Combustion apparatus

Abstract

To provide a combustion apparatus (10) capable of accurately detecting deterioration of a flame rod (15).SOLUTION: When ignition of a burner (120) is detected, deterioration of a flame rod is determined on the basis of a current value of a flame current for a deterioration determination period after the detection of the ignition. An effect of the deterioration of the flame rod appears in the current value of the flame current for the deterioration determination period after the detection of the ignition. The current value of the flame current is hardly affected by disturbance compared to an ignition delay time, and a variation of measurement results is small. Thus if the deterioration of the flame rod is determined on the basis of the current value of the flame current in the deterioration determination period after the detection of the ignition, the deterioration of the flame rod can be detected accurately.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a combustion device capable of detecting a flame formed in a burner by using a flame rod. [Background technology]

[0002] Some combustion devices that burn fuel with a burner use a flame rod to detect the flame formed on the burner, and if the flame cannot be detected, it is determined that the burner has misfired and the fuel supply is immediately stopped to stop the combustion. Here, the flame rod is a metal electrode, and the flame is detected based on the following principle. First, it is known that a flame has the property of conducting electricity. Therefore, a voltage is applied to the flame rod, and when the flame comes into contact with the flame rod, a current flows from the flame rod through the flame to the burner. The flame can be detected by detecting this current (hereinafter, flame current).

[0003] Because the flame rod becomes hot when exposed to flame, an oxide film forms on the surface of the flame rod when it is used for a long period of time. Because the oxide film has insulating properties, when an oxide film forms on the surface, it becomes difficult for a flame current to flow even when the flame comes into contact with the flame rod, and the current value of the flame current (hereinafter, the flame current value) becomes small. This phenomenon is called flame rod deterioration. If the flame rod deteriorates further, it becomes impossible to detect a flame even though one is formed in the burner, and as a result, there is a risk that it will be erroneously determined to be a misfire and combustion will be stopped.

[0004] In response to this, a technique has been proposed for detecting deterioration of a flame rod based on the ignition delay time, focusing on the fact that deterioration of the flame rod lengthens the time from when fuel supply to the burner begins to when the flame rod detects a flame (Patent Document 1). This proposed technique makes it possible to detect deterioration of the flame rod before the flame rod becomes unable to detect a flame, thereby preventing a situation in which the combustion device suddenly becomes unable to detect a flame one day and becomes unusable. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2019-74291 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, since the ignition delay time measurement results vary due to slight disturbances at the time of ignition (for example, slight fluctuations in the fuel gas supply pressure or slight movement of the air around the spark plug), the above-mentioned proposed technology had the problem of being unable to accurately detect deterioration of the flame rod.

[0007] The present invention has been made to solve the above-mentioned problems associated with the conventional technology, and realizes a combustion device capable of detecting deterioration of a flame rod with high accuracy. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the combustion device of the present invention adopts the following configuration. A combustion device having a burner for burning fuel, an ignition device for starting combustion of the fuel by igniting the burner, and a flame rod mounted at a position where the flame will come into contact with the burner when a flame is formed by the combustion, and capable of detecting the presence or absence of the flame formed on the burner by detecting a flame current flowing through the flame rod when the flame comes into contact with the flame rod, an ignition detection unit that detects ignition of the burner by detecting that a current value of the flame current exceeds a predetermined ignition judgment value when ignition is performed by the ignition device; a deterioration determination unit that determines deterioration of the flame rod based on a current value of the flame current detected during a predetermined deterioration determination period after the detection of the ignition; The present invention is characterized by comprising:

[0009] In the combustion apparatus of the present invention, when burner ignition is detected, deterioration of the flame rod is judged based on the current value of the flame current during the deterioration judgment period after the detection of ignition.

[0010] As described later, when the burner is ignited, the current value of the flame current increases rapidly and then decreases, but the current value after the decrease shows the influence of the deterioration of the flame rod. Also, the current value of the flame current after the burner is ignited has smaller variations in the measurement results due to the influence of disturbances than the ignition delay time when the burner is ignited. Therefore, if the deterioration of the flame rod is judged based on the current value of the flame current during the deterioration judgment period after the detection of ignition, it is possible to detect the deterioration of the flame rod with high accuracy.

[0011] In the combustion device of the present invention described above, deterioration of the flame rod may be judged as follows. First, an ignition judgment value, a misfire judgment value, and a deterioration judgment value are stored in advance. Here, the misfire judgment value is set to a value equal to or smaller than the ignition judgment value, and the deterioration judgment value is set to a value larger than the misfire judgment value. Then, if the current value of the flame current during the deterioration judgment period is larger than the misfire judgment value but becomes smaller than the deterioration judgment value, it is judged that the flame rod has deteriorated. Also, if the current value of the flame current becomes smaller than the misfire judgment value after burner ignition is detected, it is judged that the burner has misfired.

[0012] When the flame rod deteriorates, the current value of the flame current during the deterioration determination period becomes smaller. Furthermore, when the burner misfires, the current value of the flame current becomes even smaller. Therefore, by determining the deterioration of the flame rod as described above, it is possible to accurately determine the deterioration of the flame rod, without erroneously determining that the burner misfire is the deterioration of the flame rod.

[0013] The combustion device of the present invention described above may also be configured as follows. First, a plurality of burners are provided, and each burner is individually supplied with fuel to start combustion of the fuel, and furthermore, each burner is individually capable of stopping the supply of fuel to stop combustion of the fuel. The flame rod is formed in a rod shape, and is arranged so as to straddle areas in which flames are formed in at least two of the plurality of burners, so that the flame comes into contact with the flame rod no matter which of the two burners forms a flame. If the burner in which the flame rod detects a flame is changed during a deterioration determination period associated with ignition in a burner in which the flame rod can detect a flame, the deterioration determination period may be reset.

[0014] The current value of the flame current changes depending on the position and area of ​​the flame in contact with the flame rod. Therefore, if the burner that burns the fuel is changed during the deterioration judgment period, the current value of the flame current changes, and there is a risk that the deterioration of the flame rod cannot be judged correctly. Therefore, if the deterioration judgment period is reset when the burner that burns is changed, it becomes possible to correctly judge the deterioration of the flame rod based on the current value of the flame current during the reset deterioration judgment period.

[0015] In the combustion device of the present invention described above, the flame rod may be mounted in a cantilevered state, and the flame of at least two burners may be in contact with the flame of the flame rod, including an ignition burner that starts the combustion of fuel by an ignition device, and a flame transfer burner that starts the combustion of fuel by flame transfer formed on the ignition burner. If the flame of the flame transfer burner is a flame transfer burner that contacts the flame on the tip side of the flame rod rather than the ignition burner, and if the burner that is burning is switched from the ignition burner to the flame transfer burner during the deterioration judgment period associated with the ignition of the ignition burner, the deterioration judgment period may be extended.

[0016] The tip side of the flame rod is more susceptible to deterioration than the base side. Therefore, by doing this, it becomes possible to correctly determine the deterioration of the flame rod even when the burning burner is switched from the ignition burner to a flame transfer burner whose flame contacts the tip side of the flame rod more than the ignition burner.

[0017] In addition, in the combustion device of the present invention described above, the judgment results regarding the presence or absence of deterioration of the frame rod may be accumulated for a predetermined period or up to a predetermined number, and if the frequency of the judgment result that the frame rod has deteriorated among the multiple accumulated judgment results is higher than a predetermined threshold frequency, the occurrence of deterioration of the frame rod may be notified.

[0018] In this way, even if the deterioration of the frame rod is erroneously determined, unless the frequency of erroneous determinations becomes high, the frame rod will not be erroneously notified that it has deteriorated, thereby improving the reliability of the notification.

[0019] In addition, in the combustion device of the present invention described above, the time during which the flame rod detects a flame may be accumulated as the combustion time, and if the accumulated combustion time is shorter than a predetermined threshold combustion time, a higher threshold frequency may be used to determine whether or not to notify of the occurrence of deterioration of the flame rod compared to when the accumulated combustion time is longer than the threshold combustion time.

