JP2003185620A - Gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas sensor hard to produce a crack or breaking in the welded part between a housing and a cover on the side of gas to be measured. <P>SOLUTION: The cylindrical cover 2 on the side of gas to be measured fixed to the leading end 100 of a cylindrical housing 10 is provided so as to cover the leading end 190 of the sensor element 19 inserted into and arranged to the cylindrical housing 10. The cover 2 on the side of gas to be measured and the leading end 100 of the cylindrical housing 10 are fixed by together using caulking fixing and spot welding. Further, the difference of the coefficient of thermal expansion between the cover 2 on the side of gas to be measured and the housing is not more than 2×10<SP>-6</SP>/°C. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention is installed in an exhaust system of an internal combustion engine,
The present invention relates to a gas sensor that measures the oxygen concentration in exhaust gas.

[0002]

2. Description of the Related Art An air-fuel ratio feedback system for an internal combustion engine controls combustion by detecting the air-fuel ratio using a gas sensor installed in the exhaust system. The gas sensor used here detects the air-fuel ratio from the oxygen concentration in the exhaust gas. To do. The gas sensor has a built-in ceramic sensor element using zirconia or the like, and since the sensor element is fragile in strength,
The gas sensor is provided with a measured gas side cover that covers the tip side of the sensor element.

The structure of this gas sensor will be briefly described. A cylindrical inner cover is provided at the tip of the housing and an outer portion of the inner cover so as to cover the tip of the sensor element inserted through the tubular housing. And the tubular outer cover located on one side. The outer cover and the inner cover constitute a measured gas side cover. The base end side of the inner cover is fitted to the outer periphery of the front end portion of the housing. Then, the base end side of the outer cover is further fitted to the outer circumference of the inner cover. Then, the housing, the inner cover, and the outer cover are laser-welded over the entire circumference to be integrally joined.

[0004]

[Problems to be Solved] However, when the atmosphere around the gas sensor is exposed to an atmosphere with a temperature change from normal temperature to high temperature, the entire circumference welding is performed due to the difference in thermal expansion between the housing and the inner and outer covers. Repeated stress occurs in the welded part, and if this repeated stress is extremely large, cracks may occur in the weld and even fracture.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a gas sensor in which cracks and fractures are less likely to occur at the welded portion between the housing and the measured gas side cover. is there.

[0006]

According to a first aspect of the present invention, there is provided a cylindrical cover for a gas to be measured, which is fixed to a front end portion of a housing so as to cover a front end portion of a sensor element inserted and arranged in the cylindrical housing. The gas sensor is characterized in that the fixing between the measured gas side cover and the front end portion of the housing is a state in which caulking fixing and spot welding are used in combination (claim 1).

In the gas sensor of the first aspect of the present invention, the housing and the cover to be measured are fixed by caulking and spot welding together. In this case, when the atmosphere around the gas sensor is first exposed to a temperature-changing atmosphere from room temperature to high temperature, stress exceeding the elastic limit is generated on the housing side of the caulking fixing part, and the housing is plastically deformed. . Next, when the atmosphere around the gas sensor is exposed to an atmosphere of a temperature change of cooling from high temperature to normal temperature, stress does not occur in the housing because the heat shrinkage of the measured gas side cover is large.

Further, when the atmosphere around the gas sensor is exposed again to the atmosphere of temperature change from room temperature to high temperature, the stress is not generated in the housing since the housing has already been plastically deformed. Therefore, since no repeated stress is generated in the caulked fixing portion where the caulking is performed, neither cracks nor breaks occur.

Further, when the spot-welded portion is exposed to the atmosphere around the gas sensor in an atmosphere where the temperature changes from room temperature to high temperature or from high temperature to room temperature, repeated stress is generated, but the part to which the caulking is performed is fixed. Since it absorbs the energy of the cyclic stress at, the risk of crack initiation and fracture is reduced. As described above, according to the first aspect of the present invention, the housing is plastically deformed only by caulking and the loosening is likely to occur at the caulking fixed portion. However, by using spot welding together, the occurrence of the loosening is prevented and cracking Occurrence and breakage can be prevented.

The second aspect of the present invention has a tubular cover for a gas to be measured, which is fixed to the tip of the housing so as to cover the tip of the sensor element inserted through the tubular housing. Then, the measured gas side cover and the front end of the housing are fixed by welding, and the difference in coefficient of thermal expansion between the measured gas side cover and the housing is 2 or less.
A gas sensor is characterized in that it is within × 10 ⁻⁶ / ° C. (Claim 5).

