JP2001242121A - Gas sensor and sealing structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sealing structure capable of holding sealability, even if exposed to a high temperature over a long time, and to provide a gas sensor to which the sealing structure is applied. SOLUTION: In an oxygen sensor 1, nickel plating 71 corroded by fluoric acid (HF) generated from a sealing member 17 at a high temperature is applied to the surfaces of lead wires at the interfaces of the sealing member 17 and a plurality of the lead wires, both of which comprise a fluorine-containing resin. Therefore, if the oxygen sensor is exposed to a high temperature, nickel fluoride which is a compound of fluorine of fluoric acid and nickel of the nickel plating 71 is formed to form a sealing layer in the gaps between the sealing member 17 and a plurality of the lead wires. Accordingly, even if the oxygen sensor 1 is heated and cooled repeatedly and the elasticity of the seal member 17 deteriorates and gasp are generated between the sealing member 17 and a plurality of the lead wires, the sealing layer functions so as to seal the gaps.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas sensor which is attached to a pipe forming a flow path through which a gas to be measured such as exhaust gas flows, detects a predetermined gas component in the gas to be measured, and is used at a high temperature. The present invention relates to a lead wire sealing structure applied to such gas sensors and the like.

[0002]

2. Description of the Related Art Conventionally, various types of gas sensors, such as HC sensors and NOx sensors, are known as gas sensors for detecting a specific gas component or its concentration from a mixed gas. In this type of gas sensor, a detection element is arranged inside a metal outer cylinder, and a lead wire connected to an electrode of the detection element is drawn out from an opening provided at one end of the outer cylinder, thereby The sensor output was being taken out. A rubber seal member is elastically fitted inside the opening of the outer cylinder in order to prevent moisture or the like from entering the inside of the outer cylinder from the outside. The above-mentioned lead wire is inserted into the hole in an airtight manner so as to extend outside the outer cylinder.
Furthermore, in order to secure the adhesion between the sealing member and the lead wire, a method of elastically tightly fixing the lead wire to the sealing member by fixing the lead wire to the sealing member by externally caulking the outer cylinder in the vicinity of the opening. Had been taken.

Incidentally, such a gas sensor is often used at a high temperature, and the sealing member and the lead wire are also exposed to a high temperature due to heat conduction from the outer cylinder. For this reason, as a covering material for the sealing member and the lead wire, a material made of a fluorine-containing resin material generally having high heat resistance has been used.

[0004]

However, such a sealing member made of a fluorine-containing resin material has a large coefficient of thermal expansion, and expands itself at high temperatures. Further, as described above, a caulking force is applied to the seal member from the outside. Therefore, at high temperatures, a compressive force exceeding the elastic range may be applied to the seal member. for that reason,
When the gas sensor is used for a long time and the cycle of heating and cooling is repeated, there is a problem that the elasticity of the seal member is impaired due to thermal deterioration. Then, when the thermal deterioration of the seal member progresses, in particular, the adhesion between the seal member and the lead wire is reduced, and a gap is formed between the seal member and the outside air.

[0005] As a technique for improving the leakage property of a covered lead wire at a high temperature, as described in Japanese Utility Model Application Laid-Open No. 4-136560, the covered lead wire is crimped with a metal member at one end and covered with rubber. A technique for maintaining the sealing property of a member at a high temperature has been disclosed. However, in this method, it is difficult to crimp the covered lead wire and the metal member with good airtightness, so that there is a problem that the sealing performance at a low temperature is inferior to that using rubber.

The present invention has been made in view of such a problem, and has been applied to a seal structure capable of maintaining the sealing property even when exposed to a high temperature for a long time, and to the application of the seal structure. It is an object to provide a gas sensor.

[0007]

In view of the above problems, in the gas sensor of the present invention, a metal film is interposed between an insertion hole provided in a seal member for closing an opening of an outer cylinder and a covered lead wire. I tried to do it. The reason why the adhesion between the sealing member and the coated lead wire is reduced at a high temperature is that the sealing member cannot absorb the difference in thermal expansion between the sealing member and the coated lead wire due to elastic deformation due to the reduced elasticity of the sealing member. is there. To prevent this, the sealing member may be adhered to the covered lead wire. However, since a gas sensor is used at a very high temperature, a resin containing fluorine is often used for a lead wire and a sealing member, and a material that adheres them with high airtightness to a high temperature has not been found. The applicant has conducted intensive studies and has found that it is effective to interpose a metal film between the coated lead wire and the sealing member when joining them.

