WO2018194034A1

WO2018194034A1 - Gas sensor

Info

Publication number: WO2018194034A1
Application number: PCT/JP2018/015747
Authority: WO
Inventors: 中江　誠; 将太今田
Original assignee: 株式会社デンソー
Priority date: 2017-04-21
Filing date: 2018-04-16
Publication date: 2018-10-25

Abstract

This gas sensor is provided with a sensor element (2), and the sensor element (2) includes a solid electrolyte body (3) in the shape of a bottomed cylinder, a detecting electrode (4A) provided on an outside surface of the solid electrolyte body (3), and a reference electrode provided on an inside surface of the solid electrolyte body (3). The detecting electrode (4A) of the sensor element (2) comprises: a detecting electrode portion (41) provided in a position on a distal end side (L1) in an axial direction (L); a mounting electrode portion (43) provided in a position on a proximal end side (L2) in the axial direction (L); and a lead electrode portion (42) provided in a position joining the detecting electrode portion (41) and the mounting electrode portion (43). An insulating layer (22) is provided between a cylinder portion (31) of the solid electrolyte body (3) on the one hand, and the mounting electrode portion (43) and the lead electrode portion (42) on the other hand.

Description

Gas sensor

Cross-reference of related applications

This application is based on Japanese Patent Application No. 2017-084568 filed on Apr. 21, 2017 and Japanese Patent Application No. 2018-018540 filed on Feb. 5, 2018. The description is incorporated.

The present disclosure relates to a gas sensor having a sensor element in which an electrode is provided on a solid electrolyte body.

The gas sensor arranged in the exhaust pipe of the internal combustion engine uses the exhaust gas flowing in the exhaust pipe as a detection gas (measurement gas), and performs gas detection using the difference in oxygen concentration between this detection gas and a reference gas such as the atmosphere. Do. The gas sensor is used as an oxygen sensor for detecting whether the air-fuel ratio of the internal combustion engine determined from the composition of the exhaust gas is on the fuel rich side or the fuel lean side with respect to the theoretical air fuel ratio, and the internal combustion engine required from the exhaust gas There are uses as an air-fuel ratio sensor for quantitatively detecting the air-fuel ratio.

In a gas sensor, a bottomed cylindrical sensor element in which electrodes are arranged on the inner side surface and outer side surface of a bottomed cylindrical solid electrolyte body, or a plate-like sensor element in which electrodes are arranged on both sides of a plate-like solid electrolyte body Is used. When the gas sensor is used as an oxygen sensor, an electromotive force generated between the pair of electrodes through the solid electrolyte body is detected according to the difference in oxygen concentration between the detection gas and the reference gas. When the gas sensor is used as an air-fuel ratio sensor, a voltage is applied between the pair of electrodes, and the current flowing between the pair of electrodes via the solid electrolyte body is detected according to the oxygen concentration of the detection gas. is doing.

In the bottomed cylindrical sensor element, the detection electrode that is exposed to the detection gas is formed on the entire circumference of the tip side portion of the solid electrolyte body, and the detection unit that is heated to the target temperature by the heating unit of the heater, and the detection In many cases, it is formed into a shape having a lead portion drawn out from the portion to the proximal end side. In addition, it is known that an insulating layer is provided between the lead portion and the solid electrolyte body in order to cause oxygen movement through the solid electrolyte body only in the detection section.

Examples of such sensor elements include an oxygen sensor described in Patent Document 1. In this oxygen sensor, an insulating layer made of an insulator is provided between the solid electrolyte body and the lead portion of the detection electrode, and the area of the detection electrode that functions when performing gas detection is defined.

JP-A-6-201641

By the way, as a result of the diligent research by the inventors, in an environment where the base end side portion of the sensor element is at a high temperature of 400 ° C. or higher, the sensor output of the gas sensor originally has a stoichiometric air-fuel ratio output. Even in the state, it has been found that there is a case where the sensor output is deviated and the sensor output may not be equivalent to the theoretical air-fuel ratio. This is due to the fact that the base end portion of the sensor element is heated, so that the solid electrolyte body, the lead portion of the detection electrode and the reference electrode are activated in the base end portion of the sensor element, and the base end portion of the sensor element is activated. It was found that oxygen in the reference gas such as the atmosphere existing in the atmosphere moved through the solid electrolyte body and a leak current was generated between the lead portion of the detection electrode and the reference electrode. In particular, it has been found that a leak current is generated in a portion where the terminal fitting is mounted in the lead portion of the detection electrode.

In Patent Document 1 or the like, an insulating layer is provided for a portion of a detection electrode or a lead portion exposed to a detection gas. However, the front end portion of the sensor element is exposed to the detection gas, while the proximal end portion of the sensor element is fixed to the housing and is not exposed to the detection gas. The insulating layer in Patent Document 1 is provided to define the area of the detection electrode that functions when performing gas detection. For this reason, the insulating layer is a portion that is not exposed to the detection gas and is not considered to be provided up to the proximal end portion of the lead portion to which the terminal fitting is attached.

The present disclosure has been obtained in an attempt to provide a gas sensor capable of improving the accuracy of gas detection by preventing leakage current from being generated between the mounting electrode portion of the detection electrode and the reference electrode.

One aspect of the present disclosure includes a bottomed cylindrical solid electrolyte body in which a distal end portion of a cylindrical cylindrical portion is closed by a curved bottom portion;
A detection electrode provided at least on the outer surface of the cylindrical portion and exposed to a detection gas guided to the outside of the solid electrolyte body;
In a gas sensor comprising a sensor element that is provided at least on the inner surface of the cylindrical portion and is exposed to a reference gas guided to the inside of the solid electrolyte body,
The detection electrode is
A detection electrode provided on the entire circumference or a part of the circumference in the circumferential direction centering on the central axis at the position on the distal end side in the axial direction along the central axis of the cylinder;
A mounting electrode part that is provided on the entire circumference or a part of the circumferential direction at a position on the base end side in the axial direction and that contacts a terminal fitting mounted on the outer periphery of the cylindrical part;
A lead electrode part provided at a part of the circumferential direction at a position connecting the detection electrode part and the mounting electrode part, and having a narrow formation range in the circumferential direction compared to the mounting electrode part;
An insulating layer is provided between the cylindrical portion of the solid electrolyte body and the mounting electrode portion and the lead electrode portion to insulate the solid electrolyte body from the mounting electrode portion and the lead electrode portion. There is a gas sensor.

