Method for diagnosing gas sensor

Abstract

To provide a method for diagnosing a gas sensor which can make a precise diagnosis of failures of a gas sensor regardless of atmospheres.SOLUTION: The method for diagnosing a gas sensor diagnoses a failure in a gas sensor 21 on the basis of output from the gas sensor 21 when a charge state of storing charges in the gas sensor 21 including an action pole 21a and a counter pole 21b and a discharge state of discharging charges stored in the gas sensor 21 are switched. Also, the method determines whether the gas sensor 21 is malfunctioning on the basis of output acquired after discharge of the gas sensor 21 and a predetermined threshold value based on output before charge of the gas sensor 21.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a method for diagnosing a gas sensor, and more particularly to a method for diagnosing a gas sensor that performs a failure diagnosis of a gas sensor.

Background Art

[0002] Conventionally, a gas detection device that performs a failure diagnosis of a gas sensor has been known (see, for example, Patent Document 1).

[0003] In Patent Document 1, an alarm (gas detection device) is disclosed, which includes a gas sensor including a detection electrode and a counter electrode, a current / voltage conversion circuit that converts a current flowing through the gas sensor into a voltage, and a self-diagnosis means that performs a failure diagnosis of the gas sensor based on the output voltage of the current / voltage conversion circuit. In the alarm of this Patent Document 1, the self-diagnosis means stores and charges electric charges between the detection electrode and the counter electrode of the gas sensor, then discharges, and performs a failure diagnosis of the gas sensor based on the output voltage of the current / voltage conversion circuit at that time. Further, the self-diagnosis means performs a failure diagnosis of the gas sensor by comparing the output voltage of the current / voltage conversion circuit at a preset time point during charging and discharging of the gas sensor with a preset threshold value.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the above Patent Document 1, the self-diagnosis means diagnoses the failure of the gas sensor by comparing the output voltage of the current / voltage conversion circuit at a preset time point during charging and discharging of the gas sensor with a preset threshold value. Therefore, when the output voltage during charging and discharging of the gas sensor varies due to the presence of the gas to be detected in the atmosphere, the magnitude relationship with respect to the preset threshold value will be different. As a result, the result of the failure diagnosis of the gas sensor may vary depending on the state of the atmosphere, making it difficult to accurately diagnose the failure of the gas sensor.

[0006] This invention has been made to solve the above problems, and one object of this invention is to provide a method for diagnosing a gas sensor capable of accurately diagnosing the failure of the gas sensor regardless of the atmosphere.

Means for Solving the Problems

[0007] In order to achieve the above object, a method for diagnosing a gas sensor according to a first aspect of this invention is a diagnostic method for diagnosing the failure of a gas sensor based on the output from the gas sensor when switching between a charging state of storing charge in the gas sensor including a working electrode and a counter electrode and a discharging state of discharging the stored charge in the gas sensor. Whether the gas sensor is faulty is determined based on the output obtained after discharging the gas sensor and a predetermined threshold value based on the output before charging the gas sensor.

[0008] In the method for diagnosing a gas sensor according to the first aspect of the present invention, as described above, based on the output obtained after the discharge of the gas sensor and a predetermined threshold value based on the output before charging the gas sensor, it is determined whether the gas sensor is malfunctioning. As a result, even when the output voltage of the gas sensor varies during charging and discharging due to the presence of the gas to be detected in the atmosphere, a predetermined threshold value can be set based on the output before charging the gas sensor. Thus, when the gas sensor is charged and then discharged, since the output returns to the value before charging, a predetermined threshold value for performing the fault diagnosis can be set to an appropriate value according to the atmosphere. Consequently, the fault of the gas sensor can be accurately diagnosed regardless of the atmosphere.

[0009] The method for diagnosing a gas sensor according to the second aspect of the present invention includes a step of obtaining an output from the gas sensor before charging the gas sensor by storing charges in the gas sensor including a working electrode and a counter electrode, a step of determining a threshold value based on the output before charging the gas sensor, a step of obtaining an output after discharging the charges stored in the gas sensor, and a step of determining whether the gas sensor is malfunctioning based on the threshold value and the output after discharging the gas sensor.

