Oxygen sensor unit and hot water supply control system

Abstract

To provide an oxygen sensor unit capable of when abnormal resistance occurs in a circuit part for detecting oxygen concentration, suppressing an impact of the abnormal resistance and thus contributing to making combustion in a hot water supply facility appropriate.SOLUTION: A sensor unit 40 attached to a gas water heater includes: a detection circuit part SC including a sensor element 51 of an A / F sensor 50 and an element line SL for transmitting a detection signal indicating oxygen concentration from the sensor element 51 to a CPU 61 of a sensor substrate 60; and a heating circuit part HC including a heater resistance 52 capable of heating the sensor element 51 and a heater line HL for supplying electric power from an electric power supply part 65 provided in the sensor control substrate 60 to the heater resistance 52. The CPU 61 performs temperature control of the sensor element 51 by supplying electric power to the heater resistance 52 in accordance with a control parameter acquired from the element line SL. The CPU 61 monitors an abnormality of the detection circuit part SC on the basis of a monitoring parameter correlated with a temperature of the heater resistance 52 acquired from the heater line HL.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 discharged from a gas water heater using an oxygen sensor such as an A / F sensor and adjusting the amount of gas supplied based on the detection results (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] For the oxygen sensor described above, the temperature of the sensor element needs to be raised to an appropriate temperature (e.g., 750°C) in order to properly perform the detection function. The inventors of the present application have focused on the relationship between the temperature and resistance of the sensor element, specifically, the property that the resistance value decreases as the temperature increases, and have devised a configuration in which the temperature of the sensor element is adjusted by turning the heater on and off based on the resistance value (estimated value) of the sensor element. This resistance value is estimated, for example, from the current value or voltage value of the current flowing through the circuit section (detection circuit section) in which the sensor element is disposed.

[0005] However, in such a configuration, if abnormal resistance occurs in the circuit section due to crushing of the wiring forming the circuit section or poor connection of the connector, the above temperature adjustment is performed based on a resistance value including the abnormal resistance, which may cause the following inconvenience. That is, the abnormal resistance may cause the sensor element to be heated at an assumed temperature lower than the actual temperature of the sensor element, causing the sensor element to be heated above the appropriate temperature. If the abnormal resistance increases, the difference between the actual temperature and the assumed temperature will increase, and the appropriate temperature will be significantly exceeded. If such a situation continues, it may cause the sensor element to deteriorate or be damaged, which will hinder the optimization of combustion.

[0006] Although proper combustion is possible if abnormal resistance occurs in the circuit section and the oxygen sensor is replaced at the location where the abnormal resistance occurs, if it becomes necessary to replace the oxygen sensor, the cost and effort required to repair the hot water supply equipment will increase significantly compared to repairing only the location where the abnormal resistance occurs in the wiring, connectors, etc. Thus, there is still room for improvement in the configuration related to oxygen concentration detection in order to reduce the impact of abnormal resistance occurring in the detection circuit section and reduce repair costs and effort.

[0007] The present invention has been made in consideration of the above-mentioned problems, and its main object is to provide an oxygen sensor unit that can suppress the effects of abnormal resistance occurring in a circuit section for detecting oxygen concentration, thereby contributing to optimizing combustion in hot water supply equipment. [Means for solving the problem]

[0008] Means for solving the above problems will be described below.

[0009] Means 1. An oxygen sensor unit that is applied to a gas water heater and has an oxygen sensor that detects the oxygen concentration of the gas discharged from the gas water heater and a sensor control board to which the oxygen sensor is connected, and is capable of outputting the detected oxygen concentration to a hot water supply control device of the gas water heater, a detection circuit unit including a sensor element of the oxygen sensor and a signal transmission path for transmitting a detection signal indicating the oxygen concentration output from the sensor element to a control unit of the sensor control board; a heating circuit section including a heater resistor provided next to the sensor element and capable of heating the sensor element, and a power supply path for supplying power from a power supply section provided on the sensor control board to the heater resistor; a control parameter acquisition unit that acquires, as a control parameter, a resistance value of the sensor element or a correlation value correlated with the resistance value via the signal transmission path; a temperature control unit that controls a temperature of the sensor element to a predetermined temperature by supplying power from the power supply unit to the heater resistor in accordance with the control parameters acquired by the control parameter acquisition unit; a monitoring parameter acquisition unit that acquires a temperature of the heater resistor or a correlation value correlated with the temperature as a monitoring parameter; an abnormality monitoring unit that monitors an abnormality in the detection circuit unit based on the monitoring parameters acquired by the monitoring parameter acquisition unit; The oxygen sensor unit includes:

[0010] The temperature control unit in this means adjusts the temperature of the sensor element to a predetermined temperature (e.g., 750° C.) by supplying power from a power supply unit to a heater resistor in accordance with a control parameter that is a resistance value of the sensor element or a correlation value correlated with the resistance value. Therefore, when controlling the temperature of the sensor element, it is not necessary to obtain the temperature of the heater resistor or a monitoring parameter that is a correlation value correlated with the temperature.

[0011] However, in a configuration in which the control parameters are acquired via a signal transmission path, if abnormal resistance occurs in the signal transmission path due to crushing of the wiring forming the signal transmission path or a poor connection of a connector, the following inconvenience may occur if temperature adjustment is performed based on the control parameters affected by the abnormal resistance. That is, the abnormal resistance may cause the sensor element to be heated assuming a temperature lower than the actual temperature of the sensor element, causing the temperature of the sensor element to rise above a predetermined temperature. The temperature control unit cannot detect the occurrence of such an abnormality.

[0012] In this respect, the oxygen sensor unit shown in the present invention acquires monitoring parameters that are not necessary for the temperature control of the sensor element, and monitors the detection circuit (specifically, a predetermined section) for abnormalities based on the acquired monitoring parameters. For example, if the temperature of the sensor element exceeds a predetermined temperature, such a situation can be quickly discovered, and it is possible to take measures such as notifying the user or restricting overheating of the sensor element. This makes it possible to prevent the sensor element from being damaged in a way that makes it difficult to continue using it. This is preferable in terms of reducing the effect of abnormal resistance generated in the detection circuit and reducing the cost and effort required to repair the hot water supply equipment. In addition, the oxygen sensor unit is heated excessively, which reduces the chances of outputting a false detection result that makes it appear as if the oxygen concentration is higher than the actual oxygen concentration, and this can suitably suppress deterioration of combustion efficiency in the gas hot water heater caused by the false detection.

