JPH08160001A - Oxygen sensor structure - Google Patents

Abstract

PURPOSE: To provide an oxygen sensor structure in which a crack or craze does not occur even if it is submersed in water when a detecting element is fixed to a main body fitting via a ceramic insulator. CONSTITUTION: The platelike detecting element 3 of an oxygen sensor 1 is fixed to a glass seal 13 in a ceramic holder 11, and the holder 11 is fixed to a main body fitting 17 made of a refractory metal via a talc 15. A gap 18 is provided between the side inside the fitting 17 and the side outside the holder 11. The fitting 17 and the holder 1 are brought into contact with the more tip end side of the fitting 17 than its seat surface, and the fitting 17 supports the holder 11. More particularly, the oblique surface of the fitting 17 and the oblique surface of the holder 11 become tapered inclining to the shaft center.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor structure applied to, for example, an oxygen sensor for detecting the oxygen concentration in exhaust gas from an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, as an oxygen sensor for detecting the oxygen concentration in the exhaust gas of an internal combustion engine of an automobile or the like, an electromotive force type sensor using an oxygen ion conductive solid electrolyte (for example, zirconia) or a metal type There is a variable resistance type that uses a sensing substance such as oxide (titania), and is used for the purpose of controlling the air-fuel ratio of the internal combustion engine.

For example, in the case of a resistance change type oxygen sensor, as shown in FIG. 5 (a), a sensing substance P made of titania or the like is provided on the tip side of an alumina substrate P1 containing a heater.
2 is laminated and the output electrode P3 is arranged on the rear end side to form a plate-shaped detection element portion P4.
4 is housed in a metal shell P5 and sealed and fixed with an inorganic adhesive such as a glass seal P6.

In the case of an electromotive force type oxygen sensor, as shown in FIG. 5 (b), a bag-shaped detecting element portion P7 made of a solid electrolyte such as zirconia is housed in a metal shell P8. It has a structure in which it is fixed by swaging through a talc P9 or the like.

[0005]

However, in recent years,
LEV (Low Emission Vehicle), ULEV (UltraLo
w Emission vehicles) and other emission regulations are being strengthened, and a method of increasing the exhaust gas temperature to burn out and remove unburned components such as HC is beginning to be adopted.

When the temperature of the exhaust gas rises, in the structure of the oxygen sensor, the metal shell P5 and the glass seal P6 are used.
Due to the difference in thermal expansion between the glass seal P6 and the glass seal P6, cracks may occur in the glass seal P6 and, in some cases, even the substrate P1. As a countermeasure, the structure of the oxygen sensor is incorporated into the oxygen sensor, and as shown in FIG. 5C, for example, a plate-shaped detection element portion P10 is inserted into a cylindrical ceramic holder P11, and the ceramic holder P11 is inserted. P
A method of arranging 11 in the metal shell P12 and fixing it by caulking can be considered, but this is not always sufficient.

For example, when the oxygen sensor is mounted on the downstream side of the catalyst, the oxygen sensor may be completely immersed in water depending on the road surface condition. At that time, since the oxygen sensor is rapidly cooled from the outside, due to the difference in thermal expansion between the ceramic holder P11 and the metal shell P12, a strain remains that cannot absorb the thermal shock (by the talc P13 or the like). In addition, when the metal shell P12 is rapidly cooled, the high temperature ceramic holder P11 may be rapidly cooled to cause internal stress. In that case,
As shown in FIG. 5D, ring-shaped or vertical cracks may occur in the ceramic holder.

The present invention has been made in order to solve the above-mentioned problems, and when fixing the detection element portion to the metal shell via the ceramic insulator, even if water submersion occurs, cracks or cracks occur. It is an object of the present invention to provide an oxygen sensor structure that does not generate oxygen.

[0009]

In order to achieve the above object, the invention of claim 1 is a rod-shaped detection element portion made of ceramic, and is arranged around the detection element portion and supports the detection element portion. In a oxygen sensor structure comprising: a ceramic insulator that is provided with the metal insulator and a metal shell that is disposed around the ceramic insulator and supports the ceramic insulator, the detection element portion serves as a sealant for the ceramic insulator. The oxygen sensor structure is characterized in that the ceramic insulator is supported by the metal shell on the front end side with respect to the seat surface of the metal shell.

