Gas Sensor

Abstract

To improve water resistance of a sensor element when the gas sensor is in an inclined state. [Solution] The element chamber inlet 128, the element chamber outlet 129, and the sensor element 110 are arranged so that at least one of the distances A and B is smaller than the distance C when the angle θm of the gas sensor 100 in the tilted state is at least one of 10° to 40°. The distance A is the vertical distance between a reference point P0, which is the lower end of the inner circumferential surface of the connecting portion 134e of the inner body 134 in the vertical direction when tilted, and a point Pa, which is the lower end of the opening of the element chamber inlet 128 on the sensor element chamber 124 side in the vertical direction when tilted. The distance B is the vertical distance between the reference point P0 and a point Pb, which is the lower end of the opening of the element chamber outlet 129 on the sensor element chamber 124 side in the vertical direction when tilted. The distance C is the vertical distance between the reference point P0 and a point Pc, which is the lower end of the sensor element 110 in the vertical direction when tilted, in the vertical direction when tilted.

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] In such gas sensors, water may enter the protective cover and accumulate in the sensor element chamber. If the accumulated water adheres to the sensor element, cracks may form 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. Furthermore, gas sensors are sometimes attached to piping at an angle relative to the vertical. Therefore, there has been a demand for improving the water resistance of the sensor element when the gas sensor is in an inclined position.

[0005] The present invention has been made to solve the above problems, and its main object is to improve the water resistance of the sensor element when the gas sensor is in an inclined state. [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; an inner protective cover having a sensor element chamber therein in which the front end of the sensor element and the gas inlet are disposed; an intermediate protective cover disposed outside the inner protective cover and having an intermediate chamber formed therein as a space between the intermediate protective cover and the inner protective cover; an outer protective cover disposed outside the intermediate protective cover, the outer protective cover having an outer inlet through which the measurement gas enters from the outside and an outer outlet through which the measurement gas leaves the outside, the outer protective cover having a first gas chamber connected to the outer inlet and a second gas chamber connected to the outer outlet inside; A gas sensor comprising: the inner protective cover has a cylindrical inner body portion surrounding the sensor element, the inner body portion has a side portion in which an element chamber inlet serving as an entrance to the sensor element chamber is disposed, and a bottom portion in which an element chamber outlet serving as an exit from the sensor element chamber to the intermediate chamber is disposed, the intermediate protective cover has a cylindrical intermediate body portion that surrounds the inner body portion, and a tip portion that has a smaller diameter than the intermediate body portion and that is provided with an intermediate chamber outlet that serves as an outlet from the intermediate chamber to the second gas chamber, the intermediate protective cover and the inner protective cover form an intermediate passage configured as a space between the intermediate body portion and the inner body portion and connected to the intermediate chamber, the first gas chamber is a space formed inside the outer protective cover and outside the intermediate body and the inner protective cover, and functions as a flow path for the measurement gas from the outer inlet to the intermediate passage; the second gas chamber is a space formed inside the outer protective cover and outside the tip portion, and functions as a flow path for the measurement gas from the intermediate chamber outlet to the outer outlet; a state in which the gas sensor is tilted so that the central axis of the inner body is inclined with respect to the vertical direction and the front end of the sensor element is positioned vertically lower than the rear end, the angle between the central axis in the inclined state and the horizontal direction is defined as angle θm, the vertical direction in the inclined state is defined as an inclined vertical direction, the lower end of the inner circumferential surface of the connecting portion between the side portion and the bottom of the inner body in the inclined vertical direction is defined as a reference point, the distance between the lower end of the opening of the element chamber inlet on the sensor element chamber side in the inclined vertical direction and the reference point in the inclined vertical direction is defined as distance A, the distance between the lower end of the opening of the element chamber outlet on the sensor element chamber side in the inclined vertical direction and the reference point in the inclined vertical direction is defined as distance B, and the distance between the lower end of the sensor element in the inclined vertical direction and the reference point in the inclined vertical direction is defined as distance C, the element chamber inlet, the element chamber outlet, and the sensor element are arranged so that, when the angle θm is at least any value of 10° or more and 40° or less, at least one of the distance A and the distance B is smaller than the distance C. It is something.

[0008] In this gas sensor, the element chamber inlet, the element chamber outlet, and the sensor element are arranged so that when the angle θm in the inclined state of the gas sensor is at least any value between 10° and 40°, inclusive, at least one of the distances A and B is smaller than the distance C. In this gas sensor, when the angle θm in the inclined state is at least any value between 10° and 40°, inclusive, at least one of the openings of the element chamber inlet and the opening of the element chamber outlet is located lower than the lower end of the sensor element in the vertical direction (up and down direction when inclined). This allows water to easily escape from at least one of the openings of the element chamber inlet and the opening of the element chamber outlet before adhering to the sensor element, even if water accumulates in the sensor element chamber in the inclined state. This improves the water resistance of the sensor element when the gas sensor is in the inclined state.

[0009] [2] In the above-described gas sensor (the gas sensor described in [1] above), the element chamber inlet, the element chamber outlet, and the sensor element may be arranged so that, when the angle θm is at least any value between 10° and 40°, both the distance A and the distance B are smaller than the distance C. In this way, when the angle θm in the inclined state of the gas sensor is at least any value between 10° and 40°, both the opening of the element chamber inlet and the opening of the element chamber outlet are located at positions lower than the lower end of the sensor element. This makes it easier for water accumulated in the sensor element chamber to drain before adhering to the sensor element, thereby further improving the water resistance of the sensor element in the inclined state of the gas sensor.

[0010] [3] In the gas sensor described in [1] or [2] above, the element chamber inlet, the element chamber outlet, and the sensor element may be arranged such that, when the angle θm is at least one of 10° to 30°, at least one of the distances A and B is smaller than the distance C. In this way, the gas sensor is more suitable for an inclined state when the angle θm is at least 10° to 30°.

[0011] [4] In the above-described gas sensor (the gas sensor according to any one of [1] to [3] above), the element chamber inlet, the element chamber outlet, and the sensor element may be arranged so that at least one of the distances A and B is smaller than the distance C, regardless of whether the angle θm is a value between 10° and 30°. In this way, the gas sensor can improve the water resistance of the sensor element regardless of whether the angle θm in the tilted state is a value between 10° and 30°. Therefore, there are fewer restrictions on the angle θm when the gas sensor is used in the tilted state.

[0012] [5] In the above-described gas sensor (the gas sensor according to any one of [1] to [4] above), the element chamber inlet, the element chamber outlet, and the sensor element may be arranged so that at least one of the distances A and B is smaller than the distance C, regardless of whether the angle θm is a value between 10° and 40°. In this way, the gas sensor can improve the water resistance of the sensor element regardless of whether the angle θm in the tilted state is a value between 10° and 40°. Therefore, there are fewer restrictions on the angle θm when the gas sensor is used in the tilted state.

