JPH05283156A - High-frequency heating device - Google Patents

Abstract

PURPOSE:To surely prevent the overheat of a magnetron and extend the life of the magnetron by increasing the cooling capability when a load is small. CONSTITUTION:A blower motor 15 for cooling a magnetron 8 has a high-speed rotation terminal TH and a low-speed rotation terminal TL. When a cooking menu is inputted from an operation section 1, a controller 2 judges the magnitude of the load of a heated object on the magnetron 8. The contact 16A of a relay 16 is connected to the high-speed rotation terminal TH when the load is small based on the judged result, and the contact 16A of the relay 16 is connected to the low-speed rotation terminal TL when the load is relatively large.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency heating device such as a microwave oven.

[0002]

2. Description of the Related Art In a microwave oven, a blower or a fan is used for cooling a magnetron which generates a high frequency. Since the amount of heat generated by the magnetron varies depending on the magnitude of the high frequency output, cooling with a constant amount of air causes excess or deficiency in cooling efficiency. That is, if the cooling capacity is insufficient, the magnetron will overheat and its life will be shortened. On the other hand, if the cooling capacity is excessive, the power consumption of the blower and the like is wasted.

Therefore, for example, Japanese Utility Model Publication No. 57-30793.
As can be seen in the publication, a technique has been proposed in which the electric power supplied to the blower is changed according to the magnitude of the high frequency output to match the cooling capacity and the heat generation amount of the magnetron. However, the heat generation amount of the magnetron does not only depend on the magnitude of the high frequency output but also varies depending on the magnitude of the load impedance. That is, the size of an object to be heated such as food contained in the heating chamber and heated in the microwave oven is not constant and may be extremely small. In such a case, the load impedance viewed from the magnetron will be far from the matching value. In this case, the amount of heat generated by the magnetron increases even if the high frequency power is low.

Therefore, the above-mentioned prior art cannot prevent overheating of the magnetron, which may result in failure to extend the life of the magnetron. Recently, microwave ovens are increasingly equipped with popcorn keys for cooking popcorn, especially in the US market. In other words, a bag containing a standard amount (usually about 100 g) of popcorn is placed in the heating chamber, and the popcorn key is pressed to start heating, and the required high-frequency output and heating time etc. are controlled by the program control by the microcomputer. Is set.

However, with the above standard amount of popcorn, since the load is very small, the anode temperature of the magnetron rises rapidly in a short time. Therefore, if two or three pieces are continuously cooked, the anode temperature of the magnetron may exceed the limit value. For this reason also, it is necessary to realize the cooling capacity according to the magnitude of the load.

On the other hand, various techniques have been proposed for efficiently cooling the magnetron. One of them is the technique disclosed in Japanese Patent Laid-Open No. 1-225088.
In the prior art disclosed in this publication, the cooling efficiency of the magnetron is improved by almost eliminating the exhaust resistance of the cooling air. However, since the flow of cooling air is in a fixed direction, the part of the magnetron that faces the windward is efficiently cooled, while the stagnation of air is unavoidable in the leeward part, resulting in poor cooling efficiency. is there. This problem becomes particularly noticeable when the exhaust resistance is reduced as in the above-mentioned prior art.

More specifically, when the cooling air flow direction is constant, the temperature of the magnetron anode is measured at its outermost periphery (the lowest temperature in the anode), and a propeller fan with a small wind pressure is detected. When used, the temperature difference between the parts on the windward side and on the opposite side thereof usually reaches 30 to 40 ° C. This temperature difference becomes even larger when a sirocco fan with a large wind pressure is used, and reaches 60 to 80 ° C.

This temperature difference appears remarkably when operating under a light load, when operating for a long time, and when the reflection of cooling air on the surface of the magnetron is large. Due to such a temperature difference, even in the case of a cylindrical magnetron having a small amount of air reflection, a large thermal strain occurs even on the outer circumference where the temperature is the lowest. Therefore, even larger thermal strain occurs at the center of the magnetron and the tip of the vane near the working space. Such thermal strain increases as the anode current increases.

In consideration of this, in a model having a particularly large anode current such as a microwave oven for business use, the allowable value of the anode temperature is remarkably higher than that of a general household model having a several hundred watt output. It is suppressed. For this reason, there is a problem that a large-scale air passage is required for cooling the magnetron depending on a high-power model for business use or the like. Therefore, an object of the present invention is to solve the above-mentioned technical problems and to provide a high-frequency heating device capable of favorably cooling the high-frequency generating means and contributing to prolonging the life of the high-frequency heating means. ..

