Sensor element and gas sensor

Abstract

The invention provides a sensor element and a gas sensor, which suppress cracks caused by stress concentration in corners of an internal space. In a plate-shaped sensor element (10) extending in the axial (AX) direction and having an internal space (10G), when a cross section perpendicular to the axial direction of the internal space is observed, a protruding portion (80) extending from a corner portion toward the internal space is formed at the corner portion of a first inner surface (S1) closest to the outer surface of the sensor element in the internal space. A gap (G2) is formed between the front end of the protruding part and the first inner surface.

Description

Technical Field

[0001] The present invention relates to a sensor element and a gas sensor suitable for detecting the concentration of a specific gas contained in combustion gas or exhaust gas of, for example, a burner or an internal combustion engine. Background Art

[0002] Conventionally, a gas sensor has been used to detect the concentration of a specific component (such as oxygen) in the exhaust gas of an internal combustion engine. As such a gas sensor, the following structure is known: it has a sensor element inside itself, the sensor element is a plate-like shape in which a plurality of ceramic layers are laminated, and has a solid electrolyte body and a pair of electrodes disposed on the solid electrolyte body, and one of the electrodes faces an air (atmosphere) introduction hole (see Patent Document 1) that opens inside the element. This atmosphere introduction port communicates with the internal space of the element.

[0003] Moreover, when forming the internal space, a paste containing burnable carbon is used, but due to the shrinkage during the burning out of this paste, cracks sometimes occur from the corners of the internal space. Therefore, in order to suppress such thermal cracks, in the technique of Patent Document 1, a ceramic layer is interposed at the periphery of the internal space.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2021-51058 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] In addition, as a problem different from the above thermal cracks, if an internal space is provided in the sensor element, when a load is applied to the sensor element, stress may concentrate on the corners of the internal space and cracks may occur.

[0009] Therefore, an object of the present invention is to provide a sensor element and a gas sensor that suppress cracks caused by stress concentration at the corners of the internal space.

[0010] Means for Solving the Problems

[0011] To solve the above problems, the sensor element of the present invention is a plate-like sensor element that extends in the axial direction and has an internal space, and is characterized in that when observing a cross-section of the internal space perpendicular to the axial direction, a protrusion extending from the corner into the internal space is formed at the corner of the first inner surface closest to the outer surface of the sensor element in the internal space, and a gap is formed between the tip of the protrusion and the first inner surface.

[0012] According to this sensor element, a gap is formed between the front end of the protruding portion and the first inner surface, and the front end of the protruding portion is not constrained by the inner surface of the internal space. Therefore, when stress such as bending is applied to the sensor element, even if stress is applied to the corner of the internal space, the stress can be released by the front end of the protruding portion. As a result, cracks caused by stress concentration at the corner of the internal space can be suppressed.

[0013] In the sensor element of the present invention, the protruding portion may be mainly composed of ZrO2.

[0014] If the protruding portion is mainly composed of ZrO2, ZrO2 has high strength and undergoes a phase change and volume increase with respect to external force, so that cracks caused by stress concentration can be further suppressed.

[0015] In the sensor element of the present invention, the above internal space may also communicate with the air inlet.

[0016] According to this sensor element, by making the corner of the first inner surface a protruding portion, compared with the case where the material of the protruding portion extends over the entire surface of the first inner surface instead of the protruding portion, the volume of the internal space becomes larger and more air can be introduced.

[0017] In the sensor element of the present invention, it may also be that one of a pair of electrodes constituting a battery is disposed at a portion from the second inner surface facing the first inner surface toward the outer surface of the sensor element.

[0018] According to this sensor element, compared with the case where the electrode is disposed on the first inner surface side where the protruding portion exists, on the second inner surface side, the air flow in the internal space is less likely to be disturbed and the sensor output is stable.

[0019] In the sensor element of the present invention, it may also be that the protruding portion is porous.

[0020] If the protruding portion is porous, compared with the case where the protruding portion is solid, the volume occupied by the protruding portion in the internal space becomes smaller and the effective volume of the internal space increases.

[0021] The gas sensor of the present invention includes the sensor element and a main body fitting for holding the sensor element.

[0022] Advantages of the Invention

[0023] According to the present invention, a sensor element and a gas sensor in which cracks caused by stress concentration at the corner of the internal space are suppressed can be obtained. Brief Description of the Drawings

[0024] Figure 1 It is a cross-sectional view along the length direction of the gas sensor (NOx sensor) according to an embodiment of the present invention.

