Gas Sensors

Abstract

To provide a gas sensor that can prevent peeling of a pump electrode while ensuring good performance.SOLUTION: A gas sensor 10 comprises: a laminate 13 that includes at least one or more layers formed of solid electrolyte; a gas passage to be measured 79 that is formed in the laminate; and a pump electrode 112 that is exposed in the gas passage to be measured. The pump electrode is covered in part of a rear end side region 112R by a coating layer 182 formed on an inner face of the gas passage to be measured. The area of a portion of the pump electrode exposed in the gas passage to be measured is 4 mm2 or more. The area of a portion of a front end side region exposed in the gas passage to be measured is larger than the area of a portion of the rear end side region exposed in the gas passage to be measured. A side face of the gas passage to be measured is partitioned by a second layer 68 of the plurality of layers forming the laminate. The maximum thickness of the coating layer is smaller than the thickness of the second layer.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a gas sensor. [Background technology]

[0002] Patent Document 1 discloses a multilayer gas sensor element capable of measuring the concentration of nitrogen oxides (NOx) and the like in a measurement gas. The multilayer gas sensor element disclosed in Patent Document 1 includes a measurement gas chamber into which a measurement gas is introduced, an oxygen pump cell having a pump electrode disposed so as to face the measurement gas chamber, and a sensor cell for detecting the concentration of a specific gas in the measurement gas chamber. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2004-151018 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in conventional gas sensors, the pump electrode may peel off. When the pump electrode peels off, the detection accuracy may decrease, and detection may become impossible. In order to prevent the pump electrode from peeling off, it is possible to bury the periphery of the pump electrode, but simply burying the periphery of the pump electrode does not necessarily result in good performance.

[0005] An object of the present invention is to provide a gas sensor capable of suppressing peeling of a pump electrode while ensuring good performance. [Means for solving the problem]

[0006] A gas sensor according to one aspect of the present invention comprises a laminate including at least one layer made of a solid electrolyte, a measurement gas flow path formed in the laminate and through which a measurement gas flows when the measurement gas is introduced via a gas inlet port located at a front end side, which is one of the longitudinal directions of the laminate, and a pump electrode formed along the longitudinal direction of the measurement gas flow path and exposed in the measurement gas flow path, the pump electrode having a front end side region located at the front end side with respect to a center of the pump electrode and a rear end side region located at the rear end side opposite the front end side with respect to the center of the pump electrode, a part of the rear end side region of the pump electrode is covered with a coating layer formed on an inner surface of the measurement gas flow path, a portion of the pump electrode not covered by the coating layer is an effective area of ​​the pump electrode, and an area of ​​a portion of the pump electrode exposed in the measurement gas flow path is 4 mm 2 the area of ​​the front-end region exposed in the measurement gas flow path is larger than the area of ​​the rear-end region exposed in the measurement gas flow path, the stack further includes a first layer, a second layer adjacent to the first layer, and a third layer adjacent to the second layer, the measurement gas flow path is formed in the second layer, a bottom surface and a top surface of the measurement gas flow path are partitioned by the first layer and the third layer, a side surface of the measurement gas flow path is partitioned by the second layer, and a maximum thickness of the coating layer is smaller than a thickness of the second layer. Effect of the Invention

[0007] According to the present invention, it is possible to provide a gas sensor capable of suppressing peeling of the pump electrode while ensuring good performance. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view illustrating an example of a gas sensor according to an embodiment. [Diagram 2] 1 is a cross-sectional view showing a portion of a gas sensor according to an embodiment. [Diagram 3]3A and 3B are cross-sectional views illustrating an example of a portion of a sensor element according to one embodiment. [Figure 4] 4A to 4F are plan views showing examples of the layout of the clamped portion. [Diagram 5] 5A and 5B are cross-sectional views illustrating an example of a portion of a sensor element according to one embodiment. [Figure 6] 6A and 6B are plan views showing examples of the layout of the clamped portion. [Figure 7] 7A to 7D are plan views showing examples of the layout of the clamped portion. [Figure 8] 8A to 8C are cross-sectional views showing an example of a portion of a sensor element according to an embodiment. [Figure 9] FIG. 13 is a table showing test results. [Figure 10] FIG. 13 is a table showing test results. [Figure 11] FIG. 11 is a cross-sectional view showing a part of a gas sensor according to a modified embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] In a conventional gas sensor such as that disclosed in Patent Document 1, when the pump electrode is used repeatedly for a long period of time, platinum (Pt) contained in the pump electrode is oxidized to generate platinum oxide. Since platinum oxide is more easily sublimated than platinum, when platinum oxide is generated in the pump electrode, the platinum oxide sublimes, causing the pump electrode to peel off.

[0010] In order to prevent the pump electrode from peeling off, it is possible to bury the periphery of the pump electrode. However, simply burying the periphery of the pump electrode reduces the area of ​​contact between the pump electrode and the measured gas, resulting in an increase in the pump voltage. If the pump voltage increases, nitrogen oxides will be decomposed upstream of the measuring electrode, resulting in a decrease in detection accuracy.

[0011] As a result of extensive investigations, the present inventors have come up with the following gas sensor, which, as will be described later, can improve the resistance to peeling of the pump electrode while suppressing decomposition of nitrogen oxides upstream of the measurement electrode.

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A gas sensor according to the present invention will be described in detail below with reference to preferred embodiments and the accompanying drawings.

[0013] [One embodiment] A gas sensor according to an embodiment will be described with reference to Figures 1 to 10. Figure 1 is a cross-sectional view showing an example of the gas sensor according to the present embodiment. Figure 2 is a cross-sectional view showing a part of the gas sensor according to the present embodiment.

[0014] As shown in Fig. 1, the gas sensor 10 includes a sensor element 12. The shape of the sensor element 12 is, for example, a long rectangular parallelepiped. The longitudinal direction of the sensor element 12, i.e., the left-right direction on the paper surface of Fig. 2, is defined as the front-rear direction. The thickness direction of the sensor element 12, i.e., the up-down direction on the paper surface of Fig. 2, is defined as the up-down direction. The width direction of the sensor element 12, i.e., the direction perpendicular to the front-rear direction and the up-down direction, is defined as the left-right direction.

[0015] The gas sensor 10 is further provided with a protective cover 14 for protecting the front end side, which is one of the longitudinal directions, of the sensor element 12. The gas sensor 10 is further provided with a sensor assembly 20 including a ceramic housing 16. A metal terminal 18 is attached to the ceramic housing 16. The metal terminal 18 holds the rear end of the sensor element 12 and is electrically connected to the sensor element 12. The metal terminal 18 is attached to the ceramic housing 16 to form a connector 24.

[0016] The gas sensor 10 may be attached to a pipe 26 such as an exhaust gas pipe of a vehicle. The gas sensor 10 may be used to measure the concentration of a specific gas contained in the exhaust gas or the like that is the gas to be measured. Examples of the specific gas include, but are not limited to, nitrogen oxides and oxygen (O2).

[0017] The protective cover 14 includes an inner protective cover 14a and an outer protective cover 14b. The inner protective cover 14a is a cylindrical protective cover with a bottom that covers the front end of the sensor element 12. The outer protective cover 14b is a cylindrical protective cover with a bottom that covers the inner protective cover 14a. The inner protective cover 14a and the outer protective cover 14b are formed with a plurality of holes for allowing the measurement gas to flow through the protective cover 14. The front end of the sensor element 12 is located within the space surrounded by the inner protective cover 14a, i.e., within the sensor element chamber 28.

[0018] The sensor assembly 20 includes an element sealing body 30 that seals and fixes the sensor element 12. The sensor assembly 20 also includes a nut 32 attached to the element sealing body 30. The sensor assembly 20 also includes an outer cylinder 34 and a connector 24. The metal terminal 18 included in the connector 24 is connected to electrodes (not shown) formed on the surface of the rear end of the sensor element 12, i.e., on the upper and lower surfaces of the rear end of the sensor element 12.

[0019] The element sealing body 30 includes a cylindrical metal shell 40 and a cylindrical inner tube 42. The central axis of the metal shell 40 and the central axis of the inner tube 42 are aligned. The metal shell 40 and the inner tube 42 are fixed by welding. The ceramic supporters 44a to 44c, the powder compacts 46a and 46b, and the metal ring 48 are filled in the through holes on the inside of the metal shell 40 and the inner tube 42. The sensor element 12 is located on the central axis of the element sealing body 30 and penetrates the element sealing body 30 in the front-rear direction. The inner tube 42 is formed with reduced diameter portions 42a and 42b. The reduced diameter portion 42a is for pressing the powder compact 46b in the central axis direction of the inner tube 42. The reduced diameter portion 42b is for pressing the ceramic supporters 44a to 44c and the powder compacts 46a and 46b forward via the metal ring 48. The pressing forces from the reduced diameter portions 42a, 42b compress the powder compacts 46a, 46b between the metallic shell 40 and the sensor element 12, and between the inner cylinder 42 and the sensor element 12. As a result, the powder compacts 46a, 46b seal the space between the sensor element chamber 28 in the protective cover 14 and the space 50 in the outer cylinder 34, and fix the sensor element 12.

[0020] The nut 32 is fixed to the metal shell 40. The central axis of the nut 32 and the central axis of the metal shell 40 coincide with each other. A male thread portion is formed on the outer peripheral surface of the nut 32. A female thread portion is formed on the inner peripheral surface of a fixing member 52 welded to the pipe 26. The male thread portion formed on the outer peripheral surface of the nut 32 is inserted into the fixing member 52 having a female thread portion formed on its inner peripheral surface. In this way, the gas sensor 10 is fixed to the pipe 26 with the front end of the sensor element 12 protected by the protective cover 14 protruding into the pipe 26.

[0021] The outer cylinder 34 covers the inner cylinder 42, the sensor element 12, and the connector 24. A plurality of lead wires 54 connected to the connector 24 are drawn out from the rear end of the outer cylinder 34. The lead wires 54 are electrically connected to each electrode of the sensor element 12 via the connector 24. The gap between the outer cylinder 34 and the lead wires 54 is sealed by an elastic insulating member 56 formed by a grommet or the like. The space 50 within the outer cylinder 34 is filled with a reference gas, i.e., the atmosphere. The rear end of the sensor element 12 is located within the space 50.

[0022] As shown in FIG. 2, the sensor element 12 has a laminate 13 made up of a plurality of layers 60, 62, 64, 66, 68, and 70. A second substrate layer 62 is laminated on the first substrate layer 60. A third substrate layer 64 is laminated on the second substrate layer 62. A solid electrolyte layer 66 is laminated on the third substrate layer 64. A spacer layer 68 is laminated on the solid electrolyte layer 66. A solid electrolyte layer 70 is laminated on the spacer layer 68. For example, a solid electrolyte, more specifically, an oxygen ion conductive solid electrolyte, is used as a material for these layers 60, 62, 64, 66, 68, and 70. For example, zirconia (ZrO2) or the like may be used as an example of the oxygen ion conductive solid electrolyte. These layers 60, 62, 64, 66, 68, and 70 are highly airtight. The sensor element 12 may be manufactured as follows. That is, the ceramic green sheets corresponding to each layer are subjected to a predetermined processing and printing of a predetermined pattern. Then, these ceramic green sheets are laminated. Then, these ceramic green sheets are integrated by firing. In this manner, the sensor element 12 can be manufactured. Note that the material of these layers 60, 62, 64, 66, 68, 70 is not limited to solid electrolyte. For example, the spacer layer 68 may be an insulator layer or the like. The material of the insulator layer may be, for example, alumina.

