JP7709906B2 - Gas sensor element, gas sensor, and method of manufacturing gas sensor element - Google Patents

Description

The present invention relates to a gas sensor element, a gas sensor, and a method for manufacturing a gas sensor element.

There is known a gas sensor for measuring the concentration of a specific component (such as _NOx ) in exhaust gas from an internal combustion engine. This type of gas sensor includes a gas sensor element mainly made of ceramic. The gas sensor element includes an Ip1 cell, a Vs cell, an Ip2 cell, a first measurement chamber, a reference oxygen chamber, a second measurement chamber, etc. (See, for example, Japanese Patent Application Laid-Open No. 2003-233994).

The Ip1 cell (first pump cell) pumps oxygen in the exhaust gas between the first measurement chamber and the outside (so-called pumping).

The Vs cell (detection cell) comprises a solid electrolyte body separating the first measurement chamber and the reference oxygen chamber, a detection electrode (Vs- electrode) exposed to the atmosphere in the first measurement chamber and formed on one surface of the solid electrolyte body, and a reference electrode (Vs+ electrode) exposed to the atmosphere in the reference oxygen chamber and formed on the other surface of the solid electrolyte body. In the Vs cell, a constant minute current is passed from the detection electrode (Vs- electrode) side to the reference electrode (Vs+ electrode) side, so that a constant amount of oxygen is stored in the reference oxygen chamber. Note that excess oxygen that has accumulated in the reference oxygen chamber is released to the outside via the above-mentioned reference electrode (Vs+ electrode) and the lead wire connected thereto. The reference electrode (Vs+ electrode) and the lead wire are made of porous ceramic and are gas permeable.

The Ip2 cell (second pump cell) is for detecting the _NOx concentration, and includes a solid electrolyte body and a pair of electrodes (Ip2+ electrode, Ip2- electrode) formed on one surface of the solid electrolyte body. One electrode (Ip2+ electrode) of the Ip2 cell faces the reference electrode (Vs+ electrode) of the Vs cell with the reference oxygen chamber therebetween. The other electrode (Ip2- electrode) of the second pump cell is housed in the second measurement chamber. Such a pair of electrodes is arranged on the surface of the solid electrolyte body while being separated from each other in a plan view.

The surface of the solid electrolyte body in the Ip2 cell and the reference electrode (Vs+ electrode) of the Vs cell face each other with an insulating adhesive layer between them. In particular, the reference electrode (Vs+ electrode) has a portion (hereinafter, overlapping portion) that extends from the front end side to the rear end side of the gas sensor element so as to overlap the peripheral edge of the solid electrolyte of the second pump cell while overlapping the area (area where no electrodes are formed) between a pair of electrodes (Ip2+ electrode, Ip2- electrode) of the Ip2 cell in a plan view.

JP 2020-3286 A

In such a gas sensor element, cracks sometimes occurred along the thickness direction (stacking direction) of the insulating adhesive layer interposed between the Vs cell and the Ip2 cell in a portion sandwiched between the overlapping portion of the reference electrode (Vs+ electrode) of the Vs cell and the peripheral edge of the solid electrolyte body disposed between a pair of electrodes in the second pump cell.

When such a crack occurs, the reference oxygen chamber and the second measurement chamber are spatially connected, and there is a risk that the oxygen stored in the reference oxygen chamber will flow into the second measurement chamber. If oxygen flows into the second measurement chamber, one set of electrodes in the Ip2 cell will detect a current value larger than normal, resulting in an erroneous detection of the _NOx concentration.

These cracks are formed during the manufacture of the gas sensor element, starting from the overlapping portion of the Vs cell and growing toward the region between the electrodes of the second pump cell. The causes of the cracks include the fact that the unfired reference electrode for forming the reference electrode (Vs+ electrode) of the Vs cell is thick, resulting in a large amount of shrinkage during firing, and that the unfired adhesive layer for forming the adhesive layer, which is in contact with the unfired reference electrode, shrinks faster than the unfired reference electrode during firing.

In addition, the surface of the Ip2 cell facing the Vs cell has a more undulating surface shape in the region between a pair of electrodes (region where no electrodes are formed) and near the peripheral edge of the solid electrolyte body than in other locations. If an adhesive layer is formed between the Vs cell and the Ip2 cell while conforming to such a undulating surface shape, the amount of adhesive layer present in the portion corresponding to the surface shape tends to be relatively small. Since most of the adhesive layer is usually formed using an unfired green sheet or the like with a uniform thickness, the thickness (density) of the adhesive layer in the portion conforming to the undulating surface shape tends to be relatively small. It is presumed that the relatively small thickness (density) of the adhesive layer is one of the causes of the above-mentioned cracks.

An object of the present invention is to provide a gas sensor element etc. in which the occurrence of cracks that cause erroneous detection of _NOx concentration is suppressed in an insulating adhesive layer interposed between a first cell (Ip2 cell) and a second cell (Vs cell).

The means for solving the above problems are as follows.
a first cell having a pair of first and second electrodes arranged on the surface of the first solid electrolyte body while being separated from each other in a plan view; a second solid electrolyte body including an opposing surface facing the surface of the first insulating layer and an opposite surface on the opposite side of the opposing surface; a second cell having a third electrode arranged on the opposing surface and arranged so as to overlap the peripheral edge in a plan view, and a fourth electrode arranged on the opposite surface; and an insulating adhesive layer interposed between the first cell and the second cell, the first cell and the second cell being separated so as not to be conductive to the third electrode, the gas sensor element comprising: a first insulating layer;

<2> The gas sensor element described in <1>, in which the third electrode is made of a gas-permeable porous ceramic, and the buffer portion is made of a non-gas-permeable dense ceramic.

<3> The gas sensor element according to <1> or <2>, wherein the buffer portion is made of a ceramic containing zirconia as a main component.

<4> The gas sensor element according to any one of <1> to <3>, wherein the third electrode is made of a cermet containing platinum powder and ceramic powder.

<5> A gas sensor comprising the gas sensor element described in any one of <1> to <4>.

