JP2003057202A - Gas detection apparatus, and auto ventilation system for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas detection apparatus for reliably and readily detecting the increase in gas concentration by using simple processing, to provide a gas detection apparatus having fewer wrong determinations, and to provide an auto ventilation system for vehicles which uses the gas detection apparatus. SOLUTION: The gas detection apparatus for using a gas sensor element 11, where sensor resistance Rs changes according to gas concentration acquires a sensor output value S from a sensor resistance conversion circuit 14, calculates a base value B(n) according to B(n)=B(n-1)+k1 S(n)-B(n-1)} and B(n)=S(n) when S(n)>=S(n-1) and S(n)<S(n-1), respectively, and further calculates a difference value D(n)=S(n)-B(n). When the gas concentration increases and the difference value becomes larger than a specific concentration threshold, a concentration high signal is generated and a flap 34 is closed, a coefficient k2 that is smaller than k1 is used, and the base value B(n) is calculated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas detection device for detecting a change in the concentration of a specific gas in the environment by using a gas sensor element and an automatic ventilation system for a vehicle.

[0002]

2. Description of the Related Art Conventionally, oxidizing gas such as NOx and CO, HC (hydrocarbon) in the environment such as gas sensor element using lead-phthalocyanine or metal oxide semiconductor such as WO3 or SnO2 are reduced. Since the sensor resistance value changes due to the change in the concentration of a specific gas such as a characteristic gas, there is known a gas sensor element capable of detecting the change in the specific gas concentration due to the change in the sensor resistance value. Moreover, a gas detection device using such a gas sensor element is also known. 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 the introduction of outside air and the introduction of inside air into the vehicle interior depending on the state of contamination of the air outside the vehicle interior 2. Description of the Related Art A system and a system for detecting indoor air pollution due to smoking and controlling an air purifier are known.

In the gas detection device using such a gas sensor element, the output signal of the gas sensor element is differentiated to detect gas, and the analog differential value is A / D converted and then further digitally differentiated to the second differential. There are a method for detecting a gas by obtaining a value, a method for detecting a gas by comparing an integrated value obtained by integrating a sensor signal with the sensor signal, and the like.

[0004]

However, in a gas detection device using a gas sensor element in which electrical characteristics such as sensor resistance change due to changes in the concentration of a specific gas, the electrical characteristics (sensor resistance) of the gas sensor element are specified. It has the property of fluctuating not only due to changes in gas concentration, but also due to environmental influences such as temperature, humidity, and wind speed. Therefore, in the gas detection device using differentiation, the relative change of the output signal is detected, but this output signal is not only due to the change in the concentration of the specific gas, but also due to other environments such as temperature, humidity and wind speed. Since there is a large variation, it is not possible to clearly discriminate whether the variation is due to the concentration of the specific gas or the variation due to a disturbance such as a humidity change, only from the relative change of the output signal. Therefore, when the differential value or the second differential value of the output signal of the gas sensor element is used as described above,
It is possible to capture the time when the gas concentration fluctuates (for example, the time when the gas concentration suddenly rises), but to what extent the gas concentration change was observed, or how the gas concentration changed after that or the gas concentration decreased. It's hard to know when.

On the other hand, in a gas detection device which detects a gas by comparing the integrated value of the sensor signal with the sensor signal, the change of the integrated value is delayed with respect to the change of the concentration of the specific gas.
Once the concentration of the specific gas starts to decrease, the integrated value may become larger than the sensor output value in the concentration increasing direction. Therefore, even if the concentration of the specific gas rises again after that, the concentration of the specific gas increases because the integrated value is larger than the sensor output value, even though the concentration of the specific gas (hence, the sensor output value) starts to rise. In some cases, the rise in the gas cannot be detected, and the detection timing is delayed, so that the change in the concentration of the specific gas cannot be detected properly.

On the other hand, in JP-A-1-199142, the temporal behavior of the sensor output is tracked, the sensor output corresponding to the cleanest atmosphere is stored as a reference output, and the reference is set with the lapse of time after storage. A gas detection device is disclosed in which the output is gradually changed to the side corresponding to the contaminated atmosphere, and when the changed reference output exceeds the actual gas sensor output, the reference output is changed to the actual sensor output. According to the present invention, the increase rate of the reference output is set in advance to a value commensurate with the change in the sensor output due to the temperature / humidity fluctuation, so that the gas detection can be performed even when the temperature / humidity changes.

However, this Japanese Laid-Open Patent Publication No. 1-191414
According to the invention described in No. 2, the reference output is gradually changed to the side corresponding to the contaminated atmosphere (concentration increasing direction) with the passage of time. That is, regardless of the magnitude of the change in the sensor output, the sensor output is gradually changed at a constant rate of change with time. For example, a value obtained by adding a fixed value to the reference output is set as a new reference output and is linearly increased with time. However, the change in the concentration of the specific gas is not constant and cannot be predicted. For example, it is assumed that the gas concentration changes little by little toward the side corresponding to the contaminated atmosphere (concentration increasing direction).
In this case, when the set increase rate of the reference output is large, the reference output is higher than the sensor output (concentration increase) even though the sensor output changes to the side (concentration increasing direction) corresponding to the pollution atmosphere. Direction), the gas concentration gradually increases, and even if the gas concentration is high as a whole, the reference output (that is, the sensor output immediately before) is output.
Since the difference between the (current) sensor output does not increase and the increase in gas concentration may not be detected early.

Further, regardless of the sensor output, the reference output is gradually changed, such as linearly increasing, so that the high gas concentration is maintained for a long time such as a long tunnel and the sensor output remains high. Even if there is, the difference between the sensor output and the reference output becomes small due to the gradual increase of the reference output, and there is a problem that it is erroneously determined that the gas concentration is low. The present invention has been made in view of the above problems, using a simple process, a gas detection device capable of reliably and early detecting an increase in gas concentration,
Furthermore, it aims at providing the gas detection apparatus with few erroneous determinations, and the auto-ventilation system for vehicles using this.

[0009]

[Means for Solving the Problem, Action and Effect] A means for solving the problem is a gas detecting device using a gas sensor element whose electric characteristic changes according to the concentration of a specific gas, and using the gas sensor element, An acquisition unit that acquires the sensor output value for each time, a concentration signal generation unit that generates one of a low concentration signal and a high concentration signal, and a period in which the low concentration signal is generated by the concentration signal generation unit, First calculation means for calculating the first calculated value, and when the current sensor output value changes in the concentration increasing direction as compared with the immediately preceding sensor output value, slowly follows the current sensor output value. The first calculated value that changes is calculated using the current sensor output value, and when the current sensor output value changes in the direction of decreasing density compared to the immediately preceding sensor output value, this current sensor output value is set to the first Arithmetic Comprising a first calculation means for a value, a,
The density signal generating means replaces the density low signal when the sensor output value and the first calculated value satisfy a predetermined first relationship during a period in which the density low signal is generated. It is a gas detection device that generates a high concentration signal.

In the gas detection device of the present invention, the first calculated value is calculated during the generation period of the low concentration signal. Among them, the current sensor output value S compared to the immediately preceding sensor output value S (n-1)
When (n) changes in the density increasing direction, the first calculated value C1 (n) that changes while following the current sensor output value S (n) is calculated. That is, the sensor output value S (n)
Changes (for example, increases) in the concentration increasing direction, the first
The calculated value C1 (n) also follows this, and more slowly changes (for example, increases) in the same direction as the concentration increasing direction. Therefore, when the sensor output value S (n) changes in the direction of increasing the concentration, the first calculated value C1 (n) changes slowly after that, which causes a difference between the two. By utilizing this property, it is possible to detect an increase in the concentration of the specific gas. For example, the sensor output value S (n) and the first calculated value C1
When the difference from (n) satisfies a predetermined magnitude relationship with a predetermined first threshold value, more specifically, the sensor output value S
When the difference between (n) and the first calculated value C1 (n) becomes larger than the first threshold value, or the sensor output value S
When the ratio between (n) and the first calculated value C1 (n) satisfies a predetermined magnitude relationship with a predetermined first threshold value, the sensor output value and the first calculated value have a predetermined relationship. When satisfied,
If the concentration signal generating means generates a high concentration signal, it is possible to detect an increase in the concentration of the specific gas.

Further, for example, when the gas concentration gradually changes in the concentration increasing direction, the current sensor output value changes in the concentration increasing direction as compared with the immediately preceding sensor output value.
The current sensor output value is never substituted as the new first calculated value. Therefore, as the gas concentration increases, the sensor output value gradually changes in the concentration increasing direction, and
The calculated value changes slowly while following it, and the difference between the sensor output value and the first calculated value increases, so that the increase in gas concentration can be detected early.

On the other hand, when the current sensor output value S (n) changes in the density decreasing direction opposite to the above as compared with the immediately preceding sensor output value S (n-1), regardless of the previous progress. , The current sensor output value S (n) as the first calculated value C1
(N) (C1 (n) = S (n)). Therefore, after that, when the concentration of the specific gas increases and the sensor output value starts to change in the concentration increasing direction, the first calculated value C1 is not affected by the change in the sensor output value before that and the like.
Since (n) changes slowly while following the newly obtained sensor output value, it is possible to catch the increase in the specific gas concentration earlier. Moreover, the immediately preceding sensor output value is compared with the current sensor output value, and when the concentration changes, the current sensor output value is used as the first calculated value.
The process for obtaining the first calculated value is simple.

In the present specification, the direction of increasing the concentration means the direction in which the sensor output value changes when the concentration of the specific gas increases. For example, in the acquisition unit configured to increase the sensor output value when the concentration of the specific gas increases, the direction in which the sensor output value increases is the concentration increasing direction. On the contrary, in the acquisition means configured so that the sensor output value decreases when the concentration of the specific gas increases, the direction in which the sensor output value decreases is the concentration increasing direction. Further, the concentration decreasing direction means a direction opposite to the concentration increasing direction. Further, the "immediately before" value refers to a value obtained immediately before the considered value in a time series of values obtained in order (every predetermined time period, etc.). For example, the immediately preceding sensor output value refers to the sensor output value obtained one before (by a predetermined time period) before the sensor output value under consideration (for example, S (n- vs. S (n- 1)). In addition, the immediately preceding first calculated value refers to the first calculated value calculated last time (one time before) (for example, B (n)).
To B (n-1)). Further, as the first calculated value calculated when the current sensor output value changes in the density increasing direction compared to the immediately previous sensor output value, for example, S
When (n) is the sensor output value, B (n) = B (n-
1) + k1 {S (n) -B (n-1)}, which is a base value B (n) given by the equation, a moving average value, an integrated value, and the like.

Further, in the above-mentioned gas detecting device, the concentration signal generating means has the first relationship between the sensor output value and the first calculated value as the first relationship during a period in which the low concentration signal is being generated. It is preferable that the gas detection device generates the high concentration signal instead of the low concentration signal when the difference satisfies a predetermined magnitude relationship with respect to the predetermined first threshold value.

In the gas detector of the present invention, the difference between the sensor output value and the first calculated value is used to judge the predetermined magnitude relationship with the predetermined first threshold value, so that the gas concentration can be easily and reliably obtained. You can judge the rise of.

Further, in the gas detection device according to any one of the above, in the period in which the high concentration signal is being generated by the concentration signal generating means, the second slowly changing while following the sensor output value. A second calculation unit that calculates a calculated value using the sensor output value is provided, and the concentration signal generation unit is configured to calculate the sensor output value and the second calculated value during a period in which the high concentration signal is being generated. Is a gas detection device that generates the low concentration signal instead of the high concentration signal when the predetermined second relationship is satisfied.

