JP2021060218A - Gas sensor - Google Patents

Abstract

To suppress a sensor element from being exposed to water.SOLUTION: A gas sensor 100 comprises a sensor element 110, an inside protective cover 130 having a sensor element chamber 124 inside, and an outside protective cover 140 disposed on an outside of the inside protective cover 130. The inside protective cover 130 includes a first member 131 that encloses the sensor element 110 and a second member 135 that encloses the first member 131. The second member 135 includes a second cylindrical part 136 that encloses the first member 131, a bottom part 138e facing a tip face 110c of the sensor element 110, and a tapered part 138d provided between the second cylindrical part 136 and the bottom part 138e, with an element chamber outlet 138a disposed in the tapered part 138d. The gas sensor 100 satisfies X≥7.5 and/or Y2+667/X≤120, where X[mm] represents a distance between the tip face 110c and the bottom part 138e and Y[mm] represents a diameter of the bottom part 138e.SELECTED DRAWING: Figure 7

Description

The present invention relates to a gas sensor.

Conventionally, a gas sensor that detects a predetermined gas concentration such as NOx or oxygen in a gas to be measured such as an exhaust gas of an automobile has been known. The gas sensor is, for example, an inner protective cover having a sensor element, a sensor element chamber in which the sensor element is arranged, and an element chamber inlet and an element chamber outlet arranged, and an outer side in which an outer inlet and an outer outlet are arranged. It has a protective cover. The gas to be measured reaches the sensor element chamber from the outside of the gas sensor through the outer inlet and the element chamber inlet, and a part of the gas is introduced into the sensor element. The gas to be measured that has reached the sensor element chamber is then discharged to the outside through the element chamber outlet and the outer outlet. By the way, since the gas sensor is used at the temperature at which the sensor element is activated (for example, 850 ° C.), when the sensor element is exposed to water, the sensor element may be cracked due to thermal shock. Therefore, it has been studied to suppress the water exposure of the sensor element. For example, in Patent Document 1, the shortest distance from the outer inlet to the gas introduction port provided in the sensor element is adjusted to prevent external moisture or the like flowing in from the outer inlet from reaching the sensor element. In the gas sensor of Patent Document 1, the element chamber inlet is formed as, for example, a gap between the tubular first member surrounding the sensor element and the bottomed tubular second member surrounding the first member, and the element chamber outlet is the first. 2 It is formed on the bottom of the member. Further, for example, in Patent Document 2, the element chamber inlet is arranged on the side of the inner protective cover so as not to overlap the outer inlet in the axial direction, and the element chamber outlet is arranged on the side instead of the bottom of the inner protective cover to protect the inside. The bottom of the cover and the outer outlet overlap in the axial direction to prevent water from entering the inner protective cover directly. In the gas sensor of Patent Document 2, the side portion of the inner protective cover is provided parallel to the central axis of the inner protective cover.

JP-A-2017-223621 JP-A-2015-99142

However, in Patent Document 1, the sensor element may be exposed to water when gas suddenly flows in from the outside of the element chamber outlet. Further, Patent Document 2 has a problem that when water is present in the inner protective cover, it is difficult for water to be discharged and the sensor element is easily exposed to water.

The present invention has been made to solve such a problem, and an object of the present invention is to suppress water exposure of a sensor element.

The present invention has taken the following measures to achieve the above-mentioned main object.

The gas sensor of the present invention
A sensor element having a gas introduction port for introducing a gas to be measured and capable of detecting a specific gas concentration of the gas to be measured that has flowed into the inside from the gas introduction port.
It has a sensor element chamber in which the tip of the sensor element and the gas introduction port are arranged inside, and is one or more element chamber inlets which are inlets to the sensor element chamber and outlets from the sensor element chamber. A tubular inner protective cover in which one or more element chamber outlets are arranged, and
One or more outer inlets which are inlets of the gas to be measured from the outside and one or more outer outlets which are outlets of the gas to be measured to the outside are arranged and arranged outside the inner protective cover. With a tubular outer protective cover
With
The inner protective cover has a tubular first member surrounding the sensor element and a tubular second member surrounding the first member.
The first member and the second member form the element chamber entrance as a gap between the first member and the second member.
The second member is provided between a side portion surrounding the first member, a bottom portion provided at a position facing the tip surface of the sensor element, and the side portion and the bottom portion, and is provided from the side portion side. A tapered portion whose diameter is reduced toward the bottom side is provided, and the element chamber outlet is arranged in the tapered portion.
When the distance between the tip surface of the sensor element and the bottom of the second member is X [mm] and the diameter of the bottom of the second member is Y [mm], X ≧ 7.5 and It ^{satisfies at least one of Y 2} + 667 / X ≦ 120.

In this gas sensor, since the element chamber outlet is arranged not at the bottom but at the tapered portion, even if gas suddenly flows in from the outside of the element chamber outlet, it is difficult for the gas flow to concentrate in the sensor element direction, and the gas. It is possible to prevent water from reaching the sensor element along the flow. Further, the gas sensor is often used with its central axis tilted with respect to the vertical direction. In such a case, since the element chamber outlet is arranged in a tapered portion that is not parallel to the central axis of the inner protective cover, it is inside. The water in the protective cover is easily discharged from the element chamber outlet due to its own weight. Further, the distance X [mm] between the tip surface of the sensor element and the bottom of the second member and the diameter Y [mm] of the bottom of the second member ^{are among X ≧ 7.5 and Y 2} + 667 / X ≦ 120. When at least one of the above is satisfied, the sensor element is less likely to be exposed to water. When X ≧ 7.5 is satisfied, even if water accumulates on the bottom of the second member, it is considered that the sensor element is unlikely to be exposed to water because the distance between the accumulated water and the sensor element is sufficiently long. Further, when Y ² + 667 / X ≦ 120 is satisfied, the sensor element is less likely to be exposed to water because the distance X is relatively long, and even if the diameter Y of the bottom of the second member is relatively small and water accumulates on the bottom. Since water is likely to be discharged from the outlet of the element chamber while the amount is small, it is considered that the amount of water accumulated inside the second member is suppressed and the water exposure of the sensor element is suppressed. The smaller the diameter Y, the less likely the sensor element is to be exposed to water even if the distance X is short. As described above, the gas sensor of the present invention can suppress the water exposure of the sensor element.

In the gas sensor of the present invention, the distance X and the diameter Y ^{may satisfy Y 2} + 667 / X ≦ 112. In this way, the water exposure of the sensor element can be further suppressed.

