JP3372186B2 - Gas sensor correction method and gas concentration measurement system - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a gas sensor,
In particular, NO _{x in} exhaust gas of internal combustion engines for transportation of automobiles, ships, airplanes, etc., or in combustion gas of boilers, etc.
It relates NO _x gas sensors used to detect the gas concentration.

[0002]

2. Description of the Related Art In recent years, as exhaust gas regulations have been tightened, research has been conducted to directly measure NO _x in exhaust gas from engines and the like to control the engine and the catalyst. In particular, an oxygen ion conductor such as ZrO ₂ is used to pump oxygen to the extent that NO _x is not decomposed in the first oxygen ion pump cell, and the remaining gas containing NO _x is further pumped in the second oxygen ion pump cell. The NO _x gas sensor (concentration detector) that decomposes NO _x by releasing it and detects this decomposition as an electric current is not affected by interfering gases such as HC and CO.
Since the O _x gas concentration can be measured, it has been widely studied in recent years.

[0003]

However, according to the knowledge of the present inventor, when water is present in the gas to be measured, the water is electrolyzed and the second oxygen ion pump cell is
It has been found that there is a problem that the NO _x concentration cannot be accurately measured because not only NO _x but also an electric current caused by oxygen generated as a result of electrolysis of water flows. In particular, in lean-burn engines for gasoline and diesel engines, which have been increasing in recent years, the amount of water in the exhaust gas changes greatly depending on the operating conditions, so it is difficult to accurately measure the NO _x concentration in the exhaust gas. Do you get it.

In view of the above circumstances, the present invention is a method for correcting a gas sensor and a gas concentration measuring system capable of obtaining an accurate gas concentration by reducing or eliminating the influence of the amount of water in the gas to be measured on the gas concentration detection. The purpose is to provide.

[0005]

In the engine, there is a correlation between the excess air ratio or A / F (= oxygen concentration in the exhaust gas) and the water content in the exhaust gas, depending on the fuel used. Therefore, the present inventors have previously measured the influence of water content on the gas concentration detected by the gas sensor, and for example, the relation between the excess air ratio or the A / F value and the correction data of the concentration detected by the gas sensor. Is stored in the memory as a map, and at the time of measurement, predetermined correction data is read from the map according to the excess air ratio or A / F value determined by the operating conditions, and the detection output of the gas sensor is based on the read estimated water content. by correcting the signals, we found that it is possible to obtain a predetermined gas concentration in the correct in the exhaust gas (e.g., NO _x gas concentration).

Further, the inventors of the present invention can measure the oxygen concentration in the exhaust gas from the current value of the first oxygen ion pump cell in the gas sensor of the type using two sets of oxygen ion pump cells. Since there is a correlation with the amount of water in the inside, a correction coefficient corresponding to the current value flowing in the first oxygen ion pump cell is previously input to the memory, and a map associating this current value with the correction coefficient is prepared. Every time the gas concentration is measured, the predetermined correction coefficient in the map is read according to the current value of the first oxygen ion pump cell, and the second correction coefficient is read.
By correcting the current value of the oxygen ion pump cell,
It was also found that the influence of water can be removed to obtain an accurate gas concentration measurement. In this case, it was also found that it is possible to electrically correct the output signal of the first oxygen ion pump cell on an analog circuit without having a map in the memory. The present inventors have completed the present invention based on these findings.

In order to achieve the above object, the gas sensor correction method of the present invention is, in the first aspect, a method for detecting a predetermined gas concentration in exhaust gas of an engine, wherein an excess air amount determined by operating conditions of the engine is used. The amount of water in the exhaust gas is estimated from the rate or A / F value, and the gas concentration output signal of the gas sensor is corrected by correcting the gas concentration detection signal output by the gas sensor according to the estimated amount of water.
From the gas concentration value obtained from the concentration detection signal
And removing or reducing the influence of water content in the exhaust gas.

The second viewpoint is the same as the first viewpoint.
Preferably, the gas sensor is a NO _x sensor, the third
In the first aspect, the gas sensor is more preferably a sensor using an oxygen ion pumping action of a solid electrolyte.

A fourth viewpoint is based on the first viewpoint,
It is estimated that the ratio of air to fuel supplied to the engine corresponds to the amount of water in the exhaust gas, and based on the ratio, the gas concentration detection signal and the true gas concentration value, the gas concentration corresponding to the ratio. A map including correction data of the detection signal is prepared in advance, predetermined correction data corresponding to the ratio determined by the operating condition of the engine is read from the map, and the gas concentration detection signal is corrected by the read correction data. Is characterized by.