<6> A first cell having a first insulating layer, a first solid electrolyte body arranged on the surface side of the first insulating layer so that the peripheral end does not protrude from the surface of the first insulating layer in a plan view, a pair of first and second electrodes arranged on the surface of the first solid electrolyte body while being separated from each other in a plan view, a second solid electrolyte body including an opposing surface facing the surface of the first insulating layer and an opposite surface on the opposite side of the opposing surface, a third electrode arranged on the opposing surface and arranged so as to overlap the peripheral end in a plan view, and a fourth electrode arranged on the opposite surface, and a second cell interposed between the first cell and the second cell and including the first electrode and a first manufacturing step of manufacturing an unsintered first cell including a first green sheet for forming the first insulating layer, an unsintered first solid electrolyte body for forming the first solid electrolyte body arranged on a surface side of the first green sheet, and a pair of unsintered first and second electrodes for forming the first and second electrodes, the pair being arranged on a surface of the unsintered first solid electrolyte body in a state where the pair are separated from each other in a plan view; a second manufacturing step of manufacturing an unsintered second cell having a second green sheet for forming the second solid electrolyte body, the second green sheet including an unsintered opposing surface facing a surface of the first green sheet and an unsintered opposite surface on the opposite side of the unsintered opposing surface, an unsintered third electrode having a thickness greater than that of the unsintered first electrode and the unsintered second electrode and for forming the third electrode disposed on the unsintered opposing surface, and an unsintered fourth electrode for forming the fourth electrode disposed on the unsintered opposite surface; A method for manufacturing a gas sensor element, comprising: a bonding step of bonding the unsintered first cell and the unsintered second cell with an unsintered adhesive sheet for forming the adhesive layer between the unsintered first cell and the unsintered second cell so as to overlap the unsintered peripheral end of the body; and a firing step of firing the laminate obtained after the bonding step, in which an unsintered buffer portion for forming the buffer portion is formed on the surface of the unsintered third electrode in the second manufacturing step, the buffer portion being made of a material having a lower shrinkage start temperature than the material for forming the adhesive layer, so as to overlap the unsintered peripheral end while overlapping the area between the unsintered first electrode and the unsintered second electrode in the plan view.

According to the present invention, it is possible to provide a gas sensor element or the like in which the occurrence of cracks that cause erroneous detection of _NOx concentration is suppressed in the insulating adhesive layer interposed between the first cell (Ip2 cell) and the second cell (Vs cell).

FIG. 1 is a vertical cross-sectional view of a gas sensor according to a first embodiment. FIG. 1 is a perspective view of a gas sensor element according to a first embodiment; A cross-sectional view of line A-A in FIG. An exploded perspective view of a gas sensor element. FIG. 1 is an explanatory diagram showing the arrangement relationship of the Ip2+ electrode, the Ip2- electrode, and the Vs+ electrode in a plan view. An explanatory diagram showing an Ip2 cell in a plan view. FIG. 1 is a cross-sectional view of a stack including an Ip2 cell and a Vs cell cut along an axial direction. FIG. 1 is a cross-sectional view of a stack including an Ip2 cell and a Vs cell cut along the width direction. A flow chart showing each step in a method for manufacturing a gas sensor element. FIG. 2 is a schematic diagram illustrating a method for manufacturing a gas sensor element. FIG. 1 is a cross-sectional view of a portion of a conventional gas sensor element 10P taken along the axial direction.

<Embodiment 1>
A first embodiment of the present invention will be described below with reference to Fig. 1 to Fig. 10. Fig. 1 is a vertical cross-sectional view of a gas sensor 1 according to the first embodiment, Fig. 2 is a perspective view of a gas sensor element 10 according to the first embodiment, Fig. 3 is a cross-sectional view taken along line A-A in Fig. 2, and Fig. 4 is an exploded perspective view of the gas sensor element 10.

In FIG. 1, the axis AX of the gas sensor 1 is shown as a straight line (dotted line) along the vertical direction. In this specification, the direction along the axis AX of the gas sensor 1 may be referred to as the "longitudinal direction", and the direction perpendicular to the axis AX may be referred to as the "width direction". In this specification, the lower side of the gas sensor 1 shown in FIG. 1 is referred to as the "tip side", and the opposite side (the upper side of FIG. 1) is referred to as the "rear side". For ease of explanation, the upper sides of FIGS. 2 to 4 are referred to as the "front side (front surface side)" of the gas sensor element 10, and the lower sides thereof are referred to as the "rear side (back surface side)" of the gas sensor element 10.

The gas sensor 1 includes a gas sensor element 10 capable of detecting the concentration of _NOx and the like in exhaust gas, which is a gas to be measured (a gas to be detected). The gas sensor 1 is attached to an exhaust pipe (not shown) of an internal combustion engine when in use, and includes a cylindrical metal shell 20 having a threaded portion 21 formed at a predetermined position on its outer surface for fixing to the exhaust pipe. The gas sensor element 10 is generally in the form of a long and narrow plate extending along the axis AX, and the gas sensor element 10 is held inside the metal shell 20.

The gas sensor 1 comprises a cylindrical holding member 60 having an insertion hole 62 into which the rear end 10k of the gas sensor element 10 is inserted, and six terminal members held inside the holding member 60. For ease of explanation, only two of the six terminal members, terminal members 75 and 76, are shown in FIG. 1.

As shown in FIG. 2, a total of six electrode terminals 13-18 having a rectangular shape in plan view are formed on the rear end 10k of the gas sensor element 10. Note that FIG. 1 shows only the electrode terminals 14 and 17. The aforementioned terminal members elastically abut and electrically connect to these electrode terminals 13-18, respectively. For example, the element abutment portion 75b of the terminal member 75 elastically abuts and electrically connects to the electrode terminal 14, and the element abutment portion 76b of the terminal member 76 elastically abuts and electrically connects to the electrode terminal 17.

In addition, the six terminal members (terminal members 75, 76, etc.) are each connected to a different lead wire 71.
1 , the core wire of the lead wire 71 is crimped and held by the lead wire gripping portion 77 of the terminal member 75. Also, the core wire of the other lead wire 71 is crimped and held by the lead wire gripping portion 78 of the terminal member 76.

