JP7050584B2 - Sensor - Google Patents

Description

The present invention is a sensor including a sensing unit that detects the state of the gas to be measured, a tubular cover body that surrounds the radial circumference of the sensing unit, and a tubular housing to which the rear end side of the cover body is fixed. Regarding.

A sensor having a sensing unit that detects the state of the gas to be measured, a tubular cover body that surrounds the radial circumference of the sensing unit, and a tubular housing to which the rear end side of the cover body is fixed is known. There is.
Examples of the above sensors include gas sensors such as oxygen sensors, NOx sensors, and HC sensors for detecting the concentration of the measured gas such as exhaust gas, temperature sensors for detecting the temperature of the measured gas, and measured gas. Examples thereof include a pressure sensor for detecting pressure, a humidity sensor for detecting the humidity of the gas to be measured, and a fine particle sensor for detecting the amount of particles in the gas to be measured.

Further, as a gas sensor, there is a gas sensor whose cover body is composed of Inconel 601 (registered trademark), SUS310S, or the like (Patent Document 1). In this gas sensor, a cover body is attached to the tip of the housing by welding.

International Publication No. 2013/024579 (paragraph 0014)

However, in the cover body made of SUS310S, there is a possibility that the welded portion is oxidatively reduced in weight in the thermal cycle and the cover body may fall off. Inconel 601 (registered trademark) can prevent the welded part from being oxidized and reduced in the cold cycle and the cover body from falling off, but it is assumed that it will be exposed to high temperatures for a long time under the recent engine environment. At that time, it was found that embrittlement progressed and the cover body may be cracked.
In particular, since the rear end portion of the cover body is fixed to the tubular housing, the cover body is stressed due to the shape distortion being applied to the tubular shape, so that cracks are more likely to occur. Further, when the cover body becomes thinner as the sensor becomes smaller and lighter, cracks tend to occur more easily.

The present invention has been made in view of the present situation, and an object of the present invention is to provide a sensor which is excellent in brittleness and oxidation resistance in a high temperature environment and can suppress the occurrence of falling off or cracking of a cover body. ..

The sensor of the present invention is a sensor that extends in the axial direction from the rear end side to the front end side and is attached to the exhaust pipe of the internal combustion engine, and has a sensing unit that detects the state of the mass to be measured flowing in the exhaust pipe, and the above. In a sensor provided with a tubular cover body that surrounds the radial circumference of the sensing portion and a tubular housing to which the rear end side of the cover body is fixed, while at least a part of itself is exposed in the exhaust pipe. The cover body is Cr: 18% by mass or more and 22% by mass or less, Ni: 7% by mass or more and 12% by mass or less, Si: 1.0% by mass or more and 3.0% by mass or less, C: 0.08% by mass. Hereinafter, Mn: 2.0% by mass or less, P: 0.04% by mass or less, S: 0.01% by mass or less, Nb: 0.05% by mass or more and 0.3% by mass or less and N: 0.1% by mass. % Or more and 0.25% by mass or less, REM: 0.001% by mass or more and 0.1% by mass or less, and the balance is composed of austenite-based stainless steel composed of Fe and unavoidable impurities. ..

According to this sensor, the austenitic stainless steel constituting the cover body can be used in a high temperature environment (for example, 1050 [° C.]) as compared with SUS310S, as shown in the comparative measurement result (FIG. 2) described later. , Has the property of being less prone to embrittlement. Further, even in a high temperature environment, the austenitic stainless steel has excellent oxidation resistance and can suppress the occurrence of cracks in the cover body.
Further, since the cover body provided in the sensor of the present invention has the same strength as the conventional cover body composed of SUS310S, it can be used as a cover body in place of the conventional cover body.

In the sensor of the present invention, the cover body may be provided with a plurality of gas flow ports on the side wall.
The present invention is further effective because the cover body provided with the gas flow port tends to be more likely to be cracked by further applying processing stress when forming the flow port.

In the sensor of the present invention, the rear end portion of the side wall of the cover body may be fixed to the tip end portion of the housing via a welded portion.
Since the cover body fixed via the welded portion tends to undergo oxidative weight loss at the welded portion, the present invention is further effective.

