JP4863862B2 - Induction heating cooker - Google Patents

Description

  The present invention relates to an induction heating cooker having a plurality of heating coils.

  The conventional induction heating cooker has a heating coil divided into a plurality of inside and outside, a heating coil energization control means for controlling the energization state of the heating coil for each division unit, and a small pan detection means for detecting the size of the pan. When the small pan is detected by the small pan detecting means, there is one that reduces the leakage of magnetic flux by stopping the energization to the outer heating coil and energizing only the inner heating coil (for example, see Patent Document 1). .

Japanese Patent Laid-Open No. 11-214138 (first page, FIG. 1)

In the conventional induction heating cooker described in Patent Document 1, when the small pan is detected by the small pan detection means, the leakage magnetic flux is reduced by stopping the energization of the outer heating coil and energizing only the inner heating coil. However, since the magnetic field generated by the heating coil current changes by switching the energization state to the plurality of heating coils, the state of influence of induction heating on the heat-sensitive element arrangement portion that detects the pan temperature is Since it changes, there is a problem that accurate temperature detection cannot be performed.
The present invention was made to solve the above-described problems, and has a plurality of heating coils inside and outside, and even when the energized state of the heating coils is switched, there is little leakage magnetic flux even in a small-diameter pan, An object of the present invention is to obtain an induction heating cooker capable of accurate temperature detection.

An induction heating cooker according to the present invention includes a small-diameter heating coil having a small outer diameter and a gap in the middle, an outer heating coil disposed on the outer periphery of the small-diameter heating coil, and having the same winding direction as the small-diameter heating coil, First temperature detecting means using at least one heat sensitive element disposed in the gap of the small diameter heating coil, and at least one second heat sensitive element disposed between the small diameter heating coil and the external heating coil. Second temperature detection means using an inverter, an inverter circuit for supplying a high-frequency current to the small diameter heating coil and the external heating coil, and a heating control means for driving and controlling the inverter circuit, and the heating control means energizes only the small diameter heating coil. and a operation mode to energize control both the operation mode and the small-diameter heating coil and an outer heating coil for controlling, only the operation mode in the first temperature detecting means is energized only small heating coil Performs heating control based on the detection value, the operation mode for power control on both the small-diameter heating coil and an outer heating coil performs heating control based on the detected value of only the second temperature detection means, energized only small heating coil Compared with the operation mode to be controlled, in the operation mode in which the energization control is performed for both the small-diameter heating coil and the external heating coil, the conversion temperature for the detection values of the first temperature detection means and the second temperature detection means is set lower. Temperature characteristics are used .

In the induction heating cooker of the present invention, a small-diameter heating coil having a small outer diameter and a gap in the middle, an outer heating coil disposed on the outer periphery of the small-diameter heating coil, and having the same winding direction as the small-diameter heating coil, and a small-diameter First temperature detecting means using at least one heat sensitive element disposed in a gap of the heating coil, and at least one second heat sensitive element disposed between the small diameter heating coil and the outer heating coil. A second temperature detecting means used; an inverter circuit for supplying a high-frequency current to the small-diameter heating coil and the external heating coil; and a heating control means for driving and controlling the inverter circuit. The heating control means controls energization only for the small-diameter heating coil. operating mode and has an operation mode for energization control both of the small-diameter heating coil and the outer heating coil, only the operation mode in the first temperature detecting means is energized only small heating coil Performs heating control based on the detected value, the operation mode for power control on both the small-diameter heating coil and an outer heating coil performs heating control based on the detected value of only the second temperature detection means, energized only small heating coil Compared with the operation mode to be controlled, in the operation mode in which the energization control is performed for both the small-diameter heating coil and the external heating coil, the conversion temperature for the detection values of the first temperature detection means and the second temperature detection means is set lower. When the heating operation is performed by energizing only the small diameter heating coil, the magnetic field generated by the current flowing in the winding inside the gap portion of the small diameter heating coil and the winding outside the gap portion are used. Since the magnetic field generated by the current cancels out in the gap where the thermal element is disposed and no strong magnetic field is generated, the thermal element of the first temperature detecting means is difficult to be induction-heated and accurate. It is possible to degree detection.
In addition, when a heating operation is performed by energizing both the small diameter heating coil and the external heating coil, the magnetic field generated by the current flowing in the small diameter heating coil close to the thermal element is a magnetic field generated by the current flowing in the winding inside the thermal element. The magnetic field generated by the current flowing in the outer winding of the thermal element cancels each other and does not become strong, and the magnetic field due to the current flowing in the outer heating coil is also located at a certain distance from the thermal element. Since the heat sensitive element is not strong at the position where the heat sensitive element is disposed, there is an effect that the heat sensitive element is not so much induction-heated and accurate temperature detection is possible.

