JP3169193B2 - Gas detector - Google Patents

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, and more particularly to control of an air purifier of an automobile and detection of gas in real time in the presence of noise.

[0002]

2. Description of the Related Art It has been proposed to control air conditioning of an automobile using a gas sensor of a metal oxide semiconductor such as SnO2. The target of detection is the gas accompanying smoking.To compensate for drift due to ambient temperature and humidity of the gas sensor, changes over time, etc., it is possible to extract the envelope of the gas sensor signal and detect smoking by deviation from the envelope. Proposed.

[0003] However, the inventors have encountered the following problems in controlling an air purifier of an automobile. 1) Drift occurs in the gas sensor signal due to the operation of the air conditioner cooler and heater, the number of occupants in the automobile, and the like. The drift is large and is quick as compared with the fluctuation of the temperature and humidity of the outside air, and it is difficult to distinguish from the smoking by detecting the envelope. Therefore, especially when a large number of passengers get into a car,
The gas sensor signal increases and the air purifier operates. 2) When running with the window of the car open, noticeable noise is generated in the signal of the gas sensor. In particular, when traveling with the front and rear windows opened, a signal larger than the signal due to smoking is generated. The problem of noise also occurs when a car door is opened, and strong random noise is generated when the door is opened. A change in the sensor signal when the door is opened is difficult to distinguish from a change in the sensor signal due to smoking.

[0004] Here, as a related prior art, Japanese Patent Publication No. 3-14133 proposes that an envelope of a gas sensor signal is obtained and gas is detected based on a deviation from the envelope. Japanese Patent Application Laid-Open No. 3-271,020 discloses a problem of an air purifier for an automobile by detecting an envelope.
It has been reported that the opening of the door causes significant noise and the air purifier malfunctions.

A fundamental problem with automotive air purifiers is to quickly detect smoking. Rapid detection of smoking requires extracting small changes in the gas sensor signal, which is inconsistent with the problem of noise and drift from windows and doors.

[0006] Here, the prior art has been described for an air purifier of an automobile. However, such a problem is also the same when, for example, controlling an air purifier in a living room or detecting gas in real time in the presence of noise.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a gas detection device having a high S / N against noise.

[0008]

According to the present invention, there is provided a gas detecting apparatus for detecting a gas with a gas sensor, wherein the gas detecting means detects the gas from the gas sensor signal, and the gas detecting means detects a sharp decrease in the gas sensor signal. It is characterized in that a detecting means and a suppressing means for correcting the gas sensor signal so as to suppress the detection of the gas after the sudden detection of the gas sensor signal is detected by the decrease detecting means are provided.

Preferably, a timer is provided in the suppression means, and when the decrease detection means detects a sharp decrease in the gas sensor signal, the timer is activated to inhibit gas detection for a predetermined time. I do. Preferably, the gas detection means is configured to detect gas by differentiating a gas sensor signal. Particularly preferably, the air conditioner is controlled by the gas detecting means.

[0010]

When noise occurs due to the opening of a window or a door, the sensor signal sharply decreases. Therefore, if a sudden decrease in the sensor signal is detected and the detection of gas is suppressed thereafter, a gas detection device with less malfunction due to noise can be obtained.

[0011]

According to the present invention, it is possible to obtain a gas detection device which is less likely to malfunction due to noise such as an open window or an open door.

An embodiment will be described below. However, the present invention is to detect a sudden decrease in the gas sensor signal and suppress the detection of the gas thereafter. Is not included in the present invention.

[0013]

FIG. 1 shows a main part of an embodiment of a control device of an air purifier for an automobile. In the figure, 2 is a metal oxide semiconductor gas sensor, 4 is its heater, and 6 is its metal oxide semiconductor. The metal oxide semiconductor 6 may be, for example, SnO2, WO3, In2O3, or the like. In addition to the metal oxide semiconductor gas sensor 2, for example, a contact combustion type gas sensor utilizing a temperature change due to combustion of a combustible gas, or a proton conductor gas sensor utilizing detection of H2 and CO generated by smoking can be used. Reference numeral 8 denotes a power source such as a battery, and RL denotes a load resistance of the metal oxide semiconductor 6.

Reference numeral 10 denotes a signal processing microcomputer, which is a 4-bit one-chip microcomputer. Reference numeral 12 denotes an air purifier, for example, an electric dust collector for removing smoke accompanying smoking, and an ozone generator for removing odor accompanying smoking. Instead of the air purifier 12, a ventilation device, an outside air introduction device, and an air purification catalyst may be controlled.

