JP2003051378A - Induction heating cooker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an induction heating cooker provided with a temperature sensor capable of detecting an accurate temperature of a heated object. SOLUTION: This induction heating cooker is provided with a top plate for mounting the heated object such as a pan, a thermal element for detecting a temperature of the top plate through a heat receiving part closely contact with a rear surface of the top plate, a lead part connected to the thermal element through a joining part, a heating coil arranged beneath the top plate and wound in an annular flat plate shape, a high frequency power supply for supplying a high frequency electric current to the heating coil, a heating control part for controlling output of the high frequency power supply on the basis of output of the thermal element, a plate shaped high permeability magnetic material arranged beneath the heating coil, and a cylindrical high permeability magnetic material arranged on an inner side of the heating coil for forming a magnetic circuit in cooperation with the plate shaped high permeability magnetic material. The heat receiving part formed of non-conductive material is provided with a recessed part for covering the thermal element and the joining part, and the heat receiving part, and the thermal element and the joining part covered by the heat receiving part are arranged on an inner side of the cylindrical high permeability magnetic material.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an induction heating cooker having a function of detecting the temperature of an object to be heated.

[0002]

2. Description of the Related Art FIG. 11 shows, for example, JP-A-6-302378.
It is a schematic sectional drawing of the conventional induction heating cooking appliance disclosed by the publication. In the figure, 1 is a pan to be heated, 2 is a top plate on which the pan 1 is placed, 3 is a heating coil wound in a flat plate annular shape below the top plate 2, and 4 is a top plate 2. It is a temperature sensor attached to the back side.

The temperature sensor 4 is composed of a heat sensitive plate 4a which is a heat receiving portion and a heat sensitive element 4b such as a thermistor. The heat sensitive plate 4a is formed of a non-conductive material so as not to be inductively heated by the magnetic flux generated by the high frequency current flowing through the heating coil 3, and transmits the temperature of the top plate 2 to the heat sensitive element 4b.
Is in close contact with.

Further, the temperature sensor 4 is heated so that the temperature of the pot 1 can be detected even if the placement position of the pot 1 on the top plate 2 is slightly displaced or the outer diameter of the pot 1 is small. Coil 3
It is located in the center of. The temperature detected by the heat sensitive element 4b is input to a control unit (not shown) to control the high frequency current flowing through the heating coil 3.

Since the Dumet wire used as the lead wire of the thermistor is a ferromagnetic material made of an alloy of iron and nickel, it is induction-heated by magnetic flux. Further, the central portion of the heating coil 3 to which the temperature sensor 4 is attached is
This is the location where the generated magnetic flux concentrates. Therefore, when the output is high, the magnetic flux density at the position of the temperature sensor 4 becomes high,
The heat-sensitive element 4b and the lead wire of the temperature sensor 4 are induction-heated, causing an error in the detected temperature. In particular, the error generated in the portion where the thermistor and the Dumet wire are joined is large, which has an adverse effect on the detected temperature.

This point will be described based on experimental data. FIG. 12 shows that the pan 1 containing 1.5 liters of water is placed on the induction heating cooker having the above-mentioned configuration, and 2.5 kW.
3 shows the temporal change of the pot bottom temperature and the detected temperature when the boiling point was boiled with the heating output of. Here, the pot bottom temperature is data obtained by bringing a thermocouple into close contact with the bottom face of the pot that is in contact with water, and shows a true value. Comparing the temperatures of both during boiling, the temperature detected through the top plate 2 is higher than the actual pot bottom temperature by about 50 ° C., and it can be seen that a large error occurs due to induction heating.

[0007]

As described above, in the conventional induction heating cooker, the temperature sensor is arranged at the center of the heating coil where the magnetic flux is most concentrated. However, there is a problem in that a large error occurs in the detected temperature of the object to be heated due to induction heating.

The present invention has been made to solve the above problems, and provides an induction heating cooker including a temperature sensor capable of accurately detecting the temperature of an object to be heated while suppressing the influence of induction heating on the temperature sensor itself. The purpose is to get.