[0023] A measurement gas flow path 79 through which the measurement gas flows, i.e., a measurement gas flow section, is formed inside the sensor element 12. The measurement gas flows in the measurement gas flow path 79 in the longitudinal direction of the measurement gas flow path 79. The measurement gas flow path 79 is formed in the spacer layer 68. That is, the measurement gas flow path 79 is configured by hollowing out a part of the spacer layer 68. The side of the measurement gas flow path 79 is defined by the spacer layer 68. The bottom surface, i.e., the lower surface, of the measurement gas flow path 79 is defined by the upper surface of the solid electrolyte layer 66. The top surface, i.e., the upper surface, of the measurement gas flow path 79 is defined by the lower surface of the solid electrolyte layer 70. One end of the measurement gas flow path 79, i.e., the left part in FIG. 2, is an inlet through which the measurement gas is introduced, i.e., a gas inlet 80. The gas inlet 80 is located at the front end side, which is one side in the longitudinal direction, of the sensor element 12, that is, at the front end side, which is one side in the longitudinal direction, of the laminate 13.

[0024] In the measurement gas flow path 79, a first diffusion rate-controlling section 82 is provided at the rear of the gas inlet 80. The first diffusion rate-controlling section 82 is provided with, for example, two slits. The longitudinal direction of the slits is, for example, a direction perpendicular to the paper surface in FIG. 2. A buffer space 84 is provided at the rear of the first diffusion rate-controlling section 82. A second diffusion rate-controlling section 86 is provided at the rear of the buffer space 84. The second diffusion rate-controlling section 86 is provided with, for example, two slits. The longitudinal direction of the slits is, for example, a direction perpendicular to the paper surface in FIG. 2. A first internal space 88 is provided at the rear of the second diffusion rate-controlling section 86. The first internal space 88 is in communication with the buffer space 84 via the second diffusion rate-controlling section 86. A third diffusion rate-controlling section 90 is provided at the rear of the first internal space 88. The third diffusion rate-controlling section 90 is provided with, for example, two slits. The longitudinal direction of the slit is, for example, a direction perpendicular to the paper surface in FIG. 2. A second internal space 92 is provided behind the third diffusion rate-controlling section 90. The second internal space 92 is connected to the first internal space 88 via the third diffusion rate-controlling section 90. A fourth diffusion rate-controlling section 94 is provided behind the second internal space 92. The fourth diffusion rate-controlling section 94 is provided with, for example, one slit. The longitudinal direction of the slit is, for example, a direction perpendicular to the paper surface in FIG. 2. A third internal space 96 is provided behind the fourth diffusion rate-controlling section 94. The third internal space 96 is connected to the second internal space 92 via the fourth diffusion rate-controlling section 94. At least one of the first diffusion rate-controlling section 82, the second diffusion rate-controlling section 86, the third diffusion rate-controlling section 90, and the fourth diffusion rate-controlling section 94 may be made of a porous body.

[0025] A reference gas introduction space 98 is formed inside the sensor element 12. The measurement gas flow path 79 is located on one side in the longitudinal direction of the sensor element 12, and the reference gas introduction space 98 is located on the other side in the longitudinal direction of the sensor element 12. That is, the measurement gas flow path 79 is located on the front end side of the sensor element 12, and the reference gas introduction space 98 is located on the rear end side of the sensor element 12. The reference gas introduction space 98 is formed by hollowing out a part of the solid electrolyte layer 66. The side surface of the reference gas introduction space 98 is defined by the solid electrolyte layer 66. The lower surface of the reference gas introduction space 98 is defined by the upper surface of the third substrate layer 64. The upper surface of the reference gas introduction space 98 is defined by the lower surface of the spacer layer 68. A reference gas can be introduced into the reference gas introduction space 98. The atmosphere in the space 50 (see FIG. 1) can be the reference gas. The reference gas when measuring the concentration of nitrogen oxides is, for example, air.

[0026] An air introduction layer 100 is provided inside the sensor element 12. The air introduction layer 100 is provided, for example, between the third substrate layer 64 and the solid electrolyte layer 66. A porous material is used as the material of the air introduction layer 100. More specifically, for example, porous ceramics such as porous alumina can be used as the material of the air introduction layer 100. A part of the air introduction layer 100 is exposed in the reference gas introduction space 98. A reference gas can be introduced into the air introduction layer 100 through the reference gas introduction space 98. The air introduction layer 100 is formed so as to cover a reference electrode 102 described later. The air introduction layer 100 allows the reference gas to reach the reference electrode 102 while providing a predetermined diffusion resistance to the reference gas in the reference gas introduction space 98. A rear end of the air introduction layer 100 is exposed in the reference gas introduction space 98. The part of the air introduction layer 100 that covers the reference electrode 102 is not exposed in the reference gas introduction space 98.

[0027] A reference electrode 102 is formed on the upper surface of the third substrate layer 64. The reference electrode 102 is formed directly on the third substrate layer 64. An air introduction layer 100 that is connected to the reference gas introduction space 98 is formed around the reference electrode 102. The reference electrode 102 is covered with the air introduction layer 100 except for the portion that contacts the third substrate layer 64. As described later, the oxygen concentration (oxygen partial pressure) in the first internal space 88, the oxygen concentration in the second internal space 92, and the oxygen concentration in the third internal space 96 can be measured using the reference electrode 102. For example, a porous cermet can be used as the material of the reference electrode 102. The cermet is a material that is a composite of ceramics and metal. For example, a cermet of platinum and zirconia can be used as the material of the reference electrode 102.

[0028] The gas inlet 80 is open to the external space. A measurement gas can be introduced into the sensor element 12 from the external space through the gas inlet 80. The first diffusion rate-controlling section 82 provides a predetermined diffusion resistance to the measurement gas introduced from the gas inlet 80. The buffer space 84 guides the measurement gas introduced from the first diffusion rate-controlling section 82 to the second diffusion rate-controlling section 86. The second diffusion rate-controlling section 86 provides a predetermined diffusion resistance to the measurement gas introduced from the buffer space 84 into the first internal space 88. The measurement gas introduced into the sensor element 12 through the gas inlet 80 is introduced into the first internal space 88 through the first diffusion rate-controlling section 82, the buffer space 84, and the second diffusion rate-controlling section 86. The measurement gas may be suddenly introduced into the sensor element 12 due to pressure fluctuations in the external space. When the measurement gas is exhaust gas from an automobile, the pulsation of the exhaust pressure corresponds to the applied pressure fluctuations. Even if the measurement gas is suddenly taken into the sensor element 12 due to pressure fluctuations in the external space, the concentration fluctuations of the measurement gas are cancelled out when the measurement gas passes through the first diffusion rate-controlling section 82, the buffer space 84, and the second diffusion rate-controlling section 86. Since the measurement gas whose concentration fluctuations have been cancelled out is introduced into the first internal space 88, the concentration fluctuations of the measurement gas introduced into the first internal space 88 become almost negligible. The first internal space 88 is a space for adjusting the oxygen partial pressure in the measurement gas introduced through the second diffusion rate-controlling section 86. Such oxygen partial pressure can be adjusted by the operation of the main pump cell 110 described later.

[0029] The sensor element 12 further includes a main pump cell 110. The main pump cell 110 is an electrochemical pump cell including a pump electrode 112, an outer pump electrode 114, and a solid electrolyte layer 70 sandwiched between the pump electrode 112 and the outer pump electrode 114. The pump electrode 112 is disposed in the measurement gas flow path 79 along the flow direction of the measurement gas in the measurement gas flow path 79. The outer pump electrode 114 is disposed on the outer side of the laminate 13. The pump electrode 112 is formed on the inner surface of the first inner space 88. The outer pump electrode 114 is formed on the upper surface of the solid electrolyte layer 70. The outer pump electrode 114 is formed in a region corresponding to the region in which the pump electrode 112 is formed. The outer pump electrode 114 is exposed to the outside space, i.e., in the sensor element chamber 28 in FIG. 1.

[0030] The pump electrode 112 has a planar shape of, for example, a rectangle. The pump electrode 112 may be composed of a plurality of electrodes formed on the bottom and top surfaces of the first internal space 88. That is, the pump electrode 112 may be composed of a top pump electrode 112a and a bottom pump electrode 112b. The top pump electrode 112a and the bottom pump electrode 112b are electrically connected by a pattern or the like not shown. A longitudinal center line CL (see FIG. 4A) of the pump electrode 112 coincides with the longitudinal center axis of the first internal space 88 in a plan view. The top pump electrode 112a is formed on the top surface of the first internal space 88, i.e., on the lower surface of the solid electrolyte layer 70. The bottom pump electrode 112b is formed on the bottom surface of the first internal space 88, i.e., on the upper surface of the solid electrolyte layer 66.

[0031] The pump electrode 112 and the outer pump electrode 114 may be made of, for example, a porous cermet. For example, a cermet of platinum containing 1% gold (Au) and zirconia may be used as the material of the pump electrode 112 and the outer pump electrode 114. Note that it is preferable to use a material with a weakened reducing power for nitrogen oxides in the measured gas for the pump electrode 112 that comes into contact with the measured gas. The cermet of platinum containing 1% gold and zirconia is a material with a weakened reducing power for nitrogen oxides in the measured gas.

[0032] In the main pump cell 110, when a desired pump voltage Vp0 is applied between the pump electrode 112 and the outer pump electrode 114, a pump current Ip0 flows in a positive or negative direction between the pump electrode 112 and the outer pump electrode 114. Accordingly, oxygen in the first internal space 88 can be pumped out to the external space, or oxygen in the external space can be pumped into the first internal space 88.

[0033] The sensor element 12 further includes an oxygen partial pressure detection sensor cell 120, i.e., an oxygen partial pressure detection sensor cell for controlling the main pump. The oxygen partial pressure detection sensor cell 120 is an electrochemical sensor cell for detecting the oxygen concentration (oxygen partial pressure) in the atmosphere in the first internal space 88. The oxygen partial pressure detection sensor cell 120 is composed of a pump electrode 112, solid electrolyte layers 66, 70, a spacer layer 68, and a reference electrode 102.

[0034] By detecting the electromotive force V0 in the oxygen partial pressure detection sensor cell 120, the oxygen concentration in the atmosphere in the first internal space 88 can be grasped. Furthermore, by feedback-controlling the pump voltage Vp0 of the variable power supply 122 so that the electromotive force V0 is constant, the pump current Ip0 can be controlled. This allows the oxygen concentration in the first internal space 88 to be maintained at a predetermined constant value.

[0035] The third diffusion rate-controlling section 90 provides a predetermined diffusion resistance to the measurement gas introduced from the first internal space 88 to the second internal space 92, and guides the measurement gas to the second internal space 92. As described above, the oxygen concentration in the atmosphere of the first internal space 88 can be controlled by the main pump cell 110. The third diffusion rate-controlling section 90 provides a predetermined diffusion resistance to the measurement gas whose oxygen concentration has been controlled by the main pump cell 110.