The configuration of the microcomputer 10 is as follows. Reference numeral 14 denotes an AD converter, and reference numeral 16 denotes a differentiating circuit, which detects gas accompanying smoking by the first-order or second-order differentiation of a gas sensor signal. The time constant used for the first-order differentiation and the second-order differentiation is, for example, about 2 seconds to 10 seconds, and the time width is shortened in a range where discrimination from noise can be obtained, and gas due to smoking is promptly detected. Reference numeral 18 denotes a noise filter which detects a random, non-directional, short time constant noise of the gas sensor signal V due to noise such as wind from a window or a door. Reference numeral 20 denotes a counter which adds 1 to the differential signal △ V obtained by the differentiating circuit 16 when the threshold value is equal to or greater than the detection threshold value D, and 2 for △ V <D.
Is subtracted. The target value J of the counter 20 is determined by the signal of the noise filter 18, the larger the noise, the larger the value J. When the value of the counter 20 reaches J, the air purifier 12
To work. Reference numeral 22 denotes a stop control circuit of the air purifier 12.

FIG. 2 shows the internal configuration of the microcomputer 10. 16 performs the first order differentiation in the aforementioned differentiation circuit,
The noise filter 18 convolves and integrates the negative differential signal with a time constant k according to the equations (1) and (2). The time constant k is ΔV
When ≧ 0 continues, the time until the value of F decreases to 1 / e is about 30 to 120 seconds. Equation (1) is convolution, and equation (2) is the normalization of noise F. F = Fk + | △ V | △ V <0 (1) F ′ = F / V (2) The operator of the digital first derivative is determined by, for example, equation (3). ΔV = V1−V2 (3) (V1 is the current value of the sensor signal V, V2 is the value one second before) The stop control circuit 22 includes a memory 23 for storing the sensor signal Von when smoking is detected and a timer 24. , Multiplication circuit 25,
Expression (4) is used as a stop condition for the air purifier 12. Von (1 + T) ≧ V (4)

[0017]

Embodiment 2 FIG. 3 shows the detection of noise similar to the 0-crossing method. In FIG. 3 and subsequent figures, the same reference numerals as those in FIGS. 1 and 2 indicate the same parts. Reference numeral 31 denotes an average value calculation circuit for obtaining a time average of the sensor signal V by a simple average, convolution, or the like.
Reference numeral 32 denotes a comparison circuit, which is an average value and $ 1 and $ 2 from the average value.
Only three small detection points (の 2> △ 1) are drawn, and when the sensor signal V passes through the detection lines, the counter 3
Add 3 For example, the value of the addition is 1 when the value crosses the average value, 2 when the value crosses the average value − △ 1, and 3 when the value crosses the average value − △ 2. Reference numeral 34 denotes a timer, for example, which decrements the data of the counter 33 by one every 30 seconds, and the counter 33 is provided with a circuit for preventing occurrence of a negative number and overflow.

[0018]

Third Embodiment FIG. 4 shows a third embodiment. Reference numeral 41 denotes an edge detection circuit for further digitally differentiating the first-order differential signal △ V of the differentiating circuit 16 to obtain a digital second-order differential signal △ ² V. For example, an operator of (V1-2V2 + V3) is used for digital second-order differentiation, and detection is performed using two seconds from V1 to V3 (V1 is the current value of the sensor signal V, V3 is the sensor signal two seconds before).

[0019]

Fourth Embodiment FIG. 5 shows a fourth embodiment. According to experiments, when a window or door opens, the sensor signal V first decreases. This would be a response to the gas flow cooling the gas sensor 2. Since the sensor signal V increases in the case of smoking, a sharp decrease in the sensor signal is an indication that a window or door has been opened. In FIG. 5, reference numeral 51 denotes a noise detection circuit which determines that noise occurs when the digital first derivative signal ΔV of the sensor signal V is −B or less, and that the comparison circuit 52 determines that smoking occurs when ΔV is greater than or equal to the threshold value A. The logic circuit 53 activates the timer 34 at the time of noise detection and sets a flag. While the flag is set, the AND circuit 54 inhibits the operation of the air purifier 12. 12 is driven.
Preferably, -B is set as the threshold value, and the time for setting the flag is extended as the magnitude (absolute value) of the first derivative signal becomes larger than -B.

[0020]

Fifth Embodiment FIG. 6 shows a fifth embodiment. A differentiating circuit 16 obtains a digital first-order differential signal V of the sensor signal V, and an edge detecting circuit 41 further digitally differentiates this to obtain a digital second-order differential signal △ ² V. If the digital second derivative signal is equal to or greater than the threshold value D2, it is determined to be smoking. Digital 1
It is assumed that noise due to a window, a door, or the like is generated when the differential signal △ V is −B or less, and the timer 3
Activate 4 and set a flag. In the AND circuit 54, the air purifier 12 is operated when an edge associated with smoking occurs and there is no flag for noise.

[0021]

Sixth Embodiment FIG. 7 shows a sixth embodiment. In the figure, 71,
Reference numeral 72 denotes an addition circuit. The addition circuit 71 adds the absolute value of the change in the gas sensor signal V, and the addition circuit 72 adds the digital first derivative signal △ V of the gas sensor signal V with a sign. When noise occurs, the output of the addition circuit 71 for adding the absolute value of △ V is large, and the output of the addition circuit 72 that adds △ V with a sign is small. Thus, if these ratios are obtained by the dividing circuit 73, it is possible to distinguish between noise and smoking. This is input to the AND circuit 54, and when the smoking detection signal from the digital first-order differentiation circuit 16 is present and the noise detection signal from the division circuit 73 is not present, the air purifier 12 is driven.

