JP2001343344A - Gas detecting device, automatic flap control system for automobile, and gas detecting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas detecting device capable of appropriately detecting a change in the concentration of gas components of a gas to be measured, an automatic flap control system, using the device, for automobile, and a gas detecting method. SOLUTION: The gas detecting device 1 using a gas sensor element 2 wherein a sensor resistance value Rs is changed according to the change in the concentration of the gas components is provided with a sensor-resistance-value converting circuit 4 wherein a sensor output potential Vs falls in the case of a rise in the concentration of the gas components. Furthermore, the device 1 is provided with a decreasing peak hold circuit 5, wherein the output potential Vs is taken as a decreasing peak potential V5 when the output potential Vs is greater than the peak potential V5 and the peak potential V5 is gradually decreased with time when the output potential Vs is smaller than the peak potential V5, and a differential amplification circuit 7, a comparator 8, a switching circuit 9, which make a gas-component concentration rise signal Sg turned on when a differential between the peak potential V5 and the output potential Vs is greater than the first threshold voltage Vth1.

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 gas component in an environment using a gas sensor element, an automatic flap control system for controlling the introduction of outside air into a vehicle interior, and a gas detection method. About.

[0002]

2. Description of the Related Art Conventionally, a WO3 thin film has been used,
NOx, CO, HC (hydrocarbon) in the environment, such as gas sensor elements using phthalocyanine and SnO2
For example, a gas sensor element capable of detecting a change in the concentration of a gas component based on a change in the sensor resistance because the sensor resistance changes due to a change in the concentration of a gas component in the gas to be measured is known. Further, by using such a gas sensor element, for example, a flap for introducing outside air into an automobile interior can be opened and closed as appropriate according to the state of contamination of outside air, or detection of contamination of indoor air due to smoking can be performed by an air purifier. There are known gas detection devices and control systems for performing various controls such as control of the gas.

[0003] As a gas detection device and a control system using such a gas sensor element, for example, Japanese Patent Application Laid-Open No. 5-1 is disclosed.
In the publication No. 72773, "an updating means for updating the detected value as the lowest detected value of the pollution degree every time a detected value with a lower outside air pollution degree is detected" and a nonvolatile storage device,
There is disclosed an apparatus having "contamination degree determining means for determining the degree of outside air contamination from the rate of change of the detection value with respect to the minimum detection value of contamination degree". In this case, "the detection value detected when the vehicle is running in the cleanest air condition so far is stored in the non-volatile storage device as the lowest pollution degree detection value." The minimum pollution degree detection value indicates a constant value that is not updated any more. "

[0004]

However, the sense of smell of humans (passengers) is relative. For example, in a polluted environment, the sense of smell adapts and becomes less noticeable. On the other hand, even in such an environment, a smell is felt when a gas with a higher degree of contamination flows in. In a clean environment, even a slight inflow of pollutant gas can be felt sharply. Therefore, when the above-described control is performed, a gap is generated between humans (passengers) and the sense of smell. In addition, when the vehicle has traveled in a clean environment in the past, it is difficult to perform appropriate control such as keeping the flap closed while traveling in a polluted environment. In addition, the gas sensor element, in addition to gas components to be measured, environmental temperature and humidity in the environment,
The sensor resistance value also changes depending on the wind speed and the like. Therefore, when the temperature, the humidity, and the wind speed change, the measurement may not be properly performed.

[0005] The present invention has been made in view of the above problems, and a gas detection device capable of appropriately detecting a change in the concentration of a gas component in a gas to be measured, and an automatic flap of an automobile using the gas detection device. It is an object to provide a control system and a gas detection method.

[0006]

Means for Solving the Problems, Action and Effect The solution is a gas detecting device using a gas sensor element whose sensor resistance changes according to a change in the concentration of at least one gas component in the gas to be measured. A sensor resistance conversion circuit that supplies a current to the gas sensor element and outputs a sensor output potential according to a change in the sensor resistance value, wherein the sensor output potential decreases when the concentration of the gas component increases. A sensor resistance value converting circuit, when the sensor output potential is higher than the held gradually decreasing peak potential, the sensor output potential is set to the gradually decreasing peak potential, and the sensor output potential is higher than the held gradually decreasing peak potential. A decreasing peak hold circuit for gradually decreasing the decreasing peak potential with time, when the decreasing peak potential and the sensor output potential If the difference is greater than the first threshold voltage, a gas detection apparatus comprising: a concentration up signal generating circuit for generating a concentration up signal of the gas components, a.

The gas detector of the present invention includes a sensor resistance conversion circuit and a gradually decreasing peak hold circuit. Since the sensor resistance value conversion circuit in which the sensor output potential decreases when the concentration of the gas component increases, the gradually decreasing peak potential indicates a state where the concentration of the gas component is low (clean state). Therefore, by comparing the gradually decreasing peak potential with the sensor output potential, it can be determined whether or not the concentration of the gas component is currently increasing. Specifically, the concentration increase signal generation circuit generates the concentration increase signal of the gas component when the difference between the two is greater than the first threshold voltage.

Further, when the sensor output potential is smaller than the held gradually decreasing peak potential, the gradually decreasing peak potential gradually decreases with time. In other words, even if the sensor output potential remains low, the gradually decreasing peak potential gradually approaches the sensor output potential, and when the difference between the two decreases, the generation of the concentration increase signal is stopped. Therefore, unlike peak-holding a constant potential, a concentration rise signal is generated even when the sensor output potential drifts due to environmental changes such as temperature or humidity, or when entering a region where the concentration of gas components is low from high. The concentration increase signal is appropriately turned on / off by the circuit, and the gas component can be appropriately detected. Further, since the sensor output can be processed by an analog circuit, expensive digital elements such as a microcomputer are not required and the cost can be reduced.

Further, in the gas detection device, when the difference between the gradually decreasing peak potential and the sensor output potential is smaller than a second threshold voltage smaller than the first threshold voltage, It is preferable to provide a gas detection device including a concentration increase signal stop circuit for stopping generation of the concentration increase signal.

In this gas detection device, a difference between the gradually decreasing peak potential and the sensor output potential is compared with a first threshold voltage to generate a concentration increase signal, while a difference between the two and a first threshold voltage smaller than the first threshold voltage is generated. The generation of the concentration increase signal is stopped by comparing the threshold voltage with the threshold voltage. That is, in the determination of the concentration increase and the concentration decrease of the gas component, the threshold voltage is made different, that is, so-called hysteresis is provided. For this reason, when the difference between the sensor output potential and the gradually decreasing peak potential becomes a value near the first threshold potential or the second threshold potential, a phenomenon (chattering) in which the generation and stop of the concentration increase signal are frequently switched. Less likely to occur.

Alternatively, in the gas detection device, the concentration increase signal generation circuit and the concentration increase signal stop circuit
A hysteresis for comparing a difference between the gradually decreasing peak potential and the sensor output potential with the second threshold voltage during the generation of the concentration increasing signal and with the first threshold voltage during stopping of the concentration increasing signal; It is preferable that the gas detection device includes a comparison circuit having characteristics.

In this gas detecting device, the concentration increasing signal generating circuit and the concentration increasing signal stopping circuit compare the second threshold voltage during the generation of the concentration increasing signal and the first threshold voltage during the stop of the concentration increasing signal. Since a comparison circuit having a hysteresis characteristic for comparing with the threshold voltage is included, the difference between the gradually decreasing peak potential and the sensor output potential can be compared with each threshold potential with a simple configuration.

Further, in the gas detection device, the gradually decreasing peak hold circuit includes a peak hold circuit including a capacitor for maintaining a peak potential of the sensor output potential, and a discharge for discharging electric charges accumulated in the capacitor. Preferably, the gas detection device includes a resistor.

Since the gas detector has a discharge resistor in addition to the peak hold circuit, the peak potential maintained by the capacitor gradually decreases due to the discharge by the discharge resistor. Therefore, by doing so, a gradually decreasing peak hold circuit for easily gradually decreasing the gradually decreasing peak potential can be configured.

Further, it is preferable that an automatic flap control system for an automobile includes the above gas detecting device, wherein the discharging time constant between the capacitor and the discharging resistor in the gradually decreasing peak hold circuit is 20 to 300 seconds.

If the discharge time constant formed by the capacitor and the discharge resistor of the gas detection device is too small, the gas component concentration may be compared with the duration of the gas component concentration fluctuation detected while the vehicle is running. The gradually decreasing peak potential indicating the low concentration state can be maintained at the high potential only for a short time, and decreases in a short time to approach the current sensor output potential. Therefore, an appropriate judgment cannot be made. on the other hand,
If the discharge time constant is too large, the peak potential representing a state where the concentration of the specific gas is low will be maintained at a long and high potential, and the effect of gradually reducing the peak hold value will be poor. Inability to cope with fluctuations in the resistance value, making it impossible to make an appropriate determination Generally, in an automatic flap control system of an automobile, during normal driving, a change in gas concentration often occurs in a range of several seconds to several tens of seconds. . On the other hand, since the time constant is set to 20 to 300 seconds, appropriate measurement can be performed.

Still another solution is a gas detection device using a gas sensor element whose sensor resistance value changes according to a change in the concentration of at least one gas component in the gas to be measured. A sensor resistance conversion circuit that outputs a sensor output potential according to the sensor resistance change, wherein the sensor output potential decreases when the concentration of the gas component increases; and A / D conversion means for A / D converting the sensor output potential at predetermined intervals to output a sensor output value, and comparing the sensor output value with a current peak hold value, When the sensor output value is larger than the peak hold value, the sensor output value is set as a new peak hold value. A gradually decreasing peak hold means for setting a smaller value as a new peak hold value in place of the peak hold value; and when the difference between the peak hold value and the sensor output value is larger than a first threshold value, the gas component And a concentration-increase signal generating means for generating a concentration-increase signal.

The gas detection device of the present invention includes a sensor resistance value conversion circuit, an A / D conversion means, a gradually decreasing peak hold means, and a rising signal generation means. Since the sensor resistance value conversion circuit in which the sensor output potential decreases when the concentration of the gas component increases is used, the peak hold value indicates a state where the concentration of the gas component is low. Therefore, by comparing the peak hold value with the sensor output value, it can be determined whether or not the concentration of the gas component is currently increasing. Specifically, the concentration increase signal generation means generates a concentration increase signal of the gas component when the difference between the two is greater than the first threshold value. Moreover, when the sensor output value is smaller than the current peak hold value, the peak hold value gradually decreases with time. That is, even if the sensor output value remains low, the peak hold value gradually approaches the sensor output value, and when the difference between the two decreases, the generation of the concentration increase signal is stopped. Therefore, unlike the one that does not change the peak-held value, even if the sensor output potential drifts due to environmental changes such as temperature and humidity, or if the concentration of the gas component goes from a low to high area, the concentration increase signal The concentration increasing signal is appropriately turned on / off by the generating means, and the gas component can be appropriately detected. In addition, since the sensor output can be processed as a digital value, it is hardly affected by noise or the like, and the characteristics of the gradually decreasing peak hold means and the first threshold value can be easily changed.

