JP7319214B2 - SENSOR ELEMENT, GAS SENSOR, AND SENSOR ELEMENT MANUFACTURING METHOD - Google Patents

Description

The present invention relates to a sensor element, a gas sensor, and a method of manufacturing the sensor element, which are preferably used for detecting the gas concentration of a specific gas contained in combustion gas or exhaust gas of a combustor or an internal combustion engine, for example.

2. Description of the Related Art Conventionally, gas sensors have been used to detect the concentration of specific components (such as oxygen) in exhaust gas from internal combustion engines. This gas sensor has a sensor element inside itself, and the sensor element has a plate-like shape in which a plurality of ceramic layers are laminated, and has a solid electrolyte body and a pair of electrodes arranged on the solid electrolyte body, A configuration is known in which one of the electrodes faces an air (atmosphere) introduction hole that opens inside the element (see Patent Document 1).
As shown in FIG. 8, the air introduction hole 510 is opened at the rear end surface of the sensor element, and between the first layer 501 and the second layer 502 having dimensions of the sensor element, for example, at the end surface when viewed from the stacking direction. A third layer 503 having a U-shaped notched gap can be formed by laminating the third layer 503 .

JP 2019-2739 A

However, especially along the width direction of the device, cracks K are formed between the first layer 501 and the third layer 503 and between the second layer 502 and the third layer 503 from the air introduction hole 510 toward the outside. may occur.
If the crack K penetrates from the atmosphere introduction hole 510 to the outside, the function as the atmosphere introduction hole 510 is lost. Further, even if the crack K is small, there is a possibility that the crack K may progress and penetrate outward when the element is subjected to a thermal shock such as a thermal cycle.

The reason why such a crack K occurs is considered as follows. That is, as shown in FIG. 9, when forming the atmosphere introduction hole 510, after filling the gap of the third layer green sheet 503G, which becomes the formation region of the atmosphere introduction hole 510, with the paste 505 containing the burnable carbon, The first-layer green sheet 501G is laminated on the three-layer green sheet 503G, and the entire structure is fired to burn off the paste 505 to form the atmosphere introduction holes 510. FIG. By using the paste 505 in this way, it is possible to prevent the air introduction hole 510 from becoming defective due to deformation of the gap caused by a load applied between the first layer green sheet 501G and the second layer green sheet 50G2. .

Here, during firing, the first layer green sheet 501G and the second layer green sheet 502G can be shrunk without restriction (arrow F1 in the figure). However, even if the third layer green sheet 503G tries to shrink, it cannot shrink sufficiently because of the interference of the paste 505 until the paste 505 is burned out (arrow F2 in the figure). Therefore, it is considered that stress is applied between the layers due to the difference in degree of contraction between F1 and F2, and the above-mentioned crack K occurs.
This problem occurs not only when using a burnt-off paste but also when using a burnt-off material sheet.

Accordingly, the present invention provides a sensor element, a gas sensor, and a method for manufacturing the sensor element in which cracks between ceramic layers in contact with the internal space are suppressed in a laminated sensor element having an internal space formed by stacking ceramic layers. aim.

In order to solve the above-mentioned problems, the sensor element of the present invention comprises: a first ceramic layer and a second ceramic layer which are spaced apart in the stacking direction; and the first ceramic layer and the second ceramic layer in the stacking direction. A third ceramic layer interposed between and having a gap therein, and the gap surrounded by the first ceramic layer, the second ceramic layer and the third ceramic layer as an internal space, extending in the axial direction. In the laminated sensor element, main portions of the first ceramic layer and the third ceramic layer are disposed between the first ceramic layer and the third ceramic layer contacting the internal space at the periphery of the internal space. A fourth ceramic layer whose main component is a ceramic material different from the component ceramic material is interposed , and the fourth ceramic layer has a lower shrinkage start temperature than the first ceramic layer and the third ceramic layer. Characterized by

In the manufacture of the sensor element, if a burnable material is used to form the internal space, the green sheets that become the first ceramic layer and the second ceramic layer can shrink without restriction. On the other hand, since the voids of the green sheet that serves as the third ceramic layer are filled with the burn-off material, even if the green sheet tries to shrink, the burn-off material will sufficiently hinder it until the burn-off material is completely burned out. cannot shrink to As a result, since the green sheets adjacent to each other in the stacking direction have different degrees of shrinkage, stress may be applied between the layers and cracks may occur.
Therefore, according to this sensor element, the main component ceramic material is different between the green sheets serving as the first ceramic layer and the third ceramic layer, so that the shrinkage starts at a lower temperature (shrinkage start temperature is low). Since the fourth ceramic layer paste (or sheet) is interposed, the fourth ceramic layer paste (or sheet) shrinks toward the burnable material side to assist the shrinkage of the green sheet of the third ceramic layer, and the adjacent Reduce the difference in shrinkage between green sheets. As a result, application of stress between the first ceramic layer and the third ceramic layer can be suppressed, and cracks can be suppressed.

Moreover, according to the sensor element of the present invention, cracks can be reliably suppressed.

In the sensor element of the present invention, at the periphery of the internal space, between the second ceramic layer and the third ceramic layer contacting the internal space, the main component of the second ceramic layer and the third ceramic layer A fifth ceramic layer containing a ceramic material different from the ceramic material as a main component may be interposed , and the fifth ceramic layer may have a lower shrinkage start temperature than the second ceramic layer and the third ceramic layer.
According to this sensor element, the ceramic material as the main component is different between the green sheets serving as the second ceramic layer and the third ceramic layer, and shrinkage starts at a lower temperature (shrinkage start temperature is low). With the paste (or sheet) of the fifth ceramic layer interposed, the paste (or sheet) of the fifth ceramic layer shrinks toward the burnable material side to assist the shrinkage of the green sheet of the third ceramic layer, and the adjacent green To reduce the difference in shrinkage between sheets. As a result, it is possible to suppress stress from being applied between the second ceramic layer and the third ceramic layer, thereby suppressing cracks.