Embodiment 1 FIG.
1 is a circuit configuration diagram of an induction heating cooker according to Embodiment 1 of the present invention, FIG. 2 is a plan view showing a heating coil unit of the induction heating cooker, and FIG. 3 is a pan temperature detection of the induction heating cooker. FIG. 4 is a graph showing an example of temperature conversion characteristics of the pan temperature detection circuit, and FIG. 5 is a position of the heat-sensitive element of the induction heating cooker, showing the magnetic field generated by the current flowing through each part of the heating coil. It is explanatory drawing which shows the relationship of direction.
In FIG. 1, the induction heating cooker according to the first embodiment of the present invention is connected to an AC power source 1, and power supplied from the AC power source 1 is converted into DC power by a DC power source circuit 2. The DC power supply circuit 2 includes a rectifier diode bridge 3 that rectifies AC power, a reactor 4, and a smoothing capacitor 5.
The input power input to the DC power supply circuit 2 is detected by the input current detection means 6 and the input voltage detection means 7. The power converted into DC power by the DC power supply circuit 2 is supplied to the inverter circuit 8.

The inverter circuit 8 is two switching elements connected in series between the positive and negative buses of the DC power supply circuit 2 (hereinafter, the positive bus side switching element is referred to as an upper switch 9 and the negative bus side switching element is referred to as a lower switch 10). The diodes are connected to the switching elements in antiparallel (the positive bus side antiparallel diode is referred to as the upper diode 11 and the negative bus side antiparallel diode is referred to as the lower diode 12).
The upper switch 9 and the lower switch 10 are alternately driven by a signal from the inverter drive circuit 13, and a high frequency voltage is generated at a connection point between the upper switch 9 and the lower switch 10 that is an output point of the inverter circuit 8.
A snubber capacitor 14 and a heating coil 15 for reducing switching loss are connected to the inverter output point.

As shown in FIG. 2, the heating coil 15 includes a small-diameter heating coil 16 and an outer heating coil 17 disposed with a gap around the outer periphery thereof.
The small-diameter heating coil 16 includes an inner small-diameter inner heating coil portion 16a and an outer small-diameter outer heating coil portion 16b. A gap between the small-diameter inner heating coil portion 16a and the small-diameter outer heating coil portion 16b is provided at the bottom of the pan. Two thermosensitive elements 18 such as thermistors for detecting the temperature are arranged. These two thermosensitive elements 18 are in close contact with the back surface of a top plate (not shown) on which a heated object such as a pan is placed. The outer heating coil 17 is disposed on the outer periphery of the small diameter heating coil 16 with a gap.

When heating the large-diameter pan, current is supplied to both the small-diameter heating coil 16 and the external heating coil 17, and when heating the small-diameter pan, only the small-diameter heating coil 16 is energized. Switching between the heating of the large-diameter pan and the heating of the small-diameter pan is performed by controlling the relay 19 with the relay driving means 20.
That is, the output of the inverter circuit 8 is connected to one end of the small diameter heating coil 16, and when only the small diameter heating coil is energized, the other end of the small diameter heating coil 16 is connected to the small diameter coil resonance capacitor 21 by the relay 19.
When energizing both the small-diameter heating coil 16 and the external heating coil 17, the other end of the small-diameter heating coil 16 is connected to the external heating coil 17 by a relay 19, and both the small-diameter heating coil 16 and the external heating coil 17 are connected. The coil is connected to the negative bus via a coil resonance capacitor 22 constituting a resonance circuit.

The current flowing through the heating coil 15 is detected by the output current detection means 23, and the temperature of the pan bottom to be heated is detected by the pan temperature detection means 24 using the thermal element 18.
The control unit 25 controls the entire induction heating cooker, and in response to an input instruction from the operation input unit 26, the input current detection unit 6, the input voltage detection unit 7, the output current detection unit 23, and the pan temperature detection unit 24. While taking the detection value, the inverter drive circuit 13 is controlled to adjust the heating output.
The temperature data detected by the pan temperature detecting means 24 is used for temperature control such as deep-fried food cooking and control for preventing overheating of the object to be heated. Note that the inverter drive signal output from the control unit 25 to the inverter drive circuit 13 is a heating composed of the small-diameter heating coil resonance circuit 27 including the small-diameter heating coil 16 and the small-diameter coil resonance capacitor 21 and the small-diameter heating coil 16 and the external heating coil 16. As a drive frequency higher than the resonance frequency of both heating coil resonance circuits 28 comprising the coil 15 and both coil resonance capacitors 22, the current flowing in the resonance circuit is controlled to flow in a phase lagging from the voltage applied to the resonance circuit.

