JP2006145216A - Gas detector and auto-ventilation system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas detector capable of resuming the detection of gas at an early stage, even if the gas detector is restarted, after short-time stop or momentary interruption. <P>SOLUTION: The gas detector 10 is constituted so that a sensor output value S(n) is acquired by using a detection circuit 11, and the rise and fall in the concentration of a reducible gas is detected by using the sensor output value S(n). In the detection circuit 11, the sensor output value S(n) is changed with the sensor resistance value Rs of a gas sensor element 17 and also changed, even if the duty ratio DT of an inputted pulse signal Sc is altered. In the gas detector 10, the activation of the gas sensor element 17 is decided twice; and when the gas sensor element 17 is decided as being activated, detection of the rise and fall in the concentration of the gas is started. The second decision is performed, after the duty ratio DT of the pulse signal Sc has been altered so that the sensor output value S(n) becomes a predetermined value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a gas detection device that detects a change in the concentration of a specific gas in an environmental atmosphere and a vehicle autoventilation system.

  Conventionally, it is a gas sensor element using lead-phthalocyanine or a metal oxide semiconductor such as WO3 or SnO2, which is an oxidizing gas such as NOx in the environment or a reducing gas such as CO or HC (hydrocarbon). A gas sensor element whose sensor resistance value changes depending on the concentration change of a specific gas is known. There is also known a gas detection device that uses such a gas sensor element and can detect a change in the concentration of a specific gas by a change in the sensor resistance value. Furthermore, various control systems using this gas detection device, for example, a vehicle auto-ventilation system that performs flap opening / closing control for switching between introduction of outside air and inside air into the vehicle interior in accordance with the contamination status of the air outside the vehicle interior In addition, a system for detecting indoor air pollution due to smoking or the like and controlling an air purifier is known.

In order to appropriately react such a gas sensor element to a specific gas, it is necessary to activate the gas sensor element by heating it to about 200 to 300 ° C., for example. For this reason, conventionally, a heater is disposed in the vicinity of the gas sensor element, and the heater is energized by energizing the heater to heat the gas sensor element.
By the way, since the gas sensor element shows the property as a semiconductor according to temperature, a sensor resistance value changes with the temperature. Furthermore, when the gas sensor element is left in the air in an unheated state (for example, at room temperature), water vapor and gas components are adsorbed on the surface. For this reason, when the gas sensor element is heated to activate the gas sensor element, the gas sensor element gradually warms, so that the sensor resistance value changes with the temperature. In addition, the sensor resistance value is not stabilized by the adsorption of these components until the water vapor or gas components adsorbed on the surface are desorbed.

In other words, even when energization of the heater is started, until the gas sensor element is activated and can be used, specifically, the gas sensor element is sufficiently warmed to exhibit a property as a semiconductor, and the sensor resistance value varies depending on the gas concentration. At the same time, it took time until the sensor resistance value became stable and could be used for gas detection. Conversely, if gas detection is performed before the sensor resistance value of the gas sensor element stabilizes, the sensor resistance value may have changed due to a change in the specific gas concentration, or the sensor resistance value at the beginning of startup will be a stable value. It is difficult to distinguish whether the change is a change until the end, and erroneous detection of the change in the concentration of a specific gas is likely to occur.
Therefore, for example, in the gas detection device disclosed in Patent Document 1, after starting, the gas sensor element is activated, and after waiting for a predetermined time necessary for the sensor resistance value to stabilize, control is performed so that gas detection is started. To prevent false detection.

Even in the activated state, the sensor resistance value of the gas sensor element varies greatly depending on the outside air temperature, humidity, or the concentration of the specific gas, and the sensor resistance value may vary by several digits.
By the way, in order to detect the sensor resistance value of the gas sensor element, there is a case in which a fixed resistance (detection resistance) having a predetermined resistance value and a gas sensor element are connected in series and a circuit for dividing a predetermined DC voltage by these is used. Many. This is because the divided potential in this circuit is a value proportional to the sensor resistance value.
However, in this circuit, when the sensor resistance value is extremely large or small as described above, the divided voltage becomes a biased value close to a predetermined DC voltage or ground potential, and the fluctuation of the sensor resistance value in that state Is difficult to detect.

Therefore, the control system disclosed in Patent Document 2 proposes a system that uses a pulse signal having a repetitive waveform having a first potential state and a second potential state. This system includes a charging circuit that charges a capacitor via a charging resistor during a period in which the pulse signal is in a first potential state, and a discharging resistor in a period in which the pulse signal is in a second potential state. A discharge circuit for discharging the capacitor through the vessel. Then, a gas sensor element is used for at least one of the charging resistor and the discharging resistor, and at least one of the charging current of the charging circuit and the discharging current of the discharging circuit is changed according to the change in the sensor resistance value. Thus, the potential at one end of the capacitor (the potential at the operating point) is changed in accordance with the change in the sensor resistance value. Then, control is performed using the potential at this operating point.
According to this control system, even if the sensor resistance value of the gas sensor element fluctuates greatly, the potential of the operating point can be set to an appropriate value by changing the duty ratio of the pulse signal to an appropriate value. The potential change at the operating point due to the density change can be reliably captured.

In addition, in Patent Document 3, a plurality of fixed resistors and gas sensor elements are connected in series, and connected to a predetermined DC voltage among connection points between the plurality of fixed resistors in accordance with changes in sensor resistance values of the gas sensor elements. A control system is described in which the potential at the operating point at one end of the gas sensor element is set to a value in an appropriate range by selecting a point to be performed.
Patent Document 4 describes a control system that uses a FET instead of a detection resistor composed of a fixed resistor, forms a voltage dividing circuit with this FET and a gas sensor element, and uses a potential at a voltage dividing point (operating point). ing. In this case, by changing the gate voltage of the FET, the resistance value of the resistance between the source and the drain is changed to an appropriate value, and the potential at the operating point is set to an appropriate range.

JP 2002-156350 A JP 2001-242113 A JP 2001-183325 A JP 2001-228109 A

  By the way, in the actual use situation of a gas detection apparatus, after stopping operation | movement of a gas detection apparatus, it may restart in a short time. Alternatively, the power supply may be momentarily interrupted by the influence of vibration, noise, etc., and the operation of the gas detection device may be reset. In such a case, when the gas detection device is restarted and the heater is re-energized, the gas sensor element is activated in a short time, and the sensor resistance value also takes a stable value.

  However, even in such a case, the gas detection device described in Patent Document 1 waits for the elapse of a predetermined time every time it is started (restarted), so that the gas sensor element is already activated and the sensor resistance value is sufficiently stable. Despite this, there has been a problem that gas detection cannot be performed until the predetermined time has elapsed.

Furthermore, in the control system described in Patent Document 2 described above, if the duty ratio of the pulse signal is changed in order to keep the potential at the operating point within an appropriate value range, a capacitor, a charging resistor, a discharging resistor, Since the potential at the operating point gradually changes in accordance with the time constant determined by (1), it takes a certain amount of time to bring the potential at the operating point to a desired value.
Accordingly, if the gas detection is completed after confirming the completion of activation of the gas sensor element and then further setting the potential at the operating point to a desired value, the restart of the gas detection is further delayed. This can occur even when the techniques described in Patent Documents 3 and 4 are used.

  The present invention has been made in view of such problems, and even when the gas detection device is restarted after a short stop or instantaneous interruption, a gas detection device capable of resuming gas detection at an early stage, and this An object of the present invention is to provide a vehicle auto-ventilation system using the above.

  The solution is a gas detection device using a gas sensor element whose sensor resistance value changes according to the concentration of a specific gas in the environmental gas, and acquires the sensor output value using a detection circuit including the gas sensor element. Means for changing at least one of circuit conditions and driving conditions of the detection circuit according to a sensor resistance value of the gas sensor element; and at least one of the circuit conditions and driving conditions of the detection circuit A change instructing means for changing the sensor output value, a gas concentration raising / lowering detecting means for detecting the raising / lowering of the concentration of the specific gas using the sensor output value, and after activation of the gas detection device A plurality of activation determining means for determining whether the gas sensor element is activated or for determining whether the gas sensor element is spaced from each other; If it is determined that the gas sensor element is activated, an activation determination unit that starts detection of increase / decrease of the concentration of the specific gas by the gas concentration increase / decrease detection unit is provided, and the one or more activation determination units At least one of the activation conditions of the gas sensor element after the change instructing means changes at least one of the circuit condition and the driving condition of the detection circuit so that the sensor output value satisfies a predetermined condition. This is a gas detection device that makes a judgment on conversion.

In the gas detection device of the present invention, after the gas detection device is activated, an activation determination is made as to whether or not the gas sensor element is activated once or a plurality of times apart from each other. At least one of the circuit condition and the driving condition of the detection circuit is made by the change instruction means before the activation determination so that the sensor output value satisfies the predetermined condition for one time or any one of the plurality of times. After that, the activation of the gas sensor element is determined.
As described above, when at least one of the circuit condition and the driving condition of the detection circuit is changed in advance so that the sensor output value satisfies the predetermined condition, and it is determined whether or not the gas sensor element is activated. If it is determined that the gas concentration is activated, detection of the increase / decrease of the concentration of the specific gas by the gas concentration increase / decrease detection means can be started immediately. Thus, even when a detection circuit in which circuit conditions and driving conditions need to be appropriately changed is used as the detection circuit, gas detection can be restarted immediately after the activation of the gas detection element is completed.