[0020] If the time during which the flame rod detects the flame is short, the possibility that the flame rod is degraded is considered to be small. Therefore, if the accumulated combustion time is shorter than the threshold combustion time, a high threshold frequency is used to determine whether or not to notify the occurrence of deterioration of the flame rod, making it possible to suppress the risk of erroneously notifying the occurrence of deterioration of the flame rod. [Brief description of the drawings]

[0021] [Figure 1] 1 is an explanatory diagram illustrating a water heater 1 equipped with a combustion device 10 of the present embodiment. [Diagram 2] 1 is an explanatory diagram showing how a flame rod 15 detects a flame formed in a burner 120. FIG. [Diagram 3] 2 is an explanatory diagram showing a configuration of a controller 50 for determining deterioration of a frame rod 15. FIG. [Figure 4] FIG. 4 is an explanatory diagram showing a method for determining deterioration of the frame rod 15. [Diagram 5] 13 is an explanatory diagram showing another method for determining deterioration of the frame rod 15. FIG. [Figure 6] 13 is a flowchart of a deterioration determination process executed to determine deterioration of the flame rod 15 after the burner 120 is ignited. [Figure 7] 13 is a flowchart of a deterioration occurrence notification process for notifying the occurrence of deterioration of the frame rod 15. [Figure 8] 11 is an explanatory diagram illustrating an example of a state in which a deterioration detection frequency is calculated by reading out a predetermined number of judgment results from the most recent judgment results; FIG. [Figure 9] 11 is an explanatory diagram illustrating an example of a state in which the deterioration detection frequency is calculated by reading out a determination result for a most recent predetermined period. FIG. [Figure 10] 13 is a flowchart of a degradation occurrence notification process according to a first modified example in which a plurality of threshold frequencies are used by switching between them. [Figure 11] 10 is an explanatory diagram showing a state in which, after the small burner 12a starts combustion, the state is switched to a state in which only the medium burner 12b is burning. FIG. [Figure 12] 13 is a flowchart of the first half of the degradation determination process of a second modified example. [Figure 13] 13 is a flowchart of a second half of the deterioration determination process of the second modified example. [Figure 14] 11 is an explanatory diagram showing a flame current value obtained when the burning burner 120 is switched from the small burner 12a to the medium burner 12b during a deterioration determination period accompanying ignition of the pilot burner. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] A. Equipment configuration: FIG. 1 is an explanatory diagram illustrating a water heater 1 equipped with a combustion device 10. The water heater 1 is structured such that the combustion device 10 is mounted at a lower position inside a combustion can 11, and a heat exchanger 20 is mounted at a position above the combustion device 10 inside the combustion can 11. The combustion device 10 is equipped with a plurality of single burners 12 that combust gaseous fuel (hereinafter, fuel gas), and these single burners 12 are grouped into three groups. Note that the combustion device 10 of this embodiment will be described as combusting gaseous fuel (i.e., fuel gas), but it may also combust liquid fuel.

[0023] The combustion device 10 of the water heater 1 illustrated in FIG. 1 is equipped with a total of 16 single burners 12, which are grouped into a group 12a consisting of three single burners 12, a group 12b consisting of five single burners 12, and a group 12c consisting of eight single burners 12. As described below, the single burners 12 in the same group start and end combustion at the same time, and the single burners 12 in the same group function as one burner as a whole. Therefore, in the following, the group 12a will be referred to as the "small burner 12a", the group 12b will be referred to as the "medium burner 12b", and the group 12c will be referred to as the "large burner 12c". In addition, when it is not necessary to distinguish between the small burner 12a, the medium burner 12b, and the large burner 12c, they will be simply referred to as the burner 120. In the following description, the small burner 12a, the medium burner 12b, and the large burner 12c are described as being formed by a plurality of single burners 12, but each may be formed by one burner. That is, the combustion device 10 may be equipped with three burners with different firepower, with the burner with the smallest firepower being the small burner 12a, the burner with medium firepower being the medium burner 12b, and the burner with the highest firepower being the large burner 12c.

[0024] Each single burner 12 is provided with a gas nozzle 101 for supplying fuel gas. These gas nozzles 101 are grouped into three groups: three gas nozzles 101 to which fuel gas is supplied from the gas distribution chamber 102a, five gas nozzles 101 to which fuel gas is supplied from the gas distribution chamber 102b, and eight gas nozzles 101 to which fuel gas is supplied from the gas distribution chamber 102c. The three gas nozzles 101 to which fuel gas is supplied from the gas distribution chamber 102a supply fuel gas to the three single burners 12 forming the small burner 12a, the five gas nozzles 101 to which fuel gas is supplied from the gas distribution chamber 102b supply fuel gas to the five single burners 12 forming the medium burner 12b, and the eight gas nozzles 101 to which fuel gas is supplied from the gas distribution chamber 102c supply fuel gas to the eight single burners 12 forming the large burner 12c.

[0025] Furthermore, fuel gas is supplied to gas distribution chambers 102a, 102b, and 102c as follows. First, fuel gas is supplied from the outside to gas passage 16 of water heater 1. A main valve 17 is mounted in gas passage 16, and a proportional valve 18 is mounted downstream of main valve 17. When main valve 17 is opened, fuel gas flows into gas passage 16, and the flow rate of fuel gas at that time can be adjusted by the valve opening degree of proportional valve 18. Furthermore, when main valve 17 is closed, the flow of fuel gas flowing into gas passage 16 can be stopped.

[0026] Then, downstream of the proportional valve 18, the gas passage 16 branches into three, one of which is connected to the gas distribution chamber 102a via an electromagnetic on-off valve 19a, one of which is connected to the gas distribution chamber 102b via an electromagnetic on-off valve 19b, and the last gas passage 16 is connected to the gas distribution chamber 102c via an electromagnetic on-off valve 19c.

[0027] Therefore, when the electromagnetic on-off valve 19a is opened with the main valve 17 and the proportional valve 18 open, fuel gas is supplied to each of the single burners 12 forming the small burner 12a via the gas distribution chamber 102a, and when the electromagnetic on-off valve 19a is closed, the supply of fuel gas to each of the single burners 12 of the small burner 12a is stopped. Similarly, when the electromagnetic on-off valve 19b is opened with the main valve 17 and the proportional valve 18 open, fuel gas is supplied to each of the single burners 12 forming the medium burner 12a, and when the electromagnetic on-off valve 19b is closed, the supply of fuel gas to each of the single burners 12 of the medium burner 12a is stopped. Furthermore, when the electromagnetic on-off valve 19c is opened or closed with the main valve 17 and the proportional valve 18 open, fuel gas is supplied to each of the single burners 12 forming the large burner 12a, or the supply of fuel gas is stopped. Therefore, the combustion device 10 of this embodiment can switch the number of single burners 12 to be burned in stages by selecting a burner to be burned from the small burner 12a, the medium burner 12b, and the large burner 12c, or by changing the combination of burners to be burned. In the combustion device 10 of this embodiment, the number is switched in five stages as follows. First, when only the small burner 12a is burned, the number of single burners 12 to be burned is three, which realizes a low firepower state, and when only the medium burner 12b is burned, the number of single burners 12 to be burned is five, which realizes a medium-to-small firepower state. Furthermore, when the small burner 12a and the medium burner 12b are burned, the number of single burners 12 is eight, which realizes a medium firepower state, and when the small burner 12a and the large burner 12c are burned, the number of single burners 12 is eleven, which realizes a medium-to-large firepower state. When the small burner 12a, the medium burner 12b, and the large burner 12c are burned, the number of single burners 12 becomes 16, resulting in a high firepower state. In this specification, changing the burner to be burned may be referred to as "switching the firepower state."

