JP7769194B2 - Oxygen sensor unit and hot water supply control system - Google Patents

Description

The present invention relates to an oxygen sensor unit and a hot water supply control system having an oxygen sensor unit.

Some hot water supply systems use oxygen sensors such as A/F sensors to detect the oxygen concentration of the combustion gas emitted from a gas water heater, and adjust the amount of gas supplied based on the detection results (detected value) to optimize combustion (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 1-98818

When measuring gases with the same oxygen concentration, differences in the detected values occur due to individual differences and deterioration over time. By obtaining detected values in atmospheric conditions where the oxygen concentration is constant (20.94%) and correcting the detected values as needed using a correction value (correction coefficient) calculated based on the detected value and the reference oxygen concentration, further optimization of combustion can be expected.

Here, for the oxygen sensor described above to properly function, the sensor element must be heated (activated) to a predetermined temperature (for example, 750°C in the case of zirconia). Therefore, to properly calculate and set the correction value described above, the sensor element must be heated to the predetermined temperature under atmospheric conditions.

A heater attached to the sensor element is often used to raise the temperature of the sensor element. Because heat transfer from the heater varies depending on the distance from the heater, even if the estimated or measured temperature of the sensor element reaches a predetermined temperature, it takes some time for the temperature to become uniform across the entire sensor element. For this reason, even if the actual oxygen concentration around the sensor remains constant, the detected oxygen concentration may gradually increase even after reaching (maintaining) the predetermined temperature. If the above correction value were set during this temperature rise, there is a concern that the function of optimizing combustion may not be properly performed.

For example, if the correction value is set after a sufficient amount of time has passed since the heater started heating, it would be possible to avoid setting the correction value during the temperature rise process described above. However, the time it takes from the start of heating until the temperature reaches a uniform level varies depending on various factors, such as individual differences and deterioration levels of oxygen sensors, the oxygen sensor and ambient temperatures, and individual differences and deterioration levels of the heater. In other words, if the waiting time is set while taking various factors into consideration, the waiting time would be excessively long. This is undesirable for the following reasons. Setting the correction value requires maintaining atmospheric conditions, making it difficult to set it in parallel with boiling water. Therefore, there is a priority between boiling water and setting the correction value. If boiling water were given priority, the opportunity to set the correction value would be reduced or postponed, which could hinder further optimization of combustion. On the other hand, if the setting of the correction value were given priority, the start of boiling water would be delayed, potentially reducing user satisfaction. Furthermore, if the waiting time were set while only considering certain factors, the waiting time would be insufficient in some situations, making further optimization of combustion difficult.

As such, there is still room for improvement in the configuration related to setting the correction value when optimizing combustion by correcting the detected oxygen concentration value.

The present invention was made in consideration of the above-mentioned problems, and its primary objective is to provide an oxygen sensor unit and hot water supply control system that can correct the detected oxygen concentration value to optimize combustion, thereby improving the accuracy of setting the correction value under various conditions and shortening the waiting time required to set the correction value.

The following describes the means to solve the above problems.

Means 1. An oxygen sensor unit applied to a gas water heater,
an oxygen sensor capable of detecting the oxygen concentration of combustion gas passing through an exhaust pipe of the gas water heater;
a sensor control unit connected to the oxygen sensor, correcting the detected value of the oxygen concentration obtained from the oxygen sensor using a correction value set as a reference, and outputting the corrected detected value to the hot water supply control device of the gas hot water heater;
a heater for heating a sensor element of the oxygen sensor,
The sensor control unit
a heating control unit that starts heating of the sensor element when a preparatory condition for setting the correction value is satisfied, and that executes heating control of the heater so as to maintain the temperature of the sensor element at a predetermined temperature after the temperature of the sensor element reaches the predetermined temperature;
a convergence determination unit that repeatedly obtains the detected value from the oxygen sensor under the condition that the sensor element is heated by the heater and the inside of the exhaust pipe of the gas water heater is in an atmospheric state upon establishment of the preparation condition, and determines whether the change in the detected value is converging;
The apparatus has a correction value setting unit that, when the convergence determination unit determines that the change in the detection value has converged, sets the correction value calculated based on the detection value acquired from the oxygen sensor and a concentration reference value that indicates the oxygen concentration in the atmospheric state as the reference object.

In this configuration, the oxygen concentration detection value is repeatedly acquired from the oxygen sensor under conditions where the preparatory conditions are met, the sensor element is heated, and the exhaust pipe is in an atmospheric state (oxygen concentration = 20.97%). Then, when it is determined that the change in the detection value has converged—for example, when the amount of change is smaller than a threshold value (a threshold value assuming steady-state error) for a predetermined period of time—a correction value is set. This configuration avoids setting a correction value while the detection value is still rising. The accuracy of the correction value can be improved by setting the correction value at the appropriate timing (when the temperature reaches a predetermined temperature, becomes uniform, and the detection value stabilizes). The time from when the temperature reaches a predetermined temperature to when the temperature becomes uniform can vary depending on factors such as individual differences in the sensor element and the degree of deterioration. In this regard, this configuration eliminates the need to take these factors into account when determining the appropriate timing, making it possible to determine the appropriate timing for each situation. This is advantageous in that it minimizes the complexity of the configuration involved in setting the correction value. As detailed above, a configuration that allows the correction value to be set at the appropriate timing can contribute to further optimizing combustion through the correction function.

Because maintaining atmospheric conditions is required for setting the correction value, it is difficult to prepare for setting the correction value in parallel with boiling water, and there is a priority order between boiling water and setting the correction value. For these reasons, the long time it takes to set the correction value hinders efforts to ensure opportunities to set (e.g., update) the correction value and to prevent delays in starting boiling water. In this regard, the configuration shown in this feature sets the correction value when it is determined that the change in the detection value has converged. This configuration contributes to shortening the wait time between the temperature of the sensor element becoming uniform and the correction value being set. Considering the wait time until the correction value is set in this way is advantageous for achieving coexistence between the water boiling function and the correction value setting (update) function.

1 is a schematic diagram of a hot water supply system according to a first embodiment; FIG. 2 is a partially enlarged view of FIG. 1 showing the A/F sensor and its surroundings; FIG. 2 is a block diagram showing the electrical configuration of the sensor unit. 10 is a flowchart showing a correction coefficient setting mode process executed by a CPU of the sensor board. 10 is a flowchart showing a correction coefficient setting process. 4 is a timing chart illustrating an example of the transition of the estimated temperature of the sensor element and the transition of the detected value of the oxygen concentration. 10 is a flowchart showing a process for determining the timing for setting a correction coefficient. FIG. 1 is a schematic diagram showing the relationship between two moving averages to be compared. 5 is a schematic diagram showing the relationship between the transition of the difference between moving averages and the timing of setting a correction coefficient; 10 is a flowchart showing a setting timing determination process according to the second embodiment. 10 is a flowchart showing a setting timing determination process according to the third embodiment. 10 is a flowchart showing a setting timing determination process according to the fourth embodiment. 13 is a flowchart showing a setting timing determination process according to the fifth embodiment. 5 is a timing chart showing the transition of the detected value of oxygen concentration and the flow of setting a correction coefficient. FIG. 10 is a schematic diagram showing a modified example of the configuration related to setting of a correction coefficient. 13 is a flowchart showing a setting timing determination process according to the sixth embodiment. 13 is a flowchart showing a setting timing determination process according to the seventh embodiment. 10 is a flowchart showing a second determination process.

First Embodiment
A first embodiment will be described below with reference to the drawings. This embodiment is embodied as a hot water supply system installed in a building such as a house.

As shown in FIG. 1, the hot water supply system 10 comprises a hot water storage type gas water heater 11 and a hot water supply control device 12 that controls the hot water supply of the gas water heater 11. The gas water heater 11 is provided with a hot water storage tank 21 that stores hot water. The hot water storage tank 21 has a partition that separates the interior of the hot water storage tank 21 into upper and lower sections, with the combustion chamber 24 below this partition and the hot water storage chamber 25 above. A water supply pipe 22 is connected to the bottom of the hot water storage chamber 25, and water is supplied from the water main through this water supply pipe 22. A hot water supply pipe 23 that connects a faucet for a bath or the like to the hot water storage chamber 25 is connected to the top of the hot water storage chamber 25, and hot water is supplied through this hot water supply pipe 23.

An intake pipe 31 is connected to the combustion chamber 24, and a blower 32 is disposed in this intake pipe 31. The blower 32 is subject to drive control by the hot water supply control device 12 and operates based on a drive signal from the hot water supply control device 12. When the blower 32 operates, outside air (atmospheric air) is supplied to the combustion chamber 24 through the intake pipe 31. A nozzle of a gas supply pipe 33 is connected to a position midway through the intake pipe 31. A control valve is provided in the gas supply pipe 33, and this control valve is driven and controlled by the hot water supply control device 12 to adjust the amount of gas supplied to the intake pipe 31.

The combustion chamber 24 is equipped with a burner 34 and a spark plug 35 that combust the combustion air, which is a mixture of gas and air supplied to the combustion chamber 24 through the intake pipe 31. The combustion gas generated in the combustion chamber 24 is discharged from the combustion chamber 24 through an exhaust pipe 39 (exhaust passage) connected to the combustion chamber 24. The exhaust pipe 39 is arranged to pass through the hot water storage chamber 25 and is in contact with the water stored in the hot water storage chamber 25. As the combustion gas is discharged through the exhaust pipe 39, heat exchange occurs between the combustion gas and the water via the exhaust pipe 39. This heat exchange heats the water in the hot water storage tank 21, producing hot water.

The exhaust pipe 39 protrudes upward from the hot water storage tank 21, and an outlet for the exhaust pipe 39 is formed at this protruding portion. An A/F sensor 50 (corresponding to an "oxygen sensor") that detects the oxygen concentration of the combustion gas passing through the exhaust pipe 39 is disposed in the exhaust pipe 39 (specifically, near the outlet). The A/F sensor 50 forms a sensor unit 40 together with a sensor board 60 (corresponding to a "sensor control unit") that serves as a control board for the A/F sensor 50. The sensor board 60 is located away from the exhaust pipe 39, i.e., outside the range of influence of the exhaust heat from the gas water heater 11.

The sensor board 60 is connected to the hot water supply control device 12, which controls the amount of gas injection and other factors based on the oxygen concentration detection value input from the sensor unit 40 (sensor board 60). Specifically, feedback control is performed to ensure that the air-fuel ratio is at a preset value (theoretical air-fuel ratio). This improves the combustion efficiency of the gas hot water heater 11.

The structure of the A/F sensor 50 will now be described with reference to Figure 2 (a partially enlarged view of Figure 1). The A/F sensor 50 comprises a sensor element 51 made of zirconia and a housing 53 that houses the sensor element 51. The housing 53 is fixed to the exhaust pipe 39 so that it protrudes into the interior of the exhaust pipe 39. The housing 53 has multiple through-holes, and combustion gases that flow into the housing 53 through these through-holes are guided to the sensor element 51.

In order for the A/F sensor 50 to properly perform its detection functions, the sensor element 51 must be at an appropriate temperature (reference temperature: 750°C in this embodiment). In other words, to improve the reliability of the A/F sensor 50's detection results and optimize combustion, the sensor element 51 must be heated to the above-mentioned reference temperature and maintained at that temperature. Taking this into consideration, the A/F sensor 50 is provided with a heater resistor 52 (e.g., a ceramic heater) as an electric heater for heating the sensor element 51. In this embodiment, this reference temperature corresponds to the "predetermined temperature."

The heater resistor 52 is embedded in the sensor element 51, and heat from the heater resistor 52 is transferred to the sensor element 51, heating the sensor element 51. The heater resistor 52 is connected to the sensor board 60 (see Figure 1), and can be switched by the sensor board 60 (CPU, described below) between a powered state (heater ON) in which power is supplied and a powered state (heater OFF) in which power is not supplied.

Next, the electrical configuration of the sensor unit 40 will be described with reference to Figure 3.

The sensor unit 40 is equipped with a detection circuit SC that detects the oxygen concentration of the combustion gas and a heating circuit HC that controls the temperature of the heater resistor 52. Both the detection circuit SC and the heating circuit HC are formed to straddle the A/F sensor 50 and the sensor board 60, and the sensor board 60 is equipped with a CPU 61 that serves as a control unit that controls the heating circuit HC based on information from the detection circuit SC.

The detection circuit SC is composed of the sensor element 51 of the A/F sensor 50 and an element line SL, which is a signal transmission path that transmits a signal from the sensor element 51 to the CPU 61 via an ASIC 62 mounted on the sensor board 60. In this embodiment, the sensor element 51 generates an electromotive force corresponding to the oxygen concentration of the combustion gas. The ASIC 62 acquires the current and voltage values of the current flowing through the sensor element 51 and outputs the acquired current and voltage values to the CPU 61.

