JP6737606B2 - Induction heating steam generator - Google Patents

Description

The present invention relates to an induction heating steam generator used in a steam convection oven or the like.

The following Patent Document 1 discloses a steam generator used for a heating cooker such as a steam convection oven. This steam generator is a steam generating container that stores a predetermined amount of water to generate steam, an induction heating coil wound around the outer periphery of the steam generating container, and a high frequency radio wave in the induction heating coil housed in the steam generating container. A heating body that generates heat by supplying an electric current, a high-frequency current supply circuit that supplies a high-frequency current to the induction heating coil, and a control device that controls the operation of the high-frequency current supply circuit to control the supply of the high-frequency current to the induction heating coil. It has and. The heating element in the steam generating container heats the surrounding water by the Joule heat generated when the eddy current flows due to the effect of the magnetic field generated when the induction heating coil is supplied with the high frequency current. Generating steam.

JP, 2005-017747, A

In the steam generation device of Patent Document 1 described above, the water in the steam generation container is controlled to a predetermined amount by using the water level sensor in the water level detection tank provided adjacently, but the water level sensor malfunctions, etc. If water is not properly supplied into the steam generation container due to the above, there is a risk that the heating element will become empty and become overheated in the steam generation container. When the temperature of the heating element exceeds the Curie temperature in the steam generation container, the heating element loses magnetism and the flowing eddy current decreases, and the high frequency current supply circuit may generate an overcurrent due to a decrease in impedance. The current supply circuit could be damaged by overcurrent. In order to prevent this, when the high-frequency current supplied from the high-frequency current supply circuit exceeds a threshold value larger than a predetermined ratio (for example, 130%) of the normal current according to the output, the heating element raises the Curie temperature by emptying. It detects that the overheated state has been exceeded and controls to stop the supply of the high frequency current from the high frequency current supply circuit to the induction heating coil.

However, even if there is sufficient water (hot water) in the steam generation container, if a steam film is formed around the heating body in the steam generation container, the water in the steam generation container will be scattered around the heating body. There was a case where film heating caused by boiling at the contact surface with the steam film, and the heating element was less likely to exchange heat with the water in the steam generation container and became overheated. In this case, since the temperature rise of the heating element is slower than that in the empty heating, the temperature of the heating element rises until it exceeds the Curie temperature, which is longer than that in the empty heating, and the high frequency current from the high frequency current supply circuit is increased. However, the high current state is maintained for a long time before the temperature rises to the above-mentioned threshold value, which may cause the high-frequency current supply circuit to fail due to abnormal heat generation. On the other hand, although a failure due to abnormal heat generation can be avoided to some extent by increasing the size of the transistor forming the high frequency current supply circuit or increasing the size of the radiator or cooling fan, there is a problem that the cost is significantly increased. SUMMARY OF THE INVENTION It is an object of the present invention to make an induction heating type steam generating device less likely to cause a failure due to abnormal heat generation in a high frequency current supply circuit without increasing the cost of the high frequency current supply circuit.

In order to solve the above problems, a steam generating container that stores a predetermined amount of water to generate steam, an induction heating coil wound around the outer periphery of the steam generating container, and an induction heating coil housed in the steam generating container. A heating element that generates heat by supplying high-frequency current to the induction heating coil, a high-frequency current supply circuit that supplies high-frequency current to the induction heating coil, an ammeter that measures the current supplied from the high-frequency current supply circuit to the induction heating coil, and a high-frequency and a control device for controlling the supply of the high-frequency current to the induction heating coil by controlling the operation of the current supply circuit, the control device of the power measurement current value measured by the ammeter is supplied from the high-frequency current supply circuit The heating element exceeds the Curie temperature when it is set higher than the output corresponding current value that normally flows according to the output and exceeds the first threshold value when the heating element exceeds the Curie temperature and is in an overheated state . An induction heating steam generator that detects that an overheat condition has occurred and controls the high-frequency current supply circuit to stop supplying high-frequency current to the induction heating coil. High frequency supplied from the high frequency current supply circuit to the induction heating coil when the measured current value exceeds the second threshold value set as a value higher than the output corresponding current value and before rising to the first threshold value The present invention provides an induction heating type steam generator characterized in that the output of electric current is controlled to be temporarily reduced.