[0028] A combustion fan 13 is attached to the bottom surface of the combustion can 11, and when the combustion fan 13 is rotated, air for burning the fuel gas is supplied to the burner 120 in the combustion can 11. In addition, an ignition plug 14 for igniting the fuel gas by sending a spark to the small burner 12a, and a flame rod 15 for detecting a flame formed by burning the fuel gas in the small burner 12a and the medium burner 12b are mounted on the side surface of the combustion can 11. Here, the flame rod 15 is a rod-shaped electrode made of metal, and has a cantilever structure in which the base end side is attached to the side surface of the combustion can 11 and the tip side is protruding into the inside of the combustion can 11. The tip of the flame rod 15 protruding into the inside of the combustion can 11 is located above the medium burner 12b, and the part adjacent to the base end side of the tip part is located above the small burner 12a. In this embodiment, the fuel gas is ignited by a spark from the ignition plug 14, but the present invention is not limited to this, and the fuel gas may be ignited by heating a heater, for example. In this embodiment, one ignition plug 14 is used to generate a spark only for the small burner 12a, but the present invention is not limited to this, and three ignition plugs 14 may be installed to generate a spark individually for each of the small burner 12a, the medium burner 12b, and the large burner 12c. The ignition plug 14 in this embodiment corresponds to the "ignition device" in the present invention.

[0029] A heat exchanger 20 is mounted inside the combustion can 11 at a position above the combustion device 10, and a water supply passage 21 to which clean water is supplied and a hot water supply passage 22 for supplying hot water generated by the heat exchanger 20 are connected to the heat exchanger 20. A flow rate sensor 23 is mounted midway through the water supply passage 21 to detect the flow rate of clean water flowing into the heat exchanger 20. Furthermore, a hot water faucet 24 and the like are connected to the end of the hot water supply passage 22.

[0030] The combustion device 10 is also equipped with a controller 50. The controller 50 is mainly composed of a microcomputer, and is connected to the combustion fan 13, the ignition plug 14, the flame rod 15, the main valve 17, the proportional valve 18, the electromagnetic on-off valves 19a to 19c, the flow sensor 23, and the like. Furthermore, a remote control 50a is also connected to the controller 50. When the controller 50 detects that the user has opened the hot water faucet 24 based on the output of the flow sensor 23, it rotates the combustion fan 13 and opens the main valve 17, the proportional valve 18, and the electromagnetic on-off valve 19a to generate sparks from the ignition plug 14. Then, the small burner 12a starts combustion. Furthermore, if the heating power of the small burner 12a is insufficient for the heating power corresponding to the hot water temperature set by the remote control 50a or the water volume detected by the flow rate sensor 23, opening the electromagnetic on-off valve 19b in this state allows the flame of the small burner 12a to transfer to the medium burner 12b, thereby starting combustion in the medium burner 12b. Alternatively, opening the electromagnetic on-off valve 19c allows the flame of the small burner 12a to transfer to the large burner 12c, thereby starting combustion in the large burner 12c. Furthermore, the heating power can be adjusted by switching the burner to be burned or adjusting the opening of the proportional valve 18.

[0031] When the combustion in the burner 120 starts in this way, the high-temperature combustion exhaust gas generated by the combustion exchanges heat with clean water as it passes through the inside of the heat exchanger 20, generating hot water, which flows out of the hot water faucet 24 through the hot water supply passage 22. The combustion exhaust gas that has exchanged heat with the clean water in the heat exchanger 20 is discharged to the outside from the exhaust port 2 formed in the upper part of the combustion can 11. In addition, since the flame rod 15 is connected to the controller 50, when the combustion starts in the small burner 12a or the medium burner 12b, the controller 50 can detect the flame formed in the small burner 12a or the medium burner 12b. If the flame rod 15 cannot detect the flame even if a spark is thrown from the ignition plug 14, it is considered that the small burner 12a has not been ignited, so the small burner 12a can be ignited by throwing a spark from the ignition plug 14 again. Furthermore, if ignition is impossible or if for some reason the flame cannot be detected after ignition and combustion has begun, the supply of fuel gas can be stopped by closing the main valve 17.

[0032] FIG. 2 is an explanatory diagram showing a state where the flame formed on the small burner 12a and the medium burner 12b is detected by the flame rod 15. As shown in FIG. 2(a), when the electromagnetic on-off valve 19a is opened while a spark is being thrown from the ignition plug 14 toward the small burner 12a, combustion starts in the small burner 12a, and the flame formed on the small burner 12a comes into contact with the flame rod 15, as shown in FIG. 2(b). If the electromagnetic on-off valve 19b and the electromagnetic on-off valve 19c are also open at this time, the flame of the small burner 12a spreads, and combustion starts in the medium burner 12b and the large burner 12c, forming a flame. FIG. 2(c) shows a state where the flame is formed on the medium burner 12b and the large burner 12c. As shown in FIG. 2(c), in the combustion device 10 of this embodiment, the flame formed on the medium burner 12b also comes into contact with the flame rod 15.

[0033] When the flame comes into contact with the flame rod 15 in this way, a current called a flame current is generated in the flame rod 15. This is for the following reasons. First, the combustion of fuel gas is a kind of chemical reaction in which the fuel gas combines with oxygen in the air to generate carbon dioxide and water, and combustion heat is released along with this. However, it is known that the fuel gas does not directly combine with the oxygen in the air, but the molecules of the fuel gas are first decomposed into substances (called radicals or active species) that are smaller than the molecules and have high reactivity, and then these react with the oxygen in the air to generate carbon dioxide and water. In addition, the combustion heat is released in the process in which the radicals react with oxygen to change into carbon dioxide and water. Therefore, in the flame formed in the burner 120, a two-step reaction is simultaneously proceeding in which the fuel gas flowing out from the burner 120 is decomposed into radicals one after another, and then these radicals combine with oxygen to form carbon dioxide and water.

[0034] Moreover, radicals generally carry an electric charge. Therefore, when a flame formed on the burner 120 comes into contact with the flame rod 15 while a voltage is applied to the flame rod 15, a current (flame current) flows from the flame rod 15 toward the burner 120. Therefore, when a flame is formed on the burner 120, the flame rod 15 is mounted at a position where the flame comes into contact, and a voltage is applied to the flame rod 15, and by detecting the flame current flowing through the flame rod 15, it becomes possible to detect the flame formed on the burner 120.

[0035] Here, the flame rod 15 is made of metal because it must conduct electricity. In addition, the flame rod 15 is exposed to the flame of the burner 120, so its surface becomes hot. For this reason, when the flame rod 15 is used, an oxide film is formed on the surface, and the film gradually becomes thicker as the use continues. Since the metal oxide film does not easily conduct electricity, the flame current becomes difficult to flow when the film becomes thick. When the oxide film on the surface of the flame rod 15 becomes thick, even though a flame is formed on the burner 120, the flame current cannot be detected, and there is a risk that the combustion of the burner 120 will be stopped. The phenomenon in which the oxide film on the surface of the flame rod 15 becomes thick and it becomes difficult to detect the flame current is called deterioration of the flame rod 15. In the combustion device 10 of this embodiment, the controller 50 judges the deterioration of the frame rod 15, and when it is judged that the frame rod 15 has deteriorated, it can display that fact on the display unit of the remote control 50a to notify the user.

[0036] 3 is an explanatory diagram showing the configuration of a controller 50 capable of determining the deterioration of the flame rod 15. As shown in the figure, the controller 50 includes a combustion control unit 51, a current value detection unit 52, an ignition detection unit 53, a misfire detection unit 54, a deterioration determination unit 55, a determination result storage unit 56, a deterioration notification unit 57, and a combustion time accumulation unit 58. Note that these "units" are abstract concepts that represent the functions of the controller 50 to determine the deterioration of the flame rod 15, and do not indicate that parts corresponding to these "units" are mounted inside the controller 50. These "units" may be realized using software or hardware, or may be realized by combining software and hardware.

