JPH09210954A - Air-fuel ratio sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air-fuel ratio sensor having protection covers which can be fixed to a housing strongly and easily while the configuration remains simple. SOLUTION: An air-fuel ratio sensor is equipped with an oxygen sensor element 10, housing 41 to hold it, and protection covers 31, 32 provided with openings 21, 22. The protection covers have an inner member 31 and an outer member 32, and at the base ends of these cover members 31, 32, a flange-shaped top edge is provided in the form folded outward, and caulking is made upon putting a projection 411 on the housing 41 in pressure contact with the top edge. The top edges of the outer cover member 32 and inner cover member 31 are arranged alternately so as not to be overlapping along a closed curve running around the periphery.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a structure of an air-fuel ratio sensor for an internal combustion engine using a solid electrolyte.

[0002]

2. Description of the Related Art Adjustment of the air-fuel ratio of an internal combustion engine is extremely important for energy saving (fuel saving) and purification of exhaust gas.
As a sensor for detecting the air-fuel ratio, an electrochemical cell in which a pair of electrodes and a gas diffusion resistance layer are added to a solid electrolyte having oxygen ion conductivity is often used.
A heater unit is usually arranged inside the oxygen detection element so that a stable output can be obtained even when the exhaust gas temperature is low and when the engine is started.

That is, for example, as shown in FIG. 13, the oxygen sensor 90 has a bottomed cylindrical oxygen detecting element 91 forming an electrochemical cell, and a container 92 accommodating the oxygen detecting element 91. ing. The container 92 has a housing 93 that holds the oxygen detection element 91.
A flange 9 for mounting in the exhaust passage
31 are formed. Then, the oxygen detection element 91 is
The talc 932 is interposed and is fixed to the housing 93.

Further, a heater unit 96 is inserted inside the oxygen detecting element 91, and the heater unit 96 is inserted.
Are supported by the oxygen detection element 91 via a holder 961. The oxygen detection element 91 has a bottomed cylindrical solid electrolyte, and an inner electrode and an outer electrode. And
The electrode of the oxygen detection element 91 is connected to the signal line 97, and the heater unit 96 is connected to the power supply line 972.

On the other hand, below the housing 93 (on the tip side), there are a pair of inner and outer protective covers 941 and 942 that are inserted into the exhaust passage, and the base end portion above the housing 93 is in contact with the atmosphere. It has cover members 951 to 953. The protective covers 941 and 942 are provided with openings 943 and 944 for introducing exhaust gas, and the cover members 952 and 953 are provided with atmospheric openings 954 for introducing atmospheric air.
955 is provided.

Several methods have been proposed for fixing the inner and outer protective covers 941 and 942 to the housing 93. The first method is shown in FIG. We fixed the bottom by welding,
This is a method in which either one of the protective covers is caulked and fixed to the housing 93 (for example, Japanese Patent Laid-Open No. 5-249069). A second method of fixing the inner and outer protective covers is to fix the bottom portions of the protective covers to each other by welding, and weld either one of the protective covers to the housing 93 (KOKAI Sho 57-34443). No.

The inner and outer protective covers are attached to the housing 9
A third method for fixing the inner and outer protective covers to each other is to individually weld the inner and outer protective covers to the housing 93 and fix the inner and outer protective covers to each other (JP-A-5-26842, etc.). ). The welding work in the first to third methods is performed by a resistance welding method or the like.

As a fourth method which does not require a welding process, there is a structure disclosed in Japanese Utility Model Publication No. 6-32616. According to this method, a bent portion (skirt portion) having a U-shaped cross section is formed on the upper and lower protective covers along a circular curve having substantially the same diameter, and the bent portions are overlapped to form a double cover structure. The structure is such that the bent portion is caulked and fixed to the housing, and the ring is held in an empty portion formed inside the U-shape. The ring is for filling the void to prevent deformation and to maintain airtightness.

[0009]

However, each of the first to fourth methods of fixing the pair of inner and outer protective covers to the housing has the following problems. The first to third methods for welding the protective covers to each other or the protective cover and the housing have the following problems due to the use of the welding process.

First, in order to keep the manufacturing quality of the welded fixed portion constant, it is necessary to control the constant voltage and current in the resistance welding process and the conduction time, and to control the constant pressing force applied between the welded portions. It is necessary and not easy to manufacture. Secondly, defects such as cracks are likely to occur in the oxygen detection element due to the high temperature caused by the welding work.
In addition, the first and second welding the bottom parts of the inner and outer protective covers to each other
The second method has a third problem in that it is difficult to form an opening for taking in exhaust gas at the bottom and many openings must be provided on the side surface.

