JP2003247974A - Gas detector device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect the concentration of an object gas of detection more precisely by a gas detector device for detecting the concentration of the object gas in the gas to be measured including both the object gas and a non-object gas. <P>SOLUTION: The gas detector device S1 has a first electrode formed on one surface side of a solid electrolyte 10 and a molecule sieve 31 covering the first electrode 21. The gas detector device also has a first gas detecting means for obtaining a first detection signal based on the gas to be measured from which the object gas is removed by separating the object gas and the non-object gas with the molecule sieve 31, a second electrode 22 formed on the other surface side of the solid electrolyte 10, and a second detecting means for obtaining a second detection signal based on the gas to be measured including both the object gas and the non-object gas. The concentration of the object gas is detected by comparing and operating the first and second detection signals. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas detector for detecting the concentration of a specific type of gas to be detected in a measurement gas, for example, a gas sensor for detecting the concentration of HC (hydrocarbon) in the exhaust gas of an engine. It is suitable for use in

[0002]

2. Description of the Related Art Conventionally, in a gas detector, when detecting the concentration of a specific type of gas to be detected among measurement gases,
A method (catalyst electrode selection method) of detecting a desired gas to be detected by appropriately selecting a catalyst electrode that selectively reacts with the gas to be detected by utilizing the selectivity of the catalyst electrode is known.

However, with this catalyst electrode selection method, at present, it is difficult to select a catalyst electrode having a good selectivity, which is capable of accurately reacting only the gas to be detected among the measurement gases. Therefore, as a result, the non-detection target gas other than the detection target gas also reacts at the catalyst electrode, which makes it difficult to accurately detect the detection target gas.

Specifically, regarding the catalyst electrode selection method, P
There is an attempt to detect a hydrocarbon (gas to be detected) in exhaust gas (measurement gas) of an automobile by selecting a t-Au electrode or an oxide electrode.

However, such selectivity for hydrocarbons is determined only by the oxidation performance of the catalyst electrode, and only hydrocarbons are accurately detected among exhaust gas components in which many reducing gases (non-detection target gases) exist. Is difficult to do. Further, hydrocarbons also have various shapes such as linear, branched, and cyclic, and have different carbon numbers, and it is very difficult to detect them uniformly.

Further, the catalytic electrode has a problem that its stability is low because the selectivity of the gas reaction largely changes depending on the temperature, the oxygen concentration and the like. Further, it is conceivable to provide a plurality of catalyst electrodes in parallel according to various kinds of gas to be detected, but there is a problem that the structure is complicated and the cost becomes high.

[0007]

In the conventional method, it is difficult to accurately detect the concentration of the gas to be detected because a signal based on an extra gas to be detected other than the gas to be detected is detected. It was

In view of the above problems, the present invention is directed to a gas detection device for detecting the concentration of a specific type of gas to be detected in a measurement gas, such as a gas detection device for detecting the HC concentration in exhaust gas. The purpose of the present invention is to enable the concentration of the gas to be detected to be detected more accurately.

[0009]

In order to achieve the above object, in the invention according to claim 1, a pair of gas detecting means is provided in a gas detecting device for detecting the concentration of a gas of a specific type among measurement gases. The first gas detection means is equipped with a molecular sieve (31), and the measurement gas is passed through the molecular sieve to separate the detection target gas and the non-detection target gas in the measurement gas from the difference in molecular size. Is for obtaining a first detection signal based on the measurement gas from which the detection target gas has been removed, and the second gas detection means introduces the measurement gas without passing through the molecular sieve and separates it from the detection target gas. It is for obtaining a second detection signal based on the measurement gas in which the gas to be detected is combined, and by calculating by comparing the first detection signal and the second detection signal,
It is characterized in that the concentration of the gas to be detected is detected.

According to the present invention, the gas to be detected is removed by separating and removing the gas to be detected having a relatively large molecular size from the measurement gas by using the first gas detecting means by the molecular sieve. It is possible to obtain the first detection signal based on the measurement gas, that is, the measurement gas composed of the non-detection target gas having a relatively small molecular size.

On the other hand, in the second gas detection means, the measurement gas is introduced as it is without passing through the molecular sieve, so that the detection target gas and the non-detection target gas are combined without being separated from each other. A detection signal can be obtained.

By comparing and calculating the first detection signal and the second detection signal, a detection signal based on a relatively large gas to be detected can be obtained, so that the concentration of the gas to be detected is more accurate. Can be detected.

Here, in the invention described in claim 2, in the gas detection device according to claim 1, the second gas detection means can diffuse the measurement gas by Knudsen diffusion but does not have a molecular sieving function. It is characterized in that the measuring gas is introduced through the porous membrane (32).

In the first detecting means for introducing the measurement gas through the molecular sieve, the pores of the molecular sieve through which the measurement gas passes are small, so that individual molecules in the measurement gas freely diffuse without colliding with each other. In other words, in the molecular sieve, gas molecules diffuse by Knudsen diffusion, so the molecules are introduced at a diffusion rate according to the difference in mass and size.

On the other hand, if the second detecting means is non-Knudsen diffusion, the gas molecules introduced into the second detecting means diffuse while the molecules collide with each other.
Its diffusion rate does not depend on the mass or size of the molecule. This causes a detection error when the concentration of the gas to be detected is detected by utilizing the difference in the size of the introduced molecules between the first detection means and the second detection means.

In this respect, as in the present invention, the measurement gas is introduced into the second gas detection means through the porous membrane (32) which can diffuse the measurement gas by Knudsen diffusion but does not have a molecular sieving function. This is preferable because the diffusion mechanism of the measurement gas introduced in both detection means can be aligned with the same Knudsen diffusion. Thereby, the detection error can be reduced.

