plurality of negative characteristic heating elements in series and in parallel, a relay changeover switch and a thermostat are connected in series to the power supply, and the relay is turned on to make a plurality of The wirings of the individual negative characteristic heating elements are arranged in parallel, and when the relay is turned off, the wirings of the multiple negative characteristic heating elements are arranged in series.

[0013] Preferably, the thermostat is connected in series to each negative characteristic heating element in a state where the plurality of negative characteristic heating elements are connected in series.

[0014]

[Action]

 Before describing the operation of the present invention, the characteristics of the negative characteristic heating element will be described with reference to FIGS.

Contrary to the positive characteristic heating element, the negative characteristic heating element such as the negative characteristic ceramic heater has a large electric resistance value at the beginning of energization, and it takes a time of a minute unit to start from low power and reach a predetermined output. Takes. When the temperature of the heating element rises after energization, the electrical resistance value decreases and the output increases. In the case of a positive-characteristic heating element, the degree of change in characteristics also changes depending on the size of the heating element, but this tendency is particularly strong for negative-characteristic heating elements, and the larger the size, the slower the rate of change in electrical resistance. However, it has the characteristic that it takes time to reach the rated output. Even when the ambient temperature is low, the output increase rate is also slow. For this reason, for example, in the case of a heating device such as a heating device that wants to rapidly heat in a low temperature state, unless the size of the heating element and electric power are taken into consideration, the inconvenient characteristic that the output rises slowly as the temperature decreases Have Furthermore, if the heating element is made too small, the temperature rises by itself, and there is a safety problem in that the output exceeds the rating and runs out of control.

Therefore, in the past, only a small current was passed through the negative-characteristic heating element to use it as a temperature sensor in the appliance, and the negative-characteristic heating element was not used in the heating cooker. ..

In order to achieve the above-mentioned object, the present invention reversely uses the above-mentioned characteristics of the negative-characteristic heating element, particularly the volume and temperature rise (electrical resistance change) characteristics of the heating element. ..

FIG. 6 is a graph showing the relationship between the element temperature and the electric resistance value when the negative-characteristic heating element is energized. From this, the electric resistance value decreases as the temperature rises due to energization. I understand. FIG. 7 is a graph showing the relationship between the energization time and the electric resistance value when a voltage of 100 V is applied to three negative heating elements A, B, and C having the same initial resistance value but different volumes. The volume relationships of the three heating elements are A> B> C. In the case of a heating element having a large volume such as A, the degree of decrease in resistance value due to energization time is small, and therefore the degree of output increase and temperature increase is also small. On the contrary, in the case of a heating element having a small volume such as C, the degree of decrease in resistance value due to the energization time is large, and accordingly, the degree of output increase and temperature increase is also large. FIG. 8 is a graph showing the relationship between energization time and element temperature when a voltage of 100 V is applied to two negative-characteristic heating elements D and E having the same volume but different initial resistance values. The initial resistance values of the two heating elements are D> E. In the heating element having a large initial resistance value such as D, the degree of decrease in resistance value due to energization time is small, and therefore the degree of output increase and temperature increase is also small. On the other hand, in a heating element having a small initial resistance value such as E, the degree of decrease in resistance value due to energization time is large, and therefore, the degree of output increase and temperature increase are also large.

As described above, the change in resistance value and the temperature rise of the negative-characteristic heating element are not only affected by the initial resistance value of the heating element, but also greatly affected by the volume of the heating element.

According to the cooking device of the present invention, the connection of the plurality of negative-characteristic heat-generating bodies having the above-described characteristics is switched between series and parallel, so that the relationship between the energization time and the temperature rise is greatly changed. be able to. That is, when the connection of the negative characteristic heating element is switched in series, the volume of the heating element is large and the rated output is small, and the increase rate of the output of the heating element and the temperature increase rate are also slow. On the contrary, when the connections of the negative characteristic heating element are switched in parallel, if the volume of the heating element is appropriate or smaller than the rated output, the rate of increase in the output of the heating element and the rate of temperature increase will be high. Therefore, it is easy to make a combination of increasing the output quickly when high output is required and increasing the output as slowly as possible when low output.

