JP2019191197A - Gas sensor - Google Patents

Abstract

To suppress breakage of a ceramic member by heating.SOLUTION: The gas sensor includes: a long sensor element 20, which can detect the concentration of a specific gas in a measurement target gas; a cylindrical ceramic member 45, through which the sensor element 20 penetrates in an axial direction; a through-hole 41a, which contains the ceramic member 45 inserted therein in the axial direction; and a cylindrical housing 41, which has a space between an inner peripheral surface 42a of the through-hole 41a and the ceramic member 45, the space having a distance W1 of 20 μm or larger in a radial direction.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a gas sensor.

  Conventionally, a gas sensor that detects the concentration of a specific gas such as NOx in a gas to be measured such as an automobile exhaust gas is known. For example, Patent Literature 1 describes a gas sensor that includes a sensor element, an insulator through which the sensor element is inserted and held, a housing through which the insulator is inserted and held, and an element cover fixed to the housing.

JP 2007-178418 A

  By the way, since such a gas sensor is heated by a gas to be measured such as exhaust gas when used, the insulator expands. However, in Patent Document 1, such expansion of the insulator is not particularly taken into consideration. For this reason, stress such as cracks may occur in the insulator due to the stress applied from the housing during the expansion of the insulator.

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

  That is, the present invention adopts the following means in order to achieve the main object described above.

The gas sensor of the present invention is
A long sensor element capable of detecting a specific gas concentration in the gas to be measured;
A cylindrical ceramic member in which the sensor element penetrates the inside in the axial direction;
The ceramic member has a through hole inserted therein in the axial direction, and has a gap between the inner peripheral surface of the through hole and the ceramic member, and a radial distance W1 of the gap is 20 μm or more. A cylindrical housing which 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 existence of such a gap reduces the radial stress from the housing when the ceramic member is expanded by 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 suppress the gas (for example, the gas to be measured or the atmosphere) from flowing in the gap between the housing and the ceramic member in the axial direction, and it is difficult for the gas to condense in the gap. It becomes difficult to occur. Thereby, it can suppress that the airtightness between the one end side and other end side of a sensor element falls.

  The gas sensor of the present invention includes a protective cover that covers a tip end side of the sensor element and allows the gas to be measured to flow therein, and the ceramic member includes a cylindrical large-diameter portion and the large-diameter portion. A columnar small-diameter portion that is located closer to the protective cover than the large-diameter portion, and the distance W1 is equal to 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, a gap may exist 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 the 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 damaged because it is more easily heated by the gas to be measured. Therefore, the gap of 20 μm or more exists between the small diameter portion and the inner peripheral surface of the housing, so that, for example, compared to the case where there is a gap only between the large diameter portion and the inner peripheral surface of the housing, 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 direction distance W2 may be 5 μm or more. 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, there is a gap in the radial direction from the housing when the ceramic member expands due to heating. 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 it is difficult for the gas to condense in the gap, and for example, corrosion of the housing or the like is less likely to occur. Thereby, it can suppress that the airtightness between the one end side and other end side of a sensor element falls.

  In the gas sensor of the present invention in which the ceramic member includes a large diameter portion and a small diameter portion, a ratio W1 / W2 that is a ratio between the distance W1 and the distance W2 may be 1 or more. In this way, when the gas sensor is heated, the large-diameter portion that is not easily heated because it is far from the protective cover is more likely to come into contact with the housing before the small-diameter portion. As a result, the small-diameter portion that is likely to be thermally expanded due to being easily heated does not come into contact with the housing, or the radial stress from the housing is relieved even if contacted. Therefore, 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 housing has a first cylinder in which an inner peripheral surface constitutes a part of the through hole and the small-diameter portion is inserted therein. A cylindrical portion, an inner peripheral surface constituting a part of the through hole, the large diameter portion being inserted therein, a second cylindrical portion having a larger inner diameter than the first cylindrical portion, and the first cylinder A first step surface that is a part of the first portion and connects the inner peripheral surface of the first cylindrical portion and the inner peripheral surface of the second cylindrical portion, and the ceramic member includes: A second step surface that is a part of the large-diameter portion, connects the outer peripheral surface of the large-diameter portion and the outer peripheral surface of the small-diameter portion, and faces the first step surface; A ring-shaped sealing member disposed between the second step surface and pressed against the first step surface and the second step surface may be provided. If it carries out like this, between a 1st level | step difference surface and a 2nd level | step difference surface can be sealed because a ring-shaped sealing member exists. Therefore, it can suppress that gas distribute | circulates between a housing and a ceramic member to an axial direction, and can suppress that the airtightness between the one end side and other end side of a sensor element falls.