The detection circuit includes a gas sensor element and is configured to be able to acquire a sensor output value by an acquisition unit. By changing at least one of the circuit condition and the driving condition of the detection circuit, the sensor circuit Any circuit that can change the output value to an appropriate value or an appropriate range of values may be used. Specifically, a detection circuit described in Patent Documents 2, 3, and 4 described above and having the exemplified configuration can be used.
In addition, as a technique for changing the circuit conditions of the detection circuit, an appropriate technique may be adopted depending on the configuration of the detection circuit. For example, the circuit constants of components (for example, resistors) included in the circuit are changed. In some cases, the circuit configuration (such as connection relationships between components) is changed. More specifically, for example, in the circuit shown in the above-mentioned Patent Document 3, a resistor used for voltage division is selected from a plurality of fixed resistors connected in series, or a resistance group is connected to each other ( The resistance of the resistance between the source and the drain is changed by changing the gate voltage of the FET, as shown in Patent Document 4, in which the value of the combined resistance realized by the resistor group is changed by changing the series, parallel, etc. Something that changes the value.
In addition, as a method for changing the driving conditions of the detection circuit, an appropriate method may be adopted depending on the configuration of the detection circuit. For example, the voltage applied to the detection circuit or the frequency of the applied signal may be changed. Can be mentioned. In addition, in the circuit described in Patent Document 2, the duty ratio of the pulse signal applied to the detection circuit may be changed (PWM is performed).

  As the gas concentration increase / decrease detection means, any technique can be adopted as long as it can detect an increase or decrease in the gas concentration of a specific gas using the sensor output value acquired by the acquisition means. it can. A known detection method, for example, a method using a differential value, an integral value, or a moving average value of the sensor output value can be mentioned. When the acquired sensor output value is S (n), the reference value B (n) is B (n) = S (n) + k1 (S (n) −B (n−1)), or B (n) = S (n) + k1 (S (n) -B (n-1))-k2 (S (n) -S (nm)) Furthermore, there is a method of detecting an increase or decrease in gas concentration based on whether or not the difference D (n) = S (n) −B (n) from the sensor output value is greater than a predetermined value. Note that n is an integer representing the order of time series, m is an integer of 2 or more, and 0 <k1 <1, 0 <k2 <k1 <1.

The determination method in the activation determination means may be appropriately selected according to the properties of the gas sensor element, the configuration of the detection circuit, and the like. For example, in general, in gas sensor elements using oxide semiconductors such as WO ₃ and SnO ₂ , the sensor resistance value suddenly rises and then falls rapidly immediately after starting the gas detection device and starting heating by the heater. To do. Thereafter, the sensor resistance value gradually increases and often changes to a stable value. Note that the shorter the time until restart, the fewer changes that occur before the sensor resistance value stabilizes. Therefore, it is determined that such a gas sensor element is activated when a large variation in the sensor resistance value (and hence the sensor output value) is within a certain range. Therefore, when the sensor output value is measured at a certain time interval after starting the gas detection device, if both values do not change or are sufficiently small, it can be determined that the gas sensor element is activated. it can.
Further, in the change instructing means, the fact that the sensor output value satisfies the predetermined condition varies depending on the configuration of the detection circuit and the like. For example, there is a case where the sensor output value falls within a predetermined range. In addition, when the circuit conditions and driving conditions of the detection circuit are changed in order from the state in which the sensor output value is below the predetermined target value in the direction in which the sensor output value increases, the case where the target value is exceeded may be mentioned. It is done.

  Another solution is a gas detection device that uses a gas sensor element whose sensor resistance value changes according to the concentration of a specific gas in an environmental gas, the detection circuit including the gas sensor element, wherein the first potential state And a pulse input point to which a pulse signal having a repetitive waveform having a second potential state is input, a capacitor, and a charging resistor during a period in which the signal of the first potential state is input to the pulse input point. A charging circuit for charging the capacitor via a discharging circuit, and a discharging circuit for discharging the capacitor via a discharging resistor during a period when the signal of the second potential state is input to the pulse input point. And at least one of the charging resistor of the charging circuit and the discharging resistor of the discharging circuit includes a gas sensor element having the sensor resistance value, and the charging current of the charging circuit and At least one of the discharge currents of the discharge circuit changes according to a change in sensor resistance value of the gas sensor element, and is a detection circuit capable of changing a duty ratio of the pulse signal, and one end of the capacitor, Changing the sensor resistance value of the gas sensor element to change the duty ratio of the pulse signal applied to the pulse input point of the detection circuit and the acquisition means for acquiring the sensor output value according to the potential of the operating point where the potential changes The change instruction means for changing the sensor output value, the gas concentration rise / fall detection means for detecting the rise / fall of the concentration of the specific gas using the sensor output value, and the gas sensor after the gas detection device is started A plurality of activation judgment means for judging whether or not the element is activated, or for judging at a time from each other, If it is determined that the element is activated, an activation determination unit that starts detection of increase / decrease of the concentration of the specific gas by the gas concentration increase / decrease detection unit is provided. At least one of them activates the gas sensor element after changing the circuit condition and the driving condition of the detection circuit so that the sensor output value satisfies a predetermined condition by the change instruction means. This is a gas detection device that performs the determination.

As described above, the gas detection device of the present invention has a detection circuit including a capacitor, a charging circuit, and a discharging circuit. In this detection circuit, when the duty ratio of the pulse signal is changed, the sensor output value gradually changes according to the time constant of the charging circuit and the discharging circuit in the detection circuit.
For this reason, if the activation determination is performed first while having such a detection circuit, even if it is determined that the gas sensor element is activated, the duty ratio of the pulse signal is set to an appropriate value thereafter. Need to be changed. Then, the gas concentration increase / decrease detection means cannot detect the gas concentration increase / decrease until the change in the sensor output value accompanying the change in the duty ratio of the pulse signal is settled. Therefore, it takes time until the elevation detection is performed.
In contrast, in the gas detection apparatus of the present invention, the duty ratio of the pulse signal is changed in advance by the change instruction means so that the sensor output value satisfies the predetermined condition. Thereafter, the activation of the gas sensor element is determined. For this reason, when it is determined that the gas sensor element is activated, the gas concentration increase / decrease detection means can immediately detect the gas concentration increase / decrease. Thus, even in a gas detection device using a detection circuit that needs to change the duty ratio of the pulse signal as appropriate, gas detection can be resumed promptly after the activation of the gas detection element is completed.

  Note that the pulse signal only needs to have a repetitive waveform having the first potential state and the second potential state, and the relationship between the first potential and the second potential is, for example, one of + 5V, In addition to the potential relationship of one voltage such that the other is 0V (ground), the potential relationship of both power sources can be such that one is + 5V and the other is −5V. Furthermore, in order to change the potential at the operating point, PWM (pulse width modulation) or amplitude modulation for changing the duty ratio of the pulse signal may be performed.

In addition, the charging circuit may be any circuit that can charge the capacitor in accordance with the first potential state signal input to the pulse input point, and the discharge circuit is the second circuit input to the pulse input point. Any circuit can be used as long as it can discharge the capacitor in accordance with the signal in the potential state.
However, the circuit configuration is such that at least one of the charging current of the charging circuit and the discharging current of the discharging circuit varies depending on the sensor resistance value of the gas sensor element. For example, a charging circuit in which a charging resistor having a resistance value Rc and a capacitor having a capacitance C are connected in series to form a CR series circuit having a first time constant τ1 = CRc, or a discharging resistor having a resistance value Rd And a capacitor having an electrostatic capacity C connected in series to form a CR series circuit having a second time constant τ2 = CRd. In addition, by using an active element such as a transistor, FET, or operational amplifier, a current corresponding to the sensor resistance value of the gas sensor element or the resistance value of the resistor is passed through the capacitor to charge the capacitor or discharge the capacitor. it can.

Furthermore, in the charging circuit, the charging current to the capacitor may be configured to flow from the pulse input point to the capacitor. However, the switching element is driven by the input pulse signal, and a separate current is supplied via the switching element. The capacitor can be charged from the power source.
In the discharge circuit, the discharge current from the capacitor may flow from the capacitor toward the pulse input point. However, the switching element is driven by the input pulse signal, and the capacitor is discharged via the switching element. It can also be made.

  Note that by making the repetition period Tp of the pulse signal sufficiently small, that is, by increasing the frequency fp, the ripple of the potential at the operating point becomes small, and the potential at one end (operating point) of the capacitor becomes a substantially constant value. For this reason, even if the sensor output value is acquired by directly A / D converting the potential of the operating point in the acquisition unit, the A / D conversion value is preferably not affected by fluctuation due to charge / discharge.

  Further, as the charging resistor and the discharging resistor, a fixed resistor having a certain resistance value can be used. A variable resistor can also be used. When the variable resistor is used, it is possible to cope with a case where the sensor resistance value Rs changes over a wide range such as several digits by appropriately changing the resistance value. Alternatively, the specific variation of each gas sensor element can be absorbed by adjusting the resistance value of the variable resistor. Furthermore, a gas sensor element having other characteristics such as a resistance value changing in response to another gas different from the specific gas can be used as the resistor.

  Further, in the gas detection device, when the duty ratio is changed among the change directions of the duty ratio of the pulse signal, a direction in which the sensor output value decreases is set as an output value decrease direction. When the direction in which the sensor output value increases is defined as the output value increasing direction, the predetermined condition that the sensor output value satisfies by the change instructing means is a first time from the first time to the second time after the start. Within a predetermined period, the duty ratio of the pulse signal is changed in the direction of decreasing the output value, and the sensor output value is once set below the target value, or the sensor output value below the target value is set to the duty of the pulse signal. Whether the sensor output value is equal to or higher than the target value by changing the ratio in the direction of increasing the output value, and the activation determining means determines the duty ratio of the pulse signal as described above. The sensor output value is fixed to the duty ratio at the time when the predetermined condition is satisfied, and the sensor output value is a value within a predetermined fluctuation allowable range including the target value when a third time elapses after the second time. In this case, a gas detection device that determines that the gas sensor element is activated may be used.