In the steam generator of the induction heating type having the structure as described above, the measured current value measured by the ammeter is set higher than the output corresponding current normally flows in accordance with the output of the power supplied from the high-frequency current supply circuit When the heating element exceeds the first threshold value when the heating element exceeds the Curie temperature, the heating element detects that the heating element exceeds the Curie temperature and the high-frequency current is supplied. By controlling the high-frequency current to be stopped from the circuit to the induction heating coil, it is possible to prevent overcurrent from occurring in the high-frequency current supply circuit and prevent the steam generation container from becoming empty. be able to.

However, when a steam film is formed around the heating element in the steam generation container, the heat of the heating element is less likely to exchange heat with the water in the steam generation container due to the steam film, and the temperature of the heating element is not heated. It rises more slowly than when. At this time, by the time the measured current value measured by the ammeter exceeds the first threshold value, the high frequency current may flow from the high frequency current supply circuit at a high current for a long time, and the high frequency current supply circuit may abnormally generate heat. On the other hand, in the steam generator of the present invention, the measured current value measured by the ammeter is higher than the output corresponding current value and is set as the value before rising to the first threshold value below the first threshold value. When the second threshold value was exceeded, the output of the electric power supplied from the high-frequency current supply circuit to the induction heating coil was controlled to be temporarily reduced. As a result, even if a vapor film is formed around the heating element, the heat generation of the heating element is temporarily suppressed, so that the vapor film generated around the heating element in the steam generation container disappears, and the heating It was possible to prevent the high-frequency current from the high-frequency current supply circuit from being maintained at high current for a long time due to heat exchange between the body and the surrounding water (hot water), and to prevent abnormal heat generation in the high-frequency current supply circuit. ..

It is a schematic diagram of an induction heating type steam generator of the present invention. It is a graph which shows an output corresponding electric current value, a 1st threshold value, and a 2nd threshold value.

Below, the induction heating type steam generator of the present invention is mainly incorporated in a heating cooker such as a steam convection oven. As shown in FIG. 1, an induction heating type steam generator 10 (hereinafter, also simply referred to as a steam generator 10) includes a steam generation container 21 that stores a predetermined amount of water and generates steam, and a steam generation container. The induction heating coil 31 wound around the outer periphery of the heating element 21, the heating element 32 that is housed in the steam generation container 21 and generates heat by supplying a high frequency current to the induction heating coil 31, and a high frequency current to the induction heating coil 31. The high-frequency current supply circuit 41 for supplying, the ammeter 42 for measuring the current supplied from the high-frequency current supply circuit 41 to the induction heating coil 31, and the operation of the high-frequency current supply circuit 41 are controlled to supply the high-frequency current to the induction heating coil 31. And a control device 43 for controlling the supply.

In the steam generator 10, in order to prevent the heating element 32 in the steam generation container 21 from being in an overheated state exceeding the Curie temperature and generating an overcurrent in the high frequency current supply circuit 41, the control device 43: When the measured current value measured by the ammeter 42 exceeds the first threshold value set higher than the output corresponding current value according to the output, the heating element 32 is overheated to exceed the Curie temperature. It detects and controls to stop the supply of the high frequency current from the high frequency current supply circuit 41 to the induction heating coil 31.

Further, in the steam generator 10, a steam film is generated around the heating body 32 in the steam generation container 21, so that the heat of the heating body 32 becomes water (hot water) in the steam generation container due to the steam film. In order to prevent heat exchange from occurring and the high frequency current from the high frequency current supply circuit 41 to flow in a high current state for a long time to cause abnormal heat generation in the high frequency current supply circuit 41, the control device 43 measures with an ammeter 42. When the measured current value exceeds the second threshold value set higher than the output corresponding current value and set to the first threshold value or less, the output of the high frequency current supplied from the high frequency current supply circuit 41 to the induction heating coil 31 is temporarily stopped. It is controlled so as to lower it. Below, the steam generator 10 of this invention is explained in full detail.

As shown in FIG. 1, the steam generating container 21 has a tubular shape with upper and lower openings. The opening 21a at the upper end of the steam generating container 21 is a spout of steam, and the opening 21b at the lower end of the steam generating container 21 is a drainage port. To the upper part of the steam generation container 21, a steam lead-out tube 22 for sending steam into a cooking chamber (not shown) is connected. A drain pipe 23 is connected to a lower portion of the steam generation container 21, and water in the steam generation container 21 is drained by opening a drain valve 24 provided in the drain pipe.

