Gas detecting device and method for diagnosing gas sensor

Abstract

A gas detecting device 100 comprises a control unit 1 that performs failure diagnosis of a gas sensor 21 including a working electrode 21a and a counter electrode 21b on the basis of outputs from the gas sensor 21 when switching between a charging state in which electric charge is stored in the gas sensor 21 and a discharging state in which the electric charge accumulated in the gas sensor 21 is discharged. Then, the control unit 1 determines whether or not the gas sensor 21 has failed, on the basis of the output acquired after the gas sensor 21 is discharged and a predetermined threshold value based on the output before the gas sensor 21 is charged.

Description

Gas detection device and gas sensor diagnostic method

[0001] The present invention relates to a gas detection device and a gas sensor diagnostic method, and more particularly to a gas detection device and a gas sensor diagnostic method for diagnosing a fault in a gas sensor.

[0002] A gas detection device that performs a fault diagnosis on a gas sensor is known, for example, as disclosed in Japanese Patent Application Laid-Open No. 2011-085455.

[0003] Japanese Patent Application Laid-Open Publication No. 2011-085455 discloses an alarm (gas detection device) including a gas sensor including a sensing electrode and a counter electrode, a current / voltage conversion circuit that converts the current flowing through the gas sensor into a voltage, and self-diagnosis means that performs fault diagnosis of the gas sensor based on the output voltage of the current / voltage conversion circuit. In the alarm disclosed in Japanese Patent Application Laid-Open Publication No. 2011-085455, the self-diagnosis means accumulates an electric charge between the sensing electrode and the counter electrode of the gas sensor, charges it, and then discharges it, and performs fault diagnosis of the gas sensor based on the output voltage of the current / voltage conversion circuit at that time. The self-diagnosis means also performs fault diagnosis of the gas sensor by comparing the output voltage of the current / voltage conversion circuit at preset points during charging and discharging of the gas sensor with a preset threshold value.

[0004] JP 2011-085455 A

[0005] In the above-mentioned Japanese Patent Application Laid-Open No. 2011-085455, the self-diagnosis means diagnoses a gas sensor failure by comparing the output voltage of the current / voltage conversion circuit at predetermined times during charging and discharging of the gas sensor with a predetermined threshold value. Therefore, if the output voltage of the gas sensor during charging and discharging varies due to the presence of the gas to be detected in the atmosphere, the magnitude relationship with the predetermined threshold value will change. Therefore, the results of the gas sensor failure diagnosis may vary depending on the atmospheric conditions, making it difficult to accurately diagnose a gas sensor failure.

[0006] The present invention has been made to solve the above-mentioned problems, and one object of the present invention is to provide a gas detection device and a gas sensor diagnostic method that are capable of accurately diagnosing gas sensor failures regardless of the atmosphere.

[0007] In order to achieve the above object, a gas detection device according to a first aspect of the present invention includes a control unit that performs a fault diagnosis of the gas sensor based on the output from the gas sensor when switching between a charging state in which a charge is stored in a gas sensor including a working electrode and a counter electrode, and a discharging state in which the charge stored in the gas sensor is released, and the control unit determines whether the gas sensor has failed 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] As described above, the gas detection device according to the first aspect of the present invention includes a control unit that determines whether the gas sensor is malfunctioning based on the output obtained after discharging the gas sensor and a predetermined threshold value based on the output before charging the gas sensor. This allows the predetermined threshold value to be set based on the output of the gas sensor before charging, even if the presence of the gas to be detected in the atmosphere causes variations in the output voltage of the gas sensor during charging and discharging. This allows the output of the gas sensor to return to the value before charging when the gas sensor is charged and then discharged, so the predetermined threshold value for malfunction diagnosis can be set to an appropriate value depending on the atmosphere. As a result, malfunction of the gas sensor can be accurately diagnosed regardless of the atmosphere.

[0009] In the gas detection device according to the first aspect, the control unit preferably sets the predetermined threshold value to a value greater than the output of the gas sensor before charging. By setting the predetermined threshold value to a value greater than the output of the gas sensor before charging, it is possible to reliably prevent the output from exceeding the predetermined threshold value in the event of a malfunction, thereby making it possible to accurately determine whether or not a malfunction has occurred.

[0010] In the gas detection device according to the first aspect, the control unit preferably acquires a plurality of outputs from the gas sensor at different times after discharge and determines whether the gas sensor has malfunctioned based on all of the outputs. With this configuration, even if there is variation in the time it takes for the output voltage of the gas sensor to exceed the threshold value during charging and discharging due to individual differences between gas sensors, the control unit acquires a plurality of outputs at different times after discharge and diagnoses the gas sensor as malfunctioning if all of the outputs are below the predetermined threshold value, thereby making it possible to accurately diagnose a malfunction of the gas sensor even when there is individual difference between gas sensors.