In the gas detection device of the present invention, the predetermined condition that the sensor output value satisfies by the change instructing means is that the duty ratio of the pulse signal is changed in the output value decreasing direction within the first predetermined period, and the sensor output value is temporarily set to the target value. Whether the sensor output value is equal to or higher than the target value by changing the duty ratio in the increasing direction of the output value of the sensor output value that was originally equal to or lower than the target value. If such a condition is satisfied, at that time, the sensor output value is almost in the vicinity of the target value.
Therefore, the activation determination means observes the transition while fixing the pulse signal to the duty ratio at that time. Here, if the gas sensor element is activated and the sensor resistance value is stable, the sensor output value does not change much. On the other hand, when the activation is not completed, the sensor resistance value further varies, so that the sensor output value also varies. Therefore, if the sensor output value when the third time elapses is a value within the predetermined fluctuation allowable range, it can be determined that the gas sensor element is activated.
In addition, in this case, since the duty ratio of the pulse signal is already a value that satisfies the predetermined condition, or a value close thereto, that is, the sensor output value is close to the target value, the activation determination means activates the gas sensor element. If it is determined that the gas concentration is increased, the gas concentration increase / decrease detection means can immediately detect the increase / decrease in the concentration of the specific gas using the sensor output value.

  Note that there is a limit (theoretically exceeding 0% and less than 100%, actually, for example, 1 to 99%) in the change range of the duty ratio of the pulse signal. Therefore, even when the duty ratio is set to the upper limit value or the lower limit value, it is preferable not to perform the determination by the activation determination means when the sensor output value cannot be a value near the target value. This is because in such a case, it is not considered that the gas sensor element is activated.

  Furthermore, it is good to set it as the autoventilation system for vehicles containing the gas detection apparatus of any one of Claims 1-3.

  In these vehicle auto-ventilation systems, by using a gas detection device, gas detection can be performed at an early stage even in a short time or even after restart after a momentary interruption. The flap can be opened and closed appropriately.

  Embodiments of the present invention will be described with reference to FIGS.

  FIG. 1 shows a schematic configuration of a gas detection apparatus 10 according to the present embodiment and a vehicle auto ventilation system (hereinafter also simply referred to as a system) 100 including the same. This system 100 controls the gas detection device 10 that outputs a concentration signal LV according to the concentration change of the specific gas in the gas to be measured and the air in the interior of the automobile to either outside air intake or inside air circulation. A ventilation mechanism 30 and a flap control mechanism 40 for controlling the flap 34 of the ventilation mechanism 30 according to the density signal LV are provided.

  First, the gas detection device 10 will be described. This gas detection device 10 reacts when there is a reducing gas component such as CO and HC in the environmental gas (atmosphere in this embodiment), and the sensor resistance value Rs decreases as the concentration of the reducing gas component increases. A gas sensor element 17 of an oxide semiconductor is used. The gas sensor element 17 is disposed at a position close to a heater (not shown). The gas sensor element 17 is heated by energizing the heater and exhibits a reducing gas detection capability. The gas sensor element 17 and the heater are arranged in one container while allowing outside air to flow in to form a gas sensor, and are arranged outside the passenger compartment of the automobile. The sensor resistance value Rs of the gas sensor element 17 usually varies in the range of 5 kΩ to 1 MΩ due to environmental changes such as the concentration of reducing gas, temperature and humidity.

  In the present embodiment, the change in the sensor resistance value Rs of the gas sensor element 17 is converted into the output voltage Vout by using the detection circuit 11, and further A / D converted into the sensor output value S (n). The sensor output value S (n) is taken into the microcomputer 20, and from the state of the change, the increase and decrease of the concentration of the reducing gas are detected, and the flap 34 is opened and closed.

The detection circuit 11 shown in FIG. 1 is a circuit for driving the gas sensor element 17 to obtain an output voltage Vout according to a change in the sensor resistance value Rs of the gas sensor element 17, and as will be described later, the pulse signal Sc Input terminal (pulse input point) 18 and an output terminal (operating point) 19. The detection circuit 11 includes a capacitor 12 having a capacitance C (3.3 μF in this embodiment), a charging circuit 13 for charging the capacitor 12, and a discharging circuit 16 for discharging the capacitor 12.
Among these, the charging circuit 13 includes a charging resistor 14 having a resistance value Rc (7.5 kΩ in this embodiment) and a diode 15. In the charging circuit 13, the charging resistor 14 and the diode 15 are connected in series, one end of which is connected to the pulse input terminal 18, and the other end is connected to the one end 12 </ b> A of the capacitor 12. The other end 12B of the capacitor 12 is grounded.
On the other hand, the discharge circuit 16 includes the gas sensor element 17 described above. In the discharge circuit 16, the gas sensor element 17 is arranged in parallel with the capacitor 12, one end 17A of the gas sensor element 17 is connected to one end 12A of the capacitor 12, and the other end 17B is grounded.
Note that one end 17A of the gas sensor element 17 (one end 12A of the capacitor 12) is an operating point at which the potential changes as the sensor resistance value Rs changes. The potential of this operating point (one end 17A of the gas sensor element 17) is led to the output terminal 19. The diode 15 is connected in a direction in which the capacitor 12 side is the cathode.

The detection circuit 11 includes an A / D conversion circuit 21 and a microcomputer 20 inside. The microcomputer 20 includes a microprocessor that performs operations of a known configuration, a RAM that temporarily stores programs and data, a ROM that stores programs and data, and the like, as shown by a broken line in FIG. A circuit 21 may also be included.
The output voltage Vout of the detection circuit 11 input to the A / D conversion circuit 21 is A / D converted at predetermined intervals (in this embodiment, every 0.1 sec), and is a digital A / D conversion value sensor. The output value is S (n). n is a series of integers representing the order.
By processing the sensor output value S (n) input through the sensor input terminal 20A by the microcomputer 20, the concentration change of the reducing gas is detected from the sensor resistance value Rs of the gas sensor element 11 and the change thereof. The A / D conversion circuit 21 converts 0 to 5 V into an 8-bit digital value, and the resolution is about 20 mV (≈5 V / 2 ⁸ = 19.5 mV).

  The microcomputer 20 outputs a pulse signal Sc from the pulse output terminal 20B according to the sensor output value S (n). The detection circuit 11 is driven by the pulse signal Sc. This pulse signal Sc is a pulse signal in which two potentials of 0 V (ground potential) and +5 V appear alternately as shown in a circle in the lower part of FIG. 1, and a repetition frequency fp (fp = 2 kHz in this embodiment). The + 5V potential (first potential) is continued for time t1, and 0V (second potential) is continued for time t2. Accordingly, the duty ratio DT (%) of the pulse signal Sc is given by DT = 100t1 / (t1 + t2). The sum of t1 and t2 is the repetition period Tp (= t1 + t2). In this embodiment, the open drain terminal of the microcomputer 20 is used as the pulse output terminal 20B, and the duty ratio DT is appropriately changed while the repetition frequency fp of the pulse signal Sc is constant (fp = 2 kHz). In addition, the gas detection apparatus 10 of a present Example is a system driven with a + 5V single power supply.

Next, the operation of the detection circuit 11 will be described. First, when +5 V which is the first potential (high level) of the pulse signal Sc is applied to the pulse input terminal 18, the diode 15 is turned on, and the capacitor 12 is charged through the charging resistor 14 and the diode 15. The That is, the charging resistor 14 and the diode 15 (charging circuit 13) charge the capacitor 12 when the pulse input terminal 18 is in the first potential state. Therefore, the voltage across the capacitor 12 (output voltage Vout) rises during this period t1. The time constant (first time constant) τ1 for charging is τ1 = C · Rc · Rs / (Rc + Rs).
On the other hand, when 0 V, which is the second potential (low level) of the pulse signal Sc, is applied to the pulse input terminal 18, the diode 15 is turned off. Is done. That is, the gas sensor element 17 connected in parallel with the capacitor 12 forms a discharge circuit 16 that discharges the capacitor 12 when the pulse input terminal 18 is in the second potential state. Therefore, during this period t2, the voltage across the capacitor 12 (output voltage Vout) drops. Note that the time constant (second time constant) τ2 of this discharge is τ2 = CRs.

  Since the detection circuit 11 operates as described above, by repeatedly inputting the pulse signal Sc, the charge charged during the time t1 and the charge discharged during the time t2 are in a steady state, As shown in the upper circle in FIG. 1, the output voltage Vout has an almost constant value although it has a slight ripple of the ripple voltage Vr. Here, the frequency fp of the pulse signal Sc is preferably set to a sufficiently high frequency that is lower than the resolution of about 20 mV of the A / D conversion circuit 21, and in this embodiment, fp = 2 kHz as described above. For this reason, even if the detection circuit 11 and the A / D conversion circuit 21, that is, the output terminal 19 is directly connected to the A / D conversion circuit 21, an A / D conversion value (sensor output value S ( There is no variation in n)).

Next, in the gas detection device 10 including the detection circuit 11, changes in the output voltage Vout (sensor output value S (n)) when the sensor resistance value Rs of the gas sensor element 17 is changed are shown in FIG. In this graph, the duty ratio DT (%) of the pulse signal Sc is used as a parameter. Actually, instead of the gas sensor element 17, a variable resistor was attached to the circuit shown in FIG. 1, and the output voltage Vout was measured.
As can be easily understood, even when the duty ratio DT of the pulse signal Sc is constant, the output voltage Vout changes when the sensor resistance value Rs changes. As the sensor resistance value Rs increases, the time constant τ2 of discharge increases and it becomes difficult to discharge, and the voltage between the terminals of the capacitor 12 (output voltage Vout) increases until the charge to be charged and the charge to be discharged are balanced. Because it becomes.

  As described above, the frequency of the pulse signal fp = 2 kHz, the resistance value Rc of the charging resistor 14 is 7.5 kΩ, and the capacitance C of the capacitor 12 is 3.3 μF. As can be seen from this graph shown in FIG. 2, when the duty ratio DT is constant, the output voltage Vout increases monotonously and gradually as the sensor resistance value Rs increases. Therefore, the sensor resistance value Rs can be obtained from the output voltage Vout, and thus the sensor output value S (n) obtained by A / D converting the output voltage Vout and the duty ratio DT of the applied pulse signal. When the duty ratio DT is constant, if the sensor resistance value Rs decreases (corresponding to an increase in reducing gas concentration), the sensor output value S (n) also decreases, and the sensor resistance value Rs increases (reducing gas concentration). Sensor output value S (n) also increases. From this, it can be seen that the change in the sensor resistance value Rs and the change in the concentration of the reducing gas can be detected from the change in the sensor output value S (n).