A water level detection tank 25 is erected at a position adjacent to the steam generation container 21, and the lower part of the water level detection tank 25 is connected to the lower part of the steam generation container 21 so as to communicate therewith. A water level sensor 26 is mounted in the water level detection tank 25, and the water level sensor 26 detects the water level in the water level detection tank 25 to detect the water level in the steam generation container 21. The water level sensor 26 detects the lower limit water level L1 and the upper limit water level L2 in the steam generation container 21. A water supply pipe 27 derived from a water supply source such as a water supply is connected to the water level detection tank 25, and a water supply valve 28 is interposed in the water supply pipe 27. When the water supply valve 28 is opened and water is supplied from the water supply pipe 27 to the water level detection tank 25, the water in the water level detection tank 25 flows into the steam generation container 21 from the lower part so that the water level is the same. In this way, the water from the water supply pipe 27 is supplied to the steam generation container 21 through the water level detection tank 25.

An induction heating coil 31 is wound around the outer periphery of the steam generation container 21, and a heating body 32 is provided inside the steam generation container 21. The induction heating coil 31 generates a magnetic field around the heating body 32 when a high frequency current is supplied. The heating body 32 heats the water in the steam generating container 21, and includes a plurality of heating rods 32 a and a holder 32 b that supports the heating rods 32 a on the upper portion of the steam generating container 21. The heating rod 32a is a conductive metal rod-shaped member made of a magnetic material member, extends in the axial direction of the steam generating container 21, and is arranged at equal intervals on a concentric circle centered on the central axis of the cylindrical steam generating container 21. It is arranged. When a high frequency current is supplied to the induction heating coil 31 to generate a magnetic field around the heating rod 32a, an eddy current flows in the heating rod 32a due to the influence of the magnetic field. The heating rod 32a generates heat due to Joule heat generated by electric resistance when eddy current flows, and heats water in the steam generation container 21.

The steam generator 10 includes a high-frequency current supply circuit 41 that supplies a high-frequency current to the induction heating coil 31, an ammeter 42 that measures a current supplied from the high-frequency current supply circuit 41 to the induction heating coil 31, and a high-frequency current supply circuit. And a control device 43 for controlling the operation of 41. The high frequency current supply circuit 41 generates a high frequency current from a direct current, and a well-known IH inverter circuit is adopted in this embodiment. The high frequency current supply circuit 41 is adapted to be supplied with a direct current from an inverter circuit which converts an alternating current from a power source into a direct current. The ammeter 42 measures the output current from the high frequency current supply circuit 41 (current supplied from the high frequency current supply circuit 41 to the induction heating coil 31), and the current value measured by the ammeter 42 is the control device 43. Is output to.

The controller 43 is connected to the water level sensor 26, the water supply valve 28, the high frequency current supply circuit 41, and the ammeter 42. The control device 43 controls the opening/closing of the water supply valve 28 based on the water level detected by the water level sensor 26 by a built-in microcomputer so that the water level in the steam generation container 21 becomes a predetermined water level (a predetermined amount of water). ing. Specifically, the control device 43 opens the water supply valve 28 by the input of the detection of the lower limit water level L1 by the water level sensor 26 to start the water supply to the steam generation container 21, and the water level sensor 26 detects the upper limit water level L2. The water supply valve 28 is closed by an input to stop the water supply to the steam generation container 21, and the water level in the steam generation container 21 is controlled to a predetermined water level (between L1 and L2).

The control device 43 controls the operation of the high-frequency current supply circuit 41 so as to supply the high-frequency current according to the output of heat generation of the heating body 32 from the high-frequency current supply circuit 41 to the induction heating coil 31. .. Specifically, the control device 43 controls the set steam amount in the cooking cabinet (not shown) input to the control device 43 from the operation panel (not shown) and the cooking cabinet (not shown) input to the control device 43. ), the output of the high-frequency current supply circuit 41 is controlled so that the amount of steam required in the cooking cabinet is generated based on the exhaust temperature.

