JPS5837676B2 - induction heating cooker - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electromagnetic shield for a heating coil of an induction heating cooker.

Generally, leakage magnetic flux (lines of magnetic force) is always generated around a high-frequency induction coil, causing unnecessary radiation noise.

Similarly, the heating coil of an induction heating cooker can cause an increase in radiation noise due to leakage magnetic flux generated around the coil, malfunction of the control circuit, etc. As a countermeasure against leakage magnetic flux, an electromagnetic shield plate is usually provided around the heating coil.

The present invention aims to provide an electromagnetic shielding structure that is cheaper and more effective than conventional ones by improving this electromagnetic shielding plate.

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

FIG. 1 is a plan view showing a general electromagnetic shielding structure of an induction heating coil, in which annular shielding members 2 are arranged at desired intervals around the outer periphery of a disc-shaped heating coil 1. There is.

This electromagnetic shielding material is made of a material that is not easily subjected to induction heating, such as aluminum or copper.

When an eddy current flows through the shield ring 2 due to the magnetic field lines generated from the heating coil 1, the eddy current causes another magnetic field line, that is, a magnetic field line in the opposite direction to the magnetic field line generated by the heating coil (
A demagnetizing field) is generated, the leaking magnetic lines of force outside from the outer periphery of the shield ring are canceled out, and the lines of magnetic force are confined within the shield ring.

Therefore, the level of unnecessary radiation from the heating coil is reduced.

However, the shielding effect varies greatly depending on the shape of the shield ring, and the larger the cross-sectional area of the shield ring, and the narrower the distance between the heating coil 1 and the shield ring 2, the more The more the cross-sectional shape of the coil wraps around the heating coil, the more
It is an obvious fact that the shielding effect increases, even when considering the distribution of magnetic lines of force generated by the heating coil.

However, if a shielding structure is formed with only the shielding effect in mind, the shielding material will be provided on the entire surface of the heating coil except for the side of the pot mounting plate, which will increase the vortex loss due to the shielding material and cause the induction heating cooker to The original characteristic of high thermal efficiency is lost and the product value decreases.

In addition, in order to prevent a decrease in thermal efficiency with the above-mentioned shield structure, it is necessary to increase the distance between the heating coil and the shield material, which requires extra space, which increases the size of the device and makes the product more difficult to use. The value will drop significantly.

The present invention aims to obtain a desired shielding effect with a simple structure without the above-mentioned disadvantages such as a decrease in thermal efficiency or an increase in the size of the equipment.

Figure 2 shows the distribution of magnetic lines of force when a shielding material 2 is provided around the heating coil 1.The direction of the magnetic lines of force 7 generated by the shielding material 2 is different from the direction of the magnetic lines 6 generated by the heating coil 1. In the opposite direction, the leakage lines of magnetic force on the outside of the shielding material are canceled out, and the lines of magnetic force on the inside are multiplied.

However, depending on various conditions such as the shape and size of the shielding material, and the positional relationship with the heating coil, the amount of offset of the leakage magnetic lines of force will be more or less.

Generally, it is effective for an electromagnetic shielding circuit to have the shape of the shield material as close to a closed loop as possible along the path of the lines of magnetic force.

Therefore, the same can be said about the electromagnetic shielding of the heating coil.Since the magnetic field lines pass through the pot itself, which is heated on the top side of the heating coil, the pot itself has the same function as a shielding material, and the back side Generally, magnetic shielding is achieved by disposing a member such as a ferrite core with low loss and high dielectric constant.

This is because the ferrite core itself is provided with a path for magnetic lines of force in order to prevent the influence of leakage lines of magnetic force on the circuit components and metal chassis arranged on the back side of the heating coil.

What remains is the shielding around the periphery of the heating coil, especially the shielding between the pot and the shielding material around the periphery of the heating coil, which poses a problem against electromagnetic waves leaking from the heating coil.

FIG. 3 shows an example of a conventional shield, in which a shield ring 2a having a flat cross section is arranged around the heating coil 1.

