JP4305243B2 - Electromagnetic induction heating device - Google Patents

Description

    The present invention relates to an electromagnetic cooker used in general households and restaurants, an electromagnetic induction heating device applied to an industrial heating device used for metal melting and seamless welding, and more particularly to a means for detecting an abnormal state of a load. .

  In general, an electromagnetic induction heating device generates an eddy current in a metal to be heated by an electromagnetic induction action, and heats the metal to be heated by Joule heat due to a specific resistance of the metal. In this electromagnetic induction heating device, in the abnormal state of load (empty state) such as when the metal to be heated such as a pan is not placed or when the metal to be heated is not placed at an appropriate position It is necessary to detect this abnormal load state (hereinafter referred to as “empty detection”) and stop the output to the heating coil to prevent an accident.

  As a method for performing the sky detection, there is a method described in Patent Document 1. As shown in FIG. 4, in this method, as an empty detection condition, the condition signal of the first condition detection circuit that is output when the high-frequency current to the heating coil is larger than a predetermined value, and the power input current is below a predetermined value. A condition signal of the second condition detection circuit that is output when the current value becomes, and a detection signal of the third condition detection circuit that is output when the phase delay of the current with respect to the voltage of the power supply input section exceeds a predetermined value. Using the output of the AND circuit that receives these three signals, the automatic heating is stopped and the automatic power supply is shut off when the idling time continues for a predetermined time or more.

  On the other hand, in an electromagnetic induction heating device, a core made of a magnetic material is usually disposed in the vicinity of a heating coil. FIG. 5 is an example of an electromagnetic cooker, FIG. 5 (A) is a bottom view of a heating coil portion, and FIG. 5 (B) is a cross-sectional view along the line BB. In FIG. 5, four cores 2 made of a magnetic material having a high magnetic permeability such as ferrite are radially arranged on the lower surface side of the heating coil 1 made of a disk-shaped spiral coil. A metal to be heated such as a pan (not shown) is placed on the upper surface side of the heating coil 1. By arranging the core 2 in this manner, leakage of magnetic flux generated by the current of the heating coil 1 is reduced, and the magnetic flux density of the metal part to be heated is increased. An electromagnetic cooking device in which a core is disposed is described in Patent Document 2, for example.

In Patent Document 3, at least two or more cores having different Curie temperatures are arranged in the vicinity of the heating coil, the core is heated to the Curie temperature, the magnetic permeability rapidly decreases, and the magnetic flux density decreases rapidly. An induction heating apparatus is described that performs local heating of a member to be heated by utilizing the difference in temperature rise of the member to be heated.
Japanese Patent Laid-Open No. 5-205862 Japanese Patent Laid-Open No. 2003-347021 Japanese Unexamined Patent Publication No. 8-273382

  When the electromagnetic induction heating device is in an idle state, that is, in an abnormal load state, the high-frequency current flowing through the heating coil usually increases due to a decrease in the inductance of the heating coil. The empty detection described in the cited reference 1 uses this phenomenon as a detection condition. For example, in the case of a metal to be heated such that the pan is small and the pan bottom is thin, the heating coil current is abnormally loaded even in a normal load state. The difference between the temperature of the metal to be heated is small, and even under abnormal load conditions, the size, shape, material, etc. of the metal to be heated is not properly placed or the distance from the heating coil is long. Depending on the load condition, it is difficult to distinguish from the normal load condition. For this reason, it is difficult to detect the sky by increasing the heating coil current as a practical problem.

  In addition, as an application of the method described in the cited document 3, it is conceivable to perform empty detection from a rapid decrease in the magnetic permeability caused by an increase in the heating coil current resulting in the core being heated to the Curie temperature or higher. Since it takes a certain time for the core temperature to rise, it is impossible to detect an abnormal load condition instantaneously, and as a result, the heat loss consumed in the core before the power is shut off increases. There's a problem.

  An object of the present invention is to be able to detect an abnormal load state of an electromagnetic induction heating device quickly and reliably without causing heat loss.

