Gas sensor element and gas sensor

Abstract

To provide a gas sensor element that is superior in responsiveness to NO.SOLUTION: A gas sensor element 10 according to the present invention includes an element body 100 in which multiple ceramic sheets 121 or the like are laminated, a pump cell 110 for adjusting the oxygen concentration in a measurement target gas introduced into the element body 100, a detection chamber 160 formed inside the element body 100 in which the measurement target gas is introduced after adjusting the oxygen concentration, and a layered cathode electrode 133 which is housed in the detection chamber 160 and decomposes NO. The relation between the volume V1 of the detection chamber 160 and the volume V2 of the cathode electrode 133 in the gas sensor element 10 satisfies any one of the following conditions (A) and (B). Condition (A): The volume V1 is 0.047 mm3 or more and 0.065 mm3 or less and the volume V2 is 0.030 mm3 or more and 0.059 mm3 or less. Condition (B): The volume V1 is 0.047 mm3 or more and 0.125 mm3 or less and the volume V2 is 0.044 mm3 or more and 0.059 mm3 or less.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a gas sensor element and a gas sensor.

Background Art

[0002] A gas sensor for detecting the concentration of NO contained in the exhaust gas of an internal combustion engine is known. This type of gas sensor is a sensor that utilizes the oxygen ion conductivity of zirconia (ZrO x ) heated to a high temperature, and for the equilibrium reaction of NO with N 2 and O 2 and O 2 , by removing oxygen (O 2 ) to promote the decomposition of NO and measuring the oxygen generated by the decomposition, the concentration of NO x is determined.

[0003] As such a gas sensor, for example, a gas sensor element including a first pump cell, a detection cell, a second pump cell, a first measurement chamber, a second measurement chamber, etc. is known (see, for example, Patent Document 1).

[0004] The first pump cell pumps out or pumps in oxygen in the exhaust gas between the first measurement chamber and the outside (so-called pumping), and adjusts the oxygen concentration in the exhaust gas. By the action of this first pump cell, the oxygen concentration in the first measurement chamber is controlled to be low. The detection cell measures the oxygen concentration in the exhaust gas from which oxygen has been pumped out or pumped in by the first pump cell, and flows a current (first pump current) through the first pump cell so that the output voltage (electromotive force) corresponding to this oxygen concentration becomes constant.

[0005] The exhaust gas in the first measurement chamber whose oxygen concentration is controlled as described above is introduced into the second measurement chamber through a predetermined path in the gas sensor element. The second pump cell removes NO from the exhaust gas introduced into the second measurement chamber xThe concentration is detected. The second pump cell includes a set of electrodes, and one of the electrodes (cathode electrode, Ip2 - electrode) is housed in the second measurement chamber. NO in the exhaust gas introduced into the second space is decomposed into N 2 and O 2 at the electrode in the second measurement chamber. A second pump current flows through the second pump cell to pump out the oxygen generated by this decomposition to the other electrode (anode electrode). Since this second pump current is in a proportional relationship with the NO concentration, by measuring this second pump current, the NO x (NO) concentration in the exhaust gas can be obtained.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In conventional gas sensors, regarding the output waveform of the above - mentioned second pump current, it has been required to shorten its rise time to improve the responsiveness to NO.

[0008] An object of the present invention is to provide a gas sensor element and a gas sensor having excellent responsiveness to NO.

Means for Solving the Problems

[0009] The means for solving the above problems are as follows. That is, <1> An element body part in which a plurality of ceramic sheets are laminated, a pump cell that adjusts the oxygen concentration in a measurement target gas introduced into the element body part, a detection chamber formed inside the element body part, and the measurement target gas after the adjustment of the oxygen concentration is introduced, and a layered cathode electrode that decomposes NO and is housed in the detection chamber. The gas sensor element satisfies any one of the following condition (A) and condition (B) regarding the relationship between the volume V1 of the detection chamber and the volume V2 of the cathode electrode. Condition (A): The volume V1 is 0.047 mm 3 or more and 0.065 mm 3 or less, and the volume V2 is 0.030 mm 3 or more and 0.059 mm 3 or less Condition (B): The volume V1 is 0.047 mm 3 or more and 0.125 mm 3 or less, and the volume V2 is 0.044 mm 3 or more and 0.059 mm 3 or less

[0010] <2> The detection chamber is provided in such a way as to penetrate at least one of the plurality of ceramic sheets in the thickness direction. In the region where the detection chamber penetrates the ceramic sheet, the cross-sectional area of the detection chamber in the plane direction of the ceramic sheet is 0.05 mm 2 or more and 0.35 mm 2 or less. The gas sensor element according to <1> above.

[0011] <3> A solid electrolyte layer that forms part of the element body part and has the cathode electrode formed on its surface, and an anode electrode that is disposed on the surface of the solid electrolyte layer and receives oxygen ions generated at the cathode electrode in response to the decomposition of NO and moves through the solid electrolyte layer. The gas sensor element according to <1> or <2> above.

[0012] <4> A gas sensor including the gas sensor element according to any one of <1> to <3> above.

Advantages of the Invention

[0013] According to the present invention, a gas sensor element and a gas sensor excellent in responsiveness to NO can be provided.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0015] <Embodiment 1> Hereinafter, Embodiment 1 of the present invention will be described with reference to FIGS. 1 to 7. FIG. 1 is a longitudinal sectional view of a gas sensor (NO x sensor) 1 according to Embodiment 1, FIG. 2 is a perspective view of a gas sensor element 10 according to Embodiment 1, FIG. 3 is a cross-sectional view taken along line A-A of FIG. 2, and FIG. 4 is an exploded perspective view of the gas sensor element 10.