[0010] In the method for diagnosing a gas sensor according to the second aspect of the present invention, as described above, a step of determining whether the gas sensor is malfunctioning is provided based on the threshold value determined based on the output before charging the gas sensor and the output after discharging the gas sensor. As a result, even when the output voltage of the gas sensor varies during charging and discharging due to the presence of the gas to be detected in the atmosphere, a threshold value can be set based on the output before charging the gas sensor. Thus, when the gas sensor is charged and then discharged, since the output returns to the value before charging, a threshold value for performing the fault diagnosis can be set to an appropriate value according to the atmosphere. Consequently, a method for diagnosing a gas sensor capable of accurately diagnosing the fault of the gas sensor regardless of the atmosphere can be provided.

Advantages of the Invention

[0011] According to the present invention, as described above, regardless of the atmosphere, the failure of the gas sensor can be accurately diagnosed.

Brief Description of the Drawings

[0012]

Figure 1

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Figure 12

Figure 13

Mode for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0014] With reference to FIGS. 1 to 13, the configuration of a gas detection device 100 according to an embodiment will be described.

[0015] (Configuration of Alarm System) As shown in FIG. 1, the gas detection device 100 is configured to detect a gas to be detected and give an alarm.

[0016] As shown in FIG. 1, the gas detection device 100 includes a control unit 1, a sensor unit 2, an alarm unit 3, and a power supply unit 4.

[0017] The control unit 1 is configured to control each part of the gas detection device 100. The control unit 1 includes a processor such as an MCU (Micro Controller Unit) that executes a program to perform processing, and a memory that stores the program.

[0018] The sensor unit 2 is configured to detect a gas to be detected. The sensor unit 2 detects, for example, CO gas, methane gas, propane gas, etc. as the gas to be detected. The sensor unit 2 includes an electrochemical gas sensor. The sensor unit 2 detects the gas by changing the output voltage when the gas to be detected is present.

[0019] The alarm unit 3 is configured to give an alarm to the surroundings when the gas to be detected is detected by the sensor unit 2. The alarm unit 3 gives an alarm, for example, by a buzzer sound, a voice message, a light output, a display of information, etc. The alarm unit 3 includes, for example, a speaker, a light emitting part, a display screen, etc.

[0020] The power supply unit 4 supplies power to each part of the gas detection device 100. The power supply unit 4 includes a power conversion circuit connected to a commercial power supply. Also, the power supply unit 4 may be, for example, a battery.

[0021] As shown in FIG. 2, the sensor unit 2 includes a gas sensor 21, a constant voltage circuit unit 22, and a signal output unit 23. The gas sensor 21 includes a working electrode 21a and a counter electrode 21b.

[0022] As shown in FIG. 2, the gas sensor 21 can be represented as a circuit having a resistance component Rs, a capacitance component Cp, and a resistance component Rp. That is, each element of the gas sensor 21 as a circuit can be considered to be arranged as follows. The resistance component Rs is arranged on the working electrode 21a side and is connected in series with the capacitance component Cp and the resistance component Rp connected in parallel. The capacitance component Cp and the resistance component Rp connected in parallel are arranged on the counter electrode 21b side.

[0023] Also, a resistor R3 is provided in parallel with the gas sensor 21. Also, a resistor R4 is connected to the working electrode 21a side of the gas sensor 21. Also, a resistor R5 is connected to the counter electrode 21b side of the gas sensor 21.

[0024] The constant voltage circuit unit 22 generates a reference voltage for the sensor unit 2. The constant voltage circuit unit 22 is connected to the counter electrode 21b side of the gas sensor 21 as shown in FIG. 2. The constant voltage circuit unit 22 includes a resistor R1, a resistor R2, a capacitor C1, a capacitor C2, and an OP amplifier U1. The resistor R1 is connected to the voltage VCC supplied from the power supply unit 4. The resistor R2 is connected in series with the resistor R1 and is connected to the ground potential. The capacitor C1 is connected in parallel with the resistor R2 and in series with the resistor R1 and is connected to the ground potential. The OP amplifier U1 has its plus side connected between the resistors R1 and R2, and its minus side connected to the output. The capacitor C2 is connected between the voltage VCC of the OP amplifier U1 and the ground potential.

