Gas Sensor

Abstract

To improve water resistance of a sensor element in a gas sensor. [Solution] The gas sensor (100) includes a sensor element (110), an inner protective cover (130) having a sensor element chamber (124) therein 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 gas flow path (152) from the outside to the sensor element chamber (124), including the outer inlet (144a). The inlet gas flow path (152) has a first flow path (122a) extending upward from the outer inlet (144a). The outer inlet (144a) has a horizontal hole (144b) disposed on the outer peripheral surface of the outer protective cover (140) and opening in a direction intersecting the vertical direction. The cross-sectional area ratio (Sa / Sb) of the cross-sectional area (Sa) of a smallest flow path (123a) of the first flow path (122a) to the cross-sectional area (Sb) of a reference flow path (123b) passing through the vertical center of the horizontal hole (144b) of the first flow path (122a) is 0.716 or less.

Description

[Technical Field]

[0001] The present invention relates to a gas sensor. [Background technology]

[0002] Conventionally, gas sensors that detect the concentration of specific gases such as NOx and oxygen in a measurement gas such as automobile exhaust gas have been known. For example, Patent Document 1 describes a gas sensor including a sensor element, an inner protective cover in which the tip of the sensor element is disposed, and an outer protective cover disposed outside the inner protective cover. The inner protective cover has a sensor element chamber inside in which the tip of the sensor element is disposed, and is provided with an element chamber inlet that is an entrance to the sensor element chamber and an element chamber outlet that is an exit from the sensor element chamber. The outer protective cover is provided with an outer inlet that is an entrance from the outside of the measurement gas and an outer outlet that is an exit for the measurement gas to the outside. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7465739 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in such gas sensors, water may get inside the protective cover and adhere to the sensor element, causing cracks in the sensor element. Therefore, there has been a demand for preventing water from adhering to the sensor element, i.e., for improving the water resistance of the sensor element.

[0005] The present invention has been made to solve the above problems, and has as its main object to improve the water resistance of the sensor element in a gas sensor. [Means for solving the problem]

[0006] In order to achieve the above-mentioned main object, the present invention employs the following means.

[0007] [1] The gas sensor of the present invention is a sensor element having a front end and a rear end opposite to the front end, the sensor element having a gas inlet for introducing a measurement gas, the sensor element detecting a specific gas concentration of the measurement gas flowing into the sensor element through the gas inlet; a cylindrical inner protective cover having a sensor element chamber therein in which the front end of the sensor element and the gas inlet are disposed, the sensor element chamber having 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; a cylindrical outer protective cover having an outer inlet through which the gas under measurement enters from the outside and an outer outlet through which the gas under measurement exits to the outside, the outer protective cover being disposed outside the inner protective cover; Equipped with the outer protective cover and the inner protective cover form an inlet-side gas flow path from the outside to the sensor element chamber, which includes the outer inlet and the element chamber inlet, and an outlet-side gas flow path from the sensor element chamber to the outside, which includes the element chamber outlet and the outer outlet, a direction parallel to the axial direction of the outer protective cover and from the front end to the rear end of the sensor element is defined as an upward direction, and a direction opposite to the upward direction is defined as a downward direction, and the inlet-side gas flow path has a first flow path which is a space between the outer protective cover and the inner protective cover and which extends from the outer inlet to the upward direction, the outer inlet has a horizontal hole that is disposed on the outer peripheral surface of the outer protective cover and opens in a direction intersecting the up-down direction, a cross-sectional area ratio Sa / Sb of a minimum flow path cross-sectional area Sa, which is a portion of the first flow path with the smallest cross-sectional area perpendicular to the vertical direction, to a reference flow path cross-sectional area Sb, which is a cross-sectional portion of the first flow path that passes through the center of the horizontal hole in the vertical direction and is perpendicular to the vertical direction, is 0.716 or less; It is something.

[0008] This gas sensor has a first flow path that is a space between the outer protective cover and the inner protective cover and extends upward from the outer inlet. The cross-sectional area ratio Sa / Sb of the minimum flow path, which is the portion of the first flow path with the smallest cross-sectional area perpendicular to the vertical direction, and the cross-sectional area Sb of the reference flow path, which is perpendicular to the vertical direction and passes through the center of the horizontal 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 confirmed this through experiments and analyses.

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

[0010] [3] In the above-described gas sensor (the gas sensor according to [1] or [2]), 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 measurement gas to reach the sensor element increases, which may result in a decrease in the responsiveness of the sensor element in detecting the concentration of the specific gas. By ensuring that the cross-sectional area ratio Sa / Sb is 0.083 or more, the decrease in responsiveness in detecting the concentration of the specific gas can be suppressed. The present inventors have confirmed this through experiments and analyses.

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

[0012] [5] In the gas sensor described above (the gas sensor described in any one of [1] to [4]), the cross-sectional area Sa is 4.7 mm 2 Over 41.0mm 2 It may be the following:

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

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

[0015] [8] In the above-described gas sensor (the gas sensor described in [7]), the inner protective cover may have a cylindrical first member surrounding the sensor element and a cylindrical second member surrounding the first member and having the element chamber outlet, the element chamber inlet having a first inlet configured as a gap between the first member and the second member, an opening of the first inlet on the sensor element chamber side opening toward the downward direction, and the water passage suppressing portion may be disposed in the second member. Here, "opening toward the downward direction" includes a case where the opening is parallel to the downward direction and a case where the opening is inclined from the downward direction so as to approach the sensor element as it goes downward.