[0016] In FIG. 1, the axis AX of the gas sensor 1 is shown as a straight line (dashed-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". Further, 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 in FIG. 1) is referred to as the "rear end side". Also, for convenience of explanation, the upper side of FIGS. 2 to 5 is referred to as the "front side (surface side)" of the gas sensor element 10, and the lower side thereof is referred to as the "back side (back surface side)" of the gas sensor element 10.

[0017] The gas sensor 1 includes a gas sensor element 10 capable of detecting the concentration of NO in the exhaust gas which is the gas to be measured. x This gas sensor 1 is a NO sensor used by being mounted on an exhaust pipe (not shown) of an internal combustion engine, and includes a cylindrical main body fitting 20 in which a screw portion 21 for fixing to the exhaust pipe is formed at a predetermined position on the outer surface. The gas sensor element 10 generally has an elongated plate shape extending along the axis AX direction, and such a gas sensor element 10 is held inside the main body fitting 20. x The gas sensor 1 includes a cylindrical holding member 60 having an insertion hole 62 into which the rear end portion 10k of the gas sensor element 10 is inserted, and six terminal members held inside this holding member 60. In FIG. 1, for convenience of explanation, only two of the six terminal members, i.e., terminal members 75 and 76, are shown.

[0018] As shown in FIG. 2, a total of six electrode terminal portions 13 to 18 having a rectangular shape in plan view are formed at the rear end portion 10k of the gas sensor element 10. In FIG. 1, only the electrode terminal portions 14 and 17 are shown. The aforementioned terminal members are elastically abutted and electrically connected to these electrode terminal portions 13 to 18 respectively. For example, the element abutting portion 75b of the terminal member 75 is elastically abutted and electrically connected to the electrode terminal portion 14, and the element abutting portion 76b of the terminal member 76 is elastically abutted and electrically connected to the electrode terminal portion 17.

[0019]

[0020] ​ In addition, different lead wires 71 are electrically connected to the six terminal members (terminal members 75, 76, etc.), respectively. For example, as shown in FIG. 1, the core wire of the lead wire 71 is caulked and gripped by the lead wire gripping portion 77 of the terminal member 75. Also, the core wire of the other lead wire 71 is caulked and gripped by the lead wire gripping portion 78 of the terminal member 76.

[0021] As shown in FIG. 2, of the two main surfaces 10a and 10b at the rear end portion 10k of the gas sensor element 10, an opening-shaped air inlet 10h is provided at a location on one (front side) main surface 10a that is on the tip side of the electrode terminal portions 13 to 15 and on the rear end side of a ceramic sleeve 45 (see FIG. 1) described later. The air inlet 10h is disposed within the insertion hole 62 of the holding member 60.

[0022] The main body fitting 20 is a cylindrical member having a through hole 23 that penetrates in the axial direction of the axis AX. The main body fitting 20 includes a shelf portion 25 that projects radially inward and forms a part of the through hole 23. The main body fitting 20 holds the gas sensor element 10 within the through hole 23 in a state where the tip portion 10s of the gas sensor element 10 projects to the outside of the tip side (below in FIG. 1) of the main body fitting 20 and the rear end portion 10k of the gas sensor element 10 projects to the outside of the rear end side (above in FIG. 1) of the main body fitting 20.

[0023] Also, inside the through hole 23 of the main body fitting 20, an annular ceramic holder 42, two talc rings 43 and 44 formed by annularly filling talc powder, and a ceramic sleeve 45 are disposed. More specifically, the ceramic holder 42, the talc rings 43 and 44, and the ceramic sleeve 45 are stacked in this order from the tip side to the rear end side of the main body fitting 20 so as to surround the gas sensor element 10 extending in the axial direction of the axis AX.

[0024] A metal cup 41 is disposed between the ceramic holder 42 and the shelf portion 25 of the main fitting 20. Also, a clamping ring 46 is disposed between the ceramic sleeve 45 and the clamping portion 22 of the main fitting 20. Note that the clamping portion 22 of the main fitting 20 is clamped so as to press the ceramic sleeve 45 toward the tip side via the clamping ring 46.

[0025] On the tip portion 20b of the main fitting 20, an external protector 31 and an internal protector 32 made of metal (e.g., stainless steel) having a plurality of holes are attached by welding so as to cover the tip portion 10s of the gas sensor element 10. Also, an outer cylinder 51 is attached by welding to the rear end portion of the main fitting 20. The outer cylinder 51 generally has a cylindrical shape extending in the direction of the axis AX and surrounds the gas sensor element 10.

[0026] The holding member 60 is a cylindrical member made of an insulating material (e.g., alumina) and having an insertion hole 62 penetrating in the direction of the axis AX. In the insertion hole 62, the six terminal members (terminal members 75, 76, etc.) described above are disposed (see FIG. 1). A flange portion 65 protruding radially outward is formed at the rear end portion 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. Note that the internal support member 53 is held by a clamping portion 51g clamped inward in the radial direction of the outer cylinder 51.

[0027] 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 insulating material (e.g., alumina) and generally has a cylindrical shape. A total of six through holes 91 penetrating in the direction of the axis AX are formed in the insulating member 90. In the through holes 91, lead wire holding portions 77, 78, etc. of the terminal members described above are disposed.

[0028] Also, inside the outer cylinder 51, on the radially inner side of the rear end opening 51c disposed on the rear end side, an elastic seal member 73 made of fluororubber is arranged. A total of six cylindrical insertion holes 73c extending in the axial direction of the axis AX are formed in the 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 outside the gas sensor 1 through the insertion hole 73c of the elastic seal member 73. The elastic seal member 73 is elastically compressed and deformed in the radial direction by clamping the rear end opening 51c of the outer cylinder 51 inward in the radial direction, thereby bringing the insertion hole surface 73b into close contact with the outer peripheral surface 71b of the lead wire 71 and sealing the space between the insertion hole surface 73b and the outer peripheral surface 71b of the lead wire 71 in a watertight manner.