As shown in FIG. 2, one of the two main surfaces 10a, 10b at the rear end 10k of the gas sensor element 10 (the front side) has an open air inlet 10h at a location on the tip side of the electrode terminals 13-15 and on the rear side of the ceramic sleeve 45 (see FIG. 1) described below. The air inlet 10h is disposed within the insertion hole 62 of the holding member 60.

The metal shell 20 is a tubular member having a through hole 23 that penetrates in the direction of the axis AX. The metal shell 20 has a shelf portion 25 that protrudes radially inward and constitutes part of the through hole 23. The metal shell 20 holds the gas sensor element 10 in the through hole 23 with the tip end 10s of the gas sensor element 10 protruding outside its own tip end side (downward in FIG. 1) and the rear end 10k of the gas sensor element 10 protruding outside its own rear end side (upward in FIG. 1).

In addition, an annular ceramic holder 42, two talc rings 43, 44 filled with talc powder in an annular shape, and a ceramic sleeve 45 are arranged inside the through hole 23 of the metal shell 20. More specifically, the ceramic holder 42, the talc rings 43, 44, and the ceramic sleeve 45 are stacked in this order from the front end to the rear end of the metal shell 20, surrounding the gas sensor element 10 extending in the direction of the axis AX.

A metal cup 41 is disposed between the ceramic holder 42 and the shelf portion 25 of the metal shell 20. A crimping ring 46 is disposed between the ceramic sleeve 45 and the crimped portion 22 of the metal shell 20. The crimped portion 22 of the metal shell 20 is crimped so as to press the ceramic sleeve 45 against the tip side via the crimping ring 46.

A metal (e.g., stainless steel) external protector 31 and internal protector 32 having multiple holes are attached by welding to the tip 20b of the metal shell 20 so as to cover the tip 10s of the gas sensor element 10. An outer cylinder 51 is also attached by welding to the rear end of the metal shell 20. The outer cylinder 51 is generally cylindrical and extends in the direction of the axis AX, and surrounds the gas sensor element 10.

The holding member 60 is made of an insulating material (e.g., alumina) and is a cylindrical member 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 flange portion 65 that protrudes radially outward is formed at the rear end of the holding member 60. The holding member 60 is held by the internal support member 53 with the flange portion 65 abutting against the internal support member 53. The internal support member 53 is held by a crimped portion 51g of the outer tube 51 that is crimped radially inward.

An insulating member 90 is disposed on the rear end surface 61 of the holding member 60. The insulating member 90 is made of an insulating material (e.g., alumina) and has an overall annular shape. A total of six through holes 91 are formed in the insulating member 90, penetrating in the direction of the axis AX. The lead wire gripping portions 77, 78 of the terminal members described above are disposed in the through holes 91.

In addition, an elastic seal member 73 made of fluororubber is disposed on the radially inner side of the rear end opening 51c disposed on the rear end side of the outer tube 51. A total of six cylindrical insertion holes 73c extending in the axial direction AX are formed in this elastic seal member 73. Each insertion hole 73c is formed by the insertion hole surface 73b (cylindrical inner wall surface) of the elastic seal member 73. One lead wire 71 is inserted into each insertion hole 73c. Each lead wire 71 extends to the outside of the gas sensor 1 through the insertion hole 73c of the elastic seal member 73. The elastic seal member 73 elastically compresses and deforms in the radial direction by crimping the rear end opening 51c of the outer tube 51 radially inward, thereby tightly contacting the insertion hole surface 73b and the outer peripheral surface 71b of the lead wire 71, thereby sealing the insertion hole surface 73b and the outer peripheral surface 71b of the lead wire 71 watertightly.

3, the gas sensor element 10 includes plate-shaped insulating layers 111s, 121s, and 131s, solid electrolyte bodies 111e, 121e, and 131e, and insulators 140 and 145. The insulators 140 and 145 are each made of dense ceramic (e.g., alumina). The insulator 140 is disposed between the insulating layer 111s and the insulating layer 121s, and the insulator 145 is disposed between the insulating layer 121s and the insulating layer 131s. Furthermore, the gas sensor element 10 includes a heater 161 disposed on the back side of the solid electrolyte body 131e. The heater 161 includes two plate-shaped insulators 162 and 163 mainly made of alumina, and a heater pattern 164 embedded between them. The heater pattern 164 is made of a film-shaped pattern mainly made of platinum (Pt).

The solid electrolyte bodies 111e, 121e, and 131e each have a substantially rectangular shape in plan view. The solid electrolyte body 111e is formed so as to overlap the opening 111a provided at the tip side (left side in FIG. 4) of the plate-shaped insulating layer 111s extending in the axis AX direction. The solid electrolyte body 121e is formed so as to overlap the opening 121a provided at the tip side (left side in FIG. 4) of the plate-shaped insulating layer 121s extending in the axis AX direction. The solid electrolyte body 131e is formed on the surface of the plate-shaped insulating layer 131s extending in the axis AX direction. The insulating layer 131s corresponds to the "first insulating layer" of the present invention. The solid electrolyte bodies 111e and 121e may be formed so as to be embedded in the corresponding openings 111a and 121a, respectively, or may be formed so as to transfer a separately prepared sheet-shaped member to a predetermined location.

The solid electrolyte bodies 111e, 121e, and 131e are made of zirconia, a solid electrolyte, and have oxygen ion conductivity. A porous Ip1+ electrode 112 is provided on the front 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 front side of the Ip1+ electrode 112 is covered with a porous layer 114. An Ip1+ lead 116 is connected to the Ip1+ electrode 112. An Ip1- lead 117 is connected to the Ip1- electrode 113.

As shown in FIG. 4, a plate-shaped dense layer 118B extending in the direction of the axis AX is laminated on each surface of the Ip1+ electrode 112 and the Ip1+ lead 116. The dense layer 118B is made of a gas-impermeable material such as alumina. An opening 118Ba having a rectangular shape in a plan view is provided on the tip side of the dense layer 118B. The porous layer 114 described above is then formed to fill this opening 118Ba.

