JP4693846B2 - Induction heating device - Google Patents

Description

  The present invention relates to an induction heating apparatus in which an electric conductor is provided between an object to be heated and a heating coil.

  An induction heating device that induces and heats an eddy current in a pan or the like that becomes a load by a high-frequency magnetic field generated by a heating coil has attracted attention because of its high thermal efficiency, safety, and cleanliness. A conventional induction heating apparatus is suitable for heating an object to be heated having a high magnetic permeability such as iron. In recent years, induction heating apparatuses capable of heating an object to be heated having a low magnetic permeability and high electrical conductivity such as aluminum or copper have been developed.

There is a stray capacitance (equivalent capacity) between the heating coil and the object to be heated, and when the user touches the object to be heated, current flows from the heating coil to the ground through the stray capacitance and the internal resistance (equivalent resistance) of the user's body. Flows.
When heating an object to be heated with low magnetic permeability and high electrical conductivity, the number of turns of the heating coil is larger and the voltage applied to the heating coil is higher than when heating an object to be heated with high permeability. . Since it is dangerous to leak more than a predetermined amount of current from the high-voltage heating coil to the human body, in the case of an induction heating device that heats an object to be heated with low magnetic permeability and high electrical conductivity, leakage current will flow through the human body. There was a need to prevent.
Japanese Utility Model Laid-Open No. 50-82046 discloses an induction heating apparatus of Conventional Example 1 that uses a conductive film to prevent leakage current from flowing through the human body. A conductive film is provided on the back surface of the top plate, and the conductive film is grounded. Since most of the leakage current from the heating coil flows to the ground through the conductive film, almost no leakage current flows to the human body through the object to be heated.

  The induction heating device can adjust the heating temperature of the object to be heated by the amount of magnetic flux that reaches the object to be heated. Japanese Patent Application Laid-Open No. 7-249480 discloses an induction heating device of Conventional Example 2 in which a temperature distribution is adjusted using an annular electric conductor. The electric conductor is disposed between the heating coil and the object to be heated. The annular electrical conductor has a slit between the outer peripheral edge and the inner peripheral edge. An induced current in a direction opposite to the high frequency current of the heating coil flows on the outer peripheral edge of the electric conductor, and this induced current is blocked by a slit. An induced current flows in the opposite direction to the induced current of the outer peripheral edge (in the same direction as the heating coil) on the inner peripheral edge of the electric conductor. The induction heating device of Conventional Example 2 adjusts the strength of the magnetic field and heats the object to be heated by the high-frequency current flowing through the heating coil and the induced current flowing through the outer and inner edges of the electric conductor.

  The magnetic field generated by the heating coil extends around the heating coil. Japanese Patent Laid-Open No. 7-22170 discloses an induction heating apparatus of Conventional Example 3 that suppresses a magnetic field leaking to the surroundings. In the induction heating device of Conventional Example 3, the shield ring is disposed outside the heating coil. When a high frequency current is supplied to the heating coil, a high frequency magnetic field is generated from the heating coil. When the magnetic field is linked to the shield ring, an induced current in a direction opposite to the current of the heating coil flows through the shield ring. The shield ring generates a magnetic field due to the induced current flowing in the shield ring. The magnetic field generated by the shield ring is in the direction in which the magnetic field of the heating coil is strengthened inside the shield ring, and in the direction opposite to the magnetic field of the heating coil outside the shield ring. The shield ring cancels out the magnetic field generated by the heating coil on the outside thereof, and suppresses the leakage of the magnetic field of the heating coil to the surroundings.

Japanese Utility Model Publication No. 50-82046 JP-A-7-249480 JP-A-7-22170

In the induction heating devices of Conventional Examples 1 to 3, the conductive film that prevents leakage current from flowing through the human body, the electrical conductor that adjusts the temperature distribution, and the shield ring that prevents leakage current to the outer periphery were separate components. . Therefore, there is a problem that the induction heating apparatus having all these functions is expensive.
Furthermore, when a connection terminal is provided on a conventional electrostatic shield body in which conductive paint such as carbon and an adhesive are mixed and connected to a low potential portion, the conductive paint is not evenly applied or static. There was a problem such as weak bonding between the electric shield body and connection terminal, and the structure for ensuring reliability was complicated, and it took time to ensure reliability, such as requiring time for component inspection. .
An object of the present invention is to provide an inexpensive and reliable induction heating device for an electrostatic shield.
Another object of the present invention is to provide an induction heating device having a magnetic shielding effect that prevents a magnetic field generated by a heating coil from leaking to the outer periphery .

  In order to solve the above problems, the present invention has the following configuration.