Although a specific example has been described in these embodiments, the present invention is not limited to this. For example the digital first derivative signal △ V and digital second-order differential signal △ ² V may be determined by an analog differential regardless of the digital differential. 5 to 7
In this embodiment, the signal from the differentiating circuit 16 or the like is invalidated when noise occurs, and the air purifier 12 is not operated. On the other hand, in the embodiment of FIGS.
0 is used to delay detection when noise occurs, and for a long time (20
If the sensor signal V continues to increase monotonically, detection is limited.

[0023]

FIG. 8 shows the operation of the embodiment when the microcomputer 10 of FIG. 2 is used. 3 to 7
The operation of this embodiment is obvious from the description of FIG. The microcomputer 10 AD-converts the gas sensor signal V, for example, every second, and differentiates it first-order by the differentiating circuit 16. The ratio between the digital first derivative signal △ V and the sensor signal V is obtained, and if this value is equal to or greater than D, smoking is determined. The noise filter 18 obtains the noise amount F by integrating the differential value of the sensor signal every second by convolution with a time constant of about 30 to 120 seconds only when the differential value is negative. The noise F 'is detected from the ratio with the signal V. The target value J of the counter 20 is
J0 (for example, 2) is minimized and increased according to F 'using the constant p1, so that as the noise becomes more intense, only an increase in the sensor signal V that is monotonous for a long time is detected, and the noise is small or there is no noise. Sometimes detect smoking quickly.

FIG. 9 shows operation waveforms in each embodiment. The characteristic of the gas sensor signal V due to smoking is that the sensor signal V increases simply and monotonously as shown on the right side of FIG. Thus, for example, smoking can be detected by digitally differentiating the sensor signal V for the first order. Further, if the sensor signal V is digitally differentiated, smoking can be detected from the edge of the increase in the sensor signal V accompanying the start of smoking. As shown in the left side of FIG. 9, the characteristic of noise due to windows, doors, and the like is a random fluctuation of the sensor signal V, which is detected to suppress the smoking detection signal. The small 0 mark on the left side of FIG. 9 is an edge in the noise. When smoking is detected, the stop threshold value Von (1 + T) of the air purifier 12 is gradually increased by the timer 24, and the air purifier 12 is stopped at the point where the sensor signal V crosses. As a result, the operation time of the air purifier 12 is proportional to the increase in the sensor signal V due to smoking, and the operation time becomes longer as the amount of generated gas increases.

FIGS. 10 and 11 show a smoking signal, water vapor and odor generated by an occupant, drift of a sensor signal due to operation of an air conditioner, and noise from a door. In FIG.
The noise is shown when the vehicle is run at km / hr and two windows are opened before and after the time from 1 to 6 minutes to allow the wind to flow into the passenger compartment. In FIG. 12, the reason why the sensor resistance decreases at about 4 minutes is as follows.
This is because the truck passed around and inhaled the stench.
In these figures, the sensor resistance RS of the reciprocal of the sensor signal V is shown.
Is shown on the vertical axis, and particularly in FIGS. 10 and 11, the maximum value of the sensor resistance is normalized to 1. As shown in FIGS. 10 and 11, the drift caused by water vapor, odor and the like generated from the air conditioner and the occupant is slow, and can be distinguished from the smoking signal in FIG. 10 by the differential coefficient. Most of the noise when the door is opened can be eliminated by setting the time constant of the convolution integration to 30 seconds (when the convolution is performed every second, the constant k is 0.97). FIG.
In the case of 2, the sensor resistance continues to fluctuate randomly while the window is open, thereby preventing malfunction. When you close doors and windows,
Since the time constant of the noise filter 18 is as long as 30 to 120 seconds, the air purifier 12 does not malfunction even if the noise filter 18 temporarily drifts with a gradient equal to or higher than the detection threshold D at the beginning of the drift. Since the counter 20 is used in the embodiment shown in FIGS. 1 to 4, when the window or the door is opened, for example, when the sensor signal V exceeds the threshold value D for 50 seconds or more,
The air purifier 12 is operated, and during the drift period, for example, 20
The air purifier 12 is operated when the value exceeds D continuously for more than seconds, and when the drift is completed, the air purifier 12 is operated for 2 seconds when the value is D or more, for example. That is, the more intense the noise, the more reliable the signal is extracted at the expense of the detection speed, and the less the noise, the faster the detection.

[0026]

Embodiment 7 In FIG. 13, reference numeral 2 denotes the gas sensor described above;
Reference numeral 8 denotes the power supply. Sensor output V to load resistance RL
Is extracted using a resistor R2, and a capacitor C1 and a resistor R4
The sensor output V is differentiated by a differentiation circuit having a time constant of about 1 to 2 seconds. Resistor R so that the differential output does not become negative
3, a positive bias is applied to the differential output using R4, and this is amplified, for example, about 10 times by the amplifier circuit A1. In this way, the signal is amplified before the AD converter, and the resolution is improved.