In the gas sensor, not only an insulating layer is provided between the lead electrode portion and the solid electrolyte body in the detection electrode, but also between the mounting electrode portion and the solid electrolyte body where the terminal fitting is mounted in the detection electrode. An insulating layer is provided. Thereby, in the case where the base end side portion of the sensor element is heated to a high temperature of 400 ° C. or higher, the solid electrolyte body is activated, and oxygen moves in the reference gas contacting the base end side portion of the sensor element. Further, it is possible to prevent a leak current from being generated between the mounting electrode portion of the detection electrode and the reference electrode.

Therefore, when the gas sensor is used as an air-fuel ratio sensor, even when the proximal end portion of the sensor element is exposed to a high temperature environment of 400 ° C. or higher, an offset current is added to the output current as the sensor output near the theoretical air-fuel ratio. Can be excluded. In addition, when the gas sensor is used as an oxygen sensor, an error voltage should not be included in the output voltage as the sensor output even when the proximal end portion of the sensor element is exposed to a high temperature environment of 400 ° C. or higher. Can do.

Therefore, according to the gas sensor, it is possible to prevent leak current from being generated between the mounting electrode portion of the detection electrode and the reference electrode, and to improve the accuracy of gas detection.

In addition, although the code | symbol of the parenthesis of each component shown in 1 aspect of this indication shows the correspondence with the code | symbol in the figure in embodiment, each component is not limited only to the content of embodiment.

Objects, features, advantages, and the like of the present disclosure will become more apparent from the following detailed description with reference to the accompanying drawings. The drawings of the present disclosure are shown below.
Explanatory drawing which shows the cross section of the gas sensor concerning Embodiment 1. FIG. FIG. 3 is an explanatory diagram illustrating a formation state of detection electrodes in the sensor element according to the first embodiment. FIG. 3 is an explanatory diagram illustrating a cross section of a tip portion of a sensor element according to the first embodiment. BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows the state which has arrange | positioned the gas sensor to the exhaust pipe of the internal combustion engine concerning Embodiment 1. FIG. Explanatory drawing which shows the cross section of the front-end | tip part of the sensor element used for the other detection system concerning Embodiment 1. FIG. FIG. 3 is an explanatory diagram illustrating a formation state of detection electrodes in other sensor elements according to the first embodiment. Explanatory drawing which shows the cross section of the front-end | tip part of the other sensor element concerning Embodiment 1. FIG. The perspective view which shows the state which attaches a terminal metal fitting to the sensor element concerning Embodiment 2. FIG. Explanatory drawing which expands and shows a part of cross section of the state which attaches a terminal metal fitting to a sensor element concerning Embodiment 2. FIG. Explanatory drawing which expands and shows a part of cross section of the state which attaches a terminal metal fitting to a sensor element concerning Embodiment 3. FIG. The graph which shows the relationship between the temperature of a sensor element concerning the confirmation test 1, and the output shift amount of an air fuel ratio. The graph which shows the relationship between the thickness of an insulating layer concerning the confirmation test 2, and the output shift amount of an air fuel ratio. The graph which shows the relationship between the temperature of a sensor element concerning the confirmation test 3, and the amount of shifts of an output voltage. The graph which shows the relationship between the thickness of an insulating layer concerning the confirmation test 4, and the amount of shifts of an output voltage. The graph which shows the relationship between the inclination-angle of a taper-shaped surface concerning the confirmation test 5, and the generation number of the defect in an insulating layer.

A preferred embodiment of the gas sensor described above will be described with reference to the drawings.
<Embodiment 1>
As shown in FIGS. 1 to 3, the gas sensor 1 of the present embodiment includes a sensor element 2. The sensor element 2 includes a bottomed cylindrical solid electrolyte body 3, a detection electrode 4A, and a reference electrode 4B. The solid electrolyte body 3 has ion conductivity at the activation temperature, and includes a cylindrical tube portion 31 and a curved bottom portion 32 that closes the tip of the tube portion 31. The detection electrode 4 A is provided on the outer surface 301 of the cylindrical portion 31 and is an electrode that is exposed to the detection gas G guided to the outside of the solid electrolyte body 3. The reference electrode 4 B is an electrode that is provided on the inner side surface 302 of the cylindrical portion 31 and the bottom portion 32 and is exposed to the reference gas A guided to the inside of the solid electrolyte body 3.

The detection electrode 4A has a detection electrode portion 41, a mounting electrode portion 43, and a lead electrode portion. As shown in FIG. 2, the detection electrode portion 41 is provided on the entire circumference in the circumferential direction C centering on the central axis O at a position on the distal end side L1 in the axial direction L along the central axis O of the cylindrical portion 31. ing. As shown in FIGS. 1 and 2, the mounting electrode portion 43 is provided in a part of the circumferential direction C at a position on the base end side L 2 in the axial direction L, and is a terminal mounted on the outer periphery of the cylindrical portion 31. Contact with the metal fitting 71. As shown in FIG. 2, the lead electrode portion 42 is provided in a part of the circumferential direction C at a position where the detection electrode portion 41 and the mounting electrode portion 43 are connected. The formation range is narrow.

Between the cylindrical part 31 of the solid electrolyte body 3 and the mounting electrode part 43 and the lead electrode part 42, as shown in FIGS. 2 and 3, the solid electrolyte body 3, the mounting electrode part 43, and the lead electrode part 42 are connected. An insulating layer 22 that insulates the gaps is provided. 2, 5, 6, and 8, for the sake of simplicity, the detection electrode 4 A is shown by hatching, and the portion where the insulating layer 22 is exposed on the surface is hatched. Show.

As shown in FIG. 8, in the sensor element 2 and the gas sensor 1 of the first and second embodiments, the direction along the central axis O of the sensor element 2 is referred to as the axial direction L, and the area around the central axis O of the sensor element 2 is The direction is referred to as a circumferential direction C, and the direction radially spreading from the central axis O of the sensor element 2 is referred to as a radial direction R. In the sensor element 2 and the gas sensor 1, the side on which the bottom 32 of the sensor element 2 is provided is referred to as a distal end side L1, and the side opposite to the distal end side L1 is referred to as a proximal end side L2.

Below, it explains in full detail about the gas sensor 1 of this form.
(Internal combustion engine 8)
As shown in FIG. 4, the gas sensor 1 is disposed in an exhaust pipe 81 through which exhaust gas exhausted from an internal combustion engine (engine) 8 of the vehicle flows. The gas sensor 1 performs gas detection using the exhaust gas flowing in the exhaust pipe 81 as the detection gas G and the atmosphere as the reference gas A. The gas sensor 1 of the present embodiment is used as an air-fuel ratio sensor for determining the air-fuel ratio of the internal combustion engine 8 determined from the composition of exhaust gas. The air-fuel ratio sensor is quantitatively continuously air-fuel ratio from a fuel-rich state where the ratio of fuel to air is larger than the stoichiometric air-fuel ratio to a fuel-lean state where the ratio of fuel to air is smaller than the stoichiometric air-fuel ratio. Can be detected.