  In the gas sensor according to the aspect of the invention including the sealing member, the sealing member may have an outer diameter Dp [mm] that is equal to or smaller than the outer diameter Dc2 [mm] of the large diameter portion. If it carries out like this, a sealing member will be hard to protrude to the outer diameter side rather than the outer peripheral surface of a large diameter part. Here, when the sealing member protrudes to the outer diameter side from the outer peripheral surface of the large diameter portion, when the corner portion between the outer peripheral surface of the large diameter portion and the second step surface expands by heating, the corner In some cases, expansion of the portion is restricted by the sealing member, and thermal stress concentrates 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, the 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 having a sealing member, the sealing member is a member that is thicker on the inner diameter side than the outer diameter side in a state where it is not pressed against the first step surface and the second step surface. There may be. In this case, for example, the position of the sealing member is less likely to be displaced in the radial direction as compared with a case where the thickness of the sealing member is not pressed. Therefore, when a gas sensor repeats temperature rising / falling, it can suppress that the position of a housing and a ceramic member shifts | deviates to radial direction. Therefore, it can suppress that the airtightness between the one end side and other end side of a sensor element falls.

  In the gas sensor according to the aspect of the invention including the sealing member, the axial distance between the first step surface and the second step surface may increase as the distance from the center axis of the ceramic member approaches. If it carries out like this, the pressing force via the sealing member from a housing to a ceramic member will have a component which goes to a central axis. Therefore, when a gas sensor repeats temperature rising / falling, it can suppress that the position of a housing and a ceramic member shifts | deviates to radial direction. Therefore, it can suppress that the airtightness between the one end side and the other end side of the sensor element 20 falls.

The schematic explanatory drawing which shows a mode that the gas sensor 10 was attached to the piping 90. FIG. 1 is a longitudinal sectional view of a gas sensor 10. FIG. FIG. 3 is an enlarged view around a housing 41 and a ceramic member 45 in FIG. 2.

  Next, embodiments 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 longitudinal sectional view of the gas sensor 10, and is a sectional view taken along the line AA of FIG. FIG. 3 is an enlarged view around the housing 41 and the ceramic member 45 of FIG. In the present embodiment, the vertical direction and the horizontal direction are as shown in FIGS.

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

  As shown in FIG. 2, the gas sensor 10 includes a sensor element 20, a protective layer 25 covering at least a part of the surface of the sensor element 20, and a distal end side including the distal end surface 20a of the sensor element 20 (the lower end side in FIG. 2). 2), the element sealing body 40 for sealing and fixing the sensor element 20, the protection on the base end side (upper end side in FIG. 2) including the base end face 20 b of the sensor element 20 and the sensor element 20. And an assembly 50 for taking out the electrical signal.

The sensor element 20 has a structure in which a plurality of oxygen ion conductive solid electrolyte layers such as zirconia (ZrO ₂ ) are stacked. The sensor element 20 is an element having a long plate-like shape (cuboid shape), and has a distal end surface 20a on the lower end side, a proximal end surface 20b on the upper end side, and four surfaces perpendicular to the distal end surface 20a and the proximal end surface 20b. And. The sensor element 20 has a measurement gas introduction port (not shown) for introducing a measurement gas into the inside of the tip surface 20a, and a specific gas concentration in the measurement gas flowing into the measurement gas introduction port from the inside. 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 20 a of the sensor element 20. The protective layer 25 serves to protect 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, for example, and is a cylindrical member that allows the measurement gas to flow into the element chamber 37 from the outside. The protective cover 30 includes a bottomed cylindrical inner protective cover 31 that covers the distal end side of the sensor element 20 and a bottomed cylindrical 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 disposed. Between the inner protective cover 31 and the outer protective cover 32, there is a gas chamber 38 that 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 an element chamber outlet 34 located on the bottom surface. The outer protective cover 32 is provided with a plurality of outer inlets 35 positioned on the side surface (outer peripheral surface) and an outer outlet 36 positioned on the bottom surface.

