JP2010091526A - Gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the detection accuracy of the oxygen concentration in a gas to be measured. <P>SOLUTION: This gas sensor includes a measurement chamber 159, into which the measuring object gas (hereinafter, to be referred to as "gas") is introduced; a pump cell 111 for pumping out/in oxygen relative to the gas introduced; a measuring chamber 161 communicating with the measuring chamber 159; a pump cell 113, in which a current corresponding to a specific gas concentration in the measuring chamber 161 flows through an inside second pump electrode 145 arranged in the measurement chamber 161; a reference oxygen chamber 118, set to have a reference oxygen partial pressure atmosphere, and a detection cell 112, having a detection electrode 155 arranged in the measuring chamber 159 or in the measuring chamber 161 and a reference electrode 157, arranged in the reference oxygen chamber 118. In a cross section (electrode arrangement cross section), at a position where the detection electrode 155 is arranged on the route to a first electrode 145 of the gas introduced into the measurement chamber 159, the area of the region where the detection electrode 155 is formed occupies a half of more of the entire area of the electrode-arranged cross section. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a gas sensor that outputs a concentration signal corresponding to a specific gas concentration in a measurement target gas.

  Conventionally, as one of gas sensors that output a concentration signal corresponding to a specific gas concentration in a measurement target gas (for example, NOx concentration in exhaust gas of an internal combustion engine), a first electrode having a pair of electrodes formed on a solid electrolyte body A gas sensor including an oxygen ion pump cell, a second oxygen ion pump cell, and an oxygen partial pressure detection cell is known (see, for example, Patent Document 1).

  That is, this gas sensor has a first measurement chamber into which a measurement target gas is introduced via the first diffusion resistance unit, and pumps oxygen (in the first measurement chamber) by the first oxygen ion pump cell ( Pumping out or pumping in).

  Further, the gas sensor can detect the oxygen concentration difference between the reference oxygen chamber and the first measurement chamber whose oxygen concentration is controlled to be constant, that is, the oxygen concentration in the first measurement chamber, by the oxygen partial pressure detection cell. It is configured.

And the drive circuit which drives this gas sensor controls the 1st pump electric current which flows into a 1st oxygen ion pump cell so that the both-ends voltage of an oxygen partial pressure detection cell may become a predetermined fixed voltage (for example, 425 mV). In addition, a constant second pump voltage (for example, 450 mV) is applied to the second oxygen ion pump cell in the direction of pumping out oxygen from the second measurement chamber communicating with the first measurement chamber. At this time, the second oxygen ion pump cell The second pump current flowing through is detected. Thereby, the specific gas concentration can be detected based on the magnitude of the second pump current.
JP 2003-90820 A

  The gas sensor disclosed in Patent Document 1 passes through a surface on the first measurement chamber side of an electrode (hereinafter referred to as a detection electrode) arranged in the first measurement chamber among a pair of electrodes formed in the oxygen partial pressure detection cell. Among the measurement target gases to be detected, the oxygen concentration in the first measurement chamber is detected by the measurement target gas in contact with the detection electrode.

  However, in the gas sensor disclosed in Patent Document 1, an electrode arranged in the first measurement chamber (hereinafter referred to as a detection electrode) among a pair of electrodes formed in the oxygen partial pressure detection cell constitutes an oxygen partial pressure detection cell. It is thinly formed on the solid electrolyte body (for example, about one-fourth the height of the first measurement chamber).

  For this reason, the diffusion of the measurement target gas introduced into the first measurement chamber is insufficient, and the region near the detection electrode is separated from the detection electrode above the surface on the first measurement chamber side of the detection electrode. If there is a difference in the oxygen concentration in the measurement target gas from the region, the oxygen concentration in the measurement target gas in the region away from the detection electrode is less likely to be reflected in the detection result by the oxygen partial pressure detection cell. Thereby, in the gas sensor of the said patent document 1, there existed a problem that the detection accuracy of the oxygen concentration in measurement object gas fell.

  The present invention has been made in view of these problems, and an object of the present invention is to provide a technique for improving the detection accuracy of the oxygen concentration in the measurement target gas.