[0025] Figure 2 It is a perspective view of the sensor element.

[0026] Figure 3 It is a cross-sectional view taken along line B-B of Figure 2 .

[0027] Figure 4 It is an exploded perspective view of the sensor element.

[0028] Figure 5 It is a cross-sectional view taken along line C-C of Figure 2 .

[0029] Figure 6 It is a process chart showing an example of the manufacturing method of the sensor element according to an embodiment of the present invention. Detailed Embodiment

[0030] Hereinafter, embodiments of the present invention will be described.

[0031] Figure 1 It is a longitudinal cross-sectional view of the gas sensor (NOx sensor) 1 according to an embodiment of the present invention (a cross-sectional view cut along the length direction of the axis AX), Figure 2 It is a perspective view of the sensor element 10, Figure 3 It is a cross-sectional view taken along line B-B (axis AX) of Figure 2 , Figure 4 It is an exploded perspective view of the sensor element 10, Figure 5 It is a cross-sectional view taken along line C-C (a line orthogonal to the axis AX) of Figure 2 .

[0032] In addition, the direction along the axis AX of the sensor element (axis direction) is appropriately referred to as the "length direction". The "width direction" of the sensor element is a direction perpendicular to the "length direction (axis direction)".

[0033] The gas sensor 1 includes a sensor element 10 capable of detecting the concentration of a specific gas (NOx) in the exhaust gas as the gas to be measured, and is a NOx sensor used by being mounted on an exhaust pipe (not shown) of an internal combustion engine. The gas sensor 1 includes a cylindrical main fitting 20 having a threaded portion 21 formed at a predetermined position on the outer surface for fixing to the exhaust pipe. The sensor element 10 is in the shape of an elongated plate extending in the direction of the axis AX and is held inside the main fitting 20.

[0034] More specifically, the gas sensor 1 includes: a holding member 60 having an insertion hole 62 into which the rear end portion 10k of the sensor element 10 (the upper end portion in Figure 1 ) is inserted; and six terminal members held inside the holding member 60. In addition, inFigure 1 Only two of the six terminal components are illustrated (specifically, terminal components 75 and 76).

[0035] A total of six electrode terminal portions 13 to 18, which are rectangular in plan view, are formed at the rear end portion 10k of the sensor element 10 (only electrode terminal portions 14 and 17 are illustrated in Figure 1 ). The electrode terminal portions 13 to 18 are elastically abutted against the above-described terminal components and electrically connected. For example, the element abutting portion 75b of the terminal component 75 is elastically abutted against the electrode terminal portion 14 and electrically connected. In addition, the element abutting portion 76b of the terminal component 76 is elastically abutted against the electrode terminal portion 17 and electrically connected.

[0036] Moreover, different lead wires 71 are electrically connected to the six terminal components (such as terminal components 75 and 76) respectively. For example, as Figure 1 shown, the core wire of the lead wire 71 is pressed and held by the lead wire holding portion 77 of the terminal component 75. In addition, the core wire of the other lead wire 71 is pressed and held by the lead wire holding portion 78 of the terminal component 76.

[0037] In addition, on one of the main surfaces of the rear end portion 10k of the sensor element 10, an atmospheric introduction port 10h is opened at a position closer to the front end side than the electrode terminal portions 13 to 15 and closer to the rear end side than a ceramic sleeve 45 to be described later (see Figure 2 ). The atmospheric introduction port 10h is disposed in the insertion hole 62 of the holding member 60.

[0038] Thereby, the reference atmosphere sealed inside the outer cylinder 51 to be described later is introduced into the sensor element 10 from the atmospheric introduction port 10h.

[0039] The main body fitting 20 is a cylindrical member having a through hole 23 penetrating in the axial direction of the axis AX. The main body fitting 20 has a shelf portion 25 that forms a part of the through hole 23 in a form protruding radially inward. The main body fitting 20 holds the sensor element 10 in the through hole 23 in a state where the front end portion 10s of the sensor element 10 protrudes to the outside of its own front end side (downward in Figure 1 ) and the rear end portion 10k of the sensor element 10 protrudes to the outside of its own rear end side (upward in Figure 1 ).