In the gradually decreasing peak hold means,
When the sensor output value is smaller than the current peak hold value, as a method of setting a smaller value as a new peak hold value instead of the current peak hold value, specifically, a predetermined value is calculated from the peak hold value. A new value may be used as a new peak hold value, or a value obtained by multiplying the peak hold value by a positive predetermined ratio less than 1 (for example, 0.9) may be used.

Further, in the gas detection device, the difference between the peak hold value and the sensor output value is the first sensor value.
It is preferable that the gas detection device includes a concentration increasing signal stopping means for stopping generation of the concentration increasing signal of the gas component when the concentration is smaller than a second threshold smaller than the threshold value.

In this gas detection device, a difference between the peak hold value and the sensor output value is compared with a first threshold value to generate a concentration increase signal, while a difference between the two is smaller than a first threshold voltage. The generation of the concentration increase signal is stopped by comparing with the second threshold voltage. That is, the threshold used for determining whether the concentration of the gas component is increasing or decreasing is made different, that is, so-called hysteresis is provided. For this reason, when the difference between the sensor output value and the peak hold value becomes a value near the first threshold value or the second threshold value, the occurrence and stop of the concentration increase signal are frequently switched (chattering).
Is less likely to occur.

Still another solution is a gas detection device using a gas sensor element whose sensor resistance changes according to a change in the concentration of at least one or more gas components in the gas to be measured. A sensor resistance conversion circuit that outputs a sensor output potential according to the sensor resistance change, wherein the sensor resistance conversion circuit increases the sensor output potential when the concentration of the gas component increases. When the sensor output potential is smaller than the gradually increasing bottom potential, the sensor output potential is set to the gradually increasing bottom potential. When the sensor output potential is higher than the held gradually increasing bottom potential, A gradually increasing bottom hold circuit for gradually increasing the potential with time; and a difference between the gradually increasing bottom potential and the sensor output potential being a first threshold voltage. When is large, a gas detection apparatus comprising: a concentration up signal generating circuit for generating a concentration up signal of the gas components, a.

The gas detector of the present invention includes a sensor resistance value conversion circuit and a gradually increasing bottom hold circuit. Since the sensor resistance value conversion circuit in which the sensor output potential increases when the concentration of the gas component increases, the gradually increasing bottom potential indicates a state where the concentration of the gas component is low (clean state). Therefore, by comparing the gradually increasing bottom potential with the sensor output potential, it can be determined whether or not the concentration of the gas component is currently increasing. Specifically, the concentration increase signal generation circuit generates the concentration increase signal of the gas component when the difference between the two is greater than the first threshold voltage.

Further, when the sensor output potential is higher than the held gradually increasing bottom potential, the gradually increasing bottom potential gradually increases with time. That is, even if the sensor output potential remains high, the gradually increasing bottom potential gradually approaches the sensor output potential, and when the difference between them decreases (below the first threshold potential), finally, the concentration increase signal The occurrence will be stopped. Therefore, unlike bottom-holding a constant potential, a concentration increase signal is generated even when the sensor output potential drifts due to environmental changes such as temperature and humidity, or when entering a region where the gas component concentration is low to high. The concentration increase signal is appropriately turned on / off by the circuit, and the gas component can be appropriately detected. Further, since the sensor output can be processed by an analog circuit, expensive digital elements such as a microcomputer are not required and the cost can be reduced.

Further, in the gas detection device, when the difference between the sensor output potential and the gradually increasing bottom potential is smaller than a second threshold voltage smaller than the first threshold voltage, the gas component It is preferable to provide a gas detection device including a concentration increase signal stop circuit for stopping generation of the concentration increase signal.

In this gas detecting device, a difference between the gradually increasing bottom potential and the sensor output potential is compared with a first threshold voltage to generate a concentration increase signal, while a difference between the two and a first threshold voltage smaller than the first threshold voltage is generated. The generation of the concentration increase signal is stopped by comparing the threshold voltage with the threshold voltage. That is, in the determination of the concentration increase and the concentration decrease of the gas component, the threshold voltage is made different, that is, so-called hysteresis is provided. For this reason, when the difference between the sensor output potential and the gradually increasing bottom potential becomes a value near the first threshold potential or the second threshold potential, a phenomenon (chattering) in which generation and stop of the concentration increase signal are frequently switched is performed. Less likely to occur.

Alternatively, in the gas detection device, the concentration increase signal generation circuit and the concentration increase signal stop circuit
Hysteresis for comparing the difference between the gradually increasing bottom potential and the sensor output potential with the second threshold voltage during generation of the concentration increase signal and comparing with the first threshold voltage during stop of the concentration increase signal. It is preferable that the gas detection device includes a comparison circuit having characteristics.

In this gas detecting device, the concentration increasing signal generating circuit and the concentration increasing signal stopping circuit compare the second threshold voltage during the generation of the concentration increasing signal and the first threshold voltage during the stop of the concentration increasing signal. Since a comparison circuit having a hysteresis characteristic for comparing with the threshold voltage is included, the difference between the gradually increasing bottom potential and the sensor output potential can be compared with each threshold potential with a simple configuration.

Further, in the gas detector, the gradually increasing bottom hold circuit includes: a bottom hold circuit including a capacitor for maintaining a bottom potential of the sensor output potential; Preferably, the gas detection device includes a resistor.

Since the gas detector has a discharging resistor in addition to the bottom hold circuit, the bottom potential maintained by the capacitor gradually rises due to the discharging by the discharging resistor. Therefore, by doing so, it is possible to configure a gradually increasing bottom hold circuit that easily increases the gradually increasing bottom potential.

In addition, it is preferable to provide an automatic flap control system for an automobile, including the gas detection device, wherein a discharge time constant formed by the capacitor and the discharge resistor in the gradually increasing bottom hold circuit is 20 to 300 seconds.

If the discharge time constant formed by the capacitor and the discharge resistor of the gas detection device is too small, the gas component concentration is compared with the duration of the gas component concentration fluctuation detected while the vehicle is running. The gradually increasing bottom potential indicating the low concentration state cannot be maintained at a low potential for only a short time, and increases in a short time to approach the current sensor output potential. Therefore, an appropriate judgment cannot be made. on the other hand,
If the discharge time constant is too large, the bottom potential indicating a state where the concentration of the specific gas is low will be maintained at a long and low potential, and the effect of gradually increasing the bottom hold value will be poor. Inability to cope with fluctuations in the resistance value, making it impossible to make an appropriate determination Generally, in an automatic flap control system of an automobile, a change in gas concentration often occurs in a range of several seconds to several tens of seconds during normal running. . On the other hand, since the time constant is set to 20 to 300 seconds, appropriate measurement can be performed.

Still another solution is a gas detection device using a gas sensor element in which a sensor resistance value changes according to a change in the concentration of at least one or more gas components in a gas to be measured. A sensor resistance conversion circuit that outputs a sensor output potential according to the sensor resistance value change, wherein the sensor output potential increases when the concentration of the gas component increases; A / D conversion means for A / D converting the sensor output potential at predetermined intervals to output a sensor output value, comparing the sensor output value with a current bottom hold value, and determining whether the sensor output value is the current bottom hold value. When the sensor output value is smaller than the hold value, the sensor output value is set as a new bottom hold value. Gradually increasing bottom hold means for setting a value obtained by adding a predetermined value to a tom hold value as a new bottom hold value; and when the difference between the bottom hold value and the sensor output value is larger than a first threshold value, the gas component And a concentration increasing signal generating means for generating a concentration increasing signal.

The gas detection device of the present invention includes a sensor resistance value conversion circuit, A / D conversion means, gradually increasing bottom hold means density and rising signal generation means. Since the sensor resistance value conversion circuit in which the sensor output potential rises when the concentration of the gas component rises is used, the bottom hold value indicates a state where the concentration of the gas component is low. Therefore, by comparing the bottom hold value with the sensor output value, it can be determined whether the concentration of the gas component is currently increasing. Specifically, the concentration increase signal generation means generates a concentration increase signal of the gas component when the difference between the two is greater than the first threshold value.

Further, when the sensor output value is larger than the current bottom hold value, the bottom hold value gradually increases with time. That is, even if the sensor output value remains high, the bottom hold value gradually approaches the sensor output value, and when the difference between the two decreases, the generation of the concentration increase signal is stopped. Therefore, unlike the one that does not change the bottom-hold value, even if the sensor output potential drifts due to environmental changes such as temperature or humidity, or if the concentration of the gas component changes from low to high, the concentration increase signal is output. The concentration increasing signal is appropriately turned on / off by the generating means,
Gas components can be detected appropriately. In addition, since the sensor output can be processed as a digital value, it is hardly affected by noise or the like, and the characteristics of the gradually increasing bottom hold means, the first threshold value, and the like can be easily changed.

In the gradually increasing bottom hold means,
When the sensor output value is larger than the current bottom hold value, a larger value may be used as a new bottom hold value instead of the current bottom hold value. Use the added value as the new bottom hold value, or set the bottom hold value to 1
A value obtained by multiplying a predetermined ratio (for example, 1.1) exceeding the above value is set as a new bottom hold value.

Further, in the gas detection device, the difference between the bottom hold value and the sensor output value is determined by the first value.
It is preferable that the gas detection device includes a concentration increasing signal stopping means for stopping generation of the concentration increasing signal of the gas component when the concentration is smaller than a second threshold smaller than the threshold value.

In this gas detection device, the difference between the bottom hold value and the sensor output value is compared with a first threshold value to generate a concentration increase signal, while the difference between the two is smaller than the first threshold voltage. The generation of the concentration increase signal is stopped by comparing with the second threshold voltage. That is, the threshold used for determining whether the concentration of the gas component is increasing or decreasing is made different, that is, so-called hysteresis is provided. Therefore, when the difference between the sensor output value and the bottom hold value becomes a value near the first threshold value or the second threshold value, the occurrence and stop of the density increase signal are frequently switched (chattering).
Is less likely to occur.

