JP3873351B2 - NOx sensor element - Google Patents

Description

[0001]
【Technical field】
The present invention relates to NO, NO in a gas to be measured such as exhaust gas discharged from an automobile internal combustion engine.₂The present invention relates to a NOx sensor element for detecting the concentration of NOx gas such as.
[0002]
[Prior art]
Air pollution caused by exhaust gas has caused serious problems in modern society, and purification standards and regulations for pollutants in exhaust gas are becoming stricter year by year. Therefore, studies are underway to reduce pollutants in exhaust gas discharged from internal combustion engines such as automobiles using combustion control and catalytic converters for gasoline or diesel engines.
[0003]
In the United States, the OBD-II regulations require a function for determining whether or not a catalyst used for cleaning exhaust gas is appropriate.
In contrast, two O₂2O using a sensor₂Although a sensor monitor system has been introduced, this method is not a direct detection method for pollutants, so it is difficult to accurately detect and judge whether pollutants are actually reduced from the exhaust gas. .
[0004]
If the combustion control monitor, catalyst monitor, etc. can directly detect the NOx concentration in the exhaust gas, it is possible to more accurately and effectively reduce pollutants in the exhaust gas.
That is, for example, if the fuel injection, the EGR rate, and the like can be feedback controlled from the knowledge of the NOx concentration in the exhaust gas, the pollutant component discharged from the internal combustion engine can be reduced.
Further, for example, the deterioration of the catalyst carried on the exhaust gas purification catalytic converter can be easily determined by providing a NOx sensor on the downstream side of the exhaust gas flow from the converter.
Against this background, a NOx sensor that can be mounted on a vehicle has been desired in recent years.
[0005]
The NOx sensor used for such applications is compact and inexpensive, and may be exposed to high-temperature exhaust gas during use. Therefore, the NOx sensor needs to be difficult to deteriorate both thermally and chemically. In addition, the NOx concentration must be able to be detected continuously under actual vehicle operating conditions.
[0006]
As the NOx sensor element mounted on the NOx sensor, In₂O_Three-SnO₂, Cr₂O_Three-Nb₂O_Five, WO_ThreeVarious semiconductor oxide-based materials have been reported in the past, but the use conditions of these NOx sensor elements are limited to temperatures of 500 ° C. or lower, and there are problems with durability against water and the like. .
[0007]
NASICON (Na_ThreeZn₂Si₂PO₁₂) Or Na such as β '/ β "alumina⁺A NOx sensor element using an ion conductor as a solid electrolyte and using nitrate or nitrite has also been reported. However, since the melting points of nitrate and nitrite are low, the NOx sensor element has a problem that it is difficult to operate above 500 ° C.
[0008]
For this reason, ZrO is thermally and chemically stable and has a proven track record.₂Conventionally, a NOx sensor element as shown in FIG. 11 using a solid electrolyte body has been proposed (Japanese Patent Laid-Open No. 6-18480).
[0009]
As shown in FIG. 11, the NOx sensor element 9 includes a main body 90 made of a zirconia solid electrolyte body and three chambers 931, 932 and 933 formed inside the main body 90. The main body 90 includes oxygen pumping cells 901 and 903 and a NOx detection cell 902.
[0010]
The chamber 931 is a space formed by the outer wall 921 and the partition wall 922 in the main body 90. The chamber 933 is a space formed by the outer wall 924 and the partition wall 923 in the main body 90. Further, the chamber 932 is a space defined by a partition wall 922 and a partition wall 923.
The partition walls 922 and 923 are provided with communication ports 942 and 943 that allow the chamber 931 and the chamber 932 and the chamber 932 and the chamber 933 to communicate with each other.
The chambers 931 and 933 are provided with inlets 941 and 944 for introducing a gas to be measured.
[0011]
The NOx detection cell 902 is provided on the partition wall 923. The oxygen pumping cells 901 and 903 are provided on the outer walls 921 and 924, respectively.
The oxygen pumping cell 901 includes the outer wall 921 and a pair of Pt first electrode 911 and second electrode 912 provided on the outer wall 921. The first electrode 911 is exposed to the outside of the NOx sensor element 9, and the second electrode 912 faces the chamber 931.
[0012]
The oxygen pumping cell 903 is also composed of the outer wall 924 and a pair of Pt third electrode 913 and fourth electrode 914 provided on the outer wall 924. The fourth electrode 914 is exposed to the outside of the NOx sensor element 9, and the third electrode 913 faces the chamber 933.
