Gas sensor

Abstract

The present application provides a gas sensor that can suppress deterioration of measurement accuracy even when a contaminant gas is generated on the reference gas space side. A housing of a gas sensor that has a reference gas space inside is provided with: an outer cylinder, one end portion side of which protrudes into the outer cylinder on the other end portion side of a sensor element that has a monitoring portion; and a sealing member, which is embedded in the end portion of the outer cylinder, seals the reference gas space. The sensor element is provided with: a first electrode lead portion, which has a first electrode through portion for electrically connecting the outside and at least one cavity outer pump electrode and a first through portion insulating layer that covers the first electrode through portion; and a second electrode lead portion, which has a second electrode through portion that can electrically connect the outside and a measurement electrode and a second through portion insulating layer that covers the second electrode through portion. In a case where a diffusion resistance of the first electrode lead portion is set to A (cm －1 ) and a diffusion resistance of the second electrode lead portion is set to B (cm －1 ), A / B < 1.00.

Description

TECHNICAL FIELD

[0001] The present application relates to a gas sensor provided with a sensor element made of ceramic, and particularly relates to protection of a measurement electrode and suppression of output variation when used in a fuel-rich gas atmosphere. BACKGROUND

[0002] In the past, as a device for measuring the concentration of a prescribed gas component in a measured gas such as a combustion gas or exhaust gas in an internal combustion engine such as an engine of an automobile, a gas sensor using a solid electrolyte ceramic that is an oxygen ion conductive ceramic such as zirconia (ZrO2) to form a sensor element is well known.

[0003] This gas sensor generally has a main body portion configured such that a long strip-shaped sensor element (detection element) made of ceramic is fixed inside (hollow portion) of a metal-made housing member by a ceramic support member and a pressed powder body of ceramic such as talc, and a gas-tight seal is achieved between one end portion side where a gas introduction port for introducing a measured gas into the inside of the element where a measurement electrode and the like is located and the other end portion side where a reference gas (atmosphere) is introduced by the pressed powder body (see, for example, Patent Document 1).

[0004] The other end portion side of the housing member is a cylindrical member also called a so-called outer cylinder, and a grommet as a seal member is embedded in the tip end thereof. The space surrounded by the above-mentioned outer cylinder and grommet is a reference gas space. The grommet has through-holes into which a plurality of lead wires for electrically connecting the center element and the outside are inserted. The reference gas is usually the atmosphere existing in the outer cylinder at the time when the grommet is embedded in the outer cylinder during the production of the gas sensor, but the atmosphere entering the inside of the outer cylinder through the gap between the through-holes of the grommet and the lead wires after that can also become the reference gas.

[0005] In addition, at the other end portion of the sensor element, the reference gas is introduced from the reference gas space into the inside of the element, and a reference electrode that supplies a reference potential is provided so as to be able to come into contact with the reference gas. By bringing the reference electrode into contact with the reference gas having a constant oxygen concentration, the reference potential is kept constant, and thus a potential difference corresponding to the atmosphere around the electrode is generated between the reference electrode and the other electrode such as a measurement electrode provided in the sensor element.

[0006] It is also known that the sensor element in which the reference electrode lead-through portion connecting between the reference electrode and an electrode pad as a connection terminal is porous (see, for example, Patent Document 2).

[0007] Further, it is known that a gas sensor in which a ceramic layer is provided in such a manner that a slit portion to which a prescribed diffusion resistance is applied is formed around an outer electrode provided on an outer surface of a sensor element, and a gas sensor in which the mechanical strength of the slit portion is improved by embedding a porous body (see, for example, Patent Literature 3).

[0008] Further, it is known that a gas sensor provided with a sensor element configured such that an oxygen concentration detection unit and an oxygen pump unit are stacked in an element thickness direction with an insulating layer interposed therebetween, and a detection gas is introduced into the inside from a diffusion speed control portion formed of a porous body provided at a portion of the insulating layer (see, for example, Patent Literature 4).

[0009] Further, it is known that a gas sensor element in which the width W1 of a detection gas chamber into which a detection gas is introduced and the width W2 of a porous diffusion resistance layer disposed toward a gas introduction port of the detection gas chamber satisfy the relationship W1 < W2 (see, for example, Patent Literature 5).

[0010] Prior Art Documents

[0011] Patent Literature

[0012] Patent Literature 1: Japanese Patent No. 6401644

[0013] Patent Literature 2: Japanese Patent No. 5832479

[0014] Patent Literature 3: Japanese Patent Application Publication No. 2021-162465

[0015] Patent Literature 4: Japanese Patent Application Publication No. 2012-173146

[0016] Patent Literature 5: Japanese Patent Application Publication No. 2020-71128 SUMMARY

[0017] With the gas sensor disclosed in Patent Literature 1, the main body portion is disposed in an exhaust path from an engine and used in an exhaust gas atmosphere, and the sensor element itself is used in an environment at a high temperature such as being heated by a heater. Therefore, when use is started, the main body portion is heated to a high temperature, and at this time, sometimes, due to volatilization of oil components adhered to the inner surface of the outer cylinder or generation of gas from the rubber plug, a contaminated gas is generated, and the reference gas is contaminated with the contaminated gas. Further, as a result of the contaminated gas reaching the reference electrode, it is possible that a situation in which the reference potential, which should be maintained constant, changes, and the measurement accuracy of the gas sensor cannot be maintained, occurs. It is considered that the above situation is more likely to occur in the case where the reference electrode lead-through portion disclosed in Patent Literature 2 is porous.

[0018] In the gas sensor disclosed in Patent Literature 1, in an electrochemical pump cell composed of an outer electrode, a reference electrode, and a solid electrolyte provided between the two, oxygen is drawn from the outside of the element to the reference gas space by applying a prescribed voltage between the two electrodes, and by performing this drawing, the reference potential can be kept constant even if the reference gas is contaminated.

[0019] However, the above-mentioned contaminated gas not only reaches the reference electrode, but sometimes reaches the measurement electrode and the inner cavity closer to the gas inlet port via the electrode lead-through portion such as the measurement electrode lead-through portion. Thus, the measured gas that should have been introduced from the gas inlet port and reached the measurement electrode after the oxygen concentration was adjusted to a prescribed value is contaminated by the contaminated gas that intruded via the lead-through portion, and as a result, the measurement accuracy in the gas sensor can sometimes deteriorate. Even if the intrusion amount is small, in the case where the concentration of the measured gas component is small, the influence cannot be ignored.

[0020] For example, in Patent Literature 5, a scheme is disclosed in which, in the case where the width Wl of the measured gas chamber is made smaller than in the past so that the width of the electrode provided to the gas sensor element is also made smaller, in order to make the impedance of the electrode portion including the lead portion not change greatly, the width of the electrode lead-through portion connected to each electrode is set to be relatively larger, and thus adjusted to a prescribed electrode impedance. In the case where the width of the lead portion is made larger like this, the diffusion resistance of the lead portion becomes smaller, and the possibility of the amount of the contaminated gas that reaches via the lead portion increasing improves.

[0021] In addition, using the porous electrode lead-through portion disclosed in Patent Literature 2 also for the electrode lead-through portion other than the reference electrode lead-through portion makes it possible to suppress the amount of platinum used, and the cost decreases, but the intrusion amount of the contaminated gas via the electrode lead-through portion can possibly increase.

[0022] The present application was implemented in view of the above-mentioned problems, and aims to provide a gas sensor in which the deterioration of the measurement accuracy can be suppressed even if contaminated gas is generated on the reference gas space side.

[0023] To solve the above problems, a first aspect of the present application is a gas sensor capable of monitoring a predetermined gas component in a measured gas, characterized by comprising: a sensor element having a long strip-shaped base portion composed of a solid electrolyte having oxygen ion conductivity, and a monitoring portion provided at one end portion side; and a housing in which the sensor element is housed and fixed, the housing having: an outer cylinder having a reference gas space in which a reference gas is present, the other end portion side of the sensor element protruding into the reference gas space; and a sealing member embedded in an end portion of the outer cylinder to seal the reference gas space, the sensor element having: at least one oxygen partial pressure adjustment internal cavity that communicates with a measured gas inlet provided at the one end portion side under a predetermined diffusion resistance; a measurement internal cavity that further communicates with the at least one oxygen partial pressure adjustment internal cavity; an external cavity pump electrode provided at a position other than the at least one oxygen partial pressure adjustment internal cavity and the measurement internal cavity; at least one internal electrode provided to face the at least one oxygen partial pressure adjustment internal cavity, and capable of taking in or out oxygen between the corresponding at least one oxygen partial pressure adjustment internal cavity and the outside of the sensor element by applying a predetermined pump voltage between the at least one internal electrode and the external cavity pump electrode; a measurement electrode provided to face the measurement internal cavity, and capable of taking in or out oxygen between the measurement internal cavity and the outside of the sensor element by applying a predetermined pump voltage between the measurement electrode and the external cavity pump electrode; a first electrode lead portion having a first electrode conductor portion extending from the external cavity pump electrode for electrically connecting the outside of the sensor element and the external cavity pump electrode, and a first conductor insulating layer covering the first electrode conductor portion; a ceramic layer covering at least the first electrode lead portion; and a second electrode lead portion having a second electrode conductor portion extending from the measurement electrode for electrically connecting the outside of the sensor element and the measurement electrode, and a second conductor insulating layer covering the second electrode conductor portion, wherein a diffusion resistance of the first electrode lead portion is set to A (cm －1 ), and a diffusion resistance of the second electrode lead portion is set to B (cm －1 ), and A / B < 1.00.

