JP5204638B2 - Gas sensor - Google Patents

Description

  The present invention relates to a gas sensor.

  Conventionally, a gas sensor that detects a specific gas component such as nitrogen oxide (NOx) or oxygen and measures the concentration of the specific gas component has been used. As such a gas sensor, one having a solid electrolyte body and a pair of electrodes formed on the solid electrolyte body is known.

Japanese Patent Laid-Open No. 2004-151018

  By the way, it is known that noble metals such as Pt and Rh are used as an electrode material as in Patent Document 1, but if the electrode is formed so as to include a material containing a solid electrolyte, the durability of the electrode can be increased. (For example, adhesion between the electrode and the solid electrolyte body) can be improved. However, in order to improve the durability of the electrode, the electrode activity, which is the original role of the electrode, may be reduced by increasing the content of the solid electrolyte in the electrode. As a result, the detection accuracy of the specific gas component in the gas to be detected may decrease.

  The present invention has been made to solve at least a part of the above problems, and an object of the present invention is to provide a technique capable of achieving both durability and electrode activity.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1] A detection chamber into which a gas to be detected is introduced from the outside through a diffusion resistance portion, a solid electrolyte body, and a pair of electrodes formed on the solid electrolyte body, An internal electrode, which is one of the electrodes, is disposed in the detection chamber, and includes an oxygen pump cell that pumps or pumps oxygen into the detection gas introduced into the detection chamber. A downstream electrode, and an upstream electrode that is electrically connected to the downstream electrode and disposed upstream of the downstream electrode in the gas flow of the gas to be detected in the detection chamber, and the upstream electrode and the downstream electrode Each includes a main component of the solid electrolyte body and a conductive material, and a content of the main component of the solid electrolyte body in the upstream electrode is determined by the solid electrolyte body in the downstream electrode. Than the content of the main component, frequently, characterized in that the gas sensor.

  The upstream electrode is arranged on the upstream side of the gas flow of the gas to be detected from the downstream electrode in the detection chamber. Therefore, the detected gas exposed to the upstream electrode may have a higher oxygen concentration in the detected gas than the detected gas exposed to the downstream electrode. As a result, the oxidation of the upstream electrode is more likely to occur, and the durability of the electrode may be further reduced, but the durability of the upstream electrode is improved by containing a larger amount of the main component of the solid electrolyte body. Can be made. On the other hand, since the oxidation of the downstream electrode is less likely to occur than the upstream electrode, the content of the main component of the solid electrolyte body can be reduced to improve the electrode activity in the downstream electrode, and the specificity in the detected gas The detection accuracy of the gas component can be increased. Therefore, it is possible to achieve both durability of the internal electrode and electrode activity.

Application Example 2 The gas sensor according to Application Example 1, further including a heater for heating the gas sensor, wherein a heat generation center by the heater is disposed at a position closer to the upstream electrode than the downstream electrode. , Gas sensor.

  Some gas sensors include a heater for early detection by the gas sensor. In this case, by arranging the heat generation center of the heater at a position closer to the upstream electrode than the downstream electrode, the downstream electrode can be prevented from being heated excessively compared to the upstream electrode. Therefore, excessive deterioration of the downstream electrode can be prevented, and the detection accuracy of the specific gas component in the gas to be detected can be increased.

Application Example 3 The gas sensor according to Application Example 1 or Application Example 2, wherein the gas sensor has an overlapping portion where a part of the downstream electrode and a part of the upstream electrode overlap.

  According to this configuration, the upstream electrode and the downstream electrode can be easily conducted, the detection chamber can be made small, and the gas sensor can be miniaturized.

Application Example 4 The gas sensor according to Application Example 3, wherein the upstream electrode is in contact with the solid electrolyte body and the downstream electrode overlaps the upstream electrode in the overlapping portion.

  According to this configuration, the downstream electrode is exposed to the detection chamber in the overlapping portion while ensuring sufficient adhesion between the upstream electrode containing the greater amount of the main component of the solid electrolyte body and the solid electrolyte body. Therefore, the detection accuracy of the specific gas component in the detection gas can be enhanced over a wide range. Furthermore, the adhesion between the upstream electrode and the downstream electrode can be made compatible.

Application Example 5 In the gas sensor according to Application Example 3 or Application Example 4, the gas sensor is provided with a side wall standing from the solid electrolyte body and forming the detection chamber, and the overlapping portion is located away from the side wall. The gas sensor is formed on.

  According to this configuration, even when the formation positions of the upstream electrode and the downstream electrode are shifted, it is possible to suppress the overlapping portion between the upstream electrode and the downstream electrode from interfering with the side wall. Therefore, it is possible to prevent the occurrence of cracks caused by the overlapping portion where the electrode thickness is relatively thick interfering with the side wall.

Application Example 6 The gas sensor according to any one of Application Example 1 to Application Example 5, wherein the diffusion resistance in the detection chamber when viewed in the stacking direction of the solid electrolyte body and the internal electrode. The gas sensor is partitioned between the upstream electrode and the downstream electrode.

  According to this configuration, since the gas having an excessively high oxygen concentration flows to the downstream electrode by the adjustment of the oxygen concentration by the upstream electrode, an excessive decrease in the durability of the downstream electrode can be suppressed.

[Application Example 7] The gas sensor according to any one of Application Examples 1 to 6, wherein the content of the main component of the solid electrolyte body when the content of the conductive material in the upstream electrode is 100 wt% Is 20 wt% or more, and when the content of the conductive material in the downstream electrode is 100 wt%, the content of the main component of the solid electrolyte body is 15 wt% or less.

  According to this configuration, good durability of the upstream electrode and good activity in the downstream electrode can be realized.

Application Example 8] The gas sensor according to any one of Applications 1 to 7, the porosity of the upstream electrode is smaller than the porosity of the downstream electrode, the gas sensor.

  According to this configuration, the oxidation of the upstream electrode is more likely to occur, and the durability of the electrode may be further reduced. However, since the content of the main component of the solid electrolyte body is more contained, the upstream electrode is durable. Can be improved. On the other hand, since the oxidation of the downstream electrode is less likely to occur than the upstream electrode, the content of the main component of the solid electrolyte body can be reduced to improve the electrode activity in the downstream electrode, and the specificity in the detected gas The detection accuracy of the gas component can be increased. Therefore, it is possible to achieve both durability of the internal electrode and electrode activity.

  In addition, this invention can be implement | achieved in various aspects, for example, can be implement | achieved in aspects, such as a gas sensor system containing the gas sensor and its gas sensor, and the control apparatus of a gas sensor.

