JP2000046786A - Gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor for scarcely bringing about a leakage of a water droplet or the like in a casing even in a severer use environment with an excellent waterproofness. SOLUTION: The gas sensor 1 comprises an oxygen sensing element 2 formed in a shaft state, a cylindrical casing for containing the element 2, and a filter assembly 16 for introducing the atmosphere into the casing. In the assembly 16, a filter 53 is held in the shape for sandwiching the filter 53 between a filter holder 51 and an auxiliary filter holder 54, and the atmosphere is introduced into the casing via the filter 53 and a gas introducing hole 52. A protection cover 64 for inhibiting or suppressing direct injection of a liquid droplet or adherence of a deposit such as oil, dirt or the like to the filter 53 is provided at its outside, and a distance of 0.2 mm or more is assured between an inner surface of the cover 64 and the holder 54. Thus, the oil is scarcely stored between the both, and a ventilation via the filter 53 can be always smoothly executed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an oxygen sensor, an HC sensor,
Sensor, such as NO _X sensor, it relates to a gas sensor for detecting a test substance in the measurement object gas.

[0002]

2. Description of the Related Art Conventionally, various oxygen sensors have been developed as the above-mentioned gas sensors for use in, for example, controlling the air-fuel ratio of an automobile engine. In recent years, in particular, in order to respond to environmental protection problems such as air pollution caused by exhaust gas, the demand for an oxygen sensor for detecting the oxygen concentration in the exhaust gas has been increasing, especially for a high-performance and long-life oxygen sensor. I have.

[0003] For example, as a typical example of such an oxygen sensor, an oxygen detecting element formed in an axial shape by an oxygen ion conductive solid electrolyte such as ZrO ₂ is accommodated in a cylindrical casing, and the oxygen detecting element is connected to the oxygen detecting element. The outer surface of the tip of the detection element is brought into contact with the atmosphere to be detected, the atmosphere is introduced into the casing as a reference gas, and the oxygen concentration in the atmosphere to be detected is measured by the electromotive force of the oxygen concentration cell generated in the detection element. A structure having a rough structure is widely used.

When the above-described oxygen sensor is mounted on an automobile, it is often mounted, for example, on an exhaust pipe or the like close to the foot of the vehicle in addition to the engine room. In such a situation, the oxygen sensor should be exposed to a severe environment such as being sprayed with water droplets during running in the rain or washing a car, adhering dirt such as oil, and receiving impact from splashed pebbles. Becomes In this case, in order to protect the oxygen detecting element from the adhesion of water droplets and dirt, the structure of the casing accommodating the oxygen detecting element must be as strong as possible and have high sealing properties. However, since it is necessary to introduce air into the casing as a reference gas for the detection element, a communication part with the outside must be provided. In other words, in order to operate the oxygen sensor stably in a severe environment for a long period of time, it is necessary to increase the liquid tightness to water or the like to a certain level or more, and at the same time, to contradict the problem of securing air permeability. Need to be resolved.

[0005]

In order to meet such demands, for example, Japanese Patent Laid-Open Publication No. Hei 8-201338 discloses that a casing is provided with an air hole, which is further covered with a water-repellent filter to form a water-repellent filter. An oxygen sensor having a structure in which the intrusion of air and the like is prevented and the flow of the atmosphere can be secured is disclosed. However, when the oxygen sensor is attached to the part around the foot, the oxygen sensor may travel while strongly jumping up water such as a puddle (in particular, recently, the rapidly spreading 4
In WD off-road vehicles and the like, many drivers tend to prefer such poor road conditions).
Alternatively, if high-pressure water directly hits the filter at the time of washing the vehicle, there is a case where the above-described water-repellent filter alone cannot completely prevent water droplets or the like from entering the sensor.

[0006] Further, depending on the mounting position of the sensor, lubricating oil or the like from the part around the foot may easily adhere to the outer surface of the water repellent filter. When the outer surface of the filter is covered with oil, its air permeability is significantly impaired, and the detection accuracy is reduced.

An object of the present invention is to provide a gas sensor which is excellent in waterproofness, hardly causes deterioration of detection accuracy due to oil adhesion, and has high durability.

[0008]

Means for Solving the Problems and Functions / Effects The main part of the gas sensor according to the present invention is formed in a cylindrical casing and a shaft arranged in the casing. A detection element including a detection unit including an oxygen concentration cell element that operates using external air to be introduced as a reference gas; an auxiliary filter holding unit provided on the rear side of the casing and formed with an auxiliary gas introduction hole; A space is provided between the filter, which is disposed inside the filter holding portion so as to close the auxiliary gas introduction hole, prevents liquid permeation and allows gas permeation, and the outside of the auxiliary filter holding portion and the auxiliary filter holding portion. (Hereinafter referred to as an auxiliary gas retention space) in the form of a cylinder that covers it in a state where it has been generated, and does not prevent direct injection of droplets onto the filter or adhesion of deposits such as oil and dirt. A protective cover for controlling, an external communication portion for communicating the outside of the protective cover with the auxiliary gas retaining space, and introducing outside air into the auxiliary gas retaining space, and an auxiliary filter holding portion at a position where the auxiliary gas introducing hole is formed. The distance between the outer surface of the protective cover and the inner surface of the protective cover is 0.2 mm or more. In the present specification, the side of the oxygen detection element that is directed toward the tip in the axial direction is referred to as “front side”, and the side that is directed in the opposite direction is referred to as “rear side”.

That is, in order to introduce outside air into the casing, a filter that blocks liquid permeation and permits gas permeation, and an auxiliary filter holding portion that holds the filter are provided. By providing the protective cover on the outside of the holding portion, intrusion of water droplets, oils, and the like into the casing is further reduced. In addition, when the oxygen sensor is attached to the area around the foot of the vehicle, the vehicle runs while strongly jumping up water such as a puddle, or when high-pressure water directly hits the filter at the time of car washing, etc. By the combination, intrusion of water droplets or the like into the casing can be effectively prevented.