The invention according to claim 1 is a heating coil for inductively heating an object to be heated, a first electric conductor provided between the object to be heated and the heating coil and covering an upper portion of the heating coil, and the heating An inverter that supplies a high-frequency current to the coil, and an annular second electrode that is electrically connected to the first electrical conductor and that prevents the magnetic field of the heating coil from leaking to the surroundings. And a control circuit that drives by driving an induced current through the heating coil, and the second electrical conductor is placed in a low potential portion having a lower potential than the high potential portion of the heating coil of the control circuit. Inductive heating characterized in that electrical connection is made and the electrostatic coupling between the heating coil and the object to be heated is made smaller than when the first electrical conductor is not electrically connected to the low potential portion. Device.

In the induction heating device of the present invention, the second electric conductor is electrically connected to the low potential portion having a lower potential than the high potential portion of the heating coil , and the second electric conductor electrically connected to the low potential portion is connected. High reliability is realized by a configuration in which the temperature of the end portion is sufficiently low.
Further , the first electric conductor covering the upper part of the heating coil exhibits an electrostatic shielding effect, and the second electric conductor is provided outside the heating coil, so that the magnetic field generated by the heating coil leaks to the outer periphery. Thus, the number of components can be reduced, and an inexpensive induction heating apparatus can be realized.

According to a second aspect of the present invention, when the object to be heated is made of aluminum, copper, or a low magnetic permeability material having an electric conductivity substantially equal to or higher than that of the first electric conductor, 2. The induction heating according to claim 1 , further comprising a buoyancy reduction function for reducing a buoyancy acting on the object to be heated by an interaction between a magnetic field generated by a coil and a current induced in the object to be heated. Device.
ADVANTAGE OF THE INVENTION According to this invention, the induction heating apparatus which can heat a to-be-heated material with low magnetic permeability and high electrical conductivity like aluminum or copper, preventing that a to-be-heated material floats is realizable.

The invention according to claim 3, comprising a further ferrite outside of the heating coil, the second electrical conductors claim 1 or claim 2, characterized in that provided outside of the ferrite It is an induction heating apparatus as described in the claim.
According to the present invention, it is possible to realize an induction heating device having a high magnetic shielding effect. According to the present invention, since the second electric conductor does not block the magnetic flux emitted from the ferrite, the second electric conductor is not heated and does not reach a high temperature, and a highly efficient induction heating apparatus can be realized.

Invention according to claim 4, wherein the second electrical conductor, as claimed in any one of claims 1 or claim 2, characterized in that provided in the heating coil and substantially the same height Induction heating device.
ADVANTAGE OF THE INVENTION According to this invention, the highly efficient induction heating apparatus which prevents that the magnetic field from a heating coil leaks to an outer periphery, and prevents a 2nd electric conductor from being heated and becoming high temperature is realizable.

The invention according to claim 5, according to any one of claims 1 or claim 2, characterized in that formed integrally conductor and wherein the first electrical conductor second electrical conductors This is an induction heating device.
According to the present invention, the number of components can be reduced by integrally forming the first electric conductor having a buoyancy reduction function and the second electric conductor having an electrostatic shield function and a magnetic shielding effect, An inexpensive induction heating device can be realized.

The invention according to claim 6, before Symbol first electrical conductor, an induction heating apparatus according to any one of claims of claims 1 to 5, characterized in that it comprises a slit.
The induction heating device of the present invention reduces the amount of heat generated in the electric conductor by changing the direction and magnitude of the current induced in the electric conductor by the magnetic field generated by the heating coil by providing a slit in the electric conductor. Can do.

According to the present invention, that when can achieve an induction heating device with no possibility of reliable electric shock inexpensive both can realize an induction heating apparatus the magnetic field generated by the heating coil has a magnetic shielding effect to prevent leakage to the outer periphery The effect can be obtained.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments specifically showing the best mode for carrying out the present invention and reference embodiments will be described below with reference to the drawings.

(Reference form 1)
The induction heating apparatus of the reference form 1 is demonstrated using FIG.1 and FIG.2 . FIG. 1 is a perspective view showing a configuration of a heating coil and its surroundings of an induction heating apparatus according to Reference Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view showing a heating coil housed in an induction heating apparatus main body (not shown), a top plate fixed to the upper portion of the main body, and an object to be heated placed on the top plate.
The induction heating device according to the first embodiment of the present invention includes a heating coil 1, a holding portion 2, a ferrite core 3 (having 3a, 3b, and 3c), 4 (having 4a, 4b, and 4c), and 5 (5a). 5b, 5c.), 6 (having 6a, 6b, 6c), electric conductor 7, top plate 8, insulating plate 9, shield ring 10, terminal 13, thermistor 15, and holder 16. The object to be heated 11 is placed on the top plate 8.

