WO2020110872A1

WO2020110872A1 - Gas sensor

Info

Publication number: WO2020110872A1
Application number: PCT/JP2019/045534
Authority: WO
Inventors: 澤田　高志
Original assignee: 株式会社デンソー
Priority date: 2018-11-28
Filing date: 2019-11-21
Publication date: 2020-06-04
Also published as: JP2020085733A; JP7024696B2; DE112019005924T5

Abstract

A gas sensor (1) according to the present invention is provided with: a sensor element (2) that has a detection part (21) which is exposed to a gas (G) to be detected and an atmosphere introduction part (361) into which the atmosphere (A) is introduced; and an atmosphere cover (46) in which the atmosphere (A) to be introduced into the sensor element (2) is taken via a vent hole (461). An atmosphere path (460) within the atmosphere cover (46), said atmosphere path (460) being positioned between the vent hole (461) and the atmosphere introduction part (361), is provided with a two-layer atmosphere filter (5) which is composed of a first filter part that has a function of repelling the water in the atmosphere (A) and a second filter part that has a function of adsorbing a poisoning substance in the atmosphere (A).

Description

Gas sensor

Cross-reference of related applications

This application is based on Japanese Patent Application No. 2018-222587 filed on November 28, 2018, and the contents of the description are incorporated herein.

The present disclosure relates to a gas sensor configured so that the atmosphere is introduced therein.

The gas sensor uses, for example, exhaust gas exhausted from an internal combustion engine (engine) mounted on a vehicle as a detection target gas, detects oxygen, NOx (nitrogen oxide), etc. contained in the detection target gas, or detects the air-fuel ratio of the exhaust gas. Used for detection etc. Further, in the gas sensor, the air provided as a reference for referencing the gas to be detected is taken into the electrodes provided on the solid electrolyte body that constitutes the sensor element.

The gas sensor is attached to the exhaust pipe of an internal combustion engine, and the atmosphere around the exhaust pipe may contain various substances generated from the engine room of the vehicle. Examples of the substance in the atmosphere include Si (silicon) and S (sulfur) generated from rubber, hose, caulking, sealing, oil, rust preventive, lubricant and the like.

When a substance such as Si is mixed in the air and taken into the gas sensor, this substance may become a poisonous substance that attaches to the electrode exposed to the air and deteriorates the electrode. When the electrode is deteriorated by the poisoning substance, the performance of the sensor element may not be sufficiently exerted, and the detection accuracy and responsiveness of the gas sensor may be deteriorated.

In a conventional gas sensor, a filter that allows the atmosphere to pass through but does not allow water to pass through is provided at the inlet of the atmosphere cover that introduces the atmosphere into the gas sensor. Further, Patent Document 1 discloses a filter for a gas sensor having a first filter section that adsorbs poisoning gas under a normal temperature and normal humidity environment and a second filter section that adsorbs poisoning gas under a high temperature and high humidity environment. There is.

JP, 2005-135270, A

The filter used in the atmospheric cover of the conventional gas sensor does not have the property of not allowing permeation of poisonous substances (poisoning gas). That is, the conventional gas sensor has not been devised to protect the electrodes exposed to the atmosphere from the poisonous substances contained in the atmosphere.

On the other hand, the gas sensor filter described in Patent Document 1 is provided in a path through which a gas to be detected such as exhaust gas passes. That is, this gas sensor filter protects the electrode exposed to the gas to be detected from the poisonous substances contained in the gas to be detected.

Therefore, in order to protect the electrodes exposed to the atmosphere from water and poisonous substances, further measures are required.

The present disclosure provides a gas sensor capable of protecting an electrode of a sensor element exposed to the atmosphere from water and poisonous substances.

One aspect of the present disclosure is a sensor element having a detection unit exposed to a gas to be detected and an atmosphere introduction unit into which the atmosphere is introduced,
An atmosphere cover in which the atmosphere introduced into the sensor element is taken in through a vent,
A first filter unit having a function of repelling or trapping water in the atmosphere and an adsorbing poisoning substance in the atmosphere are provided in an atmosphere path between the vent hole and the atmosphere introducing unit in the atmosphere cover. Alternatively, the second sensor having a function of capturing the gas is provided in the gas sensor which is stacked, separated, or mixed.

In the gas sensor according to the one aspect, two types of filter units are provided in the atmosphere cover between the ventilation port and the atmosphere introducing unit in the atmosphere cover. The two types of filter sections are composed of a first filter section having a function of repelling or capturing water in the atmosphere and a second filter section having a function of adsorbing or capturing a poisonous substance in the atmosphere. There is.

Then, even when the atmosphere around the gas sensor contains water, the water can be repelled or captured by the first filter unit. This can prevent water from entering the atmosphere-introducing portion of the sensor element, and protect the electrode of the sensor element exposed to the atmosphere from being exposed to water.

Further, there is a case where the atmosphere around the gas sensor contains poisoning substances such as Si (silicon), S (sulfur), Si or S compounds, which may poison the electrode (catalyst) of the sensor element. However, this poisoning substance can be adsorbed or captured by the second filter unit. As a result, it is possible to prevent the poisoning substance from entering the atmosphere introduction portion of the sensor element, and it is possible to prevent the electrode of the sensor element exposed to the atmosphere from being poisoned.

Note that both the first filter section and the second filter section have the property of allowing the permeation of gases such as oxygen and nitrogen. When Si constitutes silicone (silicon-containing resin) or the like, it may exist as a gas poisoning substance. In this case, it is preferable that the second filter section has a function of adsorbing or capturing a gas that can be a poisoning substance in the atmosphere.

In addition, the first filter portion and the second filter portion are in a stacked state in which they are in close contact with each other, in a separated state in which they are separated from each other, or one of them is arranged inside the other, or both are mixed. It can have various forms as a mixed state.

Either of the first filter portion and the second filter portion may be arranged at a position close to the vent hole. In other words, the atmosphere can pass through the second filter unit after passing through the first filter unit, and can pass through the first filter unit after passing through the second filter unit. However, since the size of water droplets and the like is larger than the size of the poisoning substance, it is preferable that the atmosphere passes through the second filter unit after passing through the first filter unit.

As described above, according to the gas sensor of the one aspect, the electrode of the sensor element exposed to the atmosphere can be protected from water and poisonous substances.

Note that the reference numerals in parentheses of the constituent elements shown in one aspect of the present disclosure show the corresponding relationship with the reference numerals in the drawings in the embodiment, but the constituent elements are not limited to only the contents of the embodiment.