[0013] [6] In the above-described gas sensor (the gas sensor described in any one of [1] to [5] above), when a direction parallel to the central axis of the inner body is defined as an axial direction and a direction from the front end to the rear end of the sensor element along the axial direction is defined as an upward direction, the upper end of the opening of the element chamber inlet on the sensor element chamber side may be positioned higher than the lower end of the gas inlet in the axial direction. In this way, the measurement gas flowing into the sensor element chamber from the element chamber inlet is likely to reach the gas inlet before reaching the element chamber outlet. Therefore, in this gas sensor, the responsiveness of the sensor element to detect the concentration of a specific gas can be improved.

[0014] [7] In the above-described gas sensor (the gas sensor described in [6]), the lower end of the opening of the element chamber inlet on the sensor element chamber side may be positioned higher in the axial direction than the lower end of the gas inlet. This allows the measurement gas that flows into the sensor element chamber from the element chamber inlet to more easily reach the gas inlet before reaching the element chamber outlet. Therefore, in this gas sensor, the responsiveness of the sensor element to detect the concentration of a specific gas can be further improved.

[0015] [8] In the above-described gas sensor (the gas sensor according to any one of [1] to [7] above), the element chamber inlet may open midway through the intermediate passage.

[0016] [9] In the above-described gas sensor (the gas sensor according to any one of [1] to [8]), the bottom of the inner body may have a protruding portion that protrudes from the sensor element chamber toward the intermediate chamber, and the element chamber outlet may be disposed on the protruding portion. This facilitates the generation of a gas flow from the sensor element chamber through the element chamber outlet toward the intermediate chamber. This improves the responsiveness of the sensor element in detecting the concentration of a specific gas. [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] FIG. 1 is a vertical cross-sectional view of a gas sensor 100. [Figure 4] Cross section B-B of Figure 3. [Figure 5] Cross section CC of Figure 3. [Figure 6] DD cross section of Figure 3. [Figure 7] View from E in Figure 3. [Figure 8] FIG. 2 is a vertical cross-sectional view of the periphery of a sensor element chamber 124 of the gas sensor 100. [Figure 9] 9 is a partial enlarged view of the inner protective cover 131 and the sensor element 110 in FIG. 8. DETAILED DESCRIPTION OF THE INVENTION

[0018] Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic explanatory diagram of 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 longitudinal cross-sectional view of the gas sensor 100. FIG. 3 shows the cross-section of the gas sensor 100 taken along line AA in FIG. 1. FIG. 4 is a cross-sectional view taken along line BB in FIG. 3. FIG. 5 is a cross-sectional view taken along line CC in FIG. 3. FIG. 6 is a cross-sectional view taken along line DD in FIG. 3. FIG. 7 is a view seen from the E direction in FIG. 3. Note that the direction parallel to the central axis of the gas sensor 100 (particularly the inner body portion 134 of the inner protective cover 131) is defined as the axial direction, and the direction from the front end of the sensor element 110 toward the rear end (not shown) along the axial direction is defined as the upward direction. Furthermore, the direction from the rear end of the sensor element 110 toward the front end along the axial direction 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 the exhaust gas emitted from the engine as a measurement gas. Examples of specific gases include NOx, ammonia, and O2. As shown in FIG. 1, 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. As shown in FIG. 2, the gas sensor 100 is fixed in the pipe 10 with its central axis tilted relative to the vertical direction and with the front end of the sensor element 110 positioned vertically lower than the rear end. This tilted state of the gas sensor 100 is referred to as an inclined state. As shown in FIG. 2, the angle θm between the central axis of the gas sensor 100 and the horizontal direction in the inclined state is, for example, 10° to 40°.

[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 has a female thread on its inner periphery. Bolt 103 is further screwed into fixing member 12, thereby fixing housing 102 within fixing member 12. In this way, gas sensor 100 is fixed within pipe 10.

[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, long, plate-like element and has 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 so as to surround the sensor element 110. The protective cover 120 includes an inner protective cover 131, an intermediate protective cover 135, and an outer protective cover 140. The inner protective cover 131, the intermediate protective cover 135, and the outer protective cover 140 all have a cylindrical shape with a bottom. The inner protective cover 131 includes a sensor element chamber 124 therein, in which the front end of the sensor element 110 and the gas inlet 21 are disposed. The sensor element chamber 124 is a space surrounded by the inner protective cover 131. The intermediate protective cover 135 is disposed outside the inner protective cover 131. The intermediate protective cover 135 includes an intermediate chamber 125 therein, which is a space formed between the intermediate cover 135 and the inner protective cover 131. The intermediate protective cover 135 and the inner protective cover 131 form an intermediate passage 127 connected to the intermediate chamber 125. The intermediate passage 127 is formed as a space between the intermediate body portion 136 of the intermediate protective cover 135 and the inner body portion 134 of the inner protective cover 131. The outer protective cover 140 is disposed outside the intermediate protective cover 135. The outer protective cover 140 has an outer inlet 144a through which the gas under measurement enters from the outside and an outer outlet 147a through which the gas under measurement exits to the outside. The outer protective cover 140 has a first gas chamber 122 connected to the outer inlet 144a and a second gas chamber 126 connected to the outer outlet 147a inside. The first gas chamber 122 is a space formed inside the outer protective cover 140 and outside the intermediate body portion 136 of the intermediate protective cover 135 and the inner protective cover 131. The second gas chamber 126 is a space formed inside the outer protective cover 140 and outside the tip portion 138 of the intermediate protective cover 135. The gas sensor 100, the sensor element 110, the inner protective cover 131, the intermediate protective cover 135, 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 131 has a cylindrical large-diameter portion 132, a cylindrical inner body portion 134 having a diameter smaller than that of the large-diameter portion 132, a step portion 133 connecting the large-diameter portion 132 and the inner body portion 134, and the inner body portion 134. The inner body portion 134 has a bottomed, cylindrical shape that surrounds the sensor element 110. The inner body portion 134 has a side portion 134a, a bottom portion 134b, and a connecting portion 134e. The side portion 134a has a side surface along the central axis direction (up-down direction) of the inner body portion 134. An element chamber inlet 128, which serves as an inlet for the measurement gas into the sensor element chamber 124, is disposed in the side portion 134a. The bottom portion 134b is disposed below the sensor element 110. The bottom portion 134b is connected to the lower end of the side portion 134a. The bottom 134b has a protrusion 134c and an element chamber outlet 129, which serves as an outlet for the measurement gas from the sensor element chamber 124 to the intermediate chamber 125. The connection portion 134e is a portion of the inner body 134 that connects the side portion 134a and the bottom portion 134b. The connection portion 134e is a boundary portion between the side portion 134a and the bottom portion 134b, and is a corner portion between the side portion 134a and the bottom portion 134b. In this embodiment, the connection portion 134e is a rounded corner portion. The element chamber inlet 128 (horizontal hole 128b) and the element chamber outlet 129 are not disposed in the connection portion 134e. In other words, the element chamber inlet 128 (horizontal hole 128b) and the element chamber outlet 129 are not holes (square holes) provided in the corner portions of the sensor element chamber 124.