As shown in FIG. 4, a gas-impermeable dense layer 118 made of alumina or the like is disposed on the surface side of the dense layer 118B, and includes voids 10G. The voids 10G are formed inside a groove extending in the longitudinal direction (axis AX direction). A part of the porous layer 114 is exposed from the voids 10G. The voids 10G extend straight from the vicinity of the porous layer 114 to a portion communicating with the air inlet 10h in the plate-shaped dense layer 118 extending in the axis AX direction. A through hole is provided on the rear end side of the plate-shaped dense layer 118 extending in the axis AX direction to provide electrical continuity with the electrode terminals 13, 14, and 15.

In addition, a gas-impermeable dense layer 115 made of alumina or the like is laminated on the surface of the dense layer 118. By laminating the dense layer 115 in this manner, the gap 10G is blocked by the dense layer 115.

An air inlet 10h is formed in the dense layer 115 at a position that overlaps with the rear end of the gap 10G extending in the longitudinal direction (axis AX direction). The air inlet 10h is an opening that penetrates the dense layer 115 in the thickness direction. Such an air inlet 10h is connected to the gap 10G. The air inlet 10h opens toward the rear end side of the first porous body 151 described later, and can introduce air rather than exhaust gas. As a result, the Ip1+ electrode 112 is exposed to the air introduced from the air inlet 10h through the porous layer 114.

The solid electrolyte body 111e, the Ip1+ electrode 112, and the Ip1- electrode 113 constitute the Ip1 cell (first pump cell) 110 (see FIG. 3). This Ip1 cell 110 pumps oxygen in and out (so-called oxygen pumping) between the atmosphere in contact with the Ip1+ electrode 112 (the atmosphere in the gap 10G) and the atmosphere in contact with the Ip1- electrode 113 (the atmosphere in the first measurement chamber 150 described below; in other words, the measurement target gas outside the gas sensor element 10) in response to the pump current Ip1 (first pump current) flowing between the Ip1+ electrode 112 and the Ip1- electrode 113.

A porous Vs- electrode 122 is provided on the front side of the solid electrolyte body 121e. A porous Vs+ electrode (reference electrode) 123 is provided on the back side of the solid electrolyte body 121e. The Vs- electrode 122 corresponds to the "fourth electrode" of the present invention, and the Vs+ electrode 123 corresponds to the "third electrode" of the present invention. The solid electrolyte body 121e corresponds to the "second solid electrolyte body" of the present invention.

In the stacking direction, a first measurement chamber 150 is formed between the solid electrolyte body 111e and the solid electrolyte body 121e. This first measurement chamber 150 is an internal space into which the measurement target gas (exhaust gas) flowing through the exhaust passage in the exhaust pipe is first introduced into the gas sensor element 10, and is connected to the outside of the gas sensor element 10 through a first porous body (diffusion resistance portion) 151 (see Figures 2 and 4) that has gas permeability and water permeability. The first porous body 151 is provided on the side of the first measurement chamber 150 as a partition from the outside of the gas sensor element 10. Such a first porous body 151 limits the flow amount (diffusion speed) of exhaust gas into the first measurement chamber 150 per unit time. The first porous body 151 is made of porous ceramic.

At the rear end side of the first measuring chamber 150 (the right side in FIG. 3), a second porous body 152 is provided as a partition between the first measuring chamber 150 and the second measuring chamber 160 described later, which limits the amount of exhaust gas flowing per unit time.

The solid electrolyte body 121e, the Vs- electrode 122, and the Vs+ electrode 123 constitute the Vs cell (detection cell) 120. This Vs cell 120 generates an electromotive force mainly in response to the oxygen partial pressure difference between the atmospheres separated by the solid electrolyte body 121e (the atmosphere in the first measurement chamber 150 to which the Vs- electrode 122 contacts, and the atmosphere in the reference oxygen chamber 170 to which the Vs+ electrode 123 contacts). The Vs cell 120 corresponds to the "second cell" of the present invention.

A porous Ip2+ electrode 132 and a porous Ip2- electrode 133 are provided on the surface side of the solid electrolyte body 131e. The Ip2+ electrode 132 corresponds to the "first electrode" of the present invention, and the Ip2- electrode 133 corresponds to the "second electrode" of the present invention. The solid electrolyte body 131e corresponds to the "first solid electrolyte body" of the present invention.

A reference oxygen chamber 170 is formed as an isolated small space between the Ip2+ electrode 132 and the Vs+ electrode 123. This reference oxygen chamber 170 is formed by an opening 145b formed in the insulator 145. In addition, a ceramic porous body 171 is arranged on the Ip2+ electrode 132 side of the reference oxygen chamber 170 (see Figure 3).

A second measurement chamber 160 is formed at a position facing the Ip2-electrode 133 in the stacking direction. This second measurement chamber 160 is mainly composed of an opening 145c that penetrates the insulator 145 in the stacking direction (thickness direction), an opening 125 that penetrates the insulating layer 121s in the stacking direction (thickness direction), and an opening 152a that penetrates the second porous body 152 in the stacking direction (thickness direction).

The first measuring chamber 150 and the second measuring chamber 160 are in communication with each other via the second porous body 152, which has gas permeability and water permeability. Therefore, the second measuring chamber 160 is in communication with the outside of the gas sensor element 10 through the first porous body 151, the first measuring chamber 150, and the second porous body 152.

The solid electrolyte body 131e, the Ip2+ electrode 132, and the Ip2- electrode 133 constitute an Ip2 cell 130 (second pump cell) for detecting the _NOx concentration. This 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 that time, a current (second pump current) flows between the Ip2+ electrode 132 and the Ip2- electrode 133 according to the concentration of _NOx contained in the exhaust gas (measurement target gas) introduced into the second measurement chamber 160. The Ip2 cell corresponds to the "first cell" of the present invention.

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

An alumina insulating layer 128 (see FIG. 3) is formed on the surface of the insulating layer 121s, except for the Vs-electrode 122 and the like. For ease of explanation, the alumina insulating layer 128 is omitted from FIG. 4. The Vs-electrode 122 contacts the solid electrolyte body 121e through a through hole (not shown) that penetrates the alumina insulating layer 128 in the stacking direction.