[0013] Means 2: A hot water supply control system comprising the oxygen sensor unit described in Means 1, and a combustion control device that controls combustion in the gas hot water heater based on the detection result of the oxygen concentration output from the oxygen sensor unit.

[0014] According to the hot water supply control system of the present invention, even if an abnormal resistance occurs in the detection circuit of the oxygen sensor unit, it is possible to effectively suppress the inconvenience of the abnormal resistance causing a decrease in the combustion efficiency of the gas water heater or a decrease in the cleanliness of the exhaust gas. In addition, it is possible to suppress the need to replace the oxygen sensor unit when an abnormal resistance occurs in the detection circuit. This is preferable in terms of reducing the cost and effort of repairing the hot water supply control system (hot water supply equipment). [Brief description of the drawings]

[0015] [Figure 1] Schematic diagram of hot water supply equipment. [Diagram 2] FIG. 2 is a partially enlarged view of FIG. 1 showing the A / F sensor and its surroundings. [Diagram 3] FIG. 2 is a block diagram showing an electrical configuration of the sensor unit. [Figure 4] 6 is a flowchart showing a temperature adjustment process executed by a CPU of the sensor board. [Diagram 5] FIG. 4 is a schematic diagram showing the relationship between the resistance value of a sensor element and the temperature of the sensor element. [Figure 6] Schematic diagram illustrating anomalous resistance. [Figure 7] Schematic diagram showing temperature deviation when abnormal resistance occurs. [Figure 8] 6 is a flowchart showing an abnormality monitoring process executed by a CPU of the sensor board. [Figure 9] FIG. 4 is a schematic diagram showing a configuration related to estimation of a resistance value of a heater resistor. [Figure 10] FIG. 4 is a schematic diagram showing the relationship between the resistance value and temperature of a heater resistor. [Figure 11] 4 is a timing chart illustrating the behavior of a hot water supply system when abnormal resistance occurs. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described with reference to the accompanying drawings. The embodiment is embodied as a hot water supply system installed in a building such as a house.

[0017] As shown in Fig. 1, hot water supply equipment 10 includes a storage-type gas water heater 11 and a hot water supply control device 12 that controls hot water supply from 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 divides the inside of hot water storage tank 21 into upper and lower parts, and is configured so that the lower side of the partition is a combustion chamber 24 and the upper side is a hot water storage chamber 25. A water supply pipe 22 is connected to the lower part of hot water storage chamber 25, and water is supplied from a water supply 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 upper part of hot water storage chamber 25, and hot water is supplied through this hot water supply pipe 23.

[0018] An intake pipe 31 is connected to the combustion chamber 24, and a blower 32 is disposed in the intake pipe 31. The blower 32 is subject to drive control by the hot water supply control device 12, and operates based on a drive signal from the hot water supply control device 12. When the blower 32 operates, outside air is supplied to the combustion chamber 24 through the intake pipe 31. A nozzle of a gas supply pipe 33 is connected to a midpoint of the intake pipe 31. A control valve is provided in the gas supply pipe 33, and when this control valve is driven and controlled by the hot water supply control device 12, the amount of gas supplied to the intake pipe 31 is adjusted.

[0019] The combustion chamber 24 is provided with a burner 34 for burning the 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 disposed so as 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 takes place between the combustion gas and the water via the exhaust pipe 39. The water in the hot water storage tank 21 is heated by this heat exchange, and hot water is produced.

[0020] The exhaust pipe 39 protrudes upward from the ceiling of the hot water storage tank 21, and an outlet of the exhaust pipe 39 is formed in 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 that is a control board for the A / F sensor 50. The sensor board 60 is connected (wired) to the A / F sensor 50 by wiring that will be described later, and is disposed in a position away from the exhaust pipe 39, that is, in a position outside the range of influence of the exhaust heat of the gas water heater 11.

[0021] 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 detection information (detection signal) 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.

[0022] Now, with reference to Fig. 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 contains the sensor element 51, and the housing 53 is fixed to the exhaust pipe 39 so that it protrudes into the inside of the exhaust pipe 39. A plurality of through holes are formed in the housing 53, and the combustion gas that flows into the housing 53 through these through holes is guided to the sensor element 51.

[0023] In order for the A / F sensor 50 to properly exhibit its detection performance, the sensor element 51 must be at an appropriate temperature (hereinafter referred to as the reference temperature), which in this embodiment is 750° C. In other words, in order 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. Taking this into consideration, the A / F sensor 50 is provided with a heater resistor 52 (e.g., a ceramic heater) as an electric heater for heating the sensor element 51.

[0024] The heater resistor 52 is in contact with the sensor element 51, and the heat of 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 between a power-on state (heater ON) in which power is supplied by the sensor board 60 (CPU, described later) and a power-off state (heater OFF) in which power is not supplied.

[0025] Next, the electrical configuration of the sensor unit 40 will be described with reference to the block diagram of FIG.

[0026] 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 as a control unit that controls the heating circuit HC based on information from the detection circuit SC.

[0027] 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 for transmitting a detection 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 according 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.

[0028] CPU 61 identifies (estimates) the oxygen concentration based on at least one of the current value and voltage value (voltage value in this embodiment) acquired from ASIC 62. In this embodiment, the voltage value of sensor element 51 increases as the oxygen concentration decreases and decreases as the oxygen concentration increases. CPU 61 transmits information indicating the identified oxygen concentration to hot water supply control device 12 as detection information of the oxygen concentration. Hot water supply control device 12 performs combustion control (feedback control) of gas water heater 11 based on the received detection information.

[0029] Furthermore, the CPU 61 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 (see FIG. 3). 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] In the present embodiment, the ASIC 62 outputs the current value and the voltage value of the sensor element 51 to the CPU 61, but the present invention is not limited to this. The ASIC 62 may calculate the resistance value and output the calculated resistance value to the CPU 61.

[0031] 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 for supplying 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 a ground 69. The heater resistor 52 is connected to the drain side of the MOSFET 66, and the ground 69 is connected via a pull-down resistor 67 to the source side. A CPU 61 is connected to the gate of the MOSFET 66, and the CPU 61 turns the gate ON / 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.

[0032] Here, a process (temperature control process) for controlling the temperature of the heater resistor 52 (sensor element 51) by the CPU 61 will be described with reference to Fig. 4. The temperature control process is a process executed by the CPU 61 as part of regular processing.