A fifth aspect has two sets of oxygen ion pump cells of solid electrolyte, and a predetermined voltage is applied to the first oxygen ion pump cell so that NO _x does not decompose oxygen in the gas to be measured. Sufficiently pumped out, a current according to the oxygen concentration in the gas to be measured flows through the first oxygen ion pump cell, and NO _{x in} the gas left unpumped by the second oxygen ion pump cell.
Decomposing, pumping out dissociated oxygen, current corresponding to the NO _x gas concentration in the second oxygen ion pump cell flows NO _x
In the sensor, the NO _x gas concentration detection signal corresponding to the current value obtained from the second oxygen ion pump cell is corrected according to the signal corresponding to the current value obtained from the first oxygen ion pump cell, It is characterized in that the influence of the amount of water in the gas to be measured is removed or reduced from the NO _x gas concentration obtained based on the NO _x gas concentration detection signal.

A sixth viewpoint is based on the fifth viewpoint,
The current value of the first oxygen ion pump cell is estimated to correspond to the amount of water in the measured gas, the current value of the first oxygen ion pump cell, the current value obtained from the second oxygen ion pump cell, and Based on the true NO _x gas concentration,
The N corresponding to the current value of the first oxygen ion pump cell
A map including correction data for the O _x gas concentration detection signal is prepared in advance, predetermined correction data corresponding to the current value of the first oxygen ion pump cell is read from the map, and the NO _x is read according to the read correction data. It is characterized in that the gas concentration detection signal is corrected.

Further, the gas concentration measuring system of the present invention is
A gas sensor that detects a specified gas concentration in the exhaust gas of an engine.
And excess air determined by the operating conditions of the engine
Rate Estimate the amount of water in the exhaust gas from the R / A value
The gas sensor output according to the estimated water content.
Gas sensor by correcting the gas concentration detection signal
Concentration obtained from the gas concentration detection signal output by
From the value of
And a controller.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION First, a NO _x gas sensor (concentration detector) according to an embodiment of the present invention, which is provided with two sets of diffusion resistance sections, oxygen ion pump cells, and measurement chambers, respectively.
The measurement principle in will be described. 1 to 3 are diagrams for explaining the principle of NO _x gas concentration measurement, FIG. 1 is a cross-sectional view shown by hatching in FIG. 2, and FIG. 3 is a second measurement chamber pump current (second oxygen ion pump current). is a graph showing the relationship of the NO _x gas concentration. The measurement principle is as follows.

(1) Exhaust gas flows into the first measurement chamber 2 through the first diffusion hole 1 having diffusion resistance. (2) By the first oxygen ion pump cell 6, the first measurement chamber 2
Oxygen is pumped out to the extent that NO _x is not decomposed (the oxygen partial pressure in the first measurement chamber 2 is controlled by the signal output from the oxygen partial pressure detection electrode (oxygen concentration measurement cell 7)). (3) The gas in the first measurement chamber 2 (concentration-controlled 0 ₂ gas + NO _x gas) passes through the second diffusion hole 3 having diffusion resistance
It flows into the measurement chamber 4. (4) The NO _x gas in the second measurement chamber 4 is further pumped out with oxygen by the second oxygen ion pump cell 8 to generate N ₂ +.
It decomposes to O ₂ . (5) At this time, since there is a linear relationship between the second oxygen ion pump current Ip2 flowing through the second oxygen ion pump cell 8 and the NO _x gas concentration (see FIG. 3), NO _x can be detected by detecting Ip2. The gas concentration can be detected.

In the NO _x gas concentration measuring method which is measured based on such a principle, when water is present in the gas to be measured, the sensitivity (gain) is not affected, but the offset changes depending on the amount of water. Therefore, since the second oxygen ion pump current value (second measurement chamber pump current value) depends on the amount of water in the gas to be measured, it becomes impossible to accurately measure the NO _x gas concentration (see FIG. 3). Therefore, according to the present invention, the NO _x gas concentration can be accurately measured by correcting the second oxygen ion pump current value (detection signal) based on the water content or the value corresponding to the water content.

