Gas sensor

Abstract

The present application provides a gas sensor that can suppress deterioration of measurement accuracy even when contaminated 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 inside 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 (Zr02) 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 (in a 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 rubber plug as a seal member is inserted into the tip end thereof. A space surrounded by the above-mentioned outer cylinder and rubber plug is a reference gas space. The rubber plug has a through hole 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 present in the outer cylinder at the time when the rubber plug is inserted into the outer cylinder during the production of the gas sensor, but the atmosphere that enters the inside of the outer cylinder through the gap between the through hole of the rubber plug 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 other electrodes such as the measurement electrode provided in the sensor element.

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

[0007] Further, a gas sensor element is also known in which the width W1 of a measurement gas chamber into which a measurement gas is introduced and the width W2 of a porous diffusion resistance layer disposed toward a gas introduction port of the measurement gas chamber satisfy the relationship of W1 < W2 (see, for example, Patent Literature 3).

[0008] Prior Art Documents

[0009] Patent Literature

[0010] Patent Literature 1: Japanese Patent No. 6401644

[0011] Patent Literature 2: Japanese Patent No. 5832479

[0012] Patent Literature 3: Japanese Patent Application Laid-Open No. 2020-71128 SUMMARY

[0013] 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 adhering 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. Also, as a result of the contaminated gas reaching the reference electrode, it is possible that a condition occurs in which the reference potential, which should be kept constant, changes, and it is not possible to maintain the measurement accuracy of the gas sensor. It is considered that the above condition is more likely to occur in the case where the reference electrode lead-through portion is porous as disclosed in Patent Literature 2.

[0014] In the electrochemical pump unit composed of the outer electrode, the reference electrode, and the solid electrolyte disposed therebetween in the gas sensor disclosed in Patent Literature 1, by applying a prescribed voltage between the two electrodes, oxygen is able to be sucked from the outside of the element into the reference gas space, and by performing this sucking, even in the case where the reference gas is contaminated, it is possible to keep the reference potential constant.

[0015] However, the above contaminated gas not only reaches the reference electrode, but sometimes reaches the measurement electrode and the inner cavity closer to the gas introduction port via the electrode lead-through portion such as the measurement electrode lead-through portion. Then, the measurement gas that should have been introduced from the gas introduction 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 amount of intrusion is small, in the case where the concentration of the measurement object gas component is small, the influence cannot be ignored.

[0016] For example, Patent Document 3 discloses a scheme in which, in a case where the width Wl of the measured gas chamber is made smaller than in the past and 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 greatly change, the width of the electrode lead portion connected to each electrode is set to be relatively larger, and thus adjusted to a prescribed electrode impedance. In a 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 reaching via the lead portion increasing is improved.

[0017] In addition, using the porous electrode lead portion disclosed in Patent Document 2 also for the electrode lead portions other than the reference electrode lead portion makes it possible to suppress the amount of platinum used, and the cost is reduced, but the amount of the contaminated gas that intrudes via the electrode lead portion can increase.

[0018] The present application is implemented in view of the above-described problems, and aims to provide a gas sensor that can suppress deterioration of measurement accuracy even if contaminated gas is generated on the reference gas space side.

[0019] 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 inter-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 inner 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 inner electrode and the inter-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 inter-cavity pump electrode; at least one first electrode lead portion having at least one first electrode conductor 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 first conductor insulating layer covering the at least one first electrode conductor 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 at least one 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.

[0020] A second aspect of the present application is based on the gas sensor of the first aspect, characterized in that 0.02 ≤ A / B ≤ 0.27.

[0021] The gas sensor according to the third aspect of the present application, which is the gas sensor according to the first or second aspect, is characterized in that B ≥ 700 x 10 -3 (cm -1 ).

[0022] The gas sensor according to the fourth aspect of the present application, which is the gas sensor according to any one of the first to third aspects, is characterized in that the at least one internal cavity for oxygen partial pressure adjustment is a first internal cavity and a second internal cavity that are connected in series under a prescribed diffusion resistance from the inlet, the internal cavity for measurement is a third internal cavity that is connected to the second internal cavity under a prescribed diffusion resistance, and the at least one internal electrode is a main pump electrode provided in the first internal cavity and an auxiliary pump electrode provided in the second internal cavity.

[0023] Effects of the Invention

[0024] According to the first to fourth aspects of the present application, the temporary output variation of NOx concentration when a contaminated gas is generated in the reference gas space can be suppressed. Accordingly, a gas sensor in which deterioration of measurement accuracy due to generation of a contaminated gas in the reference gas space is well suppressed can be realized. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a main part cross-sectional view of the gas sensor 100 along the length direction.

[0026] Figure 2 is a vertical cross-sectional view along the element length direction that schematically shows an example of the configuration of the sensor element 101.