In order to solve the above-described problems, the present invention provides an electromagnetic induction heating apparatus in which a plurality of cores made of a magnetic material are distributed on the lower surface side of a heating coil, and a part of the plurality of cores is made to have a saturation magnetic flux density. to configure a small core, the core before Symbol part in the magnetic flux of the current flowing through the heating coil when the abnormal load is magnetically saturated, to detect an abnormality of the load from the current of the heating coil for increasing the magnetic saturation (Claim 1). In the first aspect of the invention, the core disposed in the vicinity of the heating coil is not magnetically saturated in a normal load state, but is set so that a core having a small saturation magnetic flux density is magnetically saturated due to an increase in the heating coil current in an abnormal load state. It is. When some cores are magnetically saturated, the heating coil current increases abruptly, and by detecting this rate of change, it is possible to detect the sky reliably and instantaneously. Also, if the coil power supply is shut off simultaneously with this empty detection, the core can be heated by a large heating coil current in a short time, so that heat loss can be minimized.

In the invention of claim 1, the plurality of cores can also be arranged adjacent to each other so as to partially overlap each other (invention 2). In that case, it is preferable to arrange a plurality of adjacent cores at a plurality of locations.

According to the present invention, when the load is abnormal, a part of the core disposed in the vicinity of the heating coil is magnetically saturated, so that the heating coil current can be largely changed before and after the magnetic saturation to realize reliable sky detection. Moreover, since the abnormality can be detected instantaneously and the power supply can be shut off, heat loss in the core can be suppressed, and accidents such as damage to the switching elements constituting the high frequency power supply circuit can be prevented.

  Hereinafter, based on FIGS. 1-3, embodiment of this invention in an electromagnetic cooker is described.

  FIG. 1 shows a first embodiment of the present invention, FIG. 1 (A) is a bottom view of a heating coil portion, and FIG. 1 (B) is a sectional view taken along the line BB. In FIG. 1, a plurality (four in the figure) of cores 2 are radially distributed in the vicinity of a heating coil 1 formed of a disk-shaped spiral coil, that is, on the lower surface side of the heating coil 1 in parallel with a gap. ing. The core 2 is made of a highly permeable magnetic material such as ferrite, and is formed in a columnar shape having a rectangular cross section. A metal to be heated such as a pot is placed on the upper surface side of the heating coil 1 via a top plate (not shown) made of an insulating material. When a high-frequency current flows through the heating coil 1, the metal to be heated is induction-heated, and the food material therein is cooked. At that time, the magnetic flux of the current of the heating coil 1 (heating coil current) is collected on the core 2 on the lower surface side of the heating coil 1, and the leakage magnetic flux is kept to a minimum.

In the induction heating of the metal to be heated as described above, the metal to be heated is not placed, or is not placed at an appropriate position such as left and right, or a foreign object is sandwiched between the top plate and the heating coil 1. When the distance from is increased, the inductance of the heating coil 1 decreases and the heating coil current increases with respect to the normal load state. Therefore, in such a case, it is necessary to quickly detect the sky and shut off the power supply. Therefore, in the first embodiment, the core 2 is not magnetically saturated in a normal load state, but when the heating coil current increases in an abnormal load state, at least one of them is magnetically saturated, that is, the saturation magnetic flux density is small. Is set.

Therefore, when the abnormal load state described above occurs and the heating coil current increases, at least one of the four cores 2 is magnetically saturated. However, when one of the core 2 is magnetically saturated, rapidly decreases the inductance of the heating coil 1 is the moment that the heating coil current increases rapidly as a result. Therefore, it is possible to detect the sky by detecting this sudden increase in the heating coil current. In that case, the change in the heating coil current due to the magnetic saturation of the core 2 is large compared to the presence or absence of the metal to be heated, so that it is easy to detect, and the increase in the heating coil current due to the occurrence of an abnormal load state → core Since the time required for the magnetic saturation of 2 and the rapid increase of the heating coil current is short, it is possible to detect the sky almost instantaneously from the occurrence of the abnormal load state. In the first embodiment, the four cores 2 have the same shape, dimensions, and the like, but need not necessarily be the same.

FIG. 2 shows Embodiment 2 of the present invention, FIG. 2 (A) is a bottom view of the heating coil portion, and FIG. 2 (B) is a sectional view taken along the line BB. In FIG. 2, the difference from the first embodiment is that the two cores 2 and the cores 3 are alternately arranged. Here, the core 2 and the core 3 are made of magnetic materials having different saturation magnetic flux densities, and the saturation magnetic flux density B _m2 of the core 2 is larger than the saturation magnetic flux density B _m3 of the core 3 (B _m2 > B _m3 ). . In the second embodiment, if the core 2 and the core 3 have the same shape and size and the same arrangement relationship with the heating coil 1, the magnetic flux density when the high-frequency current flows through the heating coil 1 is the same as that of the core 2 and the core 3. 3 is equal.