Further, in the invention described in claim 3, in the gas detection device according to claim 1 or 2, the first and second detection means both react the introduced oxygen with the measurement gas. For catalyst electrodes (21, 22, 21a,
21b), the first detection signal is the first
Is a signal based on the reaction between oxygen and the measurement gas in the catalyst electrode (21, 21a) of the second detection means, and the second detection signal is oxygen and the measurement gas in the catalyst electrode (22, 21b) of the second detection means. The adjusting means (30b) is a signal based on the reaction between the first detecting means and the adjusting means (30b) for making the amount of oxygen reaching the catalyst electrode of the first detecting means and the amount of oxygen reaching the catalyst electrode of the second detecting means similar. It is characterized by being provided.

According to this, in each detection means, the introduced oxygen and the measurement gas react at the catalyst electrode, and the signal based on the concentration of the remaining oxygen becomes the detection signal. Since the concentration of the introduced measurement gas is different between the first detection means and the second detection means, the concentration of oxygen remaining after the reaction is also different, which results in a difference between the first detection signal and the second detection signal. Can be generated.

Here, in the present invention, by the adjusting means, the reaction degree between oxygen and the measuring gas at the catalyst electrode of the first detecting means and the reaction between oxygen and the measuring gas at the catalyst electrode of the second detecting means. The degree can be the same. Therefore, the difference between the first detection signal and the second detection signal can be accurately obtained according to the difference in the measurement gas concentration between the first detection means and the second detection means, which is preferable.

Specifically, as the adjusting means, a pinhole (30b) through which oxygen and a measurement gas pass can be adopted as in the invention described in claim 4. It is easy to control the oxygen passage area by adjusting the diameter of the pinhole.

Further, in the invention described in claim 5, in the gas detection device according to claim 1 or 2, both the first and second detection means react the introduced oxygen with the measurement gas. For catalyst electrodes (21, 22, 21a,
21b), the first detection signal is the first
The second detection signal is a signal based on the reaction between oxygen and the measurement gas at the catalyst electrode of the second detection means, and the second detection signal is a signal based on the reaction between the oxygen and the measurement gas at the catalyst electrode of the second detection means. In at least one of the first detecting means and the second detecting means, auxiliary catalysts (31b, 3b) for reacting oxygen with the measurement gas are provided in addition to the catalyst electrode of the detecting means.
2b) is provided.

According to this, similarly to the invention of claim 3, in each detecting means, the introduced oxygen and the measurement gas react with each other at the catalyst electrode, and the signal based on the concentration of the remaining oxygen becomes the detection signal. . Since the concentration of the introduced measurement gas is different between the first detection means and the second detection means, the concentration of oxygen remaining after the reaction is also different, which results in a difference between the first detection signal and the second detection signal. Can be generated.

Here, in the present invention, the reaction efficiency between oxygen and the measurement gas in the catalyst electrode of the detecting means provided with the auxiliary catalyst can be increased, which is preferable for improving the detection sensitivity.

Further, when one of the first and second detecting means has a poor reaction efficiency and an error occurs in the comparison between the first detecting signal and the second detecting signal,
Providing an auxiliary catalyst on the side with poor reaction efficiency to increase the reaction efficiency is preferable because the reaction efficiency of both detection means can be made uniform.

Here, as in the invention described in claim 6,
When the auxiliary catalyst (31b) is provided in the first detection means, it is preferable to interpose it between the molecular sieve (31) and the catalyst electrode (21a).

Further, as in the invention described in claim 7, the second detection means introduces the measurement gas and oxygen through the porous membrane (32), and the auxiliary catalyst (32b) is used as the second catalyst.
When it is installed in the detection means of the porous membrane and the catalyst electrode (21
It is preferable to interpose it with b).

Further, as in the eighth aspect of the present invention, the pair of gas detecting means may use an electrochemical sensor.

Here, as in the invention described in claim 9,
The pair of gas detection means using the electrochemical type sensor uses a single electrochemical element, and one of the pair of electrodes (21, 22) in this electrochemical element is connected to one of the electrodes (21). A molecular sieve (31) is provided so as to cover it, and the first detection signal and the second detection signal are obtained by switching the polarity of the applied voltage applied to the pair of electrodes in the electrochemical device. Can be

According to this, one electrode of the electrochemical element is covered with the molecular sieve to form the above-mentioned first gas detecting means, and the other electrode of the electrochemical element is connected to the above-mentioned second electrode. Of the gas detection means.

Further, as in the invention described in claim 10,
The pair of gas detection means may be one using a semiconductor type sensor.

The reference numerals in parentheses for each means described above are examples showing the correspondence with specific means described in the embodiments described later.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention shown in the drawings will be described. In each of the following embodiments, the same parts are designated by the same reference numerals in the drawings for simplification of description.

(First Embodiment) FIG. 1 is a diagram schematically showing the structure of a gas detector S1 according to a first embodiment of the present invention. The present device S1 will be described as being applied to a gas sensor that detects HC (hydrocarbon) in exhaust gas (measurement gas) of an automobile engine.

In FIG. 1, one surface of a plate-shaped solid electrolyte 10 made of stabilized zirconia, perovskite or the like (see FIG. 1).
A first electrode 21 is formed on the inner surface (upper surface), and a second electrode 22 is formed on the other surface (lower surface in FIG. 1). The electrodes 21 and 22 are made of a film of platinum (Pt) or the like.

The solid electrolyte 10 is a partition wall 30 made of a ceramic having excellent heat resistance such as a dense sintered body such as alumina.
It is housed in and is separated from the outside. The internal space of the partition wall 30 is partitioned by the solid electrolyte 10 and is divided into a first space K1 on the first electrode 21 side and a second space K2 on the second electrode 22 side.

On the wall surface of the partition wall 30 which covers the first electrode 21, the molecular sieving film 31 is formed, and on the wall surface of the partition wall 30 which covers the second electrode 22, the diffusion resistor film 3 is formed.
2 are each formed as a window.

The molecular sieving film 31 is, for example, HC or CO having a carbon number of 2 or less, which is a non-detection target gas in the exhaust gas,
Only gas having a relatively small molecular size such as H ₂ is allowed to pass, but HC having a relatively large molecular size and having a carbon number of 3 or more, which is a detection target gas, is not allowed to pass. Also,
It is desirable that such a molecular sieving film 31 has a high heat resistance and a low catalytic ability, and for example, has a micropore diameter of 0.5 nm.
It can be made of silicalite-I or the like.