[0037] The combustion control unit 51 is connected to the combustion fan 13, the ignition plug 14, the flame rod 15, the main valve 17, the proportional valve 18, the electromagnetic on-off valves 19a to 19c, the flow sensor 23, etc., and performs various controls for burning the fuel gas in the burner 120 by generating sparks from the ignition plug 14, opening and closing the main valve 17 and the electromagnetic on-off valves 19a to 19c, and controlling the valve opening degree of the proportional valve 18.

[0038] The current value detection unit 52 is connected to the frame rod 15, applies a positive voltage to the frame rod 15, and detects the current value of the flame current flowing through the frame rod 15 (hereinafter, frame current value).

[0039] When the combustion control unit 51 causes a spark to fly from the ignition plug 14, the ignition detection unit 53 compares the flame current value detected by the current value detection unit 52 with a predetermined ignition judgment value. If the flame current value is greater than the ignition judgment value, it is determined that the fuel gas has been ignited by the spark and combustion has started in the small burner 12a, and outputs a message to that effect to the combustion control unit 51. Then, the combustion control unit 51 determines that combustion has started in the small burner 12a and continues the combustion operation. On the other hand, if the flame current value is smaller than the ignition judgment value, the ignition detection unit 53 determines that the fuel gas has not been ignited, and outputs a message to that effect to the combustion control unit 51. Then, the combustion control unit 51 attempts to ignite the fuel gas by flying a spark from the ignition plug 14 again. In this way, it is possible to reliably start the combustion of the fuel gas in the small burner 12a.

[0040] When combustion in the small burner 12a starts, the misfire detection unit 54 compares the flame current value detected by the current value detection unit 52 with a predetermined misfire judgment value. If the flame current value is smaller than the misfire judgment value, it is judged that the small burner 12a has misfired for some reason during combustion, and outputs that fact to the combustion control unit 51. Therefore, when the small burner 12a misfires, the combustion control unit 51 can stop the supply of fuel gas to the small burner 12a by closing the main valve 17 and the electromagnetic opening and closing valve 19a. In this embodiment, the operation of the misfire detection unit 54 is described using the combustion in the small burner 12a as an example, but the same applies to the combustion in the medium burner 12b. In addition, in this embodiment, when the large burner 12c is burning, the small burner 12a or the medium burner 12b is always burning at the same time, so when the large burner 12c is burning due to switching of the fire power state, if the flame current value is smaller than the misfire judgment value, the electromagnetic opening / closing valve 19c is also closed. In this embodiment, the misfire judgment value is set to a value smaller than the above-mentioned ignition judgment value, but the misfire judgment value may be set to the same value as the ignition judgment value.

[0041] When the ignition detection unit 53 detects ignition, the deterioration determination unit 55 obtains the flame current value from the current value detection unit 52 for a predetermined deterioration determination period to determine whether or not the flame rod 15 has deteriorated. Note that the degree of deterioration may be determined instead of whether or not the flame rod 15 has deteriorated. A method for determining whether or not the flame rod 15 has deteriorated or the degree of deterioration will be described later.

[0042] The judgment result storage unit 56 stores the judgment results obtained by the deterioration judgment unit 55. The judgment results may be stored until a predetermined upper limit is reached, and after the upper limit is reached, the older judgment results may be discarded, thereby storing the upper limit of judgment results. Alternatively, all judgment results obtained during a predetermined period in the past may be stored without setting an upper limit.

[0043] The deterioration notification unit 57 acquires the frequency at which the frame rod 15 is determined to have deteriorated based on the judgment results stored in the judgment result storage unit 56, and when the frequency is higher than a predetermined threshold frequency, displays on the remote control 50a a message indicating that the frame rod 15 has deteriorated, thereby notifying the user that the frame rod 15 has deteriorated. Note that when the deterioration judgment unit 55 determines that the frame rod 15 has deteriorated, the deterioration notification unit 57 may immediately display on the remote control 50a a message indicating that the frame rod 15 has deteriorated, to notify the user of the occurrence of deterioration, but if the occurrence of deterioration is notified based on the frequency at which the frame rod 15 is determined to have deteriorated, the risk of notifying an incorrect content can be eliminated.

[0044] The combustion time accumulation unit 58 accumulates the combustion time of the burner 120. In this embodiment, while the flame rod 15 detects a flame (i.e., while the small burner 12a or the medium burner 12b is burning), the burner 120 is considered to be burning, and the time during which the flame rod 15 detects a flame is accumulated as the combustion time. Then, when comparing the frequency at which the flame rod 15 is judged to have deteriorated with the threshold frequency, the deterioration notification unit 57 compares the frequency with a lower threshold frequency as the accumulated combustion time increases. While the time during which the flame rod 15 is exposed to a flame (i.e., the combustion time) is short, the possibility that the flame rod 15 has deteriorated is small. Therefore, if the accumulated combustion time is compared with a high threshold frequency while it is short, it becomes difficult to notify that the flame rod 15 has deteriorated, and it is possible to suppress erroneous notification of the deterioration of the flame rod 15 to the user.

[0045] B. Basic principles for determining deterioration of the flame rod 15: FIG. 4 is an explanatory diagram showing a method in which the controller 50 mounted on the combustion device 10 of this embodiment judges the deterioration of the flame rod 15. FIG. 4 shows time series data of the flame current value detected by the flame rod 15 after the spark plug 14 emits a spark. The spark plug 14 emits a spark at time 0. As shown in the figure, the flame current value increases rapidly at a point about 1 second after the spark plug 14 emits a spark, and then immediately starts to decrease. Then, after the decrease starts, the decrease rate becomes slower with the passage of time, and after about 2 seconds have passed since the decrease started, the current value starts to increase slowly. When the flame current value exceeds the ignition judgment value shown by the dashed line in the figure, it is judged that a flame is formed in the small burner 12a and ignition has occurred.

[0046] Here, the time that elapses from when the spark is thrown by the ignition plug 14 until the flame current value increases is slightly less than one second, which is believed to be because it takes time for the concentration of the fuel gas to reach the combustion range. That is, the controller 50 opens the main valve 17 and the electromagnetic opening / closing valve 19a (see FIG. 1) to supply fuel gas to the small burner 12a almost simultaneously with the throwing of a spark from the ignition plug 14, but a certain amount of time is required from the opening of the electromagnetic opening / closing valve 19a until the concentration of the fuel gas flowing out of the small burner 12a reaches the combustion range.

[0047] As shown in Fig. 4, the frame current value increases rapidly, then decreases once, and then increases slowly again. However, the inventors of the present application have found that the influence of deterioration of the frame rod 15 appears to the extent that the frame current value decreases. For example, the minimum value to which the frame current value decreases (hereinafter, the minimum current value FCmin) becomes smaller as the use time of the frame rod 15 becomes longer. In Fig. 4, the frame current value obtained by the frame rod 15 after a long period of use is shown by a broken line. Although not shown in Fig. 4, the minimum current value of the frame current shown by the broken line is smaller than the minimum current value FCmin of the frame current when it is new, shown by the solid line in the figure.

[0048] Therefore, a deterioration judgment period of a predetermined time (here, 5 seconds) is set from the time when the flame current value exceeds the ignition judgment value (the time when ignition of the burner 120 is detected), and the minimum current value FCmin of the flame current during the deterioration judgment period is detected. If the minimum current value FCmin falls below the predetermined deterioration judgment value, it is determined that the flame rod 15 has deteriorated. The deterioration judgment value is set to a value smaller than the ignition judgment value. In FIG. 4, the deterioration judgment value is represented by a two-dot chain line, and the ignition judgment value is represented by a one-dot chain line. If the flame current value falls below the misfire judgment value shown by the dashed line in FIG. 4, it is determined that the burner 120 has misfired.