[0029] As shown in FIG. 3, the gas sensor element 10 includes an element main body 100 having a plurality of plate-like insulating layers (ceramic sheets) 111s, 121s, 131s, solid electrolytes 111e, 121e, 131e formed therein, and insulators 140, 145 disposed therebetween. The insulators 140, 145 are each made of dense ceramic (for example, alumina). Further, the gas sensor element 10 includes a heater 261 disposed on the back surface side of the solid electrolyte 131e. The heater 261 includes two plate-like insulators 262, 263 mainly made of alumina and a heater pattern 264 embedded therebetween. The heater pattern 264 is made of a film-like pattern mainly made of platinum (Pt).

[0030] Note that the solid electrolytes 111e, 121e, and 131e are each substantially rectangular in plan view. The solid electrolyte 111e is formed so as to overlap an opening 111a provided on the tip side (the left side in FIG. 4) of a plate-shaped insulating layer 111s extending in the direction of the axis AX. The solid electrolyte 121e is formed so as to overlap an opening 121a provided on the tip side (the left side in FIG. 4) of a plate-shaped insulating layer 121s extending in the direction of the axis AX. The solid electrolyte 131e is formed so as to overlap an opening 131a provided on the tip side (the left side in FIG. 4) of a plate-shaped insulating layer 131s extending in the direction of the axis AX. Note that each of the solid electrolytes 111e, 121e, and 131e may be formed so as to be respectively embedded in the corresponding openings 111a, 121, and 131a, or may be formed so as to transfer a separately prepared sheet-like member to a predetermined location.

[0031] The insulators 140 and 145 are made of a fired printed layer having a smaller thickness than an insulating layer (ceramic sheet) 121s or the like.

[0032] The solid electrolytes (solid electrolyte layers) 111e, 121e, and 131e are made of zirconia, which is a solid electrolyte, and have oxygen ion conductivity. A porous Ip1+ electrode 112 is provided on the front surface side of the solid electrolyte 111e. Also, a porous Ip1− electrode 113 is provided on the back surface side of the solid electrolyte 111e. Further, the surface of the Ip1+ electrode 112 is covered with a porous layer 114. Note that an Ip1+ lead 116 is connected to the Ip1+ electrode 112 (see FIGS. 2 and 4). Also, an Ip1− lead 117 (see FIG. 4) is connected to the Ip1− electrode 113.

[0033] As shown in FIG. 4, plate-shaped dense layers 118B extending in the direction of the axis AX are laminated on the surfaces 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 plan view is provided on the tip side of the dense layer 118B. Then, the above-described porous layer 114 is formed so as to fill the opening 118Ba.

[0034] As shown in FIG. 4, on the surface side of the dense layer 118B, a gas-impermeable dense layer 118 made of alumina or the like is disposed while including voids 10G. A part of the porous layer 114 is exposed from the voids 10G. The voids 10G linearly extend from the vicinity of the porous layer 114 to the portion communicating with the air inlet 10h in the plate-shaped dense layer 118 extending in the axial direction of the axis AX. And, in the plate-shaped dense layer 118 extending in the axial direction of the axis AX, through holes for conducting with the electrode terminals 13, 14, and 15 are provided on the rear end side.

[0035] Also, 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 way, the voids 110G are blocked by the dense layer 115.

[0036] An air inlet 10h is formed at a position overlapping with the rear end of the voids 10G extending in the longitudinal direction (axial direction of the axis AX) in the dense layer 115. The air inlet 10h is composed of an opening provided so as to penetrate the dense layer 115 in the thickness direction. Such an air inlet 10h is connected to the voids 10G. The air inlet 10h opens on the rear end side of the first porous body 151 described later, and can introduce air instead of exhaust gas. Thereby, the Ip1+ electrode 112 is exposed to the air introduced from the air inlet 10h through the porous layer 114.

[0037] The solid electrolyte 111e, the Ip1+ electrode 112, and the Ip1- electrode 113 constitute the Ip1 cell (the first pump cell. An example of the pump cell of the present invention) 110. 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 void 10G) and the atmosphere in contact with the Ip1- electrode 113 (the atmosphere in the first measurement chamber 150 described later. That is, the measurement target gas outside the gas sensor element 10) according to the pump current Ip1 (the first pump current) flowing between the Ip1+ electrode 112 and the Ip1- electrode 113. The Ip1 cell 110 adjusts the oxygen concentration in the measurement target gas (exhaust gas) introduced into the element main body 100 in this way.

[0038] A porous Vs- electrode 122 is provided on the surface side of the solid electrolyte 121e. Also, a porous Vs+ electrode 123 is provided on the back side of the solid electrolyte 121e.

[0039] In the stacking direction, a first measurement chamber 150 is formed between the solid electrolyte 111e and the solid electrolyte 121e. This first measurement chamber 150 consists of an internal space S1 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 communicates with the outside of the gas sensor element 10 through a first porous body (diffusion resistance part) 151 (see FIGS. 2 and 4) having 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 rate (diffusion rate) of the exhaust gas per unit time into the first measurement chamber 150. The first porous body 151 is made of porous ceramic.

[0040] A second porous body 152 that limits the flow rate of the exhaust gas per unit time is provided on the rear end side (the right side in FIG. 3) of the first measurement chamber 150 as a partition between the first measurement chamber 150 and the second measurement chamber 160 described later.