[0009]

An induction heating cooker according to the present invention controls the temperature of a top plate through a top plate on which an object to be heated such as a pot is placed, and a heat receiving portion closely attached to the back surface of the top plate. A heat-sensitive element to detect, a lead connected to the heat-sensitive element via a joint, a heating coil wound around a flat plate arranged below the top plate, and a high-frequency power supply that supplies a high-frequency current to the heating coil. A heating control unit that controls the output of the high-frequency power source based on the output of the heat-sensitive element, a plate-shaped high-permeability magnetic material disposed below the heating coil, and a plate-shaped high-permeability magnetic material disposed inside the heating coil. A heat-receiving part is formed of a non-conductive material, and a heat-receiving part and a heat-receiving part are provided. The heat-sensitive element and the joint part covered by are arranged inside the cylindrical high-permeability magnetic material. It is intended.

In addition, a cylindrical conductive material is arranged inside the cylindrical high-permeability magnetic material, and a heat receiving portion, a heat sensitive element and a lead portion are arranged inside the cylindrical conductive material.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1. FIG. 1 is a sectional view of a heating coil central portion of an induction heating cooker according to a first embodiment of the present invention. The same or corresponding parts as those of the conventional example are designated by the same reference numerals, and different points will be described. In the figure, 5 is a flat plate-shaped lower surface ferrite made of a high-permeability magnetic material arranged below the heating coil 3, 6 is a tubular ferrite arranged inside the heating coil 3, and 7 is the heating coil 3 mounted thereon. The heating coil base, 44 is a ceramic cap thermistor, and 8 is a supporting member for the ceramic cap thermistor 44. The lower surface ferrite 5, the tubular ferrite 6 and the supporting member 8 are previously integrated with the heating coil. The ceramic cap thermistor 44 detects the temperature of the object to be heated placed on the top plate 2, and maintains a gap between the ceramic cap thermistor 44 and the inner wall of the tubular ferrite 6 by means of the support member 8 so that the back face of the top plate 2 can be detected. It is arranged so as to be in close contact with. Again 9
Is a high frequency power supply for supplying a high frequency current to the heating coil 3, 1
Reference numeral 0 denotes a heating control unit that reads the resistance value of the ceramic cap thermistor 44 to detect the pot temperature and controls the high frequency power supply 9.

FIG. 2 shows a ceramic cap thermistor 44.
It is a structural drawing of a ceramic cap thermistor 44
Is composed of a ceramic cap 44a which is non-conductive and functions as the heat sensitive plate 4a, a heat sensitive element 44b, and a dumet wire lead portion 44c. The ceramic cap thermistor 44 has a flat surface that contacts the back surface of the top plate 2 and a recess that covers at least the joint between the heat sensitive element 44b and the dumet wire lead portion 44c. FIG. 3 is a layout drawing showing the layout of the heating coil 3, the lower surface ferrite 5, the tubular ferrite 6, and the ceramic cap thermistor 44. The plate-shaped lower surface ferrite 5 is arranged radially around the tubular ferrite 6 inside the heating coil 3. Further, FIG. 4 is an explanatory diagram showing the direction of the magnetic field and the magnetic flux density generated around the heating coil 3 by a broken line and the thickness of the arrow, respectively, and the arrow A shows the direction at the moment when the current flowing through the heating coil 3 is present. There is.

The operation will be described with reference to FIGS. When the target temperature is set from the operation unit (not shown), the heating control unit 10 detects the temperature of the pan 1 from the resistance value of the ceramic cap thermistor 44, and heats the heating unit so that the detected temperature matches the target temperature. A high frequency power supply 9 that supplies a high frequency current to the coil 3 is controlled.

Since a magnetic field is generated in the direction of clockwise rotation with respect to the direction of the current, as shown in FIG. 4, the magnetic flux in the vertical direction at the central portion of the heating coil 3 is on both the left and right sides 3a of the heating coil 3.
It becomes the same with respect to the current flowing through 3b, and becomes larger by being added. The tubular ferrite 6 and the lower surface ferrite 5 cooperate to form a magnetic path. By this magnetic path, most of the magnetic flux passes through the ferrite portion of the tubular ferrite 6 made of a high-permeability magnetic material arranged in the central portion. As a result, the magnetic flux passing through the inside of the tubular ferrite 6 has a low level. In addition, in the ceramic cap thermistor 44 disposed inside the tubular ferrite 6, the ceramic cap 44a which functions as a heat receiving portion and has non-conductivity has a shape that covers the entire heat sensitive element 44b. The eddy current due to the magnetic flux is not generated, and the magnetic flux passing through the heat sensitive element 44b is further weakened. In particular, the ceramic cap 44a includes the heat sensitive element 44b and the dumet wire lead portion 4
Since it covers up to the part where 4c is joined,
The magnetic flux passing through this portion becomes small, and the error is greatly reduced.

