Gas sensor and concentration correction method in gas sensor

Abstract

The present application provides a kind of gas sensor and concentration correction method in gas sensor, even in the case where reference gas space side produces contaminated gas, can inhibit the determination precision degradation.Gas sensor control device has: concentration determination unit, which is based on the determination pump current corresponding to the concentration of the specified gas component between the determination electrode and the pump electrode outside the cavity by applying a specified pump voltage, to determine the concentration of the specified gas component;And correction processing unit, which corrects the concentration of the specified gas component determined in the concentration determination unit, the correction processing unit corrects the concentration of the specified gas component based on the correlation between the predetermined bias current value or the normalized value of bias current value and the output variation generated by the determination pump current when the gas sensor starts, the bias current value is the size of the determination pump current when the measured gas containing the specified gas component flows.

Description

Technical Field

[0001] This invention relates to gas sensors having ceramic sensor elements, and more particularly to ensuring measurement accuracy in gas sensors. Background Technology

[0002] Previously, as a device for measuring the concentration of specified gas components in combustion gases and exhaust gases in internal combustion engines such as automobile engines, gas sensors using oxygen ion conductive solid electrolyte ceramics such as zirconium oxide (ZrO2) as sensor elements were well known.

[0003] The gas sensor typically has a main body configured such that a long, strip-shaped ceramic sensor element (detection element) is fixed inside a metal housing (hollow part) by a ceramic support and a ceramic powder compact, such as talc. The powder compact ensures an airtight seal between one end of the gas inlet, which is used to introduce the gas to be measured into the element containing the measuring electrode, and another end of the reference gas (atmosphere) being introduced (see, for example, Patent Document 1).

[0004] The other end of the housing component is a cylindrical part, also known as the outer cylinder, with a rubber stopper embedded at its end as a sealing element. The space surrounded by the outer cylinder and the rubber stopper is the reference gas space. The rubber stopper has through holes for inserting several leads for connecting the central element to external electrical connections. The reference gas is usually the atmosphere present in the outer cylinder at the time the rubber stopper is embedded during the manufacturing process of the gas sensor; however, the atmosphere that subsequently enters the outer cylinder through the gap between the through holes of the rubber stopper and the leads can also serve as the reference gas.

[0005] Additionally, at the other end of the sensor element, a reference gas is introduced into the element from a reference gas space, and a reference electrode providing the reference potential is configured to contact the reference gas. By contacting the reference electrode with a reference gas of constant oxygen concentration, the reference potential is kept constant, thereby generating a potential difference between the reference electrode and other electrodes provided on the sensor element, such as the measuring electrode, corresponding to the atmosphere surrounding the electrode.

[0006] Various electrodes disposed in a sensor element are electrically connected to a connection terminal provided at the end of the element through an electrode conductive portion disposed inside the element or on the side of the element. Sensor elements in which the reference electrode conductive portion connecting the reference electrode and the electrode pad that serves as the connection terminal is porous are also known (see, for example, Patent Document 2).

[0007] In addition, gas sensor elements are known in which the width W1 of the gas chamber to which the gas to be measured is introduced and the width W2 of the porous diffusion resistance layer disposed at the gas inlet toward the gas chamber to be measured satisfy the relationship W1 < W2 (see, for example, Patent Document 3).

[0008] Existing technical documents

[0009] Patent documents

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

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

[0012] Patent Document 3: Japanese Patent Application Publication No. 2020-71128 Summary of the Invention

[0013] The gas sensor disclosed in Patent Document 1 has its main body positioned in the exhaust path from the engine and used in an exhaust atmosphere, and is used in a high-temperature environment, such as when the sensor element itself is heated by a heater. Therefore, when the main body is heated to a high temperature at the start of use, contaminating gas may sometimes be generated due to the evaporation of oil adhering to the inner surface of the outer cylinder or gas generated from the rubber stopper, and the reference gas may be contaminated by this contaminating gas. Furthermore, as a result of this contaminating gas reaching the reference electrode, the reference potential, which should be kept constant, may change, making it impossible to maintain the measurement accuracy of the gas sensor. It is believed that the above situation is more likely to occur when the reference electrode conductive part, as disclosed in Patent Document 2, is made of porous material.

[0014] In the gas sensor disclosed in Patent Document 1, an electrochemical pump unit consisting of an outer electrode, a reference electrode, and a solid electrolyte disposed between the two can draw oxygen from outside the element into the reference gas space by applying a predetermined voltage between the two electrodes. By performing this drawing, the reference potential can be kept constant even if the reference gas is contaminated.

[0015] However, the aforementioned contaminating gases not only reach the reference electrode but sometimes also reach the measuring electrode and the internal cavity closer to the gas inlet via electrode conductive parts such as the measuring electrode conductive part. Thus, the gas to be measured, which should have entered through the gas inlet and reached the measuring electrode after the oxygen concentration was adjusted to the specified value, is contaminated by the contaminating gas that enters through the conductive parts, potentially degrading the measurement accuracy of the gas sensor. Even if the amount of intrusion is small, its effect cannot be ignored when the concentration of the target gas component is low.

[0016] For example, Patent Document 3 discloses a scheme in which, when the width W1 of the gas chamber being measured is smaller than before, and thus the width of the electrodes disposed on the gas sensor element is also smaller, the width of the electrode conductive portion connected to each electrode is set to be relatively larger in order to prevent a significant change in the impedance of the electrode portion, including the lead portion, thereby adjusting to a predetermined electrode impedance. When the width of the lead portion is increased in this way, the diffusion resistance of the lead portion decreases, increasing the likelihood that the amount of contaminating gas reaching the sensor via the lead portion will increase.

[0017] In addition, the porous electrode conductive part disclosed in Patent Document 2 is also used in electrode conductive parts other than the reference electrode conductive part. This can suppress the amount of platinum used and reduce costs. However, the amount of polluting gas that enters through the electrode conductive part may increase.

[0018] The present invention was made in view of the above-mentioned problems, and its object is to provide a gas sensor that can suppress the degradation of measurement accuracy even when contaminating gas is generated on the reference gas space side.

[0019] To address the aforementioned issues, the first aspect of the present invention is a gas sensor capable of monitoring a specified gas component in a measured gas, characterized by comprising: a sensor element having a strip-shaped substrate made of an oxygen-ion-conductive solid electrolyte, and a monitoring section at one end; a housing in which the sensor element is housed and fixed; and a controller controlling the operation of the gas sensor, wherein the housing comprises: an outer cylinder having a reference gas space containing a reference gas, and the other end of the sensor element... The sensor element comprises: a side protrusion into the reference gas space; and a sealing member embedded in the end of the outer cylinder to seal the reference gas space. The sensor element includes: at least one internal cavity for adjusting oxygen partial pressure, which communicates with an inlet of the gas to be measured located at one end side under a specified diffusion resistance; a measuring internal cavity further communicating with the at least one internal cavity for adjusting oxygen partial pressure; and an external pump electrode disposed in addition to the at least one internal cavity for adjusting oxygen partial pressure and the... The controller comprises: a portion other than the internal cavity for measurement; a measuring electrode disposed facing the internal cavity for measurement; a measuring pump unit in which a measuring pump current corresponding to the concentration of the specified gas component flows between the measuring electrode and the external pump electrode of the cavity by applying a predetermined pump voltage; and a measuring electrode lead portion having a measuring electrode conductive portion extending from the measuring electrode and capable of electrically connecting the outside of the sensor element and the measuring electrode, and a measuring conductive portion insulating layer covering the measuring electrode conductive portion. The controller comprises: a concentration determination unit that determines the concentration of the specified gas component based on the measuring pump current; and a correction processing unit that corrects the concentration of the specified gas component determined by the concentration determination unit, the correction processing unit correcting the concentration of the specified gas component based on a predetermined bias current value or a standardized value of the bias current value and the output variation generated by the measuring pump current when the gas sensor is started, the bias current value being the magnitude of the measuring pump current when the measured gas without the specified gas component flows.

[0020] The second aspect of the present invention is based on the gas sensor involved in the first aspect, characterized in that the correction processing unit includes a temperature estimation unit, which estimates the temperature of the sealing component based on predetermined temperature estimation information, and corrects the concentration of the specified gas component when it is determined that the temperature of the sealing component exceeds a predetermined threshold temperature after the gas sensor is activated.

