JP3262503B2 - Induction heating rice cooker - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating type rice cooker.

[0002]

2. Description of the Related Art In an induction heating type rice cooker, a protective frame is provided inside an outer casing, and an inner pot is housed therein so as to be able to be taken out. An induction heating coil is provided on the bottom surface of the protection frame so that the inner pot is induction-heated. The induction heating coil is spirally wound, and a plurality of ferrites are provided below the coil in a radial manner from the center toward the outer diameter side.

[0003] In the induction heating type rice cooker having the above-described structure, when the coil diameter of the induction heating coil is reduced, the magnetic coupling with the pot is reduced, and the material effect is small. A space having a predetermined diameter is formed. For this reason, the lines of magnetic force generated by energization become non-uniform, and the temperature of the inner pot is low at the center and high at the middle (see the dashed line in FIG. 3). Since this causes unevenness in rice cooking, the inner pot is conventionally made to have a uniform temperature by various means as described below.

[0004] Between the bottom surface of the protective frame and the induction heating coil,
A magnetic shield is provided for suppressing the magnetic flux density at the intermediate portion (see Japanese Utility Model Laid-Open No. 5-68418). However, in this means, a part of the generated magnetic field lines is not used for heating the inner pot, and the temperature distribution of the inner pot is made uniform, so that a large amount of power is wasted.

In addition, the induction heating coil is separated and wound on an inner diameter side and an outer diameter side (see Japanese Patent Application Laid-Open No. 24988/1990). However, with this means, the winding operation of the induction heating coil is difficult, and the heating ability is inferior to the conventional one.

[0006] Further, the distance between the induction heating coil and the inner pot is increased at the intermediate portion (for example, the actual open flat hood 6-137).
No. 20). However, this means, as described above,
By not using a part of the generated magnetic field lines for heating the inner pot, in order to make the temperature distribution of the inner pot uniform, not only the wasteful power consumption is large, but also the inner pot etc. must have a special shape. Not easy to clean. In addition, a case where a desired temperature distribution cannot be obtained due to easy deformation is also assumed.

By the way, the temperature distribution of the object to be heated tends to be relatively uniform due to convection of water in the early stage of rice cooking, but tends to be non-uniform in the latter stage of rice cooking due to no convection of water. This change in the temperature distribution is strongly influenced by the difference in the capacity of the object to be heated housed in the inner pot. For this reason, in order to maintain a uniform temperature distribution, it is largely different depending on which time during cooking rice and how much the content is, and it is not possible to sufficiently cope with any of the above means.

Further, the inner pot is induction-heated by a combination of induction heating coils at the center and lower side (outer peripheral portion) of the bottom of the inner pot and a combination of induction heating coils at the center and upper side of the bottom. 2-292815). However, in this method, the induction heating coil provided at the center of the bottom surface always heats the inner pot, so that it is impossible to eliminate the variation in the temperature distribution on the bottom surface of the inner pot.

[0009]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an induction heating type rice cooker capable of efficiently heating an inner pot at a uniform temperature.

[0010]

In order to achieve the above object, according to the present invention, there is provided a protective frame, an inner pot accommodated in the protective frame, and a state in which at least a bottom surface of the protective frame is spirally wound. A coil for induction heating the inner pot,
In the induction heating type rice cooker provided with a ferrite attached below the coil, a magnetic body is disposed at a winding center of the coil, and the magnetic body is separated from a bottom surface of the inner pot during rice cooking. Are arranged so as to be changeable. According to this, the temperature distribution on the bottom surface of the inner pot can be freely changed during rice cooking, and preferable rice cooking control according to the heating state of the article to be heated can be performed.

[0011]

It is further preferable that the distance of the magnetic body can be changed according to the capacity of the object to be heated in the inner pot. According to this, it is possible to take into account the difference in the convection state due to the capacity of the object to be heated, that is, the difference in heat conduction, and it is possible to control rice cooking appropriately according to each capacity.