Objects, features, advantages, etc. of the present disclosure will be made clearer by the following detailed description with reference to the accompanying drawings. The drawings of the present disclosure are shown below.
FIG. 1 is an explanatory view showing a cross section of a gas sensor according to the first embodiment. FIG. 2 is an explanatory diagram showing an enlarged cross section of a part of the gas sensor according to the first embodiment. FIG. 3 is an explanatory diagram showing a cross section of the sensor element according to the first embodiment. FIG. 4 is a sectional view taken along line IV-IV of FIG. 3, showing the sensor element according to the first embodiment. FIG. 5 is a VV sectional view of FIG. 3 showing the sensor element according to the first embodiment. FIG. 6 is an explanatory diagram showing a cross section of the gas sensor according to the second embodiment. FIG. 7 is an explanatory diagram showing an enlarged part of the cross section of the gas sensor according to the second embodiment. FIG. 8 is an explanatory view showing an enlarged cross section of a part of the gas sensor according to the third embodiment. FIG. 9: is explanatory drawing which expands and shows a partial cross section of another gas sensor concerning Embodiment 3. As shown in FIG. FIG. 10 is an explanatory diagram showing a cross section of the first filter portion and the second filter portion according to the third embodiment. FIG. 11 is an explanatory diagram showing a cross section of another first filter portion and another second filter portion according to the third embodiment. FIG. 12 is an explanatory diagram showing a cross section of the sensor element according to the fourth embodiment. FIG. 13 is a cross-sectional view taken along line XIII-XIII of FIG. 12, showing a sensor element according to the fourth embodiment.

A preferred embodiment of the gas sensor described above will be described with reference to the drawings.
<Embodiment 1>
As shown in FIGS. 1 and 2, the gas sensor 1 of the present embodiment has a sensor element 2 having a detection unit 21 exposed to the gas G to be detected and an atmosphere introduction unit 361 into which the atmosphere A is introduced, and is introduced into the sensor element 2. Atmospheric air A that is taken in through the vent 461 is provided. In the atmosphere path 460 between the ventilation port 461 and the atmosphere introducing section 361 in the atmosphere cover 46, the first filter section 51 having a function of repelling water in the atmosphere A and the poisonous substance in the atmosphere A. And a second filter portion 52 having a function of adsorbing The 1st filter part 51 and the 2nd filter part 52 of this form are laminated|stacked on each other, and are formed as the integrated two-layer atmospheric filter 5.

As shown in FIGS. 3 to 5, the sensor element 2 of the present embodiment is provided with a plate-shaped solid electrolyte body 31 and a first main surface 301 of the solid electrolyte body 31, and is exposed to the detection target gas G. The electrode 311, the atmospheric electrode 312 provided on the second main surface 302 of the solid electrolyte body 31 exposed to the atmosphere A, and the first main surface 301 of the solid electrolyte body 31 adjacent to the detection electrode 311 are adjacent to the first main surface 301. The gas chamber 35, into which the detection target gas G is introduced via the diffusion resistance portion 32, and the second major surface 302 of the solid electrolyte body 31 are formed so as to accommodate the atmosphere electrode 312. Atmospheric duct 36. The atmosphere introducing portion 361 is formed by the rear end opening of the atmosphere duct 36.

The gas sensor 1 of this embodiment will be described below in detail.
(Gas sensor 1)
As shown in FIG. 1, the gas sensor 1 is arranged at an attachment port 71 of an exhaust pipe 7 of an internal combustion engine (engine) of a vehicle, and an exhaust gas flowing through the exhaust pipe 7 is used as a detection target gas G, and an oxygen concentration in the detection target gas G is increased. And so on. The gas sensor 1 can be used as an air-fuel ratio sensor (A/F sensor) that obtains an air-fuel ratio in an internal combustion engine based on the oxygen concentration in the exhaust gas, the unburned gas concentration, and the like. In addition to the air-fuel ratio sensor, the gas sensor 1 can be used for various purposes for obtaining oxygen concentration.

A catalyst for purifying harmful substances in the exhaust gas is arranged in the exhaust pipe 7, and the gas sensor 1 should be arranged either upstream or downstream of the catalyst in the flow direction of the exhaust gas in the exhaust pipe 7. You can also Further, the gas sensor 1 can also be arranged in the suction side pipe of the supercharger, which uses the exhaust gas to increase the density of the air sucked by the internal combustion engine. Further, the pipe in which the gas sensor 1 is arranged may be a pipe in an exhaust gas recirculation mechanism that recirculates a part of the exhaust gas exhausted from the internal combustion engine to the exhaust pipe 7 to the intake pipe of the internal combustion engine.

The air-fuel ratio sensor is quantitatively continuous from the fuel rich state where the ratio of fuel to air is higher than the theoretical air-fuel ratio to the state of fuel lean where the ratio of fuel to air is lower than the theoretical air-fuel ratio. Can be detected. In the air-fuel ratio sensor, when the diffusion resistance part (diffusion rate controlling part) 32 restricts the diffusion speed of the detection target gas G guided to the gas chamber 35, oxygen ions are generated between the detection electrode 311 and the atmospheric electrode 312. A predetermined voltage is applied to show the limiting current characteristic that a current corresponding to the amount of movement of (O ²⁻ ) is output.

In the air-fuel ratio sensor, when the air-fuel ratio on the fuel lean side is detected, when oxygen contained in the detection target gas G becomes ions and moves from the detection electrode 311 to the atmosphere electrode 312 via the solid electrolyte body 31. The current that occurs in is detected. Further, in the air-fuel ratio sensor, when the air-fuel ratio on the fuel rich side is detected, in order to react unburned gas (hydrocarbon, carbon monoxide, hydrogen, etc.) contained in the detection target gas G, the atmospheric electrode 312 is used. The oxygen that has become ions moves from the above to the detection electrode 311 through the solid electrolyte body 31, and the current generated when the unburned gas reacts with the oxygen is detected.

When the air-fuel ratio detected by the air-fuel ratio sensor becomes an air-fuel ratio on the more fuel rich side such as A/F=10 (air mass/fuel mass is 10) or less, a large amount of unburned gas is generated. In order to burn, it is necessary to transfer a sufficient amount of oxygen from the atmospheric electrode 312 to the detection electrode 311 via the solid electrolyte body 31. In this case, if the atmospheric electrode 312 is in a deteriorated state due to a poisoning substance adhering to the atmospheric electrode 312 or the atmospheric electrode 312 being oxidized by water, a catalyst that decomposes and ionizes oxygen molecules in the atmospheric electrode 312. The performance deteriorates, and it becomes difficult to send sufficient oxygen ions from the atmospheric electrode 312 to the detection electrode 311 via the solid electrolyte body 31. As a result, the air-fuel ratio detection performance on the fuel rich side deteriorates due to the decrease in the activity of the atmosphere electrode 312.