[0033] In the temperature adjustment process, first, in step S101, 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. The obtained current value and voltage value are stored in a memory attached to the CPU 61. In the following step S102, the resistance value of the sensor element 51 is calculated based on the current value and voltage value.

[0034] This resistance value includes the resistance value of the wiring 71 and the resistance value of the connector 72. However, the resistance value of the wiring 71 when no crushing occurs in the wiring 71 and the resistance value of the connector 72 when no contact failure occurs are smaller than the resistance value of the sensor element 51 and can be substantially ignored.

[0035] In the next step S103, it is determined whether the calculated current resistance value is greater than the reference resistance value. Specifically, the resistance value (e.g., 38Ω) 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. 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. In this case, an affirmative determination is made in step S103, and the process proceeds to step S104. In step S104, it is determined whether the sensor element 51 is being heated using the heating circuit HC. If an affirmative determination is made in step S104, the temperature adjustment process is terminated as it is. If a negative determination is made in step S104, the heater resistor 52 is turned on (heater ON) in step S105, and then the temperature adjustment process is terminated.

[0036] Returning to the explanation of step S103, if the resistance value of the sensor element 51 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. In this case, a negative determination is made in step S103 and the process proceeds to step S106. In step S106, it is determined whether the sensor element 51 is currently being heated using the heating circuit HC. If a negative determination is made in step S106, the temperature adjustment process is terminated. If a positive determination is made in step S106, the heater resistor 52 is put into a non-energized state (heater OFF) in step S107, and then the temperature adjustment process is terminated.

[0037] In this manner, in this embodiment, the heater resistor 52 is switched to a conducting state / non-conducting state based on the resistance value of the sensor element 51, which is correlated with the temperature of the sensor element 51. Specifically, when the temperature of the sensor element 51 has not reached the reference temperature, the heater resistor 52 is switched to a conducting state to heat the sensor element 51, and when the temperature of the sensor element 51 exceeds the reference temperature, the heater resistor 52 is switched to a non-conducting state to lower the temperature of the sensor element 51. This allows the temperature of the sensor element 51 to be maintained at the reference temperature (see FIG. 5).

[0038] Here, in the sensor unit 40 shown in this embodiment, the A / F sensor 50 and the sensor board 60 are connected via wiring 71, 75. These wiring 71, 75 realize a configuration in which the sensor board 60 can be arranged outside the range affected by the heat of the exhaust pipe 39, specifically outside the range affected by the heat of the gas water heater 11. However, in such a configuration, as shown in FIG. 6, abnormal resistance may occur in the element line SL due to crushing of the wiring 71 forming the element line SL of the detection circuit SC or poor contact of the connector 72. In the above-mentioned temperature adjustment, the resistance value of the sensor element 51 is calculated (estimated) from the acquired voltage value and current value, but the following inconvenience occurs when this resistance value includes the resistance value of the abnormal resistance.

[0039] That is, as shown in FIG. 7, the resistance value of the abnormal resistor is included in the calculated resistance value, so that the CPU 61 may erroneously determine that the resistance value of the sensor element 51 is greater than the actual resistance value. In this way, the temperature of the sensor element 51 may be erroneously determined to be lower than the actual temperature, and the temperature of the sensor element 51 may rise above the above-mentioned reference temperature. In particular, the resistance of the sensor element 51 decreases significantly as the temperature rises, so that the influence of the abnormal resistance becomes significant. If the abnormal resistance increases, the difference between the actual temperature and the expected temperature increases, and the exceedance of the reference temperature becomes significant. If such a situation continues, it may cause the deterioration of the sensor element 51 or damage the sensor element 51, which is an obstacle to optimizing combustion.

[0040] When abnormal resistance occurs in the detection circuit SC, proper combustion is possible by replacing the entire sensor element 51 including the part where abnormal resistance occurs, that is, by replacing the entire A / F sensor 50. However, when such replacement becomes necessary, the cost and labor required for repairing the hot water supply equipment 10 will be significantly increased compared to repairing only the part where abnormal resistance occurs, such as the wiring 71 or the connector 72. In this embodiment, one of the features is that, when abnormal resistance occurs in the detection circuit SC, a device is devised to suppress the influence of the abnormal resistance and to suppress the cost and labor required for repair. Specifically, one of the features is that an abnormality (occurrence of abnormal resistance) in the detection circuit SC is monitored, and when the abnormality occurs, a prompt repair is prompted, thereby suppressing damage to the sensor element 51 that makes it difficult to continue using the sensor element 51. Below, with reference to the flowchart of FIG. 8, a process for abnormality monitoring by the CPU 61 (abnormality monitoring process) will be described. The abnormality monitoring process is a process executed by the CPU 61 as part of regular processing, and is skipped while an abnormality stop signal, which will be described later, is being output or while the sensor is stopped.

[0041] In the abnormality monitoring process, first, in step S201, the resistance value (estimated value) of the sensor element 51 is confirmed. Specifically, the resistance value calculated in step S102 is read from the memory. In the following step S202, it is determined whether a high temperature abnormality (an abnormality in which the temperature exceeds the allowable upper limit) has occurred in the sensor element 51. Specifically, it is determined whether the read resistance value is smaller than the set lower limit X1. The set lower limit X1 is the resistance value when the temperature of the sensor element 51 reaches 780°C, which is the allowable upper limit, specifically 30Ω. For example, if the MOSFET 66 of the heating circuit HC has broken down and the sensor element 51 is in a state where it is excessively heated, a positive determination is made in step S202.

[0042] If the determination in step S202 is affirmative, the process proceeds to step S203, where the high temperature side error counter C1 provided in the memory is updated (specifically, incremented by 1). The high temperature side error counter C1 is a counter that stores the number of times the temperature has exceeded the upper limit of tolerance. In the following step S204, it is determined whether the value of the high temperature side error counter C1 exceeds a threshold value M.

[0043] If the value of the high temperature side error counter C1 exceeds the threshold value M, the process proceeds to step S205, where a first type abnormality stop signal is output to the hot water supply control device 12. When the hot water supply control device 12 receives this first type abnormality stop signal, it displays a message on the display screen of the hot water supply control device 12, etc., indicating that a failure has occurred in the sensor unit 40. For example, the text "Sensor failure. Please replace the sensor" is displayed. In addition, the combustion control of the gas water heater 11 is switched from feedback control using the oxygen concentration information from the sensor unit 40 to open control which does not use the information. By performing the combustion control under open control, it is possible to avoid a situation in which the hot water supply equipment 10 becomes unusable and the convenience of the hot water supply equipment 10 is reduced.