In the gas sensor of the second invention, since the difference in the coefficient of thermal expansion between the housing and the measured gas side cover is very small, almost no thermal stress is generated. Therefore, stress is less likely to accumulate when the gas sensor is exposed to a thermal cycle from room temperature to high temperature.

As described above, according to the first and second aspects of the present invention, it is possible to provide a gas sensor in which cracks and fractures are less likely to occur at the welded portion between the housing and the measured gas side cover.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The sensor element used in the gas sensor of the first and second inventions (claims 1 and 5) is an oxygen concentration, NOx concentration, HC concentration, CO concentration, When the measurement gas is the exhaust gas of the internal combustion engine, the air-fuel ratio of the combustion chamber of the internal combustion engine is measured. Also,
The sensor element may be of a laminated type or a cup type.

In the second aspect of the invention, when the difference in the coefficient of thermal expansion between the measured gas side cover and the housing is greater than 2 × 10 ^-6 / ° C, welding is performed due to thermal stress. There is a risk that cracks may occur or breaks may occur in the damaged parts.

As the material of the housing and the measured gas side cover, it is preferable to use austenitic stainless steel, ferritic stainless steel, and nickel base alloys (iron alloys containing nickel, chromium, etc.). These materials are selected so that the difference in coefficient of thermal expansion between them is within the above range. Since these materials have oxidation resistance at high temperatures, high temperature corrosion resistance, and high mechanical properties at high temperatures, they are particularly suitable for gas sensors used in corrosive atmospheres at high temperatures.

As austenitic stainless steel,
For example, SUS 310 S (16.9 × 10 ⁻⁶ /
℃), SUS 304 (18.4 × 10 ^-6 / ℃), as ferritic stainless steel, for example, SUS 43
0 (11.9 × 10 ⁻⁶ / ° C.), as a nickel-based alloy, Inconel 600 (15.5 × 10 ⁻⁶ / ° C.), Inconel 601 (16.0 × 10 ⁻⁶ / ° C.), Inconel 7
18 (14.9 × 10 ⁻⁶ / ° C.) can be used. Inconel is a registered trademark of INCO. In the above description, the numerical value in parentheses is the coefficient of linear expansion at 0 to 649 ° C.

The spot welding is preferably provided at three locations (claim 2). In this case, the housing and the measured gas side cover can be fixed without being biased in a specific direction. At two points, the space between spot-welded locations becomes at least 1/2 of the outer circumference, so it may be difficult to stably fix the housing and the measured gas side cover.

Further, it is preferable that the spot welding is provided at equal intervals (claim 3). In this case, the housing and the measured gas side cover can be fixed without being biased in a specific direction. In addition, the spot welding described above
Resistance welding or laser welding is preferred (claim 4).

It is preferable that the measured gas side cover and the housing are made of the same material (claim 6). As a result, there is no difference in the coefficient of thermal expansion, so that cracks and fractures do not occur at the welded portion between the housing and the gas side cover to be measured due to thermal stress.

Further, as for the welding and fixing between the measured gas side cover and the tip of the housing, caulking fixing and spot welding are used together (claim 7). As a result, the joint strength between the measured gas side cover and the housing can be further increased.

Further, it is preferable that the measured gas side cover has a double structure composed of an inner cover and an outer cover. As a result, the path through which the exhaust gas flows can have a labyrinth structure, so that it is possible to prevent the water and the like in the exhaust gas from adhering to the element.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. (Example 1) FIG. 1 shows a gas sensor according to the present invention.
~ It demonstrates using FIG. As shown in FIG. 1, the gas sensor 1 according to the present embodiment has a cylindrical housing fixed to the tip portion 100 of the housing 10 so as to cover the tip portion 190 of the sensor element 19 inserted and arranged in the tubular housing 10. It has a measurement gas side cover 2. The fixing between the measured gas side cover 2 and the tip portion 100 of the housing 10 uses both caulking fixing and spot welding. 1 to 3, the lower part of the drawing is the tip side of the gas sensor, and the upper part of the drawing is the base end side of the gas sensor.

