JP7111608B2 - SENSOR AND SENSOR MANUFACTURING METHOD - Google Patents

Description

The present disclosure relates to sensors and methods of manufacturing sensors.

Conventionally, the following sensors are known. The sensor comprises a measurement chamber into which the gas to be measured is introduced, a pump cell, a reference oxygen chamber and a reference cell. The pump cell pumps oxygen from the measuring chamber to the outside or pumps oxygen from the outside to the measuring chamber. The reference oxygen chamber has an atmosphere with a predetermined oxygen concentration. The reference cell generates a voltage Vs in response to the oxygen concentration difference between the measurement chamber and the reference oxygen chamber.

The pump cell includes a first solid electrolyte body, a first electrode, and a second electrode. A first electrode is formed on the first solid electrolyte body and faces the measurement chamber. A second electrode is formed on the first solid electrolyte body and faces the outside.

The reference cell comprises a second solid electrolyte body, a third electrode and a fourth electrode. A third electrode is formed on the second solid electrolyte body and faces the measurement chamber. A fourth electrode is formed on the second solid electrolyte body and faces the reference oxygen chamber (see Patent Document 1).

In the above sensor, for example, the energization amount Ip of the pump cell is feedback-controlled so that the voltage Vs of the reference cell is constant.

JP 2012-18189 A

The first electrode contains noble metal and ceramic contained in the first solid electrolyte body. A rich aging process is performed on the first electrode. When the rich aging treatment is performed, alteration progresses in the first electrode, forming a coexistence region where the noble metal and the ceramic coexist. When the coexistence region is formed, the three-phase interface between the noble metal, the solid electrolyte, and the gas is increased, so the reactivity between the first electrode and the gas is improved, and the activity of the first electrode is improved.

In conventional sensors, the side of the first electrode farther from the third electrode is more susceptible to deterioration and has higher activity than the side closer to the third electrode. Therefore, the portion of the pump cell that is far from the third electrode mainly pumps oxygen from the measurement chamber to the outside or pumps oxygen from the outside into the measurement chamber. As a result, the responsiveness of the pump cell to changes in voltage Vs was low.

It is an object of one aspect of the present disclosure to provide a sensor and method of manufacturing the sensor in which the pump cell is highly responsive to changes in the voltage Vs or current generated by the reference cell.

One aspect of the present disclosure is a sensor that includes a sensing portion. The detection unit includes a measurement chamber into which the gas to be measured is introduced, a pump cell for pumping oxygen from the measurement chamber to the outside of the element or pumping oxygen from the outside of the element to the measurement chamber, and the measurement chamber and the pump cell. , and a reference cell that generates a voltage Vs or a current according to the oxygen concentration difference from a reference space having an atmosphere of a predetermined oxygen concentration.

The pump cell includes a pump cell solid electrolyte body, a porous pump cell first electrode formed on the pump cell solid electrolyte body and facing the measurement chamber, and a pump cell solid electrolyte body formed on the and a pump cell second electrode facing the outside of the element or a space communicating with the outside of the element. The reference cell includes a reference-cell solid electrolyte body, a first reference-cell electrode facing the measurement chamber, formed on the reference-cell solid electrolyte body, and the reference-cell solid electrolyte body. and a second reference cell electrode facing the reference space. The pump-cell first electrode contains a noble metal and a ceramic contained in the pump-cell solid electrolyte body. When the surface of the first pump cell electrode facing the measurement chamber is observed under magnification, the surface includes a noble metal region made of the noble metal, a ceramic region made of the ceramic, and the noble metal and the ceramic coexist. There is a coexistence area. The width of the coexistence region in region A defined below on the surface is greater than the width of the coexistence region in region B defined below on the surface.

Area A: On the surface, the farthest part from the first reference cell electrode is defined as the farthest part. On the surface, the nearest portion is defined as the portion closest to the reference cell first electrode. Let L be the distance between the farthest part and the nearest part. On the surface, point a is a position moved from the nearest portion to the farthest portion by L/6. The inside of a circle with a radius of L/12 centered at the point a is defined as an A region.

Region B: Point b is a position on the surface that is moved by L/6 from the farthest portion toward the nearest portion. The inside of a circle with a radius of L/12 centered at the point b is defined as a B area.
In the sensor according to one aspect of the present disclosure, the side of the pump cell first electrode closer to the reference cell first electrode is more deteriorated than the side farther from the reference cell first electrode. area is expanding. Therefore, of the pump cell, mainly the portion near the first reference cell electrode pumps oxygen from the measurement chamber to the outside of the element, and pumps oxygen from the outside of the element to the measurement chamber. As a result, the pump cell is highly responsive to changes in the voltage Vs or current generated by the reference cell.

Another aspect of the present disclosure is a method of manufacturing a sensor that includes a sensing portion. The detection unit includes a measurement chamber into which a gas to be measured is introduced, a pump cell for pumping oxygen from the measurement chamber to the outside of the element or pumping oxygen from the outside of the element to the measurement chamber, and the measurement chamber. and a reference cell that generates a voltage Vs or a current according to an oxygen concentration difference from a reference space having an atmosphere of a predetermined oxygen concentration.
The pump cell includes a pump cell solid electrolyte body, a porous pump cell first electrode formed on the pump cell solid electrolyte body and facing the measurement chamber, and a pump cell solid electrolyte body formed on the a pump cell second electrode facing the outside of the element or a space communicating with the outside of the element, the reference cell being formed on the reference cell solid electrolyte body and the reference cell solid electrolyte body, A reference cell first electrode facing the chamber and a reference cell second electrode formed on the reference cell solid electrolyte body and facing the reference space.
In the sensor manufacturing method that is another aspect of the present disclosure, the temperature in region A defined below on the surface of the pump cell first electrode is higher than the temperature in region B defined below on the surface. As described above, the rich aging treatment is performed on the pump cell first electrode.