[0044] Thereafter, in step S206, the sensor unit 40 is stopped, and the abnormality monitoring process is terminated, whereby heating of the sensor element 51 and detection of the oxygen concentration are stopped.

[0045] Returning to the explanation of step S202, if a negative determination is made in step S202, that is, if the resistance value of the sensor element 51 is equal to or greater than the set lower limit X1, the process proceeds to step S207. In the following step S207, it is determined whether a low temperature abnormality (an abnormality in which the temperature falls below the allowable lower limit) has occurred in the sensor element 51. Specifically, it is determined whether the read resistance value is greater than the set upper limit X2. The set upper limit X2 is the resistance value when the temperature of the sensor element 51 is 660°C, specifically 90Ω. For example, if the heating circuit HC has broken down and the sensor element 51 is not sufficiently heated, a positive determination is made in step S207.

[0046] If the determination in step S207 is affirmative, the process proceeds to step S208, where the low temperature side error counter C2 provided in the memory is updated (specifically, incremented by 1). The low temperature side error counter C2 is a counter that stores the number of times the temperature has fallen below the allowable lower limit. In the following step S209, it is determined whether the value of the low temperature side error counter C2 exceeds a threshold value N.

[0047] If the value of low temperature side error counter C2 exceeds threshold value N, a first type abnormality stop signal is output to hot water supply control device 12 in step S205, and sensor unit 40 is stopped in step S206 to end this abnormality monitoring process.

[0048] Although not shown, the high temperature side error counter C1 and the low temperature side error counter C2 are decremented by 1 when the resistance value of the sensor element 51 is included between the set lower limit X1 and the set upper limit X2. Also, they are reset to the initial value 0 when the sensor is stopped as described above.

[0049] If a negative determination is made in any of steps S204, S207, and S209, the process proceeds to step S210. In step S210, a voltage value is obtained from the heater line HL. Specifically, a voltage value V1 (see FIG. 9) at the connection point between the heater resistor 52 and the pull-down resistor 67 is obtained.

[0050] In the next step S211, the resistance value of heater resistor 52 is calculated. Specifically, a current value I (see FIG. 9) of a current flowing through pull-down resistor 67 is calculated based on voltage value V1 acquired in step S210 and resistance value R2 of pull-down resistor 67 stored in memory. Pull-down resistor 67 is disposed in a position that is not affected by heat from heater resistor 52 or gas water heater 11, and resistance value R2 of pull-down resistor 67 stored in memory is a resistance value in the room temperature range (for example, an average value or a median value).

[0051] Next, the resistance value R1 of the heater resistor 52 is calculated based on the acquired voltage value V1, the calculated current value I, and the voltage value V0 of the power supply unit 65 stored in the memory. "Resistance value R1 = (voltage value V0 - voltage value V1) / current value I".

[0052] Thereafter, in step S212, it is determined whether or not the resistance value of the heater resistor 52 calculated in step S211 exceeds the set upper limit Y. There is a correlation between the resistance value of the heater resistor 52 and the temperature of the heater resistor 52 (the temperature of the sensor element 51), and as the temperature of the heater resistor 52 increases, the resistance value of the heater resistor 52 increases (see FIG. 10). The set upper limit Y is set to a value (e.g., 6.5Ω) that corresponds to a temperature that is higher than the temperature (780°C) corresponding to the set lower limit X1 and lower than the heat resistance temperature of the sensor element 51 (e.g., 900°C).

[0053] If it is determined in step S212 that the resistance value is equal to or less than the set upper limit Y, the abnormality monitoring process ends. If it is determined in step S212 that the resistance value is greater than the set upper limit Y, that is, if it is assumed that an abnormality has occurred, the process proceeds to step S213. In step S213, a second type abnormality stop signal is output to the hot water supply control device 12. When the hot water supply control device 12 receives this second type abnormality stop signal, a message is displayed on the display screen of the hot water supply control device 12 to the effect that abnormal resistance has occurred in the sensor unit 40. For example, the text "Please check the sensor wiring" is displayed. In addition, the combustion control of the gas water heater 11 is switched from feedback control using the oxygen concentration information from the sensor unit 40 to open control that does not use the information.

[0054] Thereafter, in step S206, the sensor unit 40 is stopped, and the abnormality monitoring process is terminated, whereby heating of the sensor element 51 and detection of the oxygen concentration are stopped.

[0055] Next, with reference to the timing chart of FIG. 11, the behavior of hot water supply equipment 10 when the above-mentioned abnormal resistance occurs will be illustrated.

[0056] At time t0 when water is not being boiled, the user removes wiring 71 to perform maintenance such as cleaning. At time t1, wiring 71 is returned to its original position, but connector 72 and connector 63 are not properly connected, and abnormal resistance occurs at the connection point between connector 72 and connector 63.

[0057] At timing t2 after the maintenance work is completed, the user performs the water boiling operation, and this operation triggers the start of water boiling (combustion control) and the start of heating by heater resistor 52 in sensor unit 40. Note that from the start of water boiling until the temperature rise of sensor element 51 is completed, the combustion control is executed as open control that does not take information from sensor unit 40 into consideration.

[0058] In the example shown in FIG. 11, an abnormal resistance occurs in the detection circuit SC of the sensor unit 40, and the resistance value of the sensor element 51 is estimated to be higher than the actual resistance value. As a result, the estimated temperature of the sensor element 51 is assumed to be lower than the actual temperature (actual temperature). For this reason, at the timing t3 after the start of heating by the heater resistor 52, the heating continues even though the actual temperature has reached the reference temperature. As a result, the actual temperature exceeds the reference temperature. At the timing t4 thereafter, specifically, at the timing before the actual temperature reaches the heat-resistant temperature, the resistance value of the heater resistor 52 reaches the above-mentioned set upper limit Y. This triggers the heating by the heater resistor 52 to be stopped, and the hot water supply equipment 10 executes an abnormality notification. In this abnormality notification, a message urging the user to check the wiring 71 of the sensor unit 40 is displayed on the display screen of the hot water supply control device 12. Note that, although the detection of the oxygen concentration has not started at this point, if the detection of the oxygen concentration is being performed, the detection is restricted so that the detection is not possible. This restriction is released by the user performing a reset operation.

