Gas sensor

Abstract

A gas sensor 100 comprises: a sensor element 110; an inner protective cover 130 having thereinside a sensor element chamber 124 in which the front end of the sensor element 110 is disposed; and an outer protective cover 140 having an outer inlet 144a. The outer protective cover 140 and the inner protective cover 130 form an inlet-side gas flow path 152 extending to the sensor element chamber 124 from the exterior including the outer inlet 144a. The inlet-side gas flow path 152 has a first flow path 122a extending upward from the outer inlet 144a. The outer inlet 144a has lateral holes 144b that are formed in the outer periphery of the outer protective cover 140 and open in a direction intersecting the vertical direction. The cross-sectional area ratio Sa / Sb of the cross-sectional area Sa of the smallest flow path 123a in the first flow path 122a to the cross-sectional area Sb of a reference flow path 123b, in the first flow path 122a, passing through the vertical centers of the lateral holes 144b is 0.716 or less.

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. With the direction parallel to the axial direction of the outer protective cover and the direction from the front end to the rear end of the sensor element being defined as upward, and the direction opposite to the upward direction being defined as downward, the inlet-side gas flow path is the space between the outer protective cover and the inner protective cover and has a first flow path extending upward from the outer inlet. The outer inlet has a transverse hole disposed on the outer circumferential surface of the outer protective cover and opening in a direction intersecting the vertical direction. The cross-sectional area ratio Sa / Sb of the minimum flow path, which is the part of the first flow path with the smallest cross-sectional area perpendicular to the vertical direction, and the reference flow path, which is the part of the first flow path that passes through the vertical center of the transverse hole and has a cross-sectional area perpendicular to the vertical direction, is 0.716 or less.

[0008] This gas sensor has a first flow path that extends upward from the outer inlet, located in the space between the outer protective cover and the inner protective cover. The cross-sectional area ratio Sa / Sb between the minimum flow path, which is the part of the first flow path with the smallest cross-sectional area perpendicular to the vertical direction, and the reference flow path Sb, which is perpendicular to the vertical direction and passes through the center of the lateral hole of the outer inlet, is 0.716 or less. This improves the water resistance of the sensor element in the gas sensor. The inventors have confirmed this through experiments and analyses.

[0009] [2] In the gas sensor described above (the gas sensor described in [1]), the cross-sectional area ratio Sa / Sb may be 0.5 or less. This can further improve the water resistance of the sensor element.

[0010] [3] In the gas sensor described above (the gas sensor described in [1] or [2] above), the cross-sectional area ratio Sa / Sb may be 0.083 or more. If the cross-sectional area ratio Sa / Sb is too small, the time it takes for the gas to be measured to reach the sensor element increases, which may reduce the responsiveness of the sensor element in detecting a specific gas concentration. By having a cross-sectional area ratio Sa / Sb of 0.083 or more, the decrease in the responsiveness of detecting a specific gas concentration can be suppressed. The inventors have confirmed this through experiments and analyses.

[0011] [4] In the gas sensor described above (the gas sensor described in any of [1] to [3] above), the cross-sectional area ratio Sa / Sb may be 0.1 or more. This will further suppress the decrease in the responsiveness of detecting specific gas concentrations.

[0012] [5] In the gas sensor described above (the gas sensor described in any of [1] to [4] above), the cross-sectional area Sa is 4.7 mm 2 41.0 mm 2 The following is also acceptable.

[0013] [6] In the gas sensor described above (the gas sensor described in any of [1] to [5] above), the volume V of the space upstream of the minimum flow path in the first flow path is 150 mm 3 The above is also acceptable. This increases the space between the outer inlet and the minimum flow path, and thus increases the volume of water that can be stored in this space, making it more difficult for water to enter the downstream side of the minimum flow path, i.e., the side of the sensor element.

[0014] [7] In the gas sensor described above (the gas sensor described in any of [1] to [6] above), the inner protective cover may have a water passage suppression portion that forms the minimum flow path by having a shape that protrudes radially outward.

[0015] [8] In the gas sensor described above (the gas sensor described in [7]), the inner protective cover has 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, and the water passage suppression part may be disposed on the second member. Here, "opens downward" includes the case where it opens parallel to the downward direction and the case where it opens inclined from the downward direction so that it approaches the sensor element as it goes downward.