Area A: On the surface, the farthest part from the first reference cell electrode is defined as the farthest part. On the surface, the nearest portion is defined as the portion closest to the reference cell first electrode. Let L be the distance between the farthest part and the nearest part. On the surface, point a is a position moved from the nearest portion to the farthest portion by L/6. The inside of a circle with a radius of L/12 centered at the point a is defined as an A region.

Region B: Point b is a position on the surface that is moved by L/6 from the farthest portion toward the nearest portion. The inside of a circle with a radius of L/12 centered at the point b is defined as a B area.
In the sensor manufactured by the sensor manufacturing method according to another aspect of the present disclosure, the side of the pump cell first electrode closer to the reference cell first electrode is closer to the reference cell first electrode than the side farther from the reference cell first electrode. As a result, deterioration progresses and the coexistence area expands. Therefore, of the pump cell, mainly the portion near the first reference cell electrode pumps oxygen from the measurement chamber to the outside of the element, and pumps oxygen from the outside of the element to the measurement chamber. As a result, the pump cell is highly responsive to changes in the voltage Vs or current generated by the reference cell.

FIG. 3 is a cross-sectional view of the NOx sensor cut along the axial direction; FIG. 2 is a perspective view showing a gas sensor element with a part in the axial direction omitted; It is explanatory drawing which expands and shows the internal structure which fracture|ruptures the front end side of a gas sensor element in the thickness direction. FIG. 4 is an explanatory diagram showing a zirconia region, a platinum region, a coexistence region, and a gap region on the surface of the first electrode; It is explanatory drawing showing the A area|region and B area|region in the surface of a 1st electrode. FIG. 4 is an explanatory diagram showing an electrical configuration connected to a gas sensor element; 3 is a photograph showing a backscattered electron image acquired in region A and the width of a coexistence region measured at 10 points in the backscattered electron image. 3 is a photograph showing a backscattered electron image obtained in region B and the width of the coexistence region measured at 10 points in the backscattered electron image.

Exemplary embodiments of the present disclosure are described with reference to the drawings.
<First Embodiment>
1. Overall Configuration of NOx Sensor 1 The overall configuration of the NOx sensor 1 will be described with reference to FIGS. 1 and 2. FIG. 1 is called the front end side of the NOx sensor, and the upper side in FIG. 1 is called the rear end side of the NOx sensor 1 hereinafter.

As shown in FIG. 1 , the NOx sensor 1 includes a metallic shell 5 , a gas sensor element 7 , a ceramic sleeve 9 , an insulating separator 13 and six lead frames 15 . 1, only a part of the six lead frames 15 is illustrated.

Each configuration will be described below. As shown in FIGS. 1 and 2, the gas sensor element 7 is a plate-shaped laminated member extending in the axial direction. The gas sensor element 7 penetrates the metal shell 5 . The tip side of the gas sensor element 7 is directed toward the exhaust gas to be measured. Exhaust gas corresponds to the gas to be measured. A detection portion 17 is formed on the tip side of the gas sensor element 7 . The detector 17 is covered with a protective layer (not shown).

As shown in FIG. 2 , electrode pads 23 , 25 , 27 , 29 , 31 and 33 are formed on the rear end side of the gas sensor element 7 . Electrode pads 23 , 25 , 27 are formed on first plate surface 19 , which is one of the outer surfaces of gas sensor element 7 . The electrode pads 29 , 31 , 33 are formed on the second plate surface 21 of the outer surface of the gas sensor element 7 that is opposite to the first plate surface 19 .

The ceramic sleeve 9 has a tubular form. The ceramic sleeve 9 is arranged to radially surround the gas sensor element 7 .
The insulating separator 13 is made of an insulating material such as alumina. The insulating separator 13 has an element insertion hole 11 extending therethrough in the axial direction. The element insertion hole 11 surrounds at least part of the gas sensor element 7 and the lead frame 15 .

The insulating separator 13 holds the lead frame 15 and the gas sensor element 7 inside the element insertion hole 11, so that the lead frame 15 is electrically connected to the electrode pads 23 to 33 of the gas sensor element 7, respectively. The lead frame 15 is also electrically connected to a lead wire 35 arranged inside the sensor from the outside, and the electric current flowing between the external device to which the lead wire 35 is connected and the electrode pads 23 to 33 . Form a current path for current.

The metal shell 5 is a substantially tubular metal member made of, for example, stainless steel. The metal shell 5 has a through-hole 37 that penetrates in the axial direction, and a shelf portion 39 that protrudes radially inward inside the through-hole 37 . A screw portion 3 for fixing to an exhaust pipe is formed on the outer surface of the metallic shell 5 .

The metal shell 5 is configured to hold the gas sensor element 7 inserted through the through hole 37 . The gas sensor element 7 held is in a state in which the detection portion 17 is arranged outside the through hole 37 on the front end side, and the electrode pads 23 to 33 are arranged outside the through hole 37 on the rear end side.

Inside the through-hole 37, an annular ceramic holder 41, powder-filled layers (talc rings) 43 and 45, and the above-mentioned ceramic sleeve 9 are arranged in this order from the tip side in a state surrounding the gas sensor element 7 in the radial direction. Laminated toward the rear end side.

A caulking ring 49 is arranged between the ceramic sleeve 9 and the rear end portion 47 of the metallic shell 5 . A metal cup 51 is arranged between the ceramic holder 41 and the shelf 39 of the metal shell 5 . The rear end portion 47 is crimped via a crimp ring 49 so as to press the ceramic sleeve 9 toward the distal end side.