[0027] Figure 3 is an example of a graph showing the change in NOx current Ip2 when the gas sensor is automatically started when operating in an atmosphere of a sample gas with a constant NOx concentration, together with the change in temperature of the rubber plug 106.

[0028] Figure 4 is a plan view showing the arrangement of the electrode lead portion including the electrode lead-through portion extending from the main pump electrode 22, the auxiliary pump electrode 51, and the measurement electrode 44.

[0029] Figure 5 is a plan view showing the arrangement of the electrode lead portion including the electrode lead-through portion extending from the external pump electrode 23.

[0030] Figure 6 is a graph for explaining the evaluation method of the output variation.

[0031] Explanation of Symbols

[0032] 1-3…first to third substrate layers, 4…first solid electrolyte layer, 5…separation layer, 6…second solid electrolyte layer, 10…gas introduction port, 11…first diffusion speed control section, 13…second diffusion speed control section, 20…first internal cavity, 21…main pump unit, 22…inner pump electrode, 22P…main pump electrode lead section, 23…outer pump electrode, 23T…terminal electrode, 30…third diffusion speed control section, 40…second internal cavity, 41…measurement pump unit, 42…reference electrode, 43…reference gas introduction cavity, 44…measurement electrode, 44P…measurement electrode lead section, 48…atmosphere introduction layer, 50…auxiliary pump unit, 51…auxiliary pump electrode, 51P…auxiliary pump electrode lead section, 60…fourth diffusion speed control section, 61…third internal cavity, 70…heater section, 100…gas sensor, 101…sensor element, 102…protective cover, 103…fixing bolt, 104…outer cylinder, 105…connector, 106…rubber plug, 107…lead wire, 120…ring-fitting member, 151…contact member, H1-H4…through hole, SP…reference gas space. DETAILED DESCRIPTION

[0033] <Configuration of gas sensor>

[0034] Figure 1 is a main part cross-sectional view of a gas sensor 100 (more specifically, a main part cross-sectional view of a main body section thereof) along a length direction according to an embodiment of the present application. In the present embodiment, the gas sensor 100 detects a prescribed gas component (for example, NOx or the like) by means of a sensor element 101 provided inside thereof. It should be noted that, Figure 1 In the present embodiment, a vertical direction is shown as a z-axis direction, and the length direction of the gas sensor 100 coincides with the z-axis direction (the same applies to the following drawings).

[0035] The gas sensor 100 is mainly configured such that the sensor element 101, a ring-fitting member 120 ring-fitted around the sensor element 101, and a cylindrical body 130 further ring-fitted around the ring-fitting member 120 and housing the ring-fitting member 120 are covered by a protective cover 102, a fixing bolt 103, and an outer cylinder 104. In other words, in outline, the gas sensor 100 is configured such that the sensor element 101 penetrates through the axial center position inside the cylindrical body 130, and the ring-fitting member 120 is ring-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 a housing (housing member) of the sensor element 101.

[0036] The sensor element 101 is a long, columnar or thin plate-like member that has an element body formed of an oxygen-ion-conducting solid electrolyte ceramic such as zirconia as a main constituent material. The sensor element 101 is disposed on the central axis in the length direction of the cylindrical body 130. Hereinafter, the direction of extension of the central axis coinciding with the length direction of the cylindrical body 130 will be referred to as the axial direction. Figure 1 In the drawings that follow as well, the axial direction coincides with the z-axis direction.

[0037] The sensor element 101 is configured to have a gas introduction port on the side of the first end portion 101a, a monitoring portion provided with 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 within 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 inside the element in proportion to the concentration of the gas component.

[0038] A prescribed range in the length direction from the first end portion 101a of the surface of the sensor element 101 is covered by the protective film 111. The protective film 111, which is 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 in accordance with the purpose. However, Figure 1 The range of formation of the protective film 111 in each of the drawings that follow is merely an example, and the actual range of formation is appropriately determined in accordance with the specific structure of the sensor element 101.

[0039] The protective cover 102 is a substantially cylindrical outer member that protects the portion of the sensor element 101 that directly contacts the measured gas during use, that is, the first end portion 101a. 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 lower side (z-axis direction negative side) of the cylindrical body 130 in the drawing.

[0040] 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. It should be noted that Figure 1 The kind, 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 manner of the measured gas flowing into the inside of the protective cover 102.

[0041] 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 a 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 side of the protection cover 102 is exposed inside the exhaust pipe.

[0042] 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 (positive side in the z-axis direction) of the cylindrical body 130 in the drawing. Inside the outer cylinder 104, the connector 105 is arranged. 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 concentration of NOx is measured.

[0043] The connector 105 has a plurality of contact members 151 that come into contact with a plurality of terminal electrodes (not shown) 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 the controller 110 and various power supplies (not shown) outside the gas sensor 100. Figure 1 The controller 110 and the various power supplies are not shown in the drawing.