Therefore, when the exhaust gas flows from the outside of the partition wall 30, the detection target gas having a relatively large molecular size is blocked by the molecular sieving film 31 and does not enter the first space K1. Only the non-detection target gas having a small molecular size can enter and exit the first space K1.

Further, the diffusion resistance film 32 is made of a porous material such as alumina, and all the exhaust gas can flow in and out. Therefore, when the exhaust gas flows from the outside of the partition wall 30, the measurement gas in which the detection target gas and the non-detection target gas are combined can enter and leave the second space K2.

A heater 40, which is a resistance heating element capable of generating heat when energized, is provided outside the partition wall 30. The heater 40 is made of, for example, a platinum film or the like. In the present embodiment, the partition wall 30 defines the main body of the sensor in the gas detection device S1.

Further, the gas detection device S1 has an external circuit (not shown) provided outside the main body of the sensor,
The electrodes 21 and 22 are electrically connected to the external circuit. Then, as shown in FIG. 1, the external circuit includes a current detection means 50, a power supply 60,
A polarity switching means 70 is provided and each electrode 21, 22 is provided.
Is connected to the power supply 60 via the current detection means 50 and the polarity switching means 70.

A voltage is applied from the power source 60 to the electrodes 21, 22 by the polarity switching means 70, and the polarity of the applied voltage applied to the pair of electrodes 21, 22 can be switched. ing. Figure 1
In this state, the first electrode 21 is the positive electrode and the second electrode 2 is
2 is the negative pole. In addition, the current detection means 50
Is for detecting the value of the current flowing between both electrodes 21, 22.

As described above, the present gas detection apparatus S1 uses a single electrochemical element in which the pair of electrodes 21 and 22 are provided on both surfaces of the solid electrolyte 10. In this embodiment,
The molecular sieving film 31, the first electrode 21 covered with the molecular sieving film 31 through the first space K1, and the solid electrolyte 10 constitute a first gas detecting means,
The second electrode 22 and the solid electrolyte 10 covered with the diffusion resistor film 32 via the space K2 of the second gas detection unit are configured.

The first gas detecting means separates the detection target gas and the non-detection target gas in the exhaust gas (measurement gas) from the difference in molecular size by the molecular sieve 31 provided, and the detection target gas is removed. It is provided to obtain the first detection signal based on the exhaust gas.

On the other hand, the second gas detection means introduces the measurement gas without passing through the molecular sieve 31, and performs the second detection based on the exhaust gas (measurement gas) in which the detection target gas and the non-detection target gas are combined. It is provided to obtain a signal.

Then, the first electrode 21 in the first detecting means and the second electrode 22 in the second gas detecting means.
Is a pair of electrodes in a single electrochemical device,
At the same time, it is a catalyst electrode for reacting the introduced oxygen with the measurement gas.

Then, the first detection signal is a signal based on the reaction between oxygen and the measurement gas in the catalyst electrode 21 of the first detection means, and the second detection signal is the signal of the second detection means. This is a signal based on the reaction between oxygen and the measurement gas at the catalyst electrode 22.

That is, in the first and second detection means, the introduced oxygen and the measurement gas are the catalyst electrodes 21 and 2.
A signal based on the concentration of the remaining oxygen that has reacted at 2 becomes a detection signal. Since the concentration of the measurement gas introduced is different between the first detection means and the second detection means, the concentration of oxygen remaining after the reaction also differs.

Then, the first electrode 21 (first space K
Oxygen ions move in the solid electrolyte 10 between the 1) side and the second electrode 22 (second space K2) side. Thereby,
A current flows between the first and second electrodes 21 and 22, and the current can be used to obtain the first detection signal and the second detection signal.

As will be described later as a detection operation, these first and second detection signals are the first electrode 21 in the first detection means and the second electrode in the second gas detection means.
It can be obtained by switching the polarity of the applied voltage applied to the electrodes 22 and.

That is, in the first embodiment, the first and second detection signals are not obtained by only the first gas detecting means and the second gas detecting means, respectively, and both gas detecting means are detected. I try to get it by combining the means.

The operation, that is, the detecting operation of the gas detector S1 of the first embodiment will be described with reference to FIGS. FIG. 2 is a diagram schematically showing the relationship between the applied voltage applied between the pair of electrodes 21 and 22 and the current flowing between the pair of electrodes 21 and 22.

Here, the first space K on the side of the first electrode 21
In No. 1, since the HC (gas to be detected) having a large molecular diameter is blocked by the molecular sieving film 31, the HC having a large molecular diameter is smaller than that in the second space K2 on the second electrode 22 side. Only, there is an excess of oxygen.

First, the case where the measurement gas (exhaust gas) is in a lean state, that is, the case where the gas concentration other than oxygen in the exhaust gas is lower than the oxygen concentration (corresponding to the case where the HC concentration is low) will be described.

The polarity switching means 70 is set to the state shown in FIG. 1 (the first electrode 21 is positive and the second electrode 22 is negative), and an appropriate voltage (in FIG. 2) is applied to the pair of electrodes 21, 22. (Corresponding to + V), the current is applied to the first electrode 2
Flows from 1 toward the second electrode 22. At this time, oxygen ions flow from the second electrode 22 to the first electrode 21.

As shown in FIG. 2, this current is obtained as a current I ₁ corresponding to the excess oxygen concentration in the lean measurement gas. That is, this current I ₁ is a current based on the measurement gas containing the gas to be detected.

On the other hand, the polarity switching means 70 is switched from the state shown in FIG. 1 (the first electrode 21 is in the minus state and the second electrode 22 is in the plus state), and the voltage applied to the pair of electrodes 21, 22 is changed. When the polarity is reversed (corresponding to -V in FIG. 2), the current flows from the second electrode 22 to the first electrode 21.