Further, as can be easily understood from the graph, this detection circuit 11 shows that measurement is possible even if the sensor resistance value Rs changes by several digits (for example, three digits from 1 kΩ to 1 MΩ).
In addition, the graph of the characteristics of the detection circuit 11 shows that the pulse signal Sc can be obtained even when the sensor resistance value Rs of the gas sensor element 17 varies greatly depending not only on the concentration of the reducing gas but also on the environment such as temperature and humidity. By changing the duty ratio DT, the output voltage Vout is changed to an appropriate value range, and it is shown that the concentration change of the specific gas can be detected with high accuracy.
For example, it is assumed that the sensor resistance value Rs changes to a value of 100 kΩ or more due to a change in the environment when a pulse signal Sc having a duty ratio DT = 90% is input to the detection circuit 11. In this case, the output voltage Vout is biased to a high value of about 4.2V. Even if the sensor resistance value Rs slightly decreases because the concentration of the reducing gas increases in this state, the change in the output voltage Vout is small because the slope of the graph is small, and it is possible to accurately detect the concentration change of the reducing gas. difficult.

On the other hand, when the duty ratio DT of the pulse signal Sc is changed to DT = 10%, the output voltage Vout becomes about 2.5 V, and the slope of the graph increases. For this reason, when the concentration of the reducing gas further increases in this state and the sensor resistance value Rs slightly decreases, the output voltage Vout changes greatly. Therefore, it is possible to accurately detect the concentration change of the reducing gas. That is, by changing the duty ratio DT in this manner, the output voltage Vout can be kept within a predetermined range, and the concentration change of the reducing gas (specific gas) can be accurately detected. In this embodiment, the operation of changing the duty ratio DT of the pulse signal Sc to an appropriate value so that the output voltage Vout and the sensor output value S (n) of the detection circuit 11 are in an appropriate predetermined range in this way. , Sometimes referred to as “combination”.
Furthermore, even when there is a variation in the characteristics of the gas sensor element 17, it is possible to measure by absorbing the variation by changing the duty ratio DT of the pulse signal Sc.

On the other hand, either a high density signal (LV = 1) or a low density signal (LV = 0) for controlling the flap drive mechanism 40 is output from the output terminal 20C of the microcomputer 20. The flap control mechanism 40 controls the flap 34 of the ventilation mechanism 30 that controls the inside air circulation and outside air intake of the automobile.
Specifically, in this embodiment, the ventilation mechanism 30 is connected to a duct 31 connected to the interior of the vehicle interior in a bifurcated manner, and an internal air intake duct 32 for taking in and circulating the internal air and an external air intake duct 33 for taking in the external air. The flap 34 for switching between and is controlled.
In the flap control mechanism 40, the flap drive circuit 41 indicates whether the concentration signal LV from the microcomputer 20 has increased or decreased in terms of the concentration of a reducing gas component such as CO, according to this embodiment. The actuator 42 such as a motor is operated according to the density signal LV. As a result, the actuator 22 rotates the flap 34 to connect either the inside air intake duct 32 or the outside air intake duct 33 to the duct 31.

  Specifically, as shown in the flowchart of FIG. 3, after performing the initial setting in step S1, the density level signal LV is acquired in step S2, and in step S3, the density signal LV is at a high level (LV = 1). It is determined whether or not there is a high density signal. Here, when No, that is, when a low concentration signal is being generated (LV = 0), since the concentration of the specific gas (reducing gas in this embodiment) is low, instructing the fully opening of the flap 34 in step S4. . Thereby, the flap 34 rotates, the outside air intake duct 33 is connected to the duct 31, and the outside air is taken into the vehicle interior. On the other hand, if Yes in step S3, that is, if a high concentration signal is being generated (LV = 1), the concentration of the reducing gas outside the passenger compartment is high, so in step S5, the flap 34 is instructed to be fully closed. As a result, the flap 34 is rotated, the inside air intake duct 32 is connected to the duct 31, the introduction of the outside air is blocked, and the inside air is circulated.

  A fan 35 that pumps air is installed in the duct 31. The flap drive circuit 21 may open and close the flap 34 only according to the concentration signal LV. For example, a microcomputer or the like is used to indicate the concentration signal LV from the gas detection device 10 as well as the broken line in the figure. As shown, the flap 34 may be opened and closed in consideration of information from, for example, a room temperature sensor, a humidity sensor, and an outside air temperature sensor.

  By the way, as described above, the gas sensor element 17 used in this embodiment needs to be activated by heating to about 200 to 300 ° C., for example. For this reason, a heater (not shown) is disposed in the vicinity of the gas sensor element 17, and the gas sensor element 17 is activated by energizing the heater to heat the gas sensor element 17. However, even if energization of the heater is started, the gas sensor element 17 is activated, the sensor resistance value Rs changes due to the concentration change of the reducing gas, and the sensor resistance value Rs is stabilized and used for gas detection. It takes time to get it. Therefore, also in the gas detection device 10 of the present embodiment, after the gas detection device 10 is started, the gas sensor element 17 is activated and a predetermined time (specifically, 30 seconds) required for the sensor resistance value Rs to become stable. After waiting for elapse of time, control is performed so as to start the gas detection to prevent erroneous detection.

  However, due to its nature, the gas detection device 10 (vehicle autoventilation system 100) may be restarted in a very short time after use and used again. For example, after driving the automobile for a long time (that is, after the gas sensor element is activated and the sensor resistance value Rs is stabilized), the vehicle is stopped and the engine is stopped. Then, after that, for example, the engine may be restarted within a few seconds to resume running. In addition, the power supply voltage of the gas detection device 10 may be decreased (instantaneous interruption) for a moment due to vibration or noise during traveling, the microcomputer 20 may be reset, and the gas detection device 10 may be restarted. .

In such a case, the gas sensor element 17 has already been activated from the beginning of restart or can be activated in a short time. That is, it should be possible to restart the gas detection and operate the system 100 in a short time. Therefore, in this embodiment, the activation of the gas sensor element 17 is determined as follows, and the gas detection is restarted in a short period after the restart.
Note that, in the gas detection device 10 (vehicle auto-ventilation system 100) having the above-described configuration, as described above, the output voltage Vout (sensor) in an appropriate range according to the sensor resistance value Rs that the gas sensor element 17 varies. It is necessary to perform “matching” by changing the duty ratio DT of the pulse signal Sc to obtain an appropriate duty ratio DT so that the change in concentration of the reducing gas can be detected by the output value S (n)). Therefore, both the determination of the activation and the combination are performed as follows.

As can be seen from the graph of FIG. 2, the sensor resistance value Rs and the output voltage Vout have a relationship in which the output voltage Vout increases as the sensor resistance value Rs increases. Accordingly, similarly, when the sensor resistance value Rs increases, the sensor output value S (n) also increases similarly. Further, as a premise, when the temperature of the gas sensor element 17 used in this embodiment is raised from a sufficiently cooled state using a heater, the sensor resistance value Rs is usually (therefore, the output voltage Vout and the sensor output value S). (n)) It has been found that immediately after the start of heating, it rises rapidly, then decreases slowly, rises slowly again, and becomes a stable value.
On the other hand, in a state where the gas sensor element 17 is not cooled (a state in which the time has not elapsed since the previous operation and has been restarted in a short time), the magnitude of the rapid increase in the sensor resistance value Rs immediately after the start of heating is reduced and is moderately slow. In many cases, the value decreases to a stable value.
Furthermore, when the gas sensor element has already been activated, the sensor resistance value Rs of the gas sensor element 17 hardly changes when the energization of the heater is stopped for a very short time, such as an instantaneous interruption of energization. However, since the duty ratio DT of the pulse signal Sc is changed to the initial value by resetting the microcomputer 20, the output voltage Vout and the sensor output value S (n) are greatly different from the values before the momentary interruption. It is possible that

In the gas detection apparatus 10 of the present embodiment, the control in the microcomputer 20 is performed according to the flowcharts shown in FIGS.
First, when the key switch of the automobile is turned on or the microcomputer 20 is reset due to noise or the like, the present control system shown in FIG. 4 is started. First, in step S11, various initial settings are performed. For example, a low density signal is generated as the density signal LV. Specifically, the density signal LV is set to a low level (LV = 0). Thereby, the flap 34 will be in the state rotated to the inside air circulation side at the beginning of starting. In addition, the time counter is activated, and the elapsed time from the activation (reactivation) is measured. Further, an alignment continuation flag is set.

  Next, the process proceeds to step S12, and it is determined whether or not 1 second has elapsed since the start (restart). When the elapsed time from the activation is less than 1 second (No), the process proceeds to step S13, and the sensor output value S (n) is acquired through the detection circuit 11 and the A / D conversion circuit 21. Then, it progresses to step S14, waits for progress of sampling time (this example 0.1 second), and returns to step S12. Accordingly, the sensor output value S (n) is acquired at every sampling time (every 0.1 second) immediately after the activation, and after 1 second has elapsed since the activation, the “first activation determination & adjustment” subroutine of step S15 is executed. move on.

In the “first activity determination & adjustment” subroutine in step S15, processing is performed according to the flow shown in FIG. First, in step S51, the first target value SM1 is substituted as the target value SM. In the present embodiment, specifically, the numerical value of the sensor output value S (n) corresponding to the output voltage Vout = 1V is set as the first target value SM1.
Next, in step S52, the current sensor output value S (n), that is, the sensor output value S (n) at the time when 1 second has elapsed since the start-up is substituted for the sensor 1-second value S1.