  The element sealing body 40 fixes the sensor element 20, and in the space (the element chamber 37 and the gas chamber 38) in the protective cover 30, which is the distal end side (lower side) of the sensor element, and the proximal end side (upper side). The space between the atmosphere side cover 74 is sealed. 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 includes a through hole 41 a in which a ceramic member 45 is inserted in an axial direction (vertical direction), a cylindrical first cylindrical portion 42, and a first cylindrical portion 42. And a cylindrical second cylindrical portion 43 connected coaxially with the first cylindrical portion 42. The first cylindrical portion 42 includes an inner peripheral surface 42a, and a first step surface 42b that connects between the upper end of the inner peripheral surface 42a and the lower end of the inner peripheral surface 43a of the second cylindrical portion 43. Yes. The first step surface 42b is a ring-shaped surface in a top view, and is closer to the protective cover 30 side (lower side) as it approaches 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. It is inclined to head. In other words, the first step surface 42b is inclined so as to be directed downward as the inner diameter side. The 2nd cylindrical part 43 is provided with the internal peripheral surface 43a with a larger internal diameter than the internal peripheral surface 42a. The inner diameter (the diameter of the inner peripheral surface 42a) of the first cylindrical portion 42 is referred to as an inner diameter dm1 [mm]. The inner diameter (the diameter of the inner peripheral surface 43a) of the second cylindrical portion 43 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 step surface 42b constitute a part of the through hole 41a. A small diameter portion 46 of the ceramic member 45 is inserted into the first tubular portion 42. A large diameter portion 47 of the ceramic member 45 is inserted into the second cylindrical portion 43. The upper end of the protective cover 30 is attached to the lower end of the first cylindrical 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. Thus, the gas sensor 10 is fixed to the pipe 90 in a state where the tip end side of the sensor element 20 and the protective cover 30 of the gas sensor 10 protrude into the pipe 90.

  The ceramic member 45 is a columnar member inserted into the through hole 41 a of the housing 41. The ceramic member 45 has a through hole coaxial with the central axis C, and the sensor element 20 passes through the inside in the axial direction. The ceramic member 45 is made of an insulating ceramic such as alumina, steatite, or zirconia. The ceramic member 45 includes a cylindrical small diameter portion 46 and a cylindrical large diameter portion 47 connected to the small diameter portion 46 coaxially with the small diameter portion 46. The small diameter portion 46 is located closer to the protective cover 30 (lower side) than the large diameter portion 47. The small diameter portion 46 includes an outer peripheral surface 46 a having an outer diameter smaller than that of the outer peripheral surface 47 a 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 step surface 47b that connects between 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 47 a faces the inner peripheral surface 43 a of the second tubular portion 43 in the radial direction. The second step surface 47b is a surface perpendicular to the central axis C and faces the first step surface 42b of the housing 41 in the vertical direction. A sealing material 49 is filled on the inner diameter side of the large diameter portion 47. The outer diameter of the small diameter portion 46 (the 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 (the 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 disposed between the first step surface 42b of the housing 41 and the second step surface 47b of the ceramic member 45, and is pressed from above and below by the first step surface 42b and the second step surface 47b. . Thereby, the sealing member 48 hermetically 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 by the diameter when the sealing member 48 was incorporated in the element sealing body 40 as shown in FIG. 3, that is, the first step surface 42b and the second step surface 47b. The diameter in the state. Moreover, it is preferable that the sealing member 48 is a member whose inner diameter side is thicker than the outer diameter side in a state where the sealing member 48 is not pressed by the first step surface 42b and the second step surface 47b. That is, it is preferable that the sealing member 48 is thicker on the inner diameter side than on the outer diameter side when no pressure is applied from the outside. In addition, the sealing member 48 may be pressed and deformed by the first step surface 42b and the second step surface 47b in a state where the sealing member 48 is 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 or 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 hermetically seals between the ceramic member 45 and the sensor element 20.

  Here, the positional relationship among the housing 41, the ceramic member 45, and the sealing member 48 of the element sealing body 40 will be described in detail. A gap exists between the inner peripheral surface of the housing 41 and the outer peripheral surface of the ceramic member 45 as shown in FIG. More specifically, a gap exists between the inner peripheral surface 42 a of the first tubular portion 42 and the outer peripheral surface 46 a of the small diameter portion 46. The radial distance W1 of the gap is 20 μm or more. Although details will be described later, when the distance W1 is 20 μm or more, damage to the ceramic member 45 due to heating during use of the gas sensor 10 can be suppressed. The distance W1 is an average value of gaps (diameter distance) over the entire circumference between the inner peripheral surface 42a and the outer peripheral surface 46a. Therefore, regardless of whether the central axes of the housing 41 and the ceramic member 45 coincide with each other, 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. Half the value of "". That is, W1 = (dm1−Dc1) / 2.

