JP4399080B2 - Gas sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gas sensor that is attached to a pipe that forms 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]
[Prior art]
Conventionally, various sensors such as an HC sensor and a NOx sensor are known as gas sensors for detecting the concentration of a specific gas component from a mixed gas.
As one of this type of gas sensor, for example, there is an outside air introduction type oxygen sensor disclosed in Japanese Patent Laid-Open No. 9-54063. In this oxygen sensor, a vent hole for introducing outside air is formed so as to penetrate the center of a seal member provided at the uppermost portion of the gas sensor in the axial direction, and the vent hole is closed with a hard water repellent filter. Therefore, it retains its breathability and waterproofness. A plurality of insertion holes are provided around the water repellent filter of the seal member, and power is supplied by inserting lead wires connected to the electrodes of the detection elements into the insertion holes.
[0003]
[Problems to be solved by the invention]
However, in the above configuration, a problem occurs when moisture adheres to the vicinity of each inlet of the plurality of lead wire insertion holes due to condensation or the like. That is, normally, the surface of the sealing member is repelled with water, so that the water adheres as water droplets. When these water droplets become large, the water droplets adhering to each lead wire insertion hole become large due to the surface tension and attract each other and gather at the center of the seal member. Then, the large water droplets formed at this time adhere to the water-repellent filter disposed in the center and cover the whole. As a result, the air permeability of the water repellent filter is impaired, and as a result, there arises a problem that the accuracy of the oxygen sensor is lowered.
[0004]
The present invention has been made in view of these problems, and an object of the present invention is to provide a gas sensor that is excellent in air permeability in a gas sensor that functions by introducing air from outside.
[0005]
[Means for Solving Problems and Effects of Invention]
In view of the above problem, in the gas sensor according to claim 1, the seal member is formed with an insertion hole through which a lead wire introduced into the reference gas space from the atmosphere side is inserted, and at least a plurality of ventilation holes. Each of the insertion hole and the ventilation hole has an opening at the upper end surface of the seal member, and at least one of the openings of the ventilation hole opens outside the opening of the insertion hole. The vent hole is closed by a breathable filter, the vent hole is closed by a water-repellent breathable filter, and the filter covers at least a part of the upper end surface of the filter. The pressing member provided in this manner and the seal member are sandwiched.

[0006]
If the openings of the vent holes are arranged in this way, even if fine water droplets accumulate in the region surrounded by the lead wire insertion holes, that is, near the central axis of the upper end surface of the seal member, Since water droplets do not adhere on the vent hole openings arranged outside the hole openings, the state of the reference gas space can be maintained well.
[0007]
The vent hole is closed by a sheet-like vent filter in order to improve waterproofness. Thus, it is preferable to use a sheet-like material for the ventilation filter because a large quantity of fresh oxygen can be supplied to the reference gas space because the quantity of ventilation can be increased.
[0008]
Furthermore, in order to arrange the filter so as to be in close contact with the upper end surface of the seal member, the filter is further pressed from the outside of the filter using a pressing member. As a result, the filter is in close contact with the sealing member at the periphery of the opening of the vent hole, so that waterproofness is improved.
[0009]
Further, as a method of closing the vent hole with a sheet-like filter, the vent filter may be arranged so as to cover from the upper end surface of the seal member so as to cover the vent hole opening from the outside. In this way, a plurality of vent holes can be covered with a single sheet-like filter, and a cylindrical member is not necessary, so that there is a great cost advantage.
[0010]
In addition, it is desirable to form a ventilation window at a position corresponding to the opening of the ventilation hole of the holding member so that air can be circulated. It is desirable that the size of the ventilation window is equal to or less than the axial thickness of the pressing member. Furthermore, the diameter of the ventilation window is more preferably 1.5 mm or less. This is because by reducing the diameter of the opening portion of the ventilation window, dust and dirt are difficult to come into contact with the filter through the ventilation window, and the air permeability of the filter is not impaired for a long time.