When the heating coil 1 is supplied with a high frequency current from a control circuit (not shown), the heating coil 1 generates a high frequency magnetic field and heats the object to be heated 11. In the present invention, the heating coil has an inner side on the high potential side and an outer side on the low potential side. The heating coil 1 is placed on the upper part of the holding unit 2.
The holding part 2 is made of a heat-resistant resin, is integrally formed with the ferrite cores 3 b to 6 b, and is positioned substantially parallel to the lower surface of the heating coil 1. The ferrite cores 3b to 6b are rod-shaped ferromagnetic bodies having four substantially rectangular parallelepipeds. The ferrite cores 3 b to 6 b are located below the heating coil 1. Ferrite cores 3a to 6a and ferrite cores 3c to 6c are provided in contact with both ends of the ferrite cores 3b to 6b. For this reason, the ferrite core is formed in a U shape whose cross section is open toward the object to be heated 11 as a whole. The holding part 2 is formed so as to cover the surface of the ferrite core (partially not covered for cooling), and the ferrite core is electrically insulated from the heating coil 1.

The electric conductor 7 is provided between the heating coil 1 and the top plate 8. Preferably, the electrical conductor 7 is placed on the insulating plate 9 just below the top plate. The electric conductor 7 is electrically insulated from the heating coil 1 by being placed on the insulating plate 9. The position of the electric conductor 7 is regulated by the three leg portions 7 b and the holding portion 2.
The electric conductor 7 is formed of an aluminum plate having a thickness of about 1 mm, and has an outer diameter and an inner diameter substantially the same as a donut shape, and a slit 7a having a width of about 6 mm extends from the outer periphery to the inner periphery. Is provided.
The electric conductor 7 has an opening 12 at the center. When viewed from the heated object 11 side, the upper end surfaces of the ferrite cores 3a to 6a that are the outer rising portions are located outside the outer periphery of the electric conductor 7, and the upper end surfaces of the ferrite cores 3c to 6c that are the inner rising portions are It is located inside the periphery of the opening 12.
A terminal 13 is connected to the leg portion 7b of the electric conductor 7, and the terminal 13 is connected to a commercial power supply potential via a capacitor 14, a potential obtained by rectifying a commercial power supply input to an inverter that supplies a high-frequency current to the heating coil 1, or the ground. Is electrically connected.

  The top plate 8, which is an insulator, is made of heat-resistant ceramics, and an aluminum heated object 11 is placed on the top plate 8 so as to face the heating coil 1. The insulating plate 9 is placed between the heating coil 1 and the electric conductor 7. The shield ring 10 is formed of a lead wire or a die-cast ring, and is provided outside the ferrite cores 3a to 6a. The thermistor 15 is fitted into the holder 16 and is brought into contact with the back surface of the top plate 8 to indirectly detect the temperature of the object to be heated 11.

  The operation of the induction heating apparatus thus assembled will be described. When a high frequency current is supplied to the heating coil 1 from a control circuit (not shown), the heating coil 1 generates a magnetic field. A current is induced on the bottom surface of the object to be heated 11 by the high frequency magnetic field generated by the heating coil 1. In the absence of the electrical conductor 7, the induced current is induced in the heated object 11 so as to cancel the magnetic field generated from the heating coil. As a result, an induction current having a direction opposite to that of the heating coil current and parallel to the heating coil current is induced in the object to be heated 11 having high electrical conductivity. Due to the interaction between the induction current and the heating coil current, a repulsive force is generated at the bottom of the object to be heated 11 to move away from the heating coil 2, and buoyancy is generated in the object to be heated 11. In particular, buoyancy occurs when the object to be heated 11 is a material having low magnetic permeability and high electrical conductivity, such as aluminum or copper.

  When there is the electric conductor 7, the magnetic field generated by the heating coil 1 is linked to the electric conductor 7 and an induced current is induced in the electric conductor 7. Since the thickness of the electric conductor 7 is about 1 mm and is greater than the penetration depth, most of the magnetic field linked to the electric conductor hardly passes through the electric conductor, and after detouring to the outer peripheral side or the inner peripheral side, it is covered. It is guided in the direction of the heated object 11. That is, the distribution of the current induced in the object to be heated 11 changes when an induced current is generated in the electric conductor 7.

The magnetic field generated by the heating coil interlinks with the electric conductor 7 and the object to be heated 11 and generates an induced current in both. The induced current induced in the object to be heated 11 is such that the magnetic field distribution generated by the heating coil 1 and the magnetic field distribution generated by superimposing the magnetic field distribution generated by the electric conductor 7 are linked to the object to be heated 11. Caused by. In this way, the current distribution induced in the object to be heated 11 is changed by the presence of the electric conductor 7 and the current distribution generated in the electric conductor 7 is further added, so that the equivalent series resistance ( The equivalent series resistance in the input impedance of the heating coil (measured using a frequency in the vicinity of the heating frequency) is increased in the same arrangement as the heated object and the electric conductor in the heated state.
When the equivalent series resistance is increased, the amount of heat generated in the object to be heated 11 is increased even with the same heating coil current. Therefore, when the same power consumption is to be obtained, the current value flowing through the heating coil can be reduced. Buoyancy acting on the object to be heated is reduced. Furthermore, the buoyancy acting on the heated object can be reduced by sharing a part of the buoyancy that the electric conductor should work on the heated object.