[0036] The second internal space 92 is a space for further adjusting the oxygen concentration of the measurement gas whose oxygen concentration has been previously adjusted in the first internal space 88. That is, the measurement gas introduced into the second internal space 92 via the third diffusion rate-controlling part 90 is further adjusted in oxygen concentration. The further adjustment of the oxygen concentration in the second internal space 92 can be performed by the auxiliary pump cell 124 described later. Since the oxygen concentration in the second internal space 92 can be kept constant with high accuracy, the gas sensor 10 can measure the concentration of nitrogen oxides with high accuracy.

[0037] The sensor element 12 further includes an auxiliary pump cell 124. The auxiliary pump cell 124 is an auxiliary electrochemical pump cell. The auxiliary pump cell 124 is composed of an auxiliary pump electrode 126, an outer pump electrode 114, and a solid electrolyte layer 70. The auxiliary pump electrode 126 is formed on the inner surface of the second inner space 92. Note that an outer electrode provided separately from the outer pump electrode 114 may be used in the auxiliary pump cell 124.

[0038] The auxiliary pump electrode 126 is formed in a cylindrical shape. The longitudinal center line of the auxiliary pump electrode 126 coincides with the longitudinal center axis of the second internal space 92 in a plan view. The auxiliary pump electrode 126 is configured by integrally forming a top surface side electrode portion 126a, a bottom surface side electrode portion 126b, and a side surface side electrode portion (not shown). The top surface side electrode portion 126a is formed on the top surface of the second internal space 92, i.e., the lower surface of the solid electrolyte layer 70. The bottom surface side electrode portion 126b is formed on the bottom surface of the second internal space 92, i.e., the upper surface of the solid electrolyte layer 66. The side surface side electrode portion is formed on the side wall portions on both sides of the second internal space 92, i.e., the side wall surface of the spacer layer 68, i.e., the inner surface. Note that, like the pump electrode 112, the auxiliary pump electrode 126 is preferably made of a material having a reduced reducing power for nitrogen oxides in the measurement gas.

[0039] In the auxiliary pump cell 124, when a voltage Vp1 is applied between the auxiliary pump electrode 126 and the outer pump electrode 114 by the variable power supply 132, a pump current Ip1 flows in a positive or negative direction between the auxiliary pump electrode 126 and the outer pump electrode 114. Accordingly, oxygen in the second internal space 92 can be pumped out to the external space, or oxygen in the external space can be pumped into the second internal space 92.

[0040] The sensor element 12 further includes an oxygen partial pressure detection sensor cell 130, i.e., an oxygen partial pressure detection sensor cell for controlling the auxiliary pump. The oxygen partial pressure detection sensor cell 130 is an electrochemical sensor cell for controlling the oxygen concentration in the atmosphere in the second internal space 92. The oxygen partial pressure detection sensor cell 130 is composed of an auxiliary pump electrode 126, a reference electrode 102, solid electrolyte layers 66, 70, and a spacer layer 68.

[0041] The voltage Vp1 is controlled based on the electromotive force V1 detected by the oxygen partial pressure detection sensor cell 130. As described above, in the auxiliary pump cell 124, a pump current Ip1 flows between the auxiliary pump electrode 126 and the outer pump electrode 114 in response to the voltage Vp1 applied between the auxiliary pump electrode 126 and the outer pump electrode 114. In this manner, oxygen pumping can be performed. The oxygen partial pressure in the atmosphere in the second internal space 92 can be controlled to a low level that does not substantially affect the measurement of the concentration of nitrogen oxides.

[0042] The signal indicative of the pump current Ip1 can be input to the oxygen partial pressure detection sensor cell 120. The oxygen partial pressure detection sensor cell 120 controls the signal indicative of the electromotive force V0 based on the signal indicative of the pump current Ip1. In this manner, control can be performed so that the gradient of the oxygen partial pressure in the measurement gas introduced into the second internal space 92 via the third diffusion rate-controlling part 90 is always constant. When the gas sensor 10 is a gas sensor for measuring the concentration of nitrogen oxides, the oxygen concentration in the atmosphere in the second internal space 92 can be set to a constant value, for example, about 0.001 ppm, by the action of the main pump cell 110 and the auxiliary pump cell 124.

[0043] The fourth diffusion rate-controlling section 94 provides a predetermined diffusion resistance to the measurement gas introduced from the second internal space 92 to the third internal space 96, and guides the measurement gas to the third internal space 96. As described above, the oxygen concentration in the atmosphere of the second internal space 92 can be controlled by the auxiliary pump cell 124. The fourth diffusion rate-controlling section 94 provides a predetermined diffusion resistance to the measurement gas whose oxygen concentration has been controlled by the auxiliary pump cell 124. The fourth diffusion rate-controlling section 94 also serves to limit the amount of nitrogen oxides flowing into the third internal space 96.

[0044] The measurement gas, the oxygen concentration of which has been adjusted in advance in the second internal space 92, is introduced into the third internal space 96 via the fourth diffusion-controlling section 94. The third internal space 96 is a space for detecting the concentration of nitrogen oxides in the measurement gas, i.e., the concentration of nitrogen oxides. The concentration of nitrogen oxides can be measured by operating a measuring pump cell 140, which will be described later.

[0045] The sensor element 12 further includes a measuring pump cell 140. The measuring pump cell 140 is an electrochemical pump cell for measuring the concentration of nitrogen oxides in the measurement gas introduced into the third internal space 96. The measuring pump cell 140 is composed of a measuring electrode 134, an outer pump electrode 114, the solid electrolyte layers 66, 70, and a spacer layer 68. The measuring electrode 134 is formed on the upper surface of the solid electrolyte layer 66. For example, a porous cermet can be used as the material of the measuring electrode 134. The measuring electrode 134 functions as a catalyst for reducing nitrogen oxides present in the atmosphere in the third internal space 96.

[0046] The measurement pump cell 140 pumps out oxygen produced by decomposing nitrogen oxides in the atmosphere surrounding the measurement electrode 134. A pump current Ip2 corresponding to the amount of oxygen pumped out by the measurement pump cell 140 can be detected.

[0047] The sensor element 12 further includes an oxygen partial pressure detection sensor cell 142, i.e., an oxygen partial pressure detection sensor cell for controlling the measurement pump. The oxygen partial pressure detection sensor cell 142 is an electrochemical sensor cell for detecting the oxygen partial pressure around the measurement electrode 134. The oxygen partial pressure detection sensor cell 142 is composed of the solid electrolyte layer 66, the measurement electrode 134, and the reference electrode 102. A variable power supply 144 can be controlled based on the electromotive force V2 detected by the oxygen partial pressure detection sensor cell 142.

[0048] The measurement gas introduced into the second internal space 92 reaches the measurement electrode 134 in the third internal space 96 through the fourth diffusion rate-controlling part 94 under the condition that the oxygen partial pressure is controlled. Nitrogen oxides in the measurement gas around the measurement electrode 134 are reduced by the measurement electrode 134 (2NO→N2+O2), and oxygen is generated around the measurement electrode 134. The generated oxygen is pumped by the measurement pump cell 140. At this time, the voltage Vp2 of the variable power supply 144 is controlled so that the electromotive force V2 detected by the oxygen partial pressure detection sensor cell 142 is constant. The amount of oxygen generated around the measurement electrode 134 is proportional to the concentration of nitrogen oxides in the measurement gas. Therefore, the concentration of nitrogen oxides in the measurement gas can be calculated based on the pump current Ip2 in the measurement pump cell 140.

[0049] The sensor element 12 further includes a sensor cell 146. The sensor cell 146 is an electrochemical sensor cell configured with the third substrate layer 64, the solid electrolyte layers 66, 70, the spacer layer 68, the outer pump electrode 114, and the reference electrode 102. Based on the electromotive force Vref obtained by the sensor cell 146, the oxygen partial pressure in the measurement gas outside the sensor element 12 can be detected.

[0050] The sensor element 12 further includes a reference gas regulating pump cell 150. The reference gas regulating pump cell 150 is an electrochemical pump cell composed of the third substrate layer 64, the solid electrolyte layers 66 and 70, the spacer layer 68, the outer pump electrode 114, and the reference electrode 102. The reference gas regulating pump cell 150 performs pumping by a control current Ip3 flowing due to a voltage Vp3 applied by a variable power supply 152 connected between the outer pump electrode 114 and the reference electrode 102. The reference gas regulating pump cell 150 can pump oxygen from the sensor element chamber 28 (see FIG. 1) located around the outer pump electrode 114 to the air introduction layer 100 located around the reference electrode 102. The voltage Vp3 of the variable power supply 152 is predetermined as a DC voltage such that the control current Ip3 is a predetermined value, i.e., a constant value of DC current.

[0051] In such a gas sensor 10, the main pump cell 110 and the auxiliary pump cell 124 are operated to supply the measurement gas, whose oxygen partial pressure is kept at a constant low value, to the measurement pump cell 140. That is, the measurement gas, whose oxygen partial pressure is kept at a value that does not substantially affect the measurement of the nitrogen oxide concentration, is supplied to the measurement pump cell 140. Then, an amount of oxygen approximately proportional to the concentration of nitrogen oxides in the measurement gas is generated by reduction of the nitrogen oxides. The oxygen thus generated is pumped out by the measurement pump cell 140. Since a pump current Ip2 flows according to the amount of oxygen pumped out by the measurement pump cell 140, it is possible to detect the concentration of nitrogen oxides in the measurement gas based on the pump current Ip2.

[0052] The sensor element 12 further includes a heater section 160 that heats the sensor element 12 and keeps it warm. The heater section 160 serves to adjust the temperature of the sensor element 12. By heating the solid electrolyte included in the sensor element 12, the oxygen ion conductivity of the solid electrolyte can be increased. The heater section 160 includes a heater connector electrode 162, a heater 164, a through hole 166, a heater insulating layer 168, a pressure relief hole 170, and a lead wire 172.

[0053] The heater connector electrode 162 is formed, for example, on the lower surface of the first substrate layer 60. By electrically connecting the heater connector electrode 162 to an external power supply, power can be supplied to the heater section 160 from the external power supply.

[0054] The heater 164 is sandwiched between the second substrate layer 62 and the third substrate layer 64 from above and below. The heater 164 is formed of, for example, an electric resistor. The heater 164 is connected to the heater connector electrode 162 via a lead wire 172 and a through hole 166. The heater 164 generates heat when power is supplied from the outside via the heater connector electrode 162. The heater 164 can heat and keep warm the solid electrolyte that forms the sensor element 12.

[0055] The region from the first internal space 88 to the third internal space 96 overlaps with the region in which the heater 164 is formed in a plan view. Therefore, the portion of the solid electrolyte provided in the sensor element 12 that requires activation can be sufficiently activated by the heater 164.

[0056] The heater insulating layer 168 is formed so as to cover the upper, lower and side surfaces of the heater 164. For example, an insulator may be used as the material of the heater insulating layer 168. More specifically, for example, porous alumina may be used as the material of the heater insulating layer 168. The heater insulating layer 168 is provided to ensure electrical insulation between the second substrate layer 62 and the heater 164, and between the third substrate layer 64 and the heater 164.

[0057] The pressure relief hole 170 penetrates the third substrate layer 64 and the atmosphere introduction layer 100, and communicates with the reference gas introduction space 98. The pressure relief hole 170 is formed for the purpose of mitigating an increase in internal pressure that accompanies a rise in temperature of the heater insulation layer 168.

[0058] In addition, the variable power sources 122, 132, 144, 152, etc. are actually connected to the respective electrodes via lead wires (not shown) formed in the sensor element 12, the connector 24 (see FIG. 1), and the lead wires 54 (see FIG. 1).