As shown in FIG. 3, in the air-fuel ratio sensor, the detection electrode 4 A provided on one surface of the solid electrolyte body 3 and exposed to the detection gas G, and the other surface of the solid electrolyte body 3 are provided. A predetermined voltage for showing the limiting current characteristic is applied by the voltage application circuit 11 between the reference electrode 4B exposed to the reference gas A and the reference electrode 4B. In addition, in the state where this voltage is applied, a limit current generated between the detection electrode 4A and the reference electrode 4B via the solid electrolyte body 3 is detected by the current detection circuit 12. In other words, when the oxygen concentration of the exhaust gas as the detection gas G changes, the movement amount and movement direction of oxygen ions (O ²⁻ ) between the detection electrode 4A and the reference electrode 4B change, and the fuel rich side and The air-fuel ratio on the fuel lean side is quantitatively detected within a predetermined detection range. As shown in FIG. 1, the voltage application circuit 11 and the current detection circuit 12 are constructed in a control device 10 such as a sensor control unit.

In the air-fuel ratio sensor, when a voltage is applied between the detection electrode 4A and the reference electrode 4B, when the air-fuel ratio is on the fuel lean side, the reference electrode is connected from the detection electrode 4A via the solid electrolyte body 3. Oxygen ions (O ²⁻ ) move to 4B. On the other hand, when the air-fuel ratio is on the fuel rich side, oxygen ions (O ²⁻ ) are transferred from the reference electrode 4B to the detection electrode 4A via the solid electrolyte body 3 as the unburned gas chemically reacts at the detection electrode 4A. Move.

As shown in FIG. 5, the gas sensor 1 is used as an oxygen sensor that determines whether the air-fuel ratio of the internal combustion engine 8 determined from the composition of the exhaust gas is on the fuel rich side or the fuel lean side by ON-OFF. You can also. The oxygen sensor is connected to the detection electrode 4A and the reference through the solid electrolyte body 3 due to the difference in oxygen concentration between the atmosphere as the reference gas A that contacts the reference electrode 4B and the exhaust gas as the detection gas G that contacts the detection electrode 4A. The electromotive force generated between the electrodes 4B is detected by the electromotive force detection circuit 13. The electromotive force detection circuit 13 is formed in the sensor control unit. The oxygen sensor can also quantitatively detect the oxygen concentration of the exhaust gas based on the electromotive force generated between the detection electrode 4A and the reference electrode 4B.

The gas sensor 1 is used to maintain the air-fuel ratio in the internal combustion engine 8 in the vicinity of the theoretical air-fuel ratio in which the catalytic activity of the three-way catalyst disposed in the exhaust pipe 81 is effectively exhibited. The gas sensor 1 can be arranged at either the upstream side position or the downstream side position of the exhaust gas flow from the arrangement position of the three-way catalyst in the exhaust pipe 81. In particular, the gas sensor 1 of the present embodiment can be used by being disposed in the exhaust pipe 81 at a downstream position where the temperature of the exhaust gas becomes lower.

As shown in FIG. 4, in the exhaust pipe 81 of this embodiment, two

catalysts

82A and 82B are arranged in the direction of the flow of the exhaust gas. The two

catalysts

82A and 82B are an upstream catalyst 82A (also referred to as an S / C (Start Converter) catalyst) located on the upstream side and a downstream catalyst 82B (U / F) located downstream of the upstream catalyst 82A. (Also called “Under Floor” catalyst). The gas sensor 1 of the present embodiment is located downstream of the upstream catalyst 82A in the exhaust pipe 81 and downstream of the downstream catalyst 82B in the exhaust pipe 81. Placed in position. In other words, the gas sensor 1 of this embodiment is disposed at a position between the upstream catalyst 82A and the downstream catalyst 82B in the direction of the exhaust gas flow in the exhaust pipe 81.

Further, another gas sensor 1A is disposed in the exhaust pipe 81 at a position upstream of the upstream catalyst 82A. This other gas sensor functions as an air-fuel ratio sensor. Then, the air-fuel ratio of the exhaust gas is detected using the two gas sensors 1 and 1A, and the ECU (engine control unit) uses the air-fuel ratio received from the two gas sensors 1 and 1A to detect the fuel injection valve in the intake pipe. The air-fuel ratio of the internal combustion engine 8 is controlled by adjusting the opening degree.

It should be noted that the gas sensor 1 of this embodiment may be disposed in the exhaust pipe 81 at a position upstream of the upstream catalyst 82A. In general, an air-fuel ratio sensor is disposed in the exhaust pipe 81 at a position upstream of the upstream catalyst 82A, and an oxygen sensor is disposed at a position downstream of the upstream catalyst 82A.

In particular, when the gas sensor 1 is disposed at a more downstream position in the exhaust pipe 81, the temperature of the exhaust gas in contact with the gas sensor 1 becomes lower, and the condensed water easily collides with the gas sensor 1. The sensor element 2 of the present embodiment uses a bottomed cylindrical (cup-shaped) solid electrolyte body 3, and is effectively prevented from being cracked by condensed water present in the exhaust pipe 81.

(Sensor element 2)
As shown in FIGS. 2 and 3, the solid electrolyte body 3 of the sensor element 2 is mainly composed of zirconia, and is stabilized by replacing a part of zirconia with a rare earth metal element or an alkaline earth metal element. It consists of zirconia or partially stabilized zirconia. The solid electrolyte body 3 can be composed of yttria stabilized zirconia or yttria partially stabilized zirconia. The solid electrolyte body 3 has ion conductivity for conducting oxygen ions (O ²⁻ ) at a predetermined activation temperature. The detection electrode 4A and the reference electrode 4B contain platinum as a noble metal exhibiting catalytic activity for oxygen.

The bottom portion 32 of the solid electrolyte body 3 is formed in a hemispherical shape, and the cylindrical portion 31 of the solid electrolyte body 3 is formed in a cylindrical shape. An opening 33 through which the reference gas A can flow into the solid electrolyte body 3 is formed at a position opposite to the bottom 32 in the axial direction L of the solid electrolyte body 3. The outer diameter of each part in the axial direction L of the cylindrical part 31 is appropriately changed in consideration of attachment to the housing 61.

