JP2002090336A - Gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor capable of introducing the outside air into a reference gas space via a gas permeable filter and securing both of a sealing property and permeability of the gas permeable filter. SOLUTION: In an oxygen sensor, the gas permeable filter 50 is constructed of a rough sheet 50a with a comparatively large thickness and a dense sheet 50b with a thickness thinner than the sheet 50a. Therefore, mechanical strength of the gas permeable filter 50 can be secured as a whole by the thick rough sheet part 50a part, while its permeability is maintained. Because of the dense sheet 50b arranged on the surface of the gas permeable filter 50, water resistance of the gas permeable filter 50 can be secured as a whole.

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, and functions by introducing atmospheric air as a reference gas from the outside.

[0002]

2. Description of the Related Art Conventionally, as a gas sensor for detecting the concentration of a specific gas component from a mixed gas, an HC sensor or N
Various types such as an Ox sensor are known. As this type of gas sensor, for example, a prior patent application (Japanese Patent Application No.
-346362), a ventilation hole for introducing outside air is formed so as to penetrate in the axial direction through the center of a seal member provided at an upper portion of the gas sensor, and a heater (heat source) installed at a lower portion of the gas sensor. By moving away from
Some devices have a configuration for preventing thermal deterioration of a ventilation filter that closes a ventilation hole. In this gas sensor, a sheet-shaped ventilation filter is inserted into a ventilation hole while being covered with a cylindrical insertion member, and is sandwiched between an outer peripheral surface of the cylindrical insertion member and an inner peripheral surface of the ventilation hole. By fixing in the air hole, the air hole is closed, and its air permeability and waterproofness are maintained.

[0003]

By the way, such a gas sensor is installed, for example, in a pipe of a vehicle. Even when a large water pressure is applied, such as when a car is washed, the gas sensor maintains its waterproofness and is installed inside the vehicle. Water must be prevented. For this purpose, it is conceivable to adopt a filter having a certain level of water resistance as a ventilation filter, that is, a filter formed of a dense porous sheet having a small porosity and a maximum pore diameter.

On the other hand, the ventilation filter inserted into the ventilation hole as described above is pulled by the frictional force between the outer peripheral surface of the cylindrical insertion member and the inner peripheral surface of the ventilation hole during the insertion. It is necessary to have a predetermined mechanical strength so as not to break even in such a state. If the thickness of the ventilation filter is too small, it is difficult to fix the filter between the outer peripheral surface of the cylindrical insertion member and the inner peripheral surface of the ventilation hole. For this reason, it is necessary to secure a predetermined thickness or more as the thickness of the ventilation filter.

[0005] However, if the predetermined thickness is ensured by the above-mentioned dense porous sheet, the air permeability deteriorates, and it is difficult to secure a necessary air flow into the reference gas space provided inside the gas sensor. Become. The present invention has been made in view of such a problem, and an object of the present invention is to provide a gas sensor that operates by introducing outside air into a reference gas space and that can guarantee both the sealing property and the gas permeability.

[0006]

SUMMARY OF THE INVENTION In view of the above problems, in the gas sensor according to the first aspect, the thickness of the sheet-shaped ventilation filter that blocks the ventilation path is made constant or more to secure the mechanical strength. In addition, in order to ensure the permeability and water resistance of the ventilation filter itself to a predetermined value or more,
A plurality of sheets made of a porous body are stacked in the thickness direction to form a ventilation filter.

[0007] That is, this air-permeable filter has a relatively large porosity and a maximum pore diameter, and a rough sheet excellent in air permeability.
A dense sheet having a relatively small porosity and a maximum pore diameter, which is inferior in air permeability to the coarse sheet but is excellent in water resistance is formed. Therefore, by increasing the thickness of the coarse sheet, it is possible to secure a certain height or more without impairing the air permeability of the gas permeable filter, and further attach a thin sheet to the coarse sheet. This makes it possible to ensure the water resistance of the ventilation filter while maintaining the permeability.

As described above, from the viewpoint of securing the thickness of the ventilation filter and its air permeability with a coarse sheet and securing water resistance with a dense sheet, increasing the number of coarse sheets and reducing the number of dense sheets It can be reduced,
In general, it is considered that as the number of sheets increases, the manufacturing cost of the ventilation filter increases. Therefore, as described in claim 2, the thickness of the dense sheet is set to be smaller than the thickness of the coarse sheet. Preferably, the number is reduced.

