Gas sensor

Abstract

This gas sensor 100 comprises: a sensor element 110; an inner protective cover 130 that has, on the inside thereof, a sensor element chamber 124 in which the front end of the sensor element 110 is disposed, an element chamber opening 125 being disposed in the inner protective cover 130; and an outer protective cover 140 having an outer opening 144a. The inner protective cover 130 has a first member 131 and a second member 135 surrounding the first member 131. The element chamber opening 125 has a first opening 127 configured as a gap between the first member 131 and the second member 135. The first member 131 has: a first cylindrical part 134 that surrounds the sensor element 110; and a bottom part 134a that is disposed below the first cylindrical part 134 and the sensor element 110 and that has an opening 134c. The opening area Sf of the opening 134c is smaller than the cross-sectional area S0, perpendicular to the axial direction, of the space inside the first cylindrical part 134.

Description

gas sensor

[0001] This invention relates to a gas sensor.

[0002] Conventionally, gas sensors are known that detect the concentration of specific gases such as NOx and oxygen in a gas to be measured, such as automobile exhaust gas. For example, Patent Document 1 describes a gas sensor comprising a sensor element, an inner protective cover in which the tip of the sensor element is placed, and an outer protective cover placed outside the inner protective cover. The inner protective cover has a sensor element chamber on its inside in which the tip of the sensor element is placed, and is provided with an element chamber inlet, which is an inlet to the sensor element chamber, and an element chamber outlet, which is an outlet from the sensor element chamber. The outer protective cover is provided with an outer inlet, which is an inlet from the outside of the gas to be measured, and an outer outlet, which is an outlet to the outside of the gas to be measured.

[0003] Patent No. 7465739

[0004] Incidentally, in such gas sensors, water can enter the protective cover and adhere to the sensor element, causing cracks in the sensor element. Therefore, there was a demand to suppress water adhesion to the sensor element, that is, to improve the water resistance of the sensor element.

[0005] This invention was made to solve these problems, and its main objective is to improve the water resistance of the sensor element in a gas sensor.

[0006] To achieve the main objectives described above, the present invention employs the following means.

[0007] [1] The gas sensor of the present invention comprises: a sensor element having a front end and a rear end opposite to the front end, a gas inlet for introducing a gas to be measured, and for detecting a specific gas concentration of the gas to be measured that has flowed into the interior from the gas inlet; a cylindrical inner protective cover having a sensor element chamber inside in which the front end of the sensor element and the gas inlet are arranged, and having an element chamber inlet which is an entrance to the sensor element chamber and an element chamber outlet which is an exit from the sensor element chamber; and a cylindrical outer protective cover disposed outside the inner protective cover, having an outer inlet which is an entrance to the gas to be measured from the outside and an outer outlet which is an exit from the gas to be measured to the outside, wherein the outer protective cover and the inner protective cover form an inlet-side gas flow path from the outside to the sensor element chamber, including the outer inlet and the element chamber inlet, and an outlet-side gas flow path from the sensor element chamber to the outside, including the element chamber outlet and the outer outlet. The inner protective cover comprises a cylindrical first member surrounding the sensor element and a cylindrical second member surrounding the first member and having an element chamber outlet. The element chamber inlet has a first inlet configured as a gap between the first member and the second member. The opening of the first inlet on the sensor element chamber side opens downward, parallel to the axial direction of the first member and in the direction from the rear end to the front end of the sensor element. The first member comprises a first cylindrical portion surrounding the sensor element and a bottom portion disposed below the first cylindrical portion and the sensor element and having an opening. The opening area Sf of the opening in the bottom portion is smaller than the cross-sectional area S0 of the space inside the first cylindrical portion perpendicular to the axial direction.

[0008] In this gas sensor, the inner protective cover has a sensor element chamber inside and an element chamber inlet which is an entrance to the sensor element chamber. The inner protective cover has a cylindrical first member surrounding the sensor element and a cylindrical second member surrounding the first member. The element chamber inlet has a first inlet which is configured as a gap between the first member and the second member. The first member has a first cylindrical portion surrounding the sensor element and a bottom portion which is disposed below the first cylindrical portion and the sensor element and has an opening. The opening area Sf of this bottom portion is smaller than the cross-sectional area S0 perpendicular to the axial direction of the space inside the first cylindrical portion. The presence of such a bottom portion in the first member prevents water from adhering to the sensor element when water enters the sensor element chamber from the first inlet. Therefore, the water resistance of the sensor element in the gas sensor can be improved. Since the bottom portion has an opening, the gas to be measured that has passed through the first inlet can pass through this opening and reach the sensor element. Here, "opening downwards" includes cases where the opening is parallel to the downward direction, and cases where the opening is inclined downwards so that it approaches the sensor element as it goes downwards.

[0009] [2] In the gas sensor described above (the gas sensor described in [1]), the bottom portion may have a shape in which the inner diameter tends to decrease as it goes downward, and the opening may be located at the lower end.

[0010] [3] In the gas sensor described above (the gas sensor described in [2]), the bottom portion may have a tapered portion in which the inner diameter decreases as it goes downward.

[0011] [4] In the gas sensor described above (the gas sensor described in any of [1] to [3] above), the aperture area Sf is 61.93 mm 2 It may be less than this. This ensures a more reliable improvement in the water resistance of the sensor element.

[0012] [5] In the gas sensor described above (the gas sensor described in any of [1] to [4] above), the aperture area Sf is 28.27 mm 2may be less than or equal to the above value. With this configuration, the water exposure resistance of the sensor element is further improved.

[0013] [6] In the gas sensor described above (the gas sensor according to any one of [1] to [5] above), the opening area Sf is 8.45 mm 2 may be greater than the above value. Here, if the opening area Sf is too small, the time required for the gas to be measured to pass through the opening and reach the sensor element increases, which may reduce the responsiveness of detection of the specific gas concentration by the sensor element. In contrast, when the opening area Sf is 8.45 mm 2 greater than the above value, a decrease in responsiveness of detection of the specific gas concentration can be suppressed.

[0014] [7] In the gas sensor described above (the gas sensor according to any one of [1] to [6] above), the opening area Sf is 12.57 mm 2 may be greater than or equal to the above value. With this configuration, a decrease in responsiveness of detection of the specific gas concentration can be more reliably suppressed.

[0015] [8] In the gas sensor described above (the gas sensor according to any one of [1] to [7] above), the element chamber inlet may have a second inlet disposed on the first member. With this configuration, since the element chamber inlet has not only the first inlet but also the second inlet, the gas to be measured easily flows into the sensor element chamber. Therefore, a decrease in responsiveness of detection of the specific gas concentration by the sensor element can be suppressed.

[0016] [9] In the gas sensor described above (the gas sensor according to [8] above), the second inlet may be positioned upward with respect to the first inlet, the upward direction being opposite to the downward direction.

[0017]

[10] In the gas sensor described above (the gas sensor according to [8] or [9] above), the opening area Ss of the second inlet is 10.60 mm 2 may be less than or equal to the above value. With this configuration, it becomes difficult for water to enter the sensor element chamber through the second inlet, so even if the second inlet is provided, the water exposure resistance of the sensor element is unlikely to decrease.

