Sensor element and gas sensor

Abstract

To provide a sensor element that is suppressed in the occurrence of crack due to stress concentration to a corner section of an internal space, and a gas sensor.SOLUTION: A plate-shaped sensor element 10 extending in an axis AX direction and having an internal space 10G is provided, when a cross section perpendicular to the axial direction of the internal space is viewed, a protrusion 80 extending from a corner toward the internal space is formed at a corner of a first inner surface S1 closest to an outer surface of the sensor element in the internal space, and a gap G2 is formed between a distal end of the protrusion and the first inner surface.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a sensor element and a gas sensor that are suitably used for detecting the concentration of a specific gas contained in combustion gas or exhaust gas from, for example, a combustor or an internal combustion engine. [Background technology]

[0002] Gas sensors have been used to detect the concentration of specific components (such as oxygen) in exhaust gas from internal combustion engines. A known gas sensor has a sensor element therein, which is a plate-like element made of a plurality of laminated ceramic layers, and which includes a solid electrolyte body and a pair of electrodes disposed on the solid electrolyte body, one of which faces an air (atmosphere) inlet opening into the element (see Patent Document 1). This air inlet is connected to the internal space of the element. When forming the internal space, a paste containing burnable carbon is used, but when this paste is burned, it shrinks, which can cause cracks to form at the corners of the internal space. Therefore, in order to suppress these thermal cracks, the technology of Patent Document 1 interposes a ceramic layer around the periphery of the internal space. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-51058 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in addition to the above-mentioned thermal cracks, if an internal space is provided in the sensor element, stress may be concentrated at the corners of the internal space when a load is applied to the sensor element, which may cause cracks.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a sensor element and a gas sensor that suppress cracks caused by stress concentration at corners of the internal space. [Means for solving the problem]

[0006] In order to solve the above problems, the sensor element of the present invention is a plate-shaped sensor element that extends in an axial direction and has an internal space, and is characterized in that, when viewed in a cross section of the internal space perpendicular to the axial direction, a protrusion extending from the corner of a first inner surface of the internal space that is closest to the outer surface of the sensor element toward the internal space is formed, and a gap is formed between the tip of the protrusion and the first inner surface.

[0007] With this sensor element, a gap is formed between the tip of the protrusion and the first inner surface, and the tip of the protrusion is not constrained by the inner surface of the internal space, so that even if stress such as bending is applied to the sensor element and stress is applied to the corners of the internal space, the stress can be released at the tip of the protrusion, thereby suppressing cracks caused by stress concentration at the corners of the internal space.

[0008] In the sensor element of the present invention, the protrusion may be made mainly of ZrO2. When the protrusions are made mainly of ZrO2, ZrO2 has high strength and undergoes a phase transition in response to an external force, increasing its volume, so that cracks due to stress concentration can be further suppressed.

[0009] In the sensor element of the present invention, the internal space may be in communication with an air inlet. According to this sensor element, by making the corners of the first inner surface protruding, the volume of the internal space is larger than when the material of the protruding portion extends over the entire surface of the first inner surface instead of the protruding portion, and more air can be introduced.

[0010] In the sensor element of the present invention, one of a pair of electrodes constituting a cell may be disposed in a region extending from a second inner surface opposite to the first inner surface toward an outer surface of the sensor element. With this sensor element, the airflow in the internal space is less likely to be disturbed on the second inner surface side, compared to when the electrodes are arranged on the first inner surface side where the protrusions are present, and the sensor output is more stable.

[0011] In the sensor element of the present invention, the protruding portion may be porous. When the protrusions are porous, the volume of the internal space that the protrusions occupy in the internal space is smaller than when the internal space is solid, and the effective volume of the internal space is increased.