Further, when a gaseous poisoning substance enters the atmosphere cover 46 through the vent hole 461 of the atmosphere cover 46, the amount of the poisoning substance invades the oxygen content of the atmosphere A introduced into the atmosphere introducing portion 361 of the sensor element 2. The pressure will decrease. It is also assumed that the poisoning substance becomes a gaseous oxide in the atmosphere cover 46 and reduces the oxygen partial pressure of the atmosphere A introduced into the atmosphere introducing unit 361. If the partial pressure of oxygen in the atmosphere cover 46 decreases, there is a possibility that sufficient oxygen cannot be supplied to the atmosphere electrode 312. Therefore, the presence of the gaseous poisoning substance or the oxide of the gaseous poisoning substance in the atmosphere cover 46 reduces the air-fuel ratio detection performance on the fuel rich side.

On the other hand, in the gas sensor 1 of the present embodiment, the first filter portion 51 and the second filter portion 52 prevent the poisonous substance and water from entering the atmosphere cover 46, particularly the atmosphere introducing portion 361. As a result, the poisoning substance is hardly attached to the air electrode 312 or the water is not oxidized, and the catalytic performance of the air electrode 312 is unlikely to be deteriorated. Further, the second filter portion 52 makes it possible to prevent the oxygen partial pressure in the atmosphere cover 46, particularly in the atmosphere introducing portion 361, from being lowered. Therefore, it is possible to suppress a decrease in the air-fuel ratio detection performance on the fuel rich side.

(Other gas sensor 1)
In addition to using the air-fuel ratio sensor, the gas sensor 1 turns ON/OFF whether the air-fuel ratio of the engine obtained from the composition of the gas G to be detected is on the fuel rich side or the fuel lean side with respect to the theoretical air-fuel ratio. It may be an oxygen sensor that is discriminated by. In the oxygen sensor, an electromotive force generated between the atmospheric electrode 312 and the detection electrode 311 is detected by the difference in oxygen concentration between the atmosphere A and the detection target gas G, and whether or not this electromotive force exceeds a predetermined threshold value. The sensor output is output. When the gas sensor 1 is used as an oxygen sensor, the use of the first filter unit 51 and the second filter unit 52 makes it possible to suppress a decrease in the oxygen concentration detection performance.

The gas sensor 1 may be a sensor that detects the concentration of a specific gas component such as NOx (nitrogen oxide). In the NOx sensor, a pump electrode that pumps oxygen from the detection electrode 311 to the atmosphere electrode 312 by applying a voltage is arranged on the upstream side of the flow of the detection target gas G that contacts the detection electrode 311. The atmosphere electrode 312 is also formed at a position facing the pump electrode via the solid electrolyte body 31. When the gas sensor 1 is used as a NOx sensor, the use of the first filter unit 51 and the second filter unit 52 makes it possible to suppress a decrease in NOx concentration detection performance.

(Sensor element 2)
As shown in FIGS. 3 to 5, the sensor element 2 of the present embodiment is formed in a long rectangular shape, and includes a solid electrolyte body 31, a detection electrode 311 as a pair of electrodes, an atmospheric electrode 312, and a first insulation. The body 33A, the second insulator 33B, the gas chamber 35, the atmospheric duct 36, and the heating element 34 are provided. The sensor element 2 is of a laminated type in which insulators 33A, 33B and a heating element 34 are laminated on a solid electrolyte body 31.

In the present embodiment, the lengthwise direction L of the sensor element 2 means a direction in which the sensor element 2 extends in a long shape. Further, a direction orthogonal to the lengthwise direction L, in which the solid electrolyte body 31 and the

insulators

33A and 33B are laminated, in other words, a direction in which the solid electrolyte body 31, the

insulators

33A and 33B and the heat generating body 34 are laminated. Is referred to as a stacking direction D. A direction orthogonal to both the lengthwise direction L and the stacking direction D is referred to as a width direction W. Further, in the longitudinal direction L of the sensor element 2, the side on which the detection portion 21 is formed is referred to as the front end side L1, and the side opposite to the front end side L1 is referred to as the rear end side L2.

(Solid electrolyte body 31, detection electrode 311, and atmospheric electrode 312)
As shown in FIGS. 3 and 4, the solid electrolyte body 31 has conductivity of oxygen ions (O ²⁻ ) at a predetermined activation temperature. The detection electrode 311 is provided on the first main surface 301 of the solid electrolyte body 31 in contact with the detection target gas G, and the atmospheric electrode 312 is the second main surface 302 of the solid electrolyte body 31 in contact with the atmosphere A. It is provided in. The detection electrode 311 and the atmospheric electrode 312 are opposed to each other with the solid electrolyte body 31 in between at the tip end side L1 of the sensor element 2 in the longitudinal direction L. At a portion of the sensor element 2 on the tip side L1 in the longitudinal direction L, a detection unit 21 including a detection electrode 311 and an atmospheric electrode 312 and a portion of the solid electrolyte body 31 sandwiched between these

electrodes

311 and 312 is provided. Has been formed. The first insulator 33A is stacked on the first main surface 301 of the solid electrolyte body 31, and the second insulator 33B is stacked on the second main surface 302 of the solid electrolyte body 31.

The solid electrolyte body 31 is composed of a zirconia-based oxide, contains zirconia as a main component (containing 50 mass% or more), and stabilized zirconia or a part thereof in which a part of the zirconia is replaced by a rare earth metal element or an alkaline earth metal element. It consists of stabilized zirconia. A part of the zirconia forming the solid electrolyte body 31 can be replaced with yttria, scandia or calcia.

The detection electrode 311 and the atmospheric electrode 312 contain platinum as a noble metal exhibiting catalytic activity for oxygen, and zirconia-based oxide as a co-material with the solid electrolyte body 31. The common material is a combination of the solid electrolyte body 31 with the detection electrode 311 and the atmosphere electrode 312 formed of the electrode material when the paste-like electrode material is printed (applied) on the solid electrolyte body 31 and the both are sintered. It is for maintaining strength.

