JP7011923B2 - Gas sensor - Google Patents

Description

The present invention relates to a gas sensor including a sensor element for performing gas detection.

The gas sensor is used, for example, to detect the concentration of oxygen contained in the detection gas or various specific gas components by using the exhaust gas flowing through the exhaust pipe of the internal combustion engine as the detection gas. Further, in the sensor element used for the gas sensor, an insulating layer is laminated on the solid electrolyte layer having ionic conductivity, and a detection gas chamber into which the detection gas is introduced and a reference gas chamber in which the reference gas such as the atmosphere is introduced. Is being formed. A detection electrode provided in the solid electrolyte layer is arranged in the detection gas chamber, and a reference electrode provided in the solid electrolyte layer is arranged in the reference gas chamber.

For example, in the oxygen sensor element of Patent Document 1, a detection electrode and a reference electrode are provided at opposite positions on both sides of a plate-shaped substrate made of a ceramic solid electrolyte, and the reference electrode is housed and the atmosphere is contained inside the substrate. It is stated that an air introduction hole to be introduced is formed. It is described that the atmospheric introduction holes are filled with porous ceramics.

Japanese Patent Application Laid-Open No. 2003-344350

The porous ceramics in the oxygen sensor element of Patent Document 1 is for preventing the introduction of moisture together with the air when the air is introduced into the atmosphere introduction hole. Further, a space portion for accommodating the detection electrode and introducing the detection gas may be formed inside the substrate, and the space portion may be filled with porous ceramics for ensuring the strength of the device. Are listed.

In the oxygen sensor element of Patent Document 1, the substrate made of a ceramic solid electrolyte forms the skeleton shape of the oxygen sensor element. In particular, both sides of the plate-shaped portion of the ceramic solid electrolyte provided with the detection electrode and the reference electrode are supported by the adjacent plate-shaped portions of the ceramic solid electrolyte of the same quality. Therefore, there is no difference in the linear expansion rate between the plate-shaped part and the adjacent plate-shaped part, and the thermal stress based on the difference in the linear expansion rate between the plate-shaped part and the adjacent plate-shaped part at the time of manufacturing the oxygen sensor element. Almost never occurs.

On the other hand, in a sensor element formed by laminating an insulating layer having insulating properties on a solid electrolyte layer having ionic conductivity, it is based on the difference in linear expansion rate between the solid electrolyte layer and the insulating layer at the time of manufacture. Thermal stress is generated. As a result, deformation such as bending may occur in the portion of the solid electrolyte layer where the detection electrode and the reference electrode are provided and which is in a free state between the detection gas chamber and the reference gas chamber. I understood. In particular, when it is desired to reduce the thickness of the solid electrolyte layer, this deformation may become remarkable. This deformation of the solid electrolyte layer extends to the detection electrode and the reference electrode and may affect the performance of the sensor element, so it is preferable to eliminate it as much as possible.

The present invention has been made in view of the above problems, and has been obtained in an attempt to provide a gas sensor capable of making it difficult for deformation such as bending to occur in a solid electrolyte layer laminated with an insulating layer.

One aspect of the present invention is a gas sensor (1) provided with a sensor element (2) for performing gas detection.
The sensor element is
The detection gas chamber (35) into which the detection gas (G) is introduced, and
The reference gas chamber (36) into which the reference gas (A) is introduced, and
It is arranged between the detection gas chamber and the reference gas chamber, and has a first main surface (301) facing the detection gas chamber and a second main surface (302) facing the reference gas chamber. , A plate-shaped solid electrolyte layer (31) having ionic conductivity,
A detection electrode (311) provided on the first main surface of the solid electrolyte layer in a state of being arranged in the detection gas chamber, and a detection electrode (311).
A reference electrode (312) provided on the second main surface of the solid electrolyte layer in a state of being arranged in the reference gas chamber, and a reference electrode (312).
A first insulating layer (33A) laminated on the first main surface of the solid electrolyte layer to form the detection gas chamber, and
A second insulating layer (33B) laminated on the second main surface of the solid electrolyte layer to form the reference gas chamber, and
A heating element (34) embedded in the second insulating layer and generating heat by energization,
Insulating first porous material arranged in the first gap (351) in the stacking direction (D) between the detection electrode and the first insulating layer in the detection gas chamber and for maintaining the first gap. (51) and
An insulating second porous material (52) arranged in the second gap (361) in the stacking direction between the reference electrode and the second insulating layer in the reference gas chamber and for maintaining the second gap. ) And, with
The porosity of the first porous material is in the gas sensor, which is larger than the porosity of the second porous material .
Another aspect of the present invention is a gas sensor (1) provided with a sensor element (2) for performing gas detection.
The sensor element is
The detection gas chamber (35) into which the detection gas (G) is introduced, and
The reference gas chamber (36) into which the reference gas (A) is introduced, and
It is arranged between the detection gas chamber and the reference gas chamber, and has a first main surface (301) facing the detection gas chamber and a second main surface (302) facing the reference gas chamber. , A plate-shaped solid electrolyte layer (31) having ionic conductivity,
A detection electrode (311) provided on the first main surface of the solid electrolyte layer in a state of being arranged in the detection gas chamber, and a detection electrode (311).
A reference electrode (312) provided on the second main surface of the solid electrolyte layer in a state of being arranged in the reference gas chamber, and a reference electrode (312).
A first insulating layer (33A) laminated on the first main surface of the solid electrolyte layer to form the detection gas chamber, and
A second insulating layer (33B) laminated on the second main surface of the solid electrolyte layer to form the reference gas chamber, and
A heating element (34) embedded in the second insulating layer and generating heat by energization,
Insulating first porous material arranged in the first gap (351) in the stacking direction (D) between the detection electrode and the first insulating layer in the detection gas chamber and for maintaining the first gap. (51) and
An insulating second porous material (52) arranged in the second gap (361) in the stacking direction between the reference electrode and the second insulating layer in the reference gas chamber and for maintaining the second gap. ) And, with
The second porous material includes an electrode-side porous layer (521) arranged on the side of the reference electrode in the stacking direction and a heating element-side porous layer (521) arranged on the heating element side in the stacking direction. It forms 522) and
The porosity of the electrode-side porous layer is larger than the porosity of the heating element-side porous layer in the gas sensor.
Yet another aspect of the present invention is a gas sensor (1) provided with a sensor element (2) for performing gas detection.
The sensor element is
The detection gas chamber (35) into which the detection gas (G) is introduced, and
The reference gas chamber (36) into which the reference gas (A) is introduced, and
It is arranged between the detection gas chamber and the reference gas chamber, and has a first main surface (301) facing the detection gas chamber and a second main surface (302) facing the reference gas chamber. , A plate-shaped solid electrolyte layer (31) having ionic conductivity,
A detection electrode (311) provided on the first main surface of the solid electrolyte layer in a state of being arranged in the detection gas chamber, and a detection electrode (311).
A reference electrode (312) provided on the second main surface of the solid electrolyte layer in a state of being arranged in the reference gas chamber, and a reference electrode (312).
A first insulating layer (33A) laminated on the first main surface of the solid electrolyte layer to form the detection gas chamber, and
A second insulating layer (33B) laminated on the second main surface of the solid electrolyte layer to form the reference gas chamber, and
A heating element (34) embedded in the second insulating layer and generating heat by energization,
An insulating first porous material arranged in the first gap (351) in the stacking direction (D) between the detection electrode and the first insulating layer in the detection gas chamber and for maintaining the first gap. (51) and
An insulating second porous material (52) arranged in the second gap (361) in the stacking direction between the reference electrode and the second insulating layer in the reference gas chamber and for maintaining the second gap. ) And, with
The solid electrolyte layer is composed of a lanthanum gallate-based oxide.
The first porous material and the second porous material are in a gas sensor composed of a ceria-based oxide.