[0016] [9] In the above-described gas sensor (the gas sensor according to [8]), the water passage suppressing portion may be located at an end portion of the second member in the upper direction. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 2 is a schematic explanatory diagram of a state in which the gas sensor 100 is attached to the pipe 10. [Figure 2] Cross section AA of Figure 1. [Figure 3] Cross section B-B of Figure 2. [Figure 4] Cross section CC of Figure 3. [Figure 5] DD cross section of Figure 3. [Figure 6] View from E in Figure 3. [Figure 7] Enlarged view of a portion of Figure 3. [Figure 8] FIG. 10 is a vertical cross-sectional view of a gas sensor 200 according to a modified example. [Figure 9] FIG. 10 is a vertical cross-sectional view of a gas sensor 300 according to a modified example. [Figure 10] FIG. 10 is a vertical cross-sectional view of a gas sensor 400 according to a modified example. [Figure 11] FIG. 10 is a vertical cross-sectional view of a gas sensor 500 according to a modified example. [Figure 12] FIG. 10 is a partial cross-sectional view of an outer inlet 144a having a square hole 144d. DETAILED DESCRIPTION OF THE INVENTION

[0018] Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram illustrating a state in which a gas sensor 100 is attached to a pipe 10. FIG. 2 is a cross-sectional view taken along line AA in FIG. 1. FIG. 3 is a cross-sectional view taken along line BB in FIG. 2. FIG. 4 is a cross-sectional view taken along line CC in FIG. 3. FIG. 4 shows a cross-section passing through the minimum flow path 123a in FIG. 3. FIG. 5 is a cross-sectional view taken along line DD in FIG. 3. FIG. 5 shows a cross-section passing through the reference flow path 123b in FIG. 3. FIG. 6 is a view seen from line E in FIG. 3. FIG. 7 is a partially enlarged view of FIG. 3. Note that the direction parallel to the axial direction of the protective cover 120 (particularly the outer protective cover 140) and extending from the front end to the rear end of the sensor element 110 (the upward direction in FIGS. 3 and 7) is defined as the upward direction, and the direction parallel to the axial direction of the protective cover 120 (particularly the outer protective cover 140) and extending from the rear end to the front end of the sensor element 110 (the downward direction in FIGS. 3 and 7) is defined as the downward direction.

[0019] As shown in Fig. 1, the gas sensor 100 is installed in a pipe 10, which is an exhaust path from a vehicle engine, and is configured to detect the concentration of a specific gas contained in exhaust gas, which is a measurement gas emitted from the engine. Examples of the specific gas include NOx, ammonia, and O2. As shown in Fig. 2, the gas sensor 100 is fixed in the pipe 10 with its central axis perpendicular to the flow of the measurement gas in the pipe 10. Alternatively, the gas sensor 100 may be fixed in the pipe 10 with its central axis perpendicular to the flow of the measurement gas in the pipe 10 and tilted at a predetermined angle (e.g., 45°) relative to the vertical direction.

[0020] As shown in FIG. 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 encapsulation body 101 that encapsulates and fixes the sensor element 110, and bolts 103 attached to the element encapsulation body 101. The element encapsulation body 101 includes a cylindrical metal housing 102, a ceramic supporter 104 that is sealed in a through-hole inside the housing 102, and a powder compact 105 that is molded from ceramic powder such as talc and that is sealed in the through-hole inside the housing 102. The sensor element 110 is located on the central axis of the element encapsulation body 101 and penetrates the element encapsulation body 101 in the vertical direction. The powder compact 105 is compressed between the housing 102 and the sensor element 110. As a result, the powder compact 105 seals the through-hole in the housing 102 and fixes the sensor element 110. Bolt 103 is a cylindrical metal member with a male thread on its outer periphery. Housing 102 of element sealing body 101 is welded to pipe 10 and inserted into fixing member 12, which is welded to pipe 10 and has a female thread on its inner periphery. Bolt 103 is further screwed into fixing member 12, thereby fixing housing 102 in fixing member 12. In this way, gas sensor 100 is fixed in pipe 10. The direction of flow of the measurement gas in pipe 10 is from left to right in FIG. 3.

[0021] The sensor element 110 includes an element body 20 and a porous protective layer 22 covering at least a portion of the surface of the element body 20. The element body 20 is an elongated, plate-like element having a structure in which multiple oxygen-ion-conductive solid electrolyte layers, such as zirconia (ZrO), are stacked. The element body 20 has a gas inlet 21 through which a measurement gas is introduced into the element body 20, and is configured to be able to detect the concentration of a specific gas in the measurement gas that flows into the element body 20 through the gas inlet 21. In this embodiment, the gas inlet 21 is open at the front end face of the element body 20 (the lower end face of the element body 20 in FIG. 3). The element body 20 includes a heater therein that heats and maintains the temperature of the element body 20 and serves to regulate the temperature. The structure of the element body 20 and the principle of detecting the concentration of a specific gas are known, and are described, for example, in Japanese Patent Application Laid-Open No. 2008-164411. The front end (the lower end in FIG. 3) and the gas inlet 21 of the sensor element 110 are disposed in 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 most of the surface of the element body 20 exposed in the sensor element chamber 124. Specifically, the porous protective layer 22 covers the entire front end surface (lower surface) of the element body 20, on which the gas inlet 21 is formed. Furthermore, of the four surfaces connected to the front end surface of the element body 20 (the top, bottom, left, and right surfaces of the element body 20 in FIG. 4 ), the porous protective layer 22 covers the side closest to the front end surface of the element body 20. The porous protective layer 22 serves to, for example, prevent moisture and the like in the gas under measurement from adhering to the element body 20, causing cracks. The porous protective layer 22 also serves to prevent oil components and the like contained in the gas under measurement from adhering to electrodes (not shown) on the surface of the element body 20. The porous protective layer 22 is made of a porous material such as porous alumina, porous zirconia, porous spinel, porous cordierite, porous titania, or porous magnesia. The porous protective layer 22 can be formed by, for example, plasma spraying, screen printing, dipping, etc. The porous protective layer 22 also covers the gas inlet 21, but since the porous protective layer 22 is a porous body, 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 disposed to surround the sensor element 110. The protective cover 120 includes a cylindrical inner protective cover 130 with a bottom that covers the front end of the sensor element 110, and a cylindrical outer protective cover 140 with a bottom that covers the inner protective cover 130. A sensor element chamber 124 is formed as a 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 a flow path for the measurement gas from the outside to the sensor element chamber 124, and an outlet gas flow path 156, which is a flow path for the measurement gas from the sensor element chamber 124 to the outside. A first gas chamber 122 and a second gas chamber 126 are also formed as spaces 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 gas sensor 100, the sensor element 110, the inner protective cover 130, and the outer protective cover 140 are coaxial with each other. The protective cover 120 is made of metal (for example, stainless steel such as SUS310S).