[0016] [9] In the gas sensor described above (the gas sensor described in [8]), the water passage suppression portion may be located at the upper end of the second member.

[0017] A schematic diagram illustrating the mounting state of the gas sensor 100 to the piping 10. A cross-sectional view along line A-A in Figure 1. A cross-sectional view along line B-B in Figure 2. A cross-sectional view along line C-C in Figure 3. A cross-sectional view along line D-D in Figure 3. A view of line E in Figure 3. A partially enlarged view of Figure 3. A longitudinal cross-sectional view of a modified gas sensor 200. A longitudinal cross-sectional view of a modified gas sensor 300. A longitudinal cross-sectional view of a modified gas sensor 400. A longitudinal cross-sectional view of a modified gas sensor 500. A partial cross-sectional view when the outer inlet 144a has a rectangular hole 144d.

[0018] 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 4 shows a cross-section passing through the minimum flow path 123a in Figure 3. Figure 5 is a cross-sectional view taken along line D-D in Figure 3. Figure 5 shows a cross-section passing through the standard flow path 123b 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 outer protective cover 140) and 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 outer protective cover 140) and 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.

[0019] 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°) with respect to the vertical.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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).

[0024] 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, and a stepped portion 133 connecting the large-diameter portion 132 and the first cylindrical portion 134. The first cylindrical portion 134 surrounds the sensor element 110. 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. Furthermore, the second member 135 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 is connected 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 (four in this embodiment) of circular lateral holes 138b formed at equal intervals along the circumferential direction of the side portion 138d. The element chamber outlet 138a is not provided 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 multiple lateral holes 138b are all the same. 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) from 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).

[0025] 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.

[0026] A plurality of protrusions 136a that protrude toward the outer circumferential surface of the first cylindrical portion 134 and are in contact with said outer circumferential surface are formed on the inner circumferential surface of the second cylindrical portion 136. As shown in FIG. 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 protrusion 136a is formed in a substantially hemispherical shape. The provision of such protrusions 136a allows the positional relationship between the first cylindrical portion 134 and the second cylindrical portion 136 to be easily fixed by the protrusions 136a. It is preferable that the protrusions 136a press the outer circumferential surface of the first cylindrical portion 134 radially inward. With this configuration, the positional relationship between the first cylindrical portion 134 and the second cylindrical portion 136 can be more reliably fixed by the protrusions 136a. The number of the protrusions 136a is not limited to four, and may be two, three, or five or more. Since the fixation between the first cylindrical portion 134 and the second cylindrical portion 136 is easily stabilized, it is preferable that the number of the protrusions 136a is three or more.

[0027] The second cylindrical portion 136 of the second member 135 has a shape protruding radially outward, and thus includes a water passage suppressing portion 136b that forms the minimum flow path 123a described later (see FIGS. 3, 4 and 7). The water passage suppressing 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 suppressing portion 136b has a tapered shape whose diameter increases from bottom to top.

[0028] 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 (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 member 135 (here, the upper end of the second cylindrical portion 136, i.e., the upper end of the water passage suppression portion 136b) to the lower end of the first member 131 (here, the lower end of the first cylindrical portion 134). 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.

[0029] 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 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). This prevents the gas to be measured flowing out from the lower opening 127b from directly hitting the surface of the sensor element 110, thereby suppressing the cooling of the sensor element 110.

[0030] 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.