The reason why the joining between the sealing member and the coated lead wire is made by interposing the metal film is unknown, but it is probably that the coated lead wire is joined to the metal and further the sealing member is joined to the metal. It is presumed that both were joined. In other words, the metal surface has a high activity by nature and has the ability to chemically bond with various substances, but if it has such a thickness that it has rigidity by itself, the coefficient of thermal expansion and rigidity with the joining member Due to the difference in the strength, the force acting to peel off exceeds the adhesive strength and does not join, but if the film state is such that the physical properties such as macroscopic coefficient of thermal expansion and rigidity are thin, the original chemical activity of metal is superior It is presumed to have a bonding force.

It is presumed that the metal film should be bonded to the sealing member and the coated lead wire in some form, but a chemical bond is preferable because the bond is strong and stable. In particular, if the seal member and the metal film are brought into close contact with each other at a high temperature, a chemical bond is generated between the seal member and the metal, so that a strong sealing property can be ensured. Similarly, it is desirable that the metal film is also chemically bonded to the coated lead wire.

The area where the metal film is formed is preferably a range sufficient for exhibiting the function of the sealing layer, and is preferably substantially equal to the length of the insertion hole provided in the sealing member. In addition, it is preferable that the lead wire is provided so as not to be interrupted in the circumferential direction. When the material of the seal member is a material containing fluorine, the fluorine promotes chemical bonding between the metal film and the seal member, and more preferable results are obtained. Fluorine reacts with hydrogen contained in the seal member when exposed to high temperatures, and hydrofluoric acid (H
F). It is considered that hydrofluoric acid has high chemical activity and reacts with the metal film to form a compound which is easily bonded to the sealing member or the covering material of the lead wire. It is preferable that the covering material of the lead wire also contains fluorine.

It has also been found that better bonding properties can be obtained when nickel is used as the metal film. As can be understood from the above assumption, the thickness of the metal film needs to be reduced to a certain degree or more.
It was found that good bondability was obtained when the thickness was 1 μm or less.

As a method of forming the metal film, there can be considered a method such as sputtering, vapor deposition, or application of an organic metal and chemically attaching the same. However, plating is advantageous in terms of cost. According to the electroless plating method, a good thin film can be formed at low cost even on the surface of a lead wire which is an insulator.

If the seal member is compressed and held by caulking the outer cylinder using an elastic body such as rubber for the seal member, the lead wire and the seal member are compressed via a metal film. Since the stress is applied to the surface, the metal film and the lead wire and the metal film and the seal member are in close contact with each other, and a better connection is obtained.

Although the gas sensor of the present invention having a seal structure which does not deteriorate its sealing performance even when used in a high-temperature environment has been described above, such a seal structure has the following features.
It is not limited to gas sensors. That is, such a seal structure is provided with a lead wire that closes an opening formed in the housing with a seal member, and penetrates an insertion hole provided in the seal member to electrically connect the inside and the outside of the housing. The same can be applied to such a case.

Even in this case, the metal film provided between the inner wall of the insertion hole and the coating surface of the coating lead wire is preferably formed by plating because it is simple and has a merit in terms of cost.

[0016]

Preferred embodiments of the present invention will be described below with reference to the drawings. In the present embodiment, the gas sensor of the present invention is configured as an oxygen sensor, and FIG. 1 is a cross-sectional view illustrating the overall configuration of the oxygen sensor.

As shown in FIG. 1, the oxygen sensor 1
A detection element 2 formed in a hollow shaft shape whose end is closed by a solid electrolyte body containing O2 as a main component, an axial ceramic heater 3 disposed in the detection element 2, a casing 10 accommodating the detection element 2, and the like. It is configured.

The casing 10 fixes the oxygen sensor 1 to a mounting portion such as an exhaust pipe, and also has a ceramic holder 6,7.
And a metal shell 9 for housing the ceramic powder 8 therein and projecting the closed end of the detection element 2 into an exhaust pipe or the like.
And extending above the metal shell 9, and from above, the detecting element 2
And an outer cylinder 16 for introducing air into the inner surface of the outer cylinder.