The details will be described below. The gas sensor 1 of this example is a sensor that is installed in the exhaust system of an automobile engine to measure the oxygen concentration and to use the measured value for combustion control. As shown in FIG. 1, a gas sensor 1 of this example includes a cylindrical housing 10 made of stainless steel, and the housing 1.
A sensor element 19 which is inserted and fixed to the element 0 through the element-side insulator 11, a measured gas side cover 2 which covers a tip portion 190 of the sensor element 19, and an atmosphere-side cover 131 which covers a base end side of the sensor element 19. Consists of. A sealing material 110 seals and fixes between the sensor element 19 and the element-side insulator 11. The sensor element 19 is an element for detecting oxygen concentration, which is formed by stacking zirconia ceramic plates and alumina ceramic plates.

Further, the atmosphere-side insulator 12 is arranged inside the atmosphere-side cover 131 on the base end side of the element-side insulator 11. Inside the atmosphere-side insulator 12, the terminal (not shown) of the sensor element 19 and the take-out spring 141 electrically contact with each other. The take-out spring 141 is electrically connected to the lead wire 143 by the connection terminal 142. Lead wire 1
43 is drawn out of the sensor. In addition, the lead wire 143 leads the output of the sensor element 19 to the outside,
Input to the sensor element 19 from an external power source (not shown).

A cylindrical outer cover 132 is fixed to the outside of the atmosphere side cover 131 via a water repellent filter 133. Both the atmosphere side cover 131 and the outer cover 132 introduce the atmosphere into the atmosphere side cover 131. Introducing hole 13
Has 0.

The measured gas side cover 2 has a double structure composed of an outer cover 21 and an inner cover 22, and has introduction holes 210 and 220 for introducing the measured gas on the side surface and a bottom surface 21.
9, 229 have bottom holes 218, 228. Inner cover 2
The inside of 2 becomes a measured gas chamber 200.

As shown in FIG. 3, the tip portion 100 of the housing 10 has an annular recess 105 which is open toward the tip side. The outer periphery of the annular recess 105 is bent inward in the radial direction during crimping, and the protrusion 101 for crimping the flanges 213 and 223 of the outer cover 21 and the inner cover 22 described later is crimped.
There is. As shown in FIG. 2, the base ends of the inner cover 21 and the outer cover 22 are bent outwardly in the radial direction so as to open in the circumferential direction to form flange portions 213 and 223. The two flange portions 213 and 223 are overlapped with each other and fit into the annular recess 102, and the protrusion 101 is bent toward the roots of the flange portions 213 and 223, whereby caulking can be achieved.

From the bent protrusion 101, the flanges 213 and 2 of the outer cover 21 and the inner cover 22 are formed.
After that, spot welding is performed on the ceiling surface 102 of the annular recess 105 of the housing 10 via 14. The welding mark is 106.
Is. As shown in FIG. 4, the spot welding is performed at three locations along the circumferential direction at equal intervals.

A durability test was conducted by exposing the gas sensor 1 having the above-mentioned configuration to a thermal cycle of heating from room temperature to 800 ° C. in the atmosphere and then cooling to room temperature for 2000 cycles. After the test, the joint state of the housing 10 with the inner cover 22 and the outer cover 21 was examined, and as a result, there was almost no change from the state before the test, and no damage occurred. Of course, the inner cover 22 and the outer cover 21 did not fall off.

The operation and effect of this example will be described. The gas sensor 1 according to the present embodiment includes an outer cover 21 and an inner cover 2 with respect to an annular recess 105 provided in the tip portion 100 of the housing 10.
The second flange portions 213 and 223 are inserted and fixed by crimping here, and spot welding is also performed. In this case, when the atmosphere around the gas sensor 1 is first exposed to an atmosphere of temperature change from room temperature to high temperature, a stress exceeding the elastic limit is generated on the housing 10 side of the caulking fixing portion, and the housing 10 is Plastically deforms. Next, when the atmosphere around the gas sensor 1 is exposed to an atmosphere of a temperature change of cooling from high temperature to normal temperature, thermal contraction of the inner cover 22 and the outer cover 21 is large, so that no stress is generated in the housing 10.

Further, when the atmosphere around the gas sensor 1 is re-exposed to the atmosphere of the temperature change from the normal temperature to the high temperature, the housing 10 is already plastically deformed, so that no stress is generated in the housing 10. Therefore, no repetitive stress is generated in the caulked fixing part, so that neither cracking nor fracture occurs.

