JPH08285805A - Gas detection apparatus - Google Patents

Abstract

PURPOSE: To provide a gas detection apparatus by which the time in which a sensor output value due to the reaction of a gas with a sensor is returned to an initial value is shortened as far as possible and whose response of a remeasurement is good. CONSTITUTION: A flow-rate decision means 303 is installed. After a gas to be detected has been passed for a prescribed time, a flow-passage changeover instruction signal 101 that an atmospheric gas is passed is input. In this case, when a sensor output value is high by a definite value or higher, the air in a large quantity is made to flow to a gas sensor 202. When the sensor output value is less than the definite value, the flow rate of the air which is made to flow to the gas sensor 202 is set to an ordinary rate.

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 discriminating between a gasoline vehicle and a light oil vehicle, for example.

[0002]

2. Description of the Related Art A gas detection device such as an oil type identification device for a refueling machine draws a vapor component from a fuel tank of a vehicle and identifies the gas type to determine whether the vehicle is a gasoline vehicle or a light oil vehicle. It is a thing. This device has been developed as a countermeasure against an engine stalling accident due to an erroneous refueling that mistakes gasoline and light oil, which has been a problem in recent years.

Conventionally, oxide semiconductor gas sensors, which are easy to handle and relatively inexpensive, have been widely used as the gas detecting means of this system.

[0004]

However, this oxide semiconductor gas sensor has a problem that the recovery characteristic is extremely poor. This will be described in detail. FIG.
It is a graph with respect to the output value of a gas sensor and the time of a switching instruction signal. Only when the switching signal is at a high level, the test gas is allowed to pass through the sensor cell (around the sensor element) for one second, for example, by the flow path switching device controlled by the switching control means, and the same thereafter. The atmosphere is flowing at a flow rate. In Fig. 4, it can be seen that the sensor output value suddenly rises when the indicator signal goes high for only 1 second and the test gas begins to flow. However, due to the reaction with the gas for only 1 second, about 20 seconds or more. It is recognized that the output does not return during the period.

In this state, re-measurement due to an operation error requires a waiting time of 20 seconds or more, and the measurement response becomes poor. Further, if re-measurement is performed before the output value returns to the initial value, the sensor output value becomes a saw-tooth shape as shown in FIG. 5, which may cause erroneous recognition.

The present invention has been made in view of the above circumstances, and shortens the time required for the sensor output value due to the reaction between the gas and the sensor to return to the initial value as much as possible, and provides a good gas response for re-measurement. The purpose is to provide.

[0007]

The present inventor has examined the characteristics of the oxide semiconductor type gas sensor having poor recovery characteristics as described above, and it is effective to pass a large amount of air through the sensor after reacting with the gas. I found out that. For example, if the flow rate of the suction device, which normally sucks at 1 liter / min, is set to 2 liter / min after recognizing the gas, the recovery is quick. However, since the output value of the sensor element is a value determined by the flow velocity and the gas component, simply increasing the flow rate will cause it to fall below the initial value V ₀ of the normal flow rate (for example, 1 liter / min), as shown in FIG. As a result, it was found that the value converged to a value of 2 liters / min, resulting in undershoot, and this was not able to achieve the purpose at all.

Therefore, if a flow rate switching means is provided and preferably a flow path switching instruction signal indicating that the test gas has been passed through and then the atmospheric gas is being passed is input, if the sensor output value is higher than a certain value, the gas sensor It was possible to solve the above-mentioned problem by causing a large amount of air to flow into the gas sensor, and when the sensor output became less than a certain value, setting the atmospheric flow rate to the gas sensor to a normal amount.

Therefore, in order to achieve the above object, the present invention provides the following gas detection device. (1) A flow path switching device capable of switching between the atmosphere and the test gas via the respective flow paths, a gas sensor, and a suction device for sending the atmosphere or the test gas to the gas sensor via the flow path switching device. A switching control means for switching the flow path switching device so that the gas to be tested is passed through for a certain time by outputting a flow path switching instruction signal; a gas judging means for detecting gas by a sensor signal of the gas sensor; A flow rate determination means for determining the suction amount of the suction device from the sensor signal and the flow path switching instruction signal of the switching control means, wherein the flow path switching instruction signal of the switching control means passes through the test gas. After that, when it is output to the flow path determining means that the atmospheric gas has passed, the flow rate determining means may flow a flow rate higher than usual when the sensor signal of the gas sensor is equal to or more than a predetermined value. The suction device controls, when the sensor signal of the gas sensor is less than the predetermined value, the gas detection device and controls the suction device so as to flow the usual amounts of flow rate. (2) The gas to be inspected is air containing vapor of gasoline or light oil, the gas sensor outputs a sensor signal according to the type of these vapors, and the gas judging means outputs the sensor from the gas sensor. The gas detection device according to (1) above, which distinguishes between gasoline and light oil by a signal. (3) The gas detection device according to (1) or (2), wherein the gas sensor is an oxide semiconductor type.