  Further, it is preferable that a gap exists also between the inner peripheral surface 43 a of the second cylindrical portion 43 and the outer peripheral surface 47 a of the large diameter portion 47. That is, the radial distance W2 of the gap may be 0 μm (no gap exists), but is preferably greater than 0 μm. Note that the distance W2 is also an average value of the gaps (radial distance) over the entire circumference in the same manner as the distance W1. Therefore, regardless of whether or not the central axes of the housing 41 and the ceramic member 45 coincide with each other, 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. Half the value of "". That is, W2 = (dm2-Dc2) / 2. Further, when the distance W2 exceeds 0 μm, the distance W2 is preferably equal to or less than the distance W1. That is, the ratio W1 / W2, which is the ratio of the distance W1 to the distance W2, is preferably 1 or more. The ratio W1 / W2 may be greater than the value 1. The ratio W1 / W2 may be a value of 100 or less, or a value of 10 or less.

  As described above, the first step surface 42 b is inclined so as to be directed toward the protective cover 30 (lower side) as it approaches the central axis C in the radial direction of the housing 41. The second step surface 47b is a surface perpendicular to the central axis C as described above. Accordingly, the first step surface 42 b and the second step surface 47 b become larger as the mutual distance in the axial direction (vertical direction) approaches the central axis C of the ceramic member 45. An angle θg (see a partially enlarged view of FIG. 3) formed by the first step surface 42b and the second step surface 47b 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 plug 73, an atmosphere side cover 74, an outer cover 75, and a disc spring 77. And. The insulator 55 is a bottomed cylindrical member, and is made of insulating ceramics like the ceramic member 45. The lower surface of the insulator 55 is in contact with the upper surface of the ceramic member 45, and is positioned coaxially with the ceramic member 45. The contact metal fitting 60 is a metal plate bent at a plurality of locations, and includes a leaf spring portion that is bent inward. A plurality of contact fittings 60 are provided on the left and right sides of the sensor element 20 (for example, two, three, etc.), and each of them comes into contact with a conduction electrode (not shown) provided on the surface of the sensor element 20. Conducted. Each end portion of the plurality of contact fittings 60 is drawn through a hole in the bottom portion on the upper side of the insulator 55 and is electrically connected to the lead wire 72 via the connection terminal 71. The lead wire 72 passes through a rubber plug 73 that closes the upper ends of the atmosphere-side cover 74 and the outer cover 75 in the vertical direction, and is drawn to the outside (outside the pipe 90 and in the atmosphere). The atmosphere-side cover 74 covers the proximal end (upper side) portion of the sensor element 20 on the outer peripheral surface of the second cylindrical portion 43. The atmosphere side cover 74 covers the insulator 55 and the rubber plug 73. The outer cover 75 covers the upper outer peripheral surface of the atmosphere-side cover 74. The atmosphere-side cover 74 and the outer cover 75 are each formed with a plurality of atmosphere introduction holes 76. A reference gas (atmosphere) serving as a reference for detecting a specific gas concentration is introduced into a reference gas introduction port (not shown) disposed on the base end face 20b of the sensor element 20 through the atmosphere introduction hole 76. The atmosphere-side cover 74 and the outer cover 75 have a crimped portion crimped in a reduced diameter near the upper end, and the rubber plug 73 is fixed by the crimped portion. The disc spring 77 is sandwiched between the atmosphere-side cover 74 and the insulator 55 at the upper and lower sides, and the insulator 55 and the ceramic member 45 are fixed by pressing the 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 to the outside (in the pipe 90) through the outer outlet 36. Then, when the gas to be measured flows into the sensor element 20 from the gas to be measured inlet when flowing through the element chamber 37, an electrical signal (for example, NOx concentration) corresponding to the specific gas concentration (for example, NOx concentration) in the gas to be measured. The sensor element 20 generates a voltage or current. The sensor element 20 generates an electrical signal corresponding to the specific gas concentration in the gas to be measured based on the reference gas introduced from the reference gas introduction port located in the atmosphere-side cover 74. By extracting this electrical signal through the contact fitting 60, the connection terminal 71, and the lead wire 72, the specific gas concentration is detected based on the electrical signal.