[0010]

In order to achieve the above object, the high frequency heating apparatus according to claim 1 is a high frequency generating means for generating a high frequency to be introduced into a heating chamber for accommodating an object to be heated. And a cooling means having a variable cooling capacity for cooling the high frequency generating means, an input means for inputting the type of the object to be heated, and a magnitude of a load on the high frequency generating means of the object to be heated. Cooling capacity control means for controlling the cooling capacity of the cooling means by determining based on the type of the object to be heated input from the means.

According to this structure, when the type of the object to be heated is input from the input means, the cooling capacity of the cooling means is changed based on the input type of the object to be heated. That is, the magnitude of the load on the high frequency generator of the object to be heated is determined based on the type of the object to be heated, and the cooling capacity is controlled correspondingly. Thus, when the heat generated by the high frequency generation means may become excessive due to the small load, the high frequency generation means can be prevented from overheating by increasing the cooling capacity of the cooling means.

The high frequency heating apparatus according to claim 2 is
The high frequency generating means for generating a high frequency to be introduced into the heating chamber for accommodating the object to be heated, the cooling fan for sending the cooling air to the high frequency generating means, and the cooling air sent by the cooling fan It is characterized in that it includes switching means for switching the flow direction in the vicinity of the high frequency generating means between a first direction and a second direction which is inverted by approximately 180 degrees from the first direction.

According to this structure, the flow direction of the cooling air sent from the cooling fan is substantially 1 by the switching means.
It is inverted by 80 degrees. For this reason, the cooling air is sent to the high-frequency generating means by switching from the first direction and the second direction, which are mutually inverted by approximately 180 degrees, not from a fixed direction. As a result, the high frequency generating means can be cooled efficiently and uniformly.

[0014]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a block diagram showing the electrical configuration of a microwave oven which is a first embodiment of the high-frequency heating apparatus of the present invention. This microwave oven responds to an input of a cooking menu or the like from an operation unit 1 which is an input unit configured by a key input device or the like, and a control unit 2 which is a cooling capacity control unit including a microcomputer and other peripheral circuits.
By controlling the size of high frequency output and heating time,
The cooking is automatically accomplished. In particular, in this embodiment, the cooking menu selection key of the operation unit 1 is provided with the popcorn key 3 for cooking a standard amount (for example, about 100 g) of popcorn. The input of the cooking menu is nothing but the input of the kind of the object to be heated.

Electric power from the commercial AC power supply 4 is applied to the primary side of the high voltage transformer 7 via the fuse 5 and the contact 6A of the relay 6. A high voltage generating circuit 9 for generating a high voltage to be supplied to a magnetron 8 which is a high frequency generating means is connected to the secondary side of the high voltage transformer 7.
Further, a heater winding 10 to be supplied to the heater of the magnetron 8 is further provided on the secondary side of the transformer 7.

The high voltage generating circuit 9 includes a high voltage capacitor 11
And a rectifier 12, and the voltage across the rectifier 12 is applied to the magnetron 8. With this configuration, current flows through the rectifier 12 while the voltage appearing on the secondary side of the high voltage transformer 7 is in the opposite direction to the magnetron 8, and at this time the high voltage capacitor 11 is charged. Then, during a period in which the voltage appearing on the secondary side of the high voltage transformer 7 is in the forward direction with respect to the magnetron 8, this voltage and the voltage across the high voltage capacitor 11 are superimposed and applied between the anode and cathode of the magnetron 8. To be done. In this way, the half-wave rectified high voltage is applied to the magnetron 8
Is applied to the magnetron 8, the magnetron 8 oscillates to generate microwaves.

This microwave is introduced into a heating chamber (not shown) for containing an object to be heated such as food. The operating voltage of the control unit 2 is created by stepping down the commercial AC voltage by the step-down transformer 13. The control unit 2 controls the relay 6 that opens and closes between the high-voltage transformer 7 and the commercial AC power supply, and controls the heating by the microwave. The adjustment of the high frequency output is achieved by intermittently closing the relay 6.

The blower motor 1 is connected in parallel to the high voltage transformer 7.
5 is connected. The blower motor 15 drives a blower (not shown) which is a cooling means for air-cooling the magnetron 8. This blower motor 1
The number 5 allows the rotation to be switched between high-speed rotation and low-speed rotation. The switching of the rotation speed is achieved by switching and connecting the contact of the relay 16 to the high speed rotation terminal TH and the low speed rotation terminal TL. The relay 16 is controlled by the control unit 2.

