JPH08100923A - Microwave oven - Google Patents

Abstract

PURPOSE: To correct the cooking time of a heater highly accurately in accordance with a detected power supply voltage while detecting the power supply voltage correctly and inform the life of the heater when the heater has arrived at the life thereof. CONSTITUTION: A microwave oven is constituted of capacitors 36, 37, connected between power supply lines 22, 23 and the earth terminal 11 of the main body of the oven, an earth inductor 17, connected between the earth terminal 11 of the main body of the oven and an earth terminal 9 for connecting an external earth and attached to the rear plate of the main body of the oven, and a detecting winding 20, detecting leakage current, which flows through the main body of the oven, and wound around the earth inductor 17. According to this constitution, a power supply voltage is detected and the life of a heater is decided based on the leakage current detected through the detecting winding 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave oven equipped with a heater for performing heater cooking such as oven cooking and grill cooking.

[0002]

2. Description of the Related Art In this type of microwave oven, when the power source voltage changes in level when cooking with a heater, the heating output of the heater fluctuates. In this case, the time for performing the heater cooking is determined according to the weight of the food to be cooked, and the heater cooking time does not change even when the power supply voltage changes. Therefore, when the power supply voltage changes, there is a problem that overheating or heating failure occurs. As a configuration for solving such a problem, a microwave oven has conventionally been provided with a power supply voltage detection circuit for detecting a power supply voltage and configured to correct the heater cooking time according to the power supply voltage detected by the power supply voltage detection circuit. Is being considered.

[0003]

In the above conventional configuration, the power supply voltage is detected based on the secondary output of the power supply transformer for the DC power supply circuit provided in the control circuit for controlling the cooking operation. If the power transformer is installed in the machine room of the microwave oven and the microwave oven is not installed properly (for example, if the intake port or the exhaust port of the machine chamber is blocked), the ambient temperature of the power transformer will be high. Can be quite high. Therefore, the power transformer is easily affected by the ambient temperature, and the detected power source voltage includes an error.

Further, although the heater is designed by setting the service life in advance, it is almost impossible for the user to recognize how long the heater has been used. On the other hand, when the total usage time of the heater reaches the design life, the insulation property of the insulation part of the heater may deteriorate and the leakage current flowing to the range main body may increase. I couldn't say it.

Therefore, an object of the present invention is to provide a microwave oven capable of accurately detecting the power supply voltage and correcting the heater cooking time with high accuracy in accordance with the detected power supply voltage. Another object of the present invention is to provide a microwave oven that can notify the user when the life of the heater has reached the end of life and can improve safety.

[0006]

The microwave oven of the present invention comprises:
A capacitive element that is connected between the power supply line and the earth terminal of the range main body and forms a part of a noise filter, is attached to the outer wall of the range main body, and is connected to the earth terminal of the range main body and an external earth connection. An inductance element that is connected between the ground terminal and the capacitive element and that constitutes the noise filter; and a detection winding that is wound around the inductance element and that detects a leakage current flowing to the range main body. It has characteristics.

In this case, it is preferable to provide voltage determining means for determining the power supply voltage based on the leakage current detected by the detection winding. Further, it is conceivable that a heater for performing heater cooking is provided and a correction means for correcting the heater cooking time based on the power supply voltage determined by the voltage determination means.

Further, it is more preferable to provide a heater for cooking the heater and a heater deterioration judging means for judging deterioration of the heater based on the leakage current detected by the detection winding. And
It is conceivable to provide a notifying means for notifying that the current value of the leakage current detected by the detection winding has reached a set value or more.

On the other hand, there is provided a heater for performing heater cooking, and a time integrating means for counting the time during which the heater cooking is being executed based on the leakage current detected by the detection winding and for integrating the measured time. It is also a preferable configuration to include a notifying unit for notifying that the heater has reached the end of its life based on the time accumulated by the time accumulating unit.

[0010]

According to the above means, the detection winding is wound around the inductance element, and the detection winding detects the leakage current flowing through the range body. Here, since it is known that there is a proportional relationship (linear relationship) between the leakage current flowing through the range body and the power supply voltage, it is possible to detect the power supply voltage by detecting the leakage current. . Further, since the inductance element is attached to the outer wall portion of the range main body, the ambient temperature of the inductance element and thus the detection winding does not rise so much even when the heater cooking is performed. Therefore, since the detection winding is less likely to be adversely affected by temperature, the power supply voltage can be accurately detected, and the heater cooking time can be corrected with high accuracy according to the detected power supply voltage.