[0040] In addition, a ring-shaped ceramic holding member 42, two talc rings 43 and 44 filled with talc powder in a ring shape, and a ceramic sleeve 45 are disposed inside the through hole 23 of the main body fitting 20. Specifically, in a state of surrounding the radial periphery of the sensor element 10, the ceramic holding member 42, the talc rings 43 and 44, and the ceramic sleeve 45 are arranged in order from the front end side in the axial direction of the main body fitting 20 ( Figure 1 the lower end side inFigure 1 The upper end side of the middle portion is arranged overlappingly.

[0041] In addition, a metal cup 41 is arranged between the ceramic holder 42 and the shelf portion 25 of the shell metal fitting 20. In addition, a fastening ring 46 is arranged between the ceramic sleeve 45 and the fastening portion 22 of the shell metal fitting 20. In addition, the fastening portion 22 of the shell metal fitting 20 is fastened in a manner that the ceramic sleeve 45 is pressed toward the front end side via the fastening ring 46.

[0042] An outer protector 31 and an inner protector 32 made of metal (specifically, stainless steel) having a plurality of holes are attached by welding to the front end portion 20b of the metal 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 metal shell 20. The outer cylinder 51 is in a cylindrical shape extending in the axis AX direction and surrounds the sensor element 10.

[0043] The holding member 60 is made of an insulating material (specifically, alumina) and is a cylindrical member having an insertion hole 62 that penetrates along the axis AX direction. The six terminal members (terminal members 75, 76, etc.) described above are arranged in the insertion hole 62 (see Figure 1 ). A flange portion 65 protruding radially outward is formed at the rear end portion of the retaining member 60. The retaining member 60 is retained by the internal support member 53 in such a manner that the flange portion 65 abuts against the internal support member 53. It should be noted that the internal support member 53 is retained by the outer tube 51 through the fastening portion 51g fastened radially inward in the outer tube 51.

[0044] An insulating member 90 is disposed on the rear end face 61 of the holding member 60. The insulating member 90 is made of an electrically insulating material (specifically, alumina) and is cylindrical. A total of six through holes 91 are formed in the insulating member 90, which penetrate along the axis AX direction. The lead wire holding portion (lead wire holding portion 77, 78, etc.) of the terminal member described above is disposed in the through hole 91.

[0045] In addition, at the rear end portion in the axial direction of the outer cylinder 51 (at Figure 1On the radially inner side of the rear end opening 51c (the upper end portion in the middle) is disposed an elastic sealing member 73 made of fluororubber. Six cylindrical insertion holes 73c extending in the direction of the axis AX are formed in total in the elastic sealing member 73. Each insertion hole 73c is formed by the insertion hole surface 73b (cylindrical inner wall surface) of the elastic sealing member 73. A lead wire 71 is inserted through 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 sealing member 73. The elastic sealing member 73 is elastically compressed and deformed in the radial direction by fastening the rear end opening 51c of the outer cylinder 51 to the radially inner side, whereby the insertion hole surface 73b is brought into close contact with the outer peripheral surface 71b of the lead wire 71, and the space between the insertion hole surface 73b and the outer peripheral surface 71b of the lead wire 71 is sealed watertightly.

[0046] On the other hand, as Figure 3 shown, the sensor element 10 includes solid electrolyte bodies 111e, 121e, 131e respectively formed in plate-like insulating layers 111s, 121s, 131s and insulators 140, 145 disposed between them, and has a structure in which they are stacked in the stacking direction. Further, in the sensor element 10, a heater 161 is stacked on the back side of the solid electrolyte body 131e. The heater 161 includes plate-like insulators 162, 163 mainly made of alumina and a heater pattern 164 (mainly made of Pt) buried therebetween.

[0047] In addition, the solid electrolyte bodies 111e, 121e, 131e are each substantially rectangular and are respectively formed in rectangular openings provided on the front end side of the insulating layers 111s, 121s, 131s. Here, in this example, the solid electrolyte bodies 111e, 131e transfer sheet-like members to predetermined positions, but the materials of the solid electrolyte bodies 111e, 131e may also be buried in the openings.

[0048] The solid electrolyte bodies 111e, 121e, 131e are made of zirconia as a solid electrolyte and have oxygen ion conductivity. A porous Ip1+ electrode 112 is provided on the surface side of the solid electrolyte body 111e. In addition, a porous Ip1- electrode 113 is provided on the back side of the solid electrolyte body 111e. Further, the surface of the Ip1+ electrode 112 is covered with a porous layer 114B.