In the sensor element of the present invention, the fourth ceramic layer may extend across the periphery of the internal space.
According to this sensor element, since the contraction force of the paste of the fourth ceramic layer is more reliably transmitted to the green sheet of the third ceramic layer, the effect of suppressing cracks is enhanced.

In the sensor element of the present invention, the fourth ceramic layer may be a porous layer.
According to this sensor element, when the fourth ceramic layer is formed on the surface of the porous layer, it does not impede ventilation of the porous layer.

In the sensor element of the present invention, the first ceramic layer and _the third ceramic layer may contain more than 50% by mass of _Al2O3 , and the fourth ceramic layer may contain more than 50% by mass of _ZrO2 . good.
According to this sensor element, the shrinkage start temperature of the fourth ceramic layer can be reliably lowered.

In the sensor element of the present invention, the fourth ceramic layer may not be exposed on the outer surfaces of the first ceramic layer and the third ceramic layer.
When the fourth ceramic layer is exposed on the outer surfaces of the first ceramic layer and the third ceramic layer, the fourth ceramic layer may be exposed to water or thermal shock may cause cracks in the fourth ceramic layer. may occur.
Therefore, by preventing the fourth ceramic layer from being exposed on the outer surfaces of the first ceramic layer and the third ceramic layer, it is possible to suppress cracks due to exposure to water or thermal shock.

In the sensor element of the present invention, the fifth ceramic layer may extend across the periphery of the internal space.
According to this sensor element, since the shrinkage force of the paste of the fifth ceramic layer is more reliably transmitted to the green sheet of the third ceramic layer, the effect of suppressing cracks is enhanced.

In the sensor element of the present invention, the fifth ceramic layer may be a porous layer.
According to this sensor element, when the fifth ceramic layer is formed on the surface of the porous layer, it does not impede ventilation of the porous layer.

In the sensor element of the present invention, the second ceramic layer and _the third ceramic layer may contain more than 50% by mass of _Al2O3 , and the fifth ceramic layer may contain more than 50% by mass of _ZrO2 . good.
According to this sensor element, the shrinkage start temperature of the fifth ceramic layer can be reliably lowered.

In the sensor element of the present invention, the fifth ceramic layer may not be exposed on the outer surfaces of the second ceramic layer and the third ceramic layer.
When the fifth ceramic layer is exposed on the outer surfaces of the second ceramic layer and the third ceramic layer, the fifth ceramic layer may be exposed to external water or thermal shock may be applied to the fifth ceramic layer, causing cracks in the fifth ceramic layer. may occur.
Therefore, by not exposing the fifth ceramic layer to the outer surfaces of the second ceramic layer and the third ceramic layer, it is possible to suppress cracks due to exposure to water or thermal shock.

A gas sensor of the present invention comprises the sensor element and a metal shell for holding the sensor element.

A method for manufacturing a sensor element according to the present invention includes: laminating a third ceramic green sheet having a void inside on the surface of a first ceramic green sheet; 3. The first ceramic layer is laminated on the surface of the ceramic green sheet and fired as a whole, the burnable material is burned off, and the first ceramic green sheet is fired, and the second ceramic green sheet is fired . A method for manufacturing a laminated sensor element extending in an axial direction and having, as an internal space, the gap surrounded by the second ceramic layer and the third ceramic layer obtained by firing the third ceramic green sheet, wherein the third ceramic green sheet Before laminating the sheet on the surface of the first ceramic green sheet, at the peripheral edge of the internal space, at a portion between the first ceramic green sheet and the third ceramic green sheet that are in contact with the burn-out material, Disposing a fourth paste or sheet containing a fourth ceramic whose main component is a ceramic material different from the main component ceramic material of the first ceramic green sheet and the third ceramic green sheet, wherein the fourth paste or sheet is and a shrinkage start temperature lower than that of the first ceramic green sheet and the third ceramic green sheet .

In the method for manufacturing a sensor element of the present invention, the second ceramic green sheet and the third 3. A fifth paste containing a fifth ceramic whose main component is a ceramic material different from the ceramic material as the main component of the ceramic green sheets and whose shrinkage start temperature is lower than that of the second ceramic green sheet and the third ceramic green sheet, or The baking may be performed after placing the sheet.

According to the present invention, in a laminated sensor element having an internal space formed by stacking ceramic layers, cracks between ceramic layers contacting the internal space can be suppressed.

1 is a longitudinal sectional view of a gas sensor (NOx sensor) according to an embodiment of the present invention; FIG. 1 is a perspective view of a sensor element; FIG. FIG. 3 is a cross-sectional view taken along line BB of FIG. 2; 3 is an exploded perspective view of the sensor element; FIG. FIG. 3 is a cross-sectional view taken along line CC of FIG. 2; It is a figure which shows the periphery of internal space. FIG. 10 is a diagram showing a method of forming an internal space using a burnable paste when manufacturing a sensor element; FIG. 3 is a cross-sectional view along the width direction of a conventional sensor element provided with air introduction holes. FIG. 9 is a diagram showing the mechanism by which cracks occur when an air introduction hole is formed using a burnable paste in manufacturing the sensor element of FIG. 8 ;

Embodiments of the present invention will be described below.
FIG. 1 is a vertical cross-sectional view of a gas sensor (NOx sensor) 1 according to an embodiment of the present invention (cross-sectional view cut in the longitudinal direction along the axis AX), FIG. 2 is a perspective view of a sensor element 10, and FIG. 2, FIG. 4 is an exploded perspective view of the sensor element 10, and FIG. 5 is a cross-sectional view along the line CC of FIG. 2 (a line perpendicular to the axis AX). .
A direction (axial direction) along the axis AX of the sensor element is appropriately referred to as a “longitudinal direction”. The “width direction” of the sensor element is a direction perpendicular to the “longitudinal direction (axial direction)”.