  The invention according to claim 1, which has been made to achieve the above object, is formed on a solid electrolyte body and a solid electrolyte body, a first measurement chamber into which a gas to be measured is introduced via a first diffusion resistance portion. A pair of first electrodes, and one of the pair of first electrodes is disposed in the first measurement chamber, and oxygen is pumped or pumped into the measurement target gas introduced into the first measurement chamber. A first oxygen ion pump cell for performing the measurement, a second measurement chamber into which the measurement target gas into which oxygen has been pumped or pumped in the first measurement chamber is introduced via the second diffusion resistance unit, a solid electrolyte body, A measurement target gas having a pair of second electrodes formed on the solid electrolyte body, one of the pair of second electrodes being disposed in the second measurement chamber, and introduced into the second measurement chamber Second oxygen ion pump that detects specific gas components The cell has a solid electrolyte body and a pair of third electrodes formed on the solid electrolyte body, and one third electrode of the pair of third electrodes is in the first measurement chamber or / and the second measurement chamber. And a gas sensor including an oxygen partial pressure detection cell disposed between one first electrode and one second electrode in a gas passage path through which a measurement target gas flows, wherein the third electrode is A location where the ratio of one third electrode to the total area of the electrode arrangement cross section is more than half when the electrode arrangement cross section of the gas passage where the third electrode is arranged is a porous electrode It is a gas sensor characterized by having.

  In the gas sensor configured as described above, the measurement target gas introduced into the first measurement chamber has an electrode arrangement cross section before reaching one second electrode (second oxygen ion pump cell) arranged in the second measurement chamber. Pass through. At this time, there is a portion where the ratio of one third electrode (hereinafter also referred to as a detection electrode) to the total area of the electrode arrangement cross section is half or more. That is, more than half of the measurement target gas passes through the inside of the detection electrode, which is a porous electrode. For this reason, oxygen in the measurement target gas can be detected over a wider range in the electrode arrangement cross section.

  Therefore, according to the gas sensor of claim 1, even if there is a difference in the oxygen concentration in the measurement target gas between the region close to the detection electrode and the region away from the detection electrode, The oxygen concentration detection accuracy can be improved.

  One third electrode may be arranged in the first measurement chamber or in the second measurement chamber. Furthermore, it may be arranged in both the first measurement chamber and the second measurement chamber. That is, the one third electrode, when viewing the gas passage, is one of the first electrode arranged in the first measurement chamber of the first oxygen ion pump cell and the second of the second oxygen ion pump cell. What is necessary is just to be arrange | positioned by one 2nd electrode arrange | positioned in a measurement chamber. Furthermore, an electrode arrangement cross section refers to an arbitrary cross section of a portion where one third electrode is arranged in the gas passage path.

  In the gas sensor according to claim 1, as described in claim 2, one third electrode covers all of the solid electrolyte body of the oxygen partial pressure detection cell in the periphery of the electrode arrangement cross section. Good.

  In this manner, the detection electrode covers all the solid electrolyte body of the oxygen partial pressure detection cell in the periphery of the electrode arrangement cross section, thereby detecting oxygen in the measurement target gas over a wider range in the electrode arrangement cross section. can do.

In the gas sensor according to claim 1, as described in claim 3, one of the third electrodes may cover the entire periphery of the electrode arrangement cross section.
As described above, the detection electrode covers the entire periphery of the electrode arrangement cross section, so that there is a difference in the oxygen concentration in the measurement target gas between the region close to and away from the solid electrolyte body of the oxygen partial pressure detection cell. Even in this case, both the measurement target gas in the close region and the measurement target gas in the distant region pass through the inside of the detection electrode, and the detection result by the oxygen partial pressure detection cell reflects both oxygen concentrations. Can be made. Therefore, the detection accuracy of the oxygen concentration of the measurement target gas can be further improved.

In the gas sensor according to claim 1, as described in claim 4, one of the third electrodes may be provided over the entire electrode arrangement cross section.
In this way, by providing the detection electrode over the entire electrode arrangement section, it is possible to reflect all the oxygen concentrations of the measurement target gas that passes through the electrode arrangement section. Therefore, the detection accuracy of the oxygen concentration of the measurement target gas can be further improved.

Further, in the gas sensor according to any one of claims 1 to 4, as described in claim 5, it is preferable that one third electrode and the second diffusion resistance portion are integrally formed.
According to the gas sensor configured as described above, it is not necessary to separately form the second diffusion resistance portion, and the configuration of the gas sensor can be simplified.

