JP7391638B2 - Sensor element and gas sensor - Google Patents

Description

The present invention relates to a sensor element and a gas sensor that are suitably used to detect the gas concentration of a specific gas contained in combustion gas or exhaust gas of, for example, a combustor or internal combustion engine, and have a pump cell.

Conventionally, gas sensors that detect the concentration of specific components (oxygen, NOx, etc.) in exhaust gas from internal combustion engines have been widely used (Patent Documents 1 and 2). For example, a typical NOx sensor has a sensor element including an oxygen pump cell 1400 as shown in FIG. Oxygen pump cell 1400 has a pair of inner electrodes 1080 and 1100 formed on both sides of solid electrolyte layer 1090, and inner electrode 1080 is exposed in measurement chamber 1070 adjacent to solid electrolyte layer 1090 in the stacking direction. On the other hand, the outer electrode 1100 faces the outside and pumps out or pumps oxygen in the exhaust gas to and from the outside. Then, a voltage (Vp voltage) is applied to the oxygen pump cell 1400 so that the output voltage (electromotive force) according to the oxygen concentration in the exhaust gas in the measurement chamber 1070 is constant, and the oxygen concentration in the measurement chamber 1070 is adjusted to NOx. It is managed to the extent that it does not decompose.

Japanese Patent Application Publication No. 2012-173146 Patent No. 4966266

However, in the case of the sensor element shown in FIG. 9, a transient noise current flows into the oxygen pump cell 1400 when the oxygen atmosphere in the gas to be measured changes, making it difficult to manage the oxygen concentration in the measurement chamber 1070. There is a problem.
In other words, when the oxygen atmosphere in the gas to be measured changes to the rich side, the oxygen concentration in the measurement chamber 1070 also becomes rich, and the pump current Ip flowing through the oxygen pump cell 1400 also decreases, as shown by the solid line C1 in FIG. is normal.
However, as shown in FIG. 9, since the gas to be measured flows into the measurement chamber 1070 via the diffusion resistance section 1200, it takes time for the gas to be measured to come into contact with the inner electrode 1080 in the measurement chamber 1070. The atmosphere remains lean. On the other hand, since the outer electrode 1100 faces the outside, the rich gas to be measured comes into contact with the outer electrode 1100 before the gas to be measured contacts the inner electrode 1080. Compared to this, the inner electrode 1080 side in the measurement chamber 1070 is leaner.
As a result, an electromotive force Ef as indicated by the arrow in FIG. 9 is generated in the oxygen pump cell 1400, a noise current flows transiently, and a noise peak as indicated by the broken line C2 in FIG. 10 occurs.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a sensor element and a gas sensor that suppress noise current in a pump cell when the oxygen atmosphere in a gas to be measured changes, and suppress a decrease in oxygen concentration management accuracy.

In order to solve the above problems, the sensor element of the present invention includes a measurement chamber, a solid electrolyte body, an inner electrode formed on the surface of the solid electrolyte body and exposed to the measurement chamber, and a surface of the solid electrolyte body. and an outer electrode formed on the outside of the measurement chamber, and the oxygen concentration in the measurement chamber is adjusted by pumping out and pumping oxygen in the gas to be measured introduced into the measurement chamber. a pump cell to be adjusted; a diffusion resistance unit disposed between the outside and the measurement chamber to adjust the diffusion rate of the gas to be measured introduced into the measurement chamber; and the gas to be measured after adjusting the oxygen concentration. A stacked sensor element extending in the axial direction and having a detection cell for measuring the concentration of a specific gas in the sensor element, the outer electrode being covered with a porous layer and preventing contact with the gas to be measured. The outer electrode is disposed within a gap surrounded by a dense layer that is impermeable to gas, and the gap communicates with an air inlet opening on the rear end side of the diffusion resistance part, and the outer electrode is connected to the porous layer. It is characterized in that it is exposed to the atmosphere introduced from the atmosphere inlet through the air inlet.

According to this sensor element, the outer electrode is placed in a gap surrounded by a dense layer to prevent contact with the gas to be measured, while the air is introduced from the air inlet port on the rear end side of the diffusion resistance section. exposed to
As a result, the outer electrode always uses the atmosphere as a reference atmosphere, so even if the oxygen atmosphere in the gas to be measured changes, the atmosphere at the outer electrode remains constant, and pump cell noise due to changes in the oxygen atmosphere in the gas to be measured The current is suppressed, and a normal pump current flows according to the oxygen atmosphere in the gas to be measured introduced from the diffusion resistance section into the measurement chamber. Therefore, it is possible to suppress a decrease in the accuracy of oxygen concentration management in the pump cell.
Furthermore, since the outer electrode is covered with a porous layer, it is possible to suppress sublimation of the electrode material of the outer electrode, which is mainly composed of a noble metal (such as Pt) when the sensor is driven.