As described above, since the ventilation filter is composed of a plurality of sheets, it is conceivable to simply use each of the plurality of sheets in an overlapping manner. Separation makes assembly work difficult. Therefore, as described in claim 3, at least a part of each of the plurality of sheets may be adhered to each other to fix them to each other to form a ventilation filter. This attachment may be performed using an adhesive, or may be performed by fusing a part of the sheet.

Further, once the inside of the ventilation filter is impregnated with oil or the like, it is difficult to remove the oil and the like, which may cause deterioration of the ventilation filter. Therefore, it is preferable to adopt a configuration in which oil and the like are repelled on the surface of the ventilation filter as much as possible.
It is preferable that a dense sheet is disposed on at least the surface on the atmosphere side of the ventilation filter.

However, when a dense sheet is provided on one surface of the ventilation filter and a rough sheet is provided on the other surface, it is sufficient if it is possible to easily determine which surface is the dense sheet. If it cannot be determined, it is difficult to arrange the dense sheet side to the atmosphere side when disposing the ventilation filter in the ventilation path.

Therefore, it is preferable to dispose dense sheets on both surfaces of the ventilation filter.
With this configuration, when assembling the ventilation filter to the ventilation path, the operator does not need to determine which one is the denser sheet each time, and can perform an efficient assembly operation.

As described above, from the viewpoint of reducing the number of sheets constituting the ventilation filter and suppressing the cost of the ventilation filter, as described in claim 6, two ventilation filters are provided. It is preferable to form one coarse sheet between the sheets. With this configuration, the ventilation filter can be configured with only one coarse sheet having a thickness and two dense sheets having a small thickness.Moreover, in the formation process of the ventilation filter, these three sheets are used. It only needs to be attached, and the manufacturing cost can be kept low.

Furthermore, in order to further enhance the sealing property of the ventilation filter, an oil-repellent coating may be applied to at least the atmosphere-side surface of the ventilation filter. However, when the oil-repellent coating is performed by impregnating the surface of the ventilation filter with the coating agent, it may be preferable to provide a rough sheet on the surface of the ventilation filter because the coating agent has better fixability.

In the case where the above-described ventilation filter is employed, the ventilation path of the gas sensor has elasticity provided on a part of a wall for isolating the reference gas space of the gas sensor from the atmosphere. It is good to be provided so that it may penetrate the seal member which has. According to this structure, when the ventilation path is closed by the ventilation filter, the ventilation filter is fixed to the sealing member which is an elastic body. This is because the waterproof property on the fixing surface of the filter is improved.

Further, when the ventilation path is formed as a through hole provided in the seal member and the ventilation filter is inserted and fixed in the through hole, the ventilation filter can be easily fixed, and the ventilation can be easily performed. Since the fixing surface of the filter is tightly adhered to the sealing member, the waterproofness of the fixing surface of the ventilation filter is further improved.

Further, when the cylindrical insertion member is inserted into the through hole and the ventilation filter is fixed between the sealing member and the cylindrical insertion member, the ventilation filter is formed by the sealing member and the cylindrical member. Since it is airtightly sandwiched between the insertion members, the waterproofness of the fixing surface of the ventilation filter is further improved.

However, in this case, if the thickness of the ventilation filter is large, it is difficult to adopt a configuration in which the ventilation filter is sandwiched between the sealing member and the cylindrical insertion member. Therefore, as described in claim 11, the thickness of the ventilation filter is preferably 0.1 mm or more and 1.0 mm or less.

From the viewpoint of ensuring the air permeability of the air-permeable filter, the dense sheet preferably has a thickness of 50 μm or less.

[0020]

Preferred embodiments of the present invention will be described below with reference to the drawings. In this embodiment, the gas sensor of the present invention is configured as an oxygen sensor, and FIG. 1 is a cross-sectional view showing 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 O ₂ as a main component, an axial ceramic heater 3 arranged in the detection element 2, a case 10 for accommodating the detection element 2, and the like. It is composed of

The case 10 fixes the oxygen sensor 1 to a mounting portion such as an exhaust pipe, accommodates the ceramic holders 6, 7 and the ceramic powder 8 therein, and closes the closed end of the detecting element 2 to the exhaust pipe or the like. It comprises a metal shell 9 projecting inward, and an outer cylinder 13 extending above the metal shell 9 and for introducing air into the inner surface of the detection element 2 from above.