  Moreover, in the gas sensor according to any one of claims 1 to 5, as described in claim 6, the porosity of one third electrode is equal to or higher than the porosity of the second diffusion resistance portion. Is preferred. Thereby, it can detect with a sufficient precision in a 2nd oxygen ion pump cell. Note that the porosity of the second diffusion resistance portion is preferably “less than 50%”, and the porosity of the third electrode may be more than that. In order to ensure the conduction of one third electrode, it is preferable that the “porosity is 80% or less”.

(First embodiment)
A first embodiment of the present invention will be described below with reference to the drawings.
In the present embodiment, a NOx sensor 1 which is a kind of gas sensor will be described. The NOx sensor 1 is mounted with a detection element (gas sensor element) for detecting a specific gas in exhaust gas to be measured and mounted on an exhaust pipe of an internal combustion engine.

FIG. 1 is a cross-sectional view showing the overall configuration of the NOx sensor 1.
As shown in FIG. 1, the NOx sensor 1 houses a detection element 2 having a plate-like shape extending in the axial direction (vertical direction in the figure) and an internal structure of the NOx sensor 1, and the NOx sensor 1 is connected to an exhaust pipe or the like. It is comprised from the casing 4 etc. which are fixed to the attachment part.

  Among these, the casing 4 includes a metal shell 5 that holds the detection element 2 and projects the detection portion 25 into the exhaust pipe and the like, and an outer cylinder 6 that extends above the metal shell 5. Yes.

  The metal shell 5 has a cylindrical main body, supports a detection element 2 from below, filling members 52 and 53 made of talc powder filled in the upper part of the support member 51, and filling members 52 and 53. A sleeve 54 or the like that presses from above is housed inside.

  In other words, an inwardly protruding step portion 55 is provided on the inner periphery on the lower end side of the metal shell 5, and the support member 51 is locked to the step portion 55 via the metal cup 56 to detect the step. Element 2 is supported from below. Filling members 52 and 53 are disposed between the inner peripheral surface of the metal shell 5 on the upper side of the support member 51 and the outer peripheral surface of the detection element 2, and a cylindrical sleeve is disposed above the filling members 52 and 53. 54 and the caulking ring 57 are sequentially inserted coaxially, and the upper end of the metal shell 5 is caulked inward (downward), so that the filling members 52 and 53 are pressurized and filled. The detection element 2 is firmly fixed to the metal shell 5. In addition, on the outer periphery on the lower end side of the metal shell 5, metal double protectors 58 and 59 having a plurality of holes are attached by welding while covering the protruding portion of the detection element 2.

  And after the lower end opening end part of the outer cylinder 6 is extrapolated to the said metal shell 5 so that the upper opening part of the metal shell 5 may be covered, welding is given to this lower end opening end part from the outside, and the outer cylinder 6 Is attached to the metal shell 5.

Further, in the vicinity of the upper end opening 61 of the outer cylinder 6, an insulating separator 7 made of ceramic and formed in a cylindrical shape is inserted.
The separator 7 has a flange portion 71 protruding outward on its outer peripheral surface, and the lower end surface of the flange portion 71 is locked by an internal support member 62 disposed in contact with the inner peripheral surface of the outer cylinder 6. Is held in the outer cylinder 6.

  The separator 7 includes an insertion hole 74 that penetrates from the rear end surface 72 toward the front end surface 73. The separator 7 accommodates a plurality of terminal fittings 8 extending from the outer electrode (not shown) arranged on the outer peripheral surface of the detection element 2 to the tip of the lead wire 9 in the insertion hole 74, and the terminal fitting 8 and the outer cylinder 6 is maintained.

  Further, the lead unit 9 connected to the outer electrode of the detection element 2 is pulled out to the upper end opening 61 of the outer cylinder 6 and the seal unit prevents moisture and oil from entering the NOx sensor 1. 10 is provided.

Next, the detection element 2 will be described. FIG. 2 is a cross-sectional view showing a schematic configuration of the detection element 2, and FIG.
As shown in FIG. 2, the detection element 2 has a structure in which a first pump cell 111, an oxygen partial pressure detection cell 112, and a second pump cell 113 are laminated via insulating layers 114 and 115 mainly composed of alumina. In the detection element 2, the heater unit 180 is stacked on the second pump cell 113 side.

  The first pump cell 111 includes a first solid electrolyte layer 131 made of zirconia having oxygen ion conductivity, an inner first pump electrode 135 and an outer first pump electrode arranged so as to sandwich the first solid electrolyte layer 131. And a first electrode 121 made of 137. The inner first pump electrode 135 and the outer first pump electrode 137 are made of platinum, a platinum alloy, cermet containing platinum and ceramics (for example, a solid electrolyte body), and the like. A protective layer 122 made of a body is formed.