In the gas sensor of the present invention, the distance X and the diameter Y may satisfy at least one of X ≦ 13 and Y ≦ 6. By doing so, it is possible to suppress water exposure of the sensor element while keeping the size of the gas sensor relatively small.

In the gas sensor of the present invention, the depth Z [mm] from the bottom of the second member to the lower end of the element chamber outlet may satisfy Z ≦ 2.5. By doing so, the water is discharged from the element chamber outlet while the amount of water accumulated at the bottom of the second member is smaller, and the amount of water accumulated inside the second member is further suppressed, so that the water exposure of the sensor element can be further suppressed. ..

In the gas sensor of the present invention, the first member and the second member are elements that are openings on the sensor element chamber side of the element chamber entrance with the direction from the rear end to the tip of the sensor element facing downward. The element chamber entrance may be formed so that the side opening opens downward. In this way, the gas to be measured flows downward into the sensor element chamber from the entrance of the element chamber separated from the sensor element by the first member, so that the water reaches the sensor element even if the gas to be measured contains water. It's hard to do. Here, "the element-side opening opens downward" means that the opening is parallel to the downward direction and the opening is inclined from the lower direction so as to approach the sensor element as the downward direction. Including the case of doing.

In the gas sensor of the present invention, the first member has a first cylindrical portion surrounding the sensor element.
The second member has a second cylindrical portion having a diameter larger than that of the first cylindrical portion.
The element chamber entrance may be a cylindrical gap between the outer peripheral surface of the first cylindrical portion and the inner peripheral surface of the second cylindrical portion.

The schematic explanatory view of the attachment state of the gas sensor 100 to the pipe 20. FIG. 1A is a cross-sectional view taken along the line AA of FIG. BB sectional view of FIG. FIG. 3 is a sectional view taken along the line CC of FIG. FIG. 3 is a cross-sectional view taken along the line CC of the outer protective cover 140 of FIG. FIG. 3D view of FIG. An enlarged view of the inner protective cover 130 of FIG. 3 and the inside thereof. The vertical sectional view of the gas sensor 200 of the modification. FIG. 8 is a sectional view taken along line FF of the outer protective cover 240 of FIG. G view of FIG. The cross-sectional view which shows the element chamber entrance 327 of the modification. The vertical sectional view of the gas sensor 400 of the modification. The graph which shows the relationship between the distance X and the diameter Y, and the water amount.

Next, a mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a schematic explanatory view of a state in which the gas sensor 100 is attached to the pipe 20. FIG. 2 is a cross-sectional view taken along the line AA of FIG. FIG. 3 is a cross-sectional view taken along the line BB of FIG. FIG. 4 is a cross-sectional view taken along the line CC of FIG. FIG. 5 is a cross-sectional view taken along the line CC of the outer protective cover 140 of FIG. Note that FIG. 5 corresponds to a diagram in which the first cylindrical portion 134, the second cylindrical portion 136, the tip portion 138, and the sensor element 110 are excluded from FIG. FIG. 6 is a view D of FIG. FIG. 7 is an enlarged view of the inner protective cover 130 of FIG. 3 and the inside thereof. The direction parallel to the axial direction of the protective cover 120 and from the front end to the rear end of the sensor element 110 (upward in FIGS. 3 and 7) is upward, and parallel to the axial direction of the protective cover 120 and behind the sensor element 110. The direction from the end to the tip (downward in FIGS. 3 and 7) is the downward direction.

As shown in FIG. 1, the gas sensor 100 is mounted in a pipe 20 which is an exhaust path from the engine of the vehicle, and NOx, ammonia, O _2, etc. contained in the exhaust gas as the gas to be measured discharged from the engine. The specific gas concentration, which is the concentration of at least one specific gas among the gas components of the above, is detected. As shown in FIG. 2, the gas sensor 100 is fixed in the pipe 20 in a state where the central axis of the gas sensor 100 is perpendicular to the flow of the gas to be measured in the pipe 20. In a state where the central axis of the gas sensor 100 is tilted by a predetermined angle (for example, any angle included between 45 ° and 80 °) with respect to the vertical direction perpendicular to the flow of the gas to be measured in the pipe 20. It may be fixed in the pipe 20.

As shown in FIG. 3, the gas sensor 100 includes _{a sensor element 110 having a function of detecting a specific gas concentration (concentration of NOx, ammonia, O 2,} etc.) in the gas to be measured, and a protective cover for protecting the sensor element 110. It is equipped with 120. Further, the gas sensor 100 includes a metal housing 102 and a metal bolt 103 having screws on the outer peripheral surface. The housing 102 is inserted into a fixing member 22 welded to the pipe 20 and provided with a female screw on the inner peripheral surface, and the housing 102 is inserted into the fixing member 22 by further inserting the bolt 103 into the fixing member 22. It is fixed in 22. As a result, the gas sensor 100 is fixed in the pipe 20. The direction in which the gas to be measured flows in the pipe 20 is the direction from left to right in FIG.

The sensor element 110 is an elongated plate-shaped element, and has an element body 110b having a structure in which a plurality of oxygen ion conductive solid electrolyte layers such as _{zirconia (ZrO 2) are laminated.} The element main body 110b has a gas introduction port 111 that introduces the gas to be measured into its own interior, and is configured to be able to detect a specific gas concentration of the gas to be measured that has flowed into the inside from the gas introduction port 111. In the present embodiment, the gas introduction port 111 is assumed to be open to the tip surface of the element body 110b (the lower surface of the element body 110b in FIG. 3). The sensor element 110 includes a heater inside which plays a role of temperature control for heating and keeping the sensor element 110 warm. The structure of such a sensor element 110 and the principle of detecting a specific gas concentration are known, and are described in, for example, Japanese Patent Application Laid-Open No. 2008-164411. The sensor element 110 has a tip (lower end in FIG. 3) and a gas introduction port 111 arranged in the sensor element chamber 124. The direction from the rear end to the tip of the sensor element 110 (downward direction) is also referred to as the tip direction.