[0025] The signal output unit 23 is connected to the gas sensor 21 and outputs a detection signal based on the power input from the gas sensor 21. The signal output unit 23 converts current into voltage and outputs a detection signal. As shown in FIG. 2, the signal output unit 23 includes a resistor R6, a resistor R7, a resistor R9, a capacitor C3, a capacitor C4, and an OP amplifier U2. The resistor R6 is connected to the working electrode 21a side of the gas sensor 21 and also connected to the minus side of the OP amplifier U2. The resistor R7 is connected to the counter electrode 21b side of the gas sensor 21 and also connected to the plus side of the OP amplifier U2. The resistor R9 and the capacitor C3 are connected in parallel to the working electrode 21a side of the gas sensor 21, together with the resistor R6 and the OP amplifier U2. The capacitor C4 is connected between the voltage VCC of the OP amplifier U2 and the ground potential.

[0026] A resistor R8 is connected between the resistor R7 and the plus side of the OP amplifier U2. The switch Q1 is connected to the resistor R8. The switch Q1 can be switched between an on state in which current flows from the resistor R8 side to the ground potential according to the on-off control signal from the control unit 1, and an off state in which no current flows from the resistor R8 side to the ground potential.

[0027] A resistor R10 is connected to the output side of the OP amplifier U2. The detection signal is output from the resistor R10 to the control unit 1. Specifically, the detection signal is amplified by an amplifier circuit and then input to the control unit 1. Also, a capacitor C5 is connected between the resistor R10 and the ground potential.

[0028] The switch Q1 switches the circuit between a charging state in which charges are stored between the working electrode 21a and the counter electrode 21b of the gas sensor 21 and a discharging state in which the charges between the working electrode 21a and the counter electrode 21b of the gas sensor 21 are released. Specifically, when the switch Q1 is in the on state, it is in a charging state in which charges are stored between the working electrode 21a and the counter electrode 21b of the gas sensor 21. Also, when the switch Q1 is in the off state, it is in a discharging state in which the charges between the working electrode 21a and the counter electrode 21b of the gas sensor 21 are released. Also, when detecting gas, the switch Q1 is in the off state.

[0029] As shown in FIG. 3, when the switch Q1 is in the off state before charging, the gas sensor 21 usually has no current flowing when there is no gas to be detected. Since no current is flowing through the gas sensor 21 before charging, due to the action of negative feedback of the operational amplifier U2, the working electrode 21a and the counter electrode 21b are at the same potential. That is, the capacitive component Cp is in a state without charge.

[0030] As shown in FIG. 4, when the switch Q1 is turned on for charging, the resistor R8 is connected to the ground potential, and the voltage on the positive side of the operational amplifier U2 is pulled down (in+ < in-). That is, the voltage on the positive side of the operational amplifier U2 becomes the voltage obtained by dividing the reference voltage Vref by the resistors R7 and R8. As a result, the balance of the input terminal voltage of the operational amplifier U2 is disrupted, and the output voltage of the operational amplifier U2 decreases.

[0031] As a result, a current flows through the path of reference voltage Vref → resistor R5 → capacitive component Cp / / resistive component Rp → resistive component Rs → resistor R4 → capacitor C3 / / resistor R9 → the output side of the operational amplifier U2. As a result, a potential difference is generated in the capacitive component Cp of the gas sensor 21, and the capacitive component Cp is charged.

