JPH11344468A - Combustible gas sensor and apparatus for measuring concentration of combustible gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately measure the concn. of combustible gas such as hydrocarbon or the like without being affected by atompshere conditions, in a combustible gas sensor measuring the concn. of the combustible gas. SOLUTION: Since all of electrodes 22b, 22c, 22d with different oxidation catalytic activity to combustible gas are present in one measuring chamber 4a in the diffusion of a gas to be measured to the measuring chamber 4a, the shape of the diffusion passage inclusive of the diffusion limiting hole 20b or porous member 32 up to the measuring chamber 4a, the shape or arrangement of the measuring chamber 4a and atmospheric conditions such as temp. or the like can made perfectly equal with each other in the measurement by all of the electrodes 22b, 22c, 22d. Therefore, diffusion states can be allowed to perfectly coincide with each other. As a result, causality of an error can be perfectly removed by the calculation of the difference between current values, and the accurate concn. of methane, that of hydrocarbon other than methane and that of all of hydrocarbons can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a flammable gas sensor and a flammable gas concentration measuring device using the flammable gas sensor.

[0002]

2. Description of the Related Art Conventionally, there has been proposed an apparatus for measuring the concentration of flammable gas such as hydrocarbons in exhaust gas for performing precise combustion control and determining the purifying performance of a three-way catalyst in an internal combustion engine or the like. Have been.

[0003] For example, JP-A-5-264501,
JP-A-5-322844, JP-A-9-29236
In Japanese Patent Publication No. 3 and the like, a measuring element having an electrode or the like having catalytic activity for oxidizing hydrocarbons and a measuring element having an electrode or the like having no catalytic activity for oxidizing hydrocarbons are provided. Then, the hydrocarbon concentration is determined from the difference in the measured oxygen concentration.

Among them, the combination of the oxygen concentration cell type and the limiting current type disclosed in JP-A-5-264501 and JP-A-9-292363 has a problem that the measurement is particularly performed in a wide range of the air-fuel ratio. It is possible.

[0005]

However, in such a wide-range air-fuel ratio sensor combining the oxygen concentration cell type and the limiting current type, there has been a problem that the measured value tends to be inaccurate. This is considered to be due to the following reasons.

That is, the wide-area air-fuel ratio sensor uses an oxygen pump to pump oxygen in the gas to be measured diffused from the space to be measured into the measurement chamber to the outside, or conversely, to pump oxygen into the measurement chamber. Then, the current value of the oxygen pump when the voltage of the oxygen concentration cell becomes the reference voltage is measured, and the oxygen concentration is measured based on this current value.

In order to measure hydrocarbons, a measuring chamber capable of oxidizing hydrocarbons in the gas to be measured which diffuses,
A measurement chamber that cannot be oxidized is provided, and the current value of the oxygen pump is individually measured, and the hydrocarbon concentration is determined from the difference between the measured values.

In such a measurement, the diffusion of the gas to be measured into the measurement chamber is greatly affected by subtle differences in the shape of the diffusion passage including the gas diffusion restricting portion up to the measurement chamber, and the shape and arrangement of the measurement chamber. It depends. As before, two measuring elements
When two are formed, it is difficult to completely match the shapes of the measuring elements, and since two are formed, their arrangements are naturally different, and a slight difference occurs in the flow of the gas to be measured. Unavoidable. Furthermore, atmospheric conditions, such as temperature, will also differ. Thus, it becomes impossible to measure both measurement elements under exactly the same conditions.

For this reason, the current values of the oxygen pumps of both measuring elements include error factors due to subtle differences in arrangement and shape, which cannot be ignored, making it difficult to measure the hydrocarbon concentration accurately.

The present invention relates to a flammable gas sensor for measuring the concentration of flammable gas such as hydrocarbon as described above.
The purpose is to measure the concentration accurately.

[0011]

According to a first aspect of the present invention, there is provided a flammable gas sensor, comprising: a measurement chamber capable of exchanging gas with a space to be measured via a gas diffusion restricting unit; Oxygen pumping means for pumping, a plurality of first electrodes disposed in the measurement chamber, and a second electrode disposed in a reference oxygen concentration space, wherein oxygen between the first electrode and the second electrode is provided. And a concentration cell that generates an electromotive force corresponding to the concentration difference, wherein the plurality of first electrodes of the concentration cell have at least two types of oxidation catalyst activities for combustible gas.

As described above, since the first electrodes having at least two types of oxidation catalyst activities for combustible gas are arranged in one measurement chamber, the first electrode and the second electrode having one type of oxidation catalyst activity are arranged. The current value of the oxygen pumping means is measured using an electrode as an oxygen concentration cell, and the current value of the oxygen pumping means is measured using the first and second electrodes having other types of oxidation catalyst activities as oxygen concentration cells. Then, if two or more types of current values are obtained and their difference is determined, the concentration of each type of combustible gas can be measured. Moreover, since all the first electrodes having different oxidation catalytic activities for the flammable gas are present in one measurement chamber, the diffusion of the gas to be measured into the measurement chamber is limited to the measurement chamber even when any of the first electrodes is used. The shape of the diffusion path including the gas diffusion restricting section, the shape and arrangement of the measurement chamber, the temperature, and the like can be completely matched. Therefore, the diffusion states can be completely matched.