As shown in FIG. 2, this current corresponds to the excess oxygen concentration in the lean measurement gas in addition to the excess oxygen concentration due to the small amount of HC having a large molecular diameter. obtained as a current I _'1 to. That is, this current I ′ ₁ is a current based on the measurement gas from which the gas to be detected is removed.

Here, the former current I ₁ becomes the second detection signal, and the latter current I ′ ₁ becomes the first detection signal. If these two detection signals are compared and calculated, for example, a current corresponding to the excess oxygen concentration corresponding to a small amount of HC having a large molecular diameter, that is, a detection target gas having a relatively large molecular size is obtained. Based detection signals can be obtained.

On the other hand, even when the measurement gas (exhaust gas) is in a rich state, that is, when the concentration of gases other than oxygen in the exhaust gas is higher than the oxygen concentration (when the HC concentration is high), the lean state is obtained. As in the case of, the pair of electrodes 2
Switching the polarity of the applied voltage with respect to 1 and 22 (+ in FIG. 2)
V, -V).

Then, when the applied voltage shown in FIG. 2 is + V, a current I ₂ corresponding to the insufficient oxygen concentration in the measurement gas in the rich state is supplied from the second electrode 22 to the first electrode.
To the electrode 21 of the.

On the other hand, when the applied voltage shown in FIG. 2 is -V, the excess oxygen concentration corresponding to the small amount of HC having a large molecular diameter is the excess oxygen concentration corresponding to the insufficient oxygen concentration in the measurement gas in the rich state (minus minus A current I ′ ₂ corresponding to the oxygen concentration minus the concentration) flows from the second electrode 22 to the first electrode 21.

Also in this case, the former current I ₂ is the second detection signal and the latter current I ′ ₂ is the first detection signal. If these two detection signals are compared and calculated, for example,
It is possible to obtain a detection signal based on a current corresponding to the excess oxygen concentration corresponding to the small amount of HC having a large molecular diameter, that is, a detection target gas having a relatively large molecular size.

FIG. 3 shows an example of the system configuration of the gas detector S1 for performing such a detecting operation.

In FIG. 3, the temperature control means 80 comprises the heater 40 and a heater control means provided in the external circuit for controlling energization of the heater 40. The storage means 90 stores the respective current values I ₁ , I ′ ₁ , I ₂ , and I ′ ₂ detected by the current detection means 50.

Further, the calculation means 100 calculates based on each current value of the storage means 90 and outputs a detection signal based on the gas to be detected. The timing setting means 110 controls the operation timings of the polarity switching means 70, the storage means 90 and the arithmetic means 100.

In the system configuration shown in FIG. 3, the sensor and the heater 40 partitioned by the partition wall 30 are formed.
Each means other than the above and power sources 50 to 110 can be provided in the external circuit. Then, based on this system configuration, the above-described detection operation can be performed and a detection signal based on the gas to be detected can be output.

In the present embodiment, attention is paid to the fact that a large number of branched hydrocarbons and cyclic hydrocarbons are contained in the unburned gas in automobiles, especially in gasoline-powered vehicles that perform stoichiometric combustion. The first constituting the gas detection means of No. 1
The electrode 21 is blocked by the molecular sieve 31 so that most of the HC to be detected is not introduced into the first electrode 21.

HC, which is the gas to be detected, is detected as a deficiency in the exhaust gas introduced into the first electrode 21 through the molecular sieve 31. As a result, the influence of the reducing gas having a small molecular size on the detection signal can be eliminated, so that the concentration of the detection target gas can be detected more accurately.

Here, FIG. 4 is a schematic cross-sectional view showing a modification of the gas detector S1 of the first embodiment. Figure 1 above
The partition wall 30 in the gas detector S1 shown in FIG. 4 is not always necessary, and as shown in FIG.
The molecular sieving film 31 and the diffusion resistor film 32 may be directly formed on the top.

Further, the gas detector S1 of the first embodiment.
In the above, the diffusion resistor film 32 constituting the second gas detecting means is a porous film which does not have a molecular sieving function and introduces a measurement gas in which a detection target gas and a non-detection target gas are combined. The resistor film 32 is preferably one that allows the measurement gas (exhaust gas in this example) to diffuse by Knudsen diffusion. This is for the following reason.

In the first detecting means for introducing the measuring gas from which the gas to be detected is removed through the molecular sieving film 31, the molecular sieving film 31 through which the measuring gas passes has a small pore size, so that the individual measuring gas has a small diameter. Molecules freely diffuse without collision.

That is, in the molecular sieving film 31, the gas molecules diffuse by Knudsen diffusion, so the gas molecules of the measurement gas are introduced at a diffusion rate according to the difference in mass and size. Specifically, in Knudsen diffusion, light-mass molecules have a high diffusion rate, and heavy-mass molecules have a low diffusion rate.

On the other hand, when the second detecting means is non-Knudsen diffusion, the gas molecules introduced into the second detecting means diffuse while the molecules collide with each other. Therefore, its diffusion rate does not depend on the mass or size of the molecule.

In the present example, the second space K1 in the second detecting means has a carbon number of 3 or more which is hardly introduced into the first space K1 in the first detecting means.
Will also be introduced. At this time, in the first space K1 and the second space K2, the second space K2 has a carbon number of 3 or more.
Since C is excessively present, the oxygen concentration around the second electrode 22 is low.

Then, the detection is carried out by utilizing the difference between the oxygen concentrations of the two spaces K1 and K2, that is, the first and second detecting means. However, if the diffusion mechanism in the second detection means, that is, the diffusion resistance film 32 is non-Knudsen diffusion unlike the first detection means, for example, HC with a large number of carbon atoms, that is, heavy HC is expected in Knudsen diffusion. It will diffuse faster than the diffusion rate.

Therefore, the amount of introduction of HC having 3 or more carbon atoms into the second space K2, which is a difference from the first detection means in the second detection means, is apparently excessive or insufficient. It becomes easy to vary.