In the gas sensor of the above aspect, when the sensor element in which the first insulating layer and the second insulating layer are laminated on the solid electrolyte layer is used, the solid electrolyte layer is devised so as to be less likely to be deformed such as bending.
Specifically, the first porous material is arranged in the detection gas chamber formed by being surrounded by the first insulating layer and the solid electrolyte layer, and is formed by being surrounded by the second insulating layer and the solid electrolyte layer. A second porous material is arranged in the reference gas chamber. The first porous material is arranged in the first gap in the stacking direction between the detection electrode and the first insulating layer, and the first gap is maintained so as not to change. The second porous material is arranged in the second gap in the stacking direction between the reference electrode and the second insulating layer, and the second gap is maintained so as not to change.

Then, at the time of manufacturing the sensor element, when the laminate of the sensor element is heated for sintering, the solid electrolyte layer and each insulating layer are affected by the difference in the linear expansion ratio between the solid electrolyte layer and each insulating layer. Thermal stress is generated at the boundary with. At this time, the first gap is maintained by the first porous material, and the second gap is maintained by the second porous material, so that the solid electrolyte layer is located between the detection gas chamber and the reference gas chamber. It is possible to prevent deformation such as bending from occurring in the portion.

Therefore, according to the gas sensor of the above aspect, it is possible to prevent the solid electrolyte layer laminated with the insulating layer from being deformed such as bending.

Each insulating layer and each porous material can be made of ceramics such as metal oxides. Each insulating layer can be formed as a dense layer having few pores formed. The porosity of each insulating layer can be, for example, 1% by volume or less so that the detection gas or the reference gas does not permeate. The porosity refers to the ratio of the volume of the pore portion to the volume of the entire outer shape including the material portion and the pore portion.

Each porous material has pores through which the detection gas or reference gas can pass. The porosity of each porous material can be, for example, 30 to 80% by volume. When the porosity of each porous material is less than 30% by volume, it becomes difficult for the detection gas or the reference gas to come into contact with the detection electrode or the reference electrode, and the reaction resistance at the detection electrode or the reference electrode may increase. On the other hand, when the porosity of each porous material exceeds 80% by volume, the strength of each porous material decreases, and each porous material cannot maintain the first gap or the second gap, and is solid. Deformation such as bending may occur in the electrolyte layer.

The "first main surface" and the "second main surface" refer to the largest surface of the solid electrolyte layer. Further, the "lamination direction" means the direction in which the first insulating layer and the second insulating layer are laminated with respect to the solid electrolyte layer.

The reference numerals in parentheses of each component shown in one aspect of the present invention indicate the correspondence with the reference numerals in the figure in the embodiment, but each component is not limited to the content of the embodiment.

The cross-sectional view which shows the gas sensor which concerns on Embodiment 1. FIG. The perspective view which shows the sensor element before stacking which concerns on Embodiment 1. FIG. The cross-sectional view which shows the sensor element which concerns on Embodiment 1. FIG. FIG. 3 is a sectional view taken along line IV-IV of FIG. 3, showing a sensor element according to the first embodiment. FIG. 6 is a cross-sectional view showing another sensor element according to the first embodiment. The cross-sectional view which shows the sensor element which concerns on Embodiment 2. FIG. 6 is a sectional view taken along the line VII-VII of FIG. 6, showing the sensor element according to the second embodiment. Explanatory drawing which shows the degree of bending of a sensor element which concerns on confirmation test 1. The graph which shows the result of having performed the complex impedance plot about the impedance of the sensor element which concerns on confirmation test 1.

A preferred embodiment of the gas sensor described above will be described.
In the gas sensor, when the porous material is arranged in the detection gas chamber and the reference gas chamber, the electrode reaction resistance when ion conduction is performed between the detection electrode and the reference electrode via the solid electrolyte layer is reduced. I am devising. Various embodiments can be adopted to reduce this electrode reaction resistance.

In the invention of the one aspect, the porosity of the first porous material is made larger than the porosity of the second porous material . The detection gas chamber is a space into which the detection gas is introduced, and the diffusion state of the detection gas in the detection gas chamber affects the output characteristics of the gas sensor. The porosity of the first porous material arranged in the detection gas chamber is preferably as large as possible on the premise that the first gap can be maintained. As a result, the detection gas can easily come into contact with the detection electrode in the detection gas chamber through the pores in the first porous material, and the diffusion state of the detection gas in the detection gas chamber can be kept good.

Then, by making the porosity of the first porous material arranged in the detection gas chamber larger than the porosity of the second porous material arranged in the reference gas chamber, the detection gas can easily come into contact with the detection electrode. Therefore, the electrode reaction resistance in the sensor element can be reduced. If the electrode reaction resistance can be reduced, the responsiveness of the gas sensor is particularly improved. The electrode reaction resistance refers to the resistance that governs the reaction at the electrode when oxygen ions are conducted between the detection electrode and the reference electrode via the solid electrolyte layer.

Further, in the invention of the other aspect, the second porous material has a porous layer on the electrode side arranged on the reference electrode side in the stacking direction and heat generation arranged on the heating element side in the stacking direction. It forms a body-side porous layer, and the porosity of the electrode-side porous layer is larger than the porosity of the heating element-side porous layer . In most cases, the volume of the reference gas chamber is larger than the volume of the detection gas chamber. Therefore, the second porous material arranged in the reference gas chamber can be easily provided in a state of two or more layers having different porosities.

By making the porosity of the porous layer on the electrode side larger than the porosity of the porous layer on the heating element side, the reference gas can easily come into contact with the reference electrode in the reference gas chamber through the pores in the second porous material. , The diffusion state of the reference gas in the vicinity of the reference electrode can be kept good. Further, the portion on the heating element side in the reference gas chamber is close to the heating element and is a portion where thermal stress is likely to occur. Therefore, since the porosity of the porous layer on the heating element side is small, it is possible to increase the strength of the portion of the second porous material where thermal stress is likely to occur. Further, the porous layer on the heating element side can easily shield the heat generated by the heating element.

When the second porous material is formed of the electrode-side porous layer and the heating element-side porous layer, the porosity of the first porous material is the porosity of the electrode-side porous layer and the heating element-side porosity. It can be larger than the average value with the porosity of the stratum. Further, the porosity of the first porous material and the porosity of the electrode-side porous layer are set to be about the same, and the porosity of the first porous material can be made larger than the porosity of the heating element-side porous layer. ..

Further, in the invention of the one aspect and the invention of the other aspect, the solid electrolyte layer is composed of a zirconia-based oxide, and the first porous material and the second porous material are ceria-based. It may be composed of at least one of an oxide and a zirconia-based oxide. When the solid electrolyte layer is composed of zirconia oxide and alumina (aluminum oxide) is used for each porous material, a reaction product may be generated between the solid electrolyte layer and each porous material. There is. Then, when the reaction product is generated, the electrode reaction resistance and the like may increase. Therefore, by combining the solid electrolyte layer composed of the zirconia-based oxide and each porous material composed of at least one of the ceria-based oxide and the zirconia-based oxide, the solid electrolyte layer and each porous material can be obtained. The formation of reaction products between them can be suppressed.

Further, in the invention of still another aspect, the solid electrolyte layer is composed of a lanthanum gallate-based oxide, and the first porous material and the second porous material are composed of a ceria-based oxide. Has been done . When zirconia (zirconium oxide) is used for each porous material when the solid electrolyte layer is composed of a lanthanum gallate-based oxide, a reaction product is generated between the solid electrolyte layer and each porous material. There is a risk. Therefore, by combining the solid electrolyte layer composed of the lanthanum gallate-based oxide and each porous material composed of the ceria-based oxide, a reaction product is generated between the solid electrolyte layer and each porous material. Can be suppressed.