Further, if a problem such as the water level sensor 26 or the water supply valve 28 occurs, water may not be properly supplied into the steam generation container 21. In this state, when a high-frequency current is supplied from the high-frequency current supply circuit 41 to the induction heating coil 31, and the heating rod 32a of the heating body 32 is continuously heated in the steam generation container 21, the heating rod 32a exchanges heat with water. Instead, it continues to generate heat and becomes overheated. When the heating rod 32a becomes overheated at the Curie temperature or higher, the eddy current flowing due to the loss of magnetism in the heating rod 32a decreases, and the high frequency current supply circuit 41 generates an overcurrent due to a decrease in impedance. 41 was likely to be damaged.

For this reason, the control device 43 exceeds the first threshold value set so that the current value measured by the ammeter 42 is higher than the output corresponding current value that normally flows according to the output of the power supplied from the high frequency current supply circuit 41. At this time, it is detected that the heating rod 32a of the heating body 32 loses magnetism and is in an overheated state, and the supply of the high frequency current from the high frequency current supply circuit 41 to the induction heating coil 31 is stopped. In this embodiment, the first threshold value is set to a current value that is 130% higher than the output corresponding current value that normally flows according to the output of the power supplied from the high-frequency current supply circuit 41 . Further, when the output of the high frequency current supply circuit 41 is set to 20% or less of the maximum output in normal use by the control device 43, in order to prevent erroneous detection due to the influence of noise or voltage fluctuation, I try not to set a threshold.

Further, when a steam film is formed around the heating rod 32a in the steam generation container 21 and film boiling occurs, the heat of the heating rod 32a is hardly exchanged with water by the steam film. At this time, the heating rod 32a becomes overheated more slowly than in the case of the above-mentioned empty heating. At this time, since the temperature of the heating rod 32a rises more slowly than in the case of no heating, until the input current of the high frequency current supply circuit 41 measured by the ammeter 42 rises to the above-mentioned first threshold value. It may take a long time, or the high current state may be maintained for a long time without rising to the above-mentioned first threshold value, and the high frequency current supply circuit 41 may generate abnormal heat.

Therefore, the control device 43 sets the current value measured by the ammeter 42 to be higher than the output corresponding current value that normally flows according to the output of the electric power supplied from the high frequency current supply circuit 41 , and the heating element 32 is Curie. The high frequency current supplied from the high frequency current supply circuit 41 to the induction heating coil 31 when the second threshold value set below the first threshold value that can detect the overheated state exceeding the temperature is exceeded. The output is controlled to be temporarily reduced (60 seconds in this embodiment) (50% lower than the output corresponding current value in this embodiment). In this embodiment, the second threshold value is set to a current value that is 110% to 130% higher than the output corresponding current value according to the output, and the output by the high frequency current from the high frequency current supply circuit 41 is normal. At 30% of the maximum output, it is set to 130% higher than the output corresponding current value like the first threshold value, and gradually increases when the output of the high frequency current from the high frequency current supply circuit 41 becomes higher than the above 30%. It is set to be low, and is set to be 110% higher when the output of electric power from the high frequency current supply circuit 41 is 100% (maximum output in normal use). Film boiling in the steam generation container 21 is unlikely to occur when the power output from the high-frequency current supply circuit 41 is low, and is more likely to occur as the power output from the high-frequency current supply circuit 41 is higher. The second threshold value is set to be lower as the power output from the circuit 41 is higher. Further, in the control device 43, when the output of electric power from the high frequency current supply circuit 41 is set to 30% or less of the maximum output in normal use, in order to prevent erroneous detection due to the influence of noise or voltage fluctuation. , The second threshold is not set either.

The operation of the steam generator 10 configured as above will be described. The inside of the cooking chamber of a heating cooking chamber (not shown) is preheated by preheat treatment or the like, the foodstuffs are stored in the cooking chamber, and the foodstuffs in the cooking chamber are heated and cooked by hot air containing steam. At this time, the steam generator 10 supplies steam to the inside of the cooking cabinet under the control of the controller 43 so that the set amount of steam is obtained. The control device 43 controls the operation of the high-frequency current supply circuit 41 to supply a high-frequency current to the induction heating coil 31 so that the inside of the cooking chamber has a set amount of steam and causes the heating rod 32a to generate heat to generate a steam generation container. Steam is generated from the water in 21. Further, since the water in the steam generation container 21 is reduced by generating steam from the steam generation container 21, the control device 43 controls opening/closing of the water supply valve 28 based on the detected water level of the water level sensor 26. The water in the steam generation container 21 is controlled so as to have a water level between the lower limit water level L1 and the upper limit water level L2.