[0018]

[11] In the gas sensor described above (the gas sensor according to any one of [8] to

[10] above), the opening area Ss of the second inlet is 7.36 mm2 It may be the following value. With this configuration, a decrease in water immersion resistance of the sensor element caused by the presence of the second inlet can be further suppressed.

[0019]

[12] In the gas sensor described above (the gas sensor according to any one of [8] to

[11] above), an opening area Ss of the second inlet is 1.18 mm 2 or more. With this configuration, the effect of suppressing a decrease in responsiveness of detection of a specific gas concentration caused by the presence of the second inlet can be obtained more reliably.

[0020]

[13] In the gas sensor described above (the gas sensor according to any one of [8] to

[12] above), an opening area Ss of the second inlet is 2.65 mm 2 or more. With this configuration, the effect of suppressing a decrease in responsiveness of detection of a specific gas concentration caused by the presence of the second inlet is further enhanced.

[0021]

[14] In the gas sensor described above (the gas sensor according to any one of [1] to

[13] above), the inlet-side gas flow path is a space between the outer protective cover and the inner protective cover, and has a first flow path extending upward from the outer inlet, the upward direction being opposite to the downward direction, and the inner protective cover and / or the outer protective cover may be provided with a water passage suppressing portion that is disposed above the outer inlet in the first flow path and has a shape narrowing a part of the first flow path. With this configuration, the water immersion resistance of the sensor element can be improved not only by the bottom portion of the first member described above but also by the water passage suppressing portion.

[0022] Schematic explanatory view showing an attached state of the gas sensor 100 to a pipe 10. A-A cross-sectional view of FIG. 1. B-B cross-sectional view of FIG. 2. C-C cross-sectional view of FIG. 3. D-D cross-sectional view of FIG. 3. E view of FIG. 3. Partial enlarged view of FIG. 3. Explanatory view showing a state where water W is accumulated in an inner protective cover 130. Longitudinal cross-sectional view of a gas sensor 900 of a comparative example. Longitudinal cross-sectional view of a gas sensor 200 according to a modified example. Longitudinal cross-sectional view of a gas sensor 300 according to a modified example. Partial cross-sectional view when an outer inlet 144a has a square hole 144d.

[0023] Next, embodiments for carrying out the present invention will be described with reference to the drawings. Figure 1 is a schematic diagram illustrating the state of attachment of the gas sensor 100 to the piping 10. Figure 2 is a cross-sectional view taken along line A-A in Figure 1. Figure 3 is a cross-sectional view taken along line B-B in Figure 2. Figure 4 is a cross-sectional view taken along line C-C in Figure 3. Figure 5 is a cross-sectional view taken along line D-D in Figure 3. Figure 6 is a view taken along line E in Figure 3. Figure 7 is a partially enlarged view of Figure 3. Note that the direction parallel to the axial direction of the protective cover 120 (especially the first member 131 of the inner protective cover 130) and moving from the front end to the rear end of the sensor element 110 (upward direction in Figures 3 and 7) is defined as the upward direction, and the direction parallel to the axial direction of the protective cover 120 (especially the first member 131 of the inner protective cover 130) and moving from the rear end to the front end of the sensor element 110 (downward direction in Figures 3 and 7) is defined as the downward direction.

[0024] As shown in Figure 1, the gas sensor 100 is installed in the piping 10, which is the exhaust path from the vehicle's engine, and is designed to detect the concentration of a specific gas contained in the exhaust gas, which is the gas to be measured, discharged from the engine. Examples of specific gases include NOx, ammonia, and O2. As shown in Figure 2, the gas sensor 100 is fixed inside the piping 10 with its central axis perpendicular to the flow of the gas to be measured inside the piping 10. Alternatively, the gas sensor 100 may be fixed inside the piping 10 with its central axis perpendicular to the flow of the gas to be measured inside the piping 10 and tilted at a predetermined angle (for example, 45° or 60°) with respect to the vertical direction.

[0025] As shown in Figure 3, the gas sensor 100 includes a sensor element 110 and a protective cover 120 that protects the sensor element 110. The gas sensor 100 also includes an element encapsulant 101 that encloses and fixes the sensor element 110, and a bolt 103 attached to the element encapsulant 101. The element encapsulant 101 includes a cylindrical metal housing 102, a ceramic supporter 104 sealed in a through hole inside the housing 102, and a compacted powder 105 made of molded ceramic powder such as talc, also sealed in a through hole inside the housing 102. The sensor element 110 is located on the central axis of the element encapsulant 101 and penetrates the element encapsulant 101 in the vertical direction. The compacted powder 105 is compressed between the housing 102 and the sensor element 110. As a result, the compacted powder 105 seals the through hole inside the housing 102 and fixes the sensor element 110. The bolt 103 is a cylindrical metal component with an external thread on its outer surface. The housing 102 of the element encapsulant 101 is welded to the pipe 10 and inserted into a fixing member 12 which has an internal thread on its inner surface. The housing 102 is further fixed inside the fixing member 12 by screwing the bolt 103 into the fixing member 12. In this way, the gas sensor 100 is fixed inside the pipe 10. The direction of flow of the gas to be measured inside the pipe 10 is from left to right in Figure 3.

[0026] The sensor element 110 comprises an element body 20 and a porous protective layer 22 that covers at least a portion of the surface of the element body 20. The element body 20 is an elongated, plate-shaped element with a structure in which multiple layers of oxygen ion conductive solid electrolyte layers, such as zirconia (ZrO2), are stacked. The element body 20 has a gas inlet 21 for introducing the gas to be measured into its interior, and is configured to detect the specific gas concentration of the gas to be measured that flows into the interior from the gas inlet 21. In this embodiment, the gas inlet 21 is assumed to open to the front end surface of the element body 20 (the lower end surface of the element body 20 in Figure 3). The element body 20 is equipped with a heater inside that plays a role in temperature control, which heats and maintains the temperature of the element body 20. The structure of such an element body 20 and the principle of detecting the specific gas concentration are publicly known, and are described, for example, in Japanese Patent Application Publication No. 2008-164411. The sensor element 110 has its front end (lower end in Figure 3) and gas inlet 21 located inside the sensor element chamber 124.

[0027] In this embodiment, the porous protective layer 22 is formed on five of the six surfaces of the element body 20, covering almost all of the surface of the element body 20 exposed within the sensor element chamber 124. Specifically, the porous protective layer 22 completely covers the front end surface (bottom surface) of the element body 20 where the gas inlet 21 is formed. The porous protective layer 22 also covers the sides of the four surfaces (the top, bottom, left, and right surfaces of the element body 20 in Figure 4) that are connected to the front end surface of the element body 20, which are closer to the front end surface. The porous protective layer 22 plays a role in preventing cracks from forming on the element body 20 due to the adhesion of moisture or other substances in the gas being measured. The porous protective layer 22 also plays a role in preventing oil components or other substances contained in the gas being measured from adhering to electrodes or other parts of the surface of the element body 20 (not shown). The porous protective layer 22 is made of a porous material such as alumina porous material, zirconia porous material, spinel porous material, cordierite porous material, titania porous material, or magnesia porous material. The porous protective layer 22 can be formed, for example, by plasma spraying, screen printing, dipping, etc. Although the porous protective layer 22 also covers the gas inlet 21, because the porous protective layer 22 is a porous material, the gas to be measured can flow through the inside of the porous protective layer 22 and reach the gas inlet 21.