[0024] A second aspect of the present application is based on the gas sensor of the first aspect, characterized in that 0.03 ≤ A / B ≤ 0.29.

[0025] The third aspect of the present invention is based on the gas sensor involved in the first or second aspect, characterized in that B ≥ 700 × 10 －3 (cm －1 ).

[0026] The fourth aspect of the present invention, based on the gas sensor involved in any of the first to third aspects, is characterized in that the gas sensor further comprises at least one third electrode lead portion, the at least one third electrode lead portion having at least one third electrode conductive portion extending from the at least one inner electrode for electrically connecting the outside of the sensor element and the at least one inner electrode, and at least one third conductive portion insulating layer covering the at least one third electrode conductive portion, wherein the diffusion resistance of the at least one third electrode lead portion is greater than or equal to the diffusion resistance of the second electrode lead portion.

[0027] The fifth aspect of the present invention is based on the gas sensor involved in any of the first to fourth aspects, characterized in that the cavity external pump electrode and the first electrode lead portion are disposed on a main surface of the substrate portion, the gas sensor further comprises a porous body region that covers the cavity external pump electrode, and the ceramic layer covers the first electrode lead portion and the porous body region.

[0028] The sixth embodiment of the present invention is based on the gas sensor involved in any of the first to fifth embodiments, characterized in that the at least one internal cavity for adjusting oxygen partial pressure is a first internal cavity and a second internal cavity that are sequentially connected from the inlet under a specified diffusion resistance; the internal cavity for measuring is a third internal cavity that is connected to the second internal cavity under a specified diffusion resistance; and the at least one inner electrode is a main pump electrode disposed in the first internal cavity and an auxiliary pump electrode disposed in the second internal cavity.

[0029] Invention Effects

[0030] According to the first to sixth aspects of the present invention, it is possible to suppress temporary fluctuations in the NOx concentration output when polluting gases are generated in the reference gas space. Accordingly, a gas sensor is realized that effectively suppresses the degradation of measurement accuracy caused by the generation of polluting gases in the reference gas space. Attached Figure Description

[0031] Figure 1 This is a cross-sectional view of the main part of the gas sensor 100 along its length.

[0032] Figure 2 This is a vertical cross-sectional view along the length of the sensor element 101, which is a schematic representation of an example of the configuration of the sensor element 101.

[0033] Figure 3 is an example of a graph showing the change in the NOx current Ip2 when the gas sensor is automatically started when operating in a test gas atmosphere with a constant NOx concentration, together with the temperature change of the rubber plug 106.

[0034] Figure 4 is a plan view showing the arrangement of the electrode lead portion including the electrode lead portion extending from the self-pumping electrode 22, the auxiliary pumping electrode 51, and the measurement electrode 44.

[0035] Figure 5 is a plan view showing the arrangement of the electrode lead portion including the electrode lead portion extending from the outer pumping electrode 23.

[0036] Figure 6 is a graph for explaining the evaluation method of the output variation amount.

[0037] Symbol explanation

[0038] 1-3... first to third substrate layers, 4... first solid electrolyte layer, 5... separation layer, 6... second solid electrolyte layer, 7... ceramic layer, 8... porous body region, 10... gas introduction port, 11... first diffusion rate control portion, 13... second diffusion rate control portion, 20... first internal cavity, 21... main pumping unit, 22... inner pumping electrode, 22P... main pumping electrode lead portion, 23... outer pumping electrode, 23L... outer pumping electrode lead portion, 23T... terminal electrode, 30... third diffusion rate control portion, 40... second internal cavity, 41... measurement pumping unit, 42... reference electrode, 43... reference gas introduction cavity, 44... measurement electrode, 44P... measurement electrode lead portion, 48... atmosphere introduction layer, 50... auxiliary pumping unit, 51... auxiliary pumping electrode, 51P... auxiliary pumping electrode lead portion, 60... fourth diffusion rate control portion, 61... third internal cavity, 70... heater portion, 100... gas sensor, 101... sensor element, 102... protective cover, 103... fixing bolt, 104... outer cylinder, 105... connector, 106... rubber plug, 107... lead wire, 120... wrap-around fitting member, 151... contact member, H1-H4... through-hole, SP... reference gas space. DETAILED DESCRIPTION

[0039] Configuration of gas sensor

[0040] Figure 1 is a (more detailed, a main portion cross-sectional view along the length direction of the main body portion of) gas sensor 100 according to the embodiment of the present application. In the present embodiment, the gas sensor 100 detects a prescribed gas component (for example, NOx, etc.) by means of a sensor element 101 provided inside thereof. It should be noted that, Figure 1In the present embodiment, the vertical direction is shown as the z-axis direction, and the length direction of the gas sensor 100 coincides with the z-axis direction (the same in the following drawings).

[0041] The gas sensor 100 is mainly composed of the sensor element 101, the ring-fitting member 120 fitted around the sensor element 101, and the cylindrical body 130 further fitted around the ring-fitting member 120 and housing the ring-fitting member 120, which are covered by the protective cover 102, the fixing bolt 103, and the outer cylinder 104. In other words, the gas sensor 100 is composed of the sensor element 101 penetrating the axial center of the cylindrical body 130, and the ring-fitting member 120 fitted around the sensor element 101 inside the cylindrical body 130. Mainly, the cylindrical body 130, the protective cover 102, and the outer cylinder 104 constitute the housing (housing member) of the sensor element 101.

[0042] The sensor element 101 is a long, columnar or thin plate-shaped member mainly composed of an element body formed of an oxygen-ion conductive solid electrolyte ceramic such as zirconia. The sensor element 101 is disposed on the central axis of the cylindrical body 130 in the length direction. Hereinafter, the extension direction of the central axis coinciding with the length direction of the cylindrical body 130 is referred to as the axial direction. Figure 1 In the following drawings, the axial direction coincides with the z-axis direction.

[0043] The sensor element 101 is composed of a monitoring portion having a gas inlet at the first end portion 101a and an internal cavity, and various electrodes and wiring patterns on the surface and inside of the element body. In the sensor element 101, the measured gas introduced into the internal cavity is reduced and even decomposed to generate oxygen ions in the internal cavity. In the gas sensor 100, the concentration of the gas component in the measured gas is calculated based on the amount of oxygen ions flowing in the element interior, which is proportional to the concentration of the gas component.

[0044] A prescribed range of the length direction of the surface of the sensor element 101 from the first end portion 101a is covered by the protective film 111. The protective film 111, also referred to as a heat shock resistant protective layer, is provided to protect the vicinity of the first end portion 101a of the sensor element 101 provided with the internal cavity, electrodes, and the like from heat shock caused by water and the like. The protective film 111 is a porous film formed of, for example, AI2O3, and has a thickness of about 10 μm to 2000 μm. The protective film 111 is preferably formed to be able to withstand a force of about 50 N or less according to the purpose. However, Figure 1 The formation range of the protective film 111 in each of the following drawings is merely an example, and the actual formation range is appropriately determined according to the specific structure of the sensor element 101.

[0045] The protective cover 102 is a substantially cylindrical outer member that protects the first end portion 101a of the sensor element 101, which is in direct contact with the measured gas during use. The protective cover 102 is welded and fixed to the outer peripheral end portion (the outer periphery of the reduced diameter portion 131 described later) of the upper side (z-axis direction positive side) of the cylindrical body 130 in the drawing.

[0046] Figure 1 In the illustrated case, the protective cover 102 has a two-layer structure of an outer cover 102a and an inner cover 102b. The outer cover 102a and the inner cover 102b are each provided with a plurality of through-holes H1 and H2, H3 and H4, through which gas can pass. Note that, Figure 1 The type, number, arrangement position, shape, and the like of the through-holes illustrated are merely examples, and can be appropriately determined in consideration of the inflow method of the measured gas flowing into the inside of the protective cover 102.