  Thus, the electric conductor has a buoyancy reduction function that reduces the buoyancy that acts on the heated pan by the magnetic field generated by the heating coil by reducing the current flowing through the heating coil when obtaining the same output. As a result, it is possible to prevent the object to be lifted or shifted when the object to be heated, which is made of aluminum or copper or has an electric conductivity substantially equal to or higher than these, and is made of a low magnetic permeability material, is heated.

  Since the electric conductor 7 is made of aluminum, it has a low magnetic permeability, and the magnetic flux is hardly absorbed by the electric conductor 7 (the amount of magnetic flux that does not reach the object to be heated does not increase). When the magnetic flux of the heating coil 1 is interlinked, the direction and distribution of the magnetic field are changed by the current induced in the electric conductor. The magnetic flux is efficiently transferred to the object to be heated 11 through the path of passing through the electric conductor 7 and interlinking with the object to be heated 11, or bypassing the electric conductor 7 and interlinking with the object to be heated 11. Can be interlinked.

The electric conductor 7 is formed in a plate shape so as to cover the heating coil 1 with the upper portion over almost the whole other than the slit 7a, that is, a part or all of the surface of the heating coil 1 on the heated object 11 side. Being done. Thus, before reaching the object to be heated 11, a part of the magnetic field generated from the heating coil 1 is efficiently linked to the electric conductor 7, bypassed from the periphery of the electric conductor 7, and heated to the object 11 to be heated. One magnetic field is interlinked.
The distance between the electric conductor 7 and the heating coil 1 is smaller than the distance between the electric conductor 7 and the object 11 to be heated, and the magnetic coupling between the electric conductor 7 and the heating coil 1 is good. The amount increases, and an induced current is distributed in the electric conductor 7 to increase the equivalent series resistance of the heating coil 1.

In the present embodiment , the size of the electric conductor 7 is determined so as to face almost the entire heating coil 1. However, the larger the area of the plate of the electric conductor 7, the more the electric conductor 7 is connected to the heating coil 1. The closer the magnetic flux of the heating coil 1 passes through the electric conductor 7 and the greater the equivalent series resistance increasing action can be increased, the closer the surface area of the electric conductor 7 is to obtain the required buoyancy reduction effect. It may be determined in consideration of conditions such as the distance between the conductor 7 and the heating coil 1 and the heat generation of the electric conductor 7.

When the slit 7a is not provided in the electric conductor 7, a circular current flows through the electric conductor and the electric conductor generates heat. Further, when a circular current in the direction opposite to the current of the heating coil flows through the electric conductor 7, the magnetic field is canceled, and the object to be heated cannot be induction-heated in that portion.
By providing the slit 7 a in the electric conductor 7, it is possible to prevent a circulating current substantially parallel to the direction opposite to the current of the heating coil 1 from flowing through the electric conductor 7 so as to circulate around the center of the heating coil 1. The circular current flowing in the opposite direction to the current flowing in the heating coil 1 induced by the electric conductor 7 is interrupted by the slit 7a, and the direction and magnitude of the current induced in the electric conductor 7 are changed. Thereby, generation | occurrence | production of a heavy current is lose | eliminated and the emitted-heat amount which generate | occur | produces in the electrical conductor 7 can be reduced. Furthermore, by placing the electric conductor 7 immediately below the top plate 8, the heat of the electric conductor 7 is radiated through the top plate 8.
By providing the slit, the buoyancy reduction effect on the article to be heated 11 may be reduced to some extent. Depending on the shape of the slit 7a, the area where the heating coils interlink, the material of the electric conductor, etc., the magnitude of the equivalent series resistance and the amount of heat generated by the electric conductor 7 are different, so select the optimum combination of these elements, What is necessary is just to determine the combination which makes the buoyancy reduction effect as large as possible and makes the heat generation amount of the electric conductor 7 acceptable.

The terminal 13 is connected to the electric conductor 7, and the terminal 13 is connected to a low potential portion (for example, a portion having a lower potential than the high potential portion of the heating coil, such as an input power supply voltage, a DC voltage after rectification thereof, or a potential close thereto). This reduces the electrostatic coupling between the high voltage portion generated in the heating coil and the object to be heated. A high-frequency high voltage generated in the heating coil is applied to the user's body via the stray capacitance between the heating coil and the object to be heated, and leakage current flowing through the user's body can be suppressed.
In other words, between the electric conductor 7 and the ground, the internal resistance (equivalent resistance) of the electric conductor 7, the stray capacitance (equivalent capacity) between the electric conductor 7 and the user's body, and the internal resistance of the user's body. (Equivalent resistance) and are connected in parallel. Since the impedance of the internal resistance (equivalent resistance) of the electric conductor 7 is very small compared to the impedance of the stray capacitance (equivalent capacitance) and the internal resistance (equivalent resistance) of the user's body, the leakage current from the heating coil 1 is Almost flows through the electric conductor 7 to the ground. Almost no current leaks to the user's body.