The gas sensor 1 is a NOx sensor equipped with a sensor element 10 capable of detecting the concentration of a specific gas (NOx) in the exhaust gas, which is the gas to be measured, and attached to an exhaust pipe (not shown) of an internal combustion engine. The gas sensor 1 includes a cylindrical metal shell 20 having a threaded portion 21 formed at a predetermined position on the outer surface thereof for fixing to an exhaust pipe. The sensor element 10 has an elongated plate shape extending in the direction of the axis AX and is held inside the metal shell 20 .
More specifically, the gas sensor 1 includes a holding member 60 having an insertion hole 62 into which the rear end portion 10k (upper end portion in FIG. 1) of the sensor element 10 is inserted, and six sensors held inside the holding member 60. and terminal members. Note that FIG. 1 shows only two terminal members (specifically, terminal members 75 and 76) out of the six terminal members.

At the rear end portion 10k of the sensor element 10, a total of six electrode terminal portions 13 to 18 (only the electrode terminal portions 14 and 17 are shown in FIG. 1) which are rectangular in plan view are formed. The electrode terminal portions 13 to 18 are electrically connected to the electrode terminal portions 13 to 18 by elastically contacting the aforementioned terminal members. For example, the element contacting portion 75b of the terminal member 75 is in elastic contact with the electrode terminal portion 14 and electrically connected thereto. Further, the element contact portion 76b of the terminal member 76 elastically contacts the electrode terminal portion 17 to electrically connect the same.
Further, different lead wires 71 are electrically connected to the six terminal members (terminal members 75, 76, etc.), respectively. For example, as shown in FIG. 1, the core wire of the lead wire 71 is crimped and gripped by the lead wire gripping portion 77 of the terminal member 75 . Further, the lead wire gripping portion 78 of the terminal member 76 crimps and grips the core wire of the other lead wire 71 .

Also, on one of the main surfaces of the rear end portion 10k of the sensor element 10, an air inlet 10h is opened on the front end side of the electrode terminal portions 13 to 15 and on the rear end side of a later-described ceramic sleeve 45. (See FIG. 2), the air inlet 10h is arranged in the insertion hole 62 of the holding member 60. As shown in FIG.
As a result, the reference atmosphere confined inside the outer cylinder 51, which will be described later, is introduced into the sensor element 10 through the atmosphere introduction port 10h.

The metal shell 20 is a tubular member having a through hole 23 penetrating in the direction of the axis AX. The metallic shell 20 has a shelf portion 25 that protrudes radially inward and constitutes a part of the through hole 23 . The metal shell 20 projects the front end portion 10s of the sensor element 10 to the outside of its front end side (downward in FIG. 1), and the rear end portion 10k of the sensor element 10 to the outside of its rear end side (upward in FIG. 1). The sensor element 10 is held in the through hole 23 with the sensor element 10 projecting outward.
Further, an annular ceramic holder 42 , two talc rings 43 and 44 annularly filled with talc powder, and a ceramic sleeve 45 are arranged inside the through hole 23 of the metallic shell 20 . Specifically, the ceramic holder 42, the talc rings 43 and 44, and the ceramic sleeve 45 surround the sensor element 10 in the radial direction. to the rear end side in the axial direction (upper end side in FIG. 1).

A metal cup 41 is arranged between the ceramic holder 42 and the shelf 25 of the metal shell 20 . A crimping ring 46 is arranged between the ceramic sleeve 45 and the crimped portion 22 of the metallic shell 20 . The crimped portion 22 of the metal shell 20 is crimped via a crimp ring 46 so as to press the ceramic sleeve 45 toward the distal end side.
An outer protector 31 and an inner protector 32 made of metal (specifically, stainless steel) having a plurality of holes are attached to the front end 20b of the metal shell 20 by welding so as to cover the front end 10s of the sensor element 10. ing. On the other hand, an outer cylinder 51 is attached to the rear end portion of the metal shell 20 by welding. The outer cylinder 51 has a tubular shape extending in the direction of the axis AX and surrounds the sensor element 10 .

The holding member 60 is a cylindrical member made of an insulating material (specifically, alumina) and having an insertion hole 62 penetrating in the direction of the axis AX. The six terminal members (terminal members 75, 76, etc.) described above are arranged in the insertion hole 62 (see FIG. 1). A rear end portion of the holding member 60 is formed with a flange portion 65 protruding radially outward. The holding member 60 is held by the internal support member 53 in such a manner that the flange portion 65 contacts the internal support member 53 . The internal support member 53 is held by the outer cylinder 51 by a crimped portion 51g that is crimped radially inward of the outer cylinder 51 .
An insulating member 90 is arranged on the rear end surface 61 of the holding member 60 . The insulating member 90 is made of an electrically insulating material (specifically, alumina) and has a cylindrical shape. A total of six through-holes 91 are formed through the insulating member 90 in the direction of the axis AX. The lead wire gripping portions (the lead wire gripping portions 77 and 78, etc.) of the terminal member described above are arranged in the through holes 91 .