A circular upper opening is formed at the upper end of the metal shell 9 by the leading edge of a flange 9a extending inward. This flange 9a is connected to the ceramic holder 6 via the ring 5. , 7 and ceramic powder 8 are fixed from above. The lower opening end of the outer cylinder 13 is fitted and mounted so as to cover the upper opening.

Further, a cylindrical seal unit 14 which forms a reference gas space together with the case 10 is fitted into the upper end opening of the outer cylinder 13 and a ventilation filter 50 disposed in a ventilation path passing through the center thereof. The outside air (oxygen) is introduced into the reference gas space via the.

The seal unit 14 has a plurality of insertion holes to be described later, and leads 20 and 21 connected to the detection element 2 and the ceramic heater 3 pass therethrough. Next, a detailed structure of the seal unit 14 will be described with reference to FIG. FIG. 2 is an exploded perspective view of the seal unit 14.

As shown in FIG. 2, the seal unit 14
Is a cylindrical sealing member 15 made of a rubber elastic body.
And a cylindrical insertion member 30 that can be inserted into a through hole 15a that passes through the center of the sealing member 15 in the axial direction, and covers an upper end (atmospheric end) of the cylindrical insertion member 30 and seals them. It comprises a sheet-shaped ventilation filter 50 which is sandwiched and fixed between the inner peripheral surface of the through hole 15 a of the member 15 and the outer peripheral surface of the cylindrical insertion member 30.

On the predetermined pitch circle centered on the through hole 15a of the seal member 15, the above-mentioned lead wires 20, 21
Four insertion holes 15b penetrating the same body in the axial direction are formed at equal intervals to insert the same. Cylindrical insertion member 3
Reference numeral 0 denotes a cylindrical shape that is open at both ends and can be fitted into the through hole 15a. A flange 30c is formed at the edge of the gas chamber side opening 30b opposite to the atmosphere side opening 30a among the two openings of the cylindrical insertion member 30.

The ventilation filter 50 is formed in a circular sheet shape as shown in FIG. 3, and for example, an unfired molded body of polytetrafluoroethylene (PTFE) is
The two types of porous fiber sheets obtained by stretching in a uniaxial direction at a heating temperature lower than the melting point are assembled in the thickness direction to prevent the transmission of a liquid mainly composed of water, such as water droplets, and a gas ( The filter is configured as a filter that allows permeation of air, water vapor, and the like.

That is, as shown in FIG. 4 which shows a cross section taken along the line AA in FIG. 3, the gas permeable filter 50 is composed of a rough sheet 50a having a predetermined air permeability and water resistance and having a thickness of about 0.2 mm. It is also composed of a dense sheet 50b having a thickness of about 50 μm, which is inferior in air permeability but excellent in water resistance,
The rough sheet 50a is formed by attaching a dense sheet 50b to both surfaces.

As shown in FIG. 2, when assembling the sealing member 15, the ventilation filter 50, and the cylindrical insertion member 30, the ventilation filter 50 is connected to the air-side end of the cylindrical insertion member 30 and the end thereof. The cylindrical insertion member 3 covers the outer peripheral surface.
0 and is inserted into the through hole 15a together with the cylindrical insertion member 30 in this state. In this way, the ventilation filter 50 is sandwiched between the outer peripheral surface of the cylindrical insertion member 30 and the inner peripheral surface of the through hole 15a, and is fixed in a state where the ventilation path is closed. At this time, when the cylindrical insertion member 30 is inserted from below the through hole 15a, the flange portion 30c is locked at the opening edge below the ventilation hole 15a, and as a result, the cylindrical insertion member is inserted into the through hole 15a. The positioning of the member 30 and the ventilation filter 50 is performed.

The sealing unit 14 thus formed
Are arranged inside the opening end 13 a of the outer cylinder 13 and are caulked in the radial direction via the outer cylinder 13. Thus, the outer cylinder 1
3 and the sealing member 15 are in close contact with each other, and the sealing property is further ensured. Then, air is introduced into the reference gas space from the atmosphere side through a ventilation path formed inside the cylindrical insertion member 30 while maintaining the air permeability and the waterproofness by the ventilation filter 50.