On the other hand, in a microwave oven equipped with a heater for cooking with a heater, when the heater reaches the end of its life,
The leakage current flowing through the range body may increase.
In such a case, since the heater deterioration is determined based on the leakage current detected by the detection winding, for example, the user can be notified that the heater has reached the end of its life, which is preferable for safety. Become.

Further, in the microwave oven provided with the heater for performing the heater cooking, the leakage current becomes larger when the heater cooking is being performed than when the heater cooking is not being performed. As a result, it is possible to measure the time during which the heater cooking is being performed based on the leakage current detected by the detection winding, and also to integrate the measured time. Then, it is possible to determine that the heater has reached the end of its life based on the time accumulated in this way, and
This can be notified.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a microwave oven with a heater will be described below with reference to the drawings. First, in FIG. 2 showing the appearance of the microwave oven with a heater,
The microwave oven main body 1 forming the outer shell of the microwave oven has a rectangular box shape as a whole, and a heating and cooking chamber (not shown) is provided inside. A door 2 for opening and closing a front opening of the cooking chamber is rotatably provided on the front surface (right end in FIG. 2) of the cooker body 1. The above range body 1
As shown in FIG. 3, includes a bottom plate 3, a rear plate 4, and a cabinet 5 having a substantially U shape so as to cover the upper surface portion and both side surface portions. The bottom plate 3, the rear plate 4, and the cabinet 5 are made of metal plates.

As shown in FIG. 3, an oven assembly 6 is placed and fixed on the bottom plate 4, and the inside of the oven assembly 6 serves as a cooking chamber. Further, a machine room (not shown) is provided on the left side of the oven assembly 6 in the range main body 1, and a magnetron 7 (see FIG. 1) for range cooking is arranged in the machine room. By supplying the high frequency (microwave) oscillated from the magnetron 7 into the heating cooking chamber, range cooking is performed in the heating cooking chamber.

A heater 8 is provided on the ceiling of the cooking chamber.
(See FIG. 1) is provided, and heating by the heater 8 is performed so that heater cooking such as oven cooking or grill cooking is performed in the heating cooking chamber. The heater 8 is, for example, a flat heater, a glass tube heater,
It is composed of a sheathed heater and the like. A heater may be provided at the bottom of the cooking chamber. Furthermore,
It is also preferable to provide a hot air supply device for supplying hot air into the cooking chamber.

On the other hand, as shown in FIG. 3, a ground terminal 9 is provided at the lower left end of the rear plate 4 (the end on the side opposite to the machine room). The ground terminal 9 is a terminal for connecting to an external ground 10 (see FIG. 1) such as a ground rod embedded in the ground. Further, a ground terminal 11 of the range main body 1 is provided at a position slightly above the ground terminal 9 at the left end of the rear plate 4. This ground terminal 11
Is a so-called body grounding terminal, and is composed of a screw hole formed in the rear plate 4 and a screw 12 screwed into the screw hole.

Now, the peripheral structure of the earth terminal 9 for connecting the external earth 10 will be described in detail with reference to FIG.
As shown in FIG. 4, the screw 1 that constitutes the ground terminal 9
3 is inserted into a slightly lower part of the middle part of a holder 14 made of insulating plastic, and is tightened and fixed by a nut 15. The holder 14 has an elongated shape. The upper portion 14a is engaged with the upper opening edge portion of the through hole 4a formed in the rear plate 4, and the lower portion 14b is connected to the rear plate 4.
The rear plate 4
Mounted on Then, in this mounted state, the rear portion of the screw 13 and the nut 15 constituting the ground terminal 9 are configured to be exposed to the outer surface side through the through hole 4a. In this case, one end of the external ground wire led from the external ground 10 is connected to the rear portion of the screw 13 and is tightened and fixed by a nut.

A housing recess 14c is formed in the front upper half of the holder 14, and the housing recess 14c is formed.
A ground inductor 17, for example, is housed and held therein as an inductance element forming a part of a noise filter (described later). This earth inductor 17
Is an annular core 18 and a winding 1 wound around the core 18.
It is composed of 9 and 9. One end 19a of the winding 19 is connected to the ground terminal 11 of the range body 1 and the other end 1
9b is connected to a ground terminal 9 for connecting an external ground 10. As a result, the earth inductor 17 is connected between the earth terminal 11 of the range body 1 and the earth terminal 9 for connecting the external earth 10. Also,
The earth inductor 17 is configured to be attached to the rear plate 4 which is the outer wall portion of the range main body 1 via the holder 14. The earth inductor 17 and the rear plate 4 of the range body 1 are insulated by a holder 14 made of an insulating material.