  Thereafter, in steps S53, S54, and S55, in the same manner as steps S12, S13, and S14, the sensor output value S (n) is set at every sampling time (every 0.1 second) until 2.5 seconds have elapsed from the start. Continue to get. Then, when 2.5 seconds have elapsed from the activation (Yes in step S53), the process proceeds to step S56.

  In step S56, whether or not | S (n) −S1 | <400 is used by using the current sensor output value S (n) (when 2.5 seconds have elapsed from the start) and the above-described sensor 1 second value S1. Judging. That is, the sensor output value S (n) at the time when 1 second has elapsed from the start and the time when 2.5 seconds have elapsed are compared, and whether or not the difference (its inclination) is smaller than a predetermined value (400 in this embodiment). Determine whether. The sensor output value S (n) of 400 is a value equivalent to about 32 mV in terms of the output voltage Vout.

  In this step S56, No, that is, when the sensor output value S (n) at the time of 2.5 seconds after the start of change has greatly changed compared to the sensor 1 second value S1, the sensor output value S ( Since n) has changed greatly and is considered unstable, the process returns to the main routine.

On the other hand, if this step S56 is Yes, that is, if the difference between the sensor 1-second value S1 and the sensor output value S (n) when 2.5 seconds have elapsed after startup is small, the sensor output value S (n) is stable. Therefore, it is considered that the gas sensor element 17 is activated. Therefore, the processing after step S57 is performed.
First, in step S57, it is determined whether or not 5 seconds have elapsed since activation (reactivation). When the elapsed time from the activation is less than 5 seconds (No), the process proceeds to step S58 to acquire the sensor output value S (n). Thereafter, the process proceeds to the “alignment process & alignment end determination process” in step T1.
After the end of step T1, the process proceeds to step S59, waits for the sampling time (0.1 second) to elapse, and returns to step S57. Accordingly, the sensor output value S (n) is acquired in step S58 and the subroutine of step T1 is repeated for a period of 2.5 seconds to 5 seconds from the start.
Then, after 5 seconds have elapsed from the start, the process proceeds to step S5A.

Here, in the “matching process & matching end determination process” in step T1, the process is performed according to the flow shown in FIG. First, in step T11, it is determined whether or not a target value or less recognition flag is set. This target value or less recognition flag is a flag that is set when the sensor output value S (n) becomes a value lower than the target value SM by the processing described below.
If this flag is cleared (No), the process proceeds to step T12. In Step T12, it is determined whether or not the current sensor output value S (n) is larger than the target value SM (the first target value SM1 is currently substituted).

If Yes, that is, if the current sensor output value S (n) is larger than the target value SM, the process proceeds to Step T13. In step T13, it is determined whether or not the duty ratio DT of the pulse signal Sc input to the detection circuit 11 is a lower limit value. In the microcomputer 20 of the present embodiment, the range of the duty ratio DT that can be taken by the pulse signal Sc is 0.4 to 99.6%, so the lower limit value in step T13 is 0.4%.
When the duty ratio DT is not the lower limit value (0.4%) (No), the process proceeds to step T14, the current duty ratio DT is reduced according to the equation DT = DT−ΔDT1, and the process proceeds to step T21. In this equation, ΔDT1 is a decrement of the duty ratio DT (ΔDT1> 0).

As can be easily understood from the graph shown in FIG. 2, even if the sensor resistance value Rs of the gas sensor element 17 in the detection circuit 11 is the same value, if the duty ratio DT of the pulse signal Sc is lowered in this way, the output voltage It can be seen that Vout is a low value, and therefore the sensor output value S (n) is also a small value. Therefore, in this embodiment, the direction in which the duty ratio DT is lowered is the output value decreasing direction in which the sensor output value is decreased, and conversely, the direction in which the duty ratio DT is increased is the output value increasing direction in which the sensor output value is increased. It is.
Therefore, if this step T14 is repeatedly executed, the duty ratio DT of the pulse signal Sc is gradually reduced. That is, the duty ratio DT is changed in the output value decreasing direction. Thereby, if it is the same sensor resistance value Rs, sensor output value S (n) will be made small gradually. Therefore, the sensor output value S (n) can be made lower than the target value SM (No in step T12). However, it is a condition that the duty ratio DT falls within the variable range (0.4 to 99.6%).

  On the other hand, when the duty ratio DT of the pulse signal Sc is the lower limit value (0.4%) at step T13 (Yes), the duty ratio DT cannot be lowered further according to step T14. “Adjustment” in which DT is changed to an appropriate value must be abandoned. Therefore, the process proceeds to step T19, the fitting completion recognition flag is set, the limit recognition flag is set, and the process proceeds to step T21. Here, the alignment completion recognition flag is a flag indicating that alignment has been completed (canceled) to change the duty ratio DT to an appropriate value. The limit recognition flag is a flag indicating that the duty ratio DT is an upper limit value (99.6%) or a lower limit value (0.4%).

In Step T12, if No, that is, if the current sensor output value S (n) is equal to or smaller than the target value SM, the process proceeds to Step T16. In step T16, a target value or less recognition flag is set.
Next, the process proceeds to step T17, where it is determined whether or not the duty ratio DT of the pulse signal Sc input to the detection circuit 11 is an upper limit value. In the present embodiment, the upper limit value in step T17 is 99.6%.
When the duty ratio DT is not the upper limit value (99.6%) (No), the process proceeds to step T18, the current duty ratio DT is increased according to the equation DT = DT + ΔDT2, and the process proceeds to step T21. In this equation, ΔDT2 is an increment of the duty ratio DT (ΔDT2> 0). It should be noted that the increment ΔDT2 and the above-described decrement ΔDT1 may be different or equal. In this embodiment, ΔDT1 = ΔDT2.

Contrary to the case of step T14 described above, even if the sensor resistance value Rs of the gas sensor element 17 is the same value, if the duty ratio DT of the pulse signal Sc is increased, the output voltage Vout becomes a high value (see FIG. 2). Therefore, the sensor output value S (n) is also a large value.
Therefore, if this step T18 is repeatedly executed, the duty ratio DT of the pulse signal Sc is gradually increased. That is, the duty ratio DT is changed in the output value increasing direction. Thereby, if the sensor resistance value Rs is the same, the sensor output value S (n) is gradually increased. Therefore, it is possible to increase the sensor output value S (n) that is below the target value SM (No in T12) and to exceed the target value SM. However, it is a condition that the duty ratio DT falls within the variable range (0.4 to 99.6%).

  On the other hand, when the duty ratio DT of the pulse signal Sc is the upper limit value (99.6%) in step T18 (Yes), the duty ratio DT cannot be increased further according to step T18. “Adjustment” in which DT is changed to an appropriate value must be abandoned. Therefore, the process proceeds to the above-described step T19, where the alignment completion recognition flag is set and the limit recognition flag is set, and then the process proceeds to step T21.

In this way, when the “below target value recognition flag” is set (step T16), when the “alignment process & alignment end determination process” in step T1 is performed, “Yes” is determined in step T11, and the process proceeds to step T15. It will go on. In step T15, as in step T12, it is determined whether or not the current sensor output value S (n) is larger than the target value SM.
If No, that is, if the current sensor output value S (n) is equal to or less than the target value SM, the process proceeds to step T16. In step T16, a recognition flag below the target value is set. Subsequently, the aforementioned steps T17, T18, T19 are performed.
On the other hand, if Yes in step T15, that is, if the current sensor output value S (n) is larger than the target value SM, the process proceeds to step T20. In order to become Yes in step T15, the target value or less recognition flag is set in step T11 before that, that is, the sensor output value S (n) becomes equal to or less than the target value SM, and step T12 or It is determined No in T15, and it is necessary to go through Step T16. As described above, the fact that the sensor output value S (n) once becomes equal to or smaller than the target value SM and then becomes larger than the target value SM means that the sensor is currently being driven by the duty ratio DT of the pulse signal Sc. This means that the value of the output value S (n) can be made substantially close to the target value SM. Therefore, in step T20, an alignment completion recognition flag is set, and the process proceeds to step T21.

In step T21, it is determined whether or not the alignment continuation flag is set. This matching continuation flag is set in step S11. Accordingly, in the subroutine of “Adjustment Process & Adjustment Completion Determination Process” in Step T1 in the “First Activity Determination & Adjustment” subroutine of Step S15, Step ST21 is always determined as Yes, and Step T22 is executed. Proceed to
If the alignment continuation flag is cleared, the process returns to the original subroutine.

In step T22, it is determined whether or not the alignment completion recognition flag is set. If this flag is cleared (No), the original subroutine (here, “first activation determination in step S15”) is determined. Return to the & fiting subroutine (FIG. 5). In this case, in the “first activation determination & adjustment” subroutine in step S15, which is repeatedly performed in the period of 2.5 to 5 seconds after activation, the “matching process & adjustment end determination process” in step T1. Each time the subroutine "" is repeatedly processed, the pulse signals are aligned in steps T14 and T18.
On the other hand, if the alignment completion recognition flag is set (Yes), the process proceeds to step T23, the alignment completion recognition flag is cleared, the recognition flag below the target value is cleared, and the process returns to the original subroutine. . That is, the target value or less recognition flag set in step T16 and the alignment end recognition flag set in step T19 or T20 are cleared in step T23.

Then, in the “first activity determination & adjustment” subroutine of step S15, when the “matching process & adjustment end determination process” subroutine of step T1 is repeatedly processed, every time step T1 is executed. In step T11, it is determined that the target value or less recognition flag is cleared (No). Therefore, the “matching process” is performed again, in which the duty ratio DT of the pulse signal Sc is changed in steps T14 and T18. That is, when the alignment continuation flag is set, the alignment processing for increasing or decreasing the duty ratio DT of the pulse signal Sc is repeatedly performed.
On the other hand, if the alignment continuation flag is cleared, the set target value below recognition flag and the alignment end recognition flag are not cleared. Even if the “end determination process” subroutine is repeatedly performed, the process returns to the original subroutine by following the paths of steps T11, T15, T20, and T21, so that the duty ratio DT of the pulse signal Sc is not changed.