[0024] The inner protective cover 130 includes a first member 131 and a second member 135. The first member 131 includes a cylindrical large-diameter portion 132, a cylindrical first cylindrical portion 134 having a smaller diameter than the large-diameter portion 132, and a step 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 includes a second cylindrical portion 136 having a larger diameter than the first cylindrical portion 134, a third cylindrical portion 137 having a smaller diameter than the second cylindrical portion 136, and a tip portion 138 having a smaller diameter than the third cylindrical portion 137. The second member 135 also has a step 136c connecting the lower end of the second cylindrical portion 136 to the upper end of the third cylindrical portion 137, and a step 137a connecting the lower end of the third cylindrical portion 137 to 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 is formed with an element chamber outlet 138a that communicates with the sensor element chamber 124 and the second gas chamber 126 and is an outlet for the measurement gas from the sensor element chamber 124. The element chamber outlet 138a has multiple (four in this embodiment) circular horizontal holes 138b formed at equal intervals along the circumferential direction of the side portion 138d. The element chamber outlets 138a are not provided at the bottom portion 138e of the tip portion 138. The diameter of the horizontal holes 138b is, for example, 0.5 mm to 2.6 mm. In this embodiment, the diameters of the multiple horizontal holes 138b are all the same. The element chamber outlet 138a is disposed below the gas inlet 21. In other words, the element chamber outlet 138a is located farther (downward) than the gas inlet 21 when viewed from the rear end of the sensor element 110 (the upper end, not shown, of the sensor element 110 in FIG. 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 inner circumferential surface of the large diameter portion 132 abuts against the housing 102, thereby fixing the first member 131 to the housing 102. The outer circumferential surface of the third cylindrical portion 137 of the second member 135 abuts against the inner circumferential surface of the outer protective cover 140, and the second member 135 is fixed by welding or the like. Note that the outer diameter of the third cylindrical portion 137 may be formed slightly larger than the inner diameter of the tip portion 146 of the outer protective cover 140, and the third cylindrical portion 137 may be press-fitted into the tip portion 146 to fix the second member 135.

[0026] The inner circumferential surface of the second cylindrical portion 136 is formed with a plurality of protrusions 136a that protrude toward and contact the outer circumferential surface of the first cylindrical portion 134. As shown in FIG. 4 , four protrusions 136a are provided, evenly spaced along the circumferential direction of the inner circumferential surface of the second cylindrical portion 136. The protrusions 136a are formed in a generally hemispherical shape. The provision of such protrusions 136a facilitates fixing 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 more reliably fixes the positional relationship between the first cylindrical portion 134 and the second cylindrical portion 136. The number of protrusions 136a is not limited to four, and may be two, three, five, or more. It is preferable to provide three or more protruding portions 136a, as this facilitates stable fixation between the first cylindrical portion 134 and the second cylindrical portion 136.

[0027] The second cylindrical portion 136 of the second member 135 has a water passage suppression portion 136b that protrudes radially outward to form a minimum flow path 123a (described later) (see FIGS. 3, 4, and 7). The water passage suppression portion 136b is located at the upper end of the second member 135, i.e., the upper end of the second cylindrical portion 136. The water passage suppression portion 136b has a tapered shape that increases in diameter from bottom to top.

[0028] The inner protective cover 130 has an element chamber inlet 125 that communicates with the first gas chamber 122 and the sensor element chamber 124 and is an inlet for the measurement gas 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 FIGS. 3, 4, and 7). The first inlet 127 is a 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 a 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 an opening on the side of the first gas chamber 122, which is the space where the outer inlet 144a is arranged, and a lower opening 127b which is an opening on the side of the sensor element chamber 124, which is the space where the gas inlet 21 is arranged. 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 closer to the rear end (upper side) of the sensor element 110 than the lower opening 127b. Therefore, in the path of the measurement gas from the outer inlet 144a to the gas inlet 21, i.e., in the inlet-side gas flow path 152, the first inlet 127 forms a flow path from the rear end (upper side) to the front end (lower side) of the sensor element 110. The first inlet 127 also forms a flow path parallel to the rear end and front end of the sensor element 110 (a flow path parallel to the up-down direction). The lower opening 127b opens into the sensor element chamber 124.

[0029] The lower opening 127b opens in a direction (downward) from the rear end to the front end of the sensor element 110 and parallel to the rear-to-front end direction (up-down direction) of the sensor element 110. That is, the lower opening 127b opens parallel to the downward direction. Therefore, the sensor element 110 is disposed at a position other than the region formed by virtually extending the first inlet 127 from the lower opening 127b (the region directly below the lower opening 127b in FIGS. 3 and 7). This prevents the measurement gas flowing out from the lower opening 127b from directly hitting the surface of the sensor element 110, thereby preventing the sensor element 110 from cooling down.

