JPH04366587A - Induction heating device - Google Patents

Abstract

PURPOSE:To improve the heating efficiency of an induction heating device. CONSTITUTION:Plates 15, 16 are provided between a heating coil 9 and a material 10 to be heated. The plates are formed of two boards, and a space layer 17 is provided between them. By passing a cooling air to the air layer 17, the heat insulation between the heating coil 9 and the material 10 to be heated is performed to prevent the heat of the material 10 to be heated from being transmitted to the heating coil 9, and the cooling effect is enhanced, whereby the heating efficiency is improved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating device, and more particularly to the structure of an insulator between the induction heating device and an object to be heated.

0002

2. Description of the Related Art Conventionally, various induction heating devices have been developed for heating metal pots.

FIG. 4 shows the circuit configuration of a conventional induction heating device. In Figure 4, commercial power supply 1 is connected to diode bridge 2.
It is rectified by a filter choke 3 and smoothed by a smoothing capacitor 4 to form a unidirectional power supply 5. The unidirectional power supply 5 is
It is connected to an inverter circuit 8 consisting of a resonant capacitor 6, a switching element 7, and the like. The inverter circuit 8 converts the output of the unidirectional power source 5 into the output of a high frequency power source and supplies it to the heating coil 9. The heating coil 9 is made of litz wire and wound into a disk shape in order to suppress an increase in loss due to the skin effect caused by high frequencies. High-frequency magnetic flux is supplied from the heating coil 9 to an object to be heated 10 such as a metal pot to generate eddy current in the metal. Joule heat is generated by this eddy current, and the object to be heated 10 is heated.

FIG. 5 shows a cross section of a heating coil portion of a conventional induction heating device. Components that are the same as those in FIG. 4 are given the same reference numerals. In FIG. 5, a ceramic plate 11 is installed on the top surface of the heating coil 9. The ceramic plate 11 that protects the heating coil 9 is non-magnetic and has very low conductivity, so there is almost no high-frequency magnetic flux loss. A ferrite 12 is installed on the lower surface of the heating coil 9 for the purpose of guiding high frequency magnetic flux. The ferrite 12 is a ferromagnetic material, through which magnetic flux easily passes, and has a small dielectric constant, so loss is small. Therefore, the high-frequency magnetic flux generated by the heating coil 9 almost exclusively causes induction loss in the object to be heated 10, making it possible to heat the object with high efficiency.

FIG. 6 shows a cutaway perspective view of a conventional induction heating device. In FIG. 6, the cooling fan rotates when the induction heating device operates, and is configured to forcibly cool the semiconductor switching element and the heating coil.

[0006]

[Problems to be Solved by the Invention] However, in such a structure, since the object to be heated 10 and the heating coil 9 are in close contact with each other with the plate 11 in between, the heat generated by the object to be heated 10 is not transferred to the plate 11. There was a problem that heat was conducted and cooling of the heating coil 9 became insufficient.

[0007] A large high-frequency current flows through the heating coil 9 of the induction heating device in order to create a strong magnetic field. The heating coil generates a large amount of heat due to copper loss due to the skin effect due to high frequency and the influence of large current. To reduce loss, we use litz copper wire twisted with coated fine wire, and we use forced cooling with a fan to suppress heat generation. However, since the object 10 to be heated by induction heating with high frequency is in close contact with the top surface of the heating coil 9 via the plate 11, heating for a long time will promote heat generation in the coil due to heat conduction from the object. However, there was a problem with insufficient cooling capacity.

[0008] In order to solve this problem, the present invention aims to provide an induction heating device having a structure in which the heat of the object to be heated 10 is not transmitted to the heating coil 9 and has high cooling efficiency.

[0009]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an inverter circuit equipped with a semiconductor switching element that converts a commercial power source into a high frequency wave, and a flat plate that receives the output of the inverter circuit and generates a high frequency magnetic flux. The heating coil is equipped with a shaped heating coil and a plate disposed on the upper surface of the heating coil, and the plate is provided with an air layer passing through the plate, and the air flow from the cooling fan is guided to the air layer.

0010

[Function] The induction heating device of the present invention has an air layer in the plate placed between the conductor of the flat heating coil and the metal object to be heated, so that the cooling air from the cooling fan is guided. The structure is such that heat from the object to be heated is not transmitted to the heating coil. This suppresses heat generation in the heating coil, making cooling easier.

[0011]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 3.

FIG. 1 shows a sectional view of a heating coil portion of an induction heating device according to the present invention. In FIG. 1, the same components as in FIG. 4 are given the same reference numerals. The heating coil 9 uses a Litz wire made by bundling several dozen thin enameled conducting wires. The resistance component of the heating coil 9 increases as the frequency increases. This is because the current flowing through the heating coil 9 is concentrated on the surface of the conductor wire due to the skin effect. At high frequencies of several tens of kilohertz, the resistance of the conductor is much greater than at commercial frequencies, and the resistance component of the heating coil increases significantly. Therefore,
Litz wire is used to increase the effective cross-sectional area of the conductor and reduce heat loss. That is, when thin wires are bundled even if they have the same cross-sectional area as a whole, the surface of the conductive wire becomes wider, so there is less heat loss due to the influence of the skin effect. Therefore, it can be said that the larger the number of thin wires, the smaller the loss. However, increasing the number of fans increases the cost, so
3, forced cooling is performed to suppress an increase in the cost of the heating coil 9, an increase in size due to an increase in cross-sectional area, and heat generation of the heating coil 9.