[0044] It should be noted that Figure 1 In the drawing, only two of the contact members 151 and the lead wire 107 are shown, but this is an example.

[0045] The cylindrical body 130 is a metal cylindrical member also referred to as a main body metal member. 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 fitted around the periphery of the grommet member 120 that is fitted around the periphery of the sensor element 101.

[0046] The cylindrical body 130 mainly has: a thick-walled main portion 130M that forms a cylindrical inner space by an inner surface 130a that is a cylindrical surface parallel to the axial direction; a reduced-diameter portion 131 that is provided at the lower end portion (z-axis direction negative side) in the drawing and is 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 portion in the axial direction in the drawing and is curved in a direction toward the axial center; and a locking portion 133 that protrudes to the outer side in the circumferential direction.

[0047] The chisel portion 132 is curved to press and fix (constrain) the ring-fitting member 120 (directly the second ceramic support 123) disposed inside from above in the drawing. Note that, as described later, the chisel portion 132 is curved after the ring-fitting member 120 is ring-fitted to the sensor element 101.

[0048] The ring-fitting member 120 includes: a first ceramic support 121, a press powder 122, and a second ceramic support 123.

[0049] 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 axial 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 ring-fitted to the sensor element 101. Note that the first ceramic support 121 is locked to the tapered surface 130b of the cylindrical body 130 from below in the drawing.

[0050] On the other hand, the press powder 122 is obtained by molding ceramic powder such as talc powder, and is disposed inside the cylindrical body 130 in a state of being ring-fitted around the sensor element 101 with the sensor element 101 inserted through the through-hole as with the first ceramic support 121 and the second ceramic support 123, and is further compressed to be integrated thereafter. More specifically, the ceramic particles that form the press powder 122 are surrounded by the first ceramic support 121 and the second ceramic support 123 and the cylindrical body 130, and are tightly packed in the space through which the sensor element 101 passes.

[0051] In the gas sensor 100, the fixation of the sensor element 101 and the ring-fitting member 120 inside the cylindrical body 130 is achieved by the locking by the tapered surface 130b of the first ceramic support 121 and the pressing from above in the drawing by the chisel portion 132 of the second ceramic support 123. Furthermore, 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 press powder 122.

[0052] <Outline configuration of sensor element>

[0053] 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 figure, 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.

[0054] 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-conducting solid electrolyte (for example, yttria-stabilized zirconia (YSZ) or the like) from the lower side in the drawing. In addition, the solid electrolytes forming the six layers are dense and airtight solid electrolytes. Hereinafter, the six layers will be collectively referred to as the solid electrolyte layers. Figure 2 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 containing the solid electrolyte is collectively referred to as the base portion.

[0055] The above-described sensor element 101 is manufactured, for example, by performing a prescribed process on a ceramic green sheet corresponding to each layer and printing a circuit pattern (for example, an electrode, an electrode lead-through portion, a lead-through portion insulating layer, and the like), and then stacking and firing them to integrate them.

[0056] On 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, a first diffusion speed control portion 11, a buffer space 12, a second diffusion speed control portion 13, a first internal cavity 20, a third diffusion speed control portion 30, a second internal cavity 40, a fourth diffusion speed control portion 60, and a third internal cavity 61 that also function as the gas introduction port 10 are formed in the order of successive communication.

[0057] 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 provided in a manner of hollowing out the separation layer 5, in which the upper portion is demarcated by the lower surface of the second solid electrolyte layer 6, the lower portion is demarcated by the upper surface of the first solid electrolyte layer 4, and the side portion is demarcated by the side surface of the separation layer 5. Note that the gas introduction port 10 can also be provided in a manner of hollowing out the separation 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 formed adjacently in a manner of being more inside than the gas introduction port 10.

[0058] 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 long slits (lengthwise slits in the direction perpendicular to the drawing). Further, the portion from the gas introduction port 10 to the third internal cavity 61, which is the innermost internal cavity, is also referred to as a gas flow-through portion.

[0059] 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 separation layer 5 and in which the side portion is 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 to a reference gas space SP inside the outer cylinder 104, and an atmosphere of reference gas is introduced from the reference gas space SP.

[0060] The atmosphere introduction layer 48 is a layer composed of porous alumina, and the 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.

[0061] The reference electrode 42 is an electrode formed in a manner of being sandwiched by the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4, and, as described above, the atmosphere 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 reference electrode 42 can be used to measure the oxygen concentration (oxygen partial pressure) in the first internal cavity 20 and the second internal cavity 40.

[0062] In the gas flow-through portion, the gas introduction port 10 (the first diffusion speed control portion 11) is a portion that is open 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.

[0063] The first diffusion speed control portion 11 is a portion that applies a prescribed diffusion resistance to the introduced measured gas.

[0064] 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.