In other words, the difference in oxygen concentration between the first space K1 and the second space K2 realized by the molecular sieving film 31 is likely to deviate from the target value. This causes a detection error when the concentration of the gas to be detected is detected by utilizing the difference in the size of the introduced molecules between the first detection means and the second detection means.

In that respect, the second gas detecting means is one in which the measuring gas can be diffused by Knudsen diffusion, but the measuring gas is introduced through the diffusion resistor film 32 as a porous film having no molecular sieving function. By doing so, the diffusion mechanism of the measurement gas introduced in both detection means can be aligned with the same Knudsen diffusion.

If the pore diameter of the diffusion resistance film 32 as a porous membrane is too large, gas molecules passing through the pores collide with each other, and if it is too small, it has a molecular sieving function. From this, specifically, the pore diameter is 10 nm to 1 μm.
By setting the size of the range to a degree, the diffusion mechanism of the measurement gas passing through the diffusion resistor film 32 can be Knudsen diffusion.

As a result, the diffusion mechanism of the first and second detection means can be adapted to the Knudsen diffusion.
The difference in oxygen concentration between the space K1 and the second space K2 can be accurately obtained. Then, the first detection signal and the second detection signal can be accurately obtained, which is preferable for improving the detection sensitivity.

Here, FIG. 4 is a schematic sectional view showing a modified example of the gas detection device S1 of the first embodiment. Figure 1 above
The partition wall 30 in the gas detector S1 shown in FIG. 4 is not always necessary, and as shown in FIG.
The molecular sieving film 31 and the diffusion resistor film 32 may be directly formed on the top. Also in this case, it is preferable that the diffusion resistor film 32 realizes Knudsen diffusion.

(Second Embodiment) FIG. 5 is a diagram showing a schematic sectional structure of a gas detector S2 according to a second embodiment of the present invention. In the first embodiment described above, the pair of gas detection means is composed of a single electrochemical element, but as shown in FIG. 5, each of the pair of gas detection means is composed of one electrochemical element. Is also good.

As shown in FIG. 5, a sensor A as an electrochemical element having an electrode 21a formed on one surface of the solid electrolyte 10 and an electrode 22a formed on the other surface, and an electrode 21b formed on one surface of the fixed electrolyte 10 and an electrode formed on the other surface. A sensor B is formed as an electrochemical element on which 22b is formed.

On one side of the solid electrolyte 10, the first electrode 21a of the sensor A is covered with the molecular sieving film 31, and the first electrode 21b of the sensor B is the diffusion resistor film 32.
It is covered by.

On the other hand, on the other surface side of the solid electrolyte 10,
Both the second electrode 22a of the sensor A and the second electrode 22b of the sensor B are covered with a porous layer 33 made of CeO ₂ or the like having an oxygen storage function of storing oxygen. A heater 40 is provided on the porous layer 33.

Although not shown in FIG. 5, each sensor A, B has a pair of electrodes 21a and 22a, 21a, respectively.
b and a power source for applying a voltage to 22b (see FIG. 6), and a current detection means for detecting a current value between a pair of electrodes (see FIG. 6)
And are provided.

FIG. 6 is a system configuration diagram of the gas detector S2 shown in FIG. In FIG. 6, temperature control means 80
Controls the heater 40 to control the temperatures of the sensor A and the sensor B.

In the sensor A, a voltage is applied between the pair of electrodes 21a and 22a by the power source 50, and
The current value between a and 22a is detected by the current detecting means 60. On the other hand, in the sensor B, a voltage is applied between the pair of electrodes 21b and 22b by the power source 50, and the pair of electrodes 2b
The current value between 1b and 22b is detected by the current detecting means 60.

Each detected current value is input to the arithmetic means 100, and the arithmetic means 100 outputs the result of the arithmetic operation by comparing the two electric current values.

The detection operation of the second embodiment is as follows. In the porous layer 33 having an oxygen storage function, exhaust gas (measurement gas) flows in and out from the exposed portion,
Oxygen is excessive in the porous layer 33. That is, the measurement gas is in a lean state on the side of the second electrodes 22a and 22b in each of the sensors A and B.

Also, the first electrode 21a of the sensor A is
On the side, due to the molecular sieving membrane 31, the HC having a large molecular diameter is
(Gas to be detected) does not enter, but on the other hand, almost all exhaust gas enters the first electrode 21b side of the sensor B through the diffusion resistor 32.

Therefore, the first electrode 2 in the sensor A is
Compared to the first electrode 21b side of the sensor B, the 1a side has a surplus of oxygen due to the small amount of HC having a large molecular diameter, and the oxygen concentration is also high.

Here, the first electrode 21a of the sensor A and the first first electrode 21b of the sensor B are catalytic electrodes for reacting the introduced oxygen with the measurement gas. Therefore, the first detection signal is a signal based on the reaction between oxygen and the measurement gas in the catalyst electrode 21a of the sensor A (first detection means), and the second detection signal is the sensor B (second detection signal). Signal) based on the reaction between oxygen and the measurement gas in the catalyst electrode 21b of (means).

Then, the pair of electrodes 21a, 2 of the sensor A,
The current value flowing through 2a (first detection signal) and the current value flowing through the pair of electrodes 21b, 22b of the sensor B (second detection signal) are different, and if these two current values are compared and calculated. Similarly to the first embodiment, it is possible to obtain the detection signal based on the detection target gas having a relatively large molecular size.

That is, according to the second embodiment, as in the first embodiment, the concentration of the gas to be detected can be detected more accurately. Furthermore, in the second embodiment,
Since the current values of the two electrochemical elements (sensors) can be obtained at the same time, there is no need for the polarity switching means for switching the polarities as in the first embodiment.

In the second embodiment, the sensor A
However, it is equipped with a molecular sieve, and the detection target gas and the non-detection target gas are separated from the difference in molecular size by the molecular sieve, and the detection gas is removed.
A first gas detecting means for obtaining the detection signal of
The sensor B constitutes a second gas detection means for obtaining a second detection signal based on the measurement gas including the detection target gas and the non-detection target gas.