On the other hand, the core 18 of the earth inductor 17 is wound with a detection winding 20 for detecting a leakage current flowing in the range body 1. Both ends of the detection winding 20 are provided with a control circuit 21 for controlling the entire cooking operation of the microwave oven.
(See FIG. 1), whereby the control circuit 21 is configured to receive the detection signal output from the detection winding 20.

Next, the electrical configuration of the microwave oven will be described with reference to FIG. In FIG. 1, one terminal 24, 25 of each of the pair of power supply lines 22, 23 is connected to a commercial AC power supply. The pair of power supply lines 22 and 23
A fuse 26 and a first door switch 27 are provided in series on one of the power supply lines 22. The second power switch 28 is connected to the other power line 23.
Is provided. A short switch 29 is connected between the power lines 22 and 23. The first
The door switch 27 and the second door switch 28 are switches that operate so as to be turned off and on in association with opening and closing of the door 2. The short switch 29 is
This is a switch that performs an on / off operation that is the reverse of the on / off operation of the first door switch 27 and the second door switch 28.

Further, a series circuit composed of the heater 8 and a heater relay 30 and a primary of a high voltage transformer (step-up transformer) 31 are provided between the power supply lines 22 and 23 on the side opposite to the power supply side of the door switches 27 and 28. A series circuit including the winding 31a and the magnetron relay 32 is connected in parallel. A series circuit including a diode 33 and a capacitor 34 having the illustrated polarities is connected between both terminals of the secondary winding 31b of the high voltage transformer 31. The cathode of the diode 33 is connected to the cathode of the magnetron 7, and the anode of the diode 33 is the magnetron 7.
Is connected to one terminal of the anode. The cathode of the magnetron 7 is connected to the earth terminal 11 of the range body 1. Further, both terminals of the anode of the magnetron 7 are connected to both terminals of the secondary winding 31c of the high voltage transformer 31. In this case, the diode 33 and the capacitor 34 form a voltage doubler rectifier circuit.

On the other hand, door switches 27 and 28 between the power lines 22 and 23, the heater 8 and the heater relay 3 are provided.
A first capacitor 35 and a series circuit including a second capacitor 36 and a third capacitor 37 are connected in parallel to a portion between the series circuit including 0s. These three capacitors 35 to 37 form a part of the noise filter. The common connection point A between the second capacitor 36 and the third capacitor 37 is connected to the ground terminal 11 of the range body 1. As a result, the second capacitor 36 is connected between the one power supply line 22 and the earth terminal 11 of the range main body 1, and the third capacitor 37 is connected between the other power supply line 23 and the earth terminal 11 of the range main body 1. It is configured to be connected.

Further, the earth terminal 11 of the range main body 1,
Between the ground terminal 9 connected to the external ground 10,
As described above, the ground inductor 17 is connected. In the case of this structure, the noise filter 38 is composed of the ground inductor 17 and the three capacitors 35 to 37. This noise filter 38 includes relays 30, 3
2. It has a function of attenuating the noise generated by each operation of the high voltage transformer 31, the magnetron 7, etc. and propagating to the external commercial AC power supply through the power supply lines 22 and 23 (power supply cord). The noise filter 38 has a known structure called a so-called earth inductor type noise filter.

Further, the heater relay 30 and the magnetron relay 32 are each configured to be on / off controlled by the control circuit 21. The control circuit 21 is mainly composed of a microcomputer and stores a control program for controlling the entire cooking operation of the microwave oven. Then, the control circuit 21
Is configured to receive a detection signal (leakage current detection signal) from the detection winding 20. With this configuration,
The control circuit 21 is configured to have respective functions as a power supply voltage determination means, a correction means, a heater deterioration determination means, a notification means, and a time integration means.

The control circuit 21 has a DC voltage circuit for supplying a DC constant voltage to a built-in microcomputer or the like. Then, both terminals of the primary winding 39a of the power transformer 39 forming a part of this DC voltage circuit are
It is connected to a portion between the power supply lines 22 and 23 and between the fuse 26 and the first capacitor 35.