100 is a new microcomputer,
102 is, for example, a 2-port AD converter, 104 is a smoking detection circuit using logarithmic differentiation of the sensor signal V, 106 is a random noise detection circuit for detecting random noise of the sensor output using the integration of | dlnV / dt | , 1
Reference numeral 08 denotes a window open detection circuit for detecting that a window or a door has been opened from a sudden decrease in the sensor output V.
Is a long-term average detection circuit for obtaining a long-term average of the sensor output V, 112 is a stop level generation circuit for generating a stop level of the air purifier, and 114 is a temporary memory of the sensor output V. 116 is a NOR gate, 118 is an AND gate, 120 and 122 are inverters, and 124 is a comparator. The window opening detection circuit 108 may not be provided.

FIG. 14 shows a signal flow in the seventh embodiment.
The sensor output V is analog-differentiated by a capacitor C1 and amplified by an amplifier circuit A1 to obtain a differential signal dV / dt of the sensor output.
Take out. This is connected to port P1 of AD converter 102.
And supplies it as a logarithmic derivative dlnV / dt to the smoking detection circuit 104, the random noise detection circuit 106, and the window open detection circuit 108. The sensor output V is applied to the port P2 of the AD converter 102 and supplied to the long-term average sensor output detection circuit 110, the air purifier stop level generation circuit 112, and the temporary memory 114.

As shown in FIG. 12, when the window is opened, the sensor resistance RS increases and the sensor output V decreases. FIG.
As shown in FIG. 11, the sensor output V also decreases when the door is opened. However, the decrease in the sensor output V when the door is opened is smaller than that when the window is opened. The window opening detection circuit 108 detects that dlnV / dt is more negative than the threshold value -X, and generates a window or door opening signal. The window opening detection circuit 108 has a built-in timer.
Start the minute timer. Random noise detection circuit 10
In step 6, a gate G is provided to pass the logarithmic differential signal only when the logarithmic differential of the sensor output V is negative. The random noise amount C stored in the memory is multiplied by the correction constant k by the multiplication circuit M to obtain k · C, and the logarithmic differentiation of the sensor output V is added by the addition circuit (absolute value subtraction because it is a negative signal). K · C-dlnV / dt is fed back to the memory, which is compared with a threshold value by a comparator C. When the threshold value is exceeded, a random signal detection circuit F2 is generated. On the other hand, the smoking detection circuit 104 calculates the logarithmic differential d (l
Since nV) / dt is larger than the threshold value k1, smoking is detected.

The long-term average detection circuit 110 of the sensor output utilizes the NOR gate 116. When there is no smoking detection signal, no random noise is detected, and there is no window open detection signal, the long-term average L of the sensor output V is obtained. To correct. For example, convolution is used to correct the long-term average L. The time constant of the long-term average is, for example, 10 minutes to 1 hour, and the correction constant is k3. This corresponds to obtaining the average value of the sensor output when the windows and doors are closed and there is no smoking. Alternatively, instead of obtaining the long-term average, the sensor output immediately before the window is opened may be stored. The sensor output long-term average detection circuit 110 calculates the ratio between the current sensor output value V and the long-term average L, and calculates the ratio V / L from the look-up table to the threshold value k1 detected by the smoking detection circuit 104 and the air cleanliness value. The correction constant k2 of the stop level in the stop level generation circuit 112 of the container is determined. As the value of V / L is smaller, the threshold value k1 for detecting smoking is increased, and the correction constant k2 of the stop level L2 of the air purifier is increased. This means that, for example, in FIG. 12, when the window is opened and the sensor output V is reduced, the smoking detection threshold value k1 is increased, and the sensitivity to smoking is reduced. When the window is closed after time 6 minutes, the sensor output V monotonously increases. During this time, the sensor output V is smaller than the long-term average L, and the detection sensitivity is lowered by increasing k1 to prevent malfunction. If smoking overlaps here, the increase in sensor output due to smoking and the increase in sensor output due to closing of the window overlap, and even if the threshold value k1 is increased, smoking can be detected. Similar effects are obtained in FIGS.
For the increased drift of the sensor output after the door is closed. When the door is open, the sensor output V
When the detection threshold value k1 for smoking is increased as the V / L is smaller with respect to the drift of the sensor output after the door is closed, malfunction due to the drift can be prevented. If smoking overlaps here, dlnV / dt is larger than usual, so that smoking can be detected.

In the embodiment shown in FIG. 13, the smoking detection signal F1 is used.
Occurs, and the air purifier 12 is driven only when there is no detection signal F2 of the random noise or the window opening signal F3. When the air purifier 12 is operated, the sensor output V before the detection of smoking is stored as an initial value of the stop level L2 of the air purifier. The air purifier 12 only removes smoke accompanying smoking and does not remove gas. Even if the air purifier 12 is operated, the sensor output V does not decrease. In accordance with the increase in the sensor output V due to smoking (peak height due to smoking), the air purifier 1
Determine the operation time of 2. Thereby, the operation time of the air purifier 12 is made to correspond to the generated smoke density. The sensor output V is not proportional to the gas concentration, but is proportional to the 0.6th power of the gas concentration. Also, the higher the background gas concentration and humidity, the smaller the increase in sensor output for gas generated by smoking. Therefore, a correction constant k2 is determined from a lookup table from the ratio V / L of the sensor output V and the long-term average value L of the sensor output,
The higher the V / L, the higher the background gas concentration and humidity, and the apparently lower sensitivity of the sensor.
The correction constant k2 of the stop level L2 is reduced.