  As described above, the gas sensor 10 is heated to a high temperature by being heated by the measurement gas because the protective cover 30 side is exposed to the measurement gas during use. For this reason, the temperature of the gas sensor 10 is repeatedly raised and lowered during use and when it is not used. And the ceramic member 45 expand | swells when the gas sensor 10 becomes high temperature at the time of use. 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 the distance W1 of this gap is 20 μm or more as described above. If such a gap exists, there will be a space that allows expansion when the ceramic member 45 is heated. Therefore, the inner peripheral surface 42a of the housing 41 and the outer peripheral surface 46a of the ceramic member 45 are not in contact with each other. Even if contact is made, the radial stress from the inner peripheral surface 42a to the outer peripheral surface 46a is reduced. Therefore, the occurrence of breakage such as cracks in the ceramic member 45 due to heating can be suppressed. In addition, the effect which suppresses the failure | damage of the ceramic member 45 by heating tends to increase, so that the distance W1 is large. For example, the distance W1 may be 50 μm or more. Moreover, it is preferable that the distance W1 is 500 micrometers or less. When the distance W1 is 500 μm or less, it is possible to suppress the gas (measured gas or reference gas) from flowing in the gap between the housing 41 and the ceramic member 45 in the axial direction. As a result, gas hardly condenses 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 hardly occurs. Therefore, it can suppress that the airtightness between the one end side (front end surface 20a side) and the other end side (base end surface 20b side) of the sensor element 20 with the element sealing body 40 as a boundary is lowered. 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 are detected. If the airtightness between the two decreases, the detection accuracy decreases. Therefore, the fall of the detection accuracy of the specific gas concentration of the gas sensor 10 can be suppressed by suppressing the fall of the airtightness between the one end side and the other end side of the sensor element 20. Note that the smaller the distance W1, the higher the effect of suppressing the decrease in airtightness. For example, the distance W1 may be 300 μm or less, or 100 μm or less.

  In addition, if there is a gap between the inner peripheral surface 43 a of the second cylindrical portion 43 and the outer peripheral surface 47 a of the large diameter portion 47, the inner peripheral surface 43 a of the housing 41 is connected to the outer peripheral surface 47 a 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. As the distance W2 is larger, the ceramic member 45 is more likely to be prevented from being damaged by heating when the gas sensor 10 is used. For example, the distance W2 is preferably 5 μm or more. The distance W2 may be 20 μm or more. Moreover, it is preferable that the distance W2 is 500 micrometers or less. When the distance W2 is 500 μm or less, as in the case where the distance W1 is 500 μm or less, the gas is less likely to condense in the gap between the inner peripheral surface 43a and the outer peripheral surface 47a. For example, the housing 41, the sealing member 48, etc. Corrosion of the member related to the airtightness of the material becomes difficult to occur. Therefore, it can suppress more that the airtightness between the one end side and the other end side of the sensor element 20 falls. Note that 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.

  Furthermore, the sealing member 48 preferably has an outer diameter Dp that is equal to or smaller than the outer diameter Dc2 of the large-diameter portion 47. In this way, the sealing member 48 is unlikely to protrude beyond the outer peripheral surface 47a of the large diameter portion 47 on the outer diameter side. Here, when the sealing member 48 protrudes to the outer diameter side of 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 step surface 47b (see FIG. 3 is expanded by heating, the expansion may be restricted by the sealing member 48. Thereby, thermal stress may concentrate on the corner | angular part 47c. Since the outer diameter Dp of the sealing member 48 is equal to or smaller than the outer diameter Dc2 of the large-diameter portion 47, the concentration of thermal stress on the corner portion 47c can be suppressed, and the ceramic member 45 is damaged by heating (particularly the corner portion 47c and its portion). (Peripheral damage) can be suppressed. The outer diameter Dp may be less than the outer diameter Dc2. Moreover, it is preferable that the sealing member 48 and the ceramic member 45 satisfy | fill following formula (1). The left side of the expression (1) indicates the radial movement of the sealing member 48 until the sealing member 48 and the ceramic member 45 are coaxially shifted from the coaxial state. Corresponds to distance. In addition, the right side of the expression (1) indicates a movement distance that does not cause a portion protruding from the outer peripheral surface 47a to the outer diameter side even when the sealing member 48 is displaced in the radial direction from the coaxial state of the sealing member 48 and the ceramic member 45. It corresponds to the maximum value of. By satisfying this expression (1), even when 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 beyond 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. The ceramic member 45 can be prevented from being damaged. Moreover, since distance W1 is 500 micrometers or less, it can suppress that the airtightness between the one end side of the sensor element 20 and the other end side falls.