A tubular protector 52 made of, for example, stainless steel is arranged on the tip side of the metal shell 5 so as to cover the tip side of the gas sensor element 7 . The protector 52 has a vent hole 53 through which the exhaust gas can pass. The protector 52 has a double protector structure consisting of an inner protector and an outer protector.

An outer cylinder 55 made of, for example, stainless steel is fixed to the rear end side of the metallic shell 5 . An opening 57 on the rear end side of the outer cylinder 55 is closed by a grommet 59 made of, for example, fluororubber.

The insulating separator 13 is held inside the outer cylinder 55 with its rear end side in contact with the grommet 59 . A holding member 61 holds the insulating separator 13 . The holding member 61 is fixed inside the outer cylinder 55 by crimping.

2. Configuration of Gas Sensor Element 7 The configuration of the gas sensor element 7 will be described with reference to FIGS. 2 to 8. FIG. As shown in FIG. 2, the gas sensor element 7 has a plate-like shape with a rectangular axial cross-section. The gas sensor element 7 has a structure in which an element portion 63 and a heater 65 are laminated. The element portion 63 and the heater 65 are each formed in a plate shape extending in the axial direction. The element portion 63 corresponds to the detection portion.

FIG. 3 shows the configuration of the tip side of the gas sensor element 7 . The gas sensor element 7 comprises, from the top in FIG. has a laminated structure. Among them, the insulating layer 67 , the first solid electrolyte body 69 , the insulating layer 71 , the second solid electrolyte body 73 , the insulating layer 75 , and the third solid electrolyte body 77 correspond to the element section 63 . The gas sensor element 7 comprises a first pump cell 83 , a reference cell 85 and a second pump cell 87 .

A first measurement chamber 89 is formed between the first solid electrolyte body 69 and the second solid electrolyte body 73 . In FIG. 3, the left end of the first measurement chamber 89 is the entrance. A first diffusion resistor portion 91 is arranged at this entrance. Exhaust gas GM is introduced into the first measurement chamber 89 from the outside of the element through the first diffusion resistance portion 91 . A second diffusion resistance section 93 is arranged at the end of the first measurement chamber 89 opposite to the entrance. The outside of the element means the outside of the gas sensor element 7 .

A second measurement chamber 95 is formed on the right side of the second diffusion resistor portion 93 in FIG. The second measurement chamber 95 communicates with the first measurement chamber 89 via the second diffusion resistor section 93 . A second measurement chamber 95 is formed between the first solid electrolyte body 69 and the third solid electrolyte body 77 . A portion corresponding to the second measurement chamber 95 is cut out of the second solid electrolyte body 73 .

Each of the first to third solid electrolyte bodies 69, 73, 77 is mainly composed of zirconia having oxygen ion conductivity. Each insulating layer 67, 71, 75, 79, 81 is mainly composed of alumina. The first and second diffusion resistors 91 and 93 are each made of porous material such as alumina. In addition, a main component means the component whose content in a ceramic layer is 50 mass % or more.

A resistance heating element 97 is embedded between the insulating layers 79 and 81 . The resistance heating element 97 extends along the horizontal direction in FIG. The resistance heating element 97 is made of platinum, for example. The insulating layers 79 and 81 and the resistance heating element 97 constitute the heater 65 . The heater 65 is in contact with the element portion 63 . The heater 65 raises the temperature of the gas sensor element 7 to a predetermined activation temperature and enhances the oxygen ion conductivity of the first to third solid electrolyte bodies 69, 73, 77 to stabilize the operation. A resistance heating element 97 corresponds to the heating element. A resistance heating element 97 is embedded between the insulating layers 79 and 81 . The insulating layers 79 and 81 and the resistance heating element 97 correspond to the heating portion.

The first pump cell 83 includes a first solid electrolyte body 69 , a first electrode 101 and a second electrode 99 . The first electrode 101 and the second electrode 99 sandwich the first solid electrolyte body 69 .
A first electrode 101 is formed on the first solid electrolyte body 69 . The first electrode 101 faces the first measurement chamber 89 . The first electrode 101 is porous. The first electrode 101 contains platinum, zirconia, and an alloy of platinum and zirconium (hereinafter referred to as a PtZr alloy). The volume ratio of the PtZr alloy in the first electrode 101 is 15% by volume or more. Zirconia corresponds to the ceramic contained in the first solid electrolyte body 69 . Platinum corresponds to the noble metal. The first solid electrolyte body 69 corresponds to a pump cell solid electrolyte body. The first electrode 101 corresponds to the pump cell first electrode. The second electrode 99 corresponds to the pump cell second electrode.

The surface of the first electrode 101 facing the first measurement chamber 89 is referred to as surface 101A. When the surface 101A is magnified and observed, for example, as shown in FIG. 4, there are a zirconia region 203 made of zirconia, a platinum region 205 made of platinum, a coexisting region 207 made of platinum, zirconia, and a PtZr alloy, and a gap region 209. do. Each region can be identified by XRD analysis. Platinum regions 205 correspond to noble metal regions. The zirconia regions 203 correspond to the ceramic regions. A coexistence region 207 is a region where noble metal and ceramic coexist.

A second electrode 99 is formed on the first solid electrolyte body 69 . The second electrode 99 faces the outside of the element. The second electrode 99 is mainly composed of platinum. The second electrode 99 is covered with a porous layer 105 . The porous layer 105 is embedded in the opening 103 of the insulating layer 67 . The porous layer 105 is made of a porous body through which gas such as oxygen can pass. Examples of the porous material include alumina and the like.