The CPU 61 determines the oxygen concentration detected by the A/F sensor 50. Specifically, a table showing the correlation between the voltage value acquired by the ASIC 62 and the oxygen concentration is stored in the memory attached to the CPU 61, and the detected oxygen concentration value (%) is determined based on this table and the voltage value (V) acquired by the ASIC 62. In the sensor unit 40 shown in this embodiment, when the oxygen concentration is low, the voltage value is small (the detected value is small), and when the oxygen concentration is high, the voltage value is large (the detected value is large).

The CPU 61 transmits the detected oxygen concentration value to the hot water supply control device 12. The hot water supply control device 12 performs combustion control (feedback control) of the gas hot water heater 11 based on the detected value. In this embodiment, the hot water supply control device 12 and the sensor unit 40 form a "hot water supply control system." It is also possible to configure the hot water supply control device 12 to transmit the acquired voltage value as a "detected value."

The CPU 61 also calculates (estimates) the resistance value of the sensor element 51 using the current and voltage values acquired from the ASIC 62. The resistance value of the sensor element 51 is correlated with the temperature of the sensor element 51. Specifically, as the temperature of the sensor element 51 decreases, the resistance of the sensor element 51 increases, and as the temperature of the sensor element 51 increases, the resistance of the sensor element 51 decreases. The CPU 61 controls the conduction of electricity to the heater resistor 52 (switching between a conducting state and a non-conducting state) based on the calculated resistance value.

The heating circuit HC includes the heater resistor 52 of the A/F sensor 50 and a heater line HL, which is a power supply path that supplies power to the heater resistor 52 from a power supply unit 65 provided on the sensor board 60. In the heater line HL, an N-type MOSFET 66 is disposed between the heater resistor 52 and ground 69. The heater resistor 52 is connected to the drain side of the MOSFET 66, and ground 69 is connected to the source side via a pull-down resistor 67. The gate of the MOSFET 66 is connected to a CPU 61, which turns the gate ON/OFF based on the calculated resistance value of the sensor element 51. This switches the heater resistor 52 between a conductive state and a non-conductive state.

Here, we will explain the temperature control process of the heater resistor 52 (sensor element 51) performed by the CPU 61. The temperature control process is performed by the CPU 61 as part of its regular processing, and the function of the CPU 61 that executes this temperature control process corresponds to the "heating control unit."

In the temperature adjustment process, the current and voltage values of the current flowing through the sensor element 51 are first obtained from the element line SL, more specifically from the ASIC 62, and the resistance value of the sensor element 51 is calculated based on these current and voltage values. In this embodiment, the resistance value of the sensor element 51 when the temperature of the sensor element 51 is the above-mentioned reference temperature (750°C) (e.g., 38 Ω) is stored as the reference resistance value in memory attached to the CPU 61, and a determination is made as to whether the calculated current resistance value is greater than the reference resistance value.

If the current resistance value is greater than the reference resistance value, it is assumed that the temperature of the sensor element 51 has not reached the reference temperature, so the heater resistor 52 is energized (heater ON) and the temperature adjustment process is terminated. If the current resistance value is equal to or less than the reference resistance value, it is assumed that the temperature of the sensor element 51 has reached the reference temperature, so the heater resistor 52 is deenergized (heater OFF) and the temperature adjustment process is terminated.

In other words, if the temperature of the sensor element 51 has not reached the reference temperature, the heater resistor 52 is energized to heat the sensor element 51, and if the temperature of the sensor element 51 exceeds the reference temperature, the heater resistor 52 is de-energized to lower the temperature of the sensor element 51. After the temperature of the sensor element 51 reaches the reference temperature, the heater resistor 52 is switched between energized (ON) and de-energized (OFF) states in short intervals to maintain the sensor element 51 at the reference temperature. This maintains the temperature of the sensor element 51 at the reference temperature.

When measuring gas with the same oxygen concentration, the A/F sensor 50 may detect different oxygen concentrations due to individual differences and deterioration over time. In other words, even if a detected value is obtained under atmospheric conditions where the oxygen concentration is constant (reference oxygen concentration: 20.94%), the detected value may not necessarily be the reference oxygen concentration, and errors may occur due to individual differences and deterioration over time. There is a concern that such errors could hinder optimization of combustion by adjusting the air-fuel ratio. This reference oxygen concentration corresponds to the "concentration reference value."

One of the features of the hot water supply control system shown in this embodiment is that a correction coefficient is determined by comparing the detected value acquired when the inside of the exhaust pipe 39 is in an atmospheric state with a reference oxygen concentration. During hot water supply, the detected value is corrected using the correction coefficient, and the corrected detected value is transmitted to the hot water supply control device 12, thereby suppressing the influence of the above-mentioned error. Specifically, the CPU 61 has two control modes: a normal mode in which the detected oxygen concentration is periodically acquired while water is being boiled, corrected using the correction coefficient, and then transmitted to the hot water supply control device 12; and a correction coefficient setting mode in which the correction coefficient is set (updated), and the correction coefficient is set (updated) as needed in the correction coefficient setting mode. Below, the correction coefficient setting mode process executed by the CPU 61 as part of its periodic processing will be described with reference to the flowchart in Figure 4.

In the correction coefficient setting mode process, first, in step S101, it is determined whether the correction coefficient setting mode is in effect. Specifically, it is determined whether a correction coefficient setting mode flag is set in the memory attached to the CPU 61. If the correction coefficient setting mode is not in effect, the process proceeds to step S102.

After the water boiling is completed, it takes some time for the air in the exhaust pipe 39 to be replaced by natural ventilation and return to atmospheric conditions. In other words, after the water boiling is completed, combustion gases will remain in the exhaust pipe 39 until at least this time has passed. In this embodiment, a time limit is specified taking this situation into consideration, and the system is configured so that switching to correction coefficient setting mode is not possible until this time limit has passed after the water boiling is completed. If the time limit has passed, a negative judgment is made in step S102 and the processing for this setting mode is terminated. If the time limit has not passed, a positive judgment is made in step S102 and the system proceeds to step S103.

In step S103, it is determined whether the conditions for starting preparation for setting the correction coefficient (preparation conditions) are met. In this embodiment, the preparation conditions are met (1) when a user or other user performs an operation to set the correction coefficient (for example, when a button for setting the correction coefficient is operated on the hot water supply control device 12), or (2) when the scheduled date and time arrives. If a negative determination is made in step S103, the process for this setting mode ends. If a positive determination is made in step S103, the process for this setting mode ends after executing the preparation process for setting the correction coefficient. In this preparation process, first, in step S104, the heater resistor 52 is energized to begin heating the sensor element 51 with the reference temperature as the target. In the following step S105, a correction coefficient setting mode flag is set in memory. This switches the control mode of the CPU 61 from normal mode to correction coefficient setting mode.

If a setting operation is performed during the time limit, that operation will be invalid. In this embodiment, the above date and time are specified so that the correction coefficient is set every month, but if the scheduled date and time arrives during the time limit, the scheduled date and time will be canceled.

Returning to the explanation of step S101, if the current control mode is the correction coefficient setting mode, a positive judgment is made in step S101 and the process proceeds to step S106. In step S106, it is determined whether or not water heating has started. In this embodiment, delays in hot water supply are suppressed by prioritizing water heating over setting the correction coefficient. If a negative judgment is made in step S106, the process proceeds to step S107. In step S107, a correction coefficient setting timing judgment process is executed to determine whether it is the appropriate timing to set the correction coefficient. Details will be described later, but if it is confirmed that the change in the detection value has converged, a correction coefficient setting timing flag is set in memory in the judgment process.

Then, in step S108, it is determined whether the correction coefficient setting timing flag is set. If the correction coefficient setting timing flag is not set, the processing for this setting mode is terminated. If the correction coefficient setting timing flag is set, the correction coefficient setting processing is executed in step S109, and then the processing for this correction coefficient setting mode is terminated. The correction coefficient setting processing will now be described with reference to the flowchart in Figure 5.

In the correction coefficient setting process, first, in step S201, it is determined whether it is time to obtain the detected oxygen concentration value from the A/F sensor 50. Specifically, if this is the first time that step S201 is performed since the correction coefficient setting timing flag was set, a positive determination is made in step S201. If this is the second or subsequent time, a positive determination is made in step S201 if the interval time has elapsed since the previous positive determination in step S201, and a negative determination is made in step S201 if the interval time has not elapsed. If a negative determination is made in step S201, the setting process is terminated. If a positive determination is made in step S201, the process proceeds to step S202, where the detected oxygen concentration value is obtained from the A/F sensor 50 and stored in memory.

In the following step S203, it is determined whether the number of acquired detection values has reached a first specified number (e.g., 10). If the first specified number has not been reached, a negative determination is made in step S203, and the setting process is terminated. If the first specified number has been reached, a positive determination is made in step S203, and the process proceeds to step S204.

In step S204, the average value of the first specified number of detection values collected in steps S201 to S203 is calculated, and the reference oxygen concentration is divided by this average value to calculate a correction coefficient. The calculated correction coefficient is then set as the reference target. Specifically, the calculated correction coefficient is saved in the reference target storage area of memory. Thereafter, detection values obtained from the A/F sensor 50 are corrected as appropriate using the currently set correction coefficient (the correction coefficient saved in the reference target storage area).

In the following step S205, the heater resistor 52 is de-energized, terminating heating of the sensor element 51. Then, in step S206, the correction coefficient setting mode flag and correction coefficient setting timing flag set in memory are erased, and in step S207, various data (collected detection values) for setting the correction coefficient stored in memory are erased, after which the setting process is terminated.

Returning to the explanation of step S106 in Figure 4, if boiling water is started during the correction coefficient setting mode, a positive determination is made in step S106 and the process proceeds to step S110. In step S110, the correction coefficient setting mode flag and correction coefficient setting timing flag set in memory are erased. Thereafter, in step S111, various data (collected detection values) for setting the correction coefficient stored in memory are erased, and the setting process ends. Note that temperature adjustment of the sensor element 51 by the heater resistor 52 is carried over to normal mode.

As mentioned above, to properly perform the detection function of the A/F sensor 50, the sensor element 51 must be activated by heating it to a reference temperature. Therefore, to properly set the correction coefficient, the sensor element 51 must be heated to the reference temperature under atmospheric conditions. Heat transfer from the heater resistor 52 varies depending on the distance from the heater resistor 52. Therefore, even if the estimated temperature of the sensor element 51 reaches a predetermined temperature, it may take some time for the temperature throughout the sensor element 51 to actually become uniform (at the predetermined temperature). For this reason, as illustrated in Figure 6, even if the actual oxygen concentration remains constant, the detected oxygen concentration may gradually increase even after the estimated temperature reaches the reference temperature (while the temperature is maintained at the reference temperature) at time t1. More specifically, although the rate of increase in the detected oxygen concentration is smaller than between time t0 (when heating begins) and time t1, the detected oxygen concentration continues to increase gradually until time t2, a certain amount of time after time t1. If the correction coefficient were set during this rising process, there is a concern that the function of optimizing combustion may not be properly performed.

For example, if the correction coefficient is set after sufficient time has passed since the heater started heating, it would be possible to avoid setting the correction coefficient during the temperature rise process described above. However, the time it takes from the start of heating until the temperature reaches a uniform level varies depending on various factors, including individual differences and deterioration levels of the A/F sensor 50 (particularly the sensor element 51), the temperature of the A/F sensor 50 and its surroundings, and individual differences and deterioration levels of the heating circuit HC (particularly the heater resistor 52). In other words, if the wait time 1 is determined while taking various factors into consideration, the wait time would be excessively long. Setting the correction coefficient requires maintaining atmospheric conditions, making it difficult to perform the setting in parallel with the water heating process. If water heating is prioritized, the opportunity to set the correction value may be reduced or postponed, hindering further optimization of combustion. Furthermore, if the wait time is determined while only certain factors are considered, the wait time may be insufficient depending on the situation, making further optimization of combustion difficult. Changing the wait time depending on the situation would require a detection means, such as a sensor, to grasp the situation, which could lead to an excessively complex hot water supply control system.

One of the features of this embodiment is that the oxygen concentration detected by the A/F sensor 50 is used to determine the timing at which the change in the detected value converges, specifically the timing at which the temperature of the sensor element 51 becomes uniform, thereby improving the accuracy of the correction coefficient while preventing the time required for setting the correction coefficient from becoming excessively long. Below, with reference to Figure 7, the configuration related to this technique, specifically the process for determining the timing at which the correction coefficient is set in step S107, will be described.

In the correction coefficient setting timing determination process, first, in step S301, it is determined whether it is time to obtain the oxygen concentration detection value from the A/F sensor 50. If the determination in step S301 is negative, the determination process ends. If the determination in step S301 is positive, the process proceeds to step S302, where the oxygen concentration detection value is obtained from the A/F sensor 50 and stored in memory. Specifically, in step S301, a positive determination is made (1) if the process of step S301 is executed for the first time since switching to correction coefficient setting mode, or (2) if an interval time has elapsed since the previous detection value was obtained. This interval time may be the same length as the interval time described in step S201, or it may be longer or shorter than the interval time described in step S201. For example, a longer interval time is preferable in order to reduce pressure on memory storage capacity.