A protective layer 21 made of a ceramic porous body is provided at the tip of the sensor element 2 so as to cover at least the entire detection electrode portion 41 of the detection electrode 4A. The protective layer 21 in the air-fuel ratio sensor of this embodiment has a function as a diffusion resistance layer that limits the diffusion of the exhaust gas as the detection gas G. When a predetermined voltage is applied between the detection electrode 4A and the reference electrode 4B, the flow rate of the detection gas G passing through the protective layer 21 is limited, and a sensor output corresponding to the oxygen concentration in the detection gas G is generated. can get. The protective layer 21 also has a function of preventing the detection electrode 4A from being poisoned and wet. Further, a porous layer for preventing the detection electrode 4A from being poisoned and exposed to water may be provided outside the protective layer 21 as a diffusion resistance layer.

When the gas sensor 1 is used as an oxygen sensor, the protective layer 21 mainly has a function of preventing the detection electrode 4A from being poisoned and wet. In this case, the protective layer 21 may be formed from a plurality of layers having different porosity, composition, and the like.

As shown in FIGS. 1 and 3, the reference electrode 4 B is provided on the entire inner surface 302 of the solid electrolyte body 3. An inner terminal fitting 72 is attached to the proximal end L2 portion of the inner side surface 302 of the solid electrolyte body 3 so as to be in contact with the proximal end L2 portion of the reference electrode 4B. Since the gas sensor 1 of the present embodiment is used as an air-fuel ratio sensor, the reference electrode 4B and the inner terminal fitting 72 become positive due to the voltage applied between the reference electrode 4B and the detection electrode 4A, and the detection electrode 4A and the terminal fitting are connected. 71 is on the negative side.

The reference electrode 4B is formed as a partial electrode in the same manner as the detection electrode 4A. The detection electrode portion located on the most distal side L1, the attachment electrode portion located on the most proximal side L2, the detection electrode portion, and the attachment electrode It can also be formed by a lead electrode part connecting the parts.

The detection electrode portion 41 of the detection electrode 4A is a part that substantially performs gas detection such as detection of an air-fuel ratio in the detection electrode 4A. In other words, only the detection electrode part 41 is provided directly on the outer surface 301 of the solid electrolyte body 3 without the insulating layer 22 among the detection electrodes 4A. And in the sensor element 2, in order to stabilize the precision which performs gas detection, in other words, in order to reduce the dispersion | variation in the output of the gas sensor 1, the area of the detection electrode part 41 is prescribed | regulated. The detection electrode unit 41 is heated to a target temperature by the heater 5 disposed inside the solid electrolyte body 3 of the sensor element 2.

The lead electrode portion 42 of the detection electrode 4A is formed at one place in the circumferential direction C of the solid electrolyte body 3. The lead electrode portion 42 is formed in parallel with the central axis O and the axial direction L of the cylindrical portion 31 of the solid electrolyte body 3. In other words, both side ends in the circumferential direction C of the lead electrode portion 42 are parallel to the axial direction L.

The mounting electrode portion 43 of the detection electrode 4A is formed in the circumferential direction C at a position on the base end side L2 of the outer surface 301 of the solid electrolyte body 3. The mounting electrode portion 43 of this embodiment is formed only in a part of the outer surface 301 of the solid electrolyte body 3 in the circumferential direction C.

As shown in FIG. 3, the insulating layer 22 provided on the outer surface 301 of the sensor element 2 is not provided between the cylinder portion 31 and the detection electrode portion 41. The insulating layer 22 is provided on the entire bottom portion 32, the entire portion between the tubular portion 31 and the lead electrode portion 42, and the entire portion between the tubular portion 31 and the mounting electrode portion 43. The mounting electrode portion 43 of this embodiment is not provided up to the base end position of the outer side surface 301 of the sensor element 2. The mounting electrode portion 43 may be provided up to the base end position of the outer side surface 301 of the sensor element 2.

In this embodiment, the insulating layer 22 is not provided at the position where the detection electrode portion 41 is formed, and the insulating layer 22 is provided at a position closer to the base end than the bottom 32 and the detection electrode portion 41. The detection electrode 4 A is continuously provided from the detection electrode portion 41 to the outer surface of the insulating layer 22 provided on the bottom portion 32. Thereby, formation of electrode 4A can be made easy. The bottom electrode portion 411 provided on the outer surface of the insulating layer 22 at the bottom portion 32 does not function as an electrode for conducting oxygen ions (O ²⁻ ) due to the presence of the insulating layer 22.

Further, as shown in FIG. 6, the mounting electrode portion 43 of the detection electrode 4A may be formed on the entire circumference in the circumferential direction C. The detection electrode portion 41 of the detection electrode 4A may not necessarily be formed on the entire circumference in the circumferential direction C. Further, as shown in FIGS. 6 and 7, the insulating layer 22 can be provided only at a position closer to the base end side than the detection electrode portion 41 and not provided on the outer surface 301 of the bottom portion 32.

As shown in FIG. 3, the detection electrode 4 A is formed by plating the outer surface 301 of the solid electrolyte body 3 with an electrode material, and the reference electrode 4 B is formed on the inner surface 302 of the solid electrolyte body 3. The material is formed by plating. The insulating layer 22 is formed by applying a paste of an insulating material to the outer surface 301 of the solid electrolyte body 3 and sintering the paste together with the solid electrolyte body 3. When forming the insulating layer 22, the formation portion of the detection electrode portion 41 on the outer surface 301 of the solid electrolyte body 3 is masked with a tape or the like. In this state, the insulating layer 22 can be prevented from being formed in the masked portion by applying the paste and peeling off the tape or the like. The insulating layer 22 is formed of an insulating material containing at least one of aluminum oxide (Al ₂ O ₃ ), spinel (MgAl ₂ O ₄ ), and insulating glass. This insulating material is generally used in the gas sensor 1, and a sufficient insulating effect can be obtained by having a high specific resistance.

The insulating layer 22 of this embodiment is formed on the outer surface 301 of the solid electrolyte body 3 so as to have a uniform thickness as much as possible. In the insulating layer 22, the minimum thickness of the part located between the cylinder part 31 and the lead electrode part 42 and between the cylinder part 31 and the mounting electrode part 43 is 4 μm or more. The minimum thickness means the thickness of the portion where the thickness is the smallest. If the minimum thickness of the insulating layer 22 is less than 4 μm, the insulating effect may not be sufficiently obtained. The thickness of the insulating layer 22 can be set to, for example, 10 μm or less from the viewpoint of manufacturing.

(Heater 5)
As shown in FIG. 3, a heater 5 for heating the solid electrolyte body 3 is disposed inside the solid electrolyte body 3 of the sensor element 2. The heater 5 includes

ceramic bases

51A and 51B and a heating element 52 made of a conductor provided on the base 51B. A heat generating portion 521 that has the smallest cross-sectional area and generates heat by Joule heat when the heat generating member 52 is energized is formed at the tip of the heat generating member 52.