[0030] As shown in FIG. 3 , the outer protective cover 140 has a cylindrical body portion 143 and a bottomed, cylindrical tip portion 146 having a smaller inner diameter than the body portion 143. The body portion 143 also has a side portion 143a having a side surface along the central axis direction (vertical direction) of the outer protective cover 140, and a step portion 143b which is the bottom of the body portion 143 and connects the side portion 143a to the tip portion 146. The central axes of the body portion 143 and the tip portion 146 are both the same as the central axis of the inner protective cover 130. The inner circumferential surface of the upper end portion of the body portion 143 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 so as to cover the outer peripheries 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 peripheral surface abuts against the outer peripheral surface of the third cylindrical portion 137. The tip portion 146 has a side portion 146a that has a side surface along the central axis direction (vertical direction) of the outer protective cover 140 and has an outer diameter smaller than the inner diameter of the side portion 143a, and a bottom portion 146b that is the bottom of the outer protective cover 140. The bottom portion 146b has a tapered portion 146c that narrows in diameter from the side portion 146a toward the lower end of the bottom portion 146b. The tip portion 146 is positioned below the body portion 143. The outer protective cover 140 has one or more (multiple, specifically 12 in this embodiment) outer inlets 144a formed in the body portion 143 as inlets for the measurement gas from the outside, and one or more outer outlets 147a formed in the tip portion 146 as outlets for the measurement gas to the outside.

[0031] The outer inlet 144a is a hole that communicates with the outside (outside) of the outer protective cover 140 and 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 step portion 143b (see FIGS. 3, 5, and 6). The horizontal holes 144b open in a direction that intersects the vertical direction, and in this embodiment, open in a direction that intersects perpendicularly with the vertical direction. The vertical holes 144c open along the vertical direction, and in this embodiment, open parallel to the vertical direction. The outer inlets 144a (horizontal holes 144b and vertical holes 144c) are circular holes. The diameter of the twelve 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 horizontal holes 144b are all the same, and the diameters of the vertical holes 144c are all the same. The diameter of the horizontal holes 144b is larger than the diameter of the vertical holes 144c. As shown in FIG. 5, the outer inlet 144a is formed so that the horizontal holes 144b and the vertical holes 144c are alternately positioned at equal intervals along the circumferential direction of the outer protective cover 140. That is, the angle formed by the line connecting the center of the horizontal hole 144b to the central axis of the outer protective cover 140 and the line connecting the center of the vertical hole 144c adjacent to that horizontal hole 144b to the central axis of the outer protective cover 140 in FIG. 5 is 30° (360° / 12 holes).

[0032] The outer outlet 147a is a hole that communicates with the outside (outside) of the outer protective cover 140 and the second gas chamber 126. The outer outlet 147a has one or more vertical holes 147c (one in this embodiment) formed in the center of the bottom 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 of the outer protective cover 140 (the side 146a of the tip portion 146 in this embodiment). The outer outlet 147a (here, the vertical hole 147c) is a circular 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 this embodiment, the diameter of the vertical hole 147c is larger than the diameters of the horizontal hole 144b and the vertical hole 144c.

[0033] As described above, the outer protective cover 140 and the inner protective cover 130 form the inlet-side gas flow path 152 and the outlet-side gas flow path 156. The inlet-side gas flow path 152 includes the outer inlet 144a, the first gas chamber 122, and the element chamber inlet 125, and the measurement gas passes through the inlet-side gas flow path 152 in this order. The outlet-side gas flow path 156 includes the element chamber outlet 138a, the second gas chamber 126, and the outer outlet 147a, and the measurement gas passes through the outlet-side gas flow path 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 the stepped portion 133, the first cylindrical portion 134, the second cylindrical portion 136, the side portion 143a, and the stepped portion 143b. The second gas chamber 126 is formed as a space between the tip portion 146 and the inner protective cover 130. More specifically, the second gas chamber 126 is a space surrounded by the step portion 137a, the tip portion 138, and the tip portion 146. Note that, since the inner peripheral surface of the tip portion 146 abuts against the outer peripheral surface of the third cylindrical portion 137, the first gas chamber 122 and the second gas chamber 126 do not directly communicate with each other.

[0034] 3 and 7, the first gas chamber 122 has a first flow path 122a. The first flow path 122a is a space between the outer protective cover 140 and the second member 135 of the inner protective cover 130, and is a flow path for the measurement gas that flows upward from the outer inlet 144a. More specifically, the first flow path 122a is a space surrounded by the side portion 143a, the step portion 143b, and the second cylindrical portion 136, and is a space below 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). 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 flow path 122a with the smallest cross-sectional area perpendicular to the vertical direction is defined as the minimum flow path 123a. Furthermore, the portion of the first flow path 122a that passes through the vertical center of the horizontal hole 144b of the outer inlet 144a and is perpendicular to the vertical direction is defined as the reference flow path 123b. In this embodiment, the cross-sectional area ratio Sa / Sb between the cross-sectional area Sa of the minimum flow path 123a and the cross-sectional area Sb of the reference flow path 123b is 0.716 or less. As described above, the water-passing suppression section 136b has a shape that protrudes radially outward, thereby reducing the cross-sectional area of ​​the first flow path 122a perpendicular to the vertical direction at the portion where the water-passing suppression section 136b is present (i.e., the first flow path 122a is narrower). The portion of the first flow path 122a near the upper end of the water-passing suppression section 136b is defined as the minimum flow path 123a. 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 that has the largest outer diameter. As shown in Figures 3 and 5, the reference 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 measurement gas within the protective cover 120 when the gas sensor 100 detects the concentration of a specific gas will be described. The measurement gas flowing through the pipe 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). The measurement gas then moves upward through the first flow path 122a, then moves downward through the first inlet 127 of the element chamber inlet 125, flows out through the lower opening 127b, and flows into the sensor element chamber 124. At least a portion of the measurement gas that flows into the sensor element chamber 124 from the lower opening 127b reaches the gas inlet 21 of the sensor element 110. When the measurement gas 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 concentration of the specific gas in the measurement gas, and the concentration of the specific gas is detected based on this electrical signal. The measurement gas in the sensor element chamber 124 flows into the second gas chamber 126 through at least one of the element chamber outlets 138a (here, the horizontal hole 138b), and then flows out through the outer outlet 147a to the outside. The output of the internal heater of the sensor element 110 is controlled by, for example, a controller (not shown) so as to maintain a predetermined temperature.