After the detection values are saved in step S302, the process proceeds to step S303, where it is determined whether the number of detection values obtained from the time the correction coefficient setting mode was entered until the present is equal to or greater than a second specified number (e.g., 30). If the number is not equal to or greater than the second specified number, a negative determination is made in step S303, and the process for determining the setting timing is terminated. If the number is equal to or greater than the second specified number, a positive determination is made in step S303, and the process proceeds to step S304. The second specified number is arbitrary and may, for example, be the same as the first specified number, or may be less than the first specified number.

In step S304, a moving average A, which is the average of the most recent N (e.g., 30) detection values, including the current detection value, is calculated, and the calculated moving average A is stored in memory. Then, in step S305, a determination is made as to whether the number of moving averages A calculated from the time the correction coefficient setting mode was entered to the present is equal to or greater than a third specified number (e.g., 50). If the number is not equal to or greater than the third specified number, the determination process ends. If the number of calculated moving averages A is equal to or greater than the third specified number, the process proceeds to step S306. In step S306, two moving averages A to be compared are selected. The following provides additional information about the selected moving averages A, with reference to Figure 8. In Figure 8, a newly calculated moving average A is distinguished as "moving average An" and a previously calculated moving average A is distinguished as "moving average Am." For ease of explanation, the interval (period) for obtaining detection values is exaggerated in Figure 8.

At time tn after switching to correction coefficient setting mode, the moving average An of the most recent N detection values, including the newly acquired detection value, is calculated. The targets of selection at time tn are the moving average An and the moving average Am calculated at time tm, which precedes time tn. The moving average Am is the average of the detection value acquired at time tm and the most recent N detection values acquired before that, and the detection values used to calculate the moving average An do not overlap with the detection values used to calculate the moving average Am. More specifically, the time from acquiring the last detection value for the moving average Am to acquiring the first detection value for the moving average An is longer than the time to collect detection values for the moving average Am and the time to collect detection values for the moving average A.

At time tn+1, when the above interval has elapsed since time tn, a moving average An+1 of the most recent N detection values, including the newly acquired detection value, is calculated. The targets of selection at time tn+1 are the moving average An+1 and the moving average Am+1 calculated before time tn+1, specifically at time tm+1, when the above interval has elapsed since time tm. At time tn+2, when the above interval has elapsed since time tn+1, a moving average An+2 of the most recent N detection values, including the newly acquired detection value, is calculated. The targets of selection at time tn+2 are the moving average An+2 and the moving average Am+2 calculated before time tn+2, specifically at time tm+2, when the above interval has elapsed since time tm+1.

Returning to the explanation of Figure 7, after moving average A is picked up in step S306, the process proceeds to step S307. In step S307, difference D, which is the absolute value of the difference between the two picked moving averages A, is calculated, and the calculated difference D is stored in memory. For example, difference Dn, which is the difference D calculated at timing tn, is (difference Dn) = |(moving average An) - (moving average Am)|.

Then, proceed to step S308 to determine whether the number of calculated differences D exceeds a fourth specified number (e.g., 10). If the determination in step S308 is negative, the determination process ends. If the determination in step S308 is positive, proceed to step S309. In step S309, the maximum value of the differences D for the most recent H times (e.g., 10 times) is identified, and in the following step S310, determine whether the maximum value is lower than a predetermined threshold. This threshold is determined based on the expected fluctuation range (upper and lower bound) of the detected value from the specifications of the A/F sensor 50 when oxygen concentration detection values are repeatedly obtained from the A/F sensor 50 under atmospheric conditions where the temperature of the sensor element 51 is equal to the reference temperature.

If a negative determination is made in step S310, the process for this determination ends. On the other hand, if a positive determination is made in step S310, the process proceeds to step S310, the correction coefficient setting timing flag is set in memory, and the process for this determination ends. In other words, if the differences D for the most recent H times are all below the threshold, it is determined that the change in the detected value has converged and the setting of the correction coefficient is permitted. In other words, if the change in the detected value has converged, it is determined that the timing is appropriate for setting the correction coefficient. Note that "convergence" refers to a state in which the temperature of the sensor element 51 has become uniform and the long-term increase (a gradual upward trend) has ended.

The first embodiment described above is expected to have the following excellent effects:

In the correction coefficient setting mode, the oxygen concentration detection value is repeatedly obtained from the A/F sensor 50 while the sensor element 51 is heated and the exhaust pipe 39 is in an atmospheric state. The correction coefficient is then set when it is determined that the change in the detection value has converged. This configuration prevents the correction coefficient from being set during the period from when the estimated temperature of the sensor element 51 equals the reference temperature until the temperature of the sensor element 51 becomes uniform, i.e., during the rising process when the oxygen concentration detection value increases slightly. Setting the correction coefficient at the appropriate timing when the temperature of the sensor element 51 has uniformed and the detection value has stabilized improves the accuracy of the correction coefficient.

The time it takes for the temperature of the sensor element 51 to be raised to the reference temperature and then stabilize at the reference temperature depends on the individual differences and degree of deterioration of the sensor element 51, the temperature of the sensor element 51 and its surroundings, and the individual differences and degree of deterioration of the heating circuit HC (particularly the heater resistor 52). In this regard, the configuration shown in this embodiment does not require control that takes into account the influence of these factors when determining the appropriate timing, making it possible to determine the appropriate timing for each situation. This is advantageous in that it prevents the configuration related to setting the correction coefficient from becoming too complicated.

As described above in detail, a configuration that allows the correction coefficient to be set at the appropriate timing can contribute to further optimizing combustion through the correction function.

Setting the correction coefficient requires maintaining atmospheric conditions. Therefore, it is difficult to simultaneously perform preparations for setting the correction coefficient and boil water, and a priority order is imposed between boiling water and setting the correction coefficient. In this embodiment, boiling water is prioritized, but such a configuration may reduce or postpone opportunities to set the correction coefficient (e.g., update opportunities), potentially hindering further optimization of combustion. In this regard, the configuration shown in this embodiment sets the correction coefficient when it is determined that the change in the detection value has converged. This configuration minimizes the wait time between the temperature of the sensor element 51 becoming uniform and the correction coefficient being set. For example, compared to a configuration in which the time until the appropriate timing is determined in advance based on the various conditions described above, this configuration prevents unnecessary wait times. Considering the wait time for setting the correction coefficient in this way is advantageous for achieving coexistence between the boiling water function and the above-mentioned correction function.

In the example shown in Figure 6, the actual oxygen concentration is constant and the change in the detected oxygen concentration value converges at time t2. However, even when the actual oxygen concentration is constant, the detected oxygen concentration value by the A/F sensor 50 can fluctuate within a certain range. In other words, when a detected value is acquired under conditions where the actual oxygen concentration is constant, the detected value will vary depending on the timing of acquisition. For this reason, simply comparing two detected values acquired at different times may result in a false determination that convergence has occurred because the difference between the two detected values acquired under conditions before convergence happens to be small, or a false determination that convergence has not yet occurred because the difference between the two detected values acquired under conditions where convergence has occurred happens to be large. Note that the detected value is correlated with the electromotive force generated in the detection circuit SC, but noise, etc., occurring in this detection circuit SC may cause the detected value to fluctuate significantly even when the actual oxygen concentration is constant.

In this embodiment, a moving average A is calculated from multiple detection values, and the difference D between the preceding and following moving averages A is referenced to determine whether the change in the detection value has converged. This reduces erroneous determinations due to the influence of detection value variation and noise, and improves the reliability of the determination result. Figure 9 shows an example of the change in difference D after entering correction coefficient setting mode. As such, a certain degree of variation also occurs in difference D. In this regard, this embodiment is configured to determine that the change in the detection value has converged when the difference D between the preceding and following moving averages A falls below the threshold value H times consecutively, thereby further improving the reliability of determining the appropriate timing for setting the correction coefficient.

Furthermore, as shown in Figure 8, the two moving averages A being compared are configured so that the detection values used to calculate each moving average A do not overlap. Specifically, a blank is provided between the detection value referenced when calculating one (earlier) moving average A and the detection value referenced when calculating the other (later) moving average A, with a detection value not referenced by either moving average A. With this configuration, each moving average A can be calculated from detection values that are separated in time, making it easier to grasp trends in change from a long-term perspective.

<Modification 1>
In the first embodiment, the two moving averages A to be compared are configured to be separated so that the detection value referenced when calculating the earlier moving average A and the detection value referenced when calculating the later moving average A do not overlap. However, it is also possible to configure the detection value referenced when calculating the earlier moving average A and the detection value referenced when calculating the later moving average A to partially overlap. Even if the detection value is affected by instantaneous noise, the noise will occur in the overlapping portion, and the noise will be reflected in both the earlier and later moving averages A. In other words, when the difference D between two moving averages A affected by noise is calculated, the influence of the noise can be removed or reduced from the difference D.

In addition, instead of a configuration in which the number of detection values (blank time) between the two moving averages A to be compared that are not referenced when calculating those moving averages A is greater (longer) than the number of detection values (collection time) referenced when calculating those moving averages A, it is also possible to configure the number of detection values (blank time) between the two moving averages A to be compared that are not referenced when calculating those moving averages A is less (shorter) than the number of detection values (collection time) referenced when calculating those moving averages A, or to configure the number of detection values (each time) to be the same.

<Modification 2>
The oxygen concentration detected by the A/F sensor 50 will rise after preparation for setting the correction coefficient begins and then stabilize. In view of this behavior, it is possible to calculate a difference (not an absolute value) by subtracting the past moving average A from the current moving average A, and to set a threshold value when this difference is on the positive side and a threshold value (second threshold value) when this difference is on the negative side. In this case, taking the above behavior into consideration, for example, the absolute value of the positive threshold value may be set to be greater than the absolute value of the negative threshold value.

<Modification 3>
In the first embodiment described above, when the difference D between the current moving average A and the previous moving average A falls below a threshold value (more specifically, when it falls below this threshold value H times in a row), it is determined that the timing is appropriate for setting the correction coefficient. However, this may be modified so that the average value of all detection values stored up to the time when preparation for setting the correction coefficient starts is calculated as needed, the difference between the current average value and the previous average value is calculated, and when this difference falls below a threshold value (for example, when it falls below this threshold value H times in a row), it is determined that the timing is appropriate for setting the correction coefficient.

Second Embodiment
In the first embodiment described above, whether or not the change in the detection value has converged is determined from the difference D of the moving average A. This embodiment is similar to the first embodiment in that the moving average A is used to determine whether or not the change in the detection value has converged, but the specific configuration related to this determination (process for determining the timing to set the correction coefficient (step S107)) is different from that of the first embodiment. Hereinafter, the process for determining the timing to set the correction coefficient in this embodiment will be described with reference to FIG. 10 . Note that the description of the configuration common to the first embodiment will be omitted as appropriate.

In this embodiment, the correction coefficient setting timing determination process determines whether it is time to obtain an oxygen concentration detection value from the A/F sensor 50 (step S401). If it is not time, the determination process ends. If it is time to obtain an oxygen concentration detection value, the oxygen concentration detection value is obtained from the A/F sensor 50 and stored in memory (step S402). It then determines whether the number of detection values obtained since the correction coefficient setting mode was entered is equal to or greater than a second specified number (step S403). If it is not equal to or greater than the second specified number, the determination process ends. If it is equal to or greater than the second specified number, a moving average A, which is the average of the most recent N detection values including the current detection value, is calculated, and the calculated moving average A is stored in memory (step S404). Note that steps S401 to S404 are the same as steps S301 to S304 described above.

After saving the moving average A in step S404, it is determined whether the number of moving averages A calculated from the time the correction coefficient setting mode was entered until the present is equal to or greater than a fifth specified number (step S405). If it is not equal to or greater than the fifth specified number, the determination process ends. If it is equal to or greater than the fifth specified number, the standard deviation SD of the moving averages A for the most recent M (e.g., three) moving averages A, including the current moving average A, is calculated, and the calculated standard deviation SD is saved in memory (step S406).

Then, it is determined whether the number of standard deviations SD calculated from the time the correction coefficient setting mode was entered until now is equal to or greater than a sixth specified number (step S407). If it is not equal to or greater than the sixth specified number, the determination process is terminated. If it is equal to or greater than the sixth specified number, the maximum value of the most recent H standard deviations SD, including the current standard deviation SD, is identified (step S408), and it is determined whether this maximum value is smaller than a predetermined threshold value (step S409). This threshold value, like the threshold value described in the first embodiment above, is determined based on the expected fluctuation range (upper and lower bound) of the detected value based on the specifications of the A/F sensor 50 when oxygen concentration detected values are repeatedly obtained from the A/F sensor 50 under atmospheric conditions where the temperature of the sensor element 51 is equal to the reference temperature.

If the maximum value is equal to or greater than the threshold, the process for this determination ends. If the maximum value is below the threshold, a correction coefficient setting timing flag is set in memory (step S410) and the process for this determination ends. In other words, if the standard deviations SD for the most recent H times are all below the threshold, it is determined that the changes in the detected values have converged and the setting of a correction coefficient is permitted.