  Therefore, in the second embodiment, neither the core 2 nor the core 3 is magnetically saturated in the normal load state. However, when the heating coil current increases in the abnormal load state, at least one of the cores 3 having a saturation magnetic flux density smaller than the core 2 is increased. Is set to be magnetically saturated. Thereby, from the increase in the heating coil current due to the magnetic saturation of the core 3, it is possible to detect the sky as in the case of the first embodiment. In that case, in the second embodiment, only a part of the plurality of (four) cores 2 and 3 are magnetically saturated and the core 2 is not magnetically saturated when the load is abnormal. In this way, by providing a difference in the current value at which the magnetic saturation occurs, there is a margin in the magnetic saturation even in an abnormal load state, for example, a large current flows through the heating coil 1 that destroys the switching element of the heating power supply. Such a situation can be prevented.

  3A and 3B show a third embodiment of the present invention, in which FIG. 3A is a bottom view of the heating coil portion, and FIG. 3B is a cross-sectional view along the line BB. In FIG. 3, a plurality (two in the drawing) of cores 2 and 3 are radially distributed at a plurality of locations (four in the drawing) in the vicinity of the heating coil 1. Are adjacent so that they partially overlap. The material of the core 2 and the core 3 does not need to be different, and the shape and dimensions may be the same.

  In such a core arrangement, when a high-frequency current flows through the heating coil 1, the magnetic flux concentrates on the cores 2 and 3 having a small magnetic resistance. In particular, the portion indicated by a dot-and-dash circle in FIG. The magnetic flux density at the end portions 2a and 3a protruding from the mating core increases. This magnetic flux concentration is larger in the abnormal load state than in the normal load state. In the normal load state, the metal to be heated and the cores 2 and 3 form the magnetic flux path above and below the heating coil 1, whereas in the abnormal load state, there is a magnetic flux path only below the heating coil 1, and ferrite This is because the distribution of the magnetic flux at the portion where the cross-sectional area of the magnetic flux rapidly decreases becomes irregular.

  Therefore, in the third embodiment, neither the core 2 nor the core 3 is magnetically saturated in the normal load state, but at least one of the cores 2 and 3 is set to be magnetically saturated in the abnormal load state. Thereby, it is possible to detect the sky from the increase of the heating coil current due to the magnetic saturation of the core 2 or the core 3. In that case, the level of the heating coil current to be magnetically saturated can be adjusted by changing the overlapping range of the core 2 and the core 3. As a result, according to the third embodiment, the core design work becomes easier as compared with the case where the magnetic saturation characteristics are adjusted by changing the material, shape / size, arrangement, etc. of the core. In the third embodiment, an example in which two cores are arranged adjacent to each other is shown. However, three or more cores may be arranged adjacent to each other. Also, the adjustment of the heating distribution of the metal to be heated can be realized by adjusting the arrangement position of the ferrite.

Embodiment 1 of the present invention is shown, in which (A) is a bottom view of a heating coil portion, and (B) is a sectional view taken along the line BB. Embodiment 2 of the present invention is shown, (A) is a bottom view of a heating coil portion, and (B) is a sectional view taken along the line BB. Embodiment 3 of the present invention is shown, in which (A) is a bottom view of a heating coil portion, and (B) is a sectional view taken along the line BB. It is a logic circuit diagram explaining a prior art. A different prior art is shown, A) is a bottom view of a heating coil portion, and (B) is a cross-sectional view along the line BB.

Explanation of symbols

1 Heating coil 2 Core 3 Core

Claims (3)

In an electromagnetic induction heating device in which a plurality of cores made of a magnetic material are distributed and arranged on the lower surface side of the heating coil, a part of the plurality of cores is configured with a core having a low saturation magnetic flux density, and the heating is performed when a load is abnormal the core of the pre-Symbol part in the magnetic flux of the current flowing through the coil is magnetically saturated, an electromagnetic induction heating device is characterized in that from the current of the heating coil for increasing the magnetic saturation to detect an abnormality of the load. 2. The electromagnetic induction heating device according to claim 1, wherein a plurality of the cores are arranged adjacent to each other so as to partially overlap each other. 3. The electromagnetic induction heating device according to claim 2, wherein a plurality of adjacent cores are further arranged at a plurality of locations.

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