[0059] 3A and 3B are cross-sectional views showing an example of a part of the sensor element according to this embodiment. Fig. 3A corresponds to the IIIA-IIIA cross section in Fig. 2. Fig. 3B shows a cross section along the longitudinal direction of the sensor element 12. Fig. 4A is a plan view showing an example of the layout of a clamped portion described later.

[0060] As shown in FIGS. 3A and 3B, a top pump electrode 112a is formed on the top surface of the first internal space 88. A bottom pump electrode 112b is formed on the bottom surface of the first internal space 88. The top pump electrode 112a and the bottom pump electrode 112b form a pump electrode 112. The longitudinal center lines of the top pump electrode 112a and the bottom pump electrode 112b, i.e., the longitudinal center line CL of the pump electrode 112, coincide with the longitudinal center axis of the first internal space 88 in a plan view. The longitudinal center axis of the first internal space 88 coincides with the longitudinal center axis of the measurement gas flow path 79.

[0061] When the pump electrode 112 is divided into two equal parts by a virtual line VL that intersects with the longitudinal direction of the measurement gas flow path 79, more specifically, by a virtual line VL that is perpendicular to the longitudinal direction of the measurement gas flow path 79, the pump electrode 112 is as follows. That is, in this case, as shown in FIG. 4A, the pump electrode 112 is divided into a front end region 112F located on the front end side and a rear end region 112R located on the rear end side opposite to the front end side. In other words, the pump electrode 112 has a front end region 112F located on the front end side with respect to the center of the pump electrode 112, and a rear end region 112R located on the rear end side with respect to the center of the pump electrode 112. As described above, the pump electrode 112 can be composed of a top surface pump electrode 112a and a bottom surface pump electrode 112b. The top surface pump electrode 112a has a front end region 112aF and a rear end region 112aR. The bottom pump electrode 112b has a front end region 112bF and a rear end region 112bR.

[0062] At least a part of the pump electrode 112 is embedded in the laminate 13 (see FIG. 2) as shown in FIG. 3A and FIG. 3B. That is, at least a part of the pump electrode 112 is sandwiched between the spacer layer 68 and the solid electrolyte layers 66, 70 as shown in FIG. 3A and FIG. 3B. More specifically, as shown in FIG. 3B, the pump electrode 112 is sandwiched between the spacer layer 68 and the solid electrolyte layers 66, 70 in a part of the rear end side region 112R. That is, the top surface side pump electrode 112a is sandwiched between the spacer layer 68 and the solid electrolyte layer 70 in a part of the rear end side region 112aR (see FIG. 4A). Also, the bottom surface side pump electrode 112b is sandwiched between the spacer layer 68 and the solid electrolyte layer 66 in a part of the rear end side region 112bR (see FIG. 4A). The part of the pump electrode 112 sandwiched between the laminate 13 is called a sandwiched part. In this embodiment, a part of the pump electrode 112 is sandwiched between the spacer layer 68 and the solid electrolyte layers 66, 70 for the following reason. That is, when the pump electrode 112 is used repeatedly for a long period of time, platinum contained in the pump electrode 112 may be oxidized and platinum oxide may be generated. In a severe usage environment such as a high temperature, platinum is more likely to be oxidized, and therefore platinum oxide is more likely to be generated. Since platinum oxide is more likely to sublime than platinum, when platinum oxide is generated in the pump electrode 112, the platinum oxide may sublime and peel off at the interface between the pump electrode 112 and the solid electrolyte layers 66, 70. Therefore, in this embodiment, in order to prevent the pump electrode 112 from peeling off, a part of the pump electrode 112 is sandwiched between the spacer layer 68 and the solid electrolyte layers 66, 70.

[0063] In the example shown in FIG. 4A, the clamped parts 180, i.e., the clamped parts 180a and 180b, are located on both sides of the pump electrode 112 with the center line CL of the pump electrode 112 as the center. When describing the clamped parts in general, the reference numeral 180 is used, and when describing each of the clamped parts, the reference numerals 180a, 180b, etc. are used. The longitudinal direction of the clamped parts 180a and 180b is the direction along the longitudinal direction of the pump electrode 112. In the example shown in FIG. 4A, the front ends of the clamped parts 180a and 180b coincide with the imaginary line VL that divides the pump electrode 112 into two equal parts. In the example shown in FIG. 4A, the rear ends of the clamped parts 180a and 180b coincide with the rear end of the pump electrode 112. In the example shown in FIG. 4A, the clamped parts 180 are disposed only in the rear end region 112R of the pump electrode 112. Such a layout in which the clamped portion 180 is disposed only in the rear end region 112R of the pump electrode 112 is referred to as a type A layout.

[0064] In order to prevent the pump electrode 112 from peeling off, it is preferable to secure a certain degree of area for the clamped portion 180. Specifically, it is preferable that the ratio of the area of ​​the clamped portion 180 to the total area of ​​the pump electrode 112 is 5% or more. Furthermore, it is more preferable that the ratio of the area of ​​the clamped portion 180 to the total area of ​​the pump electrode 112 is 10% or more.

[0065] If the area of ​​the clamped portion 180 is made excessively large, cracks will occur in the pump electrode 112 due to the difference in thermal expansion coefficient between the pump electrode 112 and the solid electrolyte layers 66 and 70, so it is preferable not to set the area of ​​the clamped portion 180 excessively large. Specifically, it is preferable to set the area of ​​the clamped portion 180 to 50% or less.

[0066] For these reasons, the ratio of the area of ​​the clamped portion 180 to the total area of ​​the pump electrode 112 is preferably 5 to 50%, and more preferably 10 to 50%. That is, the ratio of the area of ​​the portion of the pump electrode 112 that is not exposed in the measurement gas flow path 79 to the total area of ​​the pump electrode 112 is preferably 5 to 50%, and more preferably 10 to 50%.

[0067] In this embodiment, in order to obtain sufficient pumping capacity, the area of ​​the part of the pump electrode 112 exposed in the measurement gas flow path 79 is set to 4 mm 2 As described above, the pump electrode 112 is composed of the top pump electrode 112a and the bottom pump electrode 112b. Therefore, the area of ​​the part of the top pump electrode 112a exposed in the measurement gas flow path 79 is set to, for example, 2 mm 2 or more, and the area of ​​the part of the bottom pump electrode 112b exposed in the measurement gas flow path 79 is set to, for example, 2 mm 2 That is all.

[0068] In this embodiment, the area of ​​the front end region 112F exposed in the measurement gas flow path 79 is made larger than the area of ​​the rear end region 112R exposed in the measurement gas flow path 79. This is for the following reason. That is, the oxygen concentration of the measurement gas in the front end region 112F is higher than the oxygen concentration in the rear end region 112R. Ensuring a large exposed area of ​​the pump electrode 112 in the part with a higher oxygen concentration contributes to ensuring sufficient pumping capacity. On the other hand, if the area of ​​the front end region 112F exposed in the measurement gas flow path 79 is significantly smaller than the area of ​​the rear end region 112R exposed in the measurement gas flow path 79, the following occurs. That is, in such a case, an electromotive force V0 that accurately reflects the oxygen concentration in the atmosphere in the first internal space 88 cannot be obtained, resulting in an excessive increase in the pump voltage Vp0. If the pump voltage Vp0 increases excessively, the oxygen concentration in the atmosphere in the first internal space 88 cannot be accurately controlled, which leads to decomposition of nitrogen oxides and makes it impossible to accurately detect the concentration of nitrogen oxides. For this reason, in this embodiment, the area of ​​the part of the front end region 112F exposed in the measurement gas flow path 79 is made larger than the area of ​​the part of the rear end region 112R exposed in the measurement gas flow path 79.

[0069] 5A and 5B are cross-sectional views showing an example of a part of a sensor element according to this embodiment. Fig. 5A corresponds to the cross section IIIA-IIIA in Fig. 2. Fig. 5B shows a cross section along the longitudinal direction of the sensor element 12.

[0070] 5A and 5B, a part of the rear end region 112R of the pump electrode 112 is covered with a part of the coating layer 182 formed on the inner surface of the measurement gas flow path 79 (see FIG. 2). The part of the pump electrode 112 covered with the coating layer 182 is sandwiched between the solid electrolyte layers 66, 70 and the coating layer 182. That is, in the example shown in FIGS. 5A and 5B, the part of the pump electrode 112 covered with the coating layer 182 becomes the sandwiched portion 180 (see FIG. 4A). In the example shown in FIGS. 5A and 5B, the sandwiched portion 180 may be arranged in the layout shown in FIG. 4A, as in the example shown in FIGS. 3A and 3B.

[0071] FIG. 4B is a plan view showing an example of the layout of the clamped portion.

[0072] In the example shown in FIG. 4B, the clamped portion 180, i.e., the clamped portions 180c and 180d, are located on both sides of the pump electrode 112 with the center line CL of the pump electrode 112 as the center. The longitudinal direction of the clamped portions 180c and 180d is along the longitudinal direction of the pump electrode 112. In the example shown in FIG. 4B, the front ends of the clamped portions 180c and 180d are located on the rear end side with respect to a virtual line VL that divides the pump electrode 112 in half. In the example shown in FIG. 4B, the rear ends of the clamped portions 180c and 180d are located on the front end side with respect to the rear end of the pump electrode 112. In the example shown in FIG. 4B, the clamped portion 180 is disposed only in the rear end region 112R of the pump electrode 112. Therefore, the layout shown in FIG. 4B belongs to Type A.

[0073] FIG. 4C is a plan view showing an example of the layout of the clamped parts.

[0074] In the example shown in FIG. 4C, the clamped portion 180, i.e., the clamped portions 180e and 180f, are located on both sides of the pump electrode 112 with the center line CL of the pump electrode 112 as the center. The longitudinal direction of the clamped portions 180e and 180f is along the longitudinal direction of the pump electrode 112. In the example shown in FIG. 4C, the clamped portion 180, i.e., the clamped portion 180g, is further located at the end portion on the rear end side of the pump electrode 112. The longitudinal direction of the clamped portion 180g is perpendicular to the longitudinal direction of the pump electrode 112. The dimension of the clamped portion 180g in the direction perpendicular to the longitudinal direction of the pump electrode 112 is equal to the dimension of the pump electrode 112 in the direction perpendicular to the longitudinal direction of the pump electrode 112. In the example shown in Fig. 4C, the rear ends of the clamped parts 180e and 180f reach the part where the clamped part 180g is arranged in a plan view. In the example shown in Fig. 4C, the front ends of the clamped parts 180e and 180f coincide with an imaginary line VL that divides the pump electrode 112 into two equal parts. In the example shown in Fig. 4C, the clamped part 180 is arranged only in the rear end region 112R of the pump electrode 112. Therefore, the layout shown in Fig. 4C belongs to Type A.

[0075] FIG. 4D is a plan view showing the layout of the clamped parts.

[0076] In the example shown in FIG. 4D, the clamped portion 180, i.e., the clamped portions 180h and 180i, are located on both sides of the pump electrode 112 with the center line CL of the pump electrode 112 as the center. The longitudinal direction of the clamped portions 180h and 180i is along the longitudinal direction of the pump electrode 112. In the example shown in FIG. 4D, the planar shape of the clamped portions 180h and 180i is triangular. In the example shown in FIG. 4D, the width of the clamped portions 180h and 180i gradually increases from the front end side to the rear end side of the sensor element 12. In the example shown in FIG. 4D, the distance between the clamped portions 180h and 180i decreases from the front end side to the rear end side of the sensor element 12. In the example shown in FIG. 4D, the clamped portion 180 is disposed only in the rear end region 112R of the pump electrode 112. Therefore, the layout shown in FIG. 4D belongs to Type A.