[0047] The fixing bolt 103 is a ring-shaped member used when the gas sensor 100 is fixed to a measurement position. The fixing bolt 103 has a bolt portion 103a in which a thread is formed, and a holding portion 103b that holds the bolt portion 103a when the bolt portion 103a is screwed. The bolt portion 103a is screwed with a nut provided at the mounting position of the gas sensor 100. For example, by screwing the bolt portion 103a with a nut portion provided at an exhaust pipe of an automobile, the gas sensor 100 is fixed to the exhaust pipe in such a manner that the protective cover 102 side is exposed to the inside of the exhaust pipe.

[0048] The outer cylinder 104 is a cylindrical member whose one end portion (lower end portion in the drawing) is welded and fixed to the outer peripheral end portion of the upper side (z-axis direction positive side) of the cylindrical body 130 in the drawing. The connector 105 is arranged inside the outer cylinder 104. In addition, at the other end portion (upper end portion in the drawing) of the outer cylinder 104, a rubber plug 106 is embedded as a seal member. In the gas sensor 100, the space between the cylindrical body 130 and the rubber plug 106 and surrounded by the outer cylinder 104 is a reference gas space SP. In other words, the reference gas space SP is sealed by the rubber plug 106. The second end portion 101b of the sensor element 101 protrudes into the reference gas space SP. For example, the atmosphere is introduced into the reference gas space SP as a reference gas when the NOx concentration is measured.

[0049] The connector 105 has a plurality of contact members 151 that come into contact with a plurality of terminal electrodes (not illustrated) provided at the second end portion 101b of the sensor element 101. The contact members 151 are connected to a lead wire 107 that is inserted through the rubber plug 106. The lead wire 107 is connected to a controller 110 and various power sources (not illustrated) outside the gas sensor 100. Figure 1 The controller 110 and various power sources (not illustrated) outside the gas sensor 100 are connected to the lead wire 107.

[0050] It should be noted that Figure 1 The contact member 151 and the lead 107 are each shown only two, but this is an example.

[0051] The cylindrical body 130 is a cylindrical member made of metal, also referred to as a main body metal piece. Inside the cylindrical body 130, the sensor element 101 and the grommet member 120 are housed. In other words, the cylindrical body 130 is further grommeted around the grommet member 120 grommeted around the sensor element 101.

[0052] The cylindrical body 130 mainly has: a thick-walled main portion 130M that forms a cylindrical inner space by a cylindrical inner surface 130a parallel to the axis direction; a reduced diameter portion 131 provided at the lower end portion (z-axis direction negative side) in the drawing in the axis direction and thicker than the main portion 130M; a thin-walled chisel portion 132 that extends further upward from an end surface 130c of the main portion 130M at the upper end in the axis direction in the drawing and is curved toward the axis center; and a locking portion 133 that protrudes to the outer side in the circumferential direction.

[0053] The chisel portion 132 is curved to press and fix (constrain) the grommet member 120 (directly the second ceramic support 123) disposed inside from above in the drawing. It should be noted that, as described later, the chisel portion 132 is curved after the grommet member 120 is grommeted to the sensor element 101.

[0054] The grommet member 120 includes: a first ceramic support 121, a press powder 122, and a second ceramic support 123.

[0055] The first ceramic support 121 and the second ceramic support 123 are insulators made of ceramic. More specifically, a rectangular through hole (omitted from the drawing) corresponding to the cross-sectional shape of the sensor element 101 is provided at the axis center position of the first ceramic support 121 and the second ceramic support 123, and the sensor element 101 is inserted through the through hole, whereby the first ceramic support 121 and the second ceramic support 123 are grommeted to the sensor element 101. It should be noted that the first ceramic support 121 is locked to the tapered surface 130b of the cylindrical body 130 below in the drawing.

[0056] On the other hand, the compression powder body 122 is formed of ceramic powder such as talc powder, and is arranged inside the cylindrical body 130 in a state where the sensor element 101 is inserted through the through-hole and surrounded by the ring-fitting member 120, as with the first ceramic support 121 and the second ceramic support 123, and then further compressed to be integrated. More specifically, the ceramic particles that form the compression powder body 122 are surrounded by the first ceramic support 121, the second ceramic support 123, and the cylindrical body 130, and are tightly packed in the space through which the sensor element 101 is inserted.

[0057] In the gas sensor 100, the sensor element 101 inside the cylindrical body 130 and the ring-fitting member 120 are fixed by the stop by the tapered surface 130b of the first ceramic support 121 and the pressing from the upper side in the drawing by the caulking portion 132 of the second ceramic support 123. Further, the airtight seal between the first end portion 101a side and the second end portion 101b side of the sensor element 101 is achieved by the compression packing of the compression powder body 122.

[0058] <Outline of Sensor Element>

[0059] Figure 2 is a vertical sectional view along the element length direction that schematically shows an example of the configuration of the sensor element 101. Figure 2 In the drawing, the illustration of the protective film 111 provided on the first end portion 101a side of the sensor element 101 is omitted, but a controller 110 that controls the operation of each part of the gas sensor 100 and determines the NOx concentration based on the NOx current flowing through the sensor element 101 is shown together.

[0060] The sensor element 101 is a flat (long strip-shaped) ceramic element body having a structure in which six solid electrolyte layers are stacked in the order of a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, a first solid electrolyte layer 4, a separation layer 5, and a second solid electrolyte layer 6, each containing zirconia (Zr02) as an oxygen ion-conductive solid electrolyte (for example, yttria-stabilized zirconia (YSZ) or the like). Note that the solid electrolytes that form the six layers are dense and airtight solid electrolytes. Further, in the following, the upper side of each of the six layers in the drawing is simply referred to as the upper surface, and the lower side is simply referred to as the lower surface. In addition, the entire portion of the sensor element 101 that contains the solid electrolyte is collectively referred to as the base portion. Figure 2

[0061] ​The sensor element 101 is manufactured, for example, by performing prescribed processing on ceramic green sheets corresponding to the respective layers and printing of circuit patterns (e.g., electrodes, electrode lead portions, lead portion insulating layers, etc.), and then laminating them, and further performing firing to integrate them.

[0062] Between the first end portion 101a side of the sensor element 101 and between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, the first diffusion speed control portion 11, the buffer space 12, the second diffusion speed control portion 13, the first internal cavity 20, the third diffusion speed control portion 30, the second internal cavity 40, the fourth diffusion speed control portion 60, and the third internal cavity 61, which also serve as the gas introduction port 10, are adjacently formed in a manner that sequentially communicates in order.

[0063] The buffer space 12, the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61 are internal spaces (regions) of the sensor element 101 that are provided by hollowing out the partition layer 5, with the upper portion thereof being demarcated by the lower surface of the second solid electrolyte layer 6, the lower portion thereof being demarcated by the upper surface of the first solid electrolyte layer 4, and the side portions thereof being demarcated by the side surface of the partition layer 5. Note that the gas introduction port 10 can also be provided by hollowing out the partition layer 5 at the first end portion 101a, separately from the first diffusion speed control portion 11. In this case, the first diffusion speed control portion 11 is adjacently formed in a manner that is more internal than the gas introduction port 10.

[0064] The first diffusion speed control portion 11, the second diffusion speed control portion 13, the third diffusion speed control portion 30, and the fourth diffusion speed control portion 60 are each provided as two horizontally long (lengthwise direction of the opening in the direction perpendicular to the drawing) slits. Further, the portion from the gas introduction port 10 to the most internal internal cavity, the third internal cavity 61, is also referred to as a gas flow-through portion.

[0065] In addition, on the second end portion 101b side of the sensor element 101, at a position between the upper surface of the third substrate layer 3 and the lower surface of the partition layer 5, and at a position where the side portions are demarcated by the side surface of the first solid electrolyte layer 4, a reference gas introduction cavity 43 is provided. The reference gas introduction cavity 43 is open with respect to a reference gas space SP inside the outer cylinder 104, and atmosphere as reference gas is introduced from the reference gas space SP.

[0066] The atmosphere introduction layer 48 is a layer composed of porous alumina, and reference gas is introduced to the atmosphere introduction layer 48 through the reference gas introduction cavity 43. In addition, the atmosphere introduction layer 48 is formed so as to cover the reference electrode 42.