Further, when the atmosphere around the gas sensor 1 is exposed to an atmosphere with a temperature change from room temperature to high temperature or from high temperature to room temperature in the spot-welded portion, repetitive stress is generated, but caulking is performed. It absorbs the energy of repetitive stress in the part, thus reducing the risk of crack initiation and fracture. As described above, according to this example, the housing 10 is plastically deformed only by caulking, and the caulking fixing portion is likely to loosen. However, by using spot welding together, the occurrence of loosening is prevented and a crack is generated. ， Can prevent breakage.

As described above, according to this example, it is possible to provide a gas sensor in which a welded portion between the housing and the measured gas side cover is less likely to crack or break.

Further, as shown in FIGS. 5 to 9, even if the spot welding is one place, two places, four places, six places, and eight places, the spot welding of three places shown in FIGS. It is possible to obtain the same operational effect as in the case of performing.

(Embodiment 2) The structure of the gas sensor of this embodiment is as follows.
This is the same as in the first embodiment. Then, the housing is made of austenitic SUS 310 S, and the outer and inner covers are made of austenitic SUS 304. In this case, the difference in thermal expansion coefficient between the housing and the outer cover and inner cover is 1.5 × 10 ⁻⁶ / ° C. Alternatively, the housing, the outer cover, and the inner cover are all made of ferrite SUS 430.

Alternatively, the housing is made of austenitic SUS 310 S and the outer and inner covers are made of Ni.
It is composed of Inconel 600 which is a base alloy. In this case, the difference in thermal expansion between the two is 1.4 × 10 ^-6 / ° C.

The gas sensor of this example has a housing, an outer side,
Since the thermal expansion coefficient of the inner cover is small, almost no thermal stress is generated. Therefore, stress does not accumulate when the gas sensor is exposed to a thermal cycle from normal temperature to high temperature.

As described above, according to the present embodiment, it is possible to provide a gas sensor in which cracks and fractures hardly occur in the welded portion between the housing and the measured gas side cover.

[Brief description of drawings]

FIG. 1 is an overall cross-sectional explanatory view of a gas sensor according to a first embodiment.

FIG. 2 is an explanatory view of a main part of a housing, an outer cover, and an inner cover in the first embodiment.

FIG. 3 is an enlarged explanatory view of a main part of a housing front end portion in the first embodiment.

FIG. 4 is an explanatory diagram of spot welding in the first embodiment.

FIG. 5 is an explanatory diagram of spot welding provided at one location in the first embodiment.

FIG. 6 is an explanatory diagram of spot welding provided in two places in the first embodiment.

FIG. 7 is an explanatory view of spot welding provided at four places in the first embodiment.

FIG. 8 is an explanatory view of spot welding provided at six places in the first embodiment.

FIG. 9 is an explanatory diagram of spot welding provided at eight locations in the first embodiment.

[Explanation of symbols]

1. ． ． Gas sensor, 10. ． ． housing, 100, 190. ． ． Tip, 19. ． ． Gas sensor element, 2. ． ． Measured gas side cover, 21. ． ． Outer cover, 22. ． ． Inner cover,

Claims (8)

[Claims] 1. A measuring gas side cover, which is fixed to the front end of the housing so as to cover the front end of a sensor element inserted through the cylindrical housing, is provided. A gas sensor characterized in that the side cover and the front end of the housing are fixed together by caulking and spot welding. 2. The gas sensor according to claim 1, wherein the spot welding is provided at three locations. 3. The gas sensor according to claim 1 or 2, wherein the spot weldings are provided at equal intervals. 4. The gas sensor according to claim 1, wherein the spot welding is resistance welding or laser welding. 5. A measuring gas side cover having a cylindrical shape fixed to the tip of the housing so as to cover the tip of a sensor element inserted through the inside of the cylindrical housing. The side cover and the front end of the housing are fixed by welding, and the difference in thermal expansion coefficient between the measured gas side cover and the housing is within 2 × 10 ⁻⁶ / ° C. Gas sensor to do. 6. The gas sensor according to claim 5, wherein the measured gas side cover and the housing are made of the same material. 7. The welding fixing between the measured gas side cover and the front end of the housing according to claim 5 or 6, wherein caulking fixing and spot welding are used in combination. Gas sensor. 8. The method according to any one of claims 1 to 7,
A gas sensor characterized in that the measured gas side cover has a double structure including an inner cover and an outer cover.