[0049] In addition, an Ip1+ lead wire 116 is connected to the Ip1+ electrode 112 (refer to Figure 2 , Figure 4 ). In addition, the Ip1- electrode 113 is connected to an Ip1- lead wire 117 ( Figure 4 ).

[0050] In addition, as Figure 4As shown, 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 front end side of the third dense layer 118B. Moreover, a porous layer 114B is filled in the opening 118Bh.

[0051] In addition, as Figure 4 shown, a non-porous first dense layer 118 having an internal space 10G and made of alumina or the like is laminated on the surface of the third dense layer 118B. A part of the porous layer 114B protrudes from the internal space 10G. Moreover, the side surface of the Ip1+ electrode 112 is covered by the third dense layer 118B and is surrounded by the respective dense layers 115, 118, 118B.

[0052] The internal space 10G extends straight from near the porous layer 114B to a portion communicating with the air inlet 10h. Moreover, a through hole for conducting with the electrode terminal portions 13 to 15 is provided in the first dense layer 118 on the rear end side of the internal space 10G.

[0053] In addition, the dimension in the width direction of the air inlet 10h is shorter than that of the internal space 10G (refer to Figure 5 ).

[0054] Moreover, a non-porous second dense layer 115 made of alumina or the like is laminated on the surface of the first dense layer 118 to enclose the internal space 10G. Thus, the Ip1+ electrode 112 covered by the porous layer 114B is disposed in the internal space 10G surrounded by the dense layers 115, 118, thereby preventing contact with the gas to be measured.

[0055] Moreover, the position of the second dense layer 115 overlapping with the rear end of the internal space 10G is opened in a rectangular shape to form an air inlet 10h, and the internal space 10G communicates with the air inlet 10h. The air inlet 10h is opened at a position on the rear end side of a first porous body 151 to be described later, and can introduce air rather than exhaust gas. Thus, the Ip1+ electrode 112 is exposed to the air introduced from the air inlet 10h via the porous layer 114B.

[0056] The solid electrolyte body 111e and the electrodes 112, 113 constitute an Ip1 cell 110 (pump cell). The Ip1 cell 110 performs oxygen extraction and pumping (so-called oxygen pump) between the atmosphere in contact with the electrode 112 (the air in the internal space 10G different from the gas to be measured outside the sensor element 10) and the atmosphere in contact with the electrode 113 (the atmosphere in a first measurement chamber 150 to be described later, i.e., the gas to be measured outside the sensor element 10) according to the pump current Ip1 flowing between the electrodes 112, 113.

[0057] The solid electrolyte body 121e is arranged so as to face the solid electrolyte body 111e in the stacking direction with an insulator 140 therebetween. On the surface side of the solid electrolyte body 121e (the upper surface side in Figure 2 ), a porous Vs-electrode 122 is provided. Further, on the back side of the solid electrolyte body 121e ( Figure 2 the lower surface side in

[0058] ), a porous Vs+ electrode 123 is provided. Figure 2 、 Figure 4 ), a first measurement chamber 150 serving as an internal space of the sensor element is formed between the solid electrolyte body 111e and the solid electrolyte body 121e. The first measurement chamber 150 is the internal space where the gas to be measured (exhaust gas) flowing in the exhaust passage is first introduced into the sensor element 10, and is communicated with the outside of the sensor element 10 through a first porous body (diffusion resistance portion) 151 having air permeability and water permeability (refer to

[0059] ). The first porous body 151 is provided on the side of the first measurement chamber 150 as a separator from the outside of the sensor element 10, and restricts the flow rate (diffusion rate) of the exhaust gas into the first measurement chamber 150 per unit time. Figure 2 On the rear end side of the first measurement chamber 150 (

[0060] the right side in

[0061] ), a second porous body 152 that restricts the flow rate of the exhaust gas per unit time is provided as a separator between the first measurement chamber 150 and a second measurement chamber 160 described later. Figure 2 The solid electrolyte body 121e and the electrodes 122 and 123 constitute a Vs battery (detection battery) 120. The Vs battery 120 mainly generates an electromotive force based on the oxygen partial pressure difference between the atmospheres (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) separated by the solid electrolyte body 121e.

[0062] A reference oxygen chamber 170 serving as an isolated small space is formed between the Ip2+ electrode 132 and the Vs+ electrode 123. The reference oxygen chamber 170 is constituted by an opening 145b formed in the insulator 145. Further, a ceramic porous body is disposed on the Ip2+ electrode 132 side in the reference oxygen chamber 170.