[0041] The solid electrolyte 121e, the Vs - electrode 122, and the Vs + electrode 123 constitute the Vs cell (detection cell) 120. This Vs cell 120 mainly generates an electromotive force according to the oxygen partial pressure difference between the atmospheres (the atmosphere in the first measurement chamber 150 in contact with the Vs - electrode 122 and the atmosphere in the reference oxygen chamber 170 in contact with the Vs + electrode 123) separated by the solid electrolyte 121e.

[0042] On the surface side of the solid electrolyte 131e, a porous Ip2 + electrode (anode electrode) 132 and a porous Ip2 - electrode (cathode electrode) 133 are provided.

[0043] A reference oxygen chamber 170 as an isolated small space is formed between the Ip2 + electrode 132 and the Vs + electrode 123. This reference oxygen chamber 170 is constituted by an opening 145b formed in the insulator 145. Among the reference oxygen chamber 170, a porous body 171 made of ceramics is arranged on the side of the Ip2 + electrode 132 (see Figure 3).

[0044] Also, in the stacking direction, a second measurement chamber 160 composed of an internal space S2 is formed at a position facing the Ip2 - electrode (cathode electrode) 133. Details of the second measurement chamber 160 and the like will be described later.

[0045] The first measurement chamber 150 and the second measurement chamber 160 communicate with each other through a second porous body 152 having gas permeability and water permeability. Therefore, the second measurement chamber 160 communicates with the outside of the gas sensor element 10 through the first porous body 151, the first measurement chamber 150, and the second porous body 152.

[0046] The solid electrolyte 131e, the Ip2 + electrode 132, and the Ip2 - electrode 133 constitute an Ip2 cell 130 (second pump cell) for detecting the x NO concentration. This Ip2 cell 130 decomposes NO in the second measurement chamber 160 xThe original oxygen (oxygen ions) is moved to the reference oxygen chamber 170 through the solid electrolyte 131e. At this time, a current (second pump current) corresponding to the concentration of NO x contained in the exhaust gas (gas to be measured) introduced into the second measurement chamber 160 flows between the Ip2+ electrode 132 and the Ip2- electrode 133.

[0047] In this embodiment, an alumina insulating layer 119 is formed at a portion of the back surface of the insulating layer 111s excluding the Ip1- electrode 113. The Ip1- electrode 113 is in contact with the solid electrolyte 111e through a through hole 119b (see FIG. 4) penetrating the alumina insulating layer 119 in the stacking direction. Also, an alumina insulating layer 128 is formed at a portion of the surface of the insulating layer 121s excluding the Vs- electrode 122. In FIG. 4, for convenience of explanation, the alumina insulating layer 128 is omitted. The Vs- electrode 122 is in contact with the solid electrolyte 121e through a through hole (not shown) penetrating the alumina insulating layer 128 in the stacking direction.

[0048] Also, an alumina insulating layer 129 (see FIG. 3) is formed at a portion of the back surface of the insulating layer 121s excluding the Vs+ electrode 123. In FIG. 4, for convenience of explanation, the alumina insulating layer 129 is omitted. The Vs+ electrode 123 is in contact with the solid electrolyte 121e through a through hole (not shown) penetrating the alumina insulating layer 129 in the stacking direction.

[0049] Also, an alumina insulating layer 138 (see FIG. 3) is formed at a portion of the surface of the insulating layer 131s excluding the Ip2+ electrode 132 and the Ip2+ electrode 133, etc. In FIG. 4, for convenience of explanation, the alumina insulating layer 138 is omitted. The Ip2+ electrode 132 and the Ip2- electrode 133 are in contact with the solid electrolyte 131e through through holes (not shown) penetrating the alumina insulating layer 138 in the stacking direction, respectively.

[0050] Here, NO by the gas sensor 1 of this embodiment xThe method for detecting the concentration will be briefly described. The solid electrolytes 111e, 121e, and 131e of the gas sensor element 10 are heated and activated as the temperature of the heater pattern 264 rises. As a result, the Ip1 cell 110, the Vs cell 120, and the Ip2 cell 130 operate respectively.

[0051] The exhaust gas flowing through the exhaust passage (not shown) in the exhaust pipe is introduced into the first measurement chamber 150 while being restricted in the flow rate by the first porous body 151. At this time, a weak current (minute current) Icp flows from the Vs+ electrode 123 side to the Vs− electrode 122 side in the Vs cell 120. Therefore, oxygen in the exhaust gas can receive electrons from the Vs− electrode 122 in the first measurement chamber 150 on the negative electrode side, become oxygen ions, flow through the solid electrolyte 121e, and move into the reference oxygen chamber 170. That is, by flowing the current Icp between the Vs− electrode 122 and the Vs+ electrode 123, oxygen in the first measurement chamber 150 is sent into the reference oxygen chamber 170.

[0052] 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 passed through the Ip1 cell 110 so that the Ip1+ electrode 112 side becomes the negative electrode, and oxygen is drawn into the first measurement chamber 150 from the outside of the gas 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 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 out from the first measurement chamber 150 to the outside of the gas sensor element 10.

[0053] In this way, the exhaust gas whose oxygen concentration has been adjusted in the first measurement chamber 150 is introduced into the second measurement chamber 160 through the second porous body 152. NO in the exhaust gas that has come into contact with the Ip2− electrode (cathode electrode) 133 in the second measurement chamber 160 xA voltage Vp2 is applied between the Ip2+ electrode 132 and the Ip2- electrode 133, causing decomposition (reduction) into nitrogen and oxygen on the Ip2- electrode 133. The decomposed oxygen becomes oxygen ions and flows through the solid electrolyte body 131e, moving into the reference oxygen chamber 170. At this time, the residual oxygen left in the first measurement chamber 150 is similarly moved into the reference oxygen chamber 170 by the Ip2 cell 130. As a result, a current derived from NO x and a current derived from the residual oxygen flow through the Ip2 cell 130. The oxygen that has moved into the reference oxygen chamber 170 is released to the outside (atmosphere) through the Vs+ electrode 123 in contact with the inside of the reference oxygen chamber 170, the Vs+ lead, and the Ip2+ electrode 132 and the Ip2+ lead. For this reason, the Vs+ lead and the Ip2+ lead are porous.