For example, in a vehicle auto-ventilation system using a gas detection device, etc., the outside air inlet is fully closed when the gas concentration is detected to be fully closed, and the outside air inlet is fully opened when the gas concentration is detected to be low. The control for the outside air circulation may be performed. In such a case, after detecting the rise in gas concentration and fully closing the outside air inlet, when the gas concentration decreases to the same level as the gas concentration at the time of rising detection, the outside air inlet is fully opened. In order to enable control, it is preferable in the gas detection device to switch the high-concentration signal to the low-concentration signal at the time when the gas concentration decreases to the same extent as when the rise is detected. Therefore, it is considered desirable to keep the reference value, which is to be compared with the sensor output value, constant during the generation period of the high concentration signal regardless of the elapsed time.

However, as described above, the electrical characteristics of the gas sensor element are affected not only by the change in the concentration of the specific gas, but also by the environment such as temperature and humidity and the wind speed, and the concentration of the specific gas is constant. Also the sensor output value S
(N) may change gradually, that is, may drift. For example, it is assumed that an acquisition unit that increases the sensor output value as the specific gas concentration increases is used. In this case, when the concentration of the specific gas increases and then decreases, the sensor output value usually increases once and then decreases. However, here, if the sensor output value drifts in the direction of increasing during the period from the increase to the decrease of the specific gas concentration, even if the actual concentration of the specific gas decreases to the same level as before the increase, Due to the drift, the sensor output value decreases only to a value larger than the value before the increase.

In this case, even if an attempt is made to detect a decrease in the gas concentration by comparing the sensor output value with the reference value at the time of detecting the concentration increase, the sensor output value itself does not return to the value that should be returned, so that the sensor The difference between the output value and the reference value does not become small, and although the concentration of the specific gas is actually sufficiently low, it is erroneously determined that the concentration of the specific gas remains high,
There is a risk that the decrease in gas concentration cannot be determined. Then,
If such a gas detector is used in a vehicle auto-ventilation system or air purifier control system, the flap may remain closed or the fan may rotate at high speed for a long time, and It becomes difficult to control.

Therefore, as in the technique described in Japanese Patent Laid-Open No. 1-199142, the reference value changes, but does not follow the sensor output value, but gradually increases, for example, at a constant slope. When a value that linearly increases with time is used, the above-mentioned problems do not occur. This is because the difference between the sensor output value and the reference value becomes small as time passes. However, if the specific gas concentration is high for a long time, such as when entering the long tunnel described above, or if the sensor output value is held for a long time without becoming a large value, the sensor output value and the reference value And the specific gas concentration is high, a low concentration signal may eventually be generated.

On the other hand, according to the gas detector of the present invention, even in the case of the above assumption, the second calculated value slowly changes in accordance with the sensor output value, so that the sensor output value tends to increase. Even if a drift occurs, the difference between the sensor output value and the second calculated value gradually decreases with the passage of time. Therefore, when the concentration of the specific gas decreases, the predetermined second relationship can be satisfied and the low concentration signal can be generated without fail. Moreover, since the second calculated value slowly changes in accordance with the sensor output value, the second calculated value is calculated as a value that reflects the change in the sensor output value, unlike the above-described case where the reference value is increased in a predetermined pattern. Therefore, it is possible to prevent the low concentration signal from being erroneously generated despite the high concentration of the specific gas such as in the tunnel. Therefore, in a vehicle auto-ventilation system or an air purifier control system, it is possible to perform appropriate control such as opening the flap or rotating the fan at a low speed after a certain amount of time has elapsed. Contrary to the above assumption, if the sensor output value decreases due to the increase of the specific gas concentration due to the characteristics of the acquisition means, the decrease of the specific gas concentration should be similarly detected by reversing the above. You can

As described above, if the second relationship is appropriately set according to the characteristic of the acquisition means and the property of the second calculated value, the second judgment means judges whether or not the second relationship is satisfied. This makes it possible to properly detect the decrease in the specific gas concentration. Therefore, the density signal generating means can generate a density low signal instead of the density high signal. Thus, it is possible to output the concentration signal according to the level of the specific gas concentration.

Further, in the gas detection device, the concentration signal generating means sets the second relationship between the sensor output value and the second calculated value as the second relationship during a period in which the low concentration signal is being generated. It is preferable to use a gas detection device that generates the low concentration signal instead of the high concentration signal when the difference satisfies a predetermined magnitude relationship with respect to a predetermined second threshold value.

In this gas detector, the difference between the sensor output value and the second calculated value is used to judge the predetermined magnitude relationship with the predetermined second threshold value, so that the gas concentration can be easily and surely reduced. Can judge.

Further, in the gas detection device according to either of the two above, the first calculation means changes the current sensor output value in the concentration increasing direction as compared with the immediately preceding sensor output value. At times, a gas detection device that calculates the first calculated value that changes more sensitively than the second calculated value may be used.

In the gas detection device of the present invention, the first calculated value changes more sensitively than the second calculated value when calculated at the same time, that is, it follows the sensor output value relatively quickly. Here, consider a case where the sensor output value slightly changes in the density increasing direction due to the inclusion of noise during the low density signal generation period. At this time, the first calculated value rapidly changes in comparison with the case where the second calculated value is used, so the difference between the sensor output value and the first calculated value does not become a very large value. Therefore, when attempting to detect the concentration increase by utilizing this property, for example, when detecting the concentration increase using the difference or the ratio between the sensor output value and the first calculated value, erroneous detection due to noise may occur. It can be prevented. In addition, even when the sensor output value gently changes in the direction of increasing the concentration due to temperature fluctuations, etc., the first calculated value changes more quickly than the second calculated value in the case of calculation, so that the temperature change It is also possible to suppress the influence of drift due to, for example, and prevent erroneous detection.

However, when the concentration of the specific gas rises and the sensor output value changes rapidly and largely, the first calculated value cannot follow sufficiently and the difference between the sensor output value and the first calculated value becomes large. The value and the first calculated value are the predetermined first
The relationship can be satisfied, or the difference between the sensor output value and the first calculated value can satisfy a predetermined magnitude relationship with the first threshold value, and a high density signal can be generated. Thus, while suppressing the influence of noise and drift, it is possible to detect a rise in the gas concentration at a relatively early time when the rise in the specific gas concentration and generate a high concentration signal.

On the other hand, during the high density signal generation period, the sensor output value, not the first calculated value, changes following the sensor output value more slowly than the first calculated value calculated at the same time. The second calculated value is used. For this reason, the second calculated value is a value that maintains a state in which the state at the time of detecting the increase in the gas concentration is reflected more, so that the low concentration signal can be generated when the gas concentration further decreases.

Further, another solution is a gas detecting device using a gas sensor element whose electric characteristic changes according to the concentration of a specific gas, wherein the gas sensor element is used,
An acquisition means for acquiring the sensor output value S (n) at predetermined time intervals, the acquisition means increasing the sensor output value S (n) when the concentration of the specific gas increases; An integer indicating the sequence order, a density signal generating means for generating either a density low signal or a density high signal, and a base value B (n) during a period during which the density signal generating means is generating the density low signal. Is a first base value calculation means for calculating
The sensor output value S (n) is the immediately preceding sensor output value S (n
-1) or more, the base value B according to the following formula (1)
(N) is calculated and B (n) = B (n-1) + k1 {S (n) -B (n-1)} (1) where k1 is the first coefficient and 0 <k1 < 1. When the sensor output value S (n) is smaller than the immediately preceding sensor output value S (n-1), the base value B is calculated according to the following equation (2).
B (n) = S (n) for calculating (n) (2) During the period in which the high density signal is generated by the first base value calculating means and the density signal generating means, the following formula (3) Second base value calculating means for calculating the base value B (n) according to the following: B (n) = B (n-1) + k2 {S (n) -B (n-1)} (3) where k2 Is a second coefficient, 0 <k2 <k1 <1, a difference value for calculating a difference value D (n) from the sensor output value S (n) and the base value B (n) according to the following equation (4). Comprising: calculating means; and D (n) = S (n) −B (n) (4), wherein the density signal generating means is the difference value D (n).
Is larger than the concentration threshold value, the gas detector generates the high concentration signal.

First, the base value B (n) will be described. The base value B calculated according to the above equation (1) or (3) with respect to the fluctuation of the sensor output value S (n)
(N) changes following this. Here, the base value B (n) has the property that when the values of the coefficients k1 and k2 are changed, the degree of tracking the sensor output value S (n) changes, and the coefficients k1 and k2 are large (close to 1). ), The base value B (n) quickly follows the sensor output value S (n). Conversely, when the coefficients k1 and k2 are small (close to 0), the base value B (n) changes slowly, and the sensor output value S
Follow (n) slowly. Therefore, the coefficient k
When 1 and k2 are small, the base value B (n) is a value greatly influenced by the past sensor output value S (n) and the base value B (n).

The gas detection device of the present invention has, in addition to the acquisition means for acquiring the sensor output value, the first and second base value calculation means for calculating the base value B (n) having the above-mentioned characteristics. The base value is calculated while switching between the two calculation means. That is, during the period in which the low density signal is generated by the density signal generating means, the first base calculating means is used,
On the contrary, during the period when the high density signal is being generated, the base value is calculated using the second base calculating means.

First, the case of calculating the base value using the first base value calculating means will be described. When the sensor output value S (n) is equal to or more than the immediately preceding sensor output value S (n-1) during the period when the low density signal is generated, the first base value calculating means uses the above formula (1). Then, the base value is calculated. In the equation (1), the relatively large first coefficient k1 (k1>
Since k2) is used, the calculated base value B (n) follows the sensor output value S (n) in a relatively quick manner, although it is slightly behind. Therefore, while the first base value calculating means calculates the base value by the equation (1), the difference value D (n) obtained by the equation (4) is gradually changed to the sensor output value due to the temperature fluctuation or the like. Even if fluctuates,
Since the base value B (n) also changes following the change, it does not become a very large value, so gas detection can be performed while suppressing the influence of drift due to temperature change and the like. However, when the concentration of the specific gas increases and the sensor output value S (n) rapidly and largely changes (increases), the difference value D (n) increases because the base value B (n) cannot sufficiently follow. Therefore,
When this difference value D (n) exceeds the density threshold value, the density signal generating means generates a density high signal instead of the density low signal.
At the same time, the second base value calculating means is used to calculate the base value B (n).

In the period in which the low density signal is generated, the sensor output value S (n) is the sensor output value S (n) immediately before.
When it is smaller than -1), the first base value calculation means calculates the base value using the above equation (2). That is, the current sensor output value S (n) is substituted for the base value B (n). As a result, the base value B (n) changes in accordance with the sensor output value S (n) (completely follows), so that the gas concentration increases and S (n)> S (n-1). At this point, the base value B is more than the sensor output value S (n).
(N) is always a small value, and a positive difference value D (n) is generated. Therefore, regardless of the change in the gas concentration before that, the increase in the gas concentration can be grasped at an early stage.

On the other hand, in synchronism with the generation of the high density signal instead of the low density signal, the second base value using the second coefficient k2 instead of the first base value calculating means for the base value B (n). It is calculated by the calculation means. Since the second coefficient k2 used in the second base value calculation means is relatively small (k2 <k1), the change of the base value B (n) becomes slow and the tracking of the sensor output value becomes relatively slow. . As described above, the base value calculated using the relatively small second coefficient k2 is the value affected by the past sensor output value or the base value, specifically, the calculation formula of the base value B (n). The value influenced by the base value calculated by the equation (1) immediately before the time point when the equation (1) is switched to the equation (3), and therefore, the value affected by the sensor output value or the base value before the switching is changed. Has become. This can be easily understood from the fact that when k2 = 0, the base value B (n) maintains the base value immediately before switching. That is, the base value B (n) calculated by the second base value calculating means reflects the state immediately before the concentration of the specific gas rises to some extent while slowly following the sensor output value S (n). Become.