Next, embodiments of the present invention will be described in the following order based on examples.
A. First embodiment:
B. Variations:

A. First embodiment:
A1. Device configuration:
FIG. 1 is a cross-sectional view showing a gas sensor 200 as an embodiment of the present invention. This gas sensor 200 is fixed to an exhaust pipe of an internal combustion engine (engine) (not shown) and measures the concentration of nitrogen oxides (NOx) (hereinafter, the gas sensor 200 is also referred to as “NOx sensor 200”). FIG. 1 shows a cross section of the NOx sensor 200 parallel to the longitudinal direction D1. 1 is referred to as the front end direction (front end side) FWD of the NOx sensor 200, and the upper direction (upper side) in FIG. 1 is referred to as the rear end direction (rear end side) BWD of the NOx sensor 200. .

  The NOx sensor 200 includes a cylindrical metal shell 138, a plate-shaped NOx sensor element 10 (gas sensor element 10) extending in the longitudinal direction D1, a cylindrical ceramic sleeve 106 surrounding the NOx sensor element 10, and an insulating contact. A member 166 and six connection terminals 110 (two are shown in FIG. 1) are provided. A threaded portion 139 for fixing to the exhaust pipe is formed on the outer surface of the metal shell 138. The ceramic sleeve 106 is disposed so as to surround the periphery of the NOx sensor element 10 in the radial direction. The insulating contact member 166 is formed with a contact insertion hole 168 penetrating in the longitudinal direction D1. The insulating contact member 166 is disposed so that the inner wall surface of the contact insertion hole 168 surrounds the periphery of the rear end portion of the NOx sensor element 10. Each connection terminal 110 is disposed between the NOx sensor element 10 and the insulating contact member 166.

  The metal shell 138 has a substantially cylindrical shape having a through hole 154 that penetrates in the axial direction, and a shelf 152 that protrudes radially inward of the through hole 154. In the metal shell 138, the tip of the NOx sensor element 10 is arranged outside the tip side (FWD side) of the through hole 154, and the rear end side of the NOx sensor element 10 is outside the rear end side (BWD side) of the through hole 154. The NOx sensor element 10 is held in the through hole 154 so as to be arranged. The shelf 152 includes a tapered surface inclined with respect to a plane perpendicular to the longitudinal direction D1. The tapered surface is formed so that the diameter on the front end side (FWD side) is smaller than the diameter on the rear end side (BWD side).

  Inside the through hole 154 of the metal shell 138, a ceramic holder 151, powder filling layers 153 and 156 (hereinafter also referred to as talc rings 153 and 156), and a ceramic sleeve 106 are arranged in this order from the front end side to the rear end side. Are stacked. Hereinafter, the entire ceramic holder 151, talc rings 153 and 156, and the ceramic sleeve 106 correspond to a holding unit that holds the NOx sensor element 10, and are hereinafter also referred to as “holding unit 160”. Each of the holding portions 160 has an annular shape that surrounds the periphery of the NOx sensor element 10 in the radial direction. The NOx sensor element 10 is held by the holding unit 160.

  A caulking packing 157 is disposed between the ceramic sleeve 106 and the rear end portion 140 of the metal shell 138. Between the ceramic holder 151 and the shelf 152 of the metal shell 138, a metal holder 158 for holding the talc ring 153 and the ceramic holder 151 and maintaining airtightness is disposed. Note that the rear end portion 140 of the metal shell 138 is crimped so as to press the ceramic sleeve 106 toward the distal end side via the crimping packing 157.

  Moreover, as shown in FIG. 1, the external protector 142 and the internal protector 143 are attached to the outer periphery of the front end side (downward in FIG. 1) of the metal shell 138 by welding or the like. The double protectors 142 and 143 are made of a metal having a plurality of holes (for example, stainless steel) and cover the protruding portion of the NOx sensor element 10.

  An outer cylinder 144 is fixed to the outer periphery on the rear end side of the metal shell 138. A grommet 150 is disposed in the opening on the rear end side (upper side in FIG. 1) of the outer cylinder 144. A lead wire insertion hole 161 is formed in the grommet 150. Six lead wires 146 are inserted through the lead wire insertion holes 161 (only five lead wires 146 are shown in FIG. 1). These lead wires 146 are electrically connected to electrode pads (not shown) provided on the outer surface of the rear end side of the NOx sensor element 10, respectively.

  Further, an insulating contact member 166 is disposed on the rear end side (upper side in FIG. 1) of the NOx sensor element 10 protruding from the rear end portion 140 of the metal shell 138. The insulating contact member 166 is disposed around an electrode pad (not shown) formed on the rear end surface of the NOx sensor element 10. The insulating contact member 166 is formed in a cylindrical shape having a contact insertion hole 168 that penetrates in the longitudinal direction D1, and includes a flange portion 167 that protrudes radially outward from the outer surface. A holding member 169 is inserted between the insulating contact member 166 and the outer cylinder 144. The holding member 169 arranges the insulating contact member 166 inside the outer cylinder 144 by contacting the outer cylinder 144 and the flange portion 167.

  FIG. 2 is a cross-sectional view of the NOx sensor element 10. This sectional view shows a section parallel to the longitudinal direction D1. In FIG. 2, the left direction indicates the front end direction (front end side) FWD, and the right direction indicates the rear end direction (rear end side) BWD. In the NOx sensor element 10, an insulating layer 14e, a first solid electrolyte layer 11a, an insulating layer 14a, a third solid electrolyte layer 12a, an insulating layer 14b, a second solid electrolyte layer 13a, and insulating layers 14c and 14d are stacked in this order. It has a structure. These layers are stacked along a stacking direction D2 perpendicular to the longitudinal direction D1.

  A first detection chamber 16 is formed between the first solid electrolyte layer 11a and the third solid electrolyte layer 12a. 3 is a cross-sectional view taken along line AA of the NOx sensor element 10 shown in FIG. This cross-sectional view shows a cross section perpendicular to the stacking direction D2. FIG. 3 shows a part of the NOx sensor element 10 in the distal direction FWD (a part including the first detection chamber 16). FIG. 3 also shows an inner first pump electrode 11c (upstream electrode 11cU and downstream electrode 11cD) which will be described later. FIG. 3 shows two cross-sectional views on the left and right. These sectional views represent the same cross section. In these cross-sectional views, different members are hatched.

