JPS62287591A - Induction heating cooker - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention provides an induction heating cooker that supplies a high frequency output to a heating coil to induction heat a heated object. Regarding.

(Prior Art) In this type of induction heating cooker, conventionally, a plurality of copper wires are twisted together to form a so-called Litz wire, and this Litz wire is twisted into a spiral shape to form a heating coil. According to
There is a heating coil whose loss resistance against high frequencies is reduced.

(Problem to be Solved by the Invention) However, in the above configuration, in order to enable induction heating of, for example, an aluminum or copper pot, the number of turns of the heating coil is increased and the frequency of the high-frequency output supplied to the heating coil is increased. This has the disadvantage that the loss resistance of the heating coil increases due to the skin effect, resulting in poor efficiency. On the other hand, if the steel wires are made thinner and the number of twisted steel wires is increased to prevent the skin effect, the proximity effect caused by the multiple four copper wires will have a large effect, and the loss of the heating coil will increase. There is a problem of increased resistance. Furthermore, if the copper strands are made thinner, in order to obtain the same cross-sectional area, the number of strands (
For example, if the diameter of the strands is 115, the number of strands must be increased by 25 times), which makes the heating coil configuration complicated and increases the cost.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an induction heating cooker that can prevent the loss resistance of the heating coil from increasing even when the number of windings is increased and the frequency of the high-frequency output is increased.

[Structure of the Invention] (Means for Solving Problems) The induction heating cooker of the present invention is characterized in that a heating coil is constructed by twisting conductive wires coated with a magnetic layer.

(Function) Since the heating coil is constructed by twisting conductive wires coated with a magnetic layer, the skin effect and proximity effect when high frequency output is supplied to such a heating coil can be reduced.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

First, in FIG. 3, reference numeral 1 denotes a power supply device, which inputs a commercial power source 2 and outputs a predetermined DC power to an inverter device 3. 4 is a heating coil to be described later, and a resonance circuit is formed by this heating coil 4 and a resonance capacitor (not shown). A high frequency output is appropriately supplied from the inverter device 3 to this resonant circuit.

In this case, the inverter device 3 is configured to detect the resonant state of the resonant circuit and supply a high-frequency output at a frequency corresponding to the resonant state, and is configured to perform so-called feedback control. Reference numeral 5 denotes a pot serving as a heating element, which is placed on a heating coil 4 via a top plate 6, as shown in FIG. Note that 7 is a coil support plate, on which the heating coil 4 is disposed.

Now, the heating coil 4 will be explained in detail according to FIGS. 1 and 2. Reference numeral 8 denotes a conductive wire, such as a copper wire, which has a diameter of about 0.1 mm. A magnetic layer 9 covers the steel wire 8, and is formed by plating the outer periphery of the steel wire 8 with a magnetic material such as iron. Further, 10 is an insulating layer, which covers the steel wire 8 and the magnetic layer 9. The litz wire 12 is formed by twisting, for example, 320 of the strands 11 thus formed, and the heating coil 4 is constructed by winding the litz wire 12 spirally in two stages. The number of turns of the heating coil 4 can be switched between the number of turns for heating the pot 5 made of iron or non-magnetic stainless steel, and the number of turns for heating the pot 5 made of aluminum or copper.

Next, the operation of the above configuration will be explained. In general, the skin effect refers to the fact that when a high-frequency current flows through a copper wire, the i-flux density at the center of the copper wire tends to increase, but the voltage distribution in the longitudinal direction of the copper wire tends to increase. Since the surface must also have a □- value, the current density at the center decreases. In addition, the proximity effect refers to the fact that one copper wire
When several copper wires are twisted together and wound into a coil, the current within the copper wire becomes uneven due to the magnetic flux of other copper wires. In this embodiment, the steel wire 8 is coated with the magnetic layer 9, so that the magnetic flux density distribution within the steel wire 8 becomes uniform. , the current density distribution within the copper wire 8 is also made uniform, and its skin effect is reduced. Similarly, the proximity effect of the heating coil 4, which is wound with a litz wire 12 made by twisting a plurality of wires 11, is also reduced.

In FIG. 4, curve A shows the experimental results of measuring the frequency characteristics of the loss resistance of the heating coil 4. Here, curve B shows the case of a conventional heating coil that does not cover the magnetic layer 9. The reheating coil was constructed by twisting 320 steel wires each having a wire diameter of 0.1 mm, and the number of turns was 65.

According to this embodiment having such a configuration, the heating coil 4 is constructed by twisting the copper wires 8 coated with the magnetic layer 9, so that the loss resistance of the heating coil 4 can be reduced. In addition to improving efficiency, it is possible to reduce temperature rise of the heating coil 4 and improve reliability. In particular, when heating a pot 5 made of aluminum or copper, it is necessary to increase the number of turns of the heating coil 4 and to increase the frequency of the high-frequency output to be supplied. It becomes even more effective. In addition, compared to conventional heating coils, the same loss resistance can be obtained by using steel wires 8 with a larger wire diameter and by reducing the number of twisted wires, which simplifies the configuration of the heating coil 4. and lower costs.

[Effects of the Invention] As is clear from the above description, the present invention constructs a heating coil by twisting conductive wires with corrugated magnetic layers. Even when the resistance is increased, an excellent effect can be achieved in that the loss resistance of the heating coil can be prevented from increasing.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, in which Fig. 1 is a sectional view of the main part, Fig. 2 is a partially broken side view, Fig. 3 is a schematic electrical configuration diagram, and Fig. 4 shows loss of the heating coil. It is a resistance-frequency characteristic diagram. In the drawing, 4 is a heating coil, 5 is a pot (heated object), 8 is a steel wire (conductive wire), and 9 is a magnetic layer. Figure 1 Figure 2

Claims (1)

[Claims] 1. In an induction heating cooker that supplies a high frequency output to a heating coil to inductively heat a heated object, the heating coil:
An induction heating cooker characterized by being constructed by twisting conductive wires coated with a magnetic layer.