An elastic seal member 73 made of fluororubber is arranged radially inside the rear end opening 51c located at the rear end (upper end in FIG. 1) of the outer cylinder 51 in the axial direction. A total of six cylindrical insertion holes 73c extending in the direction of the axis AX are formed in the elastic seal member 73 . Each insertion hole 73 c is formed by an insertion hole surface 73 b (cylindrical inner wall surface) of the elastic seal member 73 . One lead wire 71 is inserted through each insertion hole 73c. Each lead wire 71 extends outside the gas sensor 1 through an insertion hole 73 c of the elastic seal member 73 . The elastic sealing member 73 is elastically deformed in the radial direction by crimping the rear end opening 51c of the outer cylinder 51 inward in the radial direction. The gap between the insertion hole surface 73b and the outer peripheral surface 71b of the lead wire 71 is watertightly sealed.

On the other hand, as shown in FIG. 3, the sensor element 10 includes solid electrolyte bodies 111e, 121e, and 131e formed in plate-like insulating layers 111s, 121s, and 131s, respectively, and an insulator 140 disposed therebetween. , 145, which are stacked in the stacking direction. Furthermore, in the sensor element 10, a heater 161 is laminated on the back side of the solid electrolyte body 131e. This heater 161 includes plate-shaped insulators 162 and 163 mainly made of alumina, and a heater pattern 164 (mainly made of Pt) embedded therebetween.
The solid electrolyte bodies 111e, 121e, and 131e are substantially rectangular, respectively, and are formed in rectangular openings provided on the tip side of the insulating layers 111s, 121s, and 131s, respectively. Here, in this example, the solid electrolyte bodies 111e and 131e are sheet-like members transferred to predetermined positions, but the material of the solid electrolyte bodies 111e and 131e may be embedded in the openings.

The solid electrolyte bodies 111e, 121e, and 131e are made of zirconia, which is a solid electrolyte, and have oxygen ion conductivity. A porous Ip1+ electrode 112 is provided on the surface side of the solid electrolyte body 111e. A porous Ip1-electrode 113 is provided on the back side of the solid electrolyte body 111e. Furthermore, the surface of the Ip1+ electrode 112 is covered with a porous layer 114B.
An Ip1+ lead 116 is connected to the Ip1+ electrode 112 (see FIGS. 2 and 4). Also, the Ip1-lead 117 (FIG. 4) is connected to the Ip1-electrode 113 .

Further, as shown in FIG. 4, a third dense layer 118B is laminated on the surfaces of the Ip1+ electrode 112 and the Ip1+ lead 116, and a rectangular opening 118Bh is provided on the tip side of the third dense layer 118B. The opening 118Bh is filled with the porous layer 114B.

As shown in FIG. 4, a gas-impermeable first dense layer 118 made of alumina or the like and having voids 10G is laminated on the surface of the third dense layer 118B. Part of the porous layer 114B is exposed from the gap 10G. The side surface of the Ip1+ electrode 112 is covered with the third dense layer 118B and surrounded by the dense layers 115, 118 and 118B.
The gap 10G extends straight from the vicinity of the porous layer 114B to a portion communicating with the atmosphere inlet 10h. Through holes for electrical connection with the electrode terminal portions 13 to 15 are provided in the first dense layer 118 on the rear end side of the gap 10G.
The air inlet 10h is shorter in width than the gap 10G (see FIG. 5).

Furthermore, a gas-impermeable second dense layer 115 made of alumina or the like is laminated on the surface of the first dense layer 118 to close the gap 10G. Thereby, the Ip1+ electrode 112 covered with the porous layer 114B is arranged in the gap 10G surrounded by the dense layers 115 and 118 to prevent contact with the gas to be measured.
In the second dense layer 115, the position overlapping the rear end of the gap 10G is opened in a rectangular shape to form the air inlet 10h, and the gap 10G communicates with the air inlet 10h. The air introduction port 10h is open on the rear end side of a first porous body 151, which will be described later, and can introduce air instead of exhaust gas. Thereby, the Ip1+ electrode 112 is exposed to the air introduced from the air inlet 10h through the porous layer 114B.

The solid electrolyte body 111e and electrodes 112 and 113 constitute an Ip1 cell 110 (pump cell). In the Ip1 cell 110, the atmosphere in contact with the electrode 112 (the atmosphere in the gap 10G, which is different from the measured gas outside the sensor element 10) and the Oxygen is pumped in and out (so-called oxygen pumping) with the atmosphere (the atmosphere in the first measurement chamber 150 to be described later, that is, the gas to be measured outside the sensor element 10).

Solid electrolyte body 121e is arranged so as to face solid electrolyte body 111e in the stacking direction with insulator 140 interposed therebetween. A porous Vs-electrode 122 is provided on the surface side (top side in FIG. 2) of the solid electrolyte body 121e. A porous Vs+ electrode 123 is provided on the back surface side (lower surface side in FIG. 2) of the solid electrolyte body 121e.

A first measurement chamber 150 as an internal space of the sensor element is formed between the solid electrolyte body 111e and the solid electrolyte body 121e. The first measurement chamber 150 is an internal space where the gas to be measured (exhaust gas) flowing through the exhaust passage is first introduced into the sensor element 10, and is a first porous body having gas permeability and water permeability. It communicates with the outside of the sensor element 10 through a (diffusion resistor) 151 (see FIGS. 2 and 4). The first porous body 151 is provided on the side of the first measurement chamber 150 as a partition between the sensor element 10 and the outside. speed).
On the rear end side of the first measurement chamber 150 (on the right side in FIG. 2), as a partition between the first measurement chamber 150 and a second measurement chamber 160, which will be described later, is a second measurement chamber that limits the flow rate of the exhaust gas per unit time. A biporous body 152 is provided.

The solid electrolyte body 121e and the electrodes 122, 123 constitute a Vs cell (detection cell) 120. As shown in FIG. This Vs cell 120 is mainly affected by the oxygen partial pressure difference between the atmospheres separated by the solid electrolyte body 121e (the atmosphere in the first measurement chamber 150 in contact with the electrode 122 and the atmosphere in the reference oxygen chamber 170 in contact with the electrode 123). An electromotive force is generated accordingly.