Here, in the case of the two-sensor structure as in the second embodiment, the oxygen concentration detecting means does not have to be a solid electrolyte type, but a semiconductor type using a semiconductor electrode such as SnO ₂ or TiO ₂ is used. A sensor can be used. FIG. 7 shows a modified example using a semiconductor type sensor in the present embodiment.

In FIG. 7, SnO _{2 is formed} on one surface of the substrate 11.
Semiconductor electrodes 23 and 24 made of TiO ₂ or the like are formed. One of the semiconductor electrodes 23 constitutes the sensor A, that is, the first gas detecting means, together with the molecular sieving film 31 that covers the same, and the other semiconductor electrode 24 together with the diffusion resistor film 32 that covers the sensor B, that is, the second gas. It constitutes a gas detecting means.

Also in this modification, it is possible to obtain the same operational effect as that of the gas detection device S2 shown in FIG.

Also in the second embodiment, as in the first embodiment, the diffusion resistor film 32 constituting the second gas detecting means does not have a molecular sieving function and does not detect gas to be detected. It is preferable that the porous film introduces the measurement gas combined with the target gas by Knudsen diffusion.

(Third Embodiment) FIG. 8 is a diagram showing a schematic sectional structure of a gas detector S3 according to a third embodiment of the present invention. This gas detector S3 is the same as the gas detector S3 shown in FIG.
The basic configuration is similar to the device shown in.

As shown in FIG. 8, this gas detector S3
Also, the electrode 21a on one surface of the solid electrolyte 10 and the electrode 2 on the other surface.
A sensor A as an electrochemical element having 2a formed thereon and a sensor B as an electrochemical element having an electrode 21b formed on one surface of the fixed electrolyte 10 and an electrode 22b formed on the other surface thereof are formed.

On one side of the solid electrolyte 10, the first electrode 21a of the sensor A is covered with the molecular sieving film 31, and the first electrode 21b of the sensor B is made of alumina or the like as a dense sintered body. Is located in the space K3 defined by the ceramic layer 30a.

Ceramic layer 3 which defines this space K3
0a has a pinhole 30b formed therein, and a diffusion resistor film 32 is formed on the outer surface of the ceramic layer 30a so as to cover the pinhole 30b. This diffusion resistor film 32 also does not have a molecular sieving function, but it is preferable that it realizes Knudsen diffusion.

The molecular sieving film 31 and the first sensor A
A porous film 31a made of a porous member similar to the diffusion resistor 32 is also interposed between the electrode 21a and the electrode 21a. This porous film 31a is provided in order to secure the mechanical strength of the molecular sieving film 31 and to facilitate the formation of the molecular sieving film 31.

Specifically, each electrode 21a, 22a, 21
The ceramic layer 30a is attached to the solid electrolyte 10 on which b and 22b are formed, and the diffusion resistor film 32 and the porous film 31a are laminated on the ceramic layer 30a and the solid electrolyte 10 and fired to form a layer on the porous film 31a. The molecular sieving film 31 is formed by hydrothermal synthesis.

On the other hand, on the other surface side of the solid electrolyte 10, an air introduction hole K4 defined by the ceramic layer 30a and communicating with the atmosphere is provided, and the second electrode 22a of the sensor A and the second electrode 22a of the sensor B are provided. Both of the electrodes 22b of the above are exposed to the air atmosphere by facing the air introduction hole K4. Further, as shown in FIG. 8, the ceramic layer 30a is provided with a heater 40 for controlling the temperatures of the sensors A and B.

The detection operation of the third embodiment is as follows. By introducing the atmosphere through the atmosphere introducing hole K4, the second electrodes 22a and 22b in the respective sensors A and B are
The side is the first electrode 2 through which exhaust gas (measurement gas) flows in and out.
Oxygen is in an excess state as compared with the 1a and 21b sides. That is, as in the second embodiment, the measurement gas is lean on the second electrodes 22a and 22b side of each of the sensors A and B.

In addition, the first electrode 21a of the sensor A is
On the side, due to the molecular sieving membrane 31, the HC having a large molecular diameter is
(Gas to be detected) does not enter, but on the other hand, on the first electrode 21b side of the sensor B, almost all exhaust gas enters through the diffusion resistor 32 and the pinhole 30b.

Therefore, the first electrode 2 in the sensor A is
Compared to the first electrode 21b side of the sensor B, the 1a side has a surplus of oxygen due to the small amount of HC having a large molecular diameter, and the oxygen concentration is also high.

Here, the first electrode 21a of the sensor A and the first first electrode 21b of the sensor B are catalyst electrodes for reacting the introduced oxygen with the measurement gas. Therefore, the first detection signal is a signal based on the reaction between oxygen and the measurement gas in the catalyst electrode 21a of the sensor A (first detection means), and the second detection signal is the sensor B (second detection signal). Signal) based on the reaction between oxygen and the measurement gas in the catalyst electrode 21b of (means).

Also in this embodiment, the sensor A
The current value (first detection signal) flowing through the pair of electrodes 21a, 22a of the sensor B and the current value (second detection signal) flowing through the pair of electrodes 21b, 22b of the sensor B are different. If the calculation is performed by comparison, a detection signal based on the detection target gas having a relatively large molecular size can be obtained.

Here, in the present embodiment, the first area of the sensor A, which is the catalyst electrode of the first detecting means, is adjusted by adjusting the hole area of the pinhole 30b through which oxygen and measuring gas as the adjusting means pass. It is preferable to make the amount of oxygen reaching the electrode 21a and the amount of oxygen reaching the first electrode 21b of the sensor B, which is the catalyst electrode of the second detection means, to be approximately the same.

In each of the sensors A and B, the introduced oxygen and the measuring gas react at the catalyst electrodes 21a and 21b, and the signal based on the concentration of the remaining oxygen becomes the detection signal. Since the concentration of the introduced measurement gas is different between the two sensors A and B,
The concentration of oxygen remaining after the reaction is also different, which causes a difference between the first detection signal and the second detection signal.