[0065] The second diffusion rate control section 13 is a section that applies a prescribed diffusion resistance to the measured gas introduced from the buffer space 12 to the first internal cavity 20.

[0066] When the measured gas is introduced from the outside of the sensor element 101 into the first internal cavity 20, the measured gas introduced sharply from the gas introduction port 10 into the inside of the sensor element 101 due to the pressure fluctuation of the measured gas in the outside space (pulsation of 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 fluctuation of the measured gas is eliminated by the first diffusion rate control section 11, the buffer space 12, and the second diffusion rate control section 13. Thus, the concentration fluctuation of the measured gas introduced to the first internal cavity 20 reaches almost negligible levels.

[0067] 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 section 13. The main pump unit 21 operates to adjust the oxygen partial pressure.

[0068] 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 a 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 section 22a provided on 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 provided on the upper surface (one main surface of the sensor element 101) of the second solid electrolyte layer 6 in a region corresponding to the top electrode section 22a in a manner exposed to the outside space.

[0069] The inner pump electrode 22 is formed in the solid electrolyte layers (the second solid electrolyte layer 6 and the first solid electrolyte layer 4) partitioning the first internal cavity 20 upward and downward. Specifically, the top electrode section 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 the bottom electrode section 22b is formed on the upper surface of the first solid electrolyte layer 4 constituting the bottom surface. The top electrode section 22a and the bottom electrode section 22b are connected by a conductive section provided on the side wall surface (inner surface) of the separation layer 5 constituting the two side wall sections of the first internal cavity 20 (omitted from the drawing).

[0070] The top electrode portion 22a and the bottom electrode portion 22b are provided 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.

[0071] The inner pump electrode 22 and the outer pump electrode 23 are formed as porous metal ceramic electrodes. In particular, the inner pump electrode 22, which contacts the gas to be measured, is formed using a material in which the reduction ability with respect to the NOx component in the gas to be measured is weakened. For example, as a metal ceramic electrode having a porosity of 5% to 40% and containing Au at a content of about 0.6 wt% to 1.4 wt%, an Au-Pt alloy and ZrO2 are 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.

[0072] On the other hand, the outer pump electrode 23 is formed in a rectangular shape in plan view, for example, as a metal ceramic electrode of Pt or an alloy thereof and ZrO2.

[0073] With respect to the main pump unit 21, the 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 the 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 or oxygen from the outside 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.

[0074] 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 separation layer 5, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42.

[0075] The oxygen concentration (oxygen partial pressure) in the first internal cavity 20 is obtained 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.

[0076] Further, the controller 110 performs feedback control of the main pump voltage Vp0 so that the electromotive force V0 is constant, whereby the main pump current Ip0 is controlled. As a result, the oxygen concentration in the first internal cavity 20 is maintained at a predetermined constant value.

[0077] The third diffusion rate control section 30 is a section that applies a prescribed diffusion resistance to the measured gas after the oxygen concentration (oxygen partial pressure) thereof is controlled by the action of the main pump unit 21 in the first internal cavity 20, and introduces the measured gas into the second internal cavity 40.

[0078] 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.

[0079] In the second internal cavity 40, the measured gas introduced through the third diffusion rate control section 30 after the oxygen concentration (oxygen partial pressure) thereof is adjusted in advance in the first internal cavity 20 is further subjected to adjustment of the oxygen partial pressure by the auxiliary pump unit 50.

[0080] The auxiliary pump unit 50 is an auxiliary electrochemical pump unit composed of an auxiliary pump electrode 51, the 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 the second solid electrolyte layer 6, in which the auxiliary pump electrode 51 has a top electrode section 51a provided on the lower surface of the second solid electrolyte layer 6 so as to face substantially the entire second internal cavity 40.

[0081] 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 section 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 section 51b is formed in the first solid electrolyte layer 4 constituting the bottom surface of the second internal cavity 40. Both the top electrode section 51a and the bottom electrode section 51b are formed in a rectangular shape in plan view, and are connected (omitted from the drawing) by a conductive section provided in the side wall surface (inner surface) of the separation layer 5 constituting the side wall sections of the second internal cavity 40.

[0082] Further, the auxiliary pump electrode 51 is also formed of a material that has reduced reduction ability with respect to the NOx component in the measured gas, like the inner pump electrode 22.

[0083] With respect to the auxiliary pump unit 50, under the control of the controller 110, a desired voltage (auxiliary pump voltage) Vp1 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 can be sucked from the outside space into the second internal cavity 40.

[0084] 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.

[0085] The auxiliary pump unit 50 pumps 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 lower partial pressure that has substantially no influence on the measurement of NOx.

[0086] 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, thereby controlling the gradient of the oxygen partial pressure of the measured gas introduced from the third diffusion rate control section 30 into the second internal cavity 40 to be constant at all times. 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 less due to the effects of the main pump unit 21 and the auxiliary pump unit 50.