[0054] Since the concentration of the residual oxygen left in the first measurement chamber 150 is adjusted to a predetermined value as described above, the current derived from the residual oxygen can be regarded as substantially constant. That is, the current derived from the residual oxygen has little influence on the variation of the current derived from NO x and the current (second pump current) flowing through the Ip2 cell 130 is proportional to the NO x concentration. Therefore, the current Ip2 (second pump current) flowing through the Ip2 cell 130 is measured, and based on the current value, the NO x concentration in the exhaust gas is detected.

[0055] Next, while referring to FIG. 5, the second measurement chamber 160 formed inside the gas sensor element 10 will be described. FIG. 5 is a cross-sectional view of the gas sensor element with the vicinity of the second measurement chamber 160 enlarged. For the sake of convenience of explanation, the upper side of FIG. 5 is referred to as the "upper side (upper end side)" of the second measurement chamber 160, and the lower side of FIG. 5 is referred to as the "lower side (lower end side)" of the second measurement chamber 160.

[0056] The second measurement chamber (an example of the detection chamber of the present invention) 160 contains NO in the exhaust gas, which is the gas to be measured xAn internal space S2 for detection is formed. The second measurement chamber 160 includes a cylindrical introduction chamber 161 that extends in the stacking direction (thickness direction) of the gas sensor element 10 (element main body) and has one end (upper end) closed, and a housing chamber 162 that is connected to the other end (lower end) of the introduction chamber 161 and houses the Ip2 - electrode (cathode electrode) 133 (see FIG. 5).

[0057] The introduction chamber 161 is a portion into which the exhaust gas that has passed through the second porous body 152 is introduced. As described above, it has a cylindrical shape with one end (upper end) closed. The upper end side of the introduction chamber 161 is composed of a cylindrical first peripheral wall portion 152a that surrounds a hole passing through the second porous body 152 in the thickness direction. The exhaust gas that has passed through the second porous body 152 is discharged from the first peripheral wall portion 152a and introduced into the introduction chamber 161. Note that the second porous body 152 is fitted into the rear end side (the rear end side of the gas sensor element 10) of the opening 141 provided in the insulator 140, and such a second porous body 152 separates the internal space S1 of the first measurement chamber 150 and the internal space S2 of the second measurement chamber 160 in a communicable state.

[0058] The height of the first peripheral wall portion 152a (the thickness of the second porous body 152) is, for example, about 30 μm. The upper end of the first peripheral wall portion 152a is closed by being covered with an alumina insulating layer 119 disposed between the second porous body 152 and the insulating layer 111s as shown in FIG. 5. The first peripheral wall portion 152a (the first peripheral wall portion 152a) is manufactured, for example, by printing a material for forming the second porous body 152 on the insulating layer 121s, drying the printed layer, punching holes in the dried printed layer, and firing such a printed layer.

[0059] In the introduction chamber 161, on the lower end side of the first peripheral wall portion 152a, a cylindrical second peripheral wall portion 128a that surrounds a hole passing through the alumina insulating layer 128 in the thickness direction, a cylindrical third peripheral wall portion 125 that surrounds a hole passing through the insulating layer 121s in the thickness direction, and a cylindrical fourth peripheral wall portion 129a that surrounds a hole passing through the alumina insulating layer 129 in the thickness direction are arranged in this order.

[0060] The second peripheral wall portion 128a is formed in an alumina insulating layer 128 disposed between an insulator 140 (second porous body 152) and an insulating layer 121s. The second peripheral wall portion 128a is obtained by providing holes in a printing layer for forming the alumina insulating layer 128 in a form penetrating in the thickness direction in advance by punching with a press pin or the like, and firing the printing layer. The vertical length (height) of the second peripheral wall portion 128a is, for example, about 15 μm.

[0061] The third peripheral wall portion 125 is formed in an insulating layer 121s used for a Vs cell (detection cell) 120. The third peripheral wall portion 125 is obtained by providing holes in a ceramic green sheet for forming the insulating layer 121s in a form penetrating in the thickness direction in advance by punching with a press pin or the like, and firing the ceramic green sheet (for example, thickness: 200 μm). Note that the third peripheral wall portion 125 has the longest vertical length (height) among the respective portions constituting the introduction chamber 161 and occupies most of the introduction chamber 161 (for example, 70 to 80% of the height). FIG. 5 shows the vertical length L1 (for example, about 220 μm) of the introduction chamber 161.

[0062] The fourth peripheral wall portion 129a is formed in an alumina insulating layer 129 disposed between an insulating layer 121s and an insulator 145. The fourth peripheral wall portion 129a is obtained by providing holes in a printing layer for forming the alumina insulating layer 129 in a form penetrating in the thickness direction in advance by punching with a press pin or the like, and firing the printing layer.

[0063] Thus, the introduction chamber 161 is constituted by a first peripheral wall portion 152a, an alumina insulating layer 119 of a portion closing the upper end of the first peripheral wall portion 152a, a second peripheral wall portion 128a, a third peripheral wall portion 125, and a fourth peripheral wall portion 129a. Among the internal spaces S2 of the second measurement chamber 160, the one formed by the introduction chamber 161 is referred to as an internal space S21.