[0077] FIG. 4E is a plan view showing an example of the layout of the clamped portions.

[0078] In the example shown in FIG. 4E, the clamped portions 180, i.e., clamped portions 180j and 180k, are located on both sides of the pump electrode 112 with respect to the center line CL of the pump electrode 112. The longitudinal direction of the clamped portions 180j and 180k is along the longitudinal direction of the pump electrode 112. In the example shown in FIG. 4E, the rear ends of the clamped portions 180j and 180k are located closer to the front end than the rear end of the pump electrode 112. In the example shown in FIG. 4E, the clamped portion 180, i.e., the clamped portion 180l, is further located at the end of the pump electrode 112 on the rear end side. The longitudinal direction of the clamped portion 180l is perpendicular to the longitudinal direction of the pump electrode 112. The dimension of the clamped portion 180l in a direction perpendicular to the longitudinal direction of the pump electrode 112 is smaller than the dimension of the pump electrode 112 in a direction perpendicular to the longitudinal direction of the pump electrode 112. In the example shown in FIG. 4E, the clamped portion 180j, the clamped portion 180k, and the clamped portion 180l are spaced apart from each other. In the example shown in FIG. 4E, the front ends of the clamped portions 180j and 180k coincide with a virtual line VL that divides the pump electrode 112 into two equal parts. In the example shown in FIG. 4E, the clamped portion 180 is disposed only in the rear end region 112R of the pump electrode 112. Therefore, the layout shown in FIG. 4E belongs to Type A.

[0079] FIG. 4F is a plan view showing the layout of the clamped parts.

[0080] In the example shown in FIG. 4F, the clamped portion 180, i.e., the clamped portions 180m and 180n, are located on both sides of the pump electrode 112 with the center line CL of the pump electrode 112 as the center. The longitudinal direction of the clamped portions 180m and 180n is along the longitudinal direction of the pump electrode 112. In the example shown in FIG. 4F, the width of the clamped portions 180m and 180n gradually increases from the front end side to the rear end side. In the example shown in FIG. 4F, the shape of a part of the clamped portions 180m and 180n is curved. The curved part of the clamped portions 180m and 180n is located on the center line CL side of the pump electrode 112. In the example shown in FIG. 4F, the distance between the clamped portions 180m and 180n decreases from the front end side to the rear end side of the sensor element 12. 4F, the clamped portion 180 is disposed only in the rear end region 112R of the pump electrode 112. Therefore, the layout shown in FIG.

[0081] FIG. 6A is a plan view showing an example of the layout of the clamped portion.

[0082] In the example shown in FIG. 6A, the clamped parts 180, i.e., the clamped parts 180o and 180p, are located on both sides of the pump electrode 112 with the center line CL of the pump electrode 112 as the center. The longitudinal direction of the clamped parts 180o and 180p is along the longitudinal direction of the pump electrode 112. In the example shown in FIG. 6A, the front ends of the clamped parts 180o and 180p are located on the front end side with respect to the imaginary line VL that divides the pump electrode 112 in half. In the example shown in FIG. 6A, the rear ends of the clamped parts 180o and 180p coincide with the rear end of the pump electrode 112. In the example shown in FIG. 6A, the clamped parts 180o and 180p arranged in the rear end side region 112R extend to a part of the front end side region 112F. A layout in which the clamped portions 180o, 180p arranged in the rear end region 112R extend into the front end region 112F will be referred to as Type B.

[0083] FIG. 6B is a plan view showing an example of the layout of the clamped portion.

[0084] In the example shown in FIG. 6B, the clamped portion 180, i.e., the clamped portions 180o and 180p, are arranged in the same manner as in the example shown in FIG. 6A. In the example shown in FIG. 6B, the clamped portion 180, i.e., the clamped portion 180q, is further located at the end portion on the rear end side of the pump electrode 112. The longitudinal direction of the clamped portion 180q is perpendicular to the longitudinal direction of the pump electrode 112. In the example shown in FIG. 6B, the front ends of the clamped portions 180o and 180p are located on the front end side with respect to the imaginary line VL that divides the pump electrode 112 in half. In the example shown in FIG. 6B, the rear ends of the clamped portions 180o and 180p coincide with the rear end of the pump electrode 112. In the example shown in FIG. 6B, both ends of the clamped portion 180q in the longitudinal direction reach the portions where the clamped portions 180o and 180p are arranged in a plan view. 6B, the clamped portion 180 arranged in the rear end region 112R, that is, the clamped portions 180o and 180p, extend into the front end region 112F. Therefore, the layout shown in FIG.

[0085] FIG. 7A is a plan view showing an example of the layout of the clamped portion.

[0086] In the example shown in FIG. 7A, the clamped parts 180a and 180b are arranged in the same manner as in the example shown in FIG. 4A. In the example shown in FIG. 7A, the clamped part 180, i.e., the clamped part 180r, is further located at the end of the front end side of the pump electrode 112. The longitudinal direction of the clamped part 180r is a direction perpendicular to the longitudinal direction of the pump electrode 112. The dimension of the clamped part 180r in the direction perpendicular to the longitudinal direction of the pump electrode 112 is equal to the dimension of the pump electrode 112 in the direction perpendicular to the longitudinal direction of the pump electrode 112. In the example shown in FIG. 7A, the clamped part 180r, which is different from the clamped parts 180a and 180b arranged in the rear end side region 112R, is arranged in the front end side region 112F. A layout in which a clamped portion 180r, which is separate from the clamped portions 180a, 180b arranged in the rear end region 112R, is arranged in the front end region 112F, will be referred to as Type C.

[0087] FIG. 7B is a plan view showing an example of the layout of the clamped portion.

[0088] In the example shown in FIG. 7B, the clamped parts 180a and 180b are arranged in the same manner as in the example shown in FIG. 4A. In addition, in the example shown in FIG. 7B, the clamped parts 180, i.e., the clamped parts 180s and 180t, are further located at the end of the front end side of the pump electrode 112. More specifically, the clamped parts 180s and 180t are located at the corners on both sides of the front end of the pump electrode 112. The planar shapes of the clamped parts 180s and 180t are triangular. In the example shown in FIG. 7B, the widths of the clamped parts 180s and 180t gradually narrow from the front end side to the rear end side. In the example shown in FIG. 7B, the distance between the clamped parts 180s and 180t increases from the front end side to the rear end side. In the example shown in Fig. 7B, the front ends of the clamped parts 180a, 180b coincide with a virtual line VL that bisects the pump electrode 112. In the example shown in Fig. 7B, the front ends of the clamped parts 180s, 180t coincide with the front end of the pump electrode 112. In the example shown in Fig. 7B, the clamped parts 180s, 180t that are separate from the clamped parts 180a, 180b that are arranged in the rear end region 112R are arranged in the front end region 112F. Therefore, the layout shown in Fig. 7B belongs to Type C.

[0089] FIG. 7C is a plan view showing an example of the layout of the clamped portion.

[0090] In the example shown in FIG. 7C, the clamped parts 180a and 180b are arranged in the same manner as in the example shown in FIG. 4A. In the example shown in FIG. 7C, the clamped part 180, i.e., the clamped part 180u, is further located at the end of the pump electrode 112 on the front end side. The longitudinal direction of the clamped part 180u is perpendicular to the longitudinal direction of the pump electrode 112. The dimension of the clamped part 180u in the direction perpendicular to the longitudinal direction of the pump electrode 112 is smaller than the dimension of the pump electrode 112 in the direction perpendicular to the longitudinal direction of the pump electrode 112. Both ends of the clamped part 180u in the longitudinal direction are located inside the sides of the pump electrode 112 along the longitudinal direction. In the example shown in FIG. 7C, the clamped part 180u, which is different from the clamped parts 180a and 180b arranged in the rear end side region 112R, is arranged in the front end side region 112F. Therefore, the layout shown in FIG.

[0091] FIG. 7D is a plan view showing an example of the layout of the clamped portion.

[0092] In the example shown in Fig. 7D, the clamped parts 180o and 180p are arranged similarly to the example shown in Fig. 6A. In addition, in the example shown in Fig. 7D, the clamped part 180r is further located similarly to the example shown in Fig. 7A. In the example shown in Fig. 7D, the clamped part 180r, which is separate from the clamped parts 180o and 180p arranged in the rear end side region 112R, is arranged in the front end side region 112F. Therefore, the layout shown in Fig. 7D belongs to Type C.

[0093] Figures 8A to 8C are cross-sectional views showing an example of a portion of the sensor element according to this embodiment. Figures 8A to 8C show cross sections along the longitudinal direction of sensor element 12. Figures 8A to 8C correspond to the layouts shown in Figures 7A to 7D.

[0094] In the example shown in FIG. 8A, a portion of the pump electrode 112 is sandwiched between the spacer layer 68 and the solid electrolyte layers 66, 70 in both the clamped portion 180 located in the rear end region 112R and the clamped portion 180 located in the front end region 112F.

[0095] In the example shown in FIG. 8B, a portion of the pump electrode 112 is covered with a portion of the covering layer 182 both in the clamped portion 180 located in the rear end region 112R and in the clamped portion 180 located in the front end region 112F.

[0096] In the example shown in FIG. 8C, in the sandwiched portion 180 located in the rear end region 112R, a part of the pump electrode 112 is sandwiched between the spacer layer 68 and the solid electrolyte layers 66, 70. On the other hand, in the sandwiched portion 180 located in the front end region 112F, a part of the pump electrode 112 is covered by a part of the covering layer 182. Note that, in the sandwiched portion 180 located in the rear end region 112R, a part of the pump electrode 112 may be covered by a part of the covering layer 182. And, in the sandwiched portion 180 located in the front end region 112F, a part of the pump electrode 112 may be sandwiched between the spacer layer 68 and the solid electrolyte layers 66, 70. EXAMPLES

[0097] A peeling test and a pumping capacity test were carried out on the pump electrode 112 for each of Examples 1 to 16 and Comparative Examples 1 to 5. The test results are shown in Figures 9 and 10. Figures 9 and 10 are diagrams showing tables showing the test results.

[0098] The peeling test for the pump electrode 112 was performed as follows. That is, the gas sensor 10 was placed in an air atmosphere at room temperature, and 100,000 test cycles were repeated, each cycle consisting of an on-state for 70 seconds and an off-state for 50 seconds following the on-state. In the on-state, a predetermined voltage was applied to each part of the gas sensor 10. In the off-state, no voltage was applied to each part of the gas sensor 10. In the on-state, power was supplied to the heater 164. In addition, in the on-state, signals were transmitted and received from the gas sensor 10. In the off-state, power supply to the heater 164 was stopped. In addition, in the off-state, signals were transmitted and received from the gas sensor 10. During the peeling test, the main pump cell 110 was kept operating. That is, the pump current Ip0 was kept at 15 μA. After the peeling test was completed, the pump electrode 112 was observed. X-ray CT was used for the observation of the pump electrode 112. When observing the pump electrode 112, the pump electrode 112 was cut as necessary.