In the sensor element of the present invention, a heater may be stacked on the opposite side of the dense layer when viewed in the stacking direction.
According to this sensor element, the heat of the heater is not insulated by the void, which is the case when heaters are stacked closer to the dense layer than the void (for example, buried in the dense layer). can be used more effectively and is also advantageous for rapid heating.

In the sensor element of the present invention, when viewed in a cross section perpendicular to the axial direction and along the stacking direction, when the cross-sectional area of the void is W1 and the cross-sectional area of the air inlet is W2, (1. The following relationship may be satisfied: 5×W1)≧W2≧(0.3×W1).
According to this sensor element, it is possible to prevent the strength of the sensor element from decreasing due to making the cross-sectional area of the air inlet port too wide, and to prevent the introduction of air into the void by making the cross-sectional area of the air inlet port too narrow. can be suppressed.

In the sensor element of the present invention, the atmospheric air inlet may penetrate through the dense layer and open on the front end side of the sensor element rather than the rear end thereof.
According to this sensor element, the length from the air gap to the air inlet can be shortened, and the air introduced from the air inlet can be quickly brought into contact with the outer electrode.

In the sensor element of the present invention, the outer electrode contains a noble metal and a component of the solid electrolyte body, and when a cross section is observed, the outer electrode contains a noble metal region made of the noble metal and a component of the solid electrolyte body. and a coexistence region where the noble metal and components of the solid electrolyte body coexist, and the coexistence region exists along a boundary between the noble metal region and the solid electrolyte region. You can.
According to this sensor element, it is possible to suppress variations in the electrode resistance of the outer electrode, and further suppress a decrease in the accuracy of oxygen concentration management in the pump cell.

The gas sensor of the present invention includes the sensor element and a metal shell that holds the sensor element.

According to the present invention, it is possible to obtain a sensor element and a gas sensor that suppress the noise current of the pump cell when the oxygen atmosphere in the gas to be measured changes, and suppress a decrease in the management accuracy of oxygen concentration.

FIG. 1 is a cross-sectional view along the longitudinal direction of a gas sensor (NOx sensor) according to a first embodiment of the present invention. FIG. 2 is a perspective view of a sensor element according to a first embodiment. 3 is a sectional view taken along line BB in FIG. 2. FIG. FIG. 2 is an exploded perspective view of the vicinity of the Ip1 cell (pump cell) of the sensor element according to the first embodiment. 3 is a sectional view taken along line CC in FIG. 2. FIG. FIG. 7 is a cross-sectional view along the axis of a sensor element according to a second embodiment. FIG. 7 is an exploded perspective view of the vicinity of the Ip1 cell (pump cell) of the sensor element according to the second embodiment. FIG. 7 is a cross-sectional view along the axis of a sensor element according to a third embodiment. 1 is a cross-sectional view of a sensor element with a conventional oxygen pump cell; FIG. FIG. 3 is a diagram showing noise peaks that occur in the oxygen pump cell when the oxygen atmosphere in the gas to be measured changes to a rich side.

Embodiments of the present invention will be described below.
FIG. 1 is a longitudinal cross-sectional view (a cross-sectional view cut in the longitudinal direction along the axis AX) of a gas sensor (NOx sensor) 1 according to the first embodiment of the present invention, and FIG. 2 is a cross-sectional view of the sensor according to the first embodiment. 3 is a sectional view taken along line BB (axis AX) in FIG. 2, FIG. 4 is an exploded perspective view of the sensor element 10 near the Ip1 cell (pump cell) 110, and FIG. FIG. 3 is a cross-sectional view taken along line CC (a line perpendicular to axis AX).
Note that in order to distinguish it from the "width direction" of the sensor element, the direction along the axis AX (axial direction) is appropriately referred to as the "longitudinal direction". The "width direction" of the sensor element is a direction perpendicular to the "longitudinal direction (axial direction)".

