Oxygen sensor unit and hot water supply control system

Abstract

To provide an oxygen sensor unit and a hot water supply control system which can improve setting accuracy of a correction value and can reduce waiting time related to the setting of the correction value under various situations.SOLUTION: A sensor unit 40 mounted on a gas water heater includes an A / F sensor 50 for detecting an oxygen concentration of combustion gas, and a sensor substrate 60 for correcting a detection value of the oxygen concentration with the usage of a correction coefficient set as a reference object. A CPU 61 of the sensor substrate 60 heats a sensor element 51 when a preparation condition of setting the correction coefficient is established, and adjusts temperature so as to maintain the temperature of the sensor element 51 at the prescribed temperature. After the preparation condition is established, the detection value is repeatedly acquired from the A / F sensor 50 under such situation that an inside of an exhaust pipe is in an atmospheric state, and it is determined whether the change of the detection value is converged or not. When it is determined that the change of the detection value is converged, a correction value is calculated on the basis of the detection value and a concentration reference value representing the oxygen concentration in the atmospheric state, and the correction value is set as the reference object.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an oxygen sensor unit and a hot water supply control system having an oxygen sensor unit. [Background technology]

[0002] Some hot water supply equipment optimizes combustion by detecting the oxygen concentration of the combustion gas emitted from a gas hot water heater using an oxygen sensor such as an A / F sensor and adjusting the amount of gas supplied based on the detection result (detection value) (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 1-98818 Summary of the Invention [Problem to be solved by the invention]

[0004] When measuring gases with the same oxygen concentration, differences in the detected values ​​occur due to individual differences and deterioration over time. By obtaining the detected value in atmospheric conditions where the oxygen concentration is constant (20.94%) and correcting the detected value as needed using a correction value (correction coefficient) calculated based on the detected value and the reference value of the oxygen concentration, further optimization of combustion can be expected.

[0005] In order for the oxygen sensor to properly perform its detection function, it is necessary to heat (activate) the sensor element to a predetermined temperature (for example, 750°C in the case of zirconia). Therefore, in order to properly calculate and set the correction value, it is necessary to heat the sensor element to the predetermined temperature in atmospheric conditions.

[0006] A heater attached to the sensor element is often used to heat up the sensor element. Because heat transfer from the heater varies depending on the distance from the heater, it takes some time for the temperature of the entire sensor element to become uniform even after the estimated or measured temperature of the sensor element reaches a predetermined temperature. 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 correction value were set during this temperature increase, there is a concern that the function of optimizing combustion may not be properly performed.

[0007] For example, if the correction value is set after a sufficient amount of time has elapsed since the heater started heating, setting the correction value during the heating process described above can be avoided. 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 the oxygen sensor, the oxygen sensor and ambient temperatures, and individual differences and deterioration levels of the heater. In other words, if the waiting time is specified while taking various circumstances into consideration, the waiting time will be excessively long. This is undesirable for the following reasons. Setting the correction value requires maintaining atmospheric conditions, making it difficult to perform the setting in parallel with boiling water. Therefore, there is a priority between boiling water and setting the correction value. If boiling water were prioritized, 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 prioritized, the start of boiling water would be delayed, potentially reducing user satisfaction. Furthermore, if the waiting time were specified while considering only certain circumstances, the waiting time would be insufficient under certain circumstances, making further optimization of combustion difficult.

[0008] As described above, in order to optimize combustion by correcting the detected value of the oxygen concentration, there is still room for improvement in the configuration related to setting the correction value.

[0009] The present invention has been made in consideration of the above-mentioned problems, and its main purpose is to provide an oxygen sensor unit and a hot water supply control system that can improve the accuracy of setting correction values ​​and shorten the waiting time associated with setting correction values ​​under various circumstances in order to optimize combustion by correcting the detected value of oxygen concentration. [Means for solving the problem]

[0010] The following describes means for solving the above problems.

[0011] 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; Equipped with 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; a correction value setting unit that sets, as the reference object, 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, when the convergence determination unit determines that the change in the detection value has converged; It has the following characteristics.

[0012] 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 prevents the correction value from being set while the detection value is increasing. 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 for control that takes 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 prevents the configuration for setting the correction value from becoming too complex. As described above in detail, a configuration that allows the correction value to be set at an appropriate timing can contribute to further optimizing combustion through the correction function.

[0013] 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 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 described above sets the correction value when it is determined that the change in the detection value has converged. This configuration contributes to shortening the waiting time between the temperature of the sensor element becoming uniform and the correction value being set. Considering the waiting time for setting the correction value in this way is advantageous for achieving coexistence between the boiling water function and the correction value setting (update) function. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic diagram of a hot water supply system according to a first embodiment. [Figure 2] FIG. 2 is a partially enlarged view of FIG. 1 showing the A / F sensor and its surroundings. [Figure 3] FIG. 2 is a block diagram showing the electrical configuration of the sensor unit. [Figure 4] 10 is a flowchart showing a correction coefficient setting mode process executed by a CPU of the sensor board. [Figure 5] 10 is a flowchart showing a correction coefficient setting process. [Figure 6] 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. [Figure 7] 10 is a flowchart showing a process for determining the timing for setting a correction coefficient. [Figure 8] A schematic diagram showing the relationship between two moving averages being compared. [Figure 9] 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; [Figure 10] 10 is a flowchart showing a setting timing determination process in the second embodiment. [Figure 11] 10 is a flowchart showing a setting timing determination process according to the third embodiment. [Figure 12] 10 is a flowchart showing a setting timing determination process in the fourth embodiment. [Figure 13] 13 is a flowchart showing a setting timing determination process in the fifth embodiment. [Figure 14] 5 is a timing chart showing the transition of the detected value of oxygen concentration and the flow of setting a correction coefficient. [Figure 15] FIG. 10 is a schematic diagram showing a modified example of the configuration related to setting of a correction coefficient. [Figure 16] 13 is a flowchart showing a setting timing determination process in the sixth embodiment. [Figure 17] 13 is a flowchart showing a setting timing determination process according to the seventh embodiment. [Figure 18] 10 is a flowchart showing a second determination process. DETAILED DESCRIPTION OF THE INVENTION

[0015] 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.

[0016] As shown in Figure 1, hot water supply equipment 10 includes a hot water storage type gas water heater 11 and a hot water supply control device 12 that controls the hot water supply of gas water heater 11. Gas water heater 11 is provided with a hot water storage tank 21 that stores hot water. Hot water storage tank 21 is provided with a partition that separates the interior of hot water storage tank 21 into upper and lower sections, with combustion chamber 24 below this partition and hot water storage chamber 25 above. A water supply pipe 22 is connected to the bottom of 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 hot water storage chamber 25 is connected to the top of hot water storage chamber 25, and hot water is supplied through this hot water supply pipe 23.

[0017] An intake pipe 31 is connected to combustion chamber 24, and a blower 32 is disposed in this intake pipe 31. Blower 32 is subject to drive control by hot water supply control device 12, and operates based on a drive signal from said hot water supply control device 12. When blower 32 operates, outside air (atmosphere) is supplied to combustion chamber 24 through intake pipe 31. A nozzle of gas supply pipe 33 is connected to a position midway through intake pipe 31. A control valve is provided in gas supply pipe 33, and when this control valve is driven and controlled by hot water supply control device 12, the amount of gas supplied to intake pipe 31 is adjusted.