According to the present invention, it is possible to obtain a sensor which is excellent in brittleness and oxidation resistance in a high temperature environment and can prevent the cover body from falling off or cracking.

It is sectional drawing which shows the whole structure of the all area air-fuel ratio sensor of 1st Embodiment. It is a measurement result of the comparative measurement between the first embodiment and the comparative example. It is sectional drawing which shows the whole structure of the oxygen sensor of 2nd Embodiment. It is a figure which shows the cross-sectional SEM image of the structure of the material of an Example. It is a figure which shows the cross-sectional SEM image of the structure of the material of the comparative example.

Hereinafter, embodiments to which the present invention has been applied will be described with reference to the drawings.
It is needless to say that the present invention is not limited to the following embodiments, and various forms can be adopted as long as they belong to the technical scope of the present invention.

[1. First Embodiment]
[1-1. overall structure]
FIG. 1 is a cross-sectional view showing an overall configuration of an all-region air-fuel ratio sensor 2 (hereinafter, also referred to as an air-fuel ratio sensor 2) according to an embodiment to which the present invention is applied.

The air-fuel ratio sensor 2 is a type of gas sensor, and is attached to the exhaust pipe of an internal combustion engine for use in, for example, air-fuel ratio feedback control in an automobile or various internal combustion engines. Further, the air-fuel ratio sensor 2 is configured to include a gas detection element that detects oxygen (measured gas) in the exhaust gas to be measured.

The air-fuel ratio sensor 2 includes a housing 38, a gas detection element 4, a cover body 42, a ceramic sleeve 6, an insulating contact member 66, and five connection terminals 10.
The housing 38 is a tubular member having a threaded portion 39 formed on the outer surface for fixing to the exhaust pipe of an internal combustion engine, and is made of SUS430. The gas detection element 4 has a plate-like shape extending in the axial direction (longitudinal direction of the air-fuel ratio sensor 2: vertical direction in the figure). The cover body 42 is a bottomed cylindrical member fixed to the outer periphery of the tip side of the housing 38 so as to cover the periphery of the tip portion of the gas detection element 4. The ceramic sleeve 6 is a tubular member arranged so as to surround the radial circumference of the gas detection element 4. The insulating contact member 66 is arranged so that the inner wall surface of the contact insertion hole 68 penetrating in the axial direction surrounds the periphery of the rear end portion of the gas detection element 4. The five connection terminals 10 are metal members arranged between the gas detection element 4 and the insulating contact member 66.

The gas detection element 4 has a plate-like shape extending in the axial direction, and a sensing portion 8 covered with a protective layer is formed on the front end side (lower part in the figure) directed to the gas to be measured, and the rear end side (figure). Electrode terminal portions 30, 31, 32, 34, 36 are formed on the first plate surface 21 and the second plate surface 23, which are in a positional relationship between the front and back surfaces of the outer surface (middle and upper). When the gas to be measured comes into contact with the sensing unit 8, the gas detection element 4 outputs a sensor output signal according to a state such as the concentration of the gas to be measured from the electrode terminal unit to the outside.

By arranging the connection terminal 10 between the gas detection element 4 and the insulating contact member 66, the connection terminal 10 is electrically connected to the electrode terminal portions 30, 31, 32, 34, 36 of the gas detection element 4, respectively. Further, the connection terminal 10 is also electrically connected to the lead wire 46 disposed inside the sensor from the outside, and the external device to which the lead wire 46 is connected and the electrode terminal portions 30, 31, 32, 34. , 36 to form a current path for the current flowing between them.

The housing 38 has a through hole 54 penetrating in the axial direction, and is configured in a substantially cylindrical shape having a shelf portion 52 protruding inward in the radial direction of the through hole 54. The housing 38 is provided in the through hole 54 in a state where the sensing portion 8 is arranged outside the tip end side of the through hole 54 and the electrode terminal portions 30, 31, 32, 34, 36 are arranged outside the rear end side of the through hole 54. Holds the inserted gas detection element 4. The shelf portion 52 is formed as an inwardly tapered surface having an inclination with respect to a plane perpendicular to the axial direction.

Inside the through hole 54 of the housing 38, an annular ceramic holder 51, a powder packed bed 53, 56 (hereinafter, also referred to as a talc ring 53, 56), and a state of surrounding the radial circumference of the gas detection element 4 are provided. The above-mentioned ceramic sleeves 6 are laminated in this order from the front end side to the rear end side.

A crimp packing 57 is arranged between the ceramic sleeve 6 and the rear end portion 40 of the housing 38. The rear end portion 40 of the housing 38 is crimped so as to press the ceramic sleeve 6 toward the tip end side via the crimping packing 57.

A metal holder 58 for maintaining airtightness is arranged between the ceramic holder 51 and the shelf portion 52 of the housing 38. The metal holder 58 also has a function of holding the talc ring 53 and the ceramic holder 51.

That is, the housing 38 has a configuration that surrounds the radial circumference of the gas detection element 4 with the sensing portion 8 protruding from the tip.
The gas detection element 4 has a plate-like shape having a rectangular shaft cross section in which an element portion formed in a plate shape extending in the axial direction and a heater formed in the same plate shape extending in the axial direction are laminated. Is formed in. Since the gas detection element 4 used as the air-fuel ratio sensor 2 is conventionally known, detailed description of its internal structure and the like will be omitted.

As shown in FIG. 1, in the gas detection element 4, the sensing portion 8 on the tip side (lower side in FIG. 1) protrudes from the tip of the housing 38, and the electrode terminal portions 30, 31, 32, 34 on the rear end side, 36 is fixed to the inside of the housing 38 in a state of protruding from the rear end of the housing 38.

An outer cylinder 44 is fixed to the outer periphery of the rear end side of the housing 38. In the opening on the rear end side (upper side in FIG. 1) of the outer cylinder 44, five lead wires electrically connected to the electrode terminal portions 30, 31, 32, 34, 36 of the gas detection element 4, respectively. A grommet 50 having a lead wire insertion hole 61 through which 46 (three are shown in FIG. 1) is inserted is arranged.

Further, an insulating contact member 66 is arranged on the rear end side (upper side in FIG. 1) of the gas detection element 4 protruding from the rear end portion 40 of the housing 38. The insulating contact member 66 is arranged around the electrode terminal portions 30, 31, 32, 34, 36 formed on the surface of the gas detection element 4 on the rear end side.

[1-2. Cover body composition]
The cover body 42 is formed in a bottomed cylindrical shape having a plurality of gas flow ports, and is attached to the outer periphery of the tip end side (lower side in FIG. 1) of the housing 38 in a state of covering the protruding portion of the gas detection element 4. There is. The cover body 42 is fixed to the housing 38 via the welded portion 43.

The cover body 42 is formed in a double structure including a bottomed tubular outer tubular member 81 and a bottomed tubular inner tubular member 91 arranged inside the outer tubular member 81. There is.
The outer cylindrical member 81 includes a cylindrical outer side wall 82 and an outer bottom wall 83 provided on the tip end side of the outer side wall 82. The outer cylindrical member 81 is provided with a plurality of (8 in this embodiment) outer wall gas flow ports 84 on the outer side wall 82.

The inner tubular member 91 includes a tubular inner side wall 92 arranged inside the outer side wall 82, and an inner bottom wall 93 provided on the tip end side of the inner side wall 92. The inner tubular member 91 is provided with a plurality of (8 in this embodiment) inner wall gas flow ports 94 on the inner side wall 92.

The inner side wall 92 is configured to include a fixing portion 95, a fixing step portion 96, a maximum inner diameter portion 97, a dimension changing step portion 98, and a minimum inner diameter portion 99 from the rear end side to the tip end side in the axial direction.
The dimension change step portion 98 is formed in a plate surface shape perpendicular to the axial direction, and is provided for changing the inner diameter dimension of the inner side wall 92 in the cross section perpendicular to the axial direction. The maximum inner diameter portion 97 is formed so that the inner diameter dimension in the cross section perpendicular to the axial direction is equal to the maximum inner diameter dimension of the dimension change step portion 98. The minimum inner diameter portion 99 is formed so that the inner diameter dimension in the cross section perpendicular to the axial direction is equal to the minimum inner diameter dimension of the dimension change step portion 98.

The inner wall gas flow port 94 is formed at a plurality of locations in the circumferential direction at the minimum inner diameter portion 99 of the inner side wall 92.
The inner cylindrical member 91 includes an inner bottom wall distribution port 100 for discharging the gas to be measured from the inside of the inner tubular member 91 to the outside in the inner bottom wall 93.

On the other hand, the outer wall gas flow ports 84 are formed at a plurality of locations in the circumferential direction at positions corresponding to the maximum inner diameter portion 97 of the inner side wall 92 of the outer side wall 82. That is, the outer wall gas flow port 84 is formed at a different position in the axial direction from the inner wall gas flow port 94.

Further, the outer cylindrical member 81 is configured to include an outer bottom wall distribution port 85 for discharging the measured gas from the inside of the outer tubular member 81 to the outside on the outer bottom wall 83.
The outer tubular member 81 and the inner tubular member 91 of the cover body 42 are Cr (chromium) of 18% by mass or more and 22% by mass or less, Ni (nickel) of 7% by mass or more and 12% by mass or less, 1.0. Si (silicon) of mass% or more and 3.0 mass% or less, C (carbon) of 0.08 mass% or less, Mn (manganese) of 2.0 mass% or less, P (phosphorus) of 0.04 mass% or less , S (sulfur) of 0.01% by mass or less, Nb (niob) of 0.05% by mass or more and 0.3% by mass or less, and N (nitrogen) of 0.1% by mass or more and 0.25% by mass or less, 0 It contains REM (rare earth metal) of .001% by mass or more and 0.1% by mass or less, and is composed of a material made of austenite-based stainless steel whose balance is Fe (iron) and unavoidable impurities.

C improves the brittleness of the cover body in a high temperature environment, but when the content of C exceeds 0.08% by mass, a Cr compound is likely to be produced, so that intergranular corrosion is likely to occur.
Si becomes an oxide instead of Fe to improve oxidation resistance (oxidation loss). If the Si content is less than 1.0% by mass, the effect of improving the oxidation resistance is insufficient, and if it exceeds 3.0% by mass, brittleness is likely to occur at a high temperature.
Mn improves the brittleness of the material of the present invention in a high temperature environment, but deteriorates the oxidation resistance when the Mn content exceeds 2.0% by mass.
Ni is an element that ensures heat resistance, and if the Ni content is less than 7.0% by mass, the heat resistance becomes insufficient, and if it exceeds 12.0% by mass, the raw material cost increases.
Cr is an element that ensures heat resistance, and if the Cr content is less than 18.0% by mass, the heat resistance becomes insufficient, and if it exceeds 22.0% by mass, it tends to become brittle at high temperatures.
Nb improves the high-temperature strength of the cover body in a high-temperature environment. If the Nb content is less than 0.05% by mass, the high-temperature strength cannot be secured, and if it exceeds 0.30% by mass, the toughness is lowered. ..
N needs to be contained in an amount of 0.1% by mass or more in order to improve the high temperature strength by strengthening the solid solution. However, if N is contained in excess of 0.25% by mass, brittleness is likely to occur due to the formation of Cr nitride.
Since P is an element that impairs the hot workability of austenitic stainless steel, it is preferable to reduce the content as much as possible, so the content is 0.04% by mass or less.
Since S is an element that impairs the hot workability of austenitic stainless steel like P, it is preferable to reduce the content as much as possible, so the content is preferably 0.01% by mass or less.
REM is effective in improving the high temperature oxidation resistance, improves the exfoliation property of the oxidation scale due to repeated oxidation, and lowers the oxidation rate. In order to exert such an action, it is necessary to contain REM in a total amount of 0.001% by mass or more. However, if the total content of REM exceeds 0.1% by mass, the austenitic stainless steel may be hardened and the raw material cost may increase. Therefore, when REM is contained, the total content of REM should be 0.001% by mass or more and 0.1% by mass or less.
The composition as described above prevents cracks.

The total value of each component in the material constituting the cover body 42 is 100% by mass. The balance may contain unavoidable impurities in addition to Fe. It is desirable that the number of unavoidable impurities is as small as possible.

With the above composition, the cover body is excellent in brittleness and oxidation resistance in a high temperature environment, and can prevent the cover body from falling off or cracking.

[1-3. Comparative measurement of cover material]
The comparison measurement result of the material constituting the cover body 42 (outer tubular member 81 and inner tubular member 91) of the present embodiment with SUS310S will be described.

Comparative measurements were performed for high temperature embrittlement. The component of SUS310S is 20Ni-25Cr.
In the comparative measurement of high temperature embrittlement, after holding at 1050 ° C. for 500 hours in an air atmosphere, a cross-sectional image of the structure was obtained, and it was visually determined whether or not the crystal grains were coarsened from before the test.

The measurement results of the comparative measurement are shown in FIGS. 2, 4, and 5. In FIG. 2, the material of this embodiment is described as an example, and SUS310S is described as a comparative example. 4 and 5 show cross-sectional SEM images of the structures of the materials of Examples and Comparative Examples, respectively.
As shown in the measurement results of FIG. 2, regarding the high temperature embrittlement at a high temperature (1050 ° C.), the material constituting the cover body 42 of the present embodiment had almost no crystal grains larger than those before the test. , SUS310S is considered to have coarsened crystal grains and high temperature embrittlement. From this, it can be seen that the material constituting the cover body 42 of the present embodiment is less likely to cause high temperature embrittlement at a high temperature (1050 ° C.) than SUS310S.

[1-4. effect]
As described above, in the all-region air-fuel ratio sensor 2 of the present embodiment, the cover body 42 has Cr (chromium) of 18% by mass or more and 22% by mass or less and Ni (nickel) of 7% by mass or more and 12% by mass or less. ), Si (silicon) of 1.0% by mass or more and 3.0% by mass or less, C (carbon) of 0.08% by mass or less, Mn (manganese) of 2.0% by mass or less, 0.04% by mass or less P (phosphorus), S (sulfur) of 0.01% by mass or less, Nb (niob) of 0.05% by mass or more and 0.3% by mass or less, and N of 0.1% by mass or more and 0.25% by mass or less. It contains (nitrogen), 0.001% by mass or more and 0.1% by mass or less of REM (rare earth metal), and the balance is composed of austenite-based stainless steel consisting of Fe (iron) and unavoidable impurities. ..

According to the above-mentioned comparative measurement results, the cover body 42 is less likely to be embrittled in a high temperature environment than the conventional cover body composed of SUS310S, so that cracks may occur due to the embrittlement. The sex becomes low. Further, since it has excellent oxidation resistance, it is less likely that it will fall off from the housing 38.
Therefore, according to the all-region air-fuel ratio sensor 2 of the present embodiment, the cover body 42 is excellent in brittleness and oxidation resistance in a high temperature environment, and it is possible to prevent the cover body 42 from falling off or cracking.

[2. Other embodiments]
Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and can be carried out in various embodiments without departing from the gist of the present invention.

For example, in the above embodiment, the cover body having a double structure including the outer tubular member and the inner tubular member has been described as the cover body, but the cover body is not limited to such a form. Specifically, it may be a cover body having a single structure including only an outer tubular member. Alternatively, it may be a cover body having a triple structure including an outer cylindrical member, an intermediate tubular member, and an inner tubular member.

For example, in the above embodiment, the air-fuel ratio sensor that detects the oxygen concentration in the exhaust gas has been described as an example of the sensor, but the present invention is not limited to this, and the concentration of gas types other than oxygen such as NOx sensor and HC sensor is detected. Gas sensors, temperature sensors that detect the temperature of the gas to be measured, pressure sensors that detect the pressure of the gas to be measured, humidity sensors that detect the humidity of the gas to be measured, fine particle sensors that detect the amount of particles in the gas to be measured, etc. It can be applied to a sensor attached to the exhaust pipe of an internal combustion engine to detect the state of the gas to be measured (concentration, temperature, humidity, pressure, particle amount, etc.).

Further, in the above embodiment, the tubular member made of SUS430 is exemplified as the housing, but the present invention is not limited to this, and any tubular member may be used, and an insulating porcelain tube such as a metal tube or alumina may be used. ..

Further, the gas detection element is not limited to the plate shape as described above, and may be a gas detection element having a bottomed cylindrical shape.
Here, as a second embodiment, a gas sensor 101 (oxygen sensor 101) including a cylindrical detection element 104 having a bottomed cylindrical shape will be briefly described. The oxygen sensor 101 is used, for example, for detecting the concentration of oxygen in the exhaust gas of an internal combustion engine.

A cross-sectional view showing the overall configuration of the gas sensor 101 (oxygen sensor 101) is shown in FIG.
As shown in the figure, the oxygen sensor 101 includes a bottomed cylindrical detection element 104, a housing 138, and a cover body 142.

The tubular detection element 104 is composed of a solid electrolyte body containing zirconia as a main component, and is formed in a bottomed tubular shape extending in the axial direction and having a closed tip (lower side in the figure). The tubular detection element 104 has a sensing unit 108 at its tip that comes into contact with the gas to be measured. The tubular detection element 104 is heated by a rod-shaped ceramic heater 103 arranged inside the tubular detection element 104, and is in an activated state in which oxygen can be detected.

The housing 138 surrounds the radial circumference of the tubular detection element 104 with the sensing portion 108 protruding from the tip, and houses the internal structure of the oxygen sensor 101. Further, the housing 138 is provided for fixing the oxygen sensor 101 to a mounting portion such as an exhaust pipe of an internal combustion engine.

The cover body 142 is fixed to the housing 138 so as to cover the sensing portion 108 of the tubular detection element 104. The cover body 142 is formed in a double structure including a bottomed tubular outer tubular member 181 and a bottomed tubular inner tubular member 191 arranged inside the outer tubular member 181. There is. The welded portion 143 between the cover body 142 and the housing 138 is formed by laser welding or the like.

The outer tubular member 181 and the inner tubular member 191 of the cover body 142 are each made of the same material as the cover body 42 of the first embodiment.
Therefore, the oxygen sensor 101 is excellent in brittleness and oxidation resistance in a high temperature environment, and can prevent the cover body from falling off or cracking, like the all-region air-fuel ratio sensor 2 of the first embodiment.

2 ... All area air-fuel ratio sensor (air-fuel ratio sensor), 4 ... Gas detection element, 8,108 ... Sensing part, 38,138 ... Housing, 42,142 ... Cover body, 43,143 ... Welded part, 81,181 ... Outer tubular member, 91,191 ... Inner tubular member, 101 ... Gas sensor (oxygen sensor), 104 ... Cylindrical detection element

Claims (3)

A sensor that extends in the axial direction from the rear end side to the front end side and is attached to the exhaust pipe of an internal combustion engine.
A sensing unit that detects the state of the gas to be measured flowing in the exhaust pipe, and
At least a part of itself is exposed in the exhaust pipe, and a tubular cover body that surrounds the radial circumference of the sensing portion and
A tubular housing to which the rear end side of the cover body is fixed, and
In a sensor equipped with
The cover body
Cr: 18% by mass or more and 22% by mass or less, Ni: 7% by mass or more and 12% by mass or less, Si: 1.0% by mass or more and 3.0% by mass or less, C: 0.08% by mass or less, Mn: 2. 0% by mass or less, P: 0.04% by mass or less, S: 0.01% by mass or less, Nb: 0.05% by mass or more and 0.3% by mass or less and N: 0.1% by mass or more and 0.25% by mass % Or less, REM: 0.001% by mass or more and 0.1% by mass or less, and the balance is composed of austenite-based stainless steel composed of Fe and unavoidable impurities. The sensor according to claim 1, wherein the cover body is provided with a plurality of gas flow ports on a side wall. The sensor according to claim 1 or 2, wherein the cover body has a rear end portion of a side wall fixed to a front end portion of the housing via a welded portion.

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