[0067] The reference electrode 42 is an electrode formed in a manner that it is sandwiched by the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4, and, as described above, the atmospheric gas introduction layer 48 that communicates with the reference gas introduction cavity 43 is provided around the reference electrode 42. In addition, as described later, the oxygen concentration (oxygen partial pressure) in the first internal cavity 20 and the second internal cavity 40 can be measured using the reference electrode 42.

[0068] In the gas flow passage, the gas introduction port 10 (first diffusion speed control section 11) is a portion that is opened with respect to the outside space, and the measured gas is introduced into the sensor element 101 from the outside space through the gas introduction port 10.

[0069] The first diffusion speed control section 11 is a portion that applies a prescribed diffusion resistance to the introduced measured gas.

[0070] The buffer space 12 is a space provided to guide the measured gas introduced from the first diffusion speed control section 11 to the second diffusion speed control section 13.

[0071] The second diffusion speed control section 13 is a portion that applies a prescribed diffusion resistance to the measured gas introduced from the buffer space 12 to the first internal cavity 20.

[0072] When the measured gas is introduced from the outside of the sensor element 101 into the first internal cavity 20, the measured gas that is sharply introduced into the inside of the sensor element 101 from the gas introduction port 10 due to the pressure variation of the measured gas of the outside space (pulsation of the exhaust gas pressure in the case where the measured gas is the exhaust gas of an automobile) is not directly introduced to the first internal cavity 20, but is introduced to the first internal cavity 20 after the concentration variation of the measured gas is eliminated by the first diffusion speed control section 11, the buffer space 12, and the second diffusion speed control section 13. Thus, the concentration variation of the measured gas introduced to the first internal cavity 20 reaches a level that can be almost ignored.

[0073] 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 speed control section 13. The main pump unit 21 operates to adjust the oxygen partial pressure.

[0074] The main pump unit 21 is an electrochemical pump unit composed of an inner pump electrode (also referred to as a main pump electrode) 22, an outer (cavity outer) pump electrode 23, and the second solid electrolyte layer 6 sandwiched by the inner pump electrode 22 and the outer pump electrode 23, in which the inner pump electrode 22 has a top electrode portion 22a provided on the entire surface of the lower surface of the second solid electrolyte layer 6 that faces the first internal cavity 20, and the outer pump electrode 23 is provided in a region of the upper surface (one main surface of the sensor element 101) of the second solid electrolyte layer 6 that corresponds to the top electrode portion 22a.

[0075] The inner pump electrode 22 is formed in the upper and lower solid electrolyte layers (the second solid electrolyte layer 6 and the first solid electrolyte layer 4) that divide the first internal cavity 20. Specifically, a top electrode portion 22a is formed in the lower surface of the second solid electrolyte layer 6 that constitutes the top surface of the first internal cavity 20, and a bottom electrode portion 22b is formed in the upper surface of the first solid electrolyte layer 4 that constitutes the bottom surface. The top electrode portion 22a and the bottom electrode portion 22b are connected by a conductive portion provided in the side surface (inner surface) of the partition layer 5 that constitutes the side wall of the first internal cavity 20 (omitted from the drawing).

[0076] The top electrode portion 22a and the bottom electrode portion 22b are formed in a rectangular shape in plan view. However, a configuration in which only the top electrode portion 22a is provided or a configuration in which only the bottom electrode portion 22b is provided can also be adopted.

[0077] The inner pump electrode 22 and the outer pump electrode 23 are formed as a porous metal ceramic electrode. In particular, the inner pump electrode 22 that contacts the gas to be measured is formed using a material that has reduced reduction ability with respect to the NOx component in the gas to be measured. For example, a metal ceramic electrode of an Au-Pt alloy having a porosity of 5% to 40% and containing about 0.6 wt% to 1.4 wt% of Au and ZrO2 is formed in a thickness of 5 μm to 20 μm. The weight ratio of the Au-Pt alloy and ZrO2 can be about Pt:ZrO2 = 7.0:3.0 to 5.0:5.0.

[0078] On the other hand, the outer pump electrode 23 is formed, for example, as a metal ceramic electrode of Pt or an alloy thereof and ZrO2 in a rectangular shape in plan view.

[0079] With respect to the main pump unit 21, a desired pump voltage Vp0 is applied between the inner pump electrode 22 and the outer pump electrode 23 by the variable power supply 24, and a main pump current Ip0 is caused to flow in the positive direction or the negative direction between the inner pump electrode 22 and the outer pump electrode 23, whereby oxygen in the first internal cavity 20 can be pumped out to the outside space or oxygen in the outside space can be pumped into the first internal cavity 20. Further, the pump voltage Vp0 applied between the inner pump electrode 22 and the outer pump electrode 23 in the main pump unit 21 is referred to as the main pump voltage Vp0.

[0080] In addition, in order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere of the first internal cavity 20, a main sensor unit 80 as an electrochemical sensor unit is constituted by the inner pump electrode 22, the second solid electrolyte layer 6, the partition layer 5, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42.

[0081] The oxygen concentration (oxygen partial pressure) in the first internal cavity 20 is learned by measuring the potential difference, i.e., electromotive force V0, between the inner pump electrode 22 and the reference electrode 42 in the main sensor unit 80.

[0082] Further, the controller 110 performs feedback control of the main pump voltage Vp0 so as to make the electromotive force V0 constant, thereby controlling the main pump current Ip0. Thus, the oxygen concentration in the first internal cavity 20 is maintained at a prescribed constant value.

[0083] The third diffusion rate control section 30 is a site that applies a prescribed diffusion resistance to the measured gas whose oxygen concentration (oxygen partial pressure) has been controlled by the action of the main pump unit 21 in the first internal cavity 20, and that introduces the measured gas into the second internal cavity 40.

[0084] The second internal cavity 40 is provided as a space for further adjusting the oxygen partial pressure in the measured gas introduced through the third diffusion rate control section 30. The oxygen partial pressure is adjusted by the action of the auxiliary pump unit 50. In the second internal cavity 40, the oxygen concentration of the measured gas can be adjusted with higher precision.

[0085] In the second internal cavity 40, the measured gas whose oxygen concentration (oxygen partial pressure) has been adjusted in advance in the first internal cavity 20 and then introduced through the third diffusion rate control section 30 is further subjected to adjustment of the oxygen partial pressure by the auxiliary pump unit 50.

[0086] 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, but any appropriate electrode on the outside of the sensor element 101), and a second solid electrolyte layer 6, in which the auxiliary pump electrode 51 has a top electrode portion 51a provided on the lower surface of the second solid electrolyte layer 6 so as to face substantially the entire second internal cavity 40.

[0087] The auxiliary pump electrode 51 is disposed in the second internal cavity 40 in the same manner as the inner pump electrode 22 previously disposed in the first internal cavity 20. That is, the top electrode portion 51a is formed with respect to the second solid electrolyte layer 6 constituting the top surface of the second internal cavity 40, and the bottom electrode portion 51b is formed in the first solid electrolyte layer 4 constituting the bottom surface of the second internal cavity 40. Both the top electrode portion 51a and the bottom electrode portion 51b are formed in a rectangular shape in plan view, and are connected by a conductive portion provided on the side wall surface (inner surface) of the separation layer 5 constituting the two side wall portions of the second internal cavity 40 (omitted from the drawing).

[0088] Further, the auxiliary pump electrode 51 is formed of a material that has reduced reducing ability with respect to the NOx component in the measured gas, like the inner pump electrode 22.

[0089] As for the auxiliary pump unit 50, under the control of the controller 110, a desired voltage (auxiliary pump voltage) Vpl is applied between the auxiliary pump electrode 51 and the outer pump electrode 23, whereby oxygen in the atmosphere in the second internal cavity 40 can be sucked out to the outside space, or oxygen from the outside space can be sucked into the second internal cavity 40.

[0090] Further, in order to control the oxygen partial pressure in the atmosphere in the second internal cavity 40, an auxiliary sensor unit 81 as an electrochemical sensor unit is constituted by the auxiliary pump electrode 51, the reference electrode 42, the second solid electrolyte layer 6, the separation layer 5, the first solid electrolyte layer 4, and the third substrate layer 3. In the auxiliary sensor unit 81, a potential difference, i.e., electromotive force VI, generated between the auxiliary pump electrode 51 and the reference electrode 42 in correspondence with the oxygen partial pressure in the second internal cavity 40 is detected.

[0091] The auxiliary pump unit 50 performs pumping using a variable power source 52 that controls the voltage based on the electromotive force VI detected by the above-described auxiliary sensor unit 81. Thereby, the oxygen partial pressure in the atmosphere in the second internal cavity 40 is feedback-controlled to a low partial pressure that has substantially no influence on the measurement of NOx.