Next, a preferred form of the NO _x gas sensor to which the output correcting method for the gas sensor according to the embodiment of the present invention is applied will be described. Preferably, the second measurement chamber is provided between the solid electrolyte layer provided with the pair of electrodes of the second oxygen ion pump cell and the solid electrolyte layer (oxygen concentration measurement cell) provided with the oxygen partial pressure detection electrode. Set up.

The preferred NO _x gas sensor is the first
The oxygen ion pump cell 6, the oxygen concentration measuring cell 7, and the second oxygen ion pump cell 8 are all provided in different solid electrolyte layers (see FIG. 1).
As a result, the leak current flowing between the electrodes of each cell is reduced, and the oxygen concentration in the first measurement chamber can be controlled accurately. More preferably, an insulating film such as alumina or an insulating layer is provided between the cells.

Also, preferably, a heater layer for heating the detector is laminated between the laminated solid electrolyte layers. By providing the heater layer, the first and second oxygen ion pumping capacities can be stabilized.

As the solid electrolyte of each cell, a solid solution of zirconia and yttria, a solid solution of zirconia and calcia, or the like is used. As a porous electrode formed by a method such as screen printing and sintering on both surfaces of the thin plate-like solid electrolyte layer, platinum, rhodium, palladium, rhenium, iridium, or an alloy thereof having a catalytic action is used. Preference is given to using. It is preferable to use porous ceramics as the first and second diffusion holes, for example, porous alumina ceramics.
It is preferable that the heating portion of the heater is made of a composite material of ceramics and platinum or a platinum alloy, and the lead portion is made of platinum or a platinum alloy.

The detector of the present invention can be applied to the concentration detection of CO gas, CO ₂ gas and HC gas, and NO _x
Similar to the case of detecting the gas concentration, the influence of the oxygen concentration is reduced and the target gas concentration can be measured accurately.

Other preferable features are as described in Japanese Patent Application No. 8-160812 and Japanese Patent Application No. 8-337483 by the present applicant, and if necessary, these applications will be referred to in the present application. It can be crowded.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 4 is a diagram for explaining the lateral direction of the cross-sectional view and schematic of a control system of the NO _x gas sensor correction method is preferably applied of the NO _x gas sensor according to an embodiment of the present invention, FIG. 5 is a perspective view showing a cross section of the sensor shown in FIG. 4 cut in the longitudinal direction.

The sensor shown in FIGS. 4 and 5 comprises a first oxygen ion pump cell 6 provided with a pair of electrodes 6a and 6b provided with a solid electrolyte layer sandwiched therebetween, and a pair provided with a solid electrolyte layer sandwiched therebetween. The oxygen concentration measuring cell 7 including the oxygen partial pressure detecting electrodes 7a and 7b, and the second oxygen ion pump cell 8 including the pair of electrodes 8a and 8b that sandwich the solid electrolyte layer are laminated in this order, and each solid Insulating layers are formed between the electrolyte layers. The first measurement chamber 2 is defined by the insulating layer and the solid electrolyte layer between the first oxygen ion pump cell 6 and the oxygen concentration measuring cell 7, and the second oxygen ion is similarly formed by the insulating layer and the solid electrolyte layer. The second measurement chamber 4 is defined above the pump cell 8 (see FIG. 4). Further, a plurality of first diffusion holes 1 having a diffusion resistance are provided on the wall surface surrounding the first measurement chamber 2 (see FIG. 6), and the opening of the second diffusion hole 3 is formed at the center of the first measurement chamber 2. 1 diffusion hole 1
And are separated from each other. The second diffusion hole 3 penetrates the oxygen concentration measuring cell 7 and the solid electrolyte layer to connect the first and second measuring chambers 2 and 4 with diffusion resistance.

The measurement principle of this sensor is as described above in the section of the embodiment, and the first diffusion hole 1 is provided in the first measurement chamber 2.
The electromotive force according to the oxygen concentration in the gas to be measured diffused and introduced via the pair of electrodes 7a, 7 of the oxygen concentration detection cell 7
The first oxygen ion pump cell 6 is generated by a differential amplifier or the like so that the voltage caused by the electromotive force is constant during the period b.
The voltage applied to is controlled (may be controlled using a microcomputer). Then, the excess oxygen is pumped out and the gas to be measured having a constant oxygen concentration diffuses into the second measurement chamber 4 through the second diffusion hole 3, and the pair of electrodes 8a and 8b of the second oxygen ion pump cell 8 with oxygen which the voltage remains applied further pumped in, the platinum alloy, by the catalytic action of rhodium alloy electrode, NO _x is decomposed into N ₂ and O _2, the O ₂ is as ions NO decomposed between the pair of electrodes 8a, 8b of the second oxygen ion pump cell 8 provided inside and outside the second measurement chamber 4 by conducting the solid electrolyte layer of the second oxygen ion pump cell 8.
A current Ip2 corresponding to the amount of _x gas flows. By measuring the Ip2, it can be measured NO _x gas concentration.