[0099] The evaluation criteria for the results of the peeling test on the pump electrode 112 are as follows: A: 100% of the pump electrode 112 is maintained without peeling. B: The area of ​​the portion that remains without peeling is 50% or more of the area of ​​the pump electrode 112. C: The area of ​​the portion that remains without peeling is less than 50% of the area of ​​the pump electrode 112.

[0100] The evaluation criteria for pump capacity are as follows: A: Sufficient pumping capacity is obtained. B: A reasonably good pumping capacity is obtained. C: The pump capacity is insufficient.

[0101] [Example 1] In the first embodiment, the layout of the clamped portion 180 was Type A. That is, the clamped portion 180 was arranged only in the rear end region 112R of the pump electrode 112. The total area of ​​the pump electrode 112 was 7.1 mm 2 In Example 1, the area of ​​the clamped portion 180 is 0.4 mm 2 In other words, the area of ​​the clamped portion 180 was set to be relatively small. In the first embodiment, the effective area of ​​the pump electrode 112, that is, the area of ​​the portion of the pump electrode 112 exposed in the measurement gas flow path 79, was 6.7 mm 2 The effective area of ​​the front end region 112F of the pump electrode 112, that is, the area of ​​the portion of the front end region 112F exposed in the measurement gas flow path 79, was 3.55 mm 2 The effective area of ​​the rear end region 112R of the pump electrode 112, i.e., the area of ​​the portion of the rear end region 112R exposed in the measurement gas flow path 79, was 3.15 mm 2 The ratio of the area of ​​the clamped portion 180 to the total area of ​​the pump electrode 112 was 6%. The evaluation result of the peel test of the pump electrode 112 was B. The evaluation result of the pump capacity test was A. The ratio Q of the effective area of ​​the front end region 112F to the effective area of ​​the pump electrode 112 was 53.0%. That is, the area of ​​the part of the front end region 112F exposed in the measurement gas flow path 79 was larger than the area of ​​the part of the rear end region 112R exposed in the measurement gas flow path 79.

[0102] [Example 2] In the second embodiment, the layout of the clamped portion 180 was Type A. That is, the clamped portion 180 was arranged only in the rear end region 112R of the pump electrode 112. The total area of ​​the pump electrode 112 was 7.4 mm 2 The area of ​​the clamped portion 180 is 2.2 mm 2 That is, the area of ​​the clamped portion 180 was set to be relatively large. The effective area of ​​the pump electrode 112 was set to 5.2 mm 2 The effective area of ​​the front end region 112F of the pump electrode 112 was 3.70 mm 2The effective area of ​​the rear end region 112R of the pump electrode 112 was 1.50 mm 2 The ratio of the area of ​​the clamped portion 180 to the total area of ​​the pump electrode 112 was 30%. The evaluation result of the peel test of the pump electrode 112 was A. The evaluation result of the pump capacity test was B. The ratio Q of the effective area of ​​the front end region 112F to the effective area of ​​the pump electrode 112 was 71.2%.

[0103] [Example 3] In the third embodiment, the layout of the clamped portion 180 was Type B. That is, the clamped portion 180 arranged in the rear end region 112R was extended to a part of the front end region 112F. The total area of ​​the pump electrode 112 was 7.4 mm 2 In the third embodiment, the area of ​​the clamped portion 180 is 0.7 mm 2 In other words, the area of ​​the clamped portion 180 is set to be relatively small. In the third embodiment, the effective area of ​​the pump electrode 112 is 6.7 mm 2 The effective area of ​​the front end region 112F of the pump electrode 112 was 3.60 mm 2 The effective area of ​​the rear end region 112R of the pump electrode 112 was 3.10 mm 2 The ratio of the area of ​​the clamped portion 180 to the total area of ​​the pump electrode 112 was 9%. The evaluation result of the peel test of the pump electrode 112 was B. The evaluation result of the pump capacity test was A. The ratio Q of the effective area of ​​the front end region 112F to the effective area of ​​the pump electrode 112 was 53.7%.

[0104] [Example 4] In the fourth embodiment, the layout of the clamped portion 180 was Type B. That is, the clamped portion 180 arranged in the rear end region 112R was extended to a part of the front end region 112F. The total area of ​​the pump electrode 112 was 7.3 mm 2 In the fourth embodiment, the area of ​​the clamped portion 180 is 3.2 mm 2 That is, the area of ​​the clamped portion 180 was set to be relatively large. The effective area of ​​the pump electrode 112 was set to 4.1 mm 2The effective area of ​​the front end region 112F of the pump electrode 112 was 2.45 mm 2 The effective area of ​​the rear end region 112R of the pump electrode 112 was 1.65 mm 2 The ratio of the area of ​​the clamped portion 180 to the total area of ​​the pump electrode 112 was 44%. The evaluation result of the peel test of the pump electrode 112 was A. The evaluation result of the pump capacity test was B. The ratio Q of the effective area of ​​the front end region 112F to the effective area of ​​the pump electrode 112 was 59.8%.

[0105] [Example 5] In the fifth embodiment, the layout of the clamped portion 180 was Type B. That is, the clamped portion 180 arranged in the rear end region 112R was extended to a part of the front end region 112F. The total area of ​​the pump electrode 112 was 7.5 mm 2 The area of ​​the clamped portion 180 is 1.2 mm 2 The effective area of ​​the pump electrode 112, i.e., the area of ​​the portion of the pump electrode 112 exposed in the measurement gas flow path 79, was 6.3 mm 2 The effective area of ​​the front end region 112F of the pump electrode 112 was 3.35 mm 2 The effective area of ​​the rear end region 112R of the pump electrode 112 was 2.95 mm 2 The ratio of the area of ​​the clamped portion 180 to the total area of ​​the pump electrode 112 was 16%. The evaluation result of the peel test of the pump electrode 112 was A. The evaluation result of the pump capacity test was also A. The ratio Q of the effective area of ​​the front end region 112F to the effective area of ​​the pump electrode 112 was 53.2%.

[0106] [Example 6] In the sixth embodiment, the layout of the clamped portion 180 was type B. That is, the clamped portion 180 arranged in the rear end region 112R was extended to a part of the front end region 112F. The total area of ​​the pump electrode 112 was 7.5 mm 2 In Example 6, the area of ​​the clamped portion 180 is 3.4 mm 2 The effective area of ​​the pump electrode 112 was 4.1 mm2 The effective area of ​​the front end region 112F of the pump electrode 112 was 2.55 mm 2 The effective area of ​​the rear end region 112R of the pump electrode 112 was 1.55 mm 2 The ratio of the area of ​​the clamped portion 180 to the total area of ​​the pump electrode 112 was 45%. The evaluation result of the peel test of the pump electrode 112 was A. In Example 6, the evaluation result of the pump capacity test was B. In Example 6, the ratio Q of the effective area of ​​the front end region 112F to the effective area of ​​the pump electrode 112 was 62.2%.

[0107] [Example 7] In the seventh embodiment, the layout of the clamped portion 180 was Type B. That is, the clamped portion 180 arranged in the rear end region 112R was extended to a part of the front end region 112F. The total area of ​​the pump electrode 112 was 9.0 mm 2 The area of ​​the clamped portion 180 is 1.4 mm 2 The effective area of ​​the pump electrode 112 was 7.6 mm 2 The effective area of ​​the front end region 112F of the pump electrode 112 was 4.10 mm 2 The effective area of ​​the rear end region 112R of the pump electrode 112 was 3.50 mm 2 The ratio of the area of ​​the clamped portion 180 to the total area of ​​the pump electrode 112 was 16%. The evaluation result of the peel test of the pump electrode 112 was A. In Example 7, the evaluation result of the pump capacity test was A. In Example 7, the ratio Q of the effective area of ​​the front end region 112F to the effective area of ​​the pump electrode 112 was 53.9%.

[0108] [Example 8] In the eighth embodiment, the layout of the clamped portion 180 was type B. That is, the clamped portion 180 arranged in the rear end region 112R was extended to a part of the front end region 112F. The total area of ​​the pump electrode 112 was 9.9 mm 2 In Example 8, the area of ​​the clamped portion 180 is 1.4 mm 2The effective area of ​​the pump electrode 112 was 8.5 mm 2 The effective area of ​​the front end region 112F of the pump electrode 112 was 4.45 mm 2 The effective area of ​​the rear end region 112R of the pump electrode 112 was 4.05 mm 2 In Example 8, the ratio of the area of ​​the clamped portion 180 to the total area of ​​the pump electrode 112 was 14%. In Example 8, the evaluation result of the peel test of the pump electrode 112 was A. Also, in Example 8, the evaluation result of the pump capacity test was A. In Example 8, the ratio Q of the effective area of ​​the front end region 112F to the effective area of ​​the pump electrode 112 was 52.4%.

[0109] [Example 9] In Example 9, the layout of the clamped portion 180 was Type B. That is, the clamped portion 180 arranged in the rear end region 112R was extended to a part of the front end region 112F. The total area of ​​the pump electrode 112 was 10.6 mm 2 The area of ​​the clamped portion 180 is 1.5 mm 2 The effective area of ​​the pump electrode 112 was 9.1 mm 2 The effective area of ​​the front end region 112F of the pump electrode 112 was 4.70 mm 2 The effective area of ​​the rear end region 112R of the pump electrode 112 was 4.40 mm 2 The ratio of the area of ​​the clamped portion 180 to the total area of ​​the pump electrode 112 was 14%. The evaluation result of the peel test of the pump electrode 112 was A. In Example 9, the evaluation result of the pump capacity test was A. In Example 9, the ratio Q of the effective area of ​​the front end region 112F to the effective area of ​​the pump electrode 112 was 51.6%.

[0110] [Example 10] In the tenth embodiment, the layout of the clamped portion 180 was type B. That is, the clamped portion 180 arranged in the rear end region 112R was extended to a part of the front end region 112F. The total area of ​​the pump electrode 112 was 12.3 mm 2The area of ​​the clamped portion 180 is 1.8 mm 2 The effective area of ​​the pump electrode 112 was 10.5 mm 2 The effective area of ​​the front end region 112F of the pump electrode 112 was 5.75 mm 2 The effective area of ​​the rear end region 112R of the pump electrode 112 was 4.75 mm 2 The ratio of the area of ​​the clamped portion 180 to the total area of ​​the pump electrode 112 was 15%. The evaluation result of the peel test of the pump electrode 112 was A. In Example 10, the evaluation result of the pump capacity test was A. The ratio Q of the effective area of ​​the front end region 112F to the effective area of ​​the pump electrode 112 was 54.8%.

[0111] [Example 11] In the eleventh embodiment, the layout of the clamped portion 180 was type B. That is, the clamped portion 180 arranged in the rear end region 112R was extended to a part of the front end region 112F. The total area of ​​the pump electrode 112 was 15.0 mm 2 The area of ​​the clamped portion 180 was 4.0 mm 2 The effective area of ​​the pump electrode 112 was 11.0 mm 2 The effective area of ​​the front end region 112F of the pump electrode 112 was 6.50 mm 2 The effective area of ​​the rear end region 112R of the pump electrode 112 was 4.50 mm 2 The ratio of the area of ​​the clamped portion 180 to the total area of ​​the pump electrode 112 was 27%. The evaluation result of the peel test of the pump electrode 112 was A. In Example 11, the evaluation result of the pump capacity test was A. In Example 11, the ratio Q of the effective area of ​​the front end region 112F to the effective area of ​​the pump electrode 112 was 59.1%.

