Sensor element and gas sensor

Abstract

The invention provides a sensor element and a gas sensor in which compactness and adhesion are both improved in a portion of a conductive portion that contributes to suppressing gas from reaching an inner electrode. A sensor element (101) is provided with: an element main body (102) having a solid electrolyte layer having oxygen ion conductivity; a measurement electrode (44) disposed inside the element main body (102); and a conduction section (74) in which the inner lead section (77), the side lead section (78), and the connector electrode (75a) are sequentially connected to the measurement electrode (44) in this order. At least a part of the side surface lead part (78) and / or the inner side lead part (77) is a dense part which contains a noble metal, alumina, and silica and is densely configured.

Description

Technical Field

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

[0002] In the past, the following gas sensor is known, which has a sensor element for detecting the concentration of a specific gas such as NOx in a measured gas such as the exhaust gas of an internal combustion engine (for example, see Patent Document 1). The sensor element of Patent Document 1 has: an element body, an inner electrode, a terminal portion, and a lead portion. The element body has an oxygen ion conductive solid electrolyte layer, and is in a columnar shape extending along the length direction, and has a front end and a rear end as two ends along the length direction, and a side surface as a surface along the length direction. The front end side of the element body is exposed to the measured gas. The inner electrode is arranged inside the element body. The terminal portion is arranged on the rear end side of the side of the element body. The lead portion is configured to connect the inner electrode and the terminal portion, and has an inner portion arranged inside the element body, and a side conductive portion exposed from the element body on the side. The terminal portion and the side conductive portion are respectively formed using a conductive material obtained by mixing a precious metal powder and an aluminum oxide powder. As a result, the adhesion strength between the terminal portion and the side conductive portion and the solid electrolyte body can be improved.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent No. 4628920 Summary of the invention

[0006] However, in the above-mentioned sensor element, sometimes some gas outside the sensor element (element body) moves along the inner part of the lead part and between it and the element body and inside the element body to reach the inner electrode. If the gas reaches the inner electrode, it is possible that the detection accuracy of the concentration of the specific gas is reduced. In view of this, it is considered that, for example, a dense side conductive part covers the inner part of the lead part to inhibit the gas from reaching the inner electrode. However, in the sensor element described in Patent Document 1, although the side conductive part includes aluminum oxide to improve the adhesion strength between the side conductive part and the element body, the porosity of the side conductive part tends to increase, and it is difficult to form the side conductive part densely.

[0007] The present invention has been made to solve the above-mentioned problems, and a main object of the present invention is to improve both the density and the adhesion of a portion of the conductive portion that contributes to suppressing the gas from reaching the inner electrode.

[0008] The present invention adopts the following means to achieve the above-mentioned main object.

[0009] [1] The sensor element of the present invention is used to detect the concentration of a specific gas in a gas to be measured.

[0010] The sensor element is characterized by comprising:

[0011] an element body having an oxygen ion conductive solid electrolyte layer, in a columnar shape extending in a longitudinal direction, having a front end and a rear end as both ends along the longitudinal direction and a side surface as a surface along the longitudinal direction, wherein the front end side is exposed to the measured gas;

[0012] an inner electrode disposed inside the element body; and

[0013] a conductive portion, the conductive portion having an inner conductive portion and an outer conductive portion, the inner conductive portion being arranged inside the element body and being conductively connected to the inner electrode, the outer conductive portion having a connector electrode arranged on the rear end side of the side surface, having a portion arranged on the side surface and / or a portion exposed to the outside of the sensor element on the side surface, and being conductively connected to the inner conductive portion,

[0014] A portion of the outer conductive portion that covers the inner conductive portion and / or at least a portion of the inner conductive portion is a dense portion that contains a noble metal, aluminum oxide, and silicon dioxide and is densely configured.

[0015] In this sensor element, the dense portion, which is the portion of the outer conductive portion that covers the inner conductive portion and / or at least a portion of the inner conductive portion, can improve the adhesion by including a noble metal, aluminum oxide, and silicon dioxide, and can also improve the compactness by including silicon dioxide. Therefore, the dense portion, which is the portion of the outer conductive portion that covers the inner conductive portion and / or at least a portion of the inner conductive portion, that is, the portion of the conductive portion that helps to suppress the gas from reaching the inner electrode, can improve both the compactness and the compactness. The inventors of the present invention have confirmed this through experiments, analysis, etc.

[0016] [2] In the sensor element of the present invention (the sensor element described in [1] above), when the volumes of aluminum oxide and silicon dioxide contained in the dense portion are Va [vol %] and Vs [vol %], respectively, Va / Vs ≤ 1.5 can be satisfied. This can further improve the density of the dense portion.

[0017] [3] In the sensor element of the present invention (the sensor element described in [1] or [2] above), when the volumes of the precious metal, aluminum oxide, and silicon dioxide contained in the dense portion are respectively set to Vp [vol %], Va [vol %], and Vs [vol %], 1.5 ≤ Vp / (Va + Vs) can be satisfied. This can more reliably achieve the effect of improving the compactness of the dense portion.

[0018] [4] In the sensor element of the present invention (the sensor element described in [3] above), the dense portion may satisfy 2.6≤Vp / (Va+Vs). This can further improve the density of the dense portion.

[0019] [5] In the sensor element of the present invention (the sensor element described in any one of [1] to [4] above), the dense portion may satisfy the requirement that the total mass ratio of the alkali metal and alkaline earth metal contained in the dense portion as converted into oxides is 0.1 wt% or less. This can suppress the alkali metal and / or alkaline earth metal in the dense portion from moving due to electromigration and causing the conductivity of the dense portion to decrease, thereby suppressing the decrease in the detection accuracy of the concentration of the specific gas caused by the decrease in conductivity.

[0020] [6] In the sensor element of the present invention (the sensor element described in any one of [1] to [5] above), the inner electrode may be a measurement electrode for detecting the concentration of the specific gas.

[0021] [7] In the sensor element of the present invention (the sensor element described in any one of [1] to [6] above), the element body can be a stacked body obtained by stacking a plurality of layers including the solid electrolyte layer in a stacking direction perpendicular to the length direction, wherein the stacked body has, as the side surface, a first surface and a second surface as two end surfaces in the stacking direction, and a third surface and a fourth surface as two end surfaces in a direction perpendicular to the length direction and the stacking direction, the inner conductive portion has an inner lead portion led out to the third surface or the fourth surface, and the portion of the outer conductive portion covering the inner conductive portion is a side lead portion arranged on the third surface or the fourth surface and covering the inner lead portion.

[0022] [8] In the sensor element of the present invention (the sensor element described in any one of [1] to [6] above), the element body can be a stacked body obtained by stacking multiple layers including the solid electrolyte layer in a stacking direction orthogonal to the length direction, in which the stacked body has a first surface and a second surface as the side surfaces as two end surfaces in the stacking direction, and the element body has a through hole, which includes an opening portion that is open to the first surface or the second surface on the rear end side of the side surface and penetrates one or more of the multiple layers in the stacking direction, the outer conductive portion is the connector electrode, and the inner conductive portion has a through hole conductor, which is arranged in the through hole and covered by the connector electrode.

[0023] [9] In the sensor element of the present invention (the sensor element described in any one of [1] to [6] above), the element body can be a stacked body obtained by stacking multiple layers including the solid electrolyte layer in a stacking direction orthogonal to the length direction, in which the stacked body has a first surface and a second surface as the side surfaces as two end surfaces in the stacking direction, the element body has a through hole, the through hole includes an opening portion that is open to the first surface or the second surface on the rear end side of the side surface and penetrates one or more of the multiple layers in the stacking direction, the inner conductive portion has a through hole conductor that is arranged in the through hole and exposed to the outside at the opening, and the dense portion includes at least a portion of the through hole conductor.

[0024]

[10] The sensor element of the present invention (the sensor element described in any one of [1] to [9] above) can be used in a gas sensor, which comprises: the sensor element; a shell, which is in a cylindrical shape extending along the length direction of the sensor element, has a second front end and a second rear end as two ends along the length direction, and the sensor element is arranged inside the shell; and a closing component, which closes the second rear end side of the shell.

[0025]

[11] The gas sensor of the present invention comprises: a sensor element as described in any one of [1] to [9] above; a shell, which is in a cylindrical shape extending along the length direction of the sensor element and has a second front end and a second rear end as two ends along the length direction, and the sensor element is arranged inside the shell; and a closing component, which closes the second rear end side of the shell.

[0026] This gas sensor includes the above-mentioned sensor element, and therefore can obtain the same effects as those exerted by the above-mentioned sensor element, for example, the effect of improving both the density and the adhesion of the portion of the conductive portion that helps to suppress the gas from reaching the inner electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a longitudinal cross-sectional view of the gas sensor 100 .

[0028] Figure 2 It is a cross-sectional schematic diagram schematically showing an example of the structure of the sensor element 101 .

[0029] Figure 3 It is a block diagram showing the electrical connection relationship between the control device 95 and each unit.

[0030] Figure 4 It is a perspective view of the vicinity of the rear end portion of the element body 102 .

[0031] Figure 5 It is a partial cross-sectional view in which the periphery of the conductive portion 74 corresponding to the measuring electrode 44 is enlarged.

[0032] Figure 6 2 is a partial cross-sectional view of a sensor element 201 according to a modified example.

[0033] Figure 7 2 is a partial cross-sectional view of a sensor element 301 according to a modified example.

[0034] Figure 8 FIG. 4 is a partial schematic diagram of a sensor element 401 according to a modified example.

[0035] Fig. 9 2 is a partial cross-sectional view of a sensor element 501 according to a modified example.

[0036] Fig.10 2 is a partial cross-sectional view of a sensor element 601 according to a modified example.

[0037] Description of Reference Numerals

[0038] 1…first substrate layer, 2…second substrate layer, 3…third substrate layer, 4…first solid electrolyte layer, 5…isolation layer, 6…second solid electrolyte layer, 7…adhesive layer, 10…gas inlet, 11…first diffusion rate control unit, 12…buffer space, 13…second diffusion rate control unit, 20…first internal cavity, 21…main pump unit, 22…inner pump electrode, 22a, 51a…top electrode unit, 22b, 51b…bottom electrode unit, 23…outer pump electrode, 24…variable power supply, 30…third diffusion rate control unit, 40…second internal cavity, 41…measurement pump unit, 42…reference electrode, 43…reference gas inlet space, 44…measurement electrode, 45… 5…4th diffusion rate control unit, 46…variable power supply, 48…reference gas introduction layer, 49…reference gas introduction unit, 49a…entrance, 50…auxiliary pump unit, 51…auxiliary pump electrode, 52…variable power supply, 60…4th diffusion rate control unit, 61…third internal cavity, 70…heater unit, 71a…heater, 71b…heater insulation layer, 71c…pressure release hole, 72…heater power supply, 74…conducting unit, 75, 75a to 75h, 575a…connector electrode, 76…lead wire unit, 77, 477…inner lead wire unit, 77a to 77d…first to fourth parts, 78, 278, 378…side lead wire unit, 79…lead insulation layer insulating layer, 80… oxygen partial pressure detection sensor unit for main pump control, 81… oxygen partial pressure detection sensor unit for auxiliary pump control, 82… oxygen partial pressure detection sensor unit for measuring pump control, 83… sensor unit, 95… control device, 96… control unit, 97… CPU, 98… storage unit, 100… gas sensor, 101, 201, 301, 401, 501, 601… sensor element, 102, 402… element body, 102a… first surface, 102b… second surface, 102c… third surface, 102d… fourth surface, 102e… fifth surface, 102f… sixth surface, 130… protective cover, 131… inner protective cover, 132… outer protective cover , 133…sensor element chamber, 140…sensor assembly, 141…element sealing body, 142…main metal part, 143…inner cylinder, 143a, 143b…reduced diameter portion, 144a~144c…ceramic support, 145a, 145b…powder pressed body, 146…metal ring, 147…bolt, 148…outer cylinder, 149…space, 150…connector, 155…lead wire, 157…rubber stopper, 190…pipe, 191…fixing member, 278a, 378a…first side lead wire portion, 278b, 378b…second side lead wire portion, 402h…through hole, 478, 578…through hole conductor, 479…insulating layer, 575h…hole. DETAILED DESCRIPTION

[0039] Next, the embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 is a longitudinal sectional view of a gas sensor 100 as an embodiment of the present invention. Figure 2 is a schematic sectional view schematically showing an example of the configuration of a sensor element 101 included in the gas sensor 100. Figure 3 is a block diagram showing the electrical connection relationship between the control device 95, each unit of the sensor element 101, and the heater 71a. Figure 4 is a perspective view of the periphery of the rear end portion of the element body 102 of the sensor element 101. Figure 5 is a partial sectional view obtained by magnifying the measurement electrode 44 of the sensor element 101 and the periphery of the conduction portion 74 corresponding thereto. The sensor element 101 has an elongated rectangular parallelepiped-shaped element body 102. The length direction of the element body 102 ( Figure 2 the left-right direction in it) is set as the front-rear direction, the thickness direction of the element body 102 ( Figure 2 the up-down direction in it) is set as the up-down direction, and the width direction of the element body 102 (the direction perpendicular to the front-rear direction and the up-down direction) is set as the left-right direction. Since the element body 102 is a rectangular parallelepiped, as Figure 2 , Figure 4 , Figure 5 shows, as the outer surface of the solid electrolyte layer of the element body 102, it has six surfaces: a first surface 102a (upper surface), a second surface 102b (lower surface), a third surface 102c (left side surface), a fourth surface 102d (right side surface), a fifth surface 102e (front end surface), and a sixth surface 102f (rear end surface).