Still another solution is a gas detection method using a gas sensor element in which a sensor resistance value changes according to a change in the concentration of at least one or more gas components in a gas to be measured. A sensor resistance value conversion circuit in which the sensor output potential decreases when the sensor resistance value rises, energizes the gas sensor element to output a sensor output potential corresponding to the sensor resistance value change, and the sensor output potential becomes smaller than the gradually decreasing peak potential. When large, the sensor output potential is the gradually decreasing peak potential, and when the sensor output potential is smaller than the gradually decreasing peak potential, the gradually decreasing peak potential is gradually reduced with time, and the gradually decreasing peak potential and the sensor output potential are This is a gas detection method for generating the above-mentioned concentration increase signal of the gas component when the difference is larger than a first threshold voltage.

According to the gas detection method of the present invention, the sensor output potential is output by the sensor resistance value conversion circuit, and when the sensor output potential is larger than the gradually decreasing peak potential, the sensor output potential is set to the gradually decreasing peak potential, and the gradually decreasing peak potential is set. When the difference between the gradually decreasing peak potential and the sensor output potential is larger than the first threshold voltage, a signal for increasing the concentration of the gas component is generated. Since the sensor resistance value conversion circuit in which the sensor output potential decreases when the concentration of the gas component increases, the gradually decreasing peak potential indicates a state where the concentration of the gas component is low (clean state). Therefore, when the difference between the gradually decreasing peak potential and the sensor output potential is larger than the first threshold voltage, it is determined that the concentration of the gas component is increasing, and a concentration increasing signal is generated.

Further, when the sensor output potential is smaller than the gradually decreasing peak potential, the gradually decreasing peak potential gradually decreases with time. In other words, even if the sensor output potential remains low, the gradually decreasing peak potential gradually approaches the sensor output potential, and when the difference between the two decreases, the generation of the concentration increase signal is stopped. Therefore, unlike peak-holding a constant potential, a concentration rise signal is generated even when the sensor output potential drifts due to environmental changes such as temperature or humidity, or when entering a region where the concentration of gas components is low from high. The concentration increase signal is appropriately turned on / off by the circuit, and the gas component can be appropriately detected. In addition, since the sensor output can be processed by an analog circuit, expensive digital elements such as a microcomputer are unnecessary, and gas components can be detected at low cost.

Further, in the gas detection method, when the difference between the gradually decreasing peak potential and the sensor output potential is smaller than a second threshold voltage smaller than the first threshold voltage, It is preferable to use a gas detection method for stopping the generation of the concentration increase signal.

In this gas detection method, when the difference between the gradually decreasing peak potential and the sensor output potential is larger than the first threshold voltage, a concentration increase signal is generated. On the other hand, the difference
When the second threshold voltage is lower than the second threshold voltage, the generation of the concentration increase signal is stopped. That is, in the determination of the concentration increase and the concentration decrease of the gas component, the threshold voltage is made different, that is, so-called hysteresis is provided. Therefore, the difference between the sensor output potential and the gradually decreasing peak potential is the first.
When the value becomes close to the threshold potential or the second threshold potential, a phenomenon (chattering) in which the generation and stop of the density increase signal are frequently switched is less likely to occur.

Alternatively, there is provided a gas detection method using a gas sensor element in which a sensor resistance value changes according to a change in the concentration of at least one or more gas components in a gas to be measured. The gas sensor element is energized by a sensor resistance conversion circuit in which the output potential decreases, and a sensor output potential corresponding to the change in the sensor resistance is output, and the sensor output potential is A / D-converted at predetermined intervals. The sensor output value is output, the sensor output value is compared with the current peak hold value, and when the sensor output value is larger than the current peak hold value, the sensor output value is set as a new peak hold value,
When the sensor output value is smaller than the current peak hold value, a smaller value is used as a new peak hold value instead of the current peak hold value, and a difference between the peak hold value and the sensor output value is a first threshold. It is preferable to adopt a gas detection method for generating a signal for increasing the concentration of the gas component when the value is larger than the value.

According to the gas detection method of the present invention, the sensor output potential is output by the sensor resistance value conversion circuit, A / D converted and the sensor output value is output. The sensor output value is compared with the current peak hold value. If the sensor output value is larger than the current peak hold value, the sensor output value is replaced with a new peak hold value. On the other hand, when the sensor output value is smaller than the current peak hold value, the peak hold value is gradually reduced by setting a smaller value as a new peak hold value instead of the current peak hold value. Further, when the difference between the peak hold value and the sensor output value is larger than the first threshold value, a signal for increasing the concentration of the gas component is generated. Since the sensor resistance value conversion circuit in which the sensor output potential decreases when the concentration of the gas component increases is used, the peak hold value indicates a state where the concentration of the gas component is low. Therefore, when the difference between the peak hold value and the sensor output value is larger than the first threshold value, a signal for increasing the concentration of the gas component is generated.

Moreover, when the sensor output value is smaller than the current peak hold value, the peak hold value gradually decreases with time. That is, even if the sensor output value remains low, the peak hold value gradually approaches the sensor output value, and when the difference between the two decreases (below the first threshold value), the generation of the concentration increase signal is stopped. Therefore, unlike the one that does not change the peak-held value, even if the sensor output potential drifts due to environmental changes such as temperature and humidity, or if the concentration of the gas component goes from a low to high area, the concentration increase signal The concentration increasing signal is appropriately turned on / off by the generating means, and the gas component can be appropriately detected. Further, since the sensor output is processed as a digital value, it is hardly affected by noise or the like, and the characteristics of the gradually decreasing peak hold means and the first threshold value can be easily changed.

When the sensor output value is smaller than the current peak hold value, a smaller value may be used as the new peak hold value instead of the current peak hold value. A method of subtracting a predetermined value from the value as a new peak hold value,
A positive predetermined ratio less than 1 (for example, 0.
9) and a method of setting the value multiplied by 9) as a new peak hold value.

Still another solution is a gas detection method using a gas sensor element in which a sensor resistance value changes in accordance with a change in the concentration of at least one or more gas components in the gas to be measured. When the sensor output potential rises, a sensor resistance value conversion circuit in which the sensor output potential rises, energizes the gas sensor element to output a sensor output potential corresponding to the sensor resistance value change, and the sensor output potential becomes higher than the gradually increasing bottom potential. When small, the sensor output potential is the gradually increasing bottom potential, and when the sensor output potential is greater than the gradually increasing bottom potential, the gradually increasing bottom potential is gradually increased with time, and the gradually increasing bottom potential and the sensor output potential are This is a gas detection method for generating the above-mentioned concentration increase signal of the gas component when the difference is larger than a first threshold voltage.

According to the gas detection method of the present invention, the sensor output potential is output by the sensor resistance conversion circuit, and when the sensor output potential is smaller than the gradually increasing bottom potential, the sensor output potential is set to the gradually increasing bottom potential, and the gradually increasing bottom potential is set to When the difference between the gradually increasing bottom potential and the sensor output potential is larger than the first threshold voltage, a gas component concentration increase signal is generated. Since the sensor resistance value conversion circuit in which the sensor output potential decreases when the concentration of the gas component increases is used, the gradually increasing bottom potential indicates a state where the concentration of the gas component is low (clean state). Therefore, when the difference between the gradually increasing bottom potential and the sensor output potential is larger than the first threshold voltage, it is determined that the concentration of the gas component has increased, and a concentration increase signal is generated.

Further, when the sensor output potential is larger than the gradually increasing bottom potential, the gradually increasing bottom potential gradually increases with time. In other words, even if the sensor output potential remains high, the gradually increasing bottom potential gradually approaches the sensor output potential, and when the difference between the two decreases, the generation of the concentration increase signal is stopped. Therefore, unlike bottom-holding a constant potential, a concentration increase signal is generated even when the sensor output potential drifts due to environmental changes such as temperature and humidity, or when entering a region where the gas component concentration is low to high. The concentration increase signal is appropriately turned on / off by the circuit, and the gas component can be appropriately detected. In addition, since the sensor output can be processed by an analog circuit, expensive digital elements such as a microcomputer are unnecessary, and gas components can be detected at low cost.

Further, in the gas detection method, when the difference between the gradually increasing bottom potential and the sensor output potential is smaller than a second threshold voltage smaller than the first threshold voltage, It is preferable to use a gas detection method for stopping the generation of the concentration increase signal.

In this gas detection method, when the difference between the gradually increasing bottom potential and the sensor output potential is larger than the first threshold voltage, a concentration increase signal is generated. On the other hand, the difference
When the second threshold voltage is lower than the second threshold voltage, the generation of the concentration increase signal is stopped. That is, in the determination of the concentration increase and the concentration decrease of the gas component, the threshold voltage is made different, that is, so-called hysteresis is provided. Therefore, the difference between the sensor output potential and the gradually increasing bottom potential is the first.
When the value becomes close to the threshold potential or the second threshold potential, a phenomenon (chattering) in which the generation and stop of the density increase signal are frequently switched is less likely to occur.

Alternatively, there is provided a gas detection method using a gas sensor element in which a sensor resistance value changes due to a change in the concentration of at least one or more gas components in a gas to be measured. The gas sensor element is energized by a sensor resistance conversion circuit in which the output potential rises to output a sensor output potential corresponding to the change in the sensor resistance, and the sensor output potential is A / D-converted at predetermined intervals. A sensor output value is output, the sensor output value is compared with a current bottom hold value, and when the sensor output value is smaller than the current bottom hold value, the sensor output value is set as a new bottom hold value,
When the sensor output value is larger than the current bottom hold value, a value obtained by adding a predetermined value to the bottom hold value is set as a new bottom hold value, and the difference between the bottom hold value and the sensor output value is a first threshold value. It is preferable to use a gas detection method that generates a signal indicating a rise in the concentration of the gas component when the pressure is larger than the above.

In the gas detection method according to the present invention, the sensor output potential is output by the sensor resistance value conversion circuit, and the sensor output value is output after A / D conversion. The sensor output value is compared with the current bottom hold value. If the sensor output value is smaller than the current bottom hold value, the sensor output value is replaced with a new bottom hold value. On the other hand, when the sensor output value is larger than the current bottom hold value,
Instead of the current bottom hold value, a larger value is set as a new bottom hold value, and the bottom hold value is gradually increased. When the difference between the bottom hold value and the sensor output value is larger than the first threshold value, a signal for increasing the concentration of the gas component is generated. Since the sensor resistance value conversion circuit in which the sensor output potential rises when the concentration of the gas component rises is used, the bottom hold value indicates a state where the concentration of the gas component is low. Therefore, when the difference between the bottom hold value and the sensor output value is larger than the first threshold value, a signal for increasing the concentration of the gas component is generated.