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

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

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

The metal shell 20 is a cylindrical member having a through hole 23 penetrating in the direction of the axis AX. The metal shell 20 has a shelf portion 25 that projects inward in the radial direction and forms a part of the through hole 23 . The metal shell 20 allows the distal end 10s of the sensor element 10 to protrude to the outside of its own distal end (downward in FIG. 1), and the rear end 10k of the sensor element 10 to the outside of its own rear end (upward in FIG. 1). The sensor element 10 is held in the through hole 23 in a state where it protrudes.
Further, inside the through hole 23 of the metal shell 20, an annular ceramic holder 42, two talc rings 43 and 44 filled with talc powder in an annular shape, and a ceramic sleeve 45 are arranged. Specifically, in a state surrounding the sensor element 10 in the radial direction, the ceramic holder 42, talc rings 43, 44, and ceramic sleeve 45 are arranged in this order on the axially distal end side (lower end side in FIG. 1) of the metal shell 20. They are arranged in an overlapping manner from the rear end side in the axial direction (the upper end side in FIG. 1).

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

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

Further, an elastic seal member 73 made of fluororubber is disposed inside the rear end opening 51c located at the rear end in the axial direction (the upper end in FIG. 1) of the outer cylinder 51 in the radial direction. A total of six cylindrical insertion holes 73c extending in the direction of the axis AX are formed in this elastic seal member 73. Each insertion hole 73c is formed by an insertion hole surface 73b (cylindrical inner wall surface) of the elastic seal member 73. One lead wire 71 is inserted through each insertion hole 73c. Each lead wire 71 extends to the outside of the gas sensor 1 through the insertion hole 73c of the elastic seal member 73. The elastic sealing member 73 is elastically compressed and deformed in the radial direction by crimping the rear end opening 51c of the outer cylinder 51 inward in the radial direction, thereby bringing the insertion hole surface 73b and the outer circumferential surface 71b of the lead wire 71 into close contact. In this way, the space between the insertion hole surface 73b and the outer circumferential surface 71b of the lead wire 71 is sealed watertightly.

On the other hand, as shown in FIG. 3, the sensor element 10 includes plate-shaped solid electrolyte bodies 111, 121, 131 and insulators 140, 145 disposed between them, which are stacked in the stacking direction. It has a unique structure. Furthermore, in the sensor element 10, a heater 161 is laminated on the back side of the solid electrolyte body 131. This heater 161 includes plate-shaped insulators 162 and 163 mainly made of alumina, and a heater pattern 164 (mainly made of Pt) buried therebetween.

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

Further, as shown in FIG. 4, on the surfaces of the Ip1+ electrode 112 and the Ip1+ lead 116, a gas-impermeable first dense layer 118 having a void 10G and made of alumina or the like is laminated. While the layer 114 is exposed, the Ip1+ lead 116 is covered by the outer peripheral frame portion of the first dense layer 118.
The void 10G extends straight from the vicinity of the porous layer 114 to a portion communicating with the air inlet 10h. The first dense layer 118 on the rear end side of the gap 10G is provided with through holes for electrical connection with the electrode terminal portions 13 to 15.

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

Here, the solid electrolyte body 111, the Ip1-electrode 113, and the Ip1+ electrode 112 correspond to a "solid electrolyte body," an "inner electrode," and an "outer electrode" in the claims, respectively. Further, the first measurement chamber 150 described later corresponds to a "measurement chamber" in the claims.
The solid electrolyte body 111 and the electrodes 112 and 113 constitute an Ip1 cell 110 (pump cell). This Ip1 cell 110 controls the atmosphere in contact with the electrode 112 (the atmosphere in the gap 10G, which is different from the gas to be measured outside the sensor element 10) and the atmosphere in the electrode 113, depending on the pump current Ip1 flowing between the electrodes 112 and 113. Oxygen is pumped out and pumped in (so-called oxygen pumping) with the atmosphere in contact with the sensor element (the atmosphere in the first measurement chamber 150 described later, that is, the gas to be measured outside the sensor element 10).

The solid electrolyte body 121 is arranged to face the solid electrolyte body 111 in the stacking direction with the insulator 140 in between. A porous Vs-electrode 122 is provided on the surface side (upper surface side in FIG. 2) of the solid electrolyte body 121. Further, a porous Vs+ electrode 123 is provided on the back side (lower side in FIG. 2) of the solid electrolyte body 121.

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

The solid electrolyte body 121 and the electrodes 122 and 123 constitute a Vs cell (detection cell) 120. This Vs cell 120 mainly responds to the oxygen partial pressure difference between the atmospheres separated by the solid electrolyte body 121 (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). Generates an electromotive force accordingly.