Solid electrolyte body 131e is arranged to face solid electrolyte body 121 in the stacking direction with insulator 145 interposed therebetween. A porous Ip2+ electrode 132 and a porous Ip2− electrode 133 are provided on the surface side (upper surface side in FIG. 2) of the solid electrolyte body 131e.

A reference oxygen chamber 170 as an isolated small space is formed between the Ip2+ electrode 132 and the Vs+ electrode 123 . This reference oxygen chamber 170 is constituted by an opening 145 b formed in the insulator 145 . A ceramic porous body is arranged in the reference oxygen chamber 170 on the side of the Ip2+ electrode 132 .
A second measurement chamber 160 is formed as an internal space of the sensor element at a position facing the Ip2-electrode 133 in the stacking direction. The second measurement chamber 160 includes an opening 145c passing through the insulator 145 in the stacking direction, an opening 125 passing through the solid electrolyte body 121 in the stacking direction, and an opening 141 passing through the insulator 140 in the stacking direction. It is composed of
The first measurement chamber 150 and the second measurement chamber 160 are communicated through a second porous body 152 having gas permeability and water permeability. Therefore, the second measurement chamber 160 communicates with the outside of the sensor element 10 through the first porous body 151 , the first measurement chamber 150 and the second porous body 152 .

The solid electrolyte body 131e and the electrodes 132, 133 constitute an Ip2 cell 130 (second pump cell) for detecting the NOx concentration. The Ip2 cell 130 moves oxygen (oxygen ions) derived from NOx decomposed in the second measurement chamber 160 to the reference oxygen chamber 170 through the solid electrolyte body 131e. At this time, a current flows between the electrodes 132 and 133 according to the concentration of NOx contained in the exhaust gas (gas to be measured) introduced into the second measurement chamber 160 .

Here, the third dense layer 118B, the second dense layer 115, and the first dense layer 118 correspond to the "first ceramic layer,""second ceramic layer," and "third ceramic layer," respectively. do. In addition, for each layer 115, 118B, 118, the gap 10G corresponds to the "internal space" in the claims.
Similarly, the insulating layer 121s, the insulating layer 111s, and the insulator 140 correspond to the "first ceramic layer,""second ceramic layer," and "third ceramic layer," respectively. Also, the first measurement chamber 150 corresponds to the "internal space" in the claims for each of the layers 111s, 121s, and 140. As shown in FIG.

Next, features of the present invention will be described with reference to FIGS. 4 and 5. FIG.
As shown in FIGS. 4 and 5, a fourth ceramic layer 181 is interposed between the first dense layer 118 and the third dense layer 118B in contact with the void 10G at the periphery of the void 10G forming the internal space. there is A fifth ceramic layer 191 is interposed between the second dense layer 115 and the first dense layer 118 which are in contact with the gap 10G.
Similarly, a fourth ceramic layer 182 is interposed between the insulator 140 and the insulating layer 121s in contact with the first measuring chamber 150 at the periphery of the first measuring chamber 150 forming the internal space. A fifth ceramic layer 191 is interposed between the insulating layer 111 s in contact with the first measurement chamber 150 and the insulator 140 .

Here, "at the periphery of the internal space" means, for example, a region R1 outside the periphery 10f including the periphery 10f of the gap 10G forming the internal space, or It means either the inner region R2 or both regions R1, R2.
In this embodiment, the fourth ceramic layer 181 and the fifth ceramic layer 191 extend in the width direction of the sensor element 10 and in the direction of the axis AX across the periphery of the gap 10G.
Further, the fourth ceramic layer 182 extends across the periphery of the first measurement chamber 150 in the width direction of the sensor element 10 and in the direction of the axis AX. The fifth ceramic layer 192 is formed in a region including the periphery of the first measurement chamber 150 and outside the periphery.

The fourth ceramic layer 181 is mainly composed of a ceramic material different from the ceramic material of the main component of the third dense layer 118B and the first dense layer 118 in contact therewith, and the fifth ceramic layer 191 is in contact with the third dense layer 118B. The second dense layer 115 and the first dense layer 118 are mainly composed of a ceramic material different from that of the main component.
Similarly, the fourth ceramic layer 182 is mainly composed of a ceramic material different from the ceramic material of the insulating layer 121s and the insulator 140 in contact therewith, and the fifth ceramic layer 192 is composed of the insulating layer 111s in contact therewith. The main component is a ceramic material that is different from the ceramic material that is the main component of the insulator 140 .

As described above, the fourth ceramic layer 181 is mainly composed of a ceramic material different from the ceramic material that is the main component of the third dense layer 118B and the first dense layer 118, and the fifth ceramic layer 191 is the second dense layer 115. The main component is a ceramic material different from the main component ceramic material of the first dense layer 118, and the fourth ceramic layer 181 and the fifth ceramic layer 191 start shrinking at a lower temperature (shrinkage start temperature is low). can suppress cracks between the ceramic layers 115, 118, and 118B in contact with the gap 10G.

That is, as shown in FIG. 7, when forming the voids 10G, the first dense layer green sheet 118G is laminated on the third dense layer green sheet 118BG, and the first dense layer serving as the formation region of the voids 10G. After filling the gaps between the green sheets 118G with the sheets 10p containing burn-off particles (such as carbon), the second dense layer green sheets 115G are laminated on the first dense layer green sheets 118G, and the whole is fired to form the sheet 10p. is burnt out to form a gap of 10G .
During this firing, the third dense layer green sheet 118BG and the second dense layer green sheet 115G can shrink without restriction (arrow F1 in FIG. 7). On the other hand, even if the first dense layer green sheet 118G tries to shrink, it cannot shrink sufficiently because it is hindered by the sheet 10p until the sheet 10p is completely burned out (arrow F2 in FIG. 7).