  The oxygen partial pressure detection cell 112 is a third electrode composed of a detection solid electrolyte layer 151 made of zirconia having oxygen ion conductivity, and a detection electrode 155 and a reference electrode 157 disposed so as to sandwich the detection solid electrolyte layer 151. An electrode 123 is provided. The detection electrode 155 and the reference electrode 157 are made of platinum, platinum alloy, cermet containing platinum and ceramics (for example, a solid electrolyte body), or the like.

  Further, as shown in FIG. 3, the detection electrode 155 has an area SC2 in which the detection electrode 155 is formed in the cross section SC1 in the cross section SC1 of the first measurement chamber 159 (described later) into which the measurement target gas is introduced. It is formed so as to occupy 60%.

Further, the detection electrode 155 is formed so that the porosity thereof is 60% in order to ensure the passage of the measurement target gas and to ensure the conduction of the electrode.
The detection electrode 155 is provided so as to cover the entire detection solid electrolyte layer 151 in the cross section SC1.

  Further, as shown in FIG. 2, the second pump cell 113 is disposed on the surface of the second solid electrolyte layer 141 made of zirconia having oxygen ion conductivity and the insulating layer 115 among the surfaces of the second solid electrolyte layer 141. The second electrode 125 including the inner second pump electrode 145 and the outer second pump electrode 147 is formed. The inner second pump electrode 145 and the outer second pump electrode 147 are formed of platinum, a platinum alloy, cermet containing platinum and ceramics (for example, a solid electrolyte body), or the like.

  A first measurement chamber 159 into which a measurement target gas is introduced is formed inside the detection element 2. A measurement target gas is introduced into the first measurement chamber 159 from the outside through the first diffusion resistor 116 disposed between the first pump cell 111 and the oxygen partial pressure detection cell 112.

The first diffusion resistor 116 is made of a porous body, and restricts the introduction amount (passage amount) of the measurement target gas per unit time into the first measurement chamber 159.
A second diffusion resistor 117 made of a porous material is provided on the rear end side (right side in the drawing) of the first measurement chamber 159, and the inner second pump electrode 145, the second diffusion resistor 117, A second measurement chamber 161 is formed between the two. The second measurement chamber 161 is formed so as to penetrate the oxygen partial pressure detection cell 112 in the stacking direction. In the present embodiment, the porosity of the second diffusion resistor 117 is 35%.

  Further, in addition to the second measurement chamber 161, a porous material is provided between the detection solid electrolyte layer 151 of the oxygen partial pressure detection cell 112 and the second solid electrolyte layer 141 of the second pump cell 113 in the detection element 2. A reference oxygen chamber 118 composed of a material is formed. The second measurement chamber 161 and the reference oxygen chamber 118 are formed along the second pump cell 113 in this order from the rear end side to the front end side. Further, by supplying a minute current from a gas sensor control device (not shown) to the oxygen partial pressure detection cell 112, oxygen is supplied from the first measurement chamber 159 to the reference oxygen chamber 118 via the solid electrolyte layer 151 for detection. Therefore, the reference oxygen chamber 118 is set to a predetermined oxygen partial pressure atmosphere (oxygen partial pressure atmosphere serving as a reference for concentration detection).

The reference electrode 157 of the oxygen partial pressure detection cell 112 and the outer second pump electrode 147 of the second pump cell 113 are arranged so as to face the reference oxygen chamber 118.
The heater unit 180 is configured by laminating sheet-like insulating layers 171 and 173 made of insulating ceramics such as alumina. The heater unit 180 includes a heater 175 mainly composed of Pt between the insulating layers 171 and 173.

  The detection element 2 configured as described above can pump (pump out or pump in) oxygen existing in the first measurement chamber 159 by the first pump cell 111, and the oxygen concentration can be detected by the oxygen partial pressure detection cell 112. Measures the oxygen concentration difference (oxygen partial pressure difference) between the reference oxygen chamber 118 and the first measurement chamber 159 whose (oxygen partial pressure) is controlled to be constant, that is, the oxygen concentration (oxygen partial pressure) inside the first measurement chamber 159. Is possible.