As described above in detail, by determining the timing of convergence based on the standard deviation SD calculated from the most recent M moving averages A, the accuracy can be suitably improved.

Third Embodiment
In the first and second embodiments, the moving average A of the detected values is used to determine whether the change in the detected values has converged. In this embodiment, the specific configuration related to this determination (processing for determining the timing to set the correction coefficient (step S107)) is different from that of the first embodiment, etc. Below, the processing for determining the timing to set the correction coefficient in this embodiment will be described with reference to FIG. 11 . Note that the description of the configuration common to the first embodiment, etc. will be omitted as appropriate.

In this embodiment, the process for determining the timing to set the correction coefficient determines whether it is time to obtain the detected oxygen concentration value from the A/F sensor 50 (step S501). If it is not time, the process for determining this is terminated. If it is time to obtain the detected oxygen concentration value, the detected oxygen concentration value is obtained from the A/F sensor 50 and stored in memory (step S502). Note that the processes in steps S501 to S502 are the same as those in steps S301 to S302 described above.

After the detection value is saved in step S502, the value of the detection count counter i stored in memory is incremented by "1" (step S503). The detection count counter i is a counter that stores the number of times that detection values have been acquired and saved since the correction coefficient setting mode was entered, and is cleared to "0" when the correction coefficient setting mode is terminated.

Next, it is determined whether the current detection value is equal to or less than the upper limit UL (step S504). The upper limit UL is a threshold used to determine whether the change in the detection value has converged, and is changed depending on the detection values obtained up to that point. Specifically, if the current detection value exceeds the upper limit UL, the current detection value is set as the new upper limit UL (step S505). Then, the consecutive determination counter TM stored in memory is set to the same value as the current detection count counter i (step S505), and this determination process ends. The consecutive determination counter TM is a counter used to track the number of consecutive times the upper limit UL has not been exceeded, and is cleared to "0" when the correction coefficient setting mode ends.

If the current detection value is below the upper judgment limit UL, it is determined whether the number of consecutive times the value has been below the upper judgment limit UL is a reference number (e.g., 100 times) or more (step S506). Specifically, it is determined whether the value obtained by subtracting the value of the consecutive judgment counter TM from the value of the detection count counter i is equal to or greater than the reference number. If it is not equal to or greater than the reference number, the determination process ends. If it is equal to or greater than the reference number, a correction coefficient setting timing flag is set in memory, and the determination process ends.

As detailed above, if the maximum detected value obtained up to that point is configured to be set as the upper judgment limit UL, the maximum detected value will gradually increase before stabilization, causing the upper judgment limit UL to be repeatedly updated. However, once stable, the maximum detected value will generally be smaller than the upper judgment limit UL, and updates to the upper judgment limit UL will essentially stop. If updates to the upper judgment limit UL continue to stop, it can be determined that the changes in the detected values have converged, making it possible to set the correction coefficient at the appropriate time.

In particular, the upper judgment limit UL is automatically updated when the temperature of the sensor element 51 rises over time and the detected value (maximum value) exceeds the previous upper judgment limit UL. This configuration reduces the amount of information required to determine the convergence of the detected value, making it possible to determine convergence with a simple configuration.

<Modification 1>
In the third embodiment, the upper limit of the detection value is defined by the upper judgment limit UL, but in addition, the lower limit of the detection value may be defined as the lower judgment limit, and it may be determined that the change in the detection value has converged when the detection value is continuously between the upper judgment limit UL and the lower judgment limit. By narrowing the allowable range of the detection value, it is possible to prevent an erroneous determination that the change in the detection value has converged when a situation in which the detection value temporarily fluctuates downward continues.

Note that starting to heat the sensor element 51 causes a large change in the detected value, but this change becomes more gradual as the temperature of the sensor element 51 reaches the reference temperature. Therefore, by setting the judgment lower limit to the minimum detected value obtained after the reference temperature is reached, the above-mentioned suppression effect can be more effectively exerted.

<Fourth embodiment>
In this embodiment, the configuration for determining the appropriate timing for setting the correction coefficient, specifically, the correction coefficient setting timing determination process (step S107) executed by the CPU 61, is different from those of the first to third embodiments. The correction coefficient setting timing determination process in this embodiment will be described below with reference to Fig. 12. Note that the description of the configuration common to the first embodiment and the like will be omitted as appropriate.

In this embodiment, the correction coefficient setting timing determination process first determines in step S601 whether it is time to obtain a detected oxygen concentration value from the A/F sensor 50. This determination process is configured to periodically calculate a correction coefficient separately from the correction coefficient setting process described above, and determines whether a predetermined waiting time (e.g., 3 seconds) has elapsed since the previous calculation of the correction coefficient. If this is the first time the predetermined waiting time has elapsed, a positive determination is made in step S601. From the second time onwards, a positive determination is made if an interval time (e.g., 0.1 seconds) has elapsed since the previous detection value was obtained. After the number of obtained detection values reaches a specified number (e.g., 20), negative determinations are repeated until the next predetermined waiting time has elapsed in step S601. If a negative determination is made in step S601, the determination process terminates. If a positive determination is made in step S601, the oxygen concentration detection value is obtained from the A/F sensor 50 and stored in memory.

After the detection values are saved in step S602, step S603 determines whether it is time to calculate a correction coefficient. Specifically, it determines whether the number of obtained detection values has reached the specified number. If a negative determination is made in step S603, the determination process ends. If a positive determination is made in step S603, the process proceeds to step S604, where the average of the specified number of obtained detection values is calculated, and the reference oxygen concentration is divided by this average to calculate a correction coefficient. After the correction coefficient is calculated, the detection values that were the basis for the calculation are erased.

In the following step S605, it is determined whether the correction coefficient calculated in step S604 is within an appropriate range. The appropriate range is a range that is predetermined taking into account errors that may occur due to individual differences and deterioration of the A/F sensor 50, and is pre-stored in memory associated with the CPU 61. If a negative determination is made in step S605, the calculated correction coefficient is erased and the main determination process ends. If a positive determination is made in step S605, the calculated correction coefficient is erased and the process proceeds to step S606. In step S606, a correction coefficient setting timing flag is set in memory and the main determination process ends.

Immediately after the temperature of the sensor element 51 begins to rise, the oxygen concentration detected by the A/F sensor 50 rises sharply. The correction coefficient calculated during this process deviates significantly from the appropriate range, but repeated calculation of the correction coefficient gradually brings the correction coefficient closer to the appropriate range. As the temperature of the sensor element 51 becomes uniform and the change in the detected value converges, the correction coefficient approaches the appropriate range even more. Once the correction coefficient falls within the appropriate range, the correction coefficient is calculated and set by the correction coefficient setting process.

The configuration described above makes it easy to determine the appropriate timing for setting the correction coefficient.

<Modification 1>
The specified number in this determination process is set to be smaller than the number of detection values (e.g., 30) used when calculating the correction coefficients in the correction coefficient setting process, but is not limited to this. The specified number may be larger than or the same as the number of detection values used when calculating the correction coefficients in the correction coefficient setting process. Furthermore, if the number of detection values to be acquired is set to be the same, it is preferable to share the program for acquiring the detection values and calculating the average value with the correction coefficient setting process.

Fifth Embodiment
In this embodiment, the configuration for determining the appropriate timing for setting the correction coefficient, specifically, the correction coefficient setting timing determination process (step S107) executed by the CPU 61, is different from that of the fourth embodiment. The correction coefficient setting timing determination process in this embodiment will be described below with reference to Fig. 13. Note that the description of the configuration common to the fourth embodiment will be omitted as appropriate.

In the correction coefficient setting timing determination process of this embodiment, first, in step S701, it is determined whether it is time to obtain the detected oxygen concentration value from the A/F sensor 50. If the determination in step S701 is negative, the determination process ends. If the determination in step S701 is positive, the process proceeds to step S702, where the detected oxygen concentration value is obtained from the A/F sensor 50 and stored in memory. Here, a supplementary explanation of the process in steps S701 and S702 is provided.

This determination process is configured to periodically calculate a correction coefficient separately from the correction coefficient setting process described above, and a positive determination is made in step S701 to acquire a detection value when: (1) a first waiting time (e.g., 3 seconds) has elapsed since the previous correction coefficient was calculated in this determination process; (2) the first waiting time has elapsed, an interval time (e.g., 0.1 seconds) has elapsed since the previous detection value was acquired, and the number of acquired detection values has not reached a specified number (e.g., 20); or (3) the number of acquired detection values reaches the specified number and a second waiting time (e.g., 0.5 seconds) has elapsed since the calculation of the correction coefficient described below. If none of (1) to (3) applies, this determination process ends without acquiring a detection value.

After the detection values are saved in step S702, step S703 determines whether it is time to calculate a correction coefficient. Specifically, it determines whether the number of obtained detection values has reached the specified number. If a positive determination is made in step S703, the process proceeds to step S704, where the average of the specified number of obtained detection values is calculated and the reference oxygen concentration is divided by this average to calculate a correction coefficient. The correction coefficient is then provisionally set, and the detection values used to calculate the correction coefficient are erased. Note that the provisionally set correction coefficient is used only within this determination process and is not used to correct the detection values sent to the hot water supply control device 12.

In the following step S705, the correction coefficient is calculated in the memory attached to the CPU 61, and a calculation flag is set to indicate that it has been provisionally set.

Returning to the explanation of step S703, if it is not the time to calculate the correction coefficient, a negative judgment is made in step S703 and the process proceeds to step S706. In step S706, it is determined whether the calculation flag has been set in memory. If the calculation flag has not been set, the process proceeds to step S707. In step S707, it is determined whether it is the right time to check whether the provisionally set correction coefficient is appropriate, specifically, whether the second waiting time has elapsed since the correction coefficient was calculated. If a negative judgment is made in step S707, the process proceeds to step S708 and the newly acquired detection value is corrected using the provisionally set correction coefficient when the second waiting time has elapsed.

In the following step S709, it is determined whether the correction result of step S708 (the detected value after correction) is within an appropriate range. This appropriate range is determined by taking into account errors that may occur in the reference oxygen concentration due to individual differences and deterioration of the A/F sensor 50, and is pre-stored in memory associated with the CPU 61. If a positive determination is made in step S709, the provisionally set correction coefficient is erased and the process proceeds to step S710. In step S710, a correction coefficient setting timing flag is set in memory. After executing the processing of step S710, or if a negative determination is made in step S709, the process proceeds to step S711, where the calculation flag is erased and the process for this determination ends.

Even after the estimated temperature of the sensor element 51 becomes equal to the reference temperature due to temperature rise, the detected oxygen concentration value will gradually increase until the temperature of the sensor element 51 becomes uniform. If the detected value is corrected using a provisionally set correction coefficient during this increase, the corrected detected value will match the reference oxygen concentration at the time the correction coefficient was provisionally set. In other words, the corrected detected value will generally be within the appropriate range. However, the further away the timing of obtaining the detected value is from the timing of provisionally setting the correction coefficient, the greater the degree to which the corrected detected value will deviate from the reference oxygen concentration. In other words, if the change in the detected value has not converged, the corrected detected value will fall outside the appropriate range. After that, as the change in the detected value converges, if the detected value is corrected using the provisionally set correction coefficient, the corrected value will be within the appropriate range. This configuration makes it possible to efficiently determine the appropriate timing for setting the correction coefficient.

<Modification 1>
In the fifth embodiment, the detection value is corrected and checked to see if it is within the appropriate range when the second waiting time has elapsed since the correction coefficient was provisionally set. This may be modified as follows. That is, as shown in FIG. 14 , the detection value may be periodically acquired again after the correction coefficient is provisionally set, and the provisionally set correction coefficient may be applied to each detection value to check whether it is within the appropriate range. The change in the detection value may be determined to have converged when the corrected detection value has fallen within the appropriate range a predetermined number of times in succession. If the detection value falls outside the appropriate range during the repeated checks to see if it is within the appropriate range, the first waiting time may be shortened so that the timing for provisionally setting the next correction coefficient (the start of preparation) becomes earlier the more times the detection value has fallen within the appropriate range.

<Modification 2>
If the provisionally set correction coefficient is inappropriate, a new correction coefficient may be provisionally set based on data (detection values) already collected up to that point. For example, as shown in FIG. 15 , at time t0, which is the first provisional correction coefficient setting timing after entering the correction coefficient setting mode, a correction coefficient X0 is provisionally set based on the detection values collected up to that point. Detection values continue to be collected thereafter, and at a subsequent time t1, the provisionally set correction coefficient X0 is applied to the average value of the detection values collected between time t0 and time t1. If the result (corrected detection value) is not within the appropriate range, a new correction coefficient X1 is provisionally set based on the detection value acquired at time t1 or the average value. At a subsequent time t2, the provisionally set correction coefficient X1 is applied to the average value of the detection values collected between time t1 and time t2. If the result (corrected detection value) is not within the appropriate range, a new correction coefficient X2 is provisionally set based on the detection value acquired at time t2 or the average value. Thereafter, the provisional setting of the correction coefficient and the confirmation of whether the corrected detection value is within the appropriate range are repeated until the corrected detection value is within the appropriate range. With this configuration, it is possible to suppress erroneous determinations due to fluctuations in the detected value or the influence of noise, and to suitably determine the appropriate timing for setting the correction coefficient.