[0018] The combustion chamber 24 is provided with a burner 34 that burns combustion air, which is a mixture of gas and air supplied to the combustion chamber 24 through the intake pipe 31, and a spark plug 35. 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. In the process of the combustion gas being discharged through the exhaust pipe 39, heat exchange occurs between the combustion gas and the water via the exhaust pipe 39. This heat exchange warms the water in the hot water storage tank 21, producing hot water.

[0019] The exhaust pipe 39 protrudes upward from the hot water storage tank 21, and an outlet of 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 (more specifically, near the outlet). The A / F sensor 50 constitutes a sensor unit 40 together with a sensor board 60 (corresponding to a "sensor control unit") that is a control board for the A / F sensor 50. The sensor board 60 is disposed at a position away from the exhaust pipe 39, i.e., at a position outside the range affected by the exhaust heat of the gas water heater 11.

[0020] The sensor board 60 is connected to the hot water supply control device 12, and the hot water supply control device 12 controls the amount of gas injection and the like based on the detected value of the oxygen concentration input from the sensor unit 40 (sensor board 60). Specifically, feedback control is performed so that the air-fuel ratio becomes a preset value (theoretical air-fuel ratio). This improves the combustion efficiency of the gas hot water heater 11.

[0021] 2 (a partially enlarged view of FIG. 1), the structure of the A / F sensor 50 will be described. The A / F sensor 50 comprises a sensor element 51 made of zirconia and a housing 53 that houses the sensor element 51, and the housing 53 is fixed to the exhaust pipe 39 so that it protrudes into the exhaust pipe 39. A plurality of through holes are formed in the housing 53, and combustion gas that flows into the housing 53 through these through holes is guided to the sensor element 51.

[0022] In order for the A / F sensor 50 to properly demonstrate its detection performance, the sensor element 51 must be kept at an appropriate temperature (reference temperature: 750°C in this embodiment). In other words, to improve the reliability of the detection results of the A / F sensor 50 and optimize combustion, the sensor element 51 must be heated to the above-mentioned reference temperature and maintained at that reference temperature. In consideration of this situation, 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."

[0023] 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, thereby heating the sensor element 51. The heater resistor 52 is connected to the sensor board 60 (see FIG. 1), and can be switched by the sensor board 60 (CPU, described later) between a power-on state (heater ON) in which power is supplied and a power-off state (heater OFF) in which power is not supplied.

[0024] Next, the electrical configuration of the sensor unit 40 will be described with reference to FIG.

[0025] The sensor unit 40 is provided 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 provided with a CPU 61 that serves as a control unit that controls the heating circuit HC based on information from the detection circuit SC.

[0026] The detection circuit SC is composed of a 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. The sensor element 51 shown in this embodiment generates an electromotive force corresponding to the oxygen concentration of the combustion gas. The ASIC 62 acquires the current value and voltage value of the current flowing through the sensor element 51 and outputs the acquired current value and voltage value to the CPU 61.

[0027] The CPU 61 identifies 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 a memory attached to the CPU 61, and the detected oxygen concentration value (%) is identified 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).

[0028] CPU 61 transmits the detected value of the oxygen concentration to hot water supply control device 12. Hot water supply control device 12 performs combustion control (feedback control) of gas hot water heater 11 based on the detected value. In this embodiment, a "hot water supply control system" is constructed by hot water supply control device 12 and sensor unit 40. Note that it is also possible to configure the system so that the acquired voltage value is transmitted to hot water supply control device 12 as a "detected value."

[0029] The CPU 61 also calculates (estimates) the resistance value of the sensor element 51 using the current value and voltage value 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 energization of the heater resistor 52 (switching between energized and non-energized states) based on the calculated resistance value.

[0030] 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. A CPU 61 is connected to the gate of the MOSFET 66, and the CPU 61 turns the gate on and off based on the calculated resistance value of the sensor element 51. This switches the heater resistor 52 between a conducting state and a non-conducting state.

[0031] Here, we will explain the temperature control process of the heater resistor 52 (sensor element 51) by the CPU 61. The temperature control process is a process executed as part of regular processing by the CPU 61, and the function of the CPU 61 that executes the temperature control process corresponds to a "heating control unit."

[0032] In the temperature adjustment process, first, the current value and voltage value of the current flowing through the sensor element 51 are 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 value and voltage value. In this embodiment, the resistance value (e.g., 38 Ω) of the sensor element 51 when the temperature of the sensor element 51 is the above-mentioned reference temperature (750°C) is stored as the reference resistance value in a memory attached to the CPU 61, and it is determined whether the calculated current resistance value is greater than the reference resistance value.

[0033] 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, and therefore the heater resistor 52 is turned on (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, and therefore the heater resistor 52 is turned off (heater OFF) and the temperature adjustment process is terminated.

[0034] 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 deenergized 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 deenergized (OFF) in a short period of time to maintain the sensor element 51 at the reference temperature. This keeps the temperature of the sensor element 51 at the reference temperature.

[0035] Even when measuring gases with the same oxygen concentration, the A / F sensor 50 may produce different detected oxygen concentration values ​​due to individual differences and aging. 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 aging. Such errors may hinder efforts to optimize combustion by adjusting the air-fuel ratio. This reference oxygen concentration corresponds to the "concentration reference value."

[0036] One of the features of the hot water supply control system shown in this embodiment is that a correction coefficient is determined by comparing a detection value acquired under atmospheric conditions in exhaust pipe 39 with a reference oxygen concentration, correcting the acquired detection value using the correction coefficient during hot water supply, and transmitting the corrected detection value to hot water supply control device 12, thereby suppressing the influence of the above-mentioned error. Specifically, the control modes of CPU 61 include a normal mode in which the detection value of the oxygen concentration is periodically acquired during water heating, corrected using the correction coefficient, and then transmitted to hot water supply control device 12, and a correction coefficient setting mode in which the correction coefficient is set (updated). In this correction coefficient setting mode, the correction coefficient is set (updated) as needed. Below, with reference to the flowchart in FIG. 4, a description will be given of the correction coefficient setting mode process executed by CPU 61 as part of the periodic process.

[0037] 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 a memory attached to the CPU 61. If the correction coefficient setting mode is not in effect, the process proceeds to step S102.

[0038] After the water boiling is completed, it takes a certain amount of 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 such circumstances into consideration, and the system is configured so that switching to the correction coefficient setting mode is not possible until the time limit has passed after the water boiling is completed. If the time limit has not passed, a negative determination is made in step S102 and the processing for this setting mode is terminated. If the time limit has not passed, a positive determination is made in step S102 and the system proceeds to step S103.

[0039] In step S103, it is determined whether a condition (preparation condition) for starting preparation for setting the correction coefficient is met. In this embodiment, the preparation condition is met when (1) a user or the like 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) the scheduled date and time arrives. If the determination in step S103 is negative, the process for this setting mode is terminated. If the determination in step S103 is positive, the process for this setting mode is terminated 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 start heating the sensor element 51 to the reference temperature. 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 the normal mode to the correction coefficient setting mode.

[0040] If a setting operation is performed within the time limit, the 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 within the time limit, the scheduled date and time will be canceled.

[0041] Returning to the explanation of step S101, if the current control mode is the correction coefficient setting mode, an affirmative determination 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 determination is made in step S106, the process proceeds to step S107. In step S107, a process for determining the timing to set the correction coefficient 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 determination process.

[0042] In the next 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 process for this setting mode is terminated. If the correction coefficient setting timing flag is set, the correction coefficient setting process is executed in step S109, and then the process for this correction coefficient setting mode is terminated. Here, the correction coefficient setting process will be described with reference to the flowchart in FIG. 5.