Reference cell 85 includes second solid electrolyte body 73 , third electrode 109 , and fourth electrode 111 . A third electrode 109 is formed on the second solid electrolyte body 73 . A fourth electrode 111 is formed on the second solid electrolyte body 73 . The third electrode 109 and the fourth electrode 111 sandwich the second solid electrolyte body 73 . The third electrode 109 faces the first measurement chamber 89 .
Further, when viewed from the stacking direction, the third electrode 109 is formed at a position not overlapping with the first electrode 101 . Further, the third electrode 109 is formed downstream of the first electrode 101 in the flow direction of the exhaust gas introduced from the inlet of the first measurement chamber 89 .
The fourth electrode 111 faces a reference oxygen chamber 113, which will be described later. The third electrode 109 and the fourth electrode 111 each contain platinum as a main component. The second solid electrolyte body 73 corresponds to the reference cell solid electrolyte body. The third electrode 109 corresponds to the reference cell first electrode. The fourth electrode 111 corresponds to the reference cell second electrode. In the first embodiment, the pump cell solid electrolyte body and the reference cell solid electrolyte body are separate bodies. In the first embodiment, the pump cell second electrode and the reference cell second electrode are separate bodies.

The reference oxygen chamber 113 is a portion of the insulating layer 75 cut out. The reference oxygen chamber 113 is a space surrounded by the second solid electrolyte body 73 , the third solid electrolyte body 77 and the insulating layer 75 . The inside of the reference oxygen chamber 113 has an atmosphere of a predetermined oxygen concentration. Reference oxygen chamber 113 corresponds to a reference space having an atmosphere with a predetermined oxygen concentration. In the first embodiment, the space communicating with the outside of the element and the reference space having an atmosphere with a predetermined oxygen concentration are separate spaces.

The second pump cell 87 has a third solid electrolyte body 77 , a fifth electrode 115 and a sixth electrode 117 . The fifth electrode 115 and the sixth electrode 117 are formed on one surface of the third solid electrolyte body 77 respectively. The fifth electrode 115 faces the second measurement chamber 95 . A sixth electrode 117 faces the reference oxygen chamber 113 . The fifth electrode 115 and the sixth electrode 117 are separated by an insulating layer 75 . The fifth electrode 115 and the sixth electrode 117 each contain platinum as a main component. The sixth electrode 117 is covered with a porous insulating protective layer 165 . The reference oxygen chamber 113 has a void 167 that is a space that is not filled with anything.

FIG. 5 shows the surface 101A viewed from the second solid electrolyte body 73 side. The left side in FIG. 5 is the entrance side of the first measurement chamber 89 . The right side in FIG. 5 is the exit side of the first measurement chamber 89 . On surface 101A, A region 301 and B region 303 are defined as follows.

A region 301: A farthest portion 305 is defined as the farthest portion from the third electrode 109 on the surface 101A. The nearest portion 307 is the portion closest to the third electrode 109 on the surface 101A. Let L be the distance between the farthest part 305 and the nearest part 307 . On the surface 101A, point a 309 is the position moved from the nearest portion 307 toward the farthest portion 305 by L/6. A region 301 is defined as the inside of a circle 311 having a radius of L/12 centered at point a 309 .

Region B 303: A point b 313 is a position moved from the farthest portion 305 toward the nearest portion 307 by L/6 on the surface 101A. The inside of a circle 315 with a radius of L/12 centered at the b point 313 is defined as a B area 303 .

Width W of coexistence region 207 in A region 301 is greater than width W of coexistence region 207 in B region 303 . Note that the width W of the coexistence area 207 is a value calculated as follows. The surface 101A is magnified and observed to obtain a backscattered electron image at a magnification of 8000 times. The width of each coexistence region 207 (hereinafter referred to as a local width) is measured at ten randomly selected coexistence regions 207 in the backscattered electron image. FIG. 7 shows an example of the backscattered electron image acquired in the A region 301 and the local width of the coexistence region 207 measured at 10 points in the backscattered electron image. FIG. 8 shows an example of the backscattered electron image acquired in the B region 303 and the local width of the coexistence region 207 measured at 10 points in the backscattered electron image. Let the average value of the local widths of the coexistence region 207 measured at ten locations be the width W of the coexistence region 207 .

The reason why the width W of the coexistence region 207 in the A region 301 is larger than the width W of the coexistence region 207 in the B region 303 is that the side of the first electrode 101 closer to the third electrode 109 is the third electrode. This is because the coexistence region 207 has expanded due to the deterioration progressing compared to the side farther from 109 .

Among the first electrodes 101 , the side closer to the third electrode 109 is more degraded than the side farther from the third electrode 109 , and the coexistence region 207 is expanded. Mainly, the portion close to the third electrode 109 draws oxygen from the first measurement chamber 89 to the outside of the device, and draws oxygen from the outside of the device to the first measurement chamber 89 . As a result, the responsiveness of the first pump cell 83 to changes in the voltage Vs is high.

The ratio of the width W of the coexistence region 207 in the A region 301 to the width W of the coexistence region 207 in the B region 303 (hereinafter referred to as the A/B width ratio) is preferably 1.1 or more. 0.3 or more is more preferable, and 1.5 or more is particularly preferable. When the A/B width ratio is 1.1 or more, the responsiveness of the first pump cell 83 to changes in the voltage Vs is even higher. When the A/B width ratio is 1.3 or more, the responsiveness of the first pump cell 83 to changes in the voltage Vs is even higher. When the A/B width ratio is 1.5 or more, the responsiveness of the first pump cell 83 to changes in the voltage Vs is particularly high.