[0021] The third aspect of the present invention is based on the gas sensor involved in the first or second aspect, characterized in that the calibration processing unit includes a time measuring unit, which measures the time for performing the concentration calibration of the specified gas component, and stops the calibration of the concentration of the specified gas component after the cumulative value of the time measured by the time measuring unit reaches the preset maximum required calibration time.

[0022] The fourth aspect of the present invention is a concentration correction method in a gas sensor capable of monitoring a specified gas component in a measured gas, characterized in that the gas sensor comprises: a sensor element having a strip-shaped substrate made of an oxygen ion-conductive solid electrolyte, and a monitoring section at one end; and a housing in which the sensor element is housed and fixed, the housing comprising: an outer cylinder having a reference gas space containing a reference gas, the other end of the sensor element protruding into the reference gas space; and a sealing member. A sealing component is embedded in the end of the outer cylinder to seal the reference gas space. The sensor element includes: at least one internal cavity for adjusting oxygen partial pressure, which is connected to an inlet of the gas to be measured located at one end, provided with a specified diffusion resistance; a measuring internal cavity, which is further connected to the at least one internal cavity for adjusting oxygen partial pressure; an external pump electrode disposed in a location other than the at least one internal cavity for adjusting oxygen partial pressure and the internal cavity for measuring; and a measuring electrode facing the gas. The method includes: an internal cavity for measurement; a measurement pump unit in which a measurement pump current corresponding to the concentration of the specified gas component flows between the internal cavity for measurement and the outside of the sensor element by applying a predetermined pump voltage between the measurement electrode and the external pump electrode of the cavity; and a measurement electrode lead portion having a measurement electrode conductive portion extending from the measurement electrode and capable of electrically connecting the outside of the sensor element and the measurement electrode, and a measurement conductive portion insulating layer covering the measurement conductive portion. In this case, the concentration correction method has... Note: A concentration determination step, in which the concentration of the specified gas component is determined based on the measuring pump current; and a calibration process, in which the concentration of the specified gas component determined in the concentration determination step is calibrated, wherein the concentration of the specified gas component is calibrated based on the correlation between a predetermined bias current value or a standardized value of the bias current value and the output variation generated by the measuring pump current when the gas sensor is started, wherein the bias current value is the magnitude of the measuring pump current when the measured gas without the specified gas component flows.

[0023] The fifth aspect of the present invention is based on the concentration correction method in the gas sensor involved in the fourth aspect, characterized in that the correction processing step includes a temperature estimation step, in which the temperature of the sealing component is estimated based on predetermined temperature estimation information, and in which the concentration of the specified gas component is corrected when it is determined that the temperature of the sealing component exceeds a predetermined threshold temperature after the gas sensor is activated.

[0024] The sixth aspect of the present invention is based on the concentration measurement method in the gas sensor involved in the fourth or fifth aspect, characterized in that the calibration process includes a time measurement process, in which the time for performing the concentration calibration of the specified gas component is measured, and after the cumulative value of the time measured by the time measurement process reaches the preset maximum required calibration time, the concentration calibration of the specified gas component is not performed.

[0025] Invention Effects

[0026] According to the first to sixth embodiments of the present invention, it is possible to suppress the degradation of NOx concentration measurement accuracy caused by the generation of polluting gas in the reference gas space when the gas sensor is started. Attached Figure Description

[0027] Figure 1 This is a cross-sectional view of the main part of the gas sensor 100 along its length.

[0028] 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.

[0029] Figure 3 This is a block diagram representing the functional components implemented in controller 110.

[0030] Figure 4 This is a plan view showing the arrangement of electrode lead portions including the electrode conduction portions extending from the inner pump electrode 22, the auxiliary pump electrode 51, and the measuring electrode 44.

[0031] Figure 5 This is a plan view showing the configuration of the electrode lead portion, including the electrode conduction portion extending from the outer pump electrode 23.

[0032] Figure 6 This is an example of a graph showing the change in NOx current Ip2, which automatically starts when the gas sensor operates in a sample gas atmosphere with a constant NOx concentration, together with the temperature change of the rubber stopper 106.

[0033] Figure 7This is a graph illustrating an example of the correlation between the Ip2 bias and the output variation of the NOx current Ip2.

[0034] Figure 8 This is a diagram used to illustrate the evaluation method for output variation.

[0035] Figure 9 This diagram shows the specific sequence of correction processes performed in the correction processing unit 1103.

[0036] Symbol Explanation

[0037] 1-3…First to third substrate layers, 4…First solid electrolyte layer, 5…Isolation layer, 6…Second solid electrolyte layer, 10…Gas inlet, 11…First diffusion rate control unit, 13…Second diffusion rate control unit, 20…First internal cavity, 21…Main pump unit, 22…Inner pump electrode, 22P…Main pump electrode lead, 23…Outer pump electrode, 23T…Terminal electrode, 30…Third diffusion rate control unit, 40…Second internal cavity, 41…Measurement pump unit, 42…Reference electrode, 43…Reference gas inlet cavity, 44…Measurement gas inlet… 44P… Measuring electrode lead section, 48… Atmospheric inlet layer, 50… Auxiliary pump unit, 51… Auxiliary pump electrode, 51P… Auxiliary pump electrode lead section, 60… Fourth diffusion rate 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 stopper, 107… Lead wire, 120… Surrounding assembly component, 151… Contact component, H1~H4… Through hole, SP… Reference gas space. Detailed Implementation

[0038] <Composition of Gas Sensors>

[0039] Figure 1 This is a cross-sectional view of the main portion (more specifically, its main body) of the gas sensor 100 in an embodiment of the present invention along its length. In this embodiment, the gas sensor 100 is installed in the exhaust path of an internal combustion engine (e.g., a car engine, not shown) and is used to detect predetermined gaseous components (e.g., NOx, etc.) contained in the exhaust gas flowing through the exhaust path as the gas to be measured, using a sensor element 101 provided inside it. It should be noted that... Figure 1 In the diagram, the vertical direction is shown as the z-axis, and the length direction of the gas sensor 100 is consistent with the z-axis (this is also true in the following diagrams).

[0040] The following description focuses on the case where the internal combustion engine is an automobile engine and the gas component detected by the gas sensor 100 is NOx. However, the method described in this embodiment related to the determination and correction of NOx concentration can also be applied to other gas types that can be measured and corrected based on the same principle.

[0041] The gas sensor 100 mainly comprises: a sensor element 101, a surrounding mounting component 120 mounted around it, and a cylindrical body 130 further surrounding and housing the surrounding mounting component 120, which is covered by a protective cover 102, fixing bolts 103, and an outer cylinder 104. In other words, in summary, the gas sensor 100 is configured such that the sensor element 101 extends axially through the center of the cylindrical body 130, and the surrounding mounting component 120 is mounted around the sensor element 101 inside the cylindrical body 130. Essentially, the cylindrical body 130, the protective cover 102, and the outer cylinder 104 constitute the housing (housing component) of the sensor element 101.

[0042] The sensor element 101 is a long, columnar or thin plate-shaped component whose main constituent material is a component body made of zirconium oxide or other oxygen ion-conducting solid electrolyte ceramic. The sensor element 101 is disposed on the central axis along the length direction of the cylindrical body 130. Hereinafter, the direction of extension of the central axis, which is consistent with the length direction of the cylindrical body 130, will also be referred to as the axial direction. Figure 1 In the figures below, the axis direction is consistent with the z-axis direction.

[0043] The sensor element 101 is configured to have a gas inlet and a monitoring section with an internal cavity on the first end portion 101a side, and various electrodes and wiring patterns are provided on the surface and inside of the element body. In the sensor element 101, the gas to be measured introduced into the internal cavity is reduced or even decomposed within the internal cavity to generate oxygen ions. In the gas sensor 100, the concentration of the gas component is calculated based on the direct proportionality between the amount of oxygen ions flowing inside the element and the concentration of the gas component in the gas being measured.