  As shown in FIG. 3, in this embodiment, the front end side (FWD side) of the insulating layer 14a is the front end portion 14a3 disposed at the end portion in the front end direction FWD of the NOx sensor element 10 and one of the short side direction D3. The first side wall portion 14a1 disposed on the side (left side in FIG. 3) and the second side wall portion 14a2 disposed on the other side in the short side direction D3 (right side in FIG. 3). The short direction D3 indicates a direction perpendicular to both the longitudinal direction D1 and the stacking direction D2. The distal end portion 14a3 extends from one end to the other end along the short direction D3. The two side wall portions 14a1 and 14a2 are arranged at positions separated from the front end portion 14a3 in the rear end direction BWD. Each of the two side wall portions 14a1 and 14a2 extends along the longitudinal direction D1.

  A first diffusion resistor 15a1 is disposed between the first side wall portion 14a1 and the tip end portion 14a3. A first diffusion resistor 15a2 is disposed between the second side wall portion 14a2 and the tip end portion 14a3. Hereinafter, the entire first diffusion resistors 15a1 and 15a2 are also simply referred to as “first diffusion resistors 15a”. Further, a second diffusion resistor 15b is disposed between the first side wall portion 14a1 and the second side wall portion 14a2.

  The first detection chamber 16 is surrounded by the first side wall portion 14a1, the second side wall portion 14a2, the tip end portion 14a3, the first diffusion resistor 15a, and the second diffusion resistor 15b. Then, the measurement gas GM is introduced into the first detection chamber 16 from the outside through the first diffusion resistor 15a, and the gas is discharged from the first detection chamber 16 through the second diffusion resistor 15b.

  As shown in FIG. 2, in the rear end direction BWD of the first detection chamber 16, a second detection chamber 18 communicating with the first detection chamber 16 through the second diffusion resistor 15b is formed. The second detection chamber 18 penetrates the third solid electrolyte layer 12a and is formed between the first solid electrolyte layer 11a and the second solid electrolyte layer 13a.

  A heater 50 extending along the longitudinal direction D1 is embedded between the insulating layers 14c and 14d. The heater 50 is used to stabilize the operation by raising the temperature of the gas sensor element 10 to a predetermined activation temperature and increasing the conductivity of oxygen ions in the solid electrolyte layer. The heater 50 is a heating resistor formed of a conductor such as tungsten, and generates heat by supplied power. The heater 50 is supported by the two layers 14c and 14d.

  The gas sensor element 10 includes a first oxygen pump cell 11, an oxygen concentration detection cell 12, and a second oxygen pump cell 13.

  The first oxygen pump cell 11 includes a first solid electrolyte layer 11a, an inner first pump electrode 11c (hereinafter also referred to as “first internal electrode 11c”) disposed so as to sandwich the first solid electrolyte layer 11a, and a first counter electrode. A counter electrode 11b (also referred to as an outer first pump electrode 11b) is provided. The first internal electrode 11 c faces the first detection chamber 16. Both the first inner electrode 11c and the outer first pump electrode 11b are formed mainly of platinum. The surface of the first internal electrode 11c is covered with a protective layer 11e made of a porous material. Further, a portion 11d of the insulating layer 14e facing the outer first pump electrode 11b is formed of a porous material (for example, alumina) through which a gas (for example, oxygen) can pass. The pair of electrodes 11b and 11c corresponds to “a pair of electrodes of the oxygen pump cell” in the claims. As shown in FIGS. 2 and 3, in the present embodiment, the first internal electrode 11c is divided into an upstream electrode 11cU and a downstream electrode 11cD. The reason for this will be described later.

  The oxygen concentration detection cell 12 includes a third solid electrolyte layer 12a, and a detection electrode 12b and a reference electrode 12c arranged so as to sandwich the third solid electrolyte layer 12a. The detection electrode 12b faces the first detection chamber 16 on the downstream side of the first internal electrode 11c. Both the detection electrode 12b and the reference electrode 12c are formed mainly of platinum.

  The insulating layer 14b is cut out so that the reference electrode 12c in contact with the third solid electrolyte layer 12a is disposed inside. The cutout portion is filled with a porous body to form a reference oxygen chamber 17. Oxygen is sent from the first detection chamber 16 into the reference oxygen chamber 17 by passing a weak constant current through the oxygen concentration detection cell 12 in advance. The oxygen concentration in the reference oxygen chamber 17 is maintained at a predetermined concentration. Thereby, the reference oxygen chamber 17 is used as a reference for the oxygen concentration.

  The second oxygen pump cell 13 includes a second solid electrolyte layer 13a, an inner second pump electrode 13b disposed on the surface of the second solid electrolyte layer 13a facing the second detection chamber 18, and a second counter electrode. And a counter electrode (counter electrode second pump electrode 13c). Both the inner second pump electrode 13b and the counter second pump electrode 13c are formed mainly of platinum. The counter electrode second pump electrode 13c is disposed in a cutout portion of the insulating layer 14b on the second solid electrolyte layer 13a, and faces the reference oxygen chamber 17 so as to face the reference electrode 12c. The inner second pump electrode 13 b faces the second detection chamber 18.

  In this embodiment, the solid electrolyte layers 11a, 12a and 13a are each formed using zirconia having oxygen ion conductivity (partially stabilized zirconia in this embodiment). The insulating layers 14a to 14e are formed mainly using alumina, and the first diffusion resistor 15a and the second diffusion resistor 15b are formed using a porous material such as alumina. Six layers 14e, 11a, 12a, 13a, 14c, and 14d of the eight layers of the solid electrolyte layer and the insulating layer are each formed using a raw material sheet (for example, zirconia or alumina). Ceramic sheet). Each electrode and the two insulating layers 14a and 14b are formed by screen printing on a ceramic sheet. And the NOx sensor element 10 is formed by baking the laminated body obtained by laminating | stacking each layer before baking.

  FIG. 2 also shows the control unit CU of the NOx sensor 200 (NOx sensor element 10). The control unit CU is connected to the heater 50 and the electrodes 11b, 11c, 12b, 12c, 13b, and 13c via the connection terminal 110 and the lead wire 146 shown in FIG. 1 (in this embodiment, Some of the electrodes are connected to a common lead 146). As will be described later, the control unit CU supplies power to the heater 50. The control unit CU controls the NOx sensor 200 (NOx sensor element 10) by transmitting and receiving signals to and from the electrodes 11b, 11c, 12b, 12c, 13b, and 13c. In the present embodiment, the control unit CU is an electronic circuit formed using an operational amplifier or the like. Instead, the control unit CU may be formed using a computer having a CPU and a memory.

  Next, an example of the operation of the NOx sensor element 10 will be described. First, the control unit CU is activated by starting the engine. The control unit CU supplies power to the heater 50. The heater 50 heats the first oxygen pump cell 11, the oxygen concentration detection cell 12, and the second oxygen pump cell 13 to the activation temperature. Then, the control unit CU causes a current to flow through the first oxygen pump cell 11 in accordance with the heating of the cells 11 to 13 to the activation temperature. Thereby, the first oxygen pump cell 11 pumps excess oxygen in the gas to be measured (exhaust gas) GM flowing into the first detection chamber 16 from the first internal electrode 11c toward the first counter electrode 11b.