[0049] Since the minimum current value FCmin of the frame current becomes smaller as the deterioration of the frame rod 15 progresses, the degree of deterioration of the frame rod 15 may be detected based on the minimum current value FCmin of the frame current. Alternatively, a plurality of deterioration determination values ​​may be set, and it may be determined that the deterioration of the frame rod 15 progresses as the minimum current value FCmin of the frame current falls below a smaller deterioration determination value.

[0050] 5, two deterioration judgment values ​​are set, namely, deterioration judgment value 1 and deterioration judgment value 2 smaller than deterioration judgment value 1, and when the minimum current value FCmin of the frame current is smaller than deterioration judgment value 1 but larger than deterioration judgment value 2, it can be determined that deterioration of the frame rod 15 has started, and the user is notified that it is better to prepare a replacement frame rod 15. When the minimum current value FCmin of the frame current is smaller than deterioration judgment value 2, it can be determined that deterioration of the frame rod 15 has progressed, and the user is notified that it is better to replace the frame rod 15 as soon as possible.

[0051] As explained with reference to FIG. 4 and FIG. 5, the method of determining the presence or absence of deterioration of the frame rod 15 or the degree of deterioration based on the flame current value during the deterioration determination period can determine the deterioration of the frame rod 15 with higher accuracy than the conventionally proposed determination methods. The conventionally proposed determination methods use the time (ignition delay time) from when the supply of fuel to the burner is started until the flame rod detects the flame, but the ignition delay time varies widely. The reason for this is that, as described above, the ignition delay time is considered to be due to the time from when the main valve 17 and the electromagnetic opening / closing valve 19a are opened until the concentration of the fuel gas in the small burner 12a reaches the combustion range. The time until the concentration of the fuel gas reaches the combustion range can vary due to various factors such as changes in the gas pressure of the fuel gas, deterioration of the combustion fan 13, and resistance within the combustion device 10 (resistance of the heat exchanger 20, outside wind applied to the exhaust port 2, etc.). As a result, it is difficult to accurately determine the deterioration of the frame rod 15 with the conventionally proposed determination methods.

[0052] In contrast, in the judgment method of the present embodiment described above with reference to FIG. 4, deterioration of the frame rod 15 is judged by focusing on the phenomenon that the flame current value increases and exceeds the ignition judgment value to detect ignition, and then the current value decreases, so that deterioration of the frame rod 15 can be judged without being affected even if the time until ignition is detected varies due to disturbance. In addition, since the current value changes slowly near the minimum current value FCmin of the flame current, even if noise is included in the measured flame current value, the minimum current value FCmin can be accurately detected by removing the noise using a low-pass filter. As a result, the judgment method of the present embodiment makes it possible to judge deterioration of the frame rod 15 with higher accuracy than the judgment methods proposed in the past.

[0053] C. Deterioration judgment process: FIG. 6 is a flowchart of a deterioration judgment process executed by the controller 50 mounted on the combustion device 10 of this embodiment to judge the deterioration of the flame rod 15 after the small burner 12a is ignited. In the deterioration judgment process, first, the small burner 12a is ignited by igniting the small burner 12a by igniting the small burner 12a (STEP 10), and then, it is judged whether the small burner 12a is ignited or not (STEP 11). As described above with reference to FIG. 2, when the electromagnetic opening and closing valve 19a is opened while igniting the small burner 12a with sparks being ignited, the combustion of fuel gas is normally started in the small burner 12a and the flame is detected by the flame rod 15. Therefore, if the flame is detected by the flame rod 15, it can be judged that the flame is ignited, and if the flame is not detected, it can be judged that the flame is not ignited. In this embodiment, if the flame current value detected by the flame rod 15 exceeds a predetermined ignition judgment value, it is judged that the flame is detected (see FIG. 4).

[0054] As a result, if the small burner 12a is not ignited (STEP 11: no), a spark is again generated from the ignition plug 14 (STEP 10), and then it is determined whether the small burner 12a is ignited (STEP 11). If it is determined that the small burner 12a is ignited in STEP 11 (STEP 11: yes), a predetermined time (5 seconds in this embodiment) from the detection of ignition is set as a deterioration determination period (STEP 12), and then the fact that a new deterioration determination has started is stored (STEP 13). In this embodiment, the date and time when the deterioration determination started are stored, but instead of storing the time, the order in which the deterioration determination started for each date may be stored. Alternatively, only the order in which the deterioration determination started may be stored without storing the date, and when the number of stored items reaches a predetermined upper limit number (for example, 20 items), the oldest memory may be discarded and the start of a new deterioration determination may be stored.

[0055] Next, it is determined whether the deterioration judgment period has ended (in this embodiment, whether 5 seconds have passed since the ignition was detected) (STEP 14). Immediately after the deterioration judgment period is set in STEP 12, it is determined that the deterioration judgment period has not ended (STEP 14: no), so it is determined whether the flame current value of the flame rod 15 is smaller than a predetermined deterioration judgment value (STEP 15). Here, the deterioration judgment value is set to a value smaller than the ignition judgment value and larger than the misfire judgment value. Also, as described above with reference to FIG. 4, the flame current value increases in a peak shape when the small burner 12a is ignited, so in normal cases, it is determined that the flame current value is larger than the deterioration judgment value at the beginning of the deterioration judgment period (STEP 15: no), and it is again determined whether the deterioration judgment period has ended (STEP 14). Then, if the deterioration judgment period has not ended (STEP 14: no), it is determined whether or not the frame current value is smaller than the deterioration judgment value (STEP 15), and if the frame current value is greater than the deterioration judgment value (STEP 15: no), it is again determined whether or not the deterioration judgment period has ended (STEP 14).

[0056] If it is determined that the deterioration determination period has ended while repeating such processing (STEP 14: yes), it can be determined that the flame rod 15 is not deteriorated, and the deterioration determination processing in FIG. 6 is terminated after executing the deterioration determination processing (STEP 20) described later. On the other hand, if it is within the deterioration determination period (STEP 14: no) and the flame current value is below the deterioration determination value (STEP 15: yes), it can be determined that the flame rod 15 is deteriorated. In this case, the fact that deterioration of the flame rod 15 has been detected is stored in a state associated with the start of a new deterioration determination stored in STEP 13 (STEP 16). Then, after performing the deterioration occurrence notification processing described later (STEP 20), the deterioration determination processing in FIG. 6 is terminated. Although not shown, after detecting ignition, it is always determined whether the flame current value is smaller than the misfire determination value. If the flame current value is smaller than the misfire determination value, it is considered that the burner 120 has misfired for some reason, and the solenoid opening / closing valves 19a to 19c and the main valve 17 are closed. In this manner, in the deterioration determination process of this embodiment, whenever the ignition of the burner 120 is detected (STEP 11: yes), the fact that the deterioration determination has started is stored (STEP 13), and further, if the flame rod 15 is deteriorated (STEP 16: yes), the fact that the deterioration has been detected by the deterioration determination that has started is stored (STEP 17). Then, in the deterioration occurrence notification process (STEP 20) described below, the occurrence of deterioration of the flame rod 15 is notified to the user of the water heater 1 based on these stored contents. Note that, in STEP 15 of this embodiment, it is determined whether the flame current value falls below the deterioration determination value, but it may be determined whether the flame current value continues to fall below the deterioration determination value for a predetermined period (for example, one second). In this way, even if the flame current value falls below the deterioration determination value for an extremely short time due to the influence of noise, for example, it is possible to prevent the frame rod 15 from being erroneously determined to be deteriorated.