The control unit 2 controls the relay 16 according to the cooking menu input from the operation unit 1, and the blower motor 1
The rotation state of No. 5 is switched between high speed rotation and low speed rotation. That is, the contact 16A of the relay 16 is normally connected to the low speed rotation terminal TL. When a menu in which the load of the object to be heated is expected to be small is selected, for example, when the popcorn key 3 is operated, the contact 16A is connected to the high speed rotation terminal TH.

As a result, when the heat generation amount of the magnetron 8 increases due to the small load impedance,
Since the amount of air from the blower increases, it is possible to prevent the magnetron 8 and other high-voltage electric parts from becoming overheated. As a result, the anode temperature of the magnetron 8 does not exceed the allowable value even when the load is extremely small as viewed from the magnetron 8. As a result, the service life of the magnetron 8 is extended.

There is also a case where a so-called magnetron thermostat is used which detects overheating of the magnetron 8 and stops the power supply to the magnetron 8. At this time, when the magnetron thermostat operates, the user requests repair by a serviceman. However, according to the present embodiment, overheating of the magnetron 8 can be effectively prevented, so that the number of serviceman calls can be reduced.

On the other hand, since the blower motor 15 is rotated at a high speed, the blower motor 15 will generate more heat than usual. However, in normal home use, for example, it is unthinkable to continuously cook more than 10 bags of popcorn, and the heat generation of the blower motor 15 is not a serious problem. That is, for example, in a microwave oven having an output of 700 W, it takes 3 to 4 minutes to cook 100 g of popcorn. In this case, if 10 bags of popcorn are cooked continuously, the blower motor 15 will rotate at high speed for 30 to 40 minutes. However, the heat generation of the blower motor 15 due to the high speed rotation for such a time does not pose a problem.

In the present embodiment, when the control unit 2 intermittently closes the relay 6 to adjust the high frequency output of the magnetron 8, the power supplied to the blower motor 15 also decreases. As a result, the blower motor 15 can be rotated according to the high frequency output of the magnetron 8. Therefore, the magnetron 8 can be operated at an air volume corresponding to the magnitude of the high frequency output
Will be air cooled.

The present embodiment can be modified as follows. That is, in the above embodiment, the rotation speed of the blower motor 15 is converted into two stages, but the rotation speed may be changed in three or more stages according to the cooking menu. Further, in the above embodiment, the rotation speed of the blower motor 15 is controlled by utilizing the fact that the load of the object to be heated is expected to be small in the specific cooking menu, but the operation unit controls the rotation speed. By inputting the type itself of the heated object, the blower motor 15 may be rotated at a high speed when the load of the magnetron 8 corresponding to the object to be heated is small. Further, both the type and the amount of the object to be heated may be input, and the rotation of the blower motor 15 may be controlled based on this.

FIG. 2 is a longitudinal sectional view showing the structure of the microwave oven of the second embodiment of the high-frequency heating apparatus of the present invention, showing the structure of the portion near the magnetron. This microwave oven is two magnetrons 21 and 22 and a cooling fan for cooling these magnetrons 21 and 22.
Two blowers 23 and 24 are provided. For example, the magnetron 21 supplies microwaves from above the heating chamber (not shown), and the magnetron 22 supplies microwaves from below the heating chamber. Reference numerals 48 and 49 are high-voltage transformers.

The cooling air blown out from the blower 23 is guided by the ducts 25, 26 and 27 to the magnetron 21.
Alternatively, it is guided to the magnetron 22. That is, the ducts 25, 26, 27 are flat plates and form an air flow passage together with a side plate of the microwave oven, a partition plate for the heating chamber, and the like. And, the flat ducts 25, 2
One side of 6, 27 is attached to shafts 28, 29, 30 attached near the magnetrons 21, 22,
It is rotatable in the direction of arrow R1. Furthermore, the movable ends 25a, 26a, 27a of the ducts 25, 26, 27, respectively.
Are fixed to the wires 31, respectively.

The structure relating to the blower 24 is also the same, and the ducts 35, 33 are arranged so as to be rotatable in the arrow R2 direction with respect to the shafts 32, 33, 34 mounted in the vicinity of the magnetrons 21, 22. 36 and 37 are attached. Then, each movable end 3 of the ducts 35, 36, 37
5a, 36a, 37a are fixed to the wire 31 described above.