Further, the present invention includes a configuration of three gas sensors in which any one of the following requirements is added to the above-mentioned main part. First, in the first configuration (claim 1), the distance between the outer surface of the auxiliary filter holding portion and the inner surface of the protective cover at the position where the auxiliary gas introduction hole is formed is ensured to be 0.2 mm or more. That is, even if the protective cover is provided, an external communication portion connecting the inside and the outside of the protective cover is structurally indispensable in order to secure the introduction of outside air into the casing. In this case, oil such as lubricating oil may gradually leak into the protective cover from the external communication portion from around the vehicle feet. At this time, if the distance between the outer surface of the auxiliary filter holding portion and the inner surface of the protective cover is too small, the leaked oil or the like accumulates in the gap between the two, closes the auxiliary gas introduction hole, and passes through the filter from the auxiliary gas retaining space. It may hinder the flow of outside air. Therefore, by ensuring that the distance between the outer surface of the auxiliary filter holding portion and the inner surface of the protective cover at the position where the auxiliary gas introduction hole is formed is equal to or greater than the above value, it becomes difficult for oil and the like to accumulate in the gap, and such a problem occurs. Can be difficult. The distance is more desirably 0.3 mm or more.

In the second configuration (claim 2), a cylindrical filter holding portion having a gas inlet hole formed in a wall portion is provided on the rear side of the casing. The filter is arranged outside the filter holding portion so as to close the gas introduction hole. Further, the auxiliary filter holding portion is formed in a cylindrical shape arranged outside the filter, has an auxiliary gas introduction hole formed in a wall portion, and holds the filter by being sandwiched between the filter holding portion and the filter. Is done. Then, the filter holding portion is formed by a step formed at an intermediate portion in the axial direction of the filter holding portion. Is formed so as to have a small diameter, and a gas introduction hole is formed in the wall of the second portion, and the distance between the outer surface of the auxiliary filter holding portion at the position where the auxiliary gas introduction hole is formed and the inner surface of the protective cover is set. In order to expand, the protective cover, its inner surface,
The filter holding portion has a form projecting outside the outer surface of the first portion. With this configuration, by increasing the distance between the outer surface of the auxiliary filter holding portion and the inner surface of the protective cover, it becomes difficult for oil and the like to accumulate in the gap between the outer surface of the auxiliary filter holding portion and the inner surface of the protective cover. It is possible to make it difficult to cause a problem that the circulation of the outside air from the space through the filter is hindered. In addition, when this configuration is combined with the first configuration, the effect can be further enhanced (claim 3).

On the other hand, in a third configuration (claim 4), the external communication portion includes a cover-side gas introduction hole provided so as to penetrate the protective cover at a position corresponding to the auxiliary gas retaining space. Features. By adopting this configuration, even though the protective cover is provided outside the filter, the outside air can smoothly flow into the auxiliary gas retaining space inside the protective cover. As a result, the outside air (or the atmosphere) as the reference gas can be supplied to the oxygen concentration cell element provided in the detection section without any delay, and the accuracy of oxygen detection by the oxygen concentration cell element can be improved.

When at least one of the first and second configurations is combined with the third configuration, oil and the like hardly accumulate in the gap between the outer surface of the auxiliary filter holding portion and the inner surface of the protective cover, Since the problem that the flow of the outside air passing through the filter from the auxiliary gas retaining space is prevented from occurring is less likely to occur, the supply of the outside air to the oxygen concentration cell element provided in the detection unit can be performed more smoothly, and the oxygen concentration cell element The accuracy of oxygen detection by the method can be further improved (claims 5 and 6).

The cover-side gas introduction hole and the auxiliary gas introduction hole are preferably formed so as to be displaced from each other in at least one of the axial direction and the circumferential direction of the protective cover. Since the cover-side gas introduction hole and the auxiliary gas introduction hole are formed so as to be shifted from each other, high-pressure water may fly from the outside and enter the auxiliary gas retention space from the cover-side gas introduction hole. However, it is possible to prevent this from directly hitting the auxiliary gas introduction hole, and thus it is more difficult for water droplets or the like to enter the casing. In this case, in order to enhance the effect, more preferably, the cover-side gas introduction hole and the auxiliary gas introduction hole are arranged such that when the cover-side gas introduction hole is viewed in any direction from the outside of the protective cover, the cover-side gas introduction hole is formed. It is preferable that the auxiliary gas introduction hole is formed in a positional relationship that makes it impossible to visually recognize the auxiliary gas introduction hole through the introduction hole.

In the case of an oxygen sensor or the like, for example, the gas sensor is mounted in such a manner that a detection portion on the front end side is inserted into the exhaust pipe, while the rear end side is exposed on the exhaust pipe side, and the side is exposed to water or the like. Tends to be exposed. Therefore, since the cover-side gas introduction hole is formed on the side closer to the detection unit with respect to the auxiliary gas introduction hole in the axial direction, even in such a case, water and the like hardly enter the auxiliary gas retention space. Become.

In the protective cover, the auxiliary gas introduction hole in the axial direction has at least the side farthest from the detecting section and the side close to the detecting section, at least the far side of which is formed by a circumferential annular cover joining section formed by a filter holding section. Can be bonded to the outer surface. That is, it is possible to make it more difficult for water droplets and the like to enter the inside of the protective cover by the annular cover joint. The cover joining portion can be formed on both the side farther than the detecting portion and the side closer to the detecting portion with respect to the auxiliary gas introducing hole. In this case, as the external communication portion, the above-described cover-side gas introducing hole is used. Is formed, it is possible to effectively prevent or suppress intrusion of water droplets, oil, and the like while smoothly introducing outside air into the auxiliary gas retaining space.

The external communication portion includes a groove-shaped communication portion formed between the protective cover and the filter holding portion so as to cross the circumferential cover joint formed on the side close to the detection portion. With this configuration, introduction of outside air into the protective cover can be performed without any trouble.

Such a structure can be realized relatively easily as follows. That is, a plurality of grooves having a predetermined length as external communication portions extending in the axial direction of the filter holding portion are formed at predetermined intervals along the circumferential direction on the outer peripheral surface of the filter holding portion on the front side of the gas introduction hole.
Further, the cover joint portion is formed by crimping the protective cover toward the filter holding portion so as to cross each groove, and to leave a gap between the protective cover and the filter holding portion at the bottom of the groove. The formed annular caulking portion. Thus, outside air is guided from the front opening of the gap formed between the protective cover and the filter holding portion to the gas retaining portion through the groove. in this case,
The crimping pressure and the depth of the groove may be adjusted to such an extent that the gap can be secured at the bottom of the groove.

The front edge of the protective cover can be extended to the front by a predetermined length from the end of each groove. This makes it possible to further reduce the probability that water droplets or the like enter the inside of the protective cover when the oxygen sensor is splashed.