FIG. 6 shows a schematic layout diagram for manufacturing the NO _x gas sensor shown in FIGS. 4 and 5. As shown in FIG. 6, the NO _x gas sensor is produced by a method in which green sheets made of an oxygen ion conductive solid electrolyte material are laminated and fired. The porous electrode is formed on the green sheet by screen printing.

A NO gas concentration measurement test in the gas to be measured was conducted using such a NO _x gas sensor. FIG. 7 is a diagram for explaining details of a manufacturing example and a layout of the NO _x gas sensor used for the measurement.

[Manufacturing Example] As shown in FIG. 7, the ZrO ₂ green sheet, the electrode paste, and the like are laminated in this order from the upper left to the lower left, and then from the upper right to the lower right to form an integrated detector. A paste material such as an insulating coat and an electrode is screen-printed on a predetermined ZrO ₂ green sheet to form a laminate. Next, an example of manufacturing each component such as a ZrO ₂ green sheet will be described.

[ZrO ₂ Sheet Molding] ZrO ₂ powder was calcined in an air furnace at 600 ° C. for 2 hours. 30 kg of calcined ZrO ₂ powder, 150 g of dispersant, and 10 kg of organic solvent were placed in a trommel together with 60 kg of spheroids, and mixed for about 50 hours,
A dispersion having 4 kg of an organic binder dissolved in 10 kg of an organic solvent was added thereto and mixed for 20 hours to obtain a slurry having a viscosity of about 10 Pa · s. A ZrO ₂ green sheet having a thickness of about 0.4 mm was prepared from this slurry by the doctor blade method, and dried at 100 ° C. for 1 hour.

[Printing Paste] (1) First oxygen ion pump electrode 6a, oxygen partial pressure detection electrode (oxygen reference electrode) 7b, second oxygen ion pump electrode 8
For a and 8b: Platinum powder 20g, ZrO ₂ powder 2.8g, and an appropriate amount of organic solvent are put in a raider machine (or pot mill),
Mix and disperse for 4 hours, add 2 g of organic binder dissolved in 20 g of organic solvent, add 5 g of viscosity modifier, and mix for 4 hours to prepare a paste having a viscosity of about 150 Pa · s. .

(2) For the first oxygen ion pump electrode 6b and the oxygen partial pressure detection electrode (oxygen reference electrode) 7a: Platinum powder 19.8
g, ZrO ₂ powder 2.8 g, gold powder 0.2 powder, and an appropriate amount of organic solvent are put into a raider machine (or pot mill), mixed and dispersed for 4 hours, and 2 g of organic binder is added to the organic solvent 2
What was dissolved in 0 g was added, 5 g of a viscosity modifier was further added, and the mixture was mixed for 4 hours to prepare a paste having a viscosity of about 150 Pa · s.

(3) For insulation coating and protective coating: 50 g of alumina powder and an appropriate amount of organic solvent were put in a raider machine (or pot mill), mixed for 12 hours and dissolved, and 20 g of a viscosity modifier was added, Viscosity 100Pa ・ s after mixing for 3 hours
About a paste was prepared.

(4) For Pt-containing porous material (for lead wire): 10 g of alumina powder, 1.5 g of platinum powder, 2.5 g of organic binder, 20 g of organic solvent were put in a raider machine (or pot mill) and mixed for 4 hours. , 10g of viscosity modifier was added, and 4
The mixture was mixed for a time to prepare a paste having a viscosity of about 100 Pa · s.

(5) For the first diffusion hole 1: 10 g of alumina powder having an average particle size of about 2 μm, 2 g of organic binder, 20 g of organic solvent
Put in a raider machine (or pot mill), mix,
After being dispersed, 10 g of a viscosity modifier was added and mixed for 4 hours to prepare a paste having a viscosity of about 400 Pa · s.

