JP4013419B2 - Gas sensor - Google Patents

Description

[0001]
【Technical field】
The present invention relates to a gas sensor for detecting a specific gas concentration in a gas to be measured such as an oxygen gas concentration in an exhaust gas of an automobile internal combustion engine.
[0002]
[Prior art]
Control of the air-fuel ratio of an internal combustion engine for automobiles is extremely important for energy saving (fuel saving) and exhaust gas purification. For this reason, an oxygen sensor or the like, which is a kind of gas sensor, is provided in the exhaust system to measure the oxygen gas concentration in the exhaust gas and control the combustion of the internal combustion engine.
[0003]
This has a gas contact part that comes into contact with the exhaust gas that is the gas to be measured, covers a detection element that can detect the oxygen gas concentration, a housing that holds the detection element, and the gas contact part of the detection element. And a protective cover provided with a gas hole for the gas to be measured.
[0004]
The bottom of the housing on the gas to be measured side has an inner protrusion and a caulking projection, and the bottom is surrounded by these and has an annular groove that opens to the protective cover side.
[0005]
Further, the opening end on the housing side of the protective cover has a flange portion that bends outward, the flange portion is fitted into the annular groove, and the caulking projection portion is caulked inward. The protective cover is caulked and fixed to the housing.
The protective cover is provided to protect the detection element that is weak in strength.
[0006]
[Problems to be solved]
By the way, the use environment of the gas sensor described above is in high temperature exhaust gas. Since the protective cover of the gas sensor is directly exposed to high-temperature exhaust gas, it must be made of a metal material with better heat resistance. On the other hand, since the housing has a complicated shape, it must be made of a metal material having excellent workability.
Therefore, the protective cover and the housing are made of different metal materials. However, when the gas sensor is used in a high temperature environment, the caulking and fixing between the housing and the protective cover may be loosened due to the difference in thermal expansion between the protective cover and the housing. is there.
[0007]
The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a gas sensor in which the caulking and fixing of the housing and the protective cover are strong against the cooling and heating cycle.
[0008]
[Means for solving problems]
A first aspect of the present invention is a detection element having a gas contact portion that comes into contact with a gas to be measured, a housing that holds the detection element, a gas for covering the gas contact portion of the detection element and for flowing the gas to be measured. A protective cover having a hole, a bottom portion of the housing on the gas to be measured side having an inner projecting portion and a caulking projection portion, the bottom portion being surrounded by these, opening to the protective cover side, and inward An annular groove composed of a wall surface, an outer wall surface and a ceiling surface;
Furthermore, the opening end on the housing side of the protective cover has a flange portion that bends outward, the flange portion is fitted into the annular groove, and the caulking protrusion is caulked inward. In the gas sensor formed by caulking and fixing the protective cover to the housing,
In the gas sensor, a tapered surface is provided in the annular groove from the inner wall surface to the ceiling surface.
[0009]
Next, the operation of the present invention will be described.
The most notable aspect of the present invention is that a tapered surface is provided from the inner wall surface to the ceiling surface inside the annular groove.
[0010]
By placing the flange part of the protective cover between the outer wall surface and the inner wall surface of the annular groove, and bending the caulking protrusion part inward of the annular groove, the outer wall surface and ceiling of the caulking protrusion part and the annular groove A flange part is clamped between the surfaces.
In the gas sensor according to the present invention, since the tapered surface is provided from the inner wall surface of the annular groove to the ceiling surface, the flange portion is sandwiched between the caulking projection portion and the tapered surface by bending of the caulking projection portion.
For this reason, stronger caulking can be achieved.
[0011]
If the gas sensor has a conventional structure without a tapered surface, the bent caulking projection will caulk and secure the protective cover, but the portion facing the inner wall surface of the flange will be free and the caulking will be weakened accordingly. Conceivable.
[0012]
Furthermore, thermal stress occurs due to the difference in thermal expansion coefficient between the protective cover and the housing at high temperatures, etc., but in the gas sensor according to the present invention, the portion where the flange portion and the tapered surface abut is a fulcrum. Therefore, the protective cover remains firmly caulked and fixed even when thermal stress occurs.
For this reason, according to the present invention, it is possible to provide a strong caulking structure against a cooling cycle in which the temperature fluctuates from room temperature to a high temperature of around 700 ° C., for example.