3. Configuration of Sensor Control Device 169 The configuration of the sensor control device 169 that controls the operation of the gas sensor element 7 will be described with reference to FIG. The sensor control device 169 has a microcomputer 171, an electric circuit section 173, and the like. The microcomputer 171 includes a CPU 175 that executes various calculations, a RAM 177 that stores calculation results and the like, and a ROM 179 that stores programs and the like executed by the CPU 175 .

The microcomputer 171 also includes an A/D converter 181, a signal input/output unit 185, a timer clock (not shown), and the like. The signal input/output unit 185 is connected to the electric circuit unit 173 via the A/D converter 181 and communicates with the ECU 183 .

The electric circuit section 173 is composed of a reference voltage comparison circuit 187, an Ip1 drive circuit 189, a Vs detection circuit 191, an Icp supply circuit 193, a resistance detection circuit 194, an Ip2 detection circuit 195, a Vp2 application circuit 197, and a heater drive circuit 199. be. The electric circuit section 173 is controlled by the microcomputer 171 and uses the gas sensor element 7 to detect the NOx concentration in the exhaust gas GM.

The first electrode 101, the third electrode 109, and the fifth electrode 115 are connected to a reference potential. One electrode of the resistance heating element 97 is grounded.
4. NOx Concentration Detection Processing The processing for detecting the NOx concentration in the exhaust gas GM, which is executed by the sensor control device 169 and the NOx sensor 1, will be described. A heater driving circuit 199 supplies a driving current to the resistance heating element 97 . The resistance heating element 97 raises the temperature and heats the first to third solid electrolyte bodies 69, 73, 77 to activate them. This causes the first pump cell 83, the reference cell 85, and the second pump cell 87 to operate.

The exhaust gas GM is introduced into the first measurement chamber 89 while the flow rate is restricted by the first diffusion resistance section 91 . Here, the Icp supply circuit 193 causes a weak current Icp to flow from the fourth electrode 111 to the third electrode 109 in the reference cell 85 . Therefore, oxygen in the exhaust gas GM can receive electrons from the third electrode 109 in the first measurement chamber 89 on the negative electrode side, becomes oxygen ions, flows through the second solid electrolyte body 73, and reaches the reference Move into the oxygen chamber 113 . In other words, the oxygen in the first measurement chamber 89 is sent into the reference oxygen chamber 113 by applying the current Icp between the third electrode 109 and the fourth electrode 111 .

A Vs detection circuit 191 detects a voltage Vs between the third electrode 109 and the fourth electrode 111 . The voltage Vs is a voltage corresponding to the oxygen concentration difference between the first measurement chamber 89 and the reference oxygen chamber 113 . The Vs detection circuit 191 compares the detected voltage Vs with the reference voltage (425 mV) using the reference voltage comparison circuit 187 and outputs the comparison result to the Ip1 drive circuit 189 . Here, if the oxygen concentration in the first measurement chamber 89 is adjusted so that the voltage Vs becomes constant around 425 mV, the oxygen concentration in the exhaust gas GM in the first measurement chamber 89 is set to a predetermined value (for example, 10 ^{− 8} to 10 ^-9 atm).

When the oxygen concentration of the exhaust gas GM introduced into the first measurement chamber 89 is lower than a predetermined value, the Ip1 drive circuit 189 causes the current Ip1 to flow through the first pump cell 83 so that the second electrode 99 side becomes the negative electrode. Oxygen is pumped into the first measurement chamber 89 from the outside. On the other hand, when the oxygen concentration of the exhaust gas GM introduced into the first measurement chamber 89 is higher than the predetermined value, the Ip1 drive circuit 189 supplies the current Ip1 to the first pump cell 83 so that the first electrode 101 side becomes the negative electrode. , oxygen is pumped out from the inside of the first measuring chamber 89 to the outside of the device.

The exhaust gas GM whose oxygen concentration has been adjusted in the first measurement chamber 89 is introduced into the second measurement chamber 95 via the second diffusion resistance portion 93 . By applying a voltage Vp2 between the sixth electrode 117 and the fifth electrode 115 by the Vp2 applying circuit 197, the NOx in the exhaust gas GM in contact with the fifth electrode 115 in the second measurement chamber 95 is It is decomposed into N ₂ and O ₂ on electrode 115 . The decomposed oxygen turns into oxygen ions, flows through the third solid electrolyte body 77 , and moves into the reference oxygen chamber 113 . Therefore, the current flowing through the second pump cell 87 exhibits a value corresponding to the NOx concentration.

The sensor control device 169 detects the current Ip2 flowing through the second pump cell 87 by the Ip2 detection circuit 195, and detects the NOx concentration in the exhaust gas GM from the current Ip2. Specifically, the relationship between the NOx concentration and the current Ip2 is obtained in advance, a map or the like is prepared in advance, and the measured current Ip2 is referred to the map to obtain the NOx concentration.

5. Manufacturing Method of NOx Sensor 1 A manufacturing method of the NOx sensor 1 will be described.
(5-1) Manufacturing Method of Gas Sensor Element 7 Prepare ceramic sheets as raw materials for insulating layer 67, first solid electrolyte body 69, second solid electrolyte body 73, third solid electrolyte body 77, and insulating layers 79 and 81. do. Through-holes or the like are appropriately formed in the ceramic sheet. Also, the insulating layers 71 and 75 are formed by screen printing on the ceramic sheets.

Next, in order to form each electrode 99, 101, 109, 111, 115, 117, the surface of the corresponding ceramic sheet is coated with a paste containing the material of the electrode. The paste for forming the _first electrode 101 contains platinum and ZrO2. The paste for forming other electrodes is mainly composed of platinum.

