JPS5822669Y2 - boiler - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an electric boiler with an improved temperature control method.

An electric boiler such as an electric rice cooker includes a heater for heating a pot, and a temperature switch that senses the temperature at the bottom of the pot and controls energization of the heater.

A conventional electric rice cooker has a rotatable lever with a permanent magnet and a knob attached to each end, a microswitch that is controlled to open and close according to the rotation of the lever, and a link between the permanent magnet and the pot. A magnetic shunt steel for holding the microswitch in a closed state, a spring for biasing the lever in the direction of opening the microswitch, etc. are provided, and the lever is rotated by pressing the knob. When the temperature is reached, the microswitch is closed and the heater is energized, and the permanent magnet attracts the magnetic shunt steel to keep the microswitch closed, and when the cooking temperature is reached, the magnetic force of the magnetic shunt steel decreases. The lever is configured to be returned to its old position by the biasing force of a spring.

In other words, in the conventional device as described above, the mechanical part of the temperature switch is extremely complicated and has many parts, and requires parts processing and assembly.

The disadvantage is that adjustment requires a lot of man-hours and manufacturing costs are high.

In addition, for products that also have a heat retention function by heating,
If the power plug is plugged into the outlet without pressing the knob and the microswitch is not closed, the rice will remain warm and will not cook, so the rice inside will be raw and will not cook. Fail.

Furthermore, if the knob is pressed without a pot attached, there is a risk that the microswitch will close, causing a so-called dry cooking condition.

The present invention was developed based on the above circumstances, and uses an automatic reversing temperature switch that has a sufficiently large difference between the upper and lower operating temperature limits, so that after cooking, the food is kept warm at a temperature between these two temperatures. By doing so, the structure is simple and can be manufactured at low cost, and when the power is turned on, the cooking state is automatically set without requiring any other operation, and the temperature switch operates stably. To provide an improved boiler that can maintain the temperature for a long period of time and quickly switch to a safe state when the power is turned on without a pot attached.

Hereinafter, the present invention will be described with reference to an illustrated embodiment.

FIG. 1 shows an example in which the present invention is applied to a radiant heat-retaining rice cooker, but the present invention can also be applied to various types of boilers other than rice cookers.

In the figure, an inner frame 3 having a substantially bottomed cylindrical shape is housed in an outer frame 1 having a bottomed cylindrical shape with a heat insulating material 2 interposed therebetween.

This inner frame 3 is made of a material such as aluminum that has good thermal conductivity, and is subjected to surface treatment such as chemical polishing to increase heat reflectance.
is installed.

The pot 5, which is removably housed in the inner frame 3, is held in the predetermined position shown in the figure by abutting the flange 6 formed around the upper end opening to the upper edge of the inner frame 3. The peripheral walls of the pot 5 and the inner frame 3 face each other with a very small gap in between, and the bottom walls face each other with a space 7 at a predetermined interval in between.

An outer lid 8 that covers the upper opening of the outer frame 1 is made of plastic, for example, and is rotatably supported by the outer frame 1 via a hinge member 9. It is equipped with a handle 10.

Further, the outer frame 1 and the outer lid 8 are provided with a retaining member 11 located on the opposite side of the hinge member 9, and can hold the outer lid 8 in the closed position and can be pressed by the push button 12. It is configured so that the engagement can be released.

An inner cover 14 is attached to the inner surface of the outer cover 8 via a support member 13.

The inner lid 14 is configured such that its peripheral edge is pressed against the peripheral edge of the upper opening of the pot 5 when the outer lid 8 is in the closed position.

Reference numeral 15 denotes a steam venting section, which is equipped with a ball valve 16 that can be opened and closed according to the difference between the internal pressure and the external pressure of the pot 5.

The inner frame 3 is provided with a conical cylindrical portion 17 located at the center of its bottom and protruding upward, and a stopper portion 17a is formed at the upper end.

In addition, a cylindrical portion 18 in which a person is thrust from below inside this cylindrical portion 17 is provided.
A spring seat 18 which also serves as a spring support is welded to the outer bottom of the inner frame 3.

19 is a temperature switch, and a first heat sensitive part 19 is installed on the top surface of the temperature switch.
A cylindrical flange 19b, which is a second heat-sensing part, is integrally attached to the outer periphery of the flange 19b, and has a cross-section shaped like an ellipse. A bimetallic movable contact piece C and fixed contact pieces a, l) that are brought into contact with and separated from each other by this bimetal type movable contact piece C are provided.

Such a temperature switch 19 is disposed in the cylindrical portion 17 so as to be movable up and down, and is attached to the cylindrical portion 18 of the spring seat 18.
A compression coil spring 20 is provided to surround a, and its upper and lower ends are received by the flange 19b and the spring seat 18, so that the compression coil spring 20 causes the temperature switch 19 to move inside the cylindrical portion 17. The heat-sensitive portion 19a is urged to come into elastic contact with the outer bottom surface of the pot 5.

The temperature switch 19 is set to the upper limit operating temperature Tu (fifth
(see figure) and the lower limit operating temperature TL is used. For example, Tu''=130℃, T
Lξ50°C is suitable for rice cooking.

Further, this temperature switch 19 is of a bimetal type that automatically reverses depending on the level of temperature.

On the other hand, a first heater 2 having a substantially annular shape is provided in the space 7.
1 is disposed as a boiling heater, and a second heater 22 having an annular or coil shape is wound around the outer periphery of the inner frame 3 so as to be in contact with the inner frame 3 as a part of the heat-retaining heater. There is.

These first and second heaters 21 and 22 are, for example, sheathed heaters, and their respective capacities are the same as the capacity of the pot 5.
It is set according to the heat retention temperature TH, which is set between the upper limit operating temperature Tu and the lower limit operating temperature TL.