When the object to be heated 11 is a pan made of aluminum, copper or the like having a low magnetic permeability and low resistance, the frequency flowing through the heating coil 1 becomes high, and the peak voltage applied to the heating coil 1 becomes 1 KV or higher.
If the electric conductor 7 is electrically coupled to the low potential portion as described above, the potential difference between the object to be heated 11 and the electric conductor is reduced, so that leakage occurs when the human body touches the object 11 to be heated. The current is greatly reduced. Therefore, it is safe even if the human body touches the object to be heated 11.

The electrical conductor 7 is provided with an opening 12 at the center, and the magnetic flux from the rising portions 3c to 6c of the ferrite core does not hit the electrical conductor 7 and efficiently guides the magnetic flux from the heating coil 1 to the object 11 to be heated. , Increase the heating efficiency.
The rising portions 3a to 6a of the ferrite core are positioned outside the outer periphery of the electric conductor and provided in the direction of the object to be heated so that the magnetic flux emitted from the heating coil 1 does not spread around the outside of the heating coil 1. Heating efficiency is increased by causing the magnetic flux to interlink with the object to be heated 11 efficiently.
Below the heating coil 1, magnetic flux concentrates on the ferrite cores 3 b to 6 b, which are high permeability materials, and prevents the magnetic field from expanding to the opposite side to the object to be heated 11.

Each of the ferrite cores 3a to 3c, 4a to 4c, or the ferrite cores 5a to 5c is arranged in combination with another three ferrite cores in contact with each other. Even if molded, the same effect can be obtained because of the open magnetic path. In this embodiment, both ends of the high permeability rod-shaped ferrite cores 3b to 6b provided below the heating coil 1 are raised substantially vertically by the ferrite cores 3a to 6a and the ferrite cores 3c to 6c. The angle is not the only one.
In the reference form 1, the four ferrite cores 3 to 6 are provided, but the number of ferrite cores is not limited to this. The larger the number of ferrite cores, the higher the magnetic shielding effect on the outer periphery, and the easier it is to transmit the magnetic force to the pan.

  When a high frequency current is supplied to the heating coil 1, a high frequency current is induced in the shield ring 10 by a magnetic field generated by the heating coil. The high-frequency current induced in the shield ring 10 generates a magnetic field in the same direction as the magnetic field of the heating coil inside the ring and in the opposite direction to the magnetic field generated by the heating coil outside the ring. Reduce magnetic field. In addition, if the magnetic-shielding effect by a ferrite core is enough, it is good also as a structure which does not have a shield ring.

As described above, according to the present embodiment , the electrical conductor 7 increases the equivalent series resistance of the heating coil 1 when the object to be heated 11 is disposed facing the heating coil 1, and It has a buoyancy reduction function that reduces the buoyancy that the generated magnetic field acts on the object to be heated 11. The object to be heated 11 having high electrical conductivity and low magnetic permeability such as aluminum, copper, or brass can be heated while being prevented from floating during cooking.
According to this embodiment , by connecting the electric conductor 7 directly to the low potential portion, the high frequency high voltage generated in the heating coil 1 is applied to the user's body via the stray capacitance between the heating coil and the object to be heated. Leakage current that flows through the user's body when applied can be suppressed.
According to this embodiment , the electric conductor has both functions of a buoyancy reduction function and an electrostatic shield function, so that a safe and inexpensive induction heating apparatus can be realized.

(Reference form 2)
The induction heating apparatus of the reference form 2 is demonstrated using FIG. FIG. 3 is a plan view of an electric conductor included in the induction heating device according to the second embodiment . The difference between the induction heating device of the reference form 2 and the induction heating device of the reference form 1 is the shape of the electric conductor. Since other configurations are the same as those of the first embodiment , detailed description thereof is omitted. The electric conductor of the reference form 2 will be described.
Since the reference form 1 connects the terminal 13 connected to the low potential portion to the leg portion 7b of the electric conductor 7, there is a problem that the terminal 13 becomes high temperature. When the terminal becomes hot, problems such as deterioration of reliability due to corrosion or loosening of the electrical connection occur. The electric conductor 31 of the reference form 2 is a structure which prevents the terminal 13 from becoming high temperature. The electric conductor 31 of the reference form 2 is placed between the top plate 8 and the insulating plate 9 similarly to the reference form 1, and has a buoyancy reduction function.