The heat generating portion 521 is formed in a shape meandering in the axial direction L at the tip portion of the heat generating body 52. The heat generating portion 521 is disposed at a position facing the inner peripheral side of the detection electrode portion 41 of the detection electrode 4A, and the solid electrolyte body 3, the reference electrode 4B, and the detection are performed so that the detection electrode portion 41 reaches a target temperature. The electrode 4A is heated. The heater 5 is formed by winding a sheet-like base material 51B provided with a heating element 52 around a base material 51A serving as a mandrel.

(Other configurations of the gas sensor 1)
As shown in FIG. 1, in addition to the sensor element 2 and the heater 5, the gas sensor 1 includes a housing 61 that holds the sensor element 2, a distal end side cover 62 that is attached to the distal end side L 1 of the housing 61, and a base of the housing 61. The base end side cover 63 attached to the end side L2 portion, the terminal fitting 71 attached to the outer side surface 301 of the base end side L2 portion of the sensor element 2, and the inner side surface of the base end side L2 portion of the sensor element 2 Inner terminal fitting 72 attached to 302 is provided.

(Housing 61)
As shown in FIG. 1, the housing 61 is formed with an insertion hole 611 penetrating in the axial direction L in order to hold the sensor element 2. The insertion hole 611 has a small diameter hole 612 located on the distal end side L1 in the axial direction L, and a large diameter hole 613 located on the proximal side L2 in the axial direction L and having a diameter larger than that of the small diameter hole 612. . The sensor element 2 is inserted into the small-diameter hole portion 612 and the large-diameter hole portion 613 of the insertion hole 611, and a sealing material such as talc powder and a sleeve disposed in the gap between the sensor element 2 and the large-diameter hole portion 613. 64 is held.

Further, the flange portion 34 which is the portion having the largest outer diameter in the sensor element 2 is locked to the end portion of the small-diameter hole portion 612, so that the sensor element 2 is prevented from coming out from the insertion hole 611 to the distal end side L1. ing. A caulking portion 615 that is bent toward the inner peripheral side is formed in a portion on the base end side L2 in the axial direction L of the housing 61. The sealing material 64 is compressed in the axial direction L between the caulking portion 615 and the flange portion 34, and the sensor element 2 is held by the housing 61. A portion of the sensor element 2 on the distal end side L1, particularly where the detection electrode portion 41 and the lead electrode portion 42 are formed, is disposed so as to protrude from the housing 61 to the distal end side L1 in the axial direction L.

(Front end side cover 62 and proximal end side cover 63)
As shown in FIG. 1, the portion of the housing 61 on the distal end side L1 in the axial direction L covers the portion of the sensor element 2 that protrudes from the housing 61 to the distal end side L1, and protects the sensor element 2 A cover 62 is attached. The front end side cover 62 is disposed in the exhaust pipe 81. A gas passage hole 621 for allowing the detection gas G to pass therethrough is formed in the distal end side cover 62. The front end side cover 62 can have a double structure or a single structure. The exhaust gas as the detection gas G flowing into the tip side cover 62 from the gas passage hole 621 of the tip side cover 62 passes through the protective layer 21 of the sensor element 2 and is guided to the detection electrode 4A.

The base end side cover 63 is attached to a portion of the housing 61 on the base end side L2 in the axial direction L. The proximal end cover 63 is disposed outside the exhaust pipe 81. An introduction hole 631 for introducing the atmosphere as the reference gas A into the proximal end side cover 63 is formed in a part of the proximal end side cover 63. A filter 632 that does not allow liquid to pass while allowing gas to pass is disposed in the introduction hole 631. The reference gas A introduced into the base end side cover 63 from the introduction hole 631 passes through the gap in the base end side cover 63 and is guided to the reference electrode 4B on the inner side surface 302 of the sensor element 2.

As shown in FIG. 1, a terminal fitting 71 that contacts the mounting electrode portion 43 of the detection electrode 4 A is mounted on the outer surface 301 of the base end side L 2 portion of the sensor element 2. Further, an inner terminal fitting 72 that is in contact with the base end side L2 portion of the reference electrode 4B is mounted on the inner side surface 302 of the base end side L2 portion of the sensor element 2. A lead wire 65 for electrically connecting the detection electrode 4A and the reference electrode 4B of the sensor element 2 to the external control device 10 is attached to the terminal fitting 71 and the inner terminal fitting 72. The lead wire 65 is held by a bush 66 disposed in the proximal end side cover 63.

(Function and effect)
In the gas sensor 1 of this embodiment, not only the insulating layer 22 is provided between the lead electrode portion 42 in the detection electrode 4A and the cylindrical portion 31 of the solid electrolyte body 3, but the terminal fitting 71 in the detection electrode 4A is mounted. The insulating layer 22 is provided up to the portion between the mounting electrode portion 43 which is a part and the cylindrical portion 31 of the solid electrolyte body 3. As a result, in the case where the base end L2 portion of the sensor element 2 is heated to a high temperature of 400 ° C. or higher, a leakage current is generated between the mounting electrode portion 43 of the detection electrode 4A and the reference electrode 4B. Can be prevented.

For this reason, when the gas sensor 1 is used as an air-fuel ratio sensor, even when the base end L2 portion of the sensor element 2 is exposed to a high temperature environment of 400 ° C. or higher, output as a sensor output in the vicinity of the theoretical air-fuel ratio. It is possible to prevent the offset current from being included in the current. Further, when the gas sensor 1 is used as an oxygen sensor, the output voltage as the sensor output does not include an error voltage even when the base end side L2 portion of the sensor element 2 is exposed to a high temperature environment of 400 ° C. or higher. Can be.

In the sensor element 2 having the bottomed cylindrical solid electrolyte body 3, when the temperature of the exhaust gas becomes high, the entire sensor element 2 tends to become high temperature. At this time, it was found that a minute leak current flows between the reference electrode 4B and the detection electrode 4A. In the conventional gas sensor 1, the influence of a minute leak current on the detection accuracy of the gas sensor 1 has not been regarded as a problem. However, from the viewpoint of further promoting emission reduction and fuel efficiency in recent years, the influence of minute leak currents on the detection accuracy of the gas sensor 1, particularly the stoichiometric point (the air-fuel ratio of the exhaust gas is the stoichiometric air-fuel ratio) due to the minute current. The point of detection) has become a problem. The gas sensor 1 of the present embodiment solves such a problem that has newly occurred in recent years.