[0092] Further, at the same time, the auxiliary pump current Ip1 is used to control the electromotive force of the main sensor unit 80. Specifically, the auxiliary pump current Ip1 is input as a control signal to the main sensor unit 80, and controls the electromotive force Vo thereof, whereby the gradient of the oxygen partial pressure in the measured gas introduced from the third diffusion velocity control section 30 into the second internal cavity 40 is always 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 or so due to the effects of the main pump unit 21 and the auxiliary pump unit 50.

[0093] The fourth diffusion velocity control section 60 is a site that applies a prescribed diffusion resistance to the measured gas whose oxygen concentration (oxygen partial pressure) is controlled by the action of the auxiliary pump unit 50 in the second internal cavity 40, and guides the measured gas to the third internal cavity 61.

[0094] The third internal cavity 61 is provided as a space (measured internal cavity) that performs a process of measuring the concentration of nitrogen oxides (NOx) in the measured gas introduced through the fourth diffusion velocity control section 60. In the third internal cavity 61, the measurement of the NOx concentration is performed by the action of the measurement pump unit 41. The third internal cavity 61 is introduced with the measured gas whose oxygen concentration is adjusted with high precision in the second internal cavity 40, and thus the gas sensor 100 is able to perform a high-precision measurement of the NOx concentration.

[0095] The measurement pump unit 41 is an electrochemical pump unit configured of the measurement electrode 44, the outer pump electrode 23, the second solid electrolyte layer 6, the separation layer 5, and the first solid electrolyte layer 4, in which the measurement electrode 44 is provided at a position on the upper surface of the first solid electrolyte layer 4 that faces the third internal cavity 61 and is separated from the third diffusion velocity control section 30.

[0096] The measurement electrode 44 is a porous metal ceramic electrode of a noble metal and a solid electrolyte. For example, a metal ceramic electrode formed of Pt or an alloy of Pt and another noble metal such as Rh and Zr02that is a constituent material of the sensor element 101. The measurement electrode 44 also functions as an NOx reduction catalyst that reduces NOx present in the atmosphere in the third internal cavity 61.

[0097] With respect to the measurement pump unit 41, under the control of the controller 110, oxygen generated by the decomposition of NOx in the atmosphere in the third internal cavity 61 can be pumped out, and the amount of generation thereof can be detected as a pump current Ip2.

[0098] In addition, in order to detect the oxygen partial pressure around the measurement electrode 44, a measurement sensor unit 82 that is an electrochemical sensor unit is configured of the second solid electrolyte layer 6, the separation layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the measurement electrode 44, and the reference electrode 42. The variable power supply 46 is feedback controlled based on the potential difference, i.e., electromotive force V2, between the measurement electrode 44 and the reference electrode 42 that is detected by the measurement sensor unit 82 and corresponds to the oxygen partial pressure in the third internal cavity 61.

[0099] NOx in the measured gas introduced into the third internal cavity 61 is reduced (2NO→N2+O2) by the measurement electrode 44 to generate oxygen. And, the generated oxygen is pumped by the measurement pump unit 41, at which time the voltage (measurement pump voltage) Vp2 of the variable power supply 46 is controlled so as to make the electromotive force V2 detected by the measurement sensor unit 82 constant. The amount of oxygen generated around the measurement electrode 44 is proportional to the concentration of NOx in the measured gas, and thus the NOx concentration in the measured gas is calculated using the pump current Ip2 in the measurement pump unit 41. Hereinafter, such a pump current Ip2 is also referred to as an NOx current Ip2.

[0100] In addition, if the measurement electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42 are combined to constitute an oxygen partial pressure detection mechanism as an electrochemical sensor unit, an electromotive force corresponding to a difference between the amount of oxygen generated by reduction of the NOx component in the atmosphere around the measurement electrode 44 and the amount of oxygen contained in the reference atmosphere can be detected, and thus the concentration of the NOx component in the measured gas can also be calculated.

[0101] In addition, the electrochemical sensor unit 83 is constituted by the second solid electrolyte layer 6, the separation layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the outer pump electrode 23, and the reference electrode 42, and an electromotive force Vref can be obtained using the sensor unit 83, and the oxygen partial pressure in the measured gas outside the sensor can be detected using the electromotive force Vref.

[0102] Note that, Figure 2 In the sensor element 101, the electrode lead portions including the electrode lead-through portions are provided on the inner surface or the side surface, and the electrodes of the various pump units and sensor units are electrically connected to the terminal electrodes via the electrode lead-through portions. Hereinafter, the details of the electrode lead portions including the electrode lead-through portions will be described.

[0103] The sensor element 101 also has a heater portion 70 that functions to heat and maintain the temperature of the sensor element 101 to improve the oxygen ion conductivity of the solid electrolyte that constitutes the base portion.

[0104] The heater portion 70 mainly has a heater electrode 71, a heater member 72, a heater lead-through portion 72a, a through-hole 73, a heater insulating layer 74, a pressure release hole 75, and Figure 2 The heater resistance detection lead-through portion is omitted from the drawing. In addition, the heater portion 70 is embedded in the base portion of the sensor element 101 except for the heater electrode 71.

[0105] The heater electrode 71 is an electrode formed so as to be in contact with the lower surface of the first substrate layer 1 (the other main surface of the sensor element 101).

[0106] The heater member 72 is a resistance heating body provided between the second substrate layer 2 and the third substrate layer 3. The heater member 72 is formed so as to be in contact with the heater electrode 71. Figure 2The heater member 72 is formed of Pt or mainly composed of Pt. The heater member 72 is embedded in a prescribed range of the side of the sensor element 101 having the gas flow passage in a manner to oppose the gas flow passage in the element thickness direction. The heater member 72 is provided to have a thickness of about 10 to 30 μm.

[0107] For the sensor element 101, a current is passed through the heater electrode 71 to the heater member 72, thereby causing the heater member 72 to generate heat, so that each portion of the sensor element 101 can be heated to a prescribed temperature and kept at the temperature. Specifically, the sensor element 101 is heated so that the temperature of the solid electrolyte and the electrode in the vicinity of the gas flow passage reaches about 700 to 900°C. The oxygen ion conductivity of the solid electrolyte constituting the base portion in the sensor element 101 is improved by such heating. Further, the heating temperature of the heater member 72 when the gas sensor 100 is used (when the sensor element 101 is driven) is referred to as the sensor element driving temperature.

[0108] The degree of heat generation (heater temperature) of the heater member 72 is grasped by the magnitude of the resistance value (heater resistance) of the heater member 72.

[0109] The sensor element 101 of the gas sensor 100 according to the present embodiment is provided with a ceramic layer 7 and a porous body region 8 on the second solid electrolyte layer 6 in addition to the above-described components.

[0110] The ceramic layer 7 is provided on the second solid electrolyte layer 6 and covers substantially the entire surface thereof. The ceramic layer 7 is contiguous with most of the second solid electrolyte layer 6, but is separated from the outer side pump electrode 23 and the region of the upper surface of the second solid electrolyte layer 6 in the element width direction which is located laterally of the outer side pump electrode 23 (hereinafter referred to as the electrode lateral region). The region between the outer side pump electrode 23 and the ceramic layer 7 and the region between the electrode lateral region of the second solid electrolyte layer 6 and the ceramic layer 7 are the porous body region 8. The porous body region 8 is provided to cover the outer side pump electrode 23 and expose both end portions in the element width direction, and the ceramic layer 7 is provided to cover the entire upper surface of the second solid electrolyte layer 6 including the porous body region 8 and the outer side pump electrode lead portion 23P described later.

[0111] More specifically, the ceramic layer 7 is composed of a ceramic (e.g., zirconia, alumina, etc.) which is as dense as, for example, the second solid electrolyte layer 6.

[0112] On the other hand, the porous body region 8 is composed of a porous body (for example, alumina or the like) having a porosity of about 30% to 60%. The porous body region 8 is configured so that the thickness (in other words, the distance in the element thickness direction between the outer pump electrode 23 and the ceramic layer 7) above the outer pump electrode 23 is about 25 μm to 40 μm.

[0113] For example, after the sensor element 101 excluding the ceramic layer 7 and the porous body region 8 is formed in advance, the ceramic layer 7 and the porous body region 8 are formed by a publicly known method such as printing. Alternatively, with respect to a green sheet laminate formed of the above-described six solid electrolyte layers, a material that eventually becomes the ceramic layer 7 and the porous body region 8 can be further laminated by a publicly known method such as printing, and the laminate can be fired integrally, whereby the ceramic layer 7 and the porous body region 8 can be formed.