The first electrode 911 and the second electrode 912 are connected to a power source 991, and the third electrode 913 and the fourth electrode 914 are connected to a power source 993.
[0013]
The NOx detection cell 901 includes the partition wall 922 and a pair of Pt fifth electrode 915 and sixth electrode 916 provided on the partition wall 922. The fifth electrode 915 faces the chamber 932, and the sixth electrode 916 faces the chamber 933.
The electrodes 915 and 916 are connected to a voltage measuring device 992.
[0014]
The main body 90 is provided with insulating regions 981, 982. Thereby, it is possible to prevent the voltage applied to the oxygen pumping cells 901 and 903 from being mixed with the output of the NOx detection cell 902.
[0015]
In the NOx sensor element 9, the NOx concentration is detected as follows.
A gas to be measured is introduced into the chambers 931 and 933 from the inlets 941 and 944 to the NOx sensor element 9, respectively. A voltage is applied from a power source 991, 993 to the electrodes 911, 912, 913, 914 of the oxygen pumping cells 901, 903.
As a result, the oxygen pumping cells 901 and 903 are operated, and the oxygen gas contained in the measured gas is removed in the chambers 931 and 933.
[0016]
Thereafter, the gas to be measured in the chambers 931 and 933 is introduced into the chamber 932 through the communication ports 942 and 943.
Further, in the fifth electrode 915 and the sixth electrode 916, oxygen atoms in the NOx gas in the measurement gas are reduced to oxygen ions.
[0017]
The chamber 932 and the chamber 933 differ in the amount of NOx → oxygen ion reduction between the fifth electrode and the sixth electrode due to the difference in the dimensions of the chamber and the difference in the dimensions of the gas introduction port or the communication port. Different.
Therefore, the NOx detection cell 923 functions as an oxygen concentration battery.
Therefore, the voltage measuring device 992 connected to the NOx detection cell 923 can measure the voltage between both electrodes to measure the NOx concentration in the gas to be measured.
[0018]
[Problems to be solved]
However, the NOx sensor element 9 described above has the following problems.
The NOx concentration change in the measurement gas is easily affected by the partial pressure of oxygen in the measurement gas.
That is, the oxygen gas originally contained in the gas to be measured is removed by the oxygen pumping cells 901 and 903, but the determination of how much to remove is performed by separately installing an oxygen concentration detection cell in the chamber. You can't know without it.
When there is no oxygen concentration detection cell, it is unclear whether the output of the NOx sensor element 9 is proportional to the NOx concentration in the true measured gas.
[0019]
Further, the NOx sensor element 9 has a complicated structure in which three chambers (931, 932, 933) and two introduction ports (941, 944) are provided, and it is difficult to manufacture and maintain dimensional accuracy. . The characteristics of the NOx sensor element 9 are greatly affected by the shape of the element, the chamber, the dimensional accuracy of each electrode, and the like.
Therefore, the NOx sensor element 9 has a low reliability structure.
[0020]
Further, in the NOx sensor element 9, there are 2 signal lines connected to the oxygen pumping cells 901 and 903, and 2 signal lines connected to the NOx detection cell 902. Therefore, at least 6 signal lines are connected. Is necessary (see FIG. 10). For this reason, the NOx sensor element 9 has a complicated structure from this point of view and is difficult to assemble.
In addition, when the oxygen concentration detection cell is separately provided as described above, the number of signal lines is further increased, making the structure more complicated and difficult to manufacture.
[0021]
In view of such problems, the present invention is intended to provide a NOx sensor element that can maintain high dimensional accuracy, can detect NOx concentration with high accuracy, has a simple structure, and is easy to manufacture. .
[0022]
[Means for solving problems]
  The invention according to claim 1 has a NOx detection cell, a gas diffusion resistance layer for a gas introduction path to be measured arranged on the upper surface thereof, and a function of discharging oxygen arranged on the upper surface of the gas diffusion resistance layer. With an oxygen pumping cell,
  The NOx detection cell comprises an oxygen ion conductive first solid electrolyte body, a measured gas side NOx active electrode facing the gas diffusion resistance layer, and a counter electrode provided on the opposite surface,
  The oxygen pumping cell includes an oxygen ion conductive second solid electrolyte body and a pair of electrodes provided on the surface thereof, and the area of the electrode is the same as that of the NOx active electrode to be measured in the NOx detection cell. Larger than the area,
  And the measured gas side NOx active electrodeOn the other hand, when the electrode of the oxygen pumping cell is projected, the NOx active electrode to be measured gas side is provided at a position included in the projected portion of the electrode of the oxygen pumping cell.The NOx sensor element characterized by the above-mentioned.