  The detection element 2 is driven by a gas sensor control device (not shown in FIG. 1), and the gas sensor control device drives the heater 175 so that each cell (first pump cell 111, second pump cell 113, The oxygen partial pressure detection cell 112) is heated to the activation temperature.

  The gas sensor control device drives and controls the heater 175 to heat the detection element 2 to an activation temperature (for example, 750 ° C.). In this state, the both-ends voltage Vs of the oxygen partial pressure detection cell 112 is a predetermined constant voltage. The first pump voltage Vp1 applied to the first pump cell 111 is controlled so as to be (for example, 425 mV).

  The gas sensor control device controls the first pump current Ip1 and applies a second pump voltage Vp2 having a predetermined control voltage value V0 (for example, 450 mV) to the second pump cell 113. Thereby, in the second measurement chamber 161, NOx is dissociated (reduced) by the catalytic action of the second electrode 125 constituting the second pump cell 113, and oxygen ions obtained by the dissociation are exchanged with the inner second pump electrode 145. The second pump current Ip2 flows by moving the second solid electrolyte layer 141 between the outer second pump electrode 147 and the second pump electrode I147. That is, the second pump cell 113 dissociates the specific gas component (NOx (nitrogen oxide)) to be detected present in the second measurement chamber 161 and pumps oxygen from the second measurement chamber 161 to the reference oxygen chamber 118. .

The oxygen ions (O ²⁻ ) dissociated at the inner second pump electrode 145 in the second measurement chamber 161 move to the outer second pump electrode 147 through the second solid electrolyte layer 141, and the outer second pump. The oxygen is released into the reference oxygen chamber 118 at the electrode 147 as oxygen (O ₂ ).

  That is, the gas sensor control device adjusts the oxygen concentration (oxygen partial pressure) in the first measurement chamber 159 by the pumping operation of the first pump cell 111 in a state where it is connected to the detection element 2, and the oxygen concentration in the second measurement chamber 161 ( (Oxygen partial pressure) is set to a concentration for NOx detection capable of detecting NOx, and a process of detecting the NOx concentration based on the magnitude, integrated value, etc. of the second pump current Ip2 is performed. The NOx concentration information detected by the gas sensor control device is sent to an external device (for example, engine ECU) not shown in FIG.

Next, a method for manufacturing the detection electrode 155 will be described. 4 is a cross-sectional view taken along the line AA of FIG. 2 for explaining a method of manufacturing the detection electrode 155.
First, as shown in the first step of FIG. 4, the insulating paste 214 that becomes the insulating layer 114 is applied on the solid electrolyte sheet 251 that becomes the detection solid electrolyte layer 151 when fired, except for the region that becomes the first measurement chamber 159. Print to be placed in

  Further, as shown in the second step of FIG. 4, on the solid electrolyte sheet 251, an electrode paste 255 that becomes the detection electrode 155 when printed is printed in a region where the detection electrode 155 is formed. Thereafter, a carbon paste 281 is printed on the electrode paste 255.

This electrode paste 255 is made of a Pt group powder (eg, Pt, Pd, Rh, Ru, Ir, Re) / solid electrolyte ceramics (eg, yttria stabilized or partially stabilized ZrO ₂ , scandia stabilized or partially stabilized ZrO _2). , Samaria or Gadria-added CeO ₂ , LaGaO _3, etc.) = 60 vol% / 40 vol%, Au powder = 1 vol%, sublimation material (for example, carbon, theobromine, etc.) = 100 vol%, organic binder, solvent, and plasticizer Is appropriately added and adjusted.

  After that, as shown in the third step of FIG. 4, the solid electrolyte sheet 231 that becomes the first solid electrolyte layer 131 when pressed is pressed onto the carbon paste 281 and the insulating paste 214 (arrow Y1, FIG. 4). Y2 indicates pressure bonding). Thereby, as shown in the fourth step of FIG. 4, the solid electrolyte sheet 231 is laminated on the carbon paste 281 and the insulating paste 214.

  Then, when firing is performed after all the members constituting the detection element 2 are stacked, the sublimation material in the electrode paste 255 is sublimated as shown in the fifth step of FIG. An electrode 155 is formed. Further, the carbon paste 281 is sublimated by firing, and a gap GP is formed on the detection electrode 155.