[0037] Here, the measurement gas may contain water, which may enter the protective cover 120 from the outer inlet 144a along with the measurement gas. If the water reaches the sensor element chamber 124 and adheres to the sensor element 110, cracks may occur in the sensor element 110 (particularly the element body 20). In the gas sensor 100 of this embodiment, the cross-sectional area ratio Sa / Sb is 0.716 or less, which can prevent water from adhering to the sensor element 110, i.e., improve the water resistance of the sensor element 110. The inventors confirmed this through experiments and analyses. This is thought to be because the cross-sectional area ratio Sa / Sb is 0.716 or less, which makes the cross-sectional area Sa relatively small, thereby preventing water that has entered the first flow path 122a from the outer inlet 144a from passing upward through the smallest flow path 123a.

[0038] The cross-sectional area ratio Sa / Sb is preferably 0.5 or less. This further improves the water resistance of the sensor element 110. The cross-sectional area ratio Sa / Sb may be 0.4 or less. Furthermore, the cross-sectional area ratio Sa / Sb is preferably 0.083 or more. If the cross-sectional area ratio Sa / Sb is too small, the time it takes for the measurement gas to pass through the inlet gas flow path 152 and reach the sensor element 110 increases, which may result in a decrease in the responsiveness of the sensor element 110 in detecting the concentration of the specific gas. By setting the cross-sectional area ratio Sa / Sb to 0.083 or more, the decrease in responsiveness in detecting the concentration of the specific gas can be suppressed. The inventors have confirmed this through experiments and analyses. The cross-sectional area ratio Sa / Sb is more preferably 0.1 or more. This further reduces the decrease in responsiveness in detecting the concentration of the specific gas. The cross-sectional area ratio Sa / Sb may be 0.2 or more, or 0.3 or more.

[0039] The cross-sectional area Sa is 4.7 mm 2 May be more than 5.7mm 2 It may be more than 10.0 mm 2 It may be more than 20.0 mm 2 The cross-sectional area Sa may be 41.0 mm or more. 2 May be less than 29.0 mm 2 May be less than 25.0 mm 2 The cross-sectional area Sb may be 6.58 mm 2 It may be more than 30.0 mm 2 It may be more than 50.0 mm 2 The cross-sectional area Sb may be 286 mm 2 May be less than 100mm 2 May be less than 60mm 2 It may be the following:

[0040] The vertical distance L (see FIG. 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 be, for example, 11.0 mm or less. The distance L is preferably equal to or greater than the radius of the horizontal hole 144b. In other words, the minimum flow path 123a is preferably positioned at the same level as or above the upper end of the horizontal hole 144b.

[0041] The upstream side of the smallest flow path 123a in the first flow path 122a (i.e., the side of the outer inlet 144a, here the lower side) is defined as a space 123c. In FIG. 7, the space 123c is shown by hatching. The space 123c is a 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, which is upstream of the smallest flow path 123a. The space 123c does not include the space inside the outer inlet 144a (here the space inside the horizontal hole 144b and the vertical hole 144c). The volume V of this space 123c is 150 mm 3 This is preferably equal to or greater than this. 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. Therefore, water that has entered 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 sensor element 110 side. This improves the water resistance of the sensor element 110. The volume V is 700 mm 3 It can be less than 560mm 3 The following may also be used.

[0042] According to the gas sensor 100 of this embodiment described above, the cross-sectional area ratio Sa / Sb of the cross-sectional area Sa of the minimum flow path 123a to the cross-sectional area Sb of the reference flow path 123b is 0.716 or less. This improves the water resistance of the sensor element 110. Furthermore, by making the cross-sectional area ratio Sa / Sb 0.5 or less, the water resistance of the sensor element 110 can be further improved. Furthermore, by making the cross-sectional area ratio Sa / Sb 0.083 or more, it is possible to suppress a decrease in the responsiveness of the detection of the specific gas concentration. By making the cross-sectional area ratio Sa / Sb 0.1 or more, it is possible to further suppress a decrease in the responsiveness of the detection of the specific gas concentration. Furthermore, when the volume V of the space 123c is 150 mm3 As a result, water is less likely to enter downstream of the minimum flow path 123a.

[0043] It goes without saying that the present invention is not limited to the above-described embodiment, and can be embodied in various forms as long as they fall within the technical scope of the present invention.

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

[0045] The water passage suppression portion is not limited to the water passage suppression portion 136b described above, and may be other than the water passage suppression portion 136b. For example, the water passage suppression portion 236b, 336b, or 436b shown in FIGS. 8 to 10 may be used instead of the water passage suppression portion 136b. In the modified gas sensor 200 shown in FIG. 8, the second member 135 has a second cylindrical portion 236 instead of the second cylindrical portion 136. The second cylindrical portion 236 has a tapered shape that increases in diameter from bottom to top. Therefore, the cross-sectional area of ​​the first flow path 222a perpendicular to the up-down direction decreases toward the upper side (downstream), and the upper end of the first flow path 222a becomes the smallest flow path 223a. In this case, the upper end portion of the second cylindrical portion 236 forms the smallest flow path 123a, and this portion is the water passage suppression portion 236b. Furthermore, a cross-sectional portion of the first flow path 222a passing through the center of the horizontal hole 144b of the outer inlet 144a in the vertical direction, and 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, serves as the reference flow path 223b. This gas sensor 200 also has the same features as the above-mentioned embodiment, and thus provides 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 to 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. Furthermore, if the volume V of the space 223c upstream of the minimum flow path 223a in the first flow path 222a is 150 mm 3 If this is the case, water is less likely to enter downstream of the minimum flow path 223a.