On the other hand, in the fourth method of fixing the inner and outer protective covers to the housing, the state of fixing to the housing becomes unstable unless the inner and outer bent portions (skirt portions) to be caulked and fixed are in close surface contact with each other. Therefore, the first requirement that a high degree of processing accuracy is required for the bent portion of the cover.
There is a problem. Further, there is a second problem in that it is necessary to provide a ring inside the U-shaped bent portion, and the number of parts is large.

Further, since the bent portion is caulked and fixed in a state in which two sheets are stacked, a third problem is that a large pressure contact force is required when caulking and fixing the protrusion of the housing. . The present invention has been made in view of the above conventional problems, and an object of the present invention is to provide an air-fuel ratio sensor having an excellent protective cover that can be firmly and easily fixed to a housing with a simple structure. .

[0013]

In the air-fuel ratio sensor of the first aspect of the present invention, the protective cover is caulked and fixed to the housing. Therefore, no welding process is required, and the problems of the first to third methods associated with the welding process do not occur.

In the case of caulking and fixing, the caulking and fixing portions of the inner and outer covers are flange-shaped edges formed by bending outward at the base end portions. Since the protrusions of the housing are pressed against each other, it is not necessary to provide a member such as a ring between them. This is because in the fourth method disclosed in Japanese Utility Model Publication No. 6-32616, the caulking fixing portion has a U-shaped cross-sectional shape, and it is necessary to embed a member such as a ring in the U-shaped empty portion. However, in the brim-shaped edge structure, no void is created, and therefore, a member to be embedded is not necessary.

Further, the edges which are caulked and fixed by the inner and outer covers are alternately arranged so as not to overlap each other along a closed curve that circulates the outside of the sensing element. That is, unlike the bent portion of the fourth method, the two caulking fixing portions are not stacked. Since there is no need to overlap them, a high degree of processing accuracy is not required for edge processing. Further, since the two caulking fixing portions are not overlapped with each other, a large pressure contact force is not required when caulking and fixing.

Further, since the edges of the inner and outer protective covers are alternately arranged, the positional relationship around the axial center of both covers is substantially constant. Therefore, by appropriately setting the positional relationship between the opening and the edge of both covers, the positional relationship around the axial center of the opening of the inner cover and the opening of the outer cover can be uniquely determined. Therefore, it is easy to align the openings between the covers. As described above, the air-fuel ratio sensor according to the first aspect of the present invention has an excellent protective cover that can be firmly and easily fixed to the housing with a simple structure.

Further, in the air-fuel ratio sensor according to the first aspect, the inner cover and the outer cover are not fixed by welding. Therefore, as described in the second aspect, an opening is formed at the tip of the inner cover and the outer cover. Can be provided. Therefore, an opening for taking in exhaust gas can be provided in the side surface portion and the tip portion in a well-balanced manner, and it is not necessary to provide many opening portions in the side surface portion. In addition, condensed water of exhaust gas that may stay at the bottom of the protective cover can be discharged from the opening on the bottom surface.

Further, as described in claim 2, a widening connecting portion for connecting the small-diameter body portion and the edge portion of the inner cover, and a belt-like connecting portion for connecting the body portion and the edge portion of the outer cover. The air-fuel ratio sensor according to claim 1 is characterized in that the two are prevented from overlapping with each other and that a gap is formed between the two members. Can be one. That is, an opening through which exhaust gas flows can be provided on the base end side of the protective cover.

Further, as described in claim 4, at the edges of the inner and outer covers, which are caulked and fixed, are provided an uneven portion having a waveform pulsating up and down in the direction of a closed curve that circulates the outside of the oxygen sensing element. Is preferred. By providing the corrugated concavo-convex portion without forming the edge portion into a flat surface, the strength of caulking and fixing when the protrusion of the housing is pressed against the corrugated portion can be made stronger.

Further, as described in claim 5, in addition to the first contact surface with which the edges of both the inner and outer covers which are caulked and fixed are in surface contact with the housing, from the first contact surface to the tip side. It is preferable to provide a second contact surface that is bent toward and inscribes in the body portions of the inner and outer covers. Since the second contact surface is inscribed in the body of the inner and outer covers and supports the body from the inside, the protective cover is more firmly fixed to the housing.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 As shown in FIG. 1, the present embodiment is an oxygen detection element 10 having a bottomed cylindrical solid electrolyte 11 having a closed end, a housing 41 holding the oxygen detection element 10, and an oxygen detection element. The air-fuel ratio sensor has a columnar heater unit 20 inserted inside 10, and protective covers 31 and 32 that cover the tip side of the solid electrolyte 11 and have openings 21 and 22 for introducing exhaust gas.

