JP2013228283A - Gas sensor evaluation method and gas sensor evaluation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve evaluation precision of a gas sensor for downstream-side exhaust gas.SOLUTION: Contents of respective components included in a sample gas equivalent to an exhaust gas are measured, and a model gas generated with composition in which the content of nitrogen oxide (NOx) substitutes for the content of oxygen (O) among the contents of the respective components measured with respect to the sample gas is supplied to a gas sensor, and the gas sensor is evaluated based upon sensor output characteristics to the model gas.

Description

The present invention relates to a gas sensor for detecting oxygen (O ₂ ) contained in exhaust gas of an internal combustion engine, and more particularly to a technique for evaluating such a gas sensor.

  As a gas sensor evaluation technique, it has been proposed to evaluate a gas sensor using a model gas simulating an exhaust gas of an actual vehicle (see, for example, Patent Document 1). In Patent Document 1, in order to evaluate a gas sensor installed on the exhaust side of the exhaust system of the internal combustion engine, the exhaust gas on the exhaust side (hereinafter referred to as “downstream exhaust gas”). It is described that a gas sensor is evaluated using a model gas that imitates the above.

JP 2006-17535 A

  In the evaluation of a gas sensor using model gas, in order to improve the evaluation accuracy of the gas sensor, it is required to improve the correlation with the sensor output characteristics in an actual vehicle. In particular, when the content of each component of the exhaust gas downstream of the actual vehicle is measured and the model gas generated according to the measured content of each component is used, the lean combustible component is less than the stoichiometric air-fuel ratio. In the area, the correlation with the sensor output characteristics in the actual vehicle was not enough.

  In view of the above-described problems, an object of the present invention is to provide a technique capable of improving the evaluation accuracy of a gas sensor for downstream exhaust gas.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1] In the gas sensor evaluation method in Application Example 1, the gas sensor for detecting oxygen (O ₂ ) contained in the exhaust gas at the discharge destination side of the purification device in the exhaust system of the internal combustion engine is used as the gas sensor for the model gas. A gas sensor evaluation method for evaluating based on output characteristics, wherein the plurality of components are contained in a sample gas corresponding to the exhaust gas, and include at least oxygen (O ₂ ) and nitrogen oxides (NOx). The content of each component is measured, and at least part of the content of oxygen (O ₂ ) is the same number of oxygen atoms with respect to the content of each component in the plurality of components measured for the sample gas. in terms of nitrogen oxides (NOx) with the set having a reduced content of oxygen (O ₂₎ with increasing plus the content of nitrogen oxides (NOx) In, it generates the model gas, and supplying the model gas in the gas sensor, and evaluating the output characteristic of the gas sensor.
According to this application example, the composition of the model gas in which oxygen (O ₂ ) is replaced with nitrogen oxide (NOx) can be easily obtained. In addition, by evaluating a gas sensor using a model gas in which a part of oxygen (O ₂ ) is replaced with nitrogen oxide (NOx) among sample gases containing components corresponding to exhaust gas, an actual vehicle in a lean region is obtained. Thus, the correlation with the sensor output characteristics can be improved. As a result, it is possible to improve the evaluation accuracy of the gas sensor for the downstream exhaust gas.

[Application Example 2] In the gas sensor evaluation method according to Application Example 1, the composition of the model gas is obtained by oxidizing all of the oxygen (O ₂ ) contents measured for the sample gas with nitrogen atoms having the same number of oxygen atoms. It is good also as a composition converted into a thing (NOx).
According to this application example, the correlation with the sensor output with respect to the downstream side exhaust gas can be further improved.

Application Example 3 In the gas sensor evaluation method of Application Example 1 or Application Example 2, the model gas may correspond to the exhaust gas burned at an air-fuel ratio of greater than 1.0000 and not greater than 1.0150.
According to this application example, it is possible to improve the correlation of the sensor output in the lean region that is larger than 1.0000 and equal to or smaller than 1.0150.

Application Example 4 In the gas sensor evaluation method according to any one of Application Examples 1 to 3, the gas sensor may be a zirconia oxygen sensor.
According to this application example, the evaluation accuracy of the zirconia oxygen sensor for the downstream exhaust gas can be improved.

Application Example 5 In the gas sensor evaluation method according to any one of Application Examples 1 to 4, the content of oxygen (O ₂ ) contained in the sample gas may be measured using a magnetic pressure method.
According to this application example, it is possible to improve the evaluation accuracy in the evaluation of the gas sensor for the downstream exhaust gas using the model gas generated based on the oxygen measurement result by the magnetic pressure method.