In the stop level generation circuit 112 of the air purifier, the sensor output V before the detection of smoking is stored as a stop level L2, and the stop level L2 is set at predetermined time intervals using a timer (not shown).
2 is multiplied by a modified constant k2 (0 <k2 <1), and this is set as a new stop level L2. This means that, for example, in FIG. 10, an oblique curve is drawn from the sensor resistance RS immediately before the detection of smoking to the side where RS decreases, and the air purifier 12 is operated until this curve and the actual sensor resistance RS intersect. I do. This time is a function of the valley depth of the decrease in sensor resistance due to smoking in FIG. 10 and is influenced by background humidity, flammable gas entering from outside air, and gas from previous smoking when smoking subsequently. And the time is proportional to the smoke density generated. If the vehicle air is replaced and the sensor output V decreases, the operating time of the air purifier 12 is correspondingly reduced. Necessary air purifier 12
Operating time depends on the internal volume of the vehicle, the capacity of the air purifier 12,
It is determined by the density of generated smoke. The ability of the air purifier 12 is known, and if the smoke concentration generated in the above processing is determined from the gas concentration, the air purifier 12 can be almost appropriately controlled.

Here, it has been shown that the smoking detection threshold value k1 is corrected by the ratio V / L of the sensor output V and the long-term average L. However, simply, when the ratio V / L falls below a predetermined range, the detection of smoking may be prohibited. In this case, the window or door is kept open for a long period of time, and the meaning of the stored long-term average L is lost. When V / L is equal to or less than a predetermined value, L is gradually reduced, and after a long period, V / L is reduced. May increase and the detection of smoking may be restarted.

[0034]

Eighth Embodiment FIG. 15 shows a basic configuration of an eighth embodiment. In the figure, reference numeral 202 denotes a gas sensor, for example, a metal oxide semiconductor gas sensor, a proton conductor gas sensor, a solid electrolyte gas sensor, or the like. 204 is a differentiating circuit, and 206 is a filter for generating an auxiliary signal for evaluating the reliability of the differentiated signal. A comparison circuit 208 receives a detection threshold value from the filter 206 and generates a gas detection signal when the time derivative of the sensor signal exceeds the detection threshold value.
In the embodiment, the first-order differentiating circuit is used as the differentiating circuit 204, but a second-order or higher-order differentiating circuit may be used. In the example,
The auxiliary signal is generated by the filter 206 from the signal of the gas sensor 202 itself.
6, a compensation sensor such as a humidity sensor is arranged on the input side,
The signal of the compensation sensor may be processed by the filter 206 to generate an auxiliary signal. Differentiating circuit 204, filter 2
06, the comparison circuit 208 is realized by a microcomputer, for example.

FIGS. 16 to 19 show examples of the filter 206. FIG. The noise filter 226 of FIG.
The signal 02 is second-order differentiated by the second-order differentiation circuit 222, and the integration circuit 224 performs convolution integration of the absolute value of the second-order differentiation, thereby detecting random fluctuations in the sensor signal.

FIG. 20 shows a signal waveform of the gas sensor 202 in a vehicle cabin in a case where the gas sensor 202 is used for controlling an air cleaner for an automobile. The atmosphere in the cabin can be classified into three states: a state in which doors and windows are opened, a drift period thereafter, and a stable period after the drift ends. The feature when the door or the window is opened is that the sensor signal V sharply decreases and severe random fluctuation occurs. A feature of the drift is that the sensor signal V continues to increase gradually and monotonically over a long period of time. When the drift ends, the sensor signal V becomes substantially constant. However, in reality, there is no exact stable period, and it seems that the drift speed is merely sufficiently reduced. The purpose of detection in the control of the air purifier is to detect smoking, and it is not necessary to detect smoking when the window or door is open, but only for smoking during the drift period or the stable period. The characteristic of smoking is that the sensor signal V increases rapidly.