Next, ceramic sheets are laminated to form a laminate, and the laminate is fired. At this time, the first electrode precursor is formed on the portion that will later become the first electrode 101 . The _first electrode precursor contains platinum and ZrO2. When the mass of platinum contained in the first electrode precursor is 100 parts by mass, the mass of ZrO ₂ contained in the first electrode precursor is 22 parts by mass. In the first electrode precursor, the volume occupied by platinum is 56% by volume and the volume occupied by ZrO ₂ is 44% by volume.

Next, a rich aging treatment is performed on the first electrode precursor. Conditions for the rich aging treatment are, for example, as follows.
Atmosphere of first electrode precursor: rich atmosphere Voltage between first electrode precursor and second electrode 99: 0.7 to 0.8V
Rich aging treatment time: 40-50 sec
A rich atmosphere is an atmosphere in which the ratio of oxygen is small with respect to the theoretical empty fuel ratio (λ=1). The theoretical air-fuel ratio is the mixture ratio of air and fuel that allows ideal complete combustion.

In the rich aging treatment, for example, a heater is used to heat the first electrode precursor. The heater used may be the heater 65 or an external heater.
In the rich aging process, the temperature in region A 301 of the first electrode precursor is higher than the temperature in region B 303 of the first electrode precursor. As a method of realizing such a temperature difference, for example, there is a method of making the power of the portion of the heater on the nearest portion 307 side larger than the power of the portion on the farthest portion 305 side. Specifically, there is a method in which the portion of the heater on the nearest portion 307 side is thinner than the portion on the farthest portion 305 side. The temperature of the first electrode precursor is a value measured using an infrared radiation thermometer manufactured by Chino.

Further, as a method of achieving the above temperature difference, for example, there is a method of blowing a low-temperature gas to the farthest portion 305 side of the heater to cool it.
Moreover, as a method of realizing the above temperature difference, for example, there is the following method. A heater and a first electrode precursor are contained in the chamber. The distance from the inner wall of the chamber to the first electrode precursor is increased on the farthest portion 305 side and decreased on the nearest portion 307 side. In this case, the amount of radiant heat received by the first electrode precursor from the inner wall of the chamber is small on the farthest portion 305 side and large on the nearest portion 307 side. As a result, the above temperature difference can be achieved.

Due to the rich aging treatment, deterioration progresses in the first electrode precursor, and the coexistence region 207 is generated. As a result, the first electrode 101 is formed from the first electrode precursor, and the gas sensor element 7 is completed. Since the temperature in region A 301 of the first electrode precursor is higher than the temperature in region B 303 of the first electrode precursor, the width W of coexistence region 207 in region A 301 is greater than the width W of the region 207;

The greater the difference between the temperature in region A of the first electrode precursor and the temperature in region B of the first electrode precursor (hereinafter referred to as the AB temperature difference), the greater the A/B width ratio. . By sufficiently increasing the AB temperature difference, the A/B width ratio can be 1 or more, or 1.1 or more, or 1.3 or more, or 1.5 or more.

(5-2) Method for Manufacturing Other Members Parts of the NOx sensor 1 other than the gas sensor element 7 can be manufactured by known methods.
6. Evaluation of NOx Sensor 1 The NOx sensor 1 was manufactured by the method described in the section "5. Manufacturing method of NOx sensor 1". The conditions of the rich aging treatment for the first electrode precursor were as follows.

Atmosphere of first electrode precursor in rich aging treatment: H ₂ = 2.35% by volume, H ₂ O = 10% by volume, N ₂ = remainder Atmospheric gas flow rate in rich aging treatment: 7 L/min
Voltage between first electrode precursor and second electrode 99 in rich aging treatment: 0.77 V
Rich aging treatment time: 40 sec
During the rich aging process, the temperature of the first electrode precursor in region A 301 is reduced to the first It was made higher than the temperature in the B region 303 of the electrode precursor.

In the manufactured NOx sensor 1, the width W of the coexistence region 207 in the A region 301 and the width W of the coexistence region 207 in the B region 303 were measured. Table 1 shows the measurement results. Table 1 also shows measured values of local widths at 10 points used for calculating the width W.

７．ＮＯｘセンサ１が奏する効果
（１Ａ）ＮＯｘセンサ１では、第１電極１０１のうち、第３電極１０９に近い側の方が、第３電極１０９から遠い側に比べて、変質が進行し、共存領域２０７が拡大している。そのため、第１電極１０１のうち、第３電極１０９に近い側の方が、第３電極１０９から遠い側に比べて、活性が高い。そのことにより、第１ポンプセル８３のうち、主として、第３電極１０９に近い部分が、第１測定室８９から素子外部に酸素を汲み出したり、素子外部から第１測定室８９に酸素を汲み入れたりする。その結果、電圧Ｖｓの変化に対する第１ポンプセル８３の応答性が高い。
（１Ｂ）ＮＯｘセンサ１は、ヒータ６５を備える。ヒータ６５は素子部６３に当接している。ヒータ６５は、熱伝導により、素子部６３に効率よく熱を伝えることができる。そのため、ＮＯｘセンサ１は、リッチエージング処理を効率よく行うことができる。
（１Ｃ）ＮＯｘセンサ１では、図３に示すように、ヒータ６５と、基準セル８５と、第１ポンプセル８３とが積層方向に積層されている。積層方向とは、図３における上下方向である。積層方向において、ヒータ６５と第１ポンプセル８３との間に基準セル８５が配置されている。そのため、ヒータ６５を使用した場合でも、第１ポンプセル８３の温度上昇を抑制できる。その結果、第１電極１０１の昇華や改質を抑制できる。
＜第２実施形態＞
１．第１実施形態との相違点
第２実施形態は、基本的な構成は第１実施形態と同様であるため、相違点について以下に説明する。なお、第１実施形態と同じ符号は、同一の構成を示すものであって、先行する説明を参照する。