[0012] The gas sensor of the present invention comprises the sensor element and a metallic shell that holds the sensor element. [Effects of the Invention]

[0013] According to the present invention, it is possible to obtain a sensor element and a gas sensor that are capable of suppressing cracks caused by stress concentration at the corners of the internal space. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view taken along the longitudinal direction of a gas sensor (NOx sensor) according to an embodiment of the present invention. [Figure 2] FIG. [Figure 3] FIG. 3 is a cross-sectional view taken along line BB in FIG. 2. [Figure 4] FIG. [Figure 5] FIG. 3 is a cross-sectional view taken along line CC in FIG. 2. [Figure 6] 5A to 5C are process diagrams illustrating an example of a method for manufacturing a sensor element according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present invention will be described. FIG. 1 is a longitudinal cross-sectional view (a cross-sectional view cut longitudinally along the axis AX) of a gas sensor (NOx sensor) 1 according to an embodiment of the present invention, FIG. 2 is a perspective view of a sensor element 10, FIG. 3 is a cross-sectional view taken along line BB (axis AX) in FIG. 2, FIG. 4 is an exploded perspective view of the sensor element 10, and FIG. 5 is a cross-sectional view taken along line CC (a line perpendicular to the axis AX) in FIG. 2. The direction along the axis AX of the sensor element (axial direction) is referred to as the “longitudinal direction” where appropriate. The “width direction” of the sensor element is the direction perpendicular to the “longitudinal direction (axial direction).”

[0016] The gas sensor 1 is a NOx sensor that includes a sensor element 10 capable of detecting the concentration of a specific gas (NOx) in exhaust gas, which is a measurement target gas, and is attached to an exhaust pipe (not shown) of an internal combustion engine for use. The gas sensor 1 includes a cylindrical metal shell 20 that has a threaded portion 21 formed at a predetermined position on its outer surface for fixing to the exhaust pipe. The sensor element 10 is in the form of an elongated plate 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 (the upper end portion in FIG. 1) of the sensor element 10 is inserted, and six terminal members held inside the holding member 60. Note that FIG. 1 shows only two of the six terminal members (specifically, terminal members 75 and 76).

[0017] A total of six electrode terminals 13 to 18 (only electrode terminals 14 and 17 are shown in FIG. 1 ) that are rectangular in plan view are formed at the rear end 10k of the sensor element 10. The aforementioned terminal members are elastically abutted against and electrically connected to the electrode terminals 13 to 18, respectively. For example, the element abutting portion 75b of the terminal member 75 elastically abuts against and electrically connected to the electrode terminal 14. Furthermore, the element abutting portion 76b of the terminal member 76 elastically abuts against and electrically connected to the electrode terminal 17. Furthermore, six terminal members (terminal members 75, 76, etc.) are electrically connected to different lead wires 71, respectively. For example, as shown in Fig. 1, the core wire of lead wire 71 is crimped and held by lead wire holding portion 77 of terminal member 75. Also, the core wire of another lead wire 71 is crimped and held by lead wire holding portion 78 of terminal member 76.

[0018] In addition, an air inlet 10h opens on one of the main surfaces of the rear end 10k of the sensor element 10, further forward than the electrode terminal portions 13 to 15 and further rearward than the ceramic sleeve 45 described later (see Figure 2), and the air inlet 10h is arranged within the insertion hole 62 of the holding member 60. As a result, the reference atmosphere enclosed inside the outer cylinder 51 (described later) is introduced into the inside of the sensor element 10 through the atmosphere inlet 10h.

[0019] The metal shell 20 is a cylindrical 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 sensor element 10 in the through hole 23 with the front end portion 10s of the sensor element 10 protruding outward from its own front end side (downward in FIG. 1) and the rear end portion 10k of the sensor element 10 protruding outward from its own rear end side (upward in FIG. 1). Furthermore, an annular ceramic holder 42, two talc rings 43 and 44 formed by filling talc powder in an annular shape, and a ceramic sleeve 45 are arranged inside the through hole 23 of the metallic shell 20. In detail, the ceramic holder 42, the talc rings 43 and 44, and the ceramic sleeve 45 are arranged in this order, overlapping from the axial leading end side (the lower end side in FIG. 1) of the metallic shell 20 to the axial rear end side (the upper end side in FIG. 1), so as to surround the radial periphery of the sensor element 10.