[0112] [Example 12] In the twelfth embodiment, the layout of the clamped portion 180 was type B. That is, the clamped portion 180 arranged in the rear end region 112R was extended to a part of the front end region 112F. The total area of ​​the pump electrode 112 was 15.0 mm 2The area of ​​the clamped portion 180 is 7.4 mm 2 The effective area of ​​the pump electrode 112 was 7.6 mm 2 The effective area of ​​the front end region 112F of the pump electrode 112 was 5.00 mm 2 The effective area of ​​the rear end region 112R of the pump electrode 112 was 2.60 mm 2 The ratio of the area of ​​the clamped portion 180 to the total area of ​​the pump electrode 112 was 49%. The evaluation result of the peel test of the pump electrode 112 was A. The evaluation result of the pump capacity test was A. The ratio Q of the effective area of ​​the front end region 112F to the effective area of ​​the pump electrode 112 was 65.8%.

[0113] [Example 13] In the thirteenth embodiment, the layout of the clamped portion 180 was Type B. More specifically, the layout was that shown in FIG. 6B. That is, the clamped portion 180 arranged in the rear end region 112R was extended to a part of the front end region 112F, and the clamped portion 180 was further positioned at the end of the pump electrode 112 on the rear end side. The total area of ​​the pump electrode 112 was 9.9 mm 2 The area of ​​the clamped portion 180 is 2.0 mm 2 In Example 13, the effective area of ​​the pump electrode 112 was 7.9 mm 2 The effective area of ​​the front end region 112F of the pump electrode 112 was 4.25 mm 2 The effective area of ​​the rear end region 112R of the pump electrode 112 was 3.65 mm 2 The ratio of the area of ​​the clamped portion 180 to the total area of ​​the pump electrode 112 was 20%. The evaluation result of the peel test of the pump electrode 112 was A. In Example 13, the evaluation result of the pump capacity test was A. In Example 13, the ratio Q of the effective area of ​​the front end region 112F to the effective area of ​​the pump electrode 112 was 53.8%.

[0114] [Example 14] In Example 14, the layout of the clamped parts 180 was Type C. That is, the clamped parts 180 arranged in the rear end region 112R and the clamped parts 180 different from each other were arranged in the front end region 112F. The total area of ​​the pump electrodes 112 was 9.5 mm 2 The area of ​​the clamped portion 180 is 2.3 mm 2 The effective area of ​​the pump electrode 112 was 7.2 mm 2 The effective area of ​​the front end region 112F of the pump electrode 112 was 3.69 mm 2 The effective area of ​​the rear end region 112R of the pump electrode 112 was 3.50 mm 2 The ratio of the area of ​​the clamped portion 180 to the total area of ​​the pump electrode 112 was 24%. The evaluation result of the peel test of the pump electrode 112 was A. In Example 14, the evaluation result of the pump capacity test was A. The ratio Q of the effective area of ​​the front end region 112F to the effective area of ​​the pump electrode 112 was 51.3%.

[0115] [Example 15] In Example 15, the layout of the clamped parts 180 was Type C. That is, the clamped parts 180 arranged in the rear end region 112R and the clamped parts 180 different from each other were arranged in the front end region 112F. The total area of ​​the pump electrodes 112 was 9.8 mm 2 The area of ​​the clamped portion 180 is 2.4 mm 2 The effective area of ​​the pump electrode 112 was 7.4 mm 2 The effective area of ​​the front end region 112F of the pump electrode 112 was 3.80 mm 2 The effective area of ​​the rear end region 112R of the pump electrode 112 was 3.60 mm 2 The ratio of the area of ​​the clamped portion 180 to the total area of ​​the pump electrode 112 was 24%. The evaluation result of the peel test of the pump electrode 112 was A. In Example 15, the evaluation result of the pump capacity test was A. The ratio Q of the effective area of ​​the front end region 112F to the effective area of ​​the pump electrode 112 was 51.4%.

[0116] [Example 16] In Example 16, the layout of the clamped parts 180 was Type C. That is, the clamped parts 180 arranged in the rear end region 112R and the clamped parts 180 different from each other were arranged in the front end region 112F. The total area of ​​the pump electrodes 112 was 9.9 mm 2 The area of ​​the clamped portion 180 is 2.9 mm 2 The effective area of ​​the pump electrode 112 was 7.0 mm 2 The effective area of ​​the front end region 112F of the pump electrode 112 was 3.95 mm 2 The effective area of ​​the rear end region 112R of the pump electrode 112 was 3.05 mm 2 The ratio of the area of ​​the clamped portion 180 to the total area of ​​the pump electrode 112 was 29%. The evaluation result of the peel test of the pump electrode 112 was A. In Example 16, the evaluation result of the pump capacity test was A. The ratio Q of the effective area of ​​the front end region 112F to the effective area of ​​the pump electrode 112 was 56.4%.

[0117] [Comparative Example 1] In Comparative Example 1, the total area of ​​the pump electrodes 112 is 7.5 mm 2 The area of ​​the clamped portion 180 is 0 mm 2 In other words, the clamped portion 180 was not provided. The effective area of ​​the pump electrode 112 was 7.5 mm 2 The effective area of ​​the front end region 112F of the pump electrode 112 was 3.75 mm 2 The effective area of ​​the rear end region 112R of the pump electrode 112 was 3.75 mm 2 The ratio of the area of ​​the clamped portion 180 to the total area of ​​the pump electrode 112 was 0%. The evaluation result of the peel test of the pump electrode 112 was C. The evaluation result of the pump capacity test was A. The ratio Q of the effective area of ​​the front end region 112F to the effective area of ​​the pump electrode 112 was 50.0%.

[0118] [Comparative Example 2] In Comparative Example 2, the total area of ​​the pump electrodes 112 is 9.9 mm 2 The area of ​​the clamped portion 180 is 0 mm 2In other words, the clamped portion 180 was not provided. The effective area of ​​the pump electrode 112 was 9.9 mm 2 The effective area of ​​the front end region 112F of the pump electrode 112 was 4.95 mm 2 The effective area of ​​the rear end region 112R of the pump electrode 112 was 4.95 mm 2 The ratio of the area of ​​the clamped portion 180 to the total area of ​​the pump electrode 112 was 0%. The evaluation result of the peel test of the pump electrode 112 was C. In Comparative Example 2, the evaluation result of the pump capacity test was A. In Comparative Example 2, the ratio Q of the effective area of ​​the front end region 112F to the effective area of ​​the pump electrode 112 was 50.0%.

[0119] [Comparative Example 3] In Comparative Example 3, the total area of ​​the pump electrodes 112 is 12.3 mm 2 The area of ​​the clamped portion 180 is 0 mm 2 That is, the clamped portion 180 was not provided. The effective area of ​​the pump electrode 112 was 12.3 mm 2 The effective area of ​​the front end region 112F of the pump electrode 112 was 6.15 mm 2 The effective area of ​​the rear end region 112R of the pump electrode 112 was 6.15 mm 2 The ratio of the area of ​​the clamped portion 180 to the total area of ​​the pump electrode 112 was 0%. The evaluation result of the peel test of the pump electrode 112 was C. In Comparative Example 3, the evaluation result of the pump capacity test was A. In Comparative Example 3, the ratio Q of the effective area of ​​the front end region 112F to the effective area of ​​the pump electrode 112 was 50.0%.

[0120] [Comparative Example 4] In Comparative Example 4, the total area of ​​the pump electrodes 112 is 9.8 mm 2 The area of ​​the clamped portion 180 is 6.5 mm 2 That is, the area of ​​the clamped portion 180 was set excessively large. The clamped portion 180 was disposed on the entire periphery of the pump electrode 112. The effective area of ​​the pump electrode 112 was 3.3 mm 2The effective area of ​​the front end region 112F of the pump electrode 112 was 1.65 mm 2 The effective area of ​​the rear end region 112R of the pump electrode 112 was 1.65 mm 2 The ratio of the area of ​​the clamped portion 180 to the total area of ​​the pump electrode 112 was 66%. The evaluation result of the peeling test of the pump electrode 112 was B. Cracks occurred in the pump electrode 112 due to the difference in thermal expansion coefficient between the pump electrode 112 and the solid electrolyte layers 66, 70, etc. The evaluation result of the pump capacity test was C. The ratio Q of the effective area of ​​the front end side region 112F to the effective area of ​​the pump electrode 112 was 50.0%.

[0121] [Comparative Example 5] In Comparative Example 5, the total area of ​​the pump electrodes 112 is 9.8 mm 2 The area of ​​the clamped portion 180 is 6.5 mm 2 That is, the area of ​​the clamped portion 180 was set excessively large. The clamped portion 180 was disposed on the entire periphery of the pump electrode 112. The effective area of ​​the pump electrode 112 was 3.3 mm 2 The effective area of ​​the front end region 112F of the pump electrode 112 was 1.60 mm 2 The effective area of ​​the rear end region 112R of the pump electrode 112 was 1.70 mm 2 In other words, the area of ​​the clamped portion 180 in the front end region 112F was set to be large, so that the effective area of ​​the front end region 112F of the pump electrode 112 was set to be small. The ratio of the area of ​​the clamped portion 180 to the total area of ​​the pump electrode 112 was set to 66%. The evaluation result of the peeling test of the pump electrode 112 was B. Cracks occurred in the pump electrode 112 due to the difference in thermal expansion coefficient between the pump electrode 112 and the solid electrolyte layers 66, 70, etc. The evaluation result of the pump capacity test was C. In the comparative example 5, the ratio Q of the effective area of ​​the front end region 112F to the effective area of ​​the pump electrode 112 was 48.5%.

[0122] In this manner, by setting the ratio of the area of ​​the clamped portion 180 to the total area of ​​the pump electrode 112 within the range of 5 to 50%, peeling of the pump electrode 112 can be prevented. Also, by setting the ratio of the area of ​​the clamped portion 180 to the total area of ​​the pump electrode 112 within the range of 10 to 50%, peeling of the pump electrode 112 can be more reliably prevented.

[0123] The effective area of ​​the pump electrode 112 is set to 4.0 mm 2 By setting the above, good pumping capacity can be obtained.

[0124] As described above, according to this embodiment, at least a part of the pump electrode 112 is sandwiched between the spacer layer 68 and the solid electrolyte layers 66, 70, or is covered by the covering layer 182 formed on the inner surface of the measurement gas flow path 79, so that the pump electrode 112 can be prevented from peeling off. 2 For the above reasons, good pumping ability can be ensured. According to this embodiment, the area of ​​the portion of the front end region 112F exposed in the measurement gas flow path 79 is larger than the area of ​​the portion of the rear end region 112R exposed in the measurement gas flow path 79, so that the exposed area of ​​the pump electrode 112 can be made large in the region with a higher oxygen concentration. Ensuring a large exposed area of ​​the pump electrode 112 in the region with a higher oxygen concentration contributes to ensuring sufficient pumping ability and to accurate operation of the sensor element 12. Thus, according to this embodiment, it is possible to provide a gas sensor 10 that can suppress peeling of the pump electrode 112 while ensuring good performance.

[0125] [Modified embodiment] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the gist of the present invention.

