JP5247780B2 - Gas sensor calibration method - Google Patents

Description

The present invention relates to a calibration method for a gas sensor that is used in an exhaust system of an internal combustion engine for an automobile and detects a specific component concentration in a gas to be measured.

  Air pollution caused by exhaust gas emitted from automobile internal combustion engines and the like has caused serious problems in modern society, and purification standards and regulations for pollutants in exhaust gas are becoming stricter year by year. For example, if the concentration of NOx (nitrogen oxide) in the exhaust gas is detected and the detection result is fed back to an engine combustion control monitor, a catalyst monitor, etc., it is considered that exhaust gas purification can be performed more efficiently. From such a background, there is a demand for a gas sensor that can accurately detect the NOx concentration in exhaust gas.

  An example of such a gas sensor is disclosed in Patent Document 1. The gas sensor includes a first internal space into which a gas to be measured is introduced under the first diffusion resistance, a solid electrolyte body for oxygen ion conductivity, and a pair of pump electrodes disposed in the solid electrolyte body for pump And a pump cell for adjusting the oxygen concentration in the first internal space, a second internal space in which the atmosphere in the first internal space is introduced under the second diffusion resistance, and an oxygen ion conductive solid for sensor A sensor cell having an electrolyte body and a pair of sensor electrodes disposed on the sensor solid electrolyte body and detecting a specific component concentration in the gas to be measured is provided.

  The gas sensor introduces a gas to be measured (exhaust gas) into the first internal space and applies a predetermined voltage between the pair of pump electrodes of the pump cell, whereby oxygen is taken in and out of the first internal space. The oxygen concentration in the space is controlled to a low concentration. Then, by applying a predetermined voltage between the pair of sensor electrodes of the sensor cell, the amount of oxygen ions moving through the sensor solid electrolyte body of the sensor cell, that is, the magnitude of the current flowing between the pair of sensor electrodes (sensor current value) ). This change in the sensor current value corresponds to a specific component (NOx) concentration that is a specific component. Thereby, it is possible to accurately measure the specific component (NOx) concentration regardless of the increase or decrease of the oxygen concentration in the gas to be measured (exhaust gas).

  However, in the gas sensor of Patent Document 1, it is difficult to make the shapes of the first diffusion resistance, the first internal space, the second diffusion resistance, the second internal space, and the like completely the same due to dimensional tolerances and the like. Variations occur in the sensor current value (NOx concentration dependency) with respect to the NOx concentration. Therefore, in order to detect the NOx concentration in the exhaust gas with high accuracy, it is necessary to measure the sensor current value for the NOx gas having a predetermined concentration for each sensor and calibrate the gas sensor based on this value. Further, since toxic and expensive NOx gas is used for the calibration, it is a high cost factor.

  Thus, Patent Document 2 discloses a gas sensor calibration method that uses oxygen gas as a calibration gas for calibrating the gas sensor. In this gas sensor calibration method, a correlation between a sensor current value for a predetermined concentration of oxygen gas and a sensor current value for a predetermined concentration of NOx gas is obtained in advance. Then, oxygen gas having a predetermined concentration is used as a calibration gas, the sensor current value for the NOx gas having a predetermined concentration is estimated from the sensor current value using the correlation, and the gas sensor is calibrated based on this value. Thereby, the gas sensor can be calibrated without using toxic and expensive NOx gas.

Japanese Patent No. 2885336 JP 2007-108018 A

  However, in the gas sensor disclosed in Patent Document 2, oxygen gas is used as a calibration gas. However, it is difficult to use oxygen gas such as air that is inexpensive and easy to handle. That is, normally, when detecting the NOx concentration in the exhaust gas, the concentration to be detected is on the order of ppm, and the sensor current value of the sensor cell is a minute value on the order of μA. Therefore, when obtaining the above correlation, the sensor current value for NOx gas is measured using NOx gas in the ppm order of the detection target concentration, and the sensor current value is a value on the order of μA.

  On the other hand, when the sensor current value with respect to oxygen gas is measured by using air or the like, which is oxygen gas having an oxygen concentration of about 20%, which is cheap and easy to handle, the sensor current value becomes a value on the order of mA. That is, the order of the current value between the sensor current value for NOx gas and the sensor current value for oxygen gas is greatly different. For this reason, it is difficult to accurately obtain the correlation between the two.

  Therefore, in order to accurately obtain the correlation between the sensor current value for oxygen gas and the sensor current value for NOx gas, the sensor current value for oxygen gas is as small as a μA order, similar to the sensor current value for NOx gas. Therefore, it is necessary to prepare an oxygen gas adjusted to a low concentration, and it is difficult to significantly reduce the cost.

The present invention has been made in view of such problems, and an object of the present invention is to provide a gas sensor calibration method capable of easily and accurately performing calibration of a gas sensor at low cost.

According to a first aspect of the present invention, there is provided a measurement gas chamber into which a measurement gas is introduced, a diffusion resistance portion for introducing the measurement gas into the measurement gas chamber under a predetermined diffusion resistance, and oxygen ion conductivity And a pair of pump electrodes respectively disposed on the surface on the gas chamber side to be measured and on the surface on the opposite side of the pump solid electrolyte body and oxygen in the gas chamber to be measured A pump cell for adjusting the concentration, a solid electrolyte body for oxygen ion conductive sensor, and a pair of sensor electrodes disposed on the surface on the gas chamber side to be measured and on the opposite surface of the solid electrolyte body for sensor And a sensor cell for detecting a specific component concentration in the gas to be measured introduced into the gas chamber to be measured.
Among some of the produced gas sensors, for some of the gas sensors, the pump current value Ip that flows between the pair of pump electrodes of the pump cell with respect to the oxygen gas with a predetermined concentration and the specific component gas with a predetermined concentration A correlation creating step of measuring a sensor current value Is flowing between the pair of sensor electrodes of the sensor cell and obtaining a correlation between the pump current value Ip and the sensor current value Is;
Reference current to set the reference pumping current Ip ₀ and the reference sensor current Is ₀ is the pumping current Ip and the sensor current value Is for the reference gas sensor as a reference of the plurality of gas sensors so as to satisfy the above correlation A value setting process;
With calibration gas is oxygen gas of the predetermined concentration, the pump current value measuring step of measuring the pumping current Ip _n is the pumping current Ip for the calibration gas sensor to be calibrated of the plurality of gas sensors ,
From the pumping current Ip _n, by utilizing the correlation, and the sensor current value estimation step of estimating the sensor current value Is _n is the sensor current value Is for the calibration gas sensor,
The sensor current value Is _n and the reference sensor current value Is ₀ are compared, and the sensor output characteristic of the calibration gas sensor is corrected so that the sensor output characteristic of the calibration gas sensor is equivalent to the sensor output characteristic of the reference gas sensor. And a sensor output characteristic correcting step for performing a gas sensor calibration method.