Sixth Embodiment
In the fourth and fifth embodiments, the calculated correction coefficient is used to determine the appropriate timing for setting the correction coefficient. One of the features of this embodiment is that it is designed to improve the accuracy of determining the appropriate timing for setting the correction coefficient. Hereinafter, with reference to FIG. 16 , the process for determining the timing for setting the correction coefficient in this embodiment will be described, focusing on the differences from the fourth embodiment. Note that the description of the components common to the fourth embodiment and the like will be omitted as appropriate.

The processes in steps S801 to S805 in the process for determining the timing to set the correction coefficient in this embodiment are the same as steps S601 to S605 in the fourth embodiment.

If a positive determination is made in step S805, i.e., if the calculated correction coefficient is within the appropriate range, the process proceeds to step S806, where the consecutive success count counter CC, which is a counter used to track the number of consecutive successes within the appropriate range, is incremented by "1," and the determination process ends. In other words, in this embodiment, even if the correction coefficient is within the appropriate range, this does not immediately mean that it is an appropriate time to set the correction coefficient.

If the determination in step S805 is negative, i.e., if the correction coefficient is outside the appropriate range, proceed to step S807. In step S807, a warning flag is set in memory, and in the following step S808, the consecutive success counter CC is cleared to "0" and this determination process ends. The warning flag is a flag used to determine whether the correction coefficient is within the appropriate range.

Returning to the explanation of step S803, if it is not the time to calculate the correction coefficient, the process proceeds to step S809. In step S809, it is determined whether it is time to check the conversion rate, which will be described later. Specifically, a positive determination is made in step S809 when a preset waiting time has elapsed since the correction coefficient was calculated in step S804; otherwise, a negative determination is made in step S809. If a negative determination is made in step S809, the process terminates. If a positive determination is made in step S809, the process proceeds to step S810, where it is determined whether a warning flag has been set in memory. If a warning flag has been set, the warning flag is cleared in step S811, and the process terminates. If a positive determination is made in step S810, the process proceeds to step S812, where the current detection value is corrected using the correction coefficient calculated in step S804, and the corrected detection value is stored in memory. Thereafter, the process proceeds to step S813, where the corrected detection value is divided by the uncorrected detection value to calculate the current conversion rate, and the calculated conversion rate is saved in memory.

In the following step S814, it is determined whether the value of the consecutive success counter CC is greater than a specified value (e.g., 2). That is, it is determined whether the number of consecutive times the calculated correction coefficient fell within the appropriate range is greater than the specified value. If a negative determination is made in step S814, the process ends. If a positive determination is made in step S814, the process proceeds to step S815, where the difference (absolute value) between the conversion rate using the current correction coefficient and the conversion rate using the previous correction coefficient is calculated. Then, in step S816, it is determined whether the calculated difference in conversion rate is smaller than a reference value. If a negative determination is made in step S816, the process ends. If a positive determination is made in step S816, the process sets a correction coefficient setting timing flag in memory in step S817, and the process ends. This configuration makes it possible to appropriately determine the appropriate timing for setting the correction coefficient.

In this embodiment, an example has been given of a configuration applied to the fourth embodiment that improves the accuracy of determining the appropriate timing for setting the correction coefficient by comparing conversion rates, but this configuration related to conversion rates can also be applied to the fifth embodiment.

Seventh Embodiment
In the fourth to sixth embodiments, the calculated correction coefficient is used to determine the appropriate timing for setting the correction coefficient. One of the features of this embodiment is that it is designed to improve the accuracy of determining the appropriate timing for setting the correction coefficient. Hereinafter, with reference to FIGS. 17 and 18, the process for determining the timing for setting the correction coefficient in this embodiment will be described, focusing on the differences from the fourth embodiment. Note that the description of the components common to the fourth embodiment and the like will be omitted as appropriate.

As shown in FIG. 17, in the correction coefficient setting timing determination process of this embodiment, first, in step S901, it is determined whether the value of the execution count counter DC is "0" or the conversion rate is the initial value (specifically, "0"). The execution count counter DC is a counter for keeping track of the number of times a correction coefficient has been set by the correction coefficient setting process, and is set to "0" as its initial value and is incremented by "1" each time a correction coefficient is set. Furthermore, in this embodiment, the conversion rate when the detected value is corrected using the correction coefficient temporarily set in this determination process is stored, and in step S901 it is determined whether the stored past (immediately preceding) conversion rate is 0.

If a negative judgment is made in step S901, the process proceeds to step S902, where it is determined whether the number obtained by dividing the value of the execution count counter DC by the number of times L corresponding to the correction coefficient or the validity period of the reference conversion rate (described below) is an integer. If a positive judgment is made in either step S901 or step S902, the first judgment process is executed in step S903, and then this judgment process is terminated. If a negative judgment is made in both step S901 and step S902, the second judgment process is executed in step S904, and then this judgment process is terminated. In other words, the first judgment process is executed when the correction coefficient is initially set or when the validity period has elapsed, and the second judgment process is executed otherwise.

The first determination process is basically the same as the correction coefficient setting timing determination process shown in the fourth to sixth embodiments, but a reference conversion rate is set during this process, which will serve as the reference for subsequent use. Specifically, the conversion rate when the detected value is corrected using the calculated correction coefficient is calculated, and this conversion rate is saved as the reference conversion rate. In the subsequent second determination process, this reference conversion rate is compared with the current conversion rate to determine whether the change in the detected value has converged. The second determination process will be further explained below with reference to Figure 18. Note that steps S1001 to S1004 in the second determination process are the same as steps S601 to S604 in the fourth embodiment, and therefore will not be explained here.

After the correction coefficient is calculated in step S1004, a calculation flag is set in memory in step S100, and the second determination process is terminated. Returning to the explanation of step S1003, if a negative judgment is made in step S1003, i.e., if it is determined that it is not time to calculate the correction coefficient, the process proceeds to step S1006. In step S1006, it is determined that it is time to check the conversion rate. Specifically, a positive judgment is made in step S1006 when a preset waiting time has elapsed since the correction coefficient was calculated in step S1004; otherwise, a negative judgment is made in step S1006. If a negative judgment is made in step S1006, the second determination process is terminated. If a positive judgment is made in step S1006, the process proceeds to step S1007, and it is determined whether a calculation flag has been set in memory. If the calculation flag has not been set, the second determination process is terminated. If the calculation flag is set, proceed to step S1008, where the current detection value is corrected using the correction coefficient calculated in step S1004, and the corrected detection value is stored in memory. Then proceed to step S1009, where the corrected detection value is divided by the uncorrected detection value to calculate the current conversion rate, and the calculated conversion rate is stored in memory.

In the following step S1010, the difference (absolute value) between the conversion rate using the current correction coefficient and the current reference conversion rate is calculated, and it is determined whether this difference is smaller than the reference value. If the determination in step S1010 is negative, the second determination process is terminated. If the determination in step S1010 is positive, the value of the execution count counter DC is incremented by "1" in step S1011, the calculation flag is cleared in step S1012, and a correction coefficient setting timing flag is set in memory in step S1013, thereby terminating the determination process.

By comparing the current reference conversion rate with the current conversion rate, it is possible to easily determine the appropriate timing for setting the correction coefficient. However, deterioration of the sensor unit 40 may cause the reference conversion rate itself to gradually deviate from the actual conversion rate. Therefore, by updating the reference conversion rate as needed, it is possible to prevent a decrease in the reliability of the above judgment.

<Other embodiments>
The present invention is not limited to the contents of the above-described embodiments, and may be implemented, for example, as follows. The following configurations may be applied individually to the above-described embodiments, or may be applied in combination with some or all of them. It is also possible to arbitrarily combine all or some of the various configurations shown in the above-described embodiments. In this case, it is preferable that the technical significance (effects to be achieved) of each configuration to be combined is ensured. The following configurations may be applied individually to a new configuration formed by combining the embodiments, or may be applied in combination with some or all of them.

- In each of the above embodiments, the sensor unit 40 corrects the detected oxygen concentration value and outputs the corrected detected value to the hot water supply control device 12, but this is not limited to this. The acquired detected oxygen concentration value may be output directly (without correction) to the hot water supply control device 12, and the hot water supply control device 12 may correct the detected value. In other words, it is also possible to configure the hot water supply control device 12 to perform various functions such as storing data such as detected values, determining the appropriate timing for setting the correction coefficient, and setting the correction coefficient. It is also possible to configure these functions to be shared between the sensor unit 40 and the hot water supply control device 12. For example, the hot water supply control device 12 may be configured to handle control equivalent to the correction coefficient setting mode process shown in FIG. 4, and the hot water supply control device 12 may be configured to instruct the sensor unit 40 to heat the sensor element 51 and detect the oxygen concentration when performing main controls such as controlling the boiling of water, determining whether the sensor element 51 needs to be heated, and determining the timing of correction, and the CPU 61 of the sensor unit 40 may heat the sensor element 51 and detect the oxygen concentration in response to instructions from the hot water supply control device 12.

- In the above embodiments, the acquisition of data (detected values) for determining the appropriate timing for setting the correction coefficient is initiated when heating of the sensor element 51 begins, but this is not limited to this. Considering that the detected oxygen concentration value stabilizes after the sensor element 51 reaches a predetermined temperature (750°C), the acquisition of data (detected values) for determining the appropriate timing for setting the correction coefficient may be initiated when the estimated temperature of the sensor element 51 equals the reference temperature, or when the estimated temperature of the sensor element 51 equals a specified temperature (a temperature lower than the reference temperature). In these configurations, the determination of the appropriate timing for setting the correction coefficient may be initiated when the estimated temperature of the sensor element 51 equals the reference temperature or thereafter.

- In the above embodiments, new detection values for calculating the correction coefficient are acquired after the appropriate timing for setting the correction coefficient has arrived, and the correction coefficient is calculated from these newly acquired detection values. However, this may be modified as follows. That is, when the appropriate timing for setting the correction coefficient has arrived, the correction coefficient may be calculated from the most recently acquired detection values (e.g., multiple detection values). Alternatively, the correction coefficient may be calculated from the most recently acquired detection values (e.g., multiple detection values) and a newly acquired detection value.

- In the above embodiments, the temperature of the sensor element 51 is estimated based on information from the detection circuit SC, but this does not preclude a configuration in which a thermometer is used to measure the temperature of the heater resistor 52 or the sensor element 51. It is also possible to estimate the temperature of the sensor element 51 based on information from the heating circuit HC.

- In the above embodiments, the heater resistor 52 is embedded in the sensor element 51. Even if the heater resistor 52 is placed in contact with the sensor element 51 from outside, it will take some time for the temperature of the sensor element 51 to become uniform. In other words, even after the estimated temperature reaches 750°C, the detected value may change (increase) until the temperature becomes uniform. Therefore, a practically preferable configuration can be achieved even with such a sensor structure by applying the configuration for determining the appropriate timing shown in the above embodiments.

As shown in the above embodiments, the correction coefficient for the A/F sensor 50 is set when the exhaust pipe 39 of the gas water heater 11 is in an atmospheric state. Because the air in the exhaust pipe 39 is gradually replaced with outside air, the exhaust pipe 39 will be in an atmospheric state after a certain amount of time has passed since the water boiling has finished, but this takes some time. For example, the exhaust pipe 39 may be configured to be in an atmospheric state by supplying outside air through purging and forcibly replacing the air in the exhaust pipe 39. In this case, purging may be performed when setting the correction coefficient, or the correction coefficient may be set using purging after the water boiling has finished as one of the conditions.

- After boiling water has finished or the correction coefficient has been set (including completion/interruption), if a specified continuation condition is met, the temperature control for maintaining the sensor element 51 at the reference temperature may be continued. For example, the heating control of the sensor element 51 may be continued if boiling water is started after the correction coefficient has been set, or the heating control of the sensor element 51 may be continued if the correction coefficient is set after boiling water.

- In the above embodiments, the configuration is such that, between boiling water in the gas water heater 11 and setting the correction coefficient related to the A/F sensor 50, the former is executed with priority; specifically, if a request to boil water occurs while preparation for setting the correction coefficient is underway, preparation for setting the correction coefficient is stopped and boiling water is started. This can be modified to a configuration in which, between boiling water in the gas water heater 11 and setting the correction coefficient related to the A/F sensor 50, the latter is executed with priority; specifically, if a request to boil water occurs while preparation for setting the correction coefficient is underway, boiling water is started after setting the correction coefficient is completed.