[0011] In the gas detection device configured to determine whether the gas sensor is malfunctioning based on all of the multiple outputs acquired at different times, the control unit preferably acquires the post-discharge output of the gas sensor at predetermined intervals and determines whether the gas sensor is malfunctioning or malfunctioning based on the multiple acquired outputs. This configuration reduces the processing load compared to acquiring the output continuously after discharge, because the output is acquired at predetermined intervals after discharge. Furthermore, even if the time it takes for the output to exceed the threshold after discharge varies due to individual differences between gas sensors, acquiring the output at predetermined intervals allows for accurate diagnosis of gas sensor malfunction.

[0012] In this case, the control unit preferably acquires the output at predetermined intervals longer than the time it takes to charge the gas sensor, and determines whether the gas sensor is normal or malfunctioning based on the acquired multiple outputs. With this configuration, the post-discharge output is acquired at sufficient intervals longer than the charging time, which can further reduce the processing load compared to when many outputs are acquired at short intervals.

[0013] In the gas detection device configured to determine whether the gas sensor is malfunctioning based on all of the multiple outputs acquired at different times, the control unit preferably acquires outputs at three or more different times and determines whether the gas sensor is malfunctioning or not based on the three or more acquired outputs. With this configuration, since outputs are acquired at three or more different times, it is possible to acquire outputs after discharge over a relatively long period of time and determine whether the gas sensor is malfunctioning.

[0014] In the gas detection device according to the first aspect, the control unit preferably does not perform a fault diagnosis of the gas sensor when the output satisfies a predetermined condition. With this configuration, the fault diagnosis is not performed when the output satisfies the predetermined condition, so that it is possible to prevent the detection of the target gas from being interrupted while the fault diagnosis is being performed.

[0015] In the gas detection device according to the first aspect, the control unit preferably detects the target gas based on a cumulative value of the output other than during fault diagnosis. With this configuration, the output values ​​during charging and discharging during fault diagnosis are not accumulated, thereby making it possible to prevent erroneous detection of the target gas.

[0016] A gas sensor diagnostic method according to a second aspect of the present invention is a diagnostic method for diagnosing a gas sensor for malfunction based on an output from the gas sensor when switching between a charging state in which a charge is stored in a gas sensor including a working electrode and a counter electrode, and a discharging state in which the charge stored in the gas sensor is released, and determines whether the gas sensor is malfunctioning based on the output obtained after discharging the gas sensor and a predetermined threshold value based on the output before charging the gas sensor.

[0017] In the gas sensor diagnostic method according to the second aspect of the present invention, as described above, whether or not the gas sensor is faulty is determined based on the output obtained after the gas sensor is discharged and a predetermined threshold value based on the output before the gas sensor is charged. This allows the predetermined threshold value to be set based on the output of the gas sensor before charging, even if the output voltage of the gas sensor varies between charging and discharging due to the presence of a gas to be detected in the atmosphere. This allows the output of the gas sensor to return to the value before charging when the gas sensor is charged and then discharged, so the predetermined threshold value for fault diagnosis can be set to an appropriate value depending on the atmosphere. As a result, gas sensor faults can be accurately diagnosed regardless of the atmosphere.

[0018] In the gas sensor diagnostic method according to the second aspect, it is preferable to determine whether or not the gas sensor has failed based on an output obtained after discharging the gas sensor and a predetermined threshold value based on the output before charging the gas sensor, thereby diagnosing the gas detection device including the gas sensor. This makes it possible to accurately diagnose a gas sensor failure and diagnose the gas detection device including the gas sensor regardless of the atmosphere.

[0019] A method for diagnosing a gas sensor according to a third aspect of the present invention includes the steps of: acquiring an output from a gas sensor including a working electrode and a counter electrode before the gas sensor is charged by storing an electric charge in the gas sensor; determining a threshold value based on the output from the gas sensor before charging; acquiring an output after discharging the electric charge stored in the gas sensor; and determining whether or not the gas sensor is faulty based on the threshold value and the output from the gas sensor after discharging.