FIG. 2 is a plan view of the heating coil unit of the induction heating cooker according to the first embodiment, and shows the positional relationship between the small-diameter heating coil 16 and the external heating coil 17 and the thermal element 18.
As shown in FIG. 2, the small-diameter heating coil 16 and the external heating coil 17 constituting the heating coil 15 are arranged on a coil base 29 with a substantially concentric interval. On the back surface of the coil base 29, six plate-like ferrites 30 are arranged radially so as to magnetically shield the lower surfaces of the small diameter heating coil 16 and the outer heating coil 17.
The small-diameter heating coil 16 includes an inner small-diameter inner heating coil portion 16a and an outer small-diameter outer heating coil portion 16b, and is a gap between the coil portions 16a and 16b and between the plate-like ferrite 30. Two thermosensitive elements 18 for detecting the temperature of are provided.
Since the magnetic flux generated by the current flowing through the heating coil 15 is concentrated on each ferrite 30 portion, the magnetic flux density is lower between the ferrites where the thermal elements 18 are located. It is difficult to be configured.

FIG. 3 is a block diagram of the circuit of the pan temperature detecting means 24 using the thermosensitive element 18, and FIG. 4 is a temperature conversion characteristic graph showing the relationship between the voltage value and temperature detected by the circuit of the pan temperature detecting means 24. .
As shown in FIG. 3, the pan temperature detecting means 24 includes a voltage dividing resistor 31 connected in series with the thermal element 18 connected to the positive side of the control DC power supply, and a noise removing device connected in parallel with the voltage dividing resistor 31. Capacitor 32 and an A / D converter 33 for taking in the divided voltage of the DC power supply for controlling the voltage dividing resistor 31.
The pan temperature detecting means 24 obtains the detected temperature using the temperature conversion characteristic graph of FIG. Since the thermal element 18 has a characteristic that the resistance value decreases as the temperature rises, the higher the detection voltage, the higher the temperature as shown in the graph of FIG.

FIG. 5 is a diagram showing the direction of the magnetic field generated by the current flowing in the heating coil 15, and shows the magnetic field state at the position where the thermal element 18 is disposed, by the thickness of the line and the arrow. Yes.
FIG. 5A shows a case where a high-frequency current is applied only to the small-diameter heating coil 16, and the magnetic field generated by the current flowing in the small-diameter inner heating coil portion 16a is indicated by a broken line 34 and flows to the small-diameter outer heating coil portion 16b. A magnetic field generated by the current is indicated by a broken line 35.
In the central portion (A) of the heating coil 15 and the inter-coil portion (B) between the small diameter heating coil 16 and the outer heating coil 17, a magnetic field generated by the current flowing in the small diameter inner heating coil portion 16a, and the small diameter outer heating coil portion. Since the magnetic field generated by the current flowing through 16b overlaps and strengthens in the same direction, if the thermal element 18 is disposed at this position, induction heating is likely to occur, whereas the gap between the small-diameter inner heating coil portion 16a and the small-diameter outer heating coil portion 16b. In the part (C), the thermistors 18 are less likely to be induction-heated because they reverse in the opposite directions and weaken.
In addition, in an induction heating cooker having a small diameter heating coil 16 and an external heating coil 17, when energizing only the small diameter heating coil 16 is generally performed when the heating pan is small, the small diameter heating coil 16 and the external heating coil are heated. There are many cases where the inter-coil portion (B) of the coil 17 is located away from the pan bottom and the pan bottom temperature cannot be detected.
Therefore, an accurate pan is provided by arranging the thermal element 18 in the space (C) between the small-diameter inner heating coil portion 16a and the small-diameter outer heating coil portion 16b, which does not easily cause induction heating to the thermal element 18 and is difficult to be removed from the pan bottom position. Temperature detection is possible.

FIG. 5 (b) shows the state of the magnetic field when a high-frequency current is passed through both the small diameter heating coil 16 and the external heating coil 17, and a magnetic field 34 (indicated by a broken line) generated by the current flowing through the small diameter inner heating coil portion 16a. In addition to the magnetic field 35 (indicated by a broken line) generated by the current flowing in the small-diameter outer heating coil portion 16b, the magnetic field 36 generated by the current flowing in the outer heating coil 17 is indicated by a dotted line.
In this case, the magnetic field due to the current flowing through the small-diameter heating coil 16 close to the position of the thermal element 18 includes the magnetic field due to the current flowing through the small-diameter inner heating coil portion 16a inside the thermal element 18 and the current flowing through the outer small-diameter outer heating coil portion 16b. The magnetic fields generated by the currents cancel each other and the magnetic field 36 generated by the current flowing through the external heating coil 17 is superimposed. However, since there is a space from the external heating coil 17 to the thermal element 18, the thermal element 18 is not strongly induction-heated. .