  The control unit CU controls the interelectrode voltage (interterminal voltage) of the first oxygen pump cell 11 so that the interelectrode voltage (interterminal voltage) of the oxygen concentration detection cell 12 becomes a constant voltage V1 (for example, 425 mV). The voltage of the oxygen concentration detection cell 12 represents the oxygen concentration in the detection electrode 12b. By this control, the oxygen concentration in the first detection chamber 16 is adjusted to such a degree that the NOx is slightly decomposed. When oxygen in the first detection chamber 16 is insufficient, oxygen is supplied from the outer first pump electrode 11b to the first inner electrode 11c. By switching the polarity of the voltage between the electrodes of the first oxygen pump cell 11, it is possible to switch between pumping and pumping oxygen into the first detection chamber 16.

  The gas to be measured GN whose oxygen concentration is adjusted is introduced into the second detection chamber 18 via the second diffusion resistor 15b. The control unit CU applies an interelectrode voltage (interterminal voltage) to the second oxygen pump cell 13. This voltage is set to a constant voltage such that the NOx gas in the measurement gas GN is decomposed into oxygen and nitrogen gas (a voltage higher than the control voltage value of the oxygen concentration detection cell 12, for example, 450 mV). Thereby, NOx in the measurement gas GN is decomposed into nitrogen and oxygen.

  The control unit CU supplies a second pump current to the second oxygen pump cell 13 so as to pump out oxygen generated by the decomposition of NOx from the second detection chamber 18. The second pump current increases almost in proportion to the amount (concentration) of oxygen generated by the decomposition of NOx. Therefore, the NOx concentration in the measurement gas GN can be detected by detecting the second pump current.

  Specifically, in the present embodiment, as described above, the oxygen concentration in the first detection chamber 16 is adjusted so as to decompose NOx slightly. That is, the voltage between the electrodes of the first oxygen pump cell 11 is controlled so that a small amount (constant concentration) of oxygen is contained in the measurement gas GN discharged from the first detection chamber 16. Thus, regardless of the presence or absence of NOx in the gas to be measured GM, the gas to be measured GN contains a certain concentration of oxygen. Therefore, the second pump current flowing through the second oxygen pump cell 13 has a total value of an offset (constant value) corresponding to this oxygen concentration and a gain (variable value) corresponding to the concentration of NOx in the measured gas GN. Show. In addition, it is preferable that the oxygen concentration of the measurement gas GN is small. In particular, the oxygen concentration is preferably set so that the offset is about the same as or less than the gain fluctuation range.

  Next, the configuration of the first internal electrode 11c (upstream electrode 11cU and downstream electrode 11cD) will be described. In the present embodiment, each of the upstream electrode 11cU and the downstream electrode 11cD is formed using a material containing platinum and partially stabilized zirconia. Partially stabilized zirconia is the main component of the first solid electrolyte layer 11a. Accordingly, the adhesion between the electrodes 11cU and 11cD and the first solid electrolyte layer 11a can be improved. The main component means a component having the largest weight ratio with respect to the total weight of all components.

  Incidentally, the gas to be measured GM having a high oxygen concentration can come into contact with the first internal electrode 11c (for example, when the air-fuel ratio is higher than the stoichiometric air-fuel ratio (lean)). When the oxygen concentration is high, platinum in the electrode is easily oxidized. Oxidation of platinum can cause electrode degradation (eg, platinum sublimates). And deterioration of an electrode can cause peeling from the 1st solid electrolyte layer 11a of an electrode.

  Therefore, in this embodiment, the two electrodes 11cU and 11cD are configured as follows. 4 is a cross-sectional view of the NOx sensor element 10 shown in FIG. 3 taken along the line BB. This cross-sectional view shows a cross section perpendicular to the longitudinal direction D1, and shows a cross section crossing the upstream electrode 11cU and the first diffusion resistor 15a. FIG. 4 shows a part of the periphery of the first detection chamber 16.

  As shown in FIG. 4, the first diffusion resistor 15a (15a1, 15a2) includes an inner wall 11aW of the first solid electrolyte layer 11a and an inner wall 12aW of the third solid electrolyte layer 12a (a wall facing the inner wall 11aW). Arranged between. Then, the measurement gas GM flows into the first detection chamber 16 through the first diffusion resistor 15a. As shown in FIG. 3, the upstream electrode 11cU and the downstream electrode 11cD are arranged along the longitudinal direction D1 (the downstream electrode 11cD is arranged in the rear end direction BWD of the upstream electrode 11cU). The first diffusion resistor 15a is formed in a short direction D3 perpendicular to the longitudinal direction D1 (crossing the longitudinal direction D1) as viewed from the upstream electrode 11cU. Thus, the upstream electrode 11cU is disposed on the upstream side of the gas flow in the first detection chamber 16 with respect to the downstream electrode 11cD. An upstream electrode 11cU is formed in the middle of the flow path from the first diffusion resistor 15a to the downstream electrode 11cD. When viewed along the stacking direction D2 (that is, the stacking direction of the first solid electrolyte layer 11a and the first internal electrode 11c), between the first diffusion resistor 15a and the downstream electrode 11cD in the first detection chamber 16 Is partitioned by the upstream electrode 11cU. That is, the gas cannot reach the downstream electrode 11cD from the first diffusion resistor 15a without passing through the portion facing the upstream electrode 11cU. Accordingly, the gas to be measured GM that has flowed through the first diffusion resistor 15a first contacts the upstream electrode 11cU. The gas after the oxygen concentration is adjusted by the upstream electrode 11cU comes into contact with the downstream electrode 11cD.

  As described above, the upstream electrode 11cU can be in contact with a gas having a higher oxygen concentration than the downstream electrode 11cD. Therefore, the upstream electrode 11cU is in an environment that is more likely to deteriorate than the downstream electrode 11cD. Therefore, in this example, the content of partially stabilized zirconia in the upstream electrode 11cU is set to a value larger than the content of partially stabilized zirconia in the downstream electrode 11cD (FIG. 3). In the present embodiment, the content MU of partially stabilized zirconia in the upstream electrode 11cU is 22 wt%, and the content MD of zirconia in the downstream electrode 11cD is 14 wt%. Thereby, the adhesiveness between the upstream electrode 11cU and the first solid electrolyte layer 11a can be made stronger than the adhesiveness between the downstream electrode 11cD and the first solid electrolyte layer 11a. As a result, peeling of the upstream electrode 11cU can be suppressed. That is, the overall durability of the first internal electrode 11c can be improved. Moreover, the activity in the downstream electrode 11cD can be increased as compared with the upstream electrode 11cU. As a result, it is possible to prevent an excessive decrease in the overall activity of the first internal electrode 11c. By these, durability and electrode activity can be made compatible. Moreover, the detection accuracy of the specific gas component (NOx in this embodiment) by the gas sensor 200 can be improved by preventing an excessive decrease in electrode activity.