A relay for switching the connection of a plurality of negative characteristic heating elements in series and in parallel, a relay switching switch, and a thermostat are connected in series to the power supply, and when the relay is turned on, a plurality of negative If the characteristic heating elements are connected in parallel and the relays are turned off so that multiple negative characteristic heating elements are connected in series, cooking can be done in series or in parallel. It is possible to automatically switch to series connection when the temperature rises to some extent after starting cooking at. In other words, if the switch for switching the relay is turned off, the relay will not be turned on until it is turned off, and therefore the wiring of the negative-characteristic heating element will be straight until the end. If the relay switch is turned on, the temperature is low at the beginning of energization, so the thermostat is turned on. Therefore, the relay is also turned on, and the heating element wiring is parallel. Therefore, the rate of temperature rise is high. Then, when the temperature rises to some extent, the thermostat turns off and the relay turns off, which causes the heating element connections to switch in series and the output decreases.

Furthermore, if the thermostats are connected in series to each negative characteristic heating element in a state where the plurality of negative characteristic heating elements are connected in series, the temperature rises to some extent. , Those thermostats are turned off, and the power supply to each heating element is stopped, and as a result, excessive temperature rise is suppressed.

[0023]

【Example】

 An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows a schematic configuration of the heating cooker, and FIG. 2 shows an electrical configuration thereof.

As shown in FIG. 1, the cooker includes a cooker main body (1) having a horizontal support plate (1b) at an intermediate height of the vertical cylindrical portion (1a). Two negative characteristic heating elements, that is, a first negative characteristic ceramic heater (2) and a second negative characteristic ceramic heater (3) are fixed to the upper surface of the support plate (1b) in the main body (1). Then, an appropriate cooking container (4) is placed on the heaters (2) and (3) for cooking. The main thermostat (5) is located on the lower surface of the support plate (1b) between the two heaters (2) and (3), and the first sub-thermostat (6) is located below the first heater (2). 2 The second sub-thermostat (7) is fixed to the lower part of the heater (3). The main thermostat (5) operates by detecting the temperature of the part between the two heaters (2) and (3), and controls the temperature of high output operation in the parallel connection state described later. The first sub-thermostat (6) operates by detecting the temperature of the first heater (2). The second auxiliary thermostat (7) operates by detecting the temperature of the second heater (3). Then, these sub-thermostats (6) and (7) perform temperature control of low output operation in a direct connection state described later. The temperature at which the main thermostat (5) turns off (off temperature) is high, and the temperature at which it turns on (return temperature) is low. The off temperatures of the two auxiliary thermostats (6) and (7) are equal to each other, and their return temperatures are also equal to each other. The off temperature of the sub-thermostats (6) (7) is significantly lower than the off temperature of the main thermostat (5), and the return temperature of the sub-thermostats (6) (7) is higher than the return temperature of the main thermostat (5). The difference between the off temperature and the return temperature of the sub-thermostats (6) and (7) is relatively small.

As shown in FIG. 2, the main switch (8), the main thermostat (5), the relay (9) and the output connection switch (relay switching switch) (10) are connected in series by an AC power supply (11). )It is connected to the. The common contact part (12c) of the C contact (12) of the relay (9) is connected to the part between the main switch (8) and the main thermostat (5). The a contact (13) of the relay (9) is provided between the part between the power source (11) and the changeover switch (10) and the normally closed contact part (12b) of the c contact (12). A series connection circuit of the first auxiliary thermostat (6), the first heater (2), the second auxiliary thermostat (7) and the second heater (3) is connected in parallel to the a-contact (13). The part between the first heater (2) and the second auxiliary thermostat (7) is connected to the normally open contact part (12a) of the c contact (12). The a-contact (14) of the relay (9) is connected in parallel to the first auxiliary thermostat (6), and the a-contact (15) of the relay (9) is connected in parallel to the second auxiliary thermostat (7). ..

In the above cooking device, while the main switch (8) is off, the heaters (2) and (3) are not energized and heating is not performed.