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

[0060] In the configuration in which the current value and the voltage value are obtained as the control parameters from the wiring 71 forming the element line SL, the temperature of the sensor element 51 can be easily estimated, but the above-mentioned concern about damage caused by the abnormal resistance is strong. That is, when the abnormal resistance occurs in the element line SL due to crushing of the wiring 71 or poor connection of the connector 72, the temperature of the sensor element 51 may be raised above the reference temperature by performing temperature adjustment based on the control parameters affected by the abnormal resistance. In this respect, according to the sensor unit 40 shown in the present embodiment, the monitoring parameters that are not actually necessary for the temperature control of the sensor element 51 are deliberately obtained, and the abnormality of the detection circuit SC is monitored based on the obtained monitoring parameters. For example, when the temperature of the sensor element 51 is raised above the reference temperature, such a situation can be quickly discovered. Then, by notifying the user of the fact and restricting overheating of the sensor element 51, the sensor element 51 can be prevented from being damaged, which makes it difficult to continue using it. This is preferable in terms of reducing the effect of the abnormal resistance generated in the detection circuit SC and reducing the cost and effort of repairing the hot water supply equipment 10. In addition, the sensor unit 40 (sensor element 51) is heated excessively, which reduces the chance of outputting a false detection result that makes the oxygen concentration exceed the actual oxygen concentration, and thus it is possible to suitably suppress deterioration of the combustion efficiency in the gas water heater caused by the false detection. This is also preferable in terms of preventing a decrease in the cleanliness of the exhaust gas.

[0061] In this embodiment, a voltage value is acquired from the heating circuit HC as a monitoring parameter, and the current resistance value of the heater resistor 52 is calculated from the voltage value. With such a configuration, it is possible to easily monitor whether or not a cause for exceeding the reference temperature has occurred, without adding a thermometer or the like for directly measuring the temperature of the heater resistor 52, i.e., the temperature of the sensor element 51.

[0062] As shown in this embodiment, by configuring the circuit to acquire the voltage value at the connection point between the pull-down resistor 67 mounted on the sensor board 60 and the heater resistor 52 disposed on the A / F sensor 50 as the monitoring parameter, there is no need to provide a separate circuit for acquiring the monitoring parameter, and the complexity of the configuration of the sensor unit 40 can be effectively suppressed.

[0063] The pull-down resistor 67 is also a type of resistor, and its resistance value can change depending on the temperature, just like the heater resistor 52. By arranging the pull-down resistor 67 on the sensor substrate 60 side and separating it from the heater resistor 52, it is possible to prevent the temperature of the pull-down resistor 67 from changing due to the heat generated in the heater resistor 52. By suppressing the temperature change of the heater resistor 52, it is possible to prevent the accuracy of the calculation result of the resistance value of the heater resistor 52 from decreasing drastically, even in a configuration in which the resistance value of the pull-down resistor 67 is not specified as needed depending on the situation but a pre-stored value (resistance value R2) is referenced. This allows the configuration related to the calculation of the resistance value of the heater resistor 52 to be simplified.

[0064] When calculating the current resistance value of heater resistor 52 using a value (resistance value R2) previously stored in memory, it is preferable that there is little variation in temperature in the environment in which sensor board 60 is disposed. In the configuration shown in this embodiment, A / F sensor 50 and sensor board 60 are connected via wiring 71, 75, and at least pull-down resistor 67 can be disposed so as to be outside the range affected by the heat of gas water heater 11. This makes it possible to suppress the temperature of pull-down resistor 67 from fluctuating depending on the operating conditions of gas water heater 11, etc. This is a preferable configuration for improving monitoring accuracy.

[0065] <Other embodiments> The present invention is not limited to the above-described embodiment, and may be implemented as follows. Each of the following configurations may be applied individually to the above-described embodiment, or may be applied in combination with some or all of the following configurations to the above-described embodiment.

[0066] In the above embodiment, the resistance value of the heater resistor 52 is calculated from the voltage value of the pull-down resistor 67, and the detection circuit SC is monitored for abnormality based on the calculated resistance value, but the present invention is not limited to this. For example, the temperature of the heater resistor 52, i.e., the temperature of the sensor element 51, may be estimated from the resistance value of the heater resistor 52, and the detection circuit SC may be monitored for abnormality based on the estimated temperature. In addition, considering that the voltage value of the pull-down resistor 67 is correlated with the temperature of the sensor element 51, it is also possible to monitor the detection circuit SC for abnormality based on the voltage value.

[0067] In the above embodiment, the resistance value of the heater resistor 52 is compared with the preset upper limit Y to detect an abnormality in the detection circuit SC. However, this may be modified as follows. That is, the temperature of the sensor element 51 may be estimated on the detection circuit SC side, and the temperature of the heater resistor 52 (sensor element 51) may be estimated on the heating circuit HC side, and the abnormality in at least one of the circuits may be detected by comparing the estimated results. The estimated result on the heating circuit HC side has a larger error than the estimated result on the detection circuit SC side. Therefore, for example, if the difference between the two estimated results exceeds a reference range that takes such an error into account, it is determined that an abnormality has occurred, and if it is within the reference range, it is determined that no abnormality has occurred. Also, even if heating by the heater resistor 52 starts, it takes a certain amount of time for the temperature of the sensor element 51 to reach the reference temperature. During this period (during heating), the temperature of the sensor element 51 rises later than that of the heater resistor 52, so the difference between the temperature of the sensor element 51 and that of the heater resistor 52 may become large. Therefore, by restricting the above comparison until a preset heating time has elapsed after heating has started, and then performing the comparison after the heating time has elapsed, erroneous judgments due to time lags can be suitably suppressed.

[0068] It is also possible to configure the ASIC 62 shown in the above embodiment to calculate (estimate) the resistance value of the sensor element 51 and output the calculated resistance value to the CPU 61.

[0069] The threshold values ​​M and N shown in the above embodiment may be variable values. For example, it takes a certain amount of time from when water boiling starts until the temperature of the sensor element 51 reaches the reference temperature. In consideration of this situation, it is preferable that the threshold values ​​M and N set during the period from when water boiling starts until the temperature of the sensor element 51 reaches the reference temperature be greater than the threshold values ​​M and N set after the temperature of the sensor element 51 reaches the reference temperature.