Further, the sensor element 110 includes a porous protective layer 110a that covers at least a part of the surface of the element body 110b. In the present embodiment, the porous protective layer 110a is formed on five of the six surfaces of the element body 110b and covers most of the exposed surfaces in the sensor element chamber 124. Specifically, the porous protective layer 110a covers the entire tip surface (lower surface) of the element body 110b on which the gas introduction port 111 is formed. Further, the porous protective layer 110a covers the side of the four surfaces (upper, lower, left and right surfaces in the element body 110b in FIG. 4) connected to the tip surface of the element body 110b, which is closer to the tip surface of the element body 110b. .. The porous protective layer 110a plays a role of suppressing, for example, moisture in the gas to be measured from adhering to the element main body 110b to cause cracks. Further, the porous protective layer 110a plays a role of suppressing the oil component or the like contained in the gas to be measured from adhering to the electrode or the like (not shown) on the surface of the element main body 110b. The porous protective layer 110a is made of, for example, an alumina porous body, a zirconia porous body, a spinel porous body, a cordierite porous body, a titania porous body, a magnesia porous body, or the like. The porous protective layer 110a can be formed by, for example, plasma spraying, screen printing, dipping, or the like. The porous protective layer 110a also covers the gas introduction port 111, but since the porous protective layer 110a is a porous body, the gas to be measured circulates inside the porous protective layer 110a and flows through the gas introduction port. It is possible to reach 111. The thickness of the porous protective layer 110a is, for example, 100 μm to 700 μm.

The protective cover 120 is arranged so as to surround the sensor element 110. The protective cover 120 has a bottomed tubular inner protective cover 130 that covers the tip of the sensor element 110, and a bottomed tubular outer protective cover 140 that covers the inner protective cover 130. Further, the first gas chamber 122 and the second gas chamber 126 are formed as a space surrounded by the inner protective cover 130 and the outer protective cover 140, and the sensor element chamber 124 is formed as a space surrounded by the inner protective cover 130. ing. The central axes of the gas sensor 100, the sensor element 110, the inner protective cover 130, and the outer protective cover 140 are coaxial. The protective cover 120 is made of metal (for example, stainless steel such as SUS310S).

The inner protective cover 130 includes a first member 131 and a second member 135. The first member 131 is a stepped portion connecting a cylindrical large-diameter portion 132, a cylindrical first cylindrical portion 134 having a diameter smaller than that of the large-diameter portion 132, and the large-diameter portion 132 and the first cylindrical portion 134. It has 133 and. The first cylindrical portion 134 surrounds the sensor element 110. The second member 135 has a second cylindrical portion 136 (corresponding to the side portion of the present invention) having a diameter larger than that of the first cylindrical portion 134 and a tip direction (downward) side of the sensor element 110 with respect to the second cylindrical portion 136. It has a tip portion 138 located at, and a connecting portion 137 connecting the lower end of the second cylindrical portion 136 and the upper end of the tip portion 138. The tip portion 138 has a bottom portion 138e provided at a position facing the tip surface 110c of the sensor element 110, and a tapered portion 138d whose diameter is reduced from the second cylindrical portion 136 side to the bottom portion 138e side. The bottom portion 138e is a portion surrounded by a tapered portion 138d, and the inner surface of the bottom portion 138e (the surface facing the sensor element 110) is a circular plane or a point. The tapered portion 138d is formed with one or more element chamber outlets 138a that communicate with the sensor element chamber 124 and the second gas chamber 126 and are outlets for the gas to be measured from the sensor element chamber 124. The element chamber outlet 138a has a plurality of (four in this embodiment) circular holes 138b formed at equal intervals along the circumferential direction in the tapered portion 138d. The element chamber outlet 138a is not arranged at the bottom 138e of the tip 138. The diameter of the element chamber outlet 138a is, for example, 0.5 mm to 2.6 mm. In the present embodiment, the diameters of the plurality of holes 138b are all set to the same value. The element chamber outlet 138a is formed at a position closer to the tip end direction (downward direction) of the sensor element 110 than the gas introduction port 111. In other words, the element chamber outlet 138a is located farther (downward) from the gas introduction port 111 when viewed from the rear end of the sensor element 110 (the upper end of the sensor element 110 not shown in FIG. 3).

In the second member 135, when the distance between the tip surface 110c of the sensor element 110 and the bottom portion 138e of the second member 135 is X [mm] and the diameter of the bottom portion 138e of the second member 135 is Y [mm] ( (See FIG. 7), it is provided so as to satisfy at least one of ^{X ≧ 7.5 and Y 2 + 667 / X ≦ 120.} The distance X is the distance between the virtual plane including the front end surface 110c and perpendicular to the vertical direction in FIG. 7 and the virtual plane including the inner surface of the bottom 138e and perpendicular to the vertical direction in FIG. 7. The distance X may satisfy X ≧ 667/120, and may satisfy, for example, X ≦ 13. The diameter Y is the diameter of a circular plane or point that is the inner surface of the bottom 138e. The diameter Y may satisfy Y ≧ 0, and may satisfy, for example, Y ≦ 6. The diameter (inner diameter) D [mm] of the rear end portion having the largest inner diameter among the tapered portions 138d may satisfy, for example, 4.9 ≦ D ≦ 7.4. Further, the length L [mm] of the tapered portion 138d in the vertical direction may satisfy, for example, 3.8 ≦ L ≦ 6.5. The length L is the distance between the virtual plane including the rear end surface of the tapered portion 138d and perpendicular to the vertical direction in FIG. 7 and the virtual plane including the inner surface of the bottom portion 138e and perpendicular to the vertical direction in FIG. Further, the inclination θ [°] of the inner surface of the tapered portion 138d with respect to the axial direction of the second member (vertical direction in FIG. 7) may satisfy, for example, 10 ≦ θ ≦ 80, or 10 ≦ θ ≦ 45. It may be a thing. Further, the element chamber outlet 138a may have a depth Z [mm] (see FIG. 7) from the bottom 138e of the second member 135 to the lower end of the element chamber outlet 138a satisfying, for example, Z ≦ 2.5. The distance X, the length L, and the depth Z are the vertical lengths in FIG. 7, and the diameter Y and the diameter D are the horizontal lengths in FIG. 7.

The large diameter portion 132, the first cylindrical portion 134, the second cylindrical portion 136, and the tip portion 138 have the same central axis. The inner peripheral surface of the large diameter portion 132 is in contact with the housing 102, whereby the first member 131 is fixed to the housing 102. The outer peripheral surface of the connecting portion 137 of the second member 135 is in contact with the inner peripheral surface of the outer protective cover 140 and is fixed by welding or the like. The outer diameter of the tip side (lower end side) of the connection portion 137 is formed to be slightly larger than the inner diameter of the tip portion 146 of the outer protective cover 140, and the tip portion of the connection portion 137 is press-fitted into the tip portion 146. The second member 135 may be fixed.