A preferred embodiment of the gas sensor described above will be described with reference to the drawings.
<Embodiment 1>
As shown in FIGS. 1 to 4, the gas sensor 1 of the present embodiment includes a sensor element 2 for performing gas detection. The sensor element 2 is formed as a sintered body of ceramics, and has a detection gas chamber 35, a reference gas chamber 36, a solid electrolyte layer 31, a detection electrode 311 and a reference electrode 312, a first insulating layer 33A, and a second insulating layer 33B. , A diffusion rate controlling layer 32, a heating element 34, a first porous material 51 and a second porous material 52. The detection gas chamber 35 is formed as a space into which the detection gas G is introduced. The reference gas chamber 36 is formed as a space portion into which the reference gas A is introduced.

As shown in FIGS. 3 and 4, the solid electrolyte layer 31 has ionic conductivity and is formed in a plate shape. The solid electrolyte layer 31 is arranged between the detection gas chamber 35 and the reference gas chamber 36 so as to partition the detection gas chamber 35 and the reference gas chamber 36, and is a first main surface facing the detection gas chamber 35. It has a 301 and a second main surface 302 facing the reference gas chamber 36. The detection electrode 311 is provided on the first main surface 301 of the solid electrolyte layer 31 in a state of being arranged in the detection gas chamber 35. The reference electrode 312 is provided on the second main surface 302 of the solid electrolyte layer 31 in a state of being arranged in the reference gas chamber 36. The first insulating layer 33A is laminated on the first main surface 301 of the solid electrolyte layer 31, and forms a detection gas chamber 35 together with the solid electrolyte layer 31. The second insulating layer 33B is laminated on the second main surface 302 of the solid electrolyte layer 31, and forms the reference gas chamber 36 together with the solid electrolyte layer 31.

The diffusion rate-determining layer 32 is replaced with a part of the first insulating layer 33A to form a detection gas chamber 35 together with the solid electrolyte layer 31 and the first insulating layer 33A. The diffusion rate-determining layer 32 is for controlling the diffusion of the detected gas G into the detection gas chamber 35. The heating element 34 is embedded in the second insulating layer 33B and generates heat when energized.

The first porous material 51 is formed of a porous ceramic having an insulating property. The first porous material 51 is arranged in the first gap 351 in the stacking direction D between the detection electrode 311 and the first insulating layer 33A in the detection gas chamber 35, and is used to maintain the first gap 351. .. The second porous material 52 is formed of a porous ceramic having an insulating property. The second porous material 52 is arranged in the second gap 361 in the stacking direction D between the reference electrode 312 and the second insulating layer 33B in the reference gas chamber 36, and is used to maintain the second gap 361. ..

The gas sensor 1 of this embodiment will be described in detail below.
(Internal combustion engine)
As shown in FIG. 1, the gas sensor 1 of this embodiment is attached to an exhaust pipe through which exhaust gas exhausted from an internal combustion engine (engine) of a vehicle flows. The gas sensor 1 uses the exhaust gas flowing in the exhaust pipe as the detection gas G and the atmosphere as the reference gas A for gas detection. The gas sensor 1 of this embodiment is used as an air-fuel ratio sensor for obtaining the air-fuel ratio of an internal combustion engine obtained from the composition of exhaust gas. Hereinafter, the air-fuel ratio of the internal combustion engine obtained by the gas sensor 1 may be referred to as the air-fuel ratio of the exhaust gas.

The air-fuel ratio sensor quantitatively and continuously ranges from a fuel-rich state in which the ratio of fuel to air is higher than the theoretical air-fuel ratio to a fuel lean state in which the ratio of fuel to air is lower than the theoretical air-fuel ratio. Can be detected. In the air-fuel ratio sensor, when the diffusion rate of the detection gas G guided to the detection gas chamber 35 by the diffusion rate-determining layer 32 is reduced, the amount of oxygen ions transferred between the detection electrode 311 and the reference electrode 312 is adjusted. A predetermined voltage is applied to indicate the critical current characteristic at which the current is output.

When the air-fuel ratio sensor detects the air-fuel ratio on the fuel lean side, oxygen contained in the detection gas G becomes ions and moves from the detection electrode 311 to the reference electrode 312 via the solid electrolyte layer 31. Detect the generated current. Further, when the air-fuel ratio sensor detects the air-fuel ratio on the fuel-rich side, the unburned gas (hydrocarbon, carbon monoxide, hydrogen, etc.) contained in the detected gas G is reacted from the reference electrode 312 in order to react. Ionic oxygen moves to the detection electrode 311 via the solid electrolyte layer 31, and the current generated when the unburned gas and oxygen react with each other is detected.

Further, the gas sensor 1 can also be used as a NOx sensor for detecting NOx as a specific gas component in the exhaust gas. In this case, the detection electrode 311 can be used separately as a pump electrode for discharging oxygen in the detection gas G together with the reference electrode 312 and a NOx detection electrode for detecting NOx in the detection gas G. ..

(Sensor element 2)
As shown in FIGS. 3 and 4, the sensor element 2 is a laminated type in which the insulating layers 33A and 33B and the heating element 34 are laminated on the solid electrolyte layer 31. The solid electrolyte layer 31 is composed of a zirconia-based oxide, contains zirconia as a main component (containing 50% by mass or more), and is a stabilized zirconia or a portion obtained by substituting a part of zirconia with a rare earth metal element or an alkaline earth metal element. Consists of stabilized zirconia. A portion of the zirconia constituting the solid electrolyte layer 31 can be replaced by yttria, scandia or calcia.

Further, the detection electrode 311 and the reference electrode 312 contain platinum as a noble metal exhibiting catalytic activity for oxygen and a zirconia oxide as a co-material with the solid electrolyte layer 31.

The sensor element 2 is formed in a long shape, and the heat generating portion 341 of the detection electrode 311, the reference electrode 312, the detection gas chamber 35, the diffusion rate controlling layer 32, and the heating element 34 is located at the tip end side portion in the long direction L. Have been placed. A detection unit 21 is formed at the tip end side portion of the sensor element 2 in the long direction L by a detection electrode 311 and a reference electrode 312, and a portion of a solid electrolyte layer 31 sandwiched between these electrodes 311, 312. ing.

The long direction L of the sensor element 2 means the direction in which the sensor element 2 is formed in a long shape. Further, the direction in which the solid electrolyte layer 31, the insulating layers 33A and 33B and the heating element 34 are laminated, which is orthogonal to the long direction L, is referred to as a stacking direction D. Further, the direction orthogonal to the long direction L and the stacking direction D is called the width direction W. Further, in FIGS. 1 to 4, the tip end side in the elongated direction L is indicated by L1, and the proximal end side in the elongated direction L is indicated by L2.

As shown in FIG. 2, electrode lead portions 313 and 314 for electrically connecting these electrodes 311, 312 to the outside of the gas sensor 1 are connected to the detection electrode 311 and the reference electrode 312, and the electrode lead portions are connected to the detection electrode 311 and the reference electrode 312. The 313 and 314 are pulled out to the base end side portion in the long direction L.

Further, the heating element 34 has a heating element 341 that generates heat by energization and a pair of heating element lead portions 342 connected to the heating element 341. The heating element lead portion 342 is pulled out to the proximal end side portion in the long direction L. The heating element 34 contains a conductive metal material.

As shown in FIG. 2, the heat generating portion 341 is formed in a shape meandering in the long direction L at the tip portion of the heating element 34. The heat generating portion 341 may be formed so as to meander in the width direction W. The heat generating portion 341 is arranged at a position facing the detection electrode 311 and the reference electrode 312 in the stacking direction D orthogonal to the long direction L so that the detection electrode 311 and the reference electrode 312 reach the target temperature. The solid electrolyte layer 31, the detection electrode 311 and the reference electrode 312, the insulating layers 33A, 33B and the like are heated.

The cross-sectional area of the heating element 341 is smaller than the cross-sectional area of the heating element lead portion 342, and the resistance value per unit length of the heating element 341 is higher than the resistance value per unit length of the heating element lead portion 342. This cross-sectional area means the cross-sectional area of the plane orthogonal to the extending direction of the heating element 341 and the heating element lead portion 342. When a voltage is applied to the pair of heating element lead units 342, the heat generating unit 341 generates heat due to Joule heat, and the heat generated heats the periphery of the detection unit 21.