[0023]
In the NOx detection cell, the measured gas side NOx active electrode is an electrode capable of reducing NOx gas in the measured gas into oxygen gas.
And as said to-be-measured gas side NOx active electrode, what consists of Pt, Rh, Pd, or those mixtures can be used.
The counter electrode does not need to have a NOx activity and can be made of a Pt-based material.
The NOx activation action is an action for decomposing NOx gas into N (ions) and O (ions).
[0024]
As the gas diffusion resistance layer, a porous ceramic, for example, a material made of alumina, spinel, steatite or the like can be used.
Further, it is preferable that the gas diffusion resistance layer is exposed on the side surface of the NOx sensor element so that the gas to be measured can be introduced therefrom.
This makes it easy to reduce the amount of diffusion of the gas to be measured. For this reason, the oxygen gas in the gas to be measured can be easily discharged by the oxygen pump cell.
[0025]
The gas diffusion resistance layer can be manufactured by, for example, a manufacturing method such as forming a paste as a raw material into a sheet and attaching it, or printing a paste as a raw material.
[0026]
The operation of the present invention will be described below.
In the NOx sensor element according to the present invention, the measurement gas is introduced to the measurement gas side NOx electrode through the gas diffusion resistance layer.
For this reason, the NOx sensor element according to the present invention is less prone to deformation of the element shape and can be manufactured while maintaining the dimensional accuracy as compared with the conventional NOx sensor element having a configuration in which a cavity is provided.
[0027]
The NOx sensor element can be operated if there are two signal lines for applying a voltage to the oxygen pumping cell and two signal lines for extracting the output from the NOx detection cell. Therefore, the NOx sensor element according to the present invention is easy to assemble, that is, easy to manufacture. The structure is also simple.
[0028]
As described above, according to the present invention, the dimensional accuracy can be kept high, the NOx concentration can be detected with high accuracy, and the NOx sensor element having a simple structure and easy to manufacture can be provided.
[0029]
In addition, by using the gas diffusion resistance layer, even if the flow rate of the gas to be measured fluctuates, the gas diffusion resistance layer can serve as a buffer, so that accurate NOx concentration detection can be performed. Can do.
In addition, a NOx sensor element with excellent responsiveness can be obtained because the distribution of holes through which gas passes can be easily controlled uniformly.
[0030]
Next, as in the invention of claim 2, the gas diffusion resistance layer preferably has a porosity of 1 to 20%.
As a result, the NOx concentration can be accurately measured even in an atmosphere containing a high oxygen concentration.
When the porosity is less than 1%, the applied voltage for removing oxygen can be reduced, and ZrO₂Although this is advantageous for the durability of the solid electrolyte, the gas permeation amount is small and the output value may be small. On the other hand, when it exceeds 20%, the applied voltage for removing oxygen increases and ZrO₂The durability of the solid electrolyte may be impaired.
[0031]
  next,In claim 1 aboveThe oxygen pumping cell comprises an oxygen ion conductive second solid electrolyte body and a pair of electrodes provided on the surface thereof, and the area of the electrodes is the area of the gas-side NOx active electrode to be measured in the NOx detection cell. Larger thanYes.
[0032]
As a result, the measured gas first reaches the electrode constituting the oxygen pumping cell, and then reaches the measured gas side NOx active electrode applied to the NOx detection cell.
Therefore, since the gas to be measured, from which oxygen gas has been removed in advance by the oxygen pumping cell, can reach the detection cell, a highly accurate NOx sensor element can be obtained.
[0033]
  Also,UpCoatMeasurement gas side NOx active electrode,ThatProjection image aboveIn oxygen pumping cellFormed to be included in the inner periphery of the electrode.The
[0034]
  This,acidSince the measurement gas from which oxygen gas has been removed in advance by the elementary pumping cell can reach the detection cell, a highly accurate NOx sensor element can be obtained.
[0035]
  Next, the claim3As described above, the insulating ceramic substrate is disposed on the lower surface of the NOx detection cell so as to face the counter electrode, is shielded from the gas to be measured, and forms a space extending to the atmospheric atmosphere inside the NOx sensor element. Is preferably provided.