Therefore, in the calculation of the difference between the current values of the oxygen pumping means, an error factor due to the atmospheric conditions can be completely eliminated, and an accurate flammable gas concentration can be obtained.

In the flammable gas sensor according to the second aspect,
The flammable gas to be measured is a hydrocarbon. Therefore, the concentration of the hydrocarbon can be accurately measured.

In the flammable gas sensor according to a third aspect,
The plurality of first electrodes of the concentration cell include an electrode having no oxidation catalyst activity for hydrocarbons, an electrode having oxidation catalyst activity for hydrocarbons other than methane, and an electrode having oxidation catalyst activity for hydrocarbons containing methane. It is characterized by having.

As described above, by using three types of first electrodes, one of the concentrations of the combustible gas other than hydrocarbons, the concentration of methane, the concentration of hydrocarbons other than methane, and the concentration of all hydrocarbons is obtained. More than one can be determined accurately.

A flammable gas concentration measuring apparatus according to a fourth aspect is a flammable gas concentration measuring apparatus using the flammable gas sensor according to any one of the first to third aspects, wherein a current value to the oxygen pumping means is measured. Oxygen pumping amount control means for adjusting; concentration cell voltage detection means for detecting an electromotive force between the first electrode and the second electrode of the concentration cell for each type of oxidation catalyst activity; For each type, the current value for the oxygen pumping means is changed by the oxygen pumping amount control means, and the current when the electromotive force detected by the concentration cell voltage detecting means falls within a reference voltage range is changed. Current value measuring means for measuring the value, and a concentration for measuring the concentration of each combustible gas based on the difference between the current values corresponding to the type of the oxidation catalyst activity measured by the current value measuring means. Characterized by comprising a constant section.

The current value measuring means changes the current value for the oxygen pumping means by the oxygen pumping amount control means for each type of oxidation catalyst activity, and the electromotive force detected by the concentration cell voltage detecting means is used as a reference. The current value when the voltage falls within the voltage range is measured. Thus, a current value is obtained for each type of oxidation catalyst activity in the first electrode. Then, based on the difference between the current values corresponding to the type of the oxidation catalyst activity measured by the current value measuring means, the concentration of each combustible gas is measured.

As described above, the flammable gas concentration measuring apparatus uses the flammable gas sensor in which all the first electrodes having different oxidation catalytic activities for the flammable gas are present in one measuring chamber, and thus the measured current value is measured. When calculating the difference between the first and second electrodes, the measurement errors are offset by the fact that the first electrodes are all in the same atmosphere, so that the concentration of each combustible gas can be accurately measured.

According to a fifth aspect of the present invention, in the flammable gas concentration measuring apparatus according to the fourth aspect, the control of the current value for the oxygen pumping means by the oxygen pumping amount control means is stopped to detect the concentration cell voltage. A combustible gas measuring means for measuring the presence of a combustible gas from any of the electromotive forces detected by the means; and the oxygen pumping means when the combustible gas measuring means determines that the combustible gas is present. It is characterized by comprising a quantity control means, a density measurement execution means for operating the current value measurement means and the density measurement means.

As described above, before the oxygen pumping amount control means, the current value measuring means and the concentration measuring means are operated to determine the concentration of the flammable gas, the flammable gas measuring means The presence is obtained by the electromotive force of the concentration cell, and if the value of the electromotive force indicates the presence of flammable gas, the oxygen pumping amount control means, the current value measuring means, and the concentration measuring means are operated by the concentration measurement executing means. To determine the concentration of flammable gas.

Therefore, if it is determined by the concentration cell that no flammable gas is present, the oxygen pumping amount control means takes longer time than the detection of only the electromotive force of the concentration cell,
It is not necessary to perform the process of measuring the concentration of the combustible gas by operating the current value measuring means and the concentration measuring means. For this reason,
The functions of the electronic circuit for operating the oxygen pumping amount control means, the current value measurement means, and the concentration measurement means are assigned to other processing, so that the entire processing is speeded up or unnecessary electric energy is not consumed.

[0023]

[First Embodiment] FIG. 1 is a block diagram showing a configuration of a combustible gas concentration measuring apparatus 2 to which the above-described invention is applied. This combustible gas concentration measuring device 2
Is for measuring the concentration of combustible gas in the exhaust gas of an internal combustion engine, for example.

The flammable gas concentration measuring device 2 comprises a hydrocarbon gas sensor 4 as a flammable gas sensor, various circuits 6-1.
6 and an electronic control unit (ECU) 18. Here, the hydrocarbon gas sensor 4 is shown as a sectional view.

The hydrocarbon gas sensor 4 includes a pumping cell 20, a detection cell 22, and a heater 24, as shown in an expanded view of FIG. The pumping cell 20
A diffusion limiting hole 20b is formed in a plate-like solid electrolyte 20a containing zirconia as a main component.
Around 0b, a measurement electrode 20c is formed on the upper surface side, and a reference electrode 20d is formed on the lower surface side. These electrodes 20
c and 20d are formed of a metal such as gold, which does not become a hydrocarbon oxidation catalyst. These electrodes 20c, 2
The lead portions 20e and 20f of 0d extend to terminals (not shown) existing on the base side.