Therefore, the value represented by the difference value D (n), which is the difference between the current sensor output value S (n) and the base value B (n) calculated by the second base value calculating means, is present, that is, specific. It can be considered as a value obtained by comparing the state after the gas concentration has increased with the past, that is, the state before the gas concentration has increased.
Therefore, when the concentration of the specific gas decreases again and the sensor output value S (n) decreases, the concentration of the specific gas decreases due to the difference value D (n) from the base value B (n). It can be easily determined. Then, the density signal generating means generates a density low signal instead of the density high signal. Moreover, since the second coefficient k2 can be used to adjust the gradual tracking of the base value B (n), it is possible to grasp an appropriate timing of the concentration decrease.

Further, in synchronization with the generation of the low density signal instead of the high density signal, the base value B (n) is calculated by the first base value calculating means instead of the second base value calculating means. Therefore, even if the concentration of the specific gas increases again thereafter, the increase in concentration can be detected quickly and reliably. As described above, according to the gas detection device of the present invention, two different coefficients k are calculated in calculating the base value B (n).
1, k2 are used, and different calculation methods of Expression (1) and Expression (3) are used. Therefore, by adjusting the coefficients k1 and k2, respectively, it is possible to set conditions suitable for the rising timing and the falling timing of the concentration. In addition,
The first coefficient k1 and the second coefficient k2 are the sampling cycle in the A / D conversion means used and the sensor output value S.
It may be appropriately selected in consideration of the variation range of (n).

Still another solution is a gas detection device using a gas sensor element whose electric characteristics change according to the concentration of a specific gas, wherein the sensor output value S ( n), which is an acquisition means for increasing the sensor output value S (n) when the concentration of the specific gas is increased, where n is an integer indicating a time-series order, and the concentration is low. Density signal generating means for generating either a signal or a high density signal, and a first base value calculating means for calculating a base value B (n) during a period in which the low density signal is being generated by the density signal generating means. And the sensor output value S (n) is the immediately preceding sensor output value S (n-
1) or more, the base value B according to the following formula (1)
(N) is calculated and B (n) = B (n-1) + k1 {S (n) -B (n-1)} (1) where k1 is the first coefficient and 0 <k1 < 1. When the sensor output value S (n) is smaller than the immediately preceding sensor output value S (n-1), the base value B is calculated according to the following equation (2).
B (n) = S (n) for calculating (n) (2) During the period in which the high density signal is generated by the first base value calculating means and the density signal generating means, the following formula (3) Second base value calculating means for calculating the base value B (n) according to the following: B (n) = B (n-1) + k2 {S (n) -B (n-1)} (3) where k2 Is a second coefficient, 0 <k2 <k1 <1, a difference value for calculating a difference value D (n) from the sensor output value S (n) and the base value B (n) according to the following equation (4). Comprising: calculating means; and D (n) = S (n) −B (n) (4), wherein the density signal generating means is the difference value D (n).
Is larger than the high density threshold Tu, the high density signal is generated, and when the difference value D (n) is smaller than the low density threshold Td smaller than the high density threshold Tu, It is a gas detection device that generates the low concentration signal.

In this gas detector, the first base value calculating means calculates the base value B (n) using the equation (1) or the equation (2), and the second base value calculating means in the same manner as described above. At the base value B using the equation (3)
Calculate (n). Therefore, by adjusting the coefficients k1 and k2 in the equations (1) and (3) respectively, it is possible to set conditions suitable for the rising timing and the falling timing of the concentration. Moreover, in the first base value calculating means, the formula (1) and the formula (2) are selectively used depending on the case. That is, when the sensor output value S (n) is equal to or more than the immediately preceding sensor output value S (n−1), the base value that slowly follows the sensor output value is calculated by the equation (1), and the sensor output value S When (n) is smaller than the immediately preceding sensor output value S (n-1), the base value that matches the sensor output value is calculated by the equation (2). Therefore, at the time of increasing the gas concentration, the increase in the gas concentration can be detected earlier and the high concentration signal can be generated without being affected by the change in the past sensor output value (the change in the past gas concentration).

Further, in the gas detector of the present invention, the high concentration threshold Tu and the low concentration low threshold Td smaller than this are used as the thresholds for comparison with the difference value calculated by the equation (4).
Two of them are used. Therefore, chattering before and after signal switching by the density signal generating means can be prevented.

Still another solution is a gas detection device using a gas sensor element whose electric characteristics change according to the concentration of a specific gas, wherein the sensor output value S ( n), which is an acquisition unit that decreases the sensor output value S (n) when the concentration of the specific gas rises, where n is an integer indicating a time-series order, and the concentration is low. Density signal generating means for generating either a signal or a high density signal, and a third base value calculating means for calculating a base value B (n) during a period during which the low density signal is being generated by the density signal generating means. And
The sensor output value S (n) is the immediately preceding sensor output value S
When (n-1) or less, the base value B (n) is calculated according to the following formula (5), and B (n) = B (n-1) + k3 {S (n) -B (n-1)}. (5) However, k3 is a third coefficient, and when 0 <k3 <1, the sensor output value S (n) is larger than the immediately preceding sensor output value S (n-1), the following equation (6) is obtained. According to the base value B
B (n) = S (n) for calculating (n) (6) During the period in which the high density signal is generated by the third base value calculating means and the density signal generating means, the following formula (7) is obtained. Fourth base value calculating means for calculating the base value B (n) according to the following: B (n) = B (n-1) + k4 {S (n) -B (n-1)} (7) where k4 Is a fourth coefficient, 0 <k4 <k3 <1, a difference value for calculating a difference value D (n) from the sensor output value S (n) and the base value B (n) according to the following equation (8). Comprising: calculating means; and D (n) = B (n) -S (n) (8), wherein the density signal generating means is the difference value D (n).
Is larger than the concentration threshold value, the gas detector generates the high concentration signal.

The base value B (n) calculated according to the above equation (5) or (7) changes following the fluctuation of the sensor output value S (n). This base value B
(N) has a property that the degree of tracking the sensor output value changes when the values of the coefficients k3 and k4 are changed.
When 3 and k4 are large (close to 1), the base value quickly follows the sensor output value S. Conversely, the coefficients k3 and k4
Becomes smaller (close to 0), the change in the base value becomes slower, and the sensor output value is slowly followed. Therefore, when the coefficients k3 and k4 are small, the base value becomes a value greatly influenced by the past sensor output value and the base value.

The gas detector of the present invention has, in addition to the acquisition means for acquiring the sensor output value, the third and fourth base value calculation means for calculating the base value B (n) having the above properties. The base value is calculated while switching between the two calculation means. That is, while the density signal generating means is generating the density low signal, the third base calculating means is used,
On the contrary, during the period when the high density signal is being generated, the base value is calculated by the fourth base calculating means.

First, the case of calculating the base value using the third base value calculating means will be described. When the sensor output value S (n) is less than or equal to the immediately preceding sensor output value S (n-1) during the period when the low density signal is being generated, the third base value calculating means uses the above formula (5). Then, the base value is calculated. In equation (5), the relatively large third coefficient k3 (k3>
Since k4) is used, the calculated base value B (n) follows the sensor output value S (n) in a relatively quick manner, although it is slightly behind. Therefore, while the third base value calculating means calculates the base value by the expression (5), the difference value D (n) obtained by the expression (8) is gradually changed to the sensor output value due to the temperature fluctuation or the like. Even if fluctuates,
Since the base value B (n) also changes following the change, it does not become a very large value, so gas detection can be performed while suppressing the influence of drift due to temperature change and the like. However, when the concentration of the specific gas rises and the sensor output value S (n) changes (decreases) rapidly and largely, the difference value D (n) increases because the base value B (n) cannot follow sufficiently. When this difference value D (n) exceeds the density threshold value, the density signal generating means generates a density high signal instead of the density low signal. At the same time, the fourth base value calculating means is used to calculate the base value B (n).

In the period in which the low density signal is generated, the sensor output value S (n) is the sensor output value S (n
When it is larger than −1), the third base value calculation means calculates the base value using the above equation (6). That is, the current sensor output value S (n) is substituted for the base value B (n). As a result, the base value B (n) changes (completely follows) in accordance with the sensor output value S (n), so that the gas concentration increases and S (n) <S (n-1). At this point, the base value B is more than the sensor output value S (n).
(N) is always a large value and a positive difference value D (n) is generated. Therefore, regardless of the change in the gas concentration before that, the increase in the gas concentration can be grasped at an early stage.

On the other hand, in synchronization with the generation of the high density signal instead of the low density signal, the fourth base value using the fourth coefficient k4 instead of the third base value calculating means for the base value B (n). It is calculated by the calculation means. Since the fourth coefficient k4 used in the fourth base value calculation means is relatively small (k4 <k3), the change in the base value B (n) becomes slow and the tracking of the sensor output value becomes relatively slow. . As described above, the base value calculated using the relatively small fourth coefficient k4 is a value affected by the past sensor output value or the base value, specifically, the calculation formula of the base value B (n). The value affected by the base value calculated by the equation (5) immediately before the time point when the equation (5) is switched to the equation (7), that is, the value affected by the sensor output value or the base value before the switching, Has become. This can be easily understood from the fact that when k4 = 0, the base value B (n) maintains the base value immediately before switching. That is, the base value B (n) calculated by the fourth base value calculation means reflects the state immediately before the concentration of the specific gas rises to some extent while slowly following the sensor output value S (n). Become.

Therefore, the value represented by the difference value D (n), which is the difference between the base value B (n) calculated by the fourth base value calculating means and the current sensor output value S (n), is present, that is, specific. It can be considered as a value obtained by comparing the state after the gas concentration has increased with the past, that is, the state before the gas concentration has increased. Therefore, when the concentration of the specific gas decreases again and the sensor output value S (n) increases, the base value B
From the difference value D (n) from (n), it can be easily determined that the concentration of the specific gas has decreased. Then, the density signal generating means generates a density low signal instead of the density high signal. Moreover, since the fourth coefficient k4 can be used to adjust the gradual tracking of the base value B (n), it is possible to grasp an appropriate timing of the concentration decrease.

Further, the base value B (n) is calculated by the third base value calculating means instead of the fourth base value calculating means in synchronization with the generation of the low density signal instead of the high density signal. Therefore, even if the concentration of the specific gas increases again thereafter, the increase in concentration can be detected quickly and reliably. As described above, according to the gas detection device of the present invention, two different coefficients k are calculated in calculating the base value B (n).
3, k4 are used, and different calculation methods of Expression (5) and Expression (7) are used. Therefore, by adjusting each of the coefficients k3 and k4, it is possible to set conditions suitable for the rising timing and the falling timing of the concentration. In addition,
The third coefficient k3 and the fourth coefficient k4 are the sampling cycle in the A / D conversion means used and the sensor output value S.
It may be appropriately selected in consideration of the variation range of (n).