  The partially stabilized zirconia content in the electrodes 11cU and 11cD indicates the partially stabilized zirconia content (wt%) based on the platinum content (100 wt%). For example, when a mixed material of 1.0 g of platinum and 0.2 g of zirconia is used, the content of zirconia is 0.2 / 1.0 = 20 wt%.

  FIG. 3 also shows the porosity PU and PD of the electrodes 11cU and 11cD. The porosity is obtained by observing a mirror-polished cross section of the electrode with an SEM (scanning electron microscope) and calculating the ratio of the area of the void portion to the total area of the cross section in the field of view. In this embodiment, the porosity PU of the upstream electrode 11cU is 10%, and the porosity PD of the downstream electrode 11cD is 40%. Thus, since the porosity PU of the upstream electrode 11cU is low, the adhesion between the upstream electrode 11cU and the first solid electrolyte layer 11a can be enhanced. Moreover, since the porosity PD of the downstream electrode 11cD is high, the contact between the gas and the electrode in the downstream electrode 11cD can be promoted. As a result, the activity of the downstream electrode 11cD can be increased.

  In addition, you may employ | adopt other various values as a porosity of each electrode 11cU and 11cD. In any case, the porosity PU in the upstream electrode 11cU is preferably smaller than the porosity PD in the downstream electrode 11cD. If it carries out like this, durability can be improved in the upstream electrode 11cU, and activity can be improved in the downstream electrode 11cD. However, the porosity PU in the upstream electrode 11cU may be larger than the porosity PD in the downstream electrode 11cD.

  Various methods can be adopted as a method of adjusting the porosity of each electrode 11cU, 11cD. For example, the porosity may be adjusted by adjusting the content of the organic binder added to the electrode material (the higher the organic binder content, the higher the porosity). As a material of the above-described upstream electrode 11cU, for example, a mixture of platinum (Pt), 22 wt% partially stabilized zirconia, and 7 wt% organic binder may be adopted (the content is the platinum content). It is a value used as a reference (100 wt%). As a material of the downstream electrode 11cD, for example, a mixture of platinum, 14 wt% partially stabilized zirconia, and 10 wt% organic binder may be employed. As the organic binder, various resins that can be removed by drying or baking can be used. For example, ethyl cellulose may be employed. Moreover, by adding a solvent (for example, butyl carbitol) to these mixtures, the fluidity of the material can be increased, and the electrode can be easily formed.

  FIG. 5 is a cross-sectional view of the NOx sensor element 10 shown in FIG. This cross-sectional view shows a cross section perpendicular to the short-side direction D3, and shows a cross section crossing the distal end portion 14a3, the upstream electrode 11cU, and the downstream electrode 11cD. FIG. 5 shows a part of the periphery of the first detection chamber 16. The cross-sectional view shown in FIG. 2 is also a CC cross-sectional view.

  An upstream electrode 11cU and a downstream electrode 11cD are stacked on the first solid electrolyte layer 11a (inner wall 11aW). Here, a part of the downstream electrode 11cD overlaps a part of the upstream electrode 11cU (overlapping part 11v). Thereby, the upstream electrode 11cU and the downstream electrode 11cD can be easily conducted. Further, the entire first internal electrode 11c can be reduced in size. Thereby, the 1st detection chamber 16, and by extension, the gas sensor element 10 (gas sensor 200) can be reduced in size. In the present embodiment, the upstream electrode 11cU is in contact with the first solid electrolyte layer 11a (inner wall 11aW) in the overlapping portion 11v. And the downstream electrode 11cD has overlapped on the upstream electrode 11cU. Therefore, compared with the case where the downstream electrode 11cD is sandwiched between the upstream electrode 11cU and the first solid electrolyte layer 11a, the adhesion between the upstream electrode 11cU and the first solid electrolyte layer 11a can be strengthened. Moreover, since both the electrodes 11cU and 11cD contain a common component (platinum and partially stabilized zirconia), the adhesion between these electrodes 11cU and 11cD can be strengthened. Further, since the downstream electrode 11cD is exposed to the first detection chamber 16 in the overlapping portion 11v, the detection accuracy of the specific gas component (NOx in this embodiment) in the detection gas can be increased.

  In the right sectional view of FIG. 3, the overlapping portion 11v is hatched. In the drawing, the side wall SW of the first detection chamber 16 is indicated by a bold line. In the figure, six side walls SW1 to SW6 included in the side wall SW are shown. The six side walls SW1 to SW6 are inner walls of the first side wall portion 14a1, the first inlet diffusion resistor 15a1, the tip portion 14a3, the second inlet diffusion resistor 15a2, the second side wall portion 14a2, and the second diffusion resistor 15b, respectively. It is. The sidewall SW is erected from the first solid electrolyte layer 11a. In the present embodiment, the side wall SW is connected to the inner wall 11aW of the first solid electrolyte layer 11a and is parallel to the inner wall 11aW (in the present embodiment, the first detection chamber 16 in the longitudinal direction D1 and the short direction D3). The range is defined.

  As shown in the drawing, the overlapping portion 11v is formed at a position away from the side wall SW. Therefore, even when the formation positions of the electrodes 11cU and 11cD are shifted, it is possible to suppress the thick overlapping portion 11v from interfering with the sidewall SW. For example, the problem that the overlapping portion 11v is sandwiched between the side wall SW and the first solid electrolyte layer 11a (inner wall 11aW) can be suppressed. Moreover, generation | occurrence | production of the crack which arises when the overlap part 11v interferes with the side wall SW can be prevented.

  FIG. 6 is an explanatory diagram of the center of heat generation by the heater 50. The heat generation center indicates the highest temperature portion of the NOx sensor element 10. Generally, the peak position of the temperature distribution obtained by measuring the NOx sensor element 10 with a radiation thermometer indicates the center of heat generation.

  In the upper part of FIG. 6, the same sectional view of the NOx sensor element 10 as FIG. 2 is shown. In the center of FIG. 6, a graph showing the relationship between the temperature T and the distance dt is shown. In the lower part of FIG. 6, the first internal electrode 11c and the heater 50 viewed along the stacking direction D2 are shown. In FIG. 6, the position in the longitudinal direction D1 (horizontal direction in FIG. 6) is common to the four displays.