[0040] As Figure 1 shows, the gas sensor 100 includes: a sensor element 101 having an element body 102; a protective cover 130 that protects the front end side of the element body 102; and a sensor assembly 140 having a connector 150 that conducts with the sensor element 101. As shown in the figure, the gas sensor 100 is installed in a pipe 190 such as an exhaust pipe of an internal combustion engine (diesel engine, gasoline engine, etc.) of a vehicle, and uses the exhaust gas of the internal combustion engine as the gas to be measured, so as to measure (detect) the concentration of specific gases such as NOx, O 2 , ammonia, etc. in the gas to be measured, that is, the specific gas concentration. In the present embodiment, as the specific gas concentration, the gas sensor 100 measures the NOx concentration.

[0041] The protective cover 130 includes: a bottomed cylindrical inner protective cover 131 that covers the front end portion of the element main body 102; and a bottomed cylindrical outer protective cover 132 that covers the inner protective cover 131. A plurality of holes for allowing the gas to be measured to flow through the protective cover 130 are formed in the inner protective cover 131 and the outer protective cover 132. The sensor element chamber 133 is formed as a space surrounded by the inner protective cover 131, and the front end portion of the element main body 102 is disposed in the sensor element chamber 133.

[0042] The sensor assembly 140 includes: an element enclosure 141 that encloses and fixes the sensor element 101; a bolt 147 and an outer cylinder 148 that are mounted on the element enclosure 141; and a connector 150 that contacts a connector electrode 75 formed on the surface (upper and lower surfaces) of the rear end portion of the element main body 102 of the sensor element 101 and is electrically connected to these electrodes.

[0043] The element enclosure 141 includes: a cylindrical main body metal part 142; a cylindrical inner cylinder 143 that is coaxially welded and fixed to the main body metal part 142; and ceramic supports 144a to 144c, compression powder bodies 145a, 145b, and metal rings 146 that are enclosed in through holes inside the main body metal part 142 and the inner cylinder 143. The sensor element 101 is located on the central axis of the element enclosure 141 and penetrates the element enclosure 141 in the front-rear direction. In the inner cylinder 143, there are formed: a reduced-diameter portion 143a for pressing the compression powder body 145b in the direction of the central axis of the inner cylinder 143; and a reduced-diameter portion 143b for pressing the ceramic supports 144a to 144c, the compression powder bodies 145a, 145b forward by means of the metal rings 146. The compression powder bodies 145a, 145b are compressed by the pressing forces from the reduced-diameter portions 143a, 143b between the main body metal part 142 and the inner cylinder 143 and the sensor element 101. Thus, the compression powder bodies 145a, 145b seal between the sensor element chamber 133 in the protective cover 130 and the space 149 in the outer cylinder 148, and fix the sensor element 101.

[0044] The bolt 147 is fixed coaxially with the main body metal part 142, and an external thread portion is formed on the outer peripheral surface. The external thread portion of the bolt 147 is inserted into a fixing member 191 that is welded to the pipe 190 and has an internal thread portion provided on the inner peripheral surface. Thus, the gas sensor 100 is fixed to the pipe 190 in a state where the front end portion of the element main body 102 of the sensor element 101 in the gas sensor 100 and a part of the protective cover 130 protrude into the pipe 190.

[0045] The outer cylinder 148 covers the inner cylinder 143, the sensor element 101 and the connector 150, and a plurality of lead wires 155 connected to the connector 150 are led out from the rear end to the outside. The lead wires 155 are connected to the electrodes (described later) of the sensor element 101 by means of the connector 150. At the rear end side of the outer cylinder 148, the gap between the outer cylinder 148 and the lead wires 155 is closed by a rubber plug 157. The outer cylinder 148 is formed with rivets 148a and 148b for limiting the relative movement of the rubber plug 157 in the front-rear direction relative to the outer cylinder 148. The space 149 in the outer cylinder 148 is filled with a reference gas. The rear end of the element body 102 of the sensor element 101 is arranged in the space 149.

[0046] like Figure 2 As shown in FIG. 1 , the sensor element 101 includes an element body 102, units 21, 41, 50, 80 to 83, and a heater unit 70. The element body 102 is made of zirconium dioxide (ZrO 2 ) and the like, and the six layers of the first substrate layer 1, the second substrate layer 2, the third substrate layer 3, the first solid electrolyte layer 4, the isolation layer 5, and the second solid electrolyte layer 6 are stacked in this order from the bottom in the figure. In addition, the solid electrolyte forming these six layers is a dense and airtight solid electrolyte. The element body 102 is manufactured, for example, by stacking the ceramic green sheets corresponding to each layer after performing prescribed processing and printing of circuit patterns, and then firing them to achieve integration.

[0047] On the front end side of the element body 102 and between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, the gas inlet 10, the first diffusion rate control section 11, the buffer space 12, the second diffusion rate control section 13, the first internal cavity (oxygen concentration adjustment chamber) 20, the third diffusion rate control section 30, the second internal cavity (oxygen concentration adjustment chamber) 40, the fourth diffusion rate control section 60 and the third internal cavity (measurement chamber) 61 are adjacently formed in a manner of being connected in this order.

[0048] The gas inlet port 10, the buffer space 12, the first internal cavity 20, the second internal cavity 40 and the third internal cavity 61 are the internal spaces of the sensor element 101 arranged in a manner of hollowing out the isolation layer 5. The upper part of the internal space is divided by the lower surface of the second solid electrolyte layer 6, the lower part is divided by the upper surface of the first solid electrolyte layer 4, and the side part is divided by the side surface of the isolation layer 5.

[0049] The first diffusion rate control section 11, the second diffusion rate control section 13, and the third diffusion rate control section 30 are each provided with two horizontally long (open in a direction perpendicular to the drawing and having a length direction) slits. In addition, the fourth diffusion rate control section 60 is provided with one horizontally long (open in a direction perpendicular to the drawing and having a length direction) slit, which is formed as a gap between the lower surface of the second solid electrolyte layer 6. It should be noted that the portion from the gas inlet 10 to the third internal cavity 61 is also referred to as the measured gas flow portion.

[0050] The element body 102 is provided with a reference gas introduction part 49, which allows the reference gas for measuring the NOx concentration to flow from the outside of the element body 102 to the reference electrode 42. The reference gas introduction part 49 has a reference gas introduction space 43 and a reference gas introduction layer 48. The reference gas introduction space 43 is a space provided in a manner extending from the sixth surface 102f (rear end surface) of the element body 102 toward the fifth surface 102e (front end surface) side. The reference gas introduction space 43 is provided between the upper surface of the third substrate layer 3 and the lower surface of the isolation layer 5, and is provided at a position divided by the side surface of the first solid electrolyte layer 4 on the side. The reference gas introduction space 43 is open at the rear end surface of the element body 102, and the opening functions as an inlet 49a of the reference gas introduction part 49. The reference gas is introduced into the reference gas introduction space 43 from the inlet 49a. The reference gas introduction part 49 introduces the reference gas introduced from the inlet 49a into the reference electrode 42 while giving a predetermined diffusion resistance. The reference gas is the atmosphere in this embodiment.

[0051] The reference gas introduction layer 48 is provided between the upper surface of the third substrate layer 3 and the lower surface of the first solid electrolyte layer 4. The reference gas introduction layer 48 is, for example, a porous body made of ceramics such as alumina. A portion of the upper surface of the reference gas introduction layer 48 is exposed in the reference gas introduction space 43. The reference gas introduction layer 48 is formed to cover the reference electrode 42. The reference gas introduction layer 48 allows the reference gas to flow from the reference gas introduction space 43 to the reference electrode 42.

[0052] The reference electrode 42 is an electrode formed in a manner of being sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4, and as described above, a reference gas introduction layer 48 connected to the reference gas introduction space 43 is provided around it. In addition, as described later, the reference electrode 42 can be used to measure the oxygen concentration (oxygen partial pressure) in the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61.

[0053] In the measured gas flow section, the gas inlet 10 is a portion open to the external space, and the measured gas is introduced from the external space into the sensor element 101 through the gas inlet 10. The first diffusion rate control section 11 is a portion that gives a predetermined diffusion resistance to the measured gas introduced from the gas inlet 10. The buffer space 12 is a space provided to guide the measured gas introduced from the first diffusion rate control section 11 to the second diffusion rate control section 13. The second diffusion rate control section 13 is a portion that gives a predetermined diffusion resistance to the measured gas introduced from the buffer space 12 into the first internal cavity 20. When the measured gas is introduced into the first internal cavity 20 from the outside of the sensor element 101, the measured gas that is rapidly introduced into the sensor element 101 from the gas inlet port 10 due to the pressure fluctuation of the measured gas in the external space (if the measured gas is the exhaust gas of the internal combustion engine, it is the pulsation of the exhaust pressure) is not directly introduced into the first internal cavity 20, but is introduced into the first internal cavity 20 after the pressure fluctuation of the measured gas is eliminated by the first diffusion rate control unit 11, the buffer space 12, and the second diffusion rate control unit 13. As a result, the pressure fluctuation of the measured gas introduced into the first internal cavity 20 is almost negligible. The first internal cavity 20 is provided as a space for adjusting the oxygen partial pressure in the measured gas introduced through the second diffusion rate control unit 13. The oxygen partial pressure is adjusted by operating the main pump unit 21.

[0054] The main pump unit 21 is an electrochemical pump unit composed of an inner pump electrode 22, an outer pump electrode 23, a second solid electrolyte layer 6, an isolation layer 5, and a first solid electrolyte layer 4 that serve as a current path between these electrodes, wherein the inner pump electrode 22 has a top electrode portion 22a that is arranged on substantially the entire surface of the lower surface of the second solid electrolyte layer 6 facing the first internal cavity 20, and the outer pump electrode 23 is arranged on the upper surface of the second solid electrolyte layer 6 in an area corresponding to the top electrode portion 22a so as to be exposed to the outside of the element body 102.

[0055] The inner pump electrode 22 is formed by: the solid electrolyte layer (the second solid electrolyte layer 6 and the first solid electrolyte layer 4) spanning the upper and lower parts that divide the first internal cavity 20, and the isolation layer 5 constituting the side wall. Specifically, a top electrode portion 22a is formed on the lower surface of the second solid electrolyte layer 6 constituting the top surface of the first internal cavity 20, and a bottom electrode portion 22b is formed on the upper surface of the first solid electrolyte layer 4 constituting the bottom surface of the first internal cavity 20, and a side electrode portion (not shown) is formed on the side wall surface (inner surface) of the isolation layer 5 constituting the two side wall portions of the first internal cavity 20 in a manner connecting the top electrode portion 22a and the bottom electrode portion 22b, and a tunnel-shaped structure is arranged at the location where the side electrode portion is arranged.