The detection cell 22 comprises a plate-like solid electrolyte 22a containing zirconia as a main component and three electrodes 22b, 22b,
Reference numerals 22c and 22d have a reference electrode 22e formed on the lower surface side. These electrodes 22b, 22c, and 22d are formed with platinum as a main component, but are processed so that the activity as an oxidation catalyst for hydrocarbons differs from each other as described later. The reference electrode 22e is formed of a metal such as gold or platinum. The lead portions 22f, 22f, of these electrodes 22b, 22c, 22d, 22e
22g, 22h and 22i extend to terminals (not shown) located on the base side.

The heater 24 is provided with a heater wire 24 on a flat plate-like body 24a made of an insulating ceramic such as alumina.
b is formed. Lead portions 24c and 24d at both ends of the heater wire 24b extend to terminals (not shown) existing on the base side.

A spacer 26 made of an insulating ceramic such as alumina is disposed between the pumping cell 20 and the detection cell 22. The spacer 26 has a reference electrode 20 d on the lower surface of the pumping cell 20 and a diffusion limiting hole 20.
In addition, a rectangular hole 26a is formed so that three electrodes 22b, 22c, and 22d present on the upper surface of the detection cell 22 are exposed so that the electrode b is exposed. This rectangular hole 26a
Corresponds to the measurement chamber 4a in FIG.

Between the detection cell 22 and the heater 24, two spacers 2 made of an insulating ceramic such as alumina are used.
8, 30 are arranged. Of these, the spacer 28 on the side of the detection cell 22 has the reference electrode 2 on the lower surface of the detection cell 22.
A rectangular hole 28a is formed so that 2e is exposed.
This rectangular hole 28a corresponds to the atmospheric chamber 4b as the reference oxygen concentration space in FIG. The rectangular hole 28a is open to the atmosphere by a gas passage 28b extending toward the base.

Since there is a spacer 30 having no hole between the spacer 28 and the heater 24, the heater wire 24b is not exposed to the atmosphere chamber 4b. Also,
The measurement electrode 20c and the diffusion limiting hole 20b present on the upper surface of the pumping cell 20 are protected by covering with an insulating porous body 32 such as alumina from above, thereby preventing performance degradation due to clogging or the like.

The hydrocarbon gas sensor 4 is formed by laminating and firing in the above arrangement. Here, three electrodes 22 having different oxidation catalytic activities for hydrocarbons are used.
b, 22c, 22d are hydrocarbon insensitive electrodes 22b,
Methane-insensitive electrode 22c and hydrocarbon-sensitive electrode 2
2d. The hydrocarbon-insensitive electrode 22b has the lowest catalytic ability and has an oxidation catalytic activity for hydrogen and carbon monoxide, but has no catalytic activity for hydrocarbons. The methane-insensitive electrode 22c is an electrode having the second lowest catalytic activity and has an oxidation catalytic activity for hydrogen, carbon monoxide and hydrocarbons (excluding methane), but has no catalytic activity for methane. . Hydrocarbon sensitive electrode 22
d has the highest oxidation catalytic activity and has oxidation catalytic activity on hydrogen, carbon monoxide and all hydrocarbons.

The three electrodes 22b, 22c, 22d
Are formed on the basis of platinum, but for the hydrocarbon-insensitive electrode 22b and the methane-insensitive electrode 22c, lead and gold which reduce or inactivate the hydrocarbon oxidation catalytic activity in the platinum paste at the raw material stage. The hydrocarbon gas sensor 4 can be realized by baking the hydrocarbon gas sensor 4 by blending metals such as silver, nickel, and the like at different blending ratios, and thereafter volatilizing by heat treatment or hydrogen gas treatment. The hydrocarbon sensitive electrode 22d is formed using a platinum paste as it is.

Of the electrodes provided in the hydrocarbon gas sensor 4 formed by lamination as described above, the measurement electrode 20
c is supplied with the adjusted current from the current supply circuit 6,
The current flows between the measurement electrode 20c and the reference electrode 20d. The amount of current flowing by the current supply circuit 6 is detected by the current detection circuit 8.

3 different oxidation catalyst activities for hydrocarbons
The electromotive force generated between the two electrodes 22b to 22d and the reference electrode 22e includes a first electromotive force detection circuit 12 for the hydrocarbon insensitive electrode 22b, a second electromotive force detection circuit 14 for the methane insensitive electrode 22c, and The third electromotive force detection circuit 16 detects the hydrocarbon-sensitive electrode 22d.

Electric power is supplied to the heater wire 24b from the heating circuit 10 to generate heat, thereby raising the temperature of the entire hydrocarbon gas sensor 4 to a measurable temperature. The ECU 18 includes a central processing controller (CPU) 18a, a read-only memory (ROM) 18b in which a program and a map of a concentration measurement process for each kind of flammable gas, which will be described later, are stored in advance, and a random access for temporarily storing calculation results of the CPU 18a. Memory (RAM) 1
8c, a backup RAM 18d for storing previously stored data and the like, and an input circuit 18e.
And an output circuit 18f. In addition, each part 1
8a to 18f are connected by a bus 18g.