[0013]

[0014]

[0015]

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

(First Embodiment) FIG. 1 is a sectional view of an induction heating rice cooker according to a first embodiment. In this induction heating type rice cooker, generally, a protective frame 2 is mounted in an exterior body 1 and an inner pan 3 is housed in the protective frame 2 so as to be able to be taken out.
And the upper opening of the protective frame 2 can be opened and closed by the lid 4.

The exterior body 1 is formed with a first annular projection 5 which is directed upward at the center of the upper surface of the bottom. The protective frame 2
Has a bottomed cylindrical shape, and has a second annular projection 6 directed downward at the center of the lower surface of the bottom. And, the first of the exterior body 1
The cylindrical shaft member 7 made of ferrite is positioned by the annular projection 5 and the second annular projection 6. An induction heating coil 8 is provided on the bottom surface of the protection frame 2 in a state of being spirally wound at two locations on the inner and outer circumferences from the inside to the outside with the first annular protrusion 5 as a center.
A plurality of ferrites 9 are attached to the protection frame 2 radially around the first annular projection 5.

In the induction heating type rice cooker, when the induction heating coil 8 is energized, lines of magnetic force are generated around the coil. The magnetic lines of force are strengthened by the ferrite 9 on the bottom surface side of the protection frame 2 to prevent the magnetic flux from leaking downward and to the side. Also, the magnetic coupling is strengthened at the center of the protection frame 2 by the shaft member 7, and the bottom center of the inner pan 3 is intensively heated by induction. By the induction heating, the water in the inner pot 3 convects as shown in FIG. 2, and an upward flow is formed even in the center of the inner pot 3. Therefore, the amount of heating at the middle portion of the inner and outer circumferences of the inner pot 3 is not suppressed by a magnetic shield plate or the like as in the conventional case, but as shown by a solid line in the graph of FIG. The temperature distribution of the inner pot 3 can be made uniform by increasing the amount of heating in the section. This makes it possible to obtain a favorable rice cooking state with low power consumption.

As shown in FIG. 4, the shaft member 7 is housed in a resin-made housing member 10 having a bottomed cylindrical shape. Positioning may be performed. In FIG. 4A, a flange 11 having a screw hole 11a is formed at the open end of the housing member 10, and the housing member 10 is fixed by screwing a screw 12 to the protection frame 2 through the screw hole 11a. are doing. In FIG. 4B, a male screw portion 13 is formed on the outer peripheral surface of the opening end of the housing member 10, while a female screw portion 2 a with which the male screw 14 is screwed is formed at the center of the bottom surface of the protection frame 2. ing.

Second Embodiment FIG. 5 shows an induction heating rice cooker according to a second embodiment. In this induction heating type rice cooker, the shaft member 7 made of a magnetic material can be moved up and down, and the distance to the bottom surface of the inner pot 3 can be changed. That is, the shaft member 7 moves upward by exciting the solenoid 14 disposed below the shaft member 7, and moves downward by its own weight by demagnetizing the solenoid 14. In order to smoothly move the shaft member 7 downward when the solenoid 14 is demagnetized, a spring 15 for urging the shaft member 7 downward is provided in the first annular projection 5 of the protection frame 2. You may do so.

The shaft member 7 of the induction heating type rice cooker is moved up and down by a solenoid 14 so as to be suitable for each rice cooking control processing step of preheating control processing, high heat control processing, low heat control processing, and steaming control processing, and the rice cooking situation. Is done.

During the preheating control process and the high heat control process from the start of rice cooking until the rice is cooked, the solenoid 14 is not excited and the shaft member 7 is kept down. this is,
When the shaft member 7 is brought closer to the inner pot 3 during these control processes,
As a result of the high temperature at the center of the inner pot 3, the rice may be overheated and cooked softly. Particularly, when a small amount of rice is cooked in a large-capacity rice cooker, this problem is remarkable. It is because it becomes something.

Then, when the coil 8 is energized and the inner pot 3 is induction-heated while the shaft member 7 is moved downward, the distribution of the bottom temperature of the inner pot 3 is low at the center and high at the periphery. The state shown by the one-dot chain line in the graph of FIG. At this time, since there is a lot of water in the inner pot 3, convection is actively performed. As a result, the temperature of the rice and the water to be heated becomes uniform regardless of the variation in the temperature distribution on the bottom surface of the inner pot 3. .