The first insulating layer 33A and the second insulating layer 33B are formed of alumina (aluminum oxide). The insulating layers 33A and 33B are formed as a dense layer through which the detection gas G or the reference gas A cannot permeate, and the insulating layers 33A and 33B are almost formed with pores through which the gas can pass. Not.

As shown in FIG. 2, the first insulating layer 33A is laminated with an insulating spacer 331 having a through hole 332 penetrated in the stacking direction D in order to form a detection gas chamber 35, and a through hole 331. It is formed by an insulating plate 334 for closing the 332. The diffusion rate-controlling layer 32 of this embodiment is formed adjacent to the tip end side of the detection gas chamber 35 in the long direction L. The diffusion rate-determining layer 32 is arranged in the introduction port 333 opened adjacent to the tip end side of the detection gas chamber 35 in the long direction L in the insulating spacer 331 of the first insulating layer 33A.

The detection gas chamber 35 is formed as a space portion closed by the first insulating layer 33A, the diffusion rate controlling layer 32, and the solid electrolyte layer 31. The detection gas G, which is an exhaust gas flowing in the exhaust pipe, passes through the diffusion rate-determining layer 32 and is introduced into the detection gas chamber 35.

The diffusion rate-determining layer 32 may be formed adjacent to both sides of the detection gas chamber 35 in the width direction W. In this case, the diffusion rate controlling layer 32 is arranged in the introduction port 333 opened adjacent to both sides of the detection gas chamber 35 in the width direction W in the insulating spacer 331 of the first insulating layer 33A.

The diffusion rate-determining layer 32 is formed of porous ceramics such as alumina. The diffusion rate (flow rate) of the detection gas G introduced into the detection gas chamber 35 is determined by limiting the rate at which the detection gas G permeates the pores in the diffusion rate-determining layer 32. The porosity of the diffusion rate-determining layer 32 is smaller than the porosity of the first porous material 51 arranged in the detection gas chamber 35. Porosity is expressed as the ratio of the volume of the pores to the volume of the entire outer shape including the pores.

The diffusion rate-determining of the detection gas G into the detection gas chamber 35 can be formed by using a pinhole which is a small through hole communicated with the detection gas chamber 35, in addition to using the diffusion-controlling layer 32.

As shown in FIG. 2, the second insulating layer 33B is an insulating spacer having an open hole 336 that is penetrated in the stacking direction D to form the reference gas chamber 36 and is opened on the base end side in the long direction L. It is formed by the 335, the first heater plate 337 laminated on the insulating spacer 335, and the second heater plate 338 laminated on the first heater plate 337 with the heating element 34 sandwiched between the first heater plate 337. ing.

The reference gas chamber 36 is formed as a duct for the reference gas A with the base end side in the long direction L opened. The reference gas chamber 36 is formed from the base end position of the sensor element 2 in the long direction L to a position facing the detection gas chamber 35 via the solid electrolyte layer 31. The reference electrode 312 is arranged at the tip end side portion in the reference gas chamber 36. Atmosphere as the reference gas A is introduced into the reference gas chamber 36 from the proximal end side of the sensor element 2.

As shown in FIG. 1, a porous protective layer 37 for capturing toxic substances to the detection electrode 311, condensed water generated in the exhaust pipe, and the like is formed on the entire circumference of the tip end side portion of the sensor element 2 in the long direction L. Is provided. The porous protective layer 37 is formed of porous ceramics such as alumina. The porosity of the porous protective layer 37 is larger than the porosity of the diffusion rate-determining layer 32, and the flow rate of the detection gas G that can permeate the porous layer 37 is the detection gas that can permeate the diffusion rate-determining layer 32. More than the flow rate of G.

As shown in FIGS. 3 and 4, the solid electrolyte layer 31 of the present embodiment is formed as thin as possible in order to reduce the resistance and enhance the responsiveness of the sensor element 2. The solid electrolyte layer 31 can be formed to have a thickness of 0.02 to 0.3 mm in the stacking direction D. It is difficult to form the fixed electrolyte layer 31 having a thickness of less than 0.02 mm. When the thickness of the solid electrolyte layer 31 is as thin as 0.1 mm or less, the solid electrolyte layer 31 is likely to be deformed such as bending. Therefore, in this case, the effect of arranging the porous materials 51 and 52 becomes remarkable.

The volume of the reference gas chamber 36 is larger than the volume of the detection gas chamber 35. Further, the length of the reference gas chamber 36 in the long direction L is longer than the length of the detection gas chamber 35 in the long direction L, and the thickness of the reference gas chamber 36 in the stacking direction D is the stacking direction of the detection gas chamber 35. It is larger than the thickness of D. The thickness of the reference gas chamber 36 in the stacking direction D can be, for example, 1.5 to 15 times the thickness of the detection gas chamber 35 in the stacking direction D. Further, the second gap 361 in the stacking direction D between the reference electrode 312 and the second insulating layer 33B is larger than the first gap 351 in the stacking direction D between the detection electrode 311 and the first insulating layer 33A. Unlike the detection gas chamber 35, the reference gas chamber 36 does not need to adjust the oxygen concentration, and has a large volume so that a sufficient flow rate of oxygen can pass through when gas detection is performed in the sensor element 2. It is preferable to have.

(Porous medium 51, 52)
As shown in FIGS. 3 and 4, the first porous material 51 is filled in the detection gas chamber 35, and the second porous material 52 is filled in the reference gas chamber 36. The porous materials 51 and 52 may be able to support the formation sites of the electrodes 311, 312 in the solid electrolyte layer 31 on the insulating layers 33A and 33B. Therefore, each of the porous materials 51 and 52 does not need to be completely filled in each of the gas chambers 35 and 36.

As shown in FIG. 5, the porous materials 51 and 52 may be arranged only in the gaps 351 and 361 between the electrodes 31 and 312 and the insulating layers 33A and 33B. Further, the porous materials 51 and 52 may be arranged only in a part of the gaps 351 and 361. Further, in particular, in the reference gas chamber 36, the second porous material 52 is filled only in the portion facing the detection gas chamber 35, and the second porous material 52 is filled in the portion not facing the detection gas chamber 35. You can also not.

The first porous material 51 and the second porous material 52 are formed of a porous metal oxide. Each of the porous materials 51 and 52 of this embodiment is composed of a ceria-based oxide. Ceria-based oxides have a perovskite structure, and are gadlinear-doped ceria (GDC: Ce _1-x Gd _x O _2-δ ) and sammalia-doped ceria (SDC: Ce _1-x Sm _x O _2-δ ). ), Itria-doped ceria (YDC: Ce _1-x Y _x O _2-δ ) and the like. Here, x takes a value of 0 to 0.5, δ indicates the amount of oxygen deficiency, and takes a value of 0 to 0.25.

Each of the porous materials 51 and 52 can also be composed of a zirconia-based oxide. The zirconia-based oxide can be yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (ScSZ), calcia-stabilized zirconia (CSZ), or the like, as shown for the solid electrolyte layer 31. In addition to these, the porous materials 51 and 52 include titania (TIO ₂ ), magnesia (MgO), ytria (Y ₂ O ₃ ), scandia (Sc ₂ O ₃ ), hafnia (HfO ₂ ), and the like. It may be configured by.

A large number of pores through which gas can pass are formed in each of the porous materials 51 and 52. Each of the porous materials 51 and 52 can be formed with a porosity of 30 to 80% by volume from the viewpoint of gas permeability and strength. Further, the porosity of the first porous material 51 is larger than the porosity of the second porous material 52. The porosity of the first porous material 51 can be increased by, for example, 5 to 50% by volume as compared with the porosity of the second porous material 52. Here, the porosity refers to the ratio of the volume of the pore portion to the volume of the entire outer shape of the porous material including the material portion and the pore portion.