Application Example 6 In the gas sensor evaluation method according to any one of Application Examples 1 to 5, the content of nitrogen oxide (NOx) contained in the sample gas may be measured using a chemiluminescence method.
According to this application example, the evaluation accuracy can be improved in the evaluation of the gas sensor for the downstream exhaust gas using the model gas generated based on the measurement result of nitrogen oxides by the chemiluminescence method.

Application Example 7 In the gas sensor evaluation method according to any one of Application Examples 1 to 6, the plurality of components to be measured for content in the sample gas are oxygen (O ₂ ) and nitrogen oxide (NOx). In addition to carbon dioxide (CO ₂ ), carbon monoxide (CO), hydrogen (H ₂ ), propane (C ₃ H ₈ ), propylene (C ₃ H ₆ ), methane (CH ₄ ), water (H ₂ O), nitrogen (N ₂ ), or argon (Ar) may be included.
According to this application example, the reproducibility of the downstream side exhaust gas by the model gas can be improved.

[Application Example 8] A gas sensor evaluation apparatus according to Application Example 8 is a gas sensor that detects oxygen (O ₂ ) contained in exhaust gas at a discharge destination side of a purification apparatus in an exhaust system of an internal combustion engine. A gas sensor evaluation apparatus that evaluates based on output characteristics, wherein the plurality of components are contained in a sample gas corresponding to the exhaust gas, and include at least oxygen (O ₂ ) and nitrogen oxides (NOx). , The content of each component measured for, and at least part of the content of oxygen (O ₂ ) is converted to nitrogen oxide (NOx) having the same number of oxygen atoms, and nitrogen oxide (NOx in the oxygen (O ₂₎ composition having a reduced content of together to plus increasing the content of) a gas generating unit for generating the model gas, generated by the model gas generator Characterized in that it comprises a gas supply unit for supplying the model gas in the gas sensor.
According to this application example, the composition of the model gas in which oxygen (O ₂ ) is replaced with nitrogen oxide (NOx) can be easily obtained. In addition, by evaluating a gas sensor using a model gas in which a part of oxygen (O ₂ ) is replaced with nitrogen oxide (NOx) among sample gases containing components corresponding to exhaust gas, an actual vehicle in a lean region is obtained. Thus, the correlation with the sensor output characteristics can be improved. As a result, it is possible to improve the evaluation accuracy of the gas sensor for the downstream exhaust gas.

Application Example 9 In the gas sensor evaluation apparatus according to Application Example 9, the composition of the model gas is obtained by oxidizing all the oxygen (O ₂ ) contents measured for the sample gas with nitrogen atoms having the same number of oxygen atoms. It is good also as a composition converted into a thing (NOx).
According to this application example, the correlation with the sensor output with respect to the downstream side exhaust gas can be further improved.

  The form of the present invention is not limited to the form of the gas sensor evaluation method and the gas sensor evaluation apparatus. For example, the present invention can be applied to various forms such as a gas sensor evaluation computer control method, a gas sensor manufacturing method, and a gas sensor. . Further, the present invention is not limited to the above-described embodiments, and it is needless to say that the present invention can be implemented in various forms without departing from the spirit of the present invention.

It is explanatory drawing which shows the cross-sectional structure of the gas sensor which is an example of evaluation object. It is explanatory drawing which shows an example of the usage condition of a gas sensor. It is explanatory drawing which shows the structure of a gas sensor evaluation apparatus. It is explanatory drawing which shows a gas sensor evaluation process. It is a table | surface which shows an example of the result of having measured content of each component contained in sample gas. It is a table | surface which shows an example of the composition utilized for the setting of model gas. It is a table | surface which shows an example of the composition utilized for the setting of model gas. It is a table | surface which shows an example of a composition of the model gas used for evaluation of this embodiment. It is a graph which shows the result of the comparison test of model gas.

A. Embodiment:
A-1. Gas sensor configuration:
FIG. 1 is an explanatory diagram illustrating a cross-sectional configuration of a gas sensor 10 that is an example of an evaluation target. FIG. 2 is an explanatory diagram showing an example of how the gas sensor 10 is used. FIG. 1 illustrates a cross section of the gas sensor 10 cut along the axis CA, which is the central axis of the gas sensor 10. In the description of the present embodiment, the lower side of the paper surface of the gas sensor 10 is referred to as “front end side”, and the upper side of the gas sensor 10 is referred to as “rear end side”.

The gas sensor 10 is an oxygen sensor that is attached to an exhaust system 900 of an internal combustion engine and detects oxygen (O ₂ ) contained in the exhaust gas. In this embodiment, the gas sensor 10 is a zirconia oxygen sensor using zirconia (zirconium dioxide (ZrO ₂ )).