As shown in the above embodiments, in a configuration in which the timing to set a correction coefficient is determined using the detected oxygen concentration value obtained from the A/F sensor 50, there is a possibility that the timing may continue to be determined not to be right due to unforeseen reasons such as a malfunction of the A/F sensor 50. Therefore, it is possible to add a timeout function to the determination function, and configure the current setting to be canceled if the timing does not continue and a timeout occurs. If the setting is canceled, it is advisable to continue using the previously set correction coefficient, while notifying the user that a timeout has occurred.

- In the above embodiments, calculation, judgment, and other processing is performed when a certain number of data such as detection values is acquired. However, it is also possible to measure the elapsed time using a timer counter or RTC, and perform calculation, judgment, and other processing when a certain amount of time has elapsed.

- Instead of or in addition to a configuration in which the correction coefficient is set (updated) based on user setting operations or a scheduled schedule, it is also possible to configure the correction coefficient to be set (updated) before (just before) the start of combustion control in response to a water boiling request. For example, the number of times water has been boiled may be counted, and when that number reaches a preset number, the correction coefficient may be set (updated) before (just before) the start of combustion control for the next water boiling.

- In the above embodiments, a configuration for determining the appropriate timing for setting a correction coefficient for an A/F sensor 50 applied to a storage-type hot water supply system 10 was exemplified, but this configuration can also be applied to an A/F sensor applied to an instantaneous hot water supply system. Furthermore, the configuration for setting the correction coefficient for the A/F sensor 50 shown in the above embodiments may also be applied to an A/F sensor 50 installed in other equipment having an internal combustion engine such as a gasoline engine (for example, an automobile or a generator).

<Inventions extracted from the above embodiments>
The following describes the features of the inventions extracted from the above embodiments, while indicating, as necessary, their effects, etc. Note that, for ease of understanding, the corresponding configurations in the above embodiments are indicated in parentheses as appropriate, but the invention is not limited to the specific configurations indicated in parentheses.

Feature 1. An oxygen sensor unit (sensor unit 40) applied to a gas water heater (gas water heater 11),
an oxygen sensor (A/F sensor 50) capable of detecting the oxygen concentration of combustion gas passing through an exhaust pipe (exhaust pipe 39) of the gas water heater;
a sensor control unit (sensor board 60) to which the oxygen sensor is connected, which corrects the detected value of the oxygen concentration obtained from the oxygen sensor using a correction value (correction coefficient) set as a reference, and outputs the corrected detected value to the hot water supply control device (hot water supply control device 12) of the gas hot water heater;
a heater (heater resistor 52) for heating a sensor element (sensor element 51) of the oxygen sensor,
The sensor control unit
a heating control unit (a function of executing a temperature adjustment process in the CPU 61 of the sensor substrate 60) that starts heating of the sensor element when a preparatory condition for setting the correction value (a user setting operation or a schedule) is met, and that controls the heater so as to maintain the temperature of the sensor element at a predetermined temperature (e.g., 750°C) after the temperature of the sensor element reaches the predetermined temperature;
a convergence determination unit (a function that executes a process for determining the timing of setting the correction coefficient in step S106 in the CPU 61 of the sensor board 60) that repeatedly acquires the detected value from the oxygen sensor under the condition that the sensor element is heated by the heater and the inside of the exhaust pipe of the gas water heater is in an atmospheric state (a state in which the oxygen concentration is 20.97%) upon the establishment of the preparatory condition, and determines whether the change in the detected value has converged;
An oxygen sensor unit having a correction value setting unit (a function that executes the processing of step S201 in the CPU 61 of the sensor board 60) that sets the correction value calculated based on the detection value obtained from the oxygen sensor and a concentration reference value indicating the oxygen concentration in the atmospheric state as the reference object when the convergence determination unit determines that the change in the detection value has converged.

When the temperature of the sensor element rises, the way heat is transferred varies depending on factors such as the distance from the heater. For this reason, it takes some time for the temperature of the entire sensor element to become uniform after the estimated or measured temperature of the sensor element reaches a predetermined temperature. For these reasons, even if the actual oxygen concentration around the oxygen sensor remains constant, the detected oxygen concentration value may gradually increase (slightly increase) even after the predetermined temperature is reached (while the predetermined temperature is being maintained). If the above correction value were to be set (e.g., updated) during this process of increase (slight increase) in the detected value, the function of optimizing combustion may not be properly performed.

In this regard, with this characteristic configuration, the oxygen concentration detection value is repeatedly obtained from the oxygen sensor under conditions where the preparatory conditions are met, the sensor element is heated, and the exhaust pipe is in an atmospheric state. Then, when it is determined that the change in the detection value has converged, for example, when the amount of change has become smaller than a threshold value (a threshold value that assumes steady-state error) for a predetermined period of time, a correction value is set. This configuration makes it possible to avoid setting a correction value during the temperature rise process. Then, by setting the correction value at the appropriate timing when the predetermined temperature has been reached, the temperature has become uniform, and the detection value has stabilized, the accuracy of the correction value can be improved.

Furthermore, the time it takes for the temperature to become uniform after reaching a predetermined temperature can vary depending on factors such as individual differences in the sensor element and the degree of deterioration. In this regard, with this configuration, there is no need to take into account the influence of these factors when determining the appropriate timing, and it is possible to determine the appropriate timing for each situation. This is advantageous in that it prevents the configuration related to setting the correction value from becoming too complicated.

As described above in detail, a configuration that allows the correction value to be set at the appropriate timing can contribute to further optimizing combustion through the correction function.

Because maintaining atmospheric conditions is required for setting the correction value, it is difficult to prepare for setting the correction value in parallel with boiling water, and there is a priority order between boiling water and setting the correction value. For these reasons, the long time it takes to set the correction value hinders efforts to ensure opportunities to set (e.g., update) the correction value and to prevent delays in starting boiling water. In this regard, the configuration shown in this feature sets the correction value when it is determined that the change in the detection value has converged. This configuration contributes to shortening the wait time between the temperature of the sensor element becoming uniform and the correction value being set. Considering the wait time until the correction value is set in this way is advantageous for achieving coexistence between the water boiling function and the correction value setting (update) function.

Incidentally, the "convergence determination unit" in this feature may be changed to "a timing determination unit that repeatedly acquires the detected oxygen concentration value from the oxygen sensor under conditions in which the sensor element is heated by the heater and the inside of the exhaust pipe of the gas water heater is in an atmospheric state upon the fulfillment of the preparatory condition, and determines that the timing for setting the correction value has arrived when the change in the detected value has converged," and the configuration of the "correction value setting unit" may be changed to "when the timing determination unit determines that the setting timing has arrived, sets the correction value calculated based on the detected value acquired from the oxygen sensor and a concentration reference value indicating the oxygen concentration in the atmospheric state as the reference target."

Feature 2. The sensor control unit has a temperature acquisition unit that acquires the temperature of the sensor element,
The oxygen sensor unit described in Feature 1 is configured such that, when the temperature acquired by the temperature acquisition unit is at the predetermined temperature (e.g., 750°C) and the convergence determination unit determines that the change in the detection value has converged, the correction value setting unit sets the correction value calculated based on the detection value acquired from the oxygen sensor and a concentration reference value indicating the oxygen concentration in the atmospheric state as the reference object.

As shown in this feature, the correction value is set when the change in the detection value converges when the sensor element reaches a predetermined temperature. In other words, the setting of the correction value is avoided even if an unexpected factor causes the change in the detection value to appear as if it has converged before the predetermined temperature is reached. This prevents the deviation between the actual correction value and the ideal correction value from becoming excessively large, even if the convergence is not accurately determined. This is advantageous for improving the accuracy of the correction value.

For example, the "sensor control unit" may be configured to "allow the convergence determination unit to determine whether the change in the detected value has converged when the temperature acquired by the temperature acquisition unit reaches a predetermined temperature" or "allow the setting of a correction value when the temperature acquired by the temperature acquisition unit reaches a predetermined temperature."

Feature 3. The convergence determination unit repeatedly acquires the detection values under a condition in which the sensor element is heated by the heater and the inside of the exhaust pipe of the gas water heater is in the atmospheric state upon establishment of the preparatory condition, calculates a moving average from a plurality of the detection values including the newly acquired detection value, compares the newly calculated moving average with a plurality of the moving averages including the previous moving average, and determines whether the change in the detection value has converged based on the comparison result;
The oxygen sensor unit according to Feature 1 or Feature 2, wherein when the convergence determination unit determines that the change in the detection value has converged, the correction value setting unit calculates the correction value based on the detection value acquired from the oxygen sensor and the concentration reference value indicating the oxygen concentration in the atmospheric state, and sets the calculated correction value as the reference object.

In the configuration described in this feature, oxygen concentration detection values are repeatedly acquired from the oxygen sensor under conditions where the preparatory conditions are met, the sensor element is heated, and the exhaust pipe is in an atmospheric state. A moving average is then calculated from multiple detection values, including the newly acquired detection value, and a comparison result is obtained between the newly calculated moving average and multiple moving averages, including the previous moving average, to determine whether the change in the detection value has converged. This configuration effectively embodies the technical idea described in feature 1, etc.

Due to the nature of the sensor, there will be a certain degree of variation in the detected value. In other words, even after the temperature has become uniform, the value will not remain constant, but will fluctuate (up and down) within a certain range. There is also the possibility of temporary fluctuations (up and down) due to the influence of noise, etc. The detected value described above will converge after an increasing process (a slight increase process), so the influence of such variation must be taken into account (for example, eliminated or reduced) in order to quickly determine this convergence.

In this regard, as shown in this feature, if the effects of variation and noise are smoothed (leveled) using a moving average of multiple detection values and then the convergence of the detection values is determined from that moving average, it is possible to prevent the convergence trend from being overwhelmed by the above-mentioned variation, etc. This makes it possible to minimize the time (wait time) required to determine the correction value. As described above in detail, calculating (setting) the correction value at the appropriate time is preferable for achieving the effect described in Feature 1.

Feature 4. An oxygen sensor unit (sensor unit 40) applied to a gas water heater (gas water heater 11),
an oxygen sensor (A/F sensor 50) capable of detecting the oxygen concentration of combustion gas passing through an exhaust pipe (exhaust pipe 39) of the gas water heater;
a sensor control unit (sensor board 60) to which the oxygen sensor is connected, which corrects the detected value of the oxygen concentration obtained from the oxygen sensor using a correction value (correction coefficient) set as a reference, and outputs the corrected detected value to the hot water supply control device (hot water supply control device 12) of the gas hot water heater;
a heater (heater resistor 52) for heating a sensor element (sensor element 51) of the oxygen sensor,
The sensor control unit
a heating control unit (a function of executing a temperature adjustment process in the CPU 61 of the sensor substrate 60) that starts heating of the sensor element when a preparatory condition for setting the correction value (a user setting operation or a schedule) is met, and that controls the heater so as to maintain the temperature of the sensor element at a predetermined temperature (e.g., 750°C) after the temperature of the sensor element reaches the predetermined temperature;
a timing determination unit (a function that executes the process for determining the timing of setting the correction coefficient in step S106 in the CPU 61 of the sensor board 60) that repeatedly obtains the detection value from the oxygen sensor under the condition that the sensor element is heated by the heater and the inside of the exhaust pipe of the gas water heater is in an atmospheric state (a state in which the oxygen concentration is 20.97%) upon the establishment of the preparatory condition, calculates a moving average from a plurality of the detection values including the newly obtained detection value, compares the newly calculated moving average with a plurality of the moving averages including the previous moving average, and determines whether it is time to set the correction value based on the comparison result;
An oxygen sensor unit having a correction value setting unit (a function that executes the processing of step S201 in the CPU 61 of the sensor board 60) that, when the timing determination unit determines that the set timing has arrived, calculates the correction value based on the detection value obtained from the oxygen sensor and a concentration reference value that indicates the oxygen concentration in the atmospheric state, and sets the calculated correction value as the reference object.

In the configuration described in this feature, oxygen concentration detection values are repeatedly acquired from the oxygen sensor under conditions where the preparatory conditions are met, the sensor element is heated, and the exhaust pipe is in an atmospheric state. A moving average is then calculated each time from multiple detection values, including the newly acquired detection value. When convergence of the detection values is confirmed based on the multiple moving averages, including the newly calculated moving average and the previous moving average (for example, when the difference between the moving averages or the standard deviation becomes smaller than a threshold value), it is determined that it is time to set a correction value. This configuration makes it possible to determine the timing when the temperature becomes uniform as the detection value increases (slight increase), thereby ideally realizing the technical concept described in feature 1, etc.

Due to the nature of the sensor, there will be a certain degree of variation in the detected value. In other words, even after the temperature has become uniform, the value will not remain constant, but will fluctuate (up and down) within a certain range. There is also the possibility of temporary fluctuations (up and down) due to the influence of noise, etc. The detected value described above will converge after an increasing process (a slight increase process), so the influence of such variation must be taken into account (for example, eliminated or reduced) in order to quickly determine this convergence.