  Thereby, since the decomposed oxygen used for detection is completely shielded from the measurement gas atmosphere side, measurement errors due to the generated oxygen can be eliminated.
  Further, the reason why the insulating ceramic substrate is used is that, as will be described later, this NOx sensor element is required to be provided with a heater portion as necessary, so that the NOx detection cell and the heater portion are insulated.
[0036]
  Next, the claim4As in the present invention, the NOx sensor element is preferably provided with a heater portion.
  As a result, the NOx sensor element can be quickly heated to the element activation temperature at which the NOx concentration can be detected, and the startability of the NOx sensor element in a low temperature environment can be improved.
[0037]
By the way, the oxygen pumping cell and the NOx detecting cell cannot be operated unless the NOx sensor element reaches the element activation temperature. For this reason, when the NOx sensor element is used for detecting NOx concentration in exhaust gas such as an automobile internal combustion engine, it is difficult to detect the concentration accurately because the exhaust gas temperature is low immediately after the internal combustion engine is started.
According to the present invention, since the heater for heating to the element activation temperature is provided, a NOx sensor element capable of detecting an accurate NOx concentration immediately after the internal combustion engine is started can be obtained.
[0038]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1
A NOx sensor element according to an embodiment of the present invention will be described with reference to FIGS. The NOx sensor element of this example is installed in the exhaust path of an automobile internal combustion engine and is used for combustion control of the internal combustion engine.
As shown in FIGS. 1 to 3, the NOx sensor element 1 of the present example includes a NOx detection cell 11, a gas diffusion resistance layer 13 for the gas introduction path to be measured, which is laminated on the upper surface thereof, and the gas diffusion resistance layer 13. And an oxygen pumping cell 12 having a function of discharging oxygen, which is laminated on the upper surface.
[0039]
The NOx detection cell 11 includes a first solid electrolyte body 110 having an oxygen ion conductivity, a counter electrode 112 provided on the surface thereof, an opposite surface thereof, and a measured gas side NOx facing the gas diffusion resistance layer 13. It consists of an active electrode 111.
In FIG. 1, reference numeral 16 denotes a protective sheet for protecting the electrode 121 and the lead portion 128 related to the oxygen pumping cell.
[0040]
The gas diffusion resistance layer 13 is made of alumina and has a porosity of 5% and a thickness of 200 μm.
The gas diffusion resistance layer 13 is partially provided for the NOx detection cell 11 and the oxygen pumping cell 12, and as shown in FIG. 1, a ceramic sheet 130 is provided on the right side thereof.
[0041]
The gas diffusion resistance layer 13 is exposed on the side surface of the NOx sensor element 1, and when the NOx concentration in the gas to be measured is detected, the gas to be measured is introduced from the exposed portion. .
The ceramic sheet 130 may be omitted, and the gas diffusion resistance layer 13 may be provided between the NOx detection cell 11 and the oxygen pumping cell 12.
[0042]
As shown in FIG. 1, the NOx detection cell 11 is provided with an electrode terminal 119 via a lead portion 118 for the measured gas side NOx active electrode 111.
Similarly, an electrode terminal 117 is provided for the counter electrode 112.
Although not shown in FIG. 1, the lead portion that is electrically connected to the counter electrode 112 is provided on the lower surface of the first solid electrolyte body 110. The lead portion provided on the lower surface of the first solid electrolyte body 110 and the electrode terminal 117 provided on the upper surface of the first solid electrolyte body 110 are connected by a through hole.
[0043]
As shown in FIG. 1, the oxygen pumping cell 12 includes an oxygen ion conductive second solid electrolyte body 120 and a pair of electrodes 121 and 122 provided on the surface thereof.
The oxygen pumping cell 12 is provided with an electrode terminal 129 with respect to the electrode 121 through a lead portion 128. Similarly, an electrode terminal 127 is provided for the electrode 122.
Although not shown in FIG. 1, the lead portion that is electrically connected to the counter electrode 122 is provided on the lower surface of the second solid electrolyte body 120. The lead portion provided on the lower surface of the second solid electrolyte body 120 and the electrode terminal 127 provided on the upper surface of the second solid electrolyte body 120 are connected by a through hole.