The insulating layer 22 of this embodiment not only defines the formation area of the detection electrode portion 41 and suppresses variations in the sensor output of the gas sensor 1, but also oxygen in the reference gas A such as the atmosphere moves through the solid electrolyte body 3. It is provided in order to eliminate the leakage current.
In the gas sensor 1, the solid electrolyte body 3 in the portion on the tip side L1 of the sensor element 2 including the detection electrode portion 41 of the detection electrode 4A is heated to a temperature that activates the ionic conduction of oxygen. And the part of the base end side L2 of the sensor element 2 is often not heated up to the temperature at which the solid electrolyte body 3 is activated.

However, depending on the manner of combustion in the internal combustion engine 8, the temperature of the exhaust gas may become high, and the solid electrolyte body 3 in the portion on the base end side L2 of the sensor element 2 may be heated to a temperature at which it is activated. In this case, since oxygen in the reference gas A exists around the detection electrode 4A and the reference electrode 4B, this oxygen is ionized and passes through the solid electrolyte body 3 from the detection electrode 4A to the reference electrode 4B. Can happen. In other words, an electric current is generated by the conduction of oxygen ions in the portion on the base end side L2 of the solid electrolyte body 3 where the exhaust gas as the detection gas G does not reach. This current does not flow based on the change in the composition of the detection gas G, but becomes a leak current that causes an error in detection of the air-fuel ratio or the like.

When the gas sensor 1 is used as an air-fuel ratio sensor, a voltage is applied between the detection electrode 4A and the reference electrode 4B so that the reference electrode 4B is on the positive side, so that ionized oxygen is detected by the detection electrode 4A. It is possible that a leakage current is generated by passing through the solid electrolyte body 3 from the reference electrode 4B to the reference electrode 4B. When the gas sensor 1 is used as an oxygen sensor, the oxygen concentration of the reference gas A that contacts the detection electrode 4A and the terminal fitting 71 and the oxygen concentration of the reference gas A that contacts the reference electrode 4B and the inner terminal fitting 72 are as follows. By being slightly different, it is possible that ionized oxygen passes through the solid electrolyte body 3 and a leak current is generated.

In the gas sensor 1 of this embodiment, the occurrence of such a leakage current can be prevented by the arrangement of the insulating layer 22. Therefore, according to the gas sensor 1 of the present embodiment, it is possible to prevent leak current from being generated between the mounting electrode portion 43 of the detection electrode 4A and the reference electrode 4B, thereby improving the accuracy of gas detection.

<Embodiment 2>
In the sensor element 2 of this embodiment, the method of forming the insulating layer 22 provided between the lead electrode portion 42 and the mounting electrode portion 43 of the detection electrode 4A and the cylindrical portion 31 of the solid electrolyte element is devised.
As shown in FIGS. 8 and 9, the end portion on the base end side L2 in the axial direction L of the insulating layer 22 extends from the end portion on the base end side L2 in the axial direction L of the mounting electrode portion 43 to the base end side L2. Is provided. An end portion of the insulating layer 22 on the base end side L 2 constitutes an outermost shell portion of the outer side surface 301 of the cylindrical portion 31 and is exposed on the outer side surface 301 of the cylindrical portion 31. Further, the end portion on the base end side L2 of the insulating layer 22 has a tapered surface 221 whose thickness in the radial direction R centering on the central axis O decreases toward the base end side L2 of the cylindrical portion 31. The tapered surface 221 is a surface that guides the mounting of the terminal fitting 71 that is mounted on the outer periphery of the cylindrical portion 31 from the proximal end L2 of the cylindrical portion 31 toward the distal end L1. A general portion of the insulating layer 22 excluding the end portion on the base end side L2 is provided on the outer surface 301 of the solid electrolyte body 3 so as to have a uniform thickness.

In this embodiment, when the terminal fitting 71 is attached to the solid electrolyte body 3, the terminal fitting 71 can be brought into contact with the tapered surface 221 at the end portion on the proximal side L2 of the insulating layer 22. Then, the terminal fitting 71 can be slid on the tapered surface 221. Thereby, even if the terminal fitting 71 comes into contact with the end portion of the insulating layer 22 on the base end side L2, it is possible to prevent the end portion on the base end side L2 from being peeled off or chipped.

In the present embodiment, the entire tapered surface 221 at the end portion on the base end side L2 of the insulating layer 22 is exposed. In addition to this, a mounting electrode portion 43 may be provided on the surface of the tapered surface 221 at the front end side L1. In this case, only the surface at the position of the base end side L2 of the tapered surface 221 is exposed. The tapered surface 221 constitutes the outermost shell portion of the outer side surface 301 of the cylindrical portion 31, and becomes a surface that comes into contact with the terminal fitting 71 when the terminal fitting 71 is attached to the solid electrolyte body 3.

As shown in FIG. 9, the inclination angle θ of the tapered surface 221 with respect to the axial direction L parallel to the central axis O is 60 ° or less. When the inclination angle θ of the tapered surface 221 exceeds 60 °, there is a possibility that peeling, chipping, or the like may occur at the end portion on the base end side L2 of the insulating layer 22. When the inclination angle θ of the tapered surface 221 decreases, the length in the axial direction L of the end portion on the base end side L2 of the insulating layer 22 increases. Therefore, from the viewpoint of manufacturing, the inclination angle θ of the tapered surface 221 can be set to 15 ° or more, for example.

In addition, instead of forming the tapered surface 221 at the end portion on the base end side L2 of the insulating layer 22, a curved surface may be formed at the corner portion on the base end side L2 of the insulating layer 22. Also in this case, it is possible to make it difficult for the insulating layer 22 to be peeled off or chipped.

Other configurations, operational effects, etc. of the gas sensor 1 of the present embodiment are the same as those of the first embodiment. Also in this embodiment, the components indicated by the same reference numerals as those shown in the first embodiment are the same as those in the first embodiment.

<Embodiment 3>
Also in the sensor element 2 of this embodiment, the method of forming the insulating layer 22 provided between the lead electrode portion 42 and the mounting electrode portion 43 of the detection electrode 4A and the cylindrical portion 31 of the solid electrolyte element is devised.
As shown in FIG. 10, the end portion 222 on the base end side L2 in the axial direction L of the insulating layer 22 of this embodiment is continuous from the outer surface 301 of the tube portion 31 to the end surface 311 on the base end side L2 of the tube portion 31. Is provided. The corner portion 223 of the insulating layer 22 positioned at the corner portion on the base end side L2 of the cylindrical portion 31 is preferably formed in a curved surface shape or the like. The end portion 222 of the insulating layer 22 need not be provided on the entire end surface 311 on the base end side L2 of the cylindrical portion 31. The end portion 222 of the insulating layer 22 is provided on the outer peripheral side position of the end surface 311 on the base end side L2 of the cylindrical portion 31, and is provided on the center side position of the end surface 311 on the base end side L2 of the cylindrical portion 31. Absent.