[0064] Note that the introduction chamber 161 of the second measurement chamber (detection chamber) 160 is provided in such a way as to penetrate at least one ceramic sheet (insulating layer) 121s among a plurality of ceramic sheets (insulating layers) 111s, 121s, 131s, etc. that constitute the element main body 100 in the thickness direction. In the region of the second measurement chamber 160 that penetrates the ceramic sheet (insulating layer) 121s (that is, the third peripheral wall portion 125), the cross-sectional area of the second measurement chamber 160 (introduction chamber 161) in the planar direction (the direction perpendicular to the thickness direction) of the ceramic sheet (insulating layer) 121s is 0.05 mm 2 or more and 0.35 mm 2 or less is preferable, and 0.05 mm 2 or more and 0.09 mm 2 or less is more preferable. When the cross-sectional area of the second measurement chamber 160 (introduction chamber 161) is within such a range, it is easy to satisfy the conditions (A) and (B) described later.

[0065] The accommodation chamber 162 is a part that connects to the introduction chamber 161 and accommodates the Ip2 - electrode (cathode electrode) 133 that constitutes the Ip2 cell (second pump cell) 130. As shown in FIG. 5, the accommodation chamber 162 is connected to the lower end of the introduction chamber 161 and constitutes the second measurement chamber 160 together with the introduction chamber 161. Among the internal spaces S2 of the second measurement chamber 160, the one formed by the accommodation chamber 162 is referred to as the internal space S22. The internal space S22 of the accommodation chamber 162 and the internal space S21 of the introduction chamber 161 are connected to each other, and the exhaust gas introduced into the introduction chamber 161 can move into the accommodation chamber 162.

[0066] The accommodation chamber 162 is composed of a frame - shaped fifth peripheral wall portion 145c that surrounds a hole portion penetrating the insulator 145 in the thickness direction, a porous Ip2 - electrode 133 that entirely covers the lower - end opening portion in the fifth peripheral wall portion 145c, and a part 129b of the alumina insulating layer 129 that covers a part of the upper - end opening portion in the fifth peripheral wall portion 145c.

[0067] The fifth peripheral wall portion 145c is part of the insulator 145 and forms a frame shape surrounding the internal space S22 in plan view. The fifth peripheral wall portion 145c is larger than each peripheral wall portion constituting the introduction chamber 161 in plan view. That is, the opening area (cross-sectional area) inside the fifth peripheral wall portion 145c is larger than the opening area (cross-sectional area) of the introduction chamber 161. When the upper end opening of the fifth peripheral wall portion 145c of such an accommodation chamber 162 is connected to the lower end opening of the fourth peripheral wall portion 129a of the introduction chamber 161, a part of the upper end opening of the fifth peripheral wall portion 145c protrudes outside the introduction chamber 161 (the fourth peripheral wall portion 129a) in plan view. Therefore, a part 129b of the alumina insulating layer 129 is arranged so as to cover a part of the upper end opening of the fifth peripheral wall portion 145c protruding outside in this way.

[0068] The fifth peripheral wall portion 145c is obtained by printing and forming the insulator 145 except for the region that becomes the accommodation chamber 162, printing carbon in the region that becomes the accommodation chamber 162, and firing the resulting printed layer.

[0069] The Ip2 - electrode (cathode electrode) 133 is formed on the surface of the solid electrolyte body 131e so as to entirely cover the lower end opening of the fifth peripheral wall portion 145c. The solid electrolyte body 131e constitutes a part of the element main body portion 100. The Ip2 - electrode 133 is composed of a fired printed layer and is a flat porous electrode having a predetermined thickness (film thickness). The film thickness of the Ip2 - electrode 133 is preferably 15.0 μm or more, more preferably 20.0 μm or more, preferably 55.0 μm or less, and more preferably 40.0 μm or less. When the film thickness of the Ip2 - electrode 133 is within such a range, it is easy to satisfy the conditions (A) and (B) described later.

[0070] The Ip2 + electrode (anode electrode) 132 is arranged on the surface of the solid electrolyte body 131e in the same manner as the Ip2 - electrode (cathode electrode) 133. This Ip2 + electrode (anode electrode) 132 receives oxygen ions generated at the Ip2 - electrode (cathode electrode) 133 in response to the decomposition of NO and moving through the solid electrolyte body 131e.

[0071] The gas sensor element 10 of this embodiment is configured such that either one of the following condition (A) and condition (B) is satisfied by the volume V1 of the second measurement chamber 160 and the volume V2 of the Ip2 - electrode 133. The technical basis for deriving condition (A) and condition (B) will be described later.

[0072] Condition (A): The volume V1 is 0.047 mm 3 or more and 0.065 mm 3 or less, and the volume V2 is 0.030 mm 3 or more and 0.059 mm 3 or less. Condition (B): The volume V1 is 0.047 mm 3 or more and 0.125 mm 3 or less, and the volume V2 is 0.044 mm 3 or more and 0.059 mm 3 or less.

[0073] The volume V1 of the second measurement chamber 160 is the sum of the volume of the introduction chamber 161 and the volume of the accommodation chamber 162. Note that the volume V1 of the second measurement chamber 160 is equal to the size of the internal space S2 of the second measurement chamber 160, the volume of the introduction chamber 161 is equal to the size of the internal space S21, and the volume of the accommodation chamber 162 is equal to the size of the internal space S22. In the case of this embodiment, the introduction chamber 161 is cylindrical, and its volume is obtained as the volume of a cylinder from the inner diameter (diameter) R of the introduction chamber 161 and the vertical length (height) L1 of the introduction chamber 161.