[0013]
In the conventional gas sensor having no tapered surface, the caulking and fixing of the protective cover by the caulking projection may be loosened due to thermal stress.
[0014]
As described above, according to the present invention, it is possible to provide a gas sensor in which the caulking and fixing between the housing and the protective cover are strong against the cooling / heating cycle.
[0015]
The tapered surface can be composed of a flat slope as shown in the first embodiment described later. Or it can comprise from a curved slope (refer FIG. 6 mentioned later).
Further, only one protective cover can be provided. Further, as shown in Embodiment 1 described later, a double structure including an inner cover and an outer cover may be employed. Moreover, it can also be set as a triple or more structure.
[0016]
In particular, in the case of a double or more configuration, all the covers can be provided with flange portions and all the covers can be caulked and fixed to the housing.
It is also possible to provide a flange portion only on a part of the cover and to fix only the cover to the housing by caulking. In this case, other non-caulking covers can be fixed to the caulking-fixed cover by welding or the like.
[0017]
Next, as in the invention described in claim 2, the distance between the ceiling surface of the annular groove and the flange portion of the protective cover is preferably 0.4 mm or less.
Thereby, stronger caulking can be obtained.
[0018]
When the distance is larger than 0.4 mm, when the caulking protrusion is caulked, a gap may remain between the annular groove and the flange portion, which may cause backlash.
In particular, when the protective cover is composed of an inner cover and an outer cover, the bottom of the outer cover may come into contact with the inner cover, which may prevent complete caulking and fixing. A more preferable upper limit of the distance is 0.3 mm.
[0019]
The lower limit of the distance is preferably 0.05 mm.
If the distance is less than 0.05 mm, the bent portion of the protective cover is not in contact with the taper surface of the housing, and there is a possibility that complete caulking and fixing cannot be performed.
[0020]
Considering a straight line parallel to the straight line in the axial direction of the gas sensor, the gap between the flange and the ceiling surface should be the above distance when the protective cover is simply inserted into the annular groove before caulking on this straight line. (See FIG. 2).
In addition, when the flange portion has a shape that undulates in the axial direction of the gas sensor as shown in the second embodiment, the smallest portion of the gap between the flange portion and the ceiling surface is claimed. Adopted as the distance it takes.
[0021]
Next, as in the third aspect of the invention, the flange portion of the protective cover includes a bent portion and a flat portion extending further outward than the bent portion,
The protective cover is preferably fitted into the annular groove while the bent portion is in contact with the tapered surface (see FIG. 2).
[0022]
As a result, when the thermal stress is generated, the contact portion between the bent portion and the tapered surface serves as a fulcrum, and the protective cover can be deformed. Therefore, it is possible to provide a strong caulking structure against the cooling / heating cycle.
The bent portion refers to a boundary portion between the inner side surface of the protective cover and the flange portion. Moreover, the said flat part is a part extended to the outward of the radial direction of an annular groove from a bending part (refer FIG. 2).
[0023]
Next, as in the invention described in claim 4, the protective cover comprises at least an inner cover and one or a plurality of outer covers provided outside the inner cover, both of which are outward. Bending and having a flange part consisting of a bent part and a flat part,
The inner cover is fitted to the annular groove while the bent portion is in contact with the tapered surface, while the bent portion of the outer cover is located at a position where the bent portion of the inner cover and the tapered surface are in contact with each other. Is preferably further outward.
[0024]
As a result, the caulking force received from the caulking protrusions on the outer cover and the inner cover can be applied as a large moment force with the contact portion between the bent portion and the tapered surface as a fulcrum.
Therefore, the protective cover can be caulked and fixed to the annular groove with a strong force.
[0025]
According to a fifth aspect of the present invention, it is preferable that the flange portion of the outer cover and the flange portion of the inner cover are in contact with each other at the outer end portion of the flange portion.
Thereby, the moment force with the contact portion between the bent portion and the tapered surface as a fulcrum can be utilized to the maximum extent.
[0026]
The gas sensor according to the present invention can be used for measuring oxygen gas concentration, NOx gas concentration, HC gas concentration, CO gas concentration, etc. in the gas to be measured.
Further, it can be used for measuring an air-fuel ratio in an internal combustion engine for automobiles.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1
A gas sensor according to an embodiment of the present invention will be described with reference to FIGS.
Note that the gas sensor of this example is an oxygen sensor that is installed in an exhaust system of an automobile engine and configured to measure the oxygen gas concentration in the exhaust gas that is the gas to be measured.