The protective covers 31 and 32 are made up of the solid electrolyte 11
Inner cover 31 located on the inner side close to, and this inner cover 3
1 and an outer cover 32 located on the outer side. And
As shown in FIGS. 2 and 3, at the base end portions of the inner and outer covers 31 and 32, a flange-shaped upper edge portion 3 bent outward is formed.
Six pieces of 11 and 321, respectively, are formed, and both covers 31 and 32 are protrusions 41 provided on the housing 41.
1 is pressed against the upper edge portions 311 and 321 to be caulked and fixed.

The caulked and fixed upper edge portion 321 of the outer cover 32 and the caulked and fixed upper edge portion 311 of the inner cover 31 are overlapped with each other along a closed curve that surrounds the outside of the oxygen sensing element 10. They are arranged alternately so that they do not exist. As shown in FIG. 2, the inner cover 31 includes a small-diameter body portion 310 having an opening 21 formed near the front end, a large-diameter upper edge portion 311, which is caulked and fixed, a small-diameter body portion 310, and an upper edge portion 311. It has the expansion connection part 312 which connects between.

As shown in FIG. 3, the outer cover 32 has a body portion 320 having an opening 22 and an upper edge portion 321.
And a strip-shaped connecting portion 322 that connects the body portion 320 and the upper edge portion 321. The expansion connecting portion 312 and the belt-like connecting portion 322 do not overlap with each other, and a gap 23 (FIG. 3) into which exhaust gas flows is formed between the members 312 and 322 so that the oxygen detecting element 10 has a gap. They are formed alternately in the direction of a closed curve that circulates on the outside.

That is, the expansion connecting portion 312 of the inner cover 31.
Substantially fits into the notch 323 formed between the adjacent connecting portions 322 of the outer cover 32, and both covers 3
When the 1, 32 are mounted on the housing 41, the expansion connecting portion 3
The middle bent line 313 (FIG. 2) of 12 is located above the lower end line 324 of the cutout portion 323. Therefore, both covers 3
When the components 1 and 32 are mounted on the housing 41, as shown in FIG. 3, a gap 23 is formed between the lower end lines 324 of the covers 31 and 32 and the intermediate bending line 313 indicated by the chain line.

Further, as shown in FIGS. 2 to 4, the inner and outer openings 21 and 22 are alternately arranged so as not to face each other. Then, the housing 41 has a structure shown in FIG.
As shown in FIG. 1, the first contact surface 41 that makes surface contact with the upper edge portions 311 and 321 of the inner and outer covers 31 and 32 that are caulked and fixed.
2 and a second abutment surface 413 which is bent from the first abutment surface 412 toward the front end side and is inscribed in the body portions of the inner and outer covers 31, 32.

The following is a supplementary explanation of each.
This example is an air-fuel ratio sensor 1 that detects the air-fuel ratio of an automobile engine. As shown in FIG. 1, the housing 41
Is a screw portion 414 that is screwed into a screw hole provided in the exhaust passage.
And a flange portion 415 that comes into contact with the exhaust passage, and a protrusion 411 is formed on the outside of the body. Protrusion 41
First, as shown in FIG. 5, 1 is erected upright as shown by a broken line, and the upper edges 311 and 3 of the covers 31 and 32 are provided.
The covers 31 and 32 are fixed by being pressed against 21. Further, as shown in FIG. 1, the cover members 442 and 443 located on the base end side are provided with atmospheric air inlets 444 and 445 for introducing atmospheric air into the oxygen detection element 10.

The oxygen detecting element 10 is held in the housing 41 with a talc 416 interposed. In FIG. 1, reference numeral 462 is a gasket, reference numeral 463 is a metallic ring, and reference numeral 464 is a breathable waterproof filter. A heater unit 20 is inserted inside the oxygen detection element 10, and the heater unit 20 is supported by the oxygen detection element 10 via a holder 47. A heating element (not shown) is embedded in the heater unit 20, and the heating element is connected to the power supply line 462.

The signal line 461 and the power supply line 462 are fixed to the cover members 442 and 443 via bushes. Further, an atmosphere passage (not shown) for guiding the atmosphere taken in through the air intake ports 444 and 445 to the inside of the oxygen detection element 10 is provided.

