JPS633428B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a structure for reducing electromagnetic interference in an electromagnetic induction cooking device.

Conventional configuration and problems The electromagnetic induction cooking device uses a flat heating coil.
This is a cooker that sends a high-frequency large current of 20 to 50 KHz, induces eddy currents in the bottom of the loaded pot facing the heating coil through the pot holder plate, and generates heat in the bottom of the pot using Joule heat. Due to the basic structure of an electromagnetic cooker, in which a flat heating coil emits a high-frequency, high-flux-density magnetic field that induces a large amount of power in the loaded pot, the magnetic field leaking to the outside of the cooker is extremely large. However, it has been extremely difficult to shield leakage magnetic fields because it is impossible to cover the entire device with a conductive plate to shield high frequency radiation noise.

Figure 1 shows an example of the external casing configuration of a conventional electromagnetic cooker.
It is shown in Figure 3. FIG. 2 is a cross-sectional configuration diagram of FIG. 1. In the configuration shown in FIG. 1, the side frame 2 and top rim 3 form a load pan 5 as shown in FIG.
A plate 1 made of a non-magnetic, non-conductive material is sandwiched in order to make the bottom of the pot face the heating coil 4. In the configuration shown in FIG. frame 6
It is fixed by pressure contact from above. In a conventional electromagnetic cooker, the side frame 2 and top rim 3 in FIG. 1 and the top rim 3 in FIG. Edges made of conductive material are provided around the plate 1 as supporting members for the plate 1 or as constituent members of the external casing, such as the top frame 6, but these are provided as electromagnetic shielding members. Even if there is an electromagnetic shielding effect as a result,
Since the structure is insufficient as an electromagnetic shield, the leakage magnetic field reduction effect is only about 1 dB to 2 dB at most, which is not satisfactory. The reason is the first
Points A, A', B, where the inner peripheral edge of the conductive metal member around the plate 1 and the outer peripheral edge of the heating coil 4 intersect perpendicular center lines X-X', Y-Y' shown in FIGS.
The distance L ₁ between the intersection points at B′, C, C′, D, D′,
This is because the distance difference between L ₁ and L 2 and L ₃ and L ₄ is too large in L ₂ , L _{3 ,} and L ₄ .

The basis for this will be explained in detail later.

Next, as a conventional measure to reduce leakage radiated magnetic fields, some electromagnetic cookers are provided with a shielding member as shown in FIGS. 4 and 5 inside. In this figure, a conductive shield ring 10 is arranged around the heating coil 4;
The holding structure of 0 becomes complicated, and the shield ring 1
0 receives radiant heat from the pot and becomes hot, raising the atmosphere inside the device, or because it surrounds the heating coil, it blocks the cooling air to the heating coil, increasing the temperature rise of the heating coil. Since the shield ring 10 is a conductor, it is important to ensure insulation distance inside the electromagnetic cooker, which has many electrical components and electronically controlled components to which high voltage and large current are applied. Therefore, there are problems such as various restrictions on the arrangement of parts, which impede efforts to make the entire device thinner and smaller.

OBJECTS OF THE INVENTION The present invention eliminates the above-mentioned conventional drawbacks, and aims to enhance the electromagnetic shielding effect of the conductive member located around the plate of an electromagnetic cooker.

Structure of the Invention In order to achieve the above object, the electromagnetic induction cooking device of the present invention provides an inner edge of a conductive member connected to the circumference of a plate for placing a load pan or the like located above the heating coil, and a periphery of the heating coil. The distance between the parts is defined as a predetermined value, and the distance between at least four places, that is,
Intersection points A and A', B and B', and C and C', where the outer and inner edges of the heating coil intersect with the orthogonal center lines X-X' and Y-Y' of the heating coil. ,D,
This is a configuration in which the distances L ₁ , L ₂ , L ₃ , and L ₄ between D' are made approximately equal to each other, and the effect is to reduce the leakage radiated magnetic field at the fundamental wave and the frequency near the fundamental wave generated from the electromagnetic cooker. Its structure is simple and has almost no negative effect on the internal component arrangement or cooling structure. Furthermore, the conductive material around the plate can be used as a decorative member or to protect the resin external casing from the high temperature at the bottom of the load pot. This has the effect that it can also be used as a heat-resistant member for protection.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described based on the drawings. FIG. 6 and FIG. 7 are the first embodiment,
FIG. 6 is a plan view of the electromagnetic cooker according to the present invention, and FIG. 7 is a sectional view thereof. The plate 1 is held between resin side frames 7, and a top plate 6 made of a conductive material and having a circular inner edge is disposed around the periphery of the plate 1. An important condition here is that the distance between the outer circumferential edge of the heating coil 4 and the inner circumferential edge of the top frame 6 be substantially constant. At this time, when a high-frequency current flows through the heating coil 4, an induced current flows through the top frame 6 in a concentrically distributed continuous manner, and the demagnetizing field generated by the induced current cancels the magnetic field generated by the heating coil 4 outside the top frame 6. The leakage magnetic field of an electromagnetic cooker is uniformly reduced in all directions without causing any directivity, especially near the fundamental oscillation frequency (20KHz to 50KHz).
The reduction level varies depending on the material of the top frame 6, its thickness, the diameter of the inner edge, the outer diameter of the heating coil 1, the heating coil current, etc., but the top frame 6 is made of aluminum with a thickness of 2 mm, and the diameter of the inner edge is The outer diameter of the heating coil is approximately 220 mm, and the outer diameter of the heating coil is approximately 180 mm.
When a current with a peak current of 50 A and an effective current of about 12 A at a frequency of about 25 KHz is passed through the heating coil, the maximum magnetic field strength at a position 3 m from the device is reduced by about 10 dB.