As shown in FIG. 3, an electrode lead portion 313 for electrically connecting these

electrodes

311 and 312 to the outside of the gas sensor 1 is connected to the detection electrode 311 and the atmospheric electrode 312, and the electrode lead portion 313 is , To the portion on the rear end side L2 in the lengthwise direction L.

(Gas chamber 35)
As shown in FIGS. 3 and 4, on the first main surface 301 of the solid electrolyte body 31, a gas chamber 35 surrounded by the first insulator 33A and the solid electrolyte body 31 is formed adjacently. The gas chamber 35 is formed at a position where the detection electrode 311 is housed in the first insulator 33A. The gas chamber 35 is formed as a space portion closed by the first insulator 33A, the diffusion resistance portion 32, and the solid electrolyte body 31. The detection target gas G, which is the exhaust gas flowing through the exhaust pipe 7, passes through the diffusion resistance portion 32 and is introduced into the gas chamber 35.

(Diffusion resistance part 32)
The diffusion resistance portion 32 of the present embodiment is formed adjacent to the tip side L1 of the gas chamber 35 in the longitudinal direction L. The diffusion resistance portion 32 is arranged in the first insulator 33</b>A in an inlet opening that is adjacent to the tip side L<b>1 of the gas chamber 35 in the longitudinal direction L. The diffusion resistance part 32 is formed of a porous metal oxide such as alumina. The diffusion speed (flow rate) of the detection target gas G introduced into the gas chamber 35 is determined by limiting the speed at which the detection target gas G permeates the pores in the diffusion resistance portion 32.

The diffusion resistance portion 32 may be formed adjacent to both sides of the gas chamber 35 in the width direction W. In this case, the diffusion resistance portion 32 is arranged in the first insulator 33</b>A inside the inlet opening that is adjacent to both sides of the gas chamber 35 in the width direction W. The diffusion resistance portion 32 may be formed using a pinhole which is a small through hole communicating with the gas chamber 35, instead of being formed using a porous body.

(Atmospheric duct 36)
As shown in FIGS. 3 to 5, on the second main surface 302 of the solid electrolyte body 31, an air duct 36 surrounded by the second insulator 33B and the solid electrolyte body 31 is formed adjacently. The air duct 36 is formed in the second insulator 33B from the position where the air electrode 312 is housed to the rear end position of the sensor element 2. At the rear end position of the sensor element 2 in the lengthwise direction L, a rear end opening is formed as an atmosphere introducing portion 361 of the atmosphere duct 36. The air duct 36 is formed from the rear end opening to a position facing the gas chamber 35 via the solid electrolyte body 31. The atmosphere A is introduced into the atmosphere duct 36 from the rear end opening.

The cross-sectional area of the cross section of the air duct 36 orthogonal to the long direction L is larger than the cross section of the cross section of the gas chamber 35 orthogonal to the long direction L. The thickness (width) of the air duct 36 in the stacking direction D is larger than the thickness (width) of the gas chamber 35 in the stacking direction D. Since the cross-sectional area, thickness, volume, etc. of the atmosphere duct 36 are larger than the cross-sectional area, thickness, volume, etc. of the gas chamber 35, oxygen in the atmosphere A for reacting unburned gas in the detection electrode 311 is It is possible to sufficiently supply the detection electrode 311 from the air duct 36.

(Heating element 34)
As shown in FIGS. 3 to 5, the heating element 34 is embedded in the second insulator 33B that forms the air duct 36, and the heating element 341 that generates heat when energized and the heating element lead that is connected to the heating element 341. And a portion 342. In the stacking direction D of the solid electrolyte body 31 and each of the

insulators

33A and 33B, at least a part of the heat generating portion 341 is arranged at a position overlapping the detection electrode 311 and the atmosphere electrode 312.

Further, the heating element 34 has a heating section 341 that generates heat when energized, and a pair of heating element lead sections 342 connected to the rear end side L1 of the heating section 341 in the longitudinal direction L. The heat generating portion 341 is formed by a linear conductor portion that meanders with a straight portion and a curved portion. The linear portion of the heat generating portion 341 of this embodiment is formed parallel to the longitudinal direction L. The heating element lead portion 342 is formed by a linear conductor portion. The resistance value per unit length of the heating portion 341 is larger than the resistance value per unit length of the heating element lead portion 342. The heating element lead portion 342 is extended to a portion on the rear end side L2 in the longitudinal direction L. The heating element 34 contains a conductive metal material.

The heat generating portion 341 of the present embodiment is formed in a shape meandering in the lengthwise direction L at a position on the tip side L1 of the heat generating body 34 in the lengthwise direction L. The heat generating portion 341 may be formed to meander in the width direction W. The heat generating portion 341 is arranged at a position facing the detection electrode 311 and the atmosphere electrode 312 in the stacking direction D orthogonal to the lengthwise direction L. When the heating portion 341 generates heat due to the electricity supplied from the heating element lead portion 342, the target temperature of the portion sandwiched between the

electrodes

311 and 312 in the detection electrode 311, the atmospheric electrode 312, and the solid electrolyte body 31 is targeted. Is heated to.

The cross-sectional area of the heating portion 341 is smaller than the cross-sectional area of the heating element lead portion 342, and the resistance value per unit length of the heating portion 341 is higher than the resistance value per unit length of the heating element lead portion 342. The cross-sectional area means the area of a cross section orthogonal to the extending direction of the heat generating portion 341 and the heat generating body lead portion 342. Then, when a voltage is applied to the pair of heating element lead portions 342, the heating portion 341 generates Joule heat, which heats the periphery of the detection portion 21.

(

Insulators

33A, 33B)
As shown in FIGS. 3 and 4, the first insulator 33A forms the gas chamber 35, and the second insulator 33B forms the atmospheric duct 36 and also burys the heating element 34. .. The first insulator 33A and the second insulator 33B are formed of a metal oxide such as alumina (aluminum oxide). Each of the

insulators

33A and 33B is formed as a dense body through which the gas G to be detected or the atmosphere A cannot pass, and each of the

insulators

33A and 33B has pores through which gas can pass. Not not.

(Porous layer 37)
As shown in FIG. 1, the entire circumference of the portion of the sensor element 2 on the tip side L1 in the longitudinal direction L has a porous structure for capturing poisonous substances to the detection electrode 311 and condensed water generated in the exhaust pipe 7. A quality layer 37 is provided. The porous layer 37 is made of porous ceramics (metal oxide) such as alumina. The porosity of the porous layer 37 is larger than the porosity of the diffusion resistance part 32, and the flow rate of the detection target gas G that can pass through the porous layer 37 is the detection target that can pass through the diffusion resistance part 32. It is higher than the flow rate of the gas G.