7. Effects of the NOx sensor 1 (1A) In the NOx sensor 1, the side of the first electrode 101 closer to the third electrode 109 is deteriorated more than the side farther from the third electrode 109, and the coexistence region 207 is enlarged. Therefore, the side of the first electrode 101 closer to the third electrode 109 is more active than the side farther from the third electrode 109 . As a result, the portion of the first pump cell 83 that is close to the third electrode 109 mainly pumps oxygen from the first measurement chamber 89 to the outside of the element, or pumps oxygen from the outside of the element to the first measurement chamber 89. do. As a result, the responsiveness of the first pump cell 83 to changes in the voltage Vs is high.
(1B) The NOx sensor 1 has a heater 65 . The heater 65 is in contact with the element portion 63 . The heater 65 can efficiently transfer heat to the element portion 63 by heat conduction. Therefore, the NOx sensor 1 can efficiently perform the rich aging process.
(1C) In the NOx sensor 1, as shown in FIG. 3, a heater 65, a reference cell 85, and a first pump cell 83 are stacked in the stacking direction. The stacking direction is the vertical direction in FIG. A reference cell 85 is arranged between the heater 65 and the first pump cell 83 in the stacking direction. Therefore, even when the heater 65 is used, the temperature rise of the first pump cell 83 can be suppressed. As a result, sublimation and modification of the first electrode 101 can be suppressed.
<Second embodiment>
1. Differences from First Embodiment Since the basic configuration of the second embodiment is the same as that of the first embodiment, the differences will be described below. Note that the same reference numerals as in the first embodiment indicate the same configurations, and refer to the preceding description.

In the first embodiment described above, the third electrode 109 is formed on the second solid electrolyte body 73 . In contrast, in the second embodiment, the third electrode 109 is formed on the first solid electrolyte body 69 and faces the first measurement chamber 89 . The position of the third electrode 109 is to the right in FIG. 3 compared to the first electrode 101 . Also, the third electrode 109 faces the second electrode 99 with the first solid electrolyte body 69 interposed therebetween.

In the first embodiment described above, the second solid electrolyte body 73, the third electrode 109 formed on the second solid electrolyte body 73, and the fourth electrode 111 correspond to the reference cell. In contrast, in the second embodiment, the first solid electrolyte body 69, the third electrode 109 formed on the first solid electrolyte body 69 as described above, and the second electrode 99 correspond to the reference cell. . In the second embodiment, the second electrode 99 corresponds to the second pump cell electrode and the second reference cell electrode, and the third electrode 109 formed on the first solid electrolyte body 69 corresponds to the first reference cell electrode. correspond to the electrodes.

In the second embodiment, the pump cell solid electrolyte body and the reference cell solid electrolyte body are integrated. In the second embodiment, the pump cell second electrode and the reference cell second electrode are integrated.
In the first embodiment described above, the reference oxygen chamber 113 corresponds to a reference space having an atmosphere with a predetermined oxygen concentration. In contrast, in the second embodiment, the outside of the element facing the second electrode 99 corresponds to the reference space having an atmosphere with a predetermined oxygen concentration. In the second embodiment, the space communicating with the outside of the element and the reference space having the atmosphere with the predetermined oxygen concentration are spaces with the same atmosphere.

2. Effects of the NOx Sensor 1 According to the second embodiment described in detail above, the same effects as those of the above-described first embodiment can be obtained.
<Other embodiments>
Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications can be made.

(1) The sensor of the present disclosure may be a sensor other than a NOx sensor. For example, the NOx sensor 1 described above may be a sensor in which the second pump cell 87 is removed. This sensor can be a sensor that measures the oxygen concentration in the gas to be measured based on the energization amount Ip1.

(2) The ceramic contained in the first solid electrolyte body 69 and the first electrode 101 may be other than zirconia. Ceramics other than zirconia include, for example, CeO ₂ (ceria), ThO ₂ (thoria), HfO ₂ , Bi ₂ O ₃ and the like. The noble metal contained in the first electrode 101 may be other than platinum.

(3) A member that is not formed on the first solid electrolyte body 69 may exist on the outer peripheral side of the first electrode 101 .
(4) In the first embodiment, the reference cell 85 may generate current according to the oxygen concentration difference between the first measurement chamber 89 and the reference oxygen chamber 113 . The NOx sensor 1 can feedback-control the energization amount Ip of the first pump cell 83 so that the current becomes constant.

In the second embodiment, the reference cell 85 may generate a current according to the oxygen concentration difference between the inside of the first measurement chamber 89 and the outside of the element. The NOx sensor 1 can feedback-control the energization amount Ip of the first pump cell 83 so that the current becomes constant.

(5) In the first and second embodiments, the space that the second electrode 99 faces and communicates with the outside of the element may be, for example, a channel or a room that communicates with the outside of the element.
(6) In the first embodiment, the first solid electrolyte body 69, the first solid electrolyte body 73, and the third solid electrolyte body 77 are in the form of one sheet. The first solid electrolyte body 69, the first solid electrolyte body 73, and the third solid electrolyte body 77 may be embedded inside the through-holes of the insulating layer having a shape and through-holes.
(7) A function of one component in each of the above embodiments may be assigned to a plurality of components, or a function of a plurality of components may be performed by one component. Also, part of the configuration of each of the above embodiments may be omitted. Also, at least part of the configuration of each of the above embodiments may be added, replaced, etc. with respect to the configuration of the other above embodiments. It should be noted that all aspects included in the technical idea specified by the wording in the claims are embodiments of the present disclosure.