[0046] In the gas sensor 300 of the modified example shown in FIG. 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, i.e., the upper end of the second cylindrical portion 136. The water-passage suppression portion 336b has a shape that protrudes radially outward, specifically, a shape in which the diameter of the upper end of the second cylindrical portion 136 is widened and folded back downward. This gas sensor 300 also has the same features as the above-described embodiment, and therefore can achieve 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 to 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. In addition, the volume V of the space 323c upstream of the smallest flow path 323a in the first flow path 322a is 150 mm 3 If this is the case, water is less likely to enter downstream of the minimum flow path 323a. In FIG. 9, the outer diameter of the downwardly bent portion of the water passage suppression section 336b is constant, and therefore the cross-sectional area perpendicular to the up-down direction of the first flow path 322a is the same and smallest value from the top to bottom of the region where this outer diameter is constant (region M shown in FIG. 9). In such a case, as shown in FIG. 9, the uppermost portion (the portion located most downstream) of the portion of the first flow path 322a where the cross-sectional area is smallest (i.e., region M) is defined as the minimum flow path 323a. The value of volume V is also calculated based on the minimum flow path 323a defined in this way.

[0047] In the gas sensor 400 of the modified example shown in FIG. 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 disposed at a position on the second cylindrical portion 136 of the second member 135 that is different from the upper end. The water-passage suppression portion 436b has a shape that protrudes radially outward, specifically, a substantially hemispherical shape. The ring-shaped gap between the portion of the 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 forms the minimum flow path 423a of the first flow path 422a. This gas sensor 400 also has the same features as the above-described embodiment and therefore provides the same effects. For example, if the cross-sectional area ratio Sa / Sb of the minimum flow path 423a to 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. 3 If this is the case, water is less likely to enter downstream of the smallest flow path 323a.

[0048] In the above-described embodiment, the inner protective cover 130 includes the first member 131 and the second member 135. However, the present invention is not limited to this, and the inner protective cover 130 may be a single member. For example, a gas sensor 500 of a modified example shown in FIG. 11 includes an inner protective cover 530 instead of the inner protective cover 130. The inner protective cover 530 is made of a single member and includes a large diameter portion 132, a second cylindrical portion 536 having a smaller diameter than the large diameter portion 132, a third cylindrical portion 137 having a smaller diameter than the second cylindrical portion 536, and a tip portion 138. The inner protective cover 530 also includes a step portion 133 connecting the large diameter portion 132 and the second cylindrical portion 536, a step portion 136c connecting the second cylindrical portion 536 and the third cylindrical portion 137, and a step portion 137a connecting the third cylindrical portion 137 and the tip portion 138. The element chamber inlet 125 disposed 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 inlets 528 are multiple (e.g., six) horizontal holes formed at equal intervals along the outer periphery 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 measurement gas 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 a flow path for the measurement gas that flows upward from the outer inlet 144a to the second inlet 528. The second cylindrical portion 536 has a water passage suppression portion 536b shaped similarly to the water passage suppression portion 436b in FIG. 10 . The ring-shaped gap between the portion of this water passage suppression portion 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. Furthermore, the ring-shaped gap of the first flow path 522a, which is a cross-sectional portion that passes through the center in the vertical direction of the horizontal hole 144b of the outer inlet 144a, and is 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, is the reference flow path 523b. This gas sensor 500 also has the same features as the above-described embodiment and therefore provides the same effects.For example, if the cross-sectional area ratio Sa / Sb of the cross-sectional area Sa of the minimum flow path 523a to the cross-sectional area Sb of the reference flow path 523b is 0.716 or less, it is possible to improve the water resistance of the sensor element 110. Furthermore, the volume V of the space 523c of the first flow path 522a upstream of the minimum flow path 523a is 150 mm. 3 If this is the case, water is less likely to enter downstream of the minimum flow path 523a.

[0049] In the gas sensors 100 to 400 described above, the element chamber inlet 125 only includes the first inlet 127, which is 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 only includes the second inlet 528, which is a horizontal hole provided in the second cylindrical portion 536. However, the present invention is not limited to this, and the element chamber inlet 125 may include both the first inlet 127 and the second inlet 528. For example, in the gas sensors 100 to 400, a horizontal hole similar to the second inlet 528 in FIG. 11 may be provided in the inner protective cover 130. 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 has the water passage suppression portion 136b, but this is not limited to this. For example, the outer protective cover 140 may have a water passage suppression portion that has a shape that protrudes radially inward from the inner circumferential surface to form the minimum flow path 123a. That is, the inner protective cover 130 and / or the outer protective cover 140 may have the water passage suppression portion. The same applies to the gas sensors 200 to 500 described above.

[0051] In the above-described embodiment, the outer inlet 144a has the horizontal hole 144b and the vertical hole 144c, but this is not limited thereto. The outer inlet 144a only needs to have at least the horizontal hole 144b. For example, as shown in Fig. 12, the outer inlet 144a may have a square 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 in addition to or instead of the vertical hole 144c.

[0052] In the above-described embodiment, the inner protective cover 130 includes two members, the first member 131 and the second member 135, but the first member 131 and the second member 135 may also be an integrated member.

[0053] In the above-described embodiment, the gas inlet 21 is open to the front end surface of the sensor element 110 (the lower surface of the sensor element 110 in FIG. 3), but this is not limiting. For example, the gas inlet 21 may be open to a side surface of the sensor element 110 (any of the upper, lower, left, or right surfaces of the sensor element 110 in FIG. 4).