In the vicinity of the upper opening of the outer tube 16, an insulating separator 18 formed of a ceramic tube is inserted. The separator 18 is provided with a flange 18a at an upper end thereof, and the outer cylinder 16 is caulked from the outside so that the lower end surface of the flange 18a is locked on the upper part of the outer cylinder 16 so that the inside of the outer cylinder 16 is retained. Is held in.

The upper end opening of the outer cylinder 16 has a cylindrical sealing member 1 made of fluorine rubber having excellent heat resistance.
7 are hermetically sealed by a sealing structure made of a lead wire 7, and lead wires 20 connected to the electrodes of the detecting element 2 so as to penetrate the seal member 17 and the separator 18, respectively.
A pair of lead wires (not shown) connected to the ceramic heater 3 and the ceramic heater 3 (hereinafter, these are also collectively referred to as “plural lead wires”) are arranged. The plurality of lead wires are configured such that their core wires are covered with a coating material made of a fluorine-containing resin having excellent heat resistance.

The fluorine-containing resin constituting the covering material of the seal member 17 and the lead wire is, for example, polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA), tetrafluoroethylene, or the like. Ethylene-hexafluoropropylene copolymer (FEP), polychloro-trifluoroethylene (PCTFE), ethylene-tetrafluoroethylene copolymer (ETFE), chlorotrifluoroethylene-ethylene copolymer (ECTFE), polyvinylidene fluoride ( PVDF), polyvinyl fluoride (PV
F) etc. can be used.

The details of the seal structure will be described below. As shown in FIG. 2 in an enlarged view of a portion A in FIG.
The seal member 17 provided inside the open end portion 47 of the first sensor has a vent hole 58 for introducing gas from the outside into the oxygen sensor 1 and a plurality of lead wires for passing the plurality of lead wires to be drawn out from the inside of the oxygen sensor 1. Is provided.

The plurality of insertion holes 60 are formed in parallel with the ventilation holes 58 and are arranged around the ventilation holes 58 at substantially equal intervals. And, on the outer surface of the covering material that covers each core wire of the plurality of lead wires inserted through the insertion hole 60,
Nickel plating 71 is formed on the portion to be inserted into insertion hole 60 (that is, at the interface between the plurality of lead wires and seal member 17). This nickel plating 71
It is formed by etching the surface of the covering material of the lead wire and subjecting it to electroless plating.

As described later, the nickel plating 71 is formed at a predetermined position of the coating material because the hydrofluoric acid (HF) generated by the sealing member 17 at high temperature and the nickel in the nickel plating 71 are formed. This is to enhance the sealing performance of the gap between the seal member 17 and the lead wire by forming a sealing layer by a chemical reaction of

As shown in FIG. 2, the formation area B of the nickel plating 71 in the covering material of the plurality of lead wires is longer than the height C of the sealing member 17 (that is, the length of the insertion hole 60). Or shorter, but this nickel plating 7
1 is formed so as to be located at the interface between the seal member 17 and the lead wire.
It is necessary that the sealing layer, which will be described later, formed in the gap between the insertion hole 60 and the lead wire be made so as not to be interrupted around the lead wire. Further, it is experimentally known that when the thickness of the nickel plating 71 exceeds 1 μm, the plating is easily peeled off due to bending of the lead wire when the gas sensor is used, so that the nickel plating 71 has a thickness of 1 μm.
It is preferable that the thickness be formed to be not more than μm.

The seal member 17 is provided with a plurality of lead wires to which the nickel plating 71 is applied as described above.
In a state where the water-repellent filter 50 is attached to the vent hole 58, the water-repellent filter 50 is disposed inside the open end 47 of the outer cylinder 16 and is caulked in the radial direction via the outer cylinder 16, and The sealing property between the lead wire and each lead wire is further ensured.

As described above, in the oxygen sensor 1 of the present embodiment, at the interface between the seal member 17 made of fluorine-containing resin and a plurality of lead wires, the seal member 17 Nickel plating 71 that is corroded by the generated hydrofluoric acid is applied. Therefore, when the gas sensor is exposed to a high temperature, a compound of nickel fluoride, which is a compound of fluorine of hydrofluoric acid and nickel of the nickel plating 71, is formed.
A sealing layer is formed in a gap between the lead wire and the plurality of lead wires. For this reason, even if the oxygen sensor 1 repeatedly heats and cools, the elasticity of the seal member 17 is deteriorated, and even if a gap is formed between the seal member 17 and the plurality of lead wires, the sealing layer is formed by the gap. Works to fill in.