[0126] For example, in the above embodiment, the pump electrode 112 is configured by the top pump electrode 112a and the bottom pump electrode 112b, but the present invention is not limited to this. For example, the pump electrode 112 may be configured by only the top pump electrode 112a. FIG. 11 is a cross-sectional view showing a part of a gas sensor according to a modified embodiment. In the example shown in FIG. 11, the pump electrode 112 is configured by only the top pump electrode 112a. Also, the pump electrode 112 may be configured by only the bottom pump electrode 112b.

[0127] In the above embodiment, the fourth diffusion rate-controlling portion 94 is provided between the second internal space 92 and the third internal space 96, but the present invention is not limited to this. The fourth diffusion rate-controlling portion 94 does not have to be provided between the second internal space 92 and the third internal space 96. In this case, the second internal space 92 and the third internal space 96 may be integrated. In this case, the auxiliary pump electrode 126 and the measurement electrode 134 are located in the same internal space.

[0128] The above embodiment can be summarized as follows.

[0129] The gas sensor (10) comprises a laminate (13) including at least one layer made of a solid electrolyte, a measurement gas flow path (79) formed in the laminate and through which a measurement gas flows, the measurement gas being introduced via a gas inlet (80) located on a front end side, which is one of the longitudinal directions of the laminate, and a pump electrode (112) formed along the longitudinal direction of the measurement gas flow path and exposed in the measurement gas flow path, the pump electrode having a front end region ( the pump electrode is sandwiched, in a part of the rear-end region, between a first layer (66, 70) and a second layer (68) adjacent to the first layer among a plurality of layers constituting the laminate, or is covered by a covering layer (182) formed on the inner surface of the measurement target gas flow path, and an area of ​​a portion of the pump electrode exposed in the measurement target gas flow path is 4 mm 2 or more, and the area of ​​the portion of the front end region exposed in the measurement gas flow path is larger than the area of ​​the portion of the rear end region exposed in the measurement gas flow path. With this configuration, at least a part of the pump electrode is sandwiched between the first layer and the second layer, or is covered by the covering layer formed on the inner surface of the measurement gas flow path, so that peeling of the pump electrode can be suppressed. Also, when the area of ​​the portion of the pump electrode exposed in the measurement gas flow path is 4 mm or less, 2 For the above reasons, good pumping capacity can be ensured. Furthermore, with this configuration, the area of ​​the front end region exposed in the measurement gas flow path is larger than the area of ​​the rear end region exposed in the measurement gas flow path, so that a large exposed area of ​​the pump electrode can be ensured in the region with a higher oxygen concentration. Ensuring a large exposed area of ​​the pump electrode in the region with a higher oxygen concentration contributes to ensuring sufficient pumping capacity and to accurate operation of the sensor element. Thus, with this configuration, it is possible to provide a gas sensor that can suppress peeling of the pump electrode while ensuring good performance.

[0130] The laminate may further include a third layer (70) adjacent to the second layer, the measurement gas flow path being formed in the second layer, a bottom surface and a top surface of the measurement gas flow path being partitioned by the first layer (66) and the third layer, a side surface of the measurement gas flow path being partitioned by the second layer, the pump electrodes may include a bottom-side pump electrode (112b) formed on the bottom surface of the measurement gas flow path and a top-side pump electrode (112a) formed on the top surface of the measurement gas flow path, one of the bottom-side pump electrode and the top-side pump electrode is sandwiched between the first layer and the second layer in a part of the rear-end side region or is covered by a coating layer formed on an inner surface of the measurement gas flow path, and the other of the bottom-side pump electrode and the top-side pump electrode is sandwiched between the second layer and the third layer in a part of the rear-end side region or is covered by a coating layer formed on the inner surface of the measurement gas flow path.

[0131] The ratio of the area of ​​the portion of the pump electrode that is not exposed in the measurement gas flow path to the total area of ​​the pump electrode may be 5 to 50%. With this configuration, it is possible to prevent the pump electrode from cracking and to suppress peeling of the pump electrode.

[0132] The ratio of the area of ​​the portion of the pump electrode that is not exposed in the measurement gas flow path to the total area of ​​the pump electrode may be 10 to 50%. With this configuration, it is possible to more reliably suppress peeling of the pump electrode while preventing cracks from occurring in the pump electrode.

[0133] The pump electrode may have a rectangular planar shape, and a portion of the pump electrode sandwiched between the first layer and the second layer or a portion of the pump electrode covered by the covering layer may be located at least on both sides of the pump electrode with respect to a center line (CL) of the pump electrode along the longitudinal direction of the measurement gas flow passage. Such a configuration can contribute to suppressing peeling of the pump electrode.

[0134] The pump electrode may be further sandwiched between the first layer and the second layer in at least a part of the front end region, or may be further covered by a covering layer formed on the inner surface of the measurement gas flow passage. With such a configuration, peeling of the pump electrode can be more reliably suppressed.

[0135] The pump electrode may have a front end portion sandwiched between the first layer and the second layer, or may be further covered by a covering layer formed on the inner surface of the measurement gas flow passage. With this configuration, peeling of the pump electrode can be more reliably suppressed.

[0136] The pump electrode may have a rear end that is sandwiched between the first layer and the second layer, or may be covered by a covering layer formed on the inner surface of the measurement gas flow passage. With this configuration, peeling of the pump electrode can be more reliably suppressed.

[0137] The first layer and the second layer may be made of a solid electrolyte.

[0138] The first layer may be made of a solid electrolyte, and the second layer may be made of an insulator.

[0139] The third layer may be made of a solid electrolyte. [Explanation of symbols]

[0140] 10: Gas sensor 12: Sensor element 13: Laminated body 14: Protective cover 14a: Inner protective cover 14b: Outer protective cover 16: Ceramic housing 18: Metal terminal 20: Sensor assembly 24: Connector 26: Piping 28: Sensor element chamber 30: Element sealing body 32: Nut 34: Outer tube 40: Main metal fitting 42: Inner cylinder 42a, 42b: Reduced diameter part 44a-44c: Ceramic supporter 46a, 46b: powder compact 48: metal ring 50: Space 52: Fixing member 54, 172: Lead wire 56: Elastic insulating member 60: First substrate layer 62: Second substrate layer 64: Third substrate layer 66, 70: Solid electrolyte layer 68: Spacer layer 79: Measurement gas flow path 80: Gas inlet 82: First diffusion-controlling section 84: Buffer space 86: Second diffusion limiting section 88: First inner cavity 90: Third diffusion-controlling section 92: Second internal cavity 94: Fourth diffusion-controlling section 96: Third internal space 98: Reference gas introduction space 100: Air introduction layer 102: Reference electrode 110: Main pump cell 112: Pump electrode 112aF, 112bF, 112F: Front end area 112aR, 112bR, 112R: Posterior region 112a: Top side pump electrode 112b: Bottom side pump electrode 114: Outer pump electrode 120: Oxygen partial pressure detection sensor cell for controlling main pump, Oxygen partial pressure detection sensor cell 122, 132, 144, 152: Variable power supply 124: Auxiliary pump cell 126: Auxiliary pump electrode 126a: Top electrode portion 126b: Bottom electrode portion 130: Oxygen partial pressure detection sensor cell for controlling auxiliary pump, oxygen partial pressure detection sensor cell 134: Measuring electrode 140: Measuring pump cell 142: Oxygen partial pressure detection sensor cell for measuring pump control, oxygen partial pressure detection sensor cell 146: Sensor cell 150: Reference gas adjustment pump cell 160: heater section 162: heater connector electrode 164: Heater 166: Through hole 168: Heater insulation layer 170: Pressure relief hole 180, 180a~180u: Clamped part 182: Covering layer CL: Center line Ip0, Ip1, Ip2: Pump current Ip3: Control current V0, V1, V2, Vref: electromotive force VL: virtual line Vp0: Pump voltage Vp1, Vp2, Vp3: Voltage

Claims

1. A laminate including at least one layer made of a solid electrolyte; a measurement gas flow path formed in the stack, through which a measurement gas flows, the measurement gas being introduced through a gas inlet located on a front end side, which is one of the longitudinal directions of the stack; a pump electrode formed along a longitudinal direction of the measurement gas flow passage and exposed in the measurement gas flow passage; Equipped with the pump electrode has a front end region located on the front end side with respect to a center of the pump electrode, and a rear end region located on the rear end side opposite the front end side with respect to the center of the pump electrode, the pump electrode is covered at a portion of the rear end region by a coating layer formed on an inner surface of the measurement target gas flow passage, a portion of the pump electrode that is not covered by the covering layer is an effective area of ​​the pump electrode; The area of ​​the pump electrode exposed in the measurement gas flow path is 4 mm ２ That's all. an area of ​​a portion of the front end region exposed in the measurement gas flow path is larger than an area of ​​a portion of the rear end region exposed in the measurement gas flow path, The laminate further includes a first layer, a second layer adjacent to the first layer, and a third layer adjacent to the second layer, among a plurality of layers constituting the laminate; the measurement gas flow path is formed in the second layer, a bottom surface and a top surface of the measurement gas flow passage are partitioned by the first layer and the third layer, a side surface of the measurement gas flow passage is partitioned by the second layer, A gas sensor, wherein the maximum thickness of the covering layer is smaller than the thickness of the second layer.

2. 2. The gas sensor according to claim 1, the pump electrode includes a bottom pump electrode formed on a bottom surface of the measurement target gas flow passage and a top pump electrode formed on a top surface of the measurement target gas flow passage, one of the bottom pump electrode and the top pump electrode is covered in the part of the rear end region with a first coating layer among the plurality of coating layers formed on the inner surface of the measurement gas flow path, the other of the bottom pump electrode and the top pump electrode is covered in the part of the rear end region with a second coating layer different from the first coating layer among the plurality of coating layers formed on the inner surface of the measurement gas flow path, A gas sensor, wherein the sum of the maximum thickness of the first coating layer and the maximum thickness of the second coating layer is smaller than the thickness of the second layer.

3. 3. The gas sensor according to claim 1, The gas sensor according to claim 1, wherein a ratio of an area of ​​the pump electrode that is not exposed in the measurement gas flow passage to a total area of ​​the pump electrode is 5 to 50%.

4. 4. The gas sensor according to claim 3, The gas sensor according to claim 1, wherein a ratio of an area of ​​the portion of the pump electrode that is not exposed in the measurement gas flow path to a total area of ​​the pump electrode is 10 to 50%.

5. The gas sensor according to any one of claims 1 to 4, The pump electrode has a rectangular planar shape, a portion of the pump electrode that is covered with the covering layer is located at least on both sides of the pump electrode with respect to a center line of the pump electrode that runs along the longitudinal direction of the measurement target gas flow path.

6. The gas sensor according to any one of claims 1 to 5, The pump electrode is further covered, in at least a part of the front end region, with a covering layer formed on the inner surface of the measurement gas flow passage.

7. The gas sensor according to any one of claims 1 to 6, a front end of the pump electrode is further covered with a covering layer formed on the inner surface of the measurement target gas flow passage.

8. The gas sensor according to any one of claims 1 to 7, a rear end of the pump electrode is further covered with a covering layer formed on the inner surface of the measurement target gas flow passage.

9. The gas sensor according to any one of claims 1 to 8, The gas sensor, wherein the first layer and the second layer are made of a solid electrolyte.

10. The gas sensor according to any one of claims 1 to 8, the first layer is made of a solid electrolyte; The gas sensor, wherein the second layer is made of an insulator.

11. 3. The gas sensor according to claim 2, The gas sensor, wherein the third layer is made of a solid electrolyte.

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