(6) For carbon coating: carbon powder 4
g, an organic binder 2 g, and an organic solvent 40 g were put in a raider machine (or pot mill), mixed and dispersed, 5 g of a viscosity modifier was further added, and mixed for 4 hours to prepare a paste. By forming the carbon coat by printing, for example, electrical contact between the electrodes is prevented. The carbon coat is used to form the first measurement chamber and the second measurement chamber. Since carbon is burnt out during firing, the carbon coating layer does not exist in the fired body.

For the second diffusion hole 3: 20 g of alumina powder having an average particle size of about 2 μm, 8 g of organic binder, 20 g of organic solvent,
Put into a raider machine (or pot mill), mix for 1 hour, granulate, apply a pressure of about 2 t / cm ² with a die press, and press-mold a cylindrical body with a diameter of 1.3 mm and a thickness of 0.8 mm ( Green state) was prepared. The green press-formed product is inserted into predetermined positions of the ZrO ₂ green sheets of the _second and third layers, pressure-bonded and integrated, and then fired to form the second diffusion holes in the gas sensor.

[ZrO ₂ Laminating Method] After the second and third layers are pressure bonded, the portion (diameter 1.3 mm) through which the second diffusion hole penetrates is punched out. After punching, a green cylindrical molded body to be the second diffusion hole is embedded, and 1 to 4 layers of ZrO ₂ green sheet are pressure-bonded at a pressure of 5 kg / cm ² and a pressure time of 1 minute.

[Binder Removal and Firing] The pressure-bonded molded body is debindered at 400 ° C. for 2 hours and fired at 1500 ° C. for 1 hour.

[Measurement Example] A NO _x gas sensor having the following dimensions was produced according to the above production example, and a NO _x gas concentration measurement test was conducted. The NO _x gas sensor used for the measurement has a length in the longitudinal direction of 50 mm, a width (in the lateral direction) of 4 mm, and a thickness (in the laminating direction) of 1.3 mm.
Is. The thickness of the first oxygen ion pump cell is 0.3 m
m, the length of the electrodes 6a and 6b in the longitudinal direction is 7 mm, the length in the lateral direction is 2 mm, and the length in the longitudinal direction of the first measurement chamber is 7 m.
m, the length in the lateral direction is 2 mm, the height is 50 μm, the length in the longitudinal direction of the second measurement chamber is 7 mm, and the length in the lateral direction is 2 m.
m, height 50 μm, length of the first diffusion hole in the longitudinal direction is 2 m
m, the length in the lateral direction is 1 mm, the thickness is 50 μm, and the size of the second diffusion hole is 1 mm in diameter.

The amount of water in the exhaust gas is estimated from the first oxygen ion pump current value of the NO _x gas sensor, that is, the amount of oxygen in the exhaust gas, and the gas concentration detection signal of the gas sensor, that is, the current flowing through the second oxygen ion pump cell. The gas concentration value obtained from the above was corrected.

In the NO _x gas concentration measurement test, a vehicle equipped with a 2000 cc diesel engine was used, and while changing the load conditions on the chassis, NO gas was sent from the exhaust pipe to about 1
The outputs of the NO _x gas concentration detector and the analyzer installed at the rear of the m were compared. "FT-I" which can measure water content
R "Connect the controller to .NO _x gas sensor using (HORIBA Ltd.), in accordance with the first oxygen-ion pumping current of the NO _x gas sensor, a preset correction amount, NO _x gas sensor output (second Oxygen ion pump current value, NO _x gas concentration detection signal) correction, and NO _x concentration (p
pm) can be displayed. The outline of this measurement system is shown in FIG.

The current flowing through the second oxygen ion pump cell of the NO _x gas sensor (second oxygen ion pump current)
In order to determine the correction amount of the above, a test was conducted in advance with a model gas test device, and according to the gas sensor used for the measurement, the first oxygen ion pump current 0.5 m per 1% oxygen concentration was obtained.
A, the current output of the second oxygen ion pump current 1 μA per 100 ppm of NO _x concentration, and 0.6 per 1% of water content
It was confirmed that an output increase of μA (second oxygen ion pump current) was obtained. FIG. 8 shows N according to an embodiment of the present invention.
It is a graph showing the influence of the amount of water on the NO _x gas concentration detection output of the O _x gas sensor, and illustrates the relationship between the amount of water and the increase in the output of the gas sensor. The parameters based on this result, that is, the first oxygen ion pump current value and the correction data (correction coefficient, correction parameter) of the second oxygen ion pump current value corresponding to the current value are mapped in the memory mounted on the controller. The NO _x gas concentration output from the detector is corrected according to the water content.