  In the NOx sensor 1 configured in this manner, the measurement target gas introduced into the first measurement chamber 159 is detected in the gas passage route to the inner second pump electrode 145 disposed in the second measurement chamber 161. It passes through the cross section SC1 at the position where the electrode 155 is disposed. At this time, the detection electrode 155 occupies half or more of the total area of the cross section SC1. That is, more than half of the measurement target gas passes through the inside of the detection electrode 155 that is a porous electrode. For this reason, it is possible to detect oxygen in the measurement target gas over a wider range in the cross section SC1.

  Therefore, according to the NOx sensor 1, even if there is a difference in the oxygen concentration in the measurement target gas between the region close to the detection electrode 155 and the region away from the detection electrode 155, the oxygen in the measurement target gas The density detection accuracy can be improved.

  Further, the detection electrode 155 covers all the solid electrolyte layer 151 for detection of the oxygen partial pressure detection cell 112 in the cross section SC1, thereby detecting oxygen in the measurement target gas over a wide range in the cross section SC1. Can do.

Furthermore, the porosity of the detection electrode 155 is equal to or higher than the porosity of the second diffusion resistor 117. As a result, the second pump cell 113 can accurately detect.
In the embodiment described above, the NOx sensor 1 is the gas sensor according to the present invention, the first diffusion resistor 116 is the first diffusion resistance portion according to the present invention, the first pump cell 111 is the first oxygen ion pump cell according to the present invention, the inner first The pump electrode 135 is one of the first electrodes in the present invention, the second diffusion resistor 117 is the second diffusion resistance portion in the present invention, the second pump cell 113 is the second oxygen ion pump cell in the present invention, and the inner second pump electrode 145 in the present invention. Is one second electrode in the present invention, the detection electrode 155 is one third electrode in the present invention, and the section SC1 is an electrode arrangement section in the present invention.

(Second Embodiment)
A second embodiment of the present invention will be described below with reference to the drawings. In the second embodiment, only parts different from the first embodiment will be described.

FIG. 5 is a cross-sectional view showing a schematic configuration of the detection element 2 of the second embodiment, and FIG. 6 is a cross-sectional view taken along the line AA of FIG.
As shown in FIG. 5, the detection element 2 of the second embodiment is different from the first embodiment in that the second diffusion resistor 117 is omitted. That is, the detection electrode 155 and the second diffusion resistor 117 of the second embodiment are integrally formed.

  Further, as shown in FIG. 6, the detection electrode 155 of the second embodiment is such that the area of the region SC2 where the detection electrode 155 is formed occupies the entire cross section SC1 in the cross section SC1 of the first measurement chamber 159. Is formed.

Next, the manufacturing method of the detection electrode 155 of 2nd Embodiment is demonstrated. FIG. 7 is a cross-sectional view taken along the line AA of FIG. 5 for describing the method for manufacturing the detection electrode 155 of the second embodiment.
First, as shown in the first step of FIG. 7, the insulating paste 214 that becomes the insulating layer 114 is applied on the solid electrolyte sheet 251 that becomes the detection solid electrolyte layer 151 when fired, except for the region that becomes the first measurement chamber 159. Print to be placed in

  Further, as shown in the second step of FIG. 7, on the solid electrolyte sheet 251, an electrode paste 255 that becomes the detection electrode 155 when printed is printed in a region where the detection electrode 155 is formed.

  After that, as shown in the third step of FIG. 7, the solid electrolyte sheet 231 that becomes the first solid electrolyte layer 131 when pressed is pressed onto the electrode paste 255 and the insulating paste 214 (arrows Y1, Y2 in FIG. 7). Indicates crimping). As a result, as shown in the fourth step of FIG. 7, the solid electrolyte sheet 231 is laminated on the solid electrolyte sheet 231 and the insulating paste 214.

  Then, when firing is performed after all the members constituting the detection element 2 are laminated, the sublimation material in the electrode paste 255 sublimates as shown in the fifth step of FIG. An electrode 155 is formed.

  In the NOx sensor 1 configured as described above, the detection electrode 155 is provided on the entire cross section SC1. Thereby, it is possible to reflect all the oxygen concentrations of the measurement target gas passing through the cross section SC1. Therefore, the detection accuracy of the oxygen concentration of the measurement target gas can be further improved.

The detection electrode 155 functions as the second diffusion resistor 117, and the second diffusion resistor 117 is omitted. For this reason, the configuration of the NOx sensor 1 can be simplified.
As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, As long as it belongs to the technical scope of this invention, a various form can be taken.