[0054] In the above-described embodiment, the sensor element 110 includes the porous protective layer 22, but the sensor element 110 may not include the porous protective layer 22. [Example]

[0055] Specific examples of fabricated gas sensors will be described below as examples. Experimental Examples 2 to 7 correspond to examples of the present invention, and Experimental Example 1 corresponds to a comparative example. Note that the present invention is not limited to the following examples.

[0056] [Experimental Examples 1-7] The gas sensors 100 shown in FIGS. 3 to 7 were fabricated with different cross-sectional area ratios Sa / Sb, resulting in Experimental Examples 1 to 7. In all of Experimental Examples 1 to 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 (hence the inner diameter was 14.4 mm), and the outer diameter of the portion of the second cylindrical portion 136 that was not the water passage suppression portion 136b (the portion where the reference flow path 123b was present) was set to 5.8 mm. As a result, in all of Experimental Examples 1 to 7, the cross-sectional area Sb was set to 57.177 mm 2 In Experimental Example 1, the second cylindrical portion 136 does not have the water passage suppression portion 136b, and the outer diameter of the second cylindrical portion 136 is the same value (5.8 mm) except for the portion where the protrusion 136a is present. Therefore, in Experimental Example 1, the cross-sectional area Sa is the same value (57.177 mm) as the cross-sectional area Sb. 2), and the cross-sectional area ratio Sa / Sb was 1.000. In Experimental Example 2, the maximum value of the outer radius of the water passage suppression section 136b (the radius of the portion of the outer peripheral 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 was 12.460 mm). As a result, the cross-sectional area Sa of Experimental Example 2 was 40.926 mm 2 Therefore, the cross-sectional area ratio Sa / Sb of Experimental Example 2 was 0.716. In Experimental Examples 3 to 7, the maximum values ​​of the outer radii of the water passage suppression portions 136b were 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 mm 2 , 22.002mm 2 , 5.717mm 2 , 4.764mm 2 , 4.501mm 2 Therefore, the cross-sectional area ratios Sa / Sb of 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 except for the different cross-sectional area ratios Sa / Sb as described above.

[0057] [Water resistance evaluation] The water resistance of the sensor element 110 of the gas sensors 100 of Experimental Examples 1 to 7 was evaluated. The water resistance evaluation was performed using a water exposure test apparatus described in Japanese Patent Application Laid-Open Publication No. 2019-158615. This water exposure test apparatus includes a horizontal, linear pipe with a gas flow path therein, a blower installed upstream of the pipe, a pressure fluctuation generator installed downstream of the pipe, and a chamber located in a portion of the pipe between the blower and the pressure fluctuation generator, in which the gas sensor 100 is attached. A vibrator that applies vibrations to the chamber is connected to the chamber. This water exposure test apparatus can disperse water toward the gas sensor 100 using gas simulating engine exhaust gas. In the water exposure test, the gas sensor 100 was first placed in the chamber of the water exposure test apparatus with its central axis perpendicular to the axis of the pipe and tilted 10° from the horizontal. Next, a predetermined amount of water was supplied into the pipe between the blower and the chamber. Next, a gas (atmospheric air) was supplied into the piping using a blower, the gas pressure was fluctuated using a pressure fluctuation generator, and vibrations were applied to the chamber using a vibrator. As a result, the moisture supplied into the piping was scattered toward the gas sensor 100 placed in the chamber by the gas with fluctuating pressure. 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 this temperature, cracks will occur in the sensor element 110, causing the electrical signal to indicate an abnormal value. Therefore, the presence or absence of cracks in the sensor element 110 was determined depending on whether the electrical signal indicated an abnormal value during the water exposure test. Five gas sensors 100 for each of Experimental Examples 1 to 7 were fabricated and subjected to the above-mentioned water exposure test. If none of the five gas sensors 100 had cracks in the sensor element 110, the gas sensors were judged to have very high water resistance ("A"); if one to four of the five gas sensors 100 had cracks in the sensor element 110, the gas sensors were judged to have high water resistance ("B"); and if all five gas sensors 100 had cracks in the sensor element 110, the gas sensors were judged to have low water resistance ("F").

[0058] [Responsiveness evaluation] The gas sensors 100 of Experimental Examples 1 to 7 were each attached to a pipe 10 as shown in FIGS. 1 and 2. A gas adjusted to an arbitrary oxygen concentration by mixing oxygen with atmospheric air was used as the measurement gas, and this measurement gas was flowed through the pipe 10 at a flow rate of 7 m / s. The output (electrical signal) of the sensor element 110 was measured over time when the oxygen concentration of the measurement gas flowing through the pipe was changed. The output value of the sensor element immediately before the oxygen concentration was changed was defined as 0%, and the output value when the sensor element output changed and stabilized after the oxygen concentration change was defined as 100%. The response time (sec) for detecting the specific gas concentration was defined as the elapsed time from when the output value exceeded 10% to when it exceeded 90%. A shorter response time indicates a higher response for detecting the specific gas concentration. The response time was measured multiple times for each experiment, and the average of the measurements was defined as the response time for each experiment. If the response time was less than 0.5 seconds, the responsiveness was judged to be very high ("A"), if the response time was 0.5 seconds or more but less than 0.69 seconds, the responsiveness was judged to be high ("B"), and if the response time was 0.69 seconds or more, the responsiveness was judged to be low ("F").

[0059] The cross-sectional area Sa [mm 2 ”, cross-sectional area Sb [mm 2 The evaluation results of the cross-sectional area ratio Sa / Sb, water resistance, and response are shown in Table 1.