  As shown in FIG. 2, in this embodiment, the gas sensor 10 is attached to an exhaust pipe 930 that is located on the exhaust destination side (downstream side of the exhaust gas flow) with respect to the purification device 920 in the exhaust system 900. Further, oxygen contained in the exhaust gas on the exhaust destination side (downstream exhaust gas) is detected. In the present embodiment, the front end side of the gas sensor 10 is inserted inside the exhaust pipe 930, and the rear end side of the gas sensor 10 is arranged outside the exhaust pipe 930. In the present embodiment, the purification device 920 of the exhaust system 900 is a three-way catalyst provided on the downstream side of the exhaust manifold 910, and on the downstream side of the purification device 920, an exhaust pipe 930, a silencer 940, and an exhaust gas are sequentially arranged. A tube 950 is provided.

  As shown in FIG. 1, the gas sensor 10 includes a sensor element 100, a heating element 150, a metal shell 200, a protector 300, an outer cylinder 410, a first output terminal 520, a second output terminal 530, One lead wire 570, a second lead wire 580, and a third lead wire 590 are provided.

  The sensor element 100 of the gas sensor 10 constitutes an oxygen concentration cell that outputs an electromotive force according to the oxygen partial pressure. The sensor element 100 includes a solid electrolyte body 110, an inner electrode 120, and an outer electrode 130.

The solid electrolyte body 110 of the sensor element 100 is made of a material having oxide ion conductivity (oxygen ion conductivity), and is formed in a bottomed cylindrical shape that extends along the axis CA and closes the tip side. In this embodiment, the material of the solid electrolyte body 110 is zirconium oxide (ZrO ₂ ) to which yttrium oxide (Y ₂ O ₃ ) is added, that is, yttria partially stabilized zirconia. In another embodiment, the material of the solid electrolyte body 110 is an oxide selected from calcium oxide (CaO), magnesium oxide (MgO), cerium oxide (CeO ₂ ), aluminum oxide (Al ₂ O ₃ ), and the like. Added partially stabilized zirconia may also be used.

  The inner electrode 120 of the sensor element 100 is formed so as to cover the inner side of the solid electrolyte body 110. The outer electrode 130 of the sensor element 100 is formed so as to cover the outer side of the solid electrolyte body 110. In this embodiment, the material of the inner electrode 120 and the outer electrode 130 is platinum (Pt). However, in other embodiments, it may be a platinum alloy, other noble metals, or other noble metal alloys. May be. In the present embodiment, the inner electrode 120 and the outer electrode 130 are formed by electroless plating.

  The heating element 150 of the gas sensor 10 is provided inside the sensor element 100, generates heat based on the electric power via the third lead wire 590, and heats the sensor element 100. In this embodiment, in order to improve the accuracy of the gas sensor 10, the temperature of the sensor element 100 is kept constant by adjusting the electric power supplied from the third lead wire 590 to the heating element 150.

  The metal shell 200 of the gas sensor 10 is a cylindrical metal member. The sensor element 100 is held inside the metal shell 200. A screw part 210 is formed on the outer periphery of the metal shell 200, and the gas sensor 10 is attached to the exhaust pipe 930 via the screw part 210.

  The protector 300 of the gas sensor 10 is a bottomed cylindrical metal member. The protector 300 is fixed to the distal end side of the metallic shell 200 so as to cover the sensor element 100 protruding from the distal end side of the metallic shell 200 and protects the sensor element 100. Through holes 311 and 312 are formed in protector 300 so that exhaust gas can be introduced into sensor element 100.

  The outer cylinder 410 of the gas sensor 10 is a cylindrical metal member. The outer cylinder 410 is fixed to the rear end side of the metal shell 200 so as to cover the sensor element 100, the heating element 150, the first output terminal 520, and the second output terminal 530 protruding from the rear end side of the metal shell 200. The sensor element 100, the heating element 150, the first output terminal 520, and the second output terminal 530 are protected.

  In the present embodiment, the sensor element 100 is configured to be able to introduce outside air into the sensor element 100. The outside air introduced inside the sensor element 100 is used as a reference gas that serves as a reference for the gas sensor 10 to detect oxygen from the exhaust gas.

  The first output terminal 520 of the gas sensor 10 is a conductor that electrically connects the inner electrode 120 formed in the sensor element 100 and the first lead wire 570. The second output terminal 530 of the gas sensor 10 is a conductor that electrically connects the outer electrode 130 formed on the sensor element 100 and the second lead wire 580. The first lead wire 570 and the second lead wire 580 of the gas sensor 10 are electrically connected to a processing circuit (not shown) that processes the sensor output from the gas sensor 10.