[0056] Regarding the main pump unit 21, a desired voltage Vp0 is applied between the inner pump electrode 22 and the outer pump electrode 23 so that the pump current Ip0 flows between the inner pump electrode 22 and the outer pump electrode 23 in a positive direction or a negative direction. As a result, the oxygen in the first internal cavity 20 can be sucked out to the external space, or the oxygen in the external space can be sucked into the first internal cavity 20.

[0057] In addition, in order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere in the first internal cavity 20, an electrochemical sensor unit, i.e., an oxygen partial pressure detection sensor unit 80 for main pump control, is formed by the inner pump electrode 22, the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, the third substrate layer 3 and the reference electrode 42.

[0058] The oxygen concentration (oxygen partial pressure) in the first internal cavity 20 is obtained by measuring the electromotive force (voltage V0) at the oxygen partial pressure detection sensor unit 80 for main pump control. Furthermore, the voltage Vp0 of the variable power supply 24 is feedback-controlled so that the voltage V0 becomes a target value, thereby controlling the pump current Ip0. Thus, the oxygen concentration in the first internal cavity 20 can be maintained at a predetermined constant value.

[0059] The third diffusion rate control unit 30 is a portion that provides a predetermined diffusion resistance to the gas to be measured whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump unit 21 in the first internal cavity 20 , and guides the gas to be measured to the second internal cavity 40 .

[0060] The second internal cavity 40 is provided as a space for performing the following processing: the oxygen partial pressure of the gas to be measured, which has been previously adjusted in oxygen concentration (oxygen partial pressure) in the first internal cavity 20 and then introduced through the third diffusion rate control unit 30, is further adjusted by the auxiliary pump unit 50. Thus, the oxygen concentration in the second internal cavity 40 can be kept constant with high accuracy, and thus, the gas sensor 100 can realize high-accuracy NOx concentration measurement.

[0061] The auxiliary pump unit 50 is an auxiliary electrochemical pump unit composed of an auxiliary pump electrode 51, an outer pump electrode 23 (not limited to the outer pump electrode 23, as long as it is an appropriate electrode arranged on the outer peripheral surface of the element body 102), a second solid electrolyte layer 6, an isolation layer 5 and a first solid electrolyte layer 4. The auxiliary pump electrode 51 has a top electrode portion 51a that is arranged on the lower surface of the second solid electrolyte layer 6 and faces the second internal cavity 40.

[0062] The auxiliary pump electrode 51 is arranged in the second internal cavity 40 in the same tunnel-shaped structure as the inner pump electrode 22 arranged in the first internal cavity 20. That is, a top electrode portion 51a is formed on the second solid electrolyte layer 6 constituting the top surface of the second internal cavity 40, and a bottom electrode portion 51b is formed on the first solid electrolyte layer 4 constituting the bottom surface of the second internal cavity 40, and a side electrode portion (not shown) connecting the top electrode portion 51a and the bottom electrode portion 51b is respectively formed on the two wall surfaces of the isolation layer 5 constituting the side wall of the second internal cavity 40, thereby forming a tunnel-shaped structure.

[0063] The auxiliary pump unit 50 applies a desired voltage Vp1 between the auxiliary pump electrode 51 and the outer pump electrode 23 , thereby allowing oxygen in the atmosphere in the second internal cavity 40 to be drawn out to the external space or oxygen to be drawn from the external space into the second internal cavity 40 .

[0064] In addition, in order to control the oxygen partial pressure in the atmosphere within the second internal cavity 40, an electrochemical sensor unit, namely, an auxiliary pump control oxygen partial pressure detection sensor unit 81, is formed by the auxiliary pump electrode 51, the reference electrode 42, the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4 and the third substrate layer 3.

[0065] It should be noted that the auxiliary pump unit 50 performs pumping using a variable power supply 52, and the variable power supply 52 is voltage-controlled based on the electromotive force (voltage V1) detected by the auxiliary pump control oxygen partial pressure detection sensor unit 81. As a result, the oxygen partial pressure in the atmosphere in the second internal cavity 40 is controlled to a relatively low partial pressure that has substantially no effect on the measurement of NOx.

[0066] At the same time, the pump current Ip1 is used to control the electromotive force of the oxygen partial pressure detection sensor unit 80 for main pump control. Specifically, the pump current Ip1 is input as a control signal to the oxygen partial pressure detection sensor unit 80 for main pump control, and the above-mentioned target value of the voltage V0 is controlled, thereby controlling the gradient of the oxygen partial pressure in the measured gas introduced from the third diffusion rate control unit 30 into the second internal cavity 40 to be constant. When used as a NOx sensor, the oxygen concentration in the second internal cavity 40 is maintained at a constant value of about 0.001 ppm by the action of the main pump unit 21 and the auxiliary pump unit 50.

[0067] The fourth diffusion rate control unit 60 is a portion that provides a predetermined diffusion resistance to the gas to be measured whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the auxiliary pump unit 50 in the second internal cavity 40, and guides the gas to be measured to the third internal cavity 61. The fourth diffusion rate control unit 60 has a function of limiting the amount of NOx flowing into the third internal cavity 61.

[0068] The third internal cavity 61 is provided as a space for performing the following processing: the nitrogen oxide (NOx) concentration in the measured gas is measured after the oxygen concentration (oxygen partial pressure) is adjusted in advance in the second internal cavity 40 and then introduced through the fourth diffusion rate control unit 60. The NOx concentration is measured mainly in the third internal cavity 61 by the operation of the measurement pump unit 41.

[0069] The measuring pump cell 41 measures the NOx concentration in the measured gas in the third internal cavity 61. The measuring pump cell 41 is an electrochemical pump cell composed of a measuring electrode 44, an outer pump electrode 23, a second solid electrolyte layer 6, a separator 5, and a first solid electrolyte layer 4, wherein the measuring electrode 44 is disposed on the upper surface of the first solid electrolyte layer 4 at a position facing the third internal cavity 61. The measuring electrode 44 also functions as a NOx reduction catalyst for reducing NOx present in the atmosphere in the third internal cavity 61.

[0070] The measurement pump unit 41 can suck out oxygen generated by decomposition of nitrogen oxides in the atmosphere around the measurement electrode 44 and detect the generated amount as the pump current Ip2 .

[0071] In order to detect the oxygen partial pressure around the measuring electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, the measuring electrode 44 and the reference electrode 42 constitute an electrochemical sensor unit, that is, a measuring pump control oxygen partial pressure detection sensor unit 82. The variable power supply 46 is controlled based on the electromotive force (voltage V2) detected by the measuring pump control oxygen partial pressure detection sensor unit 82.

[0072] The gas to be measured introduced into the second internal cavity 40 passes through the fourth diffusion rate control unit 60 under the condition that the oxygen partial pressure is controlled and reaches the measuring electrode 44 in the third internal cavity 61. The nitrogen oxides (NOx) in the gas to be measured around the measuring electrode 44 are reduced (2NO→N2+O2) to generate oxygen. And the generated oxygen is pumped by the measuring pump unit 41. At this time, the voltage Vp2 of the variable power supply 46 is controlled so that the voltage V2 detected by the oxygen partial pressure detection sensor unit 82 controlled by the measuring pump is constant (target value). The amount of oxygen generated around the measuring electrode 44 is proportional to the concentration of nitrogen oxides in the gas to be measured, so the concentration of nitrogen oxides in the gas to be measured is calculated using the pump current Ip2 in the measuring pump unit 41.

[0073] In addition, the measuring electrode 44, the first solid electrolyte layer 4, the third substrate layer 3 and the reference electrode 42 are combined to form an oxygen partial pressure detection mechanism as an electrochemical sensor unit, thereby being able to detect the electromotive force corresponding to the difference between the amount of oxygen generated by the reduction of the NOx component in the atmosphere around the measuring electrode 44 and the amount of oxygen contained in the reference atmosphere, thereby being able to calculate the concentration of the NOx component in the measured gas.

[0074] Furthermore, an electrochemical sensor unit 83 is formed by the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the outer pump electrode 23 and the reference electrode 42. The electromotive force (voltage Vref) obtained by the sensor unit 83 can be used to detect the oxygen partial pressure in the measured gas outside the element body 102 of the sensor element 101, specifically around the outer pump electrode 23.

[0075] With the gas sensor 100 having such a configuration, the main pump unit 21 and the auxiliary pump unit 50 are operated to supply the gas to be measured whose oxygen partial pressure is always kept at a constant low value (a value that does not substantially affect the measurement of NOx) to the measurement pump unit 41. Therefore, based on the pump current Ip2 that is approximately proportional to the concentration of NOx in the gas to be measured and flows due to the oxygen generated by the reduction of NOx being sucked out by the measurement pump unit 41, the NOx concentration in the gas to be measured can be known.

[0076] Here, each electrode 22, 23, 42, 44, 51 is described. The inner pump electrode 22, the auxiliary pump electrode 51, and the measuring electrode 44 each contain a first noble metal having catalytic activity. As the first noble metal, for example, at least any one of Pt, Rh, Ir, Ru, and Pd can be cited. The outer pump electrode 23 and the reference electrode 42 also contain the first noble metal. The inner pump electrode 22 and the auxiliary pump electrode 51 also contain a second noble metal that suppresses the catalytic activity of the first noble metal for a specific gas (NOx). As a result, the reducing ability of the inner pump electrode 22 and the auxiliary pump electrode 51 for the NOx component in the measured gas is weakened. As the second noble metal, for example, Au can be cited. The measuring electrode 44 does not contain the second noble metal. As a result, the reducing ability for the NOx component in the measured gas is higher than that of the inner pump electrode 22 and the auxiliary pump electrode 51. The measuring electrode 44 preferably contains at least one of Pt and Rh in the first noble metal, and may also contain Pt and Rh at the same time. The outer pump electrode 23 and the reference electrode 42 also preferably do not contain the second noble metal. Each of the electrodes 22, 23, 42, 44, and 51 preferably contains a noble metal and an oxide having oxygen ion conductivity (e.g., ZrO 2) metal ceramic. Each electrode 22, 23, 42, 44, 51 is preferably a porous body. In this embodiment, the inner pump electrode 22 and the auxiliary pump electrode 51 are made of Pt and ZrO containing 1% Au. 2 In addition, the outer pump electrode 23 and the reference electrode 42 are made of Pt and ZrO 2 The measuring electrode 44 is made of Pt, Rh and ZrO 2 Porous metal ceramic electrode.

[0077] The heater unit 70 has a temperature adjustment function of heating and keeping the sensor element 101 warm so as to improve the oxygen ion conductivity of the solid electrolyte of the element body 102. The heater unit 70 includes a heater 71a, a heater insulating layer 71b, and a pressure release hole 71c.

[0078] The heater 71a is a resistor formed by being sandwiched from the upper and lower sides by the second substrate layer 2 and the third substrate layer 3. The heater 71a generates heat by being supplied with power by the heater power supply 72, thereby heating and keeping warm the solid electrolyte of the element body 102 of the sensor element 101. In addition, the heater 71a is buried in the entire region from the first internal cavity 20 to the third internal cavity 61, and the entire sensor element 101 can be adjusted to a temperature that activates the solid electrolyte.

[0079] The heater insulating layer 71b is an insulating layer formed of an insulator such as alumina on the upper and lower surfaces of the heater 71a. The heater insulating layer 71b is formed to obtain electrical insulation between the second substrate layer 2 and the heater 71a, and between the third substrate layer 3 and the heater 71a.

[0080] The pressure release hole 71c is a portion that is arranged to penetrate the third substrate layer 3 and the reference gas introduction layer 48 and is connected to the reference gas introduction space 43. The purpose of forming the pressure release hole 71c is to alleviate the increase in internal pressure accompanying the temperature increase in the heater insulation layer 71b.