[0087] The fourth diffusion rate control section 60 is a site that applies a prescribed diffusion resistance to the measured gas in which the 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.

[0088] 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 rate control section 60. In the third internal cavity 61, the measurement of the NOx concentration is performed by the action of the pump unit 41. The third internal cavity 61 is introduced with the measured gas in which the 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.

[0089] 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 disposed 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.

[0090] 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.

[0091] 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.

[0092] In addition, in order to detect the oxygen partial pressure around the measurement electrode 44, a measurement sensor unit 82 as 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] Note that, Figure 2 In the sensor element 101, in order to simplify the illustration, only the wiring for electrically connecting each part outside the electrodes and sensor elements 101 that constitute the various pump units and sensor units is schematically illustrated. However, in the actual sensor element 101, an electrode lead-through portion that links the electrodes of each pump unit and sensor unit to the terminal electrode is provided on the inside or side surface. Hereinafter, the details of the electrode lead-through portion including the electrode lead-through portion are described.

[0097] The sensor element 101 also has a heater portion 70 that performs a temperature adjustment function of heating and maintaining the temperature of the sensor element 101 in order to improve the oxygen ion conductivity of the solid electrolyte that constitutes the base portion.

[0098] 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 In the present embodiment, the heater resistance detection lead-through portion is omitted from the illustration. In addition, the heater portion 70 is embedded in the base portion of the sensor element 101 except for the heater electrode 71.

[0099] 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).

[0100] The heater member 72 is a resistance heating body provided between the second substrate layer 2 and the third substrate layer 3. From Figure 2The heater member 72 is formed of Pt or mainly 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 so as 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.

[0101] For the sensor element 101, a current is passed through the heater electrode 71 to the heater member 72, whereby the heater member 72 is heated, 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.

[0102] The degree of heating (heater temperature) of the heater member 72 is grasped by the magnitude of the resistance value (heater resistance) of the heater member 72.

[0103] Note that, although Figure 2 In the gas sensor 100 having the above-described configuration, an electrode protection layer covering the outer pump electrode 23 can be provided on one main surface side of the sensor element 101 for the purpose of protecting the outer pump electrode 23.

[0104] When the concentration of NOx is measured in the gas sensor 100 having the above-described configuration, 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 to 1 ppm) where the measurement of NOx is substantially not affected is introduced into the third internal cavity 61.

[0105] Then, at the measurement electrode 44, NOx in the measured gas that has reached there is reduced, whereby oxygen is generated. The oxygen is sucked by the measurement pump unit 41, and the NOx current Ip2 that flows at the time of the sucking has a certain functional relationship (hereinafter referred to as sensitivity characteristic) with the concentration of NOx in the measured gas.

[0106] Before the gas sensor 100 is actually used, the above-mentioned sensitivity characteristics are determined in advance using a plurality of kinds of sample gases of which the NOx concentrations are known, and the data thereof are 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 flowing in correspondence with the NOx concentration in the gas to be measured is supplied to the controller 110. In the controller 110, based on the value and the determined sensitivity characteristics, the NOx concentration is sequentially calculated, and is outputted in the form of the NOx sensor detection value. Accordingly, in the gas sensor 100, the NOx concentration in the gas to be measured can be grasped approximately in real time.

[0107] <Generation of Contaminant Gas in Reference Gas Space>

[0108] In the case of a gas sensor having a configuration in which a reference gas space SP is surrounded by an outer cylinder 104 and a rubber plug 106 and which is used in a high-temperature environment, as in the gas sensor 100 according to the present embodiment, 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 a high-temperature gas condition or heat around the main body portion cannot be exhausted.

[0109] Figure 3 is an example of a graph showing a change in the NOx current Ip2 at the time when the above-mentioned gas sensor is automatically started to operate in an atmosphere of a sample gas of 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 is approximately constant.

[0110] 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 to be described later. Also, it is considered that the value of the NOx current Ip2 increases after a certain time elapses because the outer cylinder 104 and the rubber plug 106 are sufficiently heated, as a result of which the contaminant gas is completely released.

[0111] The above-mentioned 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

[0112] <Configuration of Electrode Lead Portion> ​

[0113] In the gas sensor 100 according to the present embodiment, by causing the electrode lead portion in the sensor element 101 to satisfy a prescribed condition, the generation of a contaminant gas in the reference gas space SP caused by the electrode lead portion is suppressed Figure 3 The variation in the NOx current Ip2 shown above has an effect on the measurement accuracy of the NOx concentration.

[0114] Figure 4 is a plan view showing the arrangement of the electrode lead portion including the self-pumping electrode 22 (more specifically, the bottom electrode portion 22b), the auxiliary pumping electrode 51 (more specifically, the bottom electrode portion 51b), and the measurement electrode 44, each of which extends. In addition, 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.