[0020] A metal cup 41 is disposed between the ceramic holder 42 and the shelf portion 25 of the metallic shell 20. A crimping ring 46 is disposed between the ceramic sleeve 45 and the crimped portion 22 of the metallic shell 20. The crimped portion 22 of the metallic shell 20 is crimped so as to press the ceramic sleeve 45 toward the tip end side via the crimping ring 46. An outer protector 31 and an inner protector 32 made of metal (specifically, stainless steel) and having a plurality of holes are attached by welding to the front end portion 20b of the metallic shell 20 so as to cover the front end portion 10s of the sensor element 10. On the other hand, an outer cylinder 51 is attached by welding to the rear end portion of the metallic shell 20. The outer cylinder 51 has a cylindrical shape extending in the direction of the axis AX and surrounds the sensor element 10.

[0021] The holding member 60 is made of an insulating material (specifically, alumina) and is a cylindrical member having an insertion hole 62 that penetrates in the direction of the axis AX. The six terminal members (terminal members 75, 76, etc.) described above are arranged inside 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 in such a manner that the flange portion 65 abuts against the internal support member 53. The internal support member 53 is held to the external cylinder 51 by a crimped portion 51g that is crimped radially inward of the external cylinder 51. 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 electrically insulating material (specifically, alumina) and has a cylindrical 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 (lead wire gripping portions 77, 78, etc.) of the terminal members described above are disposed in the through holes 91.

[0022] An elastic seal member 73 made of fluororubber is disposed radially inside a rear end opening 51c located at the axial rear end (upper end in FIG. 1) of the outer cylinder 51. 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 73c is defined by an 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 sealing member 73 is elastically compressed and deformed radially by crimping the rear end opening 51c of the outer tube 51 radially inward, thereby tightly adhering the insertion hole surface 73b and the outer peripheral surface 71b of the lead wire 71 and creating a watertight seal between the insertion hole surface 73b and the outer peripheral surface 71b of the lead wire 71.

[0023] 3, the sensor element 10 has a structure in which solid electrolyte bodies 111e, 121e, and 131e are formed in plate-shaped insulating layers 111s, 121s, and 131s, respectively, and insulators 140 and 145 are disposed between them, and these are stacked in the stacking direction. Furthermore, the sensor element 10 has a heater 161 stacked on the back side of the solid electrolyte body 131e. This heater 161 has 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 each substantially rectangular and are formed in rectangular openings provided at the tip ends of the insulating layers 111s, 121s, and 131s, respectively. In this example, the solid electrolyte bodies 111e and 131e are formed by transferring sheet-like members to predetermined positions, but the material of the solid electrolyte bodies 111e and 131e may also be embedded in the openings.

[0024] The solid electrolyte substrates 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 substrate 111e. A porous Ip1- electrode 113 is provided on the back side of the solid electrolyte substrate 111e. Furthermore, the front side of the Ip1+ electrode 112 is covered with a porous layer 114B. In addition, an Ip1+ lead 116 is connected to the Ip1+ electrode 112 (see FIGS. 2 and 4), and an Ip1- lead 117 (FIG. 4) is connected to the Ip1- electrode 113.

[0025] 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 a porous layer 114B.

[0026] 4, a gas-impermeable first dense layer 118 made of alumina or the like and having an internal space 10G is laminated on the surface of third dense layer 118B. A portion of porous layer 114B is exposed from internal space 10G. The side surface of Ip1+ electrode 112 is covered with third dense layer 118B and is surrounded by each of dense layers 115, 118, and 118B. The internal space 10G extends in a straight line from the vicinity of the porous layer 114B to a portion communicating with the air inlet 10h. The first dense layer 118 on the rear end side of the internal space 10G is provided with through holes for electrical connection with the electrode terminals 13-15. The width of the air inlet 10h is shorter than that of the internal space 10G (see FIG. 5).