[0074] The volume V2 of the Ip2 - electrode 133 is the volume of the portion of the Ip2 - electrode 133 that is accommodated in the accommodation chamber 162 of the second measurement chamber 160. In the case of this embodiment, in the stacking direction of the gas sensor element 10, when the Ip2 - electrode 133 is viewed in plan view, the area of the Ip2 - electrode 133 is larger than the area of the opening (opening area) of the fifth peripheral wall portion 145c of the accommodation chamber 162. Therefore, in the case of this embodiment, the product of the opening area of the fifth peripheral wall portion 145c of the accommodation chamber 162 and the thickness (film thickness) of the Ip2 - electrode 133 is the volume V2 of the Ip2 - electrode 133. In other embodiments, when the area of the Ip2 - electrode 133 is smaller than the opening area of the fifth peripheral wall portion 145c of the accommodation chamber 162, the product of the area of the Ip2 - electrode 133 and the thickness (film thickness) of the Ip2 - electrode 133 is the volume V2 of the Ip2 - electrode 133.

[0075] In the gas sensor element 10 of this embodiment, in order to configure the volume V1 of the second measurement chamber 160 and the volume V2 of the Ip2 - electrode 133 to satisfy any one of the above - mentioned conditions (A) and (B), when manufacturing the gas sensor element 10, considering that the members (laminates such as ceramic green sheets) for manufacturing the gas sensor element 10 shrink due to firing, it is necessary to set the size (cross - sectional area, etc.) of the second measurement chamber 160 and the size (thickness, etc.) of the Ip2 - electrode 133.

[0076] In the gas sensor element 10, when the relationship between the volume V1 of the second measurement chamber 160 and the volume V2 of the Ip2 - electrode 133 satisfies any one of the above - mentioned conditions (A) and (B), x the responsiveness (responsiveness to NO) of the Ip2 cell 130 for detecting the NO concentration is improved.

[0077] Specifically, when the exhaust gas (measurement target gas) containing NO flows through the exhaust passage in the exhaust pipe at a gas flow rate of 12 m / s, and the gas sensor 1 equipped with the gas sensor element 10 is mounted at a predetermined location of the exhaust pipe, when NO in the exhaust gas introduced into the second measurement chamber 160 of the gas sensor element 10 is decomposed into nitrogen and oxygen at the Ip2 - electrode 133 provided in the Ip2 cell 130, the time (rise time of the output waveform) for the output of the second pump current (current Ip2) flowing through the Ip2 cell 130 to reach from 10% to 90% is within 1 second.

[0078] Figure 6 is a graph showing the output waveform of the second pump current flowing through the Ip2 cell 130 of the gas sensor element 10. The horizontal axis of the graph shown in Figure 6 is time (seconds), and the response (%) shown on the vertical axis represents the ratio (%) of the output of the second pump current. Here, the current value at the top in the output waveform of the second pump current is set to 100%. In Figure 6, the output waveform We of the second pump current in the gas sensor 1 (gas sensor element 10) of the present embodiment is shown by a solid line. The time te for the output of the second pump current of the gas sensor 1 to reach from 10% to 90% is within 1 second. In addition, in Figure 6, as a comparative example, the output waveform Wc of the second pump current in a gas sensor that does not satisfy any of the above conditions (A) and (B) is shown by a one - dotted line. In this comparative example, the time tc for the output of the second pump current to reach from 10% to 90% exceeds 1 second.

[0079] [Test] Next, the content of the test from which the above conditions (A) and (B) were derived will be described.

[0080] (Examples 1 - 5) As Examples 1 to 5, five gas sensors each having the same basic configuration as the gas sensor (gas sensor element) of the above-described Embodiment 1 were fabricated. The inner diameter [mm] of the introduction chamber of the second measurement chamber in the gas sensor of each example was set to each value shown in Table 1. For reference, the inner diameter [mm] of the introduction chamber of the second measurement chamber in the gas sensor element before firing is also shown in Table 1. In the gas sensor of each example, considering the shrinkage after firing, the size of the inner diameter [mm] of the introduction chamber is set respectively. Further, the film thickness [mm] of the Ip2-electrode in the gas sensor of each example was set to each value shown in Table 1. The area [mm 2 of the Ip2-electrode is determined by the opening area of the accommodation chamber. For reference, the opening area of the accommodation chamber before firing was 2.13 mm 2 2.13mm

[0081] Also, the height (length in the vertical direction) L1 of the introduction chamber in each example was 0.232 mm, and the height (length in the vertical direction) L2 of the accommodation chamber was 0.024 mm.

[0082] Note that each numerical value such as the inner diameter of the introduction chamber, the height L1 of the introduction chamber, the height L2 of the accommodation portion, the film thickness of the Ip2-electrode, and the area of the Ip2-electrode in the gas sensor after firing is obtained by analyzing each cut surface obtained by cutting the gas sensor element in the longitudinal direction (axis AX direction) and the width direction with an SEM image after the evaluation of the responsiveness described later. Each numerical value is the average value of 5 samples.

[0083] (Comparative Examples 1 to 7) Except that the inner diameter [mm] of the introduction chamber of the second measurement chamber in the gas sensor and the film thickness [μm] of the Ip2-electrode were set to each value shown in Table 1, gas sensors of Comparative Examples 1 to 7 were fabricated in the same manner as in Example 1 and the like, five for each.

[0084] (Responsiveness) For the gas sensors fabricated in each example and each comparative example, the responsiveness was evaluated by the following method. With the exhaust gas passage in the exhaust pipe flowing exhaust gas with the NO concentration gradually increased from 0 ppm to 100 ppm at a gas flow rate of 12 m / s, a gas sensor was mounted at a predetermined location of the exhaust pipe. Then, for the gas sensor, the time (rise time of the output waveform) until the output of the second pump current (current Ip2) flowing through the Ip2 cell reached from 10% to 90% was determined. Such rise times were determined five times each for each example and each comparative example. Then, in accordance with the evaluation criteria shown below, the responsiveness of the gas sensors of each example and each comparative example was evaluated. The results are shown in Table 1.