Further, when the sensor output value is larger than the current bottom hold value, the bottom hold value gradually increases with time. That is, even if the sensor output value remains high, the bottom hold value gradually approaches the sensor output value, and when the difference between the two decreases, the generation of the concentration increase signal is stopped. Therefore, unlike the one that does not change the bottom-hold value, even if the sensor output potential drifts due to environmental changes such as temperature or humidity, or if the concentration of the gas component changes from low to high, the concentration increase signal is output. The concentration increasing signal is appropriately turned on / off by the generating means,
Gas components can be detected appropriately. Further, since the sensor output is processed as a digital value, it is hardly affected by noise and the like, and the characteristics of the gradually increasing bottom hold means and the first threshold value can be easily changed.

When the sensor output value is smaller than the current bottom hold value, the new bottom hold value may be set to a larger value instead of the current bottom hold value. A method in which a value obtained by adding a predetermined value to a value is used as a new bottom hold value, or a predetermined ratio exceeding 1.1 (for example, 1.1)
Is used as a new bottom hold value.

[0057]

(Embodiment 1) First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a circuit diagram of a gas detection device 1 of the present embodiment. When the gas to be measured (in the present embodiment, the atmosphere) contains a reducing gas component such as CO, the gas detection device 1 reacts with the reducing gas component to decrease the sensor resistance value Rs with an increase in the concentration of the reducing gas component. A gas sensor element 2 of a type oxide semiconductor is used. Sensor resistance value conversion circuit 4
Outputs a sensor output potential Vs corresponding to the sensor resistance value Rs of the gas sensor element 2. Specifically, a voltage obtained by dividing the power supply voltage Vcc by the gas sensor element 2 and the resistor R1 is input to the inverting input terminal of the operational amplifier OP1 via the resistor R2. On the other hand, the power supply voltage Vcc is connected to the resistors R3 and R3.
4 is input to the non-inverting input terminal of the operational amplifier OP1 and differentially amplified. As a result, the sensor output potential Vs becomes a value corresponding to the change in the sensor resistance value Rs, and when the concentration of the reducing gas component such as CO increases, the sensor output potential Vs changes in a decreasing direction. Therefore, when the sensor output potential Vs is high,
This indicates that the concentration of reducing pollutant gas components such as CO is low. Note that, in the present embodiment, the resistors R2 and R
The amplification factor given by the resistance value ratio of 5 is set to about 30 times. Further, by providing the capacitor C1 in parallel with the resistor R5, a variation in the sensor output voltage Vs due to noise is suppressed by providing a low-pass filter characteristic.

Next, the gradually decreasing peak hold circuit 5 holds the peak of the sensor output potential Vs.
Specifically, an operational amplifier OP2 whose sensor output potential Vs is input to a non-inverting input terminal, a diode D1 having an anode connected to an output terminal of the operational amplifier OP2, and a diode D1 connected to an inverting input terminal of the operational amplifier OP2. The sensor output potential Vs is peak-held by a peak hold circuit 5A including a capacitor C2 whose end is grounded. Therefore, when the sensor output potential Vs fluctuates due to a change in the sensor resistance value Rs, the peak potential thereof is held by the peak hold circuit 5A.

However, since the resistor R6 (referred to as a resistance value R6) is provided in parallel with the capacitor C2 (referred to as a capacitance value C2), the electric charge stored in the capacitor C2 is represented by a broken line. As shown in the figure, the electric charge is gradually discharged through the resistor R6 at a time constant τ1 = C2 · R6. Therefore, when the sensor output potential Vs falls below the peak potential held by the peak hold circuit 5A, the gradually decreasing peak potential V5 of the gradually decreasing peak hold circuit 5 has a gradually decreasing characteristic. In the present embodiment, the time constant τ1 = C2 · R6
= 47 seconds. As will be described later, in the automatic flap control system 10 of the automobile, during the normal traveling, the concentration change of the CO gas component often occurs in a range of several seconds to several tens of seconds. Can be detected.

As described above, in the present embodiment, when the concentration of the reducing gas component such as CO increases, the sensor output potential Vs changes in a decreasing direction. Therefore, the gradually decreasing peak potential V5 indicates a state where the concentration of the reducing contaminant gas component such as CO in the past is low. However, when the concentration of the pollutant gas component such as CO increases, that is, when the sensor output potential Vs decreases, the gradually decreasing peak potential V5 gradually decreases so as to follow it. Therefore, the gradually decreasing peak potential V5 indicates a state in which the concentration of the pollutant gas component is relatively low in the past.

Next, the operational amplifier OP of the differential amplifier circuit 7 is passed through the buffer circuit 6 comprising the operational amplifier OP3.
A buffer output potential V6, that is, a non-inverting input terminal of P4,
The gradually decreasing peak potential V5 is input. On the other hand, the operational amplifier OP
The sensor output potential Vs is input to the inversion input terminal 4. Thus, a difference between the gradually decreasing peak potential V5 and the sensor output potential Vs is obtained. This makes it possible to determine how much the current concentration of the CO gas component has changed compared to the past clean (low CO concentration) state.
In this embodiment, the amplification factor of the differential amplifier circuit 7 is set to 20 times.

Next, the differential amplified potential V7 of the differential amplifier circuit 7 is input to the inverting input terminal of the operational amplifier OP5 in the comparison circuit 8. The reference threshold potential Vth is provided by dividing the power supply potential Vp by resistors R11 and R12. However, the comparator 8 has a hysteresis characteristic because positive feedback is applied from the output terminal of the operational amplifier OP5 to the non-inverting input terminal through the resistor R13. That is, when the comparison output potential V8 is at a high potential, the threshold potential Vth is increased by the influence of this and becomes the first threshold potential Vth1. On the other hand, when the comparison output potential V8 is a low potential, the threshold potential Vth is lowered to become the second threshold voltage Vth2. In this manner, when the differential amplification potential V7 becomes a value close to the first and second threshold potentials Vth1 and Vth2, chattering in which the level of the comparison output potential V8 is frequently switched can be prevented. . However, when the influence of chattering is small, a comparison circuit having no hysteresis characteristic can be used by eliminating the resistor R13 that performs the positive feedback in the comparison circuit 8.

The comparison output potential V8 is supplied to the switching circuit 9
The detection output potential Vo which is input to the base of the transistor Q1 and is the switching output potential V9 as a collector output having the opposite phase to the comparison output potential V8 is taken out from the output terminal 3. In such a gas detection device 1, when the concentration of a reducing gas component such as CO increases, the sensor output potential Vs of the sensor resistance value conversion circuit 4 decreases, and the gradually decreasing peak potential V5 output from the gradually decreasing peak hold circuit 5 The difference between the differential amplification output V7 and the differential amplification output V7
Becomes larger. When the potential exceeds the first threshold potential Vth1, the comparison output potential V8 becomes low, and the detection output potential V8
o becomes high potential. That is, when the concentration of the reducing gas component such as CO increases, the gas component concentration increase signal Sg becomes high potential, that is, ON. Thus, the differential amplifier circuit 7,
When the difference between the gradually decreasing peak potential V5 and the sensor output potential Vs is larger than the first threshold potential Vth1, the concentration increasing signal generation circuit 789 including the comparison circuit 8 and the switching circuit 9 turns on the gas component concentration increasing signal Sg. Generate a signal. Conversely, when the concentration of the reducing gas component decreases, the concentration increase signal generation circuit 789 functions as a concentration increase signal stop circuit that stops generation of the high potential of the gas component concentration increase signal Sg, and generates the gas component concentration increase signal Sg. It is set to a low potential, that is, OFF.

Further, in the gas detector 1 of the present embodiment,
A gradually decreasing peak hold circuit 5 is used. For this reason, when the concentration of the reducing gas component increases and the state where the concentration is high (the state where the sensor resistance value Rs is low) continues, or the sensor resistance value Rs of the gas sensor element 2 is affected by humidity or the like.
Is drifted to a lower side, the electric charge of the capacitor C2 is discharged, the gradually decreasing peak potential V5 gradually decreases, and the difference from the sensor output potential Vs decreases. That is, the differential amplification output V7 decreases. When the difference falls below the second threshold potential Vth2, the comparison output potential V8 becomes high and the detection output potential Vo becomes low. That is, even if the concentration of the reducing gas component remains high or the sensor resistance value Rs drifts to the lower side, after a certain period of time, the gas component concentration increase signal Sg becomes low potential, that is, OFF. As described above, since the gas detection device 1 uses the gradually decreasing peak hold circuit 5, the gas component concentration increase signal Sg is prevented from being turned on for a long time.

Such a gas detecting device 1 is used in an automatic flap control system 10 of an automobile as shown in FIG. Specifically, the gas detection device 1 having the above-described circuit configuration including the gas sensor element 2 is connected to the electronic control assembly 16 at the output terminal 3. Specifically, in this embodiment, the electronic control assembly 16 is connected to a duct 21 that leads to the interior of the automobile, and is bifurcated to form an inside air intake duct 22 that takes in and circulates inside air, and an outside air intake duct 23 that takes in outside air. To control the flap 24 that switches between the flaps. That is, the output terminal 3
The flap driving device 17 is driven in accordance with the assembly control signal from the controller, specifically, the concentration-increasing signal Sg of the reducing gas component, the actuator 18 operates, and the flap 2
4 rotates and connects either the inside air intake duct 22 or the outside air intake duct 23 to the duct 21. In the duct 21, a fan 25 for feeding air is installed.

For example, as shown by a solid line in FIG.
When the flap 24 closes the outside air intake duct 23, the outside air is prevented from entering the room, and the duct 21 communicates with the inside air intake duct 22 to be in an inside air circulation state.
Conversely, as indicated by the dashed line, when the flap 24 closes the inside air intake duct 22, the duct 21 communicates with the outside air intake duct 23, and outside air is taken into the room.

The flap driving device 17 outputs the density increase signal S
The microcomputer includes a microcomputer that operates the actuator 18 with reference to output signals of sensors such as a room temperature sensor and an outside air temperature sensor, in addition to g. Note that the flap driving device 17 performs ON / O of the density increase signal Sg.
A flap drive circuit that operates the actuator 18 according to the FF may be used.

Next, actual measurement data in the gas detection device 1 according to the present embodiment and the automatic flap control system 10 of an automobile including the same will be described with reference to FIG. In FIG. 3, what is described at the top is a change in the output (CO concentration) of the CO analyzer simultaneously measured by a CO analyzer (model 4140-1 manufactured by Interscan). Therefore, the CO concentration in the gas to be measured (outside air) with time becomes
It is considered that this changed as shown in the graph.