When the process is shifted to the low heat control process, the water volume decreases due to water absorption and evaporation into the rice, so that the convection hardly occurs or there is no convection, and the low temperature at the bottom center of the inner pot 3 is maintained as it is. It is reflected in the temperature distribution. Therefore, the solenoid 14 is excited to move the shaft member 7 upward, thereby increasing the magnetic flux density at the center of the bottom surface of the inner pan 3, thereby suppressing the variation in the temperature distribution on the bottom surface of the inner pan 3. As a result, the temperature distribution of the object to be heated becomes uniform.

In the steaming control process, the shaft member 7 is kept moved upward for the same reason as described above.

As described above, in the second embodiment, as described in the first embodiment, the bottom temperature of the inner pot 3 is not simply maintained uniformly, but the difference in the rice cooking condition is not solved. By enabling appropriate temperature adjustment, more appropriate rice cooking can be realized. That is, in the initial stage of rice cooking, heating at the center of the bottom surface of the inner pot 3 is not so required, and in a state where uniform heating of the object to be heated by convection is possible, the shaft member 7 is kept moving downward. After that, when the convection of the object to be heated is insufficient, the shaft member 7 is moved upward, so that the distribution of the bottom temperature of the inner pot 3 is
Rice cooking control is performed in consideration of the heating state of the object to be heated.

The vertical movement of the shaft member 7 may be configured so that the shaft member 7 can be moved up and down by, for example, a rack and pinion mechanism as shown in FIG. According to this, it is not necessary to keep the excitation as in the case of the above-described solenoid 14, which is preferable in that power consumption can be suppressed. Further, by this mechanism, the vertical position in which the shaft member 7 is moved can be freely set, and the bottom surface temperature of the inner pan 3 can be more finely adjusted.

In the second embodiment, the preheating control process, the high-fire control process, and the low-fire control process are performed by the shaft member 7.
Although the heating state of the inner pan 3 is changed by changing the moving position of the inner pan 3, the shaft member 7 may be moved up and down according to the capacity. For example, in the case of a large-capacity inner pot 3, if the capacity of the object to be heated is large, even if the shaft member 7 is moved upward from the beginning, excessively heated rice cooked and becomes sticky. Since it is determined that no problem occurs, the shaft member 7 is not intentionally moved downward as described above. If the capacity of the object to be heated is small despite the large capacity of the inner pot 3, the problem may occur.
Is dealt with by moving down. The capacity of the object to be heated may be selected by a user using a switch (not shown), or may be automatically determined from the temperature rise rate of the object to be heated or the weight of the inner pot 3.

The shaft member 7 may be moved up and down in order to generate heat fluctuations in the object to be heated. For example, if the shaft member 7 is moved up and down every predetermined time during the rice cooking control, the center temperature of the bottom surface of the inner pot 3 can be raised and lowered each time, and the convection or heating state of the object to be heated is periodically changed. Can be changed to Thus, the object to be heated can be more uniformly heated, and the rice can be cooked more deliciously.

(Third Embodiment) FIG. 7 shows an induction heating rice cooker according to a third embodiment. In this induction heating type rice cooker, the coil 8 for induction heating is configured by first to fourth coils 8a, 8b, 8c, 8d. The first coil 8a is provided on the inner circumference of the bottom surface of the inner pot 3, and the second coil 8b is provided on the outer circumference thereof. The third coil 8c is disposed on the lower side of the outer periphery of the side surface of the inner pot 3, and the fourth coil 8d is disposed on the upper side. The first coil 8a and the third coil 8c, and the second coil 8b and the fourth coil 8d are each formed of the same conductive wire, and are respectively connected to the inverter circuit 15.