[0070] In addition, the above-mentioned abnormality monitoring process can be configured to be executed periodically after the sensor element 51 has been heated to the reference temperature, and the abnormality monitoring process can be configured not to be executed immediately after the water boiling process begins.

[0071] A measurement line for measuring the current value or voltage value of the current flowing through the heater resistor 52 may be provided separately from the heater line HL shown in the above embodiment.

[0072] This does not deny the possibility of directly measuring the temperature of the heater resistor 52 or the sensor element 51 using a thermometer and using the measured temperature as the monitoring parameter.

[0073] A connector may be added to the end of the wiring 71, 75 shown in the above embodiment on the A / F sensor 50 side, and the wiring 71, 75 may be configured to be detachably attached to both the sensor board 60 and the A / F sensor 50. With such a configuration, it becomes easier to replace the wiring 71, 75 when the wiring is crushed or the connector has a poor contact.

[0074] In the above embodiment, the A / F sensor 50 is disposed in the exhaust pipe 39, while the sensor board 60 is disposed at a position outside the exhaust pipe 39, specifically, outside the range (influence range) of the heat of the gas water heater 11, but the present invention is not limited to this. If the temperature variation of the pull-down resistor 67 is small enough to be negligible, the sensor board 60 can be disposed so that the pull-down resistor 67 is located within the influence range. If the temperature of the pull-down resistor 67 can change significantly, the correspondence relationship between the temperature and the resistance value of the pull-down resistor 67 may be stored in advance in a memory, and the temperature of the pull-down resistor 67 (or the environment in which the pull-down resistor 67 is disposed) may be measured, and the voltage of the pull-down resistor 67 may be calculated based on the resistance value corresponding to the current temperature of the pull-down resistor 67.

[0075] Instead of a configuration in which the sensor element 51 starts to heat up at the same time as the water is boiled when the water is boiled, it is also possible to configure the sensor element 51 to start to heat up when the water is boiled, and to start boiling water when the temperature of the sensor element 51 reaches a reference temperature.

[0076] In each of the above embodiments, the reference temperature of the sensor element 51 is set to 750°C. However, it is also possible to add a certain degree of tolerance to the reference temperature and adjust the temperature so that the temperature of the sensor element 51 falls within a range of, for example, 745°C to 755°C.

[0077] The sensor unit 40 shown in each of the above embodiments can also be applied to other devices having an internal combustion engine such as a gasoline engine (for example, an automobile or a generator).

[0078] <Inventions extracted from the above embodiments> The following describes the features of the inventions extracted from the above-mentioned embodiments, while indicating, as necessary, their effects, etc. In the following, for ease of understanding, the corresponding configurations in the above-mentioned embodiments are appropriately indicated in parentheses, but the present invention is not limited to the specific configurations indicated in parentheses.

[0079] Feature 1. An oxygen sensor unit (sensor unit 40) that is applied to a gas water heater (gas water heater 11) and has an oxygen sensor (A / F sensor 50) that detects the oxygen concentration of gas discharged from the gas water heater and a sensor control board (sensor board 60) to which the oxygen sensor is connected, and that can output the detected oxygen concentration to a hot water supply control device (hot water supply control device 12) of the gas water heater, a detection circuit section (detection circuit SC) including a sensor element (sensor element 51) of the oxygen sensor and a signal transmission path (element line SL) for transmitting a detection signal indicating the oxygen concentration output from the sensor element to a control section (CPU 61) of the sensor control board; a heating circuit unit (heating circuit HC) including a heater resistor (heater resistor 52) provided next to the sensor element and capable of heating the sensor element, and a power supply path (heater line HL) for supplying power to the heater resistor from a power supply unit (power supply unit 65) provided on the sensor control board; a control parameter acquisition unit (a function of acquiring the resistance value, and either the voltage value or the current value from the detection circuit SC in the CPU 61) that acquires the resistance value of the sensor element or a correlation value correlated with the resistance value as a control parameter via the signal transmission path; a temperature control unit (a function of executing a temperature adjustment process in a CPU 61) that controls the temperature of the sensor element to a predetermined temperature (a reference temperature, for example, 750° C.) by supplying power from the power supply unit to the heater resistor in accordance with the control parameters acquired by the control parameter acquisition unit; a monitoring parameter acquisition unit (a function of acquiring a voltage value from the heating circuit HC by the CPU 61) that acquires a temperature of the heater resistor or a correlation value correlated with the temperature as a monitoring parameter; an abnormality monitoring unit (a monitoring function in the CPU 61) that monitors an abnormality in the detection circuit unit based on the monitoring parameters acquired by the monitoring parameter acquisition unit; The oxygen sensor unit includes:

[0080] The temperature control unit according to this feature adjusts the temperature of the sensor element to a predetermined temperature (e.g., 750° C.) by supplying power from the power supply unit to the heater resistor in accordance with a control parameter that is a resistance value of the sensor element or a correlation value correlated with the resistance value. Therefore, when controlling the temperature of the sensor element, it is not necessary to obtain the temperature of the heater resistor or a monitoring parameter that is a correlation value correlated with the temperature.

[0081] However, in a configuration in which the control parameters are acquired via a signal transmission path, if abnormal resistance occurs in the signal transmission path due to crushing of the wiring forming the signal transmission path or a poor connection of a connector, the following inconvenience may occur if temperature adjustment is performed based on the control parameters affected by the abnormal resistance. That is, the abnormal resistance may cause the sensor element to be heated assuming a temperature lower than the actual temperature of the sensor element, causing the temperature of the sensor element to rise above a predetermined temperature. The temperature control unit cannot detect the occurrence of such an abnormality.

[0082] In this respect, according to the oxygen sensor unit shown in this characteristic, the monitoring parameters that are not originally necessary for the temperature control of the sensor element are acquired, and the abnormality of the detection circuit part is monitored based on the acquired monitoring parameters. For example, if the temperature of the sensor element is raised above a predetermined temperature, such a situation can be quickly discovered, and it is possible to respond by notifying the user of the situation or restricting the overheating of the sensor element. This makes it possible to prevent the sensor element from being damaged, which makes it difficult to continue using it. This is preferable in terms of reducing the effect of the abnormal resistance generated in the detection circuit part and reducing the cost and effort of repairing the hot water supply equipment. In addition, the oxygen sensor unit is excessively heated, which reduces the chance of outputting a false detection result as if the oxygen concentration is higher than the actual oxygen concentration, and the deterioration of the combustion efficiency in the gas hot water heater caused by the false detection can be preferably suppressed.