[0043] In the correction coefficient setting process, first, in step S201, it is determined whether it is time to obtain the detected value of the oxygen concentration from the A / F sensor 50. Specifically, if the determination in step S201 is executed for the first time after the correction coefficient setting timing flag is set, a positive determination is made in step S201. If it is the second or subsequent time, a positive determination is made in step S201 if an 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 value of the oxygen concentration is obtained from the A / F sensor 50 and stored in memory.

[0044] In the following step S203, it is determined whether the number of acquired detection values ​​has reached a first specified number (for example, 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, an affirmative determination is made in step S203, and the process proceeds to step S204.

[0045] In step S204, the first specified number of detection values ​​collected in steps S201 to S203 are averaged, and the reference oxygen concentration is divided by the average to calculate a correction coefficient. The calculated correction coefficient is then set as a reference target. Specifically, the calculated correction coefficient is stored in a reference target storage area in memory. Thereafter, detection values ​​obtained from the A / F sensor 50 are appropriately corrected using the currently set correction coefficient (the correction coefficient stored in the reference target storage area).

[0046] In the following step S205, the heater resistor 52 is de-energized to terminate heating of the sensor element 51. Then, in step S206, the correction coefficient setting mode flag and the correction coefficient setting timing flag set in the memory are erased, and in step S207, various data (collected detection values) for setting the correction coefficient stored in the memory are erased, and then this setting process is terminated.

[0047] Returning to the explanation of step S106 in FIG. 4, if boiling water is started during the correction coefficient setting mode, an affirmative determination is made in step S106 and the process proceeds to step S110. In step S110, the correction coefficient setting mode flag and the 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 the normal mode.

[0048] As described 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 takes some time for the temperature across the entire sensor element 51 to actually become uniform (at the predetermined temperature). For this reason, as illustrated in FIG. 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 that from time t0 when heating starts to 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 to be set during this rising process, there is a concern that the function of optimizing combustion may not be properly performed.

[0049] For example, if the correction coefficient is set after a sufficient amount of time has passed since the heater started heating, setting the correction coefficient during the temperature rise process described above can be avoided. However, the time it takes for the temperature to become uniform after the temperature rise process has started varies depending on various factors, such as 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 set while taking various factors into consideration, the wait time will be excessively long. Setting the correction coefficient requires maintaining atmospheric conditions, making it difficult to set it simultaneously with the water heating process. If water heating is prioritized, the opportunity to set the correction value will be reduced or postponed, which could hinder further optimization of combustion. Furthermore, if the wait time is set 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.

[0050] One of the features of this embodiment is that the timing at which the change in the detected value converges using the oxygen concentration detected by the A / F sensor 50, specifically the timing at which the temperature of the sensor element 51 becomes uniform, is determined to improve the accuracy of the correction coefficient while preventing the time required for setting the correction coefficient from becoming excessively long. Hereinafter, 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 with reference to Fig. 7.

[0051] In the correction coefficient setting timing determination process, first, in step S301, it is determined whether it is time to obtain a detected value of the oxygen concentration 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 detected value of the oxygen concentration is obtained from the A / F sensor 50 and stored in memory. Specifically, in step S301, a positive determination is made (1) when the process of step S301 is executed for the first time after switching to the correction coefficient setting mode, or (2) when 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 the memory storage capacity.

[0052] 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 ​​acquired 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 be, for example, the same as the first specified number, or may be smaller than the first specified number.

[0053] In step S304, a moving average A, which is the average of the most recent N detection values ​​(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 start of the correction coefficient setting mode 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 a supplementary explanation of the selected moving averages A, with reference to FIG. 8. In FIG. 8, a newly calculated moving average A is distinguished as a "moving average An" and a previously calculated moving average A is distinguished as a "moving average Am." For ease of explanation, the interval (period) for obtaining detection values ​​is exaggerated in FIG. 8.

[0054] At time tn after switching to the correction coefficient setting mode, a 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 is before 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 for collecting detection values ​​for the moving average Am and the time for collecting detection values ​​for the moving average A.

[0055] At time tn+1, when the interval has elapsed since time tn, a moving average An+1 of the most recent N detection values, including the newly acquired detection value, has been 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 interval has elapsed since time tm. At time tn+2, when the 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, has been 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 interval has elapsed since time tm+1.

[0056] Returning to the explanation of FIG. 7, after picking up the moving average A in step S306, the process proceeds to step S307. In step S307, a 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, the difference D calculated at timing tn, that is, a difference Dn, is (difference Dn)=|(moving average An)-(moving average Am)|.

[0057] Thereafter, the process proceeds to step S308, where it is determined whether the number of calculated differences D exceeds a fourth specified number (e.g., 10). If the determination in step S308 is negative, the process ends. If the determination in step S308 is positive, the process proceeds 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 subsequent step S310, it is determined whether the maximum value is lower than a predetermined threshold value. This threshold value is determined based on the fluctuation range (upper and lower bound) of the detected value that is expected from the specifications of the A / F sensor 50 when the oxygen concentration detected value is 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.

[0058] If a negative determination is made in step S310, the process for determination is terminated. On the other hand, if a positive determination is made in step S310, the process proceeds to step S310, where the correction coefficient setting timing flag is set in memory, and the process for determination is terminated. 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 detection value has converged, and setting of the correction coefficient is permitted. In other words, if the change in the detection value has converged, it is determined that it is the appropriate timing to set the correction coefficient. Note that "convergence" refers to a state in which the temperature of the sensor element 51 has become uniform and a long-term increase (a gradual upward trend) has ended.

[0059] According to the first embodiment described above in detail, the following excellent effects can be expected.

[0060] In the correction coefficient setting mode, the oxygen concentration detection value is repeatedly obtained from the A / F sensor 50 under conditions where the sensor element 51 is heated and the inside of the exhaust pipe 39 is in an atmospheric state. Then, when it is determined that the change in the detection value has converged, the correction coefficient is set. This configuration makes it possible to avoid setting the correction coefficient during the period from when the estimated temperature of the sensor element 51 becomes equal to the reference temperature until the temperature of the sensor element 51 becomes uniform, that is, during the rising process in which the detected oxygen concentration value increases slightly. Then, by setting the correction coefficient at the timing (appropriate timing) when the temperature of the sensor element 51 has become uniform and the detection value has stabilized, the accuracy of the correction coefficient can be improved.

[0061] The time required for raising the temperature of the sensor element 51 to the reference temperature and then stabilizing at the reference temperature depends on the individual differences and deterioration of the sensor element 51, the temperature of the sensor element 51 and its surroundings, and the individual differences and 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, 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 coefficient from becoming complicated.

[0062] As described above in detail, a configuration that allows the correction coefficient to be set at an appropriate timing can contribute to further optimizing combustion through the correction function.

[0063] 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. However, such a configuration may reduce or postpone opportunities to set (e.g., update) the correction coefficient, 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 waiting 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 minimizes unnecessary waiting times. Considering the waiting time for setting the correction coefficient in this way is preferable for achieving coexistence between the boiling water function and the above-mentioned correction function.

[0064] In the example shown in FIG. 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. Therefore, simply comparing two detected values ​​acquired at different times may result in a misjudgment that the difference between the two detected values ​​acquired under conditions before convergence is small, or a misjudgment that the difference between the two detected values ​​acquired under conditions where convergence is large, indicating that the concentration has not yet converged. Note that the detected value is correlated with the electromotive force generated in the detection circuit SC. However, noise or other factors generated in this detection circuit SC may cause the detected value to fluctuate significantly even when the actual oxygen concentration is constant.