For the porosity, the sensor element 2 is cut at a position including the electrodes 311, 312 in a state orthogonal to the long direction L, and the porous materials 51 and 52 on the cut surface are SEM (scanning electron microscope). Can be observed and obtained by. When observing by SEM, the cut surface is taken into the image processing apparatus, and the material portion and the pore portion in each of the porous materials 51 and 52 are binarized by the software in the image processing apparatus. Then, the ratio of the area of the pore portion to the total of the area of the material portion and the area of the pore portion can be defined as the porosity. Porosity may be expressed as either a ratio or a percentage.

By the way, since the material portion of each of the porous materials 51 and 52 is an aggregate of particles or the like, the outer shape of the porous material is difficult to determine. Porosity may be determined as the ratio of the area of the pore portion to the area within the predetermined section range on the cut surface. Further, a plurality of cut surfaces in the sensor element 2 may be observed by SEM, and the porosity may be an average value of the porosities obtained for the plurality of cut surfaces.

Further, each of the porous materials 51 and 52 can be formed by various methods. For example, the paste material containing the metal oxide particles, the resin particles and the solvent is arranged in the detection gas chamber 35 and the reference gas chamber 36. After that, when the laminate of the sensor element 2 is heated and sintered, the resin particles and the solvent can be volatilized to form the porous materials 51 and 52 made of the metal oxide particles.

Further, each of the porous materials 51 and 52 can also be formed by using a sheet material containing particles of a metal oxide. In this case, the sheet material is arranged in the detection gas chamber 35 and the reference gas chamber 36, and the sheet material is sintered together with the solid electrolyte layer 31, the insulating layers 33A, 33B, etc., so that each porous material 51 is formed. , 52 can be formed.

(Other configurations of gas sensor 1)
As shown in FIG. 1, in addition to the sensor element 2 and the like, the gas sensor 1 is connected to a first insulator 42 that holds the sensor element 2, a housing 41 that holds the first insulator 42, and a second insulator 42. A contact terminal 44 that is held by the insulator 43 and the second insulator 43 and comes into contact with the sensor element 2 is provided. Further, the gas sensor 1 is attached to the tip end side cover 45 mounted on the tip end side portion of the housing 41, and is mounted on the base end side portion of the housing 41 to cover the second insulator 43, the contact terminal 44, and the like. A bush 47 or the like for holding the lead wire 48 connected to the contact terminal 44 on the base end side cover 46 is provided.

The front end side cover 45 is arranged in the exhaust pipe of the internal combustion engine. The front end side cover 45 is formed with a gas passage hole 451 for passing the exhaust gas as the detection gas G. The tip side cover 45 may have a double structure or a single structure. The exhaust gas as the detection gas G flowing into the tip side cover 45 from the gas passage hole 451 of the tip side cover 45 passes through the porous layer 37 and the diffusion rate controlling layer 32 of the sensor element 2 and is guided to the detection electrode 311. ..

As shown in FIG. 1, the base end side cover 46 is arranged outside the exhaust pipe of the internal combustion engine. The base end side cover 46 is formed with an atmosphere introduction hole 461 for introducing the atmosphere as the reference gas A into the base end side cover 46. In the atmosphere introduction hole 461, a filter 462 that does not allow liquid to pass through but allows gas to pass through is arranged. The reference gas A introduced into the base end side cover 46 from the atmosphere introduction hole 461 passes through the gap in the base end side cover 46 and the reference gas chamber 36 and is guided to the reference electrode 312.

As shown in FIGS. 1 and 2, the contact terminal 44 is connected to each of the electrode lead portion 313 of the detection electrode 311, the electrode lead portion 314 of the reference electrode 312, and the heating element lead portion 342 of the heating element 34. A plurality of them are arranged in the second insulator 43. Further, the lead wire 48 is connected to each of the contact terminals 44.

As shown in FIGS. 1 and 3, the lead wire 48 in the gas sensor 1 is electrically connected to the sensor control device 6 that controls the gas detection in the gas sensor 1. The sensor control device 6 performs electrical control on the gas sensor 1 in cooperation with an engine control device that controls combustion operation in the engine. The sensor control device 6 includes a measurement circuit 61 for measuring the current flowing between the detection electrode 311 and the reference electrode 312, an application circuit 62 for applying a voltage between the detection electrode 311 and the reference electrode 312, and a heating element 34. An energization circuit or the like for energizing is formed. The sensor control device 6 may be built in the engine control device.

(Production method)
In the manufacture of the sensor element 2, the solid electrolyte layer 31, the insulating layers 33A and 33B, the diffusion rate-determining layer 32, the heating element 34 and the like are laminated to form a laminate, and the laminate is heated and sintered. The detection electrode 311 and the reference electrode 312 print a paste material containing platinum, a solid electrolyte, a solvent, etc. on the solid electrolyte layer 31, and when the laminate of the sensor element 2 is sintered, the platinum and the solid electrolyte are sintered. Is formed. In the first porous material 51 and the second porous material 52, when the paste material or sheet material containing the metal oxide described above is arranged in each of the gas chambers 35 and 36 and the laminate of the sensor element 2 is sintered. , Metal oxides are sintered and formed.

(Action effect)
In the sensor element 2 of the gas sensor 1 of the present embodiment, the detection gas chamber 35 is filled with the first porous material 51, and the reference gas chamber 36 is filled with the second porous material 52. The portion of the solid electrolyte layer 31 arranged between the detection gas chamber 35 and the reference gas chamber 36 is supported by the insulating layers 33A and 33B by the porous materials 51 and 52. Further, the gaps 351 and 361 in the stacking direction D between the electrodes 31 and 312 and the insulating layers 33A and 33B are maintained by the porous materials 51 and 52.

When the laminate of the sensor element 2 is heated for sintering in the manufacturing of the sensor element 2, the solid electrolyte layer is caused by the difference in the linear expansion ratio between the solid electrolyte layer 31 and the insulating layers 33A and 33B. Thermal stress is generated at the boundary between 31 and the insulating layers 33A and 33B. The linear expansion rate of zirconia constituting the solid electrolyte layer 31 is about 7 × 10 ^-6 to 2 × 10 ^-5 [K ^-1 ] at room temperature to 1000 ° C., and the linear expansion rate of alumina constituting the insulating layer. Is about 6 × 10 ^-6 to 1.5 × 10 ^-5 [K ^-1 ] at room temperature to 1000 ° C.

When thermal stress is generated at the boundary between the solid electrolyte layer 31 and the insulating layers 33A and 33B, the solid electrolyte layer 31 is distorted at a portion located between the detection gas chamber 35 and the reference gas chamber 36. The portion of the solid electrolyte layer 31 tends to bend so as to swell toward, for example, the reference gas chamber 36. At this time, the portion of the solid electrolyte layer 31 is supported by the porous materials 51 and 52 so that it can hardly be bent. As a result, distortion is less likely to occur in the electrodes 311, 312 provided on the solid electrolyte layer 31, and the output characteristics of the gas sensor 1 can be maintained satisfactorily.

Further, when the gas sensor 1 detects the air-fuel ratio as gas detection, a voltage is applied between the detection electrode 311 and the reference electrode 312. Then, the oxygen in the detection gas G introduced into the detection gas chamber 35 via the diffusion rate-controlling layer 32 is conducted through the solid electrolyte layer 31 and discharged to the reference gas chamber 36. In this state, a current is generated between the electrodes 311, 312 via the solid electrolyte layer 31 according to the oxygen concentration or the unburned gas concentration in the detection gas G supplied to the detection gas chamber 35.

At this time, the detection gas G in the detection gas chamber 35 passes through the pores in the first porous material 51 and reaches the detection electrode 311. Further, when the air-fuel ratio of the internal combustion engine is in a fuel lean state, oxygen transferred from the solid electrolyte layer 31 to the reference gas chamber 36 passes through the pores of the second porous material 52 and is discharged. Further, when the air-fuel ratio of the internal combustion engine is in a fuel-rich state, the reference gas A in the reference gas chamber 36 passes through the pores in the second porous material 52 and reaches the reference electrode 312.