Next, the filter holding portion is formed by a step formed at an intermediate portion in the axial direction of the filter holding portion. Can be formed to be smaller in diameter than the first portion. In this case, the gas introduction hole is formed in the wall of the second portion. According to this, for example, when the filter and the filter holding portion are sequentially extrapolated from the upper side in a state where the filter holding portion is set up with the second portion facing upward, the filter and the filter holding portion are applied to the step portion. The sensor can be easily assembled. in this case,
The inner diameter of the auxiliary filter holding part needs to be set smaller than the outer diameter of the first part.

In the above structure, the groove may be formed on the outer peripheral surface of the first portion. The protective cover is fixed to the first portion at the front end by an annular caulking portion, and is fixed to the outer peripheral surface of the second portion at the rear end by another caulking portion. You. Thereby, it is easy to form an auxiliary gas retaining space between the protective cover and the small-diameter second portion of the filter holding portion.

Further, the oxygen sensor of the present invention can be provided with a ceramic separator in which a plurality of lead wire insertion holes through which respective lead wires from the oxygen detection element are respectively inserted are formed so as to penetrate in the axial direction. Then, a flange-like separator-side support portion projecting from the outer peripheral surface at the axially intermediate position can be formed on the ceramic separator. The ceramic separator is directly or indirectly connected to the rear end surface of the casing at the separator-side support portion with the portion located on the front side of the separator-side support portion inside the rear end portion of the casing. They are arranged so as to abut each other. The annular caulked portion as the cover joining portion can be formed at a position corresponding to the outer peripheral surface of the flange-shaped separator-side support portion. Thus, the compression force at the time of forming the caulked portion can be received on the outer peripheral surface of the flange-shaped separator-side support portion, so that the caulked portion can be reliably formed.

The casing of the gas sensor has a main cylinder for housing the detection element and an outer cylinder member substantially cylindrically provided as a cylindrical body independent of the main cylinder, and a lead wire from the detection element itself is provided. The filter assembly can be connected to the main cylinder from the rear side while allowing the filter assembly to extend rearward and outward. The filter assembly has a cylindrical shape that is connected substantially coaxially to the main cylinder from the rear side, has an interior communicating with the interior of the main cylinder, and has one or more gas introduction holes formed in a wall portion. It can be configured to include the formed filter holding portion and a filter that is disposed so as to close the gas introduction hole of the filter holding portion and that prevents liquid permeation and allows gas permeation. in this case,
Outside air is introduced into the main cylinder through the filters and the gas introduction holes.

The gist of the feature of the above configuration is that the ventilation structure including the filter is formed as a filter assembly independently of the main cylinder, and this is connected to and integrated with the main cylinder. Thereby, the following effects are achieved. Since the assembly of the filter assembly can be performed independently of the assembly of the oxygen detection element and the like in the main cylinder, for example, the lead wire of the detection element does not interfere and the assembly work is performed extremely efficiently. be able to. Since the assembly of the components in the main cylinder and the assembly of the filter assembly can be performed in parallel, the productivity is dramatically improved. In addition, even if a failure in assembling the filter occurs, if a failure can be found at the stage of the filter assembly, the effect of the failure does not affect a completed sensor product, and waste of parts and the like hardly occurs.

The filter assembly is provided coaxially and integrally with the rear side of the main cylinder so that the inside communicates with each other, and has a filter holding portion having one or more gas introduction holes formed in a wall portion. A filter that is arranged outside the filter holding portion to close the gas introduction hole, blocks liquid permeation, and allows gas permeation, and is formed in a cylindrical shape that is disposed outside the filter, and is formed on a wall portion. One or more auxiliary gas introduction holes are formed, and an auxiliary filter holding portion for holding the filter by sandwiching it between the filter holding portion can be provided. In this case, outside air is introduced into the main cylinder from the gas introduction hole via the filter through the auxiliary gas introduction hole. That is, the filter can be securely held by the inner and outer filter holding portions, and the filter can be easily mounted on the filter holding portion. For example, when the filter is formed in a cylindrical shape, the filter is extrapolated to the filter holding portion, and the auxiliary filter holding portion is further fitted from the outside of the filter holding portion. What is necessary is just to form the filter holding | maintenance part coupling part which couple | bonds with the auxiliary filter holding | maintenance part.

A plurality of gas introduction holes and auxiliary gas introduction holes are formed at predetermined intervals along the circumferential direction with respect to the filter holding portion and the auxiliary filter holding portion at a position corresponding to each other at an intermediate portion in the axial direction. Can be. This allows the outside air to be uniformly introduced into the main cylinder from the filter assembly side. Further, for example, a cylindrical filter is arranged outside the filter holding portion so as to surround the filter holding portion in the circumferential direction, and the auxiliary filter holding portion serves as a filter holding portion coupling portion, and the filter holding portion holds the auxiliary filter holding portion. By caulking toward the portion, an annular filter caulking portion can be formed along the circumferential direction. By using the holding portion connecting portion as an annular filter caulking portion, assembling of the filter assembly is further facilitated. The annular caulking portion can be formed on both sides of the row of gas introduction holes and auxiliary gas introduction holes in the axial direction. In this case, in each caulking portion, the edge of the filter is sandwiched between the auxiliary filter holding portion and the filter holding portion, thereby bypassing the edge of the filter from the auxiliary gas introduction hole and introducing the gas into the filter holding portion. It is difficult to form a path leading to the hole, and the possibility that water or the like leaks into the inside of the filter holding part and, consequently, the inside of the main cylinder through the hole is reduced.

When the filter is formed in a cylindrical shape as described above and is arranged along the outer periphery of the filter holding portion,
The auxiliary filter holding portion can be arranged such that its rear end in the axial direction is positioned corresponding to the rear end of the filter, and can form a filter caulking portion in the circumferential direction along the rear end. Thus, the filter located between the auxiliary filter holding portion and the filter holding portion at the rear end surface position can be visually recognized. This has the following advantages. That is, when the cylindrical filter is extrapolated into the filter holding portion and the auxiliary filter holding portion is further fitted while being moved relative to the filter holding portion in the axial direction, the filter moves together with the auxiliary filter holding portion. Misalignment may occur. In this case, if the filter caulking part is formed in this state, the filter will come off from the caulking part and the seal will be incomplete, but the rear end face of the filter will be visible as described above. As a result, such a crimping failure of the filter can be easily found.

When a filter caulking portion is formed on the front edge side of the auxiliary filter holding portion, a filter confirmation exposing portion for partially exposing the filter at the filter caulking portion may be formed. This makes it easy to determine whether or not the filter is properly caulked at the caulked portion even at the front edge side of the auxiliary filter holding portion.