[0044] A protective film 111 covers a predetermined range of the surface of the sensor element 101 along its length, measured from the first end portion 101a. The purpose of the protective film 111 is to protect the area near the first end portion 101a of the sensor element 101, where internal cavities, electrodes, etc., are located, from thermal shock caused by water or the like. This protective film 111 is also called a thermal shock resistant protective layer. The protective film 111 is a porous membrane with a thickness of approximately 10 μm to 2000 μm, formed from materials such as Al₂O₃. The protective film 111 is preferably formed to withstand forces up to approximately 50 N, depending on its intended purpose. However, Figure 1The formation range of the protective film 111 in the following figures is merely an example; the actual formation range is appropriately determined based on the specific structure of the sensor element 101.

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

[0046] Figure 1 In the illustrated case, the protective cover 102 has a two-layer structure consisting of an outer cover 102a and an inner cover 102b. The outer cover 102a and the inner cover 102b are each provided with multiple through holes H1 and H2, H3 and H4 through which gas can pass. It should be noted that... Figure 1 The types, number, location, and shape of the through holes shown are merely examples and can be appropriately determined by considering the inflow pattern of the gas being measured into the protective cover 102.

[0047] The fixing bolt 103 is an annular component used to fix the gas sensor 100 to the measuring position. The fixing bolt 103 includes a threaded bolt portion 103a and a retaining portion 103b that holds the bolt portion 103a in place when screwed on. The bolt portion 103a engages with a nut provided at the mounting position of the gas sensor 100. For example, by screwing the bolt portion 103a onto a nut provided on the exhaust pipe of an automobile, the gas sensor 100 is fixed to the exhaust pipe such that the protective cover 102 side protrudes inside the exhaust pipe.

[0048] The outer cylinder 104 is a cylindrical metal component whose one end (the lower end in the attached drawing) is welded and fixed to the outer periphery of the upper side (positive side in the z-axis direction) of the cylindrical body 130 in the attached drawing. A connector 105 is disposed inside the outer cylinder 104. Additionally, a rubber stopper 106 is embedded at the other end (the upper end in the attached drawing) of the outer cylinder 104 as a sealing component. In the gas sensor 100, the space between the cylindrical body 130 and the rubber stopper 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 stopper 106. The second end portion 101b of the sensor element 101 protrudes into the reference gas space SP. For example, atmospheric air is introduced into this reference gas space SP as a reference gas for NOx concentration measurement.

[0049] The connector 105 has multiple contact parts 151 that contact multiple terminal electrodes (not shown) disposed at the second end portion 101b of the sensor element 101. The contact parts 151 are connected to leads 107 inserted through a rubber plug 106. The leads 107 are connected to the exterior of the gas sensor 100. Figure 1 The controller 110 (not shown) and various power connections.

[0050] It should be explained that Figure 1 Only two of each of the contact component 151 and lead wire 107 are shown; however, this is just an example.

[0051] The cylindrical body 130 is a metal cylindrical component, also referred to as the main metal part. The sensor element 101 and the surrounding mounting component 120 are housed inside the cylindrical body 130. In other words, the cylindrical body 130 is further surrounding the surrounding mounting component 120, which is mounted around the sensor element 101.

[0052] The cylindrical body 130 mainly comprises: a thick-walled main portion 130M, which forms a cylindrical inner space through a cylindrical inner surface 130a parallel to the axial direction; a reduced-diameter portion 131, which is provided at the lower end in the axial direction (negative side in the z-axis direction) in the figure and is thicker than the main portion 130M; a thin-walled recessed portion 132, which extends further upward from the end face 130c of the main portion 130M located at the upper end in the axial direction in the figure and bends toward the axial center; and a locking portion 133, which protrudes outward in a circumferential direction.

[0053] The punching portion 132 bends to press and secure (constrain) the internally disposed surrounding mounting component 120 (directly securing the second ceramic support 123) from above in the figure. It should be noted that, as described later, the punching portion 132 is bent after the surrounding mounting component 120 is mounted around the sensor element 101.

[0054] The surrounding assembly component 120 includes: a first ceramic support 121, a powder compactor 122, and a second ceramic support 123.

[0055] The first ceramic support 121 and the second ceramic support 123 are ceramic insulators. More specifically, a rectangular through hole (not shown) corresponding to the cross-sectional shape of the sensor element 101 is provided at the axial center of the first ceramic support 121 and the second ceramic support 123. The sensor element 101 is inserted through this through hole, thereby the first ceramic support 121 and the second ceramic support 123 are mounted around the sensor element 101. It should be noted that the first ceramic support 121 is engaged with the conical surface 130b of the cylindrical body 130 in the figure.

[0056] On the other hand, the pressed powder 122 is formed from ceramic powder such as talc powder, and is arranged inside the cylindrical body 130 in a manner similar to the first ceramic support 121 and the second ceramic support 123, with the sensor element 101 inserted through the through hole and surrounding the sensor element 101. It is then further compressed to become a single unit. More specifically, the ceramic particles forming the pressed powder 122 are surrounded by the first ceramic support 121, the second ceramic support 123, and the cylindrical body 130, and tightly fill the space through which the sensor element 101 passes.

[0057] In the gas sensor 100, in general, the sensor element 101 inside the cylindrical body 130 and the surrounding assembly part 120 are fixed by the locking action of the conical surface 130b of the first ceramic support 121 and the pressing action of the sealing portion 132 from the upper side of the second ceramic support 123 (as shown in the figure). Furthermore, an airtight seal is achieved between the first end portion 101a side and the second end portion 101b side of the sensor element 101 by the compression filling of the compressed powder 122.

[0058] <Overview of Sensor Components and Controllers>

[0059] 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. Figure 2 The illustration of the protective film 111 on the first end portion 101a side of the sensor element 101 is omitted. However, the controller 110 is shown together. The controller 110 controls the operation of each part of the gas sensor 100 and determines the NOx concentration based on the NOx current (measuring pump current) flowing through the sensor element 101.

[0060] The controller 110 includes at least one processor (not shown) and a memory (not shown). The functions of the controller 110 are implemented by the processor executing software stored in the memory. The memory is, for example, a non-volatile or volatile semiconductor memory.

[0061] Figure 3This is a block diagram illustrating the functional components implemented in the controller 110 described above. The controller 110 includes, as functional components, an element operation control unit 1101 that controls the operation of each part of the sensor element 101; a NOx concentration determination unit 1102 that determines the NOx concentration; and a correction processing unit 1103 that, under specified conditions described later, corrects the NOx concentration determined by the NOx concentration determination unit 1102. Furthermore, the correction processing unit 1103 includes: a sealing component temperature (rubber stopper temperature) estimation unit 1103A that estimates the temperature of the rubber stopper 106; a correction time measurement unit 1103B that measures the correction processing time and maintains its accumulated value (cumulative correction time); and a correction execution unit 1103C that actually performs the correction processing.

[0062] It should be noted that in this embodiment, the controller 110 includes an ECU (electronic control unit, not shown) that is electrically connected to the gas sensor 100 and controls the operation of various parts of the vehicle.

[0063] The sensor element 101 is a flat (elongated) ceramic element body, which has a structure obtained by stacking six solid electrolyte layers from bottom to top in the figure, namely a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, a first solid electrolyte layer 4, an isolation layer 5, and a second solid electrolyte layer 6, which are respectively containing zirconium oxide (ZrO2) (e.g., yttrium-stabilized zirconium oxide (YSZ)) as oxygen ion conductive solid electrolytes. Furthermore, the solid electrolyte forming these six layers is a dense and gas-tight solid electrolyte. In addition, hereinafter, sometimes... Figure 2 The upper surface of each of the six layers is referred to as the upper surface, and the lower surface is 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 substrate.

[0064] For example, the sensor element 101 can be manufactured in the following manner: the ceramic green sheets corresponding to each layer are processed in a specified manner and circuit patterns (e.g., electrodes, electrode conductive parts, conductive part insulating layers, etc.) are printed, and then they are stacked and fired to achieve integration.

[0065] 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 rate control unit 11, a buffer space 12, a second diffusion rate control unit 13, a first internal cavity 20, a third diffusion rate control unit 30, a second internal cavity 40, a fourth diffusion rate control unit 60, and a third internal cavity 61, which also serve as gas inlet 10, are formed adjacent to each other in a sequentially connected manner.

