Gas sensor

An ammonia detection section is disposed on an electrically insulating layer and includes a reference electrode, a solid electrolyte body for ammonia, and a detection electrode that are stacked in this order on the electrically insulating layer. In the ammonia detection section, a three-phase boundary is formed at the interface between the reference electrode and the solid electrolyte body for ammonia, and another three-phase boundary is formed at the interface between the detection electrode and the solid electrolyte body for ammonia. The concentration of ammonia in exhaust gas is thereby detected. The ammonia detection section includes a porous layer formed of an electrically insulating porous material and disposed between the insulating layer and the reference electrode.

This application claims the benefit of Japanese Patent Applications No. 2016-022861, filed Feb. 9, 2016 and No. 2017-017453, filed Feb. 2, 2017, all of which are incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates to a gas sensor that detects the concentration of a gas present in an atmosphere of interest.

BACKGROUND OF THE INVENTION

In recent years, a urea SCR (Selective Catalytic Reduction) system is receiving attention as a technique for cleaning NOx-containing exhaust gas emitted from internal combustion engines such as gasoline engines and diesel engines (where NOx stands for nitrogen oxides). In the urea SCR system, ammonia (NH3) is chemically reacted with nitrogen oxides (NOx) to reduce the nitrogen oxides to nitrogen (N2), and the exhaust gas containing the nitrogen oxides is thereby cleaned.

In the urea SCR system, when the amount of ammonia supplied for the nitrogen oxides is excessively large, unreacted ammonia may be contained in the exhaust gas and emitted to the outside. To reduce the emission of ammonia described above, a multi-gas sensor capable of measuring the concentrations of a plurality of gases including ammonia contained in the exhaust gas is used for the urea SCR system.

In one known multi-gas sensor, an ammonia sensor including a reference electrode, a detection electrode, and a solid electrolyte body sandwiched between these electrodes is attached to an NOx sensor (see, for example, Japanese Patent Application Laid-Open (kokai) No. 2013-221930).

Problems to be Solved by the Invention

When a stack of the reference electrode and the solid electrolyte body is formed on a green insulating layer provided on the uppermost surface of the NOx sensor and then they are co-fired, the insulating layer provided on the uppermost surface of the NOx sensor shrinks. In this case, the reference electrode becomes dense, and the area of a three-phase boundary is reduced, so that the impedance of the ammonia sensor rises. When the impedance rises, the output of the ammonia sensor is easily influenced by noise, so that the detection accuracy of the ammonia sensor may be reduced significantly.

The present invention has been made in view of the above problem, and it is an object to provide a technique for suppressing the rise in impedance due to co-firing.

SUMMARY OF THE INVENTION

Means for Solving the Problems

A first aspect of the present invention accomplished to achieve the above-described object is a gas sensor disposed on an electrically insulating member for detecting the concentration of a target gas in an atmosphere of interest. The gas sensor comprises a reference electrode, a solid electrolyte body, and a detection electrode that are stacked in this order on the electrically insulating member, a first three-phase boundary being formed at a first interface between the reference electrode and the solid electrolyte body, a second three-phase boundary being formed at a second interface between the detection electrode and the solid electrolyte body. The atmosphere of interest is a gas atmosphere to be detected by the gas sensor. Each three-phase boundary is a boundary at which the target gas comes into contact with the solid electrolyte body and one of the reference electrode and the detection electrode.

The gas sensor according to the first aspect of the present invention further comprises an insulating porous layer made of an electrically insulating porous material and disposed between the electrically insulating member and the reference electrode.

In the above-configured gas sensor of the first aspect, the insulating porous layer is disposed on the opposite side of the reference electrode from the solid electrolyte body. The insulating porous layer has many pores in its interior and on its surface. Therefore, in the insulating porous layer, the detection target gas is allowed to flow from a portion exposed to the atmosphere of interest into the interior of the insulating porous layer, and the target gas flowing inside the insulating porous layer is allowed to flow toward the reference electrode.

Therefore, the amount of the target gas flowing through the reference electrode toward the solid electrolyte body increases, and this allows an increase in the area of the three-phase boundary at which the detection target gas comes into contact with the reference electrode and the solid electrolyte body. When a stack of the reference electrode and the solid electrolyte body is formed on a green electrically insulating member and then they are co-fired, the reference electrode may become dense, and the area of the three-phase boundary may decrease. Even in this case, the increase in the inflow of the target gas through the insulating porous layer allows the reduction in the area of the three-phase boundary to be suppressed.