[0010]

The gas detecting device of the present invention is provided with the flow rate determining means, and the flow rate determining means determines the suction amount of the suction device from the sensor signal of the gas sensor and the flow path switching instruction signal of the switching control means. When the output value of the sensor signal is high, the flow rate causes a large amount of the atmosphere to restore the function of the gas sensor to flow, and when the output value of the sensor signal becomes low, the flow rate of the atmospheric air is set to a normal amount, so that the gas and the sensor The time required for the sensor output value due to the reaction to return to the initial value can be surely shortened, and the response of the remeasurement can be improved. Moreover, the sensor output value can be converged to the normal value.

Further, such a gas detecting device is particularly effective, especially when distinguishing gasoline and light oil, because the gas concentration is high and the return of the sensor is delayed. Also,
This is particularly effective when an oxide semiconductor type having poor recovery characteristics is used as the gas sensor.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a gas detection device of the present invention, and FIG. 2 is a flowchart showing a processing procedure of the flow rate determining means.

This gas detection device includes a suction device 201 such as a blower or a diaphragm pump which sucks the atmosphere or the test gas from the pipe P4 and discharges it from the pipe P5, and the suction device 20.
The gas sensor 202 is connected to the suction side of No. 1 by a pipe P4, and the flow path switching device 203 is connected to the suction side of the gas sensor 202 by a pipe P3.

This flow path switching device 203 switches between the atmosphere side pipe P2 communicating with the atmosphere side and the test gas pipe P1 communicating with the tank T of gasoline or light oil or the like so that P1 and P3 communicate with each other, or P2. And P3 are communicated with each other, and the atmosphere or the test gas is sent to the gas sensor 202 by suction of the suction device 201.

The switching of the flow path switching device 203 is performed by the output of the flow path switching instruction signal 101 from the switching control means 301. In this example, the flow path switching is switched from the atmosphere to the test gas for a predetermined time, for example, 1 second. The instruction signal 101 is output, and this is performed by driving a solenoid valve (not shown) of the flow path switching device 203 for a certain period of time.

The gas sensor 202 is, for example, an oxide semiconductor type gas sensor, and is arranged in a gas sensor cell portion (not shown) communicating with the gas flow path. The gas sensor 202 outputs sensor signals corresponding to gasoline and light oil. FIG. 4 shows changes in the output value of the oxide semiconductor gas sensor with respect to pentane, which is the main component of gasoline, with the passage of time. According to FIG. 4, when the flow path switching instruction signal 101 from the switching control means 301 becomes high level for only 1 second and gas starts to flow, the sensor output suddenly rises, but its return characteristic is very poor. It can be seen that it takes about 20 seconds or more.

The sensor signal 102 of the gas sensor 202 is
The gas is output to the gas determination unit 302, and the gasoline and the light oil are discriminated from each other based on the change in the sensor output value. Further, the sensor signal 102 of the gas sensor 202 is also output to the flow rate determination means 303, while the flow path switching instruction signal 101 of the switching control means 301 is also output to the flow rate determination means 303, and the flow rate determination means 303 uses this. From the values of the sensor signal 102 and the flow path switching instruction signal 101, a flow rate adjustment signal 103 is output to the suction amount control means 304 according to the procedure shown in FIG. 2, and suction is performed by the suction device control signal 104 of the suction amount control means 304. For example, the rotation number of the device 201 is controlled to change the suction amount.

Here, the processing procedure of the flow rate determining means 303 will be described with reference to the flowchart of FIG. First, in step 1, the normal flow mode is selected and the flow control signal 10
A signal for flowing a normal flow rate is output to 3.

Next, in step 2, it is judged whether or not the flow path switching instruction signal 101 output from the switching control means 301 to the flow rate determining means 303 is input. When the flow path switching signal 101 is input, it is determined in step 3 whether or not it is the atmosphere side switching instruction signal. If it is determined in step 3 that the signal is not the atmosphere-side switching instruction signal, it means that the gas to be detected is flowing through the gas sensor 202, so the normal flow rate selection signal 103 is directly output to the suction amount control means 304, and the gas sensor is output. The test gas flows through 202 at a normal flow rate.

When it is determined in step 3 that the signal is an atmosphere side switching instruction signal, the sensor output value F is compared with a preset threshold value THL in step 4. The sensor output value F is the threshold value T
If it is determined in step 5 that it is larger than HL, it means that it is immediately after the gas is switched to the test gas side and then to the atmosphere side. The adjustment signal 103 is sent to the suction amount control means 30.
4 is output. As a result, the gas sensor has a flow rate of the air that is twice the normal flow rate, which accelerates the return of the sensor.

In step 5, the sensor output value F is the threshold value THL.
If it is determined that it is smaller than the threshold value TH, then in step 6, the sensor output value F is equal to or less than the threshold value THL and the threshold value THL.
Is determined to be 1/10 or more. Threshold THL
If it is less than or equal to 1/10 of the threshold value THL, for example, a flow rate adjustment signal 103 for flowing a flow rate 1.5 times the normal flow rate
Is output to the suction amount control means 304, and as a result, 1.5 times the normal atmosphere flows through the gas sensor.