[0020] As described above, the gas sensor diagnostic method according to the third aspect of the present invention includes a step of determining whether the gas sensor is faulty based on a threshold value determined based on the output of the gas sensor before charging and on the output of the gas sensor after discharging. This allows the threshold value to be set based on the output of the gas sensor before charging, even if the output voltage of the gas sensor varies between charging and discharging due to the presence of a detection target gas in the atmosphere. This allows the output of the gas sensor to return to the value before charging when the gas sensor is charged and then discharged, so the threshold value for fault diagnosis can be set to an appropriate value depending on the atmosphere. As a result, a gas sensor diagnostic method can be provided that can accurately diagnose gas sensor faults regardless of the atmosphere.

[0021] According to the present invention, as described above, it is possible to accurately diagnose a failure in a gas sensor regardless of the atmosphere.

[0022] FIG. 1 is a block diagram showing the configuration of a gas detection device according to an embodiment. FIG. 2 is a diagram showing an example of an electrical circuit of a sensor unit of a gas detection device according to an embodiment. FIG. 3 is a diagram showing an electrical circuit before charging during diagnosis of a gas sensor according to an embodiment. FIG. 4 is a diagram showing an electrical circuit during charging during diagnosis of a gas sensor according to an embodiment. FIG. 5 is a diagram showing an electrical circuit during discharging during diagnosis of a gas sensor according to an embodiment. FIG. 6 is a diagram showing an example of the waveform of a detection signal during diagnosis when a gas sensor according to an embodiment is normal. FIG. 7 is a diagram showing an example of the waveform of a detection signal during diagnosis when a reference voltage of a gas sensor according to an embodiment is different. FIG. 8 is a diagram showing an example of the waveform of a detection signal during diagnosis when a detection signal returns slowly during diagnosis when a gas sensor according to an embodiment is normal. FIG. 9 is a diagram showing an electrical circuit when an open circuit failure occurs in a gas sensor according to an embodiment. FIG. 10 is a diagram showing an example of the waveform of a detection signal during diagnosis when an open circuit failure occurs in a gas sensor according to an embodiment. FIG. 11 is a diagram showing an electrical circuit when a short circuit failure occurs in a gas sensor according to an embodiment. FIG. 12 is a diagram showing an example of the waveform of a detection signal during diagnosis when a short circuit failure occurs in a gas sensor according to an embodiment. FIG. 13 is a diagram showing an example of the waveform of a detection signal during diagnosis due to aging of a gas sensor according to an embodiment.

[0023] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0024] The configuration of a gas detection device 100 according to one embodiment will be described with reference to FIGS.

[0025] (Configuration of Alarm System) As shown in FIG. 1, gas detection device 100 is configured to detect a target gas and issue an alarm.

[0026] As shown in FIG. 1, gas detection device 100 includes a control unit 1, a sensor unit 2, an alarm unit 3, and a power supply unit 4.

[0027] Control unit 1 is configured to control each unit of gas detection device 100. Control unit 1 also includes a processor such as an MCU (Micro Controller Unit) that executes programs and performs processing, and a memory that stores the programs.

[0028] The sensor unit 2 is configured to detect a target gas. The sensor unit 2 detects target gases such as CO gas, methane gas, and propane gas. The sensor unit 2 includes an electrochemical gas sensor. When the target gas is present, the sensor unit 2 detects the gas by detecting a change in output voltage.

[0029] The alarm unit 3 is configured to issue an alarm to the surrounding area when the target gas is detected by the sensor unit 2. The alarm unit 3 issues the alarm, for example, by a buzzer sound, a voice message, optical output, or information display. The alarm unit 3 includes, for example, a speaker, a light-emitting unit, a display screen, etc.

[0030] Power supply unit 4 supplies power to each component of gas detection device 100. Power supply unit 4 includes a power conversion circuit connected to a commercial power source. Power supply unit 4 may also be, for example, a battery.

[0031] 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.

[0032] 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, the elements of the circuit of the gas sensor 21 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, which are connected in parallel. The capacitance component Cp and the resistance component Rp, which are connected in parallel, are arranged on the counter electrode 21b side.

[0033] A resistor R3 is connected in parallel to the gas sensor 21. A resistor R4 is connected to the working electrode 21a side of the gas sensor 21. A resistor R5 is connected to the counter electrode 21b side of the gas sensor 21.

[0034] The constant voltage circuit 22 generates a reference voltage for the sensor unit 2. As shown in FIG. 2, the constant voltage circuit 22 is connected to the counter electrode 21b of the gas sensor 21. The constant voltage circuit 22 includes resistors R1, R2, capacitors C1, C2, and an operational amplifier U1. The resistor R1 is connected to a voltage VCC supplied from the power supply 4. The resistor R2 is connected in series with the resistor R1 and is also connected to ground potential. The capacitor C1 is connected in parallel with the resistor R2, in series with the resistor R1, and is also connected to ground potential. The operational amplifier U1 has a positive side connected between the resistors R1 and R2 and a negative side connected to the output. The capacitor C2 is connected between the voltage VCC of the operational amplifier U1 and ground potential.