[0029]

Embodiments of the present invention will be described below with reference to embodiments shown in the drawings. FIG. 1 shows the internal structure of an oxygen sensor as an embodiment of the gas sensor of the present invention. The oxygen sensor 1 includes an oxygen detecting element 2 which is a hollow shaft-shaped solid electrolyte member having a closed end, and a heating element 3 which is a shaft-shaped ceramic heater. The oxygen detecting element 2 is made of a solid electrolyte having oxygen ion conductivity. As such a solid electrolyte, Y ₂ O ₃
Although ZrO ₂ in which CaO is dissolved as a solid solution is typical, a solid solution of an oxide of another alkaline earth metal or a rare earth metal and ZrO ₂ may be used. Also,
ZrO _{2 serving} as a base may contain HfO ₂ .

Outside the intermediate portion of the oxygen detecting element 2, insulators 6, 7, made of insulating ceramic,
In addition, a metal casing 10 is provided via a ceramic powder 8 formed of talc, and the oxygen detection element 2 penetrates the casing 10 while being electrically insulated from the casing 10. The casing 10 includes a metal shell 9 having a screw portion 9b for attaching the oxygen sensor 1 to an attachment portion such as an exhaust pipe,
A main cylinder 14 as an inner cylinder member connected so that the inside communicates with one opening of the metal shell 9, and a protector 10 attached to the metal shell 9 from a side opposite to the main cylinder 14.
0 and so on. As shown in FIG. 2, a pair of electrode layers 2b and 2c are provided on the inner surface and the outer surface of the oxygen detecting element 2 so as to cover almost the entire surface. These electrode layers 2
Each of b and 2c is a reversible catalyst for a dissociation reaction of oxygen molecules for injecting oxygen into the solid electrolyte constituting the oxygen detection element 2 and a recombination reaction of oxygen for releasing oxygen from the solid electrolyte. It is configured as a porous electrode having a function (oxygen dissociation catalyst function), for example, a Pt porous electrode.

In the following description, the side of the oxygen detection element 2 that faces the closed tip in the axial direction is the “front side (or the tip side)”, and the side that faces the opposite direction is the “rear side (or the rear side)”. (End side). "

In FIG. 1, first, a cylindrical protector mounting portion 9a is formed at the front opening of the metallic shell 9, and a detecting portion 2k formed at the tip side of the oxygen detecting element 2 is formed here.
Is provided with a cap-shaped protector 100 so as to cover a predetermined space. The protector 100 is formed with a plurality of gas transmission ports 103 to 106 through which the exhaust gas passes. This enables oxygen in the exhaust gas to come into contact with the front end surface of the oxygen detection element 2.

Next, in the opening on the rear side of the metal shell 9,
The packing 1 is provided between the main cylinder 14 and the insulator 6.
The filter assembly 16 as an outer cylinder member is fitted and fixed to the main cylinder 14 from the outside. The opening on the upper end side of the filter assembly 16 in the drawing is sealed with a grommet (elastic sealing member) 17 made of rubber or the like, and a ceramic separator 18 is further provided further inward. Then, the lead wires 20 and 21 for the oxygen detecting element 2 are passed through the ceramic separator 18 and the grommet 17.
And a lead wire for the heating element 3 (not visible as a shadow of the lead wires 20 and 21).

Next, as shown in FIG. 3A, a plurality of separator-side lead wire insertion holes 72 for inserting the respective lead wires 20 and 21 are formed in the ceramic separator 18 so as to penetrate in the axial direction. A flange-shaped separator-side support portion 73 is formed at an axially intermediate position so as to protrude from the outer peripheral surface. The ceramic separator 18 has a part positioned on the front side of the separator-side support part 73 inside the rear end of the main cylinder 14.
Abuts on the rear end face of the separator 73 and the separator-side support portion 73.
It is arranged in a state where a portion located on the rear side is projected outside the main cylinder 14.

Returning to FIG. 1, one lead wire 20 for the oxygen detecting element 2 passes through the connector part 24 of the terminal fitting 23 and the lead wire part 25 following it, and the internal electrode connecting part 26 of the terminal fitting 23. It is electrically connected to the electrode layer 2c (FIG. 2) inside the oxygen detection element 2 described above. On the other hand, the other lead wire 21 is connected to a connector portion 34 of another terminal fitting 33.
And the following lead line portion 35 and external electrode connection portion 3
5b, it is electrically connected to an outside electrode layer (not shown) of the oxygen detection element 2.

Here, the oxygen detecting element 2 is heated and activated by the exhaust gas when the exhaust gas temperature is sufficiently high, but when the exhaust gas temperature is low such as when starting the engine. Is activated by forcibly heating with the heating element 3 described above. The heating element 3 is usually a ceramic heater, for example, a ceramic rod 45 mainly composed of alumina.
Is provided with a heating portion 42 having a resistance heating wire portion (not shown) formed in, for example, a meandering shape. The resistance heating wire portion is energized via a lead wire extending from the heater terminal portion 40, so that the oxygen detecting element 2
Plays a role in heating the tip (detection section) of the first electrode to a predetermined activation temperature or higher.

The heating element 3 is held in the hollow part of the oxygen detecting element 2 by the terminal fitting 23. The terminal fitting 23 has a heating element gripping portion 27 formed on the tip side of the heating element 3 (that is, on the side close to the heating section 42) with respect to the internal electrode connection section 26 described above. The heating element gripping portion 27 has a C-shaped cross-sectional shape surrounding the heating element 3. When the heating element 3 is not inserted, the heating element 3 has an inner diameter slightly smaller than the outer diameter of the heating element 3, and elastically expands as the heating element 3 is inserted. Hold. In the configuration of FIG. 1, the heating element grip portion 27 is provided only at one location on one side of the internal electrode connection portion 26.

As shown in FIG. 2, the internal electrode connection 26
Is formed so as to surround the heating element 3 by bending a plate-like portion having a plurality of saw-tooth-shaped contact portions 26a formed on both left and right edges thereof into a cylindrical shape. The frictional force between the outer peripheral surface and the inner wall surface 2a of the hollow portion of the oxygen detecting element 2 serves to position the heating element 3 in the axial direction with respect to the hollow portion. It comes into contact with and conducts with the electrode layer 2c.