[0032] As shown in FIG. 5, when the switch Q1 is turned off for discharging after charging, the resistor R8 becomes open, and the voltage on the positive side of the operational amplifier U2 returns to the original reference voltage Vref. As a result, since the potential on the negative side of the operational amplifier U2 has decreased due to charging (in+ > in-), the voltage on the output side of the operational amplifier U2 increases. As a result, a current flows through the path of the output side of the operational amplifier U2 → capacitor C3 / / resistor R9 → resistor R4 → resistive component Rs → capacitive component Cp / / resistive component Rp → resistor R5 → reference voltage Vref. As a result, the potential difference of the gas sensor 21 gradually disappears. As the elimination of the potential difference of the gas sensor 21 progresses, the output voltage from the operational amplifier U2 gradually decreases and finally converges to the state before charging.

[0033] As shown in FIG. 6, charging starts at time T0, and then, at time T1, it is switched from charging to discharging. When charging starts, the detection signal drops to 0V. Then, when it is switched from charging to discharging, the detection signal rises, exceeds the voltage before charging, and then converges to the voltage before charging.

[0034] Also, as shown in FIG. 7, due to individual differences, the reference voltage of the gas sensor 21 may be different. In this case, when discharging after charging, the detection signal converges to the reference voltage after exceeding the reference voltage which is the voltage before charging.

[0035] Also, as shown in FIG. 8, due to individual differences, when discharging after charging, the return of the voltage of the gas sensor 21 may be slow. That is, for the gas sensor 21, the time until the voltage returns after discharging after charging may vary due to individual differences.

[0036] Also, as shown in FIG. 9, when the gas sensor 21 fails due to sensor open, since the capacitance component Cp disappears, even if the switch Q1 is turned on, the gas sensor 21 is not charged. That is, when the gas sensor 21 fails due to sensor open, even if the switch Q1 is turned on and the voltage on the output side of the OP amplifier U2 drops to draw current, the gas sensor 21 is not charged. Also, since the gas sensor 21 is not charged, even if the switch Q1 is switched from the on state to the off state, the voltage of the detection signal does not rise significantly.

[0037] That is, when the gas sensor 21 fails due to sensor open, as shown in FIG. 10, even if the switch Q1 is turned on at time T0, the detection signal does not drop to 0V. Also, even if the switch Q1 is turned off at time T1, the detection signal does not exceed the original voltage and converges to the original voltage.

[0038] Also, as shown in FIG. 11, when the gas sensor 21 fails due to a sensor short circuit, the capacitive component Cp disappears. Therefore, even if the switch Q1 is turned on, the gas sensor 21 cannot be charged. That is, when the gas sensor 21 fails due to a sensor short circuit, even if the switch Q1 is turned on and the voltage on the output side of the OP amplifier U2 drops to draw current, the gas sensor 21 cannot be charged. Also, since the gas sensor 21 is not charged, even if the switch Q1 is switched from the on state to the off state, the voltage of the detection signal does not increase significantly.

[0039] That is, when the gas sensor 21 fails due to a sensor short circuit, as shown in FIG. 12, when the switch Q1 is turned on at time T0, the detection signal drops to 0V. Then, even when the switch Q1 is turned off at time T1, the detection signal does not exceed the original voltage and converges to the original voltage.

[0040] Here, in the present embodiment, the control unit 1 determines whether the gas sensor 21 is faulty based on the output of the detection signal acquired after the discharge of the gas sensor 21 and a predetermined threshold value based on the output of the detection signal before charging the gas sensor 21. Specifically, the control unit 1 determines that the gas sensor 21 is faulty based on the fact that the output of the detection signal acquired after charging and then discharging the gas sensor 21 is equal to or less than a predetermined threshold value based on the output of the detection signal before charging the gas sensor 21.

[0041] That is, the control unit 1 sets a predetermined threshold value based on the detection signal before charging the gas sensor 21. For example, as shown in FIG. 7, the control unit 1 sets a predetermined threshold value based on the detection signal before charging. In FIG. 7, in the case of the gas sensor 21 having a broken line waveform with a relatively small value of the detection signal before charging, a predetermined threshold value Th1 is set based on the detection signal before charging. Also, in the case of the gas sensor 21 having a solid line waveform with a relatively large value of the detection signal before charging, a predetermined threshold value Th2 (Th2 > Th1) is set based on the detection signal before charging.