[0063] In addition, a second measurement chamber 160, which is 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 that penetrates the insulator 145 in the stacking direction, an opening 125 that penetrates the solid electrolyte body 121 in the stacking direction, and an opening 141 that penetrates the insulator 140 in the stacking direction.

[0064] The first measurement chamber 150 and the second measurement chamber 160 communicate with each other through a second porous body 152 having air permeability and water permeability. Therefore, the second measurement chamber 160 communicates with the outside of the sensor element 10 through the first porous body 151, the first measurement chamber 150, and the second porous body 152.

[0065] 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 causes oxygen (oxygen ions) derived from NOx decomposed in the second measurement chamber 160 to move through the solid electrolyte body 131e to the reference oxygen chamber 170. 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 electrode 132 and the electrode 133.

[0066] Next, Figure 5 the characteristic part of the present invention will be described.

[0067] As Figure 5 shown, the cross - section of the internal space 10G forming the internal space perpendicular to the axis AX direction is rectangular.

[0068] And, when observing Figure 5 the cross - section, a protrusion 80 extending from the corner to the inside of the internal space 10G is formed at the corner of the first inner surface S1 closest to the outer surface of the sensor element 10 in the internal space 10G. And a gap G2 is formed between the front end of the protrusion 80 and the first inner surface S1.

[0069] In this way, a gap G2 is formed between the front end of the protrusion 80 and the first inner surface S1, and the front end of the protrusion 80 is not restricted by the inner surface of the internal space 10G. Therefore, when stress such as bending is applied to the sensor element 10, even if stress is applied to the corner of the internal space 10G, the stress can be released through the front end of the protrusion 80. As a result, cracks caused by stress concentration at the corner of the internal space 10G can be suppressed.

[0070] In addition, in this example, by forming a gap G2 between the front end of the protrusion 80 and the first inner surface S1, the front end of the protrusion 80 becomes a free end 80F. Also, the gap G2 is a part of the internal space 10G.

[0071] In addition, in this example, projecting portions 80 are respectively formed at the corner portions at both ends of the first inner surface S1.

[0072] The material constituting the projecting portion 80 is, for example, ceramics, and preferably has a main component of a ceramic material different from the ceramic material of the main component of the wall surface constituting the internal space 10G. Here, the "main component" means a component exceeding 50% by mass.

[0073] If the projecting portion 80 has ZrO2 as the main component, ZrO2 has high strength and undergoes a phase change and volume increase with respect to an external force, so that cracks caused by stress concentration can be further suppressed. In this case, as the dense layers 115, 118, 118B and the porous layer 114B constituting the wall surface of the internal space 10G, a composition containing more than 50% by mass of Al2O3 can be exemplified.

[0074] In addition, in this example, the internal space 10G forming the internal space communicates with the air inlet 10h. As described above, by providing the corner portion of the first inner surface S1 as the projecting portion 80, the volume of the internal space 10G becomes larger than the case where the material of the projecting portion 80 extends over the entire surface of the first inner surface S1 instead of the projecting portion 80, and more air can be introduced.

[0075] In addition, if the projecting portion 80 is porous, the volume occupied by the projecting portion 80 in the internal space 10G becomes smaller than the case where the projecting portion 80 is solid, and the effective volume of the internal space 10G increases.

[0076] The porosity of the projecting portion 80 is preferably 16% or more, more preferably 35% or more. The upper limit of the porosity of the projecting portion 80 is, for example, 75%. The porosity can be calculated by photographing a cross-sectional SEM image of the projecting portion and based on the ratio of the area of the pores in the field of view to the area of the projecting portion.

[0077] Moreover, as Figure 5 shown, in this example, one of the pair of electrodes 112 and 113 constituting the battery (Ip1 battery) 110 is disposed at a portion from the second inner surface S2 facing the first inner surface S1 toward the outer surface of the sensor element 10 ( Figure 5 lower side).

[0078] In this way, compared with the case where the electrode 112 is disposed on the first inner surface S1 side where the projecting portion 80 exists, the air flow in the internal space 10G is less likely to be disturbed on the second inner surface S2 side, and the sensor output is stable.

[0079] Here, the NOx concentration detection of the gas sensor 1 of the present embodiment will be briefly described.