That is, according to the sealing structure of the present embodiment, the sealing property between the sealing member 17 and the plurality of lead wires is improved when the gas sensor is manufactured at the beginning.
After the elasticity of the sealing member 17 is degraded due to thermal degradation, the sealing layer is held by the sealing layer. As a result, as a whole, the airtightness between the seal member 17 and the plurality of lead wires can be maintained for a long period of time.

The embodiments of the present invention have been described above. However, the embodiments of the present invention are not limited to the above-described embodiments, and may take various forms within the technical scope of the present invention. Needless to say. For example, in the above-described embodiment, nickel plating is used as the metal plating for forming the sealing layer. Alternatively, chrome plating, gold plating, silver plating, or the like may be used.

In the above embodiment, the metal plating is formed on the side of the plurality of lead wires. However, the metal plating may be formed on the side of the seal member 17 (that is, the insertion hole 60), or alternatively, may be formed on the side of the lead wire and the seal. It may be formed on both of the members. Further, in the above-described embodiment, the air introduction type oxygen sensor has been described. However, even when the oxygen sensor does not require a reference gas having a constant oxygen concentration such as a titania sensor or a zirconia sensor, a current flows between the electrodes. Accordingly, an oxygen sensor having a reference oxygen self-generating function that outputs a detection signal corresponding to a ratio of the oxygen concentration in the electrode side to the oxygen concentration in the gas to be measured can be similarly applied.

In this type of oxygen sensor, it is not necessary to introduce air, so that further airtightness is required. However, according to the present invention, the sealing property can be improved as described above. We can fully respond to requests.
Further, in the above embodiment, an example is shown in which the seal structure of the present invention is applied to an oxygen sensor. However, such a seal structure is not limited to the oxygen sensor, and other gas sensors or electrodes may be provided in the inner space. It is needless to say that a structure having an outer cylinder disposed therein and a lead wire connected to this electrode drawn out of the outer cylinder can be similarly applied as long as the structure is used in a high-temperature environment. Nor.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an overall configuration of an oxygen sensor according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating a structure of a seal member included in the oxygen sensor according to the embodiment.

[Explanation of symbols]

1 ... oxygen sensor 16 ... outer cylinder 17 ...
Seal member, 20, 21, ... lead wire, 50 ...
Water-repellent filter, 58: vent hole, 60: insertion hole, 71: nickel plating

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shuichi Hanai 14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi F-term (reference) 2G004 BB01 BC02 BC07 BE12 BE15 BF18 BG05 BG15 BH02 BJ02

Claims (10)

[Claims] 1. A detecting element, a covered lead connected to the detecting element, an outer cylinder for protecting at least one of the detecting element and the covered lead, and an opening formed at one end of the outer cylinder. And a sealing member made of an organic material for closing the sealing member, wherein the covered lead wire passes through an insertion hole formed in the sealing member, and covers substantially the entire periphery of the covered lead wire. A metal film interposed between the inner wall of the insertion hole and the inner wall of the insertion hole. 2. The gas sensor according to claim 1, wherein the metal film is chemically bonded to the seal member. 3. The gas sensor according to claim 1, wherein the metal film is chemically bonded to a coating material of the coated lead wire. 4. The gas sensor according to claim 1, wherein the seal member contains fluorine. 5. The gas sensor according to claim 1, wherein the metal film contains nickel. 6. The gas sensor according to claim 1, wherein the metal film has a thickness of 1 μm or less. 7. The gas sensor according to claim 1, wherein the metal film is metal plating applied to at least one surface of the inner wall of the insertion hole and the lead wire. . 8. The gas sensor according to claim 1, wherein the seal member is an elastic body, and the outer cylinder is compressed by being caulked near the opening. . 9. A housing, a sealing member made of an organic material for closing an opening formed in the housing, and an airtight insertion through an insertion hole formed in the sealing member, and extending into and out of the housing. A seal structure comprising a covered lead wire, wherein a metal film is interposed at least in part between the covered lead wire and an inner wall of the insertion hole. 10. The seal structure according to claim 9, wherein the metal film is metal plating applied to at least one surface of the inner wall of the insertion hole and the lead wire.