[0011]
As the pressing member, a heat-resistant elastic body such as fluoro rubber can be used as in the case of the sealing member, but metal, resin, ceramics, or the like may be used. When an elastic material such as rubber is used, there is a merit that there is no fear of damaging the seal member. However, since it is necessary to have waterproofness at the interface that contacts the filter, a certain degree of hardness is required. In particular, if the thickness of the pressing member is excessively thick, dust or the like tends to accumulate in the recesses of the ventilation window, so it is necessary to make the thickness below a certain level. In that case, if the rubber that is harder than the seal member is not used, the filter will not be firmly held between the presser member and the seal member, and the waterproof property may be lowered. It is desirable to form with an elastic body having a higher hardness.
[0012]
Use of hard resin, metal, or ceramic for the pressing member is advantageous because the thickness of the pressing member that covers the upper end surface of the sealing member can be reduced. This has the advantage that dust or the like does not collect in the recess of the ventilation window. Furthermore, it is excellent also in terms of heat resistance.
[0013]
Note that it is preferable that the pressing member has a shape that accommodates the sealing member therein, because the filter can be handled as a unit while being sandwiched between the sealing member and the pressing member. As an embodiment for that purpose, it is preferable to extend the side wall from the outer peripheral edge of the disc-shaped holding member to a cap shape so as to accommodate the filter and the seal member therein.
[0014]
By the way, it is preferable to arrange the lead wire insertion holes in a balanced manner in the seal member as much as possible in order to maintain good waterproofness. Therefore, if it arrange | positions on the virtual pitch circle centering on the central axis of a sealing member, the waterproofness between an insertion hole and a lead wire can be maintained favorable. In such an arrangement, when the opening of at least one vent hole is opened outside the pitch circle, water droplets hardly adhere to the opening of the vent hole, so that good air permeability can be maintained. .
[0015]
DETAILED DESCRIPTION OF THE INVENTION
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.
[0016]
As shown in the figure, the oxygen sensor 1 includes a detection element 2 formed in a hollow shaft shape whose end is closed by a solid electrolyte body mainly composed of ZrO ₂ , and a shaft-shaped ceramic disposed in the detection element 2. A heater 3, a metal shell 9 that supports the detection element 2, an outer cylinder 13 that is connected to the upper part of the metal shell 9 and forms a reference gas space inside, and a seal disposed in an upper opening 47 of the outer cylinder 13. It consists of unit 14 and the like.
[0017]
Hereinafter, the structure of the seal unit 14 will be described with reference to FIGS. 2 and 3.
2A is a plan view from above of the seal unit 14 in which the seal member 15, the holding member 16, and the water repellent filter 50 are assembled together, and FIG. The corresponding part sectional view and FIG. 10C are explanatory views of the assembly process of the seal unit 14 corresponding to the section. 3A is a component sectional view corresponding to the section BB in FIG. 2A, and FIG. 3B is an explanatory view of the assembly process of the seal unit 14 corresponding to the section. .
[0018]
As shown in FIGS. 2 and 3, the seal unit 14 includes a bottomed cylindrical pressing member 16 and a columnar sealing member 15 inserted therein. The seal unit 14 is configured in such a manner that a sheet-like water-repellent filter 50 is interposed between the pressing member 16 and the seal member 15.
[0019]
Both the sealing member 15 and the pressing member 16 use fluororubber to ensure heat resistance, but the hardness of each is different, and the hardness of the sealing member 15 is 60 to 85 in Shore hardness, and the hardness of the pressing member 16 80 to 100 are used. In addition, when a metal is used for the pressing member 16, the thickness can be reduced and heat resistance is preferable.
[0020]
As shown in the upper part of FIG. 2 (c), the holding member 16 is formed with a vent hole 16a that penetrates the center of the upper end wall in the axial direction and introduces outside air. And around this ventilation hole 16a, the four latching holes 16b for fitting the four protrusion parts 15d of the sealing member 15 mentioned later are formed in the aspect arrange | positioned at equal intervals. Further, four passages similar to those of the vent holes 16a are provided outside the pitch circle diameters of these four locking holes 16b (diameters of circles passing through the centers of the four locking holes 16b). A pore 16c is formed. The vent hole 16c is disposed so as to be positioned between the adjacent locking holes 16b. Further, the vent hole 16a and the vent hole 16c are formed from circular holes having a diameter D substantially equal to the thickness L of the upper end wall of the pressing member 16 and considerably smaller than the diameter of the locking hole 16b. And from the peripheral edge of an upper end surface, the side wall extended below is formed in the cylindrical shape.