[0037]

[Table 1] Main part of the program Read the noise filter READ VS sensor output Vs in Fig. 16 (every second) V6 = V5: V5 = V4: V4 = V3: V3 = V2: V2 = V1: V1 = VS D1 = (V1 + V2-V3-V4) / V1 First order derivative (time constant 2 seconds) D2 = (V1 + V2-2 * V3-2 * V4 + V5 + V6) / V1 2nd derivative (time constant 2 seconds) IF D2 ≦ 0 THEN F = F * (1-P) + ABS (D2) ELSE F = F * (1-P) Evaluate noise with noise filter, negative J = INT (F) * K1 + J0 Increase the threshold from J0 according to the output F of the noise filter IF D1 ≧ J THEN X = 1 Drive the air purifier with a differential signal above the threshold

Referring to Table 1 and FIG. 20, FIGS.
The operation of the sixth embodiment will be described. The sensor signal V is read every second and the first and second derivatives are performed with a time constant of 2 seconds.
When the second derivative is negative, that is, when an edge on the side where the sensor signal V decreases is detected, its absolute value is integrated. The time constant of integration is determined by a constant P, and the integration value is reduced to 1 / e every 30 seconds to 120 seconds (when there is no noise input). As is clear from FIG. 20, when the door or window is open, the sensor signal V fluctuates drastically, so that many edges are generated and the second derivative is not zero. On the other hand, in the drift period, the smoking period, or the stable period, the sensor signal V changes almost linearly and the second derivative is small. In the embodiment, in order to prevent the noise filter 226 from detecting the edge of the increase in the sensor signal due to smoking in the drift period or the stable period,
Only the negative second derivative was integrated. Therefore, the output of the noise filter 226 increases when the door or window opens, and decreases with a time constant of about 30 to 120 seconds when the door or window closes. The detection threshold value J of the first derivative signal D1 of the sensor signal V is J0
Is determined by the output of the noise filter 226 as a minimum value.
As a result, when the door or window is open, the detection threshold value J becomes large, and even if a differential signal having a gradient that cannot be distinguished from smoking temporarily occurs, malfunction can be prevented. In the early stage of the drift, the output of the noise filter 226 still remains because the time constant is as long as 30 to 120 seconds, and even if a large gradient drift occurs accidentally during this period, malfunction of the air purifier can be prevented. it can. The output of the noise filter 226 decreases when the drift ends, and the differential detection threshold value becomes minimum during the stable period. For this reason, smoking is detected even in a small differential signal in a stable period with little noise.

The detection threshold value J of the differential is calculated by the noise filter 22.
Correcting with the signal 6 also means correcting the nonlinearity of the output of the gas sensor 202. Gas sensor 2
The signal of 02 is proportional to the 0.5th power of the gas concentration or the like, and the higher the background gas concentration, the smaller the rate of change of the sensor signal V per smoking. When the doors and windows are open, ventilation is progressing, and the gas concentration in the vehicle interior is decreasing. On the other hand, during the stable period, the background gas concentration is increasing due to body odor and fragrance generated from the occupant, odor generated from the vehicle itself, odor generated from the filter of the air purifier, and the like. Therefore, suppressing the detection of smoking when the door or window is open by the noise filter 226 and speeding up the detection of smoking in the stable period facilitates the detection of smoking in the stable period when the background gas concentration is high. And has the role of correcting the non-linearity of the gas sensor 202.

FIG. 17 shows a noise filter 236 according to a modification. Table 2 shows the operation. In the noise filter 236, the signal of the gas sensor 202 is temporarily differentiated by the differentiation circuit 2
32, and the integrating circuit 234 convolves and integrates only the change on the side where the sensor signal V decreases.

[0041]

[Table 2] The main part of the program Read the noise filter READ VS sensor output Vs in Fig. 17 (every second) V4 = V3: V3 = V2: V2 = V1: V1 = VS The latest output three times before V1 Input to V4 D1 = (V1 + V2-V3-V4) / V1 First derivative (time constant 2 seconds) IF D1 ≦ 0 THEN F = F * (1-P) + ABS (D1) ELSE F = F * ( 1-P) Evaluate noise with noise filter, convolve negative difference J = INT (F) * K2 + J0 Increase threshold from J0 according to noise filter output F IF D1 ≧ J THEN X = 1 The air purifier is driven by the differential signal that is higher than the value

As is clear from FIG. 20, when the door or window is opened, the sensor signal is first reduced. After that, since the sensor signal V fluctuates randomly, a large value is obtained when the window or door is opened by adding the difference on the side where the sensor signal decreases. On the other hand, in the drift period, the smoking period, or the stable period, the sensor signal increases or is substantially constant, and the value is small even if the difference on the side where the sensor signal decreases is integrated. Therefore, the integration is performed only when the difference is negative, and this is convolved with a time constant of about 30 to 120 seconds.
36 generates a large signal, and then the doors and windows close and 6
The noise signal 236 continues to generate a signal for about 0 to 240 seconds. The time constant at which the signal decreases to 1 / e is set to 30 to 60 seconds, and the duration of the signal of the noise filter 236 is set to 60 to 240 seconds. As a result, when the door or window is open, the differential detection threshold value J is maximized, and during the drift period, the detection threshold value is set to a medium value.
In the subsequent stable period, smoking can be detected quickly by minimizing the detection threshold.