[0035] 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 a voltage and outputs the detection signal. As shown in FIG. 2 , the signal output unit 23 includes resistors R6, R7, R9, capacitors C3, C4, and an operational amplifier U2. The resistor R6 is connected to the working electrode 21a of the gas sensor 21 and to the negative side of the operational amplifier U2. The resistor R7 is connected to the counter electrode 21b of the gas sensor 21 and to the positive side of the operational amplifier U2. The resistor R9 and capacitor C3 are connected in parallel with the resistor R6 and the operational amplifier U2 on the working electrode 21a of the gas sensor 21. The capacitor C4 is connected between the voltage VCC of the operational amplifier U2 and ground potential.

[0036] A resistor R8 is connected between the resistor R7 and the positive side of the operational amplifier U2. A switch Q1 is connected to the resistor R8. The switch Q1 is switched by an on / off control signal from the control unit 1 between an on state in which a current flows from the resistor R8 side to the ground potential and an off state in which a current does not flow from the resistor R8 side to the ground potential.

[0037] A resistor R10 is connected to the output side of the operational amplifier U2. A 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. A capacitor C5 is also connected between the resistor R10 and the ground potential.

[0038] The switch Q1 switches the circuit between a charging state in which charge is accumulated between the working electrode 21a and the counter electrode 21b of the gas sensor 21 and a discharging state in which charge is released between the working electrode 21a and the counter electrode 21b of the gas sensor 21. Specifically, when the switch Q1 is turned on, the circuit is set to the charging state in which charge is accumulated between the working electrode 21a and the counter electrode 21b of the gas sensor 21. When the switch Q1 is turned off, the circuit is set to the discharging state in which charge is released between the working electrode 21a and the counter electrode 21b of the gas sensor 21. When gas is detected, the switch Q1 is turned off.

[0039] 3, when the switch Q1 is in the off state before charging, no current normally flows through the gas sensor 21 in the absence of a detection target gas. Because no current flows through the gas sensor 21 before charging, the working electrode 21a and the counter electrode 21b are at the same potential due to the negative feedback action of the operational amplifier U2. In other words, the capacitance component Cp is in a state where there is no charge.

[0040] As shown in Figure 4, when switch Q1 is turned on to charge, resistor R8 is connected to ground potential, and the voltage on the positive side of operational amplifier U2 is pulled down (in+<in-). In other words, the voltage on the positive side of operational amplifier U2 becomes the reference voltage Vref divided by resistors R7 and R8. This causes the input terminal voltages of operational amplifier U2 to become unbalanced, and the output voltage of operational amplifier U2 drops.

[0041] As a result, a current flows through the path of the reference voltage Vref, resistor R5, capacitance component Cp, resistance component Rp, resistance component Rs, resistor R4, capacitor C3, resistance R9, and the output side of the operational amplifier U2. As a result, a potential difference occurs across the capacitance component Cp of the gas sensor 21, and the capacitance component Cp is charged.

[0042] As shown in FIG. 5, when switch Q1 is turned off to discharge after charging, resistor R8 opens, and the voltage on the positive side of operational amplifier U2 returns to the original reference voltage Vref. As a result, the potential on the negative side of operational amplifier U2 drops (in+ > in-) due to charging, and the voltage on the output side of operational amplifier U2 rises. This causes current to flow from the output side of operational amplifier U2 to capacitor C3, resistor R9, resistor R4, resistor Rs, capacitor Cp, resistor Rp, resistor R5, and reference voltage Vref. As a result, the potential difference across the gas sensor 21 gradually decreases. As the potential difference across the gas sensor 21 gradually decreases, the output voltage from operational amplifier U2 gradually decreases, eventually converging to the state before charging.

[0043] 6, charging starts at time T0, and then switches from charging to discharging at time T1. When charging starts, the detection signal drops to 0 V. When charging switches from discharging to charging, the detection signal rises, exceeds the voltage before charging, and then converges to the voltage before charging.

[0044] 7, the reference voltage may vary depending on the individual gas sensor 21. In this case, when the gas sensor 21 is discharged after being charged, the detection signal exceeds the reference voltage, which is the voltage before charging, and then converges to the reference voltage.

[0045] 8, the gas sensor 21 may take a long time to recover its voltage when it is discharged after being charged, depending on the individual gas sensor 21. That is, the time it takes for the voltage to recover after being discharged after being charged may vary depending on the individual gas sensor 21.