Next, as shown in FIG. 3 (a), the filter assembly 16 has a cylindrical shape which is connected substantially coaxially to the main cylinder 14 (casing 10) from the rear and outside, and the inside of the filter assembly 16 is mainly formed. A filter holding portion 51 is provided, which communicates with the inside of the tube 14 and has a plurality of gas introduction holes 52 formed in a wall portion. And outside the filter holding portion 51,
A cylindrical filter 53 for closing the gas introduction hole 52 is arranged, and one or more (four in this embodiment) auxiliary gas introduction holes 55 are formed on the outside of the filter 53 on the wall. At the same time, the filter 53 is
A cylindrical auxiliary filter holding portion 54 that is sandwiched and held between the auxiliary filter holding portion 54 and the first auxiliary filter holding portion 54 is disposed. Specifically, the gas introduction hole 52 and the auxiliary gas introduction hole 55 are spaced from each other at predetermined intervals along the circumferential direction with respect to the filter holding portion 51 and the auxiliary filter holding portion 54 at a positional relationship corresponding to each other at the axial intermediate portions. The filter 53 is arranged so as to surround the filter holding portion 51 in the circumferential direction.

The filter holding portion 51 has a step portion 60 formed at an intermediate portion in the axial direction of the filter holding portion 51. The first portion 61 is located on the front side in the axial direction with respect to the step portion 60, and the second portion 62 is located on the rear side in the axial direction. The second portion 62 is configured to be smaller in diameter than the first portion 61, and the gas introduction hole 52 is formed in the wall of the second portion 62. Further, the auxiliary filter holding section 54 is provided with the first portion 6 of the filter holding section 51.
1 having an inner diameter smaller than the outer diameter.

The filter 53 is made of, for example, a porous fiber structure obtained by stretching an unsintered molded body of polytetrafluoroethylene (hereinafter, referred to as PTFE) in a uniaxial or more direction at a heating temperature lower than the melting point of PTFE. The body (trade name: Gore-Tex (Japan Gore-Tex Co., Ltd.)) prevents permeation of liquids mainly composed of water such as water droplets and allows permeation of gas such as air and / or water vapor. It is configured as a filter. Thereby, the air (outside air) as a reference gas is introduced into the main cylinder 14 (the casing 10) from the auxiliary gas introduction hole 55 through the filter 53 and the gas introduction hole 52, and water in a liquid state such as water droplets is removed. Intrusion into the main cylinder 14 is prevented.

Further, as shown in FIG.
Is a predetermined amount of gap between the outer surface of the filter holding portion 51 and the filter 53 so as to form an annular shape along the row of the auxiliary gas introduction holes 55, for example. 58 are formed. Further, the auxiliary filter holding portion 54 has filters 53 on both sides in the axial direction with a row of auxiliary gas introduction holes 55 arranged in the circumferential direction.
The auxiliary filter holder 54 is connected to the filter holder 5 through
1 and annular filter caulking portions 56 and 57
Are formed.

Returning to FIG. 3A, the filter holding unit 51
Sets the projecting portion of the ceramic separator 18 to the second portion 6.
2 to cover the inside thereof, and
Is disposed so as to contact the separator-side support portion 73 from the side opposite to the main cylinder 14 via the metal elastic member 74. On the other hand, the filter holding portion 51 is disposed so as to overlap with the main cylinder 14 from the outside at the distal end side, that is, the first portion 61, and the filter holding portion 51 is swaged toward the main cylinder 14 at the overlap portion. Thereby, an annular assembly connection caulking portion 75 is formed in the circumferential direction thereof. By this assembly connection caulking portion 75, the filter holding portion 51 is pressed against the main cylinder 14 so that the inner peripheral surface thereof is in an airtight state with respect to the outer peripheral surface of the main cylinder 14, and is connected thereto.

Outside the auxiliary filter holding portion 54, a cylindrical protective cover 64 is provided so as to cover it. The protective cover 64 includes, for example, the gas introduction hole 52.
(Or an auxiliary gas introduction hole 55) at a position corresponding to the auxiliary gas introduction hole 55 so as to generate an auxiliary gas retention space 65 between the filter 53 and both sides of the auxiliary gas introduction hole 52 in its own axial direction (that is, detection). The side closer to and farther from the portion 2k) is joined to the outer surface of the filter holding portion 51 by swaging portions 66 and 67 as cover joining portions.

The protective cover 64 has a form in which the inner surface extends beyond the outer surface of the first portion 61 of the filter holder 51, whereby the outer surface of the auxiliary filter holder 54 and the inner surface of the protective cover 64 are formed. The distance has been expanded. Specifically, the distance w1 between the outer surface of the auxiliary filter holding portion 54 at the position where the auxiliary gas introduction hole 55 is formed and the inner surface of the protective cover 64 is 0.2 mm or more, preferably 0.3 mm or more.
mm or more. In order to secure the protection cover 64 to the filter holding portion 51 by the caulking portion 66 on the axial front side, the distance w1 is required.
Is preferably set to 1.0 mm or less.

In the protective cover 64, the auxiliary gas retaining space 65 communicates with the outside and introduces outside air into the protective cover 64. The protective cover 64 penetrates the protective cover 64 at a position corresponding to the auxiliary gas retaining space 65 so as to penetrate therethrough. A plurality (four in the present embodiment) of cover-side gas introduction holes 64a as parts are provided at predetermined intervals in the circumferential direction. These cover side gas introduction holes 64
a is formed on the side closer to the detector 2k than the auxiliary gas introduction hole 55 in the axial direction of the protective cover 64. Specifically, as shown in FIG.
The tapered reduced-diameter portion 64b is formed by narrowing the side by forming the caulking portion 66.
The above-mentioned cover side gas introduction hole 64a is
5 are formed in a positional relationship deviated from each other. The positional relationship between the cover-side gas introduction holes 64a and the auxiliary gas introduction holes 55 is such that, when the cover-side gas introduction holes 64a are viewed in any direction from the outside of the protective cover 64, the cover-side gas introduction holes 64a. It is preferable that the setting is made such that the auxiliary gas introduction hole 55 cannot be visually recognized through the hole 64a.