The reference invention includes a measured gas chamber into which a measured gas is introduced, a diffusion resistance portion for introducing the measured gas into the measured gas chamber under a predetermined diffusion resistance, and an oxygen ion conductive pump And a pair of pump electrodes respectively disposed on the surface on the gas gas chamber side and the surface on the opposite side of the solid electrolyte material for pump and the oxygen concentration in the gas gas chamber to be measured. A pump cell to be adjusted; a solid electrolyte body for oxygen ion conductive sensor; and a pair of sensor electrodes respectively disposed on the surface of the gas chamber to be measured and the opposite surface of the solid electrolyte body for sensor A gas sensor having a sensor cell for detecting a specific component concentration in the measurement gas introduced into the measurement gas chamber,
A pump current value Ip that flows between the pair of pump electrodes of the pump cell with respect to a predetermined concentration of oxygen gas, and a sensor current value that flows between the pair of sensor electrodes of the sensor cell with respect to a specific component gas of a predetermined concentration The gas sensor is configured such that Is is determined by the diffusion resistance of the diffusion resistance portion .

  The gas sensor calibration method according to the first aspect of the invention performs the correlation creating step, the reference current value measuring step, the pump current value measuring step, the sensor current value estimating step, and the sensor output characteristic correcting step. By performing these steps, the gas sensor can be easily and accurately calibrated at low cost.

  That is, according to the present invention, in the configuration in which the pump cell and the sensor cell are disposed in the measurement gas chamber into which the measurement gas is introduced under the diffusion resistance of the diffusion resistance portion, oxygen having a predetermined concentration is provided. A major feature is that it has been found that there is a correlation between the pump current value Ip of the pump cell for gas and the sensor current value Is of the sensor cell for a specific component gas having a predetermined concentration.

  Further, since the pump current value Ip and the sensor current value Is are measured separately in the pump cell and the sensor cell, the concentrations of the oxygen gas and the specific component gas that are the measurement objects are large. Even if different, specifically, even if the order of the amount of oxygen ions and the current value that move through the solid electrolyte body for the pump and the solid electrolyte body for the sensor are greatly different, the correlation is accurate. You can ask well.

  Therefore, in the correlation creation step, the sensor current value Is is a specific component gas having a predetermined concentration to be detected. For example, if the specific component is NOx or the like, the sensor current value Is is a μA order using a specific component gas having a concentration of ppm order. The sensor current value Is is measured, and the pump current value Ip is inexpensive as a predetermined concentration of oxygen gas, and the pump current value in the order of mA using air that is easy to handle and does not require adjustment of the oxygen concentration. Ip can be measured. Even in such a case, the correlation between the pump current value Ip and the sensor current value Is can be obtained with high accuracy.

Thus, in the pump current value measuring step, it can be used an inexpensive and easy to handle air, etc. as the calibration gas, measuring the pumping current Ip _n of the calibration gas sensor. Then, in a subsequent step, by utilizing the correlation from the pumping current Ip _n, estimating the sensor current Is _n of the calibration gas sensor, further wherein the sensor current Is _n and above the reference gas sensor By comparing the reference sensor current value Is ₀ , the sensor output characteristics of the calibration gas sensor can be corrected so that the sensor output characteristics of the calibration gas sensor and the reference gas sensor are equivalent.

  Therefore, by utilizing the correlation between the pump current value Ip and the sensor current value Is, it is possible to use air that is inexpensive and easy to handle as the calibration gas, and the gas sensor can be calibrated at low cost. It can be done easily. Further, since the correlation can be obtained with high accuracy, the sensor output characteristics of the gas sensor can be calibrated with high accuracy.

In the gas sensor of the reference invention, the pump current value Ip of the pump cell for a predetermined concentration of oxygen gas and the sensor current value Is of the sensor cell for a specific component gas of a predetermined concentration are both determined by the diffusion resistance of the diffusion resistance section. It is configured to be determined. Therefore, the correlation between the pump current value Ip and the sensor current value Is can be further increased, and the correlation can be obtained with high accuracy. Thus, the gas sensor is suitable for use in the gas sensor calibration method according to the first aspect of the invention in which the sensor output characteristic is calibrated using the correlation between the pump current value Ip and the sensor current value Is. It becomes.

Thus, according to the present invention, it is possible to provide a gas sensor calibration method capable of easily and accurately performing calibration of a gas sensor at a low cost.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 3 is a developed perspective view showing the structure of the gas sensor in the first embodiment. Explanatory drawing which shows the relationship between the pump electric current value Ip and the sensor electric current value Is in Example 1. FIG. Explanatory drawing which shows the pump electric current value Ip and sensor electric current value Is of a reference | standard gas sensor and a calibration gas sensor in Example 1. FIG. FIG. 3 is an explanatory diagram illustrating the relationship between the NO concentration of the reference gas sensor and the calibration gas sensor and the sensor output value in the first embodiment. Explanatory drawing which shows the pump electric current value Ip and sensor electric current value Is of a reference | standard gas sensor and a calibration gas sensor in Example 2. FIG. Explanatory drawing which shows the structure of the gas sensor in Example 2. FIG. Explanatory drawing which shows the relationship between the height of a to-be-measured gas chamber and the sensor electric current value Is in Example 3. FIG.