[0057] D. Deterioration occurrence notification process: FIG. 7 is a flowchart of the deterioration occurrence notification process for notifying the user of the water heater 1 of the occurrence of deterioration of the frame rod 15. As shown in the figure, in the deterioration occurrence notification process, first, the judgment results of the most recent predetermined number of deterioration judgments are obtained (STEP 21). In this embodiment, the most recent 20 judgment results are obtained. Then, it is determined whether the frequency at which deterioration was detected in the obtained deterioration judgment results (hereinafter, deterioration detection frequency) is equal to or higher than a predetermined threshold frequency (STEP 22). As a result, if the deterioration detection frequency does not reach the threshold frequency (STEP 22: no), the deterioration occurrence notification process is terminated without notifying the occurrence of deterioration, but if the deterioration detection frequency reaches the threshold frequency (STEP 22: yes), the deterioration occurrence notification process is terminated after notifying the user of the occurrence of deterioration (STEP 23).

[0058] Fig. 8 is an explanatory diagram showing a specific example of determining whether or not to notify the occurrence of deterioration in the deterioration occurrence notification process. The circles shown in Fig. 8 (i.e. Fig. 8(a) and Fig. 8(b)) indicate that a deterioration determination has been made. Also, the black circles in Fig. 8 indicate that deterioration has been detected by the deterioration determination. That is, when the start of a new deterioration determination is stored in the deterioration determination process shown in Fig. 6 (STEP 13), one white circle shown in Fig. 8 is stored, and when further deterioration is detected (STEP 15: yes), the white circle is changed to a black circle (STEP 16).

[0059] In the example shown in FIG. 8(a), there is one circle for the date today, and the circle is a white circle. This indicates that only one deterioration judgment has been performed today, and no deterioration was detected in the deterioration judgment. There are four circles for the date one day ago, two of which are white circles and the remaining two are black circles. This indicates that four deterioration judgments were performed yesterday, two of which did not detect deterioration, and two of which did detect deterioration. Similarly, five deterioration judgments were performed two days ago and three days ago, and one of them detected deterioration, but the remaining four did not. Furthermore, three deterioration judgments were performed four days ago, and four of which did detect deterioration in either case.

[0060] In STEP 21 of the degradation occurrence notification process, a predetermined number (20 in this embodiment) of such degradation judgment results are read from the most recent ones. The part enclosed by a dashed-dotted rectangle in FIG. 8(a) represents the judgment results read out in this way. Then, if there are five or more judgment results (black circles) in which degradation is detected among the 20 judgment results read out, STEP 22 judges as "yes" and notifies the occurrence of degradation. In the example shown in FIG. 8(a), since there are four black circles among the 20 judgment results enclosed by the dashed-dotted rectangle, STEP 22 judges as "no", and the degradation occurrence notification process is terminated without notifying the occurrence of degradation. Also, as illustrated in FIG. 8(b), if the second degradation judgment is performed today and degradation is detected, when a predetermined number (20) of judgment results are read out from the most recent judgment results, as enclosed by a dashed-dotted rectangle in the figure, the number of black circles indicating that degradation is detected will be five. 7, the determination is "yes," and the occurrence of deterioration is notified (STEP 23). In the combustion device 10 of this embodiment, the deterioration of the flame rod 15 is notified by displaying it on the remote control 50a, but the notification may be made using other methods, such as emitting a predetermined voice or sound effect from a speaker.

[0061] In the degradation occurrence notification process shown in Fig. 7, a predetermined number of judgment results are read from the most recent judgment result, but judgment results within a predetermined period may be read instead of a predetermined number of results. For example, as shown in Fig. 9, it may be possible to determine whether or not to notify degradation by reading judgment results from today up to three days ago.

[0062] As described above, the combustion device 10 of this embodiment sets a deterioration judgment period when it detects the ignition of the burner 120, and judges the deterioration of the flame rod 15 based on the flame current value detected in the deterioration judgment period. As described above with reference to Fig. 4, the flame current value in the deterioration judgment period has a smaller variation in the measurement value compared to the ignition delay time, so the method of this embodiment can judge the deterioration of the flame rod 15 with higher accuracy than the conventional method that uses the ignition delay.

[0063] In addition, even if deterioration of the frame rod 15 is detected, it is not reported immediately, but whether or not to report the deterioration is determined based on a predetermined number of judgment results or multiple judgment results obtained over a predetermined period of time. Therefore, even if deterioration is mistakenly detected for some reason, the occurrence of deterioration is not immediately reported. As a result, it is possible to report the occurrence of deterioration with even higher reliability.

[0064] E. First Variation: In the above-described degradation occurrence notifying process, the threshold frequency used to determine whether or not to notify degradation has been described as being fixed, but a plurality of threshold frequencies having different values ​​may be switched.

[0065] 10 is a flowchart of a degradation occurrence notification process according to a first modified example in which a plurality of threshold frequencies are switched and used. This process is executed in place of the degradation occurrence notification process (STEP 20) described above in the degradation determination process of FIG.

[0066] As shown in Figure 10, in the deterioration occurrence notification process of the first modified example, similar to the deterioration occurrence notification process of the present embodiment described above using Figure 7, first, the judgment results of the most recent predetermined number of deterioration judgments (here, 20 times) are obtained (STEP 31).

[0067] Next, in the deterioration occurrence notification process of the first modification, it is determined whether or not the accumulated combustion time of the combustion device 10 has reached a predetermined threshold combustion time (here, 2000 hours) (STEP 32). In the combustion device 10 of the first modification, the time during which a flame is detected by the flame rod 15 (i.e., the time during which the flame current value is greater than the misfire judgment value) is accumulated and stored as the accumulated combustion time.

[0068] As a result, if the cumulative combustion time has reached the threshold combustion time (STEP 32: yes), the threshold frequency is set to a first threshold frequency (STEP 33). The first threshold frequency is set to a value similar to the threshold frequency of the deterioration occurrence notification process of this embodiment described above (i.e., a frequency of 5 times out of 20 times). On the other hand, if the cumulative combustion time has not reached the threshold combustion time (STEP 32: no), the threshold frequency is set to a second threshold frequency that is higher than the first threshold frequency (STEP 34). Here, the second threshold frequency is set to a frequency of 10 times out of 20 times.

[0069] Thereafter, it is determined whether the frequency at which deterioration was detected (deterioration detection frequency) in the deterioration judgment results acquired in STEP 31 is equal to or greater than a threshold frequency (STEP 35), and if the deterioration detection frequency reaches the threshold frequency (STEP 35: yes), the occurrence of deterioration is notified to the user (STEP 36), and the deterioration occurrence notification process of the first modified example is terminated. In contrast, if the deterioration detection frequency does not reach the threshold frequency (STEP 35: no), the deterioration occurrence notification process is terminated without notifying the occurrence of deterioration.

[0070] In the deterioration occurrence notification process of the first modified example described above, the threshold frequency is set to a high frequency until the cumulative combustion time reaches the threshold combustion time, so that the occurrence of deterioration is not easily notified. Since it is unlikely that the flame rod 15 is deteriorated while the cumulative combustion time is small, the threshold frequency is set to a high frequency, so that the occurrence of deterioration is not erroneously notified. On the other hand, when the flame rod 15 is really deteriorated, the deterioration is detected with a high frequency, so that the occurrence of deterioration can be notified.

[0071] In the above-described deterioration occurrence notification process of the first modified example, one threshold combustion time is stored, and the first or second threshold frequency is switched to by determining whether the cumulative combustion time is greater than the threshold combustion time. However, a plurality of threshold combustion times and a plurality of threshold frequencies may be stored, and the threshold frequency may be switched to a lower frequency as the cumulative combustion time becomes shorter by determining whether the cumulative combustion time is greater than the threshold combustion time.

[0072] F. Second Variation: In the above-mentioned embodiment and the first modified example, it has been explained that the medium burner 12b does not start burning during the deterioration judgment period after the small burner 12a is ignited by the ignition plug 14. However, in reality, during the deterioration judgment period due to the ignition of the small burner 12a, for example, the user of the water heater 1 may open the hot water faucet 24 (see FIG. 1) further, and the burning burner may switch from the small burner 12a to the medium burner 12b, or the small burner 12a and the medium burner 12b may burn simultaneously (this corresponds to the switching of the fire power state described above). The small burner 12a corresponds to the "ignition burner" of the present invention, and the medium burner 12b corresponds to the "fire transfer burner" of the present invention.