The wire 31 is arranged in a U shape so as to bypass the magnetrons 21 and 22. Then, the tip end 38a of the operating rod 38 is provided in the middle of the wire 31.
Is fixed. The operation rod 38 is provided so as to be rotatable around a fulcrum 39, and a base end portion 38b thereof is connected to an actuator 42 driven by a solenoid 40 and a spring 41.

As a result, the wire 31 can be moved in the direction of arrow R3 by exciting / demagnetizing the solenoid 40. As a result, the ducts 25, 26, 2
The positions of 7, 35, 36 and 37 can be switched between the positions indicated by the solid line and the positions indicated by the broken line in FIG. Solenoid 40
Are controlled by a control unit 50 including a microcomputer and other peripheral circuits. Thus, in this embodiment,
Duct 25,26,27,35,36,37, wire 3
1, the operation rod 38 and the solenoid 40,
Switching means is configured.

When the solenoid 40 is demagnetized, the spring force of the spring 41 causes the actuator 42 to be pulled out from the solenoid 40. As a result, the operating rod 38 is located at the position shown by the solid line in FIG. 2, and the ducts 25, 26, 27, 35, 36, 37 are located at the position shown by the solid line in FIG. At this time, the cooling air blown out from the blower 23 flows through the path L1. That is, it is guided to the magnetron 21 through the ducts 25 and 26, passes through the ducts 35 and 36, further passes through the exhaust air passage 43, and is exhausted to the outside from the exhaust port 44. On the other hand, the cooling air blown out from the blower 24 flows through the path L2. That is, after cooling the magnetron 22 through the ducts 36 and 37, the magnetron 22 is exhausted from the ducts 26 and 27 through the exhaust air passage 45 through the exhaust port 46.

On the other hand, when the solenoid 40 is excited, the actuator 42 is pulled into the solenoid 40 against the spring force of the spring 41. As a result, the operating rod 38 is in the position indicated by the broken line, which causes the ducts 25, 2
6, 27, 35, 36, 37 rotate to the positions indicated by broken lines. In this state, the cooling air from the blower 23 is
It circulates along the route L3. That is, the ducts 26, 2
After being guided to the magnetron 22 by 7 and cooling the magnetron 22, it is exhausted from the exhaust port 44 through the ducts 36 and 37 and the exhaust air passage 43. Further, the cooling air blown out from the blower 24 flows along the path L4. That is, the ducts 35 and 36 guide the magnetron 21. And this magnetron 21
After being cooled, the air is guided to the exhaust air passage 45 by the ducts 25 and 26 and is exhausted from the exhaust port 46.

In this way, the excitation of the solenoid 40 /
By degaussing, the flow of cooling air can be switched between two ways. Moreover, paying attention to the air flow in the vicinity of the magnetrons 21 and 22, the air flow in the magnetrons 21 and 22 is reversed by approximately 180 degrees by switching the air circulation path. In this embodiment, the control unit 50 periodically energizes / demagnetizes the solenoid 40. That is, the state of the solenoid 40 is reversed every fixed time Δt (for example, 1 minute). by this,
The flow direction of the cooling air blown onto the magnetrons 21 and 22 will be reversed every fixed time Δt.

As a result, the magnetron 21 is cooled uniformly from any direction, so that thermal strain can be effectively reduced and the life of the magnetron 21 can be extended. FIG. 3 is a graph showing the cooling effect of the magnetron in the present embodiment in comparison with the prior art, and shows the time change of the temperature rise value of the magnetron. The conventional technique mentioned here is a technique of blowing cooling air onto the magnetron from a certain direction.

In FIG. 3, the curves A and B correspond to the prior art, the curve A shows the temperature rise value of the magnetron anode temperature at the downstream position in the air flow direction, and the curve B at the upstream position. Shows the temperature rise value of the anode temperature of the magnetron. Curve C shows the anode temperature of the magnetron in this example. In the present embodiment, the flow direction of the cooling air changes periodically, but the curve C corresponds to the temperature of the anode part of the magnetron on the exhaust side during the period Δt immediately after the start of the operation of the microwave oven. The time change of the temperature rise on the opposite side is almost equal to the curve C except for the period of several cycles having a cycle of 2Δt immediately after the start of operation.

From the comparison between the curves A and B and the curve C, it is understood that in the present embodiment, the maximum value of the anode temperature can be greatly reduced as compared with the conventional case while using the same blower motor.
That is, the ducts 25, 26, 27, 35, 3 capable of switching the air circulation path without enlarging the blower motor itself or drastically modifying the air passage.
A large cooling effect can be obtained by a simple configuration using 6, 37 and the like. Therefore, even in a high-power microwave oven, the magnetron can be satisfactorily cooled without requiring a large air passage.