The ECU 18 outputs a signal from the output circuit 18f to the current supply circuit 6, adjusts a current flowing between the measurement electrode 20c and the reference electrode 20d, and further receives a detection signal from the current detection circuit 8 as an input. Input via circuit 18e,
The amount of current flowing between the measurement electrode 20c and the reference electrode 20d is adjusted and monitored.

The ECU 18 also controls the hydrocarbon-insensitive electrode 22 b and the reference electrode 2 via the first electromotive force detection circuit 12.
2e is detected, and the second electromotive force detection circuit 14
To detect the electromotive force between the methane-insensitive electrode 22c and the reference electrode 22e through the third electromotive force detection circuit 16
To detect the electromotive force between the hydrocarbon-sensitive electrode 22d and the reference electrode 22e.

The concentration measuring process for each kind of combustible gas performed by the ECU 18 in the above configuration will be described. The contents are shown in the flowcharts of FIGS.
Steps in the flowchart corresponding to each process are represented by “SＳ”.

When the power is turned on, the concentration measurement process for each kind of flammable gas is started after the initial setting necessary for the ECU 18. First, a heating signal is output to the heating circuit 10 to energize the heater wire 24b to generate heat (S110). Next, it is determined whether the temperature has risen to a temperature at which the hydrocarbon gas sensor 4 is activated (S120). For example, if the hydrocarbon gas sensor 4 is activated at 700 ° C., it is determined whether the temperature of the hydrocarbon gas sensor 4 has risen to 700 ° C. or more, for example, by determining whether the resistance value of the heater wire 24b corresponds to 700 ° C. The determination is made based on whether the value has been reached.

During the period when the temperature rise is not sufficient, (N
O "), and wait as it is. If it is determined that the temperature has been sufficiently raised ("YES" in S120), then the electromotive force of one of the hydrocarbon identification electrodes 22b to 22d, for example, the reference voltage between the hydrocarbon-sensitive electrode 22d and the reference electrode 22d is determined. Electrode 2
2e is detected by the measurement of the third electromotive force detection circuit 16 (S130).

At this time, since the current supply circuit 6 is not operated, the pumping cell 20 is not operated. Therefore, the inside of the measurement chamber 4a is filled with exhaust gas diffused from the external measured space, here, the inside of the exhaust pipe of the internal combustion engine via the porous body 32 and the diffusion limiting hole 20b. On the other hand, the atmosphere is introduced into the atmosphere chamber 4b as a gas having a reference oxygen concentration. Therefore, the electromotive force Vi behaves as indicated by the solid line in FIG. 6 according to the air-fuel ratio of the internal combustion engine.

Since the hydrocarbon-sensitive electrode 22d has an oxidation catalytic activity for all hydrocarbons including hydrogen, carbon monoxide, and methane, the air-fuel ratio is higher than the stoichiometric air-fuel ratio (hereinafter referred to as stoichiometric ratio). (Hereinafter referred to as rich)
When the combustion is performed in the exhaust gas, a very small amount of oxygen remaining in the exhaust gas is almost completely burned by the hydrocarbon-sensitive electrode 22d itself by the entire hydrocarbon containing hydrogen, carbon monoxide, and methane in the exhaust gas. Consume it. For this reason, it rises sharply at the boundary of the air-fuel ratio (hereinafter, referred to as lean) in which the fuel is thinner than the stoichiometric ratio, and exhibits an extremely high electromotive force as compared with the lean region. In addition, the behavior shown by the broken line in FIG. 6 is a case where the electrode does not show any oxidation catalytic activity. Since the electrode itself does not burn oxygen, an electromotive force behavior with little change corresponding to the difference in oxygen concentration is shown. It is.

Therefore, the hydrocarbon-sensitive electrode 22d
By detecting the electromotive force Vi, it is possible to sensitively detect a rich state containing hydrogen, carbon monoxide, hydrocarbons and the like in the exhaust gas. That is, in the present process, it is determined whether or not the exhaust gas contains hydrogen, carbon monoxide, hydrocarbons, and the like (rich state) based on the electromotive force Vi, based on whether or not the determination voltage V0 or higher has been reached (S140) ). As the determination voltage V0, a value substantially at the center of the rising portion in FIG. 6 is used, and differs depending on the element. For example, a value of 0.40 to 0.50 V is used.

Here, if Vi <V0 ("NO" in S140), the subsequent processing is not performed and step S13 is performed again.
0, the operation of the pumping cell 20 is stopped, the electromotive force Vi of the hydrocarbon-sensitive electrode 22d is detected (S130), and it is determined whether Vi ≧ V0 (S1).
Repeat step 40).

A combustible gas such as hydrogen, carbon monoxide, or hydrocarbon appears in the exhaust gas, and when Vi ≧ V0 ("YES" in S140), the current supply circuit 6 is driven, and the pumping cell 20 reference electrodes 20d to measurement electrodes 20c
Then, a pumping current is slightly applied (S150). The amount of pumping current Ip flowing between the measurement electrode 20c and the reference electrode 20d is precisely detected by the current detection circuit 8, and is precisely adjusted by feedback control. As a result, only oxygen is forcibly pumped into the measurement chamber 4a from the exhaust side flowing through the exhaust pipe through the pumping cell 20.

Next, the electromotive force V1 of the hydrocarbon insensitive electrode 22b is detected by the measurement of the first electromotive force detection circuit 12 (S160). The electromotive force V1 is equal to the reference voltage Vs
Is determined (S170). Reference voltage V
As s, for example, a value of 0.40 V to 0.50 V is used.