[0073] FIG. 11 is an explanatory diagram showing a state in which the burner to be burned is switched to the medium burner 12b after starting combustion in the small burner 12a (low heat state → medium-low heat state). To start combustion in the small burner 12a, first, the small burner 12a is ignited by a spark from the ignition plug 14 as shown in FIG. 11(a). Then, as shown in FIG. 11(b), a flame is formed in the small burner 12a and combustion starts. From this state, when the electromagnetic opening and closing valve 19b is opened, fuel gas flows out from the medium burner 12b, so that the flame of the small burner 12a transfers to the medium burner 12b as shown in FIG. 11(c). As a result, combustion starts in the medium burner 12b as shown in FIG. 11(d). After the combustion in the medium burner 12b has started, the electromagnetic opening / closing valve 19a is closed to stop the combustion in the small burner 12a, thereby completing the switching of the burner 120 to be burned.

[0074] Here, the flame current flowing through the flame rod 15 changes depending on the position and area of ​​the flame in contact with the flame rod 15. Therefore, when a change in the fire power state (for example, a change from the small burner 12a to the medium burner 12b) occurs, the position and area of ​​the flame in contact with the flame rod 15 changes during the deterioration determination period, so there is a risk that deterioration of the frame rod 15 cannot be detected correctly. However, even in such a case, deterioration of the frame rod 15 can be detected correctly by using the following method.

[0075] 12 and 13 are flowcharts of the deterioration judgment process of the second modified example. This process is also executed by the controller 50 mounted on the combustion device 10, similar to the deterioration judgment process of the present embodiment described above with reference to FIG. 6. In the deterioration judgment process of the second modified example, the small burner 12a is ignited by a spark from the ignition plug 14 (STEP 40), and it is determined whether the small burner 12a is ignited (STEP 41). If the small burner 12a is not ignited (STEP 41: no), the small burner 12a is ignited again (STEP 40) and it is determined whether the small burner 12a is ignited (STEP 41). If the small burner 12a is ignited (STEP 41: yes), a deterioration judgment period of a predetermined time (here, 5 seconds) is set (STEP 42), and the fact that a new deterioration judgment has started is stored (STEP 43).

[0076] Next, it is determined whether the deterioration judgment period has ended (STEP 44), and if the deterioration judgment period has not ended (STEP 44: no), it is determined whether to switch the firepower state (STEP 45). The controller 50 that executes the deterioration judgment process of FIG. 12 and FIG. 13 also controls the start and end of combustion in each burner 120, so it can determine whether to switch the firepower state. As a result, if the firepower state is to be switched (STEP 45: yes), the deterioration judgment period is reset (STEP 46). For example, if the deterioration judgment period is set to 5 seconds, when the small burner 12a is switched to the medium burner 12b (when switching from a low firepower state to a medium-low firepower state) at the point when 3 seconds have elapsed since the small burner 12a was ignited, the deterioration judgment period of 5 seconds is reset at that point, and as a result, the deterioration judgment period is extended to 8 seconds in total.

[0077] After resetting the deterioration judgment period in this way (STEP 46), the process returns to STEP 44 to determine whether the deterioration judgment period has elapsed. On the other hand, if the heating power state is not to be switched (STEP 45: no), the deterioration judgment period is not reset, and a determination is made as to whether the frame current value of the flame rod 15 is smaller than the deterioration judgment value (STEP 47). If the flame current value is larger than the deterioration judgment value (STEP 47: no), the process returns to STEP 44 to determine whether the deterioration judgment period has elapsed.

[0078] In this way, in the deterioration judgment process of the second modified example, if the firepower state is switched during the deterioration judgment period accompanying the ignition of the small burner 12a, the deterioration judgment period is reset, but other points are the same as the deterioration judgment process of this embodiment described above using Figure 6. That is, the deterioration judgment period is set with the ignition of the small burner 12a (STEP 42), and after the start of a new deterioration judgment is stored (STEP 43), the judgments of STEP 44 and STEP 47 are repeated until the deterioration judgment period has elapsed (STEP 44: yes) or the flame current value becomes smaller than the deterioration judgment value (STEP 47: yes). The reason for determining whether or not the firepower state is switched is that when the firepower state is switched, it is estimated that the burner 120 whose flame is detected by the flame rod 15 during the deterioration judgment period has been changed. However, in this embodiment, for example, when the firepower state is switched from a low firepower state to a medium-high firepower state, the burner 120 that forms the flame that contacts the flame rod 15 does not change from the small burner 12a. Therefore, the deterioration judgment period is reset only when the fire power state is switched in such a way that the burner by which the flame rod 15 actually detects the flame changes (for example, switching from a low fire power state to a medium fire power state, or switching from a medium-low fire power state to a low fire power state), and the deterioration judgment period may not be reset when the fire power state is switched in such a way that the burner by which the flame rod 15 detects the flame does not change (for example, switching from a low fire power state to a medium-high fire power state, or switching from a medium fire power state to a high fire power state).

[0079] If it is determined that the deterioration determination period has ended while repeating such processing (STEP 44: yes), the deterioration determination processing (STEP 20) described above is executed, and then the deterioration determination processing of the second modified example is terminated. On the other hand, if the frame current value falls below the deterioration determination value (STEP 47: yes), it can be determined that the frame rod 15 has deteriorated, and after storing the fact that deterioration of the frame rod 15 has been detected (STEP 48 in FIG. 13), the deterioration occurrence notification processing described above (STEP 20) is executed. Note that the deterioration occurrence notification processing may be the deterioration occurrence notification processing of the first modified example described above with reference to FIG. 10 instead of the deterioration occurrence notification processing of the present embodiment described above with reference to FIG. 7 (STEP 20). Then, after the deterioration occurrence notification processing of the present embodiment (STEP 20) or the deterioration occurrence notification processing of the first modified example (STEP 30) is executed, the deterioration determination processing of the second modified example is terminated. In the above-mentioned second modified example, the burner at the time of ignition is the small burner 12a, and when the small burner 12a is switched to the medium burner 12b, the deterioration judgment period is reset. However, this is not limited to this, and when the burners at the time of ignition are the small burner 12a and the medium burner 12b, and when the state in which the small burner 12a and the medium burner 12b are burning is switched to the state in which the medium burner 12b is burning, the flame current value changes during the deterioration judgment period, so there is a risk that the deterioration of the flame rod 15 cannot be correctly judged. Therefore, even when such a switching is performed, the deterioration judgment period may be reset.

[0080] FIG. 14 is an explanatory diagram showing the flame current value obtained when the fire power state is switched from a low fire power state to a medium-low fire power state during the deterioration judgment period associated with the ignition of the small burner 12a, that is, when the burning burner 12 is switched from the small burner 12a to the medium burner 12b. As shown by the solid line in the figure, two peaks occur in the flame current value, the first peak is a peak associated with the ignition of the small burner 12a, and the second peak is a peak associated with the ignition of the medium burner 12b. In the example shown in FIG. 14, since the second peak occurs during the deterioration judgment period associated with the ignition of the small burner 12a, it becomes difficult to correctly judge the deterioration of the flame rod 15, but this does not occur during the reset deterioration judgment period, so it becomes possible to correctly judge the deterioration of the flame rod 15.