[0066] The buffer space 12, the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61 are the internal spaces (regions) of the sensor element 101, which are formed by hollowing out the isolation layer 5. The upper part of this internal space is defined by the lower surface of the second solid electrolyte layer 6, the lower part by the upper surface of the first solid electrolyte layer 4, and the sides by the sides of the isolation layer 5. It should be noted that the gas inlet 10 can also be provided in a way that hollows out the isolation layer 5, unlike the first diffusion rate control unit 11. In this case, the first diffusion rate control unit 11 is formed adjacent to the gas inlet 10, further inside it.

[0067] The first diffusion velocity control unit 11, the second diffusion velocity control unit 13, the third diffusion velocity control unit 30, and the fourth diffusion velocity control unit 60 are all configured as two horizontally elongated slits (forming the length direction of the opening perpendicular to the drawing). Furthermore, the portion from the gas inlet 10 to the innermost internal cavity, namely the third internal cavity 61, is also referred to as the gas flow section.

[0068] Additionally, on the second end portion 101b side of the sensor element 101, between the upper surface of the third substrate layer 3 and the lower surface of the isolation layer 5, and at a position defined by the side of the first solid electrolyte layer 4, a reference gas inlet cavity 43 is provided. The reference gas inlet cavity 43 is open relative to the reference gas space SP inside the outer cylinder 104, and atmospheric air, serving as the reference gas, is introduced from the reference gas space SP.

[0069] The atmosphere inlet layer 48 is a layer composed of porous alumina. Reference gas is introduced into the atmosphere inlet layer 48 through the reference gas inlet cavity 43. In addition, the atmosphere inlet layer 48 is formed to cover the reference electrode 42.

[0070] The reference electrode 42 is an electrode formed by being sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4. As described above, an atmospheric inlet layer 48 communicating with the reference gas inlet cavity 43 is provided around it. 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.

[0071] In the gas flow section, the gas inlet 10 (first diffusion rate control section 11) is an opening relative to the external space, through which the gas to be measured is introduced from the external space into the sensor element 101.

[0072] The first diffusion rate control unit 11 is a part that applies a predetermined diffusion resistance to the introduced gas to be measured.

[0073] The buffer space 12 is a space provided for guiding the measured gas introduced from the first diffusion rate control unit 11 to the second diffusion rate control unit 13.

[0074] The second diffusion rate control unit 13 is a part that applies a predetermined diffusion resistance to the gas being measured introduced from the buffer space 12 into the first internal cavity 20.

[0075] When the gas to be measured is introduced from outside the sensor element 101 into the first internal cavity 20, the gas being measured, which is rapidly introduced into the sensor element 101 from the gas inlet 10 due to pressure fluctuations in the external space (pulsations in exhaust pressure in the case of automobile exhaust), is not directly introduced into the first internal cavity 20. Instead, it is introduced into the first internal cavity 20 after the concentration fluctuations of the gas being measured are eliminated by the first diffusion rate control unit 11, the buffer space 12, and the second diffusion rate control unit 13. As a result, the concentration fluctuations of the gas being measured introduced into the first internal cavity 20 are almost negligible.

[0076] The first internal cavity 20 is configured as a space for adjusting the oxygen partial pressure in the gas to be measured, which is introduced through the second diffusion rate control unit 13. The main pump unit 21 operates to adjust this oxygen partial pressure.

[0077] The main pump unit 21 is an electrochemical pump unit consisting of an inner pump electrode (also called the main pump electrode) 22, an outer (outside the cavity) pump electrode 23, and a second solid electrolyte layer 6 sandwiched between the inner pump electrode 22 and the outer pump electrode 23. The inner pump electrode 22 has a top electrode portion 22a disposed on the lower surface of the second solid electrolyte layer 6 facing the first internal cavity 20. The outer pump electrode 23 is disposed on the upper surface of the second solid electrolyte layer 6 (a main surface of the sensor element 101) in a manner that exposes it to the external space in the area corresponding to the top electrode portion 22a.

[0078] The inner pump electrode 22 is formed on the upper and lower solid electrolyte layers (second solid electrolyte layer 6 and first solid electrolyte layer 4) that divide the first internal cavity 20. Specifically, a top electrode portion 22a is formed on 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 on 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 conductive portions provided on the side wall surfaces (inner surfaces) of the insulating layers 5 that constitute the two side walls of the first internal cavity 20 (illustration omitted).

[0079] The top electrode portion 22a and the bottom electrode portion 22b are arranged to be rectangular when viewed from above. However, it is also possible to have only the top electrode portion 22a or only the bottom electrode portion 22b.

[0080] The inner pump electrode 22 and the outer pump electrode 23 are formed as porous cermet electrodes. Specifically, the inner pump electrode 22, which is in contact with the gas being measured, is formed using a material that reduces the reducing power of NOx components in the gas being measured. For example, it is formed as a cermet electrode of Au-Pt alloy and ZrO2 with a porosity of 5% to 40% and containing approximately 0.6 wt% to 1.4 wt% Au, with a thickness of 5 μm to 20 μm. The weight ratio of Au-Pt alloy to ZrO2 only needs to be approximately Pt:ZrO2 = 7.0:3.0 to 5.0:5.0.

[0081] On the other hand, the outer pump electrode 23 is formed, for example, as a Pt or its alloy with ZrO2 cermet electrode, and is rectangular when viewed from above.

[0082] For the main pump unit 21, under the control of the component operation control unit 1101, the desired pump voltage Vp0 is applied between the inner pump electrode 22 and the outer pump electrode 23 using the variable power supply 24, and the main pump current Ip0 flows between the inner pump electrode 22 and the outer pump electrode 23 in either a positive or negative direction. This allows oxygen from the first internal cavity 20 to be drawn out to the external space, or oxygen from the external space to be drawn into the first internal cavity 20. Furthermore, 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.

[0083] 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 is constructed as an electrochemical sensor unit, consisting of an inner pump electrode 22, a second solid electrolyte layer 6, an isolation layer 5, a first solid electrolyte layer 4, a third substrate layer 3, and a reference electrode 42.

[0084] The oxygen concentration (oxygen partial pressure) in the first internal cavity 20 is known by measuring the potential difference, i.e., the electromotive force V0, between the inner pump electrode 22 and the reference electrode 42 in the main sensor unit 80.

[0085] Furthermore, the component operation control unit 1101 performs feedback control on the main pump voltage Vp0 to keep the electromotive force V0 constant, thereby controlling the main pump current Ip0. As a result, the oxygen concentration in the first internal cavity 20 is maintained at a predetermined constant value.

[0086] The third diffusion rate control unit 30 is a component that applies a predetermined diffusion resistance to the gas to be measured after the oxygen concentration (oxygen partial pressure) has been controlled in the first internal cavity 20 by the operation of the main pump unit 21, and introduces the gas to be measured into the second internal cavity 40.

[0087] The second internal cavity 40 is configured as a space for further adjusting the oxygen partial pressure in the gas to be measured, which is introduced through the third diffusion rate control unit 30. This oxygen partial pressure is adjusted by operating the auxiliary pump unit 50. Within the second internal cavity 40, the oxygen concentration of the gas to be measured can be adjusted with greater precision.

[0088] In the second internal cavity 40, the oxygen concentration (oxygen partial pressure) of the gas to be measured, which has been pre-adjusted in the first internal cavity 20 and then introduced through the third diffusion rate control unit 30, is further adjusted by the auxiliary pump unit 50.

[0089] The auxiliary pump unit 50 is an auxiliary electrochemical pump unit consisting of an auxiliary pump electrode 51, an outer pump electrode 23 (not limited to the outer pump electrode 23, but any suitable electrode on the outside of the sensor element 101), and a second solid electrolyte layer 6. The auxiliary pump electrode 51 has a top electrode portion 51a that is generally disposed on the lower surface of the second solid electrolyte layer 6 and facing the second internal cavity 40.

[0090] 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, a top electrode portion 51a is formed relative to the second solid electrolyte layer 6 constituting the top surface of the second internal cavity 40, and a bottom electrode portion 51b is formed on the first solid electrolyte layer 4 constituting the bottom surface of the second internal cavity 40. Both the top electrode portion 51a and the bottom electrode portion 51b are formed to be rectangular when viewed from above, and are connected by conductive portions provided on the side wall surfaces (inner surfaces) of the isolation layers 5 constituting the two side walls of the second internal cavity 40 (illustration omitted).