  The graph of FIG. 6 shows the temperature distribution of the NOx sensor element 10 heated by the heater 50. The horizontal axis indicates the distance dt from the tip 10e of the NOx sensor element 10, and the vertical axis indicates the temperature T. The temperature T indicates the temperature obtained by measuring the surface of the insulating layer 14e with a radiation thermometer. This temperature distribution indicates the temperature distribution on the center line CL of the NOx sensor element 10 when viewed along the stacking direction D2. A center line CL is shown in the lower first internal electrode 11c and the heater 50 in FIG. The upper cross-sectional view of FIG. 6 is a cross-sectional view passing through the center line CL.

  As shown in the figure, in the present embodiment, there is a peak TP of temperature T at a position PP facing the upstream electrode 11cU. Although not shown, the temperature T becomes lower as the position is farther from the position PP, even with respect to the position away from the center line CL. It can be estimated that such a temperature distribution centered on the position PP is the same inside the NOx sensor element 10. Therefore, in the present embodiment, the position PP represents the position viewed along the stacking direction D2 of the heat generation center by the heater 50.

  Thus, in this example, when viewed along the stacking direction D2, the peak position PP (heat generation center) of the temperature distribution is not at the downstream electrode 11cD but at the position overlapping the upstream electrode 11cU. Therefore, the temperature of the downstream electrode 11cD can be adjusted to be equal to or lower than the temperature of the upstream electrode 11cU. As a result, it is possible to prevent excessive deterioration of the downstream electrode 11cD responsible for activity improvement. For example, when the temperature of the downstream electrode 11cD is excessively high, platinum sublimation at the downstream electrode 11cD can be promoted. However, in this embodiment, such deterioration can be suppressed. Therefore, the detection accuracy of the specific gas component (NOx in this embodiment) in the gas to be detected can be increased.

  Note that when viewed along the stacking direction D2, the heat generation center (peak position PP) may not overlap the upstream electrode 11cU. In general, the heat generation center (peak position PP) is preferably disposed at a position closer to the upstream electrode 11cU than the downstream electrode 11cD. In this way, the temperature of the downstream electrode 11cD can be adjusted to be equal to or lower than the temperature of the upstream electrode 11cU.

  Various methods can be adopted as a method of forming the heater 50 so that the heat generation center is disposed at a desired position. For example, many heat generating resistors may be arranged in a portion near the desired position of the heat generating center. As shown in FIG. 6, the heat generating center (position PP) can be arranged outside the heater 50.

A2. Electrode evaluation:
Table 1 shown below shows the relationship between the evaluation results of the electrode activity and the electrode durability (peeling) with respect to the first internal electrode 11c and the content of the main component of the electrolyte.

FIG. 7 shows an evaluation system for the evaluation of Table 1. This evaluation system ES includes an air blower BL, a gas flow path FP connected to the air blower BL, and a gas sensor 200A fixed to the gas flow path FP. As the air blower BL, a blower having a maximum capacity of ³ m ³ / min is adopted. The only difference between the gas sensor 200A for evaluation and the gas sensor 200 of the embodiment is that the entire first internal electrode 11c is formed of one electrode. The other configuration of the gas sensor 200A is the same as that of the above-described gas sensor 200 (FIGS. 1 to 6). The reason why the entire first internal electrode 11c is formed by one electrode is to evaluate the influence of the content of the main component of the electrolyte on the activity and durability of the electrode.

The evaluation method of electrode activity is as follows. The evaluation system ES is placed in an air atmosphere at room temperature (about 20 to 30 degrees Celsius). The control temperature of the NOx sensor element is about 700 degrees Celsius. Under this condition, the flow rate of the gas flow (air flow) by the air blower BL is set to 0 m / second (the flow rate represents the flow rate in the gas flow path FP). The offset in this state is measured (referred to as the first offset). Next, the flow rate of the gas flow is set to 30 m / sec. The offset in this state is measured (referred to as a second offset). According to the ratio of the difference between the first and second offsets with respect to the first offset ((second offset-first offset) / first offset: hereinafter referred to as offset change ratio), the following four-stage evaluation results Get.
A Evaluation: Offset change rate is within ± 2 ppm (parts per million) B Evaluation: Offset change rate is within ± 2 to 3 ppm C Evaluation: Offset change rate is within ± 3 to 5 ppm D Evaluation: Offset Change rate is greater than ± 5ppm

  In general, the lower the activity of the first internal electrode 11c, the lower the stability of the oxygen concentration adjustment by the first oxygen pump cell 11. Accordingly, the lower the activity of the first internal electrode 11c, the greater the amount of offset change due to a disturbance such as a change in the gas flow rate. For example, the gas sensor 200A (NOx sensor element) can be temporarily cooled by increasing the gas flow rate. Here, when the activity of the first internal electrode 11c is low, the amount of oxygen pumped out by the first oxygen pump cell 11 decreases, and the oxygen concentration (that is, offset) in the measurement gas GN can increase. Alternatively, the amount of oxygen pumped by the first oxygen pump cell 11 may decrease, and the oxygen concentration (that is, offset) in the measurement gas GN may decrease. When the activity of the first internal electrode 11c is low, the offset may vary according to various mechanisms without being limited to such a mechanism. Therefore, it can be evaluated that the smaller the ratio of the offset difference, the better the activity of the electrode.

  As shown in Table 1, the lower the content of the electrolyte main component (partially stabilized zirconia in this example) in the first internal electrode 11c, the better the evaluation of the electrode activity. This is because the smaller the content of the main component of the electrolyte, the higher the proportion of the conductive material (platinum) in the first internal electrode 11c. Further, as shown in Table 1, the electrode activity is particularly evaluated when the content of the main component of the electrolyte is 15 wt% or less. Therefore, in the downstream electrode 11cD, the content of the main component of the electrolyte is preferably 15 wt% or less. However, a value larger than 15 wt% may be adopted. The content of the main component of the electrolyte is a value based on the content (100 wt%) of the conductive material (Pt (platinum) in this embodiment).