  In the gas sensor 10, the inner electrode 120 functions as a reference electrode that is exposed to the outside air that is the reference gas, and the outer electrode 130 functions as a detection electrode that is exposed to the exhaust gas. As a result, an electromotive force is generated in the sensor element 100 according to the oxygen concentration difference between the reference gas and the exhaust gas. The electromotive force of the sensor element 100 is output as a sensor output to the outside of the gas sensor 10 via the first lead wire 570 and the second lead wire 580.

A-2. Configuration of gas sensor evaluation device:
FIG. 3 is an explanatory diagram showing the configuration of the gas sensor evaluation device 60. The gas sensor evaluation device 60 evaluates the gas sensor 10 based on the sensor output characteristics of the gas sensor 10 with respect to the model gas imitating the exhaust gas. In the present embodiment, the gas sensor evaluation device 60 uses oxygen (O ₂ ) among the content of each component measured for a plurality of components included in the sample gas corresponding to the exhaust gas that is the target of oxygen detection by the gas sensor 10. The model gas can be generated with a composition in which the content of nitrogen oxides is reduced and the content of nitrogen oxides (NOx) is increased.

  The gas sensor evaluation device 60 includes an evaluation control unit 610, a gas analysis unit 630, a result output unit 680, a gas generation unit 700, and a gas supply unit 800. In the gas sensor evaluation device 60, the model gas generated by the gas generation unit 700 is supplied to the gas sensor 10 to be evaluated attached to the gas supply unit 800.

  The gas generation unit 700 of the gas sensor evaluation device 60 generates a model gas based on a control signal from the evaluation control unit 610. The gas generation unit 700 includes storage units 711 to 719 and flow rate adjustment units 731 to 739.

The storage unit 711 of the gas generation unit 700 is a tank that stores nitrogen (N ₂ ). The flow rate adjustment unit 731 of the gas generation unit 700 adjusts the flow rate of nitrogen supplied from the storage unit 711 to the gas supply unit 800 based on the control signal from the evaluation control unit 610.

The storage unit 712 of the gas generation unit 700 is a tank that stores carbon dioxide (CO ₂ ). The flow rate adjustment unit 732 of the gas generation unit 700 adjusts the flow rate of carbon dioxide supplied from the storage unit 712 to the gas supply unit 800 based on the control signal from the evaluation control unit 610.

The storage unit 713 of the gas generation unit 700 is a tank that stores oxygen (O ₂ ). The flow rate adjustment unit 733 of the gas generation unit 700 adjusts the flow rate of oxygen supplied from the storage unit 713 to the gas supply unit 800 based on the control signal from the evaluation control unit 610.

  The storage unit 714 of the gas generation unit 700 is a tank that stores carbon monoxide (CO). The flow rate adjustment unit 734 of the gas generation unit 700 adjusts the flow rate of carbon monoxide supplied from the storage unit 714 to the gas supply unit 800 based on the control signal from the evaluation control unit 610.

The storage unit 715 of the gas generation unit 700 is a tank that stores hydrogen (H ₂ ). The flow rate adjustment unit 735 of the gas generation unit 700 adjusts the flow rate of hydrogen supplied from the storage unit 715 to the gas supply unit 800 based on the control signal from the evaluation control unit 610.

The storage unit 716 of the gas generation unit 700 is a tank that stores propane (C ₃ H ₈ ). The flow rate adjustment unit 736 of the gas generation unit 700 adjusts the flow rate of propane supplied from the storage unit 716 to the gas supply unit 800 based on the control signal from the evaluation control unit 610.

The storage unit 717 of the gas generation unit 700 is a tank that stores methane (CH ₄ ). The flow rate adjustment unit 737 of the gas generation unit 700 adjusts the flow rate of methane supplied from the storage unit 717 to the gas supply unit 800 based on the control signal from the evaluation control unit 610.

  The storage unit 718 of the gas generation unit 700 is a tank that stores nitric oxide (NO). The flow rate adjustment unit 738 of the gas generation unit 700 adjusts the flow rate of nitric oxide supplied from the storage unit 718 to the gas supply unit 800 based on the control signal from the evaluation control unit 610.

The storage unit 719 of the gas generation unit 700 is a tank that stores water (H ₂ O). The flow rate adjustment unit 739 of the gas generation unit 700 adjusts the amount of moisture supplied from the storage unit 719 to the gas supply unit 800 based on the control signal from the evaluation control unit 610. In this embodiment, moisture is added by the flow rate adjusting unit 739 to the gas containing at least one of nitrogen, carbon dioxide, and oxygen supplied from the flow rate adjusting units 731, 732, and 733.