The invention according to claim 2 is the oxygen sensor structure according to claim 1, characterized in that the oxygen sensor is an oxygen sensor using a resistance change type metal oxide as a sensing substance. . A third aspect of the invention provides the oxygen sensor structure according to the first or second aspect, wherein the detection element portion is a plate-shaped member.

The invention according to claim 4 is characterized in that the distance from the seat surface to the support portion on the tip end side is 3 / (minimum thickness A of the side portion of the metal shell) or more. The gist is the oxygen sensor structure according to any one of Items 1 to 3.

The invention of claim 5 is characterized in that the distance from the seat surface to the support portion on the tip end side is 5 / (minimum thickness A of the side portion of the metal shell) or more. The gist is the oxygen sensor structure according to any one of Items 1 to 3.

The invention of claim 6 is characterized in that a gap is provided between the inside of the side of the metal shell and the outside of the side of the ceramic insulator. The oxygen sensor structure is the gist.

According to a seventh aspect of the present invention, the metal shell on the tip end side of the seat surface supports the ceramic insulator, and a part of the stress applied inward in the radial direction of the metal shell is the ceramic insulation. The oxygen sensor structure according to any one of claims 1 to 6, characterized in that the oxygen sensor structure is dispersed in the axial direction of the body.

The invention of claim 8 is characterized in that the support portion on the side of the metal shell and the support portion on the side of the ceramic insulator on the tip side of the seat surface are inclined surfaces with respect to each other. The gist is the oxygen sensor structure according to any one of to.

The invention according to claim 9 is characterized in that a metal plate is arranged between the support portion on the metal shell side and the support portion on the ceramic insulator side on the tip side of the seat surface. The gist is the oxygen sensor structure according to any one of Items 1 to 8.

Here, the tip end side of the detection element section means the measurement target side. Further, as the sensing substance arranged and used at least on the tip side of the detection element portion, for example, a metal oxide (eg, titania) whose resistance value changes depending on the oxygen concentration can be adopted.

As the sealing agent, an inorganic material such as glass or cement can be used. The units of 3 / A and 5 / A are the same [mm] in the denominator and numerator.

[0019]

According to the first aspect of the invention, the detection element portion is sealed in the ceramic insulator by the sealant, and the ceramic insulator is supported by the metal shell on the tip side from the seating surface of the metal shell. . Therefore, even if the rear end side of the metal shell is in contact with water and is subjected to thermal stress inward, for example, the thermal stress in the support portion on the front end side is relatively small, and the heat conduction path due to rapid cooling Becomes longer,
Since the thermal shock of the ceramic insulator is mitigated, it is possible to prevent the ceramic insulator from cracking.

In the invention of claim 2, as the oxygen sensor,
For example, an oxygen sensor using a resistance change type metal oxide such as titania as a sensing substance can be adopted. According to the third aspect of the invention, a plate-shaped member such as an alumina substrate having a sensing substance such as titania laminated thereon can be used as the detection element portion.

In the invention of claim 4, when the length from the seat surface to the supporting portion is 3 / A or more, it is possible to effectively prevent cracks and breaks in the ceramic insulator. According to the invention of claim 5, when the length from the seat surface to the supporting portion is 5 / A or more, it is possible to more reliably prevent cracks and breaks in the ceramic insulator.

According to the invention of claim 6, a gap is provided between the inside of the side of the metal shell and the inside of the side of the ceramic insulator. Therefore, even if thermal stress is applied inward in the radial direction (in the direction of the central axis) due to submergence of the sensor,
Since the side surface of the ceramic insulator is not directly pressed by the gap, it is possible to prevent the occurrence of cracks or breaks.