As the water content, a calculation value obtained by assuming complete combustion from the oxygen concentration in the exhaust gas was used. Table 1 shows these calculated values, and FIG. 10 shows the relationship between the water content (calculated value) and the oxygen concentration. The excess air ratio λ is the actual supplied air amount (B) with respect to the theoretical air amount (A) required for fuel combustion.
Ratio (B / A). For example, λ = 1.2 indicates that 20% of air is larger than the theoretical air amount required for complete combustion. Since the oxygen concentration is proportional to the water content as shown in FIG. 10, it can be seen that the water content can be estimated from the current value (see FIG. 4) of the first oxygen ion pump cell which is proportional to the oxygen concentration.

[0044]

[Table 1]

Under the load conditions of three engines (see Table 2), the NO _x gas concentration to be input is changed, and the NO _x gas concentration obtained based on the detection signal output from the NO _x gas sensor (corrected value, uncorrected) Value) and the NO _x gas concentration (true concentration) output from the analyzer were compared. The results are shown in Table 3,
This is shown in FIGS. 11 and 12. 11 is not corrected NO
_x Gas sensor output and analyzer output, Figure 12 shows corrected NO _x
The gas sensor output and the analyzer output are plotted respectively.

[0046]

[Table 2]

[0047]

[Table 3]

As shown in FIG. 11, when the NO _x gas sensor output is not corrected by the amount of water, the sensitivity is not affected, but the offset changes, and the gas sensor output varies depending on the load conditions. There is. Therefore,
The NO _x gas concentration output from the gas sensor does not show a true value depending on the load condition. On the other hand, FIG.
As shown in FIG. 4, when the NO _x gas sensor output is corrected by the amount of water, the corrected gas sensor output and the analyzer output (corresponding to the true NO _x gas concentration) become equal regardless of the load condition. Therefore, the NO _x gas concentration in the exhaust gas was accurately obtained by the correction (three lines in FIG. 12 overlap, and the NO _x sensor output value and the analyzer output value almost match). I understand. The amount of water vapor in the air is less than the amount in the exhaust gas and has less effect,
In order to improve the accuracy, the moisture concentration before entering the engine may be measured with a humidity sensor.

[0049]

As described above, according to the present invention,
The influence of the amount of water in the gas to be measured on the gas concentration detection is reduced or eliminated, and an accurate gas concentration can be obtained.
In measuring the concentration of the predetermined gas in the exhaust gas discharged from the engine, the water content can be estimated from the operating conditions of the engine, and in the gas concentration detector provided with two sets of oxygen ion pump cells, The water content can be estimated from the value of the current flowing through the first oxygen ion pump cell, and the output of the gas sensor can be corrected according to the water content in the exhaust gas with a relatively simple system. Further, by previously mapping the relationship between the amount of water or a value corresponding to the amount of water and the output of the gas sensor, referring to this map according to the amount of water or the signal corresponding to the amount of water, the gas sensor can The output gas concentration detection signal can be easily corrected to obtain a more accurate gas concentration.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the principle of NO _x gas concentration measurement, and is a diagram showing a cross section in the lateral direction of a NO _x gas sensor.

FIG. 2 is a perspective view of a sensor for indicating the position of the cross section shown in FIG.

FIG. 3 is a diagram for explaining the principle of NO _x gas concentration measurement, and is a graph showing the relationship between the second measurement chamber pump current (second oxygen ion pump current) and the NO _x gas concentration.

It is a diagram for explaining a lateral direction of the cross-sectional view and schematic of a control system of the NO _x gas sensor correction method is applied of the NO _x gas sensor according to an embodiment of the present invention; FIG.

5 is a perspective view showing a cross section of the NO _x gas sensor shown in FIG. 4 cut in the longitudinal direction.

FIG. 6 is a diagram showing a schematic layout when manufacturing the NO _x gas sensor shown in FIGS. 4 and 5;

FIG. 7 is a diagram for explaining details of a manufacturing example and a layout of a NO _x gas sensor used for measurement.

FIG. 8 is a diagram for explaining a method of correcting the NO _x gas sensor according to the embodiment of the present invention, and is a graph showing the influence of the amount of water on the NO _x gas concentration detection output of the sensor.

FIG. 9 is a diagram for explaining a NO _x gas sensor correction method according to an embodiment of the present invention, and is a diagram showing a schematic configuration of a NO _x gas concentration measurement system.