[0046] 9, if the gas sensor 21 fails due to a sensor open circuit, the capacitance component Cp disappears, and therefore the gas sensor 21 is not charged even if the switch Q1 is turned on. In other words, if the gas sensor 21 fails due to a sensor open circuit, the gas sensor 21 is not charged even if the switch Q1 is turned on and the voltage on the output side of the operational amplifier U2 drops to draw current. Furthermore, because the gas sensor 21 is not charged, the voltage of the detection signal does not increase significantly even if the switch Q1 is switched from the on state to the off state.

[0047] 10, when the gas sensor 21 fails due to an open circuit, the detection signal does not drop to 0 V even when the switch Q1 is turned on at time T0. Furthermore, 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.

[0048] 11, if the gas sensor 21 fails due to a sensor short, the capacitance component Cp disappears, and therefore the gas sensor 21 is not charged even if the switch Q1 is turned on. In other words, if the gas sensor 21 fails due to a sensor short, the gas sensor 21 is not charged even if the switch Q1 is turned on and the voltage on the output side of the operational amplifier U2 drops to draw current. Furthermore, because the gas sensor 21 is not charged, the voltage of the detection signal does not increase significantly even if the switch Q1 is switched from the on state to the off state.

[0049] 12, when the switch Q1 is turned on at time T0, the detection signal drops to 0 V. 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.

[0050] In this embodiment, the control unit 1 determines whether the gas sensor 21 has failed based on the output of the detection signal obtained after discharging 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 has failed based on the output of the detection signal obtained after charging and then discharging the gas sensor 21 being equal to or less than the predetermined threshold value based on the output of the detection signal before charging the gas sensor 21.

[0051] That is, the control unit 1 sets the 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 the predetermined threshold value based on the detection signal before charging. In Fig. 7, in the case of the gas sensor 21 having a relatively small detection signal value before charging, as shown by the dashed line waveform, the predetermined threshold value Th1 is set based on the detection signal before charging. In addition, in the case of the gas sensor 21 having a relatively large detection signal value before charging, as shown by the solid line waveform, the predetermined threshold value Th2 (Th2>Th1) is set based on the detection signal before charging.

[0052] The control unit 1 also sets the predetermined threshold value to a value greater than the detection signal before charging the gas sensor 21. For example, the control unit 1 sets the predetermined threshold value to a value obtained by adding a uniform numerical value to the detection signal before charging. The control unit 1 also sets the predetermined threshold value to a value obtained by increasing the detection signal before charging by a predetermined percentage (for example, about 1% to 10%).

[0053] In this embodiment, the control unit 1 performs a fault diagnosis of the gas sensor 21 based on the detection signal from the signal output unit 23 when the switch Q1 switches between charging (ON state) and discharging (OFF state) of the gas sensor 21. Specifically, the control unit 1 acquires multiple detection signals at different times after discharging the gas sensor 21, and determines whether the gas sensor 21 has a fault based on all of the detection signals. Specifically, the control unit 1 determines that the gas sensor 21 has a fault based on the fact that all of the acquired detection signals are equal to or lower than a predetermined threshold.

[0054] For example, as shown in Fig. 6, the control unit 1 acquires the detection signal at times T2, T3, and T4 after charging and discharging. In the example shown in Fig. 6, the value of the detection signal exceeds the predetermined threshold value Th1 between times T1 and T2 after charging and discharging. In other words, 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.

[0055] 10, after charging (switch Q1 is turned on) and then discharging (switch Q1 is turned off), the detection signal does not exceed the predetermined threshold value Th1. That is, the detection signal is equal to or less than the predetermined threshold value Th1 at all of times T2, T3, and T4. In this case, the control unit 1 determines that the gas sensor 21 is faulty.

[0056] 12, after charging (switch Q1 is turned on) and then discharging (switch Q1 is turned off), the detection signal does not exceed the predetermined threshold value Th1. That is, the detection signal is equal to or less than the predetermined threshold value Th1 at all of times T2, T3, and T4. In this case, the control unit 1 determines that the gas sensor 21 is faulty.

[0057] Furthermore, if the detection signal acquired after charging and discharging the gas sensor 21 exceeds a predetermined threshold, the control unit 1 may determine that the gas sensor 21 is normal and not acquire any further detection signals for 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 discharging. The control unit 1 determines that the gas sensor 21 is normal because the detection signal acquired at time T2 exceeds the predetermined threshold Th1. The control unit 1 also does not acquire any further detection signals for fault diagnosis at subsequent times T3 and T4. In the example shown in FIG. 8 , the control unit 1 acquires a detection signal at time T2 after charging and discharging. The control unit 1 acquires a detection signal at time T3 after charging and discharging because the detection signal acquired at time T2 is equal to or smaller than the predetermined threshold Th1. The control unit 1 also acquires any further detection signals for fault diagnosis at time T4.