In this regard, as shown in this feature, if the effects of variation and noise are smoothed (leveled) using a moving average of multiple detection values and then the convergence of the detection values is determined from that moving average, it is possible to prevent the convergence trend from being overwhelmed by the above-mentioned variation, etc. This makes it possible to minimize the time (wait time) required to determine the correction value. As described above in detail, calculating (setting) the correction value at the appropriate time is preferable for achieving the effect described in Feature 1.

Feature 5. An oxygen sensor unit according to Feature 3 or Feature 4, wherein the moving averages are specified so that the detected values used to calculate one moving average do not overlap with the detected values used to calculate another moving average.

As shown by this feature, if the detected values referenced when calculating one (earlier) moving average do not overlap with the detected values referenced when calculating other (later) moving averages, each moving average can be calculated using detected values that are separated in time, making it easier to grasp trends in change from a long-term perspective and enabling appropriate determination of the convergence of changes in detected values.

Feature 6. An oxygen sensor unit according to Feature 3 or Feature 5, wherein the convergence determination unit determines that the change in the detection value has not converged if the difference between the newly calculated moving average and the previously calculated moving average is greater than a threshold value, and determines that the change in the detection value has converged if the difference between the currently calculated moving average and the previously calculated moving average is smaller than the threshold value.

After the temperature of the sensor element reaches a predetermined temperature, the difference between the previous and next moving averages becomes smaller over time. In other words, the difference between the moving averages approaches zero over time. Therefore, by comparing this difference with a threshold value to determine the convergence of the detected values, the effects described in Feature 3 and other features can be achieved with a simple configuration.

The configuration of this feature can also be applied to feature 4, resulting in an oxygen sensor unit according to feature 4, in which "the timing determination unit determines that the set timing has not arrived if the difference between the newly calculated moving average and the previously calculated moving average is greater than a threshold value, and determines that the set timing has arrived if the difference between the currently calculated moving average and the previously calculated moving average is smaller than the threshold value."

Feature 7. The oxygen sensor unit described in Feature 6, wherein the convergence determination unit determines that the change in the detection value has not converged if at least one of the newly calculated difference and a predetermined number (e.g., two) of the previously calculated differences is greater than the threshold value, and determines that the change in the detection value has converged if both the newly calculated difference and the predetermined number of the previously calculated differences are smaller than the threshold value.

As mentioned above, there is a certain degree of variability in the detected values. Therefore, as shown in this feature, by configuring the system to compare not only the newly calculated difference but also multiple differences, including differences calculated previously (in the past), with a threshold value, it is possible to effectively prevent a correction value from being determined (set) when the detected value is not stable (during the rising process described above).

Feature 8. The oxygen sensor unit described in Feature 3 or Feature 5, wherein the convergence determination unit calculates the standard deviation of the multiple calculated moving averages each time, and determines that the change in the detected value has not converged if at least one of the newly calculated standard deviation and a predetermined number (e.g., two) of the previously calculated standard deviations is greater than a threshold value, and determines that the change in the detected value has converged if both the newly calculated standard deviation and the predetermined number of the previously calculated standard deviations are smaller than the threshold value.

As shown by this feature, by configuring the system to determine that it is time to set the standard deviation when both the newly calculated standard deviation and a predetermined number of previously calculated standard deviations are smaller than the threshold value, it is possible to effectively prevent a correction value from being determined when the detected value is not stable (during the above-mentioned rising process).

Furthermore, if the configuration retains past history as standard deviation, the amount of information required to determine convergence can be reduced compared to a configuration that retains the detected values themselves. This is preferable in terms of preventing increases in memory storage capacity.

Incidentally, the configuration described in this feature can be applied to feature 4 to produce an oxygen sensor unit described in feature 4, in which "the timing determination unit calculates the standard deviation of the multiple calculated moving averages each time, and determines that the set timing has not arrived if at least one of the newly calculated standard deviation and a predetermined number (e.g., two) of the previously calculated standard deviations is greater than a threshold value, and determines that the set timing has arrived if both the newly calculated standard deviation and the predetermined number of the previously calculated standard deviations are smaller than the threshold value."

Feature 9. The convergence determination unit sets a maximum value of the detection values acquired up to that point as a determination upper limit, and determines that the detection values have converged when a plurality of detection values acquired within a predetermined time period going back from the current point in time are all smaller than the determination upper limit,
The correction value setting unit calculates the correction value based on the detection value acquired from the oxygen sensor and the concentration reference value indicating the oxygen concentration in the atmospheric state when the convergence determination unit determines that the change in the detection value has converged, and sets the calculated correction value as the reference object.

After reaching a predetermined temperature, the detected oxygen concentration value continues to increase gradually until the temperature of the sensor element becomes uniform, and then stabilizes. As shown in this feature, if the maximum detected value obtained up to that point is set as the upper judgment limit, the maximum detected value will gradually increase before stabilization, causing the upper judgment limit to be repeatedly updated. However, once stable, the maximum detected value will basically be smaller than the upper judgment limit, and updating of the upper judgment limit will essentially stop. If the system is configured to determine that the change in the detected value has converged when multiple detected values obtained within a predetermined time are all smaller than the upper judgment limit, it becomes possible to determine the convergence described in Feature 1.

In particular, the upper judgment limit is automatically updated when the temperature of the sensor element rises over time and the detected value (maximum value) exceeds the previous upper judgment limit. This configuration reduces the amount of information required to determine the convergence of the detected values, achieving the effect described in Feature 1 with a simple configuration.

Note that variations in detected values from oxygen sensors can vary depending on individual differences, but by updating the upper judgment limit and checking it multiple times, the impact of such variations on convergence judgment can be effectively suppressed.

Incidentally, when the configuration described in this feature is applied to feature 1, the description of the "convergence determination unit" may be changed to "a timing determination unit that, when the preparatory condition is met, repeatedly acquires the detection value under conditions in which the sensor element is heated by the heater and the inside of the exhaust pipe of the gas water heater is in an atmospheric state, sets the maximum of the oxygen concentration detection values acquired up to that point as an upper determination limit, and determines that the timing to set the correction value has arrived when multiple detection values acquired within a predetermined time are all smaller than the upper determination limit," and the description of the "correction value setting unit" may be changed to "a correction value setting unit that, when the timing determination unit determines that the setting timing has arrived, sets in the predetermined memory area the correction value calculated based on the detection value acquired from the oxygen sensor and a concentration reference value indicating the oxygen concentration in the atmospheric state."

Feature 10. The oxygen sensor unit of Feature 9, wherein the convergence determination unit sets the maximum of the detected values acquired up to that point as an upper determination limit and the minimum of the detected values acquired up to that point as a lower determination limit, and determines that the change in the detected values has converged if all of the detected values acquired within a predetermined time period going back from the current point in time are smaller than the upper determination limit and larger than the lower determination limit.

By defining the range of detection values using the upper judgment limit shown in Feature 9 and the lower judgment limit shown in this feature, it is possible to effectively prevent correction values from being calculated in situations where the detection values are fluctuating greatly.

The configuration described in this feature can also be modified as follows: "The oxygen sensor unit described in feature 9, wherein the sensor control unit includes a temperature acquisition unit that acquires the temperature of the sensor element, and the convergence determination unit sets the maximum of the detected values acquired up to that point as an upper determination limit and the minimum of the detected values acquired after the temperature of the sensor element reaches a predetermined temperature as a lower determination limit, and determines that the change in the detected value has converged if multiple detected values acquired within a predetermined time period from the present time after the temperature reaches the predetermined temperature are all smaller than the upper determination limit and larger than the lower determination limit." The detected value changes significantly when heating of the sensor element begins. This change becomes gradual when the temperature acquired by the temperature acquisition unit reaches the predetermined temperature. Therefore, the above-mentioned suppression effect can be more effectively achieved by setting the lower determination limit equal to the minimum of the detected values acquired after the predetermined temperature is reached.

Feature 11. The oxygen sensor unit according to any one of Features 1 to 3 and Features 5 to 10, wherein, when the convergence determination unit determines that the change in the detection value has converged, the correction value setting unit calculates the correction value using at least a portion of the detection value acquired during the current determination by the convergence determination unit.

As shown in this feature, when convergence is followed by setting a correction value, the correction value is calculated using at least some of the detection values already acquired during the convergence confirmation process, thereby shortening the time required to set the correction value compared to a configuration in which new detection values are acquired after convergence.

The configuration described in this feature can also be applied to feature 4. In this case, the statement "The convergence determination unit determined that the change in the detection value has converged" should be changed to "The timing determination unit determined that the set timing has arrived."

Feature 12. The oxygen sensor unit described in Feature 1 or Feature 2, wherein the convergence determination unit, upon satisfaction of the preparatory condition, repeatedly acquires the detected oxygen concentration value from the oxygen sensor under conditions in which the sensor element is heated by the heater and the inside of the exhaust pipe of the gas water heater is in the atmospheric state, calculates the correction value based on the acquired detected value and a concentration reference value indicating the oxygen concentration in the atmospheric state, and determines that the change in the detected value has converged if the calculated correction value is smaller than a threshold value.

According to the configuration of this feature, when the preparatory conditions are met, the sensor element is heated, and the exhaust pipe is in an atmospheric state, the oxygen concentration detection value is repeatedly acquired from the oxygen sensor. A correction value is then calculated based on the acquired detection value and a concentration reference value that indicates the oxygen concentration in an atmospheric state, and it is determined that the change in the detection value has converged if the calculated correction value is smaller than a threshold value. By using part of the correction function (the correction value) in this way to determine convergence, the effect described in Feature 1 can be achieved while preventing the configuration related to the convergence determination from becoming too complex.

Feature 13. The oxygen sensor unit according to Feature 12, wherein the correction value setting unit sets the correction value calculated by the convergence determination unit as the reference value when the convergence determination unit determines that the change in the detected value has converged.

As shown by this feature, by setting the correction value used to determine convergence as the reference value, the time required to complete the setting can be reduced compared to a configuration in which a new correction value is calculated when convergence is determined.

Feature 14. An oxygen sensor unit (sensor unit 40) applied to a gas water heater (gas water heater 11),
an oxygen sensor (A/F sensor 50) capable of detecting the oxygen concentration of combustion gas passing through an exhaust pipe (exhaust pipe 39) of the gas water heater;
a sensor control unit (sensor board 60) to which the oxygen sensor is connected, which corrects the detected value of the oxygen concentration obtained from the oxygen sensor using a correction value (correction coefficient) set as a reference, and outputs the corrected detected value to the hot water supply control device (hot water supply control device 12) of the gas hot water heater;
a heater (heater resistor 52) for heating a sensor element (sensor element 51) of the oxygen sensor,
The sensor control unit
a heating control unit (a function of executing a temperature adjustment process in the CPU 61 of the sensor substrate 60) that starts heating of the sensor element when a preparatory condition for setting the correction value (a user setting operation or a schedule) is met, and that controls the heater so as to maintain the temperature of the sensor element at a predetermined temperature (e.g., 750°C) after the temperature of the sensor element reaches the predetermined temperature;
a timing determination unit (a function that executes the process for determining the timing of setting the correction coefficient in step S106 in the CPU 61 of the sensor board 60) that repeatedly acquires the detection value from the oxygen sensor under the condition that the sensor element is heated by the heater and the inside of the exhaust pipe of the gas water heater is in an atmospheric state (a state in which the oxygen concentration is 20.97%) upon the establishment of the preparatory condition, calculates the correction value based on the acquired detection value and a concentration reference value that indicates the oxygen concentration in the atmospheric state, and determines whether it is time to set the correction value when the calculated correction value is smaller than a threshold value;
An oxygen sensor unit having a correction value setting unit (a function that executes the processing of step S201 in the CPU 61 of the sensor board 60) that sets the correction value calculated based on the detection value obtained from the oxygen sensor and a concentration reference value indicating the oxygen concentration in the atmospheric state as the reference object when the timing determination unit determines that the set timing has arrived.

According to the configuration of this feature, when the preparatory conditions are met, the sensor element is heated, and the exhaust pipe is in an atmospheric state, the oxygen concentration detection value is repeatedly acquired from the oxygen sensor. A correction value is then calculated based on the acquired detection value and a concentration reference value that indicates the oxygen concentration in an atmospheric state, and it is determined that the change in the detection value has converged if the calculated correction value is smaller than a threshold value. By using part of the correction function (the correction value) in this way to determine convergence, the effect described in Feature 1 can be achieved while preventing the configuration related to the convergence determination from becoming too complex.

Feature 15. The oxygen sensor unit described in Feature 1 or Feature 2, wherein the convergence determination unit repeatedly acquires the detected oxygen concentration value from the oxygen sensor under conditions in which the sensor element is heated by the heater and the inside of the exhaust pipe of the gas water heater is in the atmospheric state upon establishment of the preparatory condition, calculates the correction value based on the acquired detected value and the concentration reference value indicating the oxygen concentration in the atmospheric state, corrects the newly acquired detected value using the correction value after a predetermined waiting time has elapsed since calculating the correction value, and determines that the change in the detected value has converged if the result of the correction is within a reference range established based on the concentration reference value.