[0042] Further, the control unit 1 sets a value larger than the detection signal before charging the gas sensor 21 as a predetermined threshold value. For example, the control unit 1 sets, as the predetermined threshold value, a value obtained by adding a uniform numerical value to the detection signal before charging. Further, the control unit 1 sets, as the predetermined threshold value, a value obtained by increasing the detection signal before charging by a predetermined ratio (for example, about 1% to 10%).

[0043] Also, in the present embodiment, the control unit 1 performs a failure diagnosis of the gas sensor 21 based on the detection signal from the signal output unit 23 when switching the charging (on state) and discharging (off state) of the gas sensor 21 by the switch Q1. Specifically, the control unit 1 acquires a plurality of detection signals after discharging the gas sensor 21 at different times, and determines whether the gas sensor 21 is faulty based on all the detection signals. Specifically, the control unit 1 determines that the gas sensor 21 is faulty based on the fact that all the acquired detection signals are below a predetermined threshold value.

[0044] For example, as shown in FIG. 6, the control unit 1 acquires detection signals at times T2, T3, and T4 after charging and then discharging. In the example shown in FIG. 6, between time T1 and time T2 after charging and then discharging, the value of the detection signal exceeds a predetermined threshold value Th1. That is, the detection signal exceeds the predetermined threshold value Th1 at times T2, T3, and T4. In this case, the control unit 1 determines that the gas sensor 21 is normal.

[0045] Also, in the example shown in FIG. 10, after charging (switch Q1 in the on state) and then discharging (switch Q1 in the off state), the detection signal does not exceed the predetermined threshold value Th1. That is, the detection signal is below the predetermined threshold value Th1 at any of times T2, T3, and T4. In this case, the control unit 1 determines that the gas sensor 21 is faulty.

[0046] Also, in the case of the example shown in FIG. 12, after charging (switch Q1 is in the ON state) and then discharging (switch Q1 is in the OFF state), the detection signal does not exceed a predetermined threshold Th1. That is, the detection signal is equal to or less than the predetermined threshold Th1 at any of times T2, T3, and T4. In this case, the control unit 1 determines that the gas sensor 21 is malfunctioning.

[0047] Also, when the control unit 1 charges the gas sensor 21 and the detection signal obtained after discharging exceeds a predetermined threshold, the control unit 1 may determine that the gas sensor 21 is normal and stop acquiring detection signals for subsequent fault diagnosis. For example, in the example shown in FIG. 6, the control unit 1 acquires a detection signal at time T2 after charging and then discharging. Since the detection signal acquired by the control unit 1 at time T2 exceeds the predetermined threshold Th1, the control unit 1 determines that the gas sensor 21 is normal. Further, the control unit 1 does not acquire detection signals for fault diagnosis at subsequent times T3 and T4. Also, in the example shown in FIG. 8, the control unit 1 acquires a detection signal at time T2 after charging and then discharging. Since the detection signal acquired by the control unit 1 at time T2 is equal to or less than the predetermined threshold Th1, the control unit 1 acquires a detection signal at time T3 after charging and then discharging. Since the detection signal acquired by the control unit 1 at time T3 exceeds the predetermined threshold Th1, the control unit 1 determines that the gas sensor 21 is normal. Further, the control unit 1 does not acquire detection signals for fault diagnosis at the subsequent time T4.

[0048] Also, the control unit 1 acquires detection signals at every predetermined interval after charging the gas sensor 21, and determines whether the gas sensor 21 is normal or malfunctioning based on the plurality of acquired detection signals. Specifically, as shown in FIG. 6, the control unit 1 acquires detection signals at every time interval Ta starting from the start of discharging. For example, the time interval Ta is about 0.1 second to several seconds. Preferably, the time interval Ta is about 1 second.