This effect will be explained with reference to FIG. In FIG. 8, the magnetic field generated by the heating coil 4 induces a current in the conductive top frame 6. The induced current generates a demagnetizing field 9, which cancels out the magnetic field 8 caused by the heating coil current outside the top frame 6, and inside the top frame 6.
This is added to the magnetic field 9 caused by the heating coil current, and the effect of concentrating the magnetic field caused by the heating coil current inside the top frame 6 can be obtained. However, as in the external casing configuration shown in the conventional example, the shape formed by the conductive top frame 2 and top rim 3 in FIG. 1 or the inner edge of the top frame 6 in FIG. 3 is rectangular. In some cases, there is a considerable difference in the distance between the outer edge of the circular heating coil and the inner edge of the adjacent conductor in the vertical and horizontal directions, so that the magnetic field distribution pattern generated by the heating coil 4 and the magnetic field induced in the top plate 6 are different. The demagnetizing field distribution pattern due to the current differs greatly, and as a result of the superposition of the two, considerable asymmetry, ie, directivity, occurs in the magnetic field distribution. As a result, the leakage magnetic field of the electromagnetic cooker increases in a specific direction, making it ineffective as an electromagnetic shield.

Next, a second embodiment is shown in FIG. FIG. 9 is a plan view of the device, and the cross-sectional configuration diagram is the same as FIG. 7. In FIG. 9, the positional relationship between the conductive top frame 6 whose inner edge is square and the outer edge of the circular heating coil is as shown in FIG. Points A, A', B that intersect Y-Y',
At B', C, C', D, D', the distance between A and A' is L ₁
and B, the distance L between B', ₂ and C, the distance L ₃ and D between C',
They are arranged at positions that satisfy the condition that the distances L ₄ between D′ are substantially equal to each other. This case also has the effect of shielding the leakage magnetic field, and compared to the case where the distance between the inner circumferential edge of the top rim 6 and the outer circumferential edge of the heating coil 4 is uniformly constant as described in the first embodiment, the heating coil 4 Since the magnetic field distribution of the top frame 6 and the magnetic field distribution of the top frame 6 are not completely similar, the shielding effect will be approximately 6 dB (approximately 10 dB in the case of the first embodiment) under the same conditions as above, but it is sufficient as a magnetic shield. has.

A third embodiment is shown in FIGS. 10a and 10b. 10th
In Figures a and b, the heating coil 4 is circular and the inner periphery of the conductive top frame 6 is a modification of the square; In the corners, the top frame is moved closer to the heating coil 4 within the range that does not come inside the inscribed circle of the square. However, even in this case, the conditions L ₁ ≒L ₂ ≒L ₃ ≒L ₄ are satisfied. In such a case, the magnetic shielding effect is equal to or intermediate to that of the first embodiment or the second embodiment. If a part of the corner part of the square comes inside the inscribed circle, the distance between the heating coil 4 and the top frame 6 becomes particularly close at that part, which disturbs the magnetic field distribution, and the second embodiment The directivity of the magnetic field distribution becomes even sharper than in the case of , and the shielding effect is reduced accordingly.

A fourth embodiment is shown in FIG. This is the case where the heating coil 4 is circular and the inner edges of the plate 1 and the top frame 6 of the electrical conductor located around the plate are rectangular. The fifth example is the first
Shown in Figure 2. This is the case when the outer periphery of the heating coil 4 is approximately square and the inner periphery of the top frame 6, which is a conductor, is also square. In the fourth and fifth embodiments,
Naturally, the arrangement is such that the conditions L ₁ ≒L ₂ ≒L ₃ ≒L ₄ are satisfied.