  Thus, in the subroutine S15 of the “first activity determination & adjustment”, if the change in the sensor output value S (n) is small during the period of 1 to 2.5 seconds after the activation (| S1-S (n) | <400), the “adjustment” is repeated by changing the duty ratio DT of the pulse signal Sc until 5 seconds have elapsed after the activation. Thereafter, in step S5A, the alignment continuation flag is cleared, the alignment completion recognition flag is set, steps S16 to S20 of the main routine (see FIG. 4) are skipped, and the process returns to point A. Since the sensor output value S (n) is stable, that is, the sensor resistance value Rs of the gas sensor element 17 is stable at an appropriate value, the activation of the gas sensor element 17 is completed. This is because gas detection is considered possible. Therefore, after 5 seconds have elapsed from the start, the processing after step S21 is started.

In this step S21, the sensor output value S (n) is acquired, and subsequently, a subroutine for gas concentration increase / decrease detection processing shown as step S22 is performed. Subsequently, in step S23, the sampling time (0.1 seconds in this example) has elapsed, and the process returns to step S21. Thereafter, the processes of steps S21 to S23 are repeated, and the sensor output value S (n) acquired in step S21 is used to increase or decrease the concentration of the reducing gas in the subroutine (step S22) of the gas concentration increase / decrease detection process. Perform processing to detect.
Accordingly, when it is determined that the concentration of the reducing gas is high, the flap control mechanism is configured by outputting LV = 1 (high level) as the concentration signal LV from the concentration signal output terminal 20C of the microcomputer 20. 40 is used to rotate the flap 34 to circulate inside air. On the other hand, when it is determined that the concentration of the reducing gas is low, the concentration signal LV is set to LV = 0 (low level), and the flap 34 is rotated to introduce outside air.

  In addition, about the subroutine of a gas concentration raising / lowering detection process shown by this step S22, since a well-known process should just be used, the content is not explained in full detail. For example, there is a method of detecting a change in gas concentration using a differential value, an integral value, or a moving average value of sensor output values. Further, using the acquired sensor output value S (n), as a reference value B (n), B (n) = S (n) + k1 (S (n) −B (n−1)) or B ( n) = S (n) + k1 (S (n) −B (n−1)) − k2 (S (n) −S (nm)) The reference value B (n) obtained by the equation is calculated (n Is an integer indicating the order of time series, m is an integer of 2 or more, 0 <k1 <1, 0 <k2 <k1 <1). Further, there is a method of detecting an increase or decrease in gas concentration depending on whether or not the difference D (n) = S (n) −B (n) from the sensor output value is larger than a predetermined value.

  On the other hand, in the subroutine S15 of “first activation determination & adjustment”, the change in the sensor output value S (n) in the period of 1 to 2.5 seconds after the activation is large (| S1-S (n) | <400 Is not satisfied in step S56, the process returns to the main routine without performing the matching process of the pulse signal Sc, and proceeds to step S16. This is because the change in the sensor output value S (n) is large, so that the activation of the gas sensor element 17 is not sufficient and the value of the sensor resistance value Rs is considered to be unstable.

In steps S16, S17, and S18, in the same manner as in steps S12, S13, and S14 described above, the sensor output value S (n) is acquired at every sampling time (every 0.1 second) until 8 seconds have elapsed from the start. to continue. Then, when 8 seconds have elapsed since the activation (Yes in step S16), the process proceeds to step S19.
This is because the activation of the gas sensor element 17 was not sufficient in the period immediately after the activation (1 to 2, 5 seconds after the activation), and the activation is waited after a period.

  In the “second activity determination & adjustment” subroutine in step S19, processing is performed according to the flow shown in FIG. First, in step S91, the alignment continuation flag is cleared. Unlike the case of the above-mentioned “first activation determination & adjustment” subroutine (step S15), as will be described later, in this “second activation determination & adjustment” subroutine, the duty ratio DT of the pulse signal Sc is temporarily set. If it can be adjusted to an appropriate value, the duty ratio DT is maintained. This is because, after that, processing for determining whether or not the sensor output value S (n) is stable is performed.

  In step S92, the second target value SM2 is substituted as the target value SM. In the present embodiment, specifically, similarly to the first target value SM1, the numerical value of the sensor output value S (n) corresponding to Vout = 1V is set as the second target value SM2.

  Next, in steps S93 to S97 and T1, the sensor output value S (n) is continuously acquired (step S94) at every sampling time (every 0.1 second) until 12 seconds have elapsed from the start, and at step T1, A process for adjusting the duty ratio DT of the pulse signal Sc is performed. Then, when 12 seconds have elapsed from the activation (Yes in step S93), the process proceeds to step S98.

Specifically, in step S93, it is determined whether or not 12 seconds have elapsed from the start. If it has not elapsed (No), the sensor output value S (n) is acquired in step S94. Next, in step S95, it is determined whether or not an alignment end recognition flag is set. If the alignment is not completed (No), the process proceeds to the above-described “alignment process & alignment completion determination process” in step T1 (see FIG. 8). On the other hand, when the alignment completion recognition flag is set (Yes), the process proceeds to step S96, and the second alignment completion flag is set. After step T1 or step S96, the process waits for the sampling time to elapse in step S97 and returns to step S93.
In this way, in the “second activity determination & adjustment” subroutine of step S19, once the adjustment end recognition flag is set in “alignment processing & adjustment end determination processing” of step T1, the following From step S95, step S96 is selected instead of step T1, so once the duty ratio DT of the pulse signal Sc is “adjusted” to an appropriate value, the duty ratio is thereafter increased. The DT is not changed.

In the “second activity determination & alignment” subroutine (see FIG. 6) in step S19, as described above, the alignment continuation flag is cleared in step S91. For this reason, when the adjustment process is performed on the duty ratio DT of the pulse signal Sc by the processes of steps T11 to T20, it is determined No in step T21, and the “second activation determination & adjustment in step S19” is performed. It is supposed to return to the subroutine. Therefore, even when the alignment end flag is set (steps T19 and T20), the alignment recognition flag once set cannot be cleared through step T23.
It should be noted that a period during which “duration” of the duty ratio DT of the normal pulse signal Sc can be performed (the second fitting end flag is set) if the sensor resistance value Rs is stable for 4 seconds from 8 to 12 seconds after starting. Set period).

Further, when 12 seconds have elapsed from the activation (Yes in step S93), the process proceeds to step S98, and it is determined whether or not the limit recognition flag is cleared and the second fitting end flag is set. Here, if No, that is, if the limit recognition flag is set or the second matching end flag is cleared, after the setting continuation flag is reset in step S99, The process returns to the “second activity determination & adjustment” subroutine in step S19.
This is because the fact that the limit recognition flag is set means that even if the duty ratio DT is set to the upper limit value or the lower limit value, the sensor output value S (n) and the target value SM cannot be substantially equal to each other. That is to say. That is, the sensor resistance value Rs is too high or too low, and it cannot be said that the gas sensor element 17 is activated.
The fact that the second alignment end flag is cleared means that the “duration” of the duty ratio DT could not be performed in step T1 within 8 to 12 seconds after the activation. Also in this case, the sensor resistance value Rs is stable, and it cannot be said that the gas sensor element 17 is activated.

On the other hand, if the answer is Yes in step S98, in steps S9A, S9B, and S9C, in the same manner as steps S12, S13, and S14, every sampling time (every 0.1 second) until 15 seconds have passed since startup. The sensor output value S (n) is continuously acquired. Then, when 15 seconds have elapsed from the activation (Yes in step S9A), the process proceeds to step S9D.
As described below, in order to see the change up to 15 seconds after startup while maintaining the duty ratio DT of the pulse signal Sc set by “fitting” performed during the period of 8 to 12 seconds after startup. It is.

  In step S9D, the current sensor output value S (n) (that is, at the time when 15 seconds have elapsed from the start) is a value within a predetermined range including the target value SM (specifically, converted to the output voltage Vout). In the range of 0.8 to 1.2V). As described above, in the “second activation determination & adjustment” subroutine (see FIG. 6) in step S19, the duty ratio DT of the pulse signal Sc is adjusted during the period of 8 to 12 seconds after the activation. ing. Therefore, for example, at 10 seconds after the activation, the sensor output value S (n) becomes a value close to the target value SM by changing the duty ratio DT of the pulse signal Sc (T14, T18). Thereafter, since the duty ratio DT at this time is maintained, the subsequent change in the sensor output value S (n) corresponds to the change in the sensor resistance value Rs.

  Therefore, by looking at the sensor output value S (n) at 15 seconds after activation, for example, it is possible to evaluate fluctuations in the sensor output value during a period of 10 to 15 seconds after activation. Therefore, the sensor output value S (n) at 15 seconds after the activation last acquired in step S9B is within a predetermined range including the target value SM (in this example, 0.8 to 1.2 V in terms of the output voltage Vout). If it is within the range, it can be determined that the fluctuation of the sensor output value S (n) has become sufficiently small. That is, the fluctuation of the sensor resistance value Rs is sufficiently small, and it can be determined that the gas sensor element 17 is activated.

Therefore, if the sensor output value S (n) is a value within the predetermined range (Yes) in step S9D, the process proceeds to step S9E, the alignment continuation flag is cleared, and the main routine (see FIG. 4) is executed. Step S20 is skipped and the process returns to point A. After 15 seconds have elapsed from the start, the processing after step S21 is started. This is because it is considered that the gas sensor element 17 has been activated and gas detection is possible.
As described above, in this embodiment, the adjustment of the duty ratio DT of the pulse signal Sc is performed during the period of 8 to 12 seconds after the activation, and then the activation of the gas sensor element 17 is completed at the time of 15 seconds after the activation. Judging whether or not. For this reason, if it is determined that it is activated at this time, it is possible to immediately detect the gas concentration rise and fall immediately after step S21.