[0091] Furthermore, the auxiliary pump electrode 51 is also formed using a material that reduces the reduction ability of NOx components in the measured gas, just like the inner pump electrode 22.

[0092] For the auxiliary pump unit 50, under the control of the component operation control unit 1101, a desired voltage (auxiliary pump voltage) Vp1 is applied between the auxiliary pump electrode 51 and the outer pump electrode 23, thereby enabling oxygen in the atmosphere inside the second internal cavity 40 to be drawn out to the external space, or oxygen to be drawn from the external space into the second internal cavity 40.

[0093] In addition, to control the oxygen partial pressure in the atmosphere within the second internal cavity 40, an auxiliary sensor unit 81, comprising an auxiliary pump electrode 51, a reference electrode 42, a second solid electrolyte layer 6, an isolation layer 5, a first solid electrolyte layer 4, and a third substrate layer 3, serves as an electrochemical sensor unit. The auxiliary sensor unit 81 detects the potential difference, i.e., the electromotive force V1, generated between the auxiliary pump electrode 51 and the reference electrode 42 corresponding to the oxygen partial pressure within the second internal cavity 40.

[0094] The auxiliary pump unit 50 pumps using a variable power supply 52, which controls the voltage based on the electromotive force V1 detected by the auxiliary sensor unit 81. As a result, the oxygen partial pressure in the atmosphere within the second internal cavity 40 is controlled by feedback to a low partial pressure that has virtually no impact on NOx measurement.

[0095] Additionally, 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 to the main sensor unit 80 as a control signal and controls its electromotive force V0, thereby ensuring that the gradient of oxygen partial pressure in the gas to be measured, introduced from the third diffusion rate control unit 30 into the second internal cavity 40, remains constant. When used as a NOx sensor, the oxygen concentration in the second internal cavity 40 is maintained at a constant value of approximately 0.001 ppm due to the action of the main pump unit 21 and the auxiliary pump unit 50.

[0096] The fourth diffusion rate control unit 60 is a part that applies a predetermined diffusion resistance to the gas to be measured, whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the auxiliary pump unit 50 in the second internal cavity 40, and guides the gas to be measured to the third internal cavity 61.

[0097] The third internal cavity 61 is configured as a space for measuring the concentration of nitrogen oxides (NOx) in the gas to be measured, which is introduced through the fourth diffusion rate control unit 60. In the third internal cavity 61, the NOx concentration is measured by operating the measuring pump unit 41. Since the gas to be measured, whose oxygen concentration has been precisely adjusted in the second internal cavity 40, is introduced into the third internal cavity 61, the gas sensor 100 can perform highly accurate NOx concentration measurements.

[0098] The measuring pump unit 41 is used to measure the NOx concentration of the gas to be measured introduced into the third internal cavity 61. The measuring pump unit 41 is an electrochemical pump unit composed of a measuring electrode 44, an outer pump electrode 23, a second solid electrolyte layer 6, an isolation layer 5, and a first solid electrolyte layer 4. The measuring electrode 44 is disposed on the upper surface of the first solid electrolyte layer 4, facing the third internal cavity 61 and separated from the third diffusion rate control unit 30.

[0099] The measuring electrode 44 is a porous cermet electrode composed of a noble metal and a solid electrolyte. For example, it is a cermet electrode formed of Pt or an alloy of Pt and other noble metals such as Rh with ZrO2, which is the constituent material of the sensor element 101. The measuring electrode 44 also functions as a NOx reduction catalyst to reduce NOx present in the atmosphere within the third internal cavity 61.

[0100] For the measuring pump unit 41, under the control of the component operation control unit 1101, it is able to absorb the oxygen generated by the decomposition of NOx in the atmosphere of the third internal cavity 61, and can detect its generation amount as pump current Ip2.

[0101] In addition, to detect the oxygen partial pressure around the measuring electrode 44, a measuring sensor unit 82, which serves as an electrochemical sensor unit, is constructed from the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the measuring electrode 44, and the reference electrode 42. The variable power supply 46 is controlled by feedback based on the potential difference, i.e., the electromotive force V2, generated between the measuring electrode 44 and the reference electrode 42 corresponding to the oxygen partial pressure within the third internal cavity 61, detected by the measuring sensor unit 82.

[0102] NOx in the gas being measured, introduced into the third internal cavity 61, is reduced by the measuring electrode 44 (2NO→N2+O2) to generate oxygen. This generated oxygen is then pumped by the measuring pump unit 41. During this process, the voltage (measuring pump voltage) Vp2 of the variable power supply 46 is controlled to keep the electromotive force V2 detected by the measuring sensor unit 82 constant. The amount of oxygen generated around the measuring electrode 44 is proportional to the concentration of NOx in the gas being measured; therefore, the concentration of NOx in the gas being measured is calculated using the pump current Ip2 in the measuring pump unit 41. Hereinafter, this pump current Ip2 will also be referred to as the NOx current Ip2 or the measuring pump current Ip2.

[0103] Furthermore, if the measuring electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42 are combined to form an oxygen partial pressure detection mechanism as an electrochemical sensor unit, the electromotive force corresponding to the following difference can be detected, thereby allowing the determination of the concentration of NOx in the measured gas. This difference refers to the difference between the amount of oxygen generated by the reduction of NOx in the atmosphere surrounding the measuring electrode 44 and the amount of oxygen contained in the reference atmosphere.

[0104] In addition, the electrochemical sensor unit 83 is composed of the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the outer pump electrode 23 and the reference electrode 42. The electromotive force Vref can be obtained by using the sensor unit 83, and the oxygen partial pressure in the gas to be measured outside the sensor can be detected by using the electromotive force Vref.

[0105] It should be explained that Figure 2 For the sake of simplicity, only schematic diagrams are shown of the wiring used to electrically connect the electrodes constituting various pump units and sensor units to the external parts of the sensor element 101. However, in the actual sensor element 101, an electrode conduction portion is provided internally or on the side to connect the electrodes of each pump unit and sensor unit to the terminal electrodes.

[0106] Figure 4 This is a plan view showing the arrangement of electrode leads extending from electrode conductive portions, as an example, 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 measuring electrode 44. Furthermore, Figure 5 This is a plan view showing the configuration of the electrode lead portion, including the electrode conduction portion extending from the outer pump electrode 23.

[0107] Bottom electrode portion 22b, bottom electrode portion 51b, and measuring electrode 44 are all disposed on the first solid electrolyte layer 4. Furthermore, the main pump electrode conductive portion 22L, surrounded by the main pump electrode conductive portion insulating layer 22I, extends from the bottom electrode portion 22b towards the second end portion 101b; the auxiliary pump electrode conductive portion 51L, surrounded by the auxiliary pump electrode conductive portion insulating layer 51I, extends from the bottom electrode portion 51b towards the second end portion 101b; and the measuring electrode conductive portion 44L, surrounded by the measuring electrode conductive portion insulating layer 44I, extends from the measuring electrode 44 towards the second end portion 101b. On the other hand, the outer pump electrode 23 is disposed on the second solid electrolyte layer 6. Furthermore, the outer pump electrode conductive portion 23L, surrounded by the outer pump electrode conductive portion insulating layer 23I, extends from the outer pump electrode 23 towards the second end portion 101b. Through each insulating layer, insulation is achieved between each electrode conductive portion and the solid electrolyte constituting the sensor element 101.

[0108] In the following text, the region including the main pump electrode conductive section 22L and the main pump electrode conductive section insulating layer 22I, and surrounded by a solid electrolyte (mainly the first solid electrolyte layer 4 and the isolation layer 5), will be collectively referred to as the main pump electrode lead section 22P. Similarly, the region including the auxiliary pump electrode conductive section 51L and the auxiliary pump electrode conductive section insulating layer 51I, and surrounded by a solid electrolyte (mainly the first solid electrolyte layer 4 and the isolation layer 5), will be collectively referred to as the auxiliary pump electrode lead section 51P. Furthermore, the region including the measuring electrode conductive section 44L and the measuring electrode conductive section insulating layer 44I, and surrounded by a solid electrolyte (mainly the first solid electrolyte layer 4 and the isolation layer 5), will be collectively referred to as the measuring electrode lead section 44P.