A sixth embodiment is shown in FIGS. 13 and 14. FIG. 13 shows a cross-sectional structure, and FIG. 14 shows a plan view thereof. In FIG. 13, a plate 1 facing the circular heating coil 4 and having a diameter larger than the outer circumference of the heating coil 4 is fitted into the inner circumference of the conductive member 6 and integrally bonded thereto.

Note that in the above example, the shape of the inner edge of the conductor 6 was larger than the shape of the outer edge of the heating coil 4;
It may be the same or the opposite. Furthermore, if the present invention is combined with the shield structure shown in FIGS. 4 and 5 described in the conventional example, the leakage magnetic field reduction effect will be even greater as a double shield.

According to the above embodiments, the effect of reducing electromagnetic shielding due to the conductive member around the plate of the conventional electromagnetic cooker is almost non-existent under the above measurement conditions.
What used to be about 1 to 2 dB at most becomes about 6 to 10 dB. Therefore, the leakage radiation magnetic field near the fundamental frequency can be reduced with a simple structure without disposing a shield member inside. Therefore, the shield member does not adversely affect internal cooling or the arrangement of electrical components, and there is no need to consider the holding structure of the shield member. However, if the above effects are not expected, a shielding material may be provided inside. In this case, a double shielding effect can be obtained by using both the inner and outer parts, and the shield can be reliably shielded. Note that the conductive member may be formed by joining together a plurality of separately manufactured members, or may be formed integrally in advance.

Effects of the Invention As described above, according to the present invention, the following effects can be obtained.

(1) By the conductive member located around the plate,
Radiation leakage noise near the fundamental oscillation frequency emitted from the electromagnetic cooker can be reduced.

(2) Together with the shielding member inside the device, it is also possible to make the shielding more reliable.

(3) It is also possible to omit the shielding member inside the device, making it easier to make the device thinner and smaller.

[Brief explanation of the drawing]

Figures 1 and 3 are configuration diagrams of the external casing of a conventional electromagnetic cooker, Figure 2 is a cross-sectional configuration diagram of Figure 1, Figure 4 is a configuration diagram of the electromagnetic shield of a conventional induction cooker, and Figure 5 is a cross-sectional configuration diagram of FIG. 4, FIG. 6 is a plan view showing the first embodiment of the present invention, FIG. 7 is a cross-sectional configuration diagram of FIG. 6, and FIG. 8 is a shield by a conductor around the plate. 9 is a plan view showing the second embodiment of the present invention, FIGS. 10 a and b are plan views showing the third embodiment of the present invention, and FIG. 11 is a plan view showing the third embodiment of the present invention. 12 is a plan view showing the fifth embodiment of the present invention, FIG. 13 is a sectional configuration diagram of the sixth embodiment of the present invention, and FIG. 14 is a plan view showing the fifth embodiment of the present invention. FIG. 1... Plate, 2... Side frame (conductive member), 3... Top rim (conductive member), 4...
...Heating coil, 5... Load pan, 6... Top frame (conductive member), 7... Side frame (resin member).

Claims (1)

[Scope of Claims] 1. A heating device comprising a heating coil, a plate made of a non-magnetic and non-conductive material provided oppositely on the heating coil, and a conductive member continuous to the circumference of the plate, The outer peripheral edge of the coil and the inner peripheral edge of the conductive member are at intersection points A, A', B, which intersect with the orthogonal center lines X-X', Y-Y' of the heating coil, when viewed from above the plate. B', C, C',
closest to each other near D and D', at least between the intersection points,
In other words, an electromagnetic induction cooking device in which the distances L ₁ , L ₂ , L ₃ , and L ₄ between A and A', between B and B', between C and C', and between D and D' are approximately equal to each other. . 2. The electromagnetic induction cooking device according to claim 1, wherein the distance between the inner peripheral edge of the conductive member and the outer peripheral edge of the heating coil is substantially constant over the entire circumference. 3 The inner edge shape of the conductive member is approximately square;
The electromagnetic induction heating cooker according to claim 1, wherein the center point of the substantially disc-shaped heating coil and the center point of the square are substantially aligned. 4 The basic shape of the inner circumferential edge of the conductive member is approximately square, the center point of this square is made to substantially coincide with the center point of the heating coil, and part or all of the inner edges of the four corners (corners) of this square are formed. The electromagnetic induction heating cooker according to claim 1, wherein the square is located close to the center of the square.