(8) In addition to the NOx sensor described above, the present disclosure can also be implemented in various forms such as a system including the NOx sensor as a component.

Reference Signs List 1 NOx sensor 7 Gas sensor element 65 Heater 67, 71, 75, 79, 81 Insulating layer 69 First solid electrolyte body 73 Second solid electrolyte body 77 Third solid electrolyte body , 83... First pump cell, 85... Reference cell, 87... Second pump cell, 89... First measurement chamber, 91... First diffusion resistance section, 93... Second diffusion resistance section, 95... Second measurement chamber, 97... Resistance heating element 99 Second electrode 101 First electrode 103 Opening 105 Porous layer 109 Third electrode 111 Fourth electrode 113 Reference oxygen chamber 115 Fifth electrode , 117... Sixth electrode, 301... Area A, 303... Area B, 305... Farthest part, 307... Nearest part, 309... Point a, 313... Point b

Claims (7)

A sensor comprising a detection unit,
The detection unit is
a measurement chamber into which the gas to be measured is introduced;
a pump cell that pumps oxygen from the measurement chamber to the outside of the element or pumps oxygen from the outside of the element to the measurement chamber;
a reference cell that generates a voltage Vs or a current according to an oxygen concentration difference between the measurement chamber and a reference space having an atmosphere of a predetermined oxygen concentration;
with
The pump cell is
a solid electrolyte body for a pump cell;
a porous pump cell first electrode formed on the pump cell solid electrolyte body and facing the measurement chamber;
a pump cell second electrode formed on the pump cell solid electrolyte body and facing the outside of the element or a space communicating with the outside of the element;
with
The reference cell is
a solid electrolyte body for a reference cell;
a reference cell first electrode formed on the reference cell solid electrolyte body and facing the measurement chamber;
a second reference cell electrode formed on the reference cell solid electrolyte body and facing the reference space;
with
The pump cell first electrode contains a noble metal and a ceramic contained in the pump cell solid electrolyte body,
When the surface of the first pump cell electrode facing the measurement chamber is observed under magnification, the surface includes a noble metal region made of the noble metal, a ceramic region made of the ceramic, and the noble metal and the ceramic coexist. There is a coexistence area and
A sensor wherein the width of the coexistence region in the A region defined below on the surface is greater than the width of the coexistence region in the B region defined below on the surface.
Area A: On the surface, the farthest part from the first reference cell electrode is defined as the farthest part. On the surface, the nearest portion is defined as the portion closest to the reference cell first electrode. Let L be the distance between the farthest part and the nearest part. On the surface, point a is a position moved from the nearest portion to the farthest portion by L/6. The inside of a circle with a radius of L/12 centered at the point a is defined as an A region.
Region B: Point b is a position on the surface that is moved by L/6 from the farthest portion toward the nearest portion. The inside of a circle with a radius of L/12 centered at the point b is defined as a B area. A sensor according to claim 1, wherein
further comprising a heater having a heating portion in which a heating element is embedded;
A sensor in which the heat generation portion is in contact with the detection portion. 3. The sensor of claim 2, wherein
the heater, the reference cell, and the pump cell are stacked in a stacking direction,
A sensor in which the reference cell is arranged between the heater and the pump cell in the stacking direction. The sensor according to any one of claims 1 to 3,
The width of the coexistence area in the A area is 1.1 times or more the width of the coexistence area in the B area. The sensor according to any one of claims 1 to 4,
The pump cell solid electrolyte body and the reference cell solid electrolyte body are separate bodies,
the pump cell second electrode and the reference cell second electrode are separate bodies,
The sensor, wherein the reference space is a reference oxygen chamber having an atmosphere with a predetermined oxygen concentration. A method for manufacturing a sensor comprising a detection unit,
The detection unit is
a measurement chamber into which the gas to be measured is introduced;
a pump cell that pumps oxygen from the measurement chamber to the outside of the element or pumps oxygen from the outside of the element to the measurement chamber;
a reference cell that generates a voltage Vs or a current according to an oxygen concentration difference between the measurement chamber and a reference space having an atmosphere of a predetermined oxygen concentration;
with
The pump cell is
a solid electrolyte body for a pump cell;
a porous pump cell first electrode formed on the pump cell solid electrolyte body and facing the measurement chamber;
a pump cell second electrode formed on the pump cell solid electrolyte body and facing the outside of the element or a space communicating with the outside of the element;
with
The reference cell is
a solid electrolyte body for a reference cell;
a reference cell first electrode formed on the reference cell solid electrolyte body and facing the measurement chamber;
a second reference cell electrode formed on the reference cell solid electrolyte body and facing the reference space;
with
The first pump cell electrode is subjected to rich aging treatment such that the temperature in region A defined below on the surface of the first pump cell electrode is higher than the temperature in region B defined below on the surface of the first pump cell electrode. A method of manufacturing a sensor that performs
Area A: On the surface, the farthest part from the first reference cell electrode is defined as the farthest part. On the surface, the nearest portion is defined as the portion closest to the reference cell first electrode. Let L be the distance between the farthest part and the nearest part. On the surface, point a is a position moved from the nearest portion to the farthest portion by L/6. The inside of a circle with a radius of L/12 centered at the point a is defined as an A region.
Region B: Point b is a position on the surface that is moved by L/6 from the farthest portion toward the nearest portion. The inside of a circle with a radius of L/12 centered at the point b is defined as a B area. A method for manufacturing the sensor according to claim 6,
The pump cell solid electrolyte body and the reference cell solid electrolyte body are separate bodies,
the pump cell second electrode and the reference cell second electrode are separate bodies,
The sensor manufacturing method, wherein the reference space is a reference oxygen chamber having an atmosphere with a predetermined oxygen concentration.

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