According to the invention of claim 7, as the structure of the support portion on the tip side, a part of the stress applied inward in the radial direction of the metal shell is configured to be applied in the axial direction of the ceramic insulator. Therefore, even if thermal stress is applied inward in the radial direction due to submergence of the sensor, etc., the stress will be dispersed in the axial direction, so it will not be pressed so much in the radial direction, and as a result, cracks or cracks will occur. It is possible to prevent the occurrence of.

According to the eighth aspect of the present invention, the support portion on the metal shell side and the support portion on the ceramic insulator side are inclined surfaces. Therefore, as in the case of claim 7, even when a thermal stress is applied inward in the radial direction, the stress is dispersed in the axial direction at the inclined surface, and the pressing force in the radial direction decreases,
As a result, it becomes possible to prevent the occurrence of cracks and breaks.

In the ninth aspect of the invention, since the metal plate is placed between the supporting portion on the metal shell side and the supporting portion on the ceramic insulator side, the unevenness of the processing accuracy of the supporting portion results. The influence can be greatly reduced. Therefore, it is possible to disperse the thermal stress applied inward in the radial direction in the axial direction more effectively than in the case of claim 7, and reliably prevent the occurrence of cracks or breaks.

[0026]

Preferred embodiments of the present invention will be described below in order to further clarify the structure and operation of the present invention described above. In each figure, the upper side and the lower side respectively indicate the rear end side and the front end side of the oxygen sensor. (Example 1) As shown in FIG. 1, an oxygen sensor 1 of this example
Is a metal oxide whose resistance changes according to the oxygen concentration as the sensing substance used in the detection element section 3.

The detection element section 3 is formed by laminating a metal oxide 3b such as titania on the tip side (measurement target side) of a long alumina substrate 3a.
An electrode (not shown) is connected to. Terminal fittings 5 (only one of which is shown in the figure) are connected to these electrodes, and lead wires 6 and 7 for extracting signals to the outside are connected to the terminal fittings 5. In addition, a heater (not shown) is formed on the substrate 3a to heat the metal oxide 3b. The heater 8 also has a lead wire 8 and a lead wire 8 via a terminal fitting 4 (only one is shown in the figure). 9 is connected.

The detection element portion 3 is a cylindrical holding member 11 (ceramic holder) made of alumina having a collar portion 11a.
Inside, it is sealed and fixed with glass 13,
The ceramic holder 11 is fixed in a metal shell 17 made of heat-resistant metal via a talc 15. That is, the detection element unit 3 is held by the ceramic holder 11,
The shaft center is fixed so that it extends through the metal shell 17 in the vertical direction in the figure.

Further, a ceramic separator 10 through which the lead wires 6 to 9 penetrate and a waterproof sealing member 21 which is a heat resistant grommet rubber are arranged above the detecting element portion 3. There is a step 10a on the outer circumference of the ceramic separator 10, and the upper end 11b of the ceramic holder 11 is locked at the step 10a.

A metal outer cylinder 16 is fitted on the upper part 17a of the metal shell 17 and is welded all around by, for example, laser welding for waterproofing. Inside the upper portion of the metal outer cylinder 16, caulking such as hexagonal caulking, octagonal caulking, and circular caulking is performed in the radial direction, and the waterproof seal member 2 is formed.
1 is pressed and fixed.

A protective cap 19 is attached to the lower part of the metallic shell 17 to cover the periphery of the tip side of the detection element section 3 (having an opening 19a). A metal gasket 20 is annularly arranged below the seat surface of the metal shell 17. Particularly in this embodiment, a gap 18 having a width of 0.6 mm is provided between the inside of the side of the metal shell 17 and the outside of the side of the ceramic holder 11. The gap dimension is preferably in the range of 0.3 to 1.0 mm because of excellent thermal shock absorption.

Further, the metallic shell 17 and the ceramic holder 11 are in contact with each other on the tip side of the seat surface of the metallic shell 17, and the metallic shell 17 supports the ceramic holder 11 from below in the drawing. Specifically, the inclined surface of the metal shell 17 (supporting portion on the metal shell side) and the inclined surface of the ceramic holder 11 (supporting portion on the ceramic holder side) have a tapered shape inclined by about 60 degrees with respect to the axis center. There is. It is preferable that the inclination angle is in the range of 45 to 75 degrees because the supporting ability is high and the thermal shock absorption is excellent.