[0028] The protective cover 120 is positioned to surround the sensor element 110. This protective cover 120 has a bottomed cylindrical inner protective cover 130 that covers the front end of the sensor element 110, and a bottomed cylindrical outer protective cover 140 that covers the inner protective cover 130. The sensor element chamber 124 is formed as the space surrounded by the inner protective cover 130. The outer protective cover 140 and the inner protective cover 130 form an inlet gas flow path 152, which is the flow path for the gas to be measured from the outside to the sensor element chamber 124, and an outlet gas flow path 156, which is the flow path for the gas to be measured from the sensor element chamber 124 to the outside. In addition, a first gas chamber 122 and a second gas chamber 126 are formed as the space surrounded by the inner protective cover 130 and the outer protective cover 140. The first gas chamber 122 is part of the inlet gas flow path 152, and the second gas chamber 126 is part of the outlet gas flow path 156. The central axes of the gas sensor 100, sensor element 110, inner protective cover 130, and outer protective cover 140 are coaxial. The protective cover 120 is made of metal (for example, stainless steel such as SUS310S).

[0029] The inner protective cover 130 comprises a first member 131 and a second member 135. The first member 131 has a cylindrical large-diameter portion 132, a cylindrical first cylindrical portion 134 with a smaller diameter than the large-diameter portion 132, a stepped portion 133 connecting the large-diameter portion 132 and the first cylindrical portion 134, and a bottom portion 134a disposed below the first cylindrical portion 134. The first cylindrical portion 134 surrounds the sensor element 110. The bottom portion 134a is disposed below the sensor element 110. The central axis of the bottom portion 134a is coaxial with that of the first cylindrical portion 134. The upper end of the bottom portion 134a is connected to the lower end of the first cylindrical portion 134. The bottom portion 134a has a tapered portion 134b and an opening 134c. The tapered portion 134b has a shape in which the inner diameter decreases as it goes downwards. The opening 134c is a circular hole located at the lower end of the bottom portion 134a. The central axis of the opening 134c is coaxial with that of the first cylindrical portion 134. The diameter of the opening 134c is smaller than the inner diameter of the first cylindrical portion 134 and the inner diameter of the upper end of the bottom portion 134a. Therefore, the opening area Sf of the opening 134c is smaller than the cross-sectional area S0 perpendicular to the vertical direction (axial direction of the first member 131) of the space inside the first cylindrical portion 134. The area of ​​the circle whose outer shape is the inner circumferential surface of the first cylindrical portion 134 shown in Figure 4 is the cross-sectional area S0, and the area of ​​the circle of the opening 134c shown in Figure 5 is the opening area Sf.

[0030] The second member 135 has a second cylindrical portion 136 with a larger diameter than the first cylindrical portion 134, a third cylindrical portion 137 with a smaller diameter than the second cylindrical portion 136, and a tip portion 138 with a smaller diameter than the third cylindrical portion 137. The second member 135 also has a stepped portion 136c connecting the lower end of the second cylindrical portion 136 and the upper end of the third cylindrical portion 137, and a stepped portion 137a connecting the lower end of the third cylindrical portion 137 and the upper end of the tip portion 138. The tip portion 138 has a side portion 138d and a bottom portion 138e. The tip portion 138 has an element chamber outlet 138a that connects to the sensor element chamber 124 and the second gas chamber 126, and is the outlet for the gas to be measured from the sensor element chamber 124. The element chamber outlet 138a has a plurality of circular lateral holes 138b (four in this embodiment) formed at equal intervals along the circumferential direction of the side portion 138d. The element chamber outlet 138a is not located at the bottom portion 138e of the tip portion 138. The diameter of the lateral holes 138b is, for example, 0.5 mm to 2.6 mm. In this embodiment, the diameters of the plurality of lateral holes 138b are all the same value. The element chamber outlet 138a is located below the gas inlet 21. In other words, the element chamber outlet 138a is located further away (downward) than the gas inlet 21 when viewed from the rear end of the sensor element 110 (the upper end of the sensor element 110, not shown in Figure 3).

[0031] The large-diameter portion 132, the first cylindrical portion 134, the second cylindrical portion 136, the third cylindrical portion 137, and the tip portion 138 share the same central axis. The large-diameter portion 132 has its inner circumferential surface in contact with the housing 102, thereby fixing the first member 131 to the housing 102. The second member 135 has its outer circumferential surface of the third cylindrical portion 137 in contact with the inner circumferential surface of the outer protective cover 140 and is fixed by welding or the like. Alternatively, the outer diameter of the third cylindrical portion 137 may be made slightly larger than the inner diameter of the tip portion 146 of the outer protective cover 140, and the second member 135 may be fixed by press-fitting the third cylindrical portion 137 into the tip portion 146.

[0032] Multiple protrusions 136a are formed on the inner circumferential surface of the second cylindrical portion 136, projecting toward and in contact with the outer circumferential surface of the first cylindrical portion 134. As shown in Figure 4, four protrusions 136a are provided and are evenly arranged along the circumferential direction of the inner circumferential surface of the second cylindrical portion 136. The protrusions 136a are formed in a substantially hemispherical shape. The provision of such protrusions 136a makes it easier to fix the positional relationship between the first cylindrical portion 134 and the second cylindrical portion 136. Preferably, the protrusions 136a press the outer circumferential surface of the first cylindrical portion 134 radially inward. This allows the positional relationship between the first cylindrical portion 134 and the second cylindrical portion 136 to be fixed more securely by the protrusions 136a. Note that the number of protrusions 136a is not limited to four; there may be two, three, or five or more. Furthermore, it is preferable to have three or more protrusions 136a in order to facilitate the stable fixing of the first cylindrical portion 134 and the second cylindrical portion 136.