  As described above, according to the induction heating cooker of the first embodiment, both the small-diameter heating coil 16 and the small-diameter heating coil 16 and the external heating coil 17 are both energized. The thermal element 18 is arranged in the space (C) between the small-diameter inner heating coil part 16a and the small-diameter outer heating coil part 16b, which is a position where the thermal element 18 for detecting temperature is difficult to be induction-heated, and the heating coil 15 Since the position is close to the center of the pot, it is difficult to come off from the bottom of the pan, which is an object to be heated, placed on the heating coil 15, and the temperature of the pan can be accurately detected regardless of the energized state of the heating coil 15.

In addition, an induced eddy current flows in the pan bottom facing the heating coil 15 in the pan that is an object to be heated placed on the heating coil 15 so as to cancel the change in the magnetic field caused by the high-frequency current flowing in the heating coil 15. When the entire heating coil 15 is energized, the pan bottom facing the small-diameter inner heating coil portion 16a and the small-diameter outer heating coil portion 16b and the outer heating coil 17 is heated. Since it is divided into portions and widely distributed, uneven heating is suppressed.
Even when only the small-diameter heating coil 16 is energized, the pot bottom portion facing the small-diameter inner heating coil portion 16a and the small-diameter outer heating coil portion 16b generates heat, so the heating portion is divided and spreads, thereby reducing uneven heating. can do.

Embodiment 2. FIG.
FIG. 6 is a graph showing an example of temperature conversion characteristics of the pan temperature detection circuit of the induction heating cooker according to Embodiment 2 of the present invention.
As described in the first embodiment, the magnetic field at the position where the thermal element 18 is disposed is when only the small diameter heating coil 16 is energized and when both the small diameter heating coil 16 and the external heating coil 17 are energized. Therefore, as shown in FIG. 6, the thermal element 18 of the pan temperature detection circuit 24 has two temperature conversion characteristics with different detection voltages when the temperature is constant.
Therefore, when only the small-diameter heating coil 16 is energized and the magnetic field is weak, the first temperature conversion characteristic 37 shown in FIG. 6 is used, and both the small-diameter heating coil 16 and the external heating coil 17 are energized to generate the magnetic field. In the case of a strong state, the second temperature conversion characteristic 38 shown in FIG. 6 is used.

  In the second embodiment, when only the small diameter heating coil 16 is energized and the magnetic field is weak, the first temperature conversion characteristic 37 having a low detection voltage when the temperature is constant is used, and the small diameter heating coil 16 and When a current is strong and both the coils of the outer heating coil 17 are in a strong magnetic field, the heating coil is obtained by using the second temperature conversion characteristic 38 whose detected voltage is higher than the first temperature conversion characteristic 37 when the temperature is constant. By changing the superposition state of the magnetic field at the position where the thermal element 18 is arranged depending on the energization state of the heating coil, the temperature conversion characteristic according to the energization state of the heating coil is used to compensate for the difference in induction heating and more accurately detect the pan temperature. Is to do.

Embodiment 3 FIG.
FIG. 7 is a circuit configuration diagram of an induction heating cooker according to Embodiment 3 of the present invention, and FIG. 8 is a plan view showing a heating coil unit of the induction heating cooker.
7, in the third embodiment of the present invention, the same or corresponding parts as those in FIG. 1 of the first embodiment are denoted by the same reference numerals, and the description of the overlapping configuration is omitted.
In FIG. 7, the power supplied from the AC power supply 1 is converted into DC power by the DC power supply circuit 2 and supplied to the inverter circuit 8. The inverter circuit 8 has three sets of arms (hereinafter, three sets) formed by two switching elements connected in series between the positive and negative buses of the DC power supply circuit 2 and diodes connected in reverse parallel to the switching elements. These arms are referred to as a common arm 39, a small-diameter heating coil arm 40, and an external heating coil arm 41).

The common arm 39 includes an upper switch 42, a lower switch 43, an upper diode 44 connected in antiparallel with the upper switch 42, and a lower diode 45 connected in antiparallel with the lower switch 43.
The small-diameter heating coil arm 40 includes an upper switch 46, a lower switch 47, an upper diode 48 connected in antiparallel with the upper switch 46, and a lower diode 49 connected in antiparallel with the lower switch 47. ing.
The outer heating coil arm 41 includes an upper switch 50, a lower switch 51, an upper diode 52 connected in antiparallel with the upper switch 50, and a lower diode 53 connected in antiparallel with the lower switch 51. ing.