By virtue of the above-described configuration, the gas sensor of the first aspect of the present invention can suppress the rise in the impedance of the gas sensor due to co-firing.

A second aspect of the present invention accomplished to achieve the above-described object is a gas sensor disposed on an electrically insulating member for detecting the concentration of a target gas in an atmosphere of interest. The gas sensor comprises a reference electrode, a solid electrolyte body, and a detection electrode that are stacked in this order on the electrically insulating member, a first three-phase boundary being formed at a first interface between the reference electrode and the solid electrolyte body, a second three-phase boundary being formed at a second interface between the detection electrode and the solid electrolyte body.

In the gas sensor according to the second aspect of the present invention, at least part of the solid electrolyte body is porous and abuts the reference electrode.

In the above-configured gas sensor of the second aspect, the porous part of the solid electrolyte body is disposed between the non-porous part of the solid electrolyte body and the reference electrode. Therefore, in the porous part of the solid electrolyte body, the target gas is allowed to flow from a portion exposed to the atmosphere of interest into the interior of the porous part of the solid electrolyte body, and the target gas flowing inside the porous part of the solid electrolyte body is allowed to flow toward the reference electrode.

Therefore, the amount of the target gas flowing through the solid electrolyte body toward the reference electrode increases, and this allows an increase in the area of the three-phase boundary at which the target gas comes into contact with the reference electrode and the solid electrolyte body. When a stack of the reference electrode and the solid electrolyte body is formed on a green electrically insulating member and then they are co-fired, the reference electrode may become dense, and the area of the three-phase boundary may decrease. Even in this case, the increase in the inflow of the target gas through the porous part of the solid electrolyte body allows the reduction in the area of the three-phase boundary to be suppressed.

By virtue of the above-described configuration, the gas sensor of the second aspect of the present invention can suppress the rise in the impedance of the gas sensor due to co-firing.

DETAILED DESCRIPTION OF THE INVENTION

Modes for Carrying Out the Invention

First Embodiment

A multi-gas detector1in the embodiment to which the present invention is applied is used for a urea SCR (Selective Catalytic Reduction) system that is mounted on a vehicle to thereby clean nitrogen oxide (NOx)-contained exhaust gas emitted from a diesel engine. More specifically, the multi-gas detector1measures, after the NOx contained in the exhaust gas is reacted with ammonia (urea), the concentrations of nitrogen monoxide (NO), nitrogen dioxide (NO2), and ammonia contained in the resulting exhaust gas. The vehicle on which the multi-gas detector1is mounted is referred to as the “present vehicle.”

As shown inFIG. 1, the multi-gas sensor2includes a sensor element unit5, a metallic shell10, a separator34, and connection terminals38. In the following description, the side of the multi-gas sensor2on which the sensor element unit5is disposed (the lower side inFIG. 1) is referred to as a forward end side, and the side on which the connection terminals38are disposed (the upper side inFIG. 1) is referred to as a rear end side.

The sensor element unit5has a plate shape extending in the direction of an axial line O. Electrode terminal portions5A and5B are disposed at the rear end of the sensor element unit5. InFIG. 1, only the electrode terminal portions5A and5B are shown as electrode terminal portions formed in the sensor element unit5for the purpose of simplifying the drawing. However, in practice, a plurality of electrode terminal portions are formed according to the number of, for example, electrodes included in an NOx detection section101and an ammonia detection section102described later.

The metallic shell10is a tubular member, and a threaded portion11used to fix the multi-gas sensor2to an exhaust pipe of a diesel engine is formed on the external surface of the metallic shell10. The metallic shell10has a through hole12extending in the direction of the axial line O and a ledge13protruding inward in the radial direction of the through hole12. The ledge13is formed as an inward tapered surface extending from the radially outer side of the through hole12toward its center and inclined toward the forward end side.

The metallic shell10holds the sensor element unit5with its forward end protruding from the forward end of the through hole12and the rear end protruding from the rear end of the through hole12.

A ceramic holder14that is a tubular member surrounding the radial circumference of the sensor element unit5, talc rings15and16that are powder filler layers, and a ceramic sleeve17are stacked in this order inside the through hole12of the metallic shell10from the forward end side toward the rear end side.

A crimp packing18is disposed between a rear end portion of the ceramic sleeve17and a rear end portion of the metallic shell10. A metallic holder19is disposed between the ceramic holder14and the ledge13of the metallic shell10. The metallic holder19holds the talc ring15and the ceramic holder14. A rear end portion of the metallic shell10is crimped so as to press the ceramic sleeve17toward the forward end side through the crimp packing18.