In the first invention and the reference invention , the gas sensor is used, for example, for detecting deterioration of a three-way catalyst installed in an exhaust system of an internal combustion engine for a vehicle, and the like, such as NOx (nitrogen oxide) in exhaust gas. Used for NOx sensors and the like that detect the concentration of air pollutants.

  In the first invention, in the reference current value setting step, the reference gas sensor is selected from the plurality of gas sensors by selecting a gas sensor indicating the pump current value Ip and the sensor current value Is satisfying the correlation. Alternatively, a virtual gas sensor indicating the pump current value Ip and the sensor current value Is satisfying the correlation may be set, and this may be used as the reference gas sensor.

Further, the gas sensor is configured to convert and output the sensor current value Is with a predetermined amplification factor, and in the sensor output characteristic correction step, by adjusting the amplification factor of the calibration gas sensor, The sensor output characteristic of the calibration gas sensor can be corrected (claim 2).
In this case, it becomes easy to correct the sensor output characteristic of the calibration gas sensor to be equivalent to the sensor output characteristic of the reference gas sensor.

In the sensor output characteristic correction step, the sensor output characteristic of the calibration gas sensor can be corrected by changing the diffusion resistance of the diffusion resistance unit and adjusting the sensor current value Is of the calibration gas sensor ( Claim 3).
In this case, it becomes easy to correct the sensor output characteristic of the calibration gas sensor to be equivalent to the sensor output characteristic of the reference gas sensor.

In the pump current value measuring step, it is preferable to use air as the calibration gas.
In this case, the gas sensor can be easily calibrated at low cost by using the calibration gas that is inexpensive and easy to handle and does not require adjustment of the oxygen concentration.

Moreover, it is preferable that the said specific component is a nitrogen oxide (Claim 5).
In this case, the calibration of the NOx sensor for detecting the nitrogen oxide (NOx) concentration in the exhaust gas serving as the measurement gas can be easily and accurately performed at low cost.

Moreover, it is preferable that both the pump current value Ip and the sensor current value Is in the gas sensor are determined by the diffusion resistance of the diffusion resistance portion.
In this case, the correlation between the pump current value Ip and the sensor current value Is can be obtained with higher accuracy.

The height of the gas chamber to be measured is preferably 0.1 mm or more.
In this case, the diffusion resistance in the measured gas chamber can be made sufficiently smaller than the diffusion resistance of the diffusion resistance portion. Thereby, both the pump current value Ip and the sensor current value Is can be determined by the diffusion resistance of the diffusion resistance unit, and the correlation between the two can be obtained with higher accuracy.

  On the other hand, if the height of the gas chamber to be measured is less than 0.1 mm, it may be difficult to make the diffusion resistance in the gas chamber to be measured sufficiently smaller than the diffusion resistance of the diffusion resistance portion. is there. For this reason, there is a possibility that the correlation between the pump current value Ip and the sensor current value Is cannot be accurately obtained due to the influence of the diffusion resistance of the gas chamber to be measured.

Also, one of the pump electrodes of the pump cell facing the gas chamber to be measured is disposed closer to the diffusion resistance portion than one of the sensor electrodes of the sensor cell facing the gas chamber to be measured. In addition, it is preferable that the two are disposed at positions that do not face each other in the gas chamber to be measured.
In this case, both the pump current value Ip and the sensor current value Is can be determined by the diffusion resistance of the diffusion resistance unit, and the correlation between the two can be obtained with higher accuracy. it can.

In the above reference invention , the height of the gas chamber to be measured is preferably 0.1 mm or more .
In this case, the diffusion resistance in the measured gas chamber can be made sufficiently smaller than the diffusion resistance of the diffusion resistance portion. Thereby, both the pump current value Ip and the sensor current value Is can be determined by the diffusion resistance of the diffusion resistance unit.

  On the other hand, if the height of the gas chamber to be measured is less than 0.1 mm, it may be difficult to make the diffusion resistance in the gas chamber to be measured sufficiently smaller than the diffusion resistance of the diffusion resistance portion. is there. Therefore, under the influence of the diffusion resistance of the gas chamber to be measured, there is a possibility that neither the pump current value Ip nor the sensor current value Is can be determined by the diffusion resistance of the diffusion resistance portion. .

Also, one of the pump electrodes of the pump cell facing the gas chamber to be measured is disposed closer to the diffusion resistance portion than one of the sensor electrodes of the sensor cell facing the gas chamber to be measured. And it is preferable that both are arrange | positioned in the position which does not oppose in the said to-be-measured gas chamber .
In this case, both the pump current value Ip and the sensor current value Is can be determined by the diffusion resistance of the diffusion resistance unit.

Example 1
Calibration method for a gas sensor according to an embodiment of the present invention will be described with reference to FIG.
As shown in FIG. 1, the gas sensor 1 of this example is installed in an exhaust system of an automobile engine, and is used for a NOx sensor that detects the concentration of NOx (nitrogen oxide) that is a specific component in exhaust gas that is a gas to be measured. Is.
The gas sensor 1 includes a measured gas chamber 2 into which a measured gas is introduced, a diffusion resistance section 3 for introducing the measured gas into the measured gas chamber 2 under a predetermined diffusion resistance, and a measured gas chamber 2. And a sensor cell 5 for detecting a specific component (NOx) concentration in the gas to be measured introduced into the gas chamber 2 to be measured.

As shown in the figure, the pump cell 4 is disposed on the surface of the solid electrolyte body 41 for oxygen ion conductivity and on the gas chamber 2 side of the pump solid electrolyte body 41 and on the opposite surface thereof. A pair of pump electrodes 421 and 422;
The sensor cell 5 includes an oxygen ion conductive sensor solid electrolyte body 51, and a pair of sensor electrodes 521 disposed on the surface of the sensor solid electrolyte body 51 on the measurement gas chamber 2 side and the opposite surface thereof. 522. The sensor solid electrolyte body 51 is disposed opposite to the pump solid electrolyte body 41 of the pump cell 4 via the gas chamber 2 to be measured.