[0081] The gas sensor 100 further includes a control device 95. Figure 3As shown, the control device 95 includes the above-mentioned variable power supplies 24, 46, 52, the above-mentioned heater power supply 72, and a control unit 96. The control unit 96 is a microprocessor including a CPU 97 and a storage unit 98. The storage unit 98 is a non-volatile memory capable of rewriting information, and can store various programs and various data, for example. The control unit 96 is input with the voltage V0 of the main pump control oxygen partial pressure detection sensor unit 80, the voltage V1 of the auxiliary pump control oxygen partial pressure detection sensor unit 81, the voltage V2 of the measurement pump control oxygen partial pressure detection sensor unit 82, the voltage Vref of the sensor unit 83, the pump current Ip0 flowing through the main pump unit 21, the pump current Ip1 flowing through the auxiliary pump unit 50, and the pump current Ip2 flowing through the measurement pump unit 41. In addition, the control unit 96 controls the voltages Vp0, Vp1, and Vp2 output by the variable power supplies 24, 46, and 52 by outputting control signals to the variable power supplies 24, 46, and 52, thereby controlling the main pump unit 21, the measuring pump unit 41, and the auxiliary pump unit 50. The control unit 96 controls the power supplied by the heater power supply 72 to the heater 71a by outputting control signals to the heater power supply 72. The storage unit 98 also stores target values ​​V0*, V1*, and V2*, which will be described later. The CPU 97 of the control unit 96 controls each pump unit 21, 41, and 50 with reference to these target values ​​V0*, V1*, and V2*.

[0082] The control unit 96 performs auxiliary pump control processing, that is, controls the auxiliary pump unit 50 so that the oxygen concentration in the second internal cavity 40 becomes the target concentration. Specifically, the control unit 96 performs feedback control on the voltage Vp1 of the variable power supply 52 so that the voltage V1 becomes a constant value (referred to as the target value V1*), thereby controlling the auxiliary pump unit 50. The target value V1* is determined to be a predetermined low concentration value that does not substantially affect the measurement of NOx.

[0083] The control unit 96 performs the main pump control process, that is, controls the main pump unit 21 so that the pump current Ip1 flowing when the auxiliary pump unit 50 adjusts the oxygen concentration of the second internal cavity 40 by the auxiliary pump control process becomes the target current (referred to as the target value Ip1*). Specifically, the control unit 96 sets (feedback control) the target value of the voltage V0 (referred to as the target value V0*) based on the pump current Ip1 flowing due to the voltage Vp1 so that the pump current Ip1 becomes the constant target value Ip1*. In addition, the control unit 96 performs feedback control on the voltage Vp0 of the variable power supply 24 so that the voltage V0 becomes the target value V0* (that is, so that the oxygen concentration of the first internal cavity 20 becomes the target concentration). By this main pump control process, the gradient of the oxygen partial pressure in the gas to be measured introduced from the third diffusion rate control unit 30 into the second internal cavity 40 is always constant. The target value V0* is set to a value such that the oxygen concentration of the first internal cavity 20 is higher than 0% and is low. In addition, the pump current Ip0 flowing in the main pump control process changes in accordance with the oxygen concentration of the measured gas (i.e., the measured gas around the sensor element 101) flowing into the measured gas flow portion from the gas inlet 10. Therefore, the control unit 96 can also detect the oxygen concentration in the measured gas based on the pump current Ip0.

[0084] The main pump control process and the auxiliary pump control process are also collectively referred to as the adjustment pump control process. In addition, the first internal cavity 20 and the second internal cavity 40 are also collectively referred to as the oxygen concentration adjustment chamber. The main pump unit 21 and the auxiliary pump unit 50 are also collectively referred to as the adjustment pump unit. The adjustment pump control process is performed by the control unit 96 so that the adjustment pump unit adjusts the oxygen concentration of the oxygen concentration adjustment chamber.

[0085] The control unit 96 performs a measurement pump control process, that is, controls the measurement pump unit 41 so that the voltage V2 becomes a constant value (referred to as a target value V2*) (that is, so that the oxygen concentration in the third internal cavity 61 becomes a predetermined low concentration). Specifically, the control unit 96 performs feedback control on the voltage Vp2 of the variable power supply 46 so that the voltage V2 becomes the target value V2*, thereby controlling the measurement pump unit 41. Oxygen is sucked out from the third internal cavity 61 by this measurement pump control process.

[0086] By performing the measurement pump control process, oxygen is sucked out from the third internal cavity 61 in such a manner that the oxygen generated by the reduction of NOx in the measured gas in the third internal cavity 61 is substantially zero. In addition, the control unit 96 obtains the pump current Ip2 as a detection value corresponding to the oxygen generated in the third internal cavity 61 from the specific gas (here, NOx), and calculates the NOx concentration in the measured gas based on the pump current Ip2.

[0087] The storage unit 98 stores a relational expression (for example, a linear function or a quadratic function), a map, etc. as the correspondence between the pump current Ip2 and the NOx concentration. The relational expression or the map can be obtained in advance through experiments.

[0088] The control unit 96 performs a heater control process, that is, outputs a control signal to the heater power supply 72 to control so that the temperature of the heater 71a becomes a target temperature (e.g., 800°C). Here, the temperature of the heater 71a can be expressed by a formula of a linear function of the resistance value of the heater 71a. In the heater control process, the control unit 96 calculates the resistance value of the heater 71a as a value that can be regarded as the temperature of the heater 71a (a value that can be converted into a temperature), and performs feedback control on the heater power supply 72 so that the calculated resistance value becomes a target resistance value (a resistance value corresponding to the target temperature). The control unit 96 can obtain, for example, the voltage of the heater 71a and the current flowing through the heater 71a, and calculate the resistance value of the heater 71a based on the obtained voltage and current. The control unit 96 can also calculate the resistance value of the heater 71a using, for example, a three-terminal method or a four-terminal method. When the heater power supply 72 supplies power to the heater 71 a , the value of the voltage applied to the heater 71 a is changed based on a control signal from the control unit 96 , for example, to adjust the power supplied to the heater 71 a .

[0089] Should be explained, including Figure 3 The control device 95 is connected to the electrodes 22, 23, 42, 44, 51, and the heater 71a, including the variable power supplies 24, 46, 52 and the heater power supply 72, etc., through the corresponding conductive parts 74. The plurality of conductive parts 74 each have a connector electrode 75 and a lead part 76 for electrically connecting the corresponding electrodes and the connector electrode 75. Figure 4 Although all of the plurality of connector electrodes 75 are shown in the figure, only the lead wire portions 76 corresponding to the measurement electrodes 44 are shown in the figure.

[0090] The plurality of connector electrodes 75 function as terminals for electrically connecting the sensor element 101 to the outside. Figure 4As shown in FIG. 1 , a plurality of connector electrodes 75 are disposed on the rear end side of the first surface 102a (upper surface) or the second surface 102b (lower surface) of the element body 102 of the sensor element 101. Specifically, the plurality of connector electrodes 75 are connector electrodes 75a to 75d disposed in sequence from the left side on the rear end side of the first surface 102a of the element body 102, and connector electrodes 75e to 75h disposed in sequence from the left side on the rear end side of the second surface 102b of the element body 102. The connector electrodes 75a to 75d and 75h are connected (electrically connected) to the measuring electrode 44, the outer pump electrode 23, the auxiliary pump electrode 51, the inner pump electrode 22, and the reference electrode 42 via the corresponding lead portions 76, respectively. The connector electrodes 75e to 75g are connected to the heater 71a via the corresponding lead portions 76, respectively.

[0091] Here, we use Figure 4 and Figure 5 , the details of the measuring electrode 44 and the corresponding conductive portion 74 (connector electrode 75a and lead portion 76) will be described. Figure 2 Although not shown in the figure, in the element body 102, an airtight adhesive layer is provided between two adjacent layers in the stacking direction (vertical direction) of each layer 1 to 6. Therefore, the two adjacent layers are bonded by the corresponding adhesive layer. Each adhesive layer preferably has oxygen ion conductivity like each layer 1 to 6. In the present embodiment, each adhesive layer uses the same ceramic with zirconium dioxide as the main component as each layer 1 to 6. Figure 5 As shown, the adhesive layer 7 among the adhesive layers bonds the first solid electrolyte layer 4 and the isolation layer 5. The adhesive layer 7 covers most of the upper surface of the first solid electrolyte layer 4 except for the measured gas flow parts such as the buffer space 12, the first internal cavity 20, and the second internal cavity 40.

[0092] The measuring electrode 44 is provided at a position facing the third internal cavity 61 on the upper surface of the first solid electrolyte layer 4. The lead portion 76 corresponding to the measuring electrode 44 includes an inner lead portion 77 and a side lead portion 78. The inner lead portion 77 is provided inside the element body 102 and is connected (electrically connected) to the measuring electrode 44 and the side lead portion 78. Specifically, the inner lead portion 77 includes first to fourth portions 77a to 77d. The first portion 77a is provided at a position facing the third internal cavity 61 on the upper surface of the first solid electrolyte layer 4. The right end of the first portion 77a is connected to the measuring electrode 44, and the first portion 77a extends linearly to the left end of the third internal cavity 61 along the left-right direction. The right end of the second portion 77b is connected to the left end of the first portion 77a, and the second portion 77b extends linearly to a position closer to the left end of the element body 102 along the left-right direction. The front end of the third part 77c is connected to the left end of the second part 77b, and the third part 77c extends linearly along the front-back direction to the vicinity of the rear end of the element body 102. The right end of the fourth part 77d is connected to the rear end of the third part 77c, and the fourth part 77d extends linearly along the left-right direction to the left end of the element body 102. The left end of the fourth part 77d reaches (is led to) the third surface 102c (left end surface) of the element body 102, and is covered by the side lead part 78 and connected thereto. The inner lead part 77 is a conductor whose main component is a noble metal such as platinum (Pt) or a high melting point metal such as tungsten (W) and molybdenum (Mo). The inner lead part 77 is preferably a metal ceramic conductor containing a noble metal or a high melting point metal, and zirconium dioxide, which is the same as the main component of the first solid electrolyte layer 4.

[0093] The outer periphery of the second and third parts 77b and 77c of the inner lead part 77 and the part of the fourth part 77d except the left end part is surrounded by the lead insulating layer 79. The lead insulating layer 79 insulates the part of the inner lead part 77 surrounded by the lead insulating layer 79 from the first solid electrolyte layer 4 and the separator 5. It should be noted that the outer periphery of the left end part of the fourth part 77d is not surrounded by the lead insulating layer 79. Therefore, when the sensor element 101 is manufactured, it is possible to prevent the outer periphery of the left end part of the fourth part 77d from being surrounded by the lead insulating layer 79, thereby preventing the connection (electrical conduction) between the left end of the fourth part 77d and the side lead part 78 from being hindered. The lead insulating layer 79 is an insulator made of ceramics such as alumina.

[0094] The side lead portion 78 is arranged on the rear end side of the third surface 102c of the element body 102, and is connected to the inner lead portion 77 and the connector electrode 75a. Specifically, the side lead portion 78 covers the entire left end of the fourth portion 77d of the inner lead portion 77, and is arranged on the third surface 102c in a manner that its left end is not exposed to the outside of the sensor element 101. The side lead portion 78 is arranged in a manner in contact with the solid electrolyte layer. The side lead portion 78 is arranged in a manner that spans the solid electrolyte layer and the adhesive layer of the element body 102. The central portion of the right end surface of the side lead portion 78 is connected (electrically connected) to the left end of the fourth portion 77d. The upper end portion of the right end surface of the side lead portion 78 is connected to the left end surface of the front end portion of the connector electrode 75a.

[0095] The side lead portion 78 is made of a noble metal, aluminum oxide (Al 2 O 3 ) and silicon dioxide (SiO2) and is densely constructed as a conductor. Specific examples of precious metals include platinum (Pt) or platinum alloys. By including precious metals, as well as alumina and silicon dioxide in the side lead portion 78, the adhesion of the side lead portion 78 can be improved. In addition, by including silicon dioxide in the side lead portion 78, the compactness of the side lead portion 78 can also be improved. Therefore, for the side lead portion 78, both the compactness and the adhesion can be improved. The inventors of the present invention have confirmed this through experiments, analysis, etc. "Densely constructed" means that when the porosity of the side lead portion 78 is set to Rp[%], Rp is less than 3.0%. The porosity Rp of the side lead portion 78 is preferably less than 0.5%.