Further, as shown in FIG. 2, the distance H from the seat surface of the metallic shell 17 to (the upper end of) the inclined surface is 2.0 mm, and the contact length L is 2.0 mm. . This distance H
Is different in thermal shock resistance depending on the minimum thickness A of the side portion of the metal shell 17, and is preferably 3 / A or more, as described later.
/ A or more is more preferable.

As described above, in the oxygen sensor 1 of the present embodiment, the ceramic holder 11 is supported on the tip side of the seat surface of the metal shell 17, and the side surface is provided between the metal shell 17 and the ceramic holder 11. Since the metal shell 17 and the ceramic holder 11 are supported by the abutting inclined surfaces, there is a remarkable effect of being extremely strong against thermal shock.

That is, for example, when the oxygen sensor 1 is arranged on the downstream side of the catalyst and the oxygen sensor 1 is submerged in water, the rear end side is rapidly cooled, so that a large thermal stress is exerted inward in the radial direction of the metal shell 17. In addition, since the supporting portion of the ceramic holder 11 is provided below the seat surface rather than above the seat surface to which a large thermal stress is applied, the thermal stress applied to the ceramic holder 11 is relatively small. In addition, the ceramic holder 1 due to the metal shell 17 being rapidly cooled
The cooling path of No. 1 becomes longer, and the thermal shock of the ceramic holder 11 is alleviated. As a result, it is possible to prevent the ceramic holder 11 from being cracked or broken.

Further, a large thermal stress is applied above the seat surface, but since a gap 18 is provided on the side surface side between the metal shell 17 and the ceramic holder 11, the thermal stress is applied from the metal shell 17 to the ceramic holder 11. Not directly transmitted to. Therefore, also from this point, it is possible to prevent the occurrence of cracks and breaks.

Further, the metal shell 17 and the ceramic holder 1
Since 1 is supported by the abutting inclined surface, even if a thermal stress is applied in the radial direction, the thermal stress is dispersed in the radial direction and the axial direction, and a large force is exerted in the radial direction. Therefore, also from this point, it is possible to prevent the occurrence of cracks or breaks. <Experimental Example 1> Next, an experimental example performed for confirming the effect of the present embodiment will be described.

As shown in FIG. 3 (a), the oxygen sensor (upper about 60 mm) having the structure of the first embodiment is attached to a plate material through a metal gasket (stainless steel; 1.0 mm thickness),
It was heated with a burner from below. Then, as shown in FIG. 3B, the submergence of the upper part of the oxygen sensor is repeated (600
Then, the temperature of the metal shell at that time was measured with a K thermocouple.

This experiment was carried out for each of the sample No. 3 shown in Table 1 below, that is, for each of the oxygen sensors having the thickness A and the distance H (see FIG. 2) three times, and the presence or absence of cracks was examined. The results are also shown in Table 2. In Table 1, 3 / A, 5
The calculated value of / A is also shown. Further, in Test 1 of Table 1, the temperature at the time of water injection is 350 ° C., and in Test 2, the temperature is 400 ° C. which is a higher temperature (severe condition).

Further, in consideration of variations in the surface roughness of the inclined surface during manufacturing, similar experiments were conducted using the oxygen sensors of Sample Nos. 3 to 6. The results are shown in Table 2 below. The number of samples was 100 each.

[0041]

[Table 1]

[0042]

[Table 2]

As is clear from Tables 1 and 2, it can be seen that cracks are unlikely to occur when the support portion is located on the tip side of the seat surface. It should be noted that cracks tend to be less likely to occur as the support portion is located closer to the tip end side. It is also understood that the number of cracks is reduced when the distance H is 3 / A or more. Furthermore, the distance H is 5
It can be seen from, for example, sample Nos. 5 and 6 in Table 2 that the number of cracks is further reduced when / A or more. In Tables 1 and 2, ◯ indicates that the condition of 3 / A or 5 / A was satisfied, and x indicates that the condition was not satisfied. (Embodiment 2) The oxygen sensor 31 of this embodiment is shown in FIG.
As shown in, the supporting portion of the metal shell 33 (the inclined surface 33a)
A metal plate packing 37 made of, for example, a stainless steel plate or the like is arranged between the and the supporting portion (the inclined surface 35a) of the ceramic holder 35. The plate packing 37 has a ring shape, a thickness of 0.3 to 0.5 mm, and a Vickers hardness of 200 to 600.