[0021]
On the other hand, the seal member 15 has an outer diameter substantially equal to the inner diameter of the side wall of the presser member 16 and an axial length substantially equal to the axial length of the presser member 16 as shown in the lower part of FIG. It is formed as follows. Then, a ventilation hole 15a that penetrates the center of the cylindrical main body in the axial direction and introduces outside air is disposed at equal intervals around the ventilation hole 15a, and the above-described lead wires 20, 21 and the like are inserted therethrough. And four insertion holes 15b penetrating the main body in the axial direction. And the cylindrical protrusion part 15d projected coaxially around each penetration hole 15b is formed in the upper end surface, respectively. Furthermore, four vent holes 15c similar to the vent holes 15a are formed outside the pitch circle diameter of the four insertion holes 15b (see FIG. 3B). The vent holes 15a and 15c are formed so that the inner diameters thereof are equal to the inner diameter D of the vent holes 16a and 16c, and when the holding member 16 and the seal member 15 are assembled, the above-mentioned vent holes 15a and 15c are formed. It is formed at a position communicating with the pores 16a and 16c.
[0022]
The vent hole 15a and the vent hole 16a, and the vent hole 15c and the vent hole 16c constitute a vent path of the seal unit 14.
The water-repellent filter 50 is formed in a circular sheet shape having an outer diameter substantially equal to the outer diameter of the seal member 15 as shown in the cross section in the middle stage of FIG. 2 (c) and the middle stage of FIG. 3 (b). Locking holes 50a are respectively formed at positions corresponding to the stop holes 16b and the insertion holes 15b.
[0023]
The water-repellent filter 50 is made of, for example, a porous fiber structure (for example, a polytetrafluoroethylene (PTFE) green body) that is obtained by stretching in a uniaxial direction at a heating temperature lower than the melting point of PTFE. , Product name: Gore-Tex (Japan Gore-Tex Co., Ltd.) is configured as a water-repellent filter that blocks the transmission of water-based liquids such as water droplets and allows the transmission of gas (air, water vapor, etc.) Has been. Further, a porous fiber structure (trade name: Oleovent filter (Japan Gore-Tex Co., Ltd.)) further coated with an oil repellent can be used. Risk can be reduced.
[0024]
The assembly of the seal member 15, the presser member 16, and the water repellent filter 50 is performed by first connecting the four locking holes 50 a provided in the water repellent filter 50 to the four projecting portions 15 d of the corresponding seal member 15. Fit around. At this time, the water repellent filter 50 is in a state where the vent holes 15a and 15c of the seal member 15 are closed from above. Then, from this state, the seal member 15 is inserted and fitted into the presser member 16. At this time, the vent holes 16 a and 16 c provided in the holding member 16 communicate with the vent holes 15 a and 15 c provided in the seal member 15 via the water repellent filter 50, respectively. It is fixed in such a manner that it is clamped by the pressing member 16.
[0025]
The seal unit 14 thus formed is arranged inside the opening end 47 of the outer cylinder 13 and crimped in the radial direction via the outer cylinder 13, whereby the outer cylinder 13 and the seal member 15 are brought into close contact with each other. In addition, the sealing performance is more reliable.
In the above embodiment, the plurality of vent holes 15c, 16c are arranged outside the pitch circle formed by the plurality of insertion holes 15b through which the lead wires are inserted. Therefore, the plurality of vent holes 15c, 16c are leads. There is no problem of clogging due to the growth of water droplets adhering to the line. In addition, since the diameters of the vent holes 16a and 16c are considerably small, there is a low possibility that dust and dirt will reach the water repellent filter 50 through the vent holes 16a and 16c. As a result, the air permeability of the oxygen sensor 1 can be kept good.
[0026]
As mentioned above, although the Example of this invention was described, it cannot be overemphasized that embodiment of this invention can take various forms, as long as it belongs to the technical scope of this invention, without being limited to the said Example at all. Nor.