[0065] In this embodiment, a moving average A is calculated from multiple detection values, and a difference D between the preceding and following moving averages A is referenced to determine whether the change in the detection values ​​has converged. This reduces erroneous determinations due to variations in the detection values, noise, and the like, and improves the reliability of the determination results. FIG. 9 illustrates an example of a change in the difference D after the correction coefficient setting mode is entered. As such, the difference D also varies to a certain extent. In this regard, this embodiment is configured to determine that the change in the detection values ​​has converged when the difference D between the preceding and following moving averages A falls below a threshold value H consecutive times, thereby further improving the reliability of determining the appropriate timing for setting the correction coefficient.

[0066] Furthermore, as shown in Figure 8, the two moving averages A to be 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 in 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.

[0067] <Variation 1> In the first embodiment, the two moving averages A to be compared are configured so that the detection values ​​referenced when calculating the earlier moving average A and the detection values ​​referenced when calculating the later moving average A do not overlap. However, it is also possible to configure the detection values ​​referenced when calculating the earlier moving average A and the detection values ​​referenced when calculating the later moving average A so that they partially overlap. Even if the detection values ​​are 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.

[0068] 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 each detection value (each time) to be the same.

[0069] <Variation 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 the difference is on the positive side and a threshold value (second threshold value) when the difference is on the negative side. In this case, taking the above behavior into consideration, the absolute value of the positive threshold value may be set to be greater than the absolute value of the negative threshold value, for example.

[0070] <Variation 3> In the first embodiment described above, when the difference D between the current moving average A and the past moving average A falls below a threshold value (more specifically, when it falls below the 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 detected 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 past average value is calculated, and when this difference falls below the threshold value (for example, when it falls below the threshold value H times in a row), it is determined that the timing is appropriate for setting the correction coefficient.

[0071] <Second embodiment> In the first embodiment, whether or not the change in the detection value has converged is determined from the difference D of the moving average A. In this embodiment, the moving average A is used to determine whether or not the change in the detection value has converged, which is similar to the first embodiment, but 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. Hereinafter, the processing for determining the timing to set the correction coefficient in this embodiment will be described with reference to FIG. 10. Note that description of the configuration common to the first embodiment will be omitted as appropriate.

[0072] In the correction coefficient setting timing determination process of this embodiment, it is determined whether it is time to obtain a detected oxygen concentration value from the A / F sensor 50 (step S401). If it is not time, the determination process is terminated. If it is time to obtain a detected oxygen concentration value, the detected oxygen concentration value is obtained from the A / F sensor 50 and stored in memory (step S402), and it is determined whether the number of detected values ​​obtained from the start of the correction coefficient setting mode to the present 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 is terminated. If it is equal to or greater than the second specified number, a moving average A is calculated, which is the average of the most recent N detection values ​​including the current detection value, and the calculated moving average A is stored in memory (step S404). Note that the processes of steps S401 to S404 are the same as the processes of steps S301 to S304 described above.

[0073] 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 times (e.g., three times) including the current moving average A is calculated, and the calculated standard deviation SD is saved in memory (step S406).

[0074] Thereafter, it is determined whether the number of standard deviations SD calculated from the start of the correction coefficient setting mode until the present is equal to or greater than a sixth specified number (step S407). If the number is not equal to or greater than the sixth specified number, the determination process is terminated. If the number 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 the maximum value is smaller than a predetermined threshold value (step S409). This threshold value, like the threshold value described in the first embodiment, is determined based on the fluctuation range (upper and lower bounds) of the detected value that is expected from the specifications of the A / F sensor 50 when the oxygen concentration detected value is 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.

[0075] If the maximum value is equal to or greater than the threshold, the process for determination is terminated, whereas if the maximum value is below the threshold, a correction coefficient setting timing flag is set in memory (step S410) and the process for determination is terminated. In other words, if the standard deviations SD for the most recent H times are all below the threshold, it is determined that the change in the detection value has converged and the setting of the correction coefficient is permitted.

[0076] As described above in detail, if the timing of convergence is determined based on the standard deviation SD calculated from the most recent M moving averages A, the accuracy can be suitably improved.

[0077] <Third embodiment> In the first and second embodiments, the moving average A of the detection values ​​is used to determine whether the change in the detection 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.

[0078] In the process for determining the timing to set the correction coefficient in this embodiment, it is determined whether it is time to obtain a detected value of the oxygen concentration from the A / F sensor 50 (step S501). If it is not time, the process for determination ends. If it is time to obtain a detected value of the oxygen concentration, the detected value of the oxygen concentration 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 the processes in steps S301 to S302 described above.

[0079] After the detection value is saved in step S502, the value of a detection count counter i provided in memory is incremented by "1" (step S503). The detection count counter i is a counter for storing the number of times that a detection value has 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.

[0080] Next, it is determined whether the current detection value is equal to or less than the upper judgment limit UL (step S504). The upper judgment limit UL is a threshold for determining convergence of the change in the detection value, and is changed according to the detection value acquired up to that point. Specifically, if the current detection value exceeds the upper judgment limit UL, the current detection value is set as the new upper judgment limit UL (step S505). Then, the same value as the current detection number counter i is set in a consecutive determination counter TM provided in memory (step S505), and this determination process ends. The consecutive determination counter TM is a counter for keeping track of the number of consecutive times the detection limit UL has not been exceeded, and is cleared to "0" when the correction coefficient setting mode ends.

[0081] If the current detection value is equal to or less than the judgment upper limit UL, it is determined whether the number of times the value has been continuously equal to or less than the judgment upper limit UL is equal to or greater than a reference number (for example, 100 times) (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 number counter i is equal to or greater than the reference number. If the value is not equal to or greater than the reference number, the judgment process ends. If the value is equal to or greater than the reference number, a correction coefficient setting timing flag is set in memory, and the judgment process ends.

[0082] As described above in detail, if the maximum value of the detected values ​​acquired up to that point is configured to be set as the judgment upper limit UL, the maximum value of the detected values ​​will gradually increase before stabilization, causing repeated updates of the judgment upper limit UL, whereas once stable, the maximum value of the detected values ​​will basically be smaller than the judgment upper limit UL, and it is assumed that updates of the judgment upper limit UL will essentially stop. If the state in which updates of the judgment upper limit UL have stopped continues, it is determined that the changes in the detected values ​​have converged, making it possible to set the correction coefficient at an appropriate timing.

[0083] In particular, the upper 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 limit UL. This configuration reduces the amount of information required to determine the convergence of the detected values, making it possible to determine the convergence with a simple configuration.

[0084] <Variation 1> In the third embodiment, the upper limit of the detection value is defined by the upper judgment limit UL, but the lower limit of the detection value may be defined as the lower judgment limit, and the change in the detection value may be determined to have 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 the erroneous determination that the change in the detection value has converged when the detection value continues to temporarily fluctuate downward.

[0085] Note that the start of heating the sensor element 51 causes a large change in the detected value, but this change becomes gradual as the temperature of the sensor element 51 reaches the reference temperature. Therefore, by setting the judgment lower limit to the minimum value of the detected value obtained after the reference temperature is reached, the above-mentioned suppression effect can be more effectively exerted.

[0086] <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 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 etc. will be omitted as appropriate.