The external communication portion is located at a position corresponding to the caulking portion 66 and the filter holding portion 51 and the protective cover 6.
4 is also formed. Specifically, as shown in FIG. 4, a plurality of grooves 69 extending in the axial direction of the filter holding portion 51 are formed on the outer peripheral surface of the first portion 61 of the filter holding portion 51 at predetermined intervals along the circumferential direction. , These groove portions 69 constitute an external communication portion. Then, as shown in FIG. 5, the protective cover 64 is swaged toward the first portion 61 of the filter holding portion 51 so as to cross each groove 69 in the arrangement direction and at the bottom of the groove 69. The caulking portion 66 is formed in an annular shape so that a gap 70 remains between the first portion 61 and the first portion 61. In this structure, as shown in FIG. 6, the gap 70 is formed between the protective cover 64 and the first portion 61 of the filter holding portion 51 from the front opening 71 of the gap 70 formed in each groove 69. The outside air is led to the auxiliary gas retaining space 65 through the passage. On the other hand, the caulking portion 67 is formed on the outer peripheral surface of the end portion of the second portion 62.

Next, as shown in FIGS. 3 and 7, the assembly connecting and caulking portion 75 connects the filter holding portion 51 to the main cylinder 1.
4, a main caulking portion 76 formed in an annular shape in the circumferential direction, and a square cross section formed closer to the tip of the oxygen detection element 2 than the main caulking portion 76 (An octagonal cross section in the present embodiment).

Hereinafter, the main cylinder 14 of the filter assembly 16 will be described.
Is assembled as follows, for example. That is, as shown in FIG. 8A, the metal elastic member 74 is extrapolated to the ceramic separator 18, and the front end side of the ceramic separator 18 is inserted into the main cylinder 14. On the other hand, the filter assembly 16 is pre-assembled as shown in FIG. 4, and is put on the filter holder 51 from outside the ceramic separator 18 and the main cylinder 14 as shown in FIG. The oxygen detecting element 2, the heating element 3 and the like (FIG. 1) are assembled in the main cylinder 14 in advance, and the lead wires (only 20 and 21 out of the four are shown) from them are separated by the separator of the ceramic separator 18. It is passed through the side lead wire insertion hole 72 (FIG. 3A), and is further extended outward from the rear end opening of the filter support portion 51.

Subsequently, as shown in FIG.
4 and the filter assembly 16 are subjected to an axial compressive force. As a result, the metal elastic member 74 is compressed and deformed between the filter support portion 51 and the separator-side support portion 73 of the ceramic separator 18, so that the ceramic separator 18 is sandwiched between the main cylinder 14 and the filter support portion 51. Generates biasing force. And while maintaining this state,
As shown in FIG. 8C, the filter support 51 and the main cylinder 1
4 and an assembly connection crimping portion 75 is formed, and both are connected. Next, as shown in FIG. 8D, the elastic seal member 17 is fitted into the opening on the rear end side of the filter holding portion 51, and furthermore, the protective cover 64 is covered, and as shown in FIG. And 67 are formed and the assembly is completed.

The assembly connection caulking portion 75 can be formed using, for example, a caulking device 79 conceptually shown in FIG. As shown in FIGS. 9A and 9B, the caulking device 79 includes the filter support 5
1 includes a plurality of crimping punches 81 to 83 for compressing the filter support 1 from the outer side in the circumferential direction, and is arranged in a positional relationship separated by a predetermined distance in the axial direction of the filter support portion 51 as shown in FIG. First and second caulking punch units 80 and 82 are provided. Here, the first caulking punch unit 80 is for forming a main caulking portion, and the tip surfaces of the caulking punches 81 are continuous with each other to form a cylindrical surface. On the other hand, the second caulking punch unit 82 is for forming an auxiliary caulking portion, and the tip surfaces of the caulking punches 83 are connected to each other to form an octagonal cylindrical surface. Then, as shown in FIG. 9, these caulking punches 81 and 83 correspond to each other by connecting portions 84.
To form a punch segment 85, which is integrally approached and separated from the outer peripheral surface of the filter support portion 51 in the radial direction.

When the punch segments 85 arranged around the filter supporting portion 51 are moved toward the filter supporting portion 51 at the same time, the main caulking portion 76 and the auxiliary caulking portion are attached to the filter supporting portion 51. 77 are collectively formed. According to this method, the main caulking portion 76 and the auxiliary caulking portion 77 are formed simultaneously by one caulking process, so that not only is the efficiency improved, but also the following effects are achieved. . That is, the compression by the caulking punch causes the filter support portion 51 to
The crimped portion is formed by being pressed in while being locally bitten toward the surface, and a wrinkled portion or a raised portion accompanying the bite deformation is likely to be formed in the filter support portion 51 around the pressed portion. Here, the main caulking portion 76
When the auxiliary caulking portion 77 and the auxiliary caulking portion 77 are sequentially formed, the influence of a wrinkled portion or a rising portion by a caulking portion formed later affects the caulking portion formed earlier, and a problem that airtightness is likely to be deteriorated easily occurs. . However, if the crimping portions 76 and 77 are formed at the same time as described above, the influence of the wrinkled portion or the raised portion can be pooled in the region between the crimping portions 76 and 77. In the caulked portions 76 and 77, sufficient adhesion, that is, airtightness can be ensured.

As described above, the assembly of the filter assembly 16 is performed independently of the assembly of the oxygen detecting element 2 and the like in the casing 10, so that the lead wires do not interfere and the assembly work is extremely efficient. Can be done
Further, since the assembly of the components into the casing 10 and the assembly of the filter assembly 16 can be performed in parallel, the productivity is dramatically improved. Furthermore, even if a failure in assembling the filter 53 occurs, if a failure can be found at the stage of the filter assembly 16, the effect of the failure does not affect the finished sensor product, and it is unlikely that parts are wasted.

Further, the following effects are achieved by the assembly connection caulking portion 75 being constituted by the main caulking portion 76 and the auxiliary caulking portion 77 as described above. That is, in the main caulking portion 76, since the contact surface between the main cylinder 14 and the filter holding portion 51 is a cylindrical surface, the airtightness is excellent, and water or the like leaks into the main cylinder 14 from between them. Plays a role in reliably preventing However, FIG.
As schematically shown in (b), when a strong torsional force acts on the main cylinder 14 and the filter holding portion 51 due to an external impact or the like, the cylindrical contact surface causes relative rotation between the two. It is possible that slippage occurs and the airtightness is impaired.

Therefore, if the above-described auxiliary caulking portion 77 is formed, the contact surface thereof is formed in a rectangular cylindrical shape as shown in FIG. Does not easily cause relative rotation between the main cylinder 14 and the filter holding portion 51. As a result, such a relative rotation is also effectively prevented from occurring in the main caulking portion 76, and the airtightness between the main cylinder 14 and the filter holding portion 51 can be further ensured. The main caulking portion 76 and the auxiliary caulking portion 77 may be formed by exchanging the positional relationship in the axial direction. However, since the tip side of the oxygen sensor 1 is often exposed to a high temperature, airtightness is ensured. It can be said that the above-mentioned arrangement relationship in which the main caulking portion 76 in which the priority is given is far from such a heat source is more desirable.