An alumina insulating layer 129 (see FIG. 3) is formed on the back surface of the insulating layer 121s, except for the Vs+ electrode 123 and the like. For ease of explanation, the alumina insulating layer 129 is omitted in FIG. 4. The Vs+ electrode 123 contacts the solid electrolyte body 121e through a through hole (not shown) that penetrates the alumina insulating layer 129 in the stacking direction.

Now, with reference to Figures 5 to 8, the positional relationship between the Ip2+ electrode 132 and Ip2- electrode 133 of the Ip2 cell 130 and the Vs+ electrode 123 of the Vs cell 120 will be described. Figure 5 is an explanatory diagram showing the positional relationship between the Ip2+ electrode 132, the Ip2- electrode 133, and the Vs+ electrode 123 in a plan view, Figure 6 is an explanatory diagram showing the Ip2 cell 130 in a plan view, Figure 7 is a cross-sectional view of the laminate L including the Ip2 cell 130 and the Vs cell 120 cut along the axial direction, and Figure 8 is a cross-sectional view of the laminate L including the Ip2 cell 130 and the Vs cell 120 cut along the width direction.

The laminate L constitutes a part of the gas sensor element 10, and includes at least the Ip2 cell 130, the Vs cell 120, and the insulator 145. The insulator 145 corresponds to the "adhesive layer" of the present invention. The cutting direction of the cross-sectional view shown in FIG. 7 corresponds to the line B-B direction of FIG. 5, and the cutting direction of the cut surface shown in FIG. 8 corresponds to the line C-C direction of FIG. 5.

The Ip2 cell (first cell) 130 has an insulating layer (first insulating layer) 131s, a solid electrolyte body (first solid electrolyte body) 131e arranged on the surface 131s1 side so that the peripheral end 131e2 does not protrude from the surface 131s1 of the insulating layer 131s in a plan view, and a pair of Ip2+ electrodes (first electrodes) 132 and Ip2- electrodes (second electrodes) 133 arranged on the surface 131e1 of the solid electrolyte body 131e while being separated from each other in a plan view. In Figs. 5 and 6, the longitudinal lead wire 132b (see Fig. 4) connected to the Ip2+ electrode 132 and the longitudinal lead wire 133b (see Fig. 4) connected to the Ip2- electrode 133 are omitted. The solid electrolyte body 131e is formed on the surface 131s1 of the insulating layer 131s. In other words, the solid electrolyte body 131e is arranged on the surface side of the insulating layer 131s.

As shown in FIG. 6, when the Ip2 cell (first cell) 130 is viewed in plan from the front side, there is a region R between the Ip2+ electrode 132 and the Ip2- electrode 133 where no electrodes are formed. Note that the region R between the Ip2+ electrode 132 and the Ip2- electrode 133 will eventually be filled with a portion of the insulator 145.

The Vs cell (second cell) 120 has a solid electrolyte body (second solid electrolyte body) 121e including an opposing surface 121e1 that faces the surface 131s1 of the insulating layer (first insulating layer) 131s and an opposite surface 121e2 on the opposite side of the opposing surface 121e1, a Vs+ electrode (third electrode) 123 that is arranged on the opposing surface 121e1 and overlaps with the peripheral end portion 131e2 in a plan view, and a Vs- electrode (fourth electrode) 122 (see Figures 3 and 4) that is arranged on the opposite surface 121e2. Note that the Vs- electrode (fourth electrode) 122 is omitted in Figures 5, 7, and 8.

As shown in FIG. 3, the solid electrolyte body (second solid electrolyte body) 121e separates the first measurement chamber 150 and the reference oxygen chamber 170 in the gas sensor element 10. The Vs+ electrode (third electrode) 123 is exposed to the atmosphere in the reference oxygen chamber 170, and the Vs- electrode (fourth electrode) 122 is exposed to the atmosphere in the first measurement chamber 150. The Vs+ electrode (third electrode) 123 is made of a porous ceramic having gas permeability. The Vs+ electrode (third electrode) 123 is made of a cermet containing, for example, platinum powder and ceramic powder. The Vs- electrode (fourth electrode) 122 is also made of a porous ceramic having gas permeability. The Vs- electrode (fourth electrode) 122 is made of a cermet containing, for example, platinum powder and ceramic powder.

As shown in FIG. 5, the Vs+ electrode (third electrode) 123 of the Vs cell 120 faces the solid electrolyte body 131e of the Ip2 cell 130 in the stacking direction. In particular, the Vs+ electrode 123 has a portion (overlapping portion) 123a that extends from the front end side toward the rear end side of the gas sensor element 10 so as to overlap the peripheral end portion 131e2 of the solid electrolyte body 131e of the Ip2 cell 130 while overlapping the region R (region where no electrodes are formed) between the Ip2+ electrode 132 and the Ip2- electrode 133 on the solid electrolyte body 131e in a plan view.

In the Vs cell (second cell) 120, a constant amount of oxygen is stored in the reference oxygen chamber 170 by passing a constant minute current from the Vs- electrode 122 side to the Vs+ electrode 123 side. Any excess oxygen stored in the reference oxygen chamber 170 enters the inside of the Vs+ electrode 123 and travels through the inside of the elongated lead wire 123b connected to the Vs+ electrode 123 toward the rear end side of the gas sensor element 10. The oxygen is then released to the outside from the rear end 123b1 of the lead wire 123b (see FIG. 4). The Vs+ electrode 123 and the lead wire 123b are made of gas-permeable porous ceramic.

As described above, the insulator (adhesive layer) 145 is made of dense ceramic (e.g., alumina) and has insulating properties. Such an insulator (adhesive layer) 145 is interposed between the Ip2 cell (first cell) 130 and the Vs cell (second cell) 120, and bonds the Ip2 cell (first cell) 130 and the Vs cell (second cell) 120 together while the Ip2+ electrode (first electrode) 132 and the Ip2- electrode (second electrode) 133 are separated so as not to be conductive to the Vs+ electrode (third electrode) 123.