If the electromotive force V1 is not within the range of the reference voltage Vs ("NO" in S170), the pumping current amount Ip is further increased (S150), and the electromotive force V1 of the hydrocarbon insensitive electrode 22b is measured. (S160), and determines whether the electromotive force V1 has reached the reference voltage Vs (S170).
repeat.

Assuming that hydrogen, carbon monoxide, methane, and hydrocarbons other than methane (for example, propane) are all present in the exhaust gas, the oxygen concentration in the measurement chamber 4a is reduced by increasing the pumping current Ip. Fig. 7
As shown in (1), the electromotive force V1 in the hydrocarbon insensitive electrode 22b rapidly decreases at the pumping current amount Ip1, and the electromotive force V1 becomes the reference voltage Vs ("YES" in S170).

This is the same as the phenomenon described with reference to FIG. 6, and the measuring chamber 4 having increased in proportion to the amount of pumping current Ip.
This indicates that the oxygen concentration in a became stoichiometric with respect to hydrogen and carbon monoxide in the measurement chamber 4a. That is, the hydrocarbon-insensitive electrode 22b includes, among the components,
Since only hydrogen and carbon monoxide can be oxidized, it indicates that an oxygen concentration state is reached in which all of hydrogen and carbon monoxide are burned at the hydrocarbon insensitive electrode 22b.

Therefore, in step S170, "YE
S ”, the pumping current amount Ip (= Ip
1) indicates a value corresponding to the concentration of hydrogen and carbon monoxide.
It is stored in a variable I1 set in the AM 18c (S
180).

Next, the pumping current amount Ip is gradually increased (S190). And the methane insensitive electrode 22c
Is measured (S200), and it is determined whether the electromotive force V2 has reached the reference voltage Vs (S210). V
As long as 2> Vs, steps S190, S200, S
210, and gradually the pumping current amount Ip
Increase.

Also in this case, when the oxygen concentration in the measurement chamber 4a is increased by increasing the amount of pumping current Ip, as shown in FIG. 8, the electromotive force V2 at the methane insensitive electrode 22c rapidly increases at the amount of pumping current Ip2. The electromotive force V2 drops to the reference voltage Vs ("YE" in S210).
S ").

This means that the oxygen concentration in the measuring chamber 4a which increased in proportion to the pumping current Ip became stoichiometric with respect to hydrogen, carbon monoxide and hydrocarbons other than methane in the measuring chamber 4a. Is shown. That is, since the methane-insensitive electrode 22c can oxidize hydrogen, carbon monoxide, and hydrocarbons other than methane, all of the hydrogen, carbon monoxide, and hydrocarbons other than methane burn at the methane-insensitive electrode 22c. This indicates that the oxygen concentration state reached.

Therefore, in step S210, "YE
S ”, the pumping current amount Ip (= Ip
Since 2) indicates a value corresponding to the concentration of hydrocarbons other than hydrogen, carbon monoxide, and methane, the pumping current amount Ip at this time is stored in the variable I2 set in the RAM 18c (S220). ).

Next, the pumping current amount Ip is gradually increased (S230). Then, the electromotive force V3 of the hydrocarbon-sensitive electrode 22d is measured (S240), and it is determined whether or not the electromotive force V3 has reached the reference voltage Vs (S250). V3>
As long as it is Vs, steps S230, S240, S25
The process of 0 is repeated, and the pumping current amount Ip is gradually increased.

Also in this case, when the oxygen concentration in the measurement chamber 4a is increased by increasing the pumping current Ip, as shown in FIG. 9, the electromotive force V3 at the hydrocarbon-sensitive electrode 22d is rapidly increased at the pumping current Ip3. The electromotive force V3 decreases to the reference voltage Vs ("YE" in S250).
S ").

This indicates that the oxygen concentration in the measuring chamber 4a which increased in proportion to the pumping current Ip became stoichiometric with respect to hydrogen, carbon monoxide and all hydrocarbons in the measuring chamber 4a. I have. That is, since the hydrocarbon-sensitive electrode 22d can oxidize hydrogen, carbon monoxide, and all hydrocarbons, the oxygen concentration at which all of hydrogen, carbon monoxide, and all hydrocarbons are burned at the hydrocarbon-sensitive electrode 22d. Indicates that the state has been reached.

Therefore, in step S250, "YE
S ”, the pumping current amount Ip (= Ip
Since 3) indicates a value corresponding to the concentrations of hydrogen, carbon monoxide and total hydrocarbons, the pumping current Ip at this time is stored in a variable I3 set in the RAM 18c (S260).

Then, the pumping current amount Ip is returned to zero (S270), and the measuring chamber 4a by the pumping cell 20 is returned.
Stop pumping oxygen into the system. In this way, the pumping current amounts corresponding to all hydrocarbons, methane and hydrocarbons other than methane are obtained from the detected pumping current amounts I1, I2 and I3.

Here, the three electrodes 22b, 22c, 22
pumping current amounts I1, I2, and
The relationship between I3 and the exhaust component is as shown in FIG.
In the figure, A corresponds to the hydrocarbon-insensitive electrode 22b, B corresponds to the methane-insensitive electrode 22c, and C corresponds to the hydrocarbon-sensitive electrode 22d.