FIG. 10 is a graph showing the relationship between the oxygen concentration and the amount of water in exhaust gas during complete combustion.

FIG. 11 is a diagram for explaining measurement results obtained by the system shown in FIG. 9, in which uncorrected NO _x
It is a graph which shows the correlation of a gas sensor output and an analyzer output.

12 is a diagram for explaining a measurement result obtained by the system shown in FIG. 9, and is a graph showing a correlation between a corrected NO _x gas sensor output and an analyzer output.

[Explanation of symbols]

1: First diffusion hole 2: First measurement room 3: Second diffusion hole 4: Second measurement room 6: First oxygen ion pump cell 6a, 6b: electrodes 7: Oxygen concentration measuring cell 7a, 7b: electrodes 8: Second oxygen ion pump cell 8a, 8b: electrodes

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takafumi Oshima 14-18 Takatsuji-cho, Mizuho-ku, Nagoya City Japan Special Ceramics Co., Ltd. (56) Reference JP-A-63-279159 (JP, A) JP-A 8-201334 (JP, A) JP 4-43952 (JP, A) JP 10-221303 (JP, A) JP 7-333193 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 27/26-27/49

Claims (7)

(57) [Claims] 1. A method for detecting a predetermined gas concentration in an exhaust gas of an engine, the method being determined by the operating conditions of the engine.
By circle estimated from the excess air ratio or A / F value water content in the flue gas, to correct the gas concentration detection signal output from the gas sensor according to the estimated amount of water, the
Calculated from the gas concentration detection signal output by the gas sensor
Correction method of the gas sensor, characterized in that the value of the gas concentration to remove or reduce the influence of the water content of the exhaust gas was. 2. The method for correcting a gas sensor according to claim 1, wherein the gas sensor is a NO _x sensor. 3. The method for correcting a gas sensor according to claim 1, wherein the gas sensor is a sensor using an oxygen ion pumping action of a solid electrolyte. 4. The ratio of air to fuel supplied to the engine is estimated to correspond to the amount of water in the exhaust gas, and the ratio is calculated based on the ratio, the gas concentration detection signal and the true gas concentration value. A map including correction data of the corresponding gas concentration detection signal is created in advance, predetermined correction data corresponding to the ratio determined by the engine operating conditions is read from the map, and the gas concentration detection is performed by the read correction data. A signal is corrected to be corrected.
The method for correcting a gas sensor according to any one of 3 above. 5. A solid electrolyte oxygen ion pump cell is provided in two sets, a predetermined voltage is applied to the first oxygen ion pump cell, and oxygen in the gas to be measured is sufficiently pumped out so that NO _x is not decomposed, A current according to the oxygen concentration in the gas to be measured flows through the first oxygen ion pump cell, the second oxygen ion pump cell decomposes NO _x in the remaining gas and pumps out dissociated oxygen, In a NO _x sensor in which a current corresponding to the NO _x gas concentration flows in the second oxygen ion pump cell, the second oxygen ion pump cell is operated in response to a signal corresponding to a current value obtained from the first oxygen ion pump cell. NO _x gas concentration detection signal corresponding to the current value obtained by correcting the, to remove or reduce the influence of the water content of the NO _x gas concentration the measurement gas from the NO _x gas concentration obtained based on a detection signal Correction method of the gas sensor, characterized in that. 6. The current value of the first oxygen ion pump cell is estimated to correspond to the amount of water in the gas to be measured, and the current value of the first oxygen ion pump cell is calculated from the second oxygen ion pump cell. Based on the obtained current value and the true NO _x gas concentration, a map including correction data of the NO _x gas concentration detection signal corresponding to the current value of the first oxygen ion pump cell is prepared in advance, and the map is prepared from the map. 6. The method for correcting a gas sensor according to claim 5, wherein predetermined correction data corresponding to the current value of the first oxygen ion pump cell is read, and the NO _x gas concentration detection signal is corrected by the read correction data. . 7. A predetermined gas concentration in exhaust gas of an engine is detected.
Depending on the gas sensor to be emitted and the operating conditions of the engine,
Water in the exhaust gas from the total excess air ratio or A / F value
Estimate the amount and adjust the gas sensor according to the estimated water content.
By correcting the output gas concentration detection signal,
Calculated from the gas concentration detection signal output by the gas sensor
The effect of water content in the exhaust gas is removed from the measured gas concentration value.
Or a controller for reducing the
Gas concentration measuring system.