(Other configuration of gas sensor 1)
As shown in FIG. 1, the gas sensor 1 includes, in addition to the sensor element 2, a first insulator 42 holding the sensor element 2, a housing 41 holding the first insulator 42, and a second insulator connected to the first insulator 42. 43, a contact terminal 44 held by the second insulator 43 and contacting the sensor element 2. Further, the gas sensor 1 is attached to the tip end side L1 of the housing 41 and covers the tip end side portion of the sensor element 2 with the element cover 45, and is attached to the rear end side L2 of the housing 41, and the second insulator 43, An atmosphere cover 46 that covers the contact terminals 44 and the like, a bush 47 and the like for holding the lead wires 48 connected to the contact terminals 44 in the atmosphere cover 46 are provided.

The tip portion of the sensor element 2 and the element cover 45 are arranged inside the exhaust pipe 7 of the internal combustion engine. The element cover 45 is formed with a gas passage hole 451 for passing exhaust gas as the detection target gas G. The element cover 45 can have a double structure or a single structure. The exhaust gas as the detection target gas G flowing into the element cover 45 from the gas passage hole 451 of the element cover 45 passes through the porous layer 37 and the diffusion resistance portion 32 of the sensor element 2 and is guided to the detection electrode 311.

A plurality of contact terminals 44 are arranged in the second insulator 43 so as to be connected to the respective electrode lead portions 313 of the detection electrode 311 and the atmospheric electrode 312 and the heating element lead portion 342 of the heating element 34. The lead wire 48 is connected to each of the contact terminals 44.

As shown in FIGS. 1 and 3, the lead wire 48 in the gas sensor 1 is electrically connected to the sensor control device 6 that controls gas detection in the gas sensor 1. The sensor control device 6 cooperates with an engine control device that controls combustion operation in the engine to perform electric control in the gas sensor 1. The sensor control device 6 includes a measurement circuit 61 for measuring a current flowing between the detection electrode 311 and the atmospheric electrode 312, an application circuit 62 for applying a voltage between the detection electrode 311 and the atmospheric electrode 312, and a heating element 34. An energizing circuit or the like for energizing is formed. The sensor control device 6 may be built in the engine control device.

(Atmosphere cover 46 and two-layer atmospheric filter 5)
As shown in FIGS. 1 and 2, the atmosphere cover 46 is arranged outside the exhaust pipe 7 of the internal combustion engine. The gas sensor 1 of the present embodiment is mounted on a vehicle, and the vehicle body in which a part of the exhaust pipe 7 is arranged is connected to an engine room in which an internal combustion engine (engine) is arranged. Then, around the atmosphere cover 46, gases generated from various rubbers, resins, lubricants and the like in the engine room are mixed with the atmosphere A and flow.

Examples of the poisoning substances generated in the engine room include Si (silicon) and S (sulfur). Si may exist in the form of SiO ₂ (silicon dioxide), silicate (silicate) or the like. The poisoning substance refers to a substance that adheres to the air electrode 312 and deteriorates the performance of the air electrode 312. Further, the exhaust gas may contain a substance that may poison the detection electrode 311. In this case, the poisoning substance contained in the exhaust gas as the detection target gas G is captured by, for example, the porous layer 37 provided on the surface of the sensor element 2.

As shown in FIG. 2, the atmosphere cover 46 of the present embodiment includes a first atmosphere cover 46A attached to the housing 41 and a second atmosphere cover 46B that sandwiches the two-layer atmosphere filter 5 between the first atmosphere cover 46A. It is composed of and. The first atmosphere cover 46A and the second atmosphere cover 46B are formed in a cylindrical shape. The second atmosphere cover 46B overlaps the outer periphery of the first atmosphere cover 46A and is crimped to the first atmosphere cover 46A. The vent hole 461 for taking in the atmosphere A into the atmosphere cover 46 is formed on the side surface of the second atmosphere cover 46B so as to penetrate therethrough. The vent holes 461 are formed at a plurality of positions in the circumferential direction of the cylindrical second atmosphere cover 46B.

An atmosphere path 460 is formed between the first atmosphere cover 46A and the base end of the second atmosphere cover 46B. The two-layer atmospheric filter 5 of the present embodiment is sandwiched between the first atmospheric cover 46A and the second atmospheric cover 46B, and also sandwiched between the second atmospheric cover 46B and the bush 47.

The two-layer air filter 5 is formed as a sheet filter in which a sheet-shaped first filter portion 51 and a sheet-shaped second filter portion 52 are overlapped and integrated. The two-layer atmospheric filter 5 of the present embodiment is rolled into a cylindrical shape and is sandwiched between the first atmospheric cover 46A and the second atmospheric cover 46B.

The two-layer atmospheric filter 5 is arranged on the inner peripheral surface (inner side surface) of the second atmospheric cover 46B so as to cover the ventilation port 461 from the inner peripheral side of the second atmospheric cover 46B. The rear end opening of the sensor element 2 as the atmosphere introducing portion 361 of the atmosphere duct 36 is open to the space inside the atmosphere cover 46. The atmosphere path 460 of the present embodiment is formed as the entire space inside the atmosphere cover 46. The two-layer atmosphere filter 5 is arranged on the inner peripheral surface of the second atmosphere cover 46B around the ventilation port 461 so that the atmosphere A flowing through the atmosphere path 460 always passes through the two-layer atmosphere filter 5.

The first filter portion 51 and the second filter portion 52 can be formed in various three-dimensional shapes other than the sheet shape. For example, the first filter section 51 and the second filter section 52 can be formed in a block shape. Further, the first filter portion 51 and the second filter portion 52 may have a fibrous or particulate form that fills the space between the first atmosphere cover 46A and the second atmosphere cover 46B.

The atmosphere path 460 may be formed as a part of the atmosphere cover 46. In addition, the atmosphere path 460 includes the outside of the atmosphere cover 46 as long as it is a position facing the ventilation port 461. Then, the two-layer atmospheric filter 5 may be arranged at a position facing the ventilation port 461 from the outside of the atmospheric cover 46. Further, the two-layer atmospheric filter 5 may be arranged at any position on the atmospheric path 460. However, by disposing the two-layer atmospheric filter 5 at a position close to the ventilation port 461, it is possible to effectively prevent intrusion of water and poisonous substances into the atmospheric cover 46.