However, if an attempt is made to approach a closed loop with this shape, it will approach the heating coil, lowering the inductance of the heating coil more than necessary, and causing a decrease in thermal efficiency due to vortex loss.

In addition, because of the flat plate shape, it is difficult to shield the entire path of the leakage magnetic field lines, for example, the shield ring 2a
If you bring it closer to the pot side, the gap with the ferrite core 4 will increase, and the shielding effect in this area will be reduced.If you bring it closer to the ferrite core side, the gap with the pot 5 will increase, and the shielding effect in this area will decrease. .

Furthermore, if the shield ring shape is made into a cylindrical shape like 2b shown in Fig. 4, the shielding effect will be considerably greater than when it is made into a disk shape as shown in Fig. 3, but the rate of decrease in the inductance of the heating coil will be extremely large. At the same time, the rate of decrease in thermal efficiency is also significant.

According to experimental results, in the case of a cylindrical shield ring, in order to suppress the inductance reduction rate to the same rate as that of a disk-shaped shield ring, the distance between the heating coil and the heating coil must be increased by 15 to 2 times compared to that of a disk-shaped shield ring. However, it is difficult to shield leakage lines of magnetic force in the gap between the pot 5 and the ferrite core 4.

From the conventional example shown in FIGS. 2 and 3, the electromagnetic shield of the heating coil is a two-dimensional cross-sectional shield 3J, while maintaining the necessary thermal efficiency and inductance of the heating coil.
It turns out that it is very difficult to obtain the desired shielding effect.

The present invention solves the disadvantages of the conventional heating coil, such as a decrease in inductance and a decrease in thermal efficiency, by shaping the cross-sectional shape of the shield ring three-dimensionally as shown in 2c and 2d in FIGS. 5 and 6. .

In Figures 5 and 6, 1 is a heating coil, 2c, 2d
3 is an electromagnetic shielding ring, 3 is a pot mounting plate, 4 is a ferrite core for magnetic shielding, and 5 is a pot mounting plate.

The shield i2c shown in Fig. 5 has an inverted L-shaped cross section, and by arranging the horizontal part of the L shape on the pot side, the gap between the pot and the shield ring can be made small, and the cylindrical part makes it possible to reduce the leakage magnetic field. The combination of the disk-shaped part and the cylindrical part keeps the inductance of the heating coil at a predetermined level, and also prevents the reduction in thermal efficiency due to eddy loss in the shield ring itself. This is an attempt to obtain a desired shielding effect while preventing this, and the shield circuit has a shape close to a closed loop.

The shield i2d shown in FIG. 6 is the shield ring 2c shown in FIG.
This is an attempt to further improve the shielding effect of the pot 5 and the ferrite core 4 by forming a U-shaped cross section.
2 in Fig. 5, with the gap between the shield ring 2d and the
0, the shield circuit is closer to a closed loop.

Another advantage of the present invention is that to obtain the same level of shielding effect, the shield ring requires less space.

In other words, the device can be made smaller because it occupies less space than a flat or cylindrical device.

[Brief explanation of drawings]

FIG. 1 is a plan view of a heating coil of an induction heating cooker, FIGS. 2, 3, and 4 are sectional views of a conventional cooker, and FIGS. 5 and 6 are views of an embodiment of the present invention. It is a sectional view of an induction heating cooker. 1...Heating coil, 2...Electromagnetic shielding ring,...Pot mounting plate, 5...Pot to be heated. 3

Claims (1)

[Claims] 1. A heating coil in the form of a flat plate is provided below the pot mounting plate, and is equipped with a high frequency power converter that excites this heating coil, and is made of a non-magnetic metal material such as aluminum and is spaced at a predetermined interval around the outer edge of the heating coil. An induction heating cooker in which an electromagnetic shield ring is provided, and the cross-sectional shape of the electromagnetic shield ring is formed into an inverted L-shape or a U-shape.