[0025] The element chamber inlet 128 is a hole that communicates with the outside of the side portion 134a and the sensor element chamber 124. The element chamber inlet 128 has multiple (six in this embodiment) horizontal holes 128b formed at equal intervals along the outer periphery of the side portion 134a. All of the multiple horizontal holes 128b are circular holes. All of the multiple horizontal holes 128b open in a direction that intersects the vertical direction, and in this embodiment, they open in a direction that intersects perpendicularly to the vertical direction. All of the multiple horizontal holes 128b open to the intermediate passage 127.

[0026] The protruding portion 134c has a shape that protrudes from the sensor element chamber 124 side toward the intermediate chamber 125 side, i.e., from top to bottom. The protruding portion 134c has a circular shape when viewed from above (see FIGS. 4 to 6). The central axis of the protruding portion 134c is coaxial with the central axis of the inner body portion 134. The protruding portion 134c has a connecting portion 134d that connects to the portion of the bottom portion 134b other than the protruding portion 134c. The connecting portion 134d is formed so as to smoothly drop from the portion of the bottom portion 134b other than the protruding portion 134c toward the lower end of the protruding portion 134c. In other words, the shape of the lower surface of the connecting portion 134d in a cross section taken along the central axis of the protruding portion 134c is curved.

[0027] The element chamber outlet 129 is a circular vertical hole disposed in the protruding portion 134c of the bottom portion 134b. The element chamber outlet 129 opens parallel to the vertical direction. The element chamber outlet 129 is disposed in the center of the protruding portion 134c, and its central axis is coaxial with that of the inner body portion 134. The element chamber outlet 129 is disposed below the gas inlet 21.

[0028] The intermediate protective cover 135 has an intermediate body portion 136 having a larger diameter than the inner body portion 134, and a tip portion 138 having a smaller diameter than the intermediate body portion 136. The intermediate body portion 136 has a cylindrical shape that surrounds the periphery of the inner body portion 134. The intermediate body portion 136 has a side portion 136a and a step portion 136b. The step portion 136b connects the lower end of the side portion 136a to the upper end of a side portion 138d of the tip portion 138. The tip portion 138 has a side portion 138d and a bottom portion 138e. The side portion 136a and the side portion 138d both have side surfaces that are aligned along the central axis direction (up-down direction) of the intermediate protective cover 135. An intermediate chamber outlet 138a is disposed in the tip portion 138. The intermediate chamber outlet 138a communicates with the intermediate chamber 125 and the second gas chamber 126 and serves as an outlet for the measurement gas from the intermediate chamber 125 to the second gas chamber 126. The intermediate chamber outlet 138a has a plurality of (four in this embodiment) circular horizontal holes 138b formed at equal intervals along the circumferential direction of a side portion 138d of the tip portion 138. The intermediate chamber outlet 138a is not disposed in the bottom portion 138e of the tip portion 138. The intermediate chamber outlet 138a is disposed below the element chamber outlet 129.

[0029] The intermediate chamber 125 is formed as a space surrounded by the lower surface of the bottom portion 134b of the inner protective cover 131 and the inner peripheral surface of the intermediate protective cover 135. The intermediate chamber 125 is located below the sensor element 110.

[0030] The large diameter portion 132, the inner body portion 134, the intermediate body portion 136, and the tip portion 138 share the same central axis. The inner peripheral surface of the large diameter portion 132 abuts against the housing 102, thereby fixing the inner protective cover 131 to the housing 102. The outer peripheral surface of the intermediate body portion 136 of the intermediate protective cover 135 abuts against the inner peripheral surface of the second body portion 145 of the outer protective cover 140, and the intermediate protective cover 135 is fixed by welding or the like. Note that the outer diameter of the intermediate body portion 136 may be formed slightly larger than the inner diameter of the second body portion 145 of the outer protective cover 140, and the intermediate body portion 136 may be press-fitted into the second body portion 145 to fix the intermediate protective cover 135.

[0031] The inner peripheral surface of the intermediate body 136 is formed with a plurality of protruding portions 136c that protrude toward and contact the outer peripheral surface of the inner body 134. As shown in FIG. 4 , four protruding portions 136c are provided, and are evenly arranged along the circumferential direction of the inner peripheral surface of the intermediate body 136. The protruding portions 136c are formed in a substantially hemispherical shape. The provision of such protruding portions 136c makes it easier to fix the positional relationship between the inner body 134 and the intermediate body 136. Note that the protruding portions 136c preferably press the outer peripheral surface of the inner body 134 radially inward. This makes it possible to more reliably fix the positional relationship between the inner body 134 and the intermediate body 136 by the protruding portions 136c. Note that the number of protruding portions 136c is not limited to four, and may be two, three, five or more. It is preferable to provide three or more protruding portions 136c, as this facilitates stable fixation between the inner body portion 134 and the intermediate body portion 136.

[0032] As described above, the intermediate passage 127 is formed as a space between the intermediate body portion 136 of the intermediate protective cover 135 and the inner body portion 134 of the inner protective cover 131. More specifically, the intermediate passage 127 is formed as a cylindrical gap between the inner circumferential surface of the intermediate body portion 136 and the outer circumferential surface of the inner body portion 134. The intermediate passage 127 is a space from the upper end of the intermediate body portion 136 of the intermediate protective cover 135 to the lower end of the side portion 134a of the inner body portion 134 of the inner protective cover 131. The intermediate passage 127 has an upper opening 127a which is an opening on the first gas chamber 122 side, which is the space in which the outer inlet 144a is disposed, and a lower opening 127b which is an opening on the intermediate chamber 125 side. The upper opening 127a is a ring-shaped gap between the upper end of the inner circumferential surface of the intermediate body portion 136 and the outer circumferential surface of the inner body portion 134. The lower opening 127b is a ring-shaped gap between the inner circumferential surface of the intermediate body 136 and the lower end of the outer circumferential surface of the side portion 134a of the inner body 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, the intermediate passage 127 serves as a flow path for the measurement gas from the rear end (upper side) to the front end (lower side) of the sensor element 110. The intermediate passage 127 also serves as 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 to the intermediate chamber 125. The lower opening 127b opens in the direction from the rear end to the front end of the sensor element 110 (downward).

[0033] The above-mentioned element chamber inlet 128 opens midway through the intermediate passage 127. That is, the element chamber inlet 128 (here, the multiple horizontal holes 128b) is located below the upper opening 127a of the intermediate passage 127 and above the lower opening 127b.