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

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. Note that a porous body made of ceramics is arranged inside the reference oxygen chamber 170 on the Ip2+ electrode 132 side.
Further, a second measurement chamber 160 as an internal space of the sensor element is formed at a position facing the Ip2-electrode 133 in the stacking direction. The second measurement chamber 160 includes an opening 145c that passes through the insulator 145 in the stacking direction, an opening 125 that passes through the solid electrolyte body 121 in the stacking direction, and an opening 141 that passes through the insulator 140 in the stacking direction. It is made up of.
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 sensor element 10 through the first porous body 151, the first measurement chamber 150, and the second porous body 152.

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

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

Furthermore, in the present embodiment, an alumina insulating layer 128 is formed on the surface of the solid electrolyte body 121 except for the Vs-electrode 122, and the Vs-electrode 122 has a through hole ( (not shown) makes contact with the solid electrolyte body 121.
Further, an alumina insulating layer 129 is formed on the back surface of the solid electrolyte body 121 at a portion other than the Vs+ electrode 123, and the Vs+ electrode 123 is inserted into the solid electrolyte through a through hole (not shown) that penetrates the alumina insulating layer 129 in the stacking direction. Contact with electrolyte body 121.

Furthermore, in this embodiment, an alumina insulating layer 138 is formed on the surface of the solid electrolyte body 131 at a portion other than the Ip2+ electrode 132, and the Ip2+ electrode 132 is formed with a through hole (not shown) that penetrates the alumina insulating layer 138 in the stacking direction. The solid electrolyte body 131 is contacted through the solid electrolyte body 131. Further, an alumina insulating layer 138 is also formed on the surface of the solid electrolyte body 131 except for the Ip2-electrode 133, and the electrode 133 is inserted through a through hole (not shown) that penetrates the alumina insulating layer 138 in the stacking direction. It comes into contact with the solid electrolyte body 131.

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

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

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. NOx in the exhaust gas that came into 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. Oxygen becomes oxygen ions, flows through the solid electrolyte body 131, and moves 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 NOx and a current derived from residual oxygen flow through the Ip2 cell 130. Note that 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 and the Ip2+ electrode 132 and the Ip2+ lead that are in contact with the reference oxygen chamber 170. Therefore, the Vs+ lead and Ip2+ leads are porous.

Here, since the concentration of 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 considered to be approximately constant, and the current derived from NOx The effect on current fluctuations is small, and the current flowing through the Ip2 cell 130 is proportional to the NOx concentration. Therefore, the current Ip2 flowing through the Ip2 cell 130 can be detected, and the NOx concentration in the exhaust gas can be detected based on the current value.

In this embodiment, the Ip1+ electrode 112 is placed in the gap 10G surrounded by the dense layers 115 and 118, and is prevented from coming into contact with the gas to be measured, while being exposed to the atmosphere introduced from the atmosphere inlet 10h. Ru.
As a result, the Ip1+ electrode 112 always uses the atmosphere as a reference atmosphere, so even if the oxygen atmosphere in the gas to be measured changes, the atmosphere at the Ip1+ electrode 112 is kept constant, and the pump cell The noise current (broken line C2 in FIG. 10) is suppressed, and the normal pump current (solid line C1 in FIG. ) flows. Therefore, it is possible to suppress a decrease in the accuracy of oxygen concentration management in the pump cell.
Furthermore, since the Ip1+ electrode 112 is covered with the porous layer 114, it is possible to suppress sublimation of the electrode material of the Ip1+ electrode 112, which is mainly composed of a noble metal (such as Pt), when the sensor is driven.

Furthermore, in this embodiment, the heater 161 is stacked on the opposite side of the dense layers 115 and 118 (on the pump cell 110 side with respect to the gap 10G) when viewed in the stacking direction.
This prevents the heat of the heater 161 from being insulated by the air gap 10G, unlike when the heater 161 is stacked closer to the dense layers 115 and 118 than the air gap 10G (for example, buried in the dense layer 115). , the heat of the heater 161 can be used more effectively, and it is also advantageous for rapid heating.

Furthermore, in this embodiment, the air inlet 10h opens through the dense layers 115 and 118 closer to the tip than the rear end of the sensor element 10.
Thereby, the length from the air gap 10G to the air inlet 10h can be shortened, and the air introduced from the air inlet 10h can be quickly brought into contact with the Ip1+ electrode 112.