[0027] 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 internal space 10G. As a result, the Ip1+ electrode 112 covered with the porous layer 114B is disposed in the internal space 10G surrounded by the dense layers 115 and 118, preventing contact with the gas to be measured. The second dense layer 115 has a rectangular opening at a position overlapping the rear end of the internal space 10G, forming an air inlet 10h, and the internal space 10G is connected to the air inlet 10h. The air inlet 10h opens further rearward than the first porous body 151 (described later) and can introduce air rather than exhaust gas. This allows the Ip1+ electrode 112 to be exposed to the air introduced from the air inlet 10h via the porous layer 114B.

[0028] The solid electrolyte body 111e and the electrodes 112, 113 constitute an Ip1 cell (pump cell) 110. The Ip1 cell 110 pumps oxygen in and out (so-called oxygen pumping) between the atmosphere in contact with the electrode 112 (the atmosphere in the internal space 10G, which is different from the measurement gas outside the sensor element 10) and the atmosphere in contact with the electrode 113 (the atmosphere in the first measurement chamber 150, described later, i.e., the measurement gas outside the sensor element 10) in response to a pump current Ip1 flowing between the electrodes 112, 113.

[0029] The solid electrolyte body 121e is disposed opposite the solid electrolyte body 111e in the stacking direction, with the insulator 140 sandwiched therebetween. A porous Vs-electrode 122 is provided on the front surface side (upper surface 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.

[0030] A first measurement chamber 150 is formed between the solid electrolyte bodies 111e and 121e as an internal space of the sensor element. This first measurement chamber 150 is an internal space into which the measurement gas (exhaust gas) flowing through the exhaust passage is first introduced into the sensor element 10, and is in communication with the outside of the sensor element 10 through a first porous body (diffusion resistance portion) 151 (see FIGS. 2 and 4) that is gas-permeable and water-permeable. 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, and limits the amount of exhaust gas flowing into the first measurement chamber 150 per unit time (diffusion rate). A second porous body 152 is provided at the rear end side (right side in Figure 2) of the first measuring chamber 150 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.

[0031] The solid electrolyte body 121e and the electrodes 122 and 123 constitute a 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 in contact with the electrode 122 and the atmosphere in the reference oxygen chamber 170 in contact with the electrode 123).

[0032] The solid electrolyte body 131e is disposed opposite the solid electrolyte body 121 in the stacking direction, with the insulator 145 sandwiched therebetween. A porous Ip2+ electrode 132 and a porous Ip2- electrode 133 are provided on the front surface side (upper surface side in FIG. 2) of the solid electrolyte body 131e.

[0033] 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 configured by an opening 145b formed in the insulator 145. A porous ceramic body is disposed inside the reference oxygen chamber 170 on the Ip2+ electrode 132 side. A second measurement chamber 160 serving as an internal space of the sensor element is formed at a position facing the Ip2-electrode 133 in the stacking direction. The second measurement chamber 160 is composed of an opening 145c penetrating the insulator 145 in the stacking direction, an opening 125 penetrating the solid electrolyte body 121 in the stacking direction, and an opening 141 penetrating the insulator 140 in the stacking direction. The first measurement chamber 150 and the second measurement chamber 160 communicate with each other through a gas-permeable and water-permeable second porous body 152. 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.

[0034] 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 transfers 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 corresponding to the concentration of NOx contained in the exhaust gas (measurement target gas) introduced into the second measurement chamber 160 flows between the electrodes 132 and 133.