Between the output point of the common arm 39 and the output point of the small diameter heating coil arm 40, a small diameter coil load circuit 27 comprising a series circuit of the small diameter heating coil 16 and the small diameter coil resonance capacitor 21 is connected. The external heating coil load circuit 55 comprising a series circuit of the external heating coil 17 and the external coil resonance capacitor 54 is connected between the output points of the arm 41 for the external heating coil.
Snubber capacitors 56, 57, and 58 are connected to the output point of the common arm 39, the output point of the small-diameter heating coil arm 40, and the output point of the external heating coil arm 41, respectively.

  The upper switch 42 and the lower switch 43 constituting the common arm 39 are ON / OFF driven by a drive signal output from the common arm drive circuit 59, and the upper switch 46 and the lower switch 47 constituting the small diameter heating coil arm 40 are small diameter coils. ON / OFF drive is performed by a drive signal output from the arm drive circuit 60, and the upper switch 50 and the lower switch 51 constituting the outer heating coil arm 41 are ON / OFF driven by a drive signal output from the outer coil arm drive circuit 61. The

The common arm drive circuit 59 turns on / off alternately such that the lower switch 43 is turned off while the upper switch 42 of the common arm 39 is turned on, and the upper switch 42 is turned off while the lower switch 43 is turned on. The drive signal which outputs is output.
Similarly, the small-diameter coil arm drive circuit 60 outputs a drive signal for alternately turning on and off the upper switch 46 and the lower switch 47 of the small-diameter heating coil arm 40.
Further, the external arm drive circuit 61 similarly outputs a drive signal for alternately turning on and off the upper switch 50 and the lower switch 51 of the arm 41 for the external heating coil.
Note that the snubber capacitors 56, 57, and 58 respectively delay the output voltage fluctuation when the switching element is turned off in the common arm 39, the small-diameter heating coil arm 40, and the outer heating coil arm 41 to reduce the turn-off loss of the switching element. Is for.

The heating coil 15 according to the third embodiment includes a small-diameter heating coil 16 and an outer heating coil 17 disposed with a gap on the outer periphery thereof.
As shown in FIG. 8, the small-diameter heating coil 16 is composed of a small-diameter inner heating coil portion 16a wound around the center portion and a small-diameter outer heating coil portion 16b wound around the outer peripheral portion with a gap. In addition, two first thermal elements 18a are arranged in the gap between them.
In addition, an outer heating coil 17 is disposed on the outer periphery of the small diameter heating coil 16 at an interval, and two second thermal elements 18 b are disposed between the small diameter heating coil 16 and the outer heating coil 17. . And these 1st and 2nd thermal elements 18a and 18b are arrange | positioned on the straight line.

Further, a small diameter heating coil current detection means 62 and an external heating coil current detection means 63 for detecting a current flowing through the small diameter heating coil 16 and the external heating coil 17 are provided, respectively, so that the magnitude and phase of the current can be detected. .
The control unit 25 controls the entire induction heating cooker, and in response to an input instruction from the operation input unit 26, the input current detection unit 6, the input voltage detection unit 7, the small diameter heating coil current detection unit 62, and the external heating coil current. While taking in the detection value of the detection means 63, the arm drive circuits 59, 60, 61 are controlled to control the heating output.

The small-diameter heating coil 16 and the external heating coil 17 are connected so as to be wound in the same circumferential direction when viewed from the common arm 39, and the small-diameter heating coil 16 and the external heating coil 17 are simultaneously connected to the high-frequency coil. In the case of passing a current, the drive signal of each arm is controlled to flow in the same direction.
Further, the drive signal of each arm has a drive frequency higher than the resonance frequency of the small-diameter heating coil load circuit 27 and the external heating coil load circuit 55, and the current flowing through the load circuit is delayed in phase with respect to the voltage applied to the load circuit. Control to flow at.

FIG. 8 shows the heating coil unit of the induction heating cooker according to the third embodiment, and shows the positional relationship between the small-diameter heating coil 16, the outer heating coil 17, and the first and second thermal elements 18a and 18b.
As shown in FIG. 8, the small-diameter heating coil 16 and the outer heating coil 17 are disposed on the coil base 29 at a substantially concentric interval. The small-diameter heating coil 16 includes a small-diameter inner heating coil portion 16a wound around the central portion thereof, and a small-diameter outer heating coil portion 16b wound around the outer periphery thereof with a gap. Below the heating coil 15, six substantially rectangular plate-like ferrites 30 are arranged radially from the center to the outside of the heating coil 15, and the lower part of the heating coil is magnetically shielded.