[0109] The outer pump electrode conductive portion 23L is connected to the terminal electrode 23T provided at the second end portion 101b. It should be noted that... Figure 5 In the middle, the insulating layer 23I of the outer pump electrode conduction portion exists in a straight line (in a linear shape) along the outer pump electrode conduction portion 23L. However, the insulating layer 23I of the outer pump electrode conduction portion can be provided in a planar shape (in a layered shape) between the outer pump electrode 23 and the terminal electrode 23T.

[0110] On the other hand, the main pump electrode conductive section 22L, the auxiliary pump electrode conductive section 51L, and the measuring electrode conductive section 44L are mostly embedded in the interlayer wiring between the first solid electrolyte layer 4 and the isolation layer 5, but they bend towards the element side near the second end section 101b. Furthermore, although not shown in the figure, the main pump electrode conductive section 22L, the auxiliary pump electrode conductive section 51L, and the measuring electrode conductive section 44L are each surrounded by the main pump electrode conductive section insulating layer 22I, the auxiliary pump electrode conductive section insulating layer 51I, and the measuring electrode conductive section insulating layer 44I, respectively. After being connected near the element-side end via through holes in either the vertical or horizontal direction in the thickness direction, they are connected by other interlayer wiring to any of a plurality of terminal electrodes (not shown) similar to the terminal electrode 23T provided at the second end section 101b. It should be noted that in this embodiment, the electrode conductive portion being surrounded by the conductive portion insulating layer includes both the electrode conductive portion being covered by the conductive portion insulating layer and the electrode conductive portion being sandwiched by the conductive portion insulating layer.

[0111] The main pump electrode conducting section 22L, the auxiliary pump electrode conducting section 51L, the measuring electrode conducting section 44L, and the outer pump electrode conducting section 23L are preferably formed of platinum. Furthermore, the insulating layer 22I of the main pump electrode conducting section, the insulating layer 51I of the auxiliary pump electrode conducting section, the insulating layer 44I of the measuring electrode conducting section, and the insulating layer 23I of the outer pump electrode conducting section are preferably formed of alumina.

[0112] The sensor element 101 also includes a heater section 70, which performs the function of heating and maintaining the temperature of the sensor element 101 in order to improve the oxygen ion conductivity of the solid electrolyte constituting the substrate.

[0113] The heater section 70 mainly includes a heater electrode 71, a heater component 72, a heater conductive section 72a, a through hole 73, a heater insulation layer 74, a pressure relief hole 75, and Figure 2 The heater resistance detection conduction section shown in the figure is omitted. In addition, except for the heater electrode 71, the heater section 70 is embedded in the base of the sensor element 101.

[0114] The heater electrode 71 is an electrode formed in contact with the lower surface of the first substrate layer 1 (the other main surface of the sensor element 101).

[0115] The heater component 72 is a resistive heating element disposed between the second substrate layer 2 and the third substrate layer 3. Figure 2 The heater power supply (not shown) located outside the sensor element 101 supplies power to the heater member 72 via the heater electrode 71, through hole 73, and heater conduction portion 72a, which serve as the power path, thereby heating the heater member 72. The heater member 72 is formed of Pt or is formed with Pt as the main component. The heater member 72 is embedded in a predetermined range on the side of the sensor element 101 containing the gas passage, opposite to the gas passage in the element thickness direction. The heater member 72 is provided to have a thickness of approximately 10 μm to 30 μm.

[0116] For sensor element 101, under the control of element operation control unit 1101, current flows through heater electrode 71 to heater component 72, thereby heating heater component 72 and heating each part of sensor element 101 to a predetermined temperature and maintaining that temperature. Specifically, sensor element 101 is heated so that the temperature of solid electrolyte near gas flow section and electrodes reaches approximately 700°C to 900°C. This heating improves the oxygen ion conductivity of solid electrolyte constituting the matrix of sensor element 101. Furthermore, the heating temperature of heater component 72 when using gas sensor 100 (when sensor element 101 is driven) is called sensor element driving temperature.

[0117] The degree of heating of the heater component 72 (heater temperature) is controlled by the magnitude of the resistance value of the heater component 72 (heater resistance).

[0118] It should be noted that, although Figure 2The diagram is omitted. However, for the purpose of protecting the outer pump electrode 23, an electrode protective layer covering the outer pump electrode 23 may be provided on one of the main surfaces of the sensor element 101.

[0119] When measuring the NOx concentration in the gas sensor 100 with the above configuration, the element operation control unit 1101 operates the main pump unit 21 and the auxiliary pump unit 50, thereby performing feedback control to keep the oxygen concentration constant in the first internal cavity 20 and the second internal cavity 40. The gas to be measured with a constant oxygen concentration is introduced into the third internal cavity 61 and reaches the measuring electrode 44. For example, when the gas to be measured is a lean fuel atmosphere, the gas to be measured with an oxygen partial pressure sufficiently reduced to a level that has no substantial effect on the NOx measurement (e.g., 0.0001 ppm to 1 ppm) is introduced into the third internal cavity 61.

[0120] Then, at the measuring electrode 44, the NOx in the measured gas is reduced, thereby generating oxygen. This oxygen is drawn out by the measuring pump unit 41, and the NOx current Ip2 flowing during this extraction has a certain functional relationship with the concentration of NOx in the measured gas (hereinafter referred to as sensitivity characteristics).

[0121] Before actual use of the gas sensor 100, the aforementioned sensitivity characteristics are determined in advance using multiple types of sample gases with known NOx concentrations, and the data is stored in the NOx concentration determination unit 1102 (more specifically, a memory). Then, during actual use of the gas sensor 100, a signal representing the value of the NOx current Ip2 flowing corresponding to the NOx concentration in the gas being measured is provided to the NOx concentration determination unit 1102 at all times. Based on this value and the determined sensitivity characteristics, the NOx concentration is calculated sequentially in the NOx concentration determination unit 1102 and output as a NOx sensor detection value. Accordingly, the gas sensor 100 can approximately grasp the NOx concentration in the gas being measured in real time.

[0122] <Generation of pollutants in the reference gas space>

[0123] In gas sensors like the gas sensor 100 described in this embodiment, where a reference gas space SP is surrounded by an outer cylinder 104 and a rubber stopper 106 and used in high-temperature environments, contaminating gases may be generated within the reference gas space SP due to the evaporation of oil adhering to the inner surface 104a of the outer cylinder 104 or gas generated from the rubber stopper 106, resulting in changes in the NOx current Ip2. In particular, this contaminating gas is more likely to be generated under harsh conditions such as high-temperature gas conditions or when heat around the main body cannot be dissipated.

[0124] Figure 6This is an example of a graph showing the change in NOx current Ip2, which automatically starts when the gas sensor operates under a sample gas atmosphere with a constant NOx concentration, together with the temperature change of the rubber stopper 106. Figure 6 During the process, the NOx current Ip2, which should be constant, temporarily decreases after the temperature of the rubber stopper 106 rises. Then, after the temperature of the rubber stopper 106 stabilizes, it increases to the same level as the initial peak value and remains approximately constant.

[0125] think: Figure 6 The temporary decrease in NOx current is because the polluting gas generated during the heating process of the gas sensor, as described above, enters the third internal cavity 61 where the measuring electrode 44 is located through the measuring electrode lead portion described later. Furthermore, it is believed that the increase in NOx current Ip2 after a certain period of time is because the outer cylinder 104 and the rubber stopper 106 are fully heated, resulting in the complete release of the polluting gas.

[0126] The aforementioned fluctuation in the NOx current Ip2 would certainly be the primary reason for the temporary decrease in the accuracy of NOx concentration measurement in the gas sensor. Furthermore, it's not necessarily only... Figure 6 The polluting gas is generated after the use is started, as shown.

[0127] <Correlation between Ip2 bias and output variation>

[0128] In the gas sensor 100 of this embodiment, the calibration processing unit 1103 calibrates the NOx current Ip2, which changes due to the generation of polluting gas as described above, thereby ensuring the accuracy of NOx concentration measurement. This calibration utilizes Ip2 bias.