  On the other hand, if the sensor output value S (n) is outside the predetermined range (range corresponding to 0.8 to 1.2 V) in step S9D (No), the process proceeds to step S9F and the second fitting end flag is set. In addition to clearing, the matching completion recognition flag is also cleared. This is because the sensor output value S (n) and, therefore, the sensor resistance value Rs is not stable, so that the second fitting is not completed. Therefore, in step S9G, after setting the alignment continuation flag, the process returns to the main routine.

Subsequent to the “second activity determination & adjustment” subroutine in step S19, a “third adjustment” subroutine in step S20 is performed. In the “third fitting” subroutine of step S20, processing is performed according to the flow shown in FIG.
First, in step S101, the third target value SM3 is substituted as the target value SM. In the present embodiment, specifically, similarly to the first target value SM1, the numerical value of the sensor output value S (n) corresponding to Vout = 1V is set as the third target value SM3. Therefore, SM1 = SM2 = SM3.

  Next, in steps S102 to S104 and T1, the sensor output value S (n) is continuously acquired (step S103) every sampling time (every 0.1 second) until 30 seconds have elapsed from the start, and in step T1, A process for adjusting the duty ratio DT of the pulse signal Sc is performed.

Specifically, in step S102, it is determined whether or not 30 seconds have elapsed since the activation. If it has not yet elapsed (No), the sensor output value S (n) is acquired in step S103. Next, the process proceeds to the above-described “alignment process & alignment completion determination process” in step T1 (see FIG. 8). After step T1, the process waits for the sampling time to elapse in step S104 and returns to step S102.
In the “second activity determination & alignment” subroutine in step S19, the alignment continuation flag is cleared in step S91. On the other hand, in the “third fitting” subroutine in step S20, the state where the fitting continuation flag is set is maintained in step S9G. Therefore, until 30 seconds have elapsed after the activation (until “Yes” in Step S102), “Adjustment” of the duty ratio DT of the pulse signal Sc is repeated in the “Adjustment process & Adjustment completion determination process” in Step T1. To do.

  Then, when 30 seconds have elapsed from the start (Yes in step S102), the process proceeds to step S105, the alignment continuation flag is cleared, the alignment end recognition flag is set, and the process returns to the main routine.

  After returning to the main routine (see FIG. 4), as described above, steps S21 to S23 are repeated to detect the concentration rise and fall of the reducing gas. Thus, the gas detection can be started in a state in which the pulse signal Scno duty ratio DT is adjusted to an appropriate value after 30 seconds from the start by the “third adjustment” subroutine in step S20.

As can be understood from the above description, in the present embodiment, the sensor output value S in the processing of the detection circuit 11, the A / D conversion circuit 21, and steps S13, S17, S21, S54, S58, S94, S9B, and S103. The microcomputer 20 that acquires (n) corresponds to the acquisition means in the present invention.
Further, the microcomputer 20 that changes the duty ratio DT of the pulse signal Sc input to the pulse input terminal 18 of the detection circuit 11 in the processing in steps T14 and T18 corresponds to the change instruction means in the present invention.
Furthermore, in the process of step S22, the microcomputer 20 that detects the increase / decrease in the concentration of the reducing gas using the sensor output value corresponds to the gas concentration increase / decrease detection means in the present invention.
Further, in the process of step S56, the microcomputer 20 that determines whether or not | S (n) −S1 | <400 is satisfied, and in the process of step S9D, the sensor output value S (n) is within a predetermined range. Each of the microcomputers 20 for determining whether or not the value corresponds to the activation determination means in the present invention.

  Next, a specific example will be described. In the graph shown in FIG. 9, after the gas detection device 10 is restarted, it is determined that the gas sensor element 17 is activated in the “first activation determination & adjustment” subroutine in step S <b> 15, and the adjustment of the duty ratio DT is performed. It is a specific example which shows the change of sensor output value S (n) (output voltage Vout) and the change of the alignment end recognition flag when it is performed. In this graph, the sensor output value S (n) is shown as a value converted into the voltage value of the output voltage Vout of the detection circuit 11.

  In this example, the power is turned off very shortly before the restart, about 0.5 seconds, so that it can be easily understood by looking at the change in the sensor output value before the elapsed time of 0 seconds. This is an example of a so-called instantaneous interruption in which the power supply potential of the gas detection device 10 has decreased for a very short time due to noise, vibration, or the like.

In this case, the sensor output value S (n) at the time when 1 second has elapsed (steps S12 and S13) and the time when 2.5 seconds have elapsed (steps S53 and S54) from the restart (elapsed time 0 seconds) is almost equal. It is the same value. This is because the heating by the heater (not shown) is only interrupted for a very short time, so the temperature of the gas sensor element 17 hardly changed. Therefore, in the sensor output value determined by the duty ratio DT reset by the restart, This is probably because a stable value is maintained. Therefore, it is determined Yes in step S56, and thereafter, the duty ratio DT is adjusted until 5 seconds have passed (step T1). In this example, the duty ratio DT is reduced, and the sensor output value S (n) is also gradually decreased. At about 3.8 seconds after the start, the sensor output value S (n) becomes the target value SM ( The output voltage Vout is equivalent to 1V). Then, it can be seen that the realignment is performed repeatedly (a slight change in the sensor output value) until 5 seconds have passed since the start. Further, after 5 seconds have elapsed, an alignment completion recognition flag is set as indicated by a broken line (step S5A), and thereafter gas detection is performed in steps S21 to S23.
Thus, in this example, the gas detection can be resumed 5 seconds after the restart.

  Next, in the graph shown in FIG. 10, after the gas detection device 10 is restarted, the duty ratio DT is adjusted in the “second activation determination & adjustment” subroutine in step S <b> 19, and the gas sensor element 17 is activated. 11 is a specific example showing a change in the sensor output value S (n) (output voltage Vout) and a change in the alignment end recognition flag when it is determined that the adjustment is completed.

  This example shows the case where the power is turned off for a period of about 2.5 seconds before restarting, so that it can be easily understood by looking at the change in the sensor output value before the elapsed time of 0 seconds. In this example, the engine is restarted again in a short time of about a few seconds after the automobile engine is stopped.

In this case, when the time of about 30 seconds elapses after the restart, the sensor resistance value Rs is sufficiently stabilized, but even in the time of about 10 to 15 seconds after the restart, the change in the sensor resistance value is not so large. Therefore, it becomes stable to the extent that there is no problem in gas detection.
However, in this example, the sensor output value S (n) at the time when 2.5 seconds have elapsed is smaller than the sensor output value S1 at the time when 1 second has elapsed since the restart (step S52). The expression in step S56 is not satisfied. For this reason, it is determined No in step S56, and the duty ratio DT is not adjusted (duty ratio DT remains constant) in 2.5 to 5 seconds after activation.

  Next, in the subroutine of step S19, the duty ratio DT is adjusted after the elapse of 8 seconds from the start. In this example, the duty ratio DT is lowered in the period of 8 to 10 seconds after the start, and the sensor output value S (n) is also gradually reduced, and the sensor output value S (n) is adjusted to the target value SM (corresponding to 1V in the output voltage Vout) at about 10 seconds after the start-up. At this point, the fitting completion recognition flag is set as indicated by the broken line (step T20).

However, in this example, once the adjustment is performed about 10 seconds after the activation, the duty ratio DT is not changed thereafter. For this reason, the sensor output value S (n) gradually changes according to the change of the sensor resistance value Rs from the time point of 10 seconds after the activation. Then, it is determined whether or not the sensor output value S (n) at the time of 15 seconds after activation is within a predetermined range (step S9D). In this example, since it is determined that the range is within the range (a range corresponding to 0.8 to 1.2 V) (Yes), gas detection is immediately performed in steps S21 to S23.
Thus, in this example, the gas detection can be resumed 15 seconds after the restart.

  Next, the graph shown in FIG. 11 shows the sensor output value S (n when the duty ratio DT is adjusted in the “third adjustment” subroutine in step S20 after the gas detection device 10 is restarted. ) Is a specific example showing a change in (output voltage Vout) and a change in the alignment end recognition flag.

  In this example, the power is turned off for a period of 5 seconds or more before restarting so that it can be easily understood by looking at the change in the sensor output value before the elapsed time of 0 seconds. This is an example in the case where the engine is restarted after some time has elapsed after the engine of the automobile is stopped.

In this case, the sensor resistance value Rs is sufficiently stabilized after about 30 seconds after the restart, but the change in the sensor resistance value Rs is still large after about 10 to 15 seconds after the restart. .
Therefore, in this example, the sensor output value S (n) at the time when 2.5 seconds have elapsed is considerably smaller than the sensor output value S1 at the time when 1 second has elapsed since the restart (step S52). , Step S56 is not satisfied. For this reason, it is determined No in step S56, and the duty ratio DT is not adjusted (duty ratio DT remains constant) in 2.5 to 5 seconds after activation.
Therefore, in the subroutine of step S19, the duty ratio DT is adjusted after the elapse of 8 seconds. In this example, the duty ratio DT is reduced in the period of 8 to 10 seconds after the activation, and the sensor output value S (n) is gradually decreased. The sensor output value S is about 10 seconds after the activation. (N) is adjusted to the value of the target value SM (corresponding to 1 V in the output voltage Vout). At this point, the fitting completion recognition flag is once set as indicated by a broken line (step T20).

  However, unlike the previous example (see FIG. 10), if the duty ratio DT is maintained 10 seconds after the start-up after the adjustment has been completed, the sensor resistance value Rs is still unstable (continues to decrease). The sensor output value S (n) is greatly deviated from the target value SM at 15 seconds after activation. Therefore, it is determined that the value is outside the predetermined range (the range of the value corresponding to 0.8 to 1.2 V in terms of the output voltage Vout) (No in step S9D), and as shown by the broken line in FIG. Is cleared (step S9F), an alignment continuation flag is set (step S9G), and the process proceeds to a subroutine of step S20.