[0031] The outer inlet 144a is a hole communicating between the outside (exterior) of the outer protective cover 140 and the first gas chamber 122. The outer inlet 144a includes a plurality of (six in the present embodiment) lateral holes 144b formed at equal intervals on the side portion 143a, and a plurality of (six in the present embodiment) vertical holes 144c formed at equal intervals on the stepped portion 143b (see FIGS. 3, 5 and 6). The lateral holes 144b open in a direction intersecting the vertical direction, and in the present embodiment, open in a direction perpendicularly intersecting the vertical direction. The vertical holes 144c open along the vertical direction, and in the present embodiment, open parallel to the vertical direction. The outer inlet 144a (the lateral holes 144b and the vertical holes 144c) are circularly formed holes. The diameter of the twelve 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 lateral holes 144b are all the same value, and the diameters of the plurality of vertical holes 144c are all the same value. Further, the diameter of the lateral hole 144b is set to a larger value than the diameter of the vertical hole 144c. As shown in FIG. 5, the outer inlet 144a is formed such that the lateral holes 144b and the vertical holes 144c are alternately arranged at equal intervals along the circumferential direction of the outer protective cover 140. That is, an angle formed between a line connecting the center of the lateral hole 144b and the central axis of the outer protective cover 140 in FIG. 5 and a line connecting the center of the vertical hole 144c adjacent to the lateral hole 144b and the central axis of the outer protective cover 140 is 30° (360° / 12 pieces).

[0032] The outer outlet 147a is a hole communicating between the outside (exterior) of the outer protective cover 140 and the second gas chamber 126. The outer outlet 147a includes one or more (one in the present embodiment) vertical holes 147c formed at the center of the bottom portion 146b of the tip portion 146 (see FIGS. 3 and 6). Unlike the outer inlet 144a, the outer outlet 147a is not disposed 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 circularly formed hole. 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 larger value than the diameters of the lateral hole 144b and the vertical hole 144c.

[0033] 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.

[0034] 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, i.e., the upper end of the water passage suppression portion 136b). 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.

[0035] Here, the portion of the first channel 122a with the smallest cross-sectional area perpendicular to the vertical direction is defined as the minimum channel 123a. Furthermore, the portion of the first channel 122a that passes through the vertical center of the lateral hole 144b of the outer inlet 144a and has a cross-sectional area perpendicular to the vertical direction is defined as the standard channel 123b. In this embodiment, the cross-sectional area ratio Sa / Sb of the cross-sectional area Sa of the minimum channel 123a and the cross-sectional area Sb of the standard channel 123b is 0.716 or less. As described above, the water passage suppression portion 136b has a shape that protrudes radially outward, and as a result, the cross-sectional area perpendicular to the vertical direction of the first channel 122a is small in the portion where the water passage suppression portion 136b exists (i.e., the first channel 122a is narrower). The portion of the first channel 122a near the upper end of the water passage suppression portion 136b is defined as the minimum channel 123a. As shown in Figures 3 and 4, the minimum flow path 123a is a ring-shaped gap between the inner circumferential surface of the side portion 143a of the body portion 143 and the outer circumferential surface of the portion of the water passage suppression portion 136b with the largest outer diameter. As shown in Figures 3 and 5, the standard flow path 123b is a ring-shaped gap between the inner circumferential surface of the side portion 143a of the body portion 143 and the outer circumferential surface of the second cylindrical portion 136 (the portion of the second cylindrical portion 136 that is not the water passage suppression portion 136b).

[0036] 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, then moves downward through the first inlet 127 of the element chamber inlet 125, flows out from the lower opening 127b, and enters the sensor element chamber 124. At least a portion of the gas to be measured that has entered the sensor element chamber 124 from the lower opening 127b reaches the gas inlet 21 of the sensor element 110. When the gas to be measured reaches the gas inlet 21 and flows into the inside of 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. Furthermore, 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 (or lateral hole 138b in this case), and then flows out to the outside through the outer outlet 147a. The output of the internal heater of the sensor element 110 is controlled by a controller (not shown) to maintain a predetermined temperature.

[0037] 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, the above-mentioned cross-sectional area ratio Sa / Sb is 0.716 or less, which suppresses water from adhering to the sensor element 110, that is, it improves the water resistance of the sensor element 110. The inventors have confirmed this through experiments and analyses. This is thought to be because, with a cross-sectional area ratio Sa / Sb of 0.716 or less, the cross-sectional area Sa is relatively small, which suppresses water entering the first flow path 122a from the outer inlet 144a and passing upward through the minimum flow path 123a.