Further, in this embodiment, the Ip1+ electrode 112 contains a noble metal and a component of the solid electrolyte body 111, and when the cross section is observed, a noble metal region made of the noble metal and a solid body made of the components of the solid electrolyte body 111 are shown. It has an electrolyte region and a coexistence region where the noble metal and the components of the solid electrolyte body 111 coexist, and the coexistence region exists along the boundary between the noble metal region and the solid electrolyte region.
Thereby, variations in the electrode resistance of the Ip1+ electrode 112 can be suppressed, and a decrease in the accuracy of oxygen concentration management in the pump cell can be further suppressed.

Further, as shown in FIG. 5 in which the air inlet 10h is projected, in this embodiment, when the cross-sectional area of the air gap 10G is W1 and the cross-sectional area of the air inlet 10h is W2, (1.5×W1) The relationship ≧W2≧(0.3×W1) is satisfied.
This prevents the strength of the sensor element 10 from decreasing due to the cross-sectional area of the air inlet 10h being too wide, and prevents the air from being introduced into the gap 10G by making the cross-sectional area of the air inlet 10h too narrow. can be suppressed.

Next, a sensor element 10B according to a second embodiment of the present invention will be described with reference to FIGS. 6 and 7. Note that, in the sensor element 10B according to the second embodiment, between the first dense layer 118 and a composite layer including the solid electrolyte body 111e (specifically, the solid electrolyte body 111e and the insulating layer 111s, which will be described later), The sensor element according to the first embodiment except that the third dense layer 118B is interposed, and the solid electrolyte bodies 111e, 121e, and 131e are embedded in the insulating layers 111s, 121s, and 131s, respectively. 10, the explanation of the configuration of the same parts will be omitted.
FIG. 6 is a sectional view taken along the axis AX of the sensor element 10B according to the second embodiment, and FIG. 7 is an exploded perspective view of the vicinity of the Ip1 cell (pump cell) 110 of the sensor element 10B.

As shown in FIGS. 6 and 7, in the second embodiment, a third dense layer 118B is interposed between the first dense layer 118 and the composite layer, and the tip side of the third dense layer 118B is A rectangular opening 118Bh is provided in the opening 118Bh.
Then, this opening 118Bh is filled with a porous layer 114B, and an Ip1+ electrode 112 is formed on the lower surface (Ip1+ electrode 112 side) of the porous layer 114B, and the Ip1+ electrode 112 is located below the lower surface of the third dense layer 118B. It stands out. The above-mentioned protruding portion of the Ip1+ electrode 112 is covered with the solid electrolyte body 111e.
In this manner, in the second embodiment, the side surface of the Ip1+ electrode 112 is surrounded by the solid electrolyte body 111e.
Note that the solid electrolyte bodies 111e, 121e, and 131e each have a substantially rectangular shape, and rectangular openings are provided at the tip sides of the insulating layers 111s, 121s, and 131s. Solid electrolyte bodies 111e, 121e, and 131e are embedded in these openings, respectively.

In the second embodiment as well, the Ip1+ electrode 112 is placed in the gap 10G surrounded by the solid electrolyte body 111e and is prevented from coming into contact with the gas to be measured, while being exposed to the atmosphere introduced from the atmosphere inlet 10h. Ru.
As a result, the Ip1+ electrode 112 always uses the atmosphere as a reference atmosphere, so even if the oxygen atmosphere in the gas to be measured changes, the atmosphere of the Ip1+ electrode 112 is kept constant, suppressing the noise current in the pump cell, and suppressing the noise current in the pump cell. Deterioration in oxygen concentration management accuracy can be suppressed.
Furthermore, since the Ip1+ electrode 112 is covered with the porous layer 114B, sublimation of the Ip1+ electrode 112 can be suppressed.

Next, referring to FIG. 8, a sensor element 10C according to a third embodiment of the present invention will be described. Note that the sensor element 10C according to the third embodiment is the same as the sensor element 10 according to the first embodiment, except that the porous layer 114C is formed to the same thickness as the first dense layer 118. Therefore, a description of the configuration of the same parts will be omitted.
FIG. 8 shows a cross-sectional view of a sensor element 10C according to the third embodiment along the axis AX.

As shown in FIG. 8, in the third embodiment, a porous layer 114C is formed to the same thickness as the first dense layer 118.
In this way, in the third embodiment, only the side surface of the porous layer 114C covering the Ip1+ electrode 112 faces the gap 10G and is exposed to the atmosphere (arrow in FIG. 8).