After 15 seconds from the start, the adjustment of the duty ratio DT is repeated according to the subroutine of step S20 (step T1). For this reason, in this example, the duty ratio DT of the pulse signal Sc is increased in the period of 15 to 16 seconds after the startup, and the sensor output value S (n) is increased to obtain a value equivalent to 1 V in terms of the output voltage Vout. Yes. Thereafter, since the duty ratio DT is repeatedly lowered and raised, the sensor output value S (n) is a value around 1 V in terms of the output voltage Vout.
Further, after 30 seconds have elapsed since startup, after the alignment completion recognition flag is set (step S105) as shown by the broken line in FIG. 11, gas detection is performed in steps S21 to S23. Thus, in this example, the gas detection is resumed 30 seconds after the restart.

As described above, according to the present embodiment, for an instantaneous interruption of the power supply (in the case of FIG. 9), a restart after a short stop (in the case of FIG. 10), etc., 5 seconds or 15 seconds from the restart. Gas detection can be resumed in a short time.
In particular, according to the present embodiment, the duty ratio DT of the pulse signal Sc is set to an appropriate value (a value in which the sensor output value S (n) is substantially equal to the target value SM) during a period of 8 to 12 seconds after activation. The “adjustment” is performed so as to change. After that, from the change of the sensor output value S (n), it is determined whether the sensor output value Rs is stable, and thus the activation of the gas sensor element 17 is completed. For this reason, if it is determined that it is activated at the time of 15 seconds after activation, gas detection can be resumed immediately.
For this reason, there is an advantage that the gas detection can be restarted earlier than the case where “duration” of the duty ratio DT of the pulse signal Sc is performed after it is determined that it is activated.

In the above, the present invention has been described with reference to the embodiments. However, the present invention is not limited to the above embodiments, and it is needless to say that the present invention can be appropriately modified and applied without departing from the gist thereof.
For example, in the above-described embodiment, the fitting process is performed in the subroutines of steps S15, S19, and S20. At this time, the duty ratio DT is changed so that the sensor output value S (n) approaches the target value SM. The target value SM is set to Vout = 1V in any of steps S15, S19, and S20. The corresponding sensor output value S (n) was set to a numerical value (SM = SM1 = SM2 = SM3). However, in each step, the target value SM may be set to a different value.

  In the above-described embodiments, the gas sensor element that reacts with the reducing gas is used. However, a gas sensor element that reacts with an oxidizing gas such as NOx may be used. Furthermore, both a gas sensor element that reacts with a reducing gas and a gas sensor element that reacts with an oxidizing gas can be used. In this case, it is preferable to detect the increase / decrease of the concentration of the reducing gas and the increase / decrease of the oxidizing gas, and to open and close the flap 34 in total.

  Further, in the above-described embodiment, the example using the detection circuit 11 shown in FIG. 1 is shown, but a detection circuit having a circuit with another configuration as a charging circuit and a discharging circuit can also be used.

It is explanatory drawing which shows the structure of the gas detection apparatus and vehicle autoventilation system which concern on an Example. It is a graph which shows the relationship between the sensor resistance value Rs of a gas sensor element, and the output voltage Vout about the detection circuit of the gas detection apparatus which concerns on an Example using the duty ratio of the input pulse signal as a parameter. It is explanatory drawing which shows the flow of flap control in the vehicle autoventilation system concerning an Example. It is explanatory drawing which shows the flow of the main routine of the control in a microcomputer among the gas detection apparatuses concerning an Example. It is explanatory drawing which shows the content of the 1st activity judgment & adjustment routine among the control in a microcomputer concerning the gas detection apparatus of an Example. It is explanatory drawing which shows the content of the 2nd activity judgment & adjustment routine among the control in a microcomputer concerning the gas detection apparatus of an Example. It is explanatory drawing which shows the content of the 3rd activity judgment & adjustment routine among the control in a microcomputer concerning the gas detection apparatus of an Example. It is explanatory drawing which shows the content of the fitting process & fitting completion determination processing routine among the control in a microcomputer concerning the gas detection apparatus of an Example. According to the embodiment, after the gas detector is restarted, the sensor output when the gas sensor element is determined to be activated and the duty ratio is adjusted in the “first activation determination & adjustment” subroutine. It is a specific example which shows the change of value S (n) (output voltage Vout) and the change of the alignment end recognition flag. According to the embodiment, after the gas detection device is restarted, the sensor is operated when the duty ratio is adjusted and the gas sensor element is determined to be activated in the “second activation determination & adjustment” subroutine. It is a specific example showing a change of an output value S (n) (output voltage Vout) and a change of an alignment end recognition flag. According to the embodiment, the sensor output value S (n) (output voltage Vout) is changed or adjusted when the duty ratio is adjusted in the “third adjustment” subroutine after the gas detector is restarted. It is a specific example which shows the change of a completion | finish recognition flag.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Vehicle auto ventilation system 10 Gas detection apparatus 11 Detection circuit (acquisition means)
12 Capacitor 13 Charging Circuit 14 Charging Resistor Rc Resistance Value of Charging Resistor 15 Charging Diode 16 Discharging Circuit 17 Gas Sensor Element (Discharging Resistor)
Rs Sensor resistance value (resistance value of discharge resistor)
Sc Pulse signal DT (pulse signal) duty ratio ΔDT1 (duty ratio DT) decrement ΔDT2 (duty ratio DT) increment 18 Pulse input terminal (pulse input point)
19 Output terminal (operating point)
Vout output voltage (operating point potential)
20 Microcomputer 20A Sensor input terminal 20B Pulse output terminal 20C Concentration signal output terminal LV Concentration signal 21 A / D conversion circuit (acquisition means)
S (n) Sensor output value 30 Ventilation mechanism 31, 32, 33 Duct 34 Flap 35 Fan 40 Flap control mechanism 41 Flap drive circuit 42 Actuator SM Target value SM1 First target value SM2 Second target value SM3 Third target value S1 Sensor 1 second value

Claims (4)

A gas detection device using a gas sensor element whose sensor resistance value changes according to the concentration of a specific gas in an environmental gas,
An acquisition means for acquiring a sensor output value using a detection circuit including the gas sensor element,
An acquisition unit capable of changing at least one of a circuit condition and a driving condition of the detection circuit according to a sensor resistance value of the gas sensor element;
Change instruction means for changing the sensor output value by changing at least one of the circuit condition and the drive condition of the detection circuit;
Gas concentration increase / decrease detection means for detecting increase / decrease in the concentration of the specific gas using the sensor output value;
A plurality of activation determination means for determining whether or not the gas sensor element is activated after activation of the gas detection device;
When it is determined that the gas sensor element is activated, an activation determination unit that starts detection of increase / decrease of the concentration of the specific gas by the gas concentration increase / decrease detection unit is then provided,
At least one of the one or more activation determination means changes at least one of the circuit condition and the driving condition of the detection circuit so that the sensor output value satisfies a predetermined condition by the change instruction means. A gas detection device for determining whether the gas sensor element is activated after being activated. A gas detection device using a gas sensor element whose sensor resistance value changes according to the concentration of a specific gas in an environmental gas,
A detection circuit including the gas sensor element,
A pulse input point to which a pulse signal having a repetitive waveform having a first potential state and a second potential state is input;
Capacitors,
A charging circuit that charges the capacitor through a charging resistor during a period in which the signal of the first potential state is input to the pulse input point; and
A discharge circuit that discharges the capacitor through a discharge resistor during a period in which the signal of the second potential state is input to the pulse input point;
At least one of the charging resistor of the charging circuit and the discharging resistor of the discharging circuit includes a gas sensor element having the sensor resistance value,
At least one of the charging current of the charging circuit and the discharging current of the discharging circuit changes according to a change in the sensor resistance value of the gas sensor element,
A detection circuit capable of changing the duty ratio of the pulse signal;
An acquisition means for acquiring a sensor output value corresponding to the potential at the operating point at which the potential changes at one end of the capacitor and changes in the sensor resistance value of the gas sensor element;
Change instruction means for changing the sensor output value by changing the duty ratio of the pulse signal applied to the pulse input point of the detection circuit;
Gas concentration increase / decrease detection means for detecting increase / decrease in the concentration of the specific gas using the sensor output value;
A plurality of activation determination means for determining whether or not the gas sensor element is activated after activation of the gas detection device;
When it is determined that the gas sensor element is activated, an activation determination unit that starts detection of increase / decrease of the concentration of the specific gas by the gas concentration increase / decrease detection unit is then provided,
At least one of the one or more activation determination means changes at least one of the circuit condition and the driving condition of the detection circuit so that the sensor output value satisfies a predetermined condition by the change instruction means. A gas detection device for determining whether the gas sensor element is activated after being activated. The gas detection device according to claim 2,
When the duty ratio is changed among the changing directions of the duty ratio of the pulse signal, the direction in which the sensor output value decreases is defined as the output value decreasing direction, and conversely, the direction in which the sensor output value increases is defined as the output value. When going up,
The predetermined condition that the sensor output value satisfies by the change instruction means is:
Within the first predetermined period after the first time elapses and after the second time elapses,
After changing the duty ratio of the pulse signal in the direction of decreasing the output value and making the sensor output value once below the target value, or the sensor output value below the target value,
The duty ratio of the pulse signal is changed in the output value increasing direction to determine whether the sensor output value is equal to or higher than the target value.
The activation determination means includes
The duty ratio of the pulse signal is fixed to the duty ratio when the sensor output value satisfies the predetermined condition, and the sensor output value is set to the target value when a third time elapses after the second time. A gas detection device that determines that the gas sensor element is activated when the value is within a predetermined fluctuation allowable range including The vehicle autoventilation system containing the gas detection apparatus of any one of Claims 1-3.

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