On the inner peripheral surface of the second cylindrical portion 136, a plurality of protruding portions 136a are formed so as to project toward the outer peripheral surface of the first cylindrical portion 134 and are in contact with the outer peripheral surface. As shown in FIG. 4, three projecting portions 136a are provided and are evenly arranged along the circumferential direction of the inner peripheral surface of the second cylindrical portion 136. The protruding portion 136a is formed in a substantially hemispherical shape. By providing such a protruding portion 136a, the positional relationship between the first cylindrical portion 134 and the second cylindrical portion 136 can be easily fixed by the protruding portion 136a. The protruding portion 136a preferably presses the outer peripheral surface of the first cylindrical portion 134 inward in the radial direction. In this way, the positional relationship between the first cylindrical portion 134 and the second cylindrical portion 136 can be more reliably fixed by the protruding portion 136a. The number of protruding portions 136a is not limited to three, and may be two or four or more. Since the fixing between the first cylindrical portion 134 and the second cylindrical portion 136 is easy to stabilize, it is preferable that the number of protruding portions 136a is three or more.

The inner protective cover 130 forms an element chamber inlet 127 (see FIGS. 3, 4, 7) which is a gap between the first member 131 and the second member 135 and is an inlet of the gas to be measured to the sensor element chamber 124. ing. More specifically, the element chamber inlet 127 is formed as a cylindrical gap (gas flow path) between the outer peripheral surface of the first cylindrical portion 134 and the inner peripheral surface of the second cylindrical portion 136. The element chamber inlet 127 is on the side of the sensor element chamber 124, which is the space where the gas introduction port 111 is arranged, and the outer opening 128, which is the opening on the first gas chamber 122 side, which is the space where the outer inlet 144a is arranged. It has an element-side opening 129, which is an opening. The outer opening 128 is formed on the rear end side (upper side) of the sensor element 110 with respect to the element side opening 129. Therefore, in the path of the gas to be measured from the outer inlet 144a to the gas introduction port 111, the element chamber inlet 127 becomes a flow path from the rear end side (upper side) to the tip end side (lower side) of the sensor element 110. ing. Further, the element chamber inlet 127 is a flow path parallel to the rear end-tip direction of the sensor element 110 (a flow path parallel to the vertical direction).

The element-side opening 129 opens in the direction from the rear end of the sensor element 110 toward the tip (downward) and parallel to the rear end-tip direction (vertical direction) of the sensor element 110. That is, the element-side opening 129 opens parallel to the downward direction. Therefore, the sensor element 110 is arranged at a position other than the region in which the element chamber entrance 127 is virtually extended from the element-side opening 129 (the region directly below the element-side opening 129 in FIGS. 3 and 7). As a result, it is possible to prevent the gas to be measured flowing out from the element-side opening 129 from directly hitting the surface of the sensor element 110, and it is possible to prevent water from reaching the sensor element 110 along with the gas flow.

As shown in FIG. 3, the outer protective cover 140 has a cylindrical large-diameter portion 142, a cylindrical body portion 143 connected to the large-diameter portion 142 and having a smaller diameter than the large-diameter portion 142, and a bottomed portion. It has a tubular tip portion 146 having an inner diameter smaller than that of the body portion 143. Further, the body portion 143 is a stepped portion that connects the side portion 143a having a side surface along the central axial direction (vertical direction) of the outer protective cover 140 and the side portion 143a and the tip portion 146 that are the bottom portion of the body portion 143. It has 143b and. The central axes of the large diameter portion 142, the body portion 143, and the tip portion 146 are all the same as the central axis of the inner protective cover 130. The inner peripheral surface of the large-diameter portion 142 is in contact with the housing 102 and the large-diameter portion 132, whereby the outer protective cover 140 is fixed to the housing 102. The body portion 143 is located so as to cover the outer periphery of the first cylindrical portion 134 and the second cylindrical portion 136. The large diameter portion 142 and the body portion 143 may have the same diameter. The tip portion 146 is positioned so as to cover the tip portion 138, and the inner peripheral surface is in contact with the outer peripheral surface of the connection portion 137. The tip portion 146 has a side surface along the central axial direction (vertical direction) of the outer protective cover 140, a side portion 146a having an outer diameter smaller than the inner diameter of the side portion 143a, and a bottom portion 146b which is the bottom of the outer protective cover 140. And a tapered portion 146c that connects the side portion 146a and the bottom portion 146b and reduces the diameter from the side portion 146a toward the bottom portion 146b. The tip portion 146 is located on the tip direction (downward) side of the body portion 143. The outer protective cover 140 is formed on the body portion 143 and has one or more (plural, specifically 12) outer inlets 144a, which are inlets of the gas to be measured from the outside, and a tip portion 146. It has one or more outer outlets 147a, which are formed in the above and are outlets for the gas to be measured to the outside.

The outer inlet 144a is a hole leading to the outer side (outside) of the outer protective cover 140 and the first gas chamber 122. The outer inlets 144a are composed of a plurality of lateral holes 144b formed at equal intervals in the side portions 143a (six in the present embodiment) and a plurality of lateral holes 144b formed in the step portions 143b at equal intervals (six in the present embodiment). It has a vertical hole 144c (FIGS. 3 to 6). The outer inlet 144a (horizontal hole 144b and vertical hole 144c) is a hole formed in a circle. The diameter of the 12 outer inlets 144a is, for example, 0.5 mm to 2 mm. The diameter of the outer inlet 144a may be 1.5 mm or less. In the present embodiment, the diameters of the plurality of horizontal holes 144b are all set to the same value, and the diameters of the plurality of vertical holes 144c are all set to the same value. Further, the diameter of the horizontal hole 144b was set to a value larger than the diameter of the vertical hole 144c. As shown in FIGS. 4 and 5, the outer inlet 144a is formed so that the horizontal holes 144b and the vertical holes 144c are alternately located at equal intervals along the circumferential direction of the outer protective cover 140. That is, the line connecting the center of the lateral hole 144b and the central axis of the outer protective cover 140 in FIGS. 4 and 5 and the center of the vertical hole 144c adjacent to the lateral hole 144b and the central axis of the outer protective cover 140 are connected. The angle between the cover and the line is 30 ° (360 ° / 12 pieces).