Still another solution is a gas detection device using a gas sensor element whose electric characteristics change depending on the concentration of a specific gas, and the sensor output value S ( n), which is an acquisition unit that decreases the sensor output value S (n) when the concentration of the specific gas rises, where n is an integer indicating a time-series order, and the concentration is low. Density signal generating means for generating either a signal or a high density signal, and a third base value calculating means for calculating a base value B (n) during the period in which the low density signal is being generated by the density signal generating means. And the sensor output value S (n) is the immediately preceding sensor output value S (n-
1) In the case of the following, the base value B according to the following equation (5)
(N) is calculated and B (n) = B (n-1) + k3 {S (n) -B (n-1)} (5) where k3 is the third coefficient and 0 <k3 < 1. The sensor output value S (n) is the sensor output value S immediately before during the period in which the density low signal is generated by the density signal generating means.
When it is larger than (n-1), the base value B (n) is calculated according to the following equation (6): B (n) = S (n) (6) Third base value calculating means, and the density signal generation unit A fourth base value calculating means for calculating a base value B (n) according to the following equation (7) during a period in which the means outputs the high density signal, and B (n) = B (n-1) + k4 { S (n) -B (n-1)} (7) where k4 is the fourth coefficient, 0 <k4 <k3 <1, the sensor output value S (n) and the base value B (n). Therefore, the difference signal calculating means for calculating the difference value D (n) according to the following equation (8) and D (n) = B (n) −S (n) (8) , The difference value D (n)
Is larger than the high density threshold Tu, the high density signal is generated, and when the difference value D (n) is smaller than the low density threshold Td smaller than the high density threshold Tu, It is a gas detection device that generates the low concentration signal.

In this gas detection device, similarly to the above, the third base value calculating means calculates the base value B (n) using the equation (5) or the equation (6), and the fourth base value calculating means. At the base value B using the equation (7)
Calculate (n). Therefore, by adjusting the coefficients k3 and k4 in the equations (5) and (7) respectively, it is possible to set conditions suitable for the rising timing and the falling timing of the concentration. Moreover, in the third base value calculating means, the formula (5) and the formula (6) are selectively used depending on the case. That is, when the sensor output value S (n) is less than or equal to the immediately preceding sensor output value S (n-1), the base value that slowly follows the sensor output value is calculated by the equation (5), and the sensor output value S When (n) is larger than the immediately preceding sensor output value S (n-1), the base value that matches the sensor output value is calculated by the equation (6). Therefore, at the time of increasing the gas concentration, the increase in the gas concentration can be detected earlier and the high concentration signal can be generated without being affected by the change in the past sensor output value (the change in the past gas concentration).

Further, in the gas detector of the present invention, the high concentration threshold Tu and the low concentration low threshold Td smaller than this are used as thresholds for comparison with the difference value calculated by the equation (8).
Two of them are used. Therefore, chattering before and after signal switching by the density signal generating means can be prevented.

Furthermore, it is preferable to use an auto-ventilation system for a vehicle including any one of the above-described gas detection devices.

Since the vehicle automatic ventilation system of the present invention appropriately generates the high concentration signal and the low concentration signal in accordance with the change in the concentration of the specific gas, it is possible to appropriately perform the ventilation. .

Alternatively, when the outside air inlet, the gas detector described in any one of the above, and the concentration signal is a low concentration signal, the opening / closing device for the outside air inlet is fully opened, and the concentration signal indicates a high concentration. When the signal is a signal, an opening / closing instruction means for outputting an opening / closing instruction signal for fully closing the opening / closing device for the outside air inlet may be used as the vehicle automatic ventilation system.

In this vehicle auto-ventilation system, the gas detection device generates a low concentration signal and a high concentration signal in accordance with the concentration of a specific gas, and when the low concentration signal is generated, the outside air inlet port When the switchgear is fully opened and a high concentration signal is being generated, an open / close support signal for fully closing the switchgear of the outside air inlet is output. Therefore, the opening / closing device for the outside air introduction port can be appropriately driven according to the concentration of the specific gas.

[0055]

BEST MODE FOR CARRYING OUT THE INVENTION (Embodiment 1) A first embodiment of the present invention will be described with reference to FIGS. Figure 1
FIG. 1 shows a circuit diagram and a block diagram of the gas detection device 10 of the first embodiment, and a schematic configuration of a vehicle automatic ventilation system 100 including the circuit diagram and the block diagram. This system 100
Concentration signal L according to the concentration change of the measured gas (specific gas)
The gas detection device 10 that outputs V, the ventilation system 30 that rotates the flap 34 to connect either the inside air intake duct 32 or the outside air intake duct 33 to the duct 31, and the ventilation system 30 according to the concentration signal LV. Flap 3
And an electronic control assembly 20 for controlling

First, the gas detector 10 will be described.
The gas detection device 10 reacts with an oxidizing gas component such as NOx in the gas to be measured (atmosphere in the present embodiment), and the sensor resistance value Rs increases as the concentration of the oxidizing gas component increases. A gas sensor element 11 of a type oxide semiconductor is used. This gas sensor element 11
Is located outside the vehicle compartment.

Using this gas sensor element 11, a sensor resistance value conversion circuit 14, a buffer 13, and an A / D conversion circuit 15 are used.
The sensor output value acquisition circuit 19 consisting of
(N) is acquired. The sensor resistance value conversion circuit 14 outputs a sensor output potential Vs according to the sensor resistance value Rs of the gas sensor element 11. Specifically, the power supply voltage Vcc
Is divided by the gas sensor element 11 and the detection resistor 12 having the detection resistance value Rd to obtain the sensor output potential Vs at the operating point Pd.
Is output via the buffer 13.
Therefore, in this sensor resistance value conversion circuit 14, NOx
When the concentration of oxidizing gas such as increases, the sensor resistance value R
s rises, and the sensor output potential Vs rises. Output of buffer 13 (sensor output potential V
s) is input to the A / D conversion circuit 15 and digitized sensor output value S for each predetermined sampling period.
It is output as (n) and is input to the input terminal 17 of the microcomputer 16. n is a series of integers representing the order. In the sensor output value acquisition circuit 19, the density increasing direction is a direction in which the sensor output value S (n) increases,
On the contrary, the density decreasing direction is a direction in which the sensor output value S (n) decreases.

Further, from the output terminal 18 of the microcomputer 16, a concentration signal L for controlling the electronic control assembly 20, which is either a high concentration signal or a low concentration signal, is supplied.
V is output. The electronic control assembly 20 controls the flaps 34 of the ventilation system 30 which control the internal air circulation and external air intake of the vehicle. This ventilation system 30
In the present embodiment, specifically, a flap 34 for switching between a forked inside air intake duct 32 for taking in and circulating inside air and an outside air intake duct 33 for taking in outside air, which is connected in a bifurcated manner to the duct 31 connected to the interior of the automobile.
Is to control. In the electronic control assembly 20, the flap drive circuit 21 is the microcomputer 1
According to the present embodiment, the concentration signal LV from the output terminal 18 of No. 6, the actuator 22 is operated according to the concentration signal LV indicating whether the concentration of the oxidizing gas component such as NOx is increased or decreased. By rotating 34, the inside air intake duct 32 and the outside air intake duct 33
Either of them is connected to the duct 31.

For example, as shown in the flowchart of FIG. 2, after initial setting is made in step S1, step S2 is performed.
The density level signal LV is acquired in step S3, and it is determined in step S3 whether the density signal LV is a high density signal, that is, whether a high density signal is being generated. Here, when No, that is, when the low concentration signal is being generated, since the concentration of the specific gas is low, the flap 34 is instructed to be fully opened in step S4. As a result, 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 the high concentration signal is being generated, the concentration of the specific gas outside the vehicle compartment is high. As a result, the flap 34 rotates, the inside air intake duct 32 is connected to the duct 31, the outside air introduction is blocked, and the inside air is circulated.

A fan 35 for sending air under pressure is installed in the duct 31. The flap drive circuit 21
May open and close the flap 34 only in accordance with the concentration signal LV, for example, using a microcomputer or the like, in addition to the concentration signal LV by the gas detection device 10,
As shown by the broken line in the figure, the flap 34 may be opened and closed by taking into consideration information from a room temperature sensor, a humidity sensor, an outside air temperature sensor, and the like.

In the microcomputer 16, the gas sensor element 1 is processed by processing the sensor output value S (n) input from the input terminal 17 according to the flow described later.
The change in the concentration of the oxidizing gas component is detected from the sensor resistance value Rs of 1 or its change. Microcomputer 16
Although not shown in detail, has a well-known configuration, a microprocessor for performing an operation, a RAM for temporarily storing programs and data, and a ROM for holding programs and data.
Including etc. Further, a device including the A / D conversion circuit 15 can also be used.

Next, the control of the microcomputer 16 will be described with reference to the flowchart of FIG. When the vehicle engine is driven, this control system starts up. After waiting for the gas sensor element 11 to be in the activated state, initial setting is performed in step S11. As an initial setting, the initial sensor output value S (0) when the gas sensor element 11 is activated is stored as the base value B (0) (B (0) = S (0)). Further, a low density signal is generated as the density signal LV, specifically, the density signal LV is set to a low level. Then, step S12
And the sensor output value S (n) obtained by A / D converting the sensor signal, that is, the sensor output potential Vs in each sampling cycle.
Sequentially read. Next, in step S13, it is determined whether or not the concentration signal LV is currently at a high level, that is, a high concentration signal indicating that the concentration of the specific gas (oxidizing gas in this embodiment) is at a high level. Here, if No, that is, the concentration of the specific gas is low, the concentration signal LV is at a low level and a low concentration signal is generated, the process proceeds to step S14. On the other hand, if Yes, that is, if the concentration of the specific gas is high and the concentration signal LV is at the high level and the high concentration signal is generated, the process proceeds to step S17.

In step S14, the sensor output value S
It is determined whether (n) is greater than or equal to the immediately preceding sensor output value S (n-1). If S (n) ≧ S (n−1) (Yes), the process proceeds to step S15, where S (n) <
In the case of S (n-1) (No), the process proceeds to step S16.

In step S15, the previous base value B
Using (n-1) and the sensor output value S (n), the base value B (n) is calculated by the following equation (1), and the process proceeds to step S18. Formula (1): B (n) = B (n-1) +
k1 {S (n) -B (n-1)}, where the first coefficient k
1 is 0 <k1 <1. As described above, the base value B (n) calculated by the above equation (1) is the coefficient k to be used.
When 1 is in the range of 0 <k1 <1, the sensor output value S (n)
Follows changes with a delay. Therefore, the current sensor output value S (n) is the sensor output value S (n-
1) or more, that is, the current sensor output value S (n)
Is changed in the concentration increasing direction from the immediately preceding sensor output value S (n-1), the base value B (n) that follows the sensor output value S (n) with a delay is calculated in step S15. .

Then, a difference occurs between S (n) and B (n). Utilizing this property, step S19 described later is performed.
By using the difference value D (n) calculated in, it is possible to detect an increase in the concentration of the specific gas. That is, the difference value D
When (n) is larger than the first positive threshold value (concentration threshold value), if the concentration signal generating means generates a high concentration signal, an increase in the concentration of the specific gas can be detected. it can. Note that, unlike the invention described in the above-mentioned Japanese Patent Laid-Open No. 1-199142, the gas concentration increases little by little, and the current sensor output value S (n) is compared with the immediately preceding sensor output value S (n-1). Is slightly larger than the base value B, the base value is calculated in step S15.
The current sensor output value S (n) is not substituted for (n). Therefore, as the gas concentration increases, the sensor output value gradually increases, and the base value B (n) slowly changes while following the sensor output value S (n) and the base value B (n). Since the difference from n) gradually increases, an increase in gas concentration can be detected early.

On the other hand, in step S16, the base value B
Substitute the current sensor output value S (n) into (n) (B (n)
= S (n)), and proceeds to step S18. That is, when the current sensor output value S (n) is smaller than the previous (one previous) sensor output value S (n-1), that is, the current sensor output value S (n) is the previous sensor output. When the value decreases from the value S (n-1) in the density decreasing direction, the base value B
(N) is made to coincide with the sensor output value S (n) at the present time and is made to follow completely.