[0114] With the ceramic layer 7 and the porous body region 8 configured as described above, in the sensor element 101, a prescribed diffusion resistance is applied to oxygen that passes through the porous body region 8 at the time of intake and discharge of oxygen between the inside and the outside of the sensor element 101 by the outer pump electrode 23.

[0115] When the concentration of NOx is measured in the gas sensor 100 configured as described above, the main pump unit 21 and the auxiliary pump unit 50 are operated, whereby feedback control is performed so that the oxygen concentration in the first internal cavity 20 and the second internal cavity 40 is constant, and the measured gas whose oxygen concentration is constant is introduced into the third internal cavity 61 and reaches the measurement electrode 44. For example, in the case where the measured gas is a lean fuel atmosphere, the measured gas whose oxygen partial pressure is sufficiently lowered to a degree (for example, 0.0001 ppm to 1 ppm) at which the measurement of NOx is substantially not affected is introduced into the third internal cavity 61.

[0116] Then, at the measurement electrode 44, NOx in the measured gas that has reached there is reduced, whereby oxygen is generated. The oxygen is discharged by the measurement pump unit 41, and the NOx current Ip2 that flows at the time of the discharge has a certain functional relationship (hereinafter referred to as a sensitivity characteristic) with the concentration of NOx in the measured gas.

[0117] Before the gas sensor 100 is actually used, the above-described sensitivity characteristic is determined in advance using a plurality of kinds of sample gases whose NOx concentrations are known, and the data thereof is stored in the controller 110. Then, at the time of actual use of the gas sensor 100, a signal indicating the value of the NOx current Ip2 that flows in correspondence with the concentration of NOx in the measured gas is supplied to the controller 110. In the controller 110, based on the value and the determined sensitivity characteristic, the concentration of NOx is sequentially calculated, and is output in the form of a NOx sensor detection value. Accordingly, in the gas sensor 100, the concentration of NOx in the measured gas can be grasped substantially in real time.

[0118] Generation of Contaminant Gas in Reference Gas Space

[0119] In the case of a gas sensor like the gas sensor 100 according to the present embodiment, which has a configuration in which the reference gas space SP is surrounded by the outer cylinder 104 and the rubber plug 106 and which is used in a high-temperature environment, it is possible that a contaminant gas is generated in the reference gas space SP due to volatilization of oil components adhering to the inner surface 104a of the outer cylinder 104 or generation of a gas from the rubber plug 106, resulting in a change in the NOx current Ip2. In particular, this contaminant gas is likely to be generated in a severe environment in which the gas conditions are high in temperature or the heat around the main body portion cannot be dissipated.

[0120] Figure 3 is an example of a graph showing a change in the NOx current Ip2 at the time when the above-described gas sensor is automatically started to operate in an atmosphere of a sample gas in which the NOx concentration is constant, together with a change in the temperature of the rubber plug 106. Figure 3 In the graph, the NOx current Ip2, which should be constant, temporarily decreases after the temperature of the rubber plug 106 rises. Then, after the temperature of the rubber plug 106 stabilizes, it increases to the same degree as the initial peak value and becomes substantially constant.

[0121] It is considered that: Figure 3 the temporary decrease in the NOx current in the graph is because the contaminant gas generated during heating of the gas sensor, as described above, intrudes into the third internal cavity 61 in which the measurement electrode 44 is located through the measurement electrode lead portion described later. It is also considered that the value of the NOx current Ip2 increases after a certain period of time because the outer cylinder 104 and the rubber plug 106 are sufficiently heated, as a result of which the contaminant gas is completely released.

[0122] The above-described change in the NOx current Ip2 of course becomes a main cause of a temporary decrease in the measurement accuracy of the NOx concentration in the gas sensor. In addition, it is not necessarily the case that the contaminant gas is generated only after the start of use as shown in the graph. Figure 3

[0123] Configuration of Measurement Electrode Lead Portion

[0124] In the gas sensor 100 according to the present embodiment, by causing the measurement electrode lead portion in the sensor element 101 to satisfy a prescribed condition, a change in the NOx current Ip2 caused by generation of a contaminant gas in the reference gas space SP is suppressed, and the influence of the change in the NOx current Ip2 shown in the graph on the measurement accuracy of the NOx concentration is reduced. Figure 3 the change in the NOx current Ip2 shown in the graph on the measurement accuracy of the NOx concentration is reduced.

[0125] Figure 4 ​is a plan view showing the configuration of the electrode lead portion including the electrode lead portion of the electrode lead portion of the autonomous pump electrode 22 (more specifically, the bottom electrode portion 22b), the electrode lead portion of the auxiliary pump electrode 51 (more specifically, the bottom electrode portion 51b), and the electrode lead portion of the measurement electrode 44, which respectively extend, as an example thereof. In addition, Figure 5 is a plan view showing the configuration of the electrode lead portion including the electrode lead portion of the electrode lead portion of the autonomous pump electrode 22 (more specifically, the bottom electrode portion 22b), the electrode lead portion of the auxiliary pump electrode 51 (more specifically, the bottom electrode portion 51b), and the electrode lead portion of the measurement electrode 44, which respectively extend, as an example thereof. In addition,

[0126] The bottom electrode portion 22b, the bottom electrode portion 51b, and the measurement electrode 44 are each provided on the first solid electrolyte layer 4. Further, the main pump electrode lead portion 22L extends from the bottom electrode portion 22b to the second end portion 101b side, the auxiliary pump electrode lead portion 51L extends from the bottom electrode portion 51b to the second end portion 101b side, and the measurement electrode lead portion 44L extends from the measurement electrode 44 to the second end portion 101b side. On the other hand, the outer side pump electrode 23 is provided on the second solid electrolyte layer 6. Further, the outer side pump electrode lead portion 23L extends from the outer side pump electrode 23 to the second end portion 101b side.

[0127] The main pump electrode lead portion 22L, the auxiliary pump electrode lead portion 51L, the measurement electrode lead portion 44L, and the outer side pump electrode lead portion 23L are each surrounded by the main pump electrode lead portion insulating layer 22I, the auxiliary pump electrode lead portion insulating layer 51I, the measurement electrode lead portion insulating layer 44I, and the outer side pump electrode lead portion insulating layer 23I. Thereby, insulation between each electrode lead portion and the solid electrolyte constituting the sensor element 101 is achieved.

[0128] The outer side pump electrode lead portion 23L is an interlayer wiring in which a large portion thereof is buried between the second solid electrolyte layer 6 and the ceramic layer 7. However, Figure 2 In the present embodiment, the ceramic layer 7 is illustrated as extending to the second end portion 101b, but in fact, within a prescribed range from the second end portion 101b, the second solid electrolyte layer 6 is exposed, and the outer side pump electrode lead portion 23L is connected to the terminal electrode 23T provided to the exposed portion. It should be noted that, Figure 5 In the present embodiment, the outer side pump electrode lead portion insulating layer 23I exists in a straight line (in a linear shape) along the outer side pump electrode lead portion 23L, but the outer side pump electrode lead portion insulating layer 23I can be provided in a plane (in a layer shape) between the outer side pump electrode 23 and the terminal electrode 23T.

[0129] On the other hand, the main pump electrode lead 22L, the auxiliary pump electrode lead 51L, and the measurement electrode lead 44L are each an interlayer wiring in which a majority thereof is buried between the first solid electrolyte layer 4 and the separation layer 5, but is bent toward the element side in the vicinity of the second end portion 101b. Further, although not shown, the main pump electrode lead 22L, the auxiliary pump electrode lead 51L, and the measurement electrode lead 44L are each surrounded by the main pump electrode lead insulating layer 22I, the auxiliary pump electrode lead insulating layer 51I, and the measurement electrode lead insulating layer 44I, and after being connected to either of the upper and lower directions in the thickness direction via a via in the vicinity of the element side end portion, are connected to any one of a plurality of terminal electrodes, not shown, which are the same as the terminal electrode 23T provided in the second end portion 101b. Note that, in the present embodiment, the surrounding of each electrode lead by the lead insulating layer includes a mode in which the electrode lead is covered by the lead insulating layer, and a mode in which the electrode lead is sandwiched by the lead insulating layer.

[0130] The main pump electrode lead 22L, the auxiliary pump electrode lead 51L, the measurement electrode lead 44L, and the outer pump electrode lead 23L are preferably formed of platinum. Further, the main pump electrode lead insulating layer 22I, the auxiliary pump electrode lead insulating layer 51I, the measurement electrode lead insulating layer 44I, and the outer pump electrode lead insulating layer 23I are preferably formed of alumina.