[0085] <Evaluation Criteria> · When the rise time is within 1 second in all five tests ·····「〇」 · When the rise time exceeds 1 second in at least one test ·····「△」 · When the rise time exceeds 1 second in all five tests ·····「×」

[0086]

Table 1

[0087] Here, the test results of Examples 1 to 5 and Comparative Examples 1 to 7 are shown in the coordinates of FIG. 7. FIG. 7 is a diagram representing the test results of the responsiveness of the gas sensor in coordinates. The vertical axis of the coordinates shown in FIG. 7 represents the film thickness [μm] of the Ip2 - electrode, and the horizontal axis represents the inner diameter [mm] of the introduction chamber. When the results of Examples 1 to 5 and Comparative Examples 1 to 7 are plotted in such coordinates, the state as shown in FIG. 7 is obtained.

[0088] In such coordinates, from the results of Examples 3 to 5 and Comparative Examples 1 to 7, a preferable combination range Xa of the inner diameter [mm] of the introduction chamber and the film thickness [μm] of the Ip2 - electrode is derived. For the range Xa, the range of the inner diameter [mm] of the introduction chamber is 0.30 mm or more and 0.40 mm or less, and the range of the film thickness [μm] of the Ip2 - electrode is 20.0 μm or more and 40.0 μm or less.

[0089] Also, from the results of Examples 1, 2, 5 and Comparative Examples 1 to 7, the range Xb of the preferable combination of the inner diameter [mm] of the introduction chamber and the film thickness [μm] of the Ip2 - electrode is derived. Regarding the range Xb, the range of the inner diameter [mm] of the introduction chamber is 0.30 mm or more and 0.70 mm or less, and the range of the film thickness [μm] of the Ip2 - electrode is 30.0 μm or more and 40.0 μm or less.

[0090] The above - mentioned condition (A) is determined based on the range Xa, and the condition (B) is determined based on the range Xb. In Examples 1 to 5 and Comparative Examples 1 to 7, the volume of the accommodation chamber of the second measurement chamber can be regarded as substantially constant.

[0091] The output waveform of the second pump current of the gas sensor (gas sensor element) becomes steeper as the inner diameter (aperture diameter) of the introduction chamber in the second measurement chamber becomes smaller (for example, refer to the output waveform We in FIG. 6). This is presumably because the introduction chamber constitutes the second measurement chamber together with the accommodation chamber, and as the inner diameter (aperture diameter) of such an introduction chamber becomes smaller, the exchange rate of the exhaust gas (including NO) in the second measurement chamber becomes faster. From this, it is presumed that the smaller the volume V1 of the second measurement chamber, the faster the return rate of the exhaust gas. The lower limit value of the inner diameter (aperture diameter) of the introduction chamber (the lower limit value of the volume V1) is set so that a current value of the second pump current can be obtained to ensure the resolution and accuracy required for the gas sensor. Also, the upper limit value of the inner diameter (aperture diameter) of the introduction chamber (the upper limit value of the volume V1) is set to ensure the strength of the gas sensor element near the second measurement chamber.

[0092] Also, when the film thickness (volume V2) of the Ip2 - electrode is large, the site where the decomposition reaction of NO occurs increases. Therefore, it is presumed that the larger the film thickness (volume V2) of the Ip2 - electrode, the faster the exchange rate of the exhaust gas.

Explanation of symbols

[0093] 1…Gas sensor, 10…Gas sensor element, 100…Element main body part, 110…Ip1 cell (pump cell), 111s, 121s, 131s…Insulating layer (ceramic sheet), 130…Ip2 cell, 132…Ip2 + electrode (anode electrode), 133…Ip2 - electrode (cathode electrode), 160…Second measurement chamber (detection chamber), 161…Introduction chamber, 162…Accommodation chamber, V1…Volume of the detection chamber, V2…Volume of the cathode electrode

Claims

1. An element body portion in which a plurality of ceramic sheets are laminated, A pump cell that adjusts the oxygen concentration in the measurement target gas introduced into the element body portion, A detection chamber formed inside the element body portion, into which the measurement target gas after the adjustment of the oxygen concentration is introduced, A gas sensor element comprising a layered cathode electrode that is housed in the detection chamber and decomposes NO, A gas sensor element in which the relationship between the volume V1 of the detection chamber and the volume V2 of the cathode electrode satisfies any one of the following conditions (A) and (B). Condition (A): The volume V1 is 0.047 mm ３ or more and 0.065 mm ３ or less, and the volume V2 is 0.030 mm ３ or more and 0.059 mm ３ or less Condition (B): The volume V1 is 0.047 mm ３ or more and 0.125 mm ３ or less, and the volume V2 is 0.044 mm ３ or more and 0.059 mm ３ or less

2. The detection chamber is provided in such a manner as to penetrate at least one of the plurality of ceramic sheets in the thickness direction, In the region where the detection chamber penetrates the ceramic sheet, the cross-sectional area of the detection chamber in the planar direction of the ceramic sheet is 0.05 mm ２ or more and 0.35 mm ２ or less. The gas sensor element according to claim 1.

3. A solid electrolyte layer that forms part of the element body portion and has the cathode electrode formed on its surface, The gas sensor element according to claim 1 or claim 2, further comprising an anode electrode that is disposed on the surface of the solid electrolyte layer and receives oxygen ions generated at the cathode electrode in response to the decomposition of NO and that have moved through the solid electrolyte layer.

4. A gas sensor comprising the gas sensor element according to any one of claims 1 to 3.

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