Therefore, since the main component ceramic material is different between the third dense layer green sheet 118BG and the first dense layer green sheet 118G, shrinkage starts at a lower temperature (shrinkage start temperature is low). By interposing the layer paste 181p, the fourth ceramic layer paste 181p shrinks toward the sheet 10p side, assists the shrinkage of the first dense layer green sheet 118G, and reduces the difference in degree of shrinkage between F1 and F2. It suppresses stress from being applied between the layers 118BG and 118G and suppresses cracks.
Similarly, since the main component ceramic material is different between the second dense layer green sheet 115G and the first dense layer green sheet 118G, shrinkage starts at a lower temperature (shrinkage start temperature is low). By interposing the ceramic layer paste 191p, the fifth ceramic layer paste 191p shrinks toward the sheet 10p side, assists the shrinkage of the first dense layer green sheet 118G, and reduces the difference in degree of shrinkage between F1 and F2. , the application of stress between the layers 115G and 118G is suppressed, and cracks are suppressed.
The same applies to the fourth ceramic layer 182 and the fifth ceramic layer 192 in the first measurement chamber 150, so the description is omitted.

The shrinkage start temperature is defined by preparing a green sheet having the same composition as that of each ceramic layer, heating it in an air atmosphere to proceed with firing, and setting the ratio of each ceramic layer to 1.05. It means the temperature when it becomes The shrinkage ratio is also called firing shrinkage, and is calculated from the vertical or horizontal dimension of the green sheet before firing when the vertical or horizontal dimension of the ceramic layer after firing is set to 1.
In other words, the split ratio=(the vertical or horizontal dimension of the green sheet before firing)/(the same direction dimension of the ceramic layer after firing).

Alumina can be used for the layers 115, 118B, 118, 111s, 121s and 140 forming the first to third ceramic layers. Although the first to third ceramic layers do not have to have the same composition, it is preferable that they have substantially the same composition because the strength and other characteristics of each part of the element are uniform.
As the fourth ceramic layer and the fifth ceramic layer, for example, one containing more than 50% by mass of ZrO ₂ and the balance being the composition (alumina) of the first to third ceramic layers can be used. If the ZrO ₂ content exceeds 50% by mass, the shrinkage initiation temperature can be reliably lowered.
The first to third ceramic layers contain less ZrO ₂ than the fourth ceramic layer and the fifth ceramic layer (for example, more than 50% by mass of Al ₂ O ₃ and 50% by mass of ZrO ₂ %).
Specifically, the first to third ceramic layers contain 98% by mass of alumina and 2% by mass of _ZrO2 , and the fourth and fifth ceramic layers contain 80% by mass of _ZrO2 and 20% by mass of alumina. What is contained by mass % can be exemplified.

As shown in FIG. 5, if at least one of the fourth ceramic layer 181 and the fifth ceramic layer 191 extends across the periphery of the gap 10G, the fourth ceramic layer paste 181p and the fifth ceramic layer shown in FIG. Since the shrinkage force of the paste 191p is more reliably transmitted to the first dense layer green sheet 118G, the effect of suppressing cracks is enhanced.
It should be noted that "straddling the periphery" means straddling at least one of the width direction of the sensor element 10 and the direction of the axis AX, but it is more preferable to straddle both directions.

However, in the case of the fifth ceramic layer 192 shown in FIG. 5, the Ip1-electrode 113 is arranged inside the periphery of the first measurement chamber 150, so that the function of the Ip1-electrode 113 is not hindered. 192 is formed outside the periphery of the first measurement chamber 150 .
Instead of forming the fifth ceramic layer 192 outside the periphery of the first measurement chamber 150, the fifth ceramic layer 192 straddles the periphery of the first measurement chamber 150, and the inside of the periphery of the first measurement chamber 150 is Ip1- It may be formed so as to be spaced (floating) from the electrode 113 .

A fourth ceramic layer 181 shown in FIG. 5 is formed on the surface of the porous layer 114B. In such a case, the fourth ceramic layer 181 is preferably a porous layer so as not to block the ventilation of the porous layer 114B.
In order to make the fourth ceramic layer 181 a porous layer, the paste of the fourth ceramic layer 181 may contain burnt-off particles (such as carbon).

Also, when the fourth ceramic layer 181 is exposed on the outer surfaces of the second dense layer 115 and the first dense layer 118, the fourth ceramic layer 181 may be exposed to external water or thermal shock. Cracks may occur in the fourth ceramic layer 181 .
Therefore, as shown in FIG. 5, it is preferable to prevent the fourth ceramic layer 181 from being exposed to the outer surfaces of the second dense layer 115 and the first dense layer 118 .
The same is true for the fourth ceramic layer 182 and the fifth ceramic layers 191 and 192 .

Here, the NOx concentration detection by the gas sensor 1 of this embodiment will be briefly described.
As the temperature of the heater pattern 164 rises, the solid electrolyte bodies 111e, 121e, and 131e of the sensor element 10 are heated and activated. This enables the Ip1 cell 110, the Vs cell 120, and the Ip2 cell 130 to operate.
Exhaust gas flowing through the exhaust passage (not shown) is introduced into the first measurement chamber 150 while being restricted by the first porous body 151 . At this time, a weak current Icp flows through the Vs cell 120 from the electrode 123 side to the electrode 122 side. Therefore, the oxygen in the exhaust gas can receive electrons from the electrode 122 in the first measurement chamber 150 on the negative electrode side, become oxygen ions, flow through the solid electrolyte body 121, and move into the reference oxygen chamber 170. do. In other words, the oxygen in the first measurement chamber 150 is sent into the reference oxygen chamber 170 by applying the current Icp between the electrodes 122 and 123 .