[0033] This inner protective cover 130 is connected to the first gas chamber 122 and the sensor element chamber 124, and has an element chamber inlet 125 which is the inlet for the gas to be measured into the sensor element chamber 124. The element chamber inlet 125 is part of the inlet-side gas flow path 152. The element chamber inlet 125 has a first inlet 127 and a second inlet 128 (see Figures 3, 4, and 7). The first inlet 127 is the space between the first member 131 and the second member 135. More specifically, the first inlet 127 is formed as a cylindrical gap (gas flow path) between the outer circumferential surface of the first cylindrical portion 134 and the inner circumferential surface of the second cylindrical portion 136. The first inlet 127 is the space from the upper end of the second cylindrical portion 136 of the second member 135 to the lower end of the first cylindrical portion 134 of the first member 131. The first inlet 127 has an upper opening 127a, which is the opening on the first gas chamber 122 side, the space where the outer inlet 144a is located, and a lower opening 127b, which is the opening on the sensor element chamber 124 side, the space where the gas inlet 21 is located. The upper opening 127a is a ring-shaped gap between the upper end of the inner circumferential surface of the second cylindrical portion 136 and the outer circumferential surface of the first cylindrical portion 134. The lower opening 127b is a ring-shaped gap between the inner circumferential surface of the second cylindrical portion 136 and the lower end of the outer circumferential surface of the first cylindrical portion 134. The upper opening 127a is formed further back (above) the sensor element 110 than the lower opening 127b. Therefore, in the path of the gas to be measured from the outer inlet 144a to the gas inlet 21, that is, within the inlet-side gas flow path 152, the first inlet 127 is a flow path that goes from the rear end (upper side) to the front end (lower side) of the sensor element 110. Also, the first inlet 127 is a flow path parallel to the rear end-front end of the sensor element 110 (a flow path parallel in the vertical direction). The lower opening 127b opens into the sensor element chamber 124.

[0034] The lower opening 127b opens in the direction from the rear end to the front end of the sensor element 110 (downward) and is parallel to the rear end-to-front end direction (up and down direction) of the sensor element 110. In other words, the lower opening 127b opens parallel to the downward direction. Therefore, the sensor element 110 is positioned in a location other than the region that is virtually extended from the lower opening 127b to the first inlet 127 (the region directly below the lower opening 127b in Figures 3 and 7).

[0035] The second inlet 128 is located in the first member 131. More specifically, the second inlet 128 is a plurality (six in this case) of lateral holes formed at equal intervals along the outer circumference of the first cylindrical portion 134. The second inlet 128 is located above the first inlet 127. More specifically, the second inlet 128 is located above the upper opening 127a of the first inlet 127. The second inlet 128 is located above the front end (lower end in Figure 3) of the sensor element 110 and the gas inlet 21.

[0036] As shown in Figure 3, the outer protective cover 140 has a cylindrical body portion 143 and a bottomed cylindrical tip portion 146 with a smaller inner diameter than the body portion 143. The body portion 143 also has a side portion 143a that has a surface aligned with the central axis direction (vertical direction) of the outer protective cover 140, and a stepped portion 143b which is the bottom of the body portion 143 and connects the side portion 143a and the tip portion 146. The central axes of both the body portion 143 and the tip portion 146 are the same as the central axis of the inner protective cover 130. The inner circumferential surface of the portion of the body portion 143 around the upper end abuts against the housing 102 and the large diameter portion 132, thereby fixing the outer protective cover 140 to the housing 102. The body portion 143 is positioned to cover the outer circumference of the large diameter portion 132, the first cylindrical portion 134, and the second cylindrical portion 136. The tip portion 146 is positioned to cover the tip portion 138, and its inner circumferential surface is in contact with the outer circumferential surface of the third cylindrical portion 137. The tip portion 146 has a side portion 146a that has a side surface aligned with the central axis direction (vertical direction) of the outer protective cover 140 and whose outer diameter is 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. The bottom portion 146b has a tapered portion 146c that decreases in diameter from the side portion 146a towards the lower end of the bottom portion 146b. The tip portion 146 is located below the body portion 143. This outer protective cover 140 has one or more (multiple in this embodiment, specifically 12) outer inlets 144a formed in the body portion 143, which are inlets from the outside of the gas to be measured, and one or more outer outlets 147a formed in the tip portion 146, which are outlets to the outside of the gas to be measured.

[0037] The outer inlet 144a is a hole that leads from the outside of the outer protective cover 140 to the first gas chamber 122. The outer inlet 144a has a plurality of (six in this embodiment) horizontal holes 144b formed at equal intervals in the side portion 143a and a plurality of (six in this embodiment) vertical holes 144c formed at equal intervals in the stepped portion 143b (see Figures 3, 5, and 6). The horizontal holes 144b open in a direction that intersects the vertical direction, and in this embodiment, they open in a direction that intersects perpendicularly in the vertical direction. The vertical holes 144c open along the vertical direction, and in this embodiment, they open parallel to the vertical direction. The outer inlet 144a (horizontal holes 144b and vertical holes 144c) are circular holes. The diameter of these 12 outer inlets 144a is, for example, 0.5 mm to 2 mm. The diameter of the outer inlets 144a may be 1.5 mm or less. In this embodiment, the diameters of the multiple horizontal holes 144b and the multiple vertical holes 144c are all the same. Furthermore, the diameter of the horizontal holes 144b is larger than the diameter of the vertical holes 144c. As shown in Figure 5, the outer entrance 144a is formed such that the horizontal holes 144b and vertical holes 144c are alternately located at equal intervals along the circumferential direction of the outer protective cover 140. That is, the angle between the line connecting the center of the horizontal hole 144b and the central axis of the outer protective cover 140 in Figure 5, and the line connecting the center of the vertical hole 144c adjacent to the horizontal hole 144b and the central axis of the outer protective cover 140 is 30° (360° / 12 holes).

[0038] The outer outlet 147a is a hole that leads from the outside of the outer protective cover 140 to the second gas chamber 126. This outer outlet 147a has one or more (one in this embodiment) vertical holes 147c formed in the center of the bottom 146b of the tip portion 146 (see Figures 3 and 6). Unlike the outer inlet 144a, the outer outlet 147a is not located on the side of the outer protective cover 140 (in this case, the side 146a of the tip portion 146). This outer outlet 147a (in this case, the vertical hole 147c) is a circularly shaped hole. The diameter of this 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 this embodiment, the diameter of the vertical hole 147c is larger than the diameters of the horizontal hole 144b and the vertical hole 144c.

[0039] As described above, the outer protective cover 140 and the inner protective cover 130 form an inlet gas passage 152 and an outlet gas passage 156. The inlet gas passage 152 includes an outer inlet 144a, a first gas chamber 122, and an element chamber inlet 125, and the gas to be measured passes through the inlet gas passage 152 in this order. The outlet gas passage 156 includes an element chamber outlet 138a, a second gas chamber 126, and an outer outlet 147a, and the gas to be measured passes through the outlet gas passage 156 in this order. The first gas chamber 122 is formed 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 stepped portion 133, a first cylindrical portion 134, a second cylindrical portion 136, a side portion 143a, and a stepped portion 143b. The second gas chamber 126 is formed as the space between the tip portion 146 and the inner protective cover 130. More specifically, the second gas chamber 126 is the space surrounded by the stepped portion 137a, the tip portion 138, and the tip portion 146. Note that the inner circumferential surface of the tip portion 146 is in contact with the outer circumferential surface of the third cylindrical portion 137, so the first gas chamber 122 and the second gas chamber 126 are not in direct communication.

[0040] Furthermore, as shown in Figures 3 and 7, the first gas chamber 122 has a first flow path 122a. The first flow path 122a is the space between the outer protective cover 140 and the second member 135 of the inner protective cover 130, and is the flow path for the gas to be measured, moving upward from the outer inlet 144a. More specifically, the first flow path 122a is the space enclosed by the side portion 143a, the stepped portion 143b, and the second cylindrical portion 136, and is the space below the upper end of the second member 135 (in this case, the upper end of the second cylindrical portion 136). The first flow path 122a is a cylindrical gap between the inner circumferential surface of the outer protective cover 140 and the outer circumferential surface of the second cylindrical portion 136.