As shown in FIG. 5, the gas sensor element 10 of this embodiment includes a buffer portion 200 formed on the surface of the Vs+ electrode 123 so as to overlap the region R between the Ip2+ electrode 132 and the Ip2- electrode 133 in a plan view and to overlap the peripheral end portion 131e2 of the solid electrolyte body 131e. The buffer portion 200 is formed so as to cover at least the overlapping portion 123a of the Vs+ electrode 123 described above. The buffer portion 200 of this embodiment is formed in a band shape so as to follow the Vs+ electrode 123 extending in the front-rear direction. The width of the buffer portion 200 (length in the left-right direction in FIG. 5) is larger than the width of the Vs+ electrode 123 (length in the left-right direction in FIG. 5), and the buffer portion 200 is provided in the width direction so that the Vs+ electrode 123 does not protrude outward. As described above, the buffer section 200 is formed so as to cover at least the overlapping section 123a of the Vs+ electrode 123. In other embodiments, for example, the buffer section 200 may be formed in a band shape along the edge of the Vs+ electrode 123 that extends roughly in the front-rear direction and is closer to the Ip2- electrode 133 in a plan view (in this case, the edge of the Vs+ electrode 123 that is farther from the Ip2- electrode 133 in the width direction may extend outside the buffer section 200). The buffer section 200 is made of a ceramic material that has a lower shrinkage start temperature than the material used to form the insulator (adhesive layer) 145.

In this specification, the "shrinkage start temperature" refers to the temperature at which the spreading factor reaches 1.05 when green sheets having the same composition as each ceramic layer (e.g., buffer section 200, insulator 145) are prepared and heated in an air atmosphere to proceed with firing to form each ceramic layer. The spreading factor is also called the firing shrinkage factor, and is calculated by taking the vertical or horizontal dimension of the green sheet before firing as 1 when the vertical or horizontal dimension of the ceramic layer after firing is taken as 1.
That is, the allocation ratio=(longitudinal or lateral dimension of the green sheet before firing)/(dimension in the same direction of the ceramic layer after firing).

The buffer section 200 is formed by printing as described below. By providing the gas sensor element 10 of this embodiment with such a buffer section 200, the occurrence of cracks in the insulating adhesive layer (insulator) 145 interposed between the Ip2 cell (first cell) 130 and the Vs cell (second cell) 120 during the manufacture of the gas sensor element 10 is suppressed.

The buffer section 200 is made of dense, gas-impermeable ceramic. Therefore, even if it is in contact with the Vs+ electrode 123 made of porous ceramic, oxygen passing through the inside of the Vs+ electrode 123 is prevented from entering the buffer section 200. In other words, the amount of oxygen flowing per unit time through the Vs+ electrode 123 and lead wire 123b is prevented from decreasing due to the influence of the buffer section 200.

The material for forming the buffer section 200 is made of ceramic containing zirconia as the main component. In this specification, the "main component" refers to a component whose content (content ratio) in each component is 50% by mass or more. In other words, in this embodiment, the buffer section 200 contains 50% by mass or more of zirconia.

Next, a brief description will be given of a method for detecting a _NOx concentration using the gas sensor 1 of this embodiment. The solid electrolyte bodies 111e, 121e, and 131e of the gas sensor element 10 are heated and activated as the temperature of the heater pattern 164 rises. This causes the Ip1 cell 110, the Vs cell 120, and the Ip2 cell 130 to operate.

The exhaust gas flowing through the exhaust passage (not shown) in the exhaust pipe is introduced into the first measurement chamber 150 while the flow rate is restricted by the first porous body 151. At this time, a weak current (microcurrent) Icp is flowing from the Vs+ electrode 123 side to the Vs- electrode 122 side in the Vs cell 120. Therefore, the oxygen in the exhaust gas can receive electrons from the Vs- electrode 122 in the first measurement chamber 150, which is the negative electrode side, and becomes oxygen ions, flows through the solid electrolyte body 121e, and moves into the reference oxygen chamber 170. In other words, the current Icp is flowed between the Vs- electrode 122 and the Vs+ electrode 123, and the oxygen in the first measurement chamber 150 is sent into the reference oxygen chamber 170.

When the oxygen concentration of the exhaust gas introduced into the first measuring chamber 150 is lower than a predetermined value, a current Ip1 is passed through the Ip1 cell 110 so that the Ip1+ electrode 112 becomes the negative electrode, and oxygen is pumped from outside the gas sensor element 10 into the first measuring chamber 150.

In contrast, if the oxygen concentration of the exhaust gas introduced into the first measuring chamber 150 is higher than the predetermined value, a current Ip1 is passed through the Ip1 cell 110 so that the Ip1-electrode 113 side becomes the negative electrode, and oxygen is pumped from inside the first measuring chamber 150 to the outside of the gas sensor element 10.

In this way, the exhaust gas whose oxygen concentration has been adjusted in the first measuring chamber 150 is introduced into the second measuring chamber 160 through the second porous body 152. The NO _x in the exhaust gas that has come into contact with the Ip2-electrode 133 in the second measuring chamber 160 is decomposed (reduced) into nitrogen and oxygen on the Ip2-electrode 133 by applying a voltage Vp2 between the Ip2+electrode 132 and the Ip2-electrode 133, and the decomposed oxygen becomes oxygen ions and flows through the solid electrolyte body 131e, and moves into the reference oxygen chamber 170. At this time, the residual oxygen that has been left behind in the first measuring chamber 150 is also moved into the reference oxygen chamber 170 by the Ip2 cell 130. As a result, a current derived from NO _x 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) via the Vs+ electrode 123 and the Vs+ lead (lead wire 123b) that are in contact with the inside of the reference oxygen chamber 170. For this reason, the Vs+ lead is made porous.

Since the concentration of the residual oxygen left behind in the first measurement chamber 150 is adjusted to a predetermined value as described above, the current derived from the residual oxygen can be considered to be approximately constant. In other words, the current derived from the residual oxygen is little affected by fluctuations in the current derived from _NOx , and the current flowing through the Ip2 cell 130 (second pump current) is proportional to the _NOx concentration. Therefore, the current Ip2 (second pump current) flowing through the Ip2 cell 130 is measured, and the _NOx concentration in the exhaust gas is detected based on the current value.