  The ceramic member 45 includes a cylindrical large-diameter portion 47 and a cylindrical small-diameter portion 46 that is located closer to the protective cover 30 than the large-diameter portion 47 and has a smaller outer diameter than the large-diameter portion 47. is doing. The distance W1 is the distance in the radial direction of the gap 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 the large-diameter portion 47 and the small-diameter portion 46, the small-diameter portion 46 close to the protective cover 30 is easily heated by the gas to be measured and thus is easily 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 is a gap only between the large diameter portion 47 and the inner peripheral surface 43a of the housing 41. In comparison, breakage of the ceramic member 45 due to heating can be further suppressed.

  Further, the large-diameter portion 47 has a gap with the inner peripheral surface 43a of the through hole 41a, and the radial distance W2 of this gap is 5 μm or more. Thus, 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 due to heating is provided. Can be more suppressed. Moreover, since distance W2 is 500 micrometers or less, it can suppress that the airtightness between the one end side of the sensor element 20 and the other end side falls.

  Furthermore, when the ratio W1 / W2 is equal to or greater than 1, that is, the distance W2 is equal to or less than the distance W1, when the gas sensor 10 is heated, the large-diameter portion 47 is not easily heated because it is far from the protective cover 30. This makes it easier to contact the housing 41 before the small diameter portion 46. As a result, the small diameter portion 46 that is easily heated due to being easily heated does not come into contact with the housing 41, or the radial stress from the housing 41 is relieved even if the small diameter portion 46 comes into contact. Therefore, damage to the ceramic member 45 can be further suppressed.

  In addition, the gas sensor 10 is disposed between the first step surface 42b and the second step surface 47b, and is ring-shaped sealing member 48 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 step surface 42b and the second step surface 47b. Therefore, it is possible to suppress the gas from flowing between the housing 41 and the ceramic member 45 in the axial direction, and it is possible to suppress a decrease in the airtightness between the one end side and the other end side of the sensor element 20. Further, since the outer diameter Dp of the sealing member 48 is equal to or smaller than the outer diameter Dc <b> 2 of the large diameter portion 47, the sealing member 48 is less likely to protrude beyond the outer peripheral surface 47 a of the large diameter portion 47. Thereby, concentration of the thermal stress to 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.

  The sealing member 48 is a member that is thicker on the inner diameter side than the outer diameter side in a state where it is not pressed against the first step surface 42b and the second step surface 47b. Therefore, for example, the position of the sealing member 48 is less likely to be displaced in the radial direction as compared with a case where the thickness of the sealing member 48 is not pressed. Thereby, when the gas sensor 10 repeats raising / lowering temperature, it can suppress that the position of the housing 41 and the ceramic member 45 shifts | deviates to radial direction. As a result, it can suppress that the airtightness between the one end side and the other end side of the sensor element 20 falls.

  In addition, the axial distance between the first step surface 42b and the second step surface 47b increases as the distance from the central axis C of the ceramic member 45 approaches. In other words, the angle θg formed in FIG. 3 exceeds 0 °. Thereby, 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 to 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 partial enlarged view of FIG. 3, and thus has a component toward the central axis C (a rightward component in the partial enlarged view of FIG. 3). It becomes like this. 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 repeats raising / lowering temperature, it can suppress that the position of the housing 41 and the ceramic member 45 shifts | deviates to radial direction. As a result, it can suppress that the airtightness between the one end side and the other end side of the sensor element 20 falls.

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

  For example, in the above-described embodiment, the first step surface 42b is inclined downward toward the inner diameter side, but is not limited thereto. If the axial distance between the first step surface 42b and the second step surface 47b increases toward the central axis of the ceramic member 45, the radial position of the ceramic member 45 as in the embodiment described above. The effect of suppressing the shift is obtained. For example, in addition to or instead of the inclination of the first step surface 42b, the second step surface 47b may also be inclined. Specifically, the second step surface 47b may be inclined so as to be directed to the side opposite to the protective cover 30 side (upper side) as it approaches the central axis C in the radial direction of the housing 41. Further, the axial distance between the first step surface 42 b and the second step surface 47 b may decrease as the distance from the central axis C of the ceramic member 45 approaches. Alternatively, the first step surface 42b and the second step surface 47b may be parallel.