[0041] Next, the flow of the gas to be measured within the protective cover 120 when the gas sensor 100 detects a specific gas concentration will be described. The gas to be measured flowing through the piping 10 first flows into the first gas chamber 122 through at least one of the multiple outer inlets 144a (here, the horizontal hole 144b and the vertical hole 144c). Next, the gas to be measured moves upward through the first flow path 122a and then flows into the sensor element chamber 124 from the element chamber inlet 125. More specifically, of the gas to be measured that has moved upward through the first flow path 122a, a portion moves downward through the first inlet 127 and flows out from the lower opening 127b into the sensor element chamber 124, and a portion passes through the second inlet 128 and flows into the sensor element chamber 124. At least a portion of the gas to be measured that has flowed into the sensor element chamber 124 reaches the gas inlet 21 of the sensor element 110. The gas to be measured, which flows into the sensor element chamber 124 from the lower opening 127b, passes upward through the opening 134c before reaching the gas inlet 21. When the gas to be measured reaches the gas inlet 21 and flows into the sensor element 110, the sensor element 110 generates an electrical signal (voltage or current) corresponding to the specific gas concentration in the gas to be measured, and the specific gas concentration is detected based on this electrical signal. 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 (in this case, the horizontal hole 138b). The gas to be measured, including the gas that has reached the sensor element 110, and especially the gas that has reached the inside of the first member 131 in the sensor element chamber 124, passes downward through the opening 134c before flowing into the second gas chamber 126 through the element chamber outlet 138a. The gas that has reached the second gas chamber 126 flows out to the outside through the outer outlet 147a. Furthermore, the output of the internal heater of the sensor element 110 is controlled by a controller (not shown) to maintain a predetermined temperature.

[0042] In this case, the gas to be measured may contain water, and water may enter the protective cover 120 from the outer inlet 144a along with the gas to be measured. When this happens, if the water reaches the sensor element chamber 124 and adheres to the sensor element 110, cracks may occur in the sensor element 110 (especially the element body 20). In the gas sensor 100 of this embodiment, as described above, the first member 131 has a bottom portion 134a that is positioned below the first cylindrical portion 134, and the opening area Sf of the opening 134c of the bottom portion 134a is smaller than the cross-sectional area S0 of the first cylindrical portion 134. The presence of such a bottom portion 134a in the first member 131 suppresses the adhesion of water to the sensor element 110 when water enters the sensor element chamber 124 from the first inlet 127. Therefore, the water resistance of the sensor element 110 in the gas sensor 100 can be improved. This is because the portion of the bottom portion 134a other than the opening 134c (in this case, the tapered portion 134b) functions as a water adhesion suppression portion that prevents water that enters the sensor element chamber 124 (inside the second member 135) from the first inlet 127 from adhering to the sensor element 110.

[0043] Figure 8 is an explanatory diagram showing how water W accumulates inside the inner protective cover 130. Figure 8 shows how the gas sensor 100 is fixed inside the piping 10 with its central axis tilted at 60° with respect to the vertical. When the gas sensor 100 is positioned in this tilted state, water W that enters the inner protective cover 130 from the first inlet 127 tends to accumulate in the corners between the second cylindrical portion 136 and the stepped portion 136c, the corners between the third cylindrical portion 137 and the stepped portion 137a, and the corners between the side portion 138d and the bottom portion 138e. Furthermore, if the gas sensor 100 vibrates, for example due to vehicle vibration, this accumulated water W may splash around inside the inner protective cover 130 and adhere to the sensor element 110. However, as shown in Figure 8, in the gas sensor 100 of this embodiment, a bottom portion 134a exists between the inner circumferential surface of the second cylindrical portion 136 of the sensor element chamber 124 (in particular the inner circumferential surface of the corner portion mentioned above) and the sensor element 110, so even if water W splashes, it is less likely to adhere to the sensor element 110. Therefore, the water resistance of the sensor element 110 in the gas sensor 100 can be improved. In contrast, if the first member 131 does not have a bottom portion 134a, as in the comparative example gas sensor 900 shown in Figure 9, water is more likely to adhere to the sensor element 110. Note that if the sensor element chamber 124 is not tilted as shown in Figure 8, water that enters the inner protective cover 130 from the first inlet 127 tends to accumulate at the bottom portion 138e, but even in this case, the presence of the bottom portion 134a provides the effect of suppressing splashed water from adhering to the sensor element 110.

[0044] The opening area Sf is 61.93 mm². 2 It is preferable that it be less than 50 mm². This ensures a more reliable improvement in the water resistance of the sensor element. The aperture area Sf is 50 mm². 2 The following is also acceptable: 40 mm 2 The following is also acceptable: 30 mm 2 The following is also acceptable: 28.27 mm 2 The following may also be used, or 25 mm 2 The following may also be considered: The smaller the aperture area Sf, the greater the effect of improving the water resistance of the sensor element.

[0045] The aperture area Sf is 8.45 mm².2 It is preferable that the aperture area Sf is greater than the specified value. Here, if the aperture area Sf is too small, the time it takes for the gas to be measured to pass through the opening 134c and reach the sensor element 110 increases, which may reduce the responsiveness of the sensor element 110 in detecting the specific gas concentration. In contrast, an aperture area Sf of 8.45 mm is preferable. 2 By exceeding the limit, a decrease in the responsiveness of detecting specific gas concentrations can be suppressed. The aperture area Sf is 9.0 mm². 2 It may be the above, or 11.0 mm 2 The above is also acceptable, or 12.57 mm 2 It may be more than that, or 20 mm 2 The above may also be used. The larger the aperture area Sf, the more effectively the decrease in responsiveness to detecting specific gas concentrations can be suppressed.

[0046] The vertical distance L (see Figure 7) between the opening 134c and the gas inlet 21 may be, for example, 1 mm or more. The distance L may also be 7 mm or less.

[0047] Furthermore, as described above, the gas sensor 100 of this embodiment has a second inlet 128 in addition to the first inlet 127 in the element chamber inlet 125. This makes it easier for the gas to be measured to flow into the sensor element chamber 124 compared to the case where the second inlet 128 does not exist. Therefore, a decrease in the responsiveness of the sensor element 110 in detecting a specific gas concentration can be suppressed. As described above, in the gas sensor 100 of this embodiment, there is a bottom 134a between the first inlet 127 and the sensor element 110. Therefore, while the bottom 134a improves the water resistance of the sensor element 110, there is a risk that the responsiveness of detecting a specific gas concentration will decrease. In contrast, the presence of a second inlet 128 in addition to the first inlet 127 can suppress a decrease in responsiveness.