As can be easily understood by referring to the above equation (1), the base value B (n) calculated by the equation (1) is
In addition to the current sensor output value S (n), the immediately preceding base value B
It is calculated using (n-1). That is, the past base values (B (n-1), B (n-2), ...) And therefore the past sensor output values (S (n-1), S (n-2) ,. To be affected. Therefore, if the current sensor output value S
Even when (n) changes (decreases in the present embodiment) from the immediately preceding sensor output value S (n-1) in the concentration decreasing direction, the base value B (n) is continuously calculated using the equation (1). It is assumed that the calculation is continued. Here, consider a case where the gas concentration once rises, then falls, and rises again. The sensor output value increases or decreases according to the gas concentration. On the other hand, since the base value changes later than the sensor output value, if the gas concentration rises and then decreases, the base value will fall later than the sensor output value, and the base value of the sensor output value The difference between the two according to equation (4) (difference value D (n))
Is negative. In this state, when the gas concentration starts to rise again, the sensor output value starts to rise again, but the difference value D
Since it takes time for (n) to exceed the positive concentration threshold value T, detection of an increase in gas concentration may be delayed.

On the other hand, in step S16, if the current sensor output value S (n) is substituted for the base value B (n), then the gas concentration changes from a decrease to an increase and the sensor output value S (n). When the value increases, the base value B (n) is calculated in step S15 without being affected by the change in the sensor output value before that. The base value B (n) is calculated using the immediately preceding base value B (n-1), that is, the immediately preceding sensor output value S (n-1) as a starting point,
It slowly changes while following the newly obtained sensor output value S (n). Therefore, when the specific gas concentration rises, the difference between the sensor output value and the base value becomes large at an early stage.
The rise in the specific gas concentration can be caught earlier. Moreover, in step S14, the immediately preceding sensor output value S (n
-1) is compared with the current sensor output value S (n), and when the concentration is changed, the current sensor output value S (n) is set as the base value B (n) in step S16.

On the other hand, in step S17, the base value B (n) is calculated from the previous base value B (n-1) and the sensor output value S (n) using the following equation (3), and step S18 is performed. Proceed to. Formula (3): B (n) = B (n-1) +
k2 {S (n) -B (n-1)}, where the second coefficient k
2 is 0 <k2 <k1 <1. As described above, the base value B (n) has a relatively large first coefficient k1 (k1> k2) that follows the sensor output value S (n) depending on the magnitudes of the coefficients k1 and k2 used. When used (step S15), the base value B (n) follows the sensor output value S (n) relatively quickly, although it is slightly behind. On the other hand, a relatively small second coefficient k2 (k2 <k1)
When calculated by using (step S17), the change of the base value B (n) becomes slow and follows slowly.

Therefore, when the base value B (n) is calculated using the second coefficient k2 by the equation (3) in step S17,
Even if the sensor output value S (n) changes significantly, the calculated base value B (n) does not change much from the base value B (n-1) immediately before the switching.
Here, since the base value B (n-1) immediately before switching is calculated using the first coefficient k1 in step S15, a value that follows the sensor output value S (n-1) before switching. Has become. Therefore, the base value B (n) calculated in step S17 becomes a value that reflects the influence of the state in the past, that is, immediately before the switching.

Subsequent to step S15, S16 or S17, the difference value D (n) is set to D in step S18.
(N) = S (n) −B (n) is calculated according to the equation (4), and is compared with the density threshold value T (T> 0) in step S19. If D (n)> T (Yes), the process proceeds to step S20, and if D (n) ≦ T (No), the process proceeds to step S21.

If D (n)> T while the low density signal is being generated (No in step S13) until then (Yes in step S19), the sensor output value S (n ) And the base value B (n) that is calculated in step S15 and follows slightly later than this, have become large. That is, it is considered that the sensor output value S (n) increased due to the increase in the concentration of the specific gas (oxidizing gas). Until then, when the high density signal is generated (Yes in step S13), D (n)> T
If (Yes in step S19), the present sensor output value S (n) and the current sensor output value S (n) are calculated in step S17, and the past state, that is, the state immediately before the concentration of the oxidizing gas rises is reflected to some extent. It shows that the difference from the base value B (n) is still large, that is, the concentration of the oxidizing gas is not yet sufficiently reduced. Therefore, step S
At 20, a high density signal is generated or maintained. Specifically, the density signal LV is set to a high level.

On the other hand, if the density low signal has been generated until then (No in step S13), D (n) ≤
When it becomes T (No in step S19), the difference between the current sensor output value S (n) and the base value B (n) calculated in step S15 and following a little later than this is too large. However, it shows that the base value B (n) is following. That is, it is considered that the concentration of the specific gas (oxidizing gas) remains low. Alternatively, since the gas concentration continues to decrease, the base value B
It is considered that (n) is in a state of being matched with the current sensor output value S (n). Until then, in the state where the high density signal is generated (Yes in step S13),
When D (n) ≦ T (No in step S19), the sensor output value S (n) is calculated in step S17, and the state is the past state, that is, the state immediately before the concentration of the oxidizing gas rises. It is shown that the difference from the base value B (n), which reflects to some extent, is small, that is, the concentration of the oxidizing gas is sufficiently reduced. Therefore, in step S21, a low density signal is generated or maintained. Specifically, the density signal LV is set to low level.

After that, the process proceeds to step S22 from steps S20 and S21, and steps S15 and S1.
6, the previous base value B (n) calculated in S17 is stored, and after waiting for the A / D sampling time to increase in step S23, the process returns to step S12.

Next, when the NOx concentration is once increased and then decreased, and when the increase and decrease are repeated, the sensor output value S (n) and the base value B (obtained by the control according to the flowchart shown in FIG. n), the difference value D
FIG. 4 shows an example of changes in (n) and the density signal LV. In this example, the gas sensor element 11 is arranged in the wind tunnel,
Initially, clean air containing no NOx is allowed to flow at a predetermined wind speed. After that, air containing a predetermined concentration of NOx is caused to flow twice at a time interval. The sampling period was 1.0 second, the first coefficient k1 = 1/16, and the second coefficient k2 = 1/64. Further, as described above, the low density signal (low level) is generated as the density signal in the initial state.

From time 0 to about 35 seconds, clean air is flown and the sensor output value S (n) is maintained at a substantially constant value (0), although there is some fluctuation due to noise. At about time 35 seconds, the sensor output value S (n) starts to increase due to the increase in NOx concentration, and the sensor output value S (n) continues to increase until about time 210 seconds. After that, the sensor output value S (n) becomes about 210 at the time when the NOx concentration decreases.
It gradually decreases from second to t1 (= about 350 seconds). Further, at time t1 (= about 350 seconds), the sensor output value S (n) starts to increase again due to the increase in NOx concentration,
The sensor output value S (n) continues to increase until about 520 seconds. After that, the sensor output value S (n) gradually decreases as the NOx concentration decreases.

On the other hand, the base value B (n) keeps a substantially constant value while following a slight change in accordance with the sensor output value S (n) from the initial time 0 to about 35 seconds.
Therefore, the difference value D (n) is maintained at almost 0. At this time, the base value B (n) is calculated by either of steps S15 and S16. However, at the time of about 35 seconds, the sensor output value S (n) starts to increase due to the increase of the NOx concentration. Then, the current sensor output value S (n) becomes larger than the immediately preceding sensor output value S (n-1), and thus the base value B (n) is calculated by the equation (1) in step S15. However, this base value B
Since (n) slowly follows the sensor output value S (n),
Rises late. Then, the difference value D which is the difference between the two
(N) becomes large.

When the difference value D (n) exceeds the density threshold value T at about 50 seconds, the density signal LV changes from low level (low density) to high level and a high density signal is generated.
When the density signal LV is switched, thereafter, the base value B (n) is calculated by the equation (3) in step S17. Then, the base value B (n) is the sensor output value S
It gradually follows (n) and increases. Therefore, since the base value B (n) approaches the sensor output value S (n) after a long time, the difference value D (n) always approaches 0 and becomes a small value. Therefore, even if the drift occurs, the difference value D (n) always falls below the density threshold value T, and the density signal LV returns to the low level, that is, the density low signal is generated. In this example, at time 230 seconds, D (n) ≦ T, and the density signal LV changes from the high level (high density) to the low level (low density) to generate the low density signal. Further, after that, in step S13, N
Therefore, the base value B (n) is set to step S1.
5 or S16. In this example, the time is about 2
From 30 to 350 seconds, the sensor output value S (n) monotonously decreases, and during this period, the base value B (n) is given exclusively in step S16. That is, the base value B (n) shown by the broken line is the sensor output value S shown by the solid line.
It changes in agreement with (n). Therefore, the difference value D
(N) becomes 0, and the generation of the low density signal is maintained.

Thereafter, after the time t1 = about 350 seconds, the sensor output value S (n) becomes larger than the immediately preceding sensor output value S (n-1) due to the increase of the NOx concentration. Then, it is determined as Yes in Step S14, and Step S1
In step 5, the base value B (n) is calculated by the equation (1).
It can be easily understood from FIG. 4 that the base value B (n) is calculated using the value of the sensor output value S (n) (base value B (n)) immediately before the NOx concentration starts to rise as a starting point. it can. Since the base value B (n) slowly follows the sensor output value again, it increases with a delay. Then, the difference value D (n), which is the difference between the two, becomes large. When the difference value D (n) exceeds the density threshold value T at about time 370 seconds, the density signal LV changes from low level (low density) to high level, and a high density signal is generated again. Therefore, in the present embodiment, the detection delay is about 2 from the increase of the sensor output value S (n) due to the increase of the NOx concentration at time t1 (= about 350 seconds) to the detection of the increase of concentration at about time 370 seconds.
It turns out that it was 0 seconds.

After that, the base value B (n) is calculated in step S
It is calculated by Expression (3) according to 17. Then, the base value B
(N) gradually follows the sensor output value S (n) and increases. Therefore, the difference value D (n) falls below the density threshold value T at about 530 seconds, and the density signal LV returns to the low level, that is, a low density signal is generated.

(Comparative Embodiment 1) For comparison, the gas detecting apparatus 10 has the same configuration as that of Embodiment 1 described above, and steps S14 and S16 are omitted from the flowchart shown in FIG. If it is determined, the base value B (n), the base value B (n), and the like in the comparative form 1 controlled to uniformly calculate the base value in step S15.
Changes in the difference value D (n) and the density signal LV were obtained. The result is shown in FIG. However, in order to distinguish from the result of the first embodiment, in FIG. 4, the base value B (n) in this comparative embodiment is Ba (n), and the difference value D (n) is Da.
(N), the density signal LV is displayed as LVa.

According to the result of the comparative form 1, the time 0 to
In the period of about 210 seconds, the base value Ba (n) matches the base value B (n) in the first embodiment, and therefore the difference value Da (n) is also the difference value D in the first embodiment.
(N) and the density signal LVa also matches the density signal LV in the first embodiment. However, the time is about 210-35.
After 0 seconds, the base value Ba (n) is equal to the sensor output value S
It falls after (n). This is because the base value is calculated in step S15 without passing through step S16. Therefore, during this period, the sensor output value S (n)
The base value Ba (n) becomes larger than the difference value Da
(N) has a negative value. Therefore, at time t1, N again
Even if the sensor output value S (n) starts to increase due to the increase in Ox concentration, the base value Ba (n) continues to decrease.
The difference value Da (n) exceeds the density threshold value T at a time of about 390 seconds, and thereafter, the density signal LVa changes from the low level (low density) to the high level, and the high density signal is changed again. Occur.

Therefore, in this comparative embodiment, the time is about 3
Sensor output value S due to increase in NOx concentration at 50 seconds
It can be seen from the rise in (n) that the detection delay was about 40 seconds until the rise in density was detected at about 390 seconds. That is, according to the above-described control of the first embodiment, the detection delay of about 40 seconds in the first comparative example can be shortened to about 20 seconds, which is 1/2. That is, an increase in the concentration of the oxidizing gas can be surely detected early.