In the pump cell 4, the pump solid electrolyte body 41 is made of an electrolyte having oxygen ion conductivity such as zirconia or ceria.
In addition, an electrode having a low NOx decomposition activity is used for one pump electrode 421 facing the measurement gas chamber 2 in order to suppress decomposition of NOx in the measurement gas. Specifically, a porous cermet electrode containing a Pt—Au (platinum-gold) alloy is used. The content of Au in the metal component is preferably about 0.5 to 5% by weight. For the other pump electrode 422, a porous cermet electrode containing Pt is used.

In the sensor cell 5, the sensor solid electrolyte body 51 is made of an electrolyte having oxygen ion conductivity such as zirconia or ceria.
In addition, an electrode having high NOx decomposition activity is used for one sensor electrode 521 facing the measurement gas chamber 2 in order to decompose NOx in the measurement gas. Specifically, a porous cermet electrode containing a Pt—Rh (platinum-rhodium) alloy is used. The content of Rh in the metal component is preferably about 10 to 50% by weight. For the other sensor electrode 522, a porous cermet electrode containing Pt is used.

  As shown in the figure, the gas chamber 2 to be measured is formed between a solid electrolyte body for pump 41 and a solid electrolyte body for sensor 51. That is, a spacer layer 121 having an opening is interposed between the pump solid electrolyte body 41 and the sensor solid electrolyte body 51, and the pump solid electrolyte body 41 is provided in the opening of the spacer layer 121. A gas chamber 2 to be measured is formed between the sensor and the solid electrolyte body 51 for sensor. The spacer layer 121 is made of alumina.

  As shown in the figure, the diffusion resistance portion 3 is disposed on a part of the spacer layer 121 on the distal end side (left side in FIG. 1) of the gas chamber 2 to be measured. The diffusion resistance unit 3 is made of porous alumina, and communicates the measured gas chamber 2 and the outside of the gas sensor 1 at the tip of the gas sensor 1. The shape, porosity, pore diameter, etc. of the diffusion resistance part 3 are appropriately designed so that the diffusion rate of the gas to be measured introduced into the gas chamber 2 to be measured becomes a predetermined rate.

As shown in the figure, in the measured gas chamber 2, one pump electrode 421 of the pump cell 4 is disposed at a position closer to the diffusion resistance unit 3 than one sensor electrode 521 of the sensor cell 5. Further, the pump electrode 421 and the sensor electrode 521 are disposed at positions that do not face each other in the gas chamber 2 to be measured.
In the gas chamber 2 to be measured, the pump cell 4 and the sensor cell 5 are communicated with each other by a space. Moreover, the height of the gas chamber 2 to be measured is 0.1 mm or more.

Then, the gas sensor 1 of this example includes a pump current value flowing between the pair of pump electrodes 421 and 422 of the pump cell 4 when oxygen gas having a predetermined concentration is introduced into the gas chamber 2 to be measured, and a specific component having a predetermined concentration ( The sensor current value flowing between the pair of sensor electrodes 521 and 522 of the sensor cell 5 when the NOx gas is introduced into the measured gas chamber 2 is determined by the diffusion resistance of the diffusion resistance unit 3. ing.
That is, the diffusion resistance between the pump cell 4 and the sensor cell 5 is sufficiently smaller than the diffusion resistance of the diffusion resistance unit 3 and can be ignored.

  As shown in the figure, a first reference gas chamber 111 for introducing the atmosphere is formed on the surface of the pump solid electrolyte body 41 opposite to the gas chamber 2 to be measured. The first reference gas chamber 111 is formed by interposing a spacer layer 124 between the pump solid electrolyte body 41 and a heater substrate 131 described later. The other pump electrode 422 of the pump cell 4 is disposed so as to face the first reference gas chamber 111.

  Further, the ceramic heater 13 is laminated on the solid electrolyte body 41 for a pump via a spacer layer 124. The ceramic heater 13 is configured by providing, between a pair of heater substrates 131 made of alumina, a heat generating portion 132 that generates heat by energization and a lead portion 133 for supplying current to the heat generating portion 132. The spacer layer 124 is made of alumina. The heat generating part 132 is made of platinum or a platinum alloy.

  As shown in the figure, a second reference gas chamber 112 for introducing the atmosphere is formed on the surface of the sensor solid electrolyte body 51 opposite to the gas chamber 2 to be measured. The second reference gas chamber 112 is formed by interposing a spacer layer 122 between the sensor solid electrolyte 51 and the cover layer 123. The other sensor electrode 522 of the sensor cell 5 is disposed so as to face the second reference gas chamber 112. The spacer layer 122 and the cover layer 123 are made of alumina.

As shown in FIG. 2, in the pump cell 4, one pump electrode 421 has through holes 441 formed in the pump solid electrolyte body 41, the spacer layer 124, and the pair of heater substrates 131 via conductive leads 431. Through the terminal portion 451. The other pump electrode 422 is electrically connected to the terminal portion 452 through the conductive layer 432 and through the spacer layer 124 and the through hole 442 formed in the pair of heater substrates 131.
As shown in FIG. 1, the pair of pump electrodes 421 and 422 is connected to a pump circuit 46 including a power source 461 and an ammeter 462.

As shown in FIG. 2, in the sensor cell 5, one sensor electrode 521 is connected to the terminal portion through the through hole 541 formed in the sensor solid electrolyte body 51 and the spacer layers 122 and 123 via the conductive lead portion 531. 551 is electrically connected. The other sensor electrode 522 is electrically connected to the terminal portion 552 through the through hole 542 formed in the spacer layers 122 and 123 via the conductive lead portion 532.
As shown in FIG. 1, the pair of sensor electrodes 521 and 522 is connected to a sensor circuit 56 including a power source 561 and an ammeter 562.

  As shown in FIG. 2, in the heater substrate 13, the heat generating portion 132 is electrically connected to the terminal portion 135 through a pair of conductive lead portions 133 and a pair of through holes 134 formed in the heater substrate 131. ing.