Two first heat sensitive elements 18 a are disposed in the space of the small diameter heating coil 16, and a second heat sensitive element 18 b is disposed between the small diameter heating coil 16 and the outer heating coil 17.
The first thermosensitive element 18 a and the second thermosensitive element 18 b are disposed at an intermediate position where the first thermosensitive element 18 a and the second thermosensitive element 18 b do not overlap with the ferrite 30 in the same direction as viewed from the center of the heating coil 15.
Since the magnetic flux generated by the current flowing through the heating coil 15 is concentrated on the ferrite 30 having a low magnetic resistance below the heating coil, the magnetic flux passing through the arrangement positions of the first and second thermal elements 18a and 18b is reduced. The influence of induction heating on the first and second thermal elements 18a and 18b is reduced.

Next, the induction heating control process performed by the control unit 25 of the induction heating cooker according to the third embodiment of the present invention will be described with reference to FIGS.
9 is a flowchart showing the heating control process of the induction heating cooker, FIG. 10 is a waveform diagram of drive signals for energizing the small diameter heating coil and the external heating coil of the induction heating cooker, and FIG. 11 is the induction heating cooking. FIG. 12 is an explanatory diagram showing the relationship of the direction of the magnetic field generated by the current flowing in each part of the heating coil at the position of the heat sensitive element of the induction heating cooker. is there.

As shown in the flowchart of FIG. 9, first, the control unit 25 determines whether or not a heating start instruction is input from the operation input means 26 (step 1). 10 is controlled by the common arm drive circuit 59, the small diameter heating coil arm drive circuit 60, and the external heating coil arm drive circuit 61, with the small diameter heating coil 16 and the external heating coil 17 being output. The heating is started by setting the inner / outer coil mode (step 2).
The AC voltage applied to the small diameter heating coil load circuit 27 or the external heating coil load circuit 55 includes the output terminal voltage of the common arm 39, the output terminal voltage of the small diameter heating coil arm 40, or the output terminal of the external heating coil arm 41. Drive signal to the upper and lower switches 42 and 43 of the common arm 39, the drive signal to the upper and lower switches 46 and 47 of the small diameter heating coil arm 40, or the upper and lower switches 50 of the arm 41 for the external heating coil. The heating output can be controlled by adjusting the phase difference of the drive signal to 51.

Next, temperature detection is performed by the second thermal element 18b disposed between the small diameter heating coil 16 and the outer heating coil 17 (step 3), and it is determined whether the pan bottom is overheated (step 4). .
If it is not overheated, the power of the set thermal power set from the operation input means 26 is compared with the input power obtained using the detected values of the input voltage detection means 7 and the input current detection means 6 (step 5), and the input power is compared. If it is smaller, the phase difference between the common arm driving signal, the small-diameter heating coil arm driving signal, and the outer heating coil arm driving signal is increased (step 6).
If the pan bottom is overheated in Step 4 or if the input power exceeds the set power in Step 5, the common arm drive signal, the arm drive signal for the small diameter heating coil, and the arm drive signal for the external heating coil The phase difference is reduced (step 7).

Next, it is determined whether or not there is a request to switch the heating coil to be energized (step 8). The switching request of the energization heating coil is, for example, when there is an instruction input of a user switching request from the operation input unit 26, or in an imbalance between the small diameter heating coil current detection unit 62 and the external heating coil current detection unit 63 in both coil energization modes. It is assumed that there is a request when is large.
If requested, the drive signal to the arm for the outer heating coil is stopped (switched from the two-coil energization mode to the small-diameter heating coil energization mode. The drive signal waveform as shown in FIG. 11 is used) or restarted (small-diameter heating). The coil energization mode is switched to the both-coil energization mode to obtain a drive signal waveform as shown in FIG. 10), and the energization coil mode is switched (step 9).

Next, it is determined whether or not a heating stop instruction is input from the operation input means 26 (step 10). If there is no input, the energized coil mode is determined (step 11). Returning to the temperature detection process by the second thermal element 18b, in the small diameter heating coil energization mode, the temperature detection process (step 12) by the first thermal element 18a is performed, and the process proceeds to the pan bottom overheating determination process of step 4.
If it is determined in step 10 that there has been an instruction to stop heating, the drive signal to the up / down switch of each arm is stopped to stop the heating operation (step 13), and the input of the instruction to start heating in step 1 is awaited. Return to.

In the third embodiment, when only the small-diameter heating coil 16 is energized, as shown in FIG. 12A, the magnetic field 34 caused by the current flowing in the small-diameter inner heating coil portion 16a and the small-diameter outer heating coil portion 16b flow. The magnetic field 35 caused by the electric current cancels out in a substantially opposite direction in the gap of the small diameter heating coil 16, and the first thermal element 18a is hardly induction-heated, but the second thermal element 18b, which is outside the small diameter heating coil 16, has In the arrangement position, the magnetic field 34b caused by the current flowing through the small-diameter inner heating coil portion 16a and the magnetic field 35 generated by the current flowing through the small-diameter outer heating coil portion 16b are superimposed in substantially the same direction, and the second thermal element 18b is inducted. Influenced by heating.
Therefore, when only the small-diameter heating coil 16 is energized, the temperature by the first thermal element 18a is detected in step 12 shown in FIG. 9, and the effect of induction heating on the thermal element is suppressed to detect the pan temperature. can do.