The second description from the top shows changes in the sensor output potential Vs and the gradually decreasing peak potential V5 (buffer potential V6). The sensor output potential Vs is, as described above, the sensor resistance value conversion circuit 4 in the gas detection device 1.
It can be seen that the output shows a change in the characteristic opposite to the concentration of the CO analyzer described above. In other words, it can be seen that the sensor output potential Vs decreases as the CO concentration increases. Further, as can be easily understood from the above graph, the gradually decreasing peak potential V5 outputs the peak potential of the sensor output potential Vs, and when the sensor output potential Vs decreases, while maintaining the peak potential, Decreases gradually. Therefore, when the CO concentration rises sharply, the gradually decreasing peak potential V
5 maintains a relatively high potential, so there is a difference between the two. In the present embodiment, a single power supply operational amplifier OP1
Since the sensor output potential Vs is obtained by the differential amplification by the above, when the CO concentration becomes extremely high, the operating range is exceeded, and the sensor output potential Vs is regulated by the lower limit (Vs ≒ 1.1 V).

The third description from the top shows changes in the differential amplified potential V7 of the differential amplifier circuit 7 and the threshold voltage Vth input to the non-inverting input terminal of the comparator circuit 8. The differential amplification potential V7 is obtained by amplifying the difference between the above-described gradually decreasing peak potential V5 and the sensor output potential Vs. If the difference between the two becomes too large due to the regulation of the operation range of the operational amplifier OP4, the differential amplified potential V7 becomes the upper limit value (Vs ≒).
3.9V). Also, the threshold voltage Vth is
The differential amplification potential V7 is equal to the first threshold potential Vth1 (≒ 2.0
V), the second threshold potential Vth2 (≒ 1.5 V)
On the contrary, when the differential amplified potential V7 falls below the second threshold potential Vth2, the potential changes to return to the first threshold potential Vth1.

Next, what is described at the bottom is a change in the gas component concentration increase signal Sg output from the output terminal 3 of the gas detection device 1. This gas component concentration increase signal Sg
Becomes ON (high potential) when the differential amplified potential V7 exceeds a threshold potential Vth (first threshold potential Vth1),
When the differential amplification potential V7 falls below the threshold potential Vth (second threshold potential Vth2), the output becomes OFF (low potential).
Comparing the change in the gas component concentration increase signal Sg with the change in the CO concentration indicates that the gas component concentration increase signal Sg is ON when the CO concentration increases. Therefore, if this gas detection device 1 is used, an increase in the CO concentration can be reliably detected. Further, in the automatic flap control system of the automobile including the gas detection device 1, since the increase in the concentration of the reducing gas component such as CO in the outside air can be reliably detected, the outside air intake duct 23 is closed by the flap 24 accordingly. It is possible to perform appropriate control such as switching to inside air circulation.

Further, the gas detector 1 of the present embodiment is
The whole is composed of an analog circuit in which operational amplifiers, resistors, capacitors, etc. are wired. Such a gas detection device 1 has an advantage that it can be manufactured at a lower cost than a device using a microcomputer described below.

(Embodiment 2) Next, a second embodiment of the present invention will be described with reference to FIGS. In the present embodiment, similarly to the first embodiment, the present invention is applied to an automatic flap control system 20 for an automobile that controls opening and closing of a flap.
The difference is that, while the whole is configured by an analog circuit, processing is performed using a microcomputer after the output of the gas sensor element is captured. Therefore, different parts will be mainly described, and similar parts will be denoted by the same reference numerals and description thereof will be omitted or simplified.

FIG. 4 is a circuit diagram and block diagram showing an automatic flap control system 2 for an automobile according to the second embodiment.
0 is shown schematically. This automatic flap control system 20
Is a gas detection device 19, an electronic control assembly 16 similar to that shown in the first embodiment, ducts 21, 22, 2
3. It has a flap 24 and a fan 25. In this control system 20 as well, the gas detection device 19 included in
For example, an oxide semiconductor gas sensor element 11 of a type in which the sensor resistance value Rs decreases due to an increase in the concentration of a reducing gas component such as such. When the power supply potential Vcc is divided by the sensor resistance conversion circuit 26 composed of the gas sensor element 11 and the detection resistor 12 having a resistance value Rd connected in series to the gas sensor element 11, the resistance value Rs of the gas sensor element 11 changes. Accordingly, the sensor output potential Vs at the operating point Pd, which is the voltage dividing point, changes. Specifically, when the concentration of the reducing gas component such as CO increases, the sensor output potential V at the operating point Pd
It changes so that s decreases.

Therefore, the sensor output potential Vs is supplied to an A / D conversion circuit (A / D conversion means) 14 via a buffer 13.
To enter. In the present embodiment, the A / D conversion circuit 14
And the sensor output potential V at every 0.8 second sampling interval.
A / D conversion is performed on s to obtain an 8-bit digitized sensor output value S. Further, by inputting the sensor output value S to the input terminal 15A of the microcomputer 15 and performing a process according to a flow described later, the sensor resistance value Rs of the gas sensor element 11 and the change in the sensor resistance value Rs of the gas sensor element 11 are reduced. Detects changes in the concentration of gas components. Although not shown in detail, the microcomputer 15 has a known configuration, and includes a microprocessor for performing calculations, a RAM for temporarily storing programs and data, a ROM for holding programs and data, and the like. In addition, an A / D conversion circuit 14 may be included.

The microcomputer 15 has an output terminal 1
5B outputs a gas component concentration increase signal Sg. This output terminal 15B is connected to the same electronic control assembly 16 as in the first embodiment. This electronic control assembly 16
Is the same as that described in the first embodiment, and thus the description is omitted.

Next, the control of the microcomputer 15 will be described with reference to the flowchart of FIG. When the engine is driven, the control system starts up.
First, initialization is performed in step S11. Here, the initial gradually decreasing peak value is the smallest possible value of the gradually decreasing peak value. Specifically, P = 0, which corresponds to a value when the ground potential is A / D converted, is set. Thereafter, the process proceeds to step S12, where the sensor output value S obtained by A / D converting the sensor signal, that is, the sensor output potential Vs, is read every 0.8 seconds. Next, in step S13, the sensor output value S
Is compared with the gradually decreasing peak value P, and if S> P (Yes), the process proceeds to step S14. On the other hand, if S ≦ P (No), the process proceeds to step S15.

In step S14, the sensor output value S is substituted for the gradually decreasing peak value P. Thereby, the gradually decreasing peak value P
Will coincide with the peak value of the sensor output value S.
Further, in step 16, that is, when the sensor output value S is larger than the gradually decreasing peak value P (S> P), the gas component concentration increase signal Sg is turned OFF (low potential), and step S
Go to 20. On the other hand, in step S15, PS is compared with the threshold value TH. If PS> TH (Yes), the process proceeds to step S17. On the other hand, P−S ≦ TH (N
In the case of o), the process proceeds to step S18. Step S17
More specifically, when the sensor output value S greatly decreases, the gas component concentration increase signal Sg is turned ON (high potential), and the process proceeds to step S19. In step S18, that is, when the sensor output value S is smaller than the gradually decreasing peak value P and the difference is equal to or less than the threshold value TH (PS ≦ TH), the gas component concentration increase signal Sg is set to OFF (low potential). The process proceeds to step S19.

Thereafter, in step S19, a value P obtained by subtracting a predetermined value d from the gradually decreasing peak value P is added to the gradually decreasing peak value P.
Substitute -d. As a result, the gradually decreasing peak value P becomes smaller by the predetermined value d. Therefore, the peak value P is held as the gradually decreasing peak value P when passing through the step S14 (S> P), and when not passing through the step S14, that is, when S ≦ P, Step S
Each time 19 passes, the value is gradually reduced, that is, the value is gradually reduced. Next, after waiting for the A / D conversion sampling time to arrive at step S20, the process proceeds to step S1.
2 and the same process is repeated. By processing according to such a procedure, the gradually decreasing peak value P is calculated and compared with the current sensor output value S, and when the difference is larger than the threshold value TH, that is, when the CO concentration is Is exceeded, the gas component concentration increase signal Sg is turned ON. Conversely, when S> P or PS ≦ TH, that is, when the CO concentration decreases, the gas component concentration increase signal Sg can be turned off.

Thus, the microcomputer 15
By performing the above-described processing in the gas detection device 19
However, the concentration of the reducing gas component such as CO is detected, and the ON / OFF state is appropriately output from the output terminal 15B according to the change in the concentration.
The gas component concentration increase signal Sg to be turned off can be output. Accordingly, in the automatic flap control system 20 for a vehicle having the gas detection device 19 shown in FIG.
The flap 24 can be opened and closed appropriately according to the concentration of the reducing gas component such as O.

(Modification 1) Next, a modification of Embodiment 2 will be described with reference to the flowchart of FIG. In the second embodiment, the microcomputer 1
In the control of No. 5, PS was compared with one threshold TH to determine ON / OFF of the gas component concentration increase signal Sg (see FIG. 5, step S15). On the other hand, the present modified embodiment is different in that the first threshold value TH1 and the second threshold value TH2 which is a smaller value are used. Therefore, different portions will be mainly described, and description of similar portions will be omitted or simplified.

When the control system is started by driving the engine, first, in step S21, initialization is performed.
Here, the initial decreasing peak value is the smallest possible value of the decreasing peak value. Specifically, the ground potential is set to A
The value at the time of the / D conversion is set to P = 0. Thereafter, the process proceeds to step S22, where the sensor output value S is read. Next, in step S23, it is determined whether or not the gas component concentration increase signal Sg is currently ON (high potential). When the gas component concentration increase signal Sg is OFF (N
In the case of o), the process proceeds to step S24. On the other hand, when the gas component concentration increase signal Sg is ON (Yes), the process proceeds to step S25. In step S24, the sensor output value S is compared with the gradually decreasing peak value P, and if S> P (Yes), the process proceeds to step S26. On the other hand, if S ≦ P (No), the process proceeds to step S27. In step S26, the sensor output value S is substituted for the gradually decreasing peak value P, and step S3
Proceed to 3. As a result, the gradually decreasing peak value P matches the peak value of the sensor output value S.

On the other hand, in step S27, PS and the first
Compare with threshold value TH1. PS> TH1 (Ye
In the case of s), the process proceeds to step S28. Step S28
More specifically, when the sensor output value S greatly decreases, the gas component concentration increase signal Sg is turned ON (high potential), and the process proceeds to step S32. On the other hand, step S2
If P−S ≦ TH1 (No) in step 7, the process immediately proceeds to step S32. That is, the process proceeds to step S32 while maintaining the OFF state of the gas component concentration increase signal Sg.