[0096] Here, if some gas outside the sensor element 101 (element body 102) intrudes into the inside of the element body 102 from the fourth portion 77d of the inner lead portion 77 or the gap between the fourth portion 77d and the element body 102, it may move toward the measuring electrode 44 along the inner lead portion 77 and the gap between the fourth portion 77d and the element body 102 (the gap between the inner lead portion 77 and the lead insulating layer 79, the gap between the lead insulating layer 79 and the element body 102) and reach the measuring electrode 44. Examples of some gas outside the sensor element 101 include volatile organic gas generated from the rubber stopper 157 when the sensor element 101 is exposed to a high temperature environment, a small amount of measured gas intruding into the space 149 from the sensor element chamber 133, gas intruding into the inside of the outer tube 148 from the outside of the gas sensor 100 through the gap between the rubber stopper 157 and the outer tube 148, air (for example, a reference gas present in the space 149), and water vapor. If the above-mentioned gas reaches the measuring electrode 44, the oxygen concentration around the measuring electrode 44 sometimes changes, and the voltage V2 detected by the oxygen partial pressure detection sensor unit 82 controlled by the measuring pump changes, so that the amount of oxygen sucked out from the third internal cavity 61 by the measuring pump control process also changes, and the pump current Ip2 changes. For example, if the volatile organic gas generated by the rubber stopper 157 reaches the measuring electrode 44, the oxygen concentration around the measuring electrode 44 sometimes decreases, the voltage V2 increases, and the pump current Ip2 decreases. If some gas reaches the measuring electrode 44 in this way and causes the pump current Ip2 to change, the detection accuracy of the concentration of the specific gas (NOx) will be reduced. In view of this, in the present embodiment, the density of the side lead portion 78, which is the portion that covers the inner lead portion 77, that is, the portion of the conductive portion 74 that helps to inhibit the gas from reaching the measuring electrode 44, is improved. Therefore, it is possible to suppress certain gases outside the element body 102 from passing through the side lead portion 78, thereby suppressing these gases from entering the inside of the element body 102 from the fourth portion 77d of the inner lead portion 77 and the gap between it and the element body 102, and suppressing these gases from reaching the measuring electrode 44. As a result, it is possible to suppress the pump current Ip2 from changing due to these gases, thereby suppressing the reduction in the detection accuracy of the concentration of the specific gas (NOx). In addition, by suppressing the above-mentioned gas from reaching the measuring electrode 44, it is possible to suppress the degradation of the measuring electrode 44.

[0097] In addition, the adhesion of the side lead portion 78 is improved, so it is possible to suppress the side lead portion 78 from peeling off from the third surface 102c of the element body 102 during firing shrinkage during the manufacture of the sensor element 101. In addition, it is possible to suppress the side lead portion 78 from peeling off from the third surface 102c of the element body 102 due to thermal expansion and contraction of the sensor element 101.

[0098] Regarding the side lead portion 78, when the volumes of the precious metal, alumina, and silicon dioxide contained are set to Vp [Vol%], Va [Vol%], and Vs [Vol%], respectively, they can be set as follows. The side lead portion 78 preferably satisfies Va / Vs≤1.5. Thus, the compactness of the side lead portion 78 can be further improved. The side lead portion 78 can satisfy 0.1≤Va / Vs. The side lead portion 78 preferably satisfies 1.5≤Vp / (Va+Vs). Thus, the effect of improving the compactness of the side lead portion 78 can be more reliably obtained. In this case, it is more preferable to satisfy 2.6≤Vp / (Va+Vs). Accordingly, the compactness of the side lead portion 78 can be further improved. The side lead portion 78 can satisfy Vp / (Va+Vs)≤19.0. The side lead portion 78 more preferably satisfies Va / Vs≤1.5 and satisfies 1.5≤Vp / (Va+Vs). The side lead portion 78 further preferably satisfies Va / Vs≤1.5 and satisfies 2.6≤Vp / (Va+Vs). The volume Vp may be 60 Vol% or more. The volume Vp may be 95 Vol% or less. The volume Va may be 1 Vol% or more. The volume Va may be 15 Vol% or less. The volume Vs may be 2 Vol% or more, or 4 Vol% or more. The volume Vs may be 25 Vol% or less.

[0099] The side lead portion 78 preferably satisfies the following requirement: the total mass ratio of the alkali metal and alkaline earth metal contained in the side lead portion 78 as oxides is 0.1 wt% or less. Here, it is also considered that the side lead portion 78 contains a noble metal and a glass component instead of a noble metal, alumina, and silicon dioxide, thereby improving the adhesion and compactness. However, in this case, the side lead portion 78 contains a large amount of sodium oxide (Na 2 Oxides of alkali metals such as calcium oxide (CaO), magnesium oxide (MgO), and / or oxides of alkaline earth metals. In this case, due to, for example, the voltage Vp2 applied when the sensor element 101 is used, the alkali metal and / or alkaline earth metal moves due to electromigration (for example, from the inside of the side lead portion 78 to the inner lead portion 77), so that the conductivity of the side lead portion 78 decreases (the resistance value increases). As a result, the pump current Ip2 decreases, resulting in a decrease in the detection accuracy of the concentration of the specific gas (NOx). In view of this, with respect to the side lead portion 78 of the present embodiment, the adhesion and compactness are improved by including aluminum oxide and silicon dioxide, and the ratio of the total mass of the alkali metal and the alkaline earth metal converted by oxide is less than 0.1wt%, which can also suppress the decrease in the detection accuracy of the concentration of the specific gas caused by the above-mentioned electromigration.

[0100] The side lead portion 78 may be configured such that, when the thickness is set to Dc [mm], the porosity Rp and the thickness Dc satisfy Rp / Dc ≤ 145% / mm. The side lead portion 78 may also be configured such that Rp / Dc ≤ 120% / mm. The side lead portion 78 may be configured such that Rp / Dc ≥ 1.5% / mm. The side lead portion 78 may also be configured such that Rp / Dc ≥ 4.5% / mm. The porosity Rp of the side lead portion 78 may be 0.01% or more. The thickness Dc of the side lead portion 78 may be 0.001mm or more. The thickness Dc of the side lead portion 78 may be 0.080mm or less.

[0101] It should be noted that each porosity such as the porosity Rp of the side lead portion 78 is set to a value derived as follows using an image (SEM image) obtained by observation with a scanning electron microscope (SEM). First, the object to be measured is cut in such a manner that the cross section of the object to be measured (when the side lead portion 78 is the object to be measured, the cross section of the side lead portion 78 along the thickness direction) is set as the observation surface, and the cross-section surface is resin-embedded and polished to prepare an observation sample. Next, the observation surface of the observation sample is photographed with an SEM photograph (secondary electron image, acceleration voltage 15kV, magnification 1000 times, wherein when the magnification 1000 times is not appropriate, it is set to a magnification greater than 1000 times and less than 5000 times) to obtain a SEM image of the object to be measured. Next, the obtained image is subjected to image analysis, and the threshold is determined by the discriminant analysis method (Otsu's binarization) based on the brightness distribution of the brightness data of the pixels in the image. After that, based on the determined threshold, each pixel in the image is binarized into an object part and a pore part, and the area of ​​the object part and the area of ​​the pore part are calculated. Then, the ratio of the area of ​​the pore part to the total area (the total area of ​​the object part and the pore part) is derived as the porosity (unit: %).

[0102] The volumes Vp [Vol%], Va [Vol%], and Vs [Vol%] of the precious metal, alumina, and silica in the side lead portion 78 are set to the values ​​derived as follows using SEM-EDX (EDX: energy dispersive X-ray spectroscopy). First, in the same manner as the above-mentioned determination of the porosity Rp, the object to be measured is cut in such a manner that the cross section of the object to be measured is set as the observation surface, and a sample for observation is obtained. Next, element mapping is performed on multiple locations (for example, 3 locations) of the observation surface of the observation sample using SEM-EDX. Based on the results of the element mapping, the average value of the element concentration is calculated for each element of precious metal, aluminum, and silicon. Then, based on the obtained average value of the element concentration of the precious metal, the volume Vp [Vol%] is calculated. In addition, the average value of the element concentration of aluminum is converted into oxides to calculate the volume Va [Vol%], and the average value of the element concentration of silicon is converted into oxides to calculate the volume Vs [Vol%].

[0103] The ratio of the total mass of the alkali metals and alkaline earth metals in the side lead portion 78 in terms of oxide conversion is set to the value derived as follows using ICP-AES (inductively coupled plasma emission spectrometry). First, the object to be measured is peeled off from the sensor element 101, and a specified amount is weighed to obtain a sample for measurement. Next, sulfuric acid is used to dissolve the sample for measurement to obtain a dissolving solution. ICP-AES is performed using the dissolving solution to perform a qualitative analysis of the elements contained in the sample for measurement. The actual concentration value of Na is calculated using the test concentration value of Na obtained by the qualitative analysis and the calibration curve of Na obtained in advance. The actual concentration value of Na obtained is converted into oxides to calculate the mass ratio of sodium oxide in the object to be measured. The mass ratio of alkali metals and alkaline earth metals other than Na in terms of oxide conversion is also calculated according to the same steps. Using these calculation results, the ratio of the total mass of alkali metals and alkaline earth metals in the object to be measured in terms of oxide conversion is calculated.

[0104] Next, an example of a method for manufacturing the sensor element 101 of the gas sensor 100 is described below. First, six unfired ceramic green sheets containing an oxygen ion conductive solid electrolyte such as zirconium dioxide as a ceramic component are prepared. A plurality of sheet holes, necessary through holes, etc. for positioning during printing and stacking are formed in advance on the green sheet. In addition, a space that becomes a flow portion of the measured gas is set in advance on the green sheet constituting the isolation layer 5 by punching treatment, etc. A space that becomes a reference gas introduction space 43 is also pre-set on the green sheet constituting the first solid electrolyte layer 4. Then, pattern printing treatment and drying treatment for forming various patterns are performed on each ceramic green sheet corresponding to the first substrate layer 1, the second substrate layer 2, the third substrate layer 3, the first solid electrolyte layer 4, the isolation layer 5, and the second solid electrolyte layer 6, respectively. Specifically, the pattern formed is, for example, the pattern of each electrode such as the above-mentioned measuring electrode 44, the inner lead portion such as the inner lead portion 77 connected to each electrode, the lead insulation layer such as the lead insulation layer 79, the connector electrode 75, the reference gas introduction layer 48, the heater portion 70, etc. The pattern printing is performed in the following manner: the pattern forming paste prepared according to the characteristics required by each forming object is applied to the raw sheet using the known screen printing technology. The drying process is also performed using a known drying method. When the pattern printing process and the drying process are completed, the printing process and the drying process of the adhesive paste that becomes the adhesive layer (including the above-mentioned adhesive layer 7) that stacks and bonds the raw sheets corresponding to each layer to each other are performed. Then, the following pressing process is performed: the raw sheet formed with the adhesive paste is positioned using the sheet hole, and is stacked in a prescribed order and pressed under prescribed temperature and pressure conditions, thereby forming them into a stacked body. The stacked body obtained in this way contains a plurality of sensor elements 101. The laminate is cut and divided into the size of the sensor element 101. Then, a pattern to become the side lead portion 78 is formed by screen printing on the portion of the third surface 102c of the element body 102 of the sensor element 101, which is the cross-sectional surface of the laminate, and the pattern is dried. Then, the laminate is fired at a predetermined firing temperature to obtain the sensor element 101.

[0105] In addition, when forming the pattern of the inner lead portion 77 and the lead insulating layer 79 on the green sheet to be the first solid electrolyte layer 4, for example, the following can be performed. First, a pattern of a portion that covers the lower side of the inner lead portion 77 in the lead insulating layer 79 is formed on the green sheet. Next, a pattern of the inner lead portion 77 is formed. Then, a portion that covers the side and upper side of the inner lead portion 77 in the lead insulating layer 79 is formed.

[0106] In addition, the pattern forming paste of the side lead portion 78 uses a paste containing precious metals such as platinum, aluminum oxide, silicon dioxide, a binder, and a solvent. At least one of a plasticizer and a dispersing aid may be further mixed in the pattern forming paste. The pattern forming paste may be mixed with a material that becomes aluminum oxide or silicon dioxide by firing, thereby replacing aluminum oxide and silicon dioxide. For example, one or more of aluminum hydroxide, silicic acid, mullite, and kaolinite may be mixed. The porosity Rp of the side lead portion 78 may be adjusted as follows: for example, the respective proportions of the precious metals, aluminum oxide, and silicon dioxide contained in the pattern forming paste of the side lead portion 78 are adjusted, thereby adjusting the above-mentioned Va / Vs and / or Vp / (Va+Vs) of the fired side lead portion 78, thereby adjusting the porosity Rp. The thickness Dc of the side lead portion 78 can be adjusted by, for example, adjusting the viscosity of the paste for patterning the side lead portion 78 or by changing the number of printings during patterning to adjust the thickness Dc.