(Modification 1) Next, a modification of the first embodiment will be described with reference to FIGS. This modification 1 is the same gas detection device 1 as the above-mentioned embodiment 1.
0 and a vehicle automatic ventilation system 100 including the same. That is, it is a system that detects a change in the concentration of an oxidizing gas component such as NOx and opens and closes the flap 34 based on the change. However, since the processing flow in the microcomputer 16 is different and the density threshold value has a hysteresis characteristic, different portions will be mainly described, and similar portions will be denoted by the same symbols and numbers, and description thereof will be omitted or simplified. Turn into.

Microcomputer 16 of the first modification
The control in 1 will be described with reference to the flowchart of FIG. Steps S11 to S17 are the same as those in the first embodiment (see FIG. 3). In step S15,
Similarly to the first embodiment, the base value B is calculated by the equation (1).
Calculate (n). However, unlike the first embodiment, the process proceeds to step S218. Also in step S16, as in the first embodiment, the current sensor output value S is added to the base value B (n).
(N) is substituted, but unlike the first embodiment, step S
Proceed to 218. Further, also in step S17, the base value B (n) is calculated by the equation (3) as in the first embodiment. However, unlike the first embodiment, step S219.
Proceed to. Therefore, the base value B (n) obtained in steps S15 to S17 has the same property as described in the first embodiment.

Then, in step S218, the difference value D
(N) is calculated according to the equation (4) of D (n) = S (n) -B (n), and the process proceeds to step S220. Step S22
At 0, the difference value D (n) is compared with the high concentration threshold Tu. When D (n)> Tu (Yes), the process proceeds to step S222, and when D (n) ≦ Tu (No)
If so, the process directly proceeds to step S224. Step S2
The answer of 20 is Yes when the low density signal has been generated until then (No in step S13), and D (n)>
Since it is Tu, the sensor output value S (n)
And the base value B (n), which is calculated in step S15 and follows with a slight delay, becomes larger. That is, it is considered that the sensor output value S (n) increased due to the increase in the concentration of the specific gas (oxidizing gas). Therefore, in step S222, a high density signal is generated instead of the low density signal. Specifically, the density signal LV is set to a high level.

On the contrary, the reason why No is obtained in step S220 is that D (n) ≤Tu is satisfied while the low density signal is being generated (No in step S13) until then. Sensor output value S (n) of step S1
The difference from the base value B (n) calculated in step 5 and followed slightly later than this is not so large that the base value B (n)
Indicates that they are following. That is, it is considered that the concentration of the specific gas (oxidizing gas) remains low.
Alternatively, since the gas concentration continues to decrease, the base value B (n) is changed to the current sensor output value S in step S16.
It is considered that the state is matched with (n). Therefore, the low density signal is maintained and the process proceeds to step S224.

On the other hand, also in step S219, the difference value D
(N) is calculated according to the equation (4) of D (n) = S (n) −B (n), and is compared with the low concentration threshold Td in step S221. The low density threshold value Td is smaller than the high density threshold value Tu (Tu> Td). When D (n) ≦ Td (Yes), the process proceeds to step S223, and when D (n)> Td (No).
If so, the process directly proceeds to step S224. in this way,
The two thresholds of the high concentration threshold Tu and the low concentration threshold Td are used. The two thresholds are used to provide a hysteresis characteristic so that a low concentration signal and a high concentration signal may be generated. This is to prevent chattering when switching signals. The result of step S221 is Yes when the high density signal has been generated until then (Y in step S13).
es), when D (n) ≦ Td, the sensor output value S (n) and the previous state, that is, the state before the concentration of the oxidizing gas is increased are calculated in step S17. This indicates that the difference from the base value B (n), which is reflected to some extent, has become small, that is, the concentration of the oxidizing gas has sufficiently decreased. Therefore, in step S223, a low density signal is generated instead of the high density signal. Specifically, the density signal LV is set to low level.

On the contrary, the reason why No is obtained in step S221 is that D (n)> Td is satisfied while the high density signal is being generated until then (Yes in step S13). Sensor output value S (n) and step S
The difference from the base value B (n) calculated in 17 is still large, indicating that the concentration of the oxidizing gas is increasing. That is, it is considered that the concentration of the specific gas (oxidizing gas) remains high. So, keep the high concentration signal,
The process proceeds to step S224.

After that, as in the first embodiment, step S
From both 222 and S223, the process proceeds to step S224, the previous base value B (n) calculated in steps S15, S16, and S17 is stored, and A / A is calculated in step S225.
After waiting for the D sampling time to increase, the process returns to step S12.

Then, similarly to the case shown in the first embodiment, the NOx concentration is once increased, then decreased, and further increased and decreased by the control according to the flowchart shown in FIG. FIG. 6 shows an example of changes in the sensor output value S (n), the base value B (n), the difference value D (n), and the density signal LV that are obtained. As the high density threshold Tu, the same value as the density threshold T in the first embodiment was used, and as the low density threshold Td, Td = 0 was used. Further, similarly to the first comparative example, in the flowchart shown in FIG. 5, steps S14 and S16 are omitted, and if No is determined in step S13, step S13 is performed.
With respect to the comparative form 2 in which the base value is controlled by 15, the changes in the base value Bb (n), the difference value Db (n), and the density signal LVb obtained in the same manner are
It is shown in an overlapping manner in FIG.

As can be easily understood from the graph of FIG. 6, the sensor output value S (n), the base value B (n) and the difference value D (n) are the same as those in the first embodiment (see FIG. 4). Further, the base value Bb (n) and the difference value Db according to the comparison form 2
(N) is also the base value Ba (n) and the difference value Da of the comparative form 1.
Same as (n). On the other hand, the density signal LV in the first modification is slightly different from the change in the density signal LV in the first embodiment. That is, in the above-described first embodiment, D (n) is obtained at time 230 seconds and time 530 seconds.
≦ T, and the density signal LV changes from a high level (high density) to a low level (low density) to generate a low density signal, whereas in the first modification, a time slightly later than this is about 240 seconds and At time 540 seconds, D (n) ≦ Td, the density signal LV changes from the high level (high density) to the low level (low density), and a low density signal is generated. This is because two threshold values are used.

However, as in the case of comparing the density signal LV in the first embodiment with the density signal LVa in the first comparative example, the density signal LV in the first modified example and the comparative signal 2 are compared.
Comparing with the density signal LVb of the above, the modification 1 can reduce the detection delay of the density increase. That is, with the density signal LV in the first modification, the time is about 3
Sensor output value S due to increase in NOx concentration at 50 seconds
The detection delay is about 20 seconds from the rise of (n) to the detection of the density rise at the time of about 370 seconds. On the other hand, in Comparative Example 2, the detection delay is about 40 seconds from the increase of the sensor output value S (n) due to the increase of the NOx concentration at the time of about 350 seconds to the detection of the concentration increase at the time of about 390 seconds. is there.
In this way, even by the control of the first modification described above,
It can be seen that the detection delay of about 40 seconds in comparative form 2 can be shortened to about 20 seconds, which is 1/2. That is,
It is possible to reliably and early detect an increase in the concentration of the oxidizing gas.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIGS. The gas detection device 40 according to the second embodiment and the vehicle auto-ventilation system 140 including the gas detection device 40 are processed by substantially the same configuration and processing flow as those of the first embodiment, but have some differences. That is, the first embodiment
Then, as the gas sensor element 11, a gas sensor element of a type in which, when an oxidizing gas component such as NOx is present, it reacts with the oxidizing gas component to increase the sensor resistance value Rs as the concentration of the oxidizing gas component increases. On the other hand, in the second embodiment, the gas sensor element 41 is of a type that reacts with a reducing gas component such as CO or HC when it exists, and the sensor resistance value Rs decreases as the concentration of the reducing gas component increases. The difference is that the gas sensor element 41 is used. Along with this, the sensor resistance value conversion circuit 44 of the second embodiment outputs the sensor output potential Vs according to the sensor resistance value Rs of the gas sensor element 41, and when the concentration of reducing gas such as CO or HC rises. The difference is that the sensor resistance value Rs is lowered and the sensor output potential Vs is lowered.
Furthermore, the processing flow in the microcomputer 16 is slightly different. Therefore, different parts will be mainly described, and similar parts will be denoted by the same symbols and numbers, and description thereof will be omitted or simplified.

First, referring to FIG. 7, the gas detector 40
The vehicle automatic ventilation system 140 will be described. The gas detection device 40 uses the oxide semiconductor gas sensor element 41 of a type that reacts with the reducing gas as described above, and the sensor resistance value Rs decreases as the concentration of the reducing gas increases. Using this gas sensor element 41, a sensor resistance conversion circuit 44, a buffer 13, an A / D
The sensor output value acquisition circuit 49 including the conversion circuit 15 acquires the sensor output value S (n). The sensor resistance value conversion circuit 44 outputs the sensor output potential Vs according to the sensor resistance value Rs of the gas sensor element 41. In the sensor resistance conversion circuit 44, when the reducing gas concentration rises, the sensor output potential Vs at the operating point Pd falls. As in the first embodiment, the sensor output potential Vs is transferred to A through the buffer 13.
The A / D conversion circuit 15 performs A / D conversion for each sampling cycle, and the sensor output value S (n) is input to the input terminal 17 of the microcomputer 16. Contrary to the case of the first embodiment, in the sensor output value acquisition circuit 49, the sensor output value S (n) decreases in the concentration increasing direction, and the sensor output value S decreases in the conversely decreasing direction. This is the direction in which (n) increases.

Further, from the output terminal 18 of the microcomputer 16, as in the first embodiment, to control the electronic control assembly 20, either the high concentration signal or the low concentration signal indicating the high or low concentration of the reducing gas component is obtained. Concentration signal L
V is output and the electronic control assembly 20 controls the flaps 34 of the ventilation system 30 which control the internal air circulation and external air intake of the vehicle. In the microcomputer 16, the sensor output value S (n) input from the input terminal 17
Is performed according to the flow described later, and the change in the concentration of the reducing gas component is detected from the sensor resistance value Rs of the gas sensor element 41 and its change.

Next, the control of the microcomputer 16 according to this modification will be described with reference to the flowchart of FIG. When the engine of the automobile is driven, the control system starts up, waits for the gas sensor element 41 to be in an active state, and first, similarly to the first embodiment, initial setting is performed in step S11. Then, the process proceeds to step S12 to sequentially read the sensor output value S (n). Next, in step S13, it is determined whether or not a high density signal is currently generated. If the low density signal is generated (No), the process proceeds to step S314. On the other hand, if the high density signal is generated (Yes), the process proceeds to step S317.

In step S314, unlike the first embodiment, the sensor output value S (n) is the immediately preceding sensor output value S (n).
-1) Determine whether or not the following. Contrary to the case of the first embodiment, when the concentration of the specific gas (reducing gas) increases, the value of the sensor output value S (n) decreases. Here, if S (n) ≦ S (n−1) (Yes)
In step S315, S (n)> S (n-
In the case of 1) (No), the process proceeds to step S316.

In step S315, the base value B (n)
To the previous base value B (n-1) and sensor output value S (n)
Is calculated by the following equation (5) using
Proceed to 318. Formula (5): B (n) = B (n-1) + k
3 {B (n-1) -S (n)}, where the third coefficient k3
Is 0 <k3 <1. The base value B (n) calculated by the above equation (5) changes following the sensor output value S (n) with a delay when the coefficient k3 used is within the range of 0 <k3 <1. Therefore, when the current sensor output value S (n) is less than or equal to the immediately previous (one previous) sensor output value S (n-1), that is, the current sensor output value S (n) is the immediately previous sensor output value S (n). If the density is changed from (n-1), the sensor output value S (n) is determined in step S315.
A base value B (n) that follows the delay is calculated.