[0044]
The electrode terminal 117 is in electrical continuity with the electrode terminal 125 provided in the second solid electrolyte body 120 through a through hole 133 provided in the ceramic sheet 130. Similarly, the electrode terminal 119 is electrically connected to the electrode terminal 127 provided in the second solid electrolyte body 120 through a through hole 139 provided in the ceramic sheet 130.
[0045]
As shown in FIG. 2, the electrode terminals 125, 127, and 129 described above are exposed to the outside of the NOx sensor element 1 as shown in FIG. 2, and lead wires are connected thereto. The electrode terminal 125 is an electrode terminal for taking out an output from the NOx detection cell 11. The electrode terminal 129 is an electrode terminal for applying a voltage to the oxygen pumping cell 12. The electrode terminal 127 is an electrode terminal for grounding the NOx detection cell 11 and the oxygen pumping cell 12.
[0046]
Further, the measured gas side NOx active electrode 111 and the counter electrode 112 in the NOx detection cell 11 have the same shape and the same size. Similarly, the electrodes 121 and 122 in the oxygen pumping cell 12 have the same shape and size (see FIG. 4).
FIG. 4 shows a state when the electrode 122 is projected onto the measured gas side NOx active electrode 111.
[0047]
As shown in the figure, the measured gas side NOx active electrode 111 is provided at a position so as to be included in the portion where the electrode 122 is installed.
The measured gas side NOx active electrode 111 and the counter electrode 112 have a major axis of 8.5 mm and a minor axis of 1.2 mm, the electrodes 121 and 122 have a major axis of 12.0 mm and a minor axis of 3.6 mm. is there.
[0048]
An insulating ceramic base 14 is provided below the NOx detection cell 11. The insulating ceramic substrate 14 has a space 141 connected to the atmosphere provided to face the counter electrode 112.
[0049]
The NOx sensor element 1 is provided with a heater portion 15.
The heater unit 15 has a heater pattern 151 formed on the heater sheet 150 with a material mainly composed of Pt. Further, a covering sheet 159 is provided on the heater pattern 151 to cover it.
[0050]
Further, electrode terminals for energizing the heater pattern 151 are provided on the lower surface of the heater sheet 150 through lead portions 152 and through holes (not shown). The heater pattern 151 has a shape as shown in FIG. 1, and the heater pattern 151 projects the measured gas side NOx active electrode 111, the counter electrode 112, and the electrodes 121 and 122 in a projective manner. When viewed, the electrode is provided at a position that covers these electrodes.
[0051]
Next, a manufacturing method of the NOx sensor element 1 will be described.
First, the production of zirconia green sheets that will be the first solid electrolyte body 110 and the second solid electrolyte body 120 in the NOx detection cell 11 and the oxygen pumping cell 12 will be described.
[0052]
6 mol% Y₂O_ThreeAnd 94 mol% ZrO₂100 parts of yttria partially stabilized zirconia having an average particle size of 0.5 μm (parts by weight, the same applies hereinafter), 1 part of α-alumina, 5 parts of PVB (polyvinyl butyral), 10 parts of DBP (dibutyl phthalate), 10 parts of ethanol, A ceramic mixture consisting of 10 parts of toluene was prepared. Next, the ceramic mixture was mixed in a ball mill, and the slurry obtained by the mixing was molded by a doctor blade method so as to have a dry thickness of 0.4 mm to obtain a sheet compact.
[0053]
Next, the sheet compact was cut into a 5 × 70 mm rectangle.
Next, through holes required for taking out the output obtained from each electrode and the like from the same plane and for applying a voltage to be applied to each electrode from the same plane were provided in the sheet molded body.
[0054]
Next, a printing portion to be the gas-side NOx active electrode 111 to be measured was formed by screen printing using a platinum paste to which 1 to 10 wt% of Pd was added on one sheet molded body. Further, on the surface opposite to the surface provided with the printing portion, a printing portion serving as the counter electrode 112, the lead portion 118, and the electrode terminal 119 was formed by screen printing using platinum paste (see FIGS. 1 and 3).
The raw zirconia sheet | seat used as the NOx detection cell 11 was obtained by the above.
[0055]
Next, similarly to the NOx detection cell 1, the sheet compact was cut into a 5 × 70 mm rectangle to provide a through hole. Next, using a platinum paste to which 1 to 10 wt% of Au was added, a printing portion to be an electrode 122 on the measurement gas side was formed by screen printing. Further, the electrode 121, the lead portion 128, and the electrode terminals 129 and 127 were formed by screen printing on the surface opposite to the surface provided with the printing portion (see FIGS. 1 and 3).