[0028]
As shown in FIGS. 1 to 5, the gas sensor 1 of this example includes a detection element 3 having a gas contact portion that comes into contact with a gas to be measured, a housing 2 that holds the detection element 3, and a gas contact with the detection element 3. And a protective cover 10 having a gas hole 100 for circulating the gas to be measured.
[0029]
The bottom of the housing 2 on the gas to be measured side has an inner projecting portion 21 and a caulking projection portion 22. Further, the bottom portion is surrounded by them, and has an annular groove 20 that is open to the protective cover 10 side and that includes an inner wall surface 210, an outer wall surface 220, and a ceiling surface 23.
[0030]
Further, the protective cover includes an inner cover 11 and an outer cover 12, and the opening ends on the housing 2 side have flange portions 110 and 120 that bend outward. The flange portions 110 and 120 are fitted into the annular groove 20, and the inner cover 11 and the outer cover 12 are caulked and fixed to the housing 2 by caulking the caulking protrusion 22 inward. .
A tapered surface 24 is provided from the inner wall surface 21 to the ceiling surface 23 inside the annular groove 20.
As shown in FIG. 1, the angle C of the tapered surface is 45 degrees, and the height B of the tapered surface is 0.9 mm.
Further, the angle C and the height B of the tapered surface are set so that the distance F (see FIG. 2) between the ceiling surface 23 of the annular groove 20 of the housing 2 and the flange portion 110 of the inner cover 11 is 0.4 mm or less. Can be set arbitrarily.
[0031]
This will be described in detail below.
As shown in FIG. 4, the gas sensor 1 of this example includes a housing 2, an inner cover 11 and an outer cover 12, which are double protective covers 10 disposed below the housing 2, and an atmosphere side disposed above the housing 2. Cover 121-123.
The housing 2 has a substantially cylindrical shape, and a detection element 3 with a heater 39 is inserted and fixed therein.
As shown in FIG. 5, the inner diameter A of the housing is 8.2 mm.
[0032]
The atmosphere-side covers 121 to 123 include a first cover 121 that is directly caulked and fixed to the housing 2, a second cover 122 that is caulked and fixed to the upper part of the first cover 121, and a filter 129 at the upper part of the second cover 122. And a third cover 123 fixed by caulking.
[0033]
An insulator 13 is disposed inside the atmosphere-side covers 121 to 123, and a lead wire 312 connected to the output lead-out lines 31 and 32 of the detection element 3 via connection portions 311 and 321 inside the insulator 13. , 322 and the heater 39 are provided with lead wires 333.
Further, a rubber bush 14 is disposed further above the insulator 13.
[0034]
The protective cover 10 includes an outer cover 12 and an inner cover 11, and a gas hole 100 for introducing a gas to be measured is provided in both of them. The space inside the inner cover 11 functions as a gas chamber to be measured, and the gas contact portion of the detection element 3 is in contact with the gas to be measured here.
The inner cover 11 and the outer cover 12 have flange portions 110 and 120, respectively. The flange portion 110 includes a bent portion 111 and a flat portion 112 that extends further outward in the radial direction than the bent portion 111.
Similarly, the flange portion 120 of the outer cover 12 includes a bent portion 121 and a flat portion 122.
[0035]
The bottom portion of the housing 2 has an annular shape, and an annular groove 20 having an annular cross section is provided therein. A longitudinal section of the annular groove 20 is shown in FIG.
Moreover, as shown in FIG. 5, the inner diameter D of the inner cover 11 is 9.9 mm. The curvature radius of the bent portion 111 of the flange portion 110 of the inner cover 11 is 1.1 mm.
The housing 2 of this example is made of SUS430, and the inner cover 11 and the outer cover 12 are both made of SUS310S.
[0036]
Although not shown in the drawings, the detection element of the present example is configured so that a pair of electrodes are provided inside and outside a cup-type solid electrolyte body having an oxygen ion conductivity, and the oxygen gas concentration can be measured from the output of the electrodes. .
[0037]
Next, caulking and fixing of the inner cover 11 and the outer cover 12 to the annular groove 20 will be described.
As shown in FIG. 2, the inner cover 11 and the outer cover 12 are arranged so that the bent portion 111 of the flange portion 110 of the inner cover 11 contacts the tapered surface 24.