Then, a difference occurs between S (n) and B (n). Utilizing this property, step S31 described later is performed.
By using the difference value D (n) calculated in 9, it is possible to detect the increase in the concentration of the specific gas. That is, the difference value D
When (n) is larger than the first positive threshold value (concentration threshold value), if the concentration signal generating means generates a high concentration signal, an increase in the concentration of the specific gas can be detected. it can. When the sensor output value gradually decreases as the gas concentration increases, the base value B (n) follows the sensor output value S (n) and the base value B.
Since the difference from (n) gradually increases, the rise in gas concentration can be detected early.

On the other hand, in step S316, the first embodiment is performed.
Similarly to the base value B (n), the current sensor output value S
Substituting (n) (B (n) = S (n)), step S3
Proceed to 18. That is, when the current sensor output value S (n) is larger than the previous sensor output value S (n-1), that is, the current sensor output value S (n) is the previous sensor output value S (n- When the concentration is changed from 1),
The base value B (n) is made to coincide with the sensor output value S (n) at the present time so as to be completely followed.

In the same way as described in the first embodiment,
The base value B (n) calculated by the equation (5) is the current sensor output value S (n) and the immediately preceding base value B (n-1).
Is calculated using. That is, the past base value (B (n
−1), B (n−2), ..., Therefore, the past sensor output values (S (n−1), S (n−2), ...) Are also affected. This step S316 is eliminated and the sensor output value S
Even if (n) changes in the concentration decreasing direction (in this embodiment, increases), if the base value B (n) is continuously calculated using the equation (5), the detection of the increase in the gas concentration may be delayed. is there. On the other hand, in step S316, since the current sensor output value S (n) is substituted for the base value B (n), it is possible to catch the increase in the specific gas concentration earlier, as in the first embodiment.

On the other hand, in step S317, the base value B (n) is calculated from the previous base value B (n-1) and the sensor output value S (n) using the following equation (7), and step S318 is performed. Proceed to. Formula (7): B (n) = B (n-1)
+ K4 {B (n-1) -S (n)}, where the fourth coefficient k4 is 0 <k4 <k3 <1. As mentioned above,
The base value B (n) differs in the degree of tracking the sensor output value S (n) depending on the magnitude of the coefficients k3, k4 used, and when a relatively large third coefficient k3 (k3> k4) is used (step In S315), the base value B (n) follows the sensor output value S (n) a little bit, but relatively quickly. On the other hand, a relatively small fourth coefficient k4 (k4 <k
3) is used for calculation (step S317),
The change in the base value B (n) becomes slow and follows slowly.

Therefore, when the base value B (n) is calculated using the fourth coefficient k4 by the equation (7) in step S317, the calculated base value B (n) is affected by the past, that is, the state immediately before switching. Is a value that reflects.

Step S315, S316 or S3
Following step 17, in step S318, the difference value D
D (n) = B in which (n) is reversed from that of the first embodiment.
It is calculated according to the equation (8) of (n) -S (n). Thereafter, as in the first embodiment, the density threshold value T (T> 0) is compared in step S19, and if D (n)> T (Yes), the process proceeds to step S20, and D (n). If ≦ T (No), the process proceeds to step S21.

If D (n)> T while the low density signal is being generated (No in step S13) until then (Yes in step S19), the sensor output value S (n ) And the base value B (n) that is calculated in step S315 and follows slightly later than this, have become large. That is, specific gas (reducing gas)
It is conceivable that the sensor output value S (n) has decreased due to the increase in the concentration of. Until then, in the state where the high density signal is generated (Yes in step S13), D (n)>
When T is reached (Yes in step S19), the current sensor output value S (n) is calculated in step S317, and the past state, that is, the state immediately before the concentration of the reducing gas is increased is reflected to some extent. It shows that the difference with the base value B (n) being maintained is still large, that is, the concentration of the reducing gas is not yet sufficiently reduced. Therefore, in step S20, the high density signal is generated or the high density signal is maintained. Specifically, the density signal LV is set to a high level.

On the other hand, if the density low signal is being generated until then (No in step S13), D (n) ≤
When it becomes T (No in step S19), the difference between the current sensor output value S (n) and the base value B (n) calculated in step S315 and following a little later than this is too large. However, it shows that the base value B (n) is following. That is, it is considered that the concentration of the specific gas (reducing gas) remains low. Alternatively, since the gas concentration continues to decrease, it is considered that the base value B (n) is made to match the current sensor output value S (n) in step S316. Until then, the high density signal is being generated (Yes in step S13).
And D (n) ≦ T (N in step S19)
o), the sensor output value S (n) and step S317
The base value B (n) calculated in step S3 and reflecting a past state, that is, a state immediately before the concentration of the reducing gas rises to some extent.
It means that the difference between and is small, that is, the concentration of the reducing gas is sufficiently reduced. Therefore, step S
At 21, a low density signal is generated or maintained. Specifically, the density signal LV is set to low level.

Thereafter, as in the first embodiment, step S
From both 20 and S21, go to step S22,
The previous base value B (n) calculated in steps S315, S316, and S317 is stored, and A / D is calculated in step S23.
After waiting for the sampling time to increase, the process returns to step S12.

In the second embodiment, as in the above-described first embodiment, during the generation period of the low density signal (N in step S13).
o), the current sensor output value S in step S314
(N) is compared with the immediately preceding sensor output value S (n-1),
If the density is increasing, step S31
5, the base value B (n) that follows the sensor output value S (n) with a delay is calculated. On the other hand, if the base value B (n) is changing in the density decreasing direction, the sensor output value S (n) is substituted in step S316. To obtain a base value B (n). Therefore,
In the second embodiment, the graph as shown in FIG. 4 shown in the first embodiment is not presented, but steps S314 and S316 are omitted, and if No is determined in step S13, the base value is calculated in step S315. As compared with the case of performing such control, the detection delay with respect to the increase in the concentration of the reducing gas can be shortened. That is, the increase in the reducing gas concentration can be surely detected at an early stage.

(Modification 2) Further, in the same way as in Modification 1 to Embodiment 1, the density threshold value T is used in this Embodiment 2, whereas in Modification 2 the density high threshold value Tu is used. A hysteresis characteristic is provided by using two thresholds of the low density threshold Td to prevent chattering at the time of switching the density signal. The process of the second modification will be described with reference to the flowchart of FIG.

The control of the second modification is the same as that of the second embodiment from step S11 to step S317 (see FIG. 8). However, in step S315, the base value B (n) is calculated by the equation (5) as in the second embodiment. However, unlike the second embodiment, step S41
Go to 8. Also in step S316, as in the second embodiment, the current sensor output value S (n) is added to the base value B (n).
However, unlike the second embodiment, step S418
Proceed to. Further, also in step S317, the base value B (n) is calculated by the equation (7) as in the second embodiment. However, unlike the second embodiment, the process proceeds to step S419. Therefore, the base value B (n) obtained in steps S315 to S317 has the same property as the base value obtained in the second embodiment.

Then, in step S418, the difference value D
(N) is calculated according to the equation (8) of D (n) = B (n) -S (n), and the process proceeds to step S220. Step S22
At 0, the difference value D (n) is compared with the high concentration threshold Tu,
When D (n)> Tu (Yes), the process proceeds to step S222, and when D (n) ≦ Tu (No), the process directly proceeds to step S224. The result of step S220 is Yes when the low density signal has been generated until then (No in step S13) and D (n)> Tu. Therefore, the sensor output value S (n) And step S31
It is shown that the difference from the base value B (n) that is calculated in step 5 and follows slightly later than this is large. That is, it is considered that the sensor output value S (n) is increased because the concentration of the specific gas (reducing gas) is increased. Therefore,
In step S222, a high density signal is generated instead of the low density signal. Specifically, the density signal LV is set to a high level.

On the contrary, the reason why No is obtained in step S220 is that D (n) ≤Tu is satisfied while the low density signal is being generated until then (No in step S13). Sensor output value S (n) of step S3
The difference from the base value B (n) calculated in step 15 and followed slightly later than this is not so large.
It is shown that (n) is following. That is, it is considered that the concentration of the specific gas (reducing gas) remains low. Alternatively, since the gas concentration continues to decrease, it is considered that the base value B (n) matches the current sensor output value S (n) in step S316.
Therefore, the low density signal is maintained and the process proceeds to step S224.

On the other hand, also in step S419, the difference value D
(N) is calculated according to the equation (8) of D (n) = B (n) -S (n), and is compared with the low concentration threshold Td in step S221. The low concentration threshold value Td is smaller than the high concentration threshold value Tu (Tu> Td). If D (n) ≦ Td (Yes), the process proceeds to step S223, and if D (n)> Td (N).
For step o), the process directly proceeds to step S224. As described above, the reason why the two thresholds of the high concentration threshold Tu and the low concentration threshold Td are used is that the two thresholds are used to provide a hysteresis characteristic, and a low concentration signal and a high concentration signal are provided. This is in order to prevent chattering from occurring in the signals between and. The answer of Step S221 becomes Yes when the high density signal is being generated until then (Step S13).
Yes) in the case of D (n) ≦ Td, the sensor output value S (n) is calculated in step S317, and the past state, that is, the state before the concentration of the reducing gas is increased. It is shown that the difference from the base value B (n), which reflects the above-mentioned value to some extent, has become small, that is, the concentration of the reducing gas has sufficiently decreased. Therefore, in step S223, a low density signal is generated instead of the high density signal. Specifically, the density signal LV is set to low level.

On the contrary, the reason why No is obtained in step S221 is that D (n)> Td is satisfied while the high density signal is being generated until then (Yes in step S13). Sensor output value S (n) and step S
The difference from the base value B (n) calculated in 317 is still large, indicating that the concentration of the reducing gas is increasing. That is, it is considered that the concentration of the specific gas (reducing gas) remains high. So, keep the high concentration signal,
The process proceeds to step S224.

After that, as in the second embodiment, step S
From both 222 and S223, the process proceeds to step S224, the previous base value B (n) calculated in steps S315, S316, and S317 is stored, and step S225 is performed.
After waiting for the A / D sampling time to rise, the process returns to step S12.

Also in the second modification, as in the second embodiment, steps S314 and S316 are eliminated, and when a negative determination is made in step S13, step S315 is performed.
As compared with the case where the control is performed so as to calculate the base value, the detection delay with respect to the increase in the concentration of the reducing gas can be shortened. That is, the increase in the reducing gas concentration can be surely detected at an early stage.

Although the present invention has been described above with reference to the first and second embodiments and the first and second modifications, the present invention is not limited to the above-described embodiments and the like, and does not depart from the scope of the invention. Needless to say, it can be applied with appropriate changes. For example, in the above-described embodiment and the like, the sensor output potential V at the operating point Pd obtained by dividing the power supply voltage Vcc by the gas sensor elements 11 and 41 and the detection resistor 12 having the detection resistance value Rd.
gas detection device 1 for outputting s through the buffer 13
0 and 40 were used. However, the sensor resistance conversion circuit may be any circuit that outputs a sensor output potential according to the sensor resistance value Rs of the gas sensor element, and may have a circuit configuration other than the voltage dividing circuit. For example, in the first embodiment and the like, the gas sensor elements 11 and 41 are located on the ground side (lower side) of the voltage dividing circuit, and the detection resistor 12 is on the power source side (upper side) (see FIGS. 1 and 7). These may be turned upside down so that the gas sensor elements 11 and 41 are located on the power source side (upper side) of the voltage dividing circuit and the detection resistor 12 is on the ground side (lower side). However, in this case, for example, N
Since the characteristics of the sensor resistance conversion circuit are reversed, such that the sensor voltage Vs changes in the direction of decreasing when the concentration of Ox increases, it is necessary to perform processing according to it.