The operation principle of the gas sensor having the above configuration will be described.
First, the gas to be measured passes through the diffusion resistance portion 3 and is introduced into the gas chamber 2 to be measured. The amount of measurement gas introduced is determined by the diffusion resistance of the diffusion resistance unit 3.

  Next, when a voltage is applied to the pair of pump electrodes 421 and 422 of the pump cell 4 so that the other pump electrode 422 becomes a positive electrode, oxygen in the gas to be measured on one pump electrode 421 It is reduced to oxygen ions and discharged to the other pump electrode 422 side by the pumping action. Conversely, when a voltage is applied so that one pump electrode 421 becomes a positive electrode, oxygen is reduced on the other pump electrode 422 to become oxygen ions, and is discharged to the one pump electrode 421 side by the pumping action. Is done.

  In this way, by applying a voltage between the pair of pump electrodes 421 and 422 of the pump cell 4, oxygen is taken in and out of the gas chamber 2 to be measured, and the oxygen concentration in the gas chamber 2 to be reduced to a predetermined low concentration. adjust. Here, the oxygen concentration in the gas chamber 2 to be measured is preferably adjusted to 0% and held in order to suppress fluctuations in the sensor output value output from the sensor cell 5 described later.

  Next, a voltage is applied to the pair of sensor electrodes 521 and 522 of the sensor cell 5 so that the other sensor electrode 522 becomes a positive electrode. Here, since one sensor electrode 521 is a porous cermet electrode containing a Pt—Rh alloy having a high NOx decomposition activity, oxygen and NOx in the gas to be measured are reduced on the one sensor electrode 521. As a result, oxygen ions are generated and discharged to the other sensor electrode 522 side by a pumping action.

  In this way, by applying a voltage between the pair of sensor electrodes 521 and 522 of the sensor cell 5, the value of the sensor current flowing between the pair of sensor electrodes 521 and 522 changes according to the NOx concentration in the gas to be measured. To do. The sensor current value is converted into a voltage with a predetermined amplification factor and output as a sensor output value, whereby the NOx concentration in the gas to be measured can be detected.

Next, a calibration method of the gas sensor 1 of this example will be described.
As shown in FIGS. 3 to 5, the calibration method of the gas sensor 1 of the present example performs a correlation creating step, a reference current value measuring step, a pump current value measuring step, a sensor current value estimating step, and a sensor output characteristic correcting step.

  In the correlation creating step, for some gas sensors 1 among the plurality of produced gas sensors 1, a pump current value Ip flowing between the pair of pump electrodes 421 and 422 of the pump cell 4 with respect to oxygen gas having a predetermined concentration; The sensor current value Is flowing between the pair of sensor electrodes 521 and 522 of the sensor cell 5 with respect to a specific component (NOx) gas having a predetermined concentration is measured, and the correlation between the pump current value Ip and the sensor current value Is is obtained. .

In the reference current value setting step, the pump current value Ip and the reference pump current value Ip ₀ that are the sensor current value Is and the reference sensor current value Is ₀ for the reference gas sensor 1a serving as a reference for the plurality of gas sensors 1 satisfy the above correlation. Set as follows.
In the pump current value measuring step, the pump gas value Ip _n which is the pump current value Ip for the calibration gas sensors 1b and 1c to be calibrated among the plurality of gas sensors 1 using the calibration gas which is the oxygen gas of the predetermined concentration. Measure.

The sensor current measuring step, the pumping current Ip _n, by utilizing the correlation, to estimate calibration gas sensor 1b, and the sensor current value Is _n is a sensor current value Is for 1c.
In the sensor output characteristic correcting step, the sensor current value Is _n is compared with the reference sensor current value Is _0, and the calibration gas sensor is adjusted so that the sensor output characteristics of the calibration gas sensors 1b and 1c are equivalent to the sensor output characteristics of the reference gas sensor 1a. 1 sensor output characteristics are corrected.
This will be described in detail below.

First, a plurality of gas sensors 1 having the above configuration were produced. Of the plurality of gas sensors 1 produced, the pump cell 4 when eight gas sensors 1 were introduced into the measured gas chamber 2 with oxygen gas having an oxygen concentration of 20% (hereinafter referred to as 20% O ₂ gas (atmosphere)). And the sensor current value Is of the sensor cell 5 when NO gas having a NO concentration of 100 ppm (hereinafter referred to as 100 ppm NO gas) was introduced into the gas chamber 2 to be measured and plotted in FIG.
From the figure, it can be seen that there is a certain proportional relationship between the pump current value Ip and the sensor current value Is, and there is a correlation (graph S in FIG. 3).

Then, set the virtual reference gas sensor 1a as a reference of a plurality of gas sensors 1 in advance, the reference pumping current Ip ₀ and the reference sensor current Is ₀ is a pump current value Ip and the sensor current value Is of the reference gas sensor 1a It set so that the said correlation (solid line S of FIG. 4) might be satisfy | filled. In this example, as shown in FIG. 4, the reference pump current value Ip ₀ of the reference gas sensor 1a is set to 1 mA, and the reference sensor current value Is ₀ is set to 0.25 μA (broken line a in FIG. 4).

  Furthermore, the reference gas sensor 1a of this example was set so that the sensor current value Is of 0.25 μA was converted into a voltage with a predetermined amplification factor and output as a sensor output value of 1V. Therefore, the sensor output value (sensor output characteristic) with respect to the NO concentration in the reference gas sensor 1a is as shown by a solid line A in FIG.

Next, calibration was performed on the two calibration gas sensors 1b and 1c to be calibrated.
First, the calibration gas sensor 1b, were measured pump current value Ip _n of the pump cell 4 when introducing the calibration gas into the gas chamber 2 to be measured. In this example, 20% O ₂ gas (atmosphere) was used as the calibration gas. Further, as shown in FIG. 4, the pump current Ip _n was 1.6 mA (dashed line b in FIG. 4).