Next, the operation of the above structure will be described with reference to FIGS. First, the heater 8 and the magnetron 7
As shown in FIG. 5, there is a proportional relationship (linear relationship) between the leakage current I0 flowing through the range main body 1 and the power source voltage E0 of the commercial AC power source when the power is not driven. This is because when the electric capacitances of the second and third capacitors 36 and 37 are Cy, the equation of I0 = E0 / (ωCy) is satisfied. However, ω is a constant. in this case,
When the rated value (100 V) of the power supply voltage E0 is E01 and the leakage current I0 at that time (that is, in normal time) is I01, when the power supply voltage E0 fluctuates around E01 in magnitude, the leakage current I0 Fluctuates around I01 around it.

Therefore, the range main body 1
By detecting the leak current I0 flowing through the control circuit 21 and applying this detection signal to the control circuit 21, the control circuit 21 can determine (detect) the power supply voltage E0 based on the detection signal. Further, in the above embodiment, the earth inductor 17 is attached to the rear plate 4 forming the outer wall portion of the range main body 1 via the holder 14, so that even if the heater cooking is performed, the earth inductor 17 and thus the detection winding. The ambient temperature of 20 does not rise so much. In this case, in particular,
The ground inductor 17 is arranged at the lower left end of the rear plate 4 of the range body 1, and the ground inductor 17 is housed and held in the housing recess 14a of the plastic holder 14. 1
7 is hardly affected by the heat generated when the heater is cooked. Therefore, the temperature of the ground inductor 17 (that is, the detection winding 20) hardly rises during cooking with the heater.

As a result, the detection winding 20 is unlikely to be adversely affected by temperature, so that the power supply voltage E0 can be detected more accurately than in the conventional configuration. Therefore, the control circuit 21
The heater cooking time can be corrected with high accuracy according to the accurately detected power supply voltage E0.

On the other hand, in a microwave oven with a heater,
When the heater 8 reaches the end of its life, the insulation performance of the heater 8 deteriorates (decreases), so that the leakage current flowing through the range main body 1 may increase. In such a case, in the above-described embodiment, the control circuit 21 determines the deterioration of the heater 8 based on the leakage current I0 detected by the detection winding 20, and the determination result, that is, the heater 8 reaches the end of its life. It is configured to notify the user of this.

In this case, the control circuit 21 determines that the heater 8 has deteriorated, that is, the heater 8 has reached the end of its life, when the detected leakage current I0 exceeds a predetermined value (heater life judgment value). are doing. When notifying the user that the heater 8 has reached the end of its life, the control circuit 21
Sound the buzzer or display on the operation panel (eg L
The display mode indicating the above is displayed on the ED or the 7-segment type display element). As a result, unlike the conventional configuration, the user can recognize that the heater 8 has reached the end of its life by the above notification,
The use of the microwave oven is stopped, which is preferable for safety.

Further, when the heater 8 is energized and the heater cooking is being executed, the leakage current becomes larger than when it is not being executed. This is because when the heater 8 is energized, a leakage current flows through the insulating portion of the heater 8. Specifically, as shown in FIG. 6, when the heater 8 is not energized, the leakage current value is, for example, about 0.3 mA, and when the heater 8 is energized, the leakage current value is, for example, 0.35 mA.
It will be high. As a result, it is possible to determine whether or not the heater cooking is being performed based on the leakage current detected by the detection winding 20.

In the above embodiment, the control circuit 21 controls the time during which the heater cooking is executed based on the leak current detected by the detection winding 20 (heater energization time), specifically, FIG. Time t1, t2, t3 ...
Are timed and the timed times t1, t2, t3, ... Are summed. In this case, the control circuit 21 stores the integrated time in a non-volatile memory (for example, EEPROM), and is configured to be able to store and hold the integrated time even when the power is turned off. Further, the control circuit 21 compares the integrated time with the life of the heater 8 (designed life time), and when the life of the heater 8 is reached (that is, the integrated time reaches the heater life determination time). If it is determined), the fact is notified. In this case, the control circuit 21 is configured to make a buzzer sound or display a display mode indicating that the life of the heater 8 has been reached on the display of the operation panel. Therefore,
Unlike the conventional configuration, the user is notified of the heater 8 by the above notification.
Since it can be surely recognized that the product has reached the end of its life, the use of the microwave oven is stopped and repairs or the like are to be performed. For this reason, a large leakage current does not continue to flow, which is a preferable structure for safety.