In step S25, PS and the second
Compare with threshold value TH2. PS> TH2 (Ye
In the case of s), the process immediately proceeds to step S32. That is, the process proceeds to step S32 while maintaining the gas component concentration increase signal Sg in the ON state. On the other hand, PS ≦ TH2
In the case of (No), the process proceeds to step S29. The second
The threshold value TH2 is a value smaller than the above-described first threshold value TH1. In this step S29, that is, the difference between the gradually decreasing peak value P and the sensor output value S is equal to the second threshold value TH.
When the difference is less than or equal to 2 (PS ≦ TH2), that is, when the difference between the gradually decreasing peak value P and the sensor output value S becomes small, the gas component concentration increase signal Sg is set to OFF (low potential). Further, in step S30, the sensor output value S is compared with the gradually decreasing peak value P, and if S> P (Yes), the process proceeds to step S32. On the other hand, if S ≦ P (No), the process proceeds to step S31. In step S31, the sensor output value S is substituted for the gradually decreasing peak value P. As a result, the gradually decreasing peak value P matches the peak value of the sensor output value S.

Thereafter, in step S32, a value P− obtained by subtracting a predetermined value d from the gradually decreasing peak value P is added to the gradually decreasing peak value P.
Substitute d. As a result, the gradually decreasing peak value P becomes the predetermined value d.
Only a small value. Accordingly, when the gradually decreasing peak value P passes through step S26 (S> P), a larger peak value is held as the gradually decreasing peak value P. On the other hand, S ≦
In the case of P, that is, when not passing through step S26,
Every time step S32 is passed, the gradual decrease, that is, the gradual decrease peak value P is gradually reduced. Next, step S33
After waiting for the sampling time of A / D conversion to arrive, the process returns to step S22 to repeat the same processing.
In this way, the gradually decreasing peak value P is calculated, compared with the current sensor output value S, and the difference is calculated as the first threshold value T.
If it is greater than H1, that is, if the CO concentration rises above the first threshold, the gas component concentration increase signal Sg is turned ON. Conversely, if P−S ≦ TH2,
That is, when the CO concentration decreases, the gas component concentration increase signal Sg can be turned off.

In the same manner as in the second embodiment, the gradual decrease peak value P is calculated and compared with the current sensor output value S to appropriately process the gas component concentration increase signal Sg.
Can be turned on / off. Moreover, in this modification, when the gas component concentration increase signal Sg is turned ON (step S28), the difference PS and the first threshold value TH are set.
1, while the gas component concentration increase signal Sg
Is turned off (step S29), the difference PS
And the second threshold value TH2. Here, since the second threshold value TH2 is smaller than the first threshold value TH1, the ON / OFF of the gas component concentration increase signal Sg is given a hysteresis, and the difference PS is obtained. Has an advantage that it is possible to prevent chattering in which the ON / OFF of the gas component concentration increase signal Sg is frequently repeated even when the value of the second component approaches the first threshold value or the second threshold value.

(Embodiment 3) Next, a third embodiment of the present invention will be described with reference to the circuit diagram of FIG. As in the first embodiment, the gas detection device 31 according to the third embodiment includes a gas sensor element 32 that reacts with a reducing gas component such as CO to decrease the sensor resistance value Rs as the concentration of the reducing gas component increases. Used, and has substantially the same circuit configuration, but differs in that the circuit configuration of the sensor resistance value conversion circuit 34 is different and that a gradually increasing bottom hold circuit 35 is provided instead of the gradually decreasing peak hold circuit 5. Therefore, different parts will be mainly described, and description of similar parts will be omitted or simplified.

The sensor resistance conversion circuit 34 is the same as that of the first embodiment.
Similarly, the sensor output potential Vs corresponding to the sensor resistance value Rs of the gas sensor element 32 is output. However, contrary to the first embodiment, the resistor R3 is set with the gas sensor element 32 set to the ground side.
1 divides the power supply voltage Vcc. Therefore, the sensor output potential Vs becomes a value corresponding to the sensor resistance value Rs, and when the concentration of the reducing gas component such as CO increases, the sensor output potential Vs changes in a rising direction. Therefore, contrary to the first embodiment, when the sensor output potential Vs is low, it indicates that the concentration of the reducing contaminant gas component such as CO is low.

Next, instead of the gradually decreasing peak hold circuit 5 of the first embodiment, the gradually increasing bottom hold circuit 35 performs the bottom hold of the sensor output potential Vs.
Specifically, an operational amplifier OP32 having the sensor output potential Vs input to the non-inverting input terminal, a diode D31 having a cathode connected to the output terminal of the operational amplifier OP32,
By the bottom hold circuit 35A including the diode D31 and the capacitor C32 connected to the inverting input terminal of the operational amplifier OP32 and the other end connected to the power supply potential Vp,
The sensor output potential Vs is held at the bottom. Accordingly, when the sensor output potential Vs fluctuates due to a change in the sensor resistance value Rs, the bottom potential thereof is held by the bottom hold circuit 35A.

However, the capacitor C32 (capacitance value C3
2) in parallel with the power supply potential Vp.
36 (referred to as a resistance value R36), the electric charge stored in the capacitor C32 is gradually discharged through a resistor R36 with a time constant τ2 = C32 · R36 as shown by a broken line. Therefore, the bottom hold circuit 35
When the sensor output potential Vs exceeds the bottom potential held at A, the gradually decreasing bottom potential V3 of the gradually increasing bottom hold circuit 35
5 has a gradually increasing characteristic that gradually increases. In the present embodiment, the time constant τ2 = C32 · R36 = 47 seconds. As in the first embodiment, the gas detection device 3 of the present embodiment
This is to enable the automatic flap control system of vehicle 1 to appropriately detect the concentration of CO.

In this embodiment, contrary to the first embodiment, C
When the concentration of the reducing gas component such as O increases, the sensor output potential Vs changes in the increasing direction. Therefore, the gradually increasing bottom potential V35 indicates a state where the concentration of the reducing contaminant gas component such as CO in the past is low. However, the gradually increasing bottom potential V35 gradually rises so as to follow the concentration of the pollutant gas component such as CO, that is, when the sensor output potential Vs rises. Therefore, like the gradually decreasing peak potential V of the first embodiment, the gradually increasing bottom potential V35 indicates a state where the concentration of the pollutant gas component is relatively low in the past.

Thereafter, contrary to the first embodiment, the buffer potential V36, that is, the gradually increasing bottom potential V35 is input to the inverting and inverting input terminal of the differential amplifier circuit 7 through the buffer circuit 36 including the operational amplifier OP33. Also, the sensor output potential Vs is input to the non-inverting input terminal, and the sensor output potential Vs
The difference between s and the gradually increasing bottom potential V35 is calculated. This allows
It is possible to determine how much the current concentration of the CO gas component is in comparison with the past clean (low CO concentration) state.

Next, as in the first embodiment, the differential amplified potential V7 of the differential amplifier circuit 7 is compared with the threshold potential Vth by the comparator circuit 8. Since the comparison circuit 8 is a comparison circuit 8 having hysteresis characteristics, when the comparison output potential V8 is high, the first threshold potential Vth1 is relatively high. On the other hand, when the comparison output potential V8 is low, the second threshold voltage Vth2 is lower than this. By doing so, chattering of the comparison output potential V8 can be prevented. However, as in the first embodiment, when the influence of chattering is small, a comparison circuit having no hysteresis characteristic can be used by eliminating the resistor R13 that performs positive feedback in the comparison circuit 8.

Further, the comparison output potential V8 is inputted to the switching circuit 9, and the detection output potential Vo which is the switching output potential V9 is taken out from the output terminal 3. In such a gas detection device 31, when the concentration of the reducing gas component such as CO increases, the sensor output potential Vs of the sensor resistance conversion circuit 34 increases, and the gradually increasing bottom hold circuit 3
Since the difference with the gradually increasing bottom potential V35, which is the output of the differential amplifier circuit 5, increases, the differential amplified output V7 of the differential amplifier circuit 7 increases. When the voltage exceeds the first threshold Vth1, the comparison output potential V8 becomes low, and the detection output potential Vo becomes high. That is, when the concentration of the reducing gas component such as CO increases, the gas component concentration increase signal Sg becomes high potential, that is, ON. Thus, the concentration increasing signal generation circuit 7 including the differential amplifier circuit 7, the comparison circuit 8, and the switching circuit 9
89, the sensor output potential Vs and the gradually increasing bottom potential V
When the difference from 35 is greater than the first threshold potential Vth1, an ON signal is generated as the gas component concentration increase signal Sg. Conversely, when the concentration of the reducing gas component decreases, the concentration increase signal generation circuit 789 outputs the gas component concentration increase signal Sg
Functioning as a concentration increase signal stop circuit for stopping the generation of the high potential of the gas component concentration signal Sg.
F.

Further, in the gas detector 31 of the present embodiment, a gradually increasing bottom hold circuit 35 is used. Therefore, similarly to the first embodiment, when the concentration of the reducing gas component increases and the concentration continues (the sensor resistance value Rs is low), or the sensor of the gas sensor element 2 is affected by humidity or other influences. Even when the resistance value Rs drifts to the lower side, the charge of the capacitor C32 is discharged and the gradually increased bottom potential V35 gradually increases, and the difference from the sensor output potential Vs decreases. That is, the differential amplification output V7 decreases. When the difference falls below the second threshold potential Vth2, the comparison output potential V8 becomes high, and the detection output potential V
o becomes low potential. That is, even if the concentration of the reducing gas component remains high or the sensor resistance value Rs drifts to the lower side, after a certain period of time, the gas component concentration increase signal Sg becomes low potential, that is, OFF. As described above, since the gas detection device 31 uses the gradually increasing bottom hold circuit 5, the gas component concentration increase signal S
g is prevented from being turned on for a long time. Such a gas detection device 31 is used in an automatic flap control system 30 of an automobile as shown in FIG.

(Embodiment 4) Next, a fourth embodiment of the present invention will be described with reference to FIGS. In the present embodiment, the present invention is applied to an automatic flap control system 40 for an automobile which controls opening and closing of a flap as in the above-described second embodiment. Power supply potential V
The point that the relationship between the gas sensor element 41 for dividing cc and the resistor 42 is opposite to that of the second embodiment (see FIG. 4).
There is a difference in the control procedure in the microcomputer 15. Therefore, we will focus on the different parts,
Similar parts are denoted by the same reference numerals and description thereof is omitted or simplified.

FIG. 8 is a circuit diagram and a block diagram showing an automatic flap control system 4 for an automobile according to the fourth embodiment.
0 is shown schematically. This automatic flap control system 40
Is a gas detection device 49, an electronic control assembly 16 similar to that shown in the first, second, and third embodiments, and a duct 21,
2, 23, a flap 24 and a fan 25. The control system 40 also includes a gas detection device 49 included in the control system 40.
The gas sensor element 41 similar to the first and second embodiments is used. When the power supply potential Vcc is divided by a sensor resistance conversion circuit 43 composed of the gas sensor element 41 and a detection resistor 42 having a resistance value Rd connected in series with the gas sensor element 41, the resistance Rs of the gas sensor element 41 changes. Accordingly, the sensor potential Vs at the operating point Pd, which is the voltage dividing point, changes. Specifically, unlike the second embodiment, when the concentration of the reducing gas component such as CO increases, the sensor output potential V at the operating point Pd
s changes so as to increase.