By the way, the volume of the detection gas chamber 35 is smaller than the volume of the reference gas chamber 36, and since the detection gas chamber 35 is filled with the first porous material 51, it is difficult for the detection gas G to reach the detection electrode 311. Is expected to be. In particular, the diffusion state of the detected gas G in the detection gas chamber 35 greatly affects the output characteristics of the gas sensor 1.

Therefore, in the gas sensor 1 of the present embodiment, the porosity of the first porous material 51 filled in the detection gas chamber 35 is made larger than the porosity of the second porous material 52 filled in the reference gas chamber 36. ing. As a result, the detection gas G easily comes into contact with the detection electrode 311 in the detection gas chamber 35 through the pores in the first porous material 51, and the diffusion state of the detection gas G in the detection gas chamber 35 is kept good. be able to.

Further, since the volume of the reference gas chamber 36 is larger than the volume of the detection gas chamber 35, even if the porosity of the second porous material 52 is small, the reference gas A can easily reach the reference electrode 312. .. Further, the distance between the reference gas chamber 36 and the heating element 34 is smaller than the distance between the detection gas chamber 35 and the heating element 34. The second porous material 52 in the reference gas chamber 36 is easily affected by the heat generated by the heating element 34. Therefore, since the porosity of the second porous material 52 is smaller than the porosity of the first porous material 51, the solid electrolyte layer 31 can be more appropriately protected from deformation such as bending.

Therefore, the detection gas G can be easily brought into contact with the detection electrode 311, and the electrode reaction resistance in the sensor element 2 can be reduced. Thereby, the responsiveness of the gas sensor 1 can be improved. Further, the solid electrolyte layer 31 laminated with the insulating layers 33A and 33B can be prevented from being deformed such as bending, and the output characteristics of the gas sensor 1 can be well maintained.

Further, the solid electrolyte layer 31 of the present embodiment is composed of a zirconia-based oxide, and the porous materials 51 and 52 are composed of a ceria-based oxide or a zirconia-based oxide. When the solid electrolyte layer 31 is composed of a zirconia-based oxide and alumina is used for each of the porous materials 51 and 52, a reaction product is generated between the solid electrolyte layer 31 and each of the porous materials 51 and 52. May be generated. When a reaction product is produced, the electrode reaction resistance and the like may increase. Therefore, by combining the solid electrolyte layer 31 composed of the zirconia-based oxide and the porous materials 51 and 52 composed of the ceria-based oxide or the zirconia-based oxide, the solid electrolyte layer 31 and each porous material are combined. The formation of reaction products between 51 and 52 can be suppressed.

Further, the solid electrolyte layer 31 may be composed of a lanthanum gallate-based oxide, and the first porous material 51 and the second porous material 52 may be composed of a ceria-based oxide. The lanthanum gallate-based oxide has a perovskite structure and is represented by the structural formula of La _1-x A _x Ga _{1- y} By O _3-δ . However, A indicates that it is at least one of Sr, Ca, and Ba, and B indicates that it is at least one of Mg, In, Al, Ni, Fe, and Co. Further, x has a value of 0 to 0.3, y has a value of 0 to 0.3, and δ has a value of 0 to 0.5, indicating the amount of oxygen deficiency.

The lanthanum gallate oxide is, for example, LSGM: La _1-x Sr _x Ga _1-y Mg _y O _3-δ or LSGMN: La _1-x Sr _x Ga _1-yz Mg _y Ni _z O _3-δ . can do. However, z takes a value of 0 to 0.2, and the values of x, y, and δ are the same as in the case of the above-mentioned structural formula of La _1-x A _x Ga _{1- y} By O _3-δ . ..

When zirconia (zirconium oxide) is used for each of the porous materials 51 and 52 when the solid electrolyte layer 31 is composed of a lanthanum gallate-based oxide, between the solid electrolyte layer 31 and each of the porous materials 51 and 52. Reaction products may be produced. Therefore, when the solid electrolyte layer 31 is composed of a lanthanum gallate-based oxide, the porous materials 51 and 52 are composed of a ceria-based oxide, whereby the solid electrolyte layer 31 and the porous materials 51 and 52 are formed. It is possible to suppress the formation of reaction products between and.

<Embodiment 2>
In this embodiment, as shown in FIGS. 6 and 7, a gas sensor in which the second porous material 52 arranged in the reference gas chamber 36 is formed from two porous layers 521 and 522 divided in the stacking direction D. 1 is shown.
The second porous material 52 of the present embodiment has an electrode-side porous layer 521 arranged on the side of the reference electrode 312 in the stacking direction D and a heating element-side porous layer arranged on the side of the heating element 34 in the stacking direction D. It is composed of two porous layers 521 and 522 with 522. The porosity of the electrode-side porous layer 521 is larger than the porosity of the heating element-side porous layer 522.

Also in this embodiment, the volume of the reference gas chamber 36, the length in the elongated direction L, and the thickness in the stacking direction D are larger than the volume of the detection gas chamber 35, the length in the elongated direction L, and the thickness in the stacking direction D. .. Therefore, the second porous material 52 arranged in the reference gas chamber 36 can be easily provided in a state of two or more layers having different porosities.

The ratio of the thickness of the electrode-side porous layer 521 and the heating element-side porous layer 522 in the stacking direction D in the reference gas chamber 36 can be appropriately set. For example, the electrode-side porous layer 521 may be provided within the range of 1/4 to 3/4 of the thickness of the reference gas chamber 36 in the stacking direction D, and the heating element-side porous layer 522 may be provided in the remaining thickness range. can. Further, the electrode-side porous layer 521 can be provided within a range of ½ of the thickness of the reference gas chamber 36 in the stacking direction D, and the heating element-side porous layer 522 can be provided within the range of the remaining thickness.

Between the electrode-side porous layer 521 and the heating element-side porous layer 522, a porosity smaller than the porosity of the electrode-side porous layer 521 and larger than the porosity of the heating element-side porous layer 522 is provided. The intermediate porous layer having may be formed.

In this embodiment, the porosity of the electrode-side porous layer 521 is made larger than the porosity of the heating element-side porous layer 522, so that the porosity of the second porous material 52 is increased in the reference gas chamber 36. The reference gas A can be easily brought into contact with the reference electrode 312, and the diffusion state of the reference gas A in the vicinity of the reference electrode 312 can be kept good. In particular, when the gas sensor 1 is used as an air fuel ratio sensor, when the unburned gas reaches the detection electrode 311, sufficient oxygen for reacting the unburned gas at the detection electrode 311 is supplied from the reference electrode 312 to the solid electrolyte layer 31. Can be supplied to the detection electrode 311 via. Further, when the oxygen in the detection gas G is discharged, the oxygen can be appropriately discharged from the detection electrode 311 to the reference electrode 312 via the solid electrolyte layer 31.

Further, as shown in FIG. 7, the portion of the reference gas chamber 36 on the heating element 34 side is close to the heating element 34 and is a portion where thermal stress is likely to occur. In particular, the corner portion 362 on the heating element 34 side in the reference gas chamber 36 is in a state where stress concentration due to thermal stress is likely to occur. Therefore, since the porosity of the heat generating body side porous layer 522 is small, it is possible to increase the strength of the portion of the second porous material 52 where thermal stress is likely to occur. Further, the porous layer 522 on the heating element side makes it easy to shield the heat generated by the heating element 34.

Other configurations, actions and effects, etc. of the gas sensor 1 of this embodiment are the same as those of the first embodiment. Further, also in this embodiment, the components indicated by the same reference numerals as those shown in the first embodiment are the same as those in the first embodiment.

<Confirmation test 1>
In this confirmation test, regarding the sensor element 2 of the gas sensor 1 shown in the first embodiment, the porosity of the first porous material 51 in the detection gas chamber 35 and the porosity of the second porous material 522 in the reference gas chamber 36. The rate was appropriately changed, and the deflection of the solid electrolyte layer 31, the completion rate of the sensor element 2, and the electrode reaction resistance in the sensor element 2 were confirmed. Further, it was also confirmed in the same manner that the porous materials 51 and 52 were not arranged in at least one of the detection gas chamber 35 and the reference gas chamber 36.