[0131] Hereinafter, a region including the outer pump electrode lead 23L and the outer pump electrode lead insulating layer 23I and surrounded by the second solid electrolyte layer 6 and the ceramic layer 7 will be collectively referred to as an outer pump electrode lead portion 23P. Similarly, a region including the measurement electrode lead 44L and the measurement electrode lead insulating layer 44I and surrounded by the solid electrolyte (mainly the first solid electrolyte layer 4 and the separation layer 5) will be collectively referred to as a measurement electrode lead portion 44P. Further, a region including the main pump electrode lead 22L and the main pump electrode lead insulating layer 22I and surrounded by the solid electrolyte (mainly the first solid electrolyte layer 4 and the separation layer 5) will be collectively referred to as a main pump electrode lead portion 22P. Similarly, a region including the auxiliary pump electrode lead 51L and the auxiliary pump electrode lead insulating layer 51I and surrounded by the solid electrolyte (mainly the first solid electrolyte layer 4 and the separation layer 5) will be collectively referred to as an auxiliary pump electrode lead portion 51P.

[0132] In other words, the outer pump electrode lead portion 23P is inserted through the outer pump electrode lead-through portion 23L and the outer pump electrode lead-through portion insulating layer 23I. The measurement electrode lead portion 44P is inserted through the measurement electrode lead-through portion 44L and the measurement electrode lead-through portion insulating layer 44I. The main pump electrode lead portion 22P is inserted through the main pump electrode lead-through portion 22L and the main pump electrode lead-through portion insulating layer 22I. The auxiliary pump electrode lead portion 51P is inserted through the auxiliary pump electrode lead-through portion 51L and the auxiliary pump electrode lead-through portion insulating layer 51I.

[0133] Further, in the gas sensor 100 according to the present embodiment, the diffusion resistance of the measurement electrode lead portion 44P connected to the measurement electrode 44 located at the position farthest from the gas inlet port 10 in the gas flow-through portion provided in the sensor element 101 is greater than the diffusion resistance of the outer pump electrode lead portion 23P connected to the outer pump electrode 23, among the three electrode lead portions except for the outer pump electrode lead portion 23P.

[0134] That is, the gas sensor 100 according to the present embodiment is configured such that, when the diffusion resistance of the outer pump electrode lead portion 23P is set to A and the diffusion resistance of the measurement electrode lead portion 44P is set to B, the ratio A / B of the two satisfies at least the relationship A / B < 1.00.

[0135] Here, the diffusion resistance (lead-through portion diffusion resistance) of each electrode lead portion is the diffusion resistance exerted by the entire space surrounded by the solid electrolyte existing around each electrode lead portion, including the internal structure of each electrode lead-through portion and electrode lead-through portion insulating layer, on a gas moving in the space. That is, the fine gaps existing in the interiors of the electrode lead-through portion and the electrode lead-through portion insulating layer, and the gaps existing between the electrode lead-through portion and the electrode lead-through portion insulating layer, and between the electrode lead-through portion insulating layer and the surrounding solid electrolyte, all contribute to the above-described diffusion resistance.

[0136] For example, the size of the diffusion resistance of the electrode lead portion is adjusted by adjusting the porosity of the electrode lead-through portion and the insulating layer, the total length (wiring length) of the electrode lead portion, the cross-sectional area of the electrode lead portion, and the like.

[0137] Satisfying A / B < 1.00 means that, compared to a gas sensor having the same configuration except for not satisfying this condition, the outflow of the contaminated gas through the measurement electrode lead portion 44P is less likely to occur than the outflow of the contaminated gas through the outer pump electrode lead portion 23P.

[0138] In the gas sensor 100 according to the present embodiment, the main pump current Ip0 flowing through the main pump unit 21 is generally larger than the NOx current Ip2 flowing through the measurement pump unit 41, after the measured gas introduced from the gas introduction port 10 has sequentially taken in oxygen in the first internal cavity 20 and the second internal cavity 40. Therefore, even if the amount of intrusion of the contaminant gas is the same, the proportion of the output variation of the main pump current Ip0 caused by the intrusion of the contaminant gas into the outer pump electrode lead portion 23P is smaller than the proportion of the output variation of the NOx current Ip2 caused by the intrusion of the contaminant gas into the measurement electrode lead portion 44P and even into the third internal cavity 61.

[0139] By satisfying A / B < 1.00, the case where the contaminant gas preferentially intrudes into the outer pump electrode lead portion 23P is made, and the output variation of the NOx current Ip2 caused by the intrusion of the contaminant gas can be further suppressed.

[0140] For the above reasons, in the gas sensor 100 according to the present embodiment, by satisfying A / B < 1.00, even if the contaminant gas is generated in the reference gas space SP at the time of the start of use or the like, the contaminant gas can be well suppressed from flowing into the third internal cavity 61 where the measurement electrode 44 is located and contaminating the measurement electrode 44. Also, the temporary output variation amount with respect to the original value of the NOx concentration in the gas sensor 100 falls within a range permitted according to the measurement accuracy. For example, the output variation amount with respect to the NOx concentration of 100 ppm falls within a range of 20 ppm or less.

[0141] Note that, in outline, by using the above-described sensitivity characteristics, the output variation amount of the NOx current Ip2 at the time of the start of the operation of the gas sensor 100 in the atmosphere of the sample gas having a constant NOx concentration is calculated as follows. Figure 3 The change amount of the NOx current Ip2 shown in the graph (the difference between the final constant value and the value at the time of the temporary decrease) is converted into the change amount of the NOx concentration value, and the output variation amount can be calculated.

[0142] On the other hand, in the case of A / B < 0.001, the intrusion and escape of a gas other than the contaminant gas (for example, the measured gas, oxygen in the reference gas space SP) through the outer pump electrode lead portion 23P cannot be ignored, and the measurement accuracy deteriorates, and therefore, it is preferable that A / B be ≥ 0.001.

[0143] In addition, it is preferable that B be ≥ 700 x 10 －3 (cm －1 ). If the value of B is significantly lower than 700 x 10 －3 (cm －1 ), even if A / B < 1.00 is satisfied, the flow of the contaminant gas into the third internal cavity 61 through the measurement electrode lead portion 44P easily occurs. Note that, B ≥ 700 x 10－3 (cm －1 ) of the constitution Figure 1 and Figure 2 the constitution of the gas sensor shown in FIG. 1.

[0144] Preferably, the gas sensor 100 is constituted so as to satisfy the range of 0.03 ≤ A / B ≤ 0.29. In this case, the above-mentioned output variation is more favorably suppressed. For example, the output variation with respect to the NOx concentration of 500 ppm falls within the range of 10 ppm or less.

[0145] Preferably, the diffusion resistance of the main pump electrode lead portion 22P and the auxiliary pump electrode lead portion 51P is equal to or greater than the diffusion resistance B of the measurement electrode lead portion 44P. In this case, the diffusion resistance of the main pump electrode lead portion 22P and the auxiliary pump electrode lead portion 51P is also a value greater than the diffusion resistance of the outer side pump electrode lead portion 23P. Accordingly, the inflow of the contaminated gas to the first internal cavity 20 or the second internal cavity 40 through the main pump electrode lead portion 22P or the auxiliary pump electrode lead portion 51P is also favorably suppressed.

[0146] As explained above, according to the present embodiment, by constituting the gas sensor in such a manner that the diffusion resistance of the outer side pump electrode lead portion in the gas sensor is set to A, the diffusion resistance of the measurement electrode lead portion is set to B, and the relation of A / B < 1.00 is satisfied, the temporary output variation of the NOx concentration when the contaminated gas is generated in the reference gas space can be suppressed. Preferably, by constituting the gas sensor in such a manner that 0.03 ≤ A / B ≤ 0.29 is satisfied, the above-mentioned output variation can be more favorably suppressed.

[0147] Accordingly, the gas sensor in which the deterioration of the measurement accuracy caused by the generation of the contaminated gas in the reference gas space is favorably suppressed is realized.

[0148] Embodiment

[0149] As an embodiment, seven kinds of gas sensors 100 in which the combination of the magnitude of the diffusion resistance A of the outer side pump electrode lead portion 23P and the magnitude of the diffusion resistance B of the measurement electrode lead portion 44P is different within the range satisfying A / B < 1.00 (hereinafter, Embodiment 1 to Embodiment 7) were prepared, and the output variation of the NOx concentration at the time of use start was evaluated. Note that the diffusion resistance of the main pump electrode lead portion 22P and the auxiliary pump electrode lead portion 51P was equal to or greater than the diffusion resistance B of the measurement electrode lead portion 44P. In addition, the same evaluation was also performed on two kinds of gas sensors (hereinafter, Comparative Example 1 and Comparative Example 2) which were manufactured in the same manner as the embodiments except that A / B < 1.00 was not satisfied.