[0038] The cross-sectional area ratio Sa / Sb is preferably 0.5 or less. This makes it possible to further improve the water poisoning resistance of the sensor element 110. The cross-sectional area ratio Sa / Sb may be 0.4 or less. Further, the cross-sectional area ratio Sa / Sb is preferably 0.083 or more. Here, if the cross-sectional area ratio Sa / Sb is too small, the time required for the gas to be measured to pass through the inlet-side gas flow path 152 and reach the sensor element 110 increases, which may reduce the responsiveness of detection of a specific gas concentration by the sensor element 110. When the cross-sectional area ratio Sa / Sb is 0.083 or more, a decrease in responsiveness of detection of a specific gas concentration can be suppressed. The present inventors have confirmed this through experiments and analyses. The cross-sectional area ratio Sa / Sb is more preferably 0.1 or more. This makes it possible to further suppress a decrease in responsiveness of detection of a specific gas concentration. The cross-sectional area ratio Sa / Sb may be 0.2 or more, or may be 0.3 or more.

[0039] The cross-sectional area Sa may be 4.7 mm 2 or more, or may be 5.7 mm 2 or more, or may be 10.0 mm 2 or more, or may be 20.0 mm 2 or more. The cross-sectional area Sa may be 41.0 mm 2 or less, or may be 29.0 mm 2 or less, or may be 25.0 mm 2 or less. The cross-sectional area Sb may be 6.58 mm 2 or more, or may be 30.0 mm 2 or more, or may be 50.0 mm 2 or more. The cross-sectional area Sb may be 286 mm 2 or less, or may be 100 mm 2 or less, or may be 60 mm 2 or less.

[0040] The vertical distance L (see Figure 7) between the minimum flow path 123a and the reference flow path 123b may be, for example, 0.5 mm or more. The distance L may also be, for example, 11.0 mm or less. It is preferable that the distance L is greater than or equal to the radius of the lateral hole 144b. In other words, it is preferable that the position of the minimum flow path 123a is at the same level as or above the upper end of the lateral hole 144b.

[0041] Furthermore, the portion of the first flow path 122a upstream of the minimum flow path 123a (i.e., the side of the outer inlet 144a, which is the lower side in this case) is defined as space 123c. In Figure 7, space 123c is shown with hatching. Space 123c is the portion of the cylindrical gap (space) between the inner circumferential surface of the outer protective cover 140 and the outer circumferential surface of the second cylindrical portion 136 that is upstream of the minimum flow path 123a. Space 123c does not include the space within the outer inlet 144a (in this case, the space within the horizontal hole 144b and the vertical hole 144c). The volume V of this space 123c is 150 mm 3 The above is preferable. This increases the space 123c between the outer inlet 144a and the minimum flow path 123a, and also increases the volume of water that can be stored in this space 123c. As a result, water that enters the first flow path 122a from the outer inlet 144a is less likely to enter the downstream side of the minimum flow path 123a, i.e., the side of the sensor element 110. Therefore, the water resistance of the sensor element 110 can be improved. The volume V is 700 mm 3 The following is also acceptable: 560 mm 3 The following is also acceptable.

[0042] As described in detail above, the gas sensor 100 of this embodiment has a cross-sectional area ratio Sa / Sb of 0.716 or less between the cross-sectional area Sa of the minimum flow path 123a and the cross-sectional area Sb of the reference flow path 123b. This improves the water resistance of the sensor element 110. Furthermore, a cross-sectional area ratio Sa / Sb of 0.5 or less further improves the water resistance of the sensor element 110. Moreover, a cross-sectional area ratio Sa / Sb of 0.083 or more suppresses a decrease in the responsiveness of detecting a specific gas concentration. A cross-sectional area ratio Sa / Sb of 0.1 or more further suppresses a decrease in the responsiveness of detecting a specific gas concentration. And the volume V of the space 123c is 150 mm 3As a result, water is less likely to enter the area downstream of the minimum channel 123a.

[0043] 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.

[0044] For example, in the embodiment described above, the vertical centers of each of the multiple horizontal holes 144b are all at the same vertical position, but this is not limited to this. If the vertical centers of each of the multiple horizontal holes 144b are not all at the same position, the first flow path 122a is defined as the reference flow path 123b, which passes through the center of the horizontal hole 144b with the highest vertical center among the multiple horizontal holes 144b and has a cross-sectional portion perpendicular to the vertical direction.