[0129] Here, Ip2 bias refers to the magnitude (bias current value) of the pump current Ip2 flowing through the measuring pump unit 41 when the measured gas does not contain NOx. As described above, the measuring pump unit 41 draws out the oxygen generated from the decomposition of the measuring electrode 44 when the NOx contained in the almost oxygen-free measured gas reaches the third internal cavity 61. Therefore, when the measured gas does not contain NOx, there should be no pump current Ip2 flowing. However, in reality, due to the drawout of trace amounts of residual oxygen in the measured gas that enters the third internal cavity 61 through the measuring electrode lead portion 44P, the pump current Ip2 flows even when the measured gas does not contain NOx. The magnitude of the pump current Ip2 at this time is specifically referred to as Ip2 bias.

[0130] In a certain gas sensor 100, a significant amount of contaminated gas intrudes into the third internal cavity 61 through the measuring electrode lead 44P. In other words, this gas sensor 100 is inherently prone to gas intrusion (flow) from the reference gas space SP into the third internal cavity 61 through the measuring electrode lead 44P. Therefore, for such a gas sensor 100, when contaminated gas is generated, the variation in the NOx current Ip2 increases, and the Ip2 bias also increases when the measured gas does not contain NOx. That is, there is a positive correlation between the Ip2 bias and the amount of variation in the NOx current Ip2 output.

[0131] Figure 7 This is a diagram illustrating an example of the correlation between the Ip2 bias and the output variation of the NOx current Ip2. Figure 7 Yes: For six different gas sensors 100, the output variations of Ip2 bias and NOx current Ip2 are evaluated. The horizontal axis is set as Ip2 bias, and the vertical axis is set as the output variation of NOx current Ip2. Figure 7 The graph is obtained by plotting the change in Ip2 (recorded as "change in Ip2"). Figure 7 It can be seen that the output variation of Ip2 bias and NOx current Ip2 shows a strong positive correlation. The square of the correlation coefficient R, i.e., the coefficient of determination R... 2 It is 0.9965.

[0132] It should be noted that a sample gas containing neither oxygen nor NOx (O2 = 0%, NO = 0%, H2O = 3%, the remainder being N2) was used as the gas to be measured, thereby evaluating the value of the Ip2 bias.

[0133] On the other hand, in summary, by obtaining Figure 6 The output variation of NOx current Ip2 can be determined by observing the curve of NOx current Ip2 shown.

[0134] Figure 8 This is a diagram illustrating the evaluation method for this output variation. Specifically, in a sample gas atmosphere with a temperature of 1050°C, an air ratio λ = 1.05, and a NOx concentration of 100 ppm, each gas sensor is activated to control the heating of the heater section 70, so that the temperature of the rubber stopper 106 eventually reaches 300°C and remains constant. Simultaneously, the NOx current Ip2 is continuously measured, thereby obtaining... Figure 8 The curve shown is Ip2(t), which corresponds to the NOx current Ip2 as a function of time.

[0135] Although the degree of yield varies among all gas sensors, they all yield the same result. Figure 6The example shown uses the same curve Ip2(t). That is, for a period of time after the gas sensor starts operating, the NOx current Ip2 is approximately constant. However, it then decreases temporarily, becomes approximately constant as pollutant gas is produced, and after a period of time, the NOx current Ip2 starts to increase, eventually reaching approximately constant at approximately the same value as when the operation started.

[0136] but, Figure 8 In the diagram, for ease of understanding, the curve Ip2(t) is represented as a solid broken line. However, in reality, the curve Ip2(t) has slight variations, which are schematically represented by dashed lines.

[0137] When evaluating the output variation using the aforementioned curve Ip2(t), firstly, the average value av1 of the NOx current Ip2 is determined over a specified time Δt1 (e.g., 10 minutes) during which the approximately constant state transitions from a decreasing state to an increasing state. The average value is used because the seemingly constant value actually varies.

[0138] Next, we obtain the difference Δ1(t) between the value of the NOx current Ip2 after it increases and then becomes approximately constant, and the difference Δ2(t) between the maximum and minimum values ​​of the NOx current Ip2 after it increases and becomes approximately constant. Both Δ1(t) and Δ2(t) are dynamic values ​​that change in response to the changes in the value of the increased NOx current Ip2, and therefore are expressed as functions of time.

[0139] Furthermore, the state judgment that the difference Δ1(t) and the difference Δ2(t) satisfy the following equation (1) is: at the moment when the specified observation time Δtz (e.g., 60 minutes) has elapsed, the changes accompanied by the pollutant gas are eliminated, and the value of NOx current Ip2 reaches approximately constant at its original value.

[0140] The difference Δ1(t) > 2 × the difference Δ2(t) ····(1)

[0141] Based on this, the average value av2 of the NOx current Ip2 within a specified time Δt2 (e.g., 10 minutes) before the judgment time is determined, and the difference between the two is calculated.

[0142] Output variation = average value av2 - average value av1 ... (2)

[0143] <Correction of NOx Concentration>

[0144] In this embodiment, the output variation of NOx current Ip2 and the Ip2 bias satisfy the following condition: Figure 7The correlation shown is used by the correction processing unit 1103 to correct for the NOx concentration fluctuation caused by, for example, the generation of pollutant gas in the reference gas space SP when the gas sensor 100 starts operating. That is, the Ip2 bias is an inherent value for each gas sensor 100, and the correlation between the NOx current Ip2 output variation and the Ip2 bias is a general relationship that holds true among the multiple gas sensors 100. Therefore, when each gas sensor 100 is used, by substituting the bias value of that gas sensor 100 into the predetermined correlation, the NOx concentration can be corrected.

[0145] In the case of a gas sensor 100 manufactured in industrial mass production, several samples are taken from multiple manufactured gas sensors 100, and the output variation of NOx current Ip2 and Ip2 bias are calculated. Based on the obtained values, the following determination is made. Figure 7 The correlation shown is used to determine the correlation. The determined correlation is stored as correction mapping information in the correction processing unit 1103 (more specifically, a memory). On the other hand, for each gas sensor 100, when the above-mentioned sensitivity characteristics are determined immediately after manufacturing, the Ip2 bias is also determined and stored as part of the sensitivity characteristics in the NOx concentration determination unit 1102. Then, when the correction processing should be performed, the correction processing unit 1103 substitutes the Ip2 bias obtained by the NOx concentration determination unit 1102 into the pre-stored correlation, determines the output variation of the NOx current Ip2, and corrects the NOx concentration based on the determined output variation.

[0146] Figure 9 This diagram shows the specific sequence of correction processes performed in the correction processing unit 1103.

[0147] First, at the same time as the gas sensor 100 is activated, the temperature of the rubber plug 106 (sealing component temperature) is estimated using the sealing component temperature estimation unit 1103A (step S1). Normally, the activation of the gas sensor 100 is performed simultaneously with the start of the vehicle.

[0148] The temperature of the sealing component varies depending on external factors such as the temperature of the exhaust gas from the engine (which is the gas being measured), the temperature around the main body of the gas sensor 100, and the flow velocity around the main body, which changes in accordance with the vehicle's speed. In this embodiment, considering this, the relationship between the characteristic values ​​(sealing component temperature estimation factors) that affect the sealing component temperature when the vehicle is in motion (i.e., when the gas sensor 100 is activated), such as exhaust gas temperature, driving speed, and torque, and the actual sealing component temperature is determined in advance through experiments. This determined relationship is stored as mapping information (sealing component temperature estimation information) for estimating the sealing component temperature in the sealing component temperature estimation unit 1103A included in the correction processing unit 1103. Then, at the same time as the gas sensor 100 is activated, the sealing component temperature estimation unit 1103A begins to acquire the measured value of the sealing component temperature estimation factor, and continuously compares the measured value with the sealing component temperature estimation information, thereby estimating the sealing component temperature approximately in real time. It should be noted that the outer cylinder 104 is made of metal, which has higher thermal conductivity than the rubber stopper 106. Therefore, it is presumed that the gas sensor 100 reaches a higher temperature than the rubber stopper 106 when in use.

[0149] The sealing component temperature estimation unit 1103A determines whether the estimated sealing component temperature exceeds a preset threshold temperature (correction execution threshold temperature) (step S2). Here, the correction execution threshold temperature refers to the predetermined minimum temperature at which NOx concentration correction is required as the rubber stopper 106 and outer cylinder 104 heat up. For example, if NOx current Ip2 is used... Figure 6 In the case of time-varying conditions, the temperature at which the temporarily rising NOx current Ip2 decreases from its peak value by a specified value is set as the correction execution threshold temperature.