The evaluation method of electrode peeling is as follows. The evaluation system ES is placed in an air atmosphere at room temperature. The flow rate of the gas flow (air flow) by the air blower BL is set to 0 m / sec. Under this condition, the voltage between the electrodes of the first oxygen pump cell 11 is measured (referred to as a first voltage). Next, one cycle of normal control for 1 minute and control stop for 1 minute following normal control is repeated 80000 times. Under normal control, power supply to the heater 50 and transmission / reception of signals to / from the electrodes of the gas sensor 200A (NOx sensor element) are performed. By stopping the control, both power supply to the heater 50 and transmission / reception of signals to / from the electrodes of the NOx sensor element are stopped. During the 80,000 cycles, the flow rate by the air blower BL is maintained at 0 m / sec. Next, the voltage between the electrodes of the first oxygen pump cell 11 is measured under the same condition as the first voltage (referred to as a second voltage). After measuring the second voltage, the NOx sensor element is disconnected. Its cross section is the same as that shown in FIG. Then, the boundary between the first internal electrode 11c and the first solid electrolyte layer 11a in the cross section is observed using an SEM. The observation results are classified into the following three states.
(R1) The electrode 11c is not peeled off from the first solid electrolyte layer 11a over the entire boundary.
(R2) In a part of the boundary, the electrode 11c is peeled off from the first solid electrolyte layer 11a.
(R3) The electrode 11c is peeled from the first solid electrolyte layer 11a over the entire boundary.

Depending on the observation result and the ratio of the difference between the first and second voltages to the first voltage ((second voltage-first voltage) / first voltage: hereinafter referred to as voltage change ratio), the following 4 Get the evaluation result of the stage.
A evaluation: Voltage change rate is 10% or less and the observation result is the first result R1 B evaluation: Voltage change rate is within the range of 10 to 20%, and the observation result is the second result R2 C evaluation: The voltage change rate is in the range of 20 to 100%, and the observation result is the second result R2. D evaluation: The voltage change rate is greater than 100%, and the observation result is The third result is R3

  Generally, when the first internal electrode 11c is peeled off from the first solid electrolyte layer 11a, the electrical resistance between the members 11a and 11c increases, so that the same conditions (that is, the current flowing through the first oxygen pump cell 11 is the same). The interelectrode voltage of the first oxygen pump cell 11 becomes higher. Therefore, when the first internal electrode 11c is deteriorated by the cycle of 80000 times, the second voltage can be larger than the first voltage. And the 2nd voltage becomes large, so that the part peeled from the 1st solid electrolyte layer 11a of the 1st internal electrodes 11c is large. Therefore, it can be evaluated that the deterioration of the electrode progresses as the change rate of the interelectrode voltage of the first oxygen pump cell 11 increases.

  As shown in Table 1, the higher the content of the main component of the electrolyte in the first internal electrode 11c, the better the evaluation of electrode peeling. This is because the greater the content of the main component of the electrolyte, the better the adhesion between the first internal electrode 11c and the first solid electrolyte layer 11a. In addition, as shown in Table 1, the evaluation of electrode peeling is good particularly when the content of the main component of the electrolyte is 20 wt% or more. Therefore, in the upstream electrode 11cU, the content of the main component of the electrolyte is preferably 20 wt% or more. However, a value smaller than 20 wt% may be adopted.

  FIG. 8 is an explanatory diagram showing the arrangement of the electrodes 11cU and 11cD of the NOx sensor element 10 and the evaluation result of the downstream electrode 11cD in the above-described embodiment. The evaluation method of electrode activity and electrode peeling is the same as the above evaluation method. FIG. 8 shows the same cross-sectional view as FIG. In this example, regarding the downstream electrode 11cD, both electrode activity and electrode peeling are A evaluations. The reason is estimated as follows. That is, as described above, the first diffusion resistor 15a and the downstream electrode 11cD are partitioned by the upstream electrode 11cU when viewed along the stacking direction D2.

  FIG. 9 is an explanatory diagram showing the arrangement of the electrodes 11cU and 11cD of the NOx sensor element 10B having another configuration and the evaluation result of the downstream electrode 11cD. The only difference from the embodiment shown in FIG. 8 is that the boundary between the two electrodes 11cU and 11cD is shifted in the distal direction FWD. In this other configuration, regarding the downstream electrode 11cD, the electrode activity is A evaluation, but the electrode peeling is C evaluation. The reason is estimated as follows. In this other configuration, when viewed along the stacking direction D2, a gap GP is generated between the sidewall SW and the upstream electrode 11cU. Further, in the figure, two paths PG1 and PG2 through which the measurement gas GM flows are shown. The first path PG1 is a path that passes through a portion facing the upstream electrode 11cU and reaches a portion facing the downstream electrode 11cD. The second path PG2 is a path that reaches the portion facing the upstream electrode 11cU without passing through the portion facing the upstream electrode 11cU by passing through the gap GP. The gas to be measured GM passing through the second path PG2 contacts the downstream electrode 11cD without passing through the portion facing the upstream electrode 11cU. That is, a gas having a high oxygen concentration can come into contact with the downstream electrode 11cD. As a result, the deterioration of the downstream electrode 11cD is likely to proceed.

  From the above, in order to suppress the deterioration of the downstream electrode 11cD, when viewed along the stacking direction (stacking direction D2) of the first solid electrolyte layer 11a and the first internal electrode 11c, the first diffusion resistor 15a And the downstream electrode 11cD are preferably partitioned by the upstream electrode 11cU. That is, it is preferable that the upstream electrode 11cU is formed so as to block all the paths of the measurement gas GM flowing from the first diffusion resistor 15a to the downstream electrode 11cD when viewed along the stacking direction. In other words, it is preferable that all the paths of the measurement gas GM flowing from the first diffusion resistor 15a to the downstream electrode 11cD pass through a portion facing the upstream electrode 11cU when viewed along the stacking direction. In addition, as a structure of such electrodes 11cU and 11cD, not only the structure of the Example shown in FIG. 8 but various structures are employable. For example, when viewed along the stacking direction D2, the upstream electrode 11cU may be in contact with the first diffusion resistor 15a. However, a configuration as shown in FIG. 9 may be adopted.

B. Variations:
In addition, elements other than the elements claimed in the independent claims among the constituent elements in the above embodiments are additional elements and can be omitted as appropriate. The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

Modification 1:
In each of the above-described embodiments, the configuration of the NOx sensor element 10 is not limited to the configuration illustrated in FIGS. 2 to 6, and other various configurations can be employed. For example, in the embodiment shown in FIG. 3, the first diffusion resistor 15 a may be disposed at the tip portion (tip portion 14 a 3) of the NOx sensor element 10. In this case as well, when viewed in the stacking direction of the first solid electrolyte layer 11a and the first internal electrode 11c, the first diffusion resistor 15a and the downstream electrode 11cD in the first detection chamber 16 are upstream. It is preferable to be partitioned by the electrode 11cU. However, as in the embodiment shown in FIGS. 3 and 8, if the first diffusion resistor 15a is formed using a plurality of porous members separated by walls (for example, the insulating layer 14a), NOx is locally produced. It can prevent that the intensity | strength of a sensor element falls excessively. Further, the inlet of the measurement gas GM can be increased. In the embodiment shown in FIG. 2, the detection electrode 12 b may be exposed to the second detection chamber 18 instead of the first detection chamber 16. Further, the heat generation center (FIG. 6) may be disposed at a position closer to the downstream electrode 11cD than to the upstream electrode 11cU. Further, the overlapping portion 11v (FIG. 3) may be in contact with the sidewall SW. Further, the downstream electrode 11cD may not overlap the upstream electrode 11cU. For example, the upstream electrode 11cU and the downstream electrode 11cD may be electrically connected by another conductive member. Further, the first internal electrode 11c may be divided into three or more electrodes.