[0083] Feature 2: The oxygen sensor and the sensor control board are connected via wiring (wiring 71, 75), The wiring includes a signal transmission wiring (wiring 71) that forms the signal transmission path of the detection circuit unit, 2. The oxygen sensor unit according to feature 1, wherein the control parameter acquisition unit acquires at least one of a current value and a voltage value of a current flowing through the signal transmission wiring as the control parameter.

[0084] As shown in this feature, in a configuration in which at least one of a current value and a voltage value is acquired as a control parameter from a signal transmission wiring, the temperature of the sensor element can be easily estimated, but the concern shown in feature 1 becomes stronger. That is, when abnormal resistance occurs in a signal transmission path due to crushing of the wiring (signal transmission wiring) forming the signal transmission path or poor connection of a connector, the temperature adjustment is performed based on the control parameter affected by the abnormal resistance, and the temperature of the sensor element may rise above a predetermined temperature. And, as described above, the temperature control unit cannot detect the occurrence of such an abnormality. This is a factor that leads to deterioration and damage of the sensor element. By applying the technical idea shown in feature 1 to such a configuration, it is possible to suppress an excessive temperature rise of the sensor element and appropriately protect the sensor element while simplifying the configuration related to the temperature control.

[0085] Feature 3: The oxygen sensor unit according to feature 1 or 2, wherein the abnormality monitoring unit has a calculation unit (a function of calculating a resistance value in CPU 61) that calculates a current resistance value of the heater resistor from the monitoring parameters acquired by the monitoring parameter acquisition unit, and monitors, from the current resistance value calculated by the calculation unit, whether or not an abnormality has occurred in the detection circuit unit that would cause the temperature of the sensor element to exceed the predetermined temperature.

[0086] There is a correlation between the resistance value of the heater resistor and the temperature. Specifically, the higher the temperature, the higher the resistance value, and the lower the temperature, the lower the resistance value. Therefore, as shown in this feature, by calculating the current resistance value of the heater resistor from the monitoring parameters, it is possible to easily monitor whether there is a cause for exceeding the predetermined temperature without adding a thermometer or the like for directly measuring the temperature of the heater resistor, i.e., the temperature of the sensor element.

[0087] Feature 4. The heating circuit unit is A ground (ground 69) provided on the sensor control board; A pull-down resistor (pull-down resistor 67) provided between the heater resistor and the ground; having the monitoring parameter acquisition unit acquires, as the monitoring parameter, a voltage value at a connection point between the heater resistor and the pull-down resistor; The oxygen sensor unit according to feature 1 or 2, wherein the abnormality monitoring unit has a calculation unit (a function of calculating a resistance value in a CPU 61) that calculates a current resistance value of the heater resistor based on the monitoring parameters acquired by the monitoring parameter acquisition unit, a voltage value of the power supply unit, and a resistance value of the pull-down resistor.

[0088] As shown in this feature, if a configuration is adopted in which the current resistance value of the heater resistor is calculated based on a monitoring parameter (the voltage value between the heater resistor and the pull-down resistor), the voltage value of the power supply unit, and the resistance value of the pull-down resistor, the technical idea shown in feature 3 can be easily realized.

[0089] Feature 5. The pull-down resistor is provided on the sensor control board. 5. The oxygen sensor unit according to feature 4, wherein the calculation unit calculates the current resistance value of the heater resistor by using a resistance reference value that is pre-stored as a resistance value of the pull-down resistor.

[0090] The pull-down resistor is also a type of resistor, and its resistance value can change depending on the temperature, just like the heater resistor. Therefore, by disposing the pull-down resistor on the sensor control board side and separating it from the heater resistor, it is possible to prevent the temperature of the pull-down resistor from changing due to the heat generated in the heater resistor. By suppressing the temperature change of the heater resistor, it is possible to prevent the accuracy of the calculation result of the resistance value of the heater resistor from decreasing drastically, even if the resistance value of the pull-down resistor is not specified as needed depending on the situation but is instead a previously stored resistance reference value is referenced. This simplifies the configuration related to the calculation of the resistance value of the heater resistor.

[0091] Feature 6: An oxygen sensor unit as described in Feature 4 or Feature 5, in which the oxygen sensor and the sensor control board are connected via wiring (wiring 71, 75), and at least the pull-down resistor can be positioned so as to be outside the range affected by the heat of the gas water heater.

[0092] When calculating the current resistance value of the heater resistor using a resistance reference value stored in advance as described in Feature 5, it is preferable that there is little variation in temperature in the environment in which the sensor control board is disposed. Here, in the configuration described in this feature, the oxygen sensor and the sensor control board are connected via wiring, and at least the pull-down resistor can be positioned so as to be outside the range affected by the heat of the gas water heater, so that it is possible to suppress the temperature of the pull-down resistor from fluctuating depending on the operating conditions of the gas water heater, etc. This is a preferable configuration for improving monitoring accuracy.

[0093] Feature 7. The abnormality monitoring unit is A storage unit (a memory provided in the CPU 61) for storing correspondence information indicating a correspondence between the resistance value of the heater resistor and the temperature of the sensor element; an estimation unit that estimates a current temperature of the sensor element based on the current resistance value of the heater resistor calculated by the calculation unit and the correspondence relationship information stored in the storage unit; a determination unit that determines an abnormality in the detection circuit unit by comparing a current temperature of the sensor element estimated by the estimation unit with a pre-stored reference temperature; 7. The oxygen sensor unit according to any one of Features 3 to 6, further comprising:

[0094] As shown by this feature, if the current temperature of the sensor element is estimated from the resistance value of the heater resistor and the estimated temperature is compared with a pre-stored reference temperature, it is possible to determine if the temperature of the sensor element is excessively high.

[0095] Feature 8. The calculation unit is a first calculation unit, The abnormality monitoring unit a first storage unit configured to store first correspondence information indicating a correspondence relationship between a resistance value of the heater resistor and a temperature of the sensor element; a first estimation unit that estimates a current temperature of the sensor element based on a current resistance value of the heater resistor calculated by the first calculation unit and the first correspondence relationship information stored in the first storage unit; a second storage unit configured to store second correspondence information indicating a correspondence relationship between a resistance value of the sensor element and a temperature of the heater resistor; a second estimation unit that estimates a current temperature of the sensor element based on a current resistance value of the sensor element and the second correspondence relationship information stored in the second storage unit; a determination unit that determines whether the detection circuit unit is abnormal by comparing an estimation result of the first estimation unit with an estimation result of the second estimation unit; 7. The oxygen sensor unit according to claim 3, further comprising:

[0096] As shown by this feature, if the temperature of the sensor element estimated from the resistance value of the heater resistor is compared with the temperature of the sensor element estimated from the resistance value of a specified section, when the temperature of the sensor element is estimated to be lower than the actual temperature due to abnormal resistance, it can be determined that an abnormality has occurred in the detection circuit.