Therefore, first, based on the pumping current I1 at the hydrocarbon-insensitive electrode 22b and the pumping current I3 at the hydrocarbon-sensitive electrode 22d, the pumping current corresponding to the total hydrocarbon concentration THC is calculated by the following equation (1). The amount △ ITHC is calculated (S280).

[0062]

## EQU1 ## Next, based on the pumping current I2 at the methane-insensitive electrode 22c and the pumping current I3 at the hydrocarbon-sensitive electrode 22d, as shown in the following equation 2, A pumping current amount △ IMT corresponding to the methane gas concentration MT is calculated (S290).

[0063]

ΔIMT = I3−I2 (Expression 2) Next, based on the pumping current I1 at the hydrocarbon-insensitive electrode 22b and the pumping current I2 at the methane-insensitive electrode 22c, the following formula 3 is used. Then, a pumping current amount △ INMHC corresponding to the hydrocarbon gas concentration NMHC excluding methane is calculated (S300).

[0064]

## EQU3 ## Next, the amount of pumping current for each component obtained as described above is calculated as follows.
Each component concentration is obtained from the table showing the relationship between the current amount and the component concentration shown in FIG.

That is, the total hydrocarbon gas concentration THC is calculated based on the table FTHC (S310), and the methane gas concentration MT is calculated based on the table FMT (S32).
0), the hydrocarbon gas concentration NMHC excluding methane is calculated based on the table FNMHC (S330).

These concentrations THC, MT and NMHC are R
When stored in the AM 18c or the backup RAM 18d and used as data for controlling the internal combustion engine or data for failure diagnosis, or when the ECU 18 is communicating with another ECU, the ECU 18 performs processing for another ECU. It is transmitted to the ECU.

Thereafter, the process returns to the process of step S130, and the process is started from the above-described determination of the electromotive force of the hydrocarbon-sensitive electrode 22d. Thus, the concentrations of all hydrocarbons, methane, and hydrocarbons other than methane in the exhaust gas can be detected in real time.

The pumping cell 2 of the first embodiment described above
0 corresponds to oxygen pumping means, the detection cell 22 corresponds to a concentration cell, the electrodes 22b, 22c, 22d correspond to a plurality of first electrodes, the reference electrode 22e corresponds to a second electrode,
The current supply circuit 6 corresponds to oxygen pumping amount control means,
The first electromotive force detection circuit 12, the second electromotive force detection circuit 14, and the third electromotive force detection circuit 16 correspond to concentration cell voltage detection means, and the processing of steps S150 to S260 in the current detection circuit 8 and the ECU 18 measures the current value. Steps S280 to S330 correspond to processing as concentration measuring means, the processing of the third electromotive force detection circuit 16 and step S130 corresponds to flammable gas measuring means and processing thereof, and step S140. Corresponds to the processing as the concentration measurement execution means.

According to the embodiment described above, the following effects can be obtained. (I). In the hydrocarbon gas sensor 4, three types of electrodes 22b, 22c, and 22d having three types of oxidation catalytic activity for combustible gas are arranged in a single measurement chamber 4a for a concentration cell. And the reference electrode 22e are oxygen concentration cells, the methane-insensitive electrode 22c and the reference electrode 22e are oxygen concentration cells, and the hydrocarbon-sensitive electrode 22d and the reference electrode 2e.
In the case where 2e is an oxygen concentration battery, three types of current values can be obtained by measuring the current values in the pumping cells 20 respectively.

Thus, the concentration of flammable gas, methane, hydrocarbons other than methane, and total hydrocarbons can be measured from the difference between these current values. (B). In addition, the electrodes 22b, 22c, and 22d having different oxidation catalyst activities for the combustible gas are all present in one measurement chamber 4a. From this, the diffusion of the gas to be measured into the measurement chamber 4a is prevented by any of the electrodes 22b, 22c, and 22d.
Also in the measurement of the diffusion limiting hole 20b up to the measurement chamber 4a.
And the shape of the diffusion path including the porous body 32, the shape and arrangement of the measurement chamber 4a, and the atmospheric conditions such as the temperature can be completely matched, and the diffusion state can be completely matched.
Therefore, the error factor can be completely eliminated by calculation for calculating the difference between the current values, and an accurate methane concentration, a hydrocarbon concentration other than methane, and a total hydrocarbon concentration can be obtained.

(C). Before the concentration measurement processing in steps S150 to S330, the presence of the combustible gas is checked only by the electromotive force of the detection cell 22 without operating the pumping cell 20, and it is determined that the combustible gas is present.
Move on to accurate concentration measurement processing.

Therefore, if the flammable gas to be measured does not exist in the exhaust gas, it is not necessary to perform the concentration measurement processing in steps S150 to S330, which takes longer time than the detection of the electromotive force in the detection cell 22. For this reason, the ECU 1
8 is allocated to other processing, the ECU 18
Process can be accelerated, and unnecessary electric energy is not consumed.

[Other Embodiments] In the above embodiment, the supply of oxygen to the measurement chamber 4a by the pumping cell 20 is performed from the exhaust side, but a necessary amount of oxygen is pumped into the measurement chamber 4a. Since the pumping cell may be inserted, a pumping cell may be provided between the atmosphere side and the measurement chamber 4a, and oxygen may be pumped into the measurement chamber 4a from the atmosphere side.