[0043]

[Table 3] Principal part of program READ envelope VS of sensor shown in Fig. 18 Read sensor output Vs (every 1 second) V4 = V3: V3 = V2: V2 = V1: V1 = VS The latest output is three times before V1. Input to V4 D1 = (V1 + V2-V3-V4) / V1 1st derivative (time constant 2 seconds) IF T MOD 10 = 0 AND V1 ≧ VH THEN VH = VH * (1 + p2) IF T MOD 10 = 0 AND V1 ≦ VH THEN VH = VH * (1-p2) Correct the envelope value VH with the correction constant P2 every 10 seconds Q = VH / V1 Calculate the ratio between VH and V1 J = INT (Q * K3) + J0 Increase threshold value from J0 according to the value of ratio IF D1 ≧ J THEN X = 1 Drive air purifier with differential signal above threshold value

FIG. 18 shows a filter using the global filter 246. In the figure, reference numeral 242 denotes an envelope detection circuit;
4 is a division circuit. Table 3 shows the operation of the embodiment shown in FIG. When the value of the envelope following the sensor signal V with a time constant of about 30 minutes to 4 hours is obtained,
Is omitted. In other words, this value is a long-term average value of the sensor signal V. Comparing the long-term average of the sensor signal V with the current value of the sensor signal V, the current value of the sensor signal V is small when the window or door is open, and the current value of the sensor signal V is stable in the stable period or the smoking period. It will be big. Therefore, in the global filter 246 of FIG.
For example, the envelope value VH is corrected every 10 seconds, and a correction constant P2 (time constant of about 30 minutes to 4 hours) is used.
The value VH of the envelope gradually follows the sensor signal V. Instead of using the envelope, a past simple average of the sensor signals V may be used, and any value may be used as long as the past gas sensor signal is statistically obtained. The division circuit 244 obtains a ratio between the envelope value VH and the current value V1 of the gas sensor signal, thereby generating a differential detection threshold in the comparison circuit 208.

Returning to FIG. 20, the operation in this case will be described.
When the door or window is open, the sensor signal V decreases,
VH / V1 increases and the differential detection threshold value J increases. On the other hand, when the sensor signal V1 increases due to drift, VH / V
1 gradually decreases and the differential detection threshold value J gradually decreases. Then, when the period shifts to the stable period, the value of VH / V1 decreases, and accordingly, the detection threshold value J of the differentiation becomes minimum. The filter 246 of FIG. 18 also has the effect of increasing the detection threshold when the gas sensor signal V is small and compensating for the non-linearity of the gas sensor signal.

FIG. 19 shows a filter 256 using a band-pass filter for the differential signal, and Table 4 shows the operation. In FIG. 19, reference numeral 252 denotes a differentiating circuit;
Reference numeral 5 denotes a window for confirming whether the differential coefficient is within a predetermined range, and 258 denotes a counter. Window 254
When the first derivative D1 is equal to or larger than a and equal to or smaller than b, the counter 258 is incremented by 1, for example.
In the following, the counter 258 is reduced to, for example, 3/4 of the original value. Here, it is assumed that c>b> a.

[0047]

[Table 4] Main part of the program READ the differential filter of Fig. 19 VS Read the sensor output Vs (every 1 second) V4 = V3: V3 = V2: V2 = V1: V1 = VS The latest output is three times before V1. Input to V4 D1 = (V1 + V2-V3-V4) / V1 First derivative (time constant 2 seconds) IF D1 ≦ b AND D1 ≧ a THEN C2 = C2 + 1 IF D1 ≦ -C THEN C2 = INT (3 / 4 * C2) c>b> a Add the counter if the differential signal is within the drift range, subtract the counter if the sensor output decreases rapidly J = J0-C2 * K4 IF D1 ≧ J THEN X = 1 Driving the air purifier with a differential signal above the threshold

FIG. 20 shows the operation in this case. When the door or window is opened, the sensor signal V sharply decreases, so that the first-order differential signal D1 becomes -c or less, and the value of the counter 258 is rapidly reduced. . On the other hand, when the sensor signal V increases between the gradients a and b during the drift period, the window 254 opens and the counter 258 is added. As a result, as the drift progresses, the value of the counter 258 increases, and when the door or window is opened, the value of the counter 258 rapidly decreases and approaches zero. If the value of the counter 258 is large, the differential detection threshold is small, and if the value of the counter 258 is small, the differential detection threshold is large. When the door or window is open, the differential detection threshold becomes maximum, In the drift period, the detection threshold of the derivative becomes a relatively large value, and in the stable period, the detection threshold of the derivative for smoking becomes the minimum. This filter 25
6 also serves to correct the nonlinearity of the gas sensor signal and to increase the sensitivity in a stable period when the apparent sensitivity is reduced.

The operation of any of the filters shown in FIGS. 16 to 19 can be summarized as shown in FIG. The filters in FIGS. 16 to 19 all classify the atmosphere in the vehicle interior into three states: a state in which windows and doors are open, a drift state, and a stable period. For example, the filters of FIGS. 16 and 17 detect that a window or a door is open, and set the time constant of the filter to be as long as about 30 to 120 seconds to detect the initial stage of the subsequent drift. In the filter 246 of FIG. 18, the envelope value VH and the gas sensor 20
From the comparison of the signal No. 2 with the current value V1, three states are detected: a state in which the window or door is opened, a drift period, and a stable period. In the filter 256 of FIG. 19, the drift is detected in the window 254, the opening of the window or the door is detected in the window 255, and the counter 258 is decremented. Detection in this case focuses on detecting drift in window 254. When the atmosphere is classified into the three periods of the stable period, the drift period, and the opening period of the window or the door, the detection threshold value J of the derivative is corrected accordingly. As a result, as shown in FIG. 21, the detection threshold value J of the derivative increases as the noise increases. When the noise is extremely strong, the threshold value J may be set to infinity, and the detection of the derivative may be substantially prohibited.