[0048] The opening area Ss of the second entrance 128 is 10.60 mm². 2 The following is preferable. Here, if a second inlet 128 is present, water may enter the sensor element chamber 124 not only from the first inlet 127 but also from the second inlet 128. The opening area Ss is 10.60 mm². 2The following conditions make it difficult for water to enter the sensor element chamber 124 from the second inlet 128, thus preventing a decrease in the water resistance of the sensor element 110 even with the presence of the second inlet 128. In this embodiment, if the second inlet 128 is composed of multiple holes, the opening area Ss is the sum of the opening areas of the multiple holes. The opening area Ss is 10 mm². 2 The following is also acceptable: 7.36 mm 2 The following is also acceptable: 6.79 mm 2 The following may also be considered: The smaller the aperture area Ss, the greater the effect of improving the water resistance of the sensor element.

[0049] The opening area Ss is 1.18 mm². 2 The above is preferable. This makes it easier for the gas to be measured to enter the sensor element chamber 124 from the second inlet 128, thus more reliably suppressing the decrease in the responsiveness of detecting specific gas concentrations due to the presence of the second inlet 128. The aperture area Ss is 2.0 mm². 2 It may be the above, or 2.65 mm 2 The above is also acceptable, or 3.12 mm 2 The above may also be used. A larger aperture area Ss tends to suppress the decrease in responsiveness for detecting specific gas concentrations more effectively. The sum of the aperture area Sf and aperture area Ss is 17.28 mm². 2 The above is also acceptable, or 24.77 mm 2 The above is also acceptable, or 26.24 mm 2 You may leave it at that.

[0050] As described in detail above, the gas sensor 100 of this embodiment has a bottom portion 134a which prevents water from adhering to the sensor element 110 when water enters the sensor element chamber 124 from the first inlet 127. Therefore, the water resistance of the sensor element 110 in the gas sensor 100 can be improved. Also, the opening area Sf is 61.93 mm². 2 By keeping it below this value, the effect of improving the water resistance of the sensor element 110 can be obtained more reliably. (Aperture area Sf is 28.27 mm²) 2 The following conditions further improve the water resistance of the sensor element 110: An aperture area Sf of 8.45 mm². 2By exceeding the limit, the decrease in responsiveness of detecting specific gas concentrations can be suppressed. The aperture area Sf is 12.57 mm². 2 This ensures that the decrease in responsiveness of detecting specific gas concentrations can be suppressed more reliably.

[0051] Furthermore, the element chamber inlet 125 has not only a first inlet 127 but also a second inlet 128, which facilitates the flow of the gas to be measured into the sensor element chamber 124. Therefore, a decrease in the responsiveness of the sensor element 110 in detecting the specific gas concentration can be suppressed. In addition, the opening area Ss of the second inlet 128 is 10.60 mm². 2 The following conditions make it difficult for water to enter the sensor element chamber 124 from the second inlet 128, thus preventing a decrease in the water resistance of the sensor element 110 even with the presence of the second inlet 128: Opening area Ss is 7.36 mm². 2 The following conditions can further suppress the decrease in water resistance of the sensor element 110 due to the presence of the second inlet 128: The opening area Ss is 1.18 mm². 2 As a result of the above, the presence of the second inlet 128 more reliably suppresses the decrease in the responsiveness of detecting specific gas concentrations. The aperture area Ss is 2.65 mm². 2 As a result of the above, the presence of a second inlet further enhances the effect of suppressing the decrease in the responsiveness of detecting specific gas concentrations.

[0052] It goes without saying that the present invention is not limited in any way to the embodiments described above, and can be implemented in various forms as long as they fall within the technical scope of the present invention.

[0053] For example, in the embodiment described above, the bottom portion 134a had a tapered portion 134b in which the inner diameter decreased as it went downwards, but it is not limited to this, and any shape that tends to decrease in inner diameter as it goes downwards is acceptable. For example, the bottom portion 134a may have a stepped portion so that the inner diameter decreases in a stepwise manner as it goes downwards. Alternatively, as in the modified gas sensor 200 shown in Figure 10, the bottom portion 234a does not have to have a shape that tends to decrease in inner diameter as it goes downwards. The bottom portion 234a in Figure 10 has a flat plate portion 234b perpendicular to the vertical direction and an opening 234c. The opening area Sf of the opening 234c is smaller than the cross-sectional area S0 of the first cylindrical portion 134. In this gas sensor 200 as well, the same effects can be obtained with the same features as in the embodiment described above. For example, the presence of the bottom portion 234a can improve the water resistance of the sensor element 110.

[0054] In the embodiments described above, the inner protective cover 130 and / or the outer protective cover 140 may have a water passage suppression portion that is positioned above the outer inlet 144a of the first flow path 122a and has a shape that narrows a part of the first flow path 122a. For example, in the modified gas sensor 300 shown in Figure 11, the second cylindrical portion 136 of the second member 135 of the inner protective cover 130 has a water passage suppression portion 136b that protrudes radially outward. The water passage suppression portion 136b is located at the upper end of the second member 135, that is, at the upper end of the second cylindrical portion 136. The water passage suppression portion 136b has a tapered shape that expands in diameter from bottom to top. The water passage suppression portion 136b is positioned above the outer inlet 144a of the first flow path 122a and narrows a part of the first flow path 122a. In this gas sensor 300, the water passage suppression part 136b can suppress the upward movement of water that enters the first flow path 122a from the outer inlet 144a. As a result, it becomes more difficult for water to reach the element chamber inlet 125, and consequently, it becomes more difficult for water to reach the sensor element chamber 124. Therefore, the water resistance of the sensor element 110 can be improved not only by the bottom 134a of the first member 131 but also by the water passage suppression part 136b.

[0055] In the embodiment described above, the second inlet 128 was a plurality of holes, but it is not limited to this and may be a single hole. However, it is preferable that there be a plurality of second inlets 128, more preferably four or more, and even more preferably six or more.

[0056] In the embodiment described above, the opening 134c was a single hole, but it is not limited to a single hole; it may be multiple holes. In this case, the opening area Sf is the total area of ​​the multiple openings.

[0057] In the embodiment described above, the element chamber inlet 125 had a first inlet 127 and a second inlet 128, but the second inlet 128 does not necessarily have to be present.

[0058] In the embodiment described above, the second inlet 128 was located above the first inlet 127, but it is not limited to this. For example, the second inlet 128 may be located below the upper opening 127a of the first cylindrical portion 134. In this case, the second inlet 128 will open in the middle of the flow path of the first inlet 127. In this case, a portion of the gas to be measured that enters the first inlet 127 from the upper opening 127a will enter the sensor element chamber 124 from the second inlet 128, and the remainder will enter the sensor element chamber 124 from the lower opening 127b.

[0059] In the embodiment described above, the outer inlet 144a has a horizontal hole 144b and a vertical hole 144c, but it is not limited to this. The outer inlet 144a only needs to have at least a horizontal hole 144b. For example, as shown in Figure 12, the outer inlet 144a may have, in addition to or instead of the vertical hole 144c, a corner hole 144d disposed at the corner of the boundary between the side portion 143a and the bottom portion (step portion 143b) of the body portion 143.

[0060] In the embodiment described above, the inner protective cover 130 comprised two members, a first member 131 and a second member 135. However, the first member 131 and the second member 135 may be integrated into a single member.