[0034] As shown in Fig. 3, the outer protective cover 140 has a cylindrical first body portion 143, a cylindrical second body portion 145 with a smaller diameter than the first body portion 143, and a bottomed, tubular tip portion 146 with a smaller diameter than the second body portion 145. The first body portion 143 has a side portion 143a and a step portion 143b. The side portion 143a has a side surface along the central axis direction (up-down direction) of the outer protective cover 140. The step portion 143b is the bottom of the first body portion 143 and connects the side portion 143a and the second body portion 145. The second body portion 145 has a side portion 145a and a step portion 145b. The side portion 145a has a side surface along the central axis direction (up-down direction) of the outer protective cover 140. The step portion 145b is the bottom of the second body portion 145 and connects the side portion 145a and the tip portion 146. The inner circumferential surface of the second body portion 145 abuts the outer circumferential surface of the intermediate body portion 136. The tip portion 146 is positioned so as to cover the tip portion 138 of the intermediate protective cover 135. The tip portion 146 has a side portion 146a and a bottom portion 146b. The side portion 146a has a side surface along the central axis direction (up-down direction) of the outer protective cover 140. The bottom portion 146b is the bottom of the outer protective cover 140. The bottom portion 146b has a tapered portion 146c whose diameter decreases from the side portion 146a toward the lower end of the bottom portion 146b. The central axes of the first body portion 143, the second body portion 145, and the tip portion 146 are all the same as the central axis of the inner protective cover 131. The inner circumferential surface of the portion around the upper end of the first 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 first body portion 143 is positioned so as to cover the outer peripheries of the large diameter portion 132, the inner body portion 134, and the intermediate body portion 136.

[0035] The outer inlet 144a described above is formed in the first body portion 143 of the outer protective cover 140. 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 (see FIGS. 3, 6, and 7). The horizontal holes 144b open in a direction that intersects the vertical direction, and in this embodiment, open in a direction that intersects perpendicularly to the vertical direction. All of the multiple horizontal holes 144b are circular holes.

[0036] The outer outlet 147a described above is formed in the tip 146 of the outer protective cover 140. 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 (one in this embodiment) vertical holes 147c formed in the center of the bottom 146b of the tip 146 (see FIGS. 3 and 7). The outer outlet 147a is not disposed in the side of the outer protective cover 140 (here, the side 146a of the tip 146). The outer outlet 147a (here, the vertical hole 147c) is a circular hole.

[0037] The first gas chamber 122 described above is a space surrounded by the step portion 133 and side portion 134a of the inner protective cover 131, the side portion 136a of the intermediate protective cover 135, and the side portion 143a and step portion 143b of the outer protective cover 140. The second gas chamber 126 described above is a space surrounded by the step portion 136b and tip portion 138 of the intermediate protective cover 135, and the tip portion 146 of the outer protective cover 140. Note that because the inner circumferential surface of the second body portion 145 of the outer protective cover 140 abuts against the outer circumferential surface of the intermediate body portion 136 of the intermediate protective cover 135, the first gas chamber 122 and the second gas chamber 126 do not directly communicate with each other.

[0038] Next, the flow of the measurement gas inside the protective cover 120 when the gas sensor 100 detects the concentration of a specific gas will be described. The measurement gas flowing inside the pipe 10 first flows into the first gas chamber 122 through the multiple outer inlets 144a (here, at least one of the multiple horizontal holes 144b). The measurement gas then moves upward inside the first gas chamber 122 and then moves downward through the intermediate passage 127. Part of the gas in the intermediate passage 127 passes through the element chamber inlet 128 and flows into the sensor element chamber 124, and part of the gas flows into the intermediate chamber 125 through the lower opening 127b. At least part of the measurement gas that flows into the sensor element chamber 124 from the element chamber inlet 128 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 a specific gas in the measurement gas, and the concentration of the specific gas is detected based on this electrical signal. At this time, the output of the internal heater of the sensor element 110 is controlled by, for example, a controller (not shown) so that the sensor element 110 maintains a predetermined temperature. The measurement gas in the sensor element chamber 124 flows into the intermediate chamber 125 through the element chamber outlet 129. The measurement gas that flows into the intermediate chamber 125 from the upper opening 127a or the element chamber outlet 129 flows into the second gas chamber 126 through the intermediate chamber outlet 138a. The gas that reaches the second gas chamber 126 flows out to the outside through the outer outlet 147a.

[0039] As described above, the bottom 134b of the inner body 134 has a protruding portion 134c that protrudes from the sensor element chamber 124 toward the intermediate chamber 125. The element chamber outlet 129 is disposed on the protruding portion 134c. As a result, when the measurement gas flows inside the protective cover 120, the gas tends to flow from the sensor element chamber 124 through the element chamber outlet 129 toward the intermediate chamber 125. This is thought to be because, when the measurement gas moves downward inside the sensor element chamber 124, the measurement gas in the sensor element chamber 124 tends to collect at the element chamber outlet 129 because part of the upper surface of the bottom 134b (the upper surface of the protruding portion 134c) is recessed and the element chamber outlet 129 is located on the protruding portion 134c, compared to when the entire upper surface of the bottom 134b is flat. Furthermore, since a gas flow from the sensor element chamber 124 through the element chamber outlet 129 toward the intermediate chamber 125 is likely to occur, the measurement gas in the sensor element chamber 124 is more likely to be replaced with new measurement gas from outside the gas sensor 100, thereby improving the responsiveness of the sensor element 110 in detecting the concentration of a specific gas. Furthermore, compared to when the entire lower surface of the bottom 134b is flat, a part of the lower surface of the bottom 134b (the lower surface of the protruding portion 134c) protrudes downward, and therefore, gas flowing into the intermediate chamber 125 from the lower opening 127b is more likely to flow downward due to the shape of the lower surface of the protruding portion 134c. As a result, a negative pressure is likely to occur near the element chamber outlet 129 in the space within the intermediate chamber 125, and this negative pressure may act to suck the measurement gas in the sensor element chamber 124 from the element chamber outlet 129 toward the intermediate chamber 125. This action also facilitates the flow of gas from the sensor element chamber 124 through the element chamber outlet 129 toward the intermediate chamber 125, which is thought to improve the responsiveness of the sensor element 110 in detecting the concentration of a specific gas.

[0040] As described above, connecting portion 134d is formed so as to smoothly drop from the portion of bottom portion 134b other than protruding portion 134c toward the lower end of protruding portion 134c. This is thought to make it easier for gas that flows into intermediate chamber 125 from lower opening 127b to flow downward due to the shape of the lower surface of protruding portion 134c (particularly the lower surface of connecting portion 134d).