The sensor output value F is the threshold value THL in step 6.
When it is determined that the flow rate is lower than 1/10, the flow rate control signal 103 is output to the suction control means 304 so that the normal flow rate is flown. As a result, the gas having the normal flow rate is caused to flow through the gas sensor 202, and the sensor output converges to the value of the normal flow rate.

Note that this processing procedure is not limited to the PID, for example.
It is of course possible to use a control method or fuzzy control, and it is also possible to adjust the flow rate in multiple steps. [Comparative Example 1] The flow path switching control unit 301 switches the flow path switching device 203 to the tank T containing pentane for 1 second, and air containing pentane gas is flowed through the gas sensor at 1 liter / min for 1 second. A constant amount of air of 1 liter / min was kept flowing.

As a result, as shown in FIG. 7, it took about 6.42 seconds to return to 20% of the maximum output value of the sensor. [Comparative Example 2] The flow path switching control unit 203 switches the flow path switching device 203 to the tank T containing pentane for 1 second, and air containing pentane gas is supplied to the gas sensor for 1 second at a rate of 1 liter / min. 2 times 2 liters / m
A constant amount of in air was kept flowing.

As a result, as shown in FIG. 6, the output of the sensor was under-shorted, which was lower than the initial value V ₀ . [Embodiment] The flow path switching control means 203 switches the flow path switching device 203 to the tank T containing pentane for 1 second, and the gas sensor contains 1 liter of air containing pentane gas for 1 second.
After flowing at min, the sensor output value F from the above threshold THL
When the value is large, it is 2 liters / min, which is twice the normal value, and when it is less than or equal to the threshold value THL and 1/10 or more of the threshold value THL, the atmosphere at a flow rate of 1.5 liters / min which is 1.5 times the normal value is flowed. In the case of less than 1/10 of the threshold value THL, a normal flow rate of 1 liter / min of air was flowed.

As a result, as shown in FIG. 3, it takes only 3.88 seconds to recover to 20% of the peak voltage, and it is confirmed that the voltage converges to the initial value. The present invention is not limited to the embodiments described above. For example, in the above embodiment, an example in which gasoline and light oil are distinguished is shown,
Other kinds of gas may be used, and the gas sensor has a long dead time and can be applied to a kind of gas sensor that recovers by flowing air, and the procedure of the flow rate determining means is not limited to the above example. Other various modifications can be made without departing from the scope of the present invention.

[0027]

The gas detection device of the present invention allows a large amount of atmospheric flow to flow to the gas sensor when the sensor output is high, and dynamically adjusts the flow rate as a normal flow when the sensor output becomes low, thereby The recovery time can be shortened as much as possible.

Further, the gas detector of the present invention is effective for distinguishing gasoline and light oil. Further, the gas detection device of the present invention is effective for an oxide semiconductor gas sensor that requires a long time to restore.

[Brief description of drawings]

FIG. 1 is a block diagram of a gas detection device of the present invention.

FIG. 2 is a flowchart showing a processing procedure in a flow rate determining means according to the present invention.

FIG. 3 is a graph showing a relationship between a sensor output value and time in the example.

FIG. 4 is a graph showing a relationship between a sensor output value and time in a conventional example.

FIG. 5 is a graph showing a relationship between a sensor output value and time when re-measurement is performed before the sensor output does not return to the initial value.

FIG. 6 is a graph showing the relationship between the sensor output value and time when the gas sensor is flushed with air at twice the normal atmosphere.

FIG. 7 is a graph showing the relationship between the sensor output value and time when a constant flow rate of atmospheric air is passed through the gas sensor.

[Explanation of symbols]

 201 suction device 202 gas sensor 203 flow path switching device 301 switching control means 302 gas determination means 303 flow path determining means 304 suction amount control means 101 flow path switching instruction signal 102 sensor signal 103 flow rate control signal 104 suction device control signal

Claims (3)

[Claims] 1. A flow path switching device capable of switching between the atmosphere and the test gas via respective flow paths, a gas sensor, and suction for sending the atmosphere or the test gas to the gas sensor via the flow path switching device. An apparatus, a switching control unit that outputs a flow channel switching instruction signal to switch the flow channel switching device so as to pass a test gas for a certain period of time, a gas determination unit that detects a gas by a sensor signal of the gas sensor, A flow rate determining means for determining a suction amount of the suction device from a sensor signal of the gas sensor and a flow path switching instruction signal of the switching control means, wherein the flow path switching instruction signal of the switching control means is a gas to be detected. When it is output to the flow path determining means that after passing through the atmospheric gas, the flow rate determining means, when the sensor signal of the gas sensor is a predetermined value or more,
The suction device is controlled so that the flow rate is higher than usual, and when the sensor signal of the gas sensor is less than a predetermined value,
A gas detection device, characterized in that the suction device is controlled so as to flow a normal amount. 2. The test gas is air containing vapor of gasoline or light oil, the gas sensor outputs a sensor signal according to the type of these vapors, and the gas judging means outputs from the gas sensor. The gas detection device according to claim 1, wherein gasoline and light oil are discriminated by the sensor signal. 3. The gas detection device according to claim 1, wherein the gas sensor is of an oxide semiconductor type.