[0087] In the correction coefficient setting timing determination process of this embodiment, first, in step S601, it is determined 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 it is determined whether a predetermined waiting time (e.g., 3 seconds) has elapsed since the previous calculation of the correction coefficient. If this is the first timing after 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. Then, in step S601, after the number of obtained detection values ​​reaches a specified number (e.g., 20), a negative determination is made repeatedly until the next predetermined waiting time has elapsed. If a negative determination is made in step S601, the determination process is terminated. 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.

[0088] After the detection values ​​are saved in step S602, it is determined in step S603 whether it is time to calculate a correction coefficient. Specifically, it is determined whether the number of acquired detection values ​​has reached the specified number. If the determination in step S603 is negative, the determination process ends. If the determination in step S603 is positive, the process proceeds to step S604, where the average of the acquired specified number of 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.

[0089] 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 consideration errors that may occur due to individual differences and deterioration of the A / F sensor 50, and is stored in advance in a memory attached to the CPU 61. If the determination in step S605 is negative, the calculated correction coefficient is erased and the main determination process ends. If the determination in step S605 is positive, 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 the memory and the main determination process ends.

[0090] Immediately after the temperature of the sensor element 51 starts to rise, the oxygen concentration detection value of the A / F sensor 50 rises sharply. Although the correction coefficient calculated during this process deviates significantly from the appropriate range, repeated calculation of the correction coefficient gradually approaches the appropriate range. Then, as the temperature of the sensor element 51 becomes uniform and the change in the detection value converges, the correction coefficient approaches the appropriate range even more. Then, when the correction coefficient falls within the appropriate range, the correction coefficient is calculated and set by the correction coefficient setting process.

[0091] According to the configuration described above in detail, it is possible to easily determine the appropriate timing for setting the correction coefficient.

[0092] <Variation 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 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 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.

[0093] <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 and the like will be omitted as appropriate.

[0094] In the correction coefficient setting timing determination process of this embodiment, first, in step S701, it is determined whether it is time to obtain a detected value of the oxygen concentration from the A / F sensor 50. If a negative determination is made in step S701, the determination process ends. If a positive determination is made in step S701, the process proceeds to step S702, where the detected value of the oxygen concentration is obtained from the A / F sensor 50 and stored in memory. Here, a supplementary explanation will be given of the processes in steps S701 and S702.

[0095] In this determination process, a correction coefficient is calculated periodically, 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 and an interval time (e.g., 0.1 seconds) has elapsed since the previous acquisition of a detection value, 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 a correction coefficient, which will be described later. If none of (1) to (3) applies, this determination process ends without acquiring a detection value.

[0096] After the detection values ​​are saved in step S702, it is determined in step S703 whether it is time to calculate a correction coefficient. Specifically, it is determined whether the number of acquired 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 acquired specified number of 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 in this determination process and is not used to correct the detection values ​​to be sent to the hot water supply control device 12.

[0097] In the next step S705, the CPU 61 calculates the correction coefficients in the memory attached thereto and sets a calculation flag as a flag indicating that the correction coefficients have been temporarily set.

[0098] Returning to the explanation of step S703, if it is not the timing to calculate the correction coefficient, a negative determination is made in step S703 and the process proceeds to step S706. In step S706, it is determined whether the calculation flag is set in the memory. If the calculation flag is not set, the process proceeds to step S707. In step S707, it is determined whether it is the timing 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 determination is made in step S707, the process proceeds to step S708 and the newly acquired detection value when the second waiting time has elapsed is corrected using the provisionally set correction coefficient.

[0099] 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 taking into consideration errors that may occur in the reference oxygen concentration due to individual differences and deterioration of the A / F sensor 50, and is stored in advance in a memory attached to the CPU 61. If the determination in step S709 is affirmative, 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 process of step S710, or if the determination in step S709 is negative, the process proceeds to step S711, where the calculation flag is erased, and the main determination process ends.

[0100] Even after the estimated temperature of the sensor element 51 becomes equal to the reference temperature due to the temperature rise, the detected oxygen concentration value gradually increases 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 when 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 acquiring the detected value is from the timing of provisionally setting the correction coefficient, the greater the degree to which the corrected detected value deviates 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, if the change in the detected value converges, and 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 appropriately determine the appropriate timing for setting the correction coefficient.

[0101] <Variation 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 timing for starting preparation) becomes earlier the more times the detection value has fallen within the appropriate range in succession up to that point.

[0102] <Variation 2> If the provisionally set correction coefficient is inappropriate, a new correction coefficient may be provisionally set based on data (detection values) 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 time t1, the provisionally set correction coefficient X0 is applied to the average 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. At time t2, the provisionally set correction coefficient X1 is applied to the average 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. 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.

[0103] 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.

[0104] The processes of steps S801 to S805 in the correction coefficient setting timing determination process in this embodiment are the same as steps S601 to S605 in the fourth embodiment.

[0105] If the determination in step S805 is affirmative, i.e., if the calculated correction coefficient is within the appropriate range, the process proceeds to step S806, where the consecutive success counter CC, which is a counter for determining the consecutive number of times the correction coefficient has fallen within the appropriate range, is incremented by "1," and the process for determination ends. In other words, in this embodiment, even if the correction coefficient is within the appropriate range, it does not immediately mean that it is an appropriate time to set the correction coefficient.

[0106] If the determination in step S805 is negative, i.e., if the correction coefficient is outside the appropriate range, the process proceeds 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 the process for this determination ends. The warning flag is a flag for specifying whether the correction coefficient is within the appropriate determination range.

[0107] 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 ends. 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 ends. 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 stored in memory.

[0108] In the following step S814, it is determined whether the value of the consecutive success counter CC is greater than a specified value (for example, 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 for this determination is terminated. If a positive determination is made in step S814, the process proceeds to step S815, where the difference (absolute value) between the conversion rate based on the current correction coefficient and the conversion rate based on 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 for this determination is terminated. If a positive determination is made in step S816, a correction coefficient setting timing flag is set in memory in step S817, and the process for this determination is terminated. With this configuration, it is possible to appropriately determine the appropriate timing for setting the correction coefficient.

[0109] In this embodiment, an example has been given of a configuration in which the accuracy of determining the appropriate timing for setting the correction coefficient by comparing conversion rates is improved in the fourth embodiment, but this configuration related to the conversion rates can also be applied to the fifth embodiment.

[0110] 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 the present 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 configuration common to the fourth embodiment and the like will be omitted as appropriate.

[0111] 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 an 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 detection value is corrected by 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.

[0112] If a negative determination 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 later) is an integer. If a positive determination is made in either step S901 or step S902, a first determination process is executed in step S903, and then this determination process is terminated. If a negative determination is made in both step S901 and step S902, a second determination process is executed in step S904, and then this determination process is terminated. In other words, the first determination process is executed when the correction coefficient is initially set or when the validity period has elapsed, and the second determination process is executed otherwise.

[0113] 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 to serve as a 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 conversion rate at each time to determine whether the change in the detected value has converged. The second determination process will be further explained below with reference to FIG. 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 described here.

[0114] 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 determination 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, if a preset waiting time has elapsed since the correction coefficient was calculated in step S1004, a positive determination is made in step S1006; otherwise, a negative determination is made in step S1006. If a negative determination is made in step S1006, the second determination process is terminated. If a positive determination is made in step S1006, the process proceeds to step S1007, where 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, the process proceeds 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. Thereafter, the process proceeds 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.

[0115] In the next 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.