The electric conductor 31 of the reference form 2 is formed of an aluminum plate having a thickness of about 1 mm, and includes an inner peripheral portion 31a and an outer peripheral portion 31b. The outer diameter and inner diameter of the inner peripheral portion 31 a of the electric conductor 31 are substantially donut shapes that are substantially the same as the outer diameter and inner diameter of the heating coil 1. The inner peripheral portion 31a and the outer peripheral portion 31b are connected at one end 31d, and a gap 32 having a width of about 1 mm is provided between the inner peripheral portion 31a and the outer peripheral portion 31b other than the connecting portion 31d. The width of the outer peripheral portion 31b of the electric conductor is sufficiently narrower than the width of the inner peripheral portion 31a. By reducing the width of the outer peripheral portion of the electrical conductor, the amount of heat generated by the outer peripheral portion itself can be reduced, and the temperature of the outer peripheral portion 31b is lower than that of the inner peripheral portion 31a.
Furthermore, the temperature of the outer peripheral portion 31b of the electric conductor 31 decreases as the distance from the connecting portion 31d increases, and the temperature at the end of the outer peripheral portion farthest from the connecting portion 31d is the lowest. The terminal 13 connected to the low potential portion is connected to a leg portion 31c at the end portion of the outer peripheral portion provided at a location approximately ½ or more rounds away from the connection portion between the inner peripheral portion and the outer peripheral portion. Preferably and in the reference form 2, the terminal 13 connected to the low potential portion is connected to the leg portion 31c at the end of the outer peripheral portion farthest from the connection portion between the inner peripheral portion and the outer peripheral portion. The leg portion 31c is bent downward as in FIG. 1, and supports the inner peripheral portion 31a and the outer peripheral portion 31b at a predetermined height.
Further, the electrical conductor 31 is different from the first embodiment in that it has a slit 33. Since the electric conductor 31 has the slits 7a and the slit 33, the electric conductor 31 is prevented from flowing a circular current in the direction opposite to the current of the heating coil 1 and the amount of heat generated by the electric conductor 31 is reduced.
Thereby, the induction heating apparatus of the reference form 2 can prevent the terminal 13 from becoming high temperature, and can reliably prevent an electric shock.

(Reference form 3)
The induction heating apparatus of the reference form 3 is demonstrated using FIG. FIG. 4 is a plan view of an electric conductor included in the induction heating device according to the third embodiment . The difference between the induction heating device of the reference form 3 and the induction heating device of the reference form 1 is the shape of the electric conductor. Since other configurations are the same as those of the first embodiment , detailed description thereof is omitted. The electric conductor of the reference form 3 will be described.
The induction heating device according to the reference form 3 includes two symmetrical electric conductors 41 and electric conductors 42. The electric conductor 41 and the electric conductor 42 are formed of an aluminum plate having a thickness of about 1 mm. The electrical conductors 41 and 42 of the reference form 3 are placed between the top plate 8 and the insulating plate 9 similarly to the reference form 1, and have a buoyancy reduction function.

The electric conductor 41 includes an inner peripheral portion 41a and an outer peripheral portion 41b, and a gap 41e having a width of about 1 mm is provided between the inner peripheral portion 41a and the outer peripheral portion 41b except for the connecting portion 41d. The inner peripheral portion 41 a of the electric conductor 41 has a substantially sector shape having a circumferential angle of approximately 180 degrees, and the outer diameter and inner diameter thereof are substantially the same as the outer diameter and inner diameter of the heating coil 1. The outer peripheral portion 41b has a ring shape having a circumferential angle of approximately 180 degrees. The width of the outer peripheral portion 41b of the electric conductor is sufficiently narrower than the width of the inner peripheral portion 41a. By reducing the width of the outer peripheral portion 41b of the electric conductor, the amount of heat generated in the outer peripheral portion itself can be reduced, and the temperature of the outer peripheral portion 41b is lower than that of the inner peripheral portion 41a.
Furthermore, in the outer peripheral part 41b of the electric conductor 41, the temperature decreases as the distance from the connecting part 41d increases, and the end part of the outer peripheral part farthest from the connecting part 41d has the lowest temperature. The terminal 13 connected to the low potential portion is connected to the leg portion 41c at the end of the outer peripheral portion farthest from the connection portion between the inner peripheral portion and the outer peripheral portion. The leg portion 41c is bent downward as in FIG. 1, and supports the inner peripheral portion 41a and the outer peripheral portion 41b at a predetermined height. The same applies to the electric conductor 42, and the terminal 13 is connected to the leg portion 42c.
Thereby, the induction heating apparatus of the reference form 3 can prevent the terminal 13 from becoming high temperature, and can reliably prevent an electric shock.
The electric conductors 41a and 42a are provided with an opening 12 at the center, and the magnetic flux from the heating coil 1 is efficiently heated so that the magnetic flux emitted from the rising portions 3c to 6c of the ferrite core does not hit the electric conductors 41a and 42a. It leads to the thing 11, and raises heating efficiency.