[0115] 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. Furthermore, the main pumping electrode lead portion 22L extends from the bottom electrode portion 22b toward the second end portion 101b, the auxiliary pumping electrode lead portion 51L extends from the bottom electrode portion 51b toward the second end portion 101b, and the measurement electrode lead portion 44L extends from the measurement electrode 44 toward the second end portion 101b. On the other hand, the outer pumping electrode 23 is provided on the second solid electrolyte layer 6. Furthermore, the outer pumping electrode lead portion 23L extends from the outer pumping electrode 23 toward the second end portion 101b.

[0116] The main pumping electrode lead portion 22L, the auxiliary pumping electrode lead portion 51L, the measurement electrode lead portion 44L, and the outer pumping electrode lead portion 23L are each surrounded by the main pumping electrode lead portion insulating layer 22I, the auxiliary pumping electrode lead portion insulating layer 51I, the measurement electrode lead portion insulating layer 44I, and the outer pumping electrode lead portion insulating layer 23I. By this, insulation between each of the electrode lead portions and the solid electrolyte constituting the sensor element 101 is achieved.

[0117] The outer pumping electrode lead portion 23L is connected to the terminal electrode 23T provided in the second end portion 101b. Note that, Figure 5 In the present embodiment, the outer pumping electrode lead portion insulating layer 23I is present in a straight line (in a linear shape) along the outer pumping electrode lead portion 23L, but the outer pumping electrode lead portion insulating layer 23I can be provided in a plane (in a layered shape) between the outer pumping electrode 23 and the terminal electrode 23T.

[0118] On the other hand, the main pump electrode lead-through portion 22L, the auxiliary pump electrode lead-through portion 51L, and the measurement electrode lead-through portion 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-through portion 22L, the auxiliary pump electrode lead-through portion 51L, and the measurement electrode lead-through portion 44L are each surrounded by the main pump electrode lead-through portion insulating layer 22I, the auxiliary pump electrode lead-through portion insulating layer 51I, and the measurement electrode lead-through portion insulating layer 44I, and after being connected in either of the upper and lower directions in the thickness direction via a via hole 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-through portion by the lead-through portion insulating layer includes a mode in which the electrode lead-through portion is covered by the lead-through portion insulating layer and a mode in which the electrode lead-through portion is sandwiched by the lead-through portion insulating layer.

[0119] The main pump electrode lead-through portion 22L, the auxiliary pump electrode lead-through portion 51L, the measurement electrode lead-through portion 44L, and the outer pump electrode lead-through portion 23L are preferably formed of platinum. In addition, the main pump electrode lead-through portion insulating layer 22I, the auxiliary pump electrode lead-through portion insulating layer 51I, the measurement electrode lead-through portion insulating layer 44I, and the outer pump electrode lead-through portion insulating layer 23I are preferably formed of alumina.

[0120] Hereinafter, a region including the main pump electrode lead-through portion 22L and the main pump electrode lead-through portion 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-through portion 51L and the auxiliary pump electrode lead-through portion 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. Further, a region including the measurement electrode lead-through portion 44L and the measurement electrode lead-through portion 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.

[0121] In other words, the main pump electrode lead-through portion 22L and the main pump electrode lead-through portion insulating layer 22I are inserted through the main pump electrode lead portion 22P. The auxiliary pump electrode lead-through portion 51L and the auxiliary pump electrode lead-through portion insulating layer 51I are inserted through the auxiliary pump electrode lead portion 51P. The measurement electrode lead-through portion 44L and the measurement electrode lead-through portion insulating layer 44I are inserted through the measurement electrode lead portion 44P.

[0122] 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 farthest from the gas inlet 10 in the gas flow passage portion of the sensor element 101 is greater than the diffusion resistances of the main pump electrode lead portion 22P and the auxiliary pump electrode lead portion 51P connected to the inner side pump electrodes 22 and the auxiliary pump electrodes 51 located closer to the gas inlet 10 than the measurement electrode 44 in the gas flow passage portion.

[0123] That is, in the gas sensor 100 according to the present embodiment, when the diffusion resistances of the main pump electrode lead portion 22P and the auxiliary pump electrode lead portion 51P are set to A and the diffusion resistance of the measurement electrode lead portion 44P is set to B, the ratio A / B satisfies the relationship of A / B < 1.00.

[0124] Here, the diffusion resistance (diffusion resistance of the lead-through portion) of each electrode lead portion is the diffusion resistance applied 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 the electrode lead-through portion insulating layer, to 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, between the electrode lead-through portion insulating layer and the solid electrolyte around it, all contribute to the diffusion resistance.

[0125] For example, the size of the diffusion resistance of each 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.