When the controller 43 controls the operation of the high frequency current supply circuit 41 to supply the high frequency current to the induction heating coil 31, if the current value measured by the ammeter 42 becomes higher than the second threshold value, the control is performed. The device 43 controls so that the output of the high frequency current supplied from the high frequency current supply circuit 41 to the induction heating coil 31 is reduced by 50% from the set output for 60 seconds (temporarily). When the high current state is maintained in the high frequency current supply circuit 41 (the overcurrent is generated) due to the formation of the vapor film around the heating rod 32a in the vapor generation container 21, the high frequency current is generated. By temporarily reducing the output of electric power by the supply circuit 41, the steam film generated around the heating rod 32a in the steam generation container 21 disappears, and the heating rod 32a heats the surrounding water (hot water). By exchanging, the state where the high current is maintained in the high frequency current supply circuit 41 (the overcurrent is generated) is eliminated. As a result, it is possible to prevent abnormal heat generation of the high frequency current supply circuit 41, and it is erroneous that the inside of the steam generation container 21 is empty even though there is water (hot water) in the steam generation container 21. Detection can be prevented. The control device 43 controls to reduce the power output from the high frequency current supply circuit 41 for 60 seconds and then return the power output from the high frequency current supply circuit 41.

On the other hand, the high frequency current from the high frequency current supply circuit 41 became a high current (second threshold value) due to the formation of the steam film around the heating rod 32a in the steam generation container 21. Instead, due to a malfunction of the water level sensor 26, the water supply valve 28, or the like, water is not properly supplied into the steam generation container 21, and the heating rod 32a in the steam generation container 21 is overheated to the Curie temperature or higher due to empty heating. An overcurrent may occur in the high frequency current supply circuit 41 due to the state. In this case, the control device 43 may control the output of the high-frequency current supplied from the high-frequency current supply circuit 41 to the induction heating coil 31 for 60 seconds (temporarily) so as to be reduced by 50% from the set output. The high current state of the high frequency current supply circuit 41 is not resolved, and the current value measured by the ammeter 42 continues to rise. When the current value measured by the ammeter 42 exceeds the second threshold value and becomes higher than the first threshold value, the controller 43 confirms that the heating rod 32a is in an overheated state exceeding the Curie temperature due to empty heating. It detects and controls to stop the supply of the high frequency current from the high frequency current supply circuit 41 to the induction heating coil 31. As a result, abnormal heat generation of the high frequency current supply circuit 41 can be prevented, and the heating rod 32a in the steam generating container 21 can be stopped from being heated in an empty state.

10... Induction heating type steam generator, 21... Steam generation container, 31... Induction heating coil, 32... Heating body, 41... High frequency current supply circuit, 42... Ammeter, 43... Control device.

Claims (1)

A steam generation container that stores a predetermined amount of water and generates steam,
An induction heating coil wound around the outer periphery of the steam generating container,
A heating body that is housed in the steam generation container and generates heat by supplying a high-frequency current to the induction heating coil,
A high-frequency current supply circuit for supplying the high-frequency current to the induction heating coil,
A current meter for measuring the current supplied to the high-frequency current supply circuits or al the induction heating coil,
And a control device for controlling the supply of the high-frequency current to the induction heating coil by controlling the operation of the high-frequency current supplying circuit,
The control device, the measured current value measured by the ammeter is set higher than the output corresponding current value that normally flows according to the output of the power supplied from the high-frequency current supply circuit , the heating body to the Curie temperature. When the first threshold value that can detect that the overheated state is exceeded is exceeded, it is detected that the heated body is in the overheated state that exceeds the Curie temperature, and the high-frequency current supply circuit outputs the overheated state. An induction heating steam generator for controlling the induction heating coil to stop the supply of high-frequency current,
The control device, when the measured current value measured by the ammeter exceeds a second threshold value set as a value higher than the output corresponding current value and rising to the first threshold value , An induction heating steam generator, wherein the output of a high frequency current supplied from the high frequency current supply circuit to the induction heating coil is controlled to be temporarily reduced.

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