  For example, in the first embodiment, the detection electrode 155 is formed so as to cover the entire detection solid electrolyte layer 151 in the cross section SC1, but as shown in FIG. 8, all the peripheral regions of the cross section SC1 are shown. The detection electrode 155 may be formed so as to cover the surface.

  Thereby, even if there is a difference in the oxygen concentration in the measurement target gas between the region close to and away from the detection solid electrolyte layer 151 of the oxygen partial pressure detection cell 112, the measurement target gas in the close region In addition, both of the measurement target gases in the remote region pass through the inside of the detection electrode 155, and the detection result by the oxygen partial pressure detection cell 112 can reflect the oxygen concentration of both. Therefore, the detection accuracy of the oxygen concentration of the measurement target gas can be further improved.

1 is a cross-sectional view showing the overall configuration of a NOx sensor 1. FIG. It is sectional drawing which shows schematic structure of the detection element 2 of 1st Embodiment. It is a figure which shows the AA cross section of FIG. It is a figure which shows the AA cross section of FIG. 2 for demonstrating the manufacturing method of the detection electrode 155 of 1st Embodiment. It is sectional drawing which shows schematic structure of the detection element 2 of 2nd Embodiment. It is a figure which shows the AA cross section of FIG. It is a figure which shows the AA cross section of FIG. 5 for demonstrating the manufacturing method of the detection electrode 155 of 2nd Embodiment. It is a figure which shows the AA cross section of FIG. 2 about the detection electrode 155 of another embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... NOx sensor, 2 ... Detection element, 111 ... 1st pump cell, 112 ... Oxygen partial pressure detection cell, 113 ... 2nd pump cell, 114, 115 ... Insulating layer, 116 ... 1st diffusion resistor, 117 ... 2nd diffusion Resistor, 118 ... reference oxygen chamber, 119 ... introduction path, 121 ... first electrode, 123 ... third electrode, 125 ... second electrode, 131 ... first solid electrolyte layer, 135 ... inner first pump electrode, 137 ... Outer first pump electrode, 141 ... second solid electrolyte layer, 145 ... inner second pump electrode, 147 ... outer second pump electrode, 151 ... detection solid electrolyte layer, 155 ... detection electrode, 157 ... reference electrode, 159 ... First measurement chamber, 161 ... second measurement chamber

Claims (6)

A first measurement chamber into which a gas to be measured is introduced via the first diffusion resistance unit;
A solid electrolyte body and a pair of first electrodes formed on the solid electrolyte body, wherein one first electrode of the pair of first electrodes is disposed in the first measurement chamber, and the first measurement is performed. A first oxygen ion pump cell for pumping or pumping oxygen to the measurement target gas introduced into the chamber;
A second measurement chamber into which the measurement target gas into which oxygen has been pumped or pumped in the first measurement chamber is introduced via a second diffusion resistance unit;
A solid electrolyte body and a pair of second electrodes formed on the solid electrolyte body, wherein one second electrode of the pair of second electrodes is disposed in the second measurement chamber, and the second measurement is performed. A second oxygen ion pump cell for detecting a specific gas component in the measurement target gas introduced into the chamber;
A solid electrolyte body and a pair of third electrodes formed on the solid electrolyte body, wherein one third electrode of the pair of third electrodes is in the first measurement chamber or / and the second measurement chamber And a gas sensor comprising: an oxygen partial pressure detection cell disposed between the one first electrode and the one second electrode in a gas passage path through which the measurement target gas flows,
The one third electrode is a porous electrode,
When the electrode arrangement cross section of the gas passing path where the one third electrode is arranged is seen, the ratio of the one third electrode to the total area of the electrode arrangement cross section is more than half. A gas sensor characterized by that. The one third electrode is
2. The gas sensor according to claim 1, wherein all of the solid electrolyte body of the oxygen partial pressure detection cell is covered in a peripheral edge of the electrode arrangement cross section. The gas sensor according to claim 1, wherein the one third electrode covers the entire periphery of the electrode arrangement cross section. 2. The gas sensor according to claim 1, wherein the one third electrode is provided over the entire electrode arrangement cross section. The gas sensor according to any one of claims 1 to 4, wherein the one third electrode and the second diffusion resistance portion are integrally formed. The gas sensor according to any one of claims 1 to 5, wherein the porosity of the one third electrode is equal to or higher than the porosity of the second diffusion resistance portion.

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