In the third embodiment as well, the Ip1+ electrode 112 is placed in the gap 10G surrounded by the dense layers 115 and 118, and is prevented from coming into contact with the gas to be measured, while being exposed to the atmosphere introduced from the atmosphere inlet 10h. be done.
As a result, the Ip1+ electrode 112 always uses the atmosphere as a reference atmosphere, so even if the oxygen atmosphere in the gas to be measured changes, the atmosphere of the Ip1+ electrode 112 is kept constant, suppressing the noise current in the pump cell, and suppressing the noise current in the pump cell. Deterioration in oxygen concentration management accuracy can be suppressed.
Furthermore, since the Ip1+ electrode 112 is covered with the porous layer 114C, sublimation of the Ip1+ electrode 112 can be suppressed.

It goes without saying that the present invention is not limited to the above-described embodiments, but extends to various modifications and equivalents that fall within the spirit and scope of the present invention.
The air gap 10G may penetrate to the rear end of the sensor element, and the air inlet may open at the surface facing the rear end of the sensor element.
The position of the diffusion resistance portion (first porous body 151) is not limited to the side surface of the element, but may be placed on the surface facing the tip of the element.
The solid electrolyte bodies 111, 121, and 131 may be embedded in an insulating layer.

Further, the present invention can be applied to a sensor element (gas sensor) having an oxygen pump cell and a detection cell (two or more cells), and can be applied to the NOx sensor element (NOx sensor) of this embodiment. It goes without saying that the present invention is not limited to these uses, and includes various modifications and equivalents that fall within the spirit and scope of the present invention. For example, the present invention may be applied to an oxygen sensor (oxygen sensor element) that detects the oxygen concentration in a gas to be measured, an HC sensor (HC sensor element) that detects the HC concentration, and the like.

1 Gas sensor 10, 10B, 10C Sensor element 10h Air inlet 10G Gap 20 Metal shell 110 Pump cell 111, 111e Solid electrolyte body 112 Outer electrode 113 Inner electrode 114, 114B, 114C Porous layer 115, 118, 118B Dense layer 120 Detection cell (Vs cell)
150 Measurement chamber 151 Diffusion resistance section (first porous body)
161 Heater AX Longitudinal direction (axis)

Claims (6)

a measurement room;
A solid electrolyte body, an inner electrode formed on the surface of the solid electrolyte body and exposed to the measurement chamber, and an outer electrode formed on the surface of the solid electrolyte body and disposed outside the measurement chamber. a pump cell that adjusts the oxygen concentration in the measurement chamber by pumping out and pumping oxygen in the measurement gas introduced into the measurement chamber;
a diffusion resistance section that is arranged between the outside and the measurement chamber and adjusts the diffusion rate of the gas to be measured introduced into the measurement chamber;
A stacked sensor element extending in the axial direction, comprising a detection cell that measures the concentration of a specific gas in the gas to be measured after adjusting the oxygen concentration,
The outer electrode is arranged in a gap covered with a porous layer and surrounded by a gas-impermeable dense layer that prevents contact with the gas to be measured,
The void communicates with an air inlet opening on the rear end side of the diffusion resistance part, and the outer electrode is exposed to the air introduced from the air inlet through the porous layer. sensor element. 2. The sensor element according to claim 1, further comprising a heater stacked on the opposite side of the dense layer when viewed in the stacking direction. When viewed in a cross section perpendicular to the axial direction and along the stacking direction, the cross-sectional area of the void is W1, and the cross-sectional area of the air inlet is W2,
(1.5×W1)≧W2≧(0.3×W1)
The sensor element according to claim 1 or 2, wherein the sensor element satisfies the following relationship. The sensor element according to any one of claims 1 to 3, wherein the atmospheric air inlet opens through the dense layer closer to the tip than the rear end of the sensor element. The outer electrode contains a noble metal and a component of the solid electrolyte body,
and when a cross section is observed, it has a noble metal region made of the noble metal, a solid electrolyte region made of the components of the solid electrolyte body, and a coexistence region where the noble metal and the components of the solid electrolyte body coexist;
5. The sensor element according to claim 1, wherein the coexistence region exists along a boundary between the noble metal region and the solid electrolyte region. A gas sensor comprising the sensor element according to any one of claims 1 to 5 and a metal shell that holds the sensor element.

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