[0058] Furthermore, the control unit 1 acquires a detection signal at predetermined intervals after charging the gas sensor 21 and discharging it, and determines whether the gas sensor 21 is normal or malfunctioning based on the acquired detection signals. Specifically, as shown in Fig. 6, the control unit 1 acquires a detection signal at time intervals Ta from the start of discharging. For example, the time interval Ta is approximately 0.1 seconds to several seconds. Preferably, the time interval Ta is approximately 1 second.

[0059] Furthermore, after charging the gas sensor 21 and after discharging it, the control unit 1 acquires detection signals at predetermined intervals that are longer than the time it takes to charge the gas sensor 21, and determines whether the gas sensor 21 is normal or malfunctioning based on the acquired detection signals. For example, the control unit 1 acquires detection signals for determining malfunction at predetermined time intervals that are several to several tens of times the charging time.

[0060] Furthermore, the control unit 1 acquires detection signals at three or more different times after charging and discharging the gas sensor 21, and determines whether the gas sensor 21 is normal or malfunctioning based on the acquired three or more detection signals. For example, as shown in Fig. 6, the control unit 1 acquires detection signals for determining malfunctioning at three different times T2, T3, and T4 after discharging.

[0061] In this embodiment, the control unit 1 acquires, at a first time point, a first difference, which is the difference between a detection signal that exceeds the predetermined threshold after charging and discharging the gas sensor 21 and the predetermined threshold. Specifically, the control unit 1 acquires, at the first time point, the first difference, which is the difference between a detection signal that exceeds the predetermined threshold among a plurality of detection signals acquired at different times after charging and discharging the gas sensor 21 and the predetermined threshold. The control unit 1 also acquires, at a second time point later than the first time point, a second difference, which is the difference between a detection signal that exceeds the predetermined threshold after charging and discharging the gas sensor 21 and the predetermined threshold. Specifically, the control unit 1 acquires, at the second time point later than the first time point, a second difference, which is the difference between a detection signal that exceeds the predetermined threshold among a plurality of detection signals acquired at different times after charging and discharging the gas sensor 21 and the predetermined threshold. The control unit 1 then compares the first difference and the second difference to determine the degradation state of the gas sensor 21.

[0062] For example, as shown in Figure 13, if a failure is first determined at time A1, then at time A2, and then at time A3, the return of the detection signal after discharge may become slower over time. Therefore, the deterioration state is determined by comparing the difference exceeding a predetermined threshold value at each time point. The time point for determining a failure may be, for example, every day to every few months.

[0063] 13 , at time point A1, the detection signal exceeds the predetermined threshold value Th1 at time T2, so the difference at time T2 is acquired. At time point A2, the detection signal exceeds the predetermined threshold value Th1 at time T2, so the difference at time T2 is acquired. At time point A3, the detection signal exceeds the predetermined threshold value Th1 at time T3, so the difference at time T3 is acquired.

[0064] The control unit 1 determines the state of deterioration of the gas sensor 21 based on, for example, the rate of change or the amount of change in the difference at each point in time.

[0065] Furthermore, the control unit 1 sets a predetermined threshold value according to the charging time during the fault diagnosis of the gas sensor 21. Specifically, the control unit 1 changes the charging time during the fault diagnosis according to the state of the gas sensor 21. If the charging time is long, the control unit 1 sets a large predetermined threshold value based on the detection signal before charging, and if the charging time is short, the control unit 1 sets a small predetermined threshold value based on the detection signal before charging.

[0066] Furthermore, if the detection signal obtained after charging and discharging the gas sensor 21 is close to a predetermined threshold, the control unit 1 may lengthen the charging time and perform the fault diagnosis again. For example, if the detection signal after discharging during the fault diagnosis is approximately equal to the predetermined threshold and has a value that is close to or does not exceed the predetermined threshold, the control unit 1 lengthens the charging time and performs the fault diagnosis again.