Further, the outer end portions 115 and 125 of the flat portions 112 and 122 of the flange portions 110 and 120 abut against the outer wall surface 220.
At this time, the distance F between the flange portion 110 of the inner cover 11 and the ceiling surface 23 was 0.3 mm.
[0038]
After that, the flange portions 110 and 120 of the inner cover 11 and the outer cover 12 are caulked and fixed to the annular groove 20 by bending the caulking projection portion 22 inward as shown in FIG. As a result, as shown in FIG. 3, the flange portions 110 and 120 and the annular groove 20 come into contact with each other at three points X, Y, and Z, and the caulking is realized.
By this caulking, the inner cover 11 and the outer cover 12 are sandwiched between the caulking protrusion 22 and the ceiling surface 23 (between X and Y). Further, the inner cover 11 and the outer cover 12 are sandwiched between the caulking protrusion 22 and the tapered surface 24 (between X and Z).
Z is a contact portion between the bent portion 111 and the tapered surface 24.
[0039]
Further, as shown in FIG. 3, when the position where the outer cover 12 contacts the inner cover 11 is M, M is positioned outward in the radial direction from Z.
As is clear from FIG. 3, the flange portion 120 of the outer cover 12 and the flange portion 110 of the inner cover 11 are in contact with each other at the outer ends of the flange portions 110 and 120.
[0040]
The inner cover 11 and the outer cover 12 may be integrated by welding and fixing directly below the flange portions 110 and 120.
The outer end portions 115 and 125 of the flat portion of the flange portions 110 and 120 do not have to be in contact with the outer wall surface 220.
[0041]
Next, the operation of this example will be described.
In this example, when caulking is fixed, the inner cover 11 and the outer cover 12 are arranged in the annular groove 20, but as described above, the flange portions 110, 120 and the annular groove 20 abut at three points X, Y, and Z. , Strong caulking is realized.
[0042]
Furthermore, in the gas sensor 1 of this example, the protective cover 10 and the housing 2 are made of stainless steel, but the types are different, and the difference in thermal expansion coefficient is about 7 × 10 ^{−6 at} a temperature of 700 ° C.
Since the gas sensor 1 of the present example is installed in the exhaust system of the automobile internal combustion engine as described above, it is exposed to a cooling cycle from room temperature to a maximum of around 700 ° C. according to the operation / stop of the internal combustion engine. Accordingly, thermal stress is generated between the protective cover 10 and the housing 2 in a high temperature environment.
[0043]
In the gas sensor 1 of this example, since the portion where the bent portion 111 of the flange portion 110 of the inner cover 11 abuts on the tapered surface 24 becomes a fulcrum and deformation due to thermal stress occurs, the caulking projection 22 and the tapered surface 24 As a result, the protective cover 10 remains strongly restrained.
Therefore, a strong caulking structure can be provided even in a high temperature environment.
[0044]
Further, the contact position M between the outer cover 12 and the inner cover 11 is outward in the radial direction from Z of the portion where the inner cover 12 and the tapered surface 24 are in contact. Therefore, the caulking force applied to the outer cover 12 and the inner cover 11 from the caulking protrusion 22 can be applied as a large moment force with M as a fulcrum. Therefore, a strong caulking force can be easily obtained.
[0045]
As described above, according to this example, it is possible to provide a gas sensor in which the caulking and fixing between the housing and the protective cover are strong against the cooling / heating cycle.
[0046]
In addition, what consists of a laminated plate-shaped solid electrolyte body can also be used as a detection element of this example.
Further, in this example, the gas sensor functioning as an oxygen sensor has been described as an example, but the present invention can also be applied to other gas sensors such as a NOx sensor, a CO sensor, and an HC sensor.
[0047]
Further, the tapered surface 24 of the annular groove 20 of the present example is planar as is known from FIG. 1, but a curved tapered surface 24 can also be provided as shown in FIG.
Also in this case, the same effect as described above can be obtained.
[0048]
Embodiment 2
In this example, as shown in FIGS. 7 and 8, a gas sensor having a protective cover in which the flange portion is undulated will be described.
The structure of the gas sensor of this example is the same as that shown in the first embodiment.
As shown in FIGS. 7 and 8, the protective cover includes an inner cover 411 and an outer cover 412. The inner cover 411 has the same shape as that of the first embodiment, and the outer cover 412 is implemented. Although the shape is substantially the same as that of the first embodiment, as shown in FIG. 7, the flange portion 414 is provided with a concave portion 421 and a convex portion 422 so that the flange portion 414 has a corrugated cross section.