[0041] The positional relationship between the element chamber inlet 128, the element chamber outlet 129, and the sensor element 110 will now be described in detail with reference to FIG. 8. FIG. 8 is a longitudinal cross-sectional view of the periphery of the sensor element chamber 124 of the gas sensor 100. In FIG. 8, the gas sensor 100 is illustrated so that the vertical direction in the tilted state described above is parallel to the up-down direction of the drawing. FIG. 8 also illustrates, as an example, a case where the angle θm in the tilted state described above is 30°. In FIG. 8, the vertical direction in the tilted state is defined as the tilted up-down direction. The angle between the axial direction parallel to the central axis of the inner body 134 (i.e., the up-down direction of the gas sensor 100) and the vertical direction (i.e., the up-down direction when tilted) is (90°-θm), which is 60° in the example of FIG. 8.

[0042] In this state, the lower end of the inner circumferential surface of the connecting portion 134e between the side portion 134a and the bottom portion 134b of the inner body portion 134 in the vertical direction when tilted is defined as reference point P0. The lower end of the opening of the element chamber inlet 128 on the sensor element chamber 124 side in the vertical direction when tilted is defined as point Pa. In this embodiment, the element chamber inlet 128 has multiple horizontal holes 128b. In such a case, the lowermost lower end of the opening of each of the multiple horizontal holes 128b on the sensor element chamber 124 side in the vertical direction when tilted is defined as point Pa. The lower end of the opening of the element chamber outlet 129 on the sensor element chamber 124 side in the vertical direction when tilted is defined as point Pb. The lower end of the sensor element 110 in the vertical direction when tilted is defined as point Pc. In this embodiment, the sensor element 110 has an element body 20 and a porous protective layer 22. In such a case, the lower end of the entire sensor element 110 in the vertical direction when tilted is defined as point Pc, without distinguishing between the element body 20 and the porous protective layer 22. Therefore, in Fig. 8, the lower end of the porous protective layer 22 in the vertical direction when tilted is the lower end of the sensor element 110, i.e., point Pc.

[0043] The vertical distance between reference point P0 and point Pa during tilt is defined as distance A, the vertical distance between reference point P0 and point Pb during tilt is defined as distance B, and the vertical distance between reference point P0 and point Pc during tilt is defined as distance C. As shown in FIG. 8, distance A is the vertical distance between plane L0, which passes through reference point P0 and is aligned with the horizontal direction in the tilted state, and plane La, which passes through point Pa and is aligned with the horizontal direction in the tilted state. Similarly, distance B is the vertical distance between plane L0 and plane Lb, which passes through point Pb and is aligned with the horizontal direction in the tilted state. Distance C is the vertical distance between plane L0 and plane Lc, which passes through point Pc and is aligned with the horizontal direction in the tilted state. Plane L0 is a plane tangent to the inner circumferential surface of connecting portion 134e. It can also be said that the reference point P0 is the lower end of the space around the connecting portion 134e of the sensor element chamber 124 in the vertical direction when tilted, i.e., the lower end of the corner of the sensor element chamber 124 in the vertical direction when tilted. Therefore, it can also be said that the plane L0 is a plane that contacts the lower end of the corner of the sensor element chamber 124 in the vertical direction when tilted.

[0044] As can be seen from FIG. 8 , in the gas sensor 100 of this embodiment, when the angle θm is 30°, both distance A and distance B are smaller than distance C. By arranging the element chamber inlet 128, the element chamber outlet 129, and the sensor element 110 so that distances A to C have this magnitude relationship, the water resistance of the sensor element 110 can be improved when the gas sensor 100 is in an inclined state. The reason for this is explained below. First, the measurement gas may contain water, and water may enter the protective cover 120 from the outer inlet 144a along with the measurement gas. In this case, water may reach the sensor element chamber 124 and accumulate there. When the gas sensor 100 is in an inclined state, water W accumulates from the reference point P0 in the sensor element chamber 124, as shown in FIG. 8 . In this case, if at least one of distances A and B is smaller than distance C, at least one of the openings of the element chamber inlet 128 and the element chamber outlet 129 will be located vertically lower than the lower end of the sensor element 110. As a result, even if water W accumulates in the sensor element chamber 124 in an inclined state and the water level of the water W rises, the water W can easily escape from at least one of the element chamber inlet 128 and the element chamber outlet 129 to the outside of the sensor element chamber 124 (outside the inner protective cover 131) before adhering to the sensor element 110. Therefore, when the gas sensor 100 is in an inclined state, the accumulated water W can be prevented from adhering to the sensor element 110 and causing cracks in the sensor element 110 (particularly the element body 20). This can improve the water resistance of the sensor element 110 when the gas sensor 100 is in an inclined state. Moreover, in the gas sensor 100 of this embodiment, both distances A and B are smaller than distance C when the angle θm is 30°, as described above. Therefore, when the gas sensor 100 is in an inclined state, both the opening of the element chamber inlet 128 and the opening of the element chamber outlet 129 are located at positions lower in the vertical direction than the lower end of the sensor element 110. This makes it easier for water that has accumulated in the sensor element chamber 124 to drain before it adheres to the sensor element 110, thereby further improving the water resistance of the sensor element 110 when the gas sensor 100 is in an inclined state.

[0045] Although explanation using drawings is omitted, in the gas sensor 100 of this embodiment, the element chamber inlet 128, the element chamber outlet 129, and the sensor element 110 are arranged so that at least one of the distances A and B is smaller than the distance C, not only when the angle θm is 30° but also when the angle θm is any value between 10° and 40°. Therefore, the gas sensor 100 of this embodiment can further improve the water resistance of the sensor element 110 in an inclined state when the angle θm is attached to the pipe 10, regardless of whether the angle θm is any value between 10° and 40°.

[0046] In the gas sensor 100, the upper end of the opening of the element chamber inlet 128 on the sensor element chamber 124 side is located above the lower end of the gas inlet 21 in the axial direction, i.e., the vertical direction. Figure 8 shows a plane H0 that passes through the lower end of the gas inlet 21 and is perpendicular to the vertical direction (not the vertical direction when tilted), and a plane Ha that passes through the upper end of the opening of the element chamber inlet 128 on the sensor element chamber 124 side and is perpendicular to the vertical direction. In this embodiment, the gas inlet 21 opens at the lower end of the element body 20 and does not have a vertical width, so the position of the gas inlet 21 in the vertical direction is referred to as the lower end (=upper end) of the gas inlet 21. In this embodiment, the element chamber inlet 128 has multiple horizontal holes 128b. In this case, the uppermost upper end of the opening of each of the horizontal holes 128b on the sensor element chamber 124 side in the vertical direction is referred to as the upper end of the opening of the element chamber inlet 128 on the sensor element chamber 124 side. However, in this embodiment, the positions of the upper ends of the multiple horizontal holes 128b are all the same. "The upper end of the opening of the element chamber inlet 128 on the sensor element chamber 124 side is located above the lower end of the gas inlet 21 in the vertical direction" can also be rephrased as "The plane Ha in FIG. 8 is located above the plane H0 in the vertical direction." By arranging the element chamber inlet 128 and the gas inlet 21 in this positional relationship, at least a portion of the opening of the element chamber inlet 128 is located above the gas inlet 21, and therefore the gas inlet 21 is located between at least a portion of the element chamber inlet 128 and the element chamber outlet 129 in the vertical direction. This allows the measurement gas that flows into the sensor element chamber 124 from the element chamber inlet 128 to easily reach the gas inlet 21 before reaching the element chamber outlet 129. Therefore, in this gas sensor 100, the responsiveness of the sensor element 110 in detecting the concentration of a specific gas can be improved.