Further, a power switch 24 is attached to the outer frame 1 and is controlled to open and close by rotating a knob 23.

and the temperature switch 19. First heater 21. Second
The heater 22 and the power switch 24 are connected to a power plug 25 as shown in FIG. 4, for example, and the first heater 2
The heater 1 is configured to be used for cooking rice and keeping it warm, and the second heater 22 is used for keeping it warm.

Next, the operation of the rice cooker configured as described above will be explained.

Appropriate amounts of rice and water are put into the pots 5 and attached to the inner frame 3, and after the outer lid 8 and the inner lid 14 are closed, the power plug 25 is inserted into the outlet.

Now, at time to (see Figure 5), power switch 2 is turned on.
4 is closed, and the temperature switch 19 senses the pot temperature To at this time.

Generally, this temperature To is approximately equal to the water temperature in the pot 5, and when the temperature is set at about 50°C as described above, the initial temperature To is the lower limit operating temperature T of the temperature switch 19.
Since the temperature is lower than L, the temperature switch 19 is turned on between the contact pieces (C-b) as shown by the solid line in FIG.

Therefore, only the first heater 21 is energized, and the pan temperature (
Therefore, the temperature of the contents gradually increases and reaches the boiling point TB at time t1.

Then, when the rice is cooked and the liquid water in the pot 5 is almost completely gone, the pot temperature starts to rise again, rapidly rising in a relatively short period of time, and reaching the upper limit operating temperature Tu at time t3.

As a result, the temperature switch 19 performs a switching operation, and the contact piece (c-a) is turned on as shown by the broken line in FIG. The second heaters 21 and 22 are energized in series.

Therefore, since the heating temperature by these heaters 21 and 22 decreases, the temperature of the pot 5 temporarily increases slightly, but then gradually decreases, and at time t4, the temperature is maintained at T
Reach H.

As mentioned above, this heat retention temperature TH is the upper and lower limit operating temperature Tu.
, TL, and the temperature is about TH''-175°C.

In such a heat retention state, since TH>TL always holds, the temperature switch 19 never performs a return operation.

Then, when the power switch 24 is opened, the temperature switch 19 performs a switching operation between the contacts (C-b) when the sensed temperature drops to TL after a certain period of time has elapsed.
Automatically returns to initial state.

Therefore, according to this rice cooker, since the heat-sensitive part 19a of the temperature switch 19 is elastically pressed against the outer bottom surface of the pot 5 by the compression coil spring 20, the contact state is stable, and therefore The thermal conductivity between the two is also always stable.

By the way, as mentioned above, the temperature switch 19 is set between the upper limit operating temperature Tu and the lower limit operating temperature TH (differential).
If the heat sensitive part 1 is configured to rotate in one motion and is used so that the temperature in between is used as the heat retention temperature,
If the contact between 9a and the outer bottom surface of the pot 5 becomes unstable and the thermal conductivity between them also becomes unstable, the differential seen as the temperature of the pot 5 of the temperature switch 19 becomes narrower, making it impossible to obtain a stable heat retention effect. However, with the above configuration, since the thermal conductivity is stable as described above, such a fear does not arise, and the stable operation of the temperature switch 19 can be maintained for a long period of time, so that a stable heat retention effect is always achieved. That's what you get.

Next, a case will be described in which the power switch 24 is closed with the pot 5 removed.

In this case, the temperature switch 19 moves upward, and the flange portion 19b, which is the second heat-sensitive portion, is pressed against the stopper portion 17a of the inner frame 3.

Therefore, the collar portion 19b, which is the second heat-sensitive portion, is the stopper portion 17a.
That is, the temperature of the inner frame 3 is sensed.

When the pot 5 is not attached, the temperature of the inner frame 3 rises rapidly, and the temperature switch 19 senses this temperature via the second heat-sensing part, and the temperature is switched to the heat-retaining side, that is, between the contacts C and a shown in FIG. is switched so that it is closed.

Therefore, the amount of heat generated by the heater is much smaller than when cooking rice, making it extremely safe.

As described above, the present invention uses a temperature switch that senses the temperature of the pot and the temperature of the inner frame when the pot is removed. Second
Since the power supply to the heaters for boiling and keeping warm is controlled to make the rice cooking and keep warm, it is necessary to use magnetic shunt steel, permanent magnets, operating levers, springs, etc.
Since there is no need to use many types of parts such as microswitches, parts processing, assembly, and adjustment are significantly simplified, and manufacturing costs can be significantly reduced.

In addition, since the heat retention temperature is set between the upper and lower operating temperature limits of the temperature switch, the rice does not go into the cooking mode and remain warm when the power is turned on, and stable heat retention is always achieved. Furthermore, it is possible to provide a boiler that can quickly switch from an abnormal state to a safe state.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention, with FIG. 1 being a sectional view and FIG.
3 is a perspective view of the temperature switch, FIG. 4 is an electric circuit diagram, and FIG. 5 is a temperature characteristic diagram for explaining the operation. In the drawing, 5 is a pot, 17 is a cylindrical part, 18 is a spring seat, 19
19a is a temperature switch, 19a is a first heat sensitive part, 19b is a collar part (second heat sensitive part), 20 is a compression coil spring, 2
1.22 is the first. 2nd heater (heater for boiling and keeping warm)
, TH indicates the heat retention temperature, and TL and Tu indicate the operating temperature.

Claims (1)

[Scope of utility model registration request] A boiling heater and a heat-retaining heater that heat a pot that are removably installed in an inner frame, a first heat-sensitive part that is elastically pressed against the outer bottom surface of the pot by a spring means, and a first heat-sensitive part that is elastically pressed against the outer bottom surface of the pot by a spring means and a second heat-sensitive part that is elastically pressed against the stopper part of the inner frame when the inner frame is removed.