This point will be described based on experimental data. FIG. 5 shows an induction heating cooker having the above-mentioned configuration.
Under the same conditions as in FIG. 12 (1.5 liters of water is boiled with a heating output of 2.5 kW), temporal changes in the pot bottom temperature and the detected temperature are measured. Comparing the two temperatures during boiling, it can be seen that the temperature detected through the top plate 2 is higher than the actual pot bottom temperature by about 10 ° C. This value is much smaller than the difference of 50 ° C. in the conventional example, and it can be seen that the influence of induction heating is reduced.

In the present embodiment, the ceramic cap thermistor 44 and the inner wall of the tubular ferrite 6 are
I explained the structure that is held while maintaining a gap,
The same applies to the structure in which the ceramic cap thermistor 44 is held by the heat insulating member 11 as shown in FIG.

Embodiment 2. FIG. 7 is a cross-sectional view of the central portion of the heating coil of the induction heating cooker according to the second embodiment. The same or corresponding parts as those of the conventional example or the first embodiment are designated by the same reference numerals, and the description thereof will be omitted. In the figure, reference numeral 12 denotes a tubular conductive material such as an aluminum tube, which is arranged so as to be located between the tubular ferrite 6 and the support member 8. The ceramic cap thermistor 44 is held by the support member 8 so as to be in close contact with the back surface of the top plate 2 while maintaining a gap between the ceramic cap thermistor 44 and the inner wall of the tubular conductive material 12. The tubular conductive material covers the entire side surface of the temperature sensor including the Dumet wire lead portion 44c. Further, FIG. 8 is an explanatory diagram showing the direction of the magnetic field and the magnetic flux density generated around the heating coil 3 by the broken line and the thickness of the arrow, respectively. In the figure, arrow B is arrow A
The same as above, it represents the direction of the current at a certain moment.

The operation will be described with reference to FIGS. As in the first embodiment, most of the magnetic flux generated by the high-frequency current supplied to the heating coil 3 passes through the tubular ferrite 6 inside the heating coil 3, and a small amount leaks to the inside of the tubular ferrite 6. This leakage magnetic flux does not reach the inside of the tubular conductive material 12 due to the electromagnetic shielding effect of the tubular conductive material 12.
Therefore, the thermosensitive element 44b including the dumet wire lead portion 44c is completely unaffected by the induction heating due to the high frequency current flowing through the heating coil 3.

This point will be described based on experimental data. FIG. 9 shows an induction heating cooker having the above configuration,
Under the same conditions as in FIG. 12 (1.5 liters of water is boiled with a heating output of 2.5 kW), temporal changes in the pot bottom temperature and the detected temperature are measured. Comparing the pan bottom temperature and the detected temperature at the time of boiling, both are in good agreement and it is found that there is almost no effect of induction heating.

The tubular conductive material 12 may be made of a non-magnetic high conductivity material other than an aluminum tube or a copper tube. Further, in order to suppress the magnetic flux penetrating into the position of the heat sensitive element 4b, the tubular conductive material 12 may have a shape in which the diameter is narrowed from the middle as shown in FIGS. 10 (a) and 10 (b). Further, in order to enhance the heat dissipation effect of the tubular conductive material 12, a part may be blown with cooling air. Furthermore, in order to efficiently dissipate the heat generated in the tubular ferrite 6, the tubular conductive material 12 may be brought into contact with the tubular ferrite 6 and used as a radiating fin.

[0021]

The induction heating cooker of the present invention is constructed as described above and has the following effects.

Inside the tubular high permeability magnetic material, a heat-sensitive element for detecting the temperature of the top plate through a heat receiving portion closely attached to the back surface of the top plate is arranged inside a heating coil wound in a flat plate annular shape. In addition, since the heat receiving portion is formed as a non-conductive material so as to cover up to the joint portion of the heat sensitive element and the lead portion, eddy current does not flow in the heat receiving portion, and induction overheating in the joint portion is also reduced. It is possible to obtain an induction heating cooker that can detect the temperature of an object to be heated with high accuracy.