[0126] Satisfaction of A / B < 1.00 means that, compared to a gas sensor having the same configuration except that the condition is not satisfied, the outflow of the contaminant gas through the measurement electrode lead portion 44P is less likely to occur than the outflow of the contaminant gas through the main pump electrode lead portion 22P and the auxiliary pump electrode lead portion 51P.

[0127] In the gas sensor 100 according to the present embodiment, the measured gas introduced from the gas introduction port 10 reaches the third internal cavity 61 after sequentially taking in oxygen in the first internal cavity 20 and the second internal cavity 40. Normally, the main pump current Ip0 flowing through the main pump unit 21 and the auxiliary pump current Ip1 flowing through the auxiliary pump unit 50 are greater than the NOx current Ip2 flowing through the measurement pump unit 41. 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 or the auxiliary pump current Ip1 caused by the intrusion of the contaminant gas into 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 smaller than the proportion of the output variation of the NOx current Ip2 caused by the intrusion of the contaminant gas into the third internal cavity 61 through the measurement electrode lead portion 44P.

[0128] By satisfying A / B < 1.00, the output variation of the NOx current Ip2 caused by the intrusion of the contaminant gas is further suppressed in a case where the intrusion of the contaminant gas into the main pump electrode lead portion 22P or the auxiliary pump electrode lead portion 51P is prioritized.

[0129] 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 use start or the like, the contaminant gas flowing into the third internal cavity 61 where the measurement electrode 44 is located and contaminating the measurement electrode 44 can be well suppressed. 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.

[0130] Note that, in summary, by using the sensitivity characteristics described above, the output variation amount of the NOx current Ip2 at the time of 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 variation amount of the NOx current Ip2 shown in the graph (the difference between the final constant value and the value at the time of temporary decrease) is converted into the variation amount of the NOx concentration value, and the output variation amount can be calculated.

[0131] On the other hand, in a case where A / B < 0.001, the gas other than the contaminant gas (for example, the measured gas, oxygen in the reference gas introduction space SP) between the reference gas introduction space SP and the first internal cavity 20 or the second internal cavity 40 cannot be ignored, and the measurement accuracy deteriorates, and therefore, it is preferable that A / B be 0.001 or greater.

[0132] 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 , then even if A / B < 1.00 is satisfied, inflow of the contaminated gas to the third internal cavity 61 through the measuring electrode lead portion 44P is likely to occur. Note that the configuration of B ≥ 700 x 10 -3 cm -1 is Figure 1 a configuration commonly employed in the gas sensor shown in Figure 2 .

[0133] Preferably, the gas sensor 100 is configured to satisfy the range of 0.02 ≤ A / B ≤ 0.27. In this case, the above-described 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.

[0134] As explained above, according to the present embodiment, by configuring the gas sensor in such a manner that the diffusion resistance of the main pump electrode lead portion and the diffusion resistance of the auxiliary pump electrode lead portion in the gas sensor are set to A, and the diffusion resistance of the measuring electrode lead portion is set to B, and the relationship 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 configuring the gas sensor in such a manner that 0.02 ≤ A / B ≤ 0.27 is satisfied, the above-described output variation can be more favorably suppressed.

[0135] Accordingly, a 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.

[0136] Example

[0137] As an example, 10 kinds of gas sensors 100 in which the combination of the magnitude of the diffusion resistance A of the main pump electrode lead portion 22P and the magnitude of the diffusion resistance B of the measuring electrode lead portion 44P is different within the range in which A / B < 1.00 is satisfied (hereinafter, Examples 1 to 10) 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 auxiliary pump electrode lead portion 51P was made substantially the same as the diffusion resistance A of the main pump electrode lead portion 22P. In addition, the same evaluation was also performed on two kinds of gas sensors (hereinafter, Comparative Examples 1 and 2) which were made in the same manner as the examples except that A / B < 1.00 was not satisfied.

[0138] 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

[0139] In all the gas sensors, although the degree of the obtained variation differs, the same curve Ip2(t) as the example shown in Figure 3

[0140] However, Figure 6 In the curve Ip2(t), for easy understanding, the curve is illustrated as a broken line, but actually, the curve Ip2(t) has a slight variation which is schematically indicated by a dotted line.

[0141] 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 where the approximately constant state after the decrease is changed to the increase is determined. The average value is taken because the value which appears to be approximately constant is actually varied.

[0142] Next, a difference value Δl(t) between the value of the NOx current Ip2 after the state where the increase is changed to the approximately constant state 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 approximately constant state after the increase is changed are obtained. Both the above difference value Δl(t) and the difference value Δ2(t) are dynamic values which 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.

[0143] Further, the state where the difference value Δl(t) and the difference value Δ2(t) satisfy the following equation (1) is judged as the state where the variation accompanied by the contamination gas is eliminated and the value of the NOx current Ip2 reaches the approximately constant state with the original value at the time when a prescribed observation time Δtz (for example, 60 minutes) elapses.