The outer outlet 147a is a hole leading to the outer side (outside) of the outer protective cover 140 and the second gas chamber 126. The outer outlet 147a has one vertical hole 147c formed in the center of the bottom portion 146b of the tip portion 146 (see FIGS. 3, 5 and 6). Unlike the outer inlet 144a, the outer outlet 147a is not arranged on the side portion of the outer protective cover 140 (here, the side portion 146a of the tip portion 146). The outer outlet 147a (here, the vertical hole 147c) is a hole formed in a circle. The diameter of the outer outlet 147a is, for example, 0.5 mm to 2.5 mm. The diameter of the outer outlet 147a may be 1.5 mm or less. In the present embodiment, the diameter of the vertical hole 147c is set to a value larger than the diameter of the horizontal hole 144b and the vertical hole 144c.

The outer protective cover 140 and the inner protective cover 130 form a first gas chamber 122 as a space between the body portion 143 and the inner protective cover 130. More specifically, the first gas chamber 122 is a space surrounded by a step portion 133, a first cylindrical portion 134, a second cylindrical portion 136, a side portion 143a, and a step portion 143b. The sensor element chamber 124 is a space surrounded by the inner protective cover 130. The outer protective cover 140 and the inner protective cover 130 form a second gas chamber 126 as a space between the tip portion 146 and the inner protective cover 130. More specifically, the second gas chamber 126 is a space surrounded by the tip portion 138 and the tip portion 146. Since the inner peripheral surface of the tip portion 146 is in contact with the outer peripheral surface of the connecting portion 137, the first gas chamber 122 and the second gas chamber 126 are not directly communicated with each other.

Here, the flow of the gas to be measured in the protective cover 120 when the gas sensor 100 detects the specific gas concentration will be described. The gas to be measured flowing in the pipe 20 first flows into the first gas chamber 122 through at least one of the plurality of outer inlets 144a (horizontal hole 144b and vertical hole 144c). Next, the gas to be measured flows into the element chamber inlet 127 from the first gas chamber 122 via the outer opening 128, flows out from the element side opening 129 via the element chamber inlet 127, and flows into the sensor element chamber 124. To do. At least a part of the gas to be measured that has flowed into the sensor element chamber 124 from the element-side opening 129 reaches the gas introduction port 111 of the sensor element 110. When the gas to be measured reaches the gas introduction port 111 and flows into the inside of the sensor element 110, the sensor element 110 generates an electric signal (voltage or current) according to the specific gas concentration in the gas to be measured, and this electricity is generated. A specific gas concentration is detected based on the signal. Further, the gas to be measured in the sensor element chamber 124 flows into the second gas chamber 126 through at least one of the element chamber outlets 138a (hole 138b), and from there through the outer outlet 147a (vertical hole 147c). It leaks to the outside. The output of the internal heater of the sensor element 110 is controlled by, for example, a controller (not shown) so as to maintain a predetermined temperature.

By the way, coagulated water may be generated in the pipe 20 through which the exhaust gas of an automobile or the like flows. Such coagulated water enters the outer protective cover 140 from the outer inlet 144a and the outer outlet 147a due to the above-mentioned flow of the gas to be measured and the sudden gas flow when the engine is started, and further enters the element chamber inlet 127 and the element chamber. It may enter the inner protective cover 130 from the exit 138a. Water that has entered the inner protective cover 130 may reach the sensor element 110 directly or may collect on the bottom of the inner protective cover 130 (the bottom of the second member 135, that is, above the bottom 138e). The water accumulated on the bottom of the inner protective cover 130 may scatter toward the sensor element 110 due to sudden gas flow or vibration when the engine is started. Therefore, in the gas sensor 100 described above, it is assumed that the second member 135 constituting the inner protective cover 130 is provided with a tapered portion 138d on the tip end side, and the element chamber outlet 138a is arranged on the tapered portion 138d. In such a gas sensor 100, since the element chamber outlet 138a is arranged not on the bottom portion 138e but on the tapered portion 138d, even if gas suddenly flows in from the outside of the element chamber outlet 138a, the gas flow is in the direction of the sensor element 110. It is difficult for water to reach the sensor element 110 along the gas flow. Further, the gas sensor 100 is often used with its central axis tilted with respect to the vertical direction. In such a case, the element chamber outlet 138a is arranged on the tapered portion 138d which is not parallel to the central axis of the inner protective cover 130. Therefore, the water in the inner protective cover 130 is easily discharged from the element chamber outlet 138a due to its own weight. Further, in the gas sensor 100 described above, the distance X [mm] between the tip surface 110c of the sensor element 110 and the bottom 138e of the second member 135 and the diameter Y [mm] of the bottom 138e of the second member 135 are X ≧ 7. Since at least one of .5 and Y ² + 667 / X ≦ 120 is satisfied, the water exposure of the sensor element 110 is suppressed. When X ≧ 7.5 is satisfied, even if water accumulates on the bottom of the second member 135, it is considered that the sensor element 110 is unlikely to be exposed to water because the distance between the accumulated water and the sensor element 110 is sufficiently long. .. Further, when Y ² + 667 / X ≦ 120 is satisfied, the sensor element 110 is less likely to be exposed to water because the distance X is relatively long, and the diameter Y of the bottom 138e of the second member 135 is relatively small, so that water reaches the bottom. Since water is likely to be discharged from the element chamber outlet 138a while the amount of water accumulated is small, it is considered that the amount of water accumulated inside the second member 135 is suppressed and the water coverage of the sensor element 110 is suppressed. The smaller the diameter Y, the less likely the sensor element is to be exposed to water even if the distance X is short. When the distance X and the diameter Y ^{satisfy Y 2} + 667 / X ≦ 112, the water exposure of the sensor element 110 is further suppressed.

According to the gas sensor 100 of the present embodiment described in detail above, the second member 135 constituting the inner protective cover 130 is provided with a tapered portion 138d on the tip end side, and the element chamber outlet 138a is arranged on the tapered portion 138d. .. Further, the distance X [mm] between the tip surface 110c of the sensor element 110 and the bottom 138e of the second member 135 and the diameter Y [mm] of the bottom 138e of the second member 135 are X ≧ 7.5 and Y ² +667. At least one of / X ≦ 120 is satisfied. Therefore, the water exposure of the sensor element 110 is suppressed.