When the above-described cooker is operated in series connection from the beginning, the main switch (8) is turned on with the changeover switch (10) turned off. Even when the main switch (8) is turned on, the change-over switch (10) is turned on, so the relay (9) remains off, and therefore the c contact (12) is normally closed contact part (12b). ) Side, and all a-contacts (13), (14) and (15) are off. Therefore, as shown in Fig. 3, the two heaters (2) and (3) are connected to the power supply (11) in series, and the a contacts (14) (15) of the relay (9) are turned off. Therefore, the two auxiliary thermostats (6) (7) are connected to the two heaters (2) (3) in series. Since the temperature of the heaters (2) and (3) is low at the initial stage, the two auxiliary thermostats (6) and (7) are turned on, and the heaters (2) and (3) are also turned on. Thus, the state where the two heaters (2) and (3) are connected in series corresponds to the state where the heaters (2) and (3) have a large volume and a small rated output. ) The output increase rate and the temperature increase rate are also slow. Therefore, the heating of the object to be heated is gentle and the heat easily penetrates slowly into the inside. If the temperature of one of the heaters (2) and (3) rises to the off temperature of the sub-thermostats (6) and (7) while low-output heating is being performed in this way in series connection, the sub-thermostat ( Either 6) or 7) is turned off, and the two heaters (2) and (3) connected in series to this are also turned off. When the temperature of the heaters (2) and (3) drops to the return temperature of the sub-thermostats (6) and (7), the sub-thermostats (6) and (7) are turned back on and the heaters (2) and (3) are turned on again. Turns on. Even if the auxiliary thermostats (6) and (7) are turned off as described above, the volume of the heaters (2) and (3) is large and the heat capacity is large, so there is no rapid temperature drop, and therefore the object to be heated is not heated. The temperature change is small and it is easy to continue heating and control the temperature. The heating at such a low temperature is suitable, for example, for cooking a relatively thin-walled baked product such as omelet or okonomiyaki. And as a result of cooking, the surface is thinly burned, and the inside looks heated and looks good.

When operating the above cooking devices in a parallel connection state, the main switch (8) is turned on while the changeover switch (10) is turned on. At this time, the main thermostat (5) is on because the temperature of the heaters (2) and (3) is low, and the main switch (8) is on because the selector switch (10) is on. Then, the relay (9) is turned on, so that the c contact (12) is switched to the normally open contact part (12a) side, and the a contacts (13, 14) and (15) are all turned on. Therefore, as shown in FIG. 4, the two heaters (2) and (3) are connected in parallel to the power supply (11), and the a contacts (14) and (15) of the relay (9) are turned on. The heaters (2) and (3) are turned on. When the two heaters (2) and (3) are connected in parallel in this way, if the volume of the heaters (2) and (3) is appropriate or smaller than the rated output, the heaters (2) and (3) The output increase speed and the temperature increase speed become fast. Therefore, heating of the object to be heated is rapid, and heating convection is promoted in the case of a substance having a large amount of water. In the case of roasted meat, the surface is heated more than internal heating, and it is possible to form a film to prevent the outflow of the extract contained in the meat juice and the like from the inside of the meat with browning. If the temperature of the heaters (2) and (3) rises to the off temperature of the sub-thermostats (6) and (7) during high-output heating in the parallel connection state, the sub-thermostat (6) Although (7) is turned off, the two contacts (14) and (15) of the relay (9) connected in parallel with them are turned on, so the two heaters (2) and (3) are turned on. However, the heating in the parallel connection state is continued. Then, when the temperature of the heaters (2) and (3) rises to the off temperature of the main thermostat (5), the main thermostat (5) turns off, which turns off the relay (9). For this reason, the c-contact (12) of the relay (9) is switched to the normally closed contact part (12b) side, and all the a-contacts (13), (14) and (15) are turned off. As shown in 3, the two heaters (2) and (3) and the two sub-thermostats (6) and (7) are connected in series. Immediately after the connection of the heaters (2) and (3) is switched from parallel to series, the two auxiliary thermostats (6) and (7) are also off, so the heaters (2) and (3) are off. It has become. Then, when the temperature of the heaters (2) and (3) drops to the return temperature of the sub-thermostats (6) and (7), the sub-thermostats (6) and (7) are turned back on and the heaters (2) and (3) are turned on again. Is turned on, and in the same manner as above, low-output heating by the heaters (2) and (3) connected in series and temperature control by the auxiliary thermostats (6) and (7) are performed. In the case of roasted meat, by automatically switching from the parallel connection state to the series connection state in this way, it is possible to carefully heat and finish the inside of the meat. The meat thus baked is heated to the inside and becomes a delicious product containing a sufficient amount of meat extract. Normal simmering and stewing can be performed in the same automatic temperature control mode. In addition, miso soup, which has a lot of juiciness, can be heated and has a high heat-retaining effect, and is suitable for low-temperature long-term stewing of boiled beans with relatively little juiciness.