Here, the catalyst electrode 2 of each sensor A, B is adjusted by adjusting the hole area of the pinhole 30b.
The degree of reaction between oxygen and the measurement gas in 1a and 21b can be made approximately the same. Therefore, the difference between the first detection signal and the second detection signal can be accurately obtained according to the difference in the measurement gas concentration between the first detection means and the second detection means.

Specifically, it is as follows. When the adjustment using the pinhole 30b is performed, the first electrodes (catalyst electrodes) 21a and 21b of both sensors A and B pass through the molecular sieving film 31 and the diffusion resistance film 32 and have the same degree of mutual. The amount of oxygen reaches.

On the other hand, the amounts of HC reaching the first electrodes (catalyst electrodes) 21a and 21b of both sensors A and B are different, and the amount of HC to be introduced is higher in the sensor A in which the molecular sieving action is performed. The quantity is small. If the amount of oxygen reaching the catalyst electrode is the same for both sensors A and B, this HC
A signal (oxygen ion current) commensurate with the difference in the amount of is obtained.

If both sensors A and B have the catalyst electrodes 21a,
If the amount of oxygen reaching 21b is different, a signal (oxygen ion current) corresponding to the difference in amount of HC between the sensors A and B cannot be obtained, resulting in a sensitivity error. FIG. 9 is a diagram specifically showing the effect of adjustment by the pinhole 30b.

Adjustment by the pinhole 30b is performed by, for example,
Do the following: When the diameter of the pinhole 30b is changed, a mixed gas of oxygen and nitrogen (for example, oxygen 0.1
%) Is introduced into both sensors A and B, and the passing amount per unit area is calculated. If the passing amounts of the sensors A and B are the same, the oxygen reaching amount to the catalyst electrode is also the same. In this way, the size of the pinhole 30b is adjusted.

In FIG. 9, carbon monoxide,
Methane (C = 1), ethane (C = 2), propane (C =
5) of 3) and isobutane (C = 4) were used. This 5
The latter two of the types are the detection target gases. The measurement was performed under the conditions of oxygen concentration 0.1%, oxygen excess ratio λ = 1, and gas flow rate 5 liter / min.

In FIG. 9, the case where the oxygen arrival amount to the catalyst electrode is the same in both sensors A and B (the same oxygen arrival amount) is shown by a circle plot, and the diameter of the pinhole 30b is too small and the molecular sieving film 31 is shown. Side, that is, the sensor A side is large (oxygen arrival amount excess on the molecular sieving film side) is shown by a triangular plot, and the diameter of the pinhole 30b is too large and the diffusion resistance film 32 side, that is, the sensor B side is large (diffusion resistance film). The excess oxygen reaching amount) is shown by a square plot.

As can be seen from FIG. 9, when the amounts of oxygen reaching the catalyst electrode are the same in both sensors A and B, the sensitivities of methane and ethane similarly introduced into both sensors A and B are: From the comparison of the detection signals of both sensors A and B, it becomes almost 0. However, if the amount of oxygen reaching the catalyst electrode differs between the two sensors A and B, a signal corresponding to the difference in the amount of HC between the two sensors A and B cannot be obtained, resulting in an error in sensitivity.

(Fourth Embodiment) FIG. 10 is a diagram showing a schematic sectional structure of a gas detector S4 according to a fourth embodiment of the present invention. This gas detection device S4 is a partial modification of the device shown in FIG. 8 in the third embodiment.

The difference from the gas detector of the third embodiment is that at least one of the sensor A (first detecting means) and the sensor B (second detecting means) has a catalyst electrode 21a,
In addition to 21b, auxiliary catalysts 31b and 32b for reacting oxygen with the measurement gas are provided.

In this example, both sensors A and B are provided with an auxiliary catalyst. First, on the sensor A side, the molecular sieve film 3
1 and the first electrode 21a of the sensor A, the porous film 31b serving as an auxiliary catalyst is different from the porous film 31a of the third embodiment (see FIG. 8) in oxygen such as platinum particles. It carries a catalyst for reacting with the measurement gas (exhaust gas).

On the sensor B side, the pinhole 3
0b and the diffusion resistor film 32, a porous film 32b as an auxiliary catalyst is interposed so as to cover the pinhole 30b. The porous film 32b can be the same as the porous film 31a supporting the catalyst on the sensor A side in the present embodiment.

As described above, in the sensor A, the porous film 31b as the auxiliary catalyst is interposed between the molecular sieving film 31 and the first electrode (catalyst electrode) 21a, and in the sensor B, the auxiliary catalyst is used. The porous film 32b is interposed between the diffusion resistance film 32 as a porous film for introducing the measurement gas and oxygen and the first electrode (catalyst electrode) 21b.

According to this, by providing the auxiliary catalysts 31b and 32b, the reaction efficiency between oxygen and the measurement gas (exhaust gas in this example) in the catalyst electrodes 21a and 21b of the sensors A and B can be increased. Therefore, it is preferable for improving the detection sensitivity.

Further, a catalyst electrode may be provided on one of the sensors A and B. This is the catalyst electrode 21 of both sensors A and B.
One of a and 21b is effective in the case where the reaction efficiency is low and an error occurs in the comparison between the first detection signal and the second detection signal. In that case, the reaction efficiency of both the sensors A and B can be made uniform by providing an auxiliary catalyst on the side with lower reaction efficiency to increase the reaction efficiency.

FIG. 11 is a diagram showing the results of examining the specific effect of the auxiliary catalyst. In FIG. 10, the case in which the catalyst is loaded on each of the porous membranes 31b and 32b is “with auxiliary catalyst” and is loaded. When there was not, it was set as "no auxiliary catalyst."
In FIG. 11, as in the case of FIG. 9 described above, five kinds of measurement gases, carbon monoxide, methane, ethane, propane, and isobutane were used. The measurement conditions were also the same as in FIG.