[0116] 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, there is a possibility that the reference conversion rate itself will gradually deviate from the actual conversion rate due to deterioration of the sensor unit 40. Therefore, by updating the reference conversion rate as needed, it is possible to prevent a decrease in the reliability of the above determination.

[0117] <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 to the above-described embodiments. 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.

[0118] In 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, the hot water supply control device 12 may be configured to perform various functions such as storing data such as the detected value, determining the appropriate timing for setting the correction coefficient, and setting the correction coefficient. Furthermore, these functions may 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 perform control equivalent to the processing for the correction coefficient setting mode shown in Figure 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, etc., 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 be configured to heat the sensor element 51 and detect the oxygen concentration in response to instructions from the hot water supply control device 12.

[0119] In the above embodiments, the acquisition of data (detected values) for determining the appropriate timing for setting the correction coefficient is started when heating of the sensor element 51 begins, but this is not limited to this. Considering that the detected value of the oxygen concentration 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 started 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 started when the estimated temperature of the sensor element 51 equals the reference temperature or thereafter.

[0120] In the above embodiments, new detection values ​​for calculating the correction coefficients are acquired after the appropriate timing for setting the correction coefficients has arrived, and the correction coefficients are calculated from the newly acquired detection values. However, this may be modified as follows. That is, when the appropriate timing for setting the correction coefficients has arrived, the correction coefficients may be calculated from the most recently acquired detection values ​​(e.g., multiple detection values). Alternatively, the correction coefficients may be calculated from the most recently acquired detection values ​​(e.g., multiple detection values) and the newly acquired detection values.

[0121] 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 negate the possibility of using a thermometer to measure the temperatures of the heater resistor 52 and the sensor element 51. Alternatively, the temperature of the sensor element 51 may be estimated based on information from the heating circuit HC.

[0122] 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 takes 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, even with such a sensor structure, a practically preferable configuration can be realized by applying the configuration for determining the appropriate timing shown in the above embodiments.

[0123] As described 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 becomes atmospheric after a certain amount of time has passed since the water boiling operation, but this takes some time. For example, the exhaust pipe 39 may be configured to become atmospheric by supplying outside air through purging to forcibly replace 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 the fact that purging has been performed after the water boiling operation as one of the conditions.

[0124] The temperature control for maintaining the sensor element 51 at the reference temperature may be continued if a predetermined continuation condition is met after boiling water has finished or after the correction coefficient has been set (including completion / interruption). For example, the temperature control for the sensor element 51 may be continued if boiling water is started after the correction coefficient has been set, or the temperature control for the sensor element 51 may be continued if the correction coefficient is set after boiling water.

[0125] In the above embodiments, the gas water heater 11 is configured to prioritize the heating of water and the setting of a correction coefficient related to the A / F sensor 50, specifically, if a request to boil water occurs during preparation for setting the correction coefficient, the preparation for setting the correction coefficient is stopped and the heating of water is started. This may be modified to a configuration in which the gas water heater 11 is configured to prioritize the heating of water and the setting of a correction coefficient related to the A / F sensor 50, specifically, if a request to boil water occurs during preparation for setting the correction coefficient, the heating of water is started after the setting of the correction coefficient is completed.

[0126] 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 an unexpected reason 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 preferable to continue using the previously set correction coefficient while notifying the user that a timeout has occurred.

[0127] In each of the above embodiments, the configuration is such that calculation, judgment, and other processing is performed based on the fact that the number of times data such as detection values ​​has been acquired has reached a certain number. However, the configuration may also be such that the elapsed time is measured using a timer counter or RTC, and calculation, judgment, and other processing is performed based on the fact that the elapsed time has reached a certain time.

[0128] Instead of or in addition to a configuration in which the correction coefficient is set (updated) based on a user setting operation or a scheduled schedule, it is also possible to configure the correction coefficient to be set (updated) before (immediately before) the start of combustion control in response to a water boiling request. For example, the number of times water is boiled may be counted, and when that number reaches a preset number, the correction coefficient may be set (updated) before (immediately before) the start of combustion control for the next water boiling.

[0129] In the above embodiments, a configuration for determining the appropriate timing for setting the correction coefficient for the A / F sensor 50 applied to the storage-type hot water supply system 10 has been 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 mounted on other equipment having an internal combustion engine such as a gasoline engine (for example, an automobile or a generator).

[0130] <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.

[0131] 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 the sensor element (sensor element 51) of the oxygen sensor; Equipped with 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; a correction value setting unit (a function of executing the process of step S201 in the CPU 61 of the sensor board 60) that sets, as the reference object, 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 when the convergence determination unit determines that the change in the detection value has converged; The oxygen sensor unit has:

[0132] The way heat is transferred to the sensor element as it heats up 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 may gradually increase (slightly increase) even after the predetermined temperature is reached (while the predetermined temperature is being maintained). If the correction value is set (e.g., updated) during this process of increase (slight increase) in the detected value, the function of optimizing combustion may not be fully realized.

[0133] In this regard, in the configuration shown in this feature, 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 assuming a steady-state error) for a predetermined 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 a timing (appropriate timing) when the temperature has reached a predetermined temperature, become uniform, and the detection value has stabilized, the accuracy of the correction value can be improved.

[0134] Furthermore, the time it takes for the temperature to become uniform after reaching the 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, it is not necessary 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 complicated.

[0135] As described above in detail, a configuration that allows the correction value to be set at an appropriate timing can contribute to further optimizing combustion through the correction function.

[0136] 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 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 described above sets the correction value when it is determined that the change in the detection value has converged. This configuration contributes to shortening the waiting time between the temperature of the sensor element becoming uniform and the correction value being set. Considering the waiting time for setting the correction value in this way is advantageous for achieving coexistence between the boiling water function and the correction value setting (update) function.

[0137] Incidentally, the "convergence determination unit" shown in this feature may be changed to "a timing determination unit that repeatedly acquires 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 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 object."

[0138] Feature 2: The sensor control unit has a temperature acquisition unit that acquires the temperature of the sensor element, The oxygen sensor unit of feature 1, wherein when the temperature acquired by the temperature acquisition unit is 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.

[0139] As shown in this feature, by configuring the sensor element to set a correction value when the change in the detected value converges under the condition that the sensor element is at a predetermined temperature, i.e., by configuring the sensor element to avoid setting a correction value even if an accidental factor causes the change in the detected value to appear as if it has converged before the predetermined temperature is reached, it is possible to prevent 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 preferable in terms of improving the accuracy of the correction value.

[0140] 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."

[0141] Feature 3. The convergence determination unit repeatedly acquires the detection value 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, triggered by the 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.

[0142] In the configuration described in this feature, when the preparatory conditions are met, the sensor element is heated, and the exhaust pipe is in an atmospheric state, detected oxygen concentration values ​​are repeatedly obtained from the oxygen sensor. A moving average is then calculated from a plurality of detected values, including a newly obtained detected value, and a comparison result is obtained between the newly calculated moving average and a plurality of moving averages, including an earlier moving average, to determine whether the change in the detected value has converged. This configuration can suitably embody the technical idea described in feature 1 and the like.

[0143] Due to the nature of the sensor, the detected value will vary to a certain extent. 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 fluctuations must be taken into consideration (for example, eliminated or reduced) in order to quickly determine this convergence.