When a paste of an insulating material for forming the insulating layer 22 is applied to the outer surface 301 of the cylindrical portion 31 of the solid electrolyte body 3 by a roll transfer method, this paste is applied to the end surface of the proximal end L2 of the cylindrical portion 31. It can be applied up to 311. Thereafter, the paste can be sintered together with the solid electrolyte body 3 to form the insulating layer 22 from the paste.
Also in the present embodiment, as in the case of the second embodiment, even when the terminal fitting 71 contacts the corner portion 223 on the base end side L2 of the insulating layer 22, the corner portion 223 on the base end side L2 is peeled off, chipped, or the like. Can be made difficult to occur. Other configurations, operational effects, and the like in the gas sensor 1 of the present embodiment are the same as those of the first embodiment. Also in this embodiment, the components indicated by the same reference numerals as those shown in the first embodiment are the same as those in the first embodiment.

The present disclosure is not limited to each embodiment, and further different embodiments can be configured without departing from the scope of the disclosure.

<Confirmation test 1>
In this test, the relationship between the temperature of the sensor element 2 and the error that occurs in the sensor output of the gas sensor 1 used as an air-fuel ratio sensor is shown in the gas sensor 1 of the first embodiment in which the insulating layer 22 is provided on the sensor element 2 (test Product) and a gas sensor (comparative product) in which the insulating layer 22 is not provided on the sensor element 2. FIG. 11 shows how much error has occurred in the sensor output of the gas sensor 1 when the temperature [° C.] of the sensor element 2 is appropriately changed.

Since the gas sensor 1 of the first embodiment is used as an air-fuel ratio sensor, the error generated in the sensor output is an output shift amount [A / F] (amount of change in air-fuel ratio) indicating an offset amount from the detected value of the air-fuel ratio. The output shift amount is, for example, an error amount when the detected value of the air-fuel ratio is supposed to be 14.7 indicating the stoichiometric air-fuel ratio but is shown as a value slightly larger than 14.7. . The temperature of the sensor element 2 was the average value of the temperature from the portion on the distal end side L1 in the axial direction L of the sensor element 2 to the portion on the proximal end side L2. The film thickness of the general part of the insulating layer 22 was 10 μm.

As shown in the figure, in the test gas sensor 1, the output shift amount of the sensor output is almost 0 (zero) in the high temperature range where the temperature of the sensor element 2 is about 280 ° C. or more and about 540 ° C. or less. I understood that. On the other hand, in the comparative gas sensor, it was found that an output shift amount occurs when the temperature of the sensor element 2 reaches about 420 ° C. or higher, and the output shift amount increases as the temperature of the sensor element 2 increases. As a result, the gas sensor 1 for detecting the air-fuel ratio of the first embodiment suppresses a leak current generated between the reference electrode 4B and the detection electrode 4A of the sensor element 2, and an offset error due to the leak current almost occurs in the sensor output. I found out that I can do it.

<Confirmation test 2>
In this test, the relationship between the thickness of the insulating layer 22 provided on the outer surface 301 of the cylindrical portion 31 of the solid electrolyte body 3 and the error generated in the sensor output of the gas sensor 1 was confirmed. FIG. 12 shows how much error occurs in the sensor output of the gas sensor 1 of the first embodiment when the thickness [μm] of the insulating layer 22 is appropriately changed. Since the gas sensor 1 of the first embodiment is used as an air-fuel ratio sensor, the error generated in the sensor output is an output shift amount [A / F] (amount of change in air-fuel ratio) indicating an offset amount from the detected value of the air-fuel ratio.

The thickness of the insulating layer 22 was the average value of the thickness of the general portion of the insulating layer 22 excluding the end portion on the base end side L2 of the insulating layer 22 on which the tapered surface 221 was formed. The thickness of the insulating layer 22 indicates the minimum thickness of a portion of the insulating layer 22 that is located between the cylindrical portion 31 and the lead electrode portion 42 and between the cylindrical portion 31 and the mounting electrode portion 43. The temperature of the sensor element 2, which is an average value of the temperature from the portion on the distal end side L1 in the axial direction L of the sensor element 2 to the portion on the proximal end side L2, was 550 ° C.

As shown in the figure, it can be seen that the output shift amount of the sensor output increases as the thickness of the insulating layer 22 decreases. And when the thickness of the insulating layer 22 becomes thinner than 4 micrometers, it turns out that the output shift amount is increasing rapidly. When the thickness of the insulating layer 22 is less than 4 μm, the uneven protrusions formed on the surface of the solid electrolyte body 3 appear on the surface of the insulating layer 22, and the insulating layer 22 causes the solid electrolyte body 3 and the detection electrode 4A to be formed. This is considered to be because the insulation with the mounting electrode portion 43 cannot be sufficiently performed. Therefore, it can be said that the minimum thickness of the insulating layer 22 is preferably 4 μm or more in order to sufficiently obtain the insulating effect of the insulating layer 22.

<Confirmation test 3>
In this test, the relationship between the temperature of the sensor element 2 and the error that occurs in the sensor output of the gas sensor 1 used as an oxygen sensor is expressed as the gas sensor 1 of the first embodiment in which the insulating layer 22 is provided on the sensor element 2 (test product). ) And a gas sensor (comparative product) in which the sensor element 2 is not provided with the insulating layer 22. FIG. 13 shows how much error has occurred in the sensor output of the gas sensor 1 when the temperature of the sensor element 2 is appropriately changed.

The error that occurs in the sensor output is a shift in the output voltage that indicates how much the output voltage (electromotive force) of the gas sensor 1 changes when the detected gas G is at the stoichiometric air-fuel ratio when the temperature of the sensor element 2 changes. Indicated by quantity [V]. The temperature of the sensor element 2 was the average value of the temperature from the portion on the distal end side L1 in the axial direction L of the sensor element 2 to the portion on the proximal end side L2. The film thickness of the general part of the insulating layer 22 was 10 μm.

As shown in the figure, in the test gas sensor 1, the shift amount of the output voltage is close to 0 (zero) in the high temperature range where the temperature of the sensor element 2 is about 270 ° C. or more and about 600 ° C. or less. I understood. On the other hand, in the comparative gas sensor, when the temperature of the sensor element 2 reaches about 380 ° C. or higher, the output voltage shift amount occurs, and as the sensor element 2 temperature increases, the output voltage shift amount increases. It was. As a result, the gas sensor 1 for detecting the oxygen concentration according to the first embodiment suppresses a leak current generated between the reference electrode 4B and the detection electrode 4A of the sensor element 2, and an offset error due to the leak current almost occurs in the sensor output. I found out that I can do it.