[0049] Further, after charging the gas sensor 21, the control unit 1 acquires detection signals at predetermined intervals longer than the time for charging the gas sensor 21 after discharging, and determines whether the gas sensor 21 is normal or faulty based on the plurality of acquired detection signals. For example, the control unit 1 acquires detection signals for determining a fault at predetermined time intervals about several to several tens of times the charging time.

[0050] Further, after charging the gas sensor 21, the control unit 1 acquires detection signals at three or more different times after discharging, and determines whether the gas sensor 21 is normal or faulty based on the three or more acquired detection signals. For example, as shown in FIG. 6, the control unit 1 acquires detection signals for determining a fault at three different times T2, T3, and T4 after discharging.

[0051] Also, in the present embodiment, at a first time point, the control unit 1 acquires a first difference, which is a difference between a detection signal exceeding a predetermined threshold value after discharging and the predetermined threshold value, after charging the gas sensor 21. Specifically, at the first time point, the control unit 1 acquires a first difference, which is a difference between a detection signal exceeding a predetermined threshold value and the predetermined threshold value, among the plurality of detection signals acquired at different times after discharging after charging the gas sensor 21. Further, at a second time point after the first time point, the control unit 1 acquires a second difference, which is a difference between a detection signal exceeding a predetermined threshold value after discharging and the predetermined threshold value, after charging the gas sensor 21. Specifically, at the second time point after the first time point, the control unit 1 acquires a second difference, which is a difference between a detection signal exceeding a predetermined threshold value and the predetermined threshold value, among the plurality of detection signals acquired at different times after discharging after charging the gas sensor 21. Then, the control unit 1 compares the first difference and the second difference to determine the deterioration state of the gas sensor 21.

[0052] For example, as shown in FIG. 13, when the failure determination is first made at time point A1, then at time point A2, and then at time point A3, over time, the return of the detection signal after discharge may become slower. Therefore, the deterioration state is determined by comparing the differences exceeding a predetermined threshold at each time point. Note that the time points for determining the failure are, for example, time points every one day to several months.

[0053] In the example shown in FIG. 13, at time point A1, at time T2, since the detection signal exceeds the predetermined threshold Th1, the difference at time T2 is acquired. At time point A2, at time T2, since the detection signal exceeds the predetermined threshold Th1, the difference at time T2 is acquired. At time point A3, at time T3, since the detection signal exceeds the predetermined threshold Th1, the difference at time T3 is acquired.

[0054] The control unit 1 determines the deterioration state of the gas sensor 21, for example, based on the change rate or change amount of the difference at each time point.

[0055] Further, the control unit 1 sets a predetermined threshold according to the charging time during the failure diagnosis of the gas sensor 21. Specifically, the control unit 1 changes the charging time during the failure diagnosis according to the state of the gas sensor 21. Then, when the charging time is long, the control unit 1 sets a large predetermined threshold based on the detection signal before charging, and when the charging time is short, the control unit 1 sets a small predetermined threshold based on the detection signal before charging.

[0056] Also, when the detection signal acquired after discharging the gas sensor 21 after charging is near the predetermined threshold, the control unit 1 may increase the charging time and perform the failure diagnosis again. For example, when the detection signal after discharging during the failure diagnosis is approximately equal to the predetermined threshold and the detection signal is a value such that it exceeds or does not exceed the predetermined threshold, the control unit 1 increases the charging time and performs the failure diagnosis again.

[0057] Further, when the detection signal satisfies a predetermined condition, the control unit 1 does not perform a failure diagnosis of the gas sensor 21. For example, the control unit 1 may not perform a failure diagnosis of the gas sensor 21 when the detection signal detects a gas at the alarm level. That is, in the gas detection device 100 of the present embodiment, it is possible to perform a failure diagnosis of the gas sensor 21 regardless of the atmosphere. However, for example, from the viewpoint of user protection, the alarm may be prioritized, or the diagnosis may not be performed in consideration of the load on the gas sensor 21. Further, the control unit 1 may not perform a failure diagnosis of the gas sensor 21 when the output of the detection signal reaches a predetermined value once or a plurality of times within a predetermined period. Further, the control unit 1 may not perform a failure diagnosis when the output of the detection signal maintains a value equal to or greater than a predetermined value for a predetermined period.