Next, a method for manufacturing the above-mentioned gas sensor element 10 will be described with reference to Figures 9 to 11. Figure 9 is a flow diagram showing each process in the method for manufacturing the gas sensor element 10. As shown in Figure 9, the method for manufacturing the gas sensor element 10 of this embodiment includes at least a first manufacturing process S11, a second manufacturing process S12, an adhesion process S13, and a firing process S14. In addition to these processes, the method for manufacturing the gas sensor element 10 includes known processes such as a process for manufacturing the Ip1 cell 110. In this specification, a description of the known processes will be omitted. Figure 10 is an explanatory diagram that shows a schematic representation of the contents of the method for manufacturing the gas sensor element 10.

The first manufacturing process S11 is a process for manufacturing an unfired first cell 130U including a first green sheet 131sU for forming an insulating layer (first insulating layer) 131s, an unfired first solid electrolyte body 131eU for forming a solid electrolyte body (first solid electrolyte body) 131e arranged on the front side of the first green sheet 131sU, and a pair of unfired first electrodes 132U and unfired second electrodes 133U for forming a first electrode 132 and a second electrode 133, each of which is arranged on the surface of the unfired first solid electrolyte body 131eU while being separated from each other in a planar view.

The unsintered first solid electrolyte body 131eU is formed in advance on a separately prepared sheet-like member, and the unsintered first solid electrolyte body 131eU on that member is transferred to the surface 131sU1 side of the first green sheet 131sU.

A protective layer 210U, mainly composed of alumina, is formed on the surface of the unsintered first cell 130U so as to cover the unsintered first electrode 132U, the unsintered first solid electrolyte body 131eU, etc. On the surface of the unsintered first cell 130U, the unsintered second electrode 133U is not covered by the protective layer 210U and is exposed from an opening 210Ua of the protective layer 210U. The protective layer 210U is provided in a form that follows the surface shape (unevenness, etc.) of the unsintered first cell 130U. When the protective layer 210U is sintered, it eventually becomes part of the insulator 145.

The second manufacturing process S12 is a process for manufacturing an unsintered second cell 120U having a second green sheet (unsintered second solid electrolyte body) 121eU for forming a solid electrolyte body (second solid electrolyte body) 121e including an unsintered opposing surface 121eU1 that faces the surface of the first green sheet 131sU and an unsintered opposite surface 121eU2 on the opposite side of the unsintered opposing surface 121eU1, an unsintered third electrode 123U for forming a Vs+ electrode 123 disposed on the unsintered opposing surface 121eU1, and an unsintered fourth electrode 122U for forming a Vs- electrode 122 disposed on the unsintered opposite surface.

In this second manufacturing process S12, an unsintered buffer section 200U for forming the buffer section 200 is formed on the surface of the unsintered third electrode 123U so as to overlap the region RU between the unsintered first electrode 132U and the unsintered second electrode 133U in a plan view, and to overlap the unsintered peripheral end section 131eU2. The unsintered buffer section 200U is made of a material that has a lower shrinkage start temperature than the material for forming the insulator (adhesive layer) 145. Such an unsintered buffer section 200U is formed to a predetermined thickness on the surface of the unsintered third electrode 123U by printing.

The second green sheet (unfired second solid electrolyte body) 121eU is provided in the opening 121aU of the green sheet 121sU for forming the insulating layer 121s. The second green sheet 121eU has an opening 121eUa at a portion overlapping the fired second electrode 133U in a plan view. In addition, a protective layer 220U mainly composed of alumina is formed on the surface of the unfired opposing surface 121eU1 side of the unfired second cell 120U so as to cover the unfired third electrode 123U, the unfired buffer portion 200U, the green sheet 121sU, etc. The protective layer 220U is provided in a form that follows the surface shape of the unfired second cell 120U. The protective layer 220U has an opening 220Ua at a portion overlapping the unfired second electrode 133U in a plan view. When the protective layer 220U is fired, it eventually becomes part of the insulator 145.

The bonding process S13 is a process of bonding the unsintered first cell 132U and the unsintered second cell 133U with an unsintered adhesive sheet 145U interposed between the unsintered first cell 130U and the unsintered second cell 120U to form an insulator (adhesive layer) 145, so that the unsintered first electrode 132U and the unsintered second electrode 133U are separated from the unsintered third electrode 123U and the unsintered third electrode 123U overlaps the unsintered peripheral end portion 131eU2 of the unsintered first solid electrolyte body 131eU in a planar view. The unsintered adhesive sheet 145U has an opening 145Ua in the portion that overlaps the unsintered second electrode 133U in a planar view.

The firing step S14 is a step of firing the laminate obtained after the bonding step S13. In the firing step S14, the laminate is fired under predetermined temperature conditions to obtain the gas sensor element 10.

As described above, the unsintered buffer section 200U is made of a material that has a lower shrinkage start temperature than the material for forming the insulator (adhesive layer) 145. Therefore, in the firing step S14, the unsintered buffer section 200U starts to shrink before the unsintered adhesive sheet 145U, independently of the unsintered adhesive sheet 145U. Moreover, the unsintered buffer section 200U is considerably smaller in size than the unsintered adhesive sheet 145U, and the amount of shrinkage is smaller. Therefore, even if such an unsintered buffer section 200U is in contact with the unsintered third electrode 123U, the occurrence of cracks in the unsintered third electrode 123U during the shrinkage of the unsintered buffer section 200U in the firing step S14 is suppressed. In addition, even when the unsintered adhesive sheet 145U and the unsintered third electrode 123U each shrink, the presence of the unsintered buffer portion 200U prevents cracks from occurring in the sintered third electrode 123U.

Therefore, in the gas sensor element 10 obtained by the manufacturing method of the gas sensor element of this embodiment, the occurrence of cracks that may cause erroneous detection of the _NOx concentration is suppressed in the insulating adhesive layer (insulator) 145 interposed between the first cell (Ip2 cell) 130 and the second cell (Vs cell) 120.

<Conventional Example>
Next, the configuration of the conventional gas sensor element 10P will be briefly described with reference to FIG. 11. FIG. 11 is a cross-sectional view of a part of the conventional gas sensor element 10P cut along the axial direction. FIG. 11 shows a laminate LP including the Ip2 cell 130 and the Vs cell 120 as a part of the conventional gas sensor element 10P. The conventional gas sensor element 10P does not include a buffer portion 200, unlike the gas sensor element 10 of the first embodiment. That is, in the conventional gas sensor element 10P, the insulator (adhesive layer) 145P is in direct contact with the Vs+ electrode 123P. The conventional gas sensor element 10P has the same configuration as the gas sensor element 10 of the first embodiment, except that it does not include the buffer portion 200.