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

  In the embodiment described above, the ceramic member 45 includes the small diameter portion 46 and the 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 cylindrical shape without the second step 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 the gap is 20 μm or more, the ceramic member is not damaged by heating as in the above-described embodiment. The effect of suppressing is acquired. In addition to the small diameter portion 46 and the large diameter portion 47, the ceramic member 45 may include a columnar member connected coaxially thereto. Similarly, the shape of the housing 41 is not limited to the above-described embodiment.

  In the embodiment described above, there is a gap of 20 μm or more between the inner peripheral surface 42a of the first cylindrical 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. May be. Even in this case, if there is a gap having a distance of 20 μm or more between the inner peripheral surface 43a of the second cylindrical portion 43 and the outer peripheral surface 47a of the large-diameter portion 47, the effect of suppressing breakage of the ceramic member due to heating can be obtained. 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 between the ceramic member and the housing, an effect of suppressing breakage of the ceramic member due to heating can be obtained. However, since the small-diameter portion 46 is easily heated and damaged by the gas to be measured as much as the protective cover 30, the small-diameter portion 46 is between the inner peripheral surface 42 a of the first cylindrical portion 42 and the outer peripheral surface 46 a of the small-diameter portion 46. It is preferable that a gap having a distance of 20 μm or more exists.

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

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

  Below, the example which produced the gas sensor concretely is demonstrated 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. In addition, this invention is not limited to a following example.

[Experimental Examples 1 to 10]
A gas sensor having the same configuration as that of the gas sensor 10 shown in FIGS. 2 and 3 was manufactured 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. Experimental Example 1 -10. In Experimental Examples 1 to 10, the inner diameter dm2 of the second cylindrical portion 43 of the housing 41 and the outer diameter Dc2 of the large diameter portion 47 of the ceramic member 45 were both 14.5 mm. The distance W1 was adjusted by changing the outer diameter Dc1 of the small diameter portion 46 of the ceramic member 45 while keeping the inner diameter dm1 of the first cylindrical portion 42 of the housing 41 constant at 10.5 mm. 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 sealing member 48 is not pressed against the first step surface 42b and the second step surface 47b. The angle θg formed by the first step surface 42b and the second step surface 47b was 3 °.

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

[Experimental Examples 19 to 26]
Except that the distance W1 is constant at 100 μm and the distance W2 is variously changed between 10 μm and 300 μm as shown in Table 1, gas sensors having the same configurations as those of Experimental Examples 11 to 18 are manufactured. It was. The inner diameter dm1 and the outer diameter Dc1 were the same as in Experimental Example 6. The adjustment of the distance W2 is performed by changing the outer diameter Dc2 of the large-diameter portion 47 of the ceramic member 45 while making the inner diameter dm2 of the second cylindrical portion 43 of the housing 41 constant at 14.5 mm, as in Experimental Examples 11-18. I went there.

[Thermal endurance test]
About the gas sensor of Experimental Examples 1-26, the thermal endurance test was done and the presence or absence of the crack of the ceramic member 45 and the position shift was investigated. Specifically, the test was conducted as follows. After the housing 41 was heated to 600 ° C., a thermal stress that submerges the gas sensor was applied, and this was defined as one temperature raising / lowering cycle. And after repeating the temperature raising / lowering cycle 3000 times and after 6000 times, the presence or absence of the crack of the ceramic member 45 and the presence or absence of the position shift of the radial direction of the ceramic member 45 were investigated. As for the presence or absence of cracks, “A (excellent)” indicates that no cracks were observed after 6000 heating / cooling cycles, and “B (good)” indicates that no cracks were observed after 3000 repetitions. The case where cracks were observed after repeating 3000 times was evaluated as “C (impossible)”. Regarding the positional deviation, after the temperature increasing / decreasing cycle is repeated 6000 times, the position of the ceramic member 45 with respect to the housing 41 is visually displaced (when the housing 41 and the ceramic member 45 are not coaxial). “Yes”. When the position of the ceramic member 45 was not shifted in the radial direction, it was evaluated as “none”. Table 1 summarizes the distance W1, distance W2, ratio W1 / W2, and thermal endurance test results of Experimental Examples 1 to 26.