Next, the function and effect of the air-fuel ratio sensor 1 of this example will be described. The inner and outer protective covers 31, 32 of this example are
It is fixed to the housing 41 by a caulking process in which manufacturing conditions are easier to manage than welding. The caulking fixing portion of both the inner and outer covers 31, 32 of the air-fuel ratio sensor 1 is a flange-shaped upper edge portion 3 formed by bending outward at the base end portion.
11,321 and the upper edge portions 311,321 of the collar shape.
The protruding portion 411 of the housing 41 is pressed against. Therefore, no gap is formed between the two 311, 321 and 411, and it is not necessary to interpose a member such as a ring in the middle.

Further, the upper edge portion 3 of the inner and outer covers 31, 32
The reference numerals 11 and 321 are alternately arranged so as not to overlap each other along a closed curve that circulates outside the oxygen detection element 10. That is, in this example, the caulking fixing portion pressed against the same portion of the protrusion 411 is either the upper edge portion 311 of the inner cover 31 or the upper edge portion 321 of the outer cover 32, and the portion to be caulked is fixed. Two sheets are not stacked at any part.

Since it is not necessary to overlap the members 311 and 321 with each other, the upper edge portions 311 and 32 of the covers 31 and 32, respectively.
There is no need to match the shapes of 1 with high precision, and the processing is significantly easier than when two sheets are stacked. Further, since the two caulking fixing portions are not stacked, the caulking and fixing can be easily performed without requiring a large pressure contact force.

Further, since the upper edge portions 311 and 321 of the inner and outer protective covers 31 and 32 are alternately arranged, the positional relationship around the axial center of both covers 31 and 32 becomes substantially constant. Therefore, the openings 2 in both covers 31 and 32
By appropriately setting the positional relationship between the upper edge portions 311 and 321 and the upper edge portions 31 and 321, the positional relationship around the axis of the opening portion 21 of the inner cover 31 and the opening portion 22 of the outer cover 32 is uniquely determined. This facilitates the alignment of the openings 21 and 22 between the covers 31 and 32.

Further, both covers 31, 32 are attached to the housing 4
1, the expansion connecting portion 312 and the belt-like connecting portion 32 are attached.
With the structure of 2, as shown in FIG. 3, both covers 31,
Voids 23 are formed between 32. Then, as shown by the arrow in FIG. 6, the exhaust gas flows in from this void 23, and the void 23 can be used as one kind of opening, so that the number of openings 21, 22 can be reduced, and the exhaust gas Gas can be flowed in from different parts in good balance.

Then, in the housing 41, as shown in FIG. 5, the second contact surface 4 is bent from the first contact surface 412 toward the front end side and is inscribed in the body portions of the inner and outer covers 31, 32.
Since the second contact surface 413 is in contact with the inner and outer covers 31 and 32 to support the body from the inside, the protective cover is more firmly fixed to the housing. .

If the second abutment surface 413 is not provided, the body portions of the inner and outer covers 31, 32 are fixed by caulking.
Upon receiving the force that is deformed inward, the stress due to that force remains. This is also a factor that causes damage problems due to external forces due to vibrations received during use, cold heat cycles, and the like. The second contact surface 413
May be preliminarily press-fitted to the body portions of the inner and outer covers 31 and 32, or may be fitted with a gap, and the second contact surface 413 and the caulked portion may be projected by caulking. It may be sandwiched between the parts 411. As described above, the air-fuel ratio sensor 1 of this example has the excellent protective covers 31 and 32 that can be firmly and easily fixed to the housing 41 with a simple structure.

Embodiment 2 As shown in FIG. 7, this embodiment is another embodiment in which openings 21 and 22 are provided in the bottom surface 331 of the inner cover 33 and the bottom surface 341 of the outer cover 34 in the first embodiment. It is an example of an embodiment. By providing the openings 21 and 22 on the bottom surfaces 331 and 341, it is possible to reduce the number of openings 21 and 22 on the side surfaces 332 and 342 of the covers 33 and 34, and to allow the exhaust gas to flow in from different parts in a well-balanced manner. You can

In addition, the openings 21 of the bottom surfaces 331 and 341,
From 22, it is possible to discharge the condensed water of the exhaust gas and the like that stays at the bottom of the protective cover. Others are the same as those in the first embodiment.

Embodiment 3 This embodiment is another embodiment in which the bottom surface of the inner cover 35 is opened in Embodiment 1 as shown in FIG. This simplifies the structure of the inner cover 35,
Also, the step of forming an opening on the bottom surface is not necessary. Others are the same as those in the first embodiment.

Fourth Embodiment As shown in FIGS. 9 and 10, this embodiment is different from the first embodiment in that upper and lower edge portions 361 and 3 of the inner and outer protective covers 36 and 37.
The number of 71 and the number of connecting portions 362 and 372 are each four. Others are the same as in the first embodiment.