[0081] Incidentally, when the deterioration judgment period is reset as described above, the deterioration judgment period is practically extended. In the example shown in FIG. 14, the deterioration judgment period is reset when 1.5 seconds have elapsed since the ignition of the small burner 12a was detected, and the deterioration judgment period is therefore extended from 5 seconds to 6.5 seconds. If the heating power state is switched again before the extended deterioration judgment period ends, the deterioration judgment period will be further extended. However, it is not preferable for the deterioration judgment period to be too long. This is because, if the deterioration judgment period is extended, for example, the flame that was in contact with the flame rod 15 may move away from the flame rod 15 for a short time due to the influence of wind, reducing the flame current value, and there is a possibility that the flame rod 15 may be erroneously determined to be deteriorated. Therefore, an upper limit time of, for example, 10 seconds may be set for the deterioration judgment period, so that the practical deterioration judgment period does not exceed the upper limit time even when the deterioration judgment period is reset. Alternatively, an upper limit may be set for the number of times the deterioration judgment period is reset, and when the upper limit is reached, the deterioration judgment period may not be reset even if the heating power state is switched.

[0082] Alternatively, when comparing the position where the flame of the small burner 12a contacts the flame rod 15 with the position where the flame of the medium burner 12b contacts the flame rod 15, and the flame of the medium burner 12b contacts the tip side of the flame rod 15 more than the flame of the small burner 12a, the deterioration judgment period may be reset only when the burner that burns is switched to the medium burner 12b after ignition by the small burner 12a, that is, when the fire power state is switched from the low fire power state to the small / medium fire power state. For example, in the example shown in FIG. 11, as is clear from a comparison between FIG. 11(b) and FIG. 11(d), the flame of the medium burner 12b contacts the tip side of the flame rod 15 more than the flame of the small burner 12a, so in such a case, the deterioration judgment period may be reset only when the fire power state is switched from the low fire power state to the small / medium fire power state after ignition by the small burner 12a. The reason for this is as follows.

[0083] 1, the flame rod 15 is a rod-shaped metal member, and has a cantilever structure in which the base end is attached to the side of the combustion can 11 and the tip end is protruding into the inside of the combustion can 11. The tip of the flame rod 15 protruding into the inside of the combustion can 11 is located above the intermediate burner 12b, and the part adjacent to the base end side of the tip is located above the small burner 12a. For this reason, when the small burner 12a and the intermediate burner 12b are burned, the tip side of the flame rod 15 becomes hotter than the base end side, and an oxide film is easily formed on the surface, so the tip side of the flame rod 15 deteriorates faster than the base end side.

[0084] Therefore, when the fire power state is switched from a low fire power state to a medium-low fire power state, the deterioration at the tip side of the flame rod 15, which is prone to deterioration, cannot be detected unless the deterioration judgment period is reset. On the other hand, for example, when the fire power state is switched from a low fire power state to a medium fire power state, that is, when the burning burner is changed from the small burner 12a to the small burner 12a and the medium burner 12b, the flame of the small burner 12a, which is closer to the base end side and less prone to deterioration than the tip side, continues to contact the flame rod 15, so there is little need to reset the deterioration judgment period. Also, unlike the above embodiment, even if ignition is performed with a burner located at the tip side of the flame rod and the burning burner is changed from the burner located at the tip side of the flame rod to the burner near the base end side of the flame rod during the deterioration judgment period, the flame current value is easy to detect, so there is little need to reset the deterioration judgment period.

[0085] For the reasons stated above, when the flame of the small burner 12a contacts the base end side of the frame rod 15 and the flame of the medium burner 12b contacts the tip side of the frame rod 15, and after ignition by the small burner 12a the burning burner switches to the medium burner 12b, i.e., when the fire power state switches from a low fire power state to a low to medium fire power state, by resetting the deterioration judgment period, it is possible to achieve a good balance between the advantage of being able to detect deterioration at the tip side of the frame rod 15 and the disadvantage of essentially extending the deterioration judgment period.

[0086] Various embodiments and modifications have been described above, but the present invention is not limited to the above embodiments and modifications, and can be embodied in various forms without departing from the spirit of the present invention. [Explanation of symbols]

[0087] 1...water heater, 2...exhaust port, 10...combustion device, 11...combustion can, 12...single burner, 12a...small burner, 12b...medium burner, 12c...large burner, 13...combustion fan, 14...spark plug, 15...flame rod, 16...gas passage; 17...main valve; 18...proportional valve; 19a to 19c... electromagnetic on-off valve, 20... heat exchanger, 21... water supply passage, 22...hot water passage, 23...flow rate sensor, 24...hot water faucet, 50...controller, 50a...remote control unit, 51...combustion control unit, 52...current value detection unit; 53...ignition detection unit; 54...misfire detection unit; 55: deterioration determination unit; 56: determination result storage unit; 57: deterioration notification unit; 58... combustion time accumulation unit, 101... gas nozzle, 102a to 102c...gas distribution chambers, 120...burner.

Claims

1. A combustion device having a burner for burning fuel, an ignition device for starting combustion of the fuel by igniting the burner, and a flame rod mounted at a position where the flame will come into contact with the burner when a flame is formed by the combustion, and capable of detecting the presence or absence of the flame formed on the burner by detecting a flame current flowing through the flame rod when the flame comes into contact with the flame rod, an ignition detection unit that detects ignition of the burner by detecting that a current value of the flame current exceeds a predetermined ignition judgment value when ignition is performed by the ignition device; a deterioration determination unit that determines deterioration of the flame rod based on a current value of the flame current detected during a predetermined deterioration determination period after the detection of the ignition; A combustion device comprising:

2. 2. The combustion apparatus according to claim 1, a misfire detection unit that stores a predetermined misfire judgment value that is set to be equal to the ignition judgment value or a value smaller than the ignition judgment value, and detects a misfire of the burner by detecting that the current value of the flame current becomes smaller than the misfire judgment value after the ignition is detected, The deterioration determination unit is A predetermined deterioration judgment value set to a value greater than the misfire judgment value is stored, When the current value of the flame current during the deterioration judgment period is greater than the misfire judgment value but becomes smaller than the deterioration judgment value, it is judged that the flame rod has deteriorated. A combustion device characterized by:

3. 2. The combustion apparatus according to claim 1, a plurality of burners each capable of starting combustion of the fuel individually by supplying the fuel individually and stopping combustion of the fuel individually by stopping the supply of the fuel individually; The flame rod is formed in a rod shape and arranged across the areas where the flames of at least two of the burners are formed, so that the flame can be contacted even if the flame is formed by either of the two burners, The deterioration determination unit resets the deterioration determination period when the burner at which the flame rod detects the flame is changed during the deterioration determination period associated with the ignition at the burner at which the flame rod can detect the flame. A combustion device characterized by:

4. The combustion apparatus according to claim 3, The frame rod is mounted in a cantilevered manner; The at least two burners whose flame can come into contact with the flame rod include an ignition burner that starts combustion of the fuel by the ignition device, and a flame-transfer burner that starts combustion of the fuel by the flame transfer formed on the ignition burner, and the flame comes into contact with a tip side of the flame rod relative to the ignition burner, The deterioration determination unit extends the deterioration determination period when the burner that burns the fuel is switched from the ignition burner to the flame-transfer burner during the deterioration determination period associated with the ignition of the ignition burner. A combustion device characterized by:

5. The combustion device according to any one of claims 1 to 4, a judgment result storage unit that stores the judgment results regarding the presence or absence of deterioration obtained by the deterioration judgment unit for a predetermined period or up to a predetermined number; a deterioration notification unit that notifies the occurrence of deterioration in the frame rod; Equipped with The deterioration notification unit notifies the occurrence of deterioration when the occurrence frequency of the judgment result indicating that the frame rod has deteriorated is higher than a predetermined threshold frequency among the plurality of judgment results stored in the judgment result storage unit. A combustion device characterized by:

6. The combustion apparatus according to claim 5, A combustion time accumulating unit that accumulates a combustion time, which is a time during which the flame is detected by the flame rod, When the combustion time accumulated by the combustion time accumulating unit is smaller than a predetermined threshold combustion time, the deterioration notifying unit uses a higher threshold frequency than when the combustion time is greater than the threshold combustion time to determine whether or not to notify the occurrence of deterioration of the flame rod. A combustion device characterized by:

Images