For example, the arrangement and shape of the vent holes 15a, 15c, 16a, 16c and the like are not limited to those of the above-described embodiments, and can be appropriately changed for convenience of design.
[0027]
In the above embodiment, the presser member 16 can be formed of metal in order to reduce the thickness thereof. In this case, the waterproof property between the outer cylinder 13 and the side wall of the presser member 16 is sealed by caulking. Since only this can be relied upon, there is a risk that the waterproofness will be slightly reduced. Therefore, in this case, for example, the lower end of the seal member 15 is preferably expanded to form a waterproof seal surface between the seal member 15 and the outer cylinder 13 so as to supplement the sealing performance.
[0028]
Furthermore, when the presser member 16 is formed of a hard resin or ceramic that hardly deforms, the side wall cannot be caulked simultaneously with the outer cylinder 13, so in that case, in the enlarged diameter portion of the seal member 15, The outer cylinder 13 may be crimped. However, in this case, there is a possibility that the presser member 16 will fall off unless the presser member 16 is firmly fixed to the seal member 15. Therefore, it is desirable that the upper end portion of the outer cylinder 13 is bent inward so that the presser member 16 does not fall off.
[0029]
Further, as shown in FIG. 4 as a reference example of the seal structure, the sheet-like water-repellent filter 250 can be arranged by the cylindrical member 255 so as to block the plurality of vent holes 14a of the seal member 214. This figure is a cross-sectional view corresponding to the BB cross section of FIG.
[0030]
In this case, a holding member for holding the sheet-like filter in the vent hole is not necessary, and the water-repellent filter 250 is sandwiched between the cylindrical member 255 and the inner wall of the vent hole 14a.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an overall configuration of an oxygen sensor according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram showing a configuration of a seal unit according to an embodiment of the present invention.
FIG. 3 is an explanatory diagram showing a configuration of a seal unit according to an embodiment of the present invention.
FIG. 4 is an explanatory diagram showing a configuration of a seal unit according to a modification of the embodiment.
[Explanation of symbols]
1 ... oxygen sensor, 2 ... sensing element, 9 ... metal shell,
13 ... outer cylinder, 14 ... seal unit, 15 ... seal member,
15a, 15c ... vent hole, 15b ... insertion hole, 15d ... projecting part,
16 ... presser member, 16a, 16c ... vent hole, 16b ... locking hole,
20, 21 ... lead wire, 47 ... open end,
50: Water repellent filter

Claims (9)

A detecting element and a metal shell for holding the detecting element;
An outer cylinder forming a reference gas space isolated from the atmosphere on the upper end side of the detection element;
A sealing member made of an elastic body that forms the reference gas space together with the outer cylinder;
A gas sensor comprising:
The seal member is formed with an insertion hole for inserting a lead wire introduced into the reference gas space from the atmosphere side, and at least a plurality of ventilation holes,
The insertion hole and the vent hole are both an opening on the upper end surface of the sealing member,
And at least one of the openings of the vent hole opens outside the opening of the insertion hole,
The vent hole is closed by a breathable filter,
And the filter is sandwiched between a pressing member provided so as to cover at least a part of the upper end surface of the filter and the seal member,
A gas sensor. The pressing member has a side wall extending in one direction from an outer peripheral edge thereof in order to accommodate the sealing member therein;
  The gas sensor according to claim 1. A ventilation window is formed at a position facing the opening of the ventilation hole of the pressing member,
  The diameter of the ventilation window is equal to or less than the axial thickness of the pressing member,
  The gas sensor according to any one of claims 1 and 2. The vent window has a diameter of 1.5 mm or less;
  The gas sensor according to claim 3. The pressing member is made of an elastic body;
  The gas sensor according to any one of claims 1 to 4, wherein: The pressing member is made of an elastic body having a hardness higher than that of the seal member,
  The gas sensor according to claim 5. The pressing member is made of metal;
  The gas sensor according to any one of claims 1 to 6. The pressing member is made of resin;
  The gas sensor according to any one of claims 1 to 6. The opening of the insertion hole is disposed on a pitch circle centered on the axis of the seal member,
  At least one opening of the vent is disposed outside the pitch circle;
  A gas sensor according to any one of claims 1 to 8.

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