The Ip2 cell 130P has an insulating layer 131sP, a solid electrolyte body 131eP arranged on the surface 131sP1 side so that the peripheral end portion 131eP2 does not protrude from the surface 131sP1 of the insulating layer 131sP in a planar view, and a pair of Ip2+ electrode 132P and Ip2- electrode (not shown) arranged on the surface 131eP1 of the solid electrolyte body 131eP while being separated from each other in a planar view. When the Ip2 cell 130 is viewed from the front side in a planar view, there is a region RP between the Ip2+ electrode 132 and the Ip2- electrode (not shown) where no electrodes are formed, as in the first embodiment.

The Vs cell 120P has a solid electrolyte body 121eP including an opposing surface 121eP1 facing the surface 131sP1 of the insulating layer 131sP and an opposite surface 121eP2 on the opposite side of the opposing surface 121eP1, a Vs+ electrode 123P that is thicker than the Ip2+ electrode 132P and the Ip2- electrode (not shown) and is disposed on the opposing surface 121eP1 and is disposed so as to overlap the peripheral end portion 131Pe in a plan view, and a Vs- electrode (not shown) that is disposed on the opposite surface 121eP2. A longitudinal lead wire 123bP is connected to the Vs+ electrode 123P.

As shown in FIG. 11, in such a conventional gas sensor element 10P, cracks X sometimes occurred along the thickness direction (stacking direction) in the insulating adhesive layer (insulator) 145P interposed between the Vs cell 120P and the Ip2 cell 130P, in a portion sandwiched between the Vs+ electrode 123P of the Vs cell 120P and the peripheral end portion 131eP2 of the solid electrolyte body 131eP disposed near the region RP between the Ip2+ electrode 132P and the Ip2- electrode (not shown) in the Ip2 cell 130P.

1...gas sensor, 10...gas sensor element, 120...second cell, 121e...second solid electrolyte body, 121e1...opposing surface, 121e2...opposite surface, 123...third electrode, 124...fourth electrode, 130...first cell, 131s...first insulating layer, 131e...first solid electrolyte body, 131e2...peripheral end, 132...first electrode, 133...second electrode, 145...adhesive layer, 200...buffer section

Claims (6)

a first cell including a first insulating layer, a first solid electrolyte body arranged on the surface side of the first insulating layer such that a peripheral end portion does not protrude from the surface of the first insulating layer in a plan view, and a pair of first and second electrodes arranged on the surface of the first solid electrolyte body while being spaced apart from each other in a plan view;
a second cell including a second solid electrolyte body including an opposing surface facing the surface of the first insulating layer and an opposite surface on the opposite side of the opposing surface, a third electrode disposed on the opposing surface and overlapping with the peripheral edge in a plan view, and a fourth electrode disposed on the opposite surface;
a sensor element including an insulating adhesive layer interposed between the first cell and the second cell, the insulating adhesive layer adhering the first cell and the second cell in a state in which the first electrode and the second electrode are separated from each other so as not to be electrically connected to the third electrode,
a buffer portion formed on a surface of the third electrode so as to overlap with the peripheral end portion of the first solid electrolyte body while overlapping with a region between the first electrode and the second electrode in a plan view. the third electrode is made of a gas-permeable porous ceramic;
2. The gas sensor element according to claim 1, wherein the buffer portion is made of a gas-impermeable dense ceramic. The gas sensor element according to claim 1 or 2, wherein the buffer portion is made of a ceramic containing zirconia as a main component. The gas sensor element according to any one of claims 1 to 3, wherein the third electrode is made of a cermet containing platinum powder and ceramic powder. A gas sensor comprising the gas sensor element according to any one of claims 1 to 4. a first cell having a pair of first and second electrodes arranged on the surface of the first solid electrolyte body while being separated from each other in a plan view; a second solid electrolyte body including an opposing surface facing the surface of the first insulating layer and an opposite surface on the opposite side of the opposing surface; a second cell having a third electrode arranged on the opposing surface and arranged so as to overlap with the peripheral edge in a plan view, and a fourth electrode arranged on the opposite surface; and an insulating adhesive layer interposed between the first cell and the second cell, and bonding the first cell and the second cell together while the first electrode and the second electrode are separated so as not to be conductive to the third electrode,
a first manufacturing step of manufacturing an unsintered first cell including: a first green sheet for forming the first insulating layer; an unsintered first solid electrolyte body for forming the first solid electrolyte body disposed on a surface side of the first green sheet; and a pair of unsintered first and second electrodes for forming the first and second electrodes, the pair being disposed on a surface of the unsintered first solid electrolyte body while being separated from each other in a plan view;
a second production step of producing an unsintered second cell having a second green sheet for forming the second solid electrolyte body including an unsintered opposing surface opposing a surface of the first green sheet and an unsintered opposite surface on the opposite side of the unsintered opposing surface, an unsintered third electrode for forming the third electrode disposed on the unsintered opposing surface, and an unsintered fourth electrode for forming the fourth electrode disposed on the unsintered opposite surface;
a bonding step of bonding the unsintered first cell and the unsintered second cell by interposing an unsintered adhesive sheet for forming the adhesive layer between the unsintered first cell and the unsintered second cell such that the unsintered first electrode and the unsintered second electrode are separated from the unsintered third electrode and the unsintered third electrode overlaps with the unsintered peripheral end of the unsintered first solid electrolyte body in a plan view;
and a firing step of firing the laminate obtained after the bonding step,
In the second manufacturing step, an unsintered buffer portion for forming a buffer portion is formed on a surface of the unsintered third electrode so as to overlap with the unsintered peripheral end portion while overlapping with an area between the unsintered first electrode and the unsintered second electrode in the planar view. The unsintered buffer portion is made of a material having a lower shrinkage starting temperature than a material for forming the adhesive layer .