[0035] Next, the characteristic features of the present invention will be described with reference to FIG. As shown in FIG. 5, the cross section perpendicular to the axis line AX of the internal space 10G forming the internal space is rectangular. 5, a protrusion 80 extending from the corner of the first inner surface S1 of the internal space 10G, which is closest to the outer surface of the sensor element 10, toward the internal space 10G, is formed. Furthermore, a gap G2 is formed between the tip of the protrusion 80 and the first inner surface S1. In this way, a gap G2 is formed between the tip of the protrusion 80 and the first inner surface S1, and the tip of the protrusion 80 is not constrained by the inner surface of the internal space 10G, so that even if stress is applied to the corners of the internal space 10G when stress such as bending is applied to the sensor element 10, the stress can be released at the tip of the protrusion 80. As a result, cracks due to stress concentration at the corners of the internal space 10G can be suppressed. In this example, a gap G2 is formed between the tip of the protrusion 80 and the first inner surface S1, so that the tip of the protrusion 80 forms a free end 80F. The gap G2 is also part of the internal space 10G. In this example, protrusions 80 are formed at the corners on both ends of the first inner surface S1.

[0036] The material constituting the protrusion 80 is, for example, ceramic, and preferably contains a ceramic material that is different from the ceramic material that is the main component constituting the wall surface of the internal space 10G. Here, "main component" refers to a component that accounts for more than 50 mass%. When the protrusion 80 is mainly composed of ZrO2, ZrO2 has high strength and undergoes a phase transition and increases in volume in response to an external force, further suppressing cracks due to stress concentration. In this case, the dense layers 115, 118, 118B and the porous layer 114B that form the wall surfaces of the internal space 10G can be exemplified by compositions containing more than 50 mass% of Al2O3.

[0037] In this example, the internal space 10G is connected to the air inlet port 10h. By forming the corners of the first inner surface S1 as the protrusions 80 as described above, the volume of the internal space 10G is increased compared to when the material of the protrusions 80 extends over the entire surface of the first inner surface S1 instead of the protrusions 80, and more air can be introduced.

[0038] Furthermore, when the protrusion 80 is porous, the volume of the internal space 10G that the protrusion 80 occupies in the internal space 10G is smaller than when the internal space 10G is solid, and the effective volume of the internal space 10G is increased. The porosity of the protrusions 80 is preferably 16% or more, and more preferably 35% or more. The upper limit of the porosity of the protrusions 80 is, for example, 75%. The porosity can be calculated by taking a cross-sectional SEM image of the protrusions and estimating the ratio of the area of the pores to the area of the protrusions within the field of view.

[0039] Furthermore, as shown in Figure 5, in this example, one electrode 112 of a pair of electrodes 112, 113 constituting the cell (Ip1 cell) 110 is arranged in a position extending from the second inner surface S2 opposite the first inner surface S1 toward the outer surface of the sensor element 10 (the lower side of Figure 5). In this way, the airflow in the internal space 10G is less likely to be disturbed on the second inner surface S2 side, and the sensor output is more stable, compared to when the electrode 112 is disposed on the first inner surface S1 side where the protrusion 80 is present.

[0040] Here, the detection of NOx concentration by the gas sensor 1 of this embodiment will be briefly described. The solid electrolyte bodies 111e, 121e, and 131e of the sensor element 10 are heated and activated as the temperature of the heater pattern 164 rises, thereby causing 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 measuring chamber 150 while the flow rate is restricted by the first porous body 151. At this time, a weak current Icp is flowing through the Vs cell 120 from the electrode 123 side to the electrode 122 side. As a result, oxygen in the exhaust gas can receive electrons from the electrode 122 in the first measuring chamber 150, which is the negative electrode, and become oxygen ions, which flow through the solid electrolyte body 121 and migrate into the reference oxygen chamber 170. In other words, the current Icp flowing between the electrodes 122 and 123 sends oxygen from the first measuring chamber 150 into the reference oxygen chamber 170.