In the above-described embodiment, the pumping current is continuously increased while the electromotive force is sequentially detected from the hydrocarbon-insensitive electrode 22b, the methane-insensitive electrode 22c, and the hydrocarbon-sensitive electrode 22d. Alternatively, the pumping current may be continuously reduced and measured while detecting the electromotive force to the hydrocarbon-sensitive electrode 22d, the methane-insensitive electrode 22c, and the hydrocarbon-insensitive electrode 22b.

Further, since it is only necessary to detect that the electromotive force has reached the reference voltage Vs, the order of measuring the electromotive force of the electrodes 22b to 22d can be determined arbitrarily by adjusting the pumping current appropriately. it can.

In the measurement of the electromotive force of each of the electrodes 22b to 22d, the pumping current may be increased from 0 or may be decreased from an excessively large pumping current each time the electrode to be measured is changed.

In the above embodiment, the total hydrocarbon concentration, the concentration of hydrocarbons other than methane, and the methane gas concentration were individually measured and calculated. Of these, two were measured and calculated. The other one may be obtained by calculation from the difference between the two densities.

In the above-described embodiment, the total hydrocarbon concentration, the concentration of hydrocarbons other than methane, and the concentration of methane gas are determined. Further, the concentration of the hydrocarbon is determined from the current value obtained based on the electromotive force of the hydrocarbon-insensitive electrode 22b. Combustible components (H2 and CO) other than hydrocarbons may be determined.

In the processing of steps S130 and S140 for determining whether or not a combustible gas is present in the exhaust gas, the electromotive force at the hydrocarbon-sensitive electrode 22d is referred to. Alternatively, the electromotive force at the methane-insensitive electrode 22c may be used.

Also, in the processing of steps S130 and S140, referring to all three electrodes 22b, 22c and 22d, if any one of the electromotive forces is equal to or higher than the determination voltage V0, the processing from step S150 is executed. You may make it.

[0081]

According to the flammable gas sensor of the present invention, at least two types of first electrodes having at least two types of oxidizing catalytic activities for flammable gas are arranged in one measuring chamber. The first electrode and the second electrode are used as oxygen concentration cells, and the current value of the oxygen pumping means is measured. By measuring the current value of the pumping means, two or more types of current values are obtained, and if the difference between them is obtained, the concentration of each combustible gas can be measured. Moreover, since all the first electrodes having different oxidation catalytic activities for the flammable gas are present in one measurement chamber, the diffusion of the gas to be measured into the measurement chamber is limited to the measurement chamber even when any of the first electrodes is used. The shape of the diffusion path including the gas diffusion restrictor, the shape and arrangement of the measurement chamber,
The temperature and the like can be completely matched. Therefore, the diffusion states can be completely matched. Therefore,
In calculating the difference between the current values of the oxygen pumping means, it is possible to completely eliminate error factors caused by the atmospheric conditions, and to obtain an accurate flammable gas concentration.

In the flammable gas sensor according to claim 2,
Since the combustible gas to be measured is a hydrocarbon, the concentration of the hydrocarbon can be accurately measured. 4. The flammable gas sensor according to claim 3, wherein the plurality of first electrodes of the concentration cell include an electrode having no catalytic activity for oxidizing hydrocarbons, an electrode having catalytic activity for oxidizing hydrocarbons other than methane, and a carbon containing methane. An electrode having oxidation catalytic activity for hydrogen is provided. in this way,
Accurately determine one or more of the concentrations of combustible gases other than hydrocarbons, the concentration of methane, the concentration of hydrocarbons other than methane, and the concentration of total hydrocarbons by using three types of first electrodes Can be.

In the flammable gas concentration measuring device according to claim 4, the current value measuring means changes the current value for the oxygen pumping means by the oxygen pumping amount control means for each type of oxidation catalyst activity, and The current value when the electromotive force detected by the battery voltage detection means falls within the reference voltage range is measured. Thus, a current value is obtained for each type of oxidation catalyst activity in the first electrode. Then, based on the difference between the current values corresponding to the type of the oxidation catalyst activity measured by the current value measuring means, the concentration of each combustible gas is measured. The flammable gas concentration measuring device uses a flammable gas sensor in which all the first electrodes having different oxidation catalyst activities for flammable gas are present in one measurement chamber, and therefore calculates a difference between measured current values. In addition, since the first electrodes are all in the same atmosphere, the measurement error is offset, and the concentration of each combustible gas can be accurately measured.

According to a fifth aspect of the present invention, there is provided an apparatus for measuring the concentration of a flammable gas before operating the oxygen pumping amount control means, the current value measuring means and the concentration measuring means to determine the concentration of the flammable gas. The measurement means obtains the presence of the combustible gas by the electromotive force of the concentration cell, and if the value of the electromotive force indicates the presence of the combustible gas, the concentration measurement execution means controls the oxygen pumping amount control means, The value measuring means and the concentration measuring means are operated to determine the concentration of the combustible gas. Therefore, if the concentration cell determines that there is no flammable gas, the flammable gas generated by the operation of the oxygen pumping amount control means, the current value measurement means, and the concentration measurement means takes longer time than the detection of only the electromotive force of the concentration cell. It is not necessary to perform the process of measuring the concentration of the reactive gas. For this reason, the functions of the electronic circuit for operating the oxygen pumping amount control means, the current value measurement means, and the concentration measurement means are allocated to other processing, so that the entire processing is speeded up, or unnecessary electric energy is not consumed. I'm done.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a combustible gas concentration measuring device as one embodiment.