A ferrite 12 made of ferromagnetic material is arranged on the lower surface of the heating coil 9. This ferrite 12 constitutes a magnetic circuit 14 and guides the high frequency magnetic flux generated by the heating coil 9 to the object to be heated 10 . The high-frequency magnetic flux generated by the heating coil 9 has a large effect of guiding the magnetic flux and has a small loss because it is difficult for eddy current to flow in a material such as ferrite 12 which is ferromagnetic and has very low conductivity. On the other hand, the object to be heated 1
0 has higher conductivity than ferrite 12, so when magnetic flux passes through it, electromotive force is generated due to high frequency, eddy current flows, and heat is generated. The object to be heated generates heat due to copper loss caused by this eddy current.

Further, the ferrite 12 prevents the surrounding conductive metal from being inducedly heated by high-frequency magnetic flux and generating heat, thereby preventing efficiency from decreasing. Since electrical components and the like are arranged on the lower surface of the heating coil, the influence of leakage of high-frequency magnetic flux is reduced by configuring a magnetic circuit that guides the magnetic flux using the ferromagnetic ferrite 12.

Between the heating coil 9 and the object to be heated 10,
Ceramic plates 15, 16 are installed to insulate and protect the heating coil 9. plates 15, 16
consists of two plates, and an air space 17 is provided between the two plates.

The high frequency magnetic flux produced by the heating coil 9 is
It is possible to heat the object 10 by passing through the plates 15, 16 and the air layer 17 with almost no loss. Therefore, the heating coil 9 itself can heat the object 10 efficiently without generating much heat. This is the most important feature of the induction heating device. However, heating coil 9
Since the object to be heated 10 and the object to be heated are adjacent to each other, when heating is performed for a long time, the heat generated by the object to be heated 10 is transmitted to the heating coil 9 itself through the plates 15 and 16 by thermal conduction. Since the heating coil 9 uses an enamel-coated Litz wire, it generally has a heat resistance temperature of up to 100-odd degrees. However, excessive heating can cause dielectric breakdown and damage to the enamel coating. For this reason, the heating coil 9 of the induction heating device requires sufficient forced cooling, which has been a factor in reducing heating efficiency. In the present invention, heat conduction of the object to be heated is blocked by an air layer 17 provided between two plates 15 and 16. Therefore, almost no heat from the object to be heated 10 is transmitted to the heating coil 9. Therefore, the heating coil 9
Since less heat is generated, the efficiency of the device is improved, and the cost of the heating coil 9 can be reduced. Moreover, the reliability of the heating device is also improved.

13 is a cooling fan, and heating coil 9
At the same time, cooling air is sent to an air layer 17 provided between two plates 15 and 16. Heated object 10
Heat conduction from the heating coil 9 to the heated object 10 is blocked by the air layer 17, and the heat insulation effect between the heating coil 9 and the heated object 10 is significantly improved due to the air flow.

FIG. 2 shows a heating coil 9 in another embodiment.
A cross-sectional view is shown. Components that are the same as those in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted. In FIG. 2, two plates 15
, 16, a heat insulating material 17 is inserted. Therefore, the heat insulation effect between the heating coil 9 and the object to be heated 10 is further improved. Therefore, although the heating coil 9 generates heat due to its own high frequency loss, there is no temperature rise due to thermal conduction from the heated object 10. Therefore, with the above configuration, the cooling capacity of the heating coil 9 can be reduced.

FIG. 3 shows a cross-sectional perspective view of the induction heating device of the present invention. Plate 15 placed on the top surface of heating coil 9
, 16 are composed of two plates, and cooling air generated from the cooling fan 13 passes through an air layer 17 between the plates 15 and 16. The cooling fan 13 prevents the heat of the object to be heated 10 from being transmitted to the heating coil 9, and also prevents the heating coil 9 from being transferred.
and the switching element 7 attached to the heat dissipation fin.
, power semiconductor components such as the regeneration diode 18 are also cooled.

Note that, as explained above, the object to be heated 1
The purpose is to make it difficult for zero heat to be transferred to the heating coil 9. Therefore, the number of plates is not limited to two, and three or more plates may be used to form two or more air layers. Moreover, a large number of through holes through which air flows may be provided in one plate and used as an air layer.

The above configuration improves the cooling efficiency of the heating coil 9 and improves the efficiency and reliability of the device.

[0022]

Effects of the Invention As described above, the induction heating apparatus of the present invention provides the following effects. Since an air layer is provided in the plate provided between the heating coil and the object to be heated to allow cooling air to pass therethrough, the heat of the object to be heated is hardly transmitted to the heating coil. Therefore, damage to the heating coil due to heat generation can be prevented. This is especially effective when heated for a long time. Therefore, the heating efficiency of the device can be improved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a heating coil portion of an induction heating device according to an embodiment of the present invention.

[Fig. 2] Cross-sectional view of an induction heating device in another embodiment

[Figure 3] Cross-sectional perspective view of induction heating device

[Figure 4] Circuit diagram of a conventional induction heating device

[Figure 5] Cross-sectional view of the heating coil part of a conventional induction heating device

[
Figure 6: Cross-sectional perspective view of a conventional induction heating device

[Explanation of symbols]

1 Commercial power supply 7 Semiconductor switching element 8 Inverter circuit 9 Heating coil 10 Object to be heated 13 Cooling fan 15, 16 plate 17 Air layer

Claims (1)

[Claims] 1. An inverter circuit including a commercial power source, a semiconductor switching element that converts the commercial power source into a high frequency wave, a flat heating coil that receives the output of the inverter circuit and generates a high frequency magnetic flux, and an upper surface of the heating coil. An induction heating device comprising: a plate disposed in the plate; an air layer passing through the plate is provided in the plate; and an air flow from a cooling fan is guided to the air layer.