On the other hand, the progress of deterioration of the heater 8 differs depending on the magnitude of the power supply voltage. Therefore, it cannot be said that the life of the heater 8 is sufficiently accurately determined by simply measuring and integrating the execution time of the heater cooking. On the contrary,
The power supply voltage is detected based on the leakage current detected by the detection winding 20, the execution time of the timed heater cooking is adjusted based on the detected power supply voltage, and the adjusted execution time is integrated. It is possible. With this configuration, the life of the heater 8 can be determined with high accuracy.

In the above embodiment, the electric power supplied to the magnetron 7 is applied to the microwave oven whose ON / OFF is controlled by the magnetron relay 32. Instead, however, the electric power supplied to the magnetron is continuously varied by the inverter device. You may apply to the microwave oven to control.

[0035]

As is apparent from the above description, the present invention detects an inductance element in a microwave oven in which an inductance element is connected between the earth terminal of the range main body and the earth terminal for external earth connection. Since the winding is wound and the detection winding is used to detect the leakage current flowing in the range body, it is possible to accurately detect the power supply voltage based on the detected leakage current,
Therefore, there is an excellent effect that the heater cooking time can be corrected with high accuracy.

In a microwave oven equipped with a heater for cooking with a heater, the deterioration of the heater is determined based on the leakage current detected by the detection winding. It is possible to notify the user, which is a preferable structure for safety.

Further, since the time during which the heater cooking is being performed is timed based on the leakage current detected by the detection winding and the timed time is integrated, the heater is operated on the basis of the above integrated time. It becomes possible to judge that the heater has reached the end of its life, and can notify that the heater has reached the end of its life. Therefore, the user can surely recognize that the heater has reached the end of its life by the above notification, and can take measures against it.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing an embodiment of the present invention.

FIG. 2 is a side view of the entire microwave oven.

FIG. 3 is a partial perspective view with a cabinet removed.

[Figure 4] Side view of the vertical section around the ground terminal and ground inductor

FIG. 5 is a graph showing the relationship between leakage current and power supply voltage.

FIG. 6 is a time chart showing the relationship between leakage current and execution of heater cooking.

[Explanation of symbols]

1 is a range body, 3 is a bottom plate, 4 is a rear plate, 5 is a cabinet, 7 is a magnetron, 8 is a heater, 9 is a ground terminal,
10 is an external ground, 11 is a ground terminal, 14 is a holder,
17 is a ground inductor (inductance element), 18
Is a core, 19 is a winding, 20 is a detection winding, 21 is a control circuit (power supply voltage determination means, correction means, heater deterioration determination means,
(Notification means, time integration means), 22 and 23 are power lines,
Reference numeral 30 is a heater relay, 31 is a high voltage transformer, 32 is a magnetron relay, 35 is a first capacitor, 36 is a second capacitor, 37 is a third capacitor, and 38 is a noise filter.

Claims (6)

[Claims] 1. A capacitive element that is connected between a power supply line and a ground terminal of the range main body and forms a part of a noise filter; and a ground terminal of the range main body that is attached to an outer wall of the range main body. An inductance element that is connected between an earth terminal for external earth connection and that forms the noise filter together with the capacitive element, and a detection winding that is wound around the inductance element and that detects a leakage current flowing in the range body. A microwave oven comprising and. 2. The microwave oven according to claim 1, further comprising voltage determining means for determining a power supply voltage based on a leakage current detected by the detection winding. 3. The microwave oven according to claim 2, further comprising: a heater for performing heater cooking; and a correction unit that corrects the heater cooking time based on the power supply voltage determined by the voltage determination unit. . 4. A heater for cooking with a heater, and a heater deterioration judging means for judging deterioration of the heater based on a leakage current detected by the detection winding. microwave. 5. The microwave oven according to claim 1, further comprising an informing unit for informing that the current value of the leakage current detected by the detection winding has reached a set value or more. 6. A heater for performing heater cooking, and a time integrating means for counting the time during which the heater cooking is being executed based on the leakage current detected by the detection winding and for accumulating the measured time. The microwave oven according to claim 1, further comprising an informing unit that informs that the heater has reached the end of its life based on the time accumulated by the time accumulating unit.