  The gas supply unit 800 of the gas sensor evaluation device 60 supplies the model gas generated by the gas generation unit 700 to the gas sensor 10 to be evaluated. The gas supply unit 800 includes an evaluation exhaust pipe 810 and a heat generation unit 820.

  The evaluation exhaust pipe 810 of the gas supply unit 800 is a metal cylindrical body simulating the exhaust pipe 930 of an actual vehicle, and the model gas flows through the evaluation exhaust pipe 810. A heating unit 820 is provided on the upstream side of the model gas flow in the evaluation exhaust pipe 810. The downstream side of the flow of the model gas in the evaluation exhaust pipe 810 is configured so that the gas sensor 10 to be evaluated can be attached.

  In the present embodiment, the gas including at least one of nitrogen, carbon dioxide, oxygen, carbon monoxide, hydrogen, propane, methane, nitrogen monoxide, and water supplied from the flow rate adjusting units 731 to 739 in the gas generating unit 700 is Then, it is introduced into the evaluation exhaust pipe 810 from the upstream side of the heat generating portion 820.

  The heat generation unit 820 of the gas supply unit 800 adjusts the temperature of the model gas based on the control signal from the evaluation control unit 610. In the present embodiment, the heat generating portion 820 is provided on the outer periphery of the evaluation exhaust pipe 810 and adjusts the temperature of the model gas by heating the evaluation exhaust pipe 810.

  The evaluation control unit 610 of the gas sensor evaluation device 60 evaluates the evaluation target gas sensor 10 based on the sensor output output by the evaluation target gas sensor 10 attached to the gas supply unit 800. In the present embodiment, the evaluation control unit 610 stores in advance a database in which an allowable range of sensor output is set for each model gas composition, and determines whether the gas sensor 10 to be evaluated is acceptable by referring to the database. To do.

  The gas analysis unit 630 of the gas sensor evaluation device 60 analyzes the model gas in the vicinity of the evaluation target gas sensor 10 attached to the evaluation exhaust pipe 810. In the present embodiment, the gas analyzer 630 takes in the model gas from the vicinity of the gas sensor 10 to be evaluated, and analyzes the components included in the model gas. In the present embodiment, the gas analysis unit 630 is configured to be able to output the analysis result of the model gas to the evaluation control unit 610.

  The result output unit 680 of the gas sensor evaluation device 60 is configured to be able to output the evaluation result by the evaluation control unit 610. In the present embodiment, the result output unit 680 is a display device that outputs an evaluation result using an image. In other embodiments, the result output unit 680 may be an interface that outputs data indicating the evaluation result by the evaluation control unit 610 to another processing apparatus.

A-3. Gas sensor evaluation process:
FIG. 4 is an explanatory diagram showing the gas sensor evaluation process. The gas sensor evaluation process of FIG. 4 is a process for evaluating the gas sensor 10 using the gas sensor evaluation device 60.

  In the gas sensor evaluation process, first, the content of each component contained in the sample gas corresponding to the exhaust gas that is the target of oxygen detection by the gas sensor 10 is measured (step P110). Specifically, exhaust gas is acquired as a sample gas from a position SP (see FIG. 2) in the vicinity of the gas sensor 10 mounted on the exhaust pipe 930 of the exhaust system 900 of the actual vehicle, and each component contained in the sample gas is acquired. Measure the content.

  FIG. 5 is a table showing an example of the result of measuring the content of each component contained in the sample gas. FIG. 5 shows the content of each component of the sample gas measured in a state where the sensor output Vout of the gas sensor 10 is output together with the sensor output Vout.

  In the test of FIG. 5, the content of each component was measured for 18 kinds of sample gases having a sensor output Vout of 0.07 to 0.73 V (volts). Among the values shown in FIG. 5, the values of the components at the sensor output Vout = 0.60 (V) are the values of the components at the sensor output Vout = 0.55 (V) and the sensor output Vout = 0.66. It is the value estimated from the relationship between the value of each component in (V). In the present embodiment, the gas sensor 10 is designed so that the sensor output Vout is 0.60 V when the excess air ratio λ = 1.0000.