When the oxygen concentration of the exhaust gas introduced into the first measurement chamber 150 is lower than a predetermined value, the current Ip1 is passed through the Ip1 cell 110 so that the electrode 112 side becomes the negative electrode, and oxygen is pumped into the On the other hand, when the oxygen concentration of the exhaust gas introduced into the first measurement chamber 150 is higher than the predetermined value, the current Ip1 is passed through the Ip1 cell 110 so that the electrode 113 side becomes the negative electrode, and the sensor element 10 is supplied from the first measurement chamber 150. Oxygen is pumped to the outside.

Thus, the exhaust gas whose oxygen concentration has been adjusted in the first measurement chamber 150 is introduced into the second measurement chamber 160 through the second porous body 152 . NOx in the exhaust gas in contact with the electrode 133 in the second measurement chamber 160 is decomposed (reduced) into nitrogen and oxygen on the electrode 133 by applying a voltage Vp2 between the electrodes 132 and 133, and decomposed. Oxygen becomes oxygen ions, flows through the solid electrolyte body 131 , and moves into the reference oxygen chamber 170 . At this time, residual oxygen remaining in the first measurement chamber 150 is similarly moved into the reference oxygen chamber 170 by the Ip2 cell 130 . As a result, a current derived from NOx and a current derived from residual oxygen flow through the Ip2 cell 130 . The oxygen that has moved into the reference oxygen chamber 170 is released to the outside (atmosphere) through the Vs+ electrode 123 and the Vs lead and the Ip2+ electrode 132 and the Ip2+ lead that are in contact with the reference oxygen chamber 170. and Ip2+ leads are porous.

Here, since the concentration of residual oxygen left unpumped in the first measurement chamber 150 is adjusted to a predetermined value as described above, the current derived from the residual oxygen can be regarded as substantially constant, and the current derived from NOx can be regarded as It has little effect on current fluctuations, and the current flowing through the Ip2 cell 130 will be proportional to the NOx concentration. Therefore, the current Ip2 flowing through the Ip2 cell 130 can be detected, and the NOx concentration in the exhaust gas can be detected based on the current value.

In this embodiment, an alumina insulating layer 119 is formed on the back surface of the insulating layer 111s except for the Ip1-electrode 113, and the Ip1-electrode 113 has a through hole 119b penetrating the alumina insulating layer 119 in the stacking direction. (see FIG. 4), it contacts with the solid electrolyte body 111e.

Furthermore, in this embodiment, an alumina insulating layer 128 is formed on the surface of the insulating layer 121s except for the Vs-electrode 122, and the Vs-electrode 122 penetrates the alumina insulating layer 128 in the stacking direction through a through hole (see FIG. (not shown) to contact the solid electrolyte body 121e.
Furthermore, an alumina insulating layer 129 is formed on the back surface of the insulating layer 121s except for the Vs+ electrode 123, and the Vs+ electrode 123 is connected to the solid electrolyte through a through hole (not shown) penetrating the alumina insulating layer 129 in the stacking direction. Contact with body 121e.

Furthermore, in the present embodiment, an alumina insulating layer 138 is formed on the surface of the insulating layer 131s except for the Ip2+ electrode 132, and the Ip2+ electrode 132 penetrates the alumina insulating layer 138 in the stacking direction through a through hole (not shown). ) to contact the solid electrolyte body 131e. Furthermore, an alumina insulating layer 138 is also formed on the surface of the insulating layer 131s except for the Ip2-electrode 133, and the electrode 133 passes through a through hole (not shown) passing through the alumina insulating layer 138 in the stacking direction. It contacts the electrolyte body 131e.

Next, a method for manufacturing a sensor element according to an embodiment of the invention will be described.
As shown in FIG. 7, according to the method for manufacturing a sensor element according to the embodiment of the present invention, a third ceramic green sheet (first dense layer green sheet 118G) having voids formed therein by press working or the like is prepared, A sheet 10p containing a burn-out material embedded in the voids of the third ceramic green sheet is laminated on the surface of the first ceramic green sheet (third dense layer green sheet 118BG), and the second ceramic green sheet (second dense layer green sheet 118BG) is laminated. The layer green sheet 115G) is laminated on the surface of the third ceramic green sheet and the whole is fired, the sheet 10p is burned out, and the void 10G surrounded by the first ceramic layer, the second ceramic layer and the third ceramic layer is formed inside. A laminated sensor element 10 provided as a space and extending in the direction of the axis AX is obtained.

At the periphery of the internal space 10G, between the first ceramic green sheet and the third ceramic green sheet in contact with the sheet 10p, a ceramic material different from the main component ceramic material of the first ceramic green sheet and the third ceramic green sheet is provided. After applying the fourth paste 181p containing the fourth ceramic whose main component is the material, firing is performed.
If the fourth paste 181p starts shrinking at a temperature lower than that of the first ceramic green sheet and the third ceramic green sheet (lower shrinkage starting temperature), cracks can be suppressed as described above.

In the method for manufacturing a sensor element according to the embodiment of the present invention, the second ceramic green sheet and the third After applying the fifth paste 191p containing a fifth ceramic whose main component is a ceramic material different from the ceramic material that is the main component of the ceramic green sheets, the whole may be fired. In this case, firing is performed after applying the fourth paste 181p and the fifth paste 191p.
If the fifth paste 191p starts shrinking at a temperature lower than that of the second ceramic green sheet and the third ceramic green sheet (lower shrinkage starting temperature), cracks can be suppressed as described above.