The first filter unit 51 includes PTFE (polytetrafluoroethylene), PP (polypropylene), PET (polyethylene terephthalate), PE (polyethylene), PVC (polyvinyl chloride), PPS (polyphenylene sulfide), PA (polyamide), PEEK. It can be made of resin such as (polyether ether ketone), glass fiber or the like. When the first filter portion 51 is made of resin, the first filter portion 51 has a large number of pores through which air can pass. When forming the 1st filter part 51 with a fiber, the 1st filter part 51 is formed with the clearance gap through which air can pass. Further, the first filter portion 51 has water repellency that repels water, and water droplets contained in the atmosphere A are repelled by the first filter portion 51.

The second filter section 52 can be made of activated carbon, zeolite, silica gel, mesoporous silica, ion exchange membrane, carbon nanotube, or the like. The second filter unit 52 has a large number of pores through which air can pass. The large number of pores in the second filter section 52 can be made smaller than the large number of pores in the first filter section 51 because the second filter section 52 adsorbs poisoning substances smaller than water droplets. The size of the pores in the second filter portion 52 and the first filter portion 51 can be expressed as an average value. The average size of the large numbers of pores in the second filter unit 52 can be smaller than the average size of the large numbers of pores in the first filter unit 51.

The first filter section 51 of the present embodiment is arranged upstream of the flow of the atmosphere A in the atmosphere path 460 with respect to the second filter section 52. Then, the atmosphere (air) A from which water has been removed by the first filter portion 51 and poisoning substances have been removed by the second filter portion 52 is taken from the outside to the inside of the atmosphere cover 46.

By arranging the first filter section 51 upstream of the flow of the atmosphere A with respect to the second filter section 52, it is possible to prevent water from coming into contact with the second filter section 52. As a result, it is possible to effectively remove water and poisonous substances in the atmosphere A taken into the atmosphere cover 46.

Poisoning substances may be mixed in the atmosphere A in the form of gas, liquid, or solid. Then, it is considered that a part of the poisoning substance mixed in the atmosphere A is captured by the pores, gaps, etc. formed in the first filter portion 51. However, in order to remove most of the poisoning substances in the atmosphere A taken into the atmosphere cover 46, the second filter section 52 is necessary. The surface area per unit mass of the second filter unit 52 is set so that the adsorption performance or capture performance of the poisonous substance by the second filter unit 52 is higher than the capture performance of the poisonous substance by the first filter unit 51. The specific surface area is preferably larger than the specific surface area which is the surface area per unit mass of the first filter portion 51.

Further, in order to make the specific surface area of the second filter portion 52 larger than the specific surface area of the first filter portion 51, the size of the large number of pores in the second filter portion 52 is set to be the same as that of the large number of pores in the first filter portion 51. The size can be made smaller than the size, and the porosity of the second filter portion 52 can be made larger than that of the first filter portion 51. The porosity can be expressed as the ratio of the volume of pores per unit volume in the first filter portion 51 or the second filter portion 52.

The specific surface area of the first filter portion 51 can be 0.1 to 50 m ² /g, and the specific surface area of the second filter portion 52 can be 5 to 4000 m ² /g. Since the first filter portion 51 has a property of repelling water, it may have a small specific surface area, and the second filter portion 52 has a property of adsorbing poisoning substances, and thus the first filter portion 51. It is preferable that the specific surface area is larger than that. The specific surface area of the first filter portion 51 is more preferably 1 to 20 m ² /g, and the specific surface area of the second filter portion 52 is more preferably 10 to 2500 m ² /g. It is difficult in manufacturing to make the specific surface area of the first filter portion 51 less than 0.1 m ² /g or more than 50 m ² /g. Further, it is difficult to manufacture the specific surface area of the second filter portion 52 to be less than 5 m ² /g or more than 4000 m ² /g.

The specific surface area of each

filter portion

51, 52 can be measured by a gas adsorption method such as a BET adsorption isotherm method. In the gas adsorption method, the phenomenon that gas molecules and the like are adsorbed on the entire surfaces of the gaps and pores in each of the

filter parts

51 and 52 is used, and the specific surface area is obtained by measuring the amount of the gas molecules and the like. You can The specific surface area of each of the

filter parts

51 and 52 can also be measured by a transmission method. In the permeation method, a fluid is caused to flow through gaps, pores, etc. in each of the

filter parts

51 and 52, and the specific surface area can be obtained based on the difficulty of the fluid flow.

The external surface area of the second filter portion 52 is larger than the external surface area of the first filter portion 51. The external surface area means the surface area of the outermost surface as the outer surface of each

filter portion

51, 52.

The water-repellent function of the first filter unit 51 coarsens the water adsorbed on the surface of the first filter unit 51 and retains this water on the surface of the first filter unit 51, and this water is stored in the first filter unit 51. Can be used as a function of preventing penetration into Further, the water capturing function of the first filter unit 51 can be a function of preventing the water from passing through the first filter unit 51 by capturing the water in the first filter unit 51.

The first filter unit 51 may have a function of trapping water in the atmosphere A, instead of having a function of repelling water in the atmosphere A. In this case, the water in the atmosphere A is captured in the pores or gaps in the first filter section 51. The first filter unit 51 may have both a water repellent function and a water capturing function.

The function of adsorbing the poisoning substance by the second filter unit 52 is a function utilizing the van der Waals force of adsorbing the poisoning substance at the atomic level or the molecular level on the surface of the pores, gaps, etc. in the second filter unit 52. be able to. The function of capturing the poisoning substance by the second filter unit 52 is a function of preventing the poisoning substance from passing through the second filter unit 52 by capturing the poisoning substance in the second filter unit 52. Can be

Further, when the second filter portion 52 has a function of adsorbing the poisoning substance in the atmosphere A, it is adsorbed on the surface of the second filter portion 52 forming the pores or gaps. Further, the second filter unit 52 may have a function of trapping a poisoning substance in the atmosphere A instead of having a function of adsorbing the poisoning substance in the atmosphere A. In this case, the poisoning substance in the atmosphere A is captured in the pores or the gaps in the second filter unit 52. The second filter unit 52 may have both a function of adsorbing and a function of capturing poisonous substances.

The first filter section 51 and the second filter section 52 each have a property of allowing a gas such as oxygen or nitrogen to pass therethrough. When Si constitutes silicone (silicon-containing resin) or the like, it may exist as a gas poisoning substance. In this case, it is preferable that the second filter unit 52 has a function of adsorbing or capturing a gas that may be a poisoning substance in the atmosphere.