In the induction-cooked rice cooker having such a configuration,
In cooking rice, the first coil 8a and the third coil 8c,
By the combination of the second coil 8b and the fourth coil 8d, it is possible to alternately heat the center and the lower side of the bottom surface of the inner pot 3 and the outer periphery and the upper side of the bottom surface of the inner pot 3 alternately.
Thereby, the heating state of the inner pot 3 changes periodically, and the heat distribution of the inner pot 3 is made uniform by changing the convection state of the object to be heated, so that the object to be heated can be more uniformly heated. It is possible to obtain a delicious cooked state.

When the content of the object to be heated is large, the ratio of the heating time is the same, and when the content is small, the induction heating time by the combination of the first coil 8a and the third coil 8c is long, and The induction heating time by the combination of the coil 8b and the fourth coil 8d may be shortened. That is, if the content of the object to be heated is small, the object to be heated is not accommodated above the inner pot 3, so that the heating by the fourth coil 8d disposed above the side surface is suppressed. This not only promotes the convection of the object to be heated, but also reduces the power consumption by suppressing the heating of a portion not directly related to the heating of the object to be heated.

In the third embodiment, the coil 8 is constituted by the first to fourth coils 8a, 8b, 8c, 8d, but may be constituted by three or five or more coils. Of course. In this case, it is preferable that the number of coils be an even multiple so that the inductance value of the coils does not change. In addition, an inverter circuit may be provided for each coil to control the energization separately and independently.

In the third embodiment, the shaft member 7 may be provided as in the first embodiment. Further, as in the second embodiment, the shaft member 7 may be provided. The member 7 may be configured to be vertically movable.

[0036]

As is apparent from the above description, according to the induction heating type rice cooker according to the present invention, since the magnetic body is disposed at the winding center of the coil, the generated magnetic field lines are heated by the induction heating of the inner pot. This makes it possible to effectively cook rice without wasting power.

Since the distance between the magnetic body and the bottom of the inner pot can be changed during rice cooking, an appropriate heating state can be selected according to the rice cooking situation, and a more excellent cooked state can be achieved. Obtainable.

Since the distance of the magnetic body can be changed according to the capacity of the object to be heated in the inner pot, the convection of the object to be heated can be appropriately performed, and the uniform heating can be performed.

The coil is composed of a plurality of coils arranged from the center of the bottom surface of the protective frame to the outer peripheral side, and the inner pot is alternately induction-heated at predetermined time intervals by at least two coils. Therefore, the convection state of the object to be heated can be changed periodically, and the object to be heated can be uniformly heated as described above.

Since the ratio of the heating time of each coil can be changed, there is no portion that becomes insufficiently heated according to the difference in the size of the inner pot and the capacity of the object to be heated. Is possible.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an induction heating rice cooker according to a first embodiment.

FIG. 2 is a cross-sectional view showing a flowing state of an object to be heated in the induction heating rice cooker of FIG.

FIG. 3 is a sectional view and a graph showing a temperature distribution of an inner pot in the induction heating type rice cooker.

FIG. 4 is a partial cross-sectional view showing another structure to which the shaft member of FIG. 1 is attached.

FIG. 5 is a schematic partial cross-sectional view of an induction heating rice cooker according to another embodiment.

FIG. 6 is a view showing another example for raising and lowering the shaft member.

FIG. 7 is a schematic partial sectional view of an induction heating rice cooker according to still another embodiment.

[Explanation of symbols]

 2 Protective frame 3 Inner pan 7 Shaft member (magnetic material) 8 Coil 11 Ferrite

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-317176 (JP, A) JP-A-60-105192 (JP, A) JP-A-5-337042 (JP, A) JP-A-57-107 3389 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) A47J 27/00 103 H05B 6/12

Claims (2)

(57) [Claims] 1. A protection frame, an inner pot accommodated in the protection frame, and a coil arranged at least on a bottom surface of the protection frame in a spirally wound state for inductively heating the inner pot,
An induction heating rice cooker comprising a ferrite attached below the coil, wherein a magnetic body is disposed at the center of the winding of the coil, and the magnetic body is separated from the bottom surface of the inner pot during rice cooking. An induction-cooked rice cooker, characterized in that it can be changed. 2. The induction heating rice cooker according to claim 1, wherein the distance of the magnetic body can be changed according to the capacity of the object to be heated in the inner pot.