If a detection value obtained after a predetermined waiting time has elapsed since the correction value was calculated is corrected using the correction value when the detection value is rising, the correction result (corrected detection value) will deviate significantly from the concentration reference value. In contrast, if a detection value obtained after a predetermined waiting time has elapsed since the correction value was calculated is corrected using the correction value when the detection value is converging (stable), the deviation of the correction result (corrected detection value) from the concentration reference value will be reduced. Therefore, as shown in this feature, if the correction result is determined to be converging when it is within a reference range established based on the concentration reference value, the technical concept described in feature 1 and others can be effectively realized. Note that correction of the detection value is performed as needed to optimize combustion. Being able to use this correction process to determine convergence is advantageous in simplifying the control program.

It is also possible to configure the convergence determination unit so that, if the result of the correction falls outside the reference range, it newly calculates the correction value, but if the result of the correction falls within the reference range, it retains the current correction value and repeatedly acquires a new detection value, corrects the new detection value using the correction value, and determines whether the result of the correction falls within the reference range, and determines that the timing to determine the correction value has arrived based on the number of times the correction result has consecutively fallen within the reference range reaching a predetermined number of times. This configuration effectively prevents erroneous determination that the change in the detection value has converged when the correction result accidentally falls within the reference range.

Feature 16. An oxygen sensor unit (sensor unit 40) applied to a gas water heater (gas water heater 11),
an oxygen sensor (A/F sensor 50) capable of detecting the oxygen concentration of combustion gas passing through an exhaust pipe (exhaust pipe 39) of the gas water heater;
a sensor control unit (sensor board 60) to which the oxygen sensor is connected, which corrects the detected value of the oxygen concentration obtained from the oxygen sensor using a correction value (correction coefficient) set as a reference, and outputs the corrected detected value to the hot water supply control device (hot water supply control device 12) of the gas hot water heater;
a heater (heater resistor 52) for heating a sensor element (sensor element 51) of the oxygen sensor,
The sensor control unit
a heating control unit (a function of executing a temperature adjustment process in the CPU 61 of the sensor substrate 60) that starts heating of the sensor element when a preparatory condition for setting the correction value (a user setting operation or a schedule) is met, and that controls the heater so as to maintain the temperature of the sensor element at a predetermined temperature (e.g., 750°C) after the temperature of the sensor element reaches the predetermined temperature;
a timing determination unit (a function that executes the process for determining the timing of setting the correction coefficient in step S106 in the CPU 61 of the sensor board 60) that repeatedly obtains the detected value of the oxygen concentration from the oxygen sensor under the condition that the sensor element is heated by the heater and the inside of the exhaust pipe of the gas water heater is in the atmospheric state upon the establishment of the preparatory condition, calculates the correction value based on the obtained detected value and a concentration reference value that indicates the oxygen concentration in the atmospheric state, corrects the newly obtained detected value using the correction value after a predetermined waiting time has elapsed since the calculation of the correction value, and determines whether it is time to set the correction value if the result of the correction is within a reference range determined based on the concentration reference value;
An oxygen sensor unit having a correction value setting unit (a function that executes the processing of step S201 in the CPU 61 of the sensor board 60) that sets the correction value calculated based on the detection value obtained from the oxygen sensor and a concentration reference value indicating the oxygen concentration in the atmospheric state as the reference object when the timing determination unit determines that the set timing has arrived.

If a detection value obtained after a predetermined waiting time has elapsed since the correction value was calculated is corrected using the correction value when the detection value is rising, the correction result (corrected detection value) will deviate significantly from the concentration reference value. In contrast, if a detection value obtained after a predetermined waiting time has elapsed since the correction value was calculated is corrected using the correction value when the detection value is converging (stable), the deviation of the correction result (corrected detection value) from the concentration reference value will be reduced. Therefore, as shown in this feature, if the correction result is determined to be within a reference range established based on the concentration reference value, the technical concept described in feature 1 and others can be effectively realized. Note that correction of the detection value is performed as needed to optimize combustion. The ability to use this correction process to determine convergence is advantageous in simplifying the control program.

Feature 17. The heating control unit is configured to perform heating control of the heater when either a first preparation condition that is relatively infrequently met or a second preparation condition that is relatively frequently met is met as the preparation condition,
the convergence determination unit is a first determination unit that determines whether a change in the detection value has converged when the first preparation condition is satisfied,
The sensor control unit repeatedly acquires the detected oxygen concentration value from the oxygen sensor under the condition that the sensor element is heated by the heater when the second preparation condition is met and the exhaust pipe of the gas water heater is in an atmospheric state (a state in which the oxygen concentration is 20.97%), calculates the correction value based on the acquired detected value and a concentration reference value indicating the oxygen concentration in the atmospheric state, and determines that the change in the detected value has converged when the difference between the conversion rate of the detected value using the correction value and the conversion rate of the detected value using the correction value set by the correction value setting unit falls within a predetermined range.

This feature of the configuration determines whether the change in the detected value has converged based on the degree of deviation between the conversion rate when the first preparation condition is met and the conversion rate when the second preparation condition is met. By updating the criteria for determining convergence in this way, the timing of convergence can be determined accurately and quickly. However, when using an oxygen sensor for a long period of time, it is expected that the detected value will become lower or higher than before due to deterioration over time, even if it is in a stable state. Therefore, by configuring the criteria for determining convergence to be updated as needed, it is possible to prevent a deterioration in the ability to determine the timing of convergence.

Feature 18. A hot water supply control system comprising the oxygen sensor unit described in any one of Features 1 to 17 and the hot water supply control device.

This hot water supply control system allows the correction value to be set at the appropriate time, contributing to further optimization of combustion through the correction function. It also minimizes the waiting time until the correction value is set. This is advantageous in terms of achieving coexistence of the water heating function and the above-mentioned correction function.

Feature 19. An oxygen sensor (A/F sensor 50) capable of detecting the oxygen concentration of combustion gas passing through an exhaust pipe (exhaust pipe 39) of a gas water heater (gas water heater 11);
a correction unit (for example, a correction function in the CPU 61 of the sensor board 60) that corrects the detection value of the oxygen concentration detected by the oxygen sensor using a correction value (correction coefficient) set as a reference;
A hot water control system including a hot water control device (hot water control device 12) that controls combustion of the gas hot water heater based on the detection value corrected by the correction unit,
a heater (heater resistor 52) for heating a sensor element (sensor element 51) of the oxygen sensor;
a heating control unit (a function of executing a temperature adjustment process in the CPU 61 of the sensor substrate 60) that starts heating of the sensor element when a preparatory condition for setting the correction value (a user setting operation or a schedule) is met, and that controls the heater so as to maintain the temperature of the sensor element at a predetermined temperature (e.g., 750°C) after the temperature of the sensor element reaches the predetermined temperature;
a convergence determination unit (a function that executes a process for determining the timing of setting the correction coefficient in step S106 in the CPU 61 of the sensor board 60) that repeatedly acquires the detected value from the oxygen sensor under the condition that the sensor element is heated by the heater and the inside of the exhaust pipe of the gas water heater is in an atmospheric state (a state in which the oxygen concentration is 20.97%) upon the establishment of the preparatory condition, and determines whether the change in the detected value has converged;
A hot water supply control system that includes a correction value setting unit (a function that executes the processing of step S201 on the CPU 61 of the sensor board 60) that sets the correction value calculated based on the detection value obtained from the oxygen sensor and a concentration reference value indicating the oxygen concentration in the atmospheric state as the reference object when the convergence determination unit determines that the change in the detection value has converged.

This hot water supply control system allows the correction value to be set at the appropriate time, contributing to further optimization of combustion through the correction function. It also minimizes the waiting time until the correction value is set. This is advantageous in terms of achieving coexistence of the water heating function and the above-mentioned correction function.

10...Hot water supply system, 11...Gas water heater, 12...Hot water supply control device, 39...Exhaust pipe, 40...Sensor unit, 50...A/F sensor, 51...Sensor element, 52...Heater resistor, 60...Sensor board, 61...CPU.

Claims (8)

An oxygen sensor unit applied to a gas water heater,
an oxygen sensor capable of detecting the oxygen concentration of combustion gas passing through an exhaust pipe of the gas water heater;
a sensor control unit connected to the oxygen sensor, correcting the detected value of the oxygen concentration obtained from the oxygen sensor using a correction value set as a reference, and outputting the corrected detected value to the hot water supply control device of the gas hot water heater;
a heater for heating a sensor element of the oxygen sensor,
The sensor control unit
a heating control unit that starts heating of the sensor element when a preparatory condition for setting the correction value is satisfied, and that executes heating control of the heater so as to maintain the temperature of the sensor element at a predetermined temperature after the temperature of the sensor element reaches the predetermined temperature;
a convergence determination unit that repeatedly obtains the detected value from the oxygen sensor under the condition that the sensor element is heated by the heater and the inside of the exhaust pipe of the gas water heater is in an atmospheric state upon establishment of the preparation condition, and determines whether the change in the detected value is converging;
an oxygen sensor unit having a correction value setting unit that, when the convergence determination unit determines that the change in the detection value has converged , determines whether the number of detection values obtained from the oxygen sensor has reached a first specified number; if the number of detection values has reached the first specified number, calculates an average value of the first specified number of detection values; calculates a correction value by dividing a concentration reference value indicating the oxygen concentration in the atmospheric state by the average value; and sets the calculated correction value as the reference object. The oxygen sensor unit of claim 1, wherein the convergence determination unit repeatedly acquires the detection value under a condition in which the sensor element is heated by the heater and the exhaust pipe of the gas water heater is in the atmospheric state upon the fulfillment of the preparatory condition, calculates a moving average from multiple detection values including the newly acquired detection value, compares the newly calculated moving average with multiple moving averages including the previous moving average, and determines whether the change in the detection value has converged based on the comparison result. The oxygen sensor unit described in claim 2, wherein the convergence determination unit determines that the change in the detected value has not converged if the difference between the newly calculated moving average and the previously calculated moving average is greater than a threshold value, and determines that the change in the detected value has converged if the difference between the currently calculated moving average and the previously calculated moving average is smaller than the threshold value. The oxygen sensor unit described in claim 2, wherein the convergence determination unit calculates the standard deviation of the multiple calculated moving averages each time, and determines that the change in the detected value has not converged if at least one of the newly calculated standard deviation and a predetermined number of the previously calculated standard deviations is larger than a threshold value, and determines that the change in the detected value has converged if both the newly calculated standard deviation and a predetermined number of the previously calculated standard deviations are smaller than the threshold value. 2. The oxygen sensor unit according to claim 1, wherein the convergence determination unit sets the maximum value of the detection value acquired up to that point as an upper judgment limit, and determines that the detection value has converged if all of the detection values acquired within a predetermined time period going back from the current point in time are smaller than the upper judgment limit. The oxygen sensor unit of claim 1, wherein the convergence determination unit repeatedly acquires the detected oxygen concentration value from the oxygen sensor under conditions in which the sensor element is heated by the heater and the inside of the exhaust pipe of the gas water heater is in the atmospheric state upon the fulfillment of the preparatory condition, calculates the correction value based on the acquired detected value and the concentration reference value indicating the oxygen concentration in the atmospheric state, corrects the newly acquired detected value using the correction value after a predetermined waiting time has elapsed since calculating the correction value, and determines that the change in the detected value has converged if the result of the correction is within a reference range established based on the concentration reference value. An oxygen sensor unit according to any one of claims 1 to 6, wherein the correction value setting unit calculates the correction value using at least a portion of the detection value acquired during a current determination by the convergence determination unit when the convergence determination unit determines that the change in the detection value has converged. an oxygen sensor capable of detecting the oxygen concentration of combustion gas passing through the exhaust pipe of the gas water heater;
a correction unit that corrects the detected value of the oxygen concentration detected by the oxygen sensor using a correction value that is set as a reference;
A hot water control system including a hot water control device that controls combustion of the gas hot water heater based on the detection value corrected by the correction unit,
a heater for heating a sensor element of the oxygen sensor;
a heating control unit that starts heating of the sensor element when a preparatory condition for setting the correction value is satisfied, and that executes heating control of the heater so as to maintain the temperature of the sensor element at a predetermined temperature after the temperature of the sensor element reaches the predetermined temperature;
a convergence determination unit that repeatedly obtains the detected value from the oxygen sensor under the condition that the sensor element is heated by the heater and the inside of the exhaust pipe of the gas water heater is in an atmospheric state upon establishment of the preparation condition, and determines whether the change in the detected value is converging;
A hot water control system comprising: a correction value setting unit that, when the convergence determination unit determines that the change in the detection value has converged, determines whether the number of detection values obtained from the oxygen sensor has reached a first specified number; when the number of detection values has reached the first specified number, calculates the average value of the first specified number of detection values; calculates a correction value by dividing a concentration reference value indicating the oxygen concentration in the atmospheric state by the average value; and sets the calculated correction value as the reference object.