[0058] Further, the control unit 1 detects the gas to be detected based on the cumulative value of the detection signals other than during the failure diagnosis. That is, when detecting the gas to be detected, the control unit 1 starts detecting the gas in a reset state when the detection signal during the failure diagnosis is accumulated.

[0059] (Effect of the present embodiment) In the present embodiment, the following effects can be obtained.

[0060] Further, in the present embodiment, as described above, based on the output of the detection signal acquired after the discharge of the gas sensor 21 and a predetermined threshold value based on the output of the detection signal before charging the gas sensor 21, a control unit 1 for determining whether the gas sensor 21 is faulty is provided. Thereby, even when the output voltage during charging and discharging of the gas sensor 21 varies due to the presence of the gas to be detected in the atmosphere, a predetermined threshold value can be set based on the output of the detection signal before charging the gas sensor 21. As a result, when the gas sensor 21 is charged and then discharged, the output of the detection signal returns to the value before charging, so that a predetermined threshold value for performing a failure diagnosis can be set to an appropriate value according to the atmosphere. As a result, the failure of the gas sensor 21 can be accurately diagnosed regardless of the atmosphere.

[0061] Further, in the present embodiment, as described above, the control unit 1 sets a value larger than the output of the detection signal before charging the gas sensor 21 as a predetermined threshold value. Thereby, by setting the predetermined threshold value to a value larger than the detection signal before charging, it is possible to ensure that the output of the detection signal does not exceed the predetermined threshold value in the case of a failure, so that it is possible to accurately determine whether or not there is a failure.

[0062] Further, in the present embodiment, as described above, a plurality of outputs of the detection signal after the discharge of the gas sensor 21 are acquired at different times, and based on the outputs of all the detection signals, it is determined whether or not the gas sensor 21 is malfunctioning. Thereby, even when there is a variation in the time until the output voltage of the gas sensor 21 exceeds the threshold value during charging and discharging due to individual differences in the gas sensor 21, the outputs of a plurality of detection signals are acquired at different times after discharge, and when the outputs of all the detection signals are equal to or less than a predetermined threshold value, it is diagnosed as a failure. Therefore, even when there are individual differences in the gas sensor 21, it is possible to accurately diagnose the failure of the gas sensor 21.

[0063] Further, in the present embodiment, as described above, the control unit 1 acquires the output of the detection signal after the discharge of the gas sensor 21 at predetermined intervals, and based on the outputs of the plurality of acquired detection signals, determines whether the gas sensor 21 is normal or malfunctioning. Thereby, since the output of the detection signal is acquired at predetermined intervals after discharge, it is possible to reduce an increase in the processing load as compared with the case where the output of the detection signal is continuously acquired after discharge. Further, even when there is a variation in the time until the output of the detection signal exceeds the threshold value after discharge due to individual differences in the gas sensor 21, it is possible to accurately diagnose the failure of the gas sensor 21 by acquiring the output of the detection signal at predetermined intervals.

[0064] Also, in the present embodiment, as described above, the control unit 1 acquires the output of the detection signal at predetermined intervals longer than the time for charging the gas sensor 21, and determines whether the gas sensor 21 is normal or faulty based on the outputs of the plurality of acquired detection signals. Thereby, since the output of the detection signal after discharging is acquired at a sufficient time interval longer than the charging time, it is possible to further reduce the increase in the processing load compared to the case where the output of the detection signal is acquired at short time intervals.

[0065] Also, in the present embodiment, as described above, the control unit 1 acquires the output of the detection signal at three or more different times, and determines whether the gas sensor 21 is normal or faulty based on the outputs of the three or more acquired detection signals. Thereby, since the output of the detection signal is acquired at three or more timings, it is possible to acquire the output of the detection signal after discharging over a relatively long period and determine a fault.