Further, in the above-described embodiment and the like, the base value B (n) is calculated from the equation (1), the equation (3), the equation (5), and the equation (7) using the sensor output value S (n). However, it is also possible to use a value obtained by another calculation method. For example, a moving average value or an integrated value may be used. Further, in the above-described embodiment and the like, the sensor output value and the base value are used to obtain the difference value by the equations (4) and (8), and the difference between the difference value and the density threshold value is compared to determine the density. It was decided to switch signals. However, judging whether other relationships are satisfied,
The density signal may be switched. For example, there is a method of making a judgment by comparing the ratio between the sensor output value and the base value with a threshold value. Further, in the first and second modifications,
In order to prevent the chattering of the density signal, the density threshold has a hysteresis, and the density high threshold Tu and the density low threshold Td are used for switching the density signal. However, chattering of the density signal can be prevented by other methods. For example, there is a method in which once the density signal is changed, the density signal is maintained until a predetermined time elapses.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an overview of a gas detection device and a vehicle automatic ventilation system according to a first embodiment.

FIG. 2 is an explanatory diagram showing a control flow in the vehicle automatic ventilation system according to the first embodiment.

FIG. 3 is an explanatory diagram showing a control flow in a microcomputer of the gas detection device according to the first embodiment.

FIG. 4 relates to the first embodiment, and changes in the base value B (n), the difference value D (n), and the concentration signal LV with respect to changes in the sensor output value S (n) that repeatedly increase and decrease the NOx concentration. FIG. 7 is an explanatory diagram showing the above in contrast to changes in the base value Ba (n), the difference value Da (n), and the density signal LVa obtained without steps S14 and S16.

FIG. 5 is an explanatory diagram showing a control flow in a microcomputer of the gas detection device according to the first modification.

FIG. 6 is a variation of the base value B (n), the difference value D (n), and the concentration signal LV with respect to the change of the sensor output value S (n) in which the concentration of NOx is repeatedly increased and decreased according to the first modification. Is obtained without steps S314 and S316, the base value Bb (n), the difference value Db (n), and the density signal LV.
It is explanatory drawing shown in comparison with the change of b.

FIG. 7 is an explanatory diagram showing an outline of a gas detection device and a vehicle automatic ventilation system according to a second embodiment.

FIG. 8 is an explanatory diagram showing a control flow in a microcomputer of the gas detection device according to the second embodiment.

FIG. 9 is an explanatory diagram showing a control flow in a microcomputer of the gas detection device according to the second modification.

[Explanation of symbols]

100,140 Auto-ventilation system for vehicle 10,40 Gas detection device 11,41 Gas sensor element 12 Detection resistor 13 Buffer 14,44 Sensor resistance value conversion circuit 15 A / D converter 16 Microcomputer 19,49 Sensor output value acquisition circuit ( Acquisition means) 20 Electronic control assembly 21 Flap drive circuit 31, 32, 33 Duct 34 Flap

Claims (11)

[Claims] 1. A gas detection device using a gas sensor element whose electrical characteristics change depending on the concentration of a specific gas, wherein the gas sensor element is used to acquire a sensor output value at predetermined intervals. Density signal generating means for generating either a low density signal or a high density signal, and a first calculating means for calculating a first calculated value during a period in which the low density signal is being generated by the density signal generating means. When the current sensor output value changes in the concentration increasing direction compared to the immediately preceding sensor output value, the first calculated value that slowly changes while following the current sensor output value is set as the current sensor output value. And a first calculation means for setting the current sensor output value as the first calculated value when the current sensor output value changes in the density decreasing direction compared to the immediately preceding sensor output value, Above concentration The signal generating means replaces the low density signal with the high density signal when the sensor output value and the first calculated value satisfy a predetermined first relationship during a period in which the low density signal is being generated. Gas detector that generates a signal. 2. The gas detection device according to claim 1, wherein the concentration signal generating means is configured to perform the first concentration signal generation in the period during which the low concentration signal is generated.
As a relationship, when the difference between the sensor output value and the first calculated value satisfies a predetermined magnitude relationship with a predetermined first threshold value, the density high signal is generated instead of the density low signal. Gas detector. 3. The gas detection device according to claim 1 or 2, wherein the concentration signal generating means slowly follows the sensor output value while the concentration high signal is being generated. A second calculated value that changes using the sensor output value
The density signal generating means includes a calculating means, and when the sensor output value and the second calculated value satisfy a predetermined second relationship during a period in which the high density signal is generated, the high density signal is generated. A gas detection device for generating the low concentration signal instead of the signal. 4. The gas detection device according to claim 3, wherein the concentration signal generating means is configured to control the second concentration during the period in which the low concentration signal is generated.
As a relationship, when the difference between the sensor output value and the second calculated value satisfies a predetermined magnitude relationship with a predetermined second threshold value, the density low signal is generated instead of the density high signal. Gas detector. 5. The gas detection device according to claim 3, wherein the first calculation means changes the current sensor output value in the concentration increasing direction as compared with the immediately previous sensor output value. When doing, the gas detection device that calculates the first calculated value that changes more sensitively than the second calculated value. 6. A gas detection device using a gas sensor element whose electrical characteristics change according to the concentration of a specific gas, wherein the gas sensor element is used to obtain a sensor output value S (n) at predetermined time intervals. An acquisition means for increasing the sensor output value S (n) when the concentration of the specific gas increases, where n is an integer indicating a time-series order, a low concentration signal and a high concentration signal And a first base value calculating means for calculating a base value B (n) during a period in which the low density signal is being generated by the density signal generating means. The sensor output value S (n) is the immediately preceding sensor output value S (n
-1) or more, the base value B according to the following formula (1)
(N) is calculated and B (n) = B (n-1) + k1 {S (n) -B (n-1)} (1) where k1 is the first coefficient and 0 <k1 < 1. The sensor output value S (n) is the immediately preceding sensor output value S (n
−1), the base value B (n) is calculated according to the following equation (2): B (n) = S (n) (2) First base value calculating means and the density signal generating means Second base value calculating means for calculating a base value B (n) according to the following equation (3) during the period of generating the high density signal, and B (n) = B (n-1) + k2 {S ( n) -B (n-1)} (3) However, k2 is a second coefficient, and 0 <k2 <k1 <1, and from the sensor output value S (n) and the base value B (n),
The difference value calculating means for calculating the difference value D (n) according to the following equation (4), and D (n) = S (n) -B (n) (4) A gas detection device for generating the high concentration signal when the difference value D (n) is larger than a concentration threshold value. 7. A gas detection device using a gas sensor element whose electrical characteristics change according to the concentration of a specific gas, wherein the gas sensor element is used to obtain a sensor output value S (n) at predetermined time intervals. An acquisition means for increasing the sensor output value S (n) when the concentration of the specific gas increases, where n is an integer indicating a time-series order, a low concentration signal and a high concentration signal And a first base value calculating means for calculating a base value B (n) during a period in which the low density signal is being generated by the density signal generating means. The sensor output value S (n) is the immediately preceding sensor output value S (n
-1) or more, the base value B according to the following formula (1)
(N) is calculated and B (n) = B (n-1) + k1 {S (n) -B (n-1)} (1) where k1 is the first coefficient and 0 <k1 < 1. The sensor output value S (n) is the immediately preceding sensor output value S (n
−1), the base value B (n) is calculated according to the following equation (2): B (n) = S (n) (2) First base value calculating means and the density signal generating means Second base value calculating means for calculating a base value B (n) according to the following equation (3) during the period of generating the high density signal, and B (n) = B (n-1) + k2 {S ( n) -B (n-1)} (3) However, k2 is a second coefficient, and 0 <k2 <k1 <1, and from the sensor output value S (n) and the base value B (n),
The difference value calculating means for calculating the difference value D (n) according to the following equation (4), and D (n) = S (n) -B (n) (4) When the difference value D (n) is larger than the high density threshold Tu, the high density signal is generated, and the difference value D (n) is smaller than the high density threshold Tu. A gas detection device which generates the above-mentioned low concentration signal when smaller than the above. 8. A gas detection device using a gas sensor element whose electric characteristics change according to the concentration of a specific gas, wherein the sensor output value S (n) is acquired at predetermined time intervals using the gas sensor element. An acquisition means for decreasing the sensor output value S (n) when the concentration of the specific gas rises, where n is an integer indicating a time-series order, a low concentration signal and a high concentration signal And a third base value calculating means for calculating a base value B (n) during a period in which the low density signal is being generated by the density signal generating means. The sensor output value S (n) is the immediately preceding sensor output value S (n
-1) In the case of the following, the base value B according to the following equation (5)
(N) is calculated and B (n) = B (n-1) + k3 {S (n) -B (n-1)} (5) where k3 is the third coefficient and 0 <k3 < 1. The sensor output value S (n) is the immediately preceding sensor output value S (n
−1), the base value B (n) is calculated according to the following equation (6): B (n) = S (n) (6) Third base value calculating means and the density signal generating means Fourth base value calculating means for calculating a base value B (n) according to the following equation (7) during the period of generating the high density signal, and B (n) = B (n-1) + k4 {S ( n) -B (n-1)} (7) However, k4 is a fourth coefficient, and 0 <k4 <k3 <1, and from the sensor output value S (n) and the base value B (n),
The difference value calculating means for calculating the difference value D (n) according to the following equation (8), and D (n) = B (n) −S (n) (8) are provided, and the concentration signal generating means is A gas detection device for generating the high concentration signal when the difference value D (n) is larger than a concentration threshold value. 9. A gas detection device using a gas sensor element whose electric characteristics change according to the concentration of a specific gas, wherein the sensor output value S (n) is acquired at predetermined intervals using the gas sensor element. An acquisition means for decreasing the sensor output value S (n) when the concentration of the specific gas rises, where n is an integer indicating a time-series order, a low concentration signal and a high concentration signal And a third base value calculating means for calculating a base value B (n) during a period in which the low density signal is being generated by the density signal generating means. The sensor output value S (n) is the immediately preceding sensor output value S (n
-1) In the case of the following, the base value B according to the following equation (5)
(N) is calculated and B (n) = B (n-1) + k3 {S (n) -B (n-1)} (5) where k3 is the third coefficient and 0 <k3 < 1. When the sensor output value S (n) is larger than the immediately preceding sensor output value S (n-1) during the period in which the density low signal is generated by the density signal generating means, the following equation (6) B (n) = S (n) (6) for calculating the base value B (n) according to the third base value calculating means and the density signal generating means for generating the high density signal, Fourth base value calculating means for calculating a base value B (n) according to the following expression (7), and B (n) = B (n-1) + k4 {S (n) -B (n-1)} ( 7) However, k4 is a fourth coefficient, and 0 <k4 <k3 <1, and from the sensor output value S (n) and the base value B (n),
The difference value calculating means for calculating the difference value D (n) according to the following equation (8), and D (n) = B (n) −S (n) (8) When the difference value D (n) is larger than the high density threshold Tu, the high density signal is generated, and the difference value D (n) is smaller than the high density threshold Tu. A gas detection device which generates the above-mentioned low concentration signal when smaller than the above. 10. A vehicle auto-ventilation system including the gas detection device according to any one of claims 1 to 9. 11. An outside air inlet, the gas detection device according to claim 1, wherein the opening / closing device for the outside air inlet is fully opened when the concentration signal is a low concentration signal. An automatic opening / closing means for outputting an opening / closing instruction signal for fully closing the opening / closing device for the outside air inlet when the concentration signal is a high concentration signal.