[0150] Figure 6is a graph for explaining the evaluation method of the output variation amount. Specifically, under a test gas atmosphere in which the temperature is 1050°C, the air ratio λ = 1.05, and the NOx concentration is 100 ppm, each gas sensor is started up, the heating of the heater section 70 is controlled so that the temperature of the rubber plug 106 eventually reaches 300°C and is held constant, while the NOx current Ip2 is continuously measured, whereby a curve Ip2(t) equivalent to a function of the NOx current Ip2 with respect to time is obtained. Figure 6

[0151] In all the gas sensors, although the degree of the obtained variation differs, the same curve Ip2(t) as the example shown in FIG. 6 is obtained. That is, for a certain period of time after the start of the operation of the gas sensor, the NOx current Ip2 is substantially constant, but then temporarily decreases, becomes substantially constant with the generation of the contaminated gas, and after a certain period of time, the NOx current Ip2 starts to increase and eventually reaches substantially constant at substantially the same value as at the start of the operation. Figure 3

[0152] However, the curve Ip2(t) is not always the same as the example shown in FIG. 6. Figure 6 In the curve Ip2(t), for easy understanding, the curve is illustrated as a broken line of a solid line, but actually, the curve Ip2(t) has a slight variation as schematically indicated by a broken line.

[0153] In the evaluation of the output variation amount with the above curve Ip2(t) as the object, first, an average value avl of the values of the NOx current Ip2 in a prescribed time Δtl (for example, 10 minutes) from the state of substantially constant after the decrease to the increase is determined. The average value is taken because the value that appears to be substantially constant is actually varied.

[0154] Next, a difference value Δl(t) between the value of the NOx current Ip2 after the state of substantially constant after the increase and the average value avl, and a difference value Δ2(t) between the maximum value and the minimum value of the NOx current Ip2 in the state of substantially constant after the increase are obtained. Both the above difference value Δl(t) and the difference value Δ2(t) are dynamic values that vary in correspondence with the variation of the value of the NOx current Ip2 after the increase, and thus are expressed as a function of time.

[0155] Further, the state in which the difference value Δl(t) and the difference value Δ2(t) satisfy the following equation (1) is judged as the state in which the variation accompanied by the contaminated gas is eliminated and the value of the NOx current Ip2 reaches substantially constant at the original value at the time when a prescribed observation time Δtz (for example, 60 minutes) elapses.

[0156] Δl(t) > 2 x Δ2(t) (1)

[0157] ​​On this basis, the average value av2 of the value of the NOx current Ip2 over a prescribed time Δt2 (for example, 10 minutes) immediately before the judgment time is determined, and the difference between the two is calculated.

[0158] Pump current variation amount = average value av2 - average value avl... (2)

[0159] Finally, the pump current variation amount calculated in equation (2) is converted into an NOx concentration value, and the output variation amount is thereby calculated.

[0160] Table 1 is a chart that shows the diffusion resistance A of the outer pump electrode lead portion 23P, the diffusion resistance B of the measurement electrode lead portion 44P, the ratio A / B of the two, the output variation amount, and the evaluation result (the determination result of good or bad) of the output variation amount of the gas sensor involved in Examples 1 to 7 and Comparative Examples 1 and 2.

[0161] Table 1

[0162]

[0163] In the determination of good or bad of the output variation amount, the gas sensor for which the obtained output variation amount is within 10 ppm is determined to be one for which the output variation caused by the generation of the contaminant gas at the start of use is well suppressed (A determination). For this gas sensor, "A" is written in the "Determination" column of Table 1.

[0164] In addition, the gas sensor for which the obtained output variation amount exceeds 10 ppm and is within 20 ppm is determined to be one for which the output variation caused by the generation of the contaminant gas at the start of use is suppressed to a degree that is permissible depending on the measurement accuracy (B determination). For this gas sensor, "B" is written in the "Determination" column of Table 1.

[0165] On the other hand, the gas sensor for which the obtained output variation amount exceeds 20 ppm is determined to be one for which the output variation caused by the generation of the contaminant gas at the start of use is not suppressed (F determination). For this gas sensor, "F" is written in the "Determination" column of Table 1.

[0166] As shown in Table 1, the gas sensors of Example 1, Example 2, and Example 5 are A determinations. In addition, the gas sensors of Example 3, Example 4, Example 6, and Example 7 are B determinations. On the other hand, the gas sensors of Comparative Example 1 and Comparative Example 2 are F determinations.

[0167] The above results show that in the gas sensor in which the ratio A / B of the diffusion resistance A of the outer pump electrode lead portion and the diffusion resistance B of the measuring electrode lead portion satisfies the range of A / B < 1.00, even if the contaminated gas is generated in the reference gas space SP at the start and the like, the temporary output variation amount with respect to the original value of the NOx concentration falls within the range permitted according to the measurement accuracy.

[0168] Further, it is also shown that in the case where the range of 0.03 ≤ A / B ≤ 0.29 is satisfied, the output variation amount is more favorably suppressed.

Claims

1. A gas sensor capable of monitoring a prescribed gas component in a measured gas, the gas sensor characterized by comprising: a sensor element having a long strip-shaped base portion composed of a solid electrolyte having oxygen ion conductivity, and a monitoring portion provided at one end portion side; and a housing in which the sensor element is housed and fixed, the housing comprising: an outer cylinder having a reference gas space in which a reference gas is present, the other end portion side of the sensor element protruding into the reference gas space; and a sealing member embedded in an end portion of the outer cylinder, sealing the reference gas space, the sensor element comprising: at least one oxygen partial pressure adjustment internal cavity which communicates with a measured gas inlet provided at the one end portion side under a prescribed diffusion resistance; a measurement internal cavity which further communicates with the at least one oxygen partial pressure adjustment internal cavity; an external cavity pump electrode provided at a position other than the at least one oxygen partial pressure adjustment internal cavity and the measurement internal cavity; at least one internal electrode provided facing the at least one oxygen partial pressure adjustment internal cavity, and capable of taking in or out oxygen between the corresponding at least one oxygen partial pressure adjustment internal cavity and the outside of the sensor element by applying a prescribed pump voltage between the at least one internal electrode and the external cavity pump electrode; a measurement electrode provided facing the measurement internal cavity, and capable of taking in or out oxygen between the measurement internal cavity and the outside of the sensor element by applying a prescribed pump voltage between the measurement electrode and the external cavity pump electrode; a first electrode lead portion comprising a first electrode through portion for electrically connecting the outside of the sensor element and the external cavity pump electrode, extending from the external cavity pump electrode, and a first through portion insulating layer covering the first electrode through portion; a ceramic layer covering at least the first electrode lead portion; and a second electrode lead portion comprising a second electrode through portion for electrically connecting the outside of the sensor element and the measurement electrode, extending from the measurement electrode, and a second through portion insulating layer covering the second electrode through portion, A / B < 1.

00. The diffusion resistance of the first electrode lead portion is set to A, and the diffusion resistance of the second electrode lead portion is set to B, where the unit of the diffusion resistance is cm －1 In the case where 2. The gas sensor according to claim 1, characterized in that, 0.03 ≤ A / B ≤ 0.

29.

3. The gas sensor according to claim 1 or 2, characterized in that, 4. The gas sensor according to any one of claims 1 to 3, characterized in that, B ≥ 700 x 10 －3 (cm －1 ). ​ The gas sensor further includes at least one third electrode lead portion including at least one third electrode conduction portion extending from the at least one inner electrode for electrically connecting the outside of the sensor element and the at least one inner electrode, and at least one third conduction portion insulating layer covering the at least one third electrode conduction portion, The diffusion resistance of the at least one third electrode lead portion is equal to or greater than the diffusion resistance of the second electrode lead portion.

5. The gas sensor according to any one of claims 1 to 4, wherein The cavity outer pump electrode and the first electrode lead portion are provided on one main surface of the base portion, The gas sensor further includes a porous body region covering the cavity outer pump electrode, The ceramic layer covers the first electrode lead portion and the porous body region.

6. The gas sensor according to any one of claims 1 to 5, wherein The at least one oxygen partial pressure adjusting internal cavity is a first internal cavity and a second internal cavity that are sequentially connected from the inlet at a prescribed diffusion resistance, The measurement internal cavity is a third internal cavity that is connected to the second internal cavity at a prescribed diffusion resistance, The at least one inner electrode is a main pump electrode provided in the first internal cavity and an auxiliary pump electrode provided in the second internal cavity.

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