In this embodiment, if the plate packing 37 having a smooth surface is used, the supporting portion of the metal shell 33 and the ceramic holder 35 becomes smoother than that without the plate packing 37. Even if a thermal stress is applied in the radial direction, the stress can be reliably dispersed in the axial direction, and there is an effect that the adaptability to the thermal stress is high.

When the plate packing 37 is used, the inclined surface 3 between the metal shell 33 and the ceramic holder 35 is used.
Since 3a and 35a do not need to be so smooth,
There is an advantage that it is advantageous in processing. <Experimental Example 2> Further, the same experiment as in Experimental Example 1 was performed on the oxygen sensor having the structure of Example 2.
Samples Nos. 3 and 4 were used by counterboring the metal shell by the thickness of the plate packing (100 for each).
Individual). The results are shown in Table 3 below.

[0046]

[Table 3]

As is clear from Table 3, the number of cracks generated is smaller in the case where the plate packing is used than in the case where the plate packing in Table 2 is not used, which is more preferable. . The thicker the plate packing, the higher the effect. (Embodiment 3) The oxygen sensor 41 of this embodiment is shown in FIG.
As shown in, the supporting portion of the metal shell 43 (slope 43a)
The upper end 47a of the protective cap 47 is disposed between the supporting portion of the ceramic holder 45 (the inclined surface 45a). That is, the radial side surface 47 of the protective cap 47.
The upper part of b is the side surface of the metal shell 43 and the ceramic holder 4
5 and the upper end 47a thereof.
Are arranged in a tapered shape so as to spread outward, and are arranged between the inclined surfaces 43a and 45a. With this configuration, the same effect as the plate packing of the second embodiment is obtained.

The embodiments of the present invention have been described above.
The present invention is not limited to these examples, and it goes without saying that the present invention can be implemented in various modes without departing from the gist of the present invention. For example, the oxygen sensor described above is suitable because, for example, when it is arranged on the downstream side of a catalyst that purifies exhaust gas of a vehicle, it can exhibit its function even if it receives a large thermal shock due to submersion in water, etc. It is not limited to the position. For example, even if it is arranged under the floor of the vehicle, such as upstream of the catalyst, it can sufficiently exhibit its function.

[0049]

As described above in detail, in the invention of claim 1, the detection element portion is sealed by the sealant in the ceramic insulator, and the ceramic insulation is provided on the tip side from the seat surface of the metal shell. The body is supported by the metal shell. Therefore, even if the rear end side of the metal shell is exposed to water, for example, and inward in the radial direction, thermal stress is not applied to the ceramic insulator so much that cracks and cracks are prevented. It has a remarkable effect that it can be done.

According to the invention of claim 2, as the oxygen sensor,
For example, an oxygen sensor using a resistance change type metal oxide such as titania as a sensing substance can be adopted. According to the third aspect of the invention, a plate-shaped member such as an alumina substrate having a sensing substance such as titania laminated thereon can be used as the detection element portion. In particular, the plate-shaped member can be suitably attached to the metal shell having the cylindrical through hole via, for example, the cylindrical ceramic insulator having the plate cross-sectional through hole.

According to the fourth aspect of the present invention, when the distance from the seat surface to the supporting portion on the tip side is 3 / A or more, cracks and breaks in the ceramic insulator can be effectively prevented.
In the invention of claim 5, when the distance from the seat surface to the support portion on the tip end side is 5 / A or more, cracks and breaks in the ceramic insulator can be prevented more effectively.