FIG. 2 is a development view of a hydrocarbon gas sensor incorporated in the combustible gas concentration measuring device.

FIG. 3 is a flowchart of a combustible gas type concentration measurement process performed by the combustible gas concentration measuring device.

FIG. 4 is a flowchart of a combustible gas type concentration measurement process performed by the combustible gas concentration measuring device.

FIG. 5 is a flowchart of a combustible gas type concentration measurement process performed by the combustible gas concentration measuring device.

FIG. 6 is a graph showing an electromotive force generated in a concentration cell according to an air-fuel ratio of an internal combustion engine.

FIG. 7 is a graph showing an electromotive force generated in a hydrocarbon-insensitive electrode according to a pumping current amount Ip.

FIG. 8 is a graph showing an electromotive force generated in a methane-insensitive electrode according to a pumping current amount Ip.

FIG. 9 is a graph showing an electromotive force generated in a hydrocarbon-sensitive electrode according to a pumping current amount Ip.

FIG. 10 is a graph showing a relationship between pumping current amounts I1, I2, and I3 obtained for three electrodes having different sensitivities and exhaust components.

FIG. 11 is an explanatory table showing a relationship between a current amount and a component concentration.

[Explanation of symbols]

2 ... combustible gas concentration measurement device, 4 ... hydrocarbon gas sensor, 4a ... measurement room, 4b ... atmosphere room, 6 ... current supply circuit,
8 current detection circuit, 10 heating circuit, 12 first electromotive force detection circuit, 14 second electromotive force detection circuit, 16 third electromotive force detection circuit, 18 electronic control unit (ECU), 18
a: central processing controller (CPU), 18b: read-only memory (ROM), 18c: random access memory (R)
AM), 18d: backup RAM, 18e: input circuit, 18f: output circuit, 18g: bus, 20: pumping cell, 20a: solid electrolyte plate, 20b: diffusion limiting hole, 20c: measuring electrode, 20d: reference Electrode, 20e,
20f: Lead portion, 22: Detection cell, 22a: Solid electrolyte plate, 22b: Hydrocarbon insensitive electrode, 22c ...
Methane-insensitive electrode, 22d ... hydrocarbon-sensitive electrode, 2
2e: Reference electrode, 22f, 22g, 22h, 22i: Lead, 24: Heater, 24a: Plate, 24b: Heater wire, 24c, 24d: Lead, 26: Spacer, 2
6a: rectangular hole, 28: spacer, 28a: rectangular hole, 28
b: gas passage, 30: spacer, 32: porous body.

Claims (5)

[Claims] A measuring chamber capable of exchanging gas with a space to be measured via a gas diffusion limiting section; an oxygen pumping means for pumping an amount of oxygen corresponding to a current value into the measuring chamber; A concentration cell comprising: a plurality of first electrodes; and a second electrode disposed in the reference oxygen concentration space, wherein the concentration cell generates an electromotive force corresponding to an oxygen concentration difference between the first electrode and the second electrode. The combustible gas sensor, comprising: a plurality of first electrodes of the concentration cell, wherein at least two types of the first electrodes exist in an oxidation catalytic activity for a combustible gas. 2. The flammable gas sensor according to claim 1, wherein the flammable gas is a hydrocarbon. 3. The plurality of first electrodes of the concentration cell include an electrode having no oxidation catalytic activity for hydrocarbons, an electrode having an oxidation catalytic activity for hydrocarbons other than methane, and an oxidation catalytic activity for hydrocarbons containing methane. 3. The flammable gas sensor according to claim 2, further comprising an electrode. 4. A flammable gas concentration measurement device using the flammable gas sensor according to claim 1, wherein: an oxygen pumping amount control unit that adjusts a current value to the oxygen pumping unit; Concentration cell voltage detecting means for detecting an electromotive force between the first electrode and the second electrode of the concentration cell for each type of oxidation catalyst activity; and controlling the oxygen pumping amount for each type of oxidation catalyst activity. Current value measuring means for changing the current value for the oxygen pumping means by means, and measuring the current value when the electromotive force detected by the concentration cell voltage detecting means is within a reference voltage range; Concentration measuring means for measuring the concentration of each combustible gas based on the difference between the current values corresponding to the type of the oxidation catalyst activity measured by the current value measuring means. When That the combustible gas concentration measuring device. 5. The method according to claim 4, wherein the adjustment of the current value to the oxygen pumping means by the oxygen pumping amount control means is stopped, and any of the starting values detected by the concentration cell voltage detecting means is stopped. Flammable gas measuring means for measuring the presence of flammable gas from electric power, when the presence of flammable gas is measured by the flammable gas measuring means, the oxygen pumping amount control means, the current value measuring means and A combustible gas concentration measurement device, comprising: a concentration measurement execution unit for causing the concentration measurement unit to operate.