Thus, a zirconia raw sheet to be the oxygen pumping cell 12 was obtained.
[0056]
Next, the production of the alumina raw sheet to be the ceramic substrate 14, the heater sheet 150, and the covering sheet 159 will be described.
A ceramic mixture comprising 98 parts of α-alumina having an average particle size of 0.3 μm, 3 parts of 6 mol% yttria partially stabilized zirconia, 10 parts of PVB, 10 parts of DBP, 30 parts of ethanol, and 30 parts of toluene was prepared.
[0057]
Next, from this ceramic mixture, the dry thickness is 0.5 mm (for the ceramic substrate 14), 0.3 mm (for the heater sheet 150 and the covering sheet 159), and the size is 5 × 70 mm in the same manner as described above. Two types of raw alumina sheets having a rectangular shape were obtained.
Thereafter, the raw alumina sheet used as the ceramic substrate 14 was closed by cutting one end thereof, the other end being opened, and a groove having a size of 2 × 65 mm so as to form a U-shape as a whole. This becomes the space 141.
Thereafter, a printing portion to be the heater pattern 151 and the lead portion 152 was formed on the alumina raw sheet for the heater sheet 150 by screen printing using a paste containing 10 wt% alumina in Pt.
[0058]
Next, the production of an alumina raw sheet to be the gas diffusion resistance layer 13 will be described.
A ceramic mixture comprising 100 parts of α-alumina having an average particle size of 0.4 μm, 10 parts of PVB, 10 parts of DBP, 30 parts of ethanol, and 30 parts of toluene was prepared.
From the ceramic mixture, an alumina raw sheet having a rectangular shape with a dry thickness of 0.25 mm and a size of 5 × 20 mm was obtained in the same manner as described above.
[0059]
Next, the production of the raw alumina sheet to be the protective sheet 16 will be described. A ceramic mixture comprising 100 parts of α-alumina having an average particle size of 0.5 μm, 10 parts of PVB, 10 parts of DBP, 30 parts of ethanol, and 30 parts of toluene was prepared.
An alumina raw sheet having a dry thickness of 0.3 mm and a size of 5 × 50 mm was obtained from the ceramic mixture in the same manner as described above.
[0060]
Moreover, the alumina raw sheet used as the said ceramic sheet 130 was created using the ceramic mixture similar to a ceramic base | substrate and a protection sheet so that it might become a rectangle whose dry thickness is 0.25 mm and the magnitude | size is 5x50 mm.
[0061]
Each green sheet obtained as described above was provided in the order shown in FIG. 1 and a paste having pressure-sensitive adhesiveness was provided between the green sheets at room temperature, and was laminated and pressure-bonded.
Thereafter, this laminate was fired in the atmosphere at 1500 ° C. for 1 hour to obtain the NOx sensor element 1 according to this example.
[0062]
Next, a method for attaching the NOx sensor element 1 to an automobile exhaust path will be described.
As shown in FIG. 5, the NOx sensor element 1 is assembled to the gas sensor assembly 4, and the gas sensor assembly 4 is attached to the exhaust path.
The gas sensor assembly 4 covers a holder 42 that holds the NOx sensor element 1 and a cover 41 that covers the side of the holder 42 that is exposed to the exhaust gas and protects the NOx sensor element 1 from exhaust gas that is a sample gas. Become.
[0063]
Further, as shown in FIG. 3, the NOx sensor element 1 is connected to a plurality of lead wires for the purpose of drawing out the output and applying a voltage. A housing 44 for storing the lead wires includes a gas sensor. It is provided in the assembly 4.
Further, the gas sensor assembly 4 is provided with a flange 43 for fixing it to the exhaust path.
Note that the cover 41 is provided with a plurality of vent holes 410 for allowing the exhaust gas to be sample gas to circulate. The lead wires are bundled into one and drawn out as a covered wire 49 from the housing 44.
[0064]
As shown in FIG. 6, the gas sensor assembly 4 is installed on the downstream side of the three-way catalyst 53 in the exhaust pipe 50 that is the exhaust path of the automobile engine 51. The flange 43 is fixed to the exhaust path with bolts via a gasket (not shown).
An A / F sensor 52 is disposed on the upstream side of the three-way catalyst 53.