In the test of FIG. 5, the internal combustion engine of the 2008 Honda Accord SULEV (Super Ultra Low Emission Vehicle), the rotational speed 2000 rpm (per minute), the intake amount 0.3 g / cyl (gram per cylinder), the catalyst usage history The operation was performed under the condition of 150 kmile (kilomile) by changing the excess air ratio λ of the exhaust gas. In the test of FIG. 5, the excess air ratio λ was measured at a position MP (see FIG. 2) in the vicinity of the gas sensor 10. In the test of FIG. 5, among the components of the sample gas, carbon dioxide (CO ₂ ), oxygen (O ₂ ), carbon monoxide (CO), hydrogen (H ₂ ), total hydrocarbons (THC), methane (CH ₄ ), Nitrogen monoxide (NO), and water (H ₂ O).

In the present embodiment, total hydrocarbons (THC) in the sample gas are detected using a flame ionization method (FID), and oxygen (O ₂ ) in the sample gas is detected using a magnetic pressure method (MPD). Specifically, the contents of total hydrocarbons (THC) and oxygen (O ₂ ) were measured using an analyzer FMA-720 mounted on an automobile exhaust gas measuring device MEXA-7400WBS manufactured by Horiba, Ltd. .

In the present embodiment, nitrogen monoxide (NO) and carbon dioxide (CO ₂ ) in the sample gas are detected using a non-dispersive infrared absorption method (NDIR). Specifically, each content of nitric oxide (NO) and carbon dioxide (CO ₂ ) is measured using an analyzer AIA-723 mounted on an automobile exhaust gas measuring device MEXA-7400WBS manufactured by Horiba, Ltd. did.

  In the present embodiment, chemiluminescence (CLD) is used to detect nitric oxide (NO) in the sample gas. Specifically, the content of nitric oxide (NO) was measured using an analyzer CLA-720A mounted on an automobile exhaust gas measuring device MEXA-7400WBS manufactured by Horiba, Ltd.

In this embodiment, methane (CH ₄ ) in the sample gas was detected using a gas chromatographic method (GC) and a flame ionization method (FID). Specifically, the content of methane (CH ₄ ) was measured using an analyzer GFA-720 mounted on an automobile exhaust gas measuring device MEXA-7400WBS manufactured by Horiba, Ltd.

In the present embodiment, hydrogen (H ₂ ) in the sample gas is detected using sector-type mass spectrometry. Specifically, the content of hydrogen (H ₂ ) was measured using a sector type mass spectrometer MSHA-1000WSL manufactured by Horiba, Ltd.

In the present embodiment, water (H ₂ O) in the sample gas is detected using Fourier transform infrared spectroscopy (FTIR). Specifically, the content of water (H ₂ O) was measured using an engine exhaust gas analyzer MEXA-6000FT manufactured by Horiba, Ltd.

Returning to the description of FIG. 4, after measuring the content of each component of the sample gas (step P110), the content of each component measured for the sample gas is decreased and the content of oxygen (O ₂ ) is reduced. The composition of the model gas in which the content of nitrogen oxide (NOx) is increased is set (process P120).

  FIG. 6 is a table showing an example of the composition used for setting the model gas. The composition of each stage in FIG. 6 corresponds to the composition of each stage in FIG. 5, and some values are changed for the model gas. FIG. 6 shows the excess air ratio λ and its reciprocal R (1 / λ) obtained from each changed composition using the following formula 1.

[Chemical Formula] in Formula 1 is a value indicating the content (concentration) of the component represented by the corresponding chemical formula in each composition. The constant β in Equation 1 is a value indicating the ratio of nitrogen (N ₂ ) to oxygen (O ₂ ) before combustion. In this embodiment, the concentration of nitrogen (N ₂ ) is 79.01% and oxygen ( The concentration of O ₂ ) was 20.9%, and β = 3.764. The molecular term after the constant β in Equation 1 indicates the amount of nitrogen (N ₂ ) before combustion, and the denominator term after the constant β indicates the amount of fuel that could not be combusted.

In each composition of FIG. 6, the value of carbon dioxide (CO ₂ ) was fixed at 13.38%, and the value of water (H ₂ O) was fixed at 11.8%. In each composition of FIG. 6, the content of propane (C ₃ H ₈ ) corresponding to the value of total hydrocarbons (THC) in the test results of FIG. 5 was set.

In each composition of FIG. 6, the value of each component was changed according to the upper limit value and the lower limit value of each component that can be adjusted by the gas sensor evaluation device 60. Specifically, for oxygen (O ₂ ), the supply lower limit was set to 0.0030%. For carbon monoxide (CO), the lower supply limit was set to 0.0010%. For hydrogen (H ₂ ), the supply upper limit was set to 0.0170% and the supply lower limit was set to 0.0015%. For methane (CH ₄ ), the supply upper limit was set to 15 ppm.