If there is almost no fear that the above-described relative rotation occurs in the main caulking portion 76, the auxiliary caulking portion 77 can be omitted.

The dimensions of each part of the metal shell 9 shown in FIG. 11 can be set as follows, for example. K1: 2
7.6 mm, K2: 14.8 mm, K3: 12.8 mm,
K4: 9 mm, K5: 3.8 mm, K6: 2 mm, K7: 1
mm, K8: 11.9 mm, K9: 8.6 mm, K10: 9
mm, K11: 21.1 mm, K12: 6.5 mm, K13:
φ22mm, K14: φ16.88mm, K15: φ9.4
8 mm, K16: 7.5 mm, K17: 16.5 mm,
K18: φ11.6 mm, K19: φ16 mm.

On the other hand, in FIG.
Is about 54 mm, and the length L2 from the receiving surface 9d of the gasket G of the metal shell 9 to the tip end surface of the protector 100 is
Is about 29 mm. The inner diameter of the main cylinder 14 is 12.2.
mm.

Hereinafter, the operation of the oxygen sensor 1 will be described. In the oxygen sensor 1, a cover-side gas introduction hole 64a formed in the protective cover 64 shown in FIG.
The air as a reference gas is introduced into the auxiliary gas retaining space 65 through the gap 70 based on the groove 69 formed in the first portion 61 shown in FIG. 1, and further into the casing 10 via the filter 53 of the filter assembly 16. be introduced. On the other hand, the outer surface of the oxygen detecting element 2 has a protector 1
The exhaust gas introduced through the gas transmission ports 103 to 106 contacts the oxygen detection element 2, and an oxygen concentration cell electromotive force is generated in the oxygen detection element 2 according to the difference in oxygen concentration between the inner and outer surfaces. The electromotive force of the oxygen concentration cell is used as a detection signal of the oxygen concentration in the exhaust gas from the electrode layers 2 b and 2 c to the lead wires 21 and 2.
By taking it out via 20, the oxygen concentration in the exhaust gas can be detected.

With the provision of the protective cover 64,
Ejection of droplets directly to the filter 53 or attachment of deposits such as oil and dirt are effectively prevented or suppressed. Further, the protective cover 64 extends outward at a position corresponding to the auxiliary gas retaining space 65 so that the distance between the outer surface of the auxiliary filter holding portion 54 and its own inner surface is 0.2 m.
m or more (preferably 0.3 mm or more), it becomes difficult for oil or the like to accumulate in the gap between the outer surface of the auxiliary filter holding portion 54 and the inner surface of the protective cover 64. The problem that the circulation of the passed outside air is hindered is less likely to occur.

Further, although the outside of the filter 53 is covered with the protective cover 64, the cover-side gas introduction hole 64a formed in the protective cover 64 and the groove 69 formed in the filter holding portion 51 side. With the (gap 70), outside air is smoothly introduced into the auxiliary gas retaining space 65, and highly accurate detection is possible. Further, since the cover-side gas introduction hole 64a and the auxiliary gas introduction hole 55 are formed to be shifted from each other, high-pressure water comes from the outside and enters the auxiliary gas retention space 65 from the cover-side gas introduction hole 64a. The auxiliary gas introduction hole 5
5 is prevented from directly hitting water drops and the like, so that the water drops and the like do not easily enter the casing 10.

As shown in FIG. 12, the protective cover 6
4 omits the caulking part 66 shown in FIG. 3 and uses the gap 68 between the front opening and the (first part 61) of the filter holding part 51 as an external communication part, from which external air is retained as auxiliary gas. It may be introduced into the space 65. FIG.
In FIG. 4 (or FIG. 4), when outside air can be smoothly introduced into the auxiliary gas retaining space 65 by only one of the cover-side gas introduction hole 64a or the groove 69, any of these may be omitted.

In FIG. 6, when the caulking force when forming the caulked portion 66 is excessively strong, the groove 69 is too crushed, so that the gap 70 is hardly left, and the flow of gas may be hindered. . Therefore, as shown in FIG. 13, a notch 64c is formed in the protective cover 64 from the opening corresponding to the groove 69 along at least a part of each groove 69.
If the caulking portion 66 is formed at a position crossing the middle of the notches 64c, the portion of the groove 69 which is crushed by the formation of the caulking portion 66 will not be covered with the protective cover 64, so that the protective cover 64 will be smooth. Gas flow can be ensured.

In the structure shown in FIG. 3, the ceramic separator 18 can be omitted, and the rubber grommet 17 can be extended to the position of the ceramic separator 18 instead. In this case, the filter holding portion 51 can be omitted, the gas introduction hole can be formed in the grommet 17, and the filter 53 can be sandwiched and held between the grommet 17 and the auxiliary filter holding portion 54.

[0065] structure of the sensor of the present invention described above, the gas sensor other than oxygen sensor, for example, HC sensor and NO _X
The same can be applied to sensors and the like.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an oxygen sensor as one embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view showing the vicinity of a detection unit of the oxygen detection element in FIG.

FIG. 3 is an enlarged sectional view showing a part of the filter assembly of FIG. 1;

FIG. 4 is a front partial cross-sectional view of the filter assembly.

FIG. 5 is a plan sectional view of a caulked portion between the filter assembly and the protective cover, and a partially enlarged view thereof.

FIG. 6 is a partially enlarged longitudinal sectional view of the same.

FIG. 7 is an enlarged view of an assembly connection crimping portion and B-
B and CC sectional drawing.

FIG. 8 is an explanatory view of an assembling process of the oxygen sensor of FIG. 1;

FIG. 9 is a conceptual diagram of a caulking device.

FIG. 10 is an operation explanatory view of a main caulking portion and an auxiliary caulking portion in an assembly connection caulking portion.

FIG. 11 is a dimensional explanatory view of a metal shell.

FIG. 12 is a longitudinal sectional view showing a modified example of the protective cover in an assembled state.

FIG. 13 is a front view showing another modified example.