When both the heating coils of the small diameter heating coil 16 and the external heating coil 17 are energized, as shown in FIG. 12B, the magnetic field generated by the current flowing through the small diameter heating coil 16 and the current flowing through the external heating coil 17 In the gap between the small-diameter heating coil 16 and the outer heating coil 17 and cancel each other out, and the second heat sensitive element 18b raises the pan temperature (top temperature) almost without induction heating. It can be detected accurately.
Therefore, when both the heating coils are energized, the temperature is detected by the second thermal element 18b in step 3 shown in FIG. 9 to suppress the influence of induction heating on the thermistor which is the thermal element, and the energization state of the heating coil 15 It is possible to detect the pot temperature while suppressing the influence of.

  In the third embodiment, when current is supplied to both the small-diameter heating coil 16 and the external heating coil 17, the magnetic fields 34b and 35 generated by the current flowing through the small-diameter heating coil 16 and the current flowing through the external heating coil 17 are used. The temperature detection process is performed using only the second thermal element 18b disposed in the gap between the small-diameter heating coil 16 and the external heating coil 17 that is substantially opposite to the magnetic field 36b generated by However, temperature detection using the first thermal element 18a may be performed in parallel.

Embodiment 4 FIG.
FIG. 13 is a graph showing an example of temperature conversion characteristics of the pan temperature detection circuit of the induction heating cooker according to Embodiment 4 of the present invention, and FIG. 14 is a flowchart showing the heating control process of the induction heating cooker.
The first temperature conversion characteristic 62 in FIG. 13 is obtained when the temperature is obtained from the detected value of the pan temperature detection circuit 24a of the first thermal element 18a when only the small-diameter heating coil 16 is energized, and when the small-diameter heating coil 16 and the external heating are obtained. It is a temperature conversion characteristic used when calculating | requiring temperature from the detected value of the pan temperature detection circuit 24b of the 2nd thermal element 18b when supplying with electricity to both the heating coils of the coil 17. FIG.
The second temperature conversion characteristic 63 is used when the temperature is obtained from the detection value of the pan temperature detection circuit 24a of the first thermal element 18a when both the small-diameter heating coil 16 and the external heating coil 17 are energized. It is a temperature conversion characteristic.
The second temperature conversion characteristic 63 is used in a state where the influence of the magnetic field generated by the current flowing in the heating coil is more likely to occur in the first thermosensitive element 18a than the first temperature conversion characteristic 62 (within a small diameter generated in the direction of canceling each other). In addition to the magnetic field due to the current of the coil portion 16a and the small-diameter outer coil portion 16b, the magnetic field generated by the current flowing through the external heating coil 17 is also superimposed), so that the conversion temperature for the same detection value is set low.

In FIG. 14, the same or corresponding processes as those in the flowchart of FIG.
When both the heating coils of the small diameter heating coil 16 and the external heating coil 17 are energized, the second value at the time of energization of both the small diameter heating coil and the external heating coil in FIG. 13 is detected from the detected value using the first thermal element 18a. The temperature conversion characteristic 63 is used (step 3-1), and the temperature is detected using the first temperature detection characteristic 62 of FIG. 13 from the detection value using the second thermal element 18b (step 3-2). If the detected temperature exceeds a predetermined temperature, it is determined that the temperature is overheated (step 4).

  In the fourth embodiment, only the second thermal element 18b is used by performing temperature detection using the first thermal element 18a even when both the small-diameter heating coil 16 and the outer heating coil 17 are energized. Therefore, it is possible to increase the possibility that temperature detection is performed with a thermal element that has a good thermal coupling with the bottom of the pan, which is the object to be heated, and from the detection value using the first thermal element 18a. Unlike the first temperature conversion characteristic 62 when only the small-diameter heating coil 16 is energized when obtaining the detected temperature, the pan is formed using the second temperature conversion characteristic 63 that also considers the influence of the magnetic field generated by the current flowing through the outer heating coil 17. By obtaining the temperature, it is possible to compensate for the difference in induction heating and to detect the temperature more accurately.