As can be seen from FIG. 11, in the case without the auxiliary catalyst, the reaction efficiency of the sensor B was poor in this example, and a signal corresponding to the difference in the amount of HC (especially methane) between the two sensors A and B was obtained. Error occurs in the sensitivity. On the other hand, in the case of using the auxiliary catalyst, the reaction efficiency of the sensor B is corrected and the reaction efficiency of both the sensors A and B is improved. Therefore, a signal corresponding to the difference in the amount of HC between the two sensors A and B is obtained. Has been.

As described above, according to the above embodiments,
A molecular sieve 31 is provided, and the gas to be detected is separated from the gas to be detected in the gas to be measured from the difference in molecular size by passing the gas to be measured through the molecular sieve, and the gas to be detected from which the gas to be detected is removed is introduced. A pair of gas detecting means comprising a first gas detecting means and a second gas detecting means into which the measuring gas is introduced as it is without passing through the molecular sieve. The pair of gas detecting means is used. A first detection signal based on the measurement gas from which the detection target gas has been removed, and a second detection signal based on the measurement gas that is a combination of the detection target gas and the non-detection target gas, and these first detection signals are obtained. There is provided a gas detection device characterized in that the concentration of the gas to be detected is detected by comparing and calculating the signal and the second detection signal.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a gas detection device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram for explaining a gas detection operation in the first embodiment.

FIG. 3 is a diagram showing an example of a system configuration of the gas detection device according to the first embodiment.

FIG. 4 is a schematic cross-sectional view showing a gas detection device as a modified example of the first embodiment.

FIG. 5 is a schematic cross-sectional view of a gas detection device according to a second embodiment of the present invention.

FIG. 6 is a diagram showing an example of a system configuration of the gas detection device shown in FIG.

FIG. 7 is a schematic cross-sectional view showing a gas detection device as a modified example of the second embodiment.

FIG. 8 is a schematic sectional view of a gas detection device according to a third embodiment of the present invention.

FIG. 9 shows a specific effect of making the amount of oxygen reaching the catalyst electrode of the first detecting means and the amount of oxygen reaching the catalyst electrode of the second detecting means to be approximately the same by the pinhole as the adjusting means. FIG.

FIG. 10 is a schematic sectional view of a gas detection device according to a fourth embodiment of the present invention.

FIG. 11 is a diagram showing a result of examining a specific effect of an auxiliary catalyst.

[Explanation of symbols]

21, 21a, 21b ... First electrode, 22 ... Second electrode, 31 ... Molecular sieving film, 31b, 32b ... Porous film as auxiliary catalyst, 32 ... Diffusion resistor film as porous film.

Claims (10)

[Claims] 1. A gas detection device for detecting the concentration of a gas of a specific type among measurement gases, comprising a pair of gas detection means, and the first gas detection means comprises a molecular sieve (31). At the same time, the gas to be detected and the non-gas to be detected in the measurement gas are separated from the difference in molecular size by passing the measurement gas through the molecular sieve, and the first gas based on the measurement gas from which the detection gas has been removed. The second gas detection means introduces the measurement gas without passing through the molecular sieve, and combines the detection target gas and the non-detection target gas with the measurement gas. To obtain a second detection signal based on the above, and to detect the concentration of the gas to be detected by comparing and operating the first detection signal and the second detection signal. Gas detecting apparatus characterized by was Unishi. 2. The second gas detection means introduces the measurement gas through a porous membrane (32) which can diffuse the measurement gas by Knudsen diffusion but does not have a molecular sieving function. The gas detection device according to claim 1, wherein: 3. The first and second detecting means both have catalyst electrodes (21, 22, 21a, 21b) for reacting the introduced oxygen with the measurement gas, and The first detection signal is a signal based on a reaction between oxygen and the measurement gas in the catalyst electrode of the first detection means, and the second detection signal is the catalyst electrode of the second detection means. Is a signal based on the reaction between oxygen and the measurement gas in, the amount of oxygen reaching the catalyst electrode of the first detection means and the amount of oxygen reaching the catalyst electrode of the second detection means The gas detection device according to claim 1 or 2, further comprising adjustment means (30b) for making the same degree. 4. The gas detection device according to claim 3, wherein the adjusting means is a pinhole (30b) through which oxygen and the measurement gas pass. 5. The first and second detecting means both have a catalyst electrode (21, 22, 21a, 21b) for reacting the introduced oxygen with the measurement gas, The first detection signal is a signal based on a reaction between oxygen and the measurement gas in the catalyst electrode of the first detection means, and the second detection signal is the catalyst electrode of the second detection means. Is a signal based on the reaction between oxygen and the measurement gas, and at least one of the first detection means and the second detection means, oxygen and the measurement gas other than the catalyst electrode of the detection means. Auxiliary catalyst for reaction (31
b, 32b) are provided, The gas detection apparatus of Claim 1 or 2 characterized by the above-mentioned. 6. The auxiliary catalyst (31b) is provided in the first detecting means and the molecular sieve (31).
The gas detection device according to claim 5, wherein the gas detection device is interposed between the catalyst electrode and the catalyst electrode (21a). 7. The second detection means is for introducing the measurement gas and oxygen through a porous membrane (32), and the auxiliary catalyst (32b) is provided in the second detection means. The gas detection device according to claim 5, wherein the gas detection device is interposed between the porous film and the catalyst electrode (21b). 8. The gas detection device according to claim 1, wherein the pair of gas detection means uses an electrochemical sensor. 9. The pair of gas detection means uses a single electrochemical element, and one of the pair of electrodes (21, 22) in the electrochemical element is connected to one of the electrodes (21). The molecular sieve (31) is provided so as to cover, and the first detection signal and the second detection signal are obtained by switching the polarity of the applied voltage applied to the pair of electrodes in the electrochemical device. The gas detection device according to claim 8, wherein the gas detection device is configured as described above. 10. The gas detection device according to claim 1, wherein the pair of gas detection means use semiconductor type sensors.