Therefore, the sensor output potential Vs is input to the A / D conversion circuit 14 via the buffer 13 as in the second embodiment. Further, the sensor output value S is input to the input terminal 15A of the microcomputer 15 and processed according to a flow described later, and a change in the concentration of a reducing gas component such as CO is detected from a change in the sensor resistance value Rs of the gas sensor element 41. I do. The microcomputer 15 outputs a gas component concentration increase signal Sg from the output terminal 15B.
This output terminal 15B is connected to the same electronic control assembly 16 as in the first and second embodiments. The electronic control assembly 16 is the same as that described in the first embodiment, and a description thereof will be omitted.

Next, the control in the microcomputer 15 will be described with reference to the flowchart of FIG. When the control system is started up, initialization is performed in step S41, and the initial incremental bottom value is set to the largest possible value of the incremental bottom value. Specifically, the power supply potential Vcc is preferably set to a value obtained when A / D conversion is performed. Therefore, when performing 8-bit A / D conversion, B = 255. Thereafter, in step S42, the sensor output value S is read every 0.8 seconds. Next, in step S43, the sensor output value S is compared with the gradually increasing bottom value B, and S <B (Ye
In the case of s), the process proceeds to step S44. On the other hand, S ≧ B
In the case of (No), the process proceeds to step S45.

In step S44, the sensor output value S is substituted for the gradually increasing bottom value B. Thereby, the gradually increasing bottom value B
Is equal to the bottom value of the sensor output value S.
In step 46, that is, when the sensor output value S is smaller than the gradually increasing bottom value B (S <B), the gas component concentration increase signal Sg is turned off (low potential), and the process proceeds to step S50. On the other hand, in step S45, SB and the threshold T
Compare with H. If SB> TH (Yes), the process proceeds to step S47. On the other hand, if SB−TH ≦ No (No), the process proceeds to step S48. In step S47, that is, the sensor output value S is not less than the gradually increasing bottom value B, and
When the difference is larger than the threshold value TH (S−B> TH), specifically, when the sensor output value S greatly increases, the gas component concentration increase signal Sg is set to ON (high potential), and Proceed to S49. In step 48,
That is, even if the sensor output value S is larger than the gradually increasing bottom value B, when the difference is equal to or smaller than the threshold value TH (SB-TH), the gas component concentration increase signal Sg is set to OFF (low potential), and Proceed to S49.

Thereafter, in step S49, the value B + d obtained by adding the predetermined value d to the gradually increasing bottom value B is substituted for the gradually increasing bottom value B. As a result, the gradually increasing bottom value B becomes a value larger by the predetermined value d. Therefore, the gradually increasing bottom value B is calculated in step S
When the vehicle passes through step S44 (S <B), the bottom value is held as the gradually increasing bottom value B. When the vehicle does not go through step S44, that is, when S ≧ B, the bottom value is gradually increased every time this step S49 is passed. That is, the value is gradually increased. Next, in step S50, after waiting for the A / D conversion sampling time to arrive, the process returns to step S42 to repeat the same processing. By processing according to such a procedure, the gradually increasing bottom value B is calculated and compared with the current sensor output value S, and when the difference is larger than the threshold value TH, that is, when the CO concentration is Is exceeded, the gas component concentration increase signal Sg is turned ON. Conversely, if S <B or SB−TH, that is, C
When the concentration of O decreases, the gas component concentration increase signal S
g can be turned off.

By performing the above processing in the microcomputer 15, the gas detecting device 49 of the fourth embodiment also detects the concentration of the reducing gas component such as CO, and outputs the concentration from the output terminal 15B according to the change in the concentration. ON / O properly
It is possible to output a gas component concentration increase signal Sg for performing FF. Therefore, even in the automatic flap control system 40 of the automobile having the gas detection device 49 shown in FIG.
Flap 2 according to the concentration of the reducing gas component such as
4 can be opened and closed.

(Modification 2) Next, a modification of Embodiment 4 will be described with reference to the flowchart of FIG. In the fourth embodiment, under the control of the microcomputer 15, SB is compared with one threshold TH to determine ON / OFF of the gas component concentration increase signal Sg (see FIG. 8, step S45). . Similar to the relationship of the first modification to the second embodiment, the present modification differs in that a first threshold value TH1 and a second threshold value TH2 which is a smaller value are used. Therefore, different portions will be mainly described, and description of similar portions will be omitted or simplified.

When the control system starts up, initialization is performed in step S51, and the initial incremental bottom value is set to the largest possible value of the incremental bottom value. Specifically, the power supply potential Vcc is preferably set to a value obtained when A / D conversion is performed. Therefore, when performing 8-bit A / D conversion, B
= 255. After that, the sensor output value S is read in step S52. Next, in step S53,
It is determined whether the gas component concentration increase signal Sg is currently ON (high potential). Gas component concentration rise signal S
If g is OFF (No), the process proceeds to step S54. On the other hand, the gas component concentration increase signal Sg is ON (Yes).
In the case of, the process proceeds to step S55. In step S54, the sensor output value S is compared with the gradually increasing bottom value B, and S <B
If (Yes), S ≧ B (N
In the case of o), the process proceeds to step S57. Step S56
Then, the sensor output value S is substituted for the gradually increasing bottom value B, and the process proceeds to step S63. As a result, the gradually increasing bottom value B matches the bottom value of the sensor output value S.

On the other hand, in step S57, SB and the first
Compare with threshold value TH1. SB> TH1 (Ye
In the case of s), the process proceeds to step S58. Step S58
That is, when the sensor output value S is equal to or larger than the gradually increasing bottom value B (S ≧ B), and the difference (SB) is larger than the first threshold value TH1 (SB−TH> TH1), Specifically, when the sensor output value S greatly increases, the gas component concentration increase signal Sg is set to ON (high potential). On the other hand, if SB−TH ≦ TH1 (No) in step S57, the process immediately proceeds to step S62 while maintaining the gas component concentration increase signal Sg in the OFF state.

In step S55, SB and the second
Compare with threshold value TH2. SB> TH2 (Ye
s), the gas component concentration increase signal Sg immediately
The process proceeds to step S62 while maintaining the state of N. On the other hand, if SB−TH ≦ TH2 (No), the process proceeds to step S59.
Proceed to. Note that the second threshold value TH2 is a value smaller than the above-described first threshold value TH1. This step S5
9, that is, when the difference between the gradually increasing bottom value B and the sensor output value S is equal to or less than the second threshold value TH2 (S−B ≦ TH2), that is, when the difference between the sensor output value S and the gradually increasing bottom value B is When it becomes smaller, the gas component concentration increase signal Sg is set to O
FF (low potential). Further, in step S60,
The sensor output value S is compared with the gradually increasing bottom value B, and S <B (Y
In the case of es), the process proceeds to step S62. On the other hand, S ≧ B
In the case of (No), the process proceeds to step S61. Step S
At 61, the sensor output value S is substituted for the gradually increasing bottom value B. As a result, the gradually increasing bottom value B matches the bottom value of the sensor output value S.

Thereafter, in step S62, a value P + d obtained by adding the predetermined value d to the gradually increasing bottom value B is substituted for the gradually increasing bottom value B. As a result, the gradually increasing bottom value B becomes a value larger by the predetermined value d. Therefore, the gradually increasing bottom value B is calculated in step S
In the case of passing through 56 (S <B), a smaller bottom value is held as the gradually increasing bottom value B. On the other hand, when S ≧ B, that is, when the vehicle does not pass through step S56, the gradual increase, that is, the gradual increase bottom value B is gradually increased every time the vehicle passes through step S62. Next, in step S63, A /
After waiting for the D conversion sampling time to arrive, the process returns to step S52 to repeat the same processing. In this way, the gradually increasing bottom value B is calculated, compared with the current sensor output value S, and the difference is calculated as the first threshold value TH1.
Is larger than the first threshold value, that is, when the CO concentration exceeds the first threshold value, the gas component concentration increase signal Sg
Turn ON. Conversely, when SB−TH ≦ TH2, that is, when the CO concentration decreases, the gas component concentration increase signal Sg can be turned off.

Even if processing is performed in such a procedure, the fourth embodiment
Similarly to the above, the incremental bottom value B is calculated and compared with the current sensor output value S, and the gas component concentration increase signal Sg is appropriately turned on.
/ OFF. Moreover, this modification 2
Since the first threshold value TH1 and the second threshold value TH2 smaller than the first threshold value TH1 are used, the ON / OFF of the gas component concentration increase signal Sg has hysteresis, and the difference S− Even when B becomes a value close to the first threshold value or the second threshold value, the gas component concentration increase signal S
There is an advantage that chattering in which ON / OFF of g is frequently repeated is prevented.

Although the present invention has been described with reference to the first to fourth embodiments and the first and second modifications, the present invention is not limited to the above-described embodiments and modifications, and does not depart from the gist of the invention. It goes without saying that the present invention can be appropriately changed and applied within the range. For example, in each of the above embodiments, a gas sensor element that reacts with a reducing gas such as CO was used.
The present invention can also be applied to a gas sensor element that reacts with another gas. For example, an oxide semiconductor gas sensor element that reacts with an oxidizing gas such as NOx can be used. However, the characteristics of the gas sensor element that reacts with an oxidizing gas such as NOx are opposite to those of the gas sensor used in the embodiment and the like.
Has the property of rising. When a gas sensor element having such characteristics is applied to, for example, the gas detection device of the first embodiment, the positions of the resistor R1 and the gas sensor element 2 are interchanged and applied. When the concentration of the oxidizing gas component increases, the sensor output potential Vs
It is preferable to use the sensor resistance value conversion circuit 4 having a circuit configuration in which the resistance value decreases. Similarly, when applied to the second embodiment, the positions of the gas sensor element 11 and the resistor 12 are switched, and when applied to the third embodiment, the gas sensor element 32 and the resistor R are replaced.
It is preferable that the position of the gas sensor element 41 and the position of the resistor 42 be interchanged and used when the position of the gas sensor element 31 and the resistor 42 are replaced.