[0066] Also, in the present embodiment, as described above, the control unit 1 does not perform a fault diagnosis of the gas sensor 21 when the output of the detection signal satisfies a predetermined condition. Thereby, when the output of the detection signal satisfies a predetermined condition, no fault diagnosis is performed, so it is possible to suppress the detection of the gas to be detected from being interrupted during the fault diagnosis.

[0067] Also, in the present embodiment, as described above, the control unit 1 detects the gas to be detected based on the cumulative value of the output of the detection signal other than during the fault diagnosis. Thereby, since the values of the output of the detection signal during charging and discharging during the fault diagnosis are not accumulated, it is possible to suppress the misdetection of the gas to be detected.

[0068] (Modification example) It should be considered that the embodiment disclosed this time is illustrative in all respects and not restrictive. The scope of the present invention is shown not by the description of the above-described embodiment but by the claims, and further includes all changes (modification examples) within the meaning and scope equivalent to the claims.

[0069] For example, in the above embodiment, an example in which one gas sensor is provided in the gas detection device is shown, but the present invention is not limited thereto. In the present invention, a plurality of gas sensors for detecting gases with different detection targets may be provided in the gas detection device. In this case, the control unit may perform the diagnosis of the present invention on at least one gas sensor.

[0070] Further, the gas detection device may be provided with other alarm functions. For example, the gas detection device may be provided with a fire alarm (fire notification) function.

[0071] Also, in the above embodiment, an example in which detection signals are acquired at a plurality of different times after charging and discharging when diagnosing the gas sensor is shown, but the present invention is not limited thereto. In the present invention, a detection signal may be acquired at a certain one time after charging and discharging.

[0072] Also, in the above embodiment, an example in which detection signals are acquired at three different times after charging and discharging when diagnosing the gas sensor is shown, but the present invention is not limited thereto. In the present invention, detection signals may be acquired at two or a plurality of four or more different times after charging and discharging.

[0073] Also, in the above embodiment, an example in which detection signals are acquired at predetermined intervals after charging and discharging when diagnosing the gas sensor is shown, but the present invention is not limited thereto. In the present invention, when diagnosing the gas sensor, a plurality of detection signals may be acquired continuously after charging and discharging. Also, when diagnosing the gas sensor, detection signals may be acquired at different time intervals after charging and discharging.

[0074] In addition, in the above-described embodiment, an example of a configuration for determining that the gas sensor is malfunctioning is shown based on the fact that the output of the gas sensor after discharge is equal to or less than a predetermined threshold value based on the output of the gas sensor before charging. However, the present invention is not limited to this. In the present invention, it may be determined that the gas sensor is malfunctioning based on the fact that the output of the gas sensor after discharge is equal to or greater than a predetermined threshold value based on the output of the gas sensor before charging. For example, when the output increases due to charging of the gas sensor and decreases due to discharge, if the output of the gas sensor after discharge does not become smaller than the threshold value, it may be determined that the gas sensor is malfunctioning.

[0075] In addition, a predetermined range may be set from a predetermined threshold value based on the output of the gas sensor before charging, and it may be determined that there is a malfunction when the output of the gas sensor after discharge is within or outside the predetermined range.

Explanation of Reference Numerals

[0076] 1 Control unit 21 Gas sensor 21a Working electrode 21b Counter electrode 100 Gas detection device

Claims

Claim 1 In a diagnostic method for performing failure diagnosis of a gas sensor based on an output from the gas sensor when switching between a charged state of storing charge in the gas sensor including a working electrode and a counter electrode and a discharged state of discharging the charge stored in the gas sensor, a diagnostic method for a gas sensor, which determines whether the gas sensor is faulty based on the output obtained after discharging of the gas sensor and a predetermined threshold value based on the output before charging the gas sensor. Claim 2 a step of obtaining an output from the gas sensor before charging the gas sensor including a working electrode and a counter electrode to store charge; a step of determining a threshold value based on the output before charging the gas sensor; a step of obtaining an output after discharging the charge stored in the gas sensor; and a step of determining whether the gas sensor is faulty based on the threshold value and the output after discharging of the gas sensor.

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