[0144] Δl(t) > 2 x Δ2(t) (1)

[0145] ​​On this basis, the average value av2 of the value of the NOx current Ip2 over a prescribed time Δt2 (for example, 10 minutes) before the judgment time is determined, and the difference between the two is calculated.

[0146] Pump current variation amount = average value av2 - average value avl... (2)

[0147] 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.

[0148] Table 1 is a chart that shows the diffusion resistance A of the main pump electrode lead portion (in Table 1, "main pump electrode lead portion") 22P, 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 (determination result of good or bad) of the gas sensors involved in Examples 1 to 10 and Comparative Examples 1 and 2.

[0149] Table 1

[0150]

[0151] In the determination of good or bad of the output variation amount, the gas sensor for which the obtained output variation amount is 10 ppm or less is determined to have had the output variation caused by the generation of the contaminant gas at the start of use well suppressed (A determination). For this gas sensor, "A" is written in the "determination" column of Table 1.

[0152] In addition, the gas sensor for which the obtained output variation amount exceeds 10 ppm and is 20 ppm or less is determined to have had the output variation caused by the generation of the contaminant gas at the start of use suppressed to an extent that is permissible depending on the measurement accuracy (B determination). For this gas sensor, "B" is written in the "determination" column of Table 1.

[0153] On the other hand, the gas sensor for which the obtained output variation amount exceeds 20 ppm is determined to have had the output variation caused by the generation of the contaminant gas at the start of use not suppressed (F determination). For this gas sensor, "F" is written in the "determination" column of Table 1.

[0154] As shown in Table 1, the gas sensors of Examples 3 to 5, Example 7, and Example 9 are A determinations. In addition, the gas sensors of Example 1, Example 2, Example 6, Example 8, and Example 10 are B determinations. On the other hand, the gas sensors of Comparative Example 1 and Comparative Example 2 are F determinations.

[0155] The above results show that in the gas sensor in which the ratio A / B of the diffusion resistance A of the main pump electrode lead portion 22P and the diffusion resistance B of the measuring electrode lead portion 44P 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.

[0156] Further, it is also shown that in the case where the range of 0.02 ≤ A / B ≤ 0.27 is satisfied, the output variation amount is more favorably suppressed.

Claims

1. A gas sensor capable of monitoring a specified gas component in a gas to be measured. The gas sensor is characterized by having: A sensor element having a strip-shaped substrate made of a solid electrolyte with oxygen ion conductivity, and a monitoring section at one end; and The sensor element is housed and fixed inside the housing. The housing includes: An outer cylinder having an internal reference gas space containing a reference gas, and the other end of the sensor element protruding into the reference gas space; and A sealing component, embedded in the end of the outer cylinder, seals the reference gas space. The sensor element includes: At least one internal cavity for adjusting oxygen partial pressure, which is connected to the inlet of the gas to be measured provided on one end side under a specified diffusion resistance. The measuring internal cavity is further connected to the at least one oxygen partial pressure adjustment internal cavity; An external pump electrode is disposed in a location other than the at least one internal cavity for adjusting oxygen partial pressure and the internal cavity for measuring. At least one inner electrode is disposed facing the at least one internal cavity for adjusting oxygen partial pressure. By applying a predetermined pump voltage between the at least one inner electrode and the pump electrode outside the cavity, oxygen can be drawn in or drawn out between the corresponding internal cavity for adjusting oxygen partial pressure and the outside of the sensor element. A measuring electrode is disposed facing the internal cavity for measuring. By applying a predetermined pump voltage between the measuring electrode and the external pump electrode of the cavity, oxygen can be drawn in or drawn out between the internal cavity for measuring and the outside of the sensor element. At least one first electrode lead portion, the at least one first electrode lead portion having at least one first 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 first conductive portion insulating layer covering the at least one first electrode conductive portion; as well as The second electrode lead portion includes a second electrode conductive portion extending from the measuring electrode, capable of electrically connecting the exterior of the sensor element and the measuring electrode, and a second conductive portion insulating layer covering the second electrode conductive portion. Let A be the diffusion resistance of the at least one first electrode lead portion, and let B be the diffusion resistance of the second electrode lead portion, where the unit of diffusion resistance is cm. －1 In this case, A / B < 1.

00.

2. The gas sensor according to claim 1, characterized in that, 0.02≤A / B≤0.

27.

3. The gas sensor according to claim 1 or 2, characterized in that, B≥700×10 －3 (cm －1 )。 4. The gas sensor according to any one of claims 1 to 3, 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 used for measurement is a third internal cavity that communicates with the second internal cavity under a specified diffusion resistance. The at least one inner electrode is a main pump electrode disposed in the first inner cavity and an auxiliary pump electrode disposed in the second inner cavity.

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