In the invention of claim 6, since the gap is provided between the inside of the side of the metal shell and the outside of the side of the ceramic insulator, the metal shell and the ceramic insulator are in direct contact with each other on that side. Not not. Therefore, even if thermal stress is applied inward in the radial direction due to submergence of the sensor or the like, the side surface of the ceramic insulator is not directly pressed, and thus cracks and breaks can be prevented.

In the invention of claim 7, as the structure of the support portion on the tip side, a part of the stress applied inward in the radial direction of the metal shell is configured to be applied in the axial direction of the ceramic insulator. Therefore, even if a thermal stress is applied inward in the radial direction due to the immersion of the sensor in water, the stress is dispersed in the axial direction and the pressing force in the radial direction is reduced, so that cracks or breaks can be prevented.

According to the eighth aspect of the invention, since the supporting portions are inclined surfaces with each other, even if a thermal stress is applied inward in the radial direction, the stress is dispersed in the axial direction and the pressing force in the radial direction is reduced. As a result, cracks and breaks can be prevented. In the invention of claim 9, since the metal plate is sandwiched between both the supporting portions of the metal shell and the ceramic insulator, the unevenness of the surface in the supporting portions is reduced. As a result, cracks and breaks can be prevented more effectively than in the eighth aspect.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a partially broken oxygen sensor of Example 1.

FIG. 2 shows a main part of the oxygen sensor of Example 1, (a)
Is an explanatory view showing a supporting portion thereof, and (b) is an explanatory view showing a minimum thickness A of the metal shell.

FIG. 3 is an explanatory diagram showing an experimental method.

4A and 4B show another embodiment, FIG. 4A is an explanatory view showing a main part of the oxygen sensor of the first embodiment, and FIG. 4B is an explanatory view showing a main part of the oxygen sensor of the third embodiment.

FIG. 5 is an explanatory diagram showing a conventional technique.

[Explanation of symbols]

 1, 3151 ... Oxygen sensor 3 ... Detection element part 11, 35, 45 ... Ceramic holder (holding member) 17, 33, 43 ... Metal shell

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takao Kojima 14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi Nihon Special Ceramics Co., Ltd.

Claims (9)

[Claims] 1. A rod-shaped detection element portion made of ceramic, a ceramic insulator disposed around the detection element portion and supporting the detection element portion, and disposed around the ceramic insulator, In an oxygen sensor structure including a metal shell supporting a ceramic insulator, the detection element portion is sealed to the ceramic insulator with a sealant, and at a tip side of a seat surface of the metal shell. An oxygen sensor structure, wherein the ceramic insulator is supported by a metal shell. 2. The oxygen sensor structure according to claim 1, wherein the oxygen sensor is an oxygen sensor using a resistance change type metal oxide as a sensing substance. 3. The oxygen sensor structure according to claim 1, wherein the detection element section is a plate-shaped member. 4. The distance from the seat surface to the support portion on the tip end side is 3 / (minimum thickness A of the side portion of the metal shell) or more, according to any one of claims 1 to 3. The oxygen sensor structure according to any one of the above. 5. The method according to claim 1, wherein the distance from the seat surface to the support portion on the tip end side is 5 / (minimum thickness A of the side portion of the metal shell) or more. The oxygen sensor structure according to any one of the above. 6. The oxygen sensor structure according to claim 1, wherein a gap is provided between a side inner side of the metal shell and a side outer side of the ceramic insulator. 7. The structure in which the metallic shell on the tip end side of the seat surface supports the ceramic insulator is such that a part of the stress applied inward in the radial direction of the metallic shell is in the axial direction of the ceramic insulator. The oxygen sensor structure according to any one of claims 1 to 6, wherein the oxygen sensor structure is configured to be dispersed. 8. The metal shell side supporting portion and the ceramic insulator side supporting portion on the tip end side of the seat surface are inclined surfaces with respect to each other. The oxygen sensor structure described. 9. The metal plate according to claim 1, wherein a metal plate is arranged between a support portion on the side of the metal shell and a support portion on the side of the ceramic insulator on the front end side of the seat surface. The oxygen sensor structure according to any one of the above.