[0061] In the embodiment described above, the gas inlet 21 is assumed to open to the front end surface of the sensor element 110 (the lower surface of the sensor element 110 in Figure 3), but it is not limited to this. For example, it may open to the side surface of the sensor element 110 (any of the top, bottom, left, or right surfaces of the sensor element 110 in Figure 4).

[0062] In the embodiment described above, the sensor element 110 is provided with a porous protective layer 22, but it is not necessary to provide the porous protective layer 22.

[0063] In the comparative example gas sensor 900 shown in Figure 9, the front end (lower end) of the element body 20 of the sensor element 110 protrudes downward from the lower end of the first cylindrical portion 134. However, the front end of the element body 20 may be located above the lower end of the first cylindrical portion 134. In this case, the vertical distance between the front end of the element body 20 and the lower end of the first cylindrical portion 134 may be 5 mm or less, or it may be greater than 5 mm. That is, the front end of the element body 20 may be located above the lower end of the first cylindrical portion 134 by a distance greater than 5 mm.

[0064] The following describes specific examples of how gas sensors were fabricated. Experimental Examples 1-4 and 6-10 correspond to embodiments of the present invention, while Experimental Example 5 corresponds to a comparative example. However, the present invention is not limited to the following embodiments.

[0065] [Experimental Examples 1-4] The gas sensors 100 shown in Figures 3-7 were fabricated with different aperture areas Sf to form Experimental Examples 1-4. In all of Experimental Examples 1-4, the cross-sectional area S0 of the first cylindrical portion 134 was 61.93 mm². 2 The second entrance 128 has six horizontal holes with a radius of 0.5 mm (therefore the opening area Ss is 4.71 mm). 2 The aperture area Sf for experimental examples 1 to 4 was 8.45 mm². 2 12.57 mm 2 23.59 mm 2 , 28.27 mm 2 Experimental examples 1 to 4 were otherwise identical in structure.

[0066] [Experimental Example 5] A gas sensor 900 without the bottom portion 134a shown in Figure 9 was created and designated as Experimental Example 5. In Experimental Example 5, the cross-sectional area S0 and the opening area Ss were the same as in Experimental Examples 1 to 4. Since Experimental Example 5 does not have the bottom portion 134a, the opening at the lower end of the second cylindrical portion 136 was considered to correspond to the opening 134c, and the value of the opening area Sf was 61.93 mm². 2 (The same value as the cross-sectional area S0) was used.

[0067] [Experimental Examples 6-10] The same gas sensor 100 as in Experimental Example 3 was fabricated, except that the radius of the second inlet 128 was varied to create different opening areas Ss. These were then used for Experimental Examples 6-10. The opening areas Ss for Experimental Examples 6-10 were 1.18 mm² each. 2 , 2.65 mm 2 , 4.71 mm 2 7.36 mm 2 , 10.60 mm 2 Experimental Examples 6 to 10 had the same structure in all other respects. Furthermore, as can be seen from the value of the aperture area Ss above, Experimental Example 8 is essentially the same gas sensor 100 as Experimental Example 3.

[0068] [Evaluation of Water Resistance] The water resistance of the sensor element 110 was evaluated for the gas sensors 100 of Experimental Examples 1 to 10. For the evaluation of water resistance, a water exposure test apparatus described in Japanese Patent Application Publication No. 2019-158615 was used. This water exposure test apparatus comprises a pipe arranged horizontally and linearly, having a gas flow path inside; a blower installed upstream of the pipe; a pressure fluctuation generator installed downstream of the pipe; and a chamber which is part of the pipe between the blower and the pressure fluctuation generator and to which the gas sensor 100 is attached. A vibrator is connected to the chamber to apply vibration to the chamber. In this water exposure test apparatus, moisture can be scattered toward the gas sensor 100 using a gas that simulates exhaust gas from an engine. In the water exposure test, first, the gas sensor 100 was placed inside the chamber of the water exposure test apparatus with its central axis perpendicular to the axis of the pipe and tilted 10° with respect to the horizontal direction. Next, a predetermined amount of moisture was supplied into the pipe between the blower and the chamber. Next, a blower was used to supply gas (atmosphere) into the piping, a pressure fluctuation generator was used to fluctuate the gas pressure, and a vibrator was used to vibrate the chamber. As a result, the moisture supplied into the piping was scattered towards the gas sensor 100 located in the chamber by the pressure fluctuation of the gas. In this state, the heater built into the sensor element 110 was driven, and the heater power was controlled so that the temperature of the sensor element 110 reached 850°C. If water adheres to the sensor element 110 at the above temperature, a crack will occur in the sensor element 110, causing the electrical signal to show an abnormal value. Therefore, whether or not a crack occurred in the sensor element 110 was determined by whether or not the electrical signal showed an abnormal value during the water exposure test. Five gas sensors 100 were fabricated for each of Experimental Examples 1 to 10, and the above water exposure test was performed. If no cracks occurred in the sensor element 110 of any of the five sensors, it was determined that the water resistance was very high ("A"). If cracks occurred in the sensor element 110 of one to three of the five gas sensors 100, it was determined that the water resistance was high ("B"). If cracks occurred in the sensor element 110 of four or all five gas sensors 100, it was determined that the water resistance was low ("F").

[0069] [Evaluation of Responsiveness] The gas sensors 100 for Experimental Examples 1 to 10 were attached to the piping 10 in the same manner as in Figures 1 and 2. The gas to be measured was prepared by mixing oxygen with air and adjusting it to an arbitrary oxygen concentration, and this gas to be measured was flowed through the piping 10 at a flow velocity of 7 m / s. The time change in the output (electrical signal) of the sensor element 110 when the oxygen concentration of the gas to be measured flowing through the piping was then investigated. The output value of the sensor element immediately before the change in oxygen concentration was set to 0%, and the output value when the output of the sensor element changed and stabilized after the change in oxygen concentration was set to 100%. The elapsed time from when the output value exceeded 10% to when it exceeded 90% was defined as the response time (sec) for detecting the specific gas concentration. A shorter response time indicates higher responsiveness for detecting the specific gas concentration. The response time was measured multiple times for each experimental example, and the average value of each measurement was defined as the response time for each experimental example. Furthermore, a response time of less than 0.5 seconds was judged as very responsive ("A"), a response time of 0.5 seconds or more but less than 0.69 seconds was judged as high responsiveness ("B"), and a response time of 0.69 seconds or more was judged as low responsiveness ("F").

[0070] For each of the experimental examples 1 to 10, the presence or absence of the bottom 134a and the opening area Sf [mm²] 2 ], opening area Ss [mm 2 Table 1 shows the results of the water resistance evaluation and the responsiveness evaluation.