The oxygen gas permeation amounts of the first filter portion 51 and the second filter portion 52 are determined by the air-fuel ratio which is the most fuel-rich side in the internal combustion engine (when the air-fuel ratio detected by the air-fuel ratio sensor is the richest air-fuel ratio). In the case of the fuel ratio), the amount of oxygen gas to the atmospheric electrode 312 in the atmospheric duct 36 may be greater than the amount of oxygen ions required to decompose the maximum rich gas (unburned gas) in the detection electrode 311. preferable. Accordingly, even when the first filter section 51 and the second filter section 52 are used, the gas sensor 1 can accurately detect the air-fuel ratio on the richest side.

In internal combustion engines, it is assumed that the air-fuel ratio of the maximum rich gas is A/F=9 for combustion operation. Then, the oxygen gas permeation amount of the second filter unit 52 should be equal to or more than the oxygen gas amount required for the atmosphere electrode 312 when the air-fuel ratio sensor detects the air-fuel ratio on the richest side of A/F=9. You can The air-fuel ratio of the maximum rich gas may be A/F=8 instead of A/F=9.

The atmosphere A existing around the vent hole 461 of the atmosphere cover 46 is taken into the atmosphere cover 46 as the atmosphere path 460 via the first filter unit 51 and the second filter unit 52. Then, the atmosphere A that has passed through the

filter portions

51 and 52 flows into the atmosphere duct 36 from the rear end opening as the atmosphere introducing portion 361 of the atmosphere duct 36 of the sensor element 2 to the atmosphere electrode 312 in the atmosphere duct 36. Will be led.

(Effect)
In the gas sensor 1 of the present embodiment, the two-layer atmospheric filter 5 including the first filter portion 51 and the second filter portion 52 is arranged in the atmosphere cover 46 so as to cover the ventilation port 461 that serves as the inlet of the atmosphere path 460. .. The two-layer atmospheric filter 5 is composed of a first filter section 51 having a function of repelling water in the atmosphere A and a second filter section 52 having a function of adsorbing poisoning substances in the atmosphere A. ..

Then, even if the atmosphere A around the atmosphere cover 46 of the gas sensor 1 contains water, the water can be repelled by the first filter portion 51. This can prevent water from entering the rear end opening of the atmosphere duct 36 of the sensor element 2 and protect the atmosphere electrode 312 of the sensor element 2 exposed to the atmosphere A from being exposed to water. ..

Even if the atmosphere A around the atmosphere cover 46 of the gas sensor 1 contains a poisoning substance such as Si or S that may poison the atmosphere electrode 312 of the sensor element 2, this poisoning may occur. The substance can be adsorbed by the second filter unit 52. As a result, it is possible to prevent the poisoning substance from entering the rear end opening of the sensor element 2 and prevent the atmospheric electrode 312 of the sensor element 2 exposed to the atmosphere A from being poisoned. it can.

Also, the two-layer air filter 5 of the present embodiment is formed in a state of being in close contact with each other and laminated. By using this two-layer atmospheric filter 5, it is possible to easily assemble the two-layer atmospheric filter 5 to the atmospheric cover 46.

Both the first filter section 51 and the second filter section 52 have a property of allowing a gas such as oxygen or nitrogen to pass through. Then, gases such as oxygen and nitrogen, excluding water and poisonous substances, pass through the two-layer atmospheric filter 5 to the atmospheric path 460 in the atmospheric cover 46 and the atmospheric air introduction portion 361 of the atmospheric duct 36 of the sensor element 2. be introduced. Further, the second filter unit 52 hardly interferes with the permeation of oxygen, and even if the air-fuel ratio of the exhaust gas as the detection target gas G is at the fuel-rich side air-fuel ratio, it is sufficient for the atmosphere electrode 312. Any amount of oxygen can be supplied.

As described above, according to the gas sensor 1 of the present embodiment, a sufficient amount of oxygen can be supplied to the atmospheric electrode 312 of the sensor element 2, and the atmospheric electrode 312 of the sensor element 2 is protected from water and poisonous substances. Can be protected.

<Embodiment 2>
The present embodiment mainly shows a gas sensor 1 in which the shape of the sensor element 2 is different from that in the first embodiment. As shown in FIG. 6, the sensor element 2 of the present embodiment includes a cup-shaped solid electrolyte body 31, a detection electrode 311 provided on the outer peripheral surface of the solid electrolyte body 31 and exposed to the gas G to be detected, and a solid electrolyte body. It has an atmospheric electrode 312 exposed to the atmosphere A, which is provided on the inner peripheral surface of the body 31, and an atmospheric duct 36 formed on the inner peripheral side of the solid electrolyte body 31 so as to accommodate the atmospheric electrode 312. The cup-shaped solid electrolyte body 31 has a cylindrical portion 315 and a closing portion 316 that closes the tip of the cylindrical portion 315. The detection electrode 311 is provided on the outer peripheral surface of the cylindrical portion 315, and the atmospheric electrode 312 is continuously provided on the inner peripheral surface of the cylindrical portion 315 and the inner side surface of the closed portion 316.

The sensor element 2 is held on the inner peripheral side of the housing 41. A heater element 340 that generates heat when energized is arranged on the inner peripheral side of the cup-shaped solid electrolyte body 31. The heater element 340 has a ceramic base material and a heating element 34 provided on the ceramic base material. The air introduction part 361 of the present embodiment is configured by the rear end opening of the air duct 36 formed on the inner peripheral side of the solid electrolyte body 31.

As shown in FIG. 7, the atmosphere cover 46 of this embodiment can also be similar to that shown in the first embodiment. However, a space between the first atmospheric cover 46A and the second atmospheric cover 46B of the present embodiment is closed as a space in which the two-layer atmospheric filter 5 is arranged. The vent hole 461 of the atmosphere cover 46 of this embodiment is formed in both the first filter portion 51 and the second filter portion 52. Then, the atmosphere that has passed through the ventilation port 461 of the first atmospheric cover 46A passes through the two-layer atmospheric filter 5 and then passes through the ventilation port 461 of the second atmospheric cover 46B and enters the atmospheric air introduction portion 361 of the sensor element 2. be introduced.

The gas sensor 1 of the present embodiment can be used as an air-fuel ratio sensor and also as an oxygen sensor. Other configurations of the gas sensor 1 of the present embodiment are similar to those of the first embodiment. In the present embodiment as well, the two-layer air filter 5 can obtain the same operational effect as that of the first embodiment. Also in the present embodiment, the components indicated by the same reference numerals as those in the first embodiment are the same as those in the first embodiment.