Further, a tubular conductive material is provided inside the tubular high-permeability magnetic material arranged inside the heating coil wound in the form of a flat plate, and a temperature sensor composed of a heat receiving portion and a heat sensitive element is provided inside the tubular conductive material. Since the entire side surface including the temperature sensor and its leads is covered with a cylindrical conductive material, the heat-sensitive element is not affected by the high-frequency current flowing through the heating coil, and the temperature of the heated object is highly accurate. It is possible to obtain an induction heating cooker that can be detected at.

[Brief description of drawings]

FIG. 1 is a sectional view of a central portion of a heating coil unit of an induction heating cooker according to a first embodiment of the present invention.

FIG. 2 is a structural diagram of a ceramic cap thermistor used in the induction heating cooker according to the first embodiment of the present invention.

FIG. 3 is an arrangement diagram showing an arrangement relationship of a heating coil, a ferrite, and a temperature sensor of the induction heating cooker according to the first embodiment of the present invention.

FIG. 4 is a diagram illustrating a state of magnetic flux generated around the heating coil of the induction heating cooker according to the first embodiment of the present invention.

[Fig. 5] Fig. 5 is a diagram showing temporal changes in a pot bottom temperature and a detected temperature when a pot containing water is heated in the induction heating cooker according to the first embodiment of the present invention.

FIG. 6 is a cross-sectional view showing another holding structure of the ceramic cap thermistor used in the induction heating cooker according to the first embodiment of the present invention.

FIG. 7 is a sectional view of an induction heating cooker according to a second embodiment of the present invention.

FIG. 8 is a diagram showing a magnetic flux state generated around a heating coil of the induction heating cooker according to the second embodiment of the present invention.

[Fig. 9] Fig. 9 is a diagram showing a temporal change of a pot bottom temperature and a detected temperature when a pot containing water is placed on the induction heating cooker according to the second embodiment of the present invention and heated.

FIG. 10 is a diagram showing another example of the shape of a tubular conductive material used in the induction heating cooker according to the second embodiment of the present invention.

FIG. 11 is a schematic sectional view of a conventional induction heating cooker.

FIG. 12 is a view showing a temporal change of a pot bottom temperature and a detected temperature when a pot containing water is placed on a conventional induction heating cooker and heated.

[Explanation of symbols]

1 pan, 2 top plate, 3 heating coil, 4 temperature sensor,
4a Heat-sensitive plate, 4b Heat-sensitive element, 4c Dumet wire lead part, 44 Ceramic cap thermistor, 44a
Ceramic cap, 44b Thermal element, 44c Dumet wire lead part, 5 Lower surface ferrite, 6 Cylindrical ferrite, 7 Heating coil base, 8 Supporting member, 9 High frequency power supply, 10 Heating control part, 11 Insulating material, 12 Tubular conductive material, 12b Tubular conductive material, 12c tubular conductive material

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takashi Sato             1728 Omaeda, Hanazono-cho, Osato-gun, Saitama 1728               Within Mitsubishi Electric Home Equipment Co., Ltd. (72) Inventor Koichi Kinoshita             1728 Omaeda, Hanazono-cho, Osato-gun, Saitama 1728               Within Mitsubishi Electric Home Equipment Co., Ltd. F term (reference) 3K051 AB02 AB04 AC33 AD04 CD42                       CD44

Claims (2)

[Claims] 1. A top plate on which an object to be heated such as a pan is placed, a heat-sensitive element for detecting the temperature of the top plate via a heat-receiving portion closely attached to the back surface of the top plate, and a joint portion to the heat-sensitive element. A lead portion connected through the heating plate, a heating coil wound in a flat plate annular shape below the top plate, a high frequency power source for supplying a high frequency current to the heating coil, and an output of the heat sensitive element. And a heating control unit for controlling the output of the high frequency power source, a plate-shaped high-permeability magnetic material arranged below the heating coil, and a plate-shaped high-permeability magnetic material arranged inside the heating coil. A cylindrical high-permeability magnetic material that cooperates to form a magnetic path, the heat receiving portion is formed of a non-conductive material, and has a recessed portion that covers the heat sensitive element and the joint portion. The heat-sensitive element and the joint portion covered by the magnet are arranged inside the cylindrical high-permeability magnetic material. An induction heating cooker characterized by being configured as described above. 2. A tubular conductive material is disposed inside the tubular high-permeability magnetic material, and the heat receiving portion, the thermosensitive element, and the lead portion are disposed inside the tubular conductive material. The induction heating cooker according to claim 1, wherein: