JP6839236B2 - Gas sensor - Google Patents

Description

The present invention relates to a gas sensor.

Conventionally, a gas sensor that detects a specific gas concentration such as NOx in a gas to be measured such as an exhaust gas of an automobile has been known. For example, Patent Document 1 describes a gas sensor including a sensor element, an insulator that inserts and holds the sensor element, a housing that inserts and holds the insulator, and an element cover fixed to the housing.

Japanese Unexamined Patent Publication No. 2007-178418

By the way, when such a gas sensor is used, it is heated by a gas to be measured such as an exhaust gas, so that the insulator expands. However, in Patent Document 1, such expansion of the insulator is not particularly considered. Therefore, stress from the housing may be applied when the insulator is expanded, which may cause damage such as cracks in the insulator.

The present invention has been made to solve such a problem, and an object of the present invention is to suppress damage to a ceramic member due to heating.

That is, the present invention has adopted the following means in order to achieve the above-mentioned main object.

The gas sensor of the present invention
A long sensor element that can detect a specific gas concentration in the gas to be measured, and
A columnar ceramic member through which the sensor element penetrates in the axial direction,
The ceramic member has a through hole inserted in the axial direction, and has a gap between the inner peripheral surface of the through hole and the ceramic member, and the radial distance W1 of the gap is 20 μm or more. With a tubular housing that is
It is equipped with.

In this gas sensor, a gap is formed between the inner peripheral surface of the through hole of the housing and the ceramic member, and the radial distance W1 of the gap is 20 μm or more. The presence of such a gap reduces the radial stress from the housing when the ceramic member expands due to heating. Therefore, damage to the ceramic member due to heating can be suppressed.

In the gas sensor of the present invention, the distance W1 may be 500 μm or less. By doing so, it is possible to prevent gas (for example, the gas to be measured or the atmosphere) from flowing in the axial direction through the gap between the housing and the ceramic member, and it becomes difficult for the gas to condense in the gap, for example, corrosion of the housing or the like. It is less likely to occur. As a result, it is possible to suppress a decrease in airtightness between one end side and the other end side of the sensor element.

The gas sensor of the present invention includes a protective cover that covers the tip end side of the sensor element and allows the flow of the gas to be measured to flow inside, and the ceramic member has a cylindrical large-diameter portion and the large-diameter portion. It has a columnar small diameter portion that is located closer to the protective cover side and has an outer diameter smaller than that of the large diameter portion, and the distance W1 is the outer peripheral surface of the small diameter portion and the inside of the through hole. It may be the radial distance of the gap with the peripheral surface. That is, there may be a gap between the outer peripheral surface of the small diameter portion of the ceramic member and the inner peripheral surface of the through hole of the housing, and the radial distance W1 of this gap may be 20 μm or more. When the ceramic member has a large diameter portion and a small diameter portion, the small diameter portion closer to the protective cover is more likely to be heated by the gas to be measured and is therefore more likely to be damaged. Therefore, since there is a gap of 20 μm or more between the small diameter portion and the inner peripheral surface of the housing, for example, as compared with the case where there is a gap only between the large diameter portion and the inner peripheral surface of the housing, heating is performed. Damage to the ceramic member can be further suppressed.

In the gas sensor of the present invention in which the ceramic member includes a large-diameter portion and a small-diameter portion, the ceramic member has a gap between the large-diameter portion and the inner peripheral surface of the through hole, and the diameter of the gap. The distance W2 in the direction may be 5 μm or more. Since there is a gap not only between the small diameter portion and the inner peripheral surface of the housing but also between the large diameter portion and the inner peripheral surface of the housing, the ceramic member expands due to heating in the radial direction from the housing. The stress is further reduced. Therefore, damage to the ceramic member due to heating can be further suppressed.

In the gas sensor of the present invention in which the ceramic member includes a large diameter portion and a small diameter portion, the distance W2 may be 500 μm or less. By doing so, it is possible to suppress the gas from flowing in the axial direction through the gap between the housing and the ceramic member, and the gas is less likely to condense in the gap, and for example, the housing and the like are less likely to be corroded. As a result, it is possible to suppress a decrease in airtightness between one end side and the other end side of the sensor element.

In the gas sensor of the present invention in which the ceramic member includes a large-diameter portion and a small-diameter portion, the ratio W1 / W2, which is the ratio of the distance W1 to the distance W2, may be a value of 1 or more. In this way, when the gas sensor is heated, the large-diameter portion, which is far from the protective cover and therefore difficult to heat, is more likely to come into contact with the housing before the small-diameter portion. As a result, the small-diameter portion that is easily heated and easily expands thermally does not come into contact with the housing, or even if it comes into contact, the radial stress from the housing is relaxed. Therefore, damage to the ceramic member can be further suppressed.

In the gas sensor of the present invention in which the ceramic member has a large diameter portion and a small diameter portion, the housing has a first cylinder in which the inner peripheral surface forms a part of the through hole and the small diameter portion is inserted inside. The shape portion, the second tubular portion whose inner peripheral surface forms a part of the through hole and the large diameter portion is inserted inside, and the inner diameter is larger than that of the first tubular portion, and the first cylinder. The ceramic member has a first stepped surface that is a part of the shaped portion and connects the inner peripheral surface of the first tubular portion and the inner peripheral surface of the second tubular portion. It is a part of the large-diameter portion and has a second stepped surface that connects the outer peripheral surface of the large-diameter portion and the outer peripheral surface of the small-diameter portion and faces the first stepped surface. A ring-shaped sealing member that is disposed between the second stepped surface and is pressed against the first stepped surface and the second stepped surface may be provided. In this way, the presence of the ring-shaped sealing member can seal between the first stepped surface and the second stepped surface. Therefore, it is possible to suppress the gas from flowing in the axial direction between the housing and the ceramic member, and it is possible to prevent the airtightness between one end side and the other end side of the sensor element from being lowered.

In the gas sensor of the present invention in the embodiment including the sealing member, the sealing member may have an outer diameter Dp [mm] of the outer diameter Dc2 [mm] or less of the large diameter portion. In this way, the sealing member is less likely to protrude to the outer diameter side than the outer peripheral surface of the large diameter portion. Here, if the sealing member protrudes to the outer diameter side from the outer peripheral surface of the large diameter portion, the corner portion between the outer peripheral surface of the large diameter portion and the second stepped surface expands due to heating. The expansion of the portion is restricted by the sealing member, and thermal stress may be concentrated on the corner portion. When the outer diameter Dp of the sealing member is equal to or less than the outer diameter Dc2 of the large diameter portion, concentration of thermal stress on the corner portion can be suppressed, and damage to the ceramic member due to heating can be suppressed.

In the gas sensor of the present invention including the sealing member, the sealing member is a member whose inner diameter side is thicker than that of the outer diameter side in a state where the first step surface and the second step surface are not pressed. There may be. In this way, the position of the sealing member is less likely to shift in the radial direction as compared with the case where the thickness of the sealing member is uniform, for example, when the sealing member is not pressed. Therefore, when the gas sensor repeatedly raises and lowers the temperature, it is possible to prevent the housing and the ceramic member from shifting in the radial direction. Therefore, it is possible to suppress a decrease in airtightness between one end side and the other end side of the sensor element.

In the gas sensor of the present invention including the sealing member, the axial distance between the first stepped surface and the second stepped surface may increase as it approaches the central axis of the ceramic member. In this way, the pressing force from the housing to the ceramic member via the sealing member has a component toward the central axis. Therefore, when the gas sensor repeatedly raises and lowers the temperature, it is possible to prevent the housing and the ceramic member from shifting in the radial direction. Therefore, it is possible to suppress a decrease in airtightness between one end side and the other end side of the sensor element 20.

The schematic explanatory view which shows the appearance that the gas sensor 10 was attached to the pipe 90. A vertical sectional view of the gas sensor 10. An enlarged view of the periphery of the housing 41 and the ceramic member 45 in FIG.

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic explanatory view showing a state in which a gas sensor 10 according to an embodiment of the present invention is attached to a pipe 90. FIG. 2 is a vertical cross-sectional view of the gas sensor 10, and is a cross-sectional view taken along the line AA of FIG. FIG. 3 is an enlarged view of the periphery of the housing 41 and the ceramic member 45 of FIG. In this embodiment, the vertical direction and the horizontal direction are as shown in FIGS. 2 and 3.

As shown in FIG. 1, the gas sensor 10 is attached to a pipe 90 such as an exhaust gas pipe of a vehicle, and the concentration of a specific gas such _{as NOx or O 2 contained in the exhaust gas as a gas to be measured (specific gas concentration).} Is used to measure. In the present embodiment, the gas sensor 10 measures the NOx concentration as a specific gas concentration.

As shown in FIG. 2, the gas sensor 10 includes a sensor element 20, a protective layer 25 that covers at least a part of the surface of the sensor element 20, and a tip side (lower end side of FIG. 2) including the tip surface 20a of the sensor element 20. ), The element encapsulant 40 that seals and fixes the sensor element 20, and the protection of the base end side (upper end side in FIG. 2) including the base end surface 20b of the sensor element 20 and the sensor element 20. The assembly 50, which extracts the electric signal of the above, is provided.

The sensor element 20 has a structure in which a plurality of oxygen ion conductive solid electrolyte layers such as _{zirconia (ZrO 2) are laminated.} The sensor element 20 is an element having a long plate-like body shape (rectangular parallelepiped shape), and has a tip surface 20a on the lower end side, a base end surface 20b on the upper end side, and four surfaces perpendicular to the tip surface 20a and the base end surface 20b. And have. The sensor element 20 has a gas measurement port 20a (not shown) for introducing the gas to be measured into its own interior, and has a specific gas concentration in the gas to be measured that has flowed into the inside from the gas introduction port to be measured. Is configured to be detectable.

The protective layer 25 is a porous body that covers at least a part of the surface of the sensor element 20. The protective layer 25 covers most of the portion located in the element chamber 37 including the tip surface 20a of the sensor element 20. The protective layer 25 plays a role of protecting the sensor element 20 from, for example, moisture and oil components in the gas to be measured. The protective layer 25 is made of a porous body of ceramics such as alumina.

The protective cover 30 is made of a metal such as stainless steel, and is a cylindrical member that allows the inflow of the gas to be measured from the outside into the element chamber 37 inside. The protective cover 30 includes a bottomed tubular inner protective cover 31 that covers the tip end side of the sensor element 20, and a bottomed tubular outer protective cover 32 that covers the inner protective cover 31. The inner protective cover 31 has an element chamber 37 inside. The element chamber 37 is a space surrounded by the inner peripheral surface of the inner protective cover 31. In the element chamber 37, the tip side including the tip surface 20a of the sensor element 20 is arranged. Between the inner protective cover 31 and the outer protective cover 32, there is a gas chamber 38 which is a space surrounded by both covers. The inner protective cover 31 is provided with a plurality of element chamber inlets 33 located on the side surface (outer peripheral surface) and element chamber outlets 34 located on the bottom surface. The outer protective cover 32 is provided with a plurality of outer inlets 35 located on the side surface (outer peripheral surface) and outer outlets 36 located on the bottom surface.

The element encapsulant 40 fixes the sensor element 20 and is located in the space (element chamber 37 and gas chamber 38) in the protective cover 30 on the tip end side (lower side) of the sensor element and on the proximal end side (upper side). It seals the space inside a certain atmosphere side cover 74. The sensor element 20 penetrates the element sealing body 40 in the longitudinal direction (vertical direction). The element sealing body 40 includes a housing 41, a ceramic member 45, a sealing member 48, and a sealing material 49. The sensor element 20, the housing 41, the ceramic member 45, and the sealing member 48 are arranged coaxially, and their central axes coincide with the central axis C of the gas sensor 10.

The housing 41 is a cylindrical metal member made of, for example, stainless steel. As shown in FIG. 3, the housing 41 has a through hole 41a in which the ceramic member 45 is inserted in the axial direction (vertical direction), a cylindrical first tubular portion 42, and a first tubular portion 42. A cylindrical second tubular portion 43 connected coaxially with the first tubular portion 42 is provided on the upper side of the above. The first tubular portion 42 includes an inner peripheral surface 42a and a first stepped surface 42b that connects the upper end of the inner peripheral surface 42a and the lower end of the inner peripheral surface 43a of the second tubular portion 43. There is. The first stepped surface 42b is a ring-shaped surface when viewed from above, and is closer to the central axis C in the direction perpendicular to the central axis C (left-right direction), that is, in the radial direction of the housing 41, toward the protective cover 30 side (lower side). It is tilted toward you. In other words, the first stepped surface 42b is inclined so as to go downward toward the inner diameter side. The second tubular portion 43 includes an inner peripheral surface 43a having an inner diameter larger than that of the inner peripheral surface 42a. The inner diameter of the first tubular portion 42 (diameter of the inner peripheral surface 42a) is referred to as an inner diameter dm1 [mm]. The inner diameter of the second tubular portion 43 (diameter of the inner peripheral surface 43a) is referred to as an inner diameter dm2 [mm]. The inner diameter dm1 is, for example, 9 mm to 12 mm. The inner diameter dm2 is, for example, 12 mm to 16 mm. The inner peripheral surface 42a, the inner peripheral surface 43a, and the first stepped surface 42b form a part of the through hole 41a. A small diameter portion 46 of the ceramic member 45 is inserted inside the first tubular portion 42. A large diameter portion 47 of the ceramic member 45 is inserted inside the second tubular portion 43. The upper end of the protective cover 30 is attached to the lower end of the first tubular portion 42. The first tubular portion 42 is provided with a male screw portion on the outer peripheral surface, and is inserted into a fixing member 91 welded to the pipe 90 and provided with a female screw portion on the inner peripheral surface. As a result, the gas sensor 10 is fixed to the pipe 90 with the tip side of the sensor element 20 and the protective cover 30 of the gas sensor 10 protruding into the pipe 90.

The ceramic member 45 is a columnar member inserted into the through hole 41a of the housing 41. The ceramic member 45 has a through hole coaxial with the central axis C, and the sensor element 20 penetrates the inside in the axial direction. The ceramic member 45 is made of insulating ceramics such as alumina, steatite, and zirconia. The ceramic member 45 includes a columnar small-diameter portion 46 and a columnar large-diameter portion 47 coaxially connected to the small-diameter portion 46 with the small-diameter portion 46. The small diameter portion 46 is located on the protective cover 30 side (lower side) of the large diameter portion 47. The small diameter portion 46 includes an outer peripheral surface 46a having an outer diameter smaller than that of the outer peripheral surface 47a of the large diameter portion 47. The outer peripheral surface 46a faces the inner peripheral surface 42a of the first tubular portion 42 in the radial direction. The large-diameter portion 47 includes an outer peripheral surface 47a and a second stepped surface 47b that connects the lower end of the outer peripheral surface 47a and the upper end of the outer peripheral surface 46a of the small-diameter portion 46. The outer peripheral surface 47a faces the inner peripheral surface 43a of the second tubular portion 43 in the radial direction. The second stepped surface 47b is a surface perpendicular to the central axis C and faces the first stepped surface 42b of the housing 41 in the vertical direction. The inner diameter side of the large diameter portion 47 is filled with a sealing material 49. The outer diameter of the small diameter portion 46 (diameter of the outer peripheral surface 46a) is referred to as an outer diameter Dc1 [mm]. The outer diameter of the large diameter portion 47 (diameter of the outer peripheral surface 47a) is referred to as an outer diameter Dc2 [mm]. The outer diameter Dc1 is, for example, 8.96 mm to 11.96 mm. The outer diameter Dc2 is, for example, 12 mm to 16 mm.

The sealing member 48 is a ring-shaped member made of a metal such as stainless steel, nickel, or copper. The sealing member 48 is arranged between the first stepped surface 42b of the housing 41 and the second stepped surface 47b of the ceramic member 45, and is pressed from above and below by the first stepped surface 42b and the second stepped surface 47b. .. As a result, the sealing member 48 airtightly seals the gap between the housing 41 and the ceramic member 45. The outer diameter of the sealing member 48 is referred to as an outer diameter Dp [mm]. The inner diameter of the sealing member 48 is referred to as an inner diameter dp [mm]. The outer diameter Dp and the inner diameter dp were pressed against the diameter of the element sealing body 40 in the state where the sealing member 48 was incorporated, that is, the first step surface 42b and the second step surface 47b. The diameter in the state. Further, the sealing member 48 is preferably a member whose inner diameter side is thicker than that of the outer diameter side in a state where the first step surface 42b and the second step surface 47b are not pressed. That is, it is preferable that the shape of the sealing member 48 in a state where no external pressure is applied is thicker on the inner diameter side than on the outer diameter side. The sealing member 48 may be deformed by being pressed by the first stepped surface 42b and the second stepped surface 47b in a state of being incorporated in the element sealing body 40 as shown in FIG. In that case, the inner diameter side does not necessarily have to be thicker than the outer diameter side in the deformed state. The sealing material 49 is a molded body of ceramic powder such as talc, alumina powder, and boron nitride. The sealing material 49 is filled between the inner peripheral surface of the large diameter portion 47 and the sensor element 20, and airtightly seals between the ceramic member 45 and the sensor element 20.

Here, the positional relationship between the housing 41 of the element sealing body 40, the ceramic member 45, and the sealing member 48 will be described in detail. As shown in FIG. 3, there is a gap between the inner peripheral surface of the housing 41 and the outer peripheral surface of the ceramic member 45. More specifically, there is a gap between the inner peripheral surface 42a of the first tubular portion 42 and the outer peripheral surface 46a of the small diameter portion 46. The radial distance W1 of this gap is 20 μm or more. Although the details will be described later, when the distance W1 is 20 μm or more, damage to the ceramic member 45 due to heating when the gas sensor 10 is used can be suppressed. The distance W1 is an average value of the gaps (distances in the radial direction) over the entire circumference between the inner peripheral surface 42a and the outer peripheral surface 46a. Therefore, regardless of whether or not the central axes of the housing 41 and the ceramic member 45 are aligned, the distance W1 is basically "the difference between the inner diameter dm1 of the inner peripheral surface 42a and the outer diameter Dc1 of the outer peripheral surface 46a". Is half the value. That is, W1 = (dm1-Dc1) / 2.

Further, it is preferable that there is also a gap between the inner peripheral surface 43a of the second tubular portion 43 and the outer peripheral surface 47a of the large diameter portion 47. That is, the radial distance W2 of the gap may be 0 μm (there is no gap), but it is preferably more than 0 μm. The distance W2 is also the average value of the gaps (distances in the radial direction) over the entire circumference, similarly to the distance W1. Therefore, regardless of whether or not the central axes of the housing 41 and the ceramic member 45 are aligned, the distance W2 is basically "the difference between the inner diameter dm2 of the inner peripheral surface 43a and the outer diameter Dc2 of the outer peripheral surface 47a". Is half the value. That is, W2 = (dm2-Dc2) / 2. Further, when the distance W2 exceeds 0 μm, the distance W2 is preferably the distance W1 or less. That is, it is preferable that the ratio W1 / W2, which is the ratio of the distance W1 and the distance W2, is a value of 1 or more. The ratio W1 / W2 may exceed the value 1. The ratio W1 / W2 may have a value of 100 or less, or may have a value of 10 or less.

As described above, the first stepped surface 42b is inclined so as to approach the central axis C in the radial direction of the housing 41 toward the protective cover 30 side (lower side). Further, the second stepped surface 47b is a surface perpendicular to the central axis C as described above. As a result, the distance between the first stepped surface 42b and the second stepped surface 47b in the axial direction (vertical direction) increases as the distance between them approaches the central axis C of the ceramic member 45. The angle θg formed by the first stepped surface 42b and the second stepped surface 47b (see the partially enlarged view of FIG. 3) is, for example, more than 0 ° and 30 ° or less. The formed angle θg may be 5 ° or more. The formed angle θg may be 15 ° or less.

The assembly 50 includes an insulator 55, a plurality of contact fittings 60, a plurality of connection terminals 71, a plurality of lead wires 72, a rubber stopper 73, an atmosphere side cover 74, an outer cover 75, and a disc spring 77. And have. The insulating insulator 55 is a bottomed tubular member, and is made of an insulating ceramic like the ceramic member 45. The lower surface of the insulating insulator 55 is in contact with the upper surface of the ceramic member 45, and is located coaxially with the ceramic member 45. The contact metal fitting 60 is a metal plate bent at a plurality of places, and includes a leaf spring portion in a state of being bent inward. A plurality of contact fittings 60 are arranged on the left and right sides of the sensor element 20 (for example, two or three), and each of the contact metal fittings 60 comes into contact with a conduction electrode (not shown) arranged on the surface of the sensor element 20. It is conducting. Each end of the plurality of contact fittings 60 is pulled out through a hole in the upper bottom of the insulating insulator 55, and is electrically connected to the lead wire 72 via the connection terminal 71. The lead wire 72 penetrates vertically through the rubber stopper 73 that closes the upper ends of the atmospheric side cover 74 and the outer cover 75, and is pulled out to the outside (outside the pipe 90 and in the atmosphere). The atmosphere side cover 74 covers the portion of the outer peripheral surface of the second tubular portion 43 on the proximal end side (upper side) of the sensor element 20. Further, the atmospheric side cover 74 covers the insulating insulator 55 and the rubber stopper 73. The outer cover 75 covers the upper outer peripheral surface of the atmospheric side cover 74. A plurality of atmospheric introduction holes 76 are formed in the atmospheric side cover 74 and the outer cover 75, respectively. Through the atmosphere introduction hole 76, a reference gas (atmosphere) that serves as a reference for detecting a specific gas concentration is introduced into a reference gas introduction port (not shown) arranged on the base end surface 20b of the sensor element 20. The atmosphere side cover 74 and the outer cover 75 have a crimping portion crimped in a reduced diameter shape near the upper end, and the rubber stopper 73 is fixed by the crimping portion. The disc spring 77 is sandwiched between the atmospheric side cover 74 and the insulating insulator 55 at the top and bottom, and the insulating insulator 55 and the ceramic member 45 are fixed by pressing the insulating insulator 55 downward.

Next, a usage example of the gas sensor 10 thus configured will be described below. When the gas to be measured flows through the pipe 90 with the gas sensor 10 attached to the pipe 90 as shown in FIGS. 1 and 2, the gas to be measured flows through the protective cover 30. Specifically, the gas to be measured in the pipe 90 flows into the gas chamber 38 from the outer inlet 35, and flows into the element chamber 37 from the gas chamber 38 through the element chamber inlet 33. Then, the gas to be measured flows in the element chamber 37 from the element chamber inlet 33 toward the element chamber outlet 34, and flows out from the element chamber outlet 34 through the outer outlet 36 to the outside (inside the pipe 90). Then, when the gas to be measured flows into the sensor element 20 from the gas introduction port to be measured when flowing through the element chamber 37, an electric signal (for example, NOx concentration) corresponding to the specific gas concentration (for example, NOx concentration) in the gas to be measured is used. Voltage or current) is generated by the sensor element 20. The sensor element 20 generates an electric signal according to the specific gas concentration in the gas to be measured, based on the reference gas introduced inside from the reference gas introduction port located in the atmosphere side cover 74. By taking out this electric signal through the contact metal fitting 60, the connection terminal 71, and the lead wire 72, the specific gas concentration is detected based on the electric signal.

As described above, since the protective cover 30 side of the gas sensor 10 is exposed to the gas to be measured during use, the gas sensor 10 is heated by the gas to be measured and becomes high in temperature. Therefore, the temperature of the gas sensor 10 is repeatedly raised and lowered between when it is used and when it is not used. Then, when the gas sensor 10 becomes hot during use, the ceramic member 45 expands. Here, in the present embodiment, there is a gap between the inner peripheral surface 42a of the housing 41 and the outer peripheral surface 46a of the ceramic member 45, and as described above, the distance W1 of this gap is 20 μm or more. If such a gap exists, there is a space that allows expansion when the ceramic member 45 is heated, so that the inner peripheral surface 42a of the housing 41 and the outer peripheral surface 46a of the ceramic member 45 do not come into contact with each other. Or, even if they come into contact with each other, the radial stress from the inner peripheral surface 42a to the outer peripheral surface 46a is reduced. Therefore, it is possible to prevent the ceramic member 45 from being damaged such as cracks by heating. The larger the distance W1, the greater the effect of suppressing damage to the ceramic member 45 due to heating. For example, the distance W1 may be 50 μm or more. Further, the distance W1 is preferably 500 μm or less. When the distance W1 is 500 μm or less, it is possible to suppress the flow of gas (measured gas or reference gas) in the axial direction through the gap between the housing 41 and the ceramic member 45. As a result, gas is less likely to condense in the gap between the inner peripheral surface 42a and the outer peripheral surface 46a, and corrosion of members related to airtightness such as the housing 41 and the sealing member 48 is less likely to occur. Therefore, it is possible to suppress a decrease in airtightness between one end side (tip surface 20a side) and the other end side (base end surface 20b side) of the sensor element 20 with the element encapsulant 40 as a boundary. As described above, since the sensor element 20 detects the specific gas concentration in the gas to be measured in the protective cover 30 based on the reference gas in the atmosphere side cover 74, one end side and the other end side of the sensor element 20 If the airtightness between the two is reduced, the accuracy of detection is reduced. Therefore, by suppressing the decrease in airtightness between one end side and the other end side of the sensor element 20, it is possible to suppress the decrease in the detection accuracy of the specific gas concentration of the gas sensor 10. The smaller the distance W1, the greater the effect of suppressing the decrease in airtightness. For example, the distance W1 may be 300 μm or less, or 100 μm or less.

Further, if there is a gap between the inner peripheral surface 43a of the second tubular portion 43 and the outer peripheral surface 47a of the large diameter portion 47, the inner peripheral surface 43a of the housing 41 can be transferred to the outer peripheral surface 47a of the ceramic member 45. Radial stress is also reduced. Therefore, if the distance W2 exceeds 0 μm, it is possible to further suppress the occurrence of breakage such as cracks in the ceramic member 45 due to heating. The larger the distance W2, the more likely it is that damage to the ceramic member 45 due to heating during use of the gas sensor 10 can be suppressed. For example, the distance W2 is preferably 5 μm or more. The distance W2 may be 20 μm or more. Further, the distance W2 is preferably 500 μm or less. When the distance W2 is 500 μm or less, gas is less likely to condense in the gap between the inner peripheral surface 43a and the outer peripheral surface 47a, as in the case where the distance W1 is 500 μm or less. Corrosion of members related to the airtightness of the housing is less likely to occur. Therefore, it is possible to further suppress the decrease in airtightness between one end side and the other end side of the sensor element 20. The smaller the distance W2, the greater the effect of suppressing the decrease in airtightness. The distance W2 may be 300 μm or less, 100 μm or less, or 50 μm or less.

Further, the sealing member 48 preferably has an outer diameter Dp of not more than the outer diameter Dc2 of the large diameter portion 47. In this way, the sealing member 48 is less likely to protrude to the outer diameter side than the outer peripheral surface 47a of the large diameter portion 47. Here, when the sealing member 48 protrudes to the outer diameter side from the outer peripheral surface 47a of the large diameter portion 47, the corner portion 47c between the outer peripheral surface 47a of the large diameter portion 47 and the second stepped surface 47b (FIG. When the (see partially enlarged view of 3) expands due to heating, the expansion may be restricted by the sealing member 48. As a result, thermal stress may be concentrated on the corner portion 47c. When the outer diameter Dp of the sealing member 48 is equal to or less than the outer diameter Dc2 of the large diameter portion 47, it is possible to suppress the concentration of thermal stress on the corner portion 47c, and the ceramic member 45 is damaged by heating (particularly the corner portion 47c and its thereof). Damage to the surrounding area) can be suppressed. The outer diameter Dp may be less than the outer diameter Dc2. Further, it is preferable that the sealing member 48 and the ceramic member 45 satisfy the following formula (1). The left side of the equation (1) is the radial movement of the sealing member 48 from the state in which the sealing member 48 and the ceramic member 45 are coaxial to the state in which the sealing member 48 is maximally displaced in the radial direction. Corresponds to the distance. Further, the right side of the equation (1) is a moving distance in which a portion protruding from the outer peripheral surface 47a to the outer diameter side does not occur even if the sealing member 48 is displaced in the radial direction from the state where the sealing member 48 and the ceramic member 45 are coaxial. Corresponds to the maximum value of. By satisfying this equation (1), even if the position of the sealing member 48 with respect to the ceramic member 45 is displaced in the radial direction, the sealing member 48 is less likely to protrude to the outer diameter side than the outer peripheral surface 47a of the large diameter portion 47. .. The difference between the inner diameter dp of the sealing member 48 and the outer diameter Dc1 of the small diameter portion 46 may be 5 μm to 500 μm or 20 μm to 500 μm. The difference between the outer diameter Dc2 of the large diameter portion 47 and the outer diameter Dp of the sealing member 48 may be 5 μm to 500 μm.

(Dp-Dc1) / 2≤ (Dc2-Dp) / 2 (1)

According to the gas sensor 10 of the present embodiment described in detail above, there is a gap between the inner peripheral surface 42a of the through hole 41a and the ceramic member 45, and the radial distance W1 of the gap is 20 μm or more. Damage to the ceramic member 45 due to the above can be suppressed. Further, since the distance W1 is 500 μm or less, it is possible to suppress a decrease in airtightness between one end side and the other end side of the sensor element 20.

Further, the ceramic member 45 has a columnar large diameter portion 47 and a columnar small diameter portion 46 located closer to the protective cover 30 than the large diameter portion 47 and having an outer diameter smaller than that of the large diameter portion 47. doing. The distance W1 is the radial distance between the outer peripheral surface 46a of the small diameter portion 46 and the inner peripheral surface 42a of the through hole 41a. Here, when the ceramic member 45 has a large diameter portion 47 and a small diameter portion 46, the small diameter portion 46 closer to the protective cover 30 is more likely to be heated by the gas to be measured and is therefore more likely to be damaged. Therefore, when there is a gap of 20 μm or more between the small diameter portion 46 and the inner peripheral surface 42a of the housing 41, for example, there may be a gap only between the large diameter portion 47 and the inner peripheral surface 43a of the housing 41. In comparison, damage to the ceramic member 45 due to heating can be further suppressed.

Further, the large diameter portion 47 has a gap between the large diameter portion 47 and the inner peripheral surface 43a of the through hole 41a, and the radial distance W2 of this gap is 5 μm or more. As described above, since there is a gap not only between the small diameter portion 46 and the inner peripheral surface 42a of the housing 41 but also between the large diameter portion 47 and the inner peripheral surface 43a of the housing 41, the ceramic member 45 by heating is formed. Damage can be further suppressed. Further, since the distance W2 is 500 μm or less, it is possible to suppress a decrease in airtightness between one end side and the other end side of the sensor element 20.

Furthermore, when the ratio W1 / W2 is a value of 1 or more, that is, the distance W2 is a distance W1 or less, when the gas sensor 10 is heated, it is far from the protective cover 30 and therefore difficult to be heated. Is easier to contact with the housing 41 than the small diameter portion 46. As a result, the small diameter portion 46, which is easily heated and easily expands thermally, does not come into contact with the housing 41, or even if it comes into contact, the radial stress from the housing 41 is relaxed. Therefore, damage to the ceramic member 45 can be further suppressed.

Further, the gas sensor 10 is a ring-shaped sealing member 48 that is arranged between the first step surface 42b and the second step surface 47b and is pressed against the first step surface 42b and the second step surface 47b. It has. The presence of the ring-shaped sealing member 48 can seal between the first stepped surface 42b and the second stepped surface 47b. Therefore, it is possible to suppress the gas from flowing in the axial direction between the housing 41 and the ceramic member 45, and it is possible to prevent the airtightness between one end side and the other end side of the sensor element 20 from being lowered. Further, since the outer diameter Dp of the sealing member 48 is equal to or less than the outer diameter Dc2 of the large diameter portion 47, the sealing member 48 is less likely to protrude to the outer diameter side than the outer peripheral surface 47a of the large diameter portion 47. As a result, concentration of thermal stress on the corner portion 47c of the large diameter portion 47 can be suppressed, and damage to the ceramic member 45 due to heating can be suppressed.

Further, the sealing member 48 is a member whose inner diameter side is thicker than that of the outer diameter side in a state where the first step surface 42b and the second step surface 47b are not pressed. Therefore, for example, the position of the sealing member 48 is less likely to shift in the radial direction as compared with the case where the sealing member 48 has a uniform thickness when not pressed. As a result, when the gas sensor 10 repeatedly raises and lowers the temperature, it is possible to prevent the housing 41 and the ceramic member 45 from being displaced in the radial direction. As a result, it is possible to suppress a decrease in airtightness between one end side and the other end side of the sensor element 20.

Further, the distance between the first stepped surface 42b and the second stepped surface 47b in the axial direction becomes larger as it approaches the central axis C of the ceramic member 45. In other words, the angle θg formed by FIG. 3 exceeds 0 °. As a result, the pressing force from the housing 41 to the ceramic member 45 via the sealing member 48 has a component toward the central axis C. For example, when the first step surface 42b and the second step surface 47b are parallel (the angle θg formed is 0 °), the pressing force from the housing 41 to the ceramic member 45 via the sealing member 48 is parallel in the axial direction. Acts (upward). On the other hand, if the formed angle θg exceeds 0 °, the pressing force acts in the upper right direction in the partially enlarged view of FIG. 3, and therefore has a component toward the central axis C (a component pointing to the right in the partially enlarged view of FIG. 3). Will be. As a result, the housing 41 is pressed from the outer diameter side to the inner diameter side over the entire circumference of the sealing member 48. Therefore, when the gas sensor 10 repeatedly raises and lowers the temperature, it is possible to prevent the housing 41 and the ceramic member 45 from being displaced in the radial direction. As a result, it is possible to suppress a decrease in airtightness between one end side and the other end side of the sensor element 20.

It goes without saying that the present invention is not limited to the above-described embodiment, and can be implemented in various aspects as long as it belongs to the technical scope of the present invention.

For example, in the above-described embodiment, the first stepped surface 42b is inclined so as to go downward toward the inner diameter side, but the present invention is not limited to this. If the axial distance between the first stepped surface 42b and the second stepped surface 47b increases as it approaches the central axis of the ceramic member 45, the radial position of the ceramic member 45 is the same as in the above-described embodiment. The effect of suppressing deviation can be obtained. For example, in addition to or in place of the inclination of the first step surface 42b, the second step surface 47b may also be inclined. Specifically, the second stepped surface 47b may be inclined so as to approach the central axis C in the radial direction of the housing 41 toward the side (upper side) opposite to the protective cover 30 side. Further, the axial distance between the first stepped surface 42b and the second stepped surface 47b may become smaller as it approaches the central axis C of the ceramic member 45. Alternatively, the first stepped surface 42b and the second stepped surface 47b may be parallel to each other.

In the above-described embodiment, the gas sensor 10 includes the sealing member 48 between the first stepped surface 42b and the second stepped surface 47b, but the sealing member 48 may not be provided. In this case, it is preferable that the distance W2 is 0 μm so that the decrease in airtightness between one end side and the other end side of the sensor element 20 can be suppressed.

In the above-described embodiment, the ceramic member 45 includes a small diameter portion 46 and a large diameter portion 47, but the shape of the ceramic member 45 is not limited to this. For example, the ceramic member 45 may have a columnar shape that does not have the second stepped surface 47b, that is, a shape in which the outer diameter Dc1 and the outer diameter Dc2 in FIG. 3 are equal. Also in this case, if there is a gap between the inner peripheral surface of the housing and the outer peripheral surface of the ceramic member, and the distance W1 of this gap is 20 μm or more, the ceramic member is damaged by heating as in the above-described embodiment. The effect of suppressing is obtained. Further, the ceramic member 45 may have a columnar member coaxially connected to the small diameter portion 46 and the large diameter portion 47 in addition to the small diameter portion 46 and the large diameter portion 47. Similarly, the shape of the housing 41 is not limited to the above-described embodiment.

In the above-described embodiment, there is a gap of 20 μm or more between the inner peripheral surface 42a of the first tubular portion 42 and the outer peripheral surface 46a of the small diameter portion 46, but the inner peripheral surface 42a and the outer peripheral surface 46a are in contact with each other. You may. Even in this case, if there is a gap of 20 μm or more between the inner peripheral surface 43a of the second tubular portion 43 and the outer peripheral surface 47a of the large diameter portion 47, the effect of suppressing damage to the ceramic member due to heating is effective. can get. In such a case, the radial distance of the gap between the inner peripheral surface 43a and the outer peripheral surface 47a corresponds to the "distance W1" of the present invention. As described above, if there is a gap having a radial distance of 20 μm or more somewhere between the ceramic member and the housing, the effect of suppressing damage to the ceramic member due to heating can be obtained. However, since the small diameter portion 46 is more easily heated by the gas to be measured and easily damaged because it is closer to the protective cover 30, it is between the inner peripheral surface 42a of the first tubular portion 42 and the outer peripheral surface 46a of the small diameter portion 46. It is preferable that there is a gap having a distance of 20 μm or more.

In the above-described embodiment, the gas introduction port to be measured is arranged on the tip surface 20a of the sensor element 20, but the gas introduction port to be measured may be located in the element chamber 37, and the gas introduction port to be measured is the sensor. It may be arranged on another surface of the element 20. Similarly, the reference gas introduction port may be located in the atmosphere side cover 74, and may be arranged not only on the base end surface 20b of the sensor element 20 but also on another surface of the sensor element 20. Further, the sensor element 20 does not have to be provided with the gas introduction port to be measured. In this case, for example, a detection unit including a measurement electrode or the like may be arranged on the surface of the sensor element 20.

In the above-described embodiment, the sensor element 20 has a long plate-like shape, but it may be long. For example, the sensor element 20 may be cylindrical.

Hereinafter, an example in which a gas sensor is specifically manufactured will be described as an example. Experimental Examples 3 to 26 correspond to Examples of the present invention, and Experimental Examples 1 and 2 correspond to Comparative Examples. The present invention is not limited to the following examples.

[Experimental Examples 1-10]
Experimental Example 1 produced a gas sensor having the same configuration as the gas sensor 10 shown in FIGS. 2 and 3 except that the distance W2 was set to 0 μm and the distance W1 was variously changed between 0 μm and 600 μm as shown in Table 1. It was set to 10. In Experimental Examples 1 to 10, the inner diameter dm2 of the second tubular portion 43 of the housing 41 and the outer diameter Dc2 of the large diameter portion 47 of the ceramic member 45 were both set to 14.5 mm. Further, the distance W1 was adjusted by keeping the inner diameter dm1 of the first tubular portion 42 of the housing 41 constant at 10.5 mm and changing the outer diameter Dc1 of the small diameter portion 46 of the ceramic member 45. The outer diameter Dp of the sealing member 48 was 14 mm, and the inner diameter dp was 10 mm. The sealing member 48 has the same thickness on the outer diameter side and the inner diameter side in a state where the first step surface 42b and the second step surface 47b are not pressed. The angle θg formed by the first stepped surface 42b and the second stepped surface 47b was set to 3 °.

[Experimental Examples 11-18]
Gas sensors having the same configurations as those of Experimental Examples 1 to 10 were produced except that the distance W1 was kept constant at 50 μm and the distance W2 was variously changed between 5 μm and 150 μm as shown in Table 1, and Experimental Examples 11 to 18 were produced. And said. The inner diameter dm1 and the outer diameter Dc1 were the same as in Experimental Example 5. Further, the distance W2 was adjusted by keeping the inner diameter dm2 of the second tubular portion 43 of the housing 41 constant at 14.5 mm and changing the outer diameter Dc2 of the large diameter portion 47 of the ceramic member 45.

[Experimental Examples 19-26]
A gas sensor having the same configuration as that of Experimental Examples 11 to 18 was produced except that the distance W1 was kept constant at 100 μm and the distance W2 was variously changed between 10 μm and 300 μm as shown in Table 1, and Experimental Examples 19 to 26 were produced. And said. The inner diameter dm1 and the outer diameter Dc1 were the same as in Experimental Example 6. The distance W2 is adjusted by keeping the inner diameter dm2 of the second tubular portion 43 of the housing 41 constant at 14.5 mm and changing the outer diameter Dc2 of the large diameter portion 47 of the ceramic member 45 in the same manner as in Experimental Examples 11 to 18. I went there.

[Thermal durability test]
The gas sensors of Experimental Examples 1 to 26 were subjected to a thermal durability test to check for cracks and misalignment of the ceramic member 45. Specifically, the test was conducted as follows. After heating the housing 41 to 600 ° C., a cold stress was applied to submerge the gas sensor, and this was defined as one elevating temperature cycle. Then, after repeating the elevating temperature cycle 3000 times and 6000 times, the presence or absence of cracks in the ceramic member 45 and the presence or absence of radial misalignment of the ceramic member 45 were examined. Regarding the presence or absence of cracks, "A (excellent)" is defined as "A (excellent)" when no cracks are observed after repeating the temperature raising / lowering cycle 6000 times, and "B (good)" is provided when no cracks are observed after repeating 3000 times. The case where cracks were observed after repeating 3000 times was evaluated as "C (impossible)". Regarding the misalignment, when the position of the ceramic member 45 with respect to the housing 41 is visually deviated in the radial direction after repeating the temperature raising / lowering cycle 6000 times (when the housing 41 and the ceramic member 45 are no longer coaxial). "Yes". When the position of the ceramic member 45 was not displaced in the radial direction, it was evaluated as “none”. Table 1 summarizes the distance W1, the distance W2, the ratio W1 / W2, and the results of the thermal durability test of Experimental Examples 1 to 26.

As shown in Table 1, in Experimental Examples 3 to 26 in which the distance W1 is 20 μm or more, the evaluation regarding cracks is “A (excellent)” or “B (good)”, and the distance W1 is less than 20 μm. Compared with Experimental Examples 1 and 2, damage to the ceramic member 45 due to heating could be suppressed. Further, in Experimental Examples 11 to 26 in which the distance W2 exceeds 0 μm, the evaluation regarding cracks is “A (excellent)”, and the ceramic member 45 by heating is compared with Experimental Examples 3 to 10 in which the distance W2 is 0 μm. Was able to suppress the damage of. Further, in Experimental Examples 11 to 15, 19 to 23 in which the ratio W1 / W2 was a value of 1 or more, the position shift of the ceramic member 45 did not occur even if the distance W1 and the distance W2 both exceeded 0 μm. .. On the other hand, in Experimental Examples 16 to 18, 24 to 26 in which the ratio W1 / W2 was less than the value 1, misalignment occurred. Here, if the misalignment occurs, the stress in the radial direction from the housing 41 to the ceramic member 45 is biased, so that the ceramic member 45 may be easily damaged in the portion where the stress is large. Therefore, in Experimental Examples 11 to 26, the evaluation regarding cracks was "A (excellent)", but in Experimental Examples 11 to 15, 19 to 23 in which the ratio W1 / W2 was a value of 1 or more, the ratio W1 / W2 was obtained. It is considered that damage is less likely to occur as compared with Experimental Examples 16 to 18 and 24 to 26 in which the value is less than 1. For example, when the elevating temperature cycle is repeated more than 6000 times, it is considered that Experimental Examples 11 to 15, 19 to 23 are less likely to be damaged as compared with Experimental Examples 16 to 18, 24 to 26.

10 Gas sensor, 20 Sensor element, 20a tip surface, 20b base end surface, 25 protective layer, 30 protective cover, 31 inner protective cover, 32 outer protective cover, 33 element chamber inlet, 34 element chamber outlet, 35 outer inlet, 36 outer outlet , 37 element chamber, 38 gas chamber, 40 element sealant, 41 housing, 41a through hole, 42 first tubular part, 42a inner peripheral surface, 42b first stepped surface, 43 second tubular part, 43a inner circumference Surface, 45 ceramics member, 46 small diameter part, 46a outer peripheral surface, 47 large diameter part, 47a outer peripheral surface, 47b second stepped surface, 47c square part, 48 sealing member, 49 sealing material, 50 assembly, 55 insulating porcelain, 60 Contact bracket, 71 Connection terminal, 72 Lead wire, 73 Rubber stopper, 74 Atmospheric side cover, 75 Outer cover, 76 Atmospheric introduction hole, 77 Countersunk spring, 90 Piping, 91 Fixing member, C central axis.

Claims (8)

A long sensor element that can detect a specific gas concentration in the gas to be measured, and
A columnar ceramic member through which the sensor element penetrates in the axial direction,
The ceramic member has a through hole inserted in the axial direction, and has a gap between the inner peripheral surface of the through hole and the ceramic member, and the radial distance W1 of the gap is 20 μm or more. With a tubular housing that is
A protective cover that covers the tip side of the sensor element and allows the flow of the gas to be measured inside.
With
The ceramic member has a cylindrical large-diameter portion, a cylindrical small-diameter portion outer diameter is smaller than and the large-diameter portion located on the protective cover side than the large diameter portion is composed of a chisel ,
In the housing, the inner peripheral surface forms a part of the through hole and the small diameter portion is inserted into the first tubular portion, and the inner peripheral surface forms a part of the through hole and has the large diameter. A second tubular portion having a portion inserted inside and having an inner diameter larger than that of the first tubular portion, and an inner peripheral surface of the first tubular portion which is a part of the first tubular portion and the first tubular portion. It has a first stepped surface that connects the inner peripheral surface of the two tubular portions.
The ceramic member is a part of the large-diameter portion, and has a second stepped surface that connects the outer peripheral surface of the large-diameter portion and the outer peripheral surface of the small-diameter portion and faces the first stepped surface.
A ring-shaped sealing member arranged between the first step surface and the second step surface and pressed against the first step surface and the second step surface is provided.
The outer diameter Dc1 [mm] of the small diameter portion, the outer diameter Dc2 [mm] of the large diameter portion, the outer diameter Dp [mm] of the sealing member, and the inner diameter dp [mm] of the sealing member are expressed by the following equations (1). ), And the outer diameter Dp is equal to or less than the outer diameter Dc2.
(Dp-Dc1) / 2≤ (Dc2-Dp) / 2 (1)
Gas sensor. The distance W1 is 500 μm or less.
The gas sensor according to claim 1. The gas sensor according to claim 1 or 2.
The distance W1 is the radial distance of the gap between the outer peripheral surface of the small diameter portion and the inner peripheral surface of the through hole.
Gas sensor. In the ceramic member, the large diameter portion has a gap between the large diameter portion and the inner peripheral surface of the through hole, and the radial distance W2 of the gap is 5 μm or more.
The gas sensor according to claim 3. The distance W2 is 500 μm or less.
The gas sensor according to claim 4. The ratio W1 / W2, which is the ratio of the distance W1 to the distance W2, has a value of 1 or more.
The gas sensor according to claim 4 or 5. The sealing member is a member whose inner diameter side is thicker than that of the outer diameter side in a state where the first step surface and the second step surface are not pressed.
The gas sensor according to any one of claims 1 to 6. The axial distance between the first stepped surface and the second stepped surface increases as it approaches the central axis of the ceramic member.
The gas sensor according to any one of claims 1 to 7.