[Description of Signs] 1 Oxygen sensor (gas sensor) 2 Oxygen detecting element 9 Metal shell 10 Casing 14 Main cylinder 51 Filter holding part 52 Gas introduction hole 53 Filter 54 Auxiliary filter holding part 55 Auxiliary gas introduction hole 60 Step 61 First part 62 Second part 64 Protective cover 64a Cover-side gas introduction hole (external communication part) 65 Auxiliary gas retention space 69 Groove 70 Gap (external communication part)

Claims (11)

[Claims] 1. A detection device comprising: a cylindrical casing; and an oxygen concentration cell element formed in a shaft shape disposed in the casing and having a tip portion operated with outside air introduced into the casing as a reference gas. A detection element having a portion formed therein; an auxiliary filter holding portion provided on the rear side of the casing and having an auxiliary gas introduction hole formed therein; and an inside arranged inside the auxiliary filter holding portion to close the auxiliary gas introduction hole. And a filter (hereinafter, referred to as an auxiliary gas retention space) between the filter that blocks liquid permeation and allows gas permeation and the auxiliary filter holding portion outside the auxiliary filter holding portion. A protective cover having a cylindrical shape covering the filter, and a protective cover that prevents or suppresses direct injection of droplets onto the filter or adhesion of deposits such as oil and dirt; And an external communication portion for communicating the outside air into the auxiliary gas retention space, and an external surface of the auxiliary filter holding portion at a position where the auxiliary gas introduction hole is formed, A gas sensor, wherein the distance from the inner surface of the protective cover is 0.2 mm or more. 2. A detection device comprising: a tubular casing; and an oxygen concentration cell element formed in a shaft shape disposed in the casing and having a tip portion operated with outside air introduced into the casing as a reference gas. A detection element having a portion formed therein, and a step portion provided at the rear side of the casing and formed at an intermediate portion in the axial direction of the casing itself, the first portion on the front side in the axial direction with respect to the step portion, and the second portion on the rear side similarly. A cylindrical filter holding portion formed as a portion such that the second portion is smaller in diameter than the first portion, and a gas inlet hole is formed in a wall of the second portion; and the filter holding portion. The filter is disposed outside the filter so as to close the gas introduction hole, blocks liquid permeation and allows gas permeation, and is formed in a cylindrical shape disposed outside the filter, and has an auxiliary gas introduction hole formed in a wall portion. Is formed An auxiliary filter holding portion for holding the filter by being sandwiched between the filter holding portion and a space between the auxiliary filter holding portion and the outside of the auxiliary filter holding portion (hereinafter, an auxiliary gas retention space) A protective cover having a cylindrical shape that covers the filter in a state where the protective cover is formed, and a protective cover that prevents or suppresses direct spraying of droplets onto the filter or adhesion of deposits such as oil and dirt; An external communication portion that communicates the outside with the auxiliary gas retaining space and introduces the outside air into the auxiliary gas retaining space; an outer surface of the auxiliary filter holding portion at a position where the auxiliary gas introduction hole is formed; In order to increase the distance between the inner surface of the protective cover and the inner surface of the protective cover, the inner surface of the protective cover has a configuration that extends outside the outer surface of the first portion of the filter holding portion. A gas sensor characterized by the above-mentioned. 3. The gas sensor according to claim 2, wherein a distance between an outer surface of the auxiliary filter holding portion and an inner surface of the protective cover at a position where the auxiliary gas introduction hole is formed is 0.2 mm or more. 4. A detection device comprising: a cylindrical casing; and an oxygen concentration cell element formed in a shaft shape disposed in the casing and having, at its tip, an external air introduced into the casing and operating with reference air as a reference gas. A detection element having a portion formed therein; an auxiliary filter holding portion provided on the rear side of the casing and having an auxiliary gas introduction hole formed therein; and an inside arranged inside the auxiliary filter holding portion to close the auxiliary gas introduction hole. And a filter (hereinafter, referred to as an auxiliary gas retention space) between the filter that blocks liquid permeation and allows gas permeation and the auxiliary filter holding portion outside the auxiliary filter holding portion. A protective cover having a cylindrical shape covering the filter, and a protective cover that prevents or suppresses direct injection of droplets onto the filter or adhesion of deposits such as oil and dirt; And an external communication portion for communicating the outside air into the auxiliary gas storage space, the protective cover being provided at a position corresponding to the auxiliary gas storage space. A gas sensor comprising a cover-side gas introduction hole provided so as to penetrate through the gas sensor. 5. The gas sensor according to claim 4, wherein a distance between an outer surface of the auxiliary filter holding portion and an inner surface of the protective cover at a position where the auxiliary gas introduction hole is formed is 0.2 mm or more. 6. The filter holding portion has a step portion formed at an intermediate portion in the axial direction of the filter holding portion, and the filter holding portion has a first portion on the axial front side and a second portion on the rear side with respect to the step portion. Is formed so as to be smaller in diameter than the first portion, and a gas introduction hole is formed in a wall portion of the second portion, and an outer surface of the auxiliary filter holding portion at a position where the auxiliary gas introduction hole is formed. The protective cover according to claim 4, wherein the inner surface of the protective cover has a shape protruding outside the outer surface of the first portion of the filter holding portion so as to increase the distance between the inner surface of the protective cover and the inner surface of the protective cover. Gas sensor. 7. The cover-side gas introduction hole and the auxiliary gas introduction hole are formed so as to be shifted from each other in at least one of the axial direction and the circumferential direction of the protective cover. The gas sensor according to any one of the above. 8. The cover-side gas introduction hole and the auxiliary gas introduction hole are connected via the cover-side gas introduction hole when the cover-side gas introduction hole is viewed in an arbitrary direction from outside the protective cover. 8. The gas sensor according to claim 7, wherein the auxiliary gas introduction hole is formed so as not to be visually recognized. 9. The gas sensor according to claim 7, wherein the cover-side gas introduction hole is formed closer to the detection unit with respect to the auxiliary gas introduction hole in the axial direction. 10. The protective cover is configured such that, with respect to the auxiliary gas introduction hole in the axial direction, at least a side farther than the detection section and a side closer to the detection section is formed by a circumferential cover joint. The gas sensor according to claim 1, wherein the gas sensor is joined to an outer surface of the filter holding unit. 11. The cover joint portion is formed on both a side farther than the detection portion and a side closer to the detection portion with respect to the auxiliary gas introduction hole, and the external communication portion is close to the detection portion. The gas sensor according to claim 10, further comprising a groove-shaped communicating portion formed between the protective cover and the filter holding portion in a form crossing the circumferential annular cover joint formed on the side.