[0071]

[0072] As shown in Table 1, Experimental Example 1, which lacked a bottom portion 134a and therefore had an opening area Sf that was not smaller than the cross-sectional area S0, received a water resistance rating of "F". In contrast, Experimental Examples 1-4 and 6-10, which had a bottom portion 134a and an opening area Sf smaller than the cross-sectional area S0, all received a water resistance rating of "A" or "B". From these results, it was confirmed that the presence of a bottom portion 134a and an opening area Sf smaller than the cross-sectional area S0 can improve the water resistance of the sensor element 110 in the gas sensor 100. Furthermore, in Experimental Example 5, the opening area Sf was 61.93 mm. 2 Since it can be considered as such, the opening area Sf is 61.93 mm². 2It is considered preferable that it be less than [a certain value]. Furthermore, in Experimental Examples 1 to 4, where the opening area Ss is the same for all of them, the water resistance evaluation was "A", and the largest opening area Sf among Experimental Examples 1 to 4 was 28.27 mm in Experimental Example 4. 2 Therefore, from the viewpoint of water resistance, the opening area Sf is 28.27 mm². 2 The following is considered more preferable. Furthermore, among experimental examples 1 to 4, in which the aperture area Ss is the same, experimental example 1 received a responsiveness evaluation of "F", while experimental examples 2 to 4 received a responsiveness evaluation of "A". Therefore, from the viewpoint of responsiveness, the aperture area Sf is 8.45 mm. 2 An excess of 12.57 mm is preferable. 2 The above is considered more preferable.

[0073] Furthermore, among experimental examples 6 to 10, where the opening area Sf is the same, experimental example 10 received a water resistance evaluation of "B," while experimental examples 6 to 9 received a water resistance evaluation of "A." Therefore, from the viewpoint of water resistance, the opening area Ss is 10.60 mm. 2 The following is preferable: 7.36 mm 2 The following is considered more preferable. Of the experimental examples 6 to 10, experimental example 6 received a responsiveness evaluation of "B", while experimental examples 7 to 10 received a responsiveness evaluation of "A". Therefore, from the viewpoint of responsiveness, the aperture area Ss is 1.18 mm. 2 The above is preferable, 2.65 mm 2 The above is considered more preferable.

[0074] This application is based on the priority claim of Japanese Patent Application No. 2025-052925, filed on 27 March 2025, the entire contents of which are incorporated herein by reference.

[0075] This invention can be used in gas sensors that detect the concentration of specific gases, such as NOx, in a gas to be measured, such as automobile exhaust gas.

[0076] 10 Piping, 12 Fixing member, 20 Element body, 21 Gas inlet, 22 Porous protective layer, 100, 200, 300, 900 Gas sensor, 101 Element seal, 102 Housing, 103 Bolt, 104 Supporter, 105 Compacted powder, 110 Sensor element, 120 Protective cover, 122 First gas chamber, 122a First flow path, 124 Sensor element chamber, 125 Element chamber inlet, 126 Second gas chamber, 127 First inlet, 127a Upper opening, 127b Lower opening, 128 Second inlet, 130 Inner protective cover, 131 First member, 132 Large diameter section, 133 Stepped section, 134 First cylindrical section, 134a Bottom section, 134b Tapered section, 134c Opening, 135 Second member, 136 Second cylindrical section, 136a protruding section, 136b water passage suppression section, 136c stepped section, 137 third cylindrical section, 137a stepped section, 138 tip section, 138a element chamber outlet, 138b lateral hole, 138d side section, 138e bottom section, 140 outer protective cover, 143 body section, 143a side section, 143b stepped section, 144a outer inlet, 144b lateral hole, 144c vertical hole, 144d square hole, 146 tip section, 146a side section, 146b bottom section, 146c tapered section, 147a outer outlet, 147c vertical hole, 152 inlet side gas passage, 156 outlet side gas passage, 234a bottom section, 234b flat plate section, 234c opening.

Claims

1. A sensor element having a front end and a rear end opposite to the front end, and having a gas inlet for introducing a gas to be measured, for detecting a specific gas concentration of the gas to be measured that has flowed into the interior from the gas inlet; a cylindrical inner protective cover having a sensor element chamber inside in which the front end of the sensor element and the gas inlet are arranged, and having an element chamber inlet which is an entrance to the sensor element chamber and an element chamber outlet which is an exit from the sensor element chamber; a cylindrical outer protective cover having an outer inlet which is an entrance to the gas to be measured from the outside and an outer outlet which is an exit from the sensor element chamber, and disposed outside the inner protective cover, wherein the outer protective cover and the inner protective cover form an inlet-side gas flow path from the outside to the sensor element chamber, including the outer inlet and the element chamber inlet, and an outlet-side gas flow path from the sensor element chamber to the outside, including the element chamber outlet and the outer outlet. The inner protective cover comprises a cylindrical first member surrounding the sensor element and a cylindrical second member surrounding the first member and having an element chamber outlet; the element chamber inlet has a first inlet configured as a gap between the first member and the second member; the opening of the first inlet on the sensor element chamber side opens downward, parallel to the axial direction of the first member and in the direction from the rear end to the front end of the sensor element; the first member comprises a first cylindrical portion surrounding the sensor element and a bottom portion disposed below the first cylindrical portion and the sensor element and having an opening; the opening area Sf of the opening in the bottom portion is smaller than the cross-sectional area S0 perpendicular to the axial direction of the space inside the first cylindrical portion; gas sensor.

2. A gas sensor according to claim 1, wherein the bottom portion has a shape in which the inner diameter tends to decrease as it goes downward, and the opening is located at the downward end.

3. A gas sensor according to claim 2, wherein the bottom portion has a tapered portion whose inner diameter decreases as it goes downward.

4. A gas sensor according to any one of claims 1 to 3, wherein the aperture area Sf is 61.93 mm². 2 A gas sensor that is less than [value missing].

5. A gas sensor according to any one of claims 1 to 3, wherein the aperture area Sf is 28.27 mm². 2 The following is a gas sensor.

6. A gas sensor according to any one of claims 1 to 3, wherein the aperture area Sf is 8.45 mm². 2 The gas sensor is exceeding the limit.

7. A gas sensor according to any one of claims 1 to 3, wherein the aperture area Sf is 12.57 mm². 2 That's all for the gas sensor.

8. A gas sensor according to any one of claims 1 to 3, wherein the element chamber inlet has a second inlet disposed on the first member.

9. A gas sensor according to claim 8, wherein the second inlet is located in an upward direction, opposite to the downward direction, relative to the first inlet.

10. The gas sensor according to claim 8, wherein the opening area Ss of the second inlet is 10.60 mm². 2 The following is a gas sensor.

11. The gas sensor according to claim 8, wherein the opening area Ss of the second inlet is 7.36 mm². 2 The following is a gas sensor.

12. The gas sensor according to claim 8, wherein the opening area Ss of the second inlet is 1.18 mm². 2 That's all for the gas sensor.

13. The gas sensor according to claim 8, wherein the opening area Ss of the second inlet is 2.65 mm². 2 That's all for the gas sensor.

14. A gas sensor according to any one of claims 1 to 3, wherein the inlet gas flow path is the space between the outer protective cover and the inner protective cover and has a first flow path that extends upward from the outer inlet in the opposite direction to the downward direction, and the inner protective cover and / or the outer protective cover have a water passage suppression portion that is disposed above the outer inlet in the first flow path and has a shape that narrows a part of the first flow path.

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