[0150] During the period when the sealing component temperature estimation unit 1103A determines that the sealing component temperature has not exceeded the calibration execution threshold temperature (NO in step S2), the estimation of the sealing component temperature continues. This is because it is assumed that no polluting gas is generated in the temperature range where the sealing component temperature is below the calibration execution threshold temperature, and therefore, NOx concentration correction is not required. It should be noted that the sealing component temperature estimation unit 1103A continues to estimate the sealing component temperature until the calibration process stops.

[0151] On the other hand, if the sealing component temperature estimation unit 1103A determines that the sealing component temperature exceeds the calibration execution threshold temperature, the calibration time measurement unit 1103B obtains the cumulative calibration time stored at that time (step S3), and determines whether the cumulative calibration time has reached the maximum required calibration time preset during the manufacture of the gas sensor 100 and recorded in the calibration time measurement unit 1103B (more specifically, the memory) (step S4).

[0152] Here, the cumulative calibration time refers to the cumulative value of the execution time of the calibration process previously performed to deal with the generation of polluting gases. Each time the calibration process is performed, the calibration time measurement unit 1103B counts the execution time and adds the values ​​to obtain the cumulative calibration time, which is then stored for later use.

[0153] The decrease (fluctuation) in NOx current Ip2 caused by the generation of polluting gas on the inner surface 104a of the rubber stopper 106 and the outer cylinder 104 is only a temporary phenomenon that occurs when the gas sensor 100 is started shortly after initial use. Once the polluting substances evaporate and disappear, the polluting gas is no longer generated. For the gas sensor 100 after this polluting source disappears, even with heating, no polluting gas is generated during repeated use (start-up), therefore, no calibration is required. Therefore, in this embodiment, the maximum time required for calibration (maximum required calibration time) is determined in advance through experimentation and stored in the calibration time measurement unit 1103B. In other words, calibration is performed using the calibration processing unit 1103 every time the gas sensor 100 is started, until the maximum required calibration time has elapsed.

[0154] If the calibration time measurement unit 1103B determines that the accumulated calibration time has reached the maximum required calibration time (YES in step S4), it will not use the calibration processing unit 1103 for further processing. This means that, as a result of the calibration processing performed before this time, it is not necessary to perform calibration for NOx concentration to address the generation of polluting gases.

[0155] If the calibration time measurement unit 1103B determines that the accumulated calibration time has not reached the maximum required calibration time (NO in step S4), the calibration execution unit 1103C begins to calibrate the NOx concentration value determined by the NOx concentration determination unit 1102 (step S5). Specifically, the calibration execution unit 1103C substitutes the Ip2 bias value stored in the NOx concentration determination unit 1102 with mapping information representing the correlation between the output variation of the NOx current Ip2 and the Ip2 bias, and determines the calibration amount for the NOx current Ip2. Then, it substitutes this calibration amount with the sensitivity characteristics stored in the NOx concentration determination unit 1102, and calibrates the NOx concentration determined by the NOx concentration determination unit 1102 based on the obtained calibration amount, thereby calibrating the NOx concentration value determined by the NOx concentration determination unit 1102 approximately in real time. Accordingly, the NOx concentration value output from the gas sensor 100 effectively eliminates the influence of NOx current Ip2 variations caused by the generation of polluting gases.

[0156] When the calibration execution unit 1103C begins to calibrate the NOx concentration value in this manner, the calibration time measurement unit 1103B begins to count the calibration execution time (step S6). In addition, the sealing component temperature estimation unit 1103A continues to determine whether the estimated sealing component temperature is still higher than the calibration execution threshold temperature (step S7).

[0157] Then, if the sealing component temperature estimation unit 1103A determines that the estimated sealing component temperature exceeds the correction execution threshold temperature (YES in step S7), the correction time measurement unit 1103B determines whether the cumulative correction time increased due to the correction being performed has exceeded the maximum required correction time (step S8).

[0158] If, after the calibration execution begins, the temperature of the sealing component is below the calibration execution threshold temperature (NO in step S7), or the accumulated calibration time has exceeded the maximum required calibration time (YES in step S8), then calibration of the NOx concentration is no longer required. Therefore, the calibration execution performed by the calibration execution unit 1103C is stopped (step S9). At the same time, the calibration time measurement unit 1103B adds up the calibration times counted up to this moment, thereby updating the accumulated calibration time (step S10). Accordingly, the calibration processing in the calibration processing unit 1103 ends.

[0159] It should be noted that if the cumulative calibration time exceeds the maximum required calibration time (YES in step S8), and the calibration process stops, the updated cumulative calibration time will match the maximum required calibration time. In this case, NOx concentration calibration will not be performed the next time gas sensor 100 is started.

[0160] As explained above, according to this embodiment, by using the correlation between the predetermined Ip2 bias and the output variation of NOx current Ip2, the change in NOx concentration caused by the generation of pollutant gas in the reference gas space surrounded by the outer cylinder and the rubber stopper when the gas sensor is started can be corrected, thereby suppressing the temporary deterioration of the measurement accuracy of NOx concentration.

[0161] <Variation Example>

[0162] In the above embodiments, the NOx concentration is corrected based on the correlation between the Ip2 bias and the output variation of the NOx current Ip2. However, instead of the Ip2 bias, the correlation between the standardized value of the NOx current Ip2 obtained by dividing the Ip2 bias by the NOx current Ip2 when the measured gas flows with a known NOx concentration (e.g., 500 ppm) and the output variation of the NOx current Ip2 can be determined and stored in the correction processing unit 1103 as correction mapping information. The NOx concentration is then corrected based on this correlation.

[0163] The Ip2 bias is a value corresponding to the amount of oxygen remaining in the measured gas that flows in from the gas inlet 10, is drawn out, and reaches the third internal cavity 61, as well as the amount of oxygen that enters the third internal cavity 61 from the reference gas space SP through the measuring electrode lead 44P. The former depends on the diffusion resistance of the gas flow section from the gas inlet 10 to the third internal cavity 61. Therefore, instead of the Ip2 bias itself, the correlation between the output variation of the NOx current Ip2 obtained using the ratio described above has a higher correlation coefficient. The accuracy of NOx concentration correction using this correlation is better.

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; a housing in which the sensor element is housed and fixed; a controller that controls the operation of the gas sensor, 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 the end portion of the outer cylinder to seal the reference gas space, the sensor element comprising: 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 prescribed diffusion resistance; a measurement internal cavity that further communicates with the at least one oxygen partial pressure adjustment internal cavity; an internal cavity external pump electrode disposed at a position other than the at least one oxygen partial pressure adjustment internal cavity and the measurement internal cavity; a measurement electrode disposed facing the measurement internal cavity; a measurement pump unit in which a measurement pump current corresponding to the concentration of the prescribed gas component flows between the measurement electrode and the internal cavity external pump electrode by application of a prescribed pump voltage; and a measurement electrode lead portion comprising a measurement electrode lead-through portion extending from the measurement electrode that electrically connects the outside of the sensor element and the measurement electrode, and a measurement lead-through portion insulating layer covering the measurement electrode lead-through portion, the controller including a processor and a memory in which software is stored, the processor configured to: determine the concentration of the prescribed gas component based on the measurement pump current when the processor executes the software stored in the memory; estimate the temperature of the sealing member based on predetermined temperature estimation information, wherein the processor is configured to start acquiring a measured value of a sealing member temperature estimation factor at the same time as the start of the gas sensor, and continuously and continuously perform a comparison of the measured value and the temperature estimation information of the sealing member, thereby estimating the temperature of the sealing member in real time; and, in the case where it is determined that the temperature of the sealing member exceeds a prescribed threshold temperature after the start of the gas sensor, correct the concentration of the prescribed gas component based on a correlation between a predetermined bias current value or a standardized value of the bias current value and an output variation produced by the measurement pump current at the start of the gas sensor, wherein the bias current value is the magnitude of the measurement pump current when a measured gas not containing the prescribed gas component flows.

2. The gas sensor according to claim 1, wherein the processor is further configured to: measuring a time for performing the concentration correction of the prescribed gas component, and stopping the concentration correction of the prescribed gas component after a cumulative value of the time measured by the processor reaches a maximum required correction time set in advance.

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