[0144] In this regard, as shown in this feature, if the influence of variations and noise is smoothed (leveled) by using a moving average of multiple detection values ​​and then convergence of the detection values ​​is determined from the moving average, it is possible to prevent the convergence tendency from being obscured by the variations, etc. As a result, it is possible to minimize the time (waiting time) required to determine the correction value. As described above in detail, calculating (setting) the correction value at an appropriate timing is preferable in order to achieve the effect described in feature 1.

[0145] 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 the sensor element (sensor element 51) of the oxygen sensor; Equipped with 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 for 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; a correction value setting unit (a function of executing the process of step S201 in the CPU 61 of the sensor board 60) that calculates the correction value based on the detection value acquired from the oxygen sensor and a concentration reference value indicating the oxygen concentration in the atmospheric state when the timing determination unit determines that the set timing has arrived, and sets the calculated correction value as the reference object; The oxygen sensor unit has:

[0146] In 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. Then, a moving average is calculated from multiple detection values, including a newly acquired detection value, and 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), it is determined that it is time to set the correction value. This configuration makes it possible to determine the timing when the temperature becomes uniform after the detection value has gone through an increasing process (a slight increase process), thereby suitably realizing the technical idea described in feature 1 and the like.

[0147] Due to the nature of the sensor, the detected value will vary to a certain extent. 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 fluctuations must be taken into consideration (for example, eliminated or reduced) in order to quickly determine this convergence.

[0148] In this regard, as shown in this feature, if the influence of variations and noise is smoothed (leveled) by using a moving average of multiple detection values ​​and then convergence of the detection values ​​is determined from the moving average, it is possible to prevent the convergence tendency from being obscured by the variations, etc. As a result, it is possible to minimize the time (waiting time) required to determine the correction value. As described above in detail, calculating (setting) the correction value at an appropriate timing is preferable in order to achieve the effect described in feature 1.

[0149] Feature 5: The oxygen sensor unit according to Feature 3 or Feature 4, wherein the moving averages are specified so that the detection values ​​used to calculate one moving average do not overlap with the detection values ​​used to calculate another moving average.

[0150] As shown by this feature, if the detection value referenced when calculating one (earlier) moving average is configured so as not to overlap with the detection value referenced when calculating another (later) moving average, each moving average can be calculated using detection values ​​that are separated in time, making it easier to grasp the trend of change from a long-term perspective and making it possible to appropriately determine the convergence of changes in the detection values.

[0151] Feature 6: The 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 larger 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.

[0152] After the temperature of the sensor element reaches a predetermined temperature, the difference between the moving averages before and after the temperature reaches a predetermined temperature decreases over time. In other words, the difference between the moving averages approaches zero over time. Therefore, if this difference is compared with a threshold value to determine the convergence of the detected values, the effects described in Feature 3 and the like can be achieved with a simple configuration.

[0153] It is also possible to apply the configuration of this feature to feature 4, and make it so that "the timing determination unit determines that the set timing has not been reached if the difference between the newly calculated moving average and the previously calculated moving average is larger than a threshold value, and determines that the set timing has been reached if the difference between the currently calculated moving average and the previously calculated moving average is smaller than the threshold value."

[0154] Feature 7: The oxygen sensor unit according to 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 differences calculated previously 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 differences calculated previously are smaller than the threshold value.

[0155] As described above, the detected values ​​vary to a certain extent. Therefore, as shown in this feature, by configuring the system to compare not only a newly calculated difference but also multiple differences, including differences calculated previously (in the past), with the threshold, it is possible to suitably prevent the correction value from being determined (set) when the detected value is not stable (in the rising process described above).

[0156] Feature 8: The oxygen sensor unit according to Feature 3 or Feature 5, wherein the convergence determination unit calculates a standard deviation of the moving averages calculated from the plurality of moving averages each time, and determines that the change in the detection value has not converged if at least one of the newly calculated standard deviation and a predetermined number (e.g., two) of the standard deviations calculated previously is larger than a threshold value, and determines that the change in the detection value has converged if both the newly calculated standard deviation and the predetermined number of the standard deviations calculated previously are smaller than the threshold value.

[0157] As shown by this feature, the configuration determines 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, which makes it possible to effectively prevent a correction value from being determined when the detected value is not stable (during the above-mentioned rising process).

[0158] Note that if the past history is stored as a standard deviation, the amount of information required to determine convergence can be reduced compared to a configuration in which the detected value itself is stored, which is preferable in terms of suppressing an increase in memory capacity.

[0159] Incidentally, the configuration of this feature can be applied to feature 4 to make it an oxygen sensor unit according to feature 4, in which "the timing determination unit calculates the standard deviation of the moving averages calculated from the plurality of 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 standard deviations calculated previously is larger 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 standard deviations calculated previously are smaller than the threshold value."

[0160] 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 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.

[0161] The oxygen concentration detection value increases gradually even after reaching a predetermined temperature until the temperature of the sensor element becomes uniform, and then stabilizes. As shown in this feature, if the maximum detection value acquired up to that point is configured to be set as the upper judgment limit, the maximum detection value will gradually increase before stabilization, causing the upper judgment limit to be repeatedly updated. However, once stable, the maximum detection value will basically be smaller than the upper judgment limit, and updating of the upper judgment limit will essentially stop. If the configuration is such that it is determined that the change in the detection value has converged when multiple detection values ​​acquired within a predetermined time are all smaller than the upper judgment limit, it becomes possible to determine the convergence described in feature 1.

[0162] In particular, the upper limit for judgment is automatically updated when the temperature of the sensor element rises over time and the detected value (maximum value) exceeds the previous upper limit for judgment. By adopting such a configuration, the amount of information required to determine the convergence of the detected value can be reduced, and the effect described in Feature 1 can be achieved with a simple configuration.

[0163] Although variations in the detected values ​​of oxygen sensors may vary depending on individual differences, the influence of such variations on the convergence determination can be suitably suppressed by updating the determination upper limit and checking it multiple times.

[0164] Incidentally, when the configuration described in this feature is applied to feature 1, the description relating to 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 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 an atmospheric state, sets the maximum value of the oxygen concentration detection value acquired up to that point as an upper judgment limit, and determines that the timing to set the correction value has arrived when all of the multiple detection values ​​acquired within a predetermined time are smaller than the upper judgment limit," and the description relating to 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."

[0165] Feature 10: The oxygen sensor unit according to Feature 9, wherein the convergence determination unit sets the maximum value of the detection value acquired up to that point as an upper determination limit and the minimum value of the detection value acquired up to that point as a lower determination limit, and determines that the change in the detection value has converged if all of the multiple detection 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.

[0166] By defining the range of the detection value by the upper determination limit shown in Feature 9 and the lower determination limit shown in this feature, it is possible to suitably prevent the correction value from being calculated in a situation where the detection value is fluctuating greatly.

[0167] The configuration of this feature can also be modified to the oxygen sensor unit of feature 9, in which "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 values ​​has converged if multiple detected values ​​acquired within a predetermined time period from the current point in 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 temperature reaches the predetermined temperature.

[0168] Feature 11: The oxygen sensor unit according to any one of Features 1 to 3 and Features 5 to 10, wherein the correction value setting unit calculates the correction value using at least a portion of the detection value acquired during the current judgment by the convergence judgment unit when the convergence judgment unit determines that the change in the detection value has converged.

[0169] As shown in this feature, when convergence is followed by setting of a correction value, the correction value is calculated using at least a portion of the detection values ​​already acquired in the process of confirming convergence, thereby shortening the time required to set the correction value compared to a configuration in which new detection values ​​are acquired after convergence.