[0045] The water passage suppression section is not limited to the form of the water passage suppression section 136b described above, but may be of other form. For example, instead of the water passage suppression section 136b, the water passage suppression sections 236b, 336b, and 436b shown in Figures 8 to 10 may be used. In the modified gas sensor 200 shown in Figure 8, the second member 135 has a second cylindrical section 236 instead of the second cylindrical section 136. The second cylindrical section 236 has a tapered shape that expands in diameter from bottom to top. Therefore, the cross-sectional area perpendicular to the vertical direction of the first flow path 222a becomes smaller as it goes upward (downstream), and the upper end of the first flow path 222a becomes the minimum flow path 223a. In this case, the upper end portion of the second cylindrical section 236 forms the minimum flow path 123a, so this portion is the water passage suppression section 236b. Furthermore, the reference flow path 223b is the cross-sectional portion of the first flow path 222a that passes through the vertical center of the lateral hole 144b of the outer inlet 144a, and the ring-shaped gap between the inner circumferential surface of the side portion 143a of the body portion 143 and the outer circumferential surface of the second cylindrical portion 136. This gas sensor 200 also has the same features as the embodiment described above and can obtain the same effects. For example, if the cross-sectional area ratio Sa / Sb of the cross-sectional area Sa of the minimum flow path 223a and the cross-sectional area Sb of the reference flow path 223b is 0.716 or less, the water resistance of the sensor element 110 can be improved. Also, the volume V of the space 223c upstream of the minimum flow path 223a in the first flow path 222a is 150 mm 3If the above conditions are met, water will be less likely to enter the area downstream of the minimum channel 223a.

[0046] In the modified gas sensor 300 shown in Figure 9, the second cylindrical portion 136 has a water passage suppression portion 336b instead of the water passage suppression portion 136b. The water passage suppression portion 336b has a shape that protrudes radially outward, thereby forming a minimum flow path 323a. The water passage suppression portion 336b is located at the upper end of the second member 135, that is, at the upper end of the second cylindrical portion 136. Specifically, the water passage suppression portion 336b has a shape that protrudes radially outward, by widening the diameter of the upper end of the second cylindrical portion 136 and folding it downward. This gas sensor 300 also has the same features as the embodiment described above and can obtain the same effects. For example, if the cross-sectional area ratio Sa / Sb of the cross-sectional area Sa of the minimum flow path 323a and the cross-sectional area Sb of the reference flow path 123b is 0.716 or less, the water resistance of the sensor element 110 can be improved. Furthermore, the volume V of the space 323c upstream of the smallest channel 323a in the first channel 322a is 150 mm². 3 If the above conditions are met, water will have difficulty entering the area downstream of the minimum channel 323a. In Figure 9, since the outer diameter of the portion of the water passage suppression section 336b that is folded downwards is constant, the vertically perpendicular cross-sectional area of ​​the first channel 322a is the same and smallest value at all points from the upper end to the lower end of the region where this outer diameter is constant (region M shown in Figure 9). In such cases, as shown in Figure 9, the uppermost portion (the portion located furthest downstream) of the portion of the first channel 322a with the smallest cross-sectional area (i.e., region M) is defined as the minimum channel 323a. The value of volume V is also calculated based on the minimum channel 323a defined in this way.

[0047] In the modified gas sensor 400 shown in Figure 10, the second cylindrical portion 136 has a water passage suppression portion 436b instead of the water passage suppression portion 136b. The water passage suppression portion 436b has a shape that protrudes radially outward, thereby forming a minimum flow path 423a. The water passage suppression portion 436b is located at a position different from the upper end of the second cylindrical portion 136 of the second member 135. The water passage suppression portion 436b has a shape that protrudes radially outward, specifically formed in a substantially hemispherical shape. The ring-shaped gap between the part of this water passage suppression portion 436b that protrudes most radially outward and the inner circumferential surface of the side portion 143a of the body portion 143 is the minimum flow path 423a of the first flow path 422a. This gas sensor 400 also has the same features as the embodiment described above and can obtain the same effects. For example, if the cross-sectional area ratio Sa / Sb of the cross-sectional area Sa of the minimum channel 423a and the cross-sectional area Sb of the reference channel 123b is 0.716 or less, the water resistance of the sensor element 110 can be improved. Also, if the volume V of the space 423c upstream of the minimum channel 423a in the first channel 422a is 150 mm³ 3 If the above conditions are met, water will be less likely to enter the area downstream of the minimum channel 323a.