[0080] The solid electrolyte bodies 111e, 121e, and 131e of the sensor element 10 are heated and activated as the heater pattern 164 is heated. As a result, the Ip1 cell 110, the Vs cell 120, and the Ip2 cell 130 operate.

[0081] The exhaust gas flowing in the exhaust passage (not shown) is introduced into the first measurement chamber 150 while being restricted by the flow rate of the first porous body 151. At this time, in the Vs cell 120, a weak current Icp flows from the electrode 123 side to the electrode 122 side. Therefore, oxygen in the exhaust gas can receive electrons from the electrode 122 in the first measurement chamber 150, which becomes the negative electrode side, becomes an oxygen ion, flows in the solid electrolyte body 121, and moves into the reference oxygen chamber 170. That is, by flowing the current Icp between the electrodes 122 and 123, the oxygen in the first measurement chamber 150 is sent into the reference oxygen chamber 170.

[0082] When the oxygen concentration of the exhaust gas introduced into the first measurement chamber 150 is lower than a predetermined value, a current Ip1 is caused to flow through the Ip1 cell 110 with the electrode 112 side as the negative electrode, and oxygen is drawn into the first measurement chamber 150 from the outside of the sensor element 10. On the other hand, when the oxygen concentration of the exhaust gas introduced into the first measurement chamber 150 is higher than a predetermined value, a current Ip1 is caused to flow through the Ip1 cell 110 with the electrode 113 side as the negative electrode, and oxygen is sucked out from the first measurement chamber 150 to the outside of the sensor element 10.

[0083] In this way, the exhaust gas with the oxygen concentration adjusted in the first measurement chamber 150 is introduced into the second measurement chamber 160 through the second porous body 152. NOx in the exhaust gas in contact with the electrode 133 in the second measurement chamber 160 is decomposed (reduced) into nitrogen and oxygen on the electrode 133 by applying a voltage Vp2 between the electrodes 132 and 133. The decomposed oxygen becomes an oxygen ion, flows in the solid electrolyte body 131, and moves into the reference oxygen chamber 170. At this time, the residual oxygen remaining after being extracted in the first measurement chamber 150 also moves into the reference oxygen chamber 170 through the Ip2 cell 130 in the same manner. As a result, a current from the NOx and a current from the residual oxygen flow through the Ip2 cell 130. In addition, 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 wire in contact with the reference oxygen chamber 170 and the Ip2+ electrode 132 and the Ip2+ lead wire. Therefore, the Vs+ lead wire and the Ip2+ lead wire are porous.

[0084] Here, the concentration of the residual oxygen extracted in the first measurement chamber 150 is adjusted to a predetermined value as described above. Therefore, the current derived from this residual oxygen can be regarded as substantially constant, and the influence on the variation of the current derived from NOx is small. 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 this current value.

[0085] In addition, in the present embodiment, an alumina insulating layer 119 is formed at a portion on the back surface of the insulating layer 111s 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 (refer to Figure 4 ) that penetrates the alumina insulating layer 119 in the stacking direction.

[0086] Furthermore, in the present embodiment, an alumina insulating layer 128 is formed at a portion on the surface of the insulating layer 121s 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.

[0087] Furthermore, an alumina insulating layer 129 is formed at a portion on the back surface of the insulating layer 121s 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.

[0088] Furthermore, in the present embodiment, an alumina insulating layer 138 is formed at a portion on the surface of the insulating layer 131s other than the Ip2 + electrode 132, and the Ip2 + electrode 132 is in contact with 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 also formed at a portion on the surface of the insulating layer 131s other than the Ip2 - electrode 133, and the electrode 133 is in contact with the solid electrolyte body 131e through a through - hole (not shown) that penetrates the alumina insulating layer 138 in the stacking direction.

[0089] Next, with reference to Figure 6 , an example of the manufacturing method of the sensor element according to the embodiment of the present invention will be described. In addition, Figure 6 is a partial enlarged view of the sensor element 10 near the internal space 10G.

[0090] First, as shown in (a) of Figure 6 , the porous layer paste 114Bx and Figure 5The green sheets, pastes, etc. of other ceramic layers are coated at a predetermined position. And the first dense layer green sheet 118x with the hollowed-out part that becomes the internal space 10G is laminated on the porous layer paste 114Bx. And a carbon-containing burnable sheet Cp is buried in the part that becomes the internal space 10G in the first dense layer green sheet 118x.