[0067] Furthermore, the control unit 1 does not perform a fault diagnosis of the gas sensor 21 when the detection signal satisfies a predetermined condition. For example, the control unit 1 may not perform a fault diagnosis of the gas sensor 21 when the detection signal detects a gas at an alarm level. That is, while the gas detection device 100 of this embodiment is capable of performing a fault diagnosis of the gas sensor 21 regardless of the atmosphere, it may be possible to prioritize an alarm from the perspective of protecting the user or to not perform a diagnosis in consideration of the load on the gas sensor 21. The control unit 1 may also not perform a fault diagnosis of the gas sensor 21 when the output of the detection signal reaches a predetermined value one or more times within a predetermined period. The control unit 1 may also not perform a fault diagnosis when the output of the detection signal maintains a value equal to or greater than a predetermined value for a predetermined period.

[0068] Furthermore, the control unit 1 detects the target gas based on the accumulated value of the detection signals other than during the fault diagnosis. That is, when detecting the target gas, if the detection signals during the fault diagnosis have been accumulated, the control unit 1 starts gas detection in a reset state.

[0069] (Effects of this embodiment) In this embodiment, the following effects can be obtained.

[0070] Furthermore, in this embodiment, as described above, the control unit 1 is provided to determine whether the gas sensor 21 is malfunctioning based on the output of the detection signal acquired after discharging the gas sensor 21 and a predetermined threshold value based on the output of the detection signal before charging the gas sensor 21. This allows the predetermined threshold value to be set based on the output of the detection signal acquired before charging the gas sensor 21, even if the output voltage of the gas sensor 21 varies between charging and discharging due to the presence of the gas to be detected in the atmosphere. This allows the output of the detection signal acquired before charging the gas sensor 21 to return to the value before charging when the gas sensor 21 is charged and then discharged, so the predetermined threshold value for malfunction diagnosis can be set to an appropriate value depending on the atmosphere. As a result, malfunctions in the gas sensor 21 can be accurately diagnosed regardless of the atmosphere.

[0071] In this embodiment, as described above, the control unit 1 sets the predetermined threshold value to a value greater than the output of the detection signal before charging the gas sensor 21. By setting the predetermined threshold value to a value greater than the output of the detection signal before charging, it is possible to reliably prevent the output of the detection signal from exceeding the predetermined threshold value in the event of a malfunction, thereby making it possible to accurately determine whether or not a malfunction has occurred.

[0072] Furthermore, in this embodiment, as described above, a plurality of detection signal outputs are obtained at different times after discharging the gas sensor 21, and whether or not there is a malfunction in the gas sensor 21 is determined based on the outputs of all of the detection signals. As a result, even if there is variation in the time it takes for the output voltage of the gas sensor 21 to exceed a threshold value during charging and discharging due to individual differences in the gas sensor 21, the outputs of a plurality of detection signals are obtained at different times after discharging, and a malfunction is diagnosed when the outputs of all of the detection signals are equal to or less than a predetermined threshold value. Therefore, even if there is individual difference in the gas sensor 21, it is possible to accurately diagnose a malfunction in the gas sensor 21.

[0073] In the present embodiment, as described above, the control unit 1 acquires the detection signal output of the gas sensor 21 after discharge at predetermined intervals and determines whether the gas sensor 21 is normal or malfunctioning based on the acquired multiple detection signal outputs. Since the detection signal output is acquired at predetermined intervals after discharge, the processing load can be reduced compared to when the detection signal output is acquired continuously after discharge. Even if the time it takes for the detection signal output to exceed the threshold after discharge varies depending on the individual gas sensor 21, acquiring the detection signal output at predetermined intervals allows for accurate diagnosis of malfunction of the gas sensor 21.

[0074] Furthermore, in this embodiment, as described above, the control unit 1 acquires the detection signal output at predetermined intervals longer than the charging time of the gas sensor 21, and determines whether the gas sensor 21 is normal or malfunctioning based on the acquired multiple detection signal outputs. In this way, the detection signal output after discharge is acquired at sufficient time intervals longer than the charging time, which can further reduce the processing load compared to when many detection signal outputs are acquired at short time intervals.

[0075] In this embodiment, as described above, the control unit 1 acquires detection signal outputs at three or more different times and determines whether the gas sensor 21 is normal or malfunctioning based on the acquired three or more detection signal outputs. As a result, since detection signal outputs are acquired at three or more different timings, it is possible to acquire detection signal outputs after discharge over a relatively long period of time and determine whether there is a malfunction.

[0076] Furthermore, in this embodiment, as described above, when the output of the detection signal satisfies a predetermined condition, the control unit 1 does not perform a fault diagnosis of the gas sensor 21. As a result, when the output of the detection signal satisfies the predetermined condition, the fault diagnosis is not performed, and therefore it is possible to prevent the detection of the target gas from being interrupted while the fault diagnosis is being performed.