[0048] In the embodiment described above, the inner protective cover 130 had a first member 131 and a second member 135, but it is not limited to this, and the inner protective cover 130 may be a single member. For example, the modified gas sensor 500 shown in Figure 11 has an inner protective cover 530 instead of an inner protective cover 130. The inner protective cover 530 is made of a single member and has a large diameter portion 132, a second cylindrical portion 536 with a smaller diameter than the large diameter portion 132, a third cylindrical portion 137 with a smaller diameter than the second cylindrical portion 536, and a tip portion 138. The inner protective cover 530 also has a stepped portion 133 connecting the large diameter portion 132 and the second cylindrical portion 536, a stepped portion 136c connecting the second cylindrical portion 536 and the third cylindrical portion 137, and a stepped portion 137a connecting the third cylindrical portion 137 and the tip portion 138. The element chamber inlet 125, located in the inner protective cover 130, does not have a first inlet 127, but has a second inlet 528 formed in the second cylindrical portion 536. The second inlet 528 is a plurality (for example, six) of lateral holes formed at equal intervals along the outer circumference of the second cylindrical portion 536. In this gas sensor 500, the inlet-side gas flow path 152 includes the outer inlet 144a, the first gas chamber 122, and the second inlet 528, and the gas to be measured passes through the inlet-side gas flow path 152 in this order. The first gas chamber 122 has a first flow path 522a. The first flow path 522a is the space between the outer protective cover 140 and the second cylindrical portion 536 of the inner protective cover 530, and is the flow path for the gas to be measured moving upward from the outer inlet 144a to the second inlet 528. The second cylindrical portion 536 has a water passage suppression portion 536b with a shape similar to the water passage suppression portion 436b in Figure 10. The ring-shaped gap between the portion of the water passage suppression section 536b that protrudes most radially outward and the inner circumferential surface of the side portion 143a of the body portion 143 is the smallest flow path 523a of the first flow path 522a. Also, the standard flow path 523b is the cross-sectional portion of the first flow path 522a that passes through the vertical center of the lateral hole 144b of the outer inlet 144a, and the ring-shaped gap between the inner circumferential surface of the side portion 143a of the body portion 143 and the outer circumferential surface of the second cylindrical portion 536. This gas sensor 500 also has the same features as the embodiment described above and can obtain the same effects.For example, if the cross-sectional area ratio Sa / Sb of the cross-sectional area Sa of the minimum channel 523a and the cross-sectional area Sb of the reference channel 523b is 0.716 or less, the water resistance of the sensor element 110 can be improved. Also, the volume V of the space 523c upstream of the minimum channel 523a in the first channel 522a is 150 mm³. 3 If the above conditions are met, water will be less likely to enter the area downstream of the minimum channel 523a.

[0049] In the gas sensors 100 to 400 described above, the element chamber inlet 125 had only a first inlet 127, which was configured as a gap between the first member 131 and the second member 135. In the gas sensor 500 described above, the element chamber inlet 125 had only a second inlet 528, which was a lateral hole provided in the second cylindrical portion 536. However, the element chamber inlet 125 may have both the first inlet 127 and the second inlet 528. For example, in the gas sensors 100 to 400, the inner protective cover 130 may be provided with a lateral hole similar to the second inlet 528 in Figure 11. In this case, the second inlet 528 may be formed in, for example, the first cylindrical portion 134.

[0050] In the gas sensor 100 described above, the inner protective cover 130 had a water passage suppression portion 136b, but it is not limited to this. For example, the outer protective cover 140 may have a water passage suppression portion that forms a minimum flow path 123a by having a shape that protrudes radially inward from the inner circumferential surface. That is, the inner protective cover 130 and / or the outer protective cover 140 may have a water passage suppression portion. The same applies to the gas sensors 200 to 500 described above.

[0051] 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.

[0052] 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.

[0053] 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).

[0054] 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.