[0091] In addition, in the part between the boundary of the first dense layer green sheet 118x and the burnable sheet Cp and the porous layer paste 114Bx, a paste 181x containing ceramics is pre-coated in a manner that straddles the first dense layer green sheet 118x and the burnable sheet Cp.

[0092] This paste 181x inhibits the generation of cracks between the first dense layer green sheet 118x and the burnable sheet Cp during firing.

[0093] And a protrusion paste 80x is coated on the entire upper surface of the burnable sheet Cp and the upper surface of the boundary between the burnable sheet Cp and the first dense layer green sheet 118x.

[0094] Here, since the thickness of the burnable sheet Cp is thinner than the thickness of the first dense layer green sheet 118x, the protrusion paste 80x descends stepwise from the boundary between the burnable sheet Cp and the first dense layer green sheet 118x to the upper surface of the burnable sheet Cp.

[0095] Next, as shown in (b) of Figure 6 , the central part R of the protrusion paste 80x and the burnable sheet Cp is hollowed out. As shown in Figure 2 , in this example, when viewed from the upper surface, the burnable sheet Cp that becomes the internal space 10G is an elongated rectangular shape (long strip shape), and the central part R is also a rectangular shape smaller than the burnable sheet Cp.

[0096] Next, as shown in (c) of Figure 6 , the second dense layer green sheet 115x is laminated on the burnable sheet Cp and the first dense layer green sheet 118x.

[0097] Here, since the protrusion paste 80x descends stepwise on the upper surface of the burnable sheet Cp, a gap G is formed between the second dense layer green sheet 115x and the protrusion paste 80x near the central part R.

[0098] Next, as shown in (d) of Figure 6 , when the whole is fired, the burnable sheet Cp is burned out to form the internal space 10G, thus completing the sensor element 10.

[0099] Here, since there is a gap G between the green sheet 115x for the second dense layer and the paste 80x for the protrusion, as the firing progresses, the front end of the protrusion 80 becomes a free end 80F and extends into the internal space 10G.

[0100] The present invention is not limited to the above-described embodiments, and of course encompasses various modifications and equivalents within the spirit and scope of the present invention.

[0101] The internal space of the sensor element only needs to be a void, and examples include an air inlet and various measurement chambers. The shape of the internal space is also not limited.

[0102] The shape of the protrusion is also not limited.

[0103] In addition, the present invention can be applied to at least a sensor element (gas sensor) having a battery (one or more batteries), and can be applied to the NOx sensor element (NOx sensor) of the present embodiment, but is not limited to these uses, and of course also encompasses various modifications and equivalents within the spirit and scope of the present invention. For example, the present invention can also be applied to an oxygen sensor (oxygen sensor element) for detecting the oxygen concentration in the gas to be measured, an HC sensor (HC sensor element) for detecting the HC concentration, and the like.

[0104] The shape of the cross-section of the internal space S1 perpendicular to the axis O direction is not limited, and is, for example, rectangular.

[0105] Explanation of Reference Numerals

[0106] 1 Gas sensor

[0107] 10 Sensor element

[0108] 10G Internal space

[0109] 10h Air inlet

[0110] 20 Main body fitting

[0111] 80 Protrusion

[0112] 110 Battery

[0113] 112, 113 A pair of electrodes

[0114] 112 One electrode

[0115] AX Length direction (axis)

[0116] S1 First inner surface

[0117] S2 Second inner surface

[0118] G2 Void

Claims

1. A sensor element is a plate-shaped sensor element that extends in the axial direction and has an internal space. The sensor element is characterized in that when observing a cross-section perpendicular to the axial direction of the internal space, a protrusion extending from the corner portion into the internal space is formed at a corner portion of the first inner surface closest to the outer surface of the sensor element in the internal space, a gap is formed between the front end of the protrusion and the first inner surface.

2. The sensor element according to claim 1, characterized in that the protrusion is mainly composed of ZrO2.

3. The sensor element according to claim 1 or 2, characterized in that the internal space communicates with an air inlet.

4. The sensor element according to claim 1 or 2, characterized in that one of a pair of electrodes constituting a battery is disposed at a portion from the second inner surface facing the first inner surface toward the outer surface of the sensor element.

5. The sensor element according to claim 1 or 2, characterized in that the protrusion is porous.

6. A gas sensor includes a plate-shaped sensor element and a main body fitting that holds the sensor element. Among them, as the sensor element, the sensor element according to claim 1 or 2 is used.

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