In the above configuration, the lean burn precision control of the engine 51 or the deterioration detection of the three-way catalyst 53 is performed based on the signals of the NOx sensor element 1 and the A / F sensor 52 of this example.
[0065]
Next, the characteristics of the NOx sensor element according to this example were evaluated.
That is, the NOx sensor element has a temperature of 400 ° C. and a composition of 0 to 5000 ppm NO + 5% O.₂/ N₂It was exposed to a gas to be measured (1.2 liters / minute), and the temperature of the NOx sensor element itself was kept at 750 ° C., and the value of the output current from the NOx sensor element was measured.
The measurement results are shown in the diagram of FIG.
[0066]
According to the figure, it was found that the output current value from the NOx sensor element according to this example is proportional to the NO concentration in the gas to be measured.
That is, it was found that the NOx sensor element according to this example can measure the NOx concentration with high accuracy.
[0067]
Next, the gas diffusion resistance layer 13 of the NOx sensor element 1 according to this example will be described with reference to FIG.
As shown in FIG. 8, the gas diffusion resistance layer 13 controls the diffusion of the gas. For example, when the oxygen concentration in the atmospheric gas is changed, the diffusion of oxygen molecules is controlled according to each concentration, so that the sensor output is reduced. As shown in FIG. 8, it is proportional to the concentration.
[0068]
Next, the effect in this example is demonstrated.
In the NOx sensor element 1, the gas to be measured is introduced into the gas diffusion resistance layer 13.
Therefore, the NOx sensor element 1 is less likely to be deformed as compared with a NOx sensor element having a configuration in which a cavity is provided, and can be manufactured while maintaining dimensional accuracy.
[0069]
Further, since the gas diffusion resistance layer 13 is manufactured from a raw sheet, the dimensional accuracy can be improved.
Since the size of the gas diffusion resistance layer 13 affects the characteristics of the NOx sensor element, it is possible to manufacture a NOx sensor element with higher accuracy and less variation between products.
[0070]
Further, the NOx sensor element 1 of this example has a lead wire for taking out an output from the NOx detection cell 11, a lead wire for applying a voltage to the oxygen pumping cell 12, and the ground of the NOx detection cell 11 and the oxygen pumping cell 12. For this purpose, two lead wires for applying a voltage to the heater section 15 are connected, and a total of five lead wires can be operated.
Therefore, the NOx sensor element 1 can be easily assembled.
[0071]
Therefore, according to this example, the dimensional accuracy can be kept high, the NOx concentration can be detected with high accuracy, and the NOx sensor element having a simple structure and easy to manufacture can be provided.
[0072]
Embodiment 2
In the NOx sensor element of this example, as shown in FIG. 9, the oxygen pumping cell has an annular electrode.
That is, as shown in FIG. 9A, the electrode 122 in the oxygen pumping cell 12 is formed in an annular shape. Further, as shown in FIG. 9B, the projected image of the measured gas side NOx active electrode 111 in the NOx detection cell 11 is formed so as to be included in the inner peripheral portion 200 of the annularly formed electrode 122.
In addition, the structure of the NOx sensor element is the same as that of the first embodiment.
[0073]
In the NOx sensor element according to this example, the gas to be measured introduced from the gas diffusion resistance layer exposed on the side surface of the NOx sensor element first reaches the annular electrode applied to the oxygen pumping cell as in the first embodiment. To do. And the oxygen gas contained here is removed. Thereafter, it is possible to reach the measured gas side NOx active electrode applied to the NOx detection cell formed so as to be included in the inner peripheral portion of the annular electrode. For this reason, it is possible to detect the NOx concentration with high accuracy.
Others are the same as the first embodiment.
[0074]
Embodiment 3
As shown in FIG. 10, the NOx sensor element 3 of this example is provided with a protective layer for the counter electrode.
That is, as shown in FIG. 10, the NOx sensor element 3 of this example includes a NOx detection cell 11, a gas diffusion resistance layer 13 stacked on the upper surface thereof, and an oxygen layer stacked on the upper surface of the gas diffusion resistance layer 13. It consists of a pumping cell 12.
[0075]
The NOx detection cell 11 includes a first solid electrolyte body 110 having an oxygen ion conductivity, a counter electrode 112 provided on the surface thereof, an opposite surface thereof, and a measured gas side NOx facing the gas diffusion resistance layer 13. It consists of an active electrode 111.