<Confirmation test 4>
In this test, the relationship between the thickness of the insulating layer 22 provided on the outer surface 301 of the cylindrical portion 31 of the solid electrolyte body 3 and the error generated in the sensor output of the gas sensor 1 used as an oxygen sensor was confirmed. FIG. 14 shows how much error occurs in the sensor output of the gas sensor 1 of the first embodiment when the thickness [μm] of the insulating layer 22 is appropriately changed. The error that occurs in the sensor output is a shift in the output voltage that indicates how much the output voltage (electromotive force) of the gas sensor 1 changes when the detected gas G is at the stoichiometric air-fuel ratio when the thickness of the insulating layer 22 changes. Indicated by quantity [V]. The thickness of the insulating layer 22 and the temperature of the sensor element 2 are the same as in the confirmation test 2.

As shown in the figure, it can be seen that the shift amount of the output voltage increases as the thickness of the insulating layer 22 decreases. And when the thickness of the insulating layer 22 becomes thinner than 4 micrometers, it turns out that the shift amount is increasing rapidly. When the thickness of the insulating layer 22 is less than 4 μm, the uneven protrusions formed on the surface of the solid electrolyte body 3 are reflected on the surface of the insulating layer 22, and the insulating layer 22 causes the solid electrolyte body 3 and the detection electrode 4A to be formed. This is considered to be because the insulation with the mounting electrode portion 43 cannot be sufficiently performed. Therefore, it can be said that the minimum thickness of the insulating layer 22 is preferably 4 μm or more in order to sufficiently obtain the insulating effect of the insulating layer 22.

<Confirmation test 5>
In this test, with respect to the gas sensor 1 shown in the second embodiment, the inclination angle θ of the tapered surface 221 at the end of the base layer L2 of the insulating layer 22 and the number of defects such as peeling and chipping in the insulating layer 22 are generated. And confirmed the relationship. The number of occurrences of this defect was counted when peeling or chipping occurred in the insulating layer 22 when the terminal fitting 71 was mounted on the outer surface 301 of the solid electrolyte body 3. The presence or absence of peeling or chipping was confirmed 20 times for each inclination angle θ.

As shown in FIG. 15, it was found that no peeling or chipping occurred in the insulating layer 22 when the inclination angle θ of the tapered surface 221 was 60 ° or less. On the other hand, when the inclination angle θ of the tapered surface 221 exceeds 60 °, it has been found that peeling or chipping occurs several times. From this result, it can be said that the insulating layer 22 can be protected when the terminal fitting 71 is assembled to the sensor element 2 by setting the inclination angle θ of the tapered surface 221 to 60 ° or less.

Claims

A bottomed cylindrical solid electrolyte body (3) in which the tip of the cylindrical cylinder (31) is closed by a curved bottom (32);
A detection electrode (4A) provided on at least the outer surface (301) of the cylindrical portion and exposed to a detection gas (G) guided to the outside of the solid electrolyte body;
A gas sensor comprising a sensor element (2) provided at least on an inner surface (302) of the cylindrical portion and having a reference electrode (4B) exposed to a reference gas (G) guided to the inside of the solid electrolyte body In 1)
The detection electrode is
Detecting electrode portions provided on the entire circumference or a part of the circumferential direction (C) centered on the central axis line at a position on the distal end side in the axial direction (L) along the central axis line (O) of the cylindrical portion ( 41),
A mounting electrode portion (43) that is provided on the entire circumference or a part of the circumferential direction at a position on the base end side in the axial direction and that contacts a terminal fitting (71) mounted on the outer periphery of the cylindrical portion;
A lead electrode portion (42) provided in a part of the circumferential direction at a position connecting the detection electrode portion and the mounting electrode portion and having a narrower formation range in the circumferential direction than the mounting electrode portion; And
Between the cylindrical portion of the solid electrolyte body and the mounting electrode portion and the lead electrode portion, there is an insulating layer (22) that insulates the solid electrolyte body from the mounting electrode portion and the lead electrode portion. A gas sensor is provided.
An electromotive force generated between the detection electrode and the reference electrode via the solid electrolyte body due to a difference in oxygen concentration between the reference gas in contact with the reference electrode and the detection gas in contact with the detection electrode. The gas sensor according to claim 1, configured to detect.
A diffusion resistance layer (21) that covers at least the entire detection electrode portion of the detection electrode and restricts diffusion of the detection gas is provided on the outer surface of the cylindrical portion of the solid electrolyte body,
The device is configured to detect a limit current generated between the detection electrode and the reference electrode via the solid electrolyte body in a state where a voltage is applied between the detection electrode and the reference electrode. Item 2. The gas sensor according to Item 1.
An end portion on the base end side in the axial direction of the insulating layer is provided to a base end side rather than an end portion on the base end side in the axial direction of the mounting electrode portion, and is exposed to an outer surface of the cylindrical portion. And the axial base end side of the cylindrical portion so as to guide the terminal fitting mounted on the outer periphery of the cylindrical portion from the base end side in the axial direction of the cylindrical portion toward the distal end side. The gas sensor according to any one of claims 1 to 3, further comprising a tapered surface (221) in which a thickness in a radial direction (R) centering on the central axis decreases.
The gas sensor according to claim 4, wherein an inclination angle of the tapered surface with respect to the central axis is 60 ° or less.
The end (222) on the base end side in the axial direction of the insulating layer is continuously provided from the outer surface of the tube portion to the end surface (311) on the base end side of the tube portion. 4. The gas sensor according to any one of items 1 to 3.
The gas sensor according to any one of claims 1 to 6, wherein a minimum thickness of a portion of the insulating layer located between the cylindrical portion and the mounting electrode portion and the lead electrode portion is 4 μm or more.
The solid electrolyte body contains zirconia,
The reference electrode and the detection electrode contain a noble metal,
The gas sensor according to any one of claims 1 to 7, wherein the insulating layer contains at least one of aluminum oxide, spinel, and insulating glass.
The gas sensor is disposed in an exhaust pipe (81) of an internal combustion engine (8) through which exhaust gas as the detection gas flows.
In the exhaust pipe, one catalyst (82A) or a plurality of catalysts (82A, 82B) are arranged in the direction of the flow of the exhaust gas,
The gas sensor according to any one of claims 1 to 8, wherein the gas sensor is arranged downstream of at least one of the catalysts in the flow of the exhaust gas in the exhaust pipe.