<Embodiment 3>
In this embodiment, the first filter unit 51 and the second filter unit 52 have different configurations from those in the first embodiment. As shown in FIG. 8, the first filter section 51 and the second filter section 52 may be separated from each other and arranged in the atmosphere cover 46. In this case, the first filter portion 51 is arranged at a position that covers the vent hole 461 of the first atmosphere cover 46A, and the second filter portion 52 is provided inside the second atmosphere cover 46B as a part of the atmosphere path 460. Can be placed. Further, the second filter portion 52 can be arranged, for example, at a position that covers the rear end opening portion of the air duct 36 of the sensor element 2 as the air introduction portion 361.

Further, when the first filter section 51 and the second filter section 52 are separated from each other, the second filter section 52 may be provided in the gap between the second insulator 43 and the lead wire 48, for example, as shown in FIG. 9. It can also be arranged.

Further, the second filter portion 52 is arranged on the upstream side of the flow of the atmosphere A in the atmosphere path 460 inside the atmosphere cover 46, and the first filter portion 51 is on the downstream side of the flow of the atmosphere A with respect to the second filter portion 52. It can also be placed in. Further, as shown in FIG. 10, the first filter portion 51 and the second filter portion 52 may be formed into a sheet shape and may be alternately laminated a plurality of times.

The first filter unit 51 and the second filter unit 52 may be mixed with each other. Specifically, as shown in FIG. 11, the second filter units 52 can be dispersed and arranged in the first filter unit 51. The second filter part 52 can be kneaded in a dispersed state in the first filter part 51 when molding the first filter part 51 made of a resin material.

When the first filter unit 51 and the second filter unit 52 are mixed with each other, one of the first filter unit 51 and the second filter unit 52 is disposed inside the other, the first filter unit One of 51 and the second filter part 52 is dispersed in the other base material, a state in which pieces of the first filter part 51 and the second filter part 52 formed in a lump are joined, and the like are included. ..

Other configurations of the gas sensor 1 of the present embodiment are similar to those of the first embodiment. Also in the present embodiment, the same operational effect as in the case of the first embodiment can be obtained by the first filter unit 51 and the second filter unit 52. Also in the present embodiment, the components indicated by the same reference numerals as those in the first embodiment are the same as those in the first embodiment.

<Embodiment 4>
In this embodiment, as shown in FIGS. 12 and 13, the sensor element 2 does not have the air duct 36, and the air introduction part 361 forms a gap between the solid electrolyte body 31B and the insulator 33E in the sensor element 2. The gas sensor 1 will be described. The

solid electrolyte bodies

31A and 31B of the present embodiment are composed of a long plate-shaped first solid electrolyte body 31A and a long plate-shaped second solid electrolyte body 31B. The gas chamber 35 is formed between the first solid electrolyte body 31A and the second solid electrolyte body 31B.

Also in the gas sensor 1 of the present embodiment, the configuration of the atmosphere cover 46 and the like arranged around the sensor element 2 is the same as that of the first embodiment. The atmosphere cover 46 is formed with a vent 461 for taking in the atmosphere A into the atmosphere cover 46, and the atmosphere cover 46 covers the vent 461 so as to cover the first filter portion 51 and the second filter. The part 52 is arranged.

The first main surface of the first solid electrolyte body 31A exposed to the detection target gas G in the gas chamber 35 and the first main surface of the first solid electrolyte body 31A opposite to the first main surface exposed to the detection target gas G via the porous body 38. A pair of

electrodes

311A and 312A for pumping out oxygen in the detection target gas G in the gas chamber 35 is arranged on the two main surfaces. The third main surface of the second solid electrolyte body 31B exposed to the detection target gas G in the gas chamber 35 and the fourth main surface facing the insulator 33E and opposite to the third main surface are provided. A pair of

electrodes

311 and 312 for detecting the air-fuel ratio of the detection target gas G in the gas chamber 35 are arranged.

The air introduction part 361 of the present embodiment has a gap (interface) between the second solid electrolyte body 31B and the insulator 33E and a gap (interface) between the electrode lead portion 313 of the electrode 312 and the second solid electrolyte body 31B in the sensor element 2. ), a gap (interface) between the electrode lead portion 313 of the electrode 312 and the insulator 33E, or the like. Then, the atmosphere A taken into the atmosphere cover 46 is supplied to the electrode 312 on the fourth main surface of the second solid electrolyte body 31B via the gap (interface).

In this embodiment, the electrode 312 on the fourth main surface of the second solid electrolyte body 31B is supplied with the atmosphere A from which water and poisonous substances have been removed by the first filter portion 51 and the second filter portion 52. This makes it possible to protect the electrode of the sensor element 2 in contact with the atmosphere A from water and poisonous substances.

The present disclosure is not limited to each embodiment, and further different embodiments can be configured without departing from the gist thereof. Further, the present disclosure includes various modifications, modifications within the equivalent range, and the like. Furthermore, the technical idea of the present disclosure also includes combinations and forms of various constituent elements that are assumed from the present disclosure.

Claims

A sensor element (2) having a detection part (21) exposed to the gas to be detected (G) and an atmosphere introduction part (361) into which the atmosphere (A) is introduced;
An atmosphere cover (46) through which air introduced into the sensor element is taken in through a vent (461),
A first filter unit (51) having a function of repelling or trapping water in the atmosphere is provided in the atmosphere path (460) between the ventilation port and the atmosphere introducing unit in the atmosphere cover, and The gas sensor (1), which is provided by being laminated, separated or mixed with the second filter part (52) having a function of adsorbing or trapping the poisoning substance.
The gas sensor according to claim 1, wherein a specific surface area which is a surface area per unit mass of the second filter portion is larger than the specific surface area of the first filter portion.
The specific surface area of the first filter portion is 1 to 20 m 2 /g,
The gas sensor according to claim 2 , wherein the specific surface area of the second filter portion is 10 to 2500 m 2 /g.
The gas sensor according to any one of claims 1 to 3, wherein the first filter section is arranged upstream of the atmosphere flow in the atmosphere path with respect to the second filter section.
The gas sensor according to any one of claims 1 to 3, wherein the second filter portion is arranged in a distributed manner in the first filter portion.
The first filter unit and the second filter unit are laminated or mixed with each other to form an integrated sheet filter,
The gas sensor according to any one of claims 1 to 3, wherein the sheet filter is arranged on an inner surface of the atmosphere cover in a state of covering the vent hole.