[0097] In addition, when the second estimation unit estimates the current temperature of the sensor element, the resistance value, which is a control parameter acquired by the control parameter acquisition unit, may be used, or the resistance value may be calculated from the correlation value, which is a control parameter.

[0098] Feature 9. The oxygen sensor unit according to Feature 8, wherein the determination unit is configured not to perform the determination until a preset heating time has elapsed since heating of the sensor element by the heater resistor has begun.

[0099] Even after heating by the heater resistor starts, it takes a certain amount of time for the temperature of the sensor element to reach a predetermined temperature. During this time, it is expected that the difference between the temperature of the sensor element and the temperature of the heater resistor will become large. Therefore, by configuring the device so that a judgment is made after a preset heating time has elapsed after heating starts, erroneous judgments can be suitably suppressed.

[0100] Feature 10. The abnormality monitoring unit is a first abnormality monitoring unit, The oxygen sensor unit according to any one of features 1 to 9, further comprising a second abnormality monitoring unit that monitors an abnormality in the detection circuit unit based on the control parameters acquired by the control parameter acquisition unit.

[0101] Generally, the temperature of the heater resistor or a monitoring parameter that is a correlation value correlated with the temperature varies widely. Therefore, by providing a second abnormality monitoring unit in addition to the abnormality monitoring unit, it is possible to monitor abnormalities in the detection circuit unit other than abnormalities caused by abnormal resistors.

[0102] Feature 11. A notification unit that notifies the occurrence of an abnormality when the first abnormality monitoring unit or the second abnormality monitoring unit determines that an abnormality has occurred in the detection circuit unit, The oxygen sensor unit according to feature 10, wherein the notification unit makes the notification in a manner that makes it possible to distinguish between a case in which an abnormality is determined to have occurred by the first abnormality monitoring unit and a case in which an abnormality is determined to have occurred by the second abnormality monitoring unit.

[0103] As described in Feature 1, etc., when abnormal resistance occurs in the wiring or connector, the abnormal resistance can be eliminated by repairing the wiring or connector, making it unnecessary to replace the oxygen sensor itself. Here, when the second abnormality monitoring means is used in combination, it is expected that the oxygen sensor (oxygen sensor unit) may need to be replaced. Therefore, when an abnormality is notified, by making it possible to identify which monitoring unit determined the abnormality, it is possible to reduce the opportunity for unnecessary replacement of the oxygen sensor (oxygen sensor unit).

[0104] Feature 12. A hot water control system comprising an oxygen sensor unit according to any one of features 1 to 11, and a combustion control device that controls combustion in the gas hot water heater based on the detection result of the oxygen concentration output from the oxygen sensor unit.

[0105] According to the hot water supply control system having this feature, even if an abnormal resistance occurs in the detection circuit of the oxygen sensor unit, it is possible to effectively suppress the inconvenience of the abnormal resistance causing a decrease in the combustion efficiency of the gas water heater or a decrease in the cleanliness of the exhaust gas. In addition, it is possible to suppress the need to replace the oxygen sensor unit when an abnormal resistance occurs in the detection circuit. This is preferable in terms of reducing the cost and effort of repairing the hot water supply control system (hot water supply equipment). [Explanation of symbols]

[0106] 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, 65...power supply unit, 67...pull-down resistor, 71, 75...wiring, 72, 76...connector, HC...heating circuit, HI...heater line, SC...detection circuit, SI...element line, TG...reference temperature, Y...setting upper limit.

Claims

1. An oxygen sensor unit that is applied to a gas water heater, has an oxygen sensor that detects the oxygen concentration of gas discharged from the gas water heater, and a sensor control board to which the oxygen sensor is connected, and is capable of outputting the detected oxygen concentration to a hot water supply control device of the gas water heater, a detection circuit unit including a sensor element of the oxygen sensor and a signal transmission path for transmitting a detection signal indicating the oxygen concentration output from the sensor element to a control unit of the sensor control board; a heating circuit section including a heater resistor provided next to the sensor element and capable of heating the sensor element, and a power supply path for supplying power from a power supply section provided on the sensor control board to the heater resistor; a control parameter acquisition unit that acquires, as a control parameter, a resistance value of the sensor element or a correlation value correlated with the resistance value via the signal transmission path; a temperature control unit that controls a temperature of the sensor element to a predetermined temperature by supplying power from the power supply unit to the heater resistor in accordance with the control parameters acquired by the control parameter acquisition unit; a monitoring parameter acquisition unit that acquires a temperature of the heater resistor or a correlation value correlated with the temperature as a monitoring parameter; an abnormality monitoring unit that monitors an abnormality in the detection circuit unit based on the monitoring parameters acquired by the monitoring parameter acquisition unit; The oxygen sensor unit includes:

2. The oxygen sensor unit according to claim 1, wherein the abnormality monitoring unit has a calculation unit that calculates a current resistance value of the heater resistor from the monitoring parameters acquired by the monitoring parameter acquisition unit, and monitors whether an abnormality has occurred in the detection circuit unit that would cause the temperature of the sensor element to exceed the predetermined temperature based on the current resistance value calculated by the calculation unit.

3. The heating circuit unit includes: A ground provided on the sensor control board; a pull-down resistor provided between the heater resistor and the ground; having the monitoring parameter acquisition unit acquires, as the monitoring parameter, a voltage value at a connection point between the heater resistor and the pull-down resistor; 2. The oxygen sensor unit according to claim 1, wherein the abnormality monitoring unit has a calculation unit that calculates a current resistance value of the heater resistor based on the monitoring parameters acquired by the monitoring parameter acquisition unit, a voltage value of the power supply unit, and a resistance value of the pull-down resistor.

4. A hot water control system comprising an oxygen sensor unit as described in any one of claims 1 to 3, and a combustion control device that controls the combustion of the gas hot water heater based on the detection result of the oxygen concentration output from the oxygen sensor unit.

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