  Moreover, as a pattern of the heater 50, not only the pattern shown in FIG. 6 but other various patterns are employable. Further, the configuration of the gas sensor 200 is not limited to the configuration shown in FIG. 1, and various configurations can be employed.

Modification 2:
In each of the above-described embodiments, the conductive material of the electrode is not limited to platinum, and other various conductive materials can be employed. For example, gold or silver may be used. Moreover, various materials can be adopted as the material of the other members.

Modification 3:
In each of the above-described embodiments, the gas sensor (gas sensor element) is not limited to the NOx sensor shown in FIG. 2, and other various sensors (elements) can be employed. For example, an air-fuel ratio sensor (oxygen sensor) including a first oxygen pump cell and an oxygen concentration detection cell may be employed. As a configuration of such an air-fuel ratio sensor, a configuration in which the second detection chamber 18 and the second oxygen pump cell 13 are omitted from the gas sensor element 10 shown in FIG. 2 can be adopted.

It is sectional drawing which shows the gas sensor 200 as one Example of this invention. 2 is a cross-sectional view of a NOx sensor element 10. FIG. FIG. 3 is a cross-sectional view of the NOx sensor element 10 shown in FIG. FIG. 4 is a BB cross-sectional view of the NOx sensor element 10 shown in FIG. 3. FIG. 4 is a CC cross-sectional view of the NOx sensor element 10 shown in FIG. 3. It is explanatory drawing of the heat_generation | fever center by the heater. It is explanatory drawing which shows an evaluation system. It is explanatory drawing which shows arrangement | positioning of electrode 11cU and 11cD, and the evaluation result of downstream electrode 11cD. It is explanatory drawing which shows arrangement | positioning of the electrodes 11cU and 11cD of the NOx sensor element 10B of another structure, and the evaluation result of the downstream electrode 11cD.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Gas sensor element 10e ... Tip 11 ... 1st oxygen pump cell 11a ... 1st solid electrolyte layer 11b ... Outer side 1st pump electrode 11c ... Inner 1st pump electrode 11e ... Protective layer 11v ... Overlapping part 11cU ... Upstream electrode 11cD ... Downstream electrode 11aW ... Inner wall (surface)
DESCRIPTION OF SYMBOLS 12 ... Oxygen concentration detection cell 12a ... 3rd solid electrolyte layer 12b ... Detection electrode 12c ... Reference electrode 12aW ... Inner wall 13 ... 2nd oxygen pump cell 13a ... 2nd solid electrolyte layer 13b ... Inner 2nd pump electrode 13c ... Counter electrode 2nd pump Electrodes 14a, 14b, 14c, 14d, 14e ... insulating layer 14a1 ... first side wall 14a2 ... second side wall 14a3 ... tip 15a ... first diffusion resistor 15a1 ... first inlet diffusion resistor 15a2 ... second inlet diffusion Resistor 15b ... Second diffusion resistor 16 ... First detection chamber 17 ... Reference oxygen chamber 18 ... Second detection chamber 50 ... Heater 106 ... Ceramic sleeve 110 ... Connecting terminal 138 ... Metal fitting 139 ... Screw 140 ... Rear end 142 ... External protector 143 ... Internal protector 144 ... Outer tube 146 ... Lead wire 150 ... Grommet 151 ... Ceramic Cholder 152 ... shelf 153 ... talc ring (powder packed bed)
154... Through hole 157. Packing 158. Metal holder 160. Holding part 161. ... Gas to be measured GN ... Gas to be measured PP ... Peak position FP ... Gas flow path GP ... Gap ES ... Evaluation system CU ... Control part SW ... Side wall PG1 ... First path PG2 ... Second path

Claims (8)

A detection chamber into which a gas to be detected is introduced from the outside via a diffusion resistance unit;
A solid electrolyte body and a pair of electrodes formed on the solid electrolyte body, and an internal electrode which is one of the pair of electrodes is disposed in the detection chamber and introduced into the detection chamber An oxygen pump cell that pumps or pumps oxygen to the gas to be detected;
In the gas sensor with
The internal electrode includes a downstream electrode, and an upstream electrode that is electrically connected to the downstream electrode and disposed upstream of the downstream electrode in the gas flow of the gas to be detected in the detection chamber.
Each of the upstream electrode and the downstream electrode includes a main component of the solid electrolyte body and a conductive material,
The content of the main component of the solid electrolyte body in the upstream electrode is larger than the content of the main component of the solid electrolyte body in the downstream electrode.
A gas sensor. The gas sensor according to claim 1, further comprising:
A heater for heating the gas sensor;
The heat generation center by the heater is disposed at a position closer to the upstream electrode than the downstream electrode,
Gas sensor. The gas sensor according to claim 1 or 2, wherein
Having an overlapping portion where a part of the downstream electrode and a part of the upstream electrode overlap;
Gas sensor. The gas sensor according to claim 3,
In the overlapping portion, the upstream electrode contacts the solid electrolyte body, and the downstream electrode overlaps the upstream electrode.
Gas sensor. The gas sensor according to claim 3 or 4, wherein
Standing up from the solid electrolyte body, comprising a side wall forming the detection chamber,
The overlapping portion is formed at a position away from the side wall,
Gas sensor. A gas sensor according to any one of claims 1 to 5,
When viewed along the stacking direction of the solid electrolyte body and the internal electrode, the diffusion resistance portion in the detection chamber and the downstream electrode are partitioned by the upstream electrode,
Gas sensor. The gas sensor according to any one of claims 1 to 6,
When the content of the conductive material in the upstream electrode is 100 wt%, the content of the main component of the solid electrolyte body is 20 wt% or more,
When the content of the conductive material in the downstream electrode is 100 wt%, the content of the main component of the solid electrolyte body is 15 wt% or less.
Gas sensor. A gas sensor according to any one of claims 1 to 7,
Porosity in the upstream electrode is smaller than the porosity of the downstream electrode, the gas sensor.

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