Various components thus set (carbon dioxide (CO ₂ ), oxygen (O ₂ ), carbon monoxide (CO), hydrogen (H ₂ ), propane (C ₃ H ₈ ), methane (CH ₄ ), monoxide The remaining components other than nitrogen (NO) and water (H ₂ O) were nitrogen (N ₂ ), and the content of nitrogen (N ₂ ) in each composition of FIG. 6 was set.

  FIG. 7 shows the composition used for setting the model gas shown in FIG. 6 from 1.000 to ± 0.10%, ± 0.20%, ± 0.30%, ± 0.50%, ± 1 It is a table | surface which shows content of each component corresponding to each of the excess air ratio (lambda) changed by each change rate of 0.000% and +/- 1.50%.

FIG. 8 is a table showing an example of the composition of the model gas used for the evaluation of this embodiment. The composition of each stage in FIG. 8 corresponds to the composition of each stage in FIG. 7, and is used to reduce the oxygen (O ₂ ) content and increase the nitrogen oxide (NOx) content. The value has changed. In the example of FIG. 8, in the lean region where the excess air ratio λ is from 1.0010 to 1.0150, all of the oxygen (O ₂ ) content is the same as that of nitrogen monoxide (NO) having the same number of oxygen atoms. As a quantity, it was set as the composition converted using the above-mentioned numerical formula 1.

  Returning to the description of FIG. 4, after setting the composition of the model gas (process P120), the gas sensor 10 to be evaluated is prepared (process P130), and the gas sensor 10 is attached to the gas sensor evaluation apparatus 60 (process P140). Then, the model gas produced | generated according to the set composition is supplied to the gas sensor 10, and the gas sensor 10 is evaluated based on the sensor output characteristic with respect to model gas (process P150). After evaluating the gas sensor 10, when evaluating the other gas sensor 10 to be evaluated, the other gas sensor 10 to be evaluated is attached to the gas sensor evaluation device 60 (process P140) and evaluated in the same manner (step 140). Step P150).

A-4. Model gas comparison test:
FIG. 9 is a graph showing the results of a model gas comparison test. FIG. 9 shows the sensor output characteristics of the gas sensor 10 with respect to various gases, with the excess air ratio λ on the horizontal axis and the sensor output Vout on the vertical axis. In the comparative test of FIG. 9, the sensor output characteristics of the replacement model gas, which is the model gas of FIG. 8 in which all of oxygen (O ₂ ) is replaced with nitric oxide (NO), and the model gas of FIG. The sensor output characteristics with the reproduced model gas were measured and compared with the sensor output characteristics when mounted on an actual vehicle (the same vehicle as in the test of FIG. 5).

  In the comparative test of FIG. 9, when measuring the sensor output characteristics by the replacement model gas and the reproduced model gas, the gas sensor 10 is attached to the gas sensor evaluation device 60, the temperature of the model gas is 450 ° C., and the flow rate of the model gas is 40L. The value of the sensor output Vout was measured in a static state where the sensor output Vout of the gas sensor 10 was stable for each model gas having each composition having different excess air ratio λ under the condition of / min (liter per minute). In the comparative test of FIG. 9, for each of the replacement model gas and the reproduction model gas, the sensor output in the state where the sensor element 100 of the gas sensor 10 is heated to 600 ° C. and the state where the sensor element 100 of the gas sensor 10 is heated to 800 ° C. Characteristics were measured.

  In the comparison test of FIG. 9, when measuring the sensor output characteristics of the actual vehicle, the sensor output Vout of the gas sensor 10 is in a static state where the sensor output Vout of the gas sensor 10 is stable under the same conditions as the test of FIG. 5. While measuring the value, the excess air ratio λ of the exhaust gas was measured at a position MP (see FIG. 2) in the vicinity of the gas sensor 10.

  As shown in FIG. 9, in the lean region where the excess air ratio λ is larger than 1.0000, the sensor output characteristics by the replacement model gas are compared with the sensor output characteristics by the reproduced model gas in the actual vehicle. The value is close, and the correlation with the sensor output characteristics in the actual vehicle is excellent.

A-5. effect:
According to the embodiment described above, by evaluating the gas sensor 10 using the replacement model gas (composition of FIG. 8) in which oxygen (O ₂ ) is replaced with nitric oxide (NO), as shown in FIG. Thus, it is possible to improve the correlation with the sensor output characteristics of the actual vehicle in the lean region. As a result, it is possible to improve the evaluation accuracy of the gas sensor 10 for downstream exhaust gas.

B. Other embodiments:
As mentioned above, although embodiment of this invention was described, this invention is not limited to such embodiment at all, Of course, it can implement with a various form within the range which does not deviate from the meaning of this invention.