  In Embodiments 2 and 4 described above, the temperature of the bottom of the pan is changed using different temperature conversion characteristics when energizing only the small diameter heating coil 16 and when energizing both the small diameter heating coil 16 and the external heating coil 17. Although the temperature (top plate temperature) is obtained, the detected temperature is obtained by the temperature conversion characteristic in a predetermined coil energized state, and the detected temperature is corrected in the coil energized state other than the predetermined (for example, when the detected temperature is X ° C, The value of a linear function such as aX + b may be used as the detected value).

Embodiment 5 FIG.
In the third embodiment, the first thermal element 18a and the second thermal element 18b are arranged in a straight line. However, as shown in FIG. 15, the first thermal element 18a and the second thermal element 18b are arranged. By arranging the thermal element 18b in a different direction, even if the position of the pan placed on the heating coil is shifted in any direction, up, down, left, or right, any one of the thermal elements may be located below the pan bottom. Becomes high, and stable temperature detection becomes possible.

Embodiment 6 FIG.
In the third and fifth embodiments, the first heat sensitive element 18a provided in the gap of the small diameter heating coil 16 or the second heat sensitive element 18b provided between the small diameter heating coil 16 and the outer heating coil 17 is provided. Although the example provided with two or more was shown, as shown in FIG. 16, it is good also as a structure which aimed at the reduction of cost by arrange | positioning a thermal element one each.

The circuit block diagram of the induction heating cooking appliance which concerns on Embodiment 1 of this invention. The top view which shows the heating coil unit of the induction heating cooking appliance. The block diagram of the pan temperature detection circuit of the induction heating cooking appliance. The graph which shows an example of the temperature conversion characteristic of the same pan temperature detection circuit. Explanatory drawing which shows the relationship of the direction of the magnetic field produced by the electric current which flows into each part of a heating coil in the arrangement position of the thermal element of the induction heating cooking appliance. The graph which shows an example of the temperature conversion characteristic of the pan temperature detection circuit of the induction heating cooking appliance which concerns on Embodiment 2 of this invention. The circuit block diagram of the induction heating cooking appliance which concerns on Embodiment 3 of this invention. The top view which shows the heating coil unit of the induction heating cooking appliance. The flowchart which shows the heating control process of the induction heating cooking appliance. The wave form diagram of the drive signal which supplies with electricity to the small diameter heating coil and external heating coil of the induction heating cooking appliance. The wave form diagram of the drive signal which supplies electricity only to a small diameter heating coil in the induction heating cooking appliance. Explanatory drawing which shows the relationship of the direction of the magnetic field produced by the electric current which flows into each part of a heating coil in the arrangement position of the thermal element of the induction heating cooking appliance. The graph which shows an example of the temperature conversion characteristic of the pan temperature detection circuit of the induction heating cooking appliance which concerns on Embodiment 4 of this invention. The flowchart which shows the heating control process of the induction heating cooking appliance. The top view which shows the heating coil unit of the induction heating cooking appliance which concerns on Embodiment 5 of this invention. The top view which shows the heating coil unit of the induction heating cooking appliance which concerns on Embodiment 6 of this invention.

Explanation of symbols

  1 AC power supply, 2 DC power supply circuit, 8 inverter circuit, 13 inverter drive circuit, 15 heating coil, 16 small diameter heating coil, 17 outer heating coil, 18 thermal element, 19 relay, 20 relay drive means, 24 pan temperature detection means, 25 control part, 26 operation input means.

Claims (2)

A small diameter heating coil having a small outer diameter and a gap in the middle,
An outer heating coil disposed on the outer periphery of the small diameter heating coil and having the same winding direction as the small diameter heating coil;
First temperature detection means using at least one thermal element disposed in the gap of the small diameter heating coil;
Second temperature detection means using at least one second thermal element disposed between the small-diameter heating coil and the outer heating coil;
An inverter circuit for supplying a high-frequency current to the small-diameter heating coil and the external heating coil;
Heating control means for driving and controlling the inverter circuit;
It said heating control means,
An operation mode for controlling energization of only the small diameter heating coil, and an operation mode for controlling energization of both the small diameter heating coil and the external heating coil,
In the operation mode in which energization control is performed only for the small diameter heating coil, heating control is performed based on the detection value of only the first temperature detection means , and in the operation mode in which energization control is performed for both the small diameter heating coil and the outer heating coil, the second Perform heating control based on the detected value of only the temperature detection means,
Compared to the operation mode in which only the small diameter heating coil is energized, the first temperature detection unit and the second temperature detection unit are in the operation mode in which the energization control is performed on both the small diameter heating coil and the external heating coil. An induction heating cooker using a temperature characteristic in which the conversion temperature for the detected value is set low . A plate-like ferrite is arranged radially with respect to the center of the coil below the small-diameter heating coil and the external heating coil, and a thermal element of the temperature detecting means is arranged between the ferrites. The induction heating cooker according to claim 1 .

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