As shown in FIG. 8, the deflection of the solid electrolyte layer 31 is the sensor element by SEM shown in the first embodiment for the test products 1 to 8 of the sensor element 2 manufactured by sintering the laminated body of the sensor element 2. The cut surface of No. 2 was observed and measured as the degree of bending M (−) in the cross section of the solid electrolyte layer 31. The degree of deflection M is the maximum displacement amount in the stacking direction D of the portion of the solid electrolyte layer 31 arranged between the detection gas chamber 35 and the reference gas chamber 36 in the stacking direction D, and the bending direction M in the stacking direction D of the solid electrolyte layer 31. It is a value represented by M = d / t when the thickness is t (mm). The larger the value, the larger the amount of deflection, and when it is 0 (zero), it indicates that there was no deflection.

The completion rate of the sensor element 2 confirms the quality of the electrical conductivity between the detection electrode 311 and the reference electrode 312 in the test products 1 to 8 of the sensor element 2 after manufacturing. When there was sufficient continuity, it became 0.9, and as the value decreased from 0.9, the continuity deteriorated, and when it was 0.2, there was almost no continuity. show.

The electrode reaction resistance (Ω) is shown as a value in the state of being heated to 500 ° C. for the test products 1 to 8 of the sensor element 2 after manufacturing. For the electrode reaction resistance, an AC voltage measuring method is used, and an AC voltage whose frequency is changed from 0.01 Hz to 1 MHz is applied between the detection electrode 311 and the reference electrode 312, and the detection electrode is interposed through the solid electrolyte layer 31. The impedance between 311 and the reference electrode 312 was measured.

As shown in FIG. 9, this impedance is represented by performing a complex impedance plot in a graph having a horizontal axis showing a real number component and a vertical axis showing an imaginary number component, and the result of the semicircular plot appearing in the complex impedance plot. Analyzed by. In the complex impedance plot, the ohmic resistance based on the material component of the solid electrolyte layer 31 and each electrode 311, 312 and the reaction component of the solid electrolyte layer 31 and each electrode 311, 312 are based on the position where the value of the real component is small. The electrode reaction resistance and the gas diffusion resistance based on the diffusion rate of the detected gas G appear. Then, the electrode reaction resistance (Ω) was obtained by extracting from the complex impedance plot. The larger the electrode reaction resistance, the larger the reaction resistance in the sensor element 2, and the worse the responsiveness in the sensor element 2.

The deflection of the solid electrolyte layer 31, the completion rate of the sensor element 2, and the electrode reaction resistance are all measured or confirmed for the sensor element 2 after manufacturing and before use.

Table 1 shows the results of measuring or confirming the deflection of the solid electrolyte layer 31, the completion rate of the sensor element 2, and the electrode reaction resistance for the test products 1 to 8 having different porosities of the porous materials 51 and 52.

The porosity of each of the porous materials 51 and 52 is shown as the volume of the pores in the total volume of the porous materials 51 and 52 including the pores. In the test products 1 to 3, when the porosity of each of the porous materials 51 and 52 is 1, it indicates that the porous materials 51 and 52 are not arranged in the gas chambers 35 and 36. Further, the closer the porosity is to 0, the smaller the porosity.

From the results in Table 1, the porosity of each of the porous materials 51 and 52 is in the range of 0.3 to 0.8 (30 to 80% by volume), and that of the first porous material 51 in the detection gas chamber 35. In the case of the test products 5 and 6 having a porosity larger than the porosity of the second porous material 52 in the reference gas chamber 36, it was found that the bending, the completion rate and the electrode reaction resistance were all good.

On the other hand, in the case of the test products 1 to 3 having no first porous material 51 or second porous material 52, it was found that not only the bending was large but also the completion rate was poor. It is considered that the reason why the completion rate is poor is that the electrodes 311, 312 provided on the solid electrolyte layer 31 are distorted due to the bending. Further, as shown in the results of the test products 2 and 3, it was found that the electrode reaction resistance increases when the porosity of the porous materials 51 and 52 in any of the gas chambers 35 and 36 is small. .. It is considered that the reason for this is that the porosity of the porous materials 51 and 52 is small, so that the flow of the detected gas G or the reference gas A in any of the gas chambers 35 and 36 is poor.

Further, it was found that in the case of the test product 4 in which the porosity of the first porous material 51 is smaller than the porosity of the second porous material 52, the electrode reaction resistance is larger than that of the test products 5 and 6. .. It is considered that the reason for this is that the porosity of the first porous material 51 is small and the diffusion state of the detected gas G in the detected gas chamber 35 is deteriorated.

Further, it was found that in the case of the experimental products 7 and 8 having a large porosity of at least one of the porous materials 51 and 52, the bending becomes large and the completion rate is worse than that of the test products 5 and 6. It is considered that the reason for this is that the porous materials 51 and 52 cannot sufficiently support the solid electrolyte layer 31.

Although not shown in Table 1, the electrode reaction resistance when the porosity of each of the porous materials 51 and 52 was 0.3 (30% by volume) was not very excellent. Further, when the porosity of each of the porous materials 51 and 52 was 0.8 (80% by volume), the deflection and the completion rate of the sensor element 2 of the sensor element 2 (test product 7) were not very excellent. The porosity of each of the porous materials 51 and 52 can be a value of 0.3 or 0.8 alone, but if both are set to 0.3 or 0.8, the characteristics of the sensor element 2 are improved. It's difficult to do.

More specifically, the porosity of the first porous material 51 is preferably 0.4 to 0.8 (40 to 80% by volume), and the porosity of the second porous material 52 is the first. It was found that the porosity of the porous material 51 was smaller than that of the porous material 51, and it was preferably 0.3 to 0.7 (30 to 70% by volume).

<Confirmation test 2>
In this confirmation test, regarding the sensor element 2 of the gas sensor 1 shown in the second embodiment, the pore ratio of the electrode-side porous layer 521 in the reference gas chamber 36 and the heating element-side porous layer 522 in the reference gas chamber 36 The porosity was appropriately changed, and the deflection of the solid electrolyte layer 31, the completion rate of the sensor element 2, and the electrode reaction resistance in the sensor element 2 were confirmed. The porosity of the first porous material 51 in the detection gas chamber 35 was 0.7 (70% by volume).

The ratio of the range in which the electrode-side porous layer 521 is arranged and the range in which the heating element-side porous layer 522 is arranged within the range of the thickness of the reference gas chamber 36 in the stacking direction D is 1: 1. Further, the meanings of the deflection of the solid electrolyte layer 31, the completion rate of the sensor element 2, and the electrode reaction resistance are the same as in the case of the confirmation test 1.

Table 2 shows the results of measuring or confirming the deflection of the solid electrolyte layer 31, the completion rate of the sensor element 2, and the electrode reaction resistance for the test products 9 to 12 having different porosities of the porous materials 51 and 52.

From the results in Table 2, the porosity of each of the porous layers 521 and 522 is in the range of 0.3 to 0.8 (30 to 80% by volume), and the porosity of the electrode-side porous layer 521 is the heating element-side porosity. In the case of the test products 10 and 11 having a porosity larger than that of the layer 522, it was found that the deflection, the completion rate and the electrode reaction resistance were all good.

On the other hand, in the case of the test product 9 in which both the porosity of the electrode-side porous layer 521 and the porosity of the heating element-side porous layer 522 are large as 0.8, the deflection is large and compared with the test products 10 and 11. It turned out that the completion rate also deteriorated. Further, it was found that in the case of the test product 12 in which the porosity of the electrode-side porous layer 521 is as small as 0.3, the electrode reaction resistance is larger than that in the test products 10 and 11.