An outer protector21and an inner protector22are disposed at a forward end portion of the metallic shell10. The outer protector21and the inner protector22are tubular members formed from a metallic material such as stainless steel having a closed forward end. The inner protector22covers a forward end portion of the sensor element unit5and is welded to the metallic shell10, and the outer protector21covers the inner protector22and is welded to the metallic shell10.

A forward end portion of an outer tube31formed into a tubular shape is fixed to a rear end portion of the metallic shell10. A grommet32is disposed in a rear end opening of the outer tube31so as to close the opening.

Lead wire insertion holes33into which lead wires41are inserted are formed in the grommet32. The lead wires41are electrically connected to the electrode terminal portions5A and5B of the sensor element unit5.

A separator34is a tubular member disposed rearward of the sensor element unit5. A space formed inside the separator34is an insertion hole35passing through the separator34in the direction of the axial line O. A flange portion36protruding radially outward is formed on the outer surface of the separator34.

A rear end portion of the sensor element unit5is inserted into the insertion hole35of the separator34, and the electrode terminal portions5A and5B are disposed inside the separator34.

A tubular holding member37is disposed between the separator34and the outer tube31. The holding member37is in contact with the flange portion36of the separator34and also with the inner surface of the outer tube31and thereby holds the separator34such that the separator34is fixed to the outer tube31.

The connection terminals38are members disposed inside the insertion hole35of the separator34and are electrically conductive members that electrically connect the electrode terminal portions5A and5B of the sensor element unit5to their respective lead wires41. InFIG. 1, only two connection terminals38are shown for the purpose of simplifying the drawing.

As shown inFIG. 2, a controller3of the multi-gas detector1is electrically connected to an electronic control unit200mounted on the present vehicle. The electronic control unit200receives data representing the concentrations of NO, NO2, and ammonia in exhaust gas that are computed by the controller3. Then the electronic control unit200performs processing for controlling the operating conditions of the diesel engine according to the data received and also performs cleaning processing for NOx accumulated on a catalyst.

The sensor element unit5includes the NOx detection section101and the ammonia detection section102.

The NOx detection section101is formed by sequentially stacking an insulating layer113, a ceramic layer114, an insulating layer115, a ceramic layer116, an insulating layer117, a ceramic layer118, an insulating layer119, and an insulating layer120. The insulating layers113,115,117,119, and120are formed mainly of alumina.

The NOx detection section101includes a first measurement chamber121formed between the ceramic layer114and the ceramic layer116. In the NOx detection section101, the exhaust gas is introduced from the outside into the interior of the first measurement chamber121through a diffusion resistor122that is disposed between the ceramic layer114and the ceramic layer116so as to be adjacent to the first measurement chamber121. The diffusion resistor122is formed of a porous material such as alumina.

The NOx detection section101further includes a first pumping cell130. The first pumping cell130includes a solid electrolyte layer131and pumping electrodes132and133.

The solid electrolyte layer131is formed mainly of zirconia having oxygen ion conductivity. A part of the ceramic layer114is removed from a region exposed to the first measurement chamber121, and the resulting space is filled with the solid electrolyte layer131instead of the ceramic layer114.

The pumping electrodes132and133are formed mainly of platinum. The pumping electrode132is disposed on the solid electrolyte layer131so as to be exposed to the first measurement chamber121. The pumping electrode133is disposed on the solid electrolyte layer131on the side opposite the pumping electrode132with the solid electrolyte layer131sandwiched between the pumping electrodes132and133. The insulating layer113is removed from a region in which the pumping electrode133is disposed and from a region around the pumping electrode133, and the resulting space is filled with a porous material134instead of the insulating layer113. The porous material134allows gas (oxygen) migration between the pumping electrode133and the outside.

The NOx detection section101further includes an oxygen concentration detection cell140. The oxygen concentration detection cell140includes a solid electrolyte layer141, a detection electrode142, and a reference electrode143.

The solid electrolyte layer141is formed mainly of zirconia having oxygen ion conductivity. A part of the ceramic layer116is removed from a region rearward of the solid electrolyte layer131, and the resulting space is filled with the solid electrolyte layer141instead of the ceramic layer116.

The detection electrode142and the reference electrode143are formed mainly of platinum. The detection electrode142is disposed on the solid electrolyte layer141so as to be exposed to the first measurement chamber121. The reference electrode143is disposed on the solid electrolyte layer141on the side opposite the detection electrode142with the solid electrolyte layer141sandwiched between the detection electrode142and the reference electrode143.