[0107] It should be noted that the particles contained in the pattern forming paste of the side lead portion 78, especially the particles of aluminum oxide and silicon dioxide, sometimes contain alkali metals and / or alkaline earth metals as impurities. With regard to these particles, by using high-purity particles or preparing the pattern forming paste by mixing with other raw materials after washing, the ratio of the total mass of the alkali metals and alkaline earth metals contained in the side lead portion 78 in terms of oxide conversion can be made 0.1wt% or less.

[0108] After that, the gas sensor 100 in which the sensor element 101 is embedded is manufactured. For example, the element sealing body 141 is installed on the sensor element 101 to seal and fix it, and the protective cover 130 is installed on the front end side of the element body 102 of the sensor element 101 in the element sealing body 141. In addition, the connector 150 and the lead wire 155 are installed on the rear end side of the element body 102 of the sensor element 101 in a manner that is conductive with the connector electrode 75. Furthermore, the outer cylinder 148 is installed on the rear end side of the element body 102 in the element sealing body 141, and the lead wire 155 is led out from the outer cylinder 148 to the outside, and the outer cylinder 148 is welded and fixed to the main metal fitting 142. Next, the lead wire 155 is passed through the through hole of the rubber plug 157, the rubber plug 157 is inserted into the outer cylinder 148, and the outer cylinder 148 is reduced in diameter by riveting to form the riveted parts 148a and 148b, and the rubber plug 157 and the outer cylinder 148 are fixed. Then, the control device 95 and the sensor element 101 are connected via the lead wire 155. In this way, the gas sensor 100 is obtained.

[0109] Next, a usage example of the gas sensor 100 is described. The CPU 97 of the control unit 96 first controls the heater power supply 72 to supply power to the heater 71a, and controls the heater 71a so that the temperature becomes the target temperature (e.g., 800°C, etc.). The CPU 97 obtains a value that can be converted to, for example, the temperature of the heater 71a (e.g., the resistance value or current value of the heater 71a), and based on the value, performs feedback control on the heater power supply 72, thereby controlling the temperature of the heater 71a. When the temperature of the heater 71a reaches the target temperature (or near the target temperature), the CPU 97 starts the control of the above-mentioned pump units 21, 41, and 50 (adjustment pump control processing and measurement pump control processing), and the above-mentioned acquisition of the voltages V0, V1, V2, and Vref from the sensor units 80 to 83. In this state, when the measured gas is introduced from the gas inlet 10, the measured gas passes through the first diffusion rate control unit 11, the buffer space 12, and the second diffusion rate control unit 13 to reach the first internal cavity 20. Next, in the first internal cavity 20 and the second internal cavity 40, the oxygen concentration of the measured gas is adjusted by the main pump unit 21 and the auxiliary pump unit 50, and the adjusted measured gas reaches the third internal cavity 61. Then, the CPU 97 detects the NOx concentration in the measured gas based on the obtained pump current Ip2 and the corresponding relationship stored in the storage unit 98.

[0110] Here, the correspondence between the components of the present embodiment and the components of the present invention is clarified. The first substrate layer 1, the second substrate layer 2, the third substrate layer 3, the first solid electrolyte layer 4, the isolation layer 5 and the second solid electrolyte layer 6 of the present embodiment are respectively equivalent to the solid electrolyte layers of the present invention, the element body 102 is equivalent to the element body, the first to fourth surfaces 102a to 102d are equivalent to the side surfaces, the measuring electrode 44 is equivalent to the inner electrode, the conductive portion 74 is equivalent to the conductive portion, the inner lead portion 77 is equivalent to the inner conductive portion, the connector electrode 75a and the side lead portion 78 are equivalent to the outer conductive portion, and the side lead portion 78 is equivalent to the dense portion. In addition, the protective cover 130 and the sensor assembly 140 are equivalent to the housing, and the rubber stopper 157 is equivalent to the sealing member.

[0111] In the sensor element 101 provided in the gas sensor 100 of the present embodiment described in detail above, the side lead portion 78 covers the left end of the fourth portion 77d of the inner lead portion 77 and is densely constructed by containing a noble metal, aluminum oxide, and silicon dioxide. As a result, the side lead portion 78, which is a portion of the conductive portion 74 that helps to suppress the gas from reaching the measuring electrode 44, can be improved in both density and adhesion. In addition, since the side lead portion 78 is dense, it is possible to suppress some gases outside the sensor element 101 (element body 102) such as volatile organic gas generated by the rubber stopper 157 from passing through the side lead portion 78, and to suppress these gases from entering the inside of the element body 102 from the fourth portion 77d of the inner lead portion 77 and the gap between it and the element body 102, thereby suppressing these gases from reaching the measuring electrode 44. As a result, it is possible to suppress the pump current Ip2 from changing due to these gases, and suppress the reduction in the detection accuracy of the concentration of the specific gas (NOx). In addition, due to the high adhesion of the side lead portion 78, it is possible to suppress the side lead portion 78 from peeling off from the third surface 102c of the element body 102 during the firing shrinkage during the manufacture of the sensor element 101. In addition, it is possible to suppress the side lead portion 78 from peeling off from the third surface 102c of the element body 102 due to the thermal expansion and contraction of the sensor element 101. In addition, it is possible to suppress the side lead portion 78 from leaving from the third surface 102c due to the stress applied from the outside (contact with the jig, etc.) when the fired sensor element 101 flows in the manufacturing process.

[0112] In the sensor element 101 , the side lead portion 78 is configured to satisfy Va / Vs≦1.5, thereby further improving the density of the side lead portion 78 and further suppressing some gas outside the element body 102 from passing through the side lead portion 78 .

[0113] Furthermore, in the sensor element 101, the side lead portion 78 is configured to satisfy 1.5≤Vp / (Va+Vs). Thus, the effect of improving the compactness of the side lead portion 78 can be more reliably obtained. In addition, the side lead portion 78 is configured to satisfy 2.6≤Vp / (Va+Vs). Thus, the compactness of the side lead portion 78 can be further improved.

[0114] Furthermore, in the sensor element 101, the side lead portion 78 is configured to satisfy a ratio of the total mass of the alkali metal and alkaline earth metal contained in the side lead portion 78 as converted into oxides of 0.1 wt% or less. This can suppress the alkali metal and / or alkaline earth metal in the side lead portion 78 from moving due to electromigration and causing a decrease in the conductivity of the side lead portion 78, thereby suppressing a decrease in the detection accuracy of the concentration of the specific gas caused by the decrease in conductivity.

[0115] It should be noted that the present invention is not limited to the above-mentioned embodiment and can be implemented in various forms as long as it belongs to the technical scope of the present invention.

[0116] For example, in the above embodiment, the side lead portion 78 is composed of one layer, but the present invention is not limited thereto. Figure 6 A sensor element 201 according to a modified example of Figure 7 As shown in the sensor element 301 of the modified example, the side lead portion 78 can be replaced by the side lead portions 278 and 378. The side lead portions 278 and 378 are respectively composed of two layers. It should be noted that the side lead portions 278 and 378 can also be composed of three or more layers instead of two layers.

[0117] Figure 6 In the sensor element 201, the side lead portion 278 is generally in the shape of a rectangular parallelepiped, and has a first side lead portion 278a and a second side lead portion 278b. The first side lead portion 278a is in the shape of a rectangular parallelepiped, and covers the entire left end of the fourth portion 77d of the inner lead portion 77, thereby being arranged on the third surface 102c (left side surface) of the element body 102 in a manner that the left end is not exposed to the outside of the sensor element 101. The second side lead portion 278b is in the shape of a rectangular parallelepiped, and is arranged on the left end surface of the first side lead portion 278a. In this case, the first side lead portion 278a is a portion of the conductive portion 74 that helps to inhibit the gas from reaching the measuring electrode 44. Therefore, with respect to the first side lead portion 278a, it is sufficient to be configured as a dense portion of the present invention in the same manner as the side lead portion 78 of the sensor element 101.

[0118] Figure 7In the sensor element 301, the side lead portion 378 is generally in a substantially rectangular parallelepiped shape, and includes a first side lead portion 378a and a second side lead portion 378b. The first side lead portion 378a is in a substantially rectangular parallelepiped shape, and covers the entire left end of the fourth portion 77d of the inner lead portion 77, thereby being arranged on the third surface 102c (left side surface) of the element body 102 in such a manner that the left end is not exposed to the outside of the sensor element 301. The second side lead portion 378b covers the five surfaces of the first side lead portion 378a except the right end surface, and is in contact with the third surface 102c of the element body 102, thereby being arranged in such a manner that the fourth portion 77d of the inner lead portion 77 and the first side lead portion 378a are not exposed to the outside of the sensor element 301. In this case, the first side lead portion 378a and the second side lead portion 378b are both portions of the conductive portion 74 that contribute to suppressing the gas from reaching the measuring electrode 44. Therefore, the first side lead portion 378a may be configured as the dense portion of the present invention, the second side lead portion 378b may be configured as the dense portion of the present invention, or the entire side lead portion 378 may be configured as the dense portion of the present invention. Therefore, the components of the first side lead portion 378a, the second side lead portion 378b, and the entire side lead portion 378 that are configured as the dense portion of the present invention may be configured in the same manner as the side lead portion 78 of the sensor element 101.

[0119] In the above embodiment, the connector electrode 75a is connected to the measuring electrode 44 via the inner lead portion 77 and the side lead portion 78, but the present invention is not limited thereto. Figure 8As shown in the sensor element 401 of the modified example, the element body 102 can be replaced by the element body 402, and the inner lead portion 77 and the side lead portion 78 can be replaced by the inner lead portion 477 and the through-hole conductor 478. The element body 402 of the sensor element 401 has a through hole 402h. The through hole 402h includes an opening portion that is open on the first surface 102a of the element body 402, and penetrates the isolation layer 5 and the second solid electrolyte layer 6 in the stacking direction (up and down direction). The inner lead portion 477 is arranged between the first solid electrolyte layer 4 and the isolation layer 5 in the same manner as the inside of the element body 402, specifically, the inner lead portion 77 of the sensor element 101. It should be noted that at least a portion of the inner lead portion 477 is surrounded by a lead insulation layer (not shown) in the same manner as the inner lead portion 77. The through-hole conductor 478 is disposed in the through-hole 402h via the insulating layer 479, and the lower end is connected to the inner lead portion 477, and the entire upper end is covered by the connector electrode 75a in a manner not exposed to the outside of the sensor element 401 and connected thereto. In this case, the connector electrode 75a is equivalent to the outer conductive portion of the present invention. In addition, the connector electrode 75a is a portion of the conductive portion 74 that helps to suppress the gas from reaching the measuring electrode 44. Therefore, the connector electrode 75a can be configured as a dense portion of the present invention in the same manner as the side lead portion 78 of the sensor element 101.

[0120] In the sensor element 401, the connector electrode 75a is composed of one layer, but it may be composed of two or three layers or more. Figure 6 , Figure 7 The side lead portions 278 and 378 of the sensor elements 201 and 301 of the modified examples are considered in the same manner.

[0121] In the above-mentioned sensor elements 101, 201, 301, and 401, the portion of the outer conductive portion that covers the inner conductive portion is constituted as the dense portion of the present invention. However, the dense portion of the present invention only needs to include the portion of the outer conductive portion that covers the inner conductive portion and / or at least a portion of the inner conductive portion. For example, in the sensor elements 101, 201, and 301, the inner conductive portion, that is, at least a portion of the inner lead portion 77, can be constituted as the dense portion of the present invention in the same manner as the side lead portion 78 of the sensor element 101. In the sensor element 401, the inner conductive portion, that is, at least a portion of the inner lead portion 477 and the through-hole conductor 478, can be constituted as the dense portion of the present invention in the same manner as the side lead portion 78 of the sensor element 101. If at least a portion of the inner conductive portion is dense, it is possible to suppress some gas outside the sensor element 101 (element body 102) from moving along the inside of the inner conductive portion toward the measuring electrode 44 side. In addition, if the close adhesion of the dense portion in the inner conductive portion is high, it is also possible to suppress the gas from moving toward the measuring electrode 44 along the gap between the portion and the element body 102. Accordingly, when at least a portion of the inner conductive portion is configured as the dense portion of the present invention, it is also possible to suppress some gas outside the sensor element 101 (element body 102) from reaching the measuring electrode 44.