Then, the pump current value Ip _n calibration gas sensor 1b, by using the pre-obtained the correlation (solid line S in FIG. 4), were estimated sensor current Is _n calibration gas sensor 1b. In this embodiment, as shown in FIG. 4, the pump current value Ip _n calibration gas sensor 1b is deduced from it is 1.6 mA, the sensor current Is _n and 0.4Myuei (broken line b in FIG. 4).
From this sensor current value Is _n , when the calibration gas sensor 1b is voltage-converted with the same amplification factor as that of the reference sensor 1a and a sensor output value is output, the sensor output value (sensor output characteristic) with respect to the NO concentration is indicated by a broken line B in FIG. It becomes like this.

Then, was compared with the reference sensor current Is ₀ of the sensor current Is _n and the reference gas sensor 1a of the calibration gas sensor 1b, the reference sensor current Is ₀ is to be 0.625 times the sensor current Is _n all right. Based on this, the gain at the time of voltage conversion of the calibration gas sensor 1b was set to 0.625 times that of the reference sensor 1a. As a result, the sensor output characteristics of the calibration gas sensor 1b were corrected, and the sensor output characteristics of the reference gas sensor 1a could be aligned (broken line B → solid line A in FIG. 5).

On the other hand, for the calibration gas sensor 1c, it was determined pump current value Ip _n of the pump cell 4 when introducing the calibration gas into the gas chamber 2 to be measured. In this embodiment, as shown in FIG. 4, the pump current Ip _n was 0.8 mA (broken line c in FIG. 4).

Then, the calibration from the pump current Ip _n of the gas sensor 1b, by utilizing the previously obtained correlation between the pumping current Ip and the sensor current value Is (solid line S in FIG. 4), the calibration gas sensor 1b of the sensor current value Is _n was estimated. In this embodiment, as shown in FIG. 4, the pump current value Ip _n calibration gas sensor 1b is deduced from it is 0.8 mA, the sensor current Is _n and 0.2 .mu.A (broken line c in FIG. 4).
From this sensor current value Is _n , when the calibration gas sensor 1c is voltage-converted with the same amplification factor as that of the reference sensor 1a and a sensor output value is output, the sensor output value (sensor output characteristic) with respect to the NO concentration is indicated by a broken line C in FIG. It becomes like this.

Next, when the sensor current value Is _n of the calibration gas sensor 1c is compared with the reference sensor current value Is _{0 of the} reference gas sensor 1a, the reference sensor current value Is ₀ is 1.25 times the sensor current value Is _n. all right. Based on this, the gain at the time of voltage conversion of the calibration gas sensor 1b was set to 1.25 times that of the reference sensor 1a. As a result, the sensor output characteristics of the calibration gas sensor 1c were corrected, and the sensor output characteristics of the reference gas sensor 1a could be aligned (broken line C → solid line A in FIG. 5).

Next, the effect of the gas sensor calibration method of this example will be described.
The gas sensor calibration method of this example performs the correlation creating step, the reference current value measuring step, the pump current value measuring step, the sensor current value estimating step, and the sensor output characteristic correcting step. Then, by performing these steps, the gas sensor 1 can be calibrated easily and accurately at low cost.

  That is, in the gas sensor calibration method of this example, in the configuration in which the pump cell 4 and the sensor cell 5 are disposed in the gas chamber 2 to be measured, into which the gas to be measured is introduced under the diffusion resistance of the diffusion resistance unit 3. A major feature is that it has been found that there is a correlation between the pump current value Ip of the pump cell 4 for a predetermined concentration of oxygen gas and the sensor current value Is of the sensor cell 5 for a specific component (NOx) gas of a predetermined concentration.

  In addition, since the pump current value Ip and the sensor current value Is are measured separately by the pump cell 4 and the sensor cell 5, respectively, the concentrations of the oxygen gas and the specific component gas that are the measurement objects are greatly different. However, specifically, even when the amount of oxygen ions moving through the pump solid electrolyte body 41 and the sensor solid electrolyte body 51 and the order of the current values are greatly different, the above correlation is obtained accurately. be able to.

  Therefore, in the correlation creation step, the sensor current value Is is a μA order using a specific component gas having a predetermined concentration to be detected, for example, NO gas having a concentration of ppm order if the specific component is NOx as in this example. The pump current value Ip is measured as a pump current value Ip in the order of mA using an atmosphere that is inexpensive as a predetermined concentration of oxygen gas and does not require adjustment of the oxygen concentration and is easy to handle. can do. Even in such a case, the correlation between the pump current value Ip and the sensor current value Is can be obtained with high accuracy.

Thereby, the pump current value measuring step, can be inexpensive with easy to handle air as calibration gas, measuring the calibration gas sensor 1b, and the pump current Ip _n of 1c. The reference sensor subsequent in step, by the pumping current Ip _n utilizing the correlation, the calibration gas sensor 1b, estimates the sensor current Is _n of 1c, further sensor current Is _n and the reference gas sensor 1a by comparing a current value is _0, calibration gas sensor 1b, as the sensor output characteristics of the 1c and the reference gas sensor 1a is equal can be corrected calibration gas sensor 1b, and the sensor output characteristics of 1c.

  As described above, by utilizing the correlation between the pump current value Ip and the sensor current value Is, it is possible to use an inexpensive and easy-to-handle atmosphere as the calibration gas, and easily calibrate the gas sensor 1 at a low cost. be able to. In addition, since the correlation can be obtained with high accuracy, the sensor output characteristics of the gas sensor 1 can be calibrated with high accuracy.

  The gas sensor 1 is configured to convert the sensor current value Is into a voltage with a predetermined amplification factor and output it. In the sensor output characteristic correction step, the calibration is performed by adjusting the amplification factor of the calibration gas sensors 1b and 1c. The sensor output characteristics of the gas sensors 1b and 1c are corrected. Therefore, it becomes easy to correct the sensor output characteristics of the calibration gas sensors 1b and 1c so as to be equivalent to the sensor output characteristics of the reference gas sensor 1a.

  In the pump current value measuring step, the atmosphere is used as a calibration gas. By using an air that is inexpensive and easy to handle and does not require adjustment of the oxygen concentration as the calibration gas, the gas sensor 1 can be easily calibrated at low cost.