Further, if the distance X and the diameter Y ^{satisfy Y 2} + 667 / X ≦ 112, the water exposure of the sensor element 110 can be further suppressed. Further, if the distance X and the diameter Y satisfy at least one of X ≦ 13 and Y ≦ 6, water exposure of the sensor element 110 can be suppressed while keeping the dimensions of the gas sensor 100 relatively small. Furthermore, if the depth Z (≧ 0) [mm] from the bottom 138e of the second member 135 to the lower end of the element chamber outlet 138a is Z ≦ 2.5, the amount of water accumulated at the bottom of the second member 135 is increased. Water is discharged from the element chamber outlet 138a before it is less. As a result, the amount of water accumulated inside the second member 135 is further suppressed, so that the water exposure of the sensor element 110 can be further suppressed.

Then, in the gas sensor 100, the first member 131 and the second member 135 form the element chamber inlet 127 so that the element side opening 129 opens downward. As a result, the gas to be measured flows downward into the sensor element chamber 124 from the element chamber inlet 127 separated from the sensor element 110 by the first member 131, so that the water can be discharged even if the gas to be measured contains water. It is difficult to reach the sensor element 110.

Needless to say, 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, the shape of the protective cover 120 is not limited to the above-described embodiment. The shape of the protective cover 120, the shape, number, arrangement, etc. of the element chamber inlet 127, the element chamber outlet 138a, the outer inlet 144a, and the outer outlet 147a may be appropriately changed. For example, the tip portion 146 of the outer protective cover 140 has a bottomed tubular shape and has a side portion 146a, a bottom portion 146b, and a tapered portion 146c, but the tapered portion 146c may be omitted in a cylindrical shape. Further, for example, in the outer inlet 144a, the horizontal holes 144b and the vertical holes 144c are alternately formed along the circumferential direction of the outer protective cover 140, but the horizontal holes and the vertical holes are formed in the same phase. You may be. FIG. 8 is a vertical cross-sectional view (of the gas sensor 100) of the gas sensor 200 in which the tip portion 146 of the outer protective cover 140 of FIG. BB cross-sectional view). 9 is a sectional view taken along line FF of the outer protective cover 240 of FIG. 8, and FIG. 10 is a G view of FIG. In FIGS. 8 to 10, the same components as those of the gas sensor 100 are designated by the same reference numerals, and detailed description thereof will be omitted. As shown in FIG. 8, the protective cover 220 of the gas sensor 200 includes an outer protective cover 240 instead of the outer protective cover 140. The outer protective cover 240 has an outer inlet 244a instead of the outer inlet 144a. The outer inlet 244a includes a plurality of (six in this case) horizontal holes 244b formed in the side portion 143a at equal intervals and a plurality of (six in this case) vertical holes 144c formed in the stepped portion 143b at equal intervals. have. In the outer inlet 244a, the horizontal holes 244b and the vertical holes 144c are formed in the same phase at equal intervals (here, 60 ° intervals) along the circumferential direction of the outer protective cover 240. Further, the outer protective cover 240 has a tip portion 246 having a bottomed tubular shape (cylindrical shape) and an inner diameter smaller than that of the body portion 143 instead of the tip portion 146. The tip portion 246 has a side surface along the central axial direction (vertical direction in FIG. 8) of the outer protective cover 240, and has a side portion 246a whose outer diameter is smaller than the inner diameter of the side portion 143a and a bottom portion of the outer protective cover 240. It has a bottom 246b and a certain bottom. Further, an outer outlet 247a, which is an outlet for the gas to be measured to the outside, is formed at the tip portion 246. The outer outlet 247a has a plurality of (here, 6) vertical holes 247c formed at equal intervals along the circumferential direction of the outer protective cover 240 at the bottom 246b of the tip portion 246 (FIGS. 8, 9, and 6). 10). Even in such a gas sensor 200, since the sensor element 110 and the inner protective cover 130 satisfy the above-mentioned conditions, the same effects as those in the above-described embodiment can be obtained.

In the above-described embodiment, the element chamber inlet 127 is a cylindrical gap between the first cylindrical portion 134 of the first member 131 and the second cylindrical portion 136 of the second member 135, but the present invention is not limited to this. The chamber entrance may have any shape as long as it is a gap between the first member 131 and the second member 135. For example, the entrance of the element chamber may be a gap inclined from the vertical direction in FIG. 3 (see also FIG. 12 described later). Further, the number of element chamber inlets 127 is not limited to one, but may be plural (see also FIG. 11 described later). The outer inlet 144a and the outer outlet 147a are not limited to the holes, but may be gaps between a plurality of members constituting the protective cover 120, and the number of each may be one or more. Further, although the outer inlet 144a has a horizontal hole 144b and a vertical hole 144c, it may have only one of them. Further, in addition to or in place of the horizontal hole 144b and the vertical hole 144c, a square hole may be formed at the corner of the boundary between the side portion 143a and the step portion 143b. Similarly, the outer outlet 147a may have one or more of a horizontal hole, a vertical hole, and a square hole. Further, the outer outlet 147a may have a through hole provided in the tapered portion 146c.

In the above-described embodiment, the protruding portion 136a is formed on the inner peripheral surface of the second cylindrical portion 136, but the present invention is not limited to this. It suffices that at least one surface of the outer peripheral surface of the first cylindrical portion 134 and the inner peripheral surface of the second cylindrical portion 136 is formed with a plurality of projecting portions projecting toward the other surface and in contact with the surface. Further, in the above-described embodiment, as shown in FIGS. 3 and 4, the outer peripheral surface of the portion of the second cylindrical portion 136 in which the protruding portion 136a is formed is recessed inward, but the outer peripheral surface is not limited to this. Does not have to be dented. Further, the protruding portion 136a is not limited to the hemispherical shape and may have any shape. The protruding portion 136a may not be formed on the outer peripheral surface of the first cylindrical portion 134 and the inner peripheral surface of the second cylindrical portion 136.

In the above-described embodiment, the element chamber inlet 127 is a tubular gap between the outer peripheral surface of the first cylindrical portion 134 and the inner peripheral surface of the second cylindrical portion 136, but the present invention is not limited to this. For example, a recess (groove) is formed in at least one of the outer peripheral surface of the first cylindrical portion and the inner peripheral surface of the second cylindrical portion, and the element chamber entrance is the first cylindrical portion and the second cylindrical portion formed by the recess. It may be a gap with the cylindrical portion. FIG. 11 is a cross-sectional view showing the element chamber entrance 327 of the modified example. As shown in FIG. 11, the outer peripheral surface of the first cylindrical portion 334 and the inner peripheral surface of the second cylindrical portion 336 (corresponding to the side portion of the present invention) are in contact with each other, and the outer peripheral surface of the first cylindrical portion 334 is in contact with the outer peripheral surface. A plurality of (4 in FIG. 11) recesses 334a are formed at equal intervals. The gap between the recess 334a and the inner peripheral surface of the second cylindrical portion 336 is the element chamber entrance 327.