(Embodiment 1)
The induction heating apparatus according to the first embodiment will be described with reference to FIGS. FIG. 5 is a plan view of an electric conductor included in the induction heating apparatus according to the first embodiment . FIG. 6 shows a heating coil 1 housed in an induction heating apparatus main body (not shown), electric conductors 51 and 52, a top plate 8 fixed to the upper part of the main body, and an object to be heated placed on the top plate 8. FIG. In FIG. 6, the same parts as those in FIG. Induction heating device an induction heating apparatus is different from the reference in the form 1 of the first embodiment is that no separate shield ring 10 and having an electrical conductor 51 and 52 of different shapes. Since other configurations are the same as those of the first embodiment , detailed description thereof is omitted. The electric conductor of Embodiment 1 is demonstrated.
The electric conductor according to the first embodiment includes a first electric conductor 51 and a second electric conductor 52. The first electric conductor 51 and the second electric conductor 52 are integrally formed of a single aluminum plate. The first electric conductor 51 and the second electric conductor 52 are connected by a connecting portion 52d, and a gap 53 is provided in other areas. In the first embodiment , the first electric conductor 51 and the second electric conductor 52 are different from each other in height with respect to the holding unit 2 (or the heating coil 1), and a step 52e is provided between the two at the connection unit 52d. .

The first electric conductor 51 is provided between the top plate 8 and the insulating plate 9. First electrical conductor 51 of the first embodiment, having substantially the same function as electrical conductors 7 of Reference Embodiment 1. The first electric conductor 51 has a substantially sector shape in which the outer diameter and inner diameter are substantially the same as the outer diameter and inner diameter of the heating coil 1 and have a circumferential angle slightly smaller than 360 degrees. Twelve. The first electric conductor 51 increases the equivalent series resistance of the heating coil 1 when the object to be heated 11 is disposed facing the heating coil 1 to reduce the buoyancy acting on the object to be heated 11. It has a function. Since the first electric conductor 51 has the slits 7 a and 33, the first electric conductor 51 is prevented from flowing a circular current in the direction opposite to the current of the heating coil 1, and the first electric conductor 51 generates a heat. Reduce.

The first electric conductor 51 is provided with an opening 12 at the center, and the magnetic flux from the heating coil 1 is efficiently generated so that the magnetic flux emitted from the rising portions 3c to 6c of the ferrite core does not hit the first electric conductor 51. It leads to the article to be heated 11 and increases the heating efficiency.
In the gap 53 between the first electric conductor 51 and the second electric conductor 52, the rising portions 3a to 6a of the ferrite core are provided in the direction of the object to be heated. The magnetic flux from the heating coil 1 is efficiently guided to the object to be heated 11 so that the magnetic flux emitted from the rising portions 3a to 6a of the ferrite core does not strike the first electric conductor 51 and the second electric conductor 52. Further, the second electric conductor 52 constituting the shield ring (closed loop) prevents the magnetic flux emitted from the heating coil 1 from spreading outside the second electric conductor 52. With this configuration, the magnetic flux efficiently interlinks with the article 11 to be heated, thereby realizing high heating efficiency. The width of the gap 53 is wider than that of the first embodiment . The width of the gap 53 is optimally designed based on various conditions such as the height difference between the rising portions 3 a to 6 a of the ferrite core and the first electric conductor 51 and the second electric conductor 52. In the first embodiment , since the first electric conductor 51 and the second electric conductor 52 are integrally formed of a single aluminum plate, the first electric conductor 51 and the second electric conductor 52 are disposed between each other. If the height difference is large, it is necessary to widen the gap 53.

  When the first electric conductor 51 is placed immediately below the top plate 8, the heat of the first electric conductor is radiated through the top plate 8. The closer the first electric conductor 51 is to the heating coil 1, the more magnetic flux of the heating coil 1 passes through the first electric conductor 51, thereby increasing the equivalent series resistance increasing action. It becomes hot. The position of the first electric conductor 51 may be determined in consideration of conditions such as a buoyancy reduction function and heat generation of the first electric conductor.

The second electric conductor 52 is annular and is provided outside the heating coil 1 and the ferrite cores 3a to 6a. Second electrical conductors 52, relative height magnetic flux from heating coil 1 for half 径及 beauty height of the optimum (heating coil 1 to prevent spread outside the second electrical conductors 52 ). The optimum radius and height of the circumference to which the second electric conductor 52 is attached can be determined by experiment. The second electric conductor 52 has substantially the same effect as the shield ring 10. When a high frequency current is supplied to the heating coil 1, a high frequency current is induced in the second electric conductor 52 by a magnetic field generated by the heating coil. The high-frequency current induced in the second electric conductor 52 generates a magnetic field in the same direction as the magnetic field of the heating coil inside the ring and in the opposite direction to the magnetic field generated by the heating coil outside the ring. Reduce the magnetic field leaking to the outer periphery.