[0041] If the oxygen concentration of the exhaust gas introduced into the first measuring chamber 150 is lower than a predetermined value, current Ip1 is passed through the Ip1 cell 110 so that the electrode 112 side becomes negative, and oxygen is pumped into the first measuring chamber 150 from outside the sensor element 10. On the other hand, if the oxygen concentration of the exhaust gas introduced into the first measuring chamber 150 is higher than a predetermined value, current Ip1 is passed through the Ip1 cell 110 so that the electrode 113 side becomes negative, and oxygen is pumped out of the first measuring chamber 150 to outside the sensor element 10.

[0042] 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. NOx in the exhaust gas that has come into contact with the electrode 133 in the second measuring 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 the decomposed oxygen becomes oxygen ions that flow through the solid electrolyte body 131 and move into the reference oxygen chamber 170. At this time, the residual oxygen that was left behind in the first measuring chamber 150 also moves into the reference oxygen chamber 170 by the Ip2 cell 130. As a result, a current derived from NOx and a current derived from the residual oxygen flow through the Ip2 cell 130. The oxygen that moves into the reference oxygen chamber 170 is released to the outside (atmosphere) through the Vs+ electrode 123 and Vs lead, and the Ip2+ electrode 132 and Ip2+ lead, which are in contact with the inside of the reference oxygen chamber 170. For this reason, the Vs+ lead and Ip2+ lead are porous.

[0043] Here, because the concentration of residual oxygen left unpumped in the first measuring chamber 150 is adjusted to a predetermined value as described above, the current derived from that residual oxygen can be considered to be approximately constant and is little affected by fluctuations in the current derived from NOx, so that the current flowing through the Ip2 cell 130 is 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.

[0044] In this embodiment, an alumina insulating layer 119 is formed on the rear surface of the insulating layer 111s in a region other than the Ip1-electrode 113, and the Ip1-electrode 113 is in contact with the solid electrolyte body 111e through a through-hole 119b (see FIG. 4) that penetrates the alumina insulating layer 119 in the stacking direction.

[0045] Furthermore, in this embodiment, an alumina insulating layer 128 is formed on the surface of the insulating layer 121s in a region other than the Vs-electrode 122, and the Vs-electrode 122 is in contact with the solid electrolyte body 121e through a through-hole (not shown) that penetrates the alumina insulating layer 128 in the stacking direction. Furthermore, an alumina insulating layer 129 is formed on the rear surface of the insulating layer 121s in a region other than the Vs+ electrode 123, and the Vs+ electrode 123 is in contact with the solid electrolyte body 121e through a through-hole (not shown) that penetrates the alumina insulating layer 129 in the stacking direction.

[0046] Furthermore, in this embodiment, an alumina insulating layer 138 is formed on the surface of the insulating layer 131s in a region excluding the Ip2+ electrode 132, and the Ip2+ electrode 132 contacts the solid electrolyte body 131e through a through-hole (not shown) that penetrates the alumina insulating layer 138 in the stacking direction. Furthermore, an alumina insulating layer 138 is formed on the surface of the insulating layer 131s in a region excluding the Ip2- electrode 133, and the electrode 133 contacts the solid electrolyte body 131e through a through-hole (not shown) that penetrates the alumina insulating layer 138 in the stacking direction.

[0047] Next, an example of a method for manufacturing a sensor element according to an embodiment of the present invention will be described with reference to Fig. 6. Fig. 6 is a partially enlarged view showing the sensor element 10 near the internal space 10G. First, as shown in Fig. 6(a), porous layer paste 114Bx is applied to a predetermined position along with the green sheets and pastes of the other ceramic layers shown in Fig. 5. Then, first dense layer green sheet 118x, which has a hollowed-out portion that will become internal space 10G, is laminated on porous layer paste 114Bx. Furthermore, a burnable sheet Cp containing carbon is embedded in the portion of first dense layer green sheet 118x that will become internal space 10G. In addition, at the boundary between the first dense layer green sheet 118x and the burn-dissipating sheet Cp, a ceramic-containing paste 181x is applied in advance to the area between the porous layer paste 114Bx and the first dense layer green sheet 118x and the burn-dissipating sheet Cp. This paste 181x prevents cracks from occurring between the first dense layer green sheet 118x and the burn-away sheet Cp during firing.