[0055] The following describes specific examples of how gas sensors were fabricated. Experimental Examples 2 to 7 correspond to embodiments of the present invention, while Experimental Example 1 corresponds to a comparative example. However, the present invention is not limited to the following embodiments.

[0056] [Experimental Examples 1-7] The gas sensors 100 shown in Figures 3-7 were manufactured with different cross-sectional area ratios Sa / Sb to form Experimental Examples 1-7. In all of Experimental Examples 1-7, the inner radius of the side portion 143a of the body portion 143 of the outer protective cover 140 was set to 7.2 mm (therefore the inner diameter is 14.4 mm), and the outer diameter of the portion of the second cylindrical portion 136 that is not the water passage suppression portion 136b (the portion where the reference flow path 123b exists) was set to 5.8 mm. As a result, in all of Experimental Examples 1-7, the cross-sectional area Sb was 57.177 mm². 2 In Experimental Example 1, the second cylindrical portion 136 did not have a water passage suppression portion 136b, and the outer diameter of the second cylindrical portion 136 was the same value (5.8 mm) throughout, except for the portion where the protrusion 136a was located. Therefore, in Experimental Example 1, the cross-sectional area Sa was the same value as the cross-sectional area Sb (57.177 mm). 2 ) and the cross-sectional area ratio Sa / Sb became 1.000. In Experimental Example 2, the maximum outer radius of the water passage suppression section 136b (the radius of the part of the outer surface of the water passage suppression section 136b that forms the smallest flow path 123a) was set to 6.230 mm (therefore the outer diameter is 12.460 mm). As a result, the cross-sectional area Sa of Experimental Example 2 was 40.926 mm². 2Therefore, the cross-sectional area ratio Sa / Sb in Experimental Example 2 was 0.716. In Experimental Examples 3 to 7, the maximum outer radius of the water passage suppression section 136b was set to 6.538 mm, 6.696 mm, 7.073 mm, 7.094 mm, and 7.100 mm, respectively. As a result, the cross-sectional area Sa of Experimental Examples 3 to 7 was 28.571 mm². 2 , 22.002 mm 2 5.717 mm 2 4.764 mm 2 , 4.501 mm 2 Therefore, the cross-sectional area ratios Sa / Sb for experimental examples 3 to 7 were 0.500, 0.385, 0.100, 0.083, and 0.079, respectively. Experimental examples 1 to 7 had the same structure as each other, except that the cross-sectional area ratios Sa / Sb were different as described above.

[0057] [Evaluation of Water Resistance] The water resistance of the sensor element 110 was evaluated for the gas sensors 100 of Experimental Examples 1 to 7. 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 7, 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 four 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 all five gas sensors 100, it was determined that the water resistance was low ("F").

[0058] [Evaluation of Responsiveness] The gas sensors 100 from Experimental Examples 1 to 7 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 changed was 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 used 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").

[0059] Cross-sectional area Sa [mm²] for each of Experimental Examples 1 to 7 2 ”, cross-sectional area Sb [mm 2 Table 1 shows the results of the evaluation of the cross-sectional area ratio Sa / Sb, water resistance, and responsiveness.

[0060]

[0061] As shown in Table 1, Experimental Example 1, with a cross-sectional area ratio Sa / Sb of 1.0, received a water resistance rating of "F," while Experimental Examples 2 to 7, with a cross-sectional area ratio Sa / Sb of 0.716 or less, all received a water resistance rating of "A" or "B." From these results, it was confirmed that a cross-sectional area ratio Sa / Sb of 0.716 or less can improve the water resistance of the sensor element 110 in the gas sensor 100. Furthermore, a comparison between Experimental Example 2, with a water resistance rating of "B," and Experimental Examples 3 to 7, with a water resistance rating of "A," confirmed that a cross-sectional area ratio Sa / Sb of 0.5 or less further improves the water resistance of the sensor element 110.