[0170] The configuration of this feature can also be applied to feature 4. In this case, the description "the convergence determination unit determines that the change in the detection value has converged" should be changed to "the timing determination unit determines that the set timing has arrived."

[0171] Feature 12: The oxygen sensor unit according to Feature 1 or Feature 2, wherein the convergence determination unit repeatedly acquires the detected oxygen concentration 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 the atmospheric state upon the fulfillment of the preparatory condition, 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.

[0172] According to the configuration of this feature, 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. 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 a part of the correction function (the correction value) in this way to determine convergence, the effect of feature 1 can be achieved while preventing the configuration related to the convergence determination from becoming complicated.

[0173] 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 object when the convergence determination unit determines that the change in the detection value has converged.

[0174] As shown by this feature, by setting the correction value used to determine convergence as the reference value as is, the time required to complete the setting can be shortened compared to a configuration in which a new correction value is calculated when convergence is determined.

[0175] 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 the sensor element (sensor element 51) of the oxygen sensor; Equipped with 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 a process for determining the timing for 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; a correction value setting unit (a function of executing the process of step S201 in the CPU 61 of the sensor board 60) that sets, as the reference object, 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 when the timing determination unit determines that the set timing has arrived; The oxygen sensor unit has:

[0176] According to the configuration of this feature, 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. 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 a part of the correction function (the correction value) in this way to determine convergence, the effect of feature 1 can be achieved while preventing the configuration related to the convergence determination from becoming complicated.

[0177] Feature 15. The oxygen sensor unit according to Feature 1 or Feature 2, wherein the convergence determination unit repeatedly acquires the detected oxygen concentration 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 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.

[0178] When the detected value is increasing, if the detected value acquired after a predetermined waiting time has elapsed since the correction value was calculated is corrected using the correction value, the correction result (corrected detected value) will deviate significantly from the concentration reference value. In contrast, when the detected value is converging (stable), if the detected value acquired after a predetermined waiting time has elapsed since the correction value was calculated is corrected using the correction value, the deviation of the corrected result (corrected detected value) from the concentration reference value is suppressed. Therefore, as shown in this feature, if the correction result is determined to be converging when it is within a reference range determined based on the concentration reference value, the technical idea described in Feature 1 and the like can be suitably realized. The correction of the detected value is performed as needed to optimize combustion. The ability to divert this correction flow to determine convergence is advantageous in simplifying the control program.

[0179] It is also possible to configure the convergence determination unit such that "when the result of the correction falls outside the reference range, the convergence determination unit newly calculates the correction value, while retaining the current correction value when the result of the correction falls within the reference range, the convergence determination unit 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." With this configuration, it is possible to suitably prevent erroneous determination that the change in the detection value has converged when the correction result accidentally falls within the reference range.

[0180] 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 the sensor element (sensor element 51) of the oxygen sensor; Equipped with 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 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 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 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; a correction value setting unit (a function of executing the process of step S201 in the CPU 61 of the sensor board 60) that sets, as the reference object, 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 when the timing determination unit determines that the set timing has arrived; The oxygen sensor unit has:

[0181] When the detected value is increasing, if the detected value acquired after a predetermined waiting time has elapsed since the correction value was calculated is corrected using the correction value, the correction result (corrected detected value) will deviate significantly from the concentration reference value. In contrast, when the detected value is converging (stable), if the detected value acquired after a predetermined waiting time has elapsed since the correction value was calculated is corrected using the correction value, the deviation of the corrected result (corrected detected value) from the concentration reference value is suppressed. Therefore, as shown in this feature, if the configuration determines that the timing to set the correction value has arrived when the correction result is within a reference range determined based on the concentration reference value, the technical idea described in Feature 1 and the like can be suitably realized. Note that the correction of the detected value is performed as needed to optimize combustion. The ability to divert this correction flow to determine convergence is advantageous in simplifying the control program.

[0182] Feature 17. The heating control unit is configured to control the heating 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 the change in the detection value has converged when the first preparation condition is satisfied, The oxygen sensor unit described in any one of Features 1 to 16 (excluding Features 4, 14, and 16), wherein the sensor control unit repeatedly acquires the detected value of the oxygen concentration from the oxygen sensor under conditions in which the sensor element is heated by the heater upon the fulfillment of the second preparation condition 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%), 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.

[0183] According to this feature, whether the change in the detected value has converged is determined based on the degree of deviation of the conversion rate when the second preparation condition is met from the conversion rate when the first 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 an oxygen sensor is used for a long period of time, it is expected that the detected value will become lower or higher than before due to aging, even if it is in a stable state. Therefore, by configuring the criteria for determining convergence to be updated as needed, a deterioration in the ability to determine the timing of convergence can be suppressed.

[0184] Feature 18: A hot water supply control system including the oxygen sensor unit according to any one of Features 1 to 17 and the hot water supply control device.

[0185] This hot water supply control system allows the correction value to be set at the appropriate timing, contributing to further optimization of combustion through the correction function. It also minimizes the waiting time until the correction value is set. This is preferable for achieving coexistence of the water heating function and the above-mentioned correction function.

[0186] 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 substrate 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 supply control device (hot water supply control device 12) that controls combustion of the gas hot water heater based on the detection value corrected by the correction unit; A hot water supply control system comprising: 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 correction value setting unit (a function of executing the process of step S201 in the CPU 61 of the sensor board 60) that sets, as the reference object, 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 when the convergence determination unit determines that the change in the detection value has converged; A hot water control system comprising:

[0187] This hot water supply control system allows the correction value to be set at the appropriate timing, contributing to further optimization of combustion through the correction function. It also minimizes the waiting time until the correction value is set. This is preferable for achieving coexistence of the water heating function and the above-mentioned correction function. [Explanation of symbols]

[0188] 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

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; Equipped with 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; a correction value setting unit that, when it is determined by the convergence determination unit that the change in the detection value has converged, determines whether or not the number of the detection values ​​acquired from the oxygen sensor has reached a first specified number, calculates an average value of the first specified number of the detection values ​​if the number of the detection values ​​has reached the first specified number, calculates a correction value by dividing a concentration reference value that indicates 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 has:

2. 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.

3. 3. The oxygen sensor unit according to claim 2, 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.

4. 3. The oxygen sensor unit according to claim 2, wherein the convergence determination unit calculates the standard deviation of the moving averages calculated each time, and determines that the change in the detection value has not converged if at least one of the newly calculated standard deviation and a predetermined number of the standard deviations calculated previously is larger than a threshold value, and determines that the change in the detection value has converged if both the newly calculated standard deviation and the predetermined number of the standard deviations calculated previously are smaller than the threshold value.

5. 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.

6. 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 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 standard range determined based on the concentration reference value.

7. 7. The oxygen sensor unit according to claim 1, wherein the correction value setting unit calculates the correction value using at least a portion of the detection value acquired during the current judgment by the convergence judgment unit when the convergence judgment unit determines that the change in the detection value has converged.

8. 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 supply control device that controls combustion in the gas hot water heater based on the detection value corrected by the correction unit; A hot water supply control system comprising: 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 correction value setting unit that, when it is determined by the convergence determination unit that the change in the detection value has converged, determines whether or not the number of the detection values ​​acquired from the oxygen sensor has reached a first specified number, calculates an average value of the first specified number of the detection values ​​if the number of the detection values ​​has reached the first specified number, calculates a correction value by dividing a concentration reference value that indicates the oxygen concentration in the atmospheric state by the average value, and sets the calculated correction value as the reference object; A hot water control system comprising:

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