For example, as in the composition of the model gas in FIG. 8, the total amount of oxygen (O ₂ ) is not converted as the content of nitric oxide (NO) having the same number of oxygen atoms, but oxygen (O ₂ ). Part of the content of ₂ ) may be converted as the content of nitric oxide (NO) having the same number of oxygen atoms.

In the embodiment of the present invention, nitrogen (N ₂ ) is used as the inert gas. However, the present invention is not limited to this, and argon (Ar) or the like may be used. Further, propylene (C ₃ H ₆ ) or the like may be used instead of propane (C ₃ H ₈ ).

DESCRIPTION OF SYMBOLS 10 ... Gas sensor 60 ... Gas sensor evaluation apparatus 100 ... Sensor element 110 ... Solid electrolyte body 120 ... Inner electrode 130 ... Outer electrode 150 ... Heat generating body 200 ... Main metal fitting 210 ... Screw part 300 ... Protector 311, 312 ... Through-hole 410 ... Outer cylinder 520 ... First output terminal 530 ... Second output terminal 570 ... First lead wire 580 ... Second lead wire 590 ... Third lead wire 610 ... Evaluation control unit 630 ... Gas analysis unit 680 ... Result output unit 700 ... Gas generation unit 711 to 719... Storage unit 731 to 739. Exhaust pipe CA ... axis MP ... position SP ... position

Claims (9)

A gas sensor evaluation method for evaluating a gas sensor for detecting oxygen (O ₂ ) contained in exhaust gas at a discharge destination side of a purification device in an exhaust system of an internal combustion engine based on output characteristics of the gas sensor with respect to a model gas,
A plurality of components contained in a sample gas corresponding to the exhaust gas, wherein at least a plurality of components including oxygen (O ₂ ) and nitrogen oxide (NOx), the content of each component is measured;
With respect to the content of each component in the plurality of components measured for the sample gas, at least a part of the content of oxygen (O ₂ ) is converted to nitrogen oxide (NOx) having the same number of oxygen atoms. The model gas is generated with a composition in which the content of nitrogen oxide (NOx) is increased and the content of oxygen (O ₂ ) is decreased.
A gas sensor evaluation method comprising: supplying the model gas to the gas sensor and evaluating an output characteristic of the gas sensor. The composition of the model gas is a composition obtained by converting all of the oxygen (O ₂ ) content measured for the sample gas into nitrogen oxides (NOx) having the same number of oxygen atoms. The gas sensor evaluation method according to claim 1.   3. The gas sensor evaluation method according to claim 1, wherein the model gas corresponds to the exhaust gas burned at an air-fuel ratio of greater than 1.0000 and equal to or less than 1.0150. 4.   The gas sensor evaluation method according to any one of claims 1 to 3, wherein the gas sensor is a zirconia oxygen sensor. 5. The gas sensor evaluation method according to claim 1, wherein the content of oxygen (O ₂ ) contained in the sample gas is measured using a magnetic pressure method.   The gas sensor evaluation method according to any one of claims 1 to 5, wherein a content of nitrogen oxide (NOx) contained in the sample gas is measured using a chemiluminescence method. In addition to oxygen (O ₂ ) and nitrogen oxides (NOx), the plurality of components whose contents are to be measured in the sample gas include carbon dioxide (CO ₂ ), carbon monoxide (CO), hydrogen ( H ₂ ), propane (C ₃ H ₈ ), propylene (C ₃ H ₆ ), methane (CH ₄ ), water (H ₂ O), nitrogen (N ₂ ), argon (Ar) The gas sensor evaluation method according to any one of claims 1 to 6, wherein: A gas sensor evaluation device that evaluates a gas sensor that detects oxygen (O ₂ ) contained in exhaust gas at a discharge destination side of a purification device in an exhaust system of an internal combustion engine based on output characteristics of the gas sensor with respect to a model gas,
With respect to the content of each component measured for a plurality of components included in the sample gas corresponding to the exhaust gas and including at least oxygen (O ₂ ) and nitrogen oxide (NOx), At least a part of the content of oxygen (O ₂ ) is converted to nitrogen oxide (NOx) having the same number of oxygen atoms to increase the content of nitrogen oxide (NOx) and increase the oxygen (O _2). ) With a composition in which the content is reduced, a gas generating unit that generates the model gas;
A gas sensor evaluation apparatus comprising: a gas supply unit configured to supply the model gas generated by the model gas generation unit to the gas sensor. The composition of the model gas is a composition obtained by converting all of the oxygen (O ₂ ) content measured for the sample gas into nitrogen oxides (NOx) having the same number of oxygen atoms. The gas sensor evaluation apparatus according to claim 8.

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