[0122] In the sensor element 401, the upper end of the through-hole conductor 478 is covered by the connector electrode 75a, but the present invention is not limited to this. Fig. 9As shown in the sensor element 501 of the modified example, the connector electrode 75a is replaced by a connector electrode 575a, and the through-hole conductor 478 is replaced by a through-hole conductor 578. The through-hole conductor 578 is arranged in the through-hole 402h through the insulating layer 579 in the same manner as the through-hole conductor 478, and the lower end is connected to the inner lead portion 477. The connector electrode 575a has a circular hole 575h, and the outer peripheral portion of the hole 575h at the lower end surface of the connector electrode 575a is connected to the outer peripheral portion of the upper end of the through-hole conductor 578. Therefore, the portion of the upper end of the through-hole conductor 578 other than the outer peripheral portion is exposed to the outside of the sensor element 501. In this case, it is sufficient to configure the inner conductive portion, that is, at least a portion of the inner lead portion 477 and the through-hole conductor 578 as the dense portion of the present invention in the same manner as the side lead portion 78 of the sensor element 101. For example, the portion including the portion of the through-hole conductor 578 exposed to the outside of the sensor element 501 may be configured as the dense portion of the present invention, or the through-hole conductor 578 as a whole may be configured as the dense portion of the present invention. It should be noted that, in addition to this, the connector electrode 575a may also be configured as the dense portion of the present invention in the same manner as the side lead portion 78. In this way, it is possible to suppress the gas outside the sensor element 501 (element body 102) from passing through the connector electrode 575a and from invading the periphery of the through-hole conductor 578, specifically, the gap between the through-hole conductor 578 and the insulating layer 579, and the gap between the insulating layer 579 and the through hole 402h.

[0123] In the above embodiment, the conductive portion 74 corresponding to the measuring electrode 44 is described. However, the conductive portion 74 corresponding to any one of the inner pump electrode 22, the auxiliary pump electrode 51, and the reference electrode 42 may be provided in the same manner. For example, in the case where the conductive portion 74 corresponding to the measuring electrode 44 includes the connector electrode 75a, the lead portion 76 including the inner lead portion 77 and the side lead portion 78, and the conductive portion 74 corresponding to the inner pump electrode 22 includes the connector electrode 75h, the lead portion including the inner lead portion and the side lead portion, the side lead portion may be configured as the dense portion of the present invention in the same manner as the side lead portion 78. In addition, at least a part of the inner lead portion may be configured as the dense portion of the present invention in addition to or in place of the side lead portion.

[0124] In the above embodiment, the oxygen concentration adjustment chamber has a first internal cavity 20 and a second internal cavity 40, but the present invention is not limited thereto. For example, the oxygen concentration adjustment chamber may further include another internal cavity, or one of the first internal cavity 20 and the second internal cavity 40 may be omitted. Similarly, in the above embodiment, the adjustment pump unit has a main pump unit 21 and an auxiliary pump unit 50, but the present invention is not limited thereto. For example, the adjustment pump unit may further include another pump unit, or one of the main pump unit 21 and the auxiliary pump unit 50 may be omitted. For example, when the oxygen concentration of the measured gas can be sufficiently reduced only by the main pump unit 21, the auxiliary pump unit 50 may be omitted. When the auxiliary pump unit 50 is omitted, the control unit 96 only performs the main pump control process as the adjustment pump control process. In addition, in the main pump control process, the setting of the target value V0* based on the pump current Ip1 described above may be omitted. Specifically, a predetermined target value V0 * is stored in advance in the storage unit 98 , and the control unit 96 performs feedback control on the voltage Vp0 of the variable power supply 24 so that the voltage V0 reaches the target value V0 *, thereby controlling the main pump unit 21 .

[0125] In the above embodiment, the sensor element 101 of the gas sensor 100 includes the first internal cavity 20, the second internal cavity 40 and the third internal cavity 61, but the present invention is not limited thereto. Fig.10 As shown in a sensor element 601 of a modified example, the third internal cavity 61 may not be provided. Fig.10 In the sensor element 601 of the modified example, between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, the gas inlet 10, the first diffusion rate control part 11, the buffer space 12, the second diffusion rate control part 13, the first internal cavity 20, the third diffusion rate control part 30 and the second internal cavity 40 are adjacently formed in a manner of being connected in this order. In addition, the measuring electrode 44 is arranged on the upper surface of the first solid electrolyte layer 4 in the second internal cavity 40. The measuring electrode 44 is covered by the fourth diffusion rate control part 45. The fourth diffusion rate control part 45 is made of aluminum oxide (Al 2 O 3 ) or other ceramic porous bodies. The fourth diffusion rate control unit 45 plays the role of limiting the amount of NOx flowing into the measuring electrode 44, similarly to the fourth diffusion rate control unit 60 in the above-mentioned embodiment. In addition, the fourth diffusion rate control unit 45 also plays a role as a protective film for the measuring electrode 44. The top electrode portion 51a of the auxiliary pump electrode 51 is formed to be directly above the measuring electrode 44. Even the sensor element 601 of this structure can detect the NOx concentration using the measuring pump unit 41, similarly to the above-mentioned embodiment. Fig.10In the sensor element 601 , the periphery of the measuring electrode 44 functions as a measuring chamber. That is, the periphery of the measuring electrode 44 functions similarly to the third internal cavity 61 .

[0126] In the above embodiment, the outer pump electrode 23 has the functions of an electrode paired with the inner pump electrode 22 of the main pump cell 21 (also referred to as an outer main pump electrode), an electrode paired with the auxiliary pump electrode 51 of the auxiliary pump cell 50 (also referred to as an outer auxiliary pump electrode), and an electrode paired with the measuring electrode 44 of the measuring pump cell 41 (also referred to as an outer measuring electrode), but the present invention is not limited thereto. Any one or more of the outer main pump electrode, the outer auxiliary pump electrode, and the outer measuring electrode may be provided outside the element body 102 in contact with the measured gas, separate from the outer pump electrode 23.

[0127] In the above embodiment, the sensor element 101 detects the NOx concentration in the measured gas, but is not limited to this, as long as the concentration of the specific gas in the measured gas is detected. For example, the concentration of oxides other than NOx can be set as the specific gas concentration. In the case where the specific gas is an oxide, similarly to the above embodiment, oxygen is generated when the specific gas itself is reduced in the third internal cavity 61, so the measurement pump unit 41 can obtain a detection value corresponding to the oxygen (for example, pump current Ip2) to detect the specific gas concentration. In addition, the specific gas can also be a non-oxide such as ammonia. In the case where the specific gas is a non-oxide, by converting the specific gas into an oxide (for example, if it is ammonia, it is converted into NO), oxygen is generated when the converted gas is reduced in the third internal cavity 61, so the measurement pump unit 41 can obtain a detection value corresponding to the oxygen (for example, pump current Ip2) to detect the specific gas concentration. For example, the inner pump electrode 22 of the first internal cavity 20 acts as a catalyst, and ammonia can be converted into NO in the first internal cavity 20.

[0128] In the above embodiment, the element body 102 of the sensor element 101 is a stacked body having a plurality of solid electrolyte layers (layers 1 to 6), but the present invention is not limited thereto. The element body 102 only needs to include at least one oxygen ion conductive solid electrolyte layer. Figure 2 In the embodiment, the layers 1 to 5 other than the second solid electrolyte layer 6 may be layers made of materials other than the solid electrolyte layer (e.g., layers made of aluminum oxide). In this case, the electrodes of the sensor element 101 only need to be arranged on the second solid electrolyte layer 6. For example, Figure 2The measuring electrode 44 only needs to be arranged on the lower surface of the second solid electrolyte layer 6. In addition, the reference gas introduction space 43 can be arranged in the isolation layer 5 instead of being arranged in the first solid electrolyte layer 4, the reference gas introduction layer 48 can be arranged between the second solid electrolyte layer 6 and the isolation layer 5 instead of being arranged between the first solid electrolyte layer 4 and the third substrate layer 3, and the reference electrode 42 can be arranged at a position behind the third internal cavity 61 and on the lower surface of the second solid electrolyte layer 6. In the case where the stacked body also includes a layer other than the solid electrolyte layer, the dense portion of the present invention can be in contact with the solid electrolyte layer in the same manner as the side lead portion 78 of the above-mentioned embodiment, or can be in contact with a layer composed of a material other than the solid electrolyte layer (for example, a layer composed of aluminum oxide).

[0129] In the above embodiment, the control unit 96 sets the target value V0* of the voltage V0 based on the pump current Ip1 (feedback control) so that the pump current Ip1 becomes the target value Ip1*, and performs feedback control on the pump voltage Vp0 so that the voltage V0 becomes the target value V0*, but other controls may be performed. For example, the control unit 96 may also perform feedback control on the pump voltage Vp0 based on the pump current Ip1 so that the pump current Ip1 becomes the target value Ip1*. That is, the control unit 96 may omit obtaining the voltage V0 from the main pump control oxygen partial pressure detection sensor unit 80 and setting the target value V0*, and directly control the pump voltage Vp0 based on the pump current Ip1 (or even control the pump current Ip0).

[0130] In the above-mentioned embodiment, the form of the gas sensor 100 including the sensor element 101 , 201 , etc. is described. Of course, the form of the sensor element 101 , 201 , etc. used in the gas sensor 100 may be adopted.

[0131] Example

[0132] Hereinafter, as an example, an example of producing a sensor element will be described in detail. It should be noted that the present invention is not limited to the following example.

[0133] [Examples 1 to 8, Comparative Examples 1 to 3]

[0134] Using the above manufacturing method, make Figure 2 The sensor element 101 shown, or making Figure 1The gas sensor 100 shown is used as Examples 1 to 8. It should be noted that when manufacturing the sensor element 101, the ceramic green sheet is obtained by mixing zirconium dioxide particles to which 4 mol% of yttrium trioxide as a stabilizer is added, an organic binder and an organic solvent and molding them by tape casting. In addition, the paste used for pattern formation of the side lead portion 78 uses a paste containing precious metals, alumina and silica. In Examples 1 to 8, various changes are made to the volumes Vp [vol%], Va [vol%], and Vs [vol%] of the precious metals, alumina, and silica of the side lead portion 78 as shown in Table 1 below. This is achieved by changing the ratio of the precious metals, alumina, and silica contained in the paste used for pattern formation of the side lead portion 78. In addition, as shown in Table 1 below, various changes are made to the volumes Vp [vol%], Va [vol%], and Vs [vol%] of the precious metal, aluminum oxide, and silicon dioxide of the side lead portion 78, and a sensor element 101 in which the side lead portion 78 does not contain one of aluminum oxide and silicon dioxide and a gas sensor 100 having the sensor element 101 are produced as comparison examples 1 to 3.

[0135] [Table 1]

[0136]

[0137] [Evaluation of density]

[0138] The porosity Rp[%] of the side lead portion 78 was measured by the above method for the sensor elements 101 of Examples 1 to 8 and Comparative Examples 1 to 3. When the porosity Rp was less than 0.5%, the density was evaluated as very high (A), when the porosity Rp was 0.5% or more and less than 3%, the density was evaluated as relatively high (B), and when the porosity Rp was 3.0% or more, the density was evaluated as relatively low (F).

[0139] [Evaluation of Adhesion]

[0140] For the sensor elements 101 of Examples 1 to 8 and Comparative Example 3, a test for measuring the adhesion strength of the side lead portion 78 relative to the third surface 102c of the element body 102 was performed according to the well-known Sebastian method (see "Thin Film Handbook" edited by the Japan Society for the Promotion of Science and the Thin Film Committee No. 131 [Ohm Co., Ltd.]. Specifically, first, the sensor element 101 was cut into a predetermined size, and a test piece in which the side lead portion 78 was arranged on the third surface 102c was prepared. Next, a copper stud pin with a diameter of 1.3 mm was adhered to the side lead portion 78 of the test piece by means of an epoxy adhesive. Thereafter, a force was applied using a universal testing machine so that the side lead portion 78 of the test piece was peeled off from the third surface 102c by means of the stud pin. And, when the epoxy adhesive was destroyed before the side lead portion 78 was peeled off from the element body 102 and the stud pin and the side lead portion 78 were separated, the adhesion of the side lead portion 78 was evaluated as high (A). On the other hand, when the side lead portion 78 was peeled off from the element body 102 before the stud pin and the side lead portion 78 were separated, the adhesion of the side lead portion 78 was evaluated as low (F). In addition, for Comparative Examples 1 and 2, as shown in Table 1, the evaluation of the tightness was "low (F)", and therefore the evaluation of the tightness was omitted.