The NOx detection section101further includes a reference oxygen chamber146. The reference oxygen chamber146is a through hole formed by removing the insulating layer117from a region in which the reference electrode143is disposed and from a region around the reference electrode143.

The NOx detection section101further includes a second measurement chamber148. The second measurement chamber148is formed rearward of the detection electrode142and the reference electrode143so as to pass through the solid electrolyte layer141and the insulating layer117. In the NOx detection section101, the exhaust gas discharged from the first measurement chamber121is introduced into the second measurement chamber148.

The NOx detection section101further includes a second pumping cell150. The second pumping cell150includes a solid electrolyte layer151and pumping electrodes152and153.

The solid electrolyte layer151is formed mainly of zirconia having oxygen ion conductivity. The ceramic layer118is removed from a region exposed to the reference oxygen chamber146and the second measurement chamber148and a region around this exposed region, and the resulting space is filled with the solid electrolyte layer151instead of the ceramic layer118.

The pumping electrodes152and153are formed mainly of platinum. The pumping electrode152is disposed on the solid electrolyte layer151so as to be exposed to the second measurement chamber148. The pumping electrode153is disposed on the solid electrolyte layer151so as to be opposed to the reference electrode143with the reference oxygen chamber146therebetween. A porous material147is disposed inside the reference oxygen chamber146so as to cover the pumping electrode153.

The NOx detection section101further includes a heater160. The heater160is a heat-generating resistor that is formed mainly of platinum and generates heat when energized and is disposed between the insulating layers119and120.

The ammonia detection section102is formed on the outer surface of the NOx detection section101, more specifically on the insulating layer120. The ammonia detection section102is disposed at substantially the same position, with respect to the direction of the axial line O (the horizontal direction inFIG. 2), as the reference electrode143in the NOx detection section101.

The ammonia detection section102has a structure formed by stacking a porous layer211, a reference electrode212, a solid electrolyte body213for ammonia, and a detection electrode214in this order.

The porous layer211is formed of the same material as the material of the porous material134and is disposed in contact with the surface of the insulating layer120.

The reference electrode212is formed mainly of platinum (Pt) serving as an electrode material and more specifically formed of a material containing Pt and zirconium oxide (ZrO2). The solid electrolyte body213for ammonia is formed of an oxygen ion-conductive material such as yttria-stabilized zirconia (YSZ). The reference electrode212is a dense layer having a smaller porosity than the porous layer211. The detection electrode214is formed mainly of gold (Au) serving as an electrode material and more specifically formed of a material containing Au and zirconium oxide (ZrO2).

Therefore, a three-phase boundary at which ammonia comes into contact with the reference electrode212and the solid electrolyte body213for ammonia is formed at the interface between the reference electrode212and the solid electrolyte body213for ammonia. Similarly, another three-phase boundary at which ammonia comes into contact with the detection electrode214and the solid electrolyte body213for ammonia is formed at the interface between the detection electrode214and the solid electrolyte body213for ammonia.

The entire ammonia detection section102is covered with a porous protecting layer220. The protecting layer220is configured to prevent adhesion of a poisoning material to the detection electrode214and to control the diffusion rate of ammonia flowing from the outside into the ammonia detection section102.

The controller3includes a control circuit180and a microcomputer190.

The control circuit180is an analog circuit disposed on a circuit board. The control circuit180includes an Ip1drive circuit181, a Vs detection circuit182, a reference voltage comparator183, an Icp supply circuit184, a Vp2application circuit185, an Ip2detection circuit186, a heater drive circuit187, and an electromotive force detection circuit188.

The pumping electrode132, the detection electrode142, and the pumping electrode152are connected to a reference potential. The pumping electrode133is connected to the Ip1drive circuit181. The reference electrode143is connected to the Vs detection circuit182and the Icp supply circuit184. The pumping electrode153is connected to the Vp2application circuit185and the Ip2detection circuit186. The heater160is connected to the heater drive circuit187.

The Ip1drive circuit181applies a voltage Vp1between the pumping electrode132and the pumping electrode133to supply a first pumping current Ip1and detects the supplied first pumping current Ip1.

The Vs detection circuit182detects the voltage Vs between the detection electrode142and the reference electrode143and outputs the detection result to the reference voltage comparator183.