[0060] [Table 1]

[0061] As shown in Table 1, Experimental Example 1, in which the cross-sectional area ratio Sa / Sb was 1.0, was evaluated as "F" for water resistance, whereas Experimental Examples 2 to 7, in which the cross-sectional area ratio Sa / Sb was 0.716 or less, were all evaluated as "A" or "B" for water resistance. These results confirm 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, in which the water resistance was evaluated as "B," and Experimental Examples 3 to 7, in which the water resistance was evaluated as "A," confirms 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, Experimental Example 7, in which the cross-sectional area ratio Sa / Sb was 0.079, was evaluated as "F" in responsiveness, whereas Experimental Examples 1 to 6, in which the cross-sectional area ratio Sa / Sb was 0.083 or greater, were all evaluated as "A" or "B" in responsiveness. These results confirm that a cross-sectional area ratio Sa / Sb of 0.083 or greater can suppress a decrease in responsiveness in detecting the concentration of a specific gas in the gas sensor 100. Furthermore, a comparison between Experimental Example 6, in which the responsiveness ratio was evaluated as "B," and Experimental Examples 1 to 5, in which the responsiveness ratio was evaluated as "A," confirms that a cross-sectional area ratio Sa / Sb of 0.1 or greater can further suppress a decrease in responsiveness in detecting the concentration of a specific gas.

[0063] From these results, it was confirmed that if the cross-sectional area ratio Sa / Sb is 0.083 or more and 0.716 or less, the water resistance of the sensor element 110 is improved and a decrease in the responsiveness of the detection of the specific gas concentration can be suppressed. [Explanation of symbols]

[0064] 10 piping, 12 fixing member, 20 element body, 21 gas inlet, 22 porous protective layer, 100, 200, 300, 400, 500 gas sensor, 101 element sealing body, 102 housing, 103 bolt, 104 supporter, 105 powder compact, 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 portion, 133 Step portion, 134 First cylindrical portion, 135 Second member, 136, 236, 536 Second cylindrical portion, 136a Protruding portion, 136b, 236b, 336b, 436b, 536b Water passage suppressing portion, 136c Step portion, 137 Third cylindrical portion, 137a Step portion, 138, 338 Tip portion, 138a, 338a Element chamber outlet, 138b Horizontal hole, 138d Side portion, 138e Bottom portion, 140 Outer protective cover, 143 Body portion, 143a Side portion, 143b Step portion, 144a Outer inlet, 144b Horizontal hole, 144c vertical hole, 144d square hole, 146 tip portion, 146a side portion, 146b bottom portion, 146c tapered portion, 147a outer outlet, 147c vertical hole, 152 inlet side gas flow passage, 156 outlet side gas flow passage, 234a body portion, 234b first cylindrical portion, 342 large diameter portion, 346d square portion, 347b horizontal hole, 528 second inlet.

Claims

1. a sensor element having a front end and a rear end opposite to the front end, the sensor element having a gas inlet for introducing a measurement gas, the sensor element detecting a specific gas concentration of the measurement gas flowing into the sensor element through the gas inlet; a cylindrical inner protective cover having a sensor element chamber therein in which the front end of the sensor element and the gas inlet are disposed, the sensor element chamber having 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; a cylindrical outer protective cover having an outer inlet through which the gas under measurement enters from the outside and an outer outlet through which the gas under measurement exits to the outside, the outer protective cover being disposed outside the inner protective cover; Equipped with the outer protective cover and the inner protective cover form an inlet-side gas flow path from the outside to the sensor element chamber, which includes the outer inlet and the element chamber inlet, and an outlet-side gas flow path from the sensor element chamber to the outside, which includes the element chamber outlet and the outer outlet, a direction parallel to the axial direction of the outer protective cover and from the front end to the rear end of the sensor element is defined as an upward direction, and a direction opposite to the upward direction is defined as a downward direction, and the inlet-side gas flow path has a first flow path which is a space between the outer protective cover and the inner protective cover and which extends from the outer inlet toward the upward direction, the outer inlet has a horizontal hole disposed on the outer peripheral surface of the outer protective cover and opening in a direction intersecting the axial direction, a cross-sectional area ratio Sa / Sb of a minimum flow path cross-sectional area Sa, which is a portion of the first flow path with the smallest cross-sectional area perpendicular to the axial direction, to a reference flow path cross-sectional area Sb, which is a cross-sectional portion of the first flow path that passes through the center of the axial direction of the horizontal hole and is perpendicular to the axial direction, is 0.716 or less, the inner protective cover includes a cylindrical first member that surrounds the sensor element, and a cylindrical second member that surrounds the first member and has the element chamber outlet, the element chamber inlet has a first inlet configured as a gap between the first member and the second member, an opening of the first inlet on the sensor element chamber side facing downward; The first flow path is a space between the outer protective cover and the second member. Gas sensor.

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

3. 3. The gas sensor according to claim 1, The cross-sectional area ratio Sa / Sb is 0.083 or more. Gas sensor.

4. 3. The gas sensor according to claim 1, The cross-sectional area ratio Sa / Sb is 0.1 or more. Gas sensor.

5. 3. The gas sensor according to claim 1, The cross-sectional area Sa is 4.7 mm 2 Over 41.0 mm 2 Below is the Gas sensor.

6. 3. The gas sensor according to claim 1, The volume V of the space upstream of the smallest flow path in the first flow path is 150 mm 3 That's all. Gas sensor.

7. 3. The gas sensor according to claim 1, The inner protective cover has a water passage suppression portion that has a shape that protrudes radially outward to form the minimum flow path. Gas sensor.

8. 8. The gas sensor according to claim 7, The water passage suppression portion is disposed on the second member. Gas sensor.

9. 9. The gas sensor according to claim 8, The water passage suppression portion is located at an end portion of the second member in the upward direction. Gas sensor.

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