[0048] Furthermore, a paste 80x for protrusions is applied to the entire upper surface of the burn-dissipating sheet Cp and to the upper surface of the boundary between the burn-dissipating sheet Cp and the green sheet 118x for the first dense layer. Here, since the thickness of the burn-off sheet Cp is thinner than the thickness of the green sheet 118x for the first dense layer, the paste 80x for the protrusions rises in a step from the boundary between the burn-off sheet Cp and the green sheet 118x for the first dense layer toward the upper surface of the burn-off sheet Cp.

[0049] Next, as shown in Fig. 6(b), the paste 80x for protrusions and the central portion R of the burn-off sheet Cp are hollowed out. As shown in Fig. 2, in this example, the burn-off sheet Cp, which becomes the internal space 10G when viewed from above, has a long and narrow rectangular shape (strip shape), and the central portion R is also a rectangle smaller than the burn-off sheet Cp.

[0050] Next, as shown in FIG. 6(c), a second dense layer green sheet 115x is laminated on the burn-off sheet Cp and the first dense layer green sheet 118x. Here, since the protrusion paste 80x falls with a step on the upper surface of the burnable sheet Cp, a gap G is formed near the central portion R between the second dense layer green sheet 115x and the protrusion paste 80x.

[0051] Next, as shown in FIG. 6(d), when the entire assembly is fired, the burnable sheet Cp is burned away, forming an internal space 10G, and the sensor element 10 is completed. Here, since there is a gap G between the second dense layer green sheet 115x and the protrusion paste 80x, the tip of the protrusion 80 becomes a free end 80F as it is fired, and extends toward the internal space 10G.

[0052] It goes without saying that the present invention is not limited to the above-described embodiments, but covers various modifications and equivalents that fall within the spirit and scope of the present invention. The internal space of the sensor element may be an air gap, such as an air inlet or a measuring chamber. The shape of the internal space is not limited. The shape of the protrusion is not limited. Furthermore, the present invention is applicable 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, but it goes without saying that the present invention is not limited to these applications and covers various modifications and equivalents that fall 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 a gas to be measured, an HC sensor (HC sensor element) that detects the HC concentration, etc. The shape of the cross section of the internal space S1 perpendicular to the axis O direction is not limited, but may be rectangular, for example. [Explanation of symbols]

[0053] 1 Gas sensor 10 Sensor element 10G internal space 10H Atmospheric inlet 20 Metal body 80 Protrusion 110 cells 112, 113 Pair of electrodes 112 One electrode AX Longitudinal direction (axis) S1 First inner surface S2 Second inner surface G2 void

Claims

1. A plate-shaped sensor element extending in an axial direction and having an internal space, When a cross section of the internal space is viewed perpendicular to the axial direction, a protrusion extending from a corner of a first inner surface of the internal space that is closest to an outer surface of the sensor element is formed at the corner toward the internal space, The sensor element is characterized in that a gap is formed between the tip of the protrusion and the first inner surface.

2. The protrusion is made of ZrO ２ 2. The sensor element according to claim 1, wherein the main component is

3. 3. The sensor element according to claim 1, wherein the internal space communicates with an air inlet.

4. 3. The sensor element according to claim 1, wherein one of a pair of electrodes constituting a cell is arranged in a region extending from a second inner surface opposite the first inner surface toward an outer surface of the sensor element.

5. 3. The sensor element according to claim 1, wherein the protrusion is porous.

6. A gas sensor comprising a plate-shaped sensor element and a metal shell that holds the sensor element, A gas sensor using the sensor element according to claim 1 or 2 as the sensor element.

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