The reference voltage comparator183compares a reference voltage (e.g., 425 mV) with the output from the Vs detection circuit182(the voltage Vs) and outputs the comparison result to the Ip1drive circuit181. The Ip1drive circuit181controls the direction and magnitude of the first pumping current Ip1such that the voltage Vs becomes equal to the reference voltage to thereby adjust the concentration of oxygen in the first measurement chamber121to a prescribed value at which decomposition of NOx does not occur.

The Icp supply circuit184causes a weak current Icp to flow between the detection electrode142and the reference electrode143. Oxygen is thereby fed from the first measurement chamber121to the reference oxygen chamber146through the solid electrolyte layer141, and the concentration of oxygen in the reference oxygen chamber146is set to be a prescribed oxygen concentration serving as a reference.

The Vp2application circuit185applies a constant voltage Vp2(e.g., 450 mV) between the pumping electrode152and the pumping electrode153. In the second measurement chamber148, NOx is dissociated (reduced) through the catalytic action of the pumping electrodes152and153included in the second pumping cell150. The oxygen ions obtained as a result of the dissociation migrate in the solid electrolyte layer151between the pumping electrode152and the pumping electrode153, so that a second pumping current Ip2flows. The Ip2detection circuit186detects the second pumping current Ip2.

The heater drive circuit187applies a positive voltage for energizing the heater160to one end of the heater160, which is a heat-generating resistor, and applies a negative voltage for energizing the heater160to the other end of the heater160to thereby drive the heater160.

The electromotive force detection circuit188detects the electromotive force between the reference electrode212and the detection electrode214(hereinafter referred to as an ammonia electromotive force EMF) and outputs a signal representing the detection result to the microcomputer190.

The microcomputer190includes a CPU191, a ROM192, a RAM193, and a signal input/output unit194.

The CPU191executes a process for controlling the sensor element unit5according to a program stored in the ROM192. The signal input/output unit194is connected to the Ip1drive circuit181, the Vs detection circuit182, the Ip2detection circuit186, the heater drive circuit187, and the electromotive force detection circuit188. The CPU191outputs a driving signal to the heater drive circuit187through the signal input/output unit194to control the heater160.

The CPU191executes a process for removing the influence of the oxygen concentration from the value of the second pumping current Ip2and from the ammonia electromotive force EMF on the basis of various data stored in the ROM192and further executes a process for computing NOx concentrations such as the concentration of NO and the concentration of NO2and the concentration of ammonia. No particular limitation is imposed on these processes, and processes described in, for example, Japanese Patent Application Laid-Open (kokai) No. 2011-075546 may be used.

The above-configured ammonia detection section102is disposed on the electrically insulating layer120and has a structure including the reference electrode212, the solid electrolyte body213for ammonia, and the detection electrode214that are stacked in this order on the insulating layer120. In the ammonia detection section102, a three-phase boundary is formed at the interface between the reference electrode212and the solid electrolyte body213for ammonia, and another three-phase boundary is formed at the interface between the detection electrode214and the solid electrolyte body213for ammonia. The concentration of ammonia in the exhaust gas is thereby detected.

The ammonia detection section102includes the porous layer211formed of an electrically insulating porous material and disposed between the insulating layer120and the reference electrode212.

In the above-configured ammonia detection section102, the porous layer211is disposed on the opposite side of the reference electrode212from the solid electrolyte body213for ammonia. The porous layer211has many pores in its interior and on its surface. Therefore, in the porous layer211, ammonia is allowed to flow from a portion exposed to the exhaust gas into the interior of the porous layer211, and the ammonia flowing inside the porous layer211is allowed to flow toward the reference electrode212.

Therefore, the amount of ammonia flowing through the reference electrode212toward the solid electrolyte body213for ammonia increases, and this allows an increase in the area of the three-phase boundary at which ammonia comes into contact with the reference electrode212and the solid electrolyte body213for ammonia. When a stack of the reference electrode212and the solid electrolyte body213for ammonia is formed on a green insulating layer120and then they are co-fired, the reference electrode212may become dense, and the area of the three-phase boundary may decrease. Even in this case, the increase in the inflow of ammonia through the porous layer211allows the reduction in the area of the three-phase boundary to be suppressed.

In the ammonia detection section102, the rise in impedance of the ammonia detection section102due to co-firing can be suppressed in the manner described above.

FIG. 3is a complex impedance plot for a structure prepared by stacking a porous layer, a reference electrode, and a solid electrolyte body on a substrate as shown inFIG. 4(A)and for a structure prepared by stacking a reference electrode and a solid electrolyte body on a substrate as shown inFIG. 4(B). A curve L1inFIG. 3is a complex impedance plot for the structure shown inFIG. 4(A), and a curve L2inFIG. 3is a complex impedance plot for the structure shown inFIG. 4(B).

