Induction heating type rice cooker

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Industrial application field]

The present invention relates mainly to an electric rice cooker used for home use and utilizing induction heating.

【0002】

[Conventional technology]

Conventional electric rice cookers generally use electric heater wires as a heating source for many years, but recently, those using an induction heating coil as a heating source have been manufactured and delicious rice cooking is possible. It has come to be widely used. An example of the configuration of a conventional electric rice cooker using this type of induction heating coil will be described with reference to FIG.

【0003】

In FIG. 4, reference numeral 21 denotes a main body case, and the lid 30 is attached by the upper end hinge portion 31 so as to be openable and closable. 24 is a pan made of a magnetic metal such as stainless steel on the outside and a two-layer metal plate made of a material with good thermal conductivity such as aluminum on the inside, attached at the upper end of the main body case 21, and a protective frame made of heat-resistant plastic. It is detachably stored in 22. 29a and 29b are induction heating coils, which are excited by the output of the inverter 23 and magnetically couple with the magnetic metal layer of the pot 24 to heat the pot 24. 26 is pressed against the bottom of the pan 24 from the through hole 32 of the protective frame 24 by a spring 27 held in the sensor case 28 fixed to the protective frame 22 by the sensor. Reference numeral 25 denotes a side heater, which mainly heats the heat. When rice and water are put in the pot 24 and the power switch (not shown) is turned on, the output of the inverter 23 is applied to the induction heating coils 29a and 29b, the bottom and bottom sides of the pot 24 generate heat, and the aluminum layer inside the pot. The heat is propagated and rice cooking is started. The heating according to the rice cooking process is controlled by the temperature signal measured by the sensor 28 by the control circuit built in the inverter 23. When the rice cooking is completed, the temperature of the pot rises sharply, so the output of the inverter 23 is stopped by the control circuit by this temperature signal, and the state shifts to the heat retention state. In general, in order to cook delicious rice, it is most important to use good equipment and to improve the water and heat. The best heating can be achieved by improving the heating method, improving the temperature distribution of the pot, and accurately capturing the temperature signal for controlling the heating. Therefore, in order to measure the temperature of the pot 24 in a stable manner, it was indispensable to provide a through hole in the protective frame 22 so that the sensor 26 could freely appear and disappear and press-contact the bottom surface of the pot 24 with the spring 27. However, in this configuration, there is a problem that foreign matter is placed on the sensor or foreign matter or water enters between the through hole 32 of the protective frame 22 and the sensor, and basically the sensor and the pan are thermally conducted by contact. There was a problem that the error could not be avoided.

【0004】

[Problems to be Solved by the Invention]

The conventional problem to be solved by the present invention is to provide a through hole on the bottom or side of the protective frame for storing the pot in order to control the heating of rice and turn off the power when the rice is cooked. The output of the inverter has been controlled according to the rice cooking process by contacting the pot with the signal from the sensor and calculating it with a microcomputer. Therefore, there is a risk that dust and water will flow into the protective frame that houses the pot, and many design measures have been required. Further, in order to ensure the contact between the pot and the sensor, it is necessary to press the sensor against the pot with a spring or the like to ensure the free movement of the sensor for the support device.

【0005】

In addition, when a foreign substance intervenes between the sensor and the pot, a large error occurs, which causes a problem that the rice cannot be cooked. An object of the present invention is to solve such a conventional problem, and it is possible to cook rice stably by utilizing the temperature and magnetic characteristics of the material of the pot without using the above sensor.

【0006】

[Means for solving problems]

In the present invention, in order to achieve the above object, the constituent material of the pot is a material having a Curie temperature, the Curie temperature is matched with the cooking temperature of rice, and the induction heating coil and the pot change according to the rice cooking process. It is configured to detect changes in magnetic coupling and control rice cooking.

【0007】

[Action]

The electric rice cooker of the present invention cooks rice according to the above configuration, and since the Curie temperature of the magnetic material constituting the pot is set to the cooking end temperature of the rice, the magnetic material constituting the pot is used at the same time as the rice cooking is completed. It is possible to detect a change in which the magnetic permeability sharply decreases and the magnetic coupling with the induction heating coil sharply decreases, detect the temperature of the pot in non-contact with the pot, and turn off the power.

【0008】

Furthermore, even if the control circuit malfunctions, the temperature of the pot does not rise above the Curie temperature, which is extremely safe.

【0009】

[Example]

Hereinafter, examples of the present invention will be described with reference to the drawings. In FIG. 1, 1 is a main body case in which an upper frame 12 is fixed to an upper end portion and a lid 5 is attached by a hinge portion 13 so as to be openable and closable. A protective frame 2 made of heat-resistant plastic is fixed to the upper frame 12 at its upper end. The pot 3 is detachably housed in the protective frame 2. Reference numeral 4a is an induction coil for heating the bottom of the pan, which is connected to the inverter portion 6 together with the induction coil 4b for heating the bottom of the pan. 8 is fixed to the upper part of the side surface of the protective frame 2 by the pan side heating heater and heats the pan 3 from the side surface. Reference numeral 9 denotes a lid heater that is fixed to the heat radiating plate 10 and heats the pot 3 from the upper surface via the inner lid 11. The pot 2 is made of a magnetic alloy, and the Curie temperature of this magnetic material is adjusted to a cooking end temperature of about 140 ° C.