In the above-described embodiment, the element chamber inlet 127 is a flow path parallel to the rear end-tip direction of the sensor element 110 (a flow path parallel to the vertical direction in FIG. 3), but the present invention is not limited to this. For example, the element chamber entrance may be a flow path inclined from the vertical direction so as to approach the sensor element 110 as it goes downward. FIG. 12 is a vertical cross-sectional view of the gas sensor 400 of the modified example in this case. In FIG. 12, the same components as those of the gas sensors 100 and 200 are designated by the same reference numerals, and detailed description thereof will be omitted. As shown in FIG. 12, the protective cover 420 of the gas sensor 400 includes an inner protective cover 430 instead of the inner protective cover 130. The inner protective cover 430 includes a first member 431 and a second member 435. Compared to the first member 131, the first member 431 does not include the first cylindrical portion 134, but instead has a cylindrical body portion 434a and a cylindrical first cylindrical portion 434b whose diameter decreases downward. It has. The first cylindrical portion 434b is connected to the body portion 434a at the upper end portion. The second member 435 does not have the second cylindrical portion 136 as compared with the second member 135, but instead has a cylindrical second cylindrical portion 436 (corresponding to the side portion of the present invention) whose diameter decreases downward. I have. The second cylindrical portion 436 is connected to the tip portion 138 via the connecting portion 137. The outer peripheral surface of the first cylindrical portion 434b and the inner peripheral surface of the second cylindrical portion 436 are not in contact with each other, and the gap formed by both is the element chamber entrance 427. The element chamber inlet 427 has an outer opening 428 which is an opening on the first gas chamber 122 side and an element side opening 429 which is an opening on the sensor element chamber 124 side. Due to the shapes of the first cylindrical portion 434b and the second cylindrical portion 436, the element chamber inlet 427 is inclined from the vertical direction so as to approach the sensor element 110 (approaching the central axis of the inner protective cover 430) as it goes downward. It is a flow path. Similarly, the element-side opening 429 is inclined from the vertical direction so as to approach the sensor element 110 as it goes downward. When the element chamber inlet 427 is a flow path inclined in the vertical direction or the element side opening 429 is inclined in the vertical direction as described above, the sensor element chamber is formed from the element side opening 429. The direction in which the gas to be measured flowing out to 124 flows is a direction inclined from the vertical direction. As a result, the same effect as that of the element chamber entrance 127 and the element side opening 129 of the above-described embodiment can be obtained. That is, since the gas to be measured flows downward into the sensor element chamber 124 from the element chamber inlet 427 separated from the sensor element 110 by the first member 431, the water is used as the sensor even if the gas to be measured contains water. It is difficult to reach the element 110. As a result, the water exposure of the sensor element 110 can be suppressed. Further, in FIG. 12, the width of the element chamber entrance 427 becomes narrower toward the lower side of the sensor element 110. Therefore, the opening area of the element side opening 429 is smaller than the opening area of the outer opening 428. As a result, the gas to be measured flows in from the outer opening 428 and flows out from the element side opening 429, so that the flow velocity of the gas to be measured at the time of outflow is higher than that at the time of inflow. Therefore, the responsiveness of the specific gas concentration detection can be improved. In FIG. 12, the element chamber inlet 427 is a flow path inclined from the vertical direction, the element side opening 429 is inclined from the vertical direction to open, and the opening area of the element side opening 429 is the outer opening. Although it is made smaller than the opening area of the portion 428, one or more of these three features may be omitted, or the gas sensor may have one or more of these three features. May be good. Even in such a gas sensor 400, since the sensor element 110 and the inner protective cover 130 satisfy the above-mentioned conditions, the same effects as those in the above-described embodiment can be obtained. Although the gas sensor 400 of FIG. 12 has an outer protective cover 240 similar to that of the gas sensor 200, it may have an outer protective cover 140 similar to that of the gas sensor 100.

In the above-described embodiment, the first gas chamber 122 and the second gas chamber 126 are not directly communicated with each other, but the first gas chamber 122 and the second gas chamber 126 may be directly communicated with each other. Good. For example, a gap may be provided for communicating the first gas chamber 122 and the second gas chamber 126 by separating the inner peripheral surface of the tip portion 146 from the outer peripheral surface of the connecting portion 137.

In the above-described embodiment, the gas introduction port 111 is open to the tip surface of the element body 110b (the lower surface of the element body 110b in FIG. 3), but the present invention is not limited to this. For example, it may be opened on the side surface of the element body 110b (the top, bottom, left and right surfaces of the element body 110b in FIG. 4).

In the above-described embodiment, the sensor element 110 includes the porous protective layer 110a, but the sensor element 110 may not include the porous protective layer 110a. In that case, the lower surface of the element body 110b becomes the front end surface of the sensor element 110.

Hereinafter, an example in which a gas sensor is specifically manufactured will be described as an example. Experimental Examples 1 to 10 correspond to Examples of the present invention, and Experimental Examples 11 to 15 correspond to Comparative Examples. The present invention is not limited to the following examples.

[Experimental Example 1]
The gas sensor 100 shown in FIGS. 3 to 7 was used as Experimental Example 1. In Experimental Example 1, as the inner protective cover 130, the diameter Y of the bottom portion 138e is 3.41 mm, the diameter D of the rear end portion of the tapered portion 138d is 7.37 mm, and the vertical length L of the tapered portion 138d is 5.20 mm. The diameter of each hole 138b of the element chamber outlet 138a is 1.5 mm, and the depth Z from the bottom 138e to the lower end of the element chamber outlet 138a is 1.00 mm. Further, the sensor element 110 is arranged at a position where the distance X between the front end surface 110c and the bottom portion 138e is 6.76 mm.

[Experimental Examples 2 to 15]
Experimental Examples 2 to 15 are the same as the gas sensor 100 of Experimental Example 1 except that the diameter Y of the bottom 138e is set to the value shown in Table 1 and the sensor element 110 is arranged at a position where the distance X is the value shown in Table 1. did.