In this embodiment, the differential detection signal J is corrected instead of invalidating the differential signal when noise is detected. I will explain another meaning of this. For example, even when the window or door is open, the sensor signal V may continue to increase monotonously for about 30 seconds. Where 2
If a filter having a time constant of about 0 second is used and the differential detection signal is invalidated by the filter signal, a malfunction may occur with a short time constant. However, if the time constant of the filter 206 is lengthened here, a dead time occurs during the drift period after the window or door is closed. However, in practice, when smoking is performed during the drift period, the sensor signal increase due to smoking is added to the increase in sensor signal due to drift, and the differential coefficient of the sensor signal becomes larger. Therefore, if the detected threshold value J is corrected according to the magnitude of the noise and the time constant of the filter 206 is increased to, for example, about 30 to 120 seconds, the noise can be removed without causing a dead time in the drift period.

[Brief description of the drawings]

FIG. 1 is a block diagram of an air conditioning control device according to an embodiment.

FIG. 2 is a block diagram of a main part of an air conditioning control device according to the embodiment.

FIG. 3 is a main block diagram of an air conditioning control device according to a second embodiment.

FIG. 4 is a block diagram of a main part of an air conditioning control device according to a third embodiment.

FIG. 5 is a block diagram of a main part of an air conditioning control device according to a fourth embodiment.

FIG. 6 is a block diagram of a main part of an air conditioning control device according to a fifth embodiment.

FIG. 7 is a block diagram of a main part of an air conditioning control device according to a sixth embodiment.

FIG. 8 is a flowchart showing an operation algorithm of the first embodiment.

FIG. 9 is a characteristic diagram of a gas sensor signal, showing a detection principle of the present invention.

FIG. 10 is a characteristic diagram showing gas sensor signals in the vehicle when the door is opened and when smoking is performed.

FIG. 11 is a characteristic diagram showing gas sensor signals in the vehicle when the door is opened and when the vehicle drifts.

FIG. 12 is a characteristic diagram showing a gas sensor signal when a window is opened.

FIG. 13 is a block diagram of a main part of an air conditioning control device according to a seventh embodiment.

FIG. 14 is a diagram showing a signal flow in the air conditioning control device according to the seventh embodiment.

FIG. 15 is a block diagram of a gas detector according to an eighth embodiment.

FIG. 16 is a block diagram of a noise filter used in the eighth embodiment.

FIG. 17 is a block diagram of another noise filter.

FIG. 18 is a block diagram of a global filter used in the eighth embodiment.

FIG. 19 is a block diagram of a differential filter used in the eighth embodiment.

FIG. 20 is a characteristic diagram of a gas sensor signal in a vehicle cabin.

FIG. 21 is a characteristic diagram showing a relationship between noise and a detection threshold value for differentiation of a gas sensor signal in the eighth embodiment.

[Explanation of symbols]

 2 Gas sensor 4 Heater 6 Metal oxide semiconductor 8 Power supply 10 Microcomputer 12 Air purifier 14 AD converter 16 Differentiation circuit 18 Noise filter 20 Counter 22 Stop control circuit 31 Average value calculation circuit 32 Comparison circuit 33 Counter 34 Timer 41 Edge detection circuit 51 Noise detection circuit 52 Comparison circuit 54 AND circuit 71 Addition circuit 72 Addition circuit R2 to R4 Resistance C1 Capacitor A1 Amplification circuit 100 Microcomputer 102 Two-port AD converter 104 Smoking detection circuit 106 Random noise detection circuit 108 Window open detection circuit 110 Sensor output Long term average detection circuit 112 Air purifier stop level generation circuit 114 Temporary memory of sensor output

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 27/04 G01N 27/12

Claims (4)

(57) [Claims] 1. An apparatus for detecting gas with a gas sensor, comprising: gas detection means for detecting gas from a gas sensor signal; drop detection means for detecting a sharp drop in the gas sensor signal; A gas detection device, comprising: a suppression unit for correcting the gas detection unit so as to suppress detection of gas after detecting a sharp decrease in the gas sensor signal. 2. A timer is provided in the suppression means, and when the decrease detection means detects a sharp decrease in the gas sensor signal,
2. The gas detecting device according to claim 1, wherein a timer is started and gas detection is prohibited for a predetermined time. 3. The gas detection device according to claim 2, wherein said gas detection means is configured to detect gas by differentiating a gas sensor signal. 4. The gas detecting device according to claim 1, wherein the air conditioner is controlled by the gas detecting means.