The second electric conductor 52 has three leg parts 52 b and fixes the leg part 52 b to the holding part 2. The width of the second electric conductor 52 is sufficiently narrower than the width of the first electric conductor 51. The second electric conductor 52 is away from the heating coil 1 and is difficult to receive the magnetic flux from the heating coil 1. For this reason, the calorific value of the second electric conductor itself can be reduced, and the temperature of the second electric conductor 52 is lower than that of the first electric conductor 51. Further, the temperature of the second electric conductor 52 decreases as the distance from the connecting portion 52d with the first electric conductor 51 increases. The terminal 13 is connected to a leg portion 52b (provided at a position approximately 180 degrees away from the connecting portion 52d) farthest from the connecting portion between the second electric conductor 52 and the first electric conductor 51. The terminal 13 is connected to a low potential portion (for example, a commercial power source potential, a potential obtained by rectifying a commercial power source input by an inverter that supplies a high-frequency current to the heating coil 1, or the ground) via a capacitor 14. Thereby, the electrostatic coupling between the high voltage portion generated in the heating coil and the object to be heated is reduced. A high-frequency high voltage generated in the heating coil is applied to the user's body via the stray capacitance between the heating coil and the object to be heated, and leakage current flowing through the user's body can be suppressed.
The leg portion 52b is configured to be bent downward from the second electric conductor 52 at the base portion 52f as in FIG. 1, and the first electric conductor 51 and the second electric conductor have a predetermined height. (In the first embodiment , the height of the first electric conductor 51 is different from the height of the second electric conductor 52).

In the above embodiment and reference embodiments , the electric conductor may be formed of a material having high conductivity other than aluminum.
In the above embodiment and reference embodiments , the same effect can be obtained even if the electric conductor is formed by die casting. For example, the cross section of the second electric conductor 52 can be formed in an L shape by configuring the electric conductor of the first embodiment by die casting.
In the first embodiment , the second electric conductor 52 is provided at substantially the same height as the heating coil 1 (the height between the mounting height of the first electric conductor 51 and the upper surface of the holding portion 2). Instead of this, the second electric conductor 52 may be provided at the same height as the first electric conductor 51 or on the upper surface of the holding portion 2.
Incidentally, this reference embodiment 1-3, had done only in one place of the pin 13 the connection between each electric conductor and the low-potential portion Oite to the first embodiment (the commercial power source potential and the ground, etc.), a plurality The safety can be further improved by providing a configuration in which the reliability is simply increased or current is passed between a plurality of terminals to detect the presence or absence of connection and the heating coil 1 is energized only when the connection is good.

  The present invention is useful for an induction heating apparatus such as an induction heating cooker.

The perspective view which shows the structure of the induction heating apparatus of the reference form 1 of this invention. Sectional drawing which shows the structure of the induction heating apparatus of the reference form 1 of this invention The top view of the electrical conductor of the induction heating apparatus of the reference form 2 of this invention The top view of the electrical conductor of the induction heating apparatus of the reference form 3 of this invention The top view of the electrical conductor of the induction heating apparatus of Embodiment 1 of this invention Sectional drawing which shows the structure of the induction heating apparatus of Embodiment 1 of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heating coil 2 Holding part 3, 4, 5, 6 Ferrite core 7, 31, 41, 42 Electric conductor 8 Top plate 9 Insulating plate 10 Shield ring 11 Heated object 13 Terminal 51 First electric conductor 52 Second electric conductor

Claims (6)

A heating coil for inductively heating an object to be heated;
A first electric conductor provided between the object to be heated and the heating coil and covering an upper portion of the heating coil ;
An inverter for supplying a high frequency current to the heating coil;
An annular second electrical conductor that is electrically connected to the first electrical conductor and prevents the magnetic field of the heating coil from leaking to the surroundings; and
A control circuit that drives the heating coil by passing an induction current;
Have
The second electrical conductor is electrically connected to a low potential portion having a lower potential than the high potential portion of the heating coil of the control circuit, and electrostatic coupling between the heating coil and the object to be heated is performed in the first circuit. The induction heating apparatus is characterized in that the electrical conductor is made smaller than when the electrical conductor is not electrically connected to the low potential portion . When induction heating is performed on an object to be heated made of aluminum, copper, or a low-permeability material having an electric conductivity substantially equal to or higher than the above, the first electric conductor includes the magnetic field generated by the heating coil and the object to be heated. The induction heating apparatus according to claim 1 , wherein the induction heating apparatus has a buoyancy reduction function for reducing a buoyancy acting on the object to be heated by interaction with an electric current induced in the object. Further comprising ferrite on the outside of the heating coil,
Induction heating apparatus according to any one of claims 1 or claim 2 wherein the second electrical conductor and which are located outside of the ferrite. Said second electrical conductor, the induction heating apparatus according to any one of claims 1 or claim 2, characterized in that provided in the heating coil and substantially the same height. Induction heating apparatus according to any one of claims 1 or claim 2, characterized in that to form the said first electrical conductor second electrical conductors integral conductor. Before SL first electrical conductor, the induction heating device according to claim 1, characterized in that a slit to one of claims 5.

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