As shown inFIG. 3, by disposing the porous layer between the substrate and the reference electrode, the impedance can be reduced.

In the embodiment described above, the ammonia detection section102is the gas sensor of the first aspect of the present invention, and the insulating layer120is the insulating member in the first aspect. The solid electrolyte body213for ammonia is the solid electrolyte body in the first aspect, and the porous layer211is the insulating porous layer in the first aspect.

The exhaust gas is the atmosphere of interest in the first aspect, and ammonia is the detection target gas in the first aspect.

Second Embodiment

A second embodiment of the present invention will next be described with reference toFIG. 5. In the second embodiment, differences from the first embodiment will be described. The same reference numerals as those in the first embodiment indicate the same components, and their description will be omitted.

A multi-gas detector1in the second embodiment is different from the multi-gas detector1in the first embodiment in that an ammonia detection section302is provided instead of the ammonia detection section102.

As shown inFIG. 5, the ammonia detection section302is formed on the insulating layer120and has a structure including the reference electrode212, a solid electrolyte body313for ammonia, and the detection electrode214that are stacked in this order.

The solid electrolyte body313for ammonia includes a porous layer313aand a non-porous layer313b.

The porous layer313ais a porous layer formed of the same material as the material of the solid electrolyte body213for ammonia (i.e., an oxygen ion-conductive material such as yttria-stabilized zirconia (YSZ)) and is formed on the reference electrode212.

The non-porous layer313bis a non-porous layer formed of the same material as the material of the solid electrolyte body213for ammonia and is formed on the porous layer313a.

The above-configured ammonia detection section302is disposed on the electrically insulating layer120and has a structure including the reference electrode212, the solid electrolyte body313for ammonia, and the detection electrode214that are stacked in this order on the insulating layer120. In the ammonia detection section302, a three-phase boundary is formed at the interface between the reference electrode212and the solid electrolyte body313for ammonia, and another three-phase boundary is formed at the interface between the detection electrode214and the solid electrolyte body313for ammonia. The concentration of ammonia in the exhaust gas is thereby detected.

In the ammonia detection section302, a portion of the solid electrolyte body313for ammonia that is in contact with the reference electrode212is porous.

As described above, in the ammonia detection section302, the porous layer313ais disposed between the non-porous layer313band the reference electrode212. Therefore, in the porous layer313a, ammonia is allowed to flow from a portion313aexposed to the exhaust gas into the interior of the porous layer313a, and the ammonia flowing inside the porous layer313ais allowed to flow toward the reference electrode212.

Therefore, the amount of ammonia flowing through the solid electrolyte body313for ammonia toward the reference electrode212increases, and this allows an increase in the area of the three-phase boundary at which ammonia comes into contact with the reference electrode212and the solid electrolyte body313for ammonia. When a stack of the reference electrode212and the solid electrolyte body313for ammonia is formed on a green insulating layer120and then they are co-fired, the reference electrode212may become dense, and the area of the three-phase boundary may decrease. Even in this case, the increase in the inflow of ammonia through the porous layer313aallows the reduction in the area of the three-phase boundary to be suppressed.

In the ammonia detection section302, the rise in impedance of the ammonia detection section302due to co-firing can be suppressed in the manner described above.

In the embodiment described above, the ammonia detection section302is the gas sensor of the second aspect of the present invention, and the solid electrolyte body313for ammonia is the solid electrolyte body in the second aspect.

While the embodiments of the present invention have been described, the present invention is not limited to these embodiments. The present invention can be implemented in various forms so long as they fall within the technical scope of the invention.

For example, in one of the embodiments, the ammonia detection section102having a stacked structure including the reference electrode212, the solid electrolyte body213for ammonia, and the detection electrode214detects the concentration of ammonia. However, the present invention is not limited to the gas sensor that detects the concentration of ammonia. Specifically, the present invention is applicable to any gas sensor for detecting the concentration of a gas other than ammonia, so long as the gas sensor has a stacked structure including a reference electrode, a solid electrolyte body, and a detection electrode.

In one of the embodiments, the ammonia detection section102is formed on the outer surface of the NOx detection section101. However, the present invention is not limited to the ammonia detection section formed on the gas sensor. The ammonia detection section102may be formed on any electrically insulating member.

DESCRIPTION OF REFERENCE NUMERALS