[0047] Furthermore, in the gas sensor 100, the lower end of the opening of the element chamber inlet 128 on the sensor element chamber 124 side is located above the lower end of the gas inlet 21 in the vertical direction. FIG. 8 shows a plane Hb that passes through the lower end of the opening of the element chamber inlet 128 on the sensor element chamber 124 side and is perpendicular to the vertical direction. "The lower end of the opening of the element chamber inlet 128 on the sensor element chamber 124 side is located above the lower end of the gas inlet 21 in the vertical direction" can also be rephrased as "The plane Hb in FIG. 8 is located above the plane H0 in the vertical direction." By arranging the element chamber inlet 128 and the gas inlet 21 in this positional relationship, the entire opening of the element chamber inlet 128 is located above the gas inlet 21, and therefore the gas inlet 21 is located between the entire element chamber inlet 128 and the element chamber outlet 129 in the vertical direction. This allows the measurement gas that has flowed into the sensor element chamber 124 from the element chamber inlet 128 to more easily reach the gas inlet 21 before reaching the element chamber outlet 129. Therefore, in this gas sensor 100, the responsiveness of the sensor element 110 in detecting the concentration of a specific gas can be further improved.

[0048] The planes H0, Ha, Hb and their positional relationships are determined based on the above-mentioned axial direction, that is, the vertical direction, regardless of the vertical direction when tilted (that is, regardless of the angle θm).

[0049] The distance A can be adjusted by, for example, adjusting the vertical position of the element chamber inlet 128 or adjusting the diameter of the horizontal hole 128b of the element chamber inlet 128. For example, the lower the element chamber inlet 128 is positioned in the vertical direction, the easier it is to reduce the distance A, which makes it easier to achieve the effect of improving the water resistance of the sensor element 110 in an inclined state. However, if the element chamber inlet 128 is positioned lower in the vertical direction, the positions of the planes Ha and Hb also move lower. For this reason, it is preferable to position the element chamber inlet 128 lower in the range where the plane Ha is positioned above the plane H0, and it is more preferable to position the element chamber inlet 128 lower in the range where the plane Hb is positioned above the plane H0.

[0050] The distance B can be adjusted, for example, by adjusting the vertical position of the element chamber outlet 129 (i.e., the vertical distance between the sensor element 110 and the element chamber outlet 129), by adjusting the diameter of the element chamber outlet 129, or by adjusting the inner diameter of the inner body 134. Because the element chamber outlet 129 is located vertically below the gas inlet 21, adjusting the vertical position of the element chamber outlet 129 to reduce the distance B does not reduce the responsiveness of the detection of the specific gas concentration. Therefore, it is preferable to position the element chamber outlet 129 and the sensor element 110 so that the distance B is at least smaller than the distance C when the angle θm is at least any value between 10° and 40°. This arrangement facilitates achieving both water resistance of the sensor element 110 in an inclined state and responsiveness of the detection of the specific gas concentration.

[0051] The above-mentioned distance C can be adjusted, for example, by adjusting the vertical position of the sensor element 110, adjusting the width of the element body 20, adjusting the thickness of the porous protective layer 22, or adjusting the inner diameter of the inner body portion 134.

[0052] According to the gas sensor 100 of this embodiment described above, the element chamber inlet 128, the element chamber outlet 129, and the sensor element 110 are arranged so that when the angle θm in the inclined state of the gas sensor 100 is at least any value between 10° and 40°, at least one of the distances A and B is smaller than the distance C. This improves the water resistance of the sensor element 110 when the gas sensor 100 is in the inclined state. Note that "when the angle θm is at least any value between 10° and 40°, at least one of the distances A and B is smaller than the distance C" means, in other words, that "when the angle θm is changed (when the inclined state is changed), the distances A to C change, but the value of the angle θm at which at least one of the distances A and B is smaller than the distance C is within the range between 10° and 40°."

[0053] Furthermore, in the gas sensor 100, the element chamber inlet 128, the element chamber outlet 129, and the sensor element 110 are arranged so that, when the angle θm is at least any value between 10° and 40°, both distances A and B are smaller than distance C. This further improves the water resistance of the sensor element 110 when the gas sensor 100 is in an inclined state.

[0054] Furthermore, in the gas sensor 100, the element chamber inlet 128, the element chamber outlet 129, and the sensor element 110 are arranged so that when the angle θm is at least any value between 10° and 30°, inclusive, at least one of the distances A and B is smaller than the distance C. This makes the gas sensor 100 more suitable for an inclined state when the angle θm is between 10° and 30°, inclusive.

[0055] In the gas sensor 100, the element chamber inlet 128, the element chamber outlet 129, and the sensor element 110 are arranged so that at least one of the distances A and B is smaller than the distance C regardless of whether the angle θm is a value between 10° and 30°. This provides the gas sensor 100 with the effect of improving the water resistance of the sensor element 110 regardless of whether the angle θm in the tilted state is a value between 10° and 30°. This reduces the restrictions on the angle θm when the gas sensor 100 is used in the tilted state.

[0056] Furthermore, in the gas sensor 100, the element chamber inlet 128, the element chamber outlet 129, and the sensor element 110 are arranged so that at least one of the distances A and B is smaller than the distance C regardless of whether the angle θm is a value between 10° and 40°. This provides the gas sensor 100 with the effect of improving the water resistance of the sensor element 110 regardless of whether the angle θm in the tilted state is a value between 10° and 40°. Therefore, there are fewer restrictions on the angle θm when the gas sensor 100 is used in the tilted state.

[0057] Furthermore, in the gas sensor 100, the upper end of the opening of the element chamber inlet 128 on the sensor element chamber 124 side is located higher in the axial direction than the lower end of the gas inlet 21. This can improve the responsiveness of the sensor element 110 to detect the concentration of a specific gas. Furthermore, in the gas sensor 100, the lower end of the opening of the element chamber inlet 128 on the sensor element chamber 124 side is located higher in the axial direction than the lower end of the gas inlet 21. This can further improve the responsiveness of the sensor element 110 to detect the concentration of a specific gas.

[0058] Furthermore, the bottom 134b of the inner body 134 has a protruding portion 134c that protrudes from the sensor element chamber 124 side toward the intermediate chamber 125 side. The element chamber outlet 129 is disposed in the protruding portion 134c. This improves the responsiveness of the sensor element 110 in detecting the concentration of a specific gas.

[0059] 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.

[0060] For example, in the gas sensor 100 of the above-described embodiment, it is preferable that the element chamber inlet 128, the element chamber outlet 129, and the sensor element 110 are arranged so that both the distance A and the distance B are smaller than the distance C, regardless of whether the angle θm is a value between 10° and 30°. Furthermore, it is more preferable that the element chamber inlet 128, the element chamber outlet 129, and the sensor element 110 are arranged so that both the distance A and the distance B are smaller than the distance C, regardless of whether the angle θm is a value between 10° and 40°. For example, these aspects can be realized by increasing the inner diameter of the inner body portion 134 or the diameter of the element chamber outlet 129 compared to the gas sensor 100 of the above-described embodiment.

[0061] Although not described in the above-described embodiment, as shown in FIG. 9, the vertical distance between plane L0 and plane Ld, which is tangent to the inner circumferential surface of connection portion 134d of protrusion 134c and extends horizontally in the tilted state, is defined as distance D. This distance D is preferably smaller than distance C. Furthermore, distance D is more preferably equal to or smaller than distance B. FIG. 9 is a partial enlarged view of the inner protective cover 131 and sensor element 110 shown in FIG. 8. Plane Ld is a plane that is tangent to a portion of the inner circumferential surface of connection portion 134d of protrusion 134c that is the lower surface (the surface facing upward) in the tilted state and extends horizontally in the tilted state. Note that FIG. 9 indicates the point where plane Ld and connection portion 134d meet as point Pd. If distance D is greater than distance B—in other words, if point Pd is located higher than point Pb in the vertical direction in the tilted state—water W accumulating in the sensor element chamber 124 from reference point P0 will flow over connection portion 134d before reaching the element chamber outlet 129. Therefore, if distance D is too large, it may be difficult for water W to escape from element chamber outlet 129. From this perspective, as described above, distance D is preferably smaller than distance C, and more preferably, distance D is equal to or smaller than distance B. Note that if distance A is smaller than distance C, problems are unlikely to occur even if distance D is large and water is difficult to escape from element chamber outlet 129. Therefore, when "at least one of distances A and B is smaller than distance C," it is preferable to further satisfy at least one of the first condition that "distance A is smaller than distance C" and the second condition that "both distances B and D are smaller than distance C," and it is more preferable to satisfy both the first and second conditions. For example, when "at least one of distances A and B is smaller than distance C when angle θm is at least any value between 10° and 40°," it is preferable to satisfy at least one of the first and second conditions at that value of angle θm, and it is preferable to satisfy both the first and second conditions. Furthermore, for example, if "at least one of distance A and distance B is smaller than distance C regardless of whether angle θm is a value between 10° and 30°," it is preferable that "at least one of the first and second conditions is satisfied regardless of whether angle θm is a value between 10° and 30°."Furthermore, it is preferable that "both the first and second conditions are satisfied when the angle θm is any value between 10° and 30°." The same applies when the angle θm is within the other ranges.

[0062] In the above-described FIG. 8, in the tilted state, the reference point P0 and points Pa to Pc all appear on the same cross section (the cross section shown in FIG. 8). In the above-described FIG. 9, point Pd also appears on the same cross section. However, even in the same tilted state, i.e., even when the angle θm is the same, if the rotational position around the central axis of the inner body portion 134 is different, the position of the horizontal hole 128b along the circumferential direction of the side portion 134a relative to the central axis (also referred to as the phase of the horizontal hole 128b) changes, and point Pa may not appear on the cross section shown in FIG. 8 or 9. Even in such cases, point Pa and distance A can be determined based on the above-described definition, but the value of distance A will change depending on the phase of the horizontal hole 128b even for the same protective cover 120 and the same tilted state. However, distance A is the minimum value within the range of distance A that changes depending on the phase of the horizontal hole 128b. In other words, when point Pa is located on the cross section of horizontal hole 128b shown in Figures 8 and 9 (a cross section passing through the central axis of inner body portion 134 and along the vertical direction when tilted), distance A is the distance between reference point P0 and point Pa in the vertical direction when tilted. If distance A defined in this way is smaller than distance C, an effect is obtained in which water in sensor element chamber 124 can easily escape through horizontal hole 128b, at least in an inclined state in which gas sensor 100 is attached so that horizontal hole 128b has such a phase. Note that it is preferable that the maximum value of the range of distance A, which changes depending on the phase of horizontal hole 128b, is also smaller than distance C. This effect is obtained in which water in sensor element chamber 124 can easily escape through horizontal hole 128b, regardless of the phase of horizontal hole 128b when gas sensor 100 is actually attached to pipe 10.

[0063] Although not explained in the above-described embodiment, distance A is defined as a positive value when point Pa is located above reference point P0 in the vertical direction when tilted. The same applies to distances B to D. Therefore, for example, distance B may be a negative value. Specifically, if the downward protrusion height of protrusion 134c from bottom 134b is greater than in the above-described embodiment, point Pb in FIG. 8 may be located below reference point P0 in the vertical direction when tilted, in which case distance B will be a negative value. If distance B is a negative value and distance C is a positive value, distance B will be smaller than distance C.

[0064] In the above-described embodiment, in the gas sensor 100, the upper end of the opening of the element chamber inlet 128 on the sensor element chamber 124 side is located above the lower end of the gas inlet 21 in the axial direction, but this is not limiting. The upper end of the opening of the element chamber inlet 128 on the sensor element chamber 124 side may also be located below the lower end of the gas inlet 21.

[0065] In the above-described embodiment, the element chamber entrance 128 has multiple horizontal holes 128b, but this is not a limitation and the number of horizontal holes 128b may be one. However, it is preferable that the element chamber entrance 128 (horizontal holes 128b) has multiple entrances, more preferably four or more, even more preferably six or more, and even more preferably eight or more. The greater the number of entrances 128 (horizontal holes 128b), the smaller the difference between the maximum and minimum values ​​of distance A, which changes depending on the phase of the horizontal holes 128b described above, and not only the minimum value of distance A but also the maximum value of distance A is more likely to be smaller than distance C.

[0066] In the above-described embodiment, the element chamber outlet 129 is a single hole, but the present invention is not limited to this and may be a plurality of holes.

[0067] In the above-described embodiment, the element chamber inlet 128 opens midway through the intermediate passage 127, but this is not limiting. For example, the element chamber inlet 128 may be located above the upper opening 127a in the inner body portion 134.