In a normal metal resistance wire heating element, when the connection of two heating elements having the same resistance value is switched from parallel to series, the overall resistance value increases four times and the output is 1 / It drops to 4. On the other hand, in the case of the negative characteristic ceramic heater, the changes in the output increase rate and the temperature increase rate in the same manner are larger than those in the metal resistance wire heating element. Also, in the case of a negative characteristic ceramic heater, even when the heater volume is smaller than the rated output in the parallel connection state, the excessive inrush current does not flow instantaneously immediately after energization like the positive characteristic heating element, and Since it increases gradually, it can be dealt with by the control by the main thermostat (5) as described above.

FIG. 5 shows a heating cooker different from the above.

In this case, two negative characteristic ceramic heaters (2) and (3) are directly attached to the outer surface of the bottom of the cooking vessel (16), and an object to be heated is put in the vessel (16) for cooking. I am supposed to do it. Others can be configured similarly to the above embodiment.

If the OFF temperature and the return temperature of the thermostats (5), (6) and (7) are made variable so as to allow a wide range of temperature settings, a more delicate temperature adjustment suitable for the purpose of cooking can be performed.

If the number of negative characteristic heating elements is increased, the rate of change in power at the time of switching between series and parallel is further increased, and flexibility is further increased. In other words, as the number of negative-characteristic heating elements increases, the overall volume in the serial connection state increases, the output drops significantly, and the time to reach the low rated output is delayed, resulting in an extremely weak heating state.

[0035]

[Effect of the device]

 According to the cooking device of the present invention, as described above, the connection between the plurality of negative characteristic heating elements is switched between series and parallel, whereby the relationship between the energization time and the temperature rise can be greatly changed. Therefore, temperature control is extremely easy, and it is easy to make a combination of increasing the output quickly when high output is required and increasing the output as slowly as possible when low output.

A relay for switching the connection of a plurality of negative characteristic heating elements in series and in parallel, a relay switching switch, and a thermostat are connected in series to the power supply, and when the relay is turned on, a plurality of negative If the characteristic heating elements are connected in parallel and the relays are turned off so that multiple negative characteristic heating elements are connected in series, cooking can be done in series or in parallel. It is possible to automatically switch to series connection when the temperature rises to some extent after starting cooking at.

If the thermostat is connected in series to each negative characteristic heating element in the state where the plurality of negative characteristic heating elements are connected in series, the temperature will be as high as possible. When the temperature rises, those thermostats are turned off, and the power supply to each heating element is stopped, and as a result, an excessive temperature rise is suppressed.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a heating cooker showing an embodiment of the present invention.

FIG. 2 is an electric circuit diagram showing an example of an electric configuration of the heating cooker shown in FIG.

FIG. 3 is an explanatory diagram showing a main part of a circuit in a state where two negative characteristic ceramic heaters are connected in series.

FIG. 4 is an explanatory diagram showing a main part of a circuit in a state where two negative characteristic ceramic heaters are connected in parallel.

FIG. 5 is a vertical sectional view of a heating cooker according to another embodiment of the present invention.

FIG. 6 is a graph showing the relationship between the temperature and the electric resistance value of a negative characteristic ceramic heater.

FIG. 7 is a graph showing the relationship between the energization time and the electric resistance value of a negative characteristic ceramic heater.

FIG. 8 is a graph showing a relationship between an energization time and a temperature of a negative characteristic ceramic heater.

[Explanation of symbols]

(1) Cooker body (2) (3) Negative characteristic ceramic heater (negative characteristic heating element) (4) Cooking vessel (5) Main thermostat (6) (7) Sub thermostat (8) Main switch (9) Relay ( 10) Output selector switch (switch for relay selection) (11) AC power supply (16) Cooking container

Claims (3)

[Scope of utility model registration request] 1. A heating cooker using a negative-characteristic heating element comprising a plurality of negative-characteristic heating elements, and the connection of these heating elements can be switched between series and parallel. 2. A relay for switching connection of a plurality of negative characteristic heating elements in series and in parallel, a relay switching switch and a thermostat are connected in series to a power source,
The connection of the plurality of negative characteristic heating elements is parallel when the relay is turned on, and the connection of the plurality of negative characteristic heating elements is connected in series when the relay is turned off. A heating cooker that uses a negative heating element. 3. The negative characteristic heating element according to claim 2, wherein a thermostat is connected in series to each negative characteristic heating element in a state where the plurality of negative characteristic heating elements are connected in series. Cooker using.