[0062] Furthermore, in Experimental Example 7, where the cross-sectional area ratio Sa / Sb was 0.079, the responsiveness evaluation was "F," whereas in Experimental Examples 1 to 6, where the cross-sectional area ratio Sa / Sb was 0.083 or higher, the responsiveness evaluation was "A" or "B." From these results, it was confirmed that a cross-sectional area ratio Sa / Sb of 0.083 or higher can suppress the decrease in responsiveness of detecting specific gas concentrations in the gas sensor 100. In addition, from a comparison between Experimental Example 6, where the responsiveness evaluation was "B," and Experimental Examples 1 to 5, where the responsiveness evaluation was "A," it was confirmed that a cross-sectional area ratio Sa / Sb of 0.1 or higher can further suppress the decrease in responsiveness of detecting specific gas concentrations.

[0063] These results confirm that if the cross-sectional area ratio Sa / Sb is between 0.083 and 0.716, the water resistance of the sensor element 110 is improved, and the decrease in the responsiveness of detecting specific gas concentrations is suppressed.

[0064] This application is based on the priority claim of Japanese Patent Application No. 2025-052924, filed on 27 March 2025, the entire contents of which are incorporated herein by reference.

[0065] 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.

[0066] 10 Piping, 12 Fixing member, 20 Element body, 21 Gas inlet, 22 Porous protective layer, 100, 200, 300, 400, 500 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, 222a, 322a, 422a, 522a First flow path, 123a, 223a, 323a, 423a, 523a Minimum flow path, 123b, 223b, 523b Reference flow path, 123c, 223c, 323c, 423c, 523c Space, 124 Sensor element chamber, 125 Element chamber inlet, 126 Second gas chamber, 127 First inlet, 127a Upper opening, 127b Lower opening, 130, 530 Inner protective cover, 131 First member, 132 Large diameter section, 133 Stepped section, 134 First cylindrical section, 135 Second member, 136, 236, 536 Second cylindrical section, 136a Protruding section, 136b, 236b, 336b, 436b, 536b Water passage suppression section, 136c Stepped section, 137 Third cylindrical section, 137a Stepped section, 138, 338 Tip section, 138a, 338a Element chamber outlet, 138b Side hole, 138d Side section, 138e Bottom section, 140 Outer protective cover, 143 Body section, 143a Side section, 143b Stepped section, 144a Outer inlet, 144b Horizontal hole, 144c Vertical hole, 144d Square hole, 146 Tip, 146a Side, 146b Bottom, 146c Tapered section, 147a Outer outlet, 147c Vertical hole, 152 Inlet gas passage, 156 Outlet gas passage, 234a Body, 234b First cylindrical section, 342 Large diameter section, 346d Square section, 347b Horizontal hole, 528 Second inlet.

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. A gas sensor 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 extending upward from the outer inlet, with the direction from the front end to the rear end of the sensor element being the upward direction and the direction opposite to the upward direction being the downward direction, the outer inlet has a transverse hole disposed on the outer circumferential surface of the outer protective cover and opening in a direction intersecting the vertical direction, and the cross-sectional area ratio Sa / Sb of the minimum flow path, which is the smallest portion of the first flow path with the smallest cross-sectional area perpendicular to the vertical direction, and the reference flow path, which is the portion of the first flow path that passes through the vertical center of the transverse hole and has a cross-sectional area perpendicular to the vertical direction, is 0.716 or less.

2. A gas sensor according to claim 1, wherein the cross-sectional area ratio Sa / Sb is 0.5 or less.

3. A gas sensor according to claim 1 or 2, wherein the cross-sectional area ratio Sa / Sb is 0.083 or more.

4. A gas sensor according to claim 1 or 2, wherein the cross-sectional area ratio Sa / Sb is 0.1 or more.

5. A gas sensor according to claim 1 or 2, wherein the cross-sectional area Sa is 4.7 mm². 2 41.0 mm 2 The following is a gas sensor.

6. A gas sensor according to claim 1 or 2, wherein the volume V of the space upstream of the minimum flow path in the first flow path is 150 mm 3 That's all for the gas sensor.

7. A gas sensor according to claim 1 or 2, wherein the inner protective cover has a water passage suppression portion that forms the minimum flow path by having a shape that protrudes radially outward.

8. A gas sensor according to claim 7, wherein 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, and the water passage suppression part is disposed on the second member.

9. A gas sensor according to claim 8, wherein the water passage suppression portion is located at the upper end of the second member.

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