  Further, the gas sensor 1 has a diffusion resistance of the diffusion resistance unit 3 in which the pump current value Ip of the pump cell 4 with respect to oxygen gas of a predetermined concentration and the sensor current value Is of the sensor cell 5 with respect to a specific component (NOx) gas of predetermined concentration are both. It is comprised so that it may be determined by. Therefore, the correlation between the pump current value Ip and the sensor current value Is can be further increased, and the correlation can be obtained with high accuracy.

  Moreover, the height of the gas chamber 2 to be measured is 0.1 mm or more. Therefore, the diffusion resistance in the measured gas chamber 2 can be made sufficiently smaller than the diffusion resistance of the diffusion resistance portion 3. As a result, both the pump current value Ip and the sensor current value Is can be determined by the diffusion resistance of the diffusion resistance unit 3, and the correlation between the two can be obtained with higher accuracy.

  Also, one pump electrode 421 of the pump cell 4 facing the measured gas chamber 2 is disposed at a position closer to the diffusion resistance unit 3 than one sensor electrode 521 of the sensor cell 5 facing the measured gas chamber 2. And both are arrange | positioned in the position which does not oppose in the to-be-measured gas chamber 2. As shown in FIG. Therefore, both the pump current value Ip and the sensor current value Is can be determined by the diffusion resistance of the diffusion resistance unit 3, and the correlation between the two can be obtained with higher accuracy.

  Thus, according to this example, it is possible to provide a gas sensor calibration method capable of easily and accurately performing calibration of the gas sensor 1 at low cost, and the gas sensor 1 suitable for using the method.

(Example 2)
This example shows another example of the gas sensor calibration method.
In this example, as in Example 1, the correlation creation process and the reference current value measurement process were performed, and then the two calibration gas sensors 1b and 1c to be calibrated were calibrated. In addition, the structure of the gas sensor 1 is the same as that of Example 1 (refer FIG. 1, FIG. 2).
Hereinafter, the pump current value measuring step, the sensor current value estimating step, and the sensor output characteristic correcting step will be described.

First, the calibration gas sensor 1b, were measured pump current value Ip _n of the pump cell 4 when introducing the calibration gas into the gas chamber 2 to be measured. In this embodiment, as shown in FIG. 6, the pump current Ip _n was 1.6 mA (dashed line b in FIG. 6).

Then, the calibration from the pump current Ip _n of the gas sensor 1b, by utilizing the previously determined correlation between the pumping current Ip and the sensor current value Is (solid line S in FIG. 6), the calibration gas sensor 1b of the sensor current value Is _n was estimated. In this embodiment, as shown in FIG. 6, the pump current value Ip _n calibration gas sensor 1b is deduced from it is 1.6 mA, the sensor current Is _n and 0.4Myuei (broken line b in FIG. 6).

Then, was compared with the reference sensor current Is ₀ of the sensor current Is _n and the reference gas sensor 1a of the calibration gas sensor 1b, the reference sensor current Is ₀ is to be 0.625 times the sensor current Is _n all right. Based on this, as shown in FIG. 7, a porous body 31 that further serves as diffusion resistance was disposed outside the diffusion resistance portion 3. Thereby, as shown in FIG. 6, the pump cell current value Ip of the calibration gas sensor 1b was adjusted to 1 mA which is the reference pump current value Ip ₀ of the reference gas sensor 1a (broken line b → broken line a in FIG. 6).

  As a result, as shown in FIG. 6, the sensor current value Is of the calibration gas sensor 1b is 0.25 μA, and as shown in FIG. 5, the sensor output characteristics of the calibration gas sensor 1b can be aligned with the sensor output characteristics of the reference gas sensor 1a. (Solid line A in FIG. 5).

On the other hand, for the calibration gas sensor 1c, it was determined pump current value Ip _n of the pump cell 4 when introducing the calibration gas into the gas chamber 2 to be measured. In this embodiment, as shown in FIG. 6, the pump current Ip _n was 0.8 mA (broken line c in FIG. 6).

Then, a calibration from the pump current Ip _n of the gas sensor 1b, by utilizing the previously obtained correlation between the pumping current Ip and the sensor current value Is (solid line S in FIG. 6), the calibration gas sensor 1b of the sensor current value Is _n was estimated. In this embodiment, as shown in FIG. 6, the pump current value Ip _n calibration gas sensor 1b is deduced from it is 0.8 mA, the sensor current Is _n and 0.2 .mu.A (broken line c in FIG. 6).

Next, when the sensor current value Is _n of the calibration gas sensor 1c is compared with the reference sensor current value Is _{0 of the} reference gas sensor 1a, the reference sensor current value Is ₀ is 1.25 times the sensor current value Is _n. all right. Based on this, as shown in FIG. 1, the tip of the gas sensor 1 (left side in FIG. 1) was cut to shorten the length of the diffusion resistance unit 3 in the direction in which the gas to be measured is communicated. Thereby, as shown in FIG. 6, the pump cell current value Ip of the calibration gas sensor 1c was adjusted to 1 mA which is the reference pump current value Ip ₀ of the reference gas sensor 1a (broken line c → broken line a in FIG. 6).

  As a result, as shown in FIG. 6, the sensor current value Is of the calibration gas sensor 1c is 0.25 μA, and as shown in FIG. 5, the sensor output characteristics of the calibration gas sensor 1b can be aligned with the sensor output characteristics of the reference gas sensor 1a. (Solid line A in FIG. 5).

Next, the effect of the gas sensor calibration method of this example will be described.
In this example, in the sensor output characteristic correction step, the sensor output characteristics of the calibration gas sensors 1b and 1c are corrected by changing the diffusion resistance of the diffusion resistance unit 3 and adjusting the sensor current value Is of the calibration gas sensors 1b and 1c. To do. Therefore, it becomes easy to correct the sensor output characteristics of the calibration gas sensors 1b and 1c so as to be equivalent to the sensor output characteristics of the reference gas sensor 1a.
In addition, the same effects as those of the first embodiment are obtained.