The oxygen pumping cell 12 includes an oxygen ion conductive second solid electrolyte body 120 and a pair of electrodes 121 and 122 provided on the surface thereof. The surface of the electrode 121 is covered with a protective sheet 16.
[0076]
A ceramic base 34 is provided on the lower surface of the NOx detection cell 11, and a heater portion 35 is provided on the lower surface thereof. The heater unit 35 includes a heater sheet 350 provided with a heater pattern 351 and a covering sheet 359 covering the heater pattern 351.
[0077]
The ceramic base 34 and the heater section 35 are provided with a space 341, which is a space for discharging oxygen from the NOx sensor cell 11.
The space 341 is provided so as to face the counter electrode 112 in the NOx sensor cell 11, and the surface of the counter electrode 112 is covered with a protective layer 30.
Others are the same as the first embodiment.
[0078]
The NOx sensor element 3 according to this example does not require a closed space for removing oxygen discharged from the NOx detection cell, and the element structure is simplified.
The other effects are the same as those of the first embodiment.
[Brief description of the drawings]
1 is an exploded perspective view of a NOx sensor element according to Embodiment 1;
FIG. 2 is a perspective view of a NOx sensor element according to Embodiment 1;
3 is a cross-sectional view of the NOx sensor element taken along the line AA in FIG. 2 according to the first embodiment.
FIG. 4 is an explanatory diagram showing a positional relationship between a measured gas side NOx active electrode of the NOx detection cell and an electrode of the oxygen pumping cell according to the first embodiment.
FIG. 5 is an explanatory view showing a gas sensor assembly in which a NOx sensor element is assembled according to Embodiment 1;
6 is an explanatory view showing a state in which the gas sensor assembly according to the first embodiment is attached to the exhaust path of the automobile. FIG.
7 is a diagram showing the relationship between the current value, which is the output of the NOx sensor element, and the NO concentration in the gas to be measured according to Embodiment 1. FIG.
FIG. 8 is a diagram showing the properties of a gas diffusion resistance layer according to Embodiment 1;
9A is an explanatory diagram showing an electrode in an oxygen pumping cell, and FIG. 9B is an explanatory diagram showing a measured gas side NOx active electrode in a NOx detection cell according to Embodiment 2. FIG.
10 is an explanatory view showing a NOx sensor element in which a protective layer is provided on a counter electrode according to Embodiment 3. FIG.
FIG. 11 is an explanatory diagram of a NOx sensor element having three chambers according to a conventional example.
[Explanation of symbols]
1. . . NOx sensor element,
11. . . NOx detection cell,
110. . . First solid electrolyte,
111. . . Measured gas side NOx active electrode,
112. . . Counter electrode,
12 . . Oxygen pumping cell,
120. . . Second solid electrolyte,
121, 122. . . electrode,
13. . . Gas diffusion resistance layer,
14 . . Insulating ceramic substrate,
141. . . space,
15. . . Heater section,

Claims (4)

And a NOx detection cell, a gas diffusion resistance layer for the gas introduction path to be measured stacked on the upper surface thereof, and an oxygen pumping cell having a function of discharging oxygen stacked on the upper surface of the gas diffusion resistance layer. ,
The NOx detection cell comprises an oxygen ion conductive first solid electrolyte body, a measured gas side NOx active electrode facing the gas diffusion resistance layer, and a counter electrode provided on the opposite surface,
The oxygen pumping cell comprises an oxygen ion conductive second solid electrolyte body and a pair of electrodes provided on the surface thereof, and the area of the electrode is the same as that of the NOx active electrode to be measured in the NOx detection cell. Larger than the area,
Further, when the electrode of the oxygen pumping cell is projected onto the measured gas side NOx active electrode, the measured gas side NOx active electrode is included in the projected portion of the electrode of the oxygen pumping cell. A NOx sensor element, characterized in that the NOx sensor element is provided .   The NOx sensor element according to claim 1, wherein the gas diffusion resistance layer has a porosity of 1 to 20%.   3. The insulating ceramic according to claim 1 or 2, wherein an insulating ceramic is disposed on a lower surface of the NOx detection cell so as to face the counter electrode, is shielded from a gas to be measured, and forms a space extending to an atmospheric atmosphere inside the NOx sensor element. A NOx sensor element comprising a base.   The NOx sensor element according to any one of claims 1 to 3, wherein the NOx sensor element is provided with a heater portion.

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