Others are the same as the first embodiment.
[0049]
The effect of this example will be described.
A concave portion 421 and a convex portion 422 are provided on the flange portion 414 of the outer cover 412 of the gas sensor of this example.
For this reason, when the outer cover 412 and the inner cover 411 are fixed to the annular groove 20 of the housing 2 in the same manner as in the first embodiment, it is possible to obtain a caulking structure in which loosening does not easily occur.
[0050]
That is, by laminating the flange portions 413 and 414, the thickness of the flange portion 414 is increased by the height and dent due to the influence of the concave portion 421 and the convex portion 422. Since caulking is performed in this state, the concave portion 421 and the convex portion 422 are deformed and fixed in a slightly thin state.
Therefore, the flange portion 414 after caulking and fixing is in a state in which the concave portion 421 and the convex portion 422 maintain the action of an elastic force to return the thickness of the flange portion 414 to the original state.
[0051]
Therefore, even when the caulking projection 22 of the housing 2 is loosened due to, for example, thermal stress at high temperature, the flange 414 extends in the thickness direction by an elastic force so as to compensate for the loosening, thereby preventing the loosening.
Therefore, it is possible to maintain a very strong caulking.
The other effects are the same as those of the first embodiment.
[Brief description of the drawings]
FIG. 1 is a cross-sectional explanatory view of a main part of a housing according to Embodiment 1;
FIG. 2 is a cross-sectional explanatory view of main parts of a housing and a protective cover before caulking and fixing in the first embodiment.
3 is a cross-sectional explanatory view of main parts of a housing and a protective cover after caulking and fixing in Embodiment 1; FIG.
4 is a cross-sectional explanatory view of a gas sensor in Embodiment 1. FIG.
FIG. 5 is a sectional development explanatory view of a housing and a protective cover in the first embodiment.
6 is a cross-sectional explanatory view of a main part of an annular groove having a curved tapered surface in Embodiment 1. FIG.
7 is a development view of a protective cover in Embodiment 2. FIG.
FIG. 8 is a cross-sectional explanatory view of main parts of a housing and a protective cover after caulking and fixing in a second embodiment.
[Explanation of symbols]
1. . . Gas sensor,
2. . . housing,
20. . . Annular groove,
21. . . Inward protrusion,
210. . . Inner wall,
22. . . Caulking projections,
220. . . Outside wall,
23. . . Ceiling surface,
24. . . Tapered surface,
3. . . Sensing element,

Claims (5)

A detection element having a gas contact portion that comes into contact with the gas to be measured; a housing that holds the detection element; a protective cover that covers the gas contact portion of the detection element and has a gas hole for circulating the gas to be measured; The bottom of the housing to be measured gas side has an inner protrusion and a caulking projection, and the bottom is surrounded by these, opens to the protective cover side, and has an inner wall surface, an outer wall surface, and a ceiling surface. An annular groove composed of
Furthermore, the opening end on the housing side of the protective cover has a flange portion that bends outward, the flange portion is fitted into the annular groove, and the caulking protrusion is caulked inward. In the gas sensor formed by caulking and fixing the protective cover to the housing,
A gas sensor characterized in that a tapered surface is provided from the inner wall surface to the ceiling surface inside the annular groove. The gas sensor according to claim 1, wherein a distance between a ceiling surface of the annular groove and a flange portion of the protective cover is 0.4 mm or less. In Claim 1 or 2, the flange part of the said protective cover consists of a bending part and the flat part extended further outward from this bending part,
The gas sensor according to claim 1, wherein the protective cover is fitted into the annular groove while the bent portion is in contact with the tapered surface. 4. The protective cover according to claim 1, wherein the protective cover includes at least an inner cover and one or a plurality of outer covers provided outside the inner cover, both of which are bent outward. And a flange portion composed of a bent portion and a flat portion,
The inner cover is fitted to the annular groove while the bent portion is in contact with the tapered surface, while the bent portion of the outer cover is located at a position where the bent portion of the inner cover and the tapered surface are in contact with each other. A gas sensor characterized by being further outward. 5. The gas sensor according to claim 4, wherein the flange portion of the outer cover and the flange portion of the inner cover are in contact with each other at an outer end portion of the flange portion.

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