It goes without saying that the present invention is not limited to the above-described embodiments, but extends to various modifications and equivalents within the spirit and scope of the present invention.
The internal space of the sensor element may be a gap, and examples thereof include an air introduction hole and various measurement chambers. The shape of the internal space is also not limited.
The burn-out material may be in the form of a sheet or a paste.
Further, the present invention can be applied to a sensor element (gas sensor) having at least one detection cell (one or more cells), and can be applied to the NOx sensor element (NOx sensor) of the present embodiment. It goes without saying that the present invention is not limited to specific applications, and that various modifications and equivalents are included within the spirit and scope of the present invention. For example, the present invention may be applied to an oxygen sensor (oxygen sensor element) that detects the oxygen concentration in the gas to be measured, an HC sensor (HC sensor element) that detects the HC concentration, and the like.

Reference Signs List 1 gas sensor 10 sensor element 10f peripheral edge of internal space 10G internal space (gap)
150 Internal space (first measurement room)
10p Sheet containing burn-out material 20 Metal shell 118B First ceramic layer (third dense layer)
121s First ceramic layer (insulating layer)
115 Second ceramic layer (second dense layer)
111s Second ceramic layer (insulating layer)
118 third ceramic layer (first dense layer)
140 third ceramic layer (insulator)
181, 182 fourth ceramic layer 191, 192 fifth ceramic layer 118BG first ceramic layer green sheet 115G second ceramic layer green sheet 118G third ceramic layer green sheet 181p fourth paste 191p fifth paste AX longitudinal direction (axis)

Claims (13)

a first ceramic layer and a second ceramic layer spaced apart in the stacking direction;
a third ceramic layer interposed between the first ceramic layer and the second ceramic layer in the stacking direction and having a void therein;
A laminated sensor element extending in an axial direction and having the gap surrounded by the first ceramic layer, the second ceramic layer, and the third ceramic layer as an internal space, the sensor element comprising:
A ceramic material different from the main component ceramic material of the first ceramic layer and the third ceramic layer is placed between the first ceramic layer and the third ceramic layer in contact with the internal space at the periphery of the internal space. A fourth ceramic layer containing as a main component is interposed ,
The sensor element , wherein the fourth ceramic layer has a shrinkage start temperature lower than that of the first ceramic layer and the third ceramic layer . A ceramic material different from the main component ceramic material of the second ceramic layer and the third ceramic layer is placed between the second ceramic layer and the third ceramic layer in contact with the internal space at the periphery of the internal space. A fifth ceramic layer containing as a main component is interposed,
2. The sensor element according to claim 1 , wherein the fifth ceramic layer has a shrinkage start temperature lower than that of the second ceramic layer and the third ceramic layer . 3. The sensor element according to claim 1 , wherein said fourth ceramic layer extends across the periphery of said internal space . A sensor element according to any one of claims 1 to 3, characterized in that said fourth ceramic layer is a porous layer . The first ceramic layer and the third ceramic layer contain more than 50% by mass of Al ₂ O ₃ ,
Sensor element according to any one of the preceding claims, characterized in that the fourth ceramic layer comprises more than 50% by weight of ZrO ₂ . The sensor element according to any one of claims 1 to 5 , wherein the fourth ceramic layer is not exposed on the outer surfaces of the first ceramic layer and the third ceramic layer . The sensor element according to claim 2 or any one of claims 3 to 6 depending on claim 2, wherein the fifth ceramic layer extends across the periphery of the internal space. A sensor element according to claim 2 or any one of claims 3 to 7 depending on claim 2, characterized in that said fifth ceramic layer is a porous layer . The second ceramic layer and the third ceramic layer contain more than 50% by mass of Al ₂ O ₃ ,
Sensor element according to claim 2 or any one of claims 3 to 8 depending on claim 2, characterized in that the fifth ceramic layer comprises more than 50% by weight of ZrO ₂ . Claim 2 or any one of Claims 3 to 9 depending on Claim 2, wherein the fifth ceramic layer is not exposed to the outer surfaces of the second ceramic layer and the third ceramic layer. A sensor element as described in . A gas sensor comprising the sensor element according to any one of claims 1 to 10 and a metal shell for holding the sensor element. Laminating a third ceramic green sheet having voids inside on the surface of the first ceramic green sheet,
filling the void with a burnable material;
A first ceramic layer obtained by laminating a second ceramic green sheet on the surface of the third ceramic green sheet and firing the whole, burning off the burnable material, and firing the first ceramic green sheet; A method for manufacturing a stacked sensor element extending in the axial direction, wherein the void surrounded by the second ceramic layer formed by firing the ceramic green sheets and the third ceramic layer formed by firing the third ceramic green sheets is provided as an internal space. There is
Before laminating the third ceramic green sheet on the surface of the first ceramic green sheet, at the periphery of the internal space, between the first ceramic green sheet and the third ceramic green sheet that are in contact with the burn-out material. a fourth paste or sheet containing a fourth ceramic whose main component is a ceramic material different from the main component ceramic material of the first ceramic green sheet and the third ceramic green sheet,
The method for manufacturing a sensor element, wherein the fourth paste or sheet has a shrinkage start temperature lower than that of the first ceramic green sheet and the third ceramic green sheet. A ceramic material, which is the main component of the second ceramic green sheet and the third ceramic green sheet, is placed between the second ceramic green sheet and the third ceramic green sheet in contact with the burn-out material at the periphery of the internal space. After arranging a fifth paste or sheet containing a fifth ceramic having a lower shrinkage start temperature than the second ceramic green sheet and the third ceramic green sheet, the baking is performed. A method for manufacturing a sensor element according to claim 12, characterized by :

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