[Evaluation of water coverage]
For the evaluation of the water cover amount, the water cover test apparatus described in Japanese Patent Application Laid-Open No. 2019-158615 was used. This water exposure test device has a pipe that has a gas flow path inside and is arranged horizontally and linearly, a blower (blower) that is installed upstream of the pipe, and a pressure fluctuation that is installed on the downstream side of the pipe. It includes a generator and a chamber in which a gas sensor is mounted, which is part of the piping between the blower and the pressure fluctuation generator. A vibration exciter that applies vibration to the chamber is connected to the chamber. In this water exposure test device, water can be scattered toward the gas sensor by a gas that imitates the exhaust gas from the engine. In the water test, first, the gas sensor was placed in the chamber of the water test device with the central axis of the gas sensor perpendicular to the axis of the pipe and tilted by 10 ° with respect to the horizontal direction. Next, a predetermined amount of water was supplied into the pipe between the blower and the chamber. Subsequently, gas (atmosphere) was supplied into the pipe using a blower, the pressure of the gas was fluctuated using a pressure fluctuation generator, and vibration was applied to the chamber by a vibrator. As a result, the water supplied into the pipe is scattered toward the gas sensor arranged in the chamber by the gas whose pressure fluctuates. In this state, the heater built in the sensor element was driven, and the heater power was controlled so that the temperature of the sensor element became a predetermined target value between 100 and 200 ° C. The control value of the heater power at this time was applied to the relationship between the heater power derived in advance and the water cover amount to obtain the water cover amount of the sensor element in each gas sensor. Then, the one with a water coverage of 2.5 μL or less is “A (excellent)”, the one with an excess of 2.5 μL of 4.0 μL or less is “B (good)”, and the one with an excess of 4.0 μL is “F (impossible)”. The judgment was made as. The results are summarized in Table 1 and FIG.

From Table 1 and FIG. 13, it was found that when the distance X satisfies X ≧ 7.5 mm, the amount of water received is zero regardless of the value of Y. Further, even when X ≧ 7.5 mm is not satisfied, the amount of water received tends to be suppressed by reducing the diameter Y as the distance X decreases, and the distance X and the diameter Y tend to be Y ² ≦ −. It was found that when the relationship of 667 / X + 120 was satisfied, the water intake was suppressed to 4.0 μL or less. Furthermore, it was found that when the distance X and the diameter Y ^{satisfy the relationship of Y 2} ≤ -667 / X + 112, the water intake is suppressed to 2.5 μL or less. The distance X and the diameter Y are ^{not particularly limited as long as they satisfy the relationship of X ≧ 7.5 mm or Y 2} ≦ −667 / X + 120, but may be, for example, X ≦ 13 mm or Y ≦ 6 mm. In such a range, it is considered that water exposure can be suppressed while keeping the size of the gas sensor relatively small.

20 Piping, 22 Fixing member, 100, 200, 400 Gas sensor, 102 housing, 103 volt, 110 sensor element, 110a porous protective layer, 110b element body, 110c tip surface, 111 gas inlet, 120, 220, 420 protection Cover, 122 1st gas chamber, 124 sensor element chamber, 126 2nd gas chamber 127,327,427 element chamber inlet, 128,428 outer opening, 129,429 element side opening, 130,430 inner protective cover, 131,431 1st member, 132 large diameter part, 133 stepped part, 134,334 1st cylindrical part, 135,435 2nd member, 136,336,436 2nd cylindrical part, 136a protruding part, 137 connection part, 138 Tip, 138a element chamber outlet, 138b hole, 138d side, 138e bottom, 140,240 outer protective cover, 142 large diameter, 143 body, 143a side, 143b step, 144a outer entrance, 144b side hole, 144c vertical hole, 146,246 tip part, 146a, 246a side part, 146b, 246b bottom part, 146c taper part, 147a, 247a outer outlet, 147c, 247c vertical hole, 334a recess, 434a body part, 434b first cylindrical part.

Claims (6)

A sensor element having a gas introduction port for introducing a gas to be measured and capable of detecting a specific gas concentration of the gas to be measured that has flowed into the inside from the gas introduction port.
It has a sensor element chamber in which the tip of the sensor element and the gas introduction port are arranged inside, and is one or more element chamber inlets which are inlets to the sensor element chamber and outlets from the sensor element chamber. A tubular inner protective cover in which one or more element chamber outlets are arranged, and
One or more outer inlets which are inlets of the gas to be measured from the outside and one or more outer outlets which are outlets of the gas to be measured to the outside are arranged and arranged outside the inner protective cover. With a tubular outer protective cover
With
The inner protective cover has a tubular first member surrounding the sensor element and a tubular second member surrounding the first member.
The first member and the second member form the element chamber entrance as a gap between the first member and the second member.
The second member is provided between a side portion surrounding the first member, a bottom portion provided at a position facing the tip surface of the sensor element, and the side portion and the bottom portion, and is provided from the side portion side. A tapered portion whose diameter is reduced toward the bottom side is provided, and the element chamber outlet is arranged in the tapered portion.
When the distance between the tip surface of the sensor element and the bottom of the second member is X [mm] and the diameter of the bottom of the second member is Y [mm], X ≧ 7.5 and A gas sensor that satisfies at least one of ^{Y 2 + 667 / X ≦ 120.} The gas sensor according to claim 1, wherein the distance X and the diameter Y ^{satisfy Y 2 + 667 / X ≦ 112.} The gas sensor according to claim 1 or 2, wherein the distance X and the diameter Y satisfy at least one of X ≦ 13 and Y ≦ 6. The gas sensor according to any one of claims 1 to 3, wherein the depth Z [mm] from the bottom of the second member to the lower end of the element chamber outlet satisfies Z ≦ 2.5. In the first member and the second member, the direction from the rear end to the tip of the sensor element is downward, and the element-side opening, which is the opening on the sensor element chamber side of the element chamber entrance, is below. The element chamber entrance is formed so as to open in the direction.
The gas sensor according to any one of claims 1 to 4. The first member has a first cylindrical portion that surrounds the sensor element.
The second member has a second cylindrical portion having a diameter larger than that of the first cylindrical portion.
The element chamber entrance is a cylindrical gap between the outer peripheral surface of the first cylindrical portion and the inner peripheral surface of the second cylindrical portion.
The gas sensor according to any one of claims 1 to 5.

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