【0010】

The circuit configuration and operation of the proposed rice cooker will be described with reference to FIG. Reference numeral 12 is a power supply, and the inverter circuit 6 is connected to the power supply. The operation of the inverter circuit 6 is controlled by the control circuit 7, and the pot 3 is induced and heated by the induction heating coils 4a and b. The inverter circuit 6 is composed of a rectifier 66, a choke coil 64 constituting a filter circuit, smoothing capacitors 67 and 65, a resonance capacitor 63 switching element 61, and a diode 62. Reference numeral 71 denotes a magnetic coupling detecting means. When the output of the inverter 6 is applied to the induction heating coils 4a and b to heat the magnetically coupled pot 3 and cook rice, the temperature of the pot 3 changes according to the rice cooking process. The change in the magnetic coupling between the pot 3 and the induction heating coils 4a and 4b is detected, and this signal is sent to the control circuit 7 to control the output of the inverter 6. On the other hand, the control circuit 7 operates the relay driving means 72 by the signal from the magnetic coupling detecting means 71 to control the side heater 8 and the lid heater 9 in accordance with the rice cooking process. Put rice and water in pot 3, connect to the power supply, turn on the power supply 12 switch 14 and start cooking rice.

【0011】

Cooking rice begins with a flooding process. A signal from the control circuit 7 is sent to the inverter 6 so that the heating power corresponds to the rice cooking process stored in the computer of the control circuit 7 in advance, and the output of the inverter 6 is applied to the induction heating coils 4a and b to heat the pot 3. Heat. At the same time, the control circuit 7 also sends a signal to the relay drive circuit 72 to energize the side heater 8 and the lid heater 9. When the time of the flooding process elapses, the control circuit 7 maximizes the output of the inverter 6, and the induction coils 4a and b heat the pot 3 with the maximum power to cook rice.

【0012】

When the rice is cooked after boiling, some of the water in the pot evaporates and most of it is absorbed by the rice, and the temperature of the pot 3 rises sharply above the equilibrium temperature during boiling. When the pot temperature reaches the Curie temperature of 140 ° C of the pot material, the pot material rapidly loses its magnetism, the electromagnetic coupling with the induction heating coils 4a and b sharply decreases, and the exciting current to the induction heating coils 4a and b also rapidly decreases. Decreases to. The magnetic coupling detection means 71 catches this change and sends a signal to the control circuit 7, which turns off the output of the inverter 6, and also sends a signal to the relay drive means 72 to turn off the lid heater 9 and the side heater 8 to cook rice. Is finished. In general, magnetic materials have hysteresis in their characteristics, so even if the pot material reaches the Curie temperature and the power to the induction coils 4a and b drops and the pot temperature rises, the exciting current does not increase immediately. Therefore, it is possible to switch off accurately.

【0013】

As described above, according to this embodiment, the Curie temperature of the magnetic material of the pot for cooking rice is set to 140 ° C, which is the end temperature of cooking rice, so that the pot and the induction heating coil are connected at the same time as the rice cooking is completed. The magnetic coupling drops rapidly. Since this change is detected and heating is controlled, the temperature of the pot can be measured non-contactly, and there is no need to equip a special sensor. Therefore, stable rice cooking is always possible, and the protective frame for storing the pot does not need to be provided with holes for installing the sensor on the bottom or side surface, and the rice cooker has a simple structure and is easy to handle.

【0014】

In the above embodiment, the pot 3 is a single-layer type, but as shown in FIG. 3a, the inside of the pot 3 is an aluminum layer 3a, and the outside is a magnetic material layer 3b so that the Curie temperature becomes equal to the cooking end temperature. In addition, the thickness of the inner aluminum layer 3a may be made thicker than the thickness of the magnetic material layer 3b in order to enhance the thermal conductivity. Further, as shown in FIG. 3b, the magnetic material layer 3b may be formed on the aluminum layer 3a only at the portion facing the induction heating coil 4.

【0015】

[Effect of the invention]

As described above in the examples, the electric rice cooker of the present invention sets the Curie temperature of the magnetic material of the cooking pot to the cooking end temperature of the rice, and the magnetism of the pot and the induction heating coil decreases sharply with the completion of rice cooking. By providing a control device that detects changes in the coupling and turns off the power, even if the control device breaks down without the need for a special sensor, the pot temperature does not rise above the Curie temperature, enabling safe and accurate rice cooking. It is possible to provide an excellent rice cooker that is simplified by greatly reducing the number of components of the rice cooker body.

[Simple explanation of drawings]

[Figure 1]

Breaking side view of the main part of the rice cooker in one embodiment of the present invention [Figure 2]

Block circuit diagram of the rice cooker [Fig. 3]

Cross-sectional view of a main part of a rice cooker pot showing another embodiment of the present invention. [Fig. 4]

Breaking side view of the main part of the conventional induction heating type rice cooker [Explanation of symbols]

1 Body case 2 Protective frame 3 pot 4a Induction coil for heating the bottom of the pot 4b Induction coil for heating the bottom of the pan 5 lid 6 Inverter section 7 Control circuit 8 side heater 9 Lid heater 10 Lid heat dissipation plate 11 Inner lid