As described above, in the oxygen sensor 1 of the present embodiment, most of the ventilation filter 50 has a rough sheet 50.
Since it is composed of a, it is possible to secure a necessary amount of ventilation into the reference gas space without particularly impairing the air permeability. Also, on the surface of the rough sheet 50a,
Since the dense sheet 50b having excellent water resistance is adhered, predetermined water resistance of the entire ventilation filter 50 is secured.

Further, the thickness of the entire ventilation filter 50 can be increased by the portion of the rough sheet 50a, and its mechanical strength can be secured. 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 as long as they fall within the technical scope of the present invention. Nor.

For example, in the above embodiment, the ventilation filter 50 is composed of one coarse sheet 50a and two dense sheets 50b.
And a plurality of dense sheets 50b may be laminated. For example, a relatively thin rough sheet may be provided on the uppermost layer (atmosphere side) of the ventilation filter 50 shown in FIG. 4 and an oil-repellent coat may be applied to the sheet. The reason for this is that the coating agent is easily impregnated into the coarse coat, and the risk of adhering oil and the like being vaporized and entering the reference gas space can be further reduced.

[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 exploded perspective view of a seal unit constituting the oxygen sensor according to the embodiment.

FIG. 3 is an explanatory diagram of a ventilation filter constituting the seal unit of the embodiment.

FIG. 4 is an explanatory diagram of a ventilation filter of an example.

[Explanation of symbols]

1 ... oxygen sensor, 2 ... detection element, 9 ...
Metal shell, 10: Case, 14: Seal unit, 15: Seal member, 15a: Through hole,
30 ... cylindrical insertion member, 50 ... ventilation filter, 50a ... coarse sheet, 50b ... dense sheet

Claims (12)

[Claims] 1. A detection element for detecting a gas component to be measured based on a reference gas, and one end of the detection element is held so as to be exposed to the gas to be measured, and a reference gas space is provided at the other end of the detection element. Forming a case, a ventilation path for introducing air from the atmosphere side to the reference gas space, and a ventilation filter formed in a sheet shape having a predetermined thickness and arranged so as to close the ventilation path. A gas sensor provided, wherein the ventilation filter is at least a coarse sheet made of a porous body and having a predetermined air permeability and water resistance, and also made of a porous body and inferior in air permeability to the coarse sheet to have water resistance. A gas sensor comprising a plurality of sheets including an excellent dense sheet and a plurality of sheets overlapped in a thickness direction thereof. 2. The gas sensor according to claim 1, wherein the thickness of the dense sheet is smaller than the thickness of the coarse sheet. 3. The gas sensor according to claim 1, wherein the ventilation filter is formed by attaching at least a part of each of the plurality of sheets to each other. 4. The gas sensor according to claim 1, wherein the gas permeable filter is formed by arranging the dense sheet at least on a surface on the atmosphere side. 5. The gas sensor according to claim 1, wherein the dense sheet is formed on both surfaces of the ventilation filter. 6. The gas sensor according to claim 1, wherein the ventilation filter is formed by sandwiching one coarse sheet between two dense sheets. . 7. The gas sensor according to claim 1, wherein an oil-repellent coat is applied to at least a surface of the ventilation filter on the atmosphere side. 8. A wall for isolating the reference gas space from the atmosphere, a part of the wall is a seal member made of an elastic body, and the ventilation path is provided through the seal member. The gas sensor according to claim 1, wherein: 9. The air passage according to claim 1, wherein the air passage is a through hole provided in the seal member, and the air filter is inserted into the through hole. Gas sensor. 10. A cylindrical insertion member is inserted into the through hole, and the ventilation filter is sandwiched and fixed between an inner surface of the through hole and an outer surface of the cylindrical insertion member. The gas sensor according to claim 9, wherein: 11. The thickness of the ventilation filter is 0.1 m.
2. The length is not less than m and not more than 1.0 mm.
The gas sensor according to any one of claims 10 to 10. 12. The gas sensor according to claim 1, wherein the thickness of the dense sheet is 50 μm or less.