[0077] In this embodiment, as described above, the control unit 1 detects the target gas based on the cumulative value of the detection signal output during periods other than the fault diagnosis. This prevents the cumulative value of the detection signal output during charging and discharging during the fault diagnosis, thereby preventing erroneous detection of the target gas.

[0078] (Modifications) The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the description of the above-mentioned embodiments, and includes all modifications (modifications) within the meaning and scope of the claims.

[0079] For example, in the above embodiment, an example was shown in which the gas detection device is provided with one gas sensor, but the present invention is not limited to this. In the present invention, the gas detection device may be provided with multiple gas sensors for detecting different detection target gases. In this case, the control unit may perform the diagnosis of the present invention on at least one of the gas sensors.

[0080] The gas detection device may also have other alarm functions, for example, a fire alarm (fire alarm) function.

[0081] In the above embodiment, an example is shown in which detection signals are acquired at a plurality of different times after charging and discharging when diagnosing a gas sensor, but the present invention is not limited to this. In the present invention, a detection signal may be acquired at a single time after charging and discharging.

[0082] In the above embodiment, an example is shown in which detection signals are acquired at three different times after charging and discharging when diagnosing a gas sensor, but the present invention is not limited to this. In the present invention, detection signals may be acquired at two or four or more different times after charging and discharging.

[0083] In the above embodiment, an example was shown in which a detection signal is acquired at predetermined intervals after charging and discharging when diagnosing a gas sensor, but the present invention is not limited to this. In the present invention, when diagnosing a gas sensor, a plurality of detection signals may be acquired consecutively after charging and discharging. Furthermore, when diagnosing a gas sensor, a detection signal may be acquired at different time intervals after charging and discharging.

[0084] In the above embodiment, the gas sensor is determined to be faulty when 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, the gas sensor may be determined to be faulty when 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 of the gas sensor increases upon charging and decreases upon discharging, the gas sensor may be determined to be faulty when the output of the gas sensor after discharge does not become smaller than the threshold value.

[0085] In addition, a predetermined range may be set from a predetermined threshold value based on the output of the gas sensor before charging, and if the output of the gas sensor after discharging is within or outside the predetermined range, it may be determined that a malfunction has occurred.

[0086] 1 Control unit 21 Gas sensor 21a Working electrode 21b Counter electrode 100 Gas detection device

Claims

1. A gas detection device comprising a control unit that diagnoses a failure of a gas sensor based on an output from the gas sensor when switching between a charged state in which charge is stored in the gas sensor including a working electrode and a counter electrode and a discharged state in which the charge stored in the gas sensor is discharged, wherein the control unit determines whether the gas sensor has failed 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.

2. The gas detection device according to claim 1, wherein the control unit sets a value larger than the output before charging the gas sensor as the predetermined threshold value.

3. The gas detection device according to claim 1, wherein the control unit acquires a plurality of the outputs after discharging of the gas sensor at different times and determines whether the gas sensor has failed based on all of the outputs.

4. The gas detection device according to claim 3, wherein the control unit acquires the output after discharging of the gas sensor at predetermined intervals and determines whether the gas sensor is normal or has failed based on the plurality of acquired outputs.

5. The gas detection device according to claim 4, wherein the control unit acquires the output at the predetermined intervals longer than the time for charging the gas sensor and determines whether the gas sensor is normal or has failed based on the plurality of acquired outputs.

6. The gas detection device according to claim 3, wherein the control unit acquires the output at three or more different times and determines whether the gas sensor is normal or has failed based on the three or more acquired outputs.

7. The gas detection device according to claim 1, wherein the control unit does not perform a failure diagnosis of the gas sensor when the output satisfies a predetermined condition.

8. The gas detection device according to claim 1, wherein the control unit detects a gas to be detected based on an accumulated value of the output other than during a failure diagnosis.

9. A diagnostic method for a gas sensor that diagnoses a failure of the gas sensor based on an output from the gas sensor when switching between a charged state in which charge is stored in the gas sensor including a working electrode and a counter electrode and a discharged state in which the charge stored in the gas sensor is discharged, wherein it is determined whether the gas sensor has failed 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.

10. Based on the output obtained after discharging the gas sensor and a predetermined threshold value based on the output before charging the gas sensor, determine whether the gas sensor is malfunctioning, and perform a diagnosis of the gas detection device including the gas sensor. The gas sensor diagnosis method according to claim 9.

11. A step of obtaining an output from the gas sensor before charging the gas sensor including a working electrode and a counter electrode by storing 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 malfunctioning based on the threshold value and the output after discharging the gas sensor. A gas sensor diagnosis method comprising:

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