(Example 3)
In this example, as shown in FIG. 8, the influence of the height of the gas chamber 2 to be measured on the sensor current value Is of the sensor cell 5 is examined.
In this example, first, a plurality of gas sensors 1 having different heights of the gas chamber 2 to be measured were prepared. In addition, the structure of the gas sensor 1 is the same as that of Example 1 (refer FIG. 1, FIG. 2). The measured gas chamber 2 has a width of 3.0 mm and a length of 8.0 mm.

Next, for each gas sensor 1, the sensor current value Is of the sensor cell 5 when 100 ppm NO gas was introduced into the measured gas chamber 2 was measured. The diffusion resistance unit 3 is set so that the pump current value Ip of the pump cell 4 when the 20% O ₂ gas is introduced into the gas chamber 2 to be measured is 1 mA.
The measurement results are shown in FIG.

FIG. 8 shows the relationship between the height (mm) of the gas chamber to be measured and the sensor current value Is (μA).
From the figure, it can be seen that the sensor current value Is of the sensor cell 5 decreases as the height of the gas chamber 2 to be measured decreases. This is because the diffusion resistance in the measured gas chamber 2 increases as the height of the measured gas chamber 2 decreases. That is, the sensor current value Is is affected not only by the diffusion resistance of the diffusion resistance unit 3 but also by the diffusion resistance in the gas chamber 2 to be measured.

  On the other hand, it can be seen that the sensor current value Is of the sensor cell 5 becomes substantially constant as the height of the gas chamber 2 to be measured increases. In this example, the sensor current value Is of the sensor cell 5 becomes substantially constant by setting the height of the gas chamber 2 to be measured to 0.1 mm or more. This is because the diffusion resistance in the measured gas chamber 2 becomes sufficiently small when the height of the measured gas chamber 2 increases. That is, the sensor current value Is is determined by the diffusion resistance of the diffusion resistance unit 3 without being affected by the diffusion resistance in the gas chamber 2 to be measured.

  From the above results, by setting the height of the measured gas chamber 2 to 0.1 mm or more, the diffusion resistance in the measured gas chamber 2 can be made sufficiently smaller than the diffusion resistance of the diffusion resistance portion 3. The pump current value Ip and the sensor current value Is can both be determined by the diffusion resistance of the diffusion resistance unit 3, and the correlation between the two can be obtained with higher accuracy.

DESCRIPTION OF SYMBOLS 1 Gas sensor 2 Gas chamber to be measured 3 Diffusion resistance part 4 Pump cell 5 Sensor cell

Claims (8)

A gas chamber to be measured into which a gas to be measured is introduced, a diffusion resistance portion for introducing the gas to be measured under a predetermined diffusion resistance into the gas chamber to be measured, and a solid electrolyte body for oxygen ion conductive pump And a pump cell for adjusting the oxygen concentration in the gas chamber to be measured, and a pair of pump electrodes respectively disposed on the surface on the gas gas chamber side and the surface on the opposite side of the pump solid electrolyte body A solid electrolyte body for oxygen ion conductive sensor, and a pair of sensor electrodes respectively disposed on the surface of the sensor solid electrolyte body on the gas gas measuring chamber side and on the opposite surface. A gas sensor calibration method comprising a sensor cell for detecting a specific component concentration in a gas to be measured introduced into a measurement gas chamber,
Among some of the produced gas sensors, for some of the gas sensors, the pump current value Ip that flows between the pair of pump electrodes of the pump cell with respect to the oxygen gas with a predetermined concentration and the specific component gas with a predetermined concentration A correlation creating step of measuring a sensor current value Is flowing between the pair of sensor electrodes of the sensor cell and obtaining a correlation between the pump current value Ip and the sensor current value Is;
Reference current to set the reference pumping current Ip ₀ and the reference sensor current Is ₀ is the pumping current Ip and the sensor current value Is for the reference gas sensor as a reference of the plurality of gas sensors so as to satisfy the above correlation A value setting process;
With calibration gas is oxygen gas of the predetermined concentration, the pump current value measuring step of measuring the pumping current Ip _n is the pumping current Ip for the calibration gas sensor to be calibrated of the plurality of gas sensors ,
From the pumping current Ip _n, by utilizing the correlation, and the sensor current value estimation step of estimating the sensor current value Is _n is the sensor current value Is for the calibration gas sensor,
The sensor current value Is _n and the reference sensor current value Is ₀ are compared, and the sensor output characteristic of the calibration gas sensor is corrected so that the sensor output characteristic of the calibration gas sensor is equivalent to the sensor output characteristic of the reference gas sensor. And a sensor output characteristic correcting step for performing a gas sensor calibration method.   2. The gas sensor calibration method according to claim 1, wherein the gas sensor is configured to convert the sensor current value Is with a predetermined amplification factor and output the voltage, and in the sensor output characteristic correction step, the calibration gas sensor A gas sensor calibration method, wherein the sensor output characteristics of the calibration gas sensor are corrected by adjusting the amplification factor. In the calibration method of the gas sensor according to claim 1, in the above sensor output characteristic correction process, to change the diffusion resistance of the diffusion resistance portion, by adjusting the sensor current Is _n of the calibration gas sensor, the calibration gas sensor A gas sensor calibration method comprising correcting the sensor output characteristics of the gas sensor.   The gas sensor calibration method according to any one of claims 1 to 3, wherein the pump current value measurement step uses air as the calibration gas.   5. The gas sensor calibration method according to claim 1, wherein the specific component is nitrogen oxide.   6. The gas sensor calibration method according to claim 1, wherein the pump current value Ip and the sensor current value Is in the gas sensor are both determined by a diffusion resistance of the diffusion resistance unit. A gas sensor calibration method characterized by the above.   7. The gas sensor calibration method according to claim 6, wherein a height of the gas chamber to be measured is 0.1 mm or more. The gas sensor according to claim 6 or 7, wherein one of the pump electrodes of the pump cell facing the gas chamber to be measured is more than the one of the sensor electrodes of the sensor cell facing the gas chamber to be measured. A method for calibrating a gas sensor, characterized in that the gas sensor is disposed at a position close to the diffusion resistance portion, and both are disposed at positions not facing each other in the gas chamber to be measured .

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