  As shown in Table 1, in each of Experimental Examples 3 to 26 in which the distance W1 is 20 μm or more, the evaluation regarding the crack 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 each of Experimental Examples 11 to 26 in which the distance W2 exceeds 0 μm, the evaluation regarding the crack is “A (excellent)”, and the ceramic member 45 by heating compared to the Experimental Examples 3 to 10 in which the distance W2 is 0 μm. It was possible to further suppress the damage. Further, in Experimental Examples 11 to 15 and 19 to 23 in which the ratio W1 / W2 is equal to or greater than 1, even when both the distance W1 and the distance W2 exceed 0 μm, the ceramic member 45 is not displaced. . On the other hand, in Experimental Examples 16 to 18 and 24 to 26 in which the ratio W1 / W2 is less than 1, a positional deviation occurred. Here, when the positional deviation occurs, the radial stress from the housing 41 to the ceramic member 45 is biased, and the ceramic member 45 may be easily damaged at a portion where the stress is large. Therefore, in all of the experimental examples 11 to 26, the evaluation regarding the crack was “A (excellent)”, but in the experimental examples 11 to 15 and 19 to 23 in which the ratio W1 / W2 is 1 or more, the ratio W1 / W2 It is considered that breakage is less likely to occur as compared with Experimental Examples 16 to 18 and 24 to 26 in which is less than 1. For example, when the temperature increasing / decreasing cycle is further repeated over 6000 times, it is considered that the experimental examples 11 to 15 and 19 to 23 are less likely to be damaged than the experimental examples 16 to 18 and 24 to 26.

  DESCRIPTION OF SYMBOLS 10 Gas sensor, 20 Sensor element, 20a Front end 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 sealing body, 41 Housing, 41a Through hole, 42 1st cylindrical part, 42a Inner peripheral surface, 42b 1st level | step difference surface, 43 2nd cylindrical part, 43a Inner periphery Surface, 45 ceramic member, 46 small diameter portion, 46a outer peripheral surface, 47 large diameter portion, 47a outer peripheral surface, 47b second step surface, 47c corner portion, 48 sealing member, 49 sealing material, 50 assembly, 55 insulator, 60 Contact metal fitting, 71 Connection terminal, 72 Lead wire, 73 Rubber plug, 74 Air side cover, 75 Outer cover, 76 Air introduction hole, 77 Disc spring, 9 0 piping, 91 fixing member, C central axis.

Claims (10)

A long sensor element capable of detecting a specific gas concentration in the gas to be measured;
A cylindrical ceramic member in which the sensor element penetrates the inside in the axial direction;
The ceramic member has a through hole inserted therein in the axial direction, and has a gap between the inner peripheral surface of the through hole and the ceramic member, and a radial distance W1 of the gap is 20 μm or more. A cylindrical housing which is
Gas sensor equipped with. The distance W1 is 500 μm or less.
The gas sensor according to claim 1. The gas sensor according to claim 1 or 2,
A protective cover that covers the tip side of the sensor element and allows the gas to be measured to flow inside;
With
The ceramic member has a cylindrical large-diameter portion, and a cylindrical small-diameter portion that is located closer to the protective cover than the large-diameter portion and has an outer diameter smaller than the large-diameter portion,
The distance W1 is a radial distance of a gap between the outer peripheral surface of the small diameter portion and the inner peripheral surface of the through hole.
Gas sensor. The ceramic member has a gap between the large diameter portion and an inner peripheral surface of the through hole, and a 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. A ratio W1 / W2 that is a ratio of the distance W1 and the distance W2 is a value of 1 or more.
The gas sensor according to claim 4 or 5. The gas sensor according to any one of claims 3 to 6,
The housing includes a first cylindrical portion in which an inner peripheral surface forms part of the through hole and the small diameter portion is inserted therein, and an inner peripheral surface forms part of the through hole and the large diameter. A second cylindrical part having a larger inner diameter than the first cylindrical part, a part of the first cylindrical part, an inner peripheral surface of the first cylindrical part, and the first cylindrical part. A first step surface connecting the inner peripheral surface of the two cylindrical portions,
The ceramic member has a second step surface that is a part of the large-diameter portion, connects the outer peripheral surface of the large-diameter portion and the outer peripheral surface of the small-diameter portion, and faces the first step surface,
A ring-shaped sealing member disposed between the first step surface and the second step surface and pressed against the first step surface and the second step surface;
Gas sensor equipped with. The sealing member has an outer diameter Dp [mm] that is equal to or smaller than an outer diameter Dc2 [mm] of the large diameter portion.
The gas sensor according to claim 7. The sealing member is a member in which the inner diameter side is thicker than the outer diameter side in a state where the sealing member is not pressed against the first step surface and the second step surface.
The gas sensor according to claim 7 or 8. The axial distance between the first step surface and the second step surface increases as the distance from the central axis of the ceramic member increases.
The gas sensor according to any one of claims 7 to 9.