Embodiment 5 As shown in FIGS. 11 and 12, this embodiment is similar to Embodiment 4 except that the upper edge portions 381 and 391 of the inner and outer covers 38 and 39, which are caulked and fixed, detect the oxygen. An uneven portion having a waveform that pulsates vertically in the direction of a closed curve that circulates on the outside of the element 10 is provided. Since the upper and lower edge portions 381 and 391 are not flat surfaces and are provided with corrugated uneven portions,
When the protrusion 411 of the housing 41 is pressed into contact with the protrusion 41, the concave and convex portions bite into the protrusion 411, and the caulking fixing strength can be made more stable and strong. Others are the same as those in the fourth embodiment.

In the drawings of the embodiments, the exhaust gas introduction openings for ventilation are provided in the body of both the inner and outer covers, but it is not always necessary to provide openings for each cover. As shown in the example of FIG. 3, only the void 23 formed when the inner and outer covers are caulked and fixed may be used as the opening for taking in the exhaust gas.

[Brief description of drawings]

FIG. 1 is a sectional view of an air-fuel ratio sensor according to a first embodiment (FIG. 4).
XX sectional view).

FIG. 2 is a perspective view of an inner cover according to the first embodiment.

FIG. 3 is a perspective view of an outer cover according to the first embodiment.

FIG. 4 is a sectional view taken along line YY of FIG. 1;

5 is a partially enlarged view of the distal end portion of FIG. 1 showing the shape of the housing before caulking with a broken line.

FIG. 6 is a diagram showing an exhaust gas flowing into a void in an enlarged view of a part of a tip portion of FIG. 1 by an arrow.

FIG. 7 is a cross-sectional view showing a distal end portion of a housing and a protective cover according to the second embodiment.

FIG. 8 is a cross-sectional view showing a distal end portion of a housing and a protective cover according to the third embodiment.

FIG. 9 is a perspective view of an inner cover according to the fourth embodiment.

FIG. 10 is a perspective view of an outer cover according to the fourth embodiment.

FIG. 11 is a perspective view of an inner cover according to the fifth embodiment.

FIG. 12 is a perspective view of an outer cover according to a fifth embodiment.

FIG. 13 is a sectional view of a conventional air-fuel ratio sensor.

[Explanation of symbols]

 1. . . Air-fuel ratio sensor, 10. . . Oxygen sensing element, 21, 22. . . Openings, 31, 32. . . Protective cover, 41. . . Housing, 411. . . Protrusion,

Claims (5)

[Claims] 1. An oxygen sensing element having a sensing part made of a solid electrolyte, a housing for holding the oxygen sensing element, and a protective cover having an opening for covering the tip side of the solid electrolyte and introducing exhaust gas. The protective cover has an inner cover located inside the solid electrolyte and an outer cover located outside the inner cover, and the base ends of both the inner and outer covers. Has a brim-shaped edge portion bent outward, and the both covers are caulked and fixed by pressing a protrusion provided on the housing onto the edge portion. The edge of the inner cover to be crimped and the edge of the inner cover to be crimped are alternately arranged so as not to overlap each other along a closed curve that surrounds the axis of the oxygen sensing element. An air-fuel ratio sensor characterized by being arranged. 2. The air-fuel ratio sensor according to claim 1, wherein the inner cover and the outer cover are formed with openings at their tip ends. 3. The inner cover according to claim 1, wherein the inner cover has a small-diameter body portion near the tip, a large-diameter edge portion that is caulked and fixed, and the small-diameter body portion and the edge portion. The outer cover has a body portion, the edge portion, and a strip-shaped connection portion connecting the body portion and the edge portion. The open connection part and the band-shaped connection part are alternately arranged along a closed curve that circulates around the axis of the oxygen detection element so as not to overlap each other and to form a gap between the two members through which exhaust gas flows. An air-fuel ratio sensor characterized by being formed. 4. The edge portion of each of the inner and outer covers, which is caulked and fixed, faces a direction of a closed curve that circulates around an axis of the oxygen detection element according to any one of claims 1 to 3. The air-fuel ratio sensor is characterized in that it is provided with a corrugated portion that pulsates vertically. 5. The first contact surface according to claim 1, wherein the housing has a first contact surface that comes into surface contact with edges of the inner and outer covers that are fixed by crimping, and the first contact surface.
An air-fuel ratio sensor, comprising: a second contact surface that is bent from the contact surface toward the front end side and is inscribed in the body portions of the inner and outer covers.