Moreover, since the circulation direction of the cooling air is reversed, it is naturally possible to greatly reduce the thermal strain of the magnetrons 21 and 22, which contributes to the extension of the life of the magnetrons 21 and 22. Further, as a result of the large improvement in cooling efficiency, the load on the magnetrons 21 and 22 is small, so that even if the heat generation amount of these magnetrons 21 and 22 increases,
22 can be cooled well. As a result, the temperature rise of the magnetrons 21 and 22 is moderated, so that the risk of thermal destruction of the ceramic or the like forming the magnetrons 21 and 22 is greatly reduced. This also achieves a long life of the magnetrons 21 and 22.

The present embodiment can be modified as follows. That is, the fixed ducts are provided at the positions of the ducts 25 and 37 indicated by the broken line in FIG. 2 and the positions of the ducts 27 and 35 indicated by the solid line in FIG. On the other hand, a movable duct that rotates about the positions of reference numerals a1, a2, a3, and a4 in FIG. 2 is provided. Then, by rotating the movable duct, the cooling air from the blowers 23 and 24 is switched between the magnetron 21 side and the magnetron 22 side to be guided.
The flow direction of the cooling air guided to 22 can be reversed by approximately 180 degrees.

Further, in the above embodiment, the flow direction of the cooling air is periodically reversed, but the flow direction does not need to be periodically reversed. For example, the exhaust temperature is detected and this detection is performed. You may make it perform according to a result.
Furthermore, although two magnetrons are used and two blowers are used in the above embodiment, the number of magnetrons and blowers may be one, or three or more. ..

[0039]

According to the high frequency heating apparatus of the first aspect, the cooling capacity is controlled according to the magnitude of the load on the high frequency generating means of the object to be heated. Thus, when the heat generated by the high frequency generation means may become excessive due to the small load, the high frequency generation means can be prevented from overheating by increasing the cooling capacity of the cooling means. This allows
The life of the high frequency generating means can be extended.

Further, according to the high frequency heating apparatus of the second aspect, the high frequency generating means can be efficiently and uniformly cooled by switching the flow direction of the cooling air.
As a result, the cooling fan does not need to have an excessively high capacity and a large air passage is not required, and the high-frequency generating means can be satisfactorily cooled with a simple configuration.

Moreover, as a result of being able to cool the high frequency generating means uniformly, it is possible to suppress the thermal strain that occurs in this high frequency generating means, which can contribute to the extension of the life of the high frequency generating means. Further, even when the load is small, the temperature of the high-frequency generating means rises slowly as a result of efficient cooling. As a result, thermal shock to the components of the high frequency generating means can be suppressed, and the life of the high frequency generating means can be extended.

[Brief description of drawings]

FIG. 1 is a block diagram showing an electrical configuration of a microwave oven which is a first embodiment of a high-frequency heating device of the present invention.

FIG. 2 is a block diagram showing an electrical configuration of a microwave oven which is a second embodiment of the high-frequency heating device of the present invention.

FIG. 3 is a graph showing the cooling effect of the magnetron in comparison with the prior art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Operation part (input means) 2 Control part (cooling capacity control means) 3 Popcorn key 8 Magnetron (high frequency generation means) 15 Blower motor (cooling means) 16 Relay TL low speed rotation terminal TH High speed rotation terminal 21,22 Magnetron (high frequency generation means) ) 23, 24 Blower (cooling fan) 25-27 Duct 31 Wire 35-37 Duct 38 Operation rod 40 Solenoid 42 Actuator

Claims (2)

[Claims] 1. A high frequency generating means for generating a high frequency to be introduced into a heating chamber for accommodating an object to be heated, a cooling means having a variable cooling capacity for cooling the high frequency generating means, and an object to be heated. The input means for inputting the type and the magnitude of the load on the high frequency generating means of the object to be heated are
A high-frequency heating device comprising: a cooling capacity control unit that controls the cooling capacity of the cooling unit by determining based on the type of the object to be heated input from the input unit. 2. A high frequency generating means for generating a high frequency to be introduced into a heating chamber for accommodating an object to be heated, a cooling fan for sending cooling air to the high frequency generating means, and a cooling fan for supplying the cooling air. Switching means for switching the flow direction of the cooling air in the vicinity of the high frequency generating means between a first direction and a second direction which is approximately 180 degrees inverted from the first direction. High frequency heating device.