<Confirmation test 3>
In this confirmation test, the ohmic resistance (Ω) and the electrode reaction resistance (Ω) in the sensor element 2 were measured when the materials used for the solid electrolyte layer 31 and the porous materials 51 and 52 were changed. The solid electrolyte layer 31 is composed of yttria-stabilized zirconia (YSZ) or lanthanum gallate oxide (LSGM: La _1-x Sr _x Ga _1-y Mg _y O _3-δ (x = 0.2, y = 0.2). , Δ = 0.2)), and the porous materials 51 and 52 were alumina (AlO ₂ ), yttria-stabilized zirconia (YSZ), or ceria oxide (GDC: Ce _0.9 Gd _0.1 O _1.95 ).

The ohmic resistance and the electrode reaction resistance were determined as values at 500 ° C. based on the complex impedance plot (FIG. 9) shown in Confirmation Test 1.

Table 3 shows the measurement results of the test products 13 to 19 in which the materials used for the solid electrolyte layer 31 and the porous materials 51 and 52 were changed.

When the solid electrolyte layer 31 is composed of yttria-stabilized zirconia, the test products 13 and the porous materials 51 and 52 in which the porous materials 51 and 52 are not arranged in the gas chambers 35 and 36 are provided. Regarding the test product 14 composed of alumina, the test product 15 in which the porous materials 51 and 52 are composed of yttria-stabilized zirconia, and the test product 16 in which the porous materials 51 and 52 are composed of ceria oxide. It turns out that the ohmic resistance does not decrease so much. However, the value of the ohmic resistance in these cases was obtained as a value that can sufficiently withstand practical use.

When the solid electrolyte layer 31 is composed of a lanthanum gallate-based oxide, each of the porous materials 51 and 52 is composed of a test product 17 composed of alumina, and each of the porous materials 51 and 52 is composed of yttria-stabilized zirconia. It was found that the electrode reaction resistance of the tested product 18 was not so small. It is considered that the reason for this is that a reaction product was formed between the solid electrolyte layer 31 and the porous material.

On the other hand, for the test product 19 in which the solid electrolyte layer 31 is composed of a lanthanum gallate-based oxide and the porous materials 51 and 52 are composed of a ceria-based oxide, both the ohmic resistance and the electrode reaction resistance are small and good. It turned out that there was. In this case, the combination of the solid electrolyte layer 31 and the porous materials 51 and 52 is considered to be the most appropriate.

The present invention is not limited to each embodiment, and further different embodiments can be configured without departing from the gist thereof. In addition, the present invention includes various modifications, modifications within a uniform range, and the like.

1 Gas sensor 2 Sensor element 31 Solid electrolyte layer 311 Detection electrode 312 Reference electrode 33A, 33B Insulation layer 34 Heat generator 35 Detection gas chamber 36 Reference gas chamber 51, 52 Porous material

Claims (6)

A gas sensor (1) provided with a sensor element (2) for performing gas detection.
The sensor element is
The detection gas chamber (35) into which the detection gas (G) is introduced, and
The reference gas chamber (36) into which the reference gas (A) is introduced, and
It is arranged between the detection gas chamber and the reference gas chamber, and has a first main surface (301) facing the detection gas chamber and a second main surface (302) facing the reference gas chamber. , A plate-shaped solid electrolyte layer (31) having ionic conductivity,
A detection electrode (311) provided on the first main surface of the solid electrolyte layer in a state of being arranged in the detection gas chamber, and a detection electrode (311).
A reference electrode (312) provided on the second main surface of the solid electrolyte layer in a state of being arranged in the reference gas chamber, and a reference electrode (312).
A first insulating layer (33A) laminated on the first main surface of the solid electrolyte layer to form the detection gas chamber, and
A second insulating layer (33B) laminated on the second main surface of the solid electrolyte layer to form the reference gas chamber, and
A heating element (34) embedded in the second insulating layer and generating heat by energization,
Insulating first porous material arranged in the first gap (351) in the stacking direction (D) between the detection electrode and the first insulating layer in the detection gas chamber and for maintaining the first gap. (51) and
An insulating second porous material (52) arranged in the second gap (361) in the stacking direction between the reference electrode and the second insulating layer in the reference gas chamber and for maintaining the second gap. ) And, with
A gas sensor in which the porosity of the first porous material is larger than the porosity of the second porous material . A gas sensor (1) provided with a sensor element (2) for performing gas detection.
The sensor element is
The detection gas chamber (35) into which the detection gas (G) is introduced, and
The reference gas chamber (36) into which the reference gas (A) is introduced, and
It is arranged between the detection gas chamber and the reference gas chamber, and has a first main surface (301) facing the detection gas chamber and a second main surface (302) facing the reference gas chamber. , A plate-shaped solid electrolyte layer (31) having ionic conductivity,
A detection electrode (311) provided on the first main surface of the solid electrolyte layer in a state of being arranged in the detection gas chamber, and a detection electrode (311).
A reference electrode (312) provided on the second main surface of the solid electrolyte layer in a state of being arranged in the reference gas chamber, and a reference electrode (312).
A first insulating layer (33A) laminated on the first main surface of the solid electrolyte layer to form the detection gas chamber, and
A second insulating layer (33B) laminated on the second main surface of the solid electrolyte layer to form the reference gas chamber, and
A heating element (34) embedded in the second insulating layer and generating heat by energization,
Insulating first porous material arranged in the first gap (351) in the stacking direction (D) between the detection electrode and the first insulating layer in the detection gas chamber and for maintaining the first gap. (51) and
An insulating second porous material (52) arranged in the second gap (361) in the stacking direction between the reference electrode and the second insulating layer in the reference gas chamber and for maintaining the second gap. ) And, with
The second porous material includes an electrode-side porous layer (521) arranged on the side of the reference electrode in the stacking direction and a heating element-side porous layer (521) arranged on the heating element side in the stacking direction. It forms 522) and
A gas sensor in which the porosity of the electrode-side porous layer is larger than the porosity of the heating element-side porous layer . A gas sensor (1) provided with a sensor element (2) for performing gas detection.
The sensor element is
The detection gas chamber (35) into which the detection gas (G) is introduced, and
The reference gas chamber (36) into which the reference gas (A) is introduced, and
It is arranged between the detection gas chamber and the reference gas chamber, and has a first main surface (301) facing the detection gas chamber and a second main surface (302) facing the reference gas chamber. , A plate-shaped solid electrolyte layer (31) having ionic conductivity,
A detection electrode (311) provided on the first main surface of the solid electrolyte layer in a state of being arranged in the detection gas chamber, and a detection electrode (311).
A reference electrode (312) provided on the second main surface of the solid electrolyte layer in a state of being arranged in the reference gas chamber, and a reference electrode (312).
A first insulating layer (33A) laminated on the first main surface of the solid electrolyte layer to form the detection gas chamber, and
A second insulating layer (33B) laminated on the second main surface of the solid electrolyte layer to form the reference gas chamber, and
A heating element (34) embedded in the second insulating layer and generating heat by energization,
Insulating first porous material arranged in the first gap (351) in the stacking direction (D) between the detection electrode and the first insulating layer in the detection gas chamber and for maintaining the first gap. (51) and
An insulating second porous material (52) arranged in the second gap (361) in the stacking direction between the reference electrode and the second insulating layer in the reference gas chamber and for maintaining the second gap. ) And, with
The solid electrolyte layer is composed of a lanthanum gallate-based oxide.
The first porous material and the second porous material are gas sensors composed of ceria-based oxides . The first porous material is filled in the detection gas chamber, and is
The gas sensor according to any one of claims 1 to 3, wherein the second porous material is filled in the reference gas chamber. The gas sensor according to any one of claims 1 to 4 , wherein the second gap is larger than the first gap. The solid electrolyte layer is composed of a zirconia-based oxide.
The gas sensor according to claim 1 or 2 , wherein the first porous material and the second porous material are composed of at least one of a ceria-based oxide and a zirconia-based oxide.

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