[0141] Table 1 summarizes the volumes Vp [vol %], Va [vol %], Vs [vol %], Va / Vs, Vp / (Va+Vs) of the side lead portions 78 of Examples 1 to 8 and Comparative Examples 1 to 3, the evaluation results of compactness, and the evaluation results of adhesion.

[0142] As can be seen from Table 1, the compactness of Comparative Examples 1 and 2 not containing silica was evaluated as "low (F)", while the compactness of Examples 1 to 8 and Comparative Example 3 containing silica was evaluated as "very high (A)" or "high (B)". Therefore, it is believed that the compactness can be improved by including silica. In addition, the adhesion of Comparative Example 3 not containing alumina was evaluated as "low (F)", while the adhesion of Examples 1 to 8 containing alumina and silica was evaluated as "high (A)". Therefore, it is believed that the adhesion can be improved by including alumina and silica.

[0143] In addition, when comparing Examples 3, 6 to 8 in which the total volume of aluminum oxide and silicon dioxide is the same (Va+Vs=20 [vol%]), the compactness of Example 6, which does not satisfy Va / Vs≤1.5, is evaluated as "relatively high (B)", while the compactness of Examples 3, 7 to 8, which satisfy Va / Vs≤1.5, is evaluated as "very high (A)". Therefore, it is considered that by satisfying Va / Vs≤1.5, the compactness of the side lead portion 78 can be further improved.

[0144] It should be noted that Examples 1 to 8 all satisfy 1.5≤Vp / (Va+Vs), and the compactness is evaluated as "very high (A)" or "relatively high (B)". In addition, when comparing Examples 1 to 5 and 7 to 8 that satisfy Va / Vs≤1.5, the compactness of Example 4 that does not satisfy 2.6≤Vp / (Va+Vs) is evaluated as "relatively high (B)", while the compactness of Examples 1 to 3, 5, and 7 to 8 that satisfy 2.6≤Vp / (Va+Vs) is evaluated as "very high (A)". Therefore, it is believed that by satisfying 2.6≤Vp / (Va+Vs), the compactness of the side lead portion 78 can be further improved.

[0145] [Examples 9 to 11]

[0146] A sensor element 101 and a gas sensor 100 having the same values ​​of volume Vp [vol %], Va [vol %], and Vs [vol %] as those of Examples 1 and 2 were prepared as Examples 9 and 10, respectively. In addition, as shown in Table 2 below, the raw material ratio of the paste for patterning the side lead portion 78 was changed so that the side lead portion 78 contained sodium oxide, and a sensor element 101 and a gas sensor 100 of Example 11 were prepared.

[0147] Table 2

[0148]

[0149] [Determination of alkali metals and alkaline earth metals]

[0150] For the side lead portion 78 of Examples 9 to 11, the above-mentioned method is used to measure the ratio of the total mass of the alkali metal and alkaline earth metal contained in the oxide conversion. Specifically, first, the side lead portion 78 is peeled off from the sensor element 101, and 0.5 g is weighed to obtain a sample for measurement, and the sample for measurement is placed in a PTFE container. Next, 7.5 mL of a sulfuric acid solution with a ratio of water to sulfuric acid of 1:3 is added to the PTFE container, and then the PTFE container is placed in a stainless steel container and sealed with a lid. The stainless steel container is placed in a constant temperature bath and maintained at 230°C for 24 hours, excluding the heating time and the cooling time, so that the sample for measurement is dissolved to obtain a solution. Water is added to the solution to prepare a 50 mL sample. Using the sample, ICP-AES is performed to perform a qualitative analysis of the elements contained in the sample. The actual concentration value of Na is obtained by using the test concentration value of Na obtained by the qualitative analysis and the calibration curve of Na obtained in advance. The actual concentration value of Na is converted into oxides to calculate the sodium oxide (Na 2The mass ratio of the alkali metals and alkaline earth metals other than Na in terms of oxide conversion is also calculated using the same procedure. Using these calculation results, the total mass ratio of the alkali metals and alkaline earth metals in the side lead portion 78 in terms of oxide conversion is calculated.

[0151] [Evaluation of electrical conductivity]

[0152] For the gas sensors 100 of Examples 9 to 11, whether the conductivity of the side lead portion 78 is reduced after the endurance test is evaluated. First, the bias current of the pump current Ip2 before the endurance test is investigated as follows. The gas sensors 100 of Examples 9 to 11 are respectively installed in the piping in such a manner that the front end side of the element body 102 of the sensor element 101 protrudes into the piping, and a model gas containing no NOx, specifically a model gas in which the base gas is nitrogen and the oxygen concentration is 0%, and the NOx concentration is 0 ppm, is prepared and made to flow through the piping as the measured gas. At the same time, the heater control process is started, and when the heater 71a reaches 800°C, the adjustment pump control process and the measurement pump control process are started, and the pump current Ip2 flowing in this state is measured as the bias current (the pump current Ip2 flowing when the measured gas does not contain NOx). Next, the endurance test is performed. Specifically, for the gas sensors 100 of Examples 9 to 11, the exhaust gas of the diesel generator is made to flow through the pipe as the measured gas, and the heater control process, the adjustment pump control process, and the measurement pump control process are continuously executed. The temperature of the side lead portion 78 at this time is 280°C. This state is maintained for 2000 hours. Then, the bias current of the pump current Ip2 after the endurance test is measured by the same method as before the endurance test. After that, for the gas sensors 100 of Examples 9 to 11, the change (difference) of the bias current before and after the endurance test is calculated, and the change is converted into NOx concentration [ppm], and the value is used as the bias variation. Here, when the conductivity of the side lead portion 78 decreases (the resistance value increases) due to the endurance test, even if the NOx concentration is the same, the pump current Ip2 flowing through the side lead portion 78 will become a different value. Therefore, when the above-mentioned bias variation is within 7 ppm, the effect of suppressing the decrease in conductivity of the side lead portion 78 is evaluated to be high (A). When the bias variation is greater than 7 ppm, the effect of suppressing the decrease in conductivity of the side lead portion 78 is evaluated to be low (B).

[0153] The volumes Vp [vol %], Va [vol %], Vs [vol %] of the side lead portion 78 of Examples 9 to 11, the volume Vn [vol %] of sodium oxide, the ratio of the total mass of alkali metals and alkaline earth metals converted to oxides, and the evaluation results of the effect of suppressing the decrease in conductivity are summarized in Table 2.

[0154] As can be seen from Table 2, the effect of suppressing the decrease in conductivity of Example 11, in which the total mass ratio of alkali metals and alkaline earth metals in terms of oxide conversion exceeds 0.10wt%, is evaluated as "low (B)", while the effects of suppressing the decrease in conductivity of Examples 9 and 10, in which the total mass ratio of alkali metals and alkaline earth metals in terms of oxide conversion is less than 0.10wt%, are both evaluated as "high (A)". It is believed that in Examples 9 and 10, the alkali metals and / or alkaline earth metals contained in the side lead portion 78 are small (the total mass ratio in terms of oxide conversion is less than 0.10wt%), so the decrease in conductivity of the side lead portion 78 caused by their movement based on electromigration is suppressed.

[0155] Industrial Applicability

[0156] The present invention can be used for a sensor element for detecting the concentration of a specific gas such as NOx in a measured gas such as exhaust gas of an internal combustion engine, and a gas sensor including the sensor element.

Claims

1. A sensor element for detecting the concentration of a specific gas in a gas to be measured, comprising: an element body having an oxygen ion conductive solid electrolyte layer, in a columnar shape extending in a longitudinal direction, having a front end and a rear end as both ends along the longitudinal direction and a side surface as a surface along the longitudinal direction, wherein the front end side is exposed to the measured gas; an inner electrode disposed inside the element body; and a conductive portion, the conductive portion having an inner conductive portion and an outer conductive portion, the inner conductive portion being arranged inside the element body and being conductively connected to the inner electrode, the outer conductive portion having a connector electrode arranged on the rear end side of the side surface, having a portion arranged on the side surface and / or a portion exposed to the outside of the sensor element on the side surface, and being conductively connected to the inner conductive portion, A portion of the outer conductive portion that covers the inner conductive portion and / or at least a portion of the inner conductive portion is a dense portion that contains a noble metal, aluminum oxide, and silicon dioxide and is densely configured.

2. The sensor element according to claim 1, characterized in that Regarding the dense portion, when the volumes of aluminum oxide and silicon dioxide contained are respectively represented by Va [vol %] and Vs [vol %], Va / Vs≤1.5 is satisfied.

3. The sensor element according to claim 1 or 2, characterized in that Regarding the dense portion, when the volumes of the noble metal, alumina, and silica contained are respectively represented by Vp [vol %], Va [vol %], and Vs [vol %], 1.5 ≤ Vp / (Va + Vs).

4. The sensor element according to claim 3, characterized in that The dense portion satisfies 2.6≤Vp / (Va+Vs).

5. The sensor element according to claim 1 or 2, characterized in that: The dense portion satisfies that the ratio of the total mass of the alkali metal and the alkaline earth metal contained in the dense portion as converted into oxides is 0.1 wt % or less.

6. The sensor element according to claim 1 or 2, characterized in that The inner electrode is a measuring electrode for detecting the concentration of the specific gas.

7. The sensor element according to claim 1 or 2, characterized in that: The element body is a stacked body in which a plurality of layers including the solid electrolyte layer are stacked in a stacking direction orthogonal to the longitudinal direction. The stacked body has, as the side surfaces, a first surface and a second surface as two end surfaces in the stacking direction, and a third surface and a fourth surface as two end surfaces in a direction orthogonal to the longitudinal direction and the stacking direction, The inner conducting portion includes an inner lead portion led out to the third surface or the fourth surface, The portion of the outer conductive portion that covers the inner conductive portion is a side lead portion that is disposed on the third surface or the fourth surface and covers the inner lead portion.

8. The sensor element according to claim 1 or 2, characterized in that The element body is a stacked body in which a plurality of layers including the solid electrolyte layer are stacked in a stacking direction orthogonal to the longitudinal direction. The stacked body has, as the side surfaces, a first surface and a second surface as two end surfaces in the stacking direction, The element body has a through hole including an opening portion opened on the first surface or the second surface at the rear end side of the side surface, and penetrating one or more of the plurality of layers in the stacking direction. The outer conductive portion is the connector electrode, The inner conducting portion includes a through-hole conductor disposed in the through-hole and covered by the connector electrode.

9. The sensor element according to claim 1 or 2, characterized in that: The element body is a stacked body in which a plurality of layers including the solid electrolyte layer are stacked in a stacking direction orthogonal to the longitudinal direction. The stacked body has, as the side surfaces, a first surface and a second surface as two end surfaces in the stacking direction, The element body has a through hole including an opening portion opened on the first surface or the second surface at the rear end side of the side surface, and penetrating one or more of the plurality of layers in the stacking direction. The inner conductive portion includes a through-hole conductor, which is disposed in the through-hole and exposed to the outside at the opening. The dense portion includes at least a portion of the through-hole conductor.

10. The sensor element according to claim 1 or 2, characterized in that The sensor element is used for a gas sensor, and the gas sensor has: the sensor element; a housing in the shape of a tube extending along the length direction of the sensor element and having a second front end and a second rear end as two ends along the length direction, wherein the sensor element is disposed inside the housing; and A closing member that closes the second rear end side of the housing.

11. A gas sensor, characterized in that: have: The sensor element according to claim 1 or 2; a housing in the shape of a tube extending along the length direction of the sensor element and having a second front end and a second rear end as two ends along the length direction, wherein the sensor element is disposed inside the housing; and A closing member that closes the second rear end side of the housing.

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