In the first embodiment, the buffer circuit 6 is interposed between the gradually decreasing peak hold circuit 5 and the differential amplifier circuit 7. However, the operational amplifier OP3 and the discharging resistor R6
By using the resistors R8 and R10 of the differential amplifier circuit 7 as discharge resistors, the circuit configuration of the gas detection circuit 1 can be further simplified. Also,
In the second embodiment and the first modification, the gradually decreasing peak value P
Is a value P−d obtained by subtracting a predetermined value d from the gradually decreasing peak value P.
(See steps S19 and S32)
However, a value k1 · P obtained by multiplying a gradually decreasing peak value P by a predetermined value k1 (0 <k1 <1, for example, k1 = 0.95) is substituted for the gradually decreasing peak value P (P = k1 · P) so that the value gradually decreases. You may do it. Similarly, in Embodiment 4 and Modification 2, the value B + d obtained by adding the predetermined value d to the gradually increasing bottom value B is substituted for the gradually increasing bottom value B, and the value is gradually increased (Steps S49 and S62).
), A value k2 · B obtained by multiplying the gradually increasing bottom value B by a predetermined value k2 (k2> 1, for example, k2 = 1.05) is assigned to the gradually increasing bottom value B (B = k2 · B) so that the value gradually increases. You may do it.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a gas detection device according to a first embodiment.

FIG. 2 is an explanatory diagram showing an outline of an automatic flap control system for an automobile according to the first embodiment;

FIG. 3 is a graph showing measured data for explaining an actual operation of the gas detection device according to the first embodiment.

FIG. 4 is an explanatory diagram showing an outline of a gas detection device and an automatic flap control system of an automobile according to a second embodiment.

FIG. 5 is a flowchart illustrating a processing procedure in the gas detection device according to the second embodiment.

FIG. 6 is a flowchart illustrating a processing procedure in a gas detection device according to a first modification.

FIG. 7 is a circuit diagram showing a gas detection device according to a third embodiment.

FIG. 8 is an explanatory diagram showing an outline of a gas detection device and an automatic flap control system of an automobile according to a fourth embodiment.

FIG. 9 is a flowchart illustrating a processing procedure in the gas detection device according to the fourth embodiment.

FIG. 10 is a flowchart showing a processing procedure in a gas detection device according to a second modification.

[Explanation of symbols]

 1,19,31,49 Gas detector 2,11,32,41 Gas sensor element 4,26,34,43 Sensor resistance value conversion circuit 5 Gradual decrease peak hold circuit 6 Buffer circuit 7 Differential amplifier circuit 8 Comparison circuit 789 Concentration increase Signal generation circuit 35 Incremental bottom hold circuit 10, 20, 30, 40 Automatic flap control system 16 Electronic control assembly 17 Flap drive 18 Actuator 24 Flap

Continued on front page F term (reference) 2G046 AA01 AA11 CA09 DC14 DC16 DC17 DC18 EB01 FB02 FE28 FE39 FE46 2G060 AA01 AB08 AE19 AF07 BA01 HC07 HC10 HC13 HE10

Claims (18)

[Claims] 1. A gas detection device using a gas sensor element whose sensor resistance changes according to a change in the concentration of at least one or more gas components in a gas to be measured. A sensor resistance conversion circuit that outputs a sensor output potential according to a value change, wherein the sensor resistance conversion circuit decreases the sensor output potential when the concentration of the gas component increases; When the sensor output potential is larger than the potential, the sensor output potential is set to the gradually decreasing peak potential. When the sensor output potential is smaller than the held gradually decreasing peak potential, the gradually decreasing peak potential gradually decreases with time. A gradually decreasing peak hold circuit, and a difference between the gradually decreasing peak potential and the sensor output potential is a first value.
A gas detection device comprising: a concentration increase signal generation circuit that generates a concentration increase signal of the gas component when the voltage is higher than a threshold voltage. 2. The gas detection device according to claim 1, wherein a difference between the gradually decreasing peak potential and the sensor output potential is smaller than a second threshold voltage smaller than the first threshold voltage. A gas detection device including a concentration increase signal stop circuit for stopping generation of the concentration increase signal of the gas component. 3. The gas detection device according to claim 2, wherein the concentration increase signal generation circuit and the concentration increase signal stop circuit determine a difference between the gradually decreasing peak potential and the sensor output potential with the concentration increase signal. A gas detection device, comprising: a comparison circuit having a hysteresis characteristic for comparing with the second threshold voltage during generation and comparing with the first threshold voltage when the concentration increase signal is stopped. 4. The gas detection device according to claim 3, wherein the gradually decreasing peak hold circuit includes a capacitor for maintaining a peak potential of the sensor output potential, and a charge stored in the capacitor. And a discharge resistor for discharging the gas. 5. An automatic flap control for an automobile, comprising the gas detection device according to claim 4, wherein the discharging time constant between the capacitor and the discharging resistor in the gradually decreasing peak hold circuit is 20 to 300 seconds. system. 6. A gas detecting device using a gas sensor element whose sensor resistance value changes according to a change in the concentration of at least one or more gas components in a gas to be measured. A sensor resistance value conversion circuit that outputs a sensor output potential according to a value change, wherein the sensor output value decreases when the concentration of the gas component increases; A / D conversion means for performing A / D conversion at each interval to output a sensor output value, and comparing the sensor output value with a current peak hold value, wherein the sensor output value is larger than the current peak hold value Sometimes, the sensor output value is set as a new peak hold value, and when the sensor output value is smaller than the current peak hold value, the peak hold value is substituted. Difference between decreasing peak hold means, and the peak hold value and the sensor output value to the new peak hold value smaller than this Te is first
A gas concentration increasing means for generating a concentration increasing signal of the gas component when the gas concentration is larger than the threshold value. 7. The gas detection device according to claim 6, wherein a difference between the peak hold value and the sensor output value is smaller than a second threshold value smaller than the first threshold value. A gas detection device provided with a concentration increasing signal stopping means for stopping generation of the concentration increasing signal of the gas component. 8. A gas detecting device using a gas sensor element whose sensor resistance value changes according to a change in the concentration of at least one or more gas components in a gas to be measured. A sensor resistance conversion circuit for outputting a sensor output potential in accordance with a value change, wherein the sensor resistance conversion circuit increases the sensor output potential when the concentration of the gas component increases; When the sensor output potential is smaller than the potential, the sensor output potential is set to the gradually increasing bottom potential. When the sensor output potential is larger than the held gradually increasing bottom potential, the gradually increasing bottom potential is gradually increased with time. An increasing bottom hold circuit, and a difference between the increasing bottom potential and the sensor output potential is a first value.
A gas detection device comprising: a concentration increase signal generation circuit that generates a concentration increase signal of the gas component when the voltage is higher than a threshold voltage. 9. The gas detection device according to claim 8, wherein a difference between the sensor output potential and the gradually increasing bottom potential is smaller than a second threshold voltage smaller than the first threshold voltage. A gas detection device including a concentration increase signal stop circuit for stopping generation of the concentration increase signal of the gas component. 10. The gas detection device according to claim 9, wherein the concentration increase signal generation circuit and the concentration increase signal stop circuit determine a difference between the gradually increasing bottom potential and the sensor output potential with the concentration increase signal. A gas detection device, comprising: a comparison circuit having a hysteresis characteristic for comparing with the second threshold voltage during generation and comparing with the first threshold voltage when the concentration increase signal is stopped. 11. The gas detection device according to claim 10, wherein the gradually increasing bottom hold circuit includes a bottom hold circuit including a capacitor for maintaining a bottom potential of the sensor output potential, and a charge stored in the capacitor. And a discharge resistor for discharging the gas. 12. An automatic flap control for an automobile, comprising the gas detection device according to claim 11, wherein a discharge time constant between the capacitor and the discharge resistor in the gradually increasing bottom hold circuit is 20 to 300 seconds. system. 13. A gas detecting device using a gas sensor element whose sensor resistance value changes according to a change in the concentration of at least one or more gas components in a gas to be measured. A sensor resistance conversion circuit that outputs a sensor output potential according to a change in value, wherein the sensor resistance conversion circuit increases the sensor output potential when the concentration of the gas component increases; A / D conversion means for performing A / D conversion at each interval to output a sensor output value, and comparing the sensor output value with a current bottom hold value, wherein the sensor output value is smaller than the current bottom hold value Sometimes, the sensor output value is set as a new bottom hold value, and when the sensor output value is larger than the current bottom hold value, And increasing bottom hold means for a value obtained by adding a value with a new bottom-hold value, the difference between the bottom hold value and the sensor output value is first
A gas concentration increasing means for generating a concentration increasing signal of the gas component when the gas concentration is larger than the threshold value. 14. The gas detection device according to claim 13, wherein a difference between the bottom hold value and the sensor output value is smaller than a second threshold value smaller than the first threshold value. A gas detection device provided with a concentration increasing signal stopping means for stopping generation of the concentration increasing signal of the gas component. 15. A gas detection method using a gas sensor element in which a sensor resistance value changes according to a change in the concentration of at least one or more gas components in a gas to be measured, wherein the sensor detects when the concentration of the gas component increases. When the sensor resistance conversion circuit in which the output potential decreases, the gas sensor element is energized to output a sensor output potential corresponding to the change in the sensor resistance, and when the sensor output potential is greater than the gradually decreasing peak potential, The sensor output potential is set to the gradually decreasing peak potential. When the sensor output potential is smaller than the gradually decreasing peak potential, the gradually decreasing peak potential is gradually decreased with time. The difference between the gradually decreasing peak potential and the sensor output potential is the first.
A gas detection method for generating a signal for increasing the concentration of the gas component when the voltage is higher than a threshold voltage. 16. The gas detection method according to claim 15, wherein a difference between the gradually decreasing peak potential and the sensor output potential is smaller than a second threshold voltage smaller than the first threshold voltage. And a gas detection method for stopping generation of the gas component concentration increase signal. 17. A gas detection method using a gas sensor element in which a sensor resistance value changes according to a change in the concentration of at least one or more gas components in a gas to be measured, wherein the sensor detects when the concentration of the gas component increases. When the output potential rises, a sensor resistance value conversion circuit energizes the gas sensor element to output a sensor output potential corresponding to the change in the sensor resistance value. When the sensor output potential is smaller than the gradually increasing bottom potential, The sensor output potential is the gradually increasing bottom potential. When the sensor output potential is greater than the gradually increasing bottom potential, the gradually increasing bottom potential is gradually increased with time.
A gas detection method for generating a signal for increasing the concentration of the gas component when the voltage is higher than a threshold voltage. 18. The gas detection method according to claim 17, wherein a difference between the gradually increasing bottom potential and the sensor output potential is smaller than a second threshold voltage smaller than the first threshold voltage. And a gas detection method for stopping generation of the gas component concentration increase signal.