[0068] 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 (either the top, bottom, left, or right surface of the sensor element 110 in FIG. 4). In this case, the upper and lower ends of the gas inlet 21 are positioned at different positions in the vertical direction.

[0069] 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.

[0070] In the above-described embodiment, the bottom portion 134b has the protrusion 134c, but this is not limiting. For example, the entire lower surface of the bottom portion 134b may be flat.

[0071] The gas sensor 100 of the above-described embodiment may be configured as a gas sensor 100 having the above-described feature of the protruding portion 134c where the element chamber outlet 129 is disposed, without having the above-described feature of the positional relationship (for example, the magnitude relationship between the distances A to C, or the positional relationship between the planes H0, Ha, and Hb) between the element chamber inlet 128, the element chamber outlet 129, and the sensor element 110. Even in this case, the feature of the protruding portion 134c makes it easier to generate a flow of the measurement gas from the sensor element chamber 124 through the element chamber outlet 129 toward the intermediate chamber 125, thereby improving the responsiveness of the sensor element 110 in detecting the concentration of a specific gas. [Explanation of symbols]

[0072] 10 piping, 12 fixing member, 20 element body, 21 gas inlet, 22 porous protective layer, 100 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, 124 sensor element chamber, 125 intermediate chamber, 126 second gas chamber, 127 intermediate passage, 127a upper opening, 127b lower opening, 128 element chamber inlet, 128b horizontal hole, 129 element chamber outlet, 131 inner protective cover, 132 large diameter portion, 133 step portion, 134 inner body portion, 134a side portion, 134b bottom portion, 134c protrusion portion, 134d connection portion, 134e connection portion, 135 Intermediate protective cover, 136 intermediate body portion, 136a side portion, 136b stepped portion, 136c protruding portion, 138 tip portion, 138a intermediate chamber outlet, 138b horizontal hole, 138d side portion, 138e bottom portion, 140 outer protective cover, 143 first body portion, 143a side portion, 143b stepped portion, 144a outer inlet, 144b horizontal hole, 145 second body portion, 145a side portion, 145b stepped portion, 146 tip portion, 146a side portion, 146b bottom portion, 146c tapered portion, 147a outer outlet, 147c vertical hole.

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; an inner protective cover having a sensor element chamber therein in which the front end of the sensor element and the gas inlet are disposed; an intermediate protective cover disposed outside the inner protective cover and having an intermediate chamber formed therein as a space between the intermediate protective cover and the inner protective cover; an outer protective cover disposed outside the intermediate protective cover, the outer protective cover having an outer inlet through which the measurement gas enters from the outside and an outer outlet through which the measurement gas leaves the outside, the outer protective cover having a first gas chamber connected to the outer inlet and a second gas chamber connected to the outer outlet inside; A gas sensor comprising: the inner protective cover has a cylindrical inner body portion surrounding the sensor element, the inner body portion has a side portion in which an element chamber inlet serving as an entrance to the sensor element chamber is disposed, and a bottom portion in which an element chamber outlet serving as an exit from the sensor element chamber to the intermediate chamber is disposed, the intermediate protective cover has a cylindrical intermediate body portion that surrounds the inner body portion, and a tip portion that has a smaller diameter than the intermediate body portion and that is provided with an intermediate chamber outlet that serves as an outlet from the intermediate chamber to the second gas chamber, the intermediate protective cover and the inner protective cover form an intermediate passage configured as a space between the intermediate body portion and the inner body portion and connected to the intermediate chamber, the first gas chamber is a space formed inside the outer protective cover and outside the intermediate body and the inner protective cover, and functions as a flow path for the measurement gas from the outer inlet to the intermediate passage; the second gas chamber is a space formed inside the outer protective cover and outside the tip portion, and functions as a flow path for the measurement gas from the intermediate chamber outlet to the outer outlet; a state in which the gas sensor is tilted so that the central axis of the inner body is inclined with respect to the vertical direction and the front end of the sensor element is positioned vertically lower than the rear end, the angle between the central axis in the inclined state and the horizontal direction is defined as angle θm, the vertical direction in the inclined state is defined as angle θm, the lower end of the inner circumferential surface of the connecting portion between the side portion and the bottom of the inner body in the vertical direction when tilted is defined as a reference point, the distance between the lower end of the opening of the element chamber inlet on the sensor element chamber side in the vertical direction when tilted and the reference point in the vertical direction when tilted is defined as distance A, the distance between the lower end of the opening of the element chamber outlet on the sensor element chamber side in the vertical direction when tilted and the reference point in the vertical direction when tilted is defined as distance B, and the distance between the lower end of the sensor element in the vertical direction when tilted and the reference point in the vertical direction when tilted is defined as distance C, the element chamber inlet, the element chamber outlet, and the sensor element are arranged such that, when the angle θm is at least any value between 10° and 40°, at least one of the distance A and the distance B is smaller than the distance C. Gas sensor.

2. 2. The gas sensor according to claim 1, the element chamber inlet, the element chamber outlet, and the sensor element are arranged such that, when the angle θm is at least any value between 10° and 40°, both the distance A and the distance B are smaller than the distance C. Gas sensor.

3. 3. The gas sensor according to claim 1, the element chamber inlet, the element chamber outlet, and the sensor element are arranged such that, when the angle θm is at least any value between 10° and 30°, at least one of the distance A and the distance B is smaller than the distance C. Gas sensor.

4. 3. The gas sensor according to claim 1, When the angle θm is any value between 10° and 30°, the element chamber inlet, the element chamber outlet, and the sensor element are arranged so that at least one of the distance A and the distance B is smaller than the distance C. Gas sensor.

5. 3. The gas sensor according to claim 1, When the angle θm is any value between 10° and 40°, the element chamber inlet, the element chamber outlet, and the sensor element are arranged so that at least one of the distance A and the distance B is smaller than the distance C. Gas sensor.

6. 3. The gas sensor according to claim 1, when a direction parallel to the central axis of the inner body portion is defined as an axial direction and a direction from the front end to the rear end of the sensor element along the axial direction is defined as an upward direction, an upper end of the opening of the element chamber inlet on the sensor element chamber side is located higher than a lower end of the gas inlet in the axial direction. Gas sensor.

7. 7. The gas sensor according to claim 6, a lower end of the opening of the element chamber inlet on the sensor element chamber side is located higher than a lower end of the gas inlet in the axial direction; Gas sensor.

8. 3. The gas sensor according to claim 1, the element chamber inlet opens midway through the intermediate passage; Gas sensor.

9. 3. The gas sensor according to claim 1, the bottom of the inner body portion has a protruding portion that protrudes from the sensor element chamber side toward the intermediate chamber side, the element chamber outlet is disposed in the protruding portion; Gas sensor.

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