Gas Sensor

Abstract

Improves response in detecting specific gas concentrations. [Solution] The gas sensor 100 includes an inner protective cover 131, an intermediate protective cover 135, and an outer protective cover 140. The inner protective cover 131 has a sensor element chamber 124 therein, in which the front end of the sensor element 110 and the gas inlet 21 are disposed. The intermediate protective cover 135 is disposed outside the inner protective cover 131, and has an intermediate chamber 125 therein, which is a space formed between the inner protective cover 131 and the intermediate protective cover 135. The intermediate protective cover 135 and the inner protective cover 131 form an intermediate passage 127 connected to the intermediate chamber 125. When the flow path cross-sectional area of ​​a lower opening 127b of the intermediate passage 127, which is an outlet for the measured gas to the intermediate chamber 125, is defined as S1, and the flow path cross-sectional area of ​​a gas passage inlet 151a of the gas passage 151, which is an inlet for the measured gas from the intermediate passage 127 side, is defined as S2, the ratio S2 / S1 is 1.00 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, there has been a demand for improving the response of the sensor element in detecting the concentration of a specific gas.

[0005] The present invention has been made to solve such problems, and a main object of the present invention is to improve the response of detection of the concentration of a specific gas. [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 an inner 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 body portion has an intermediate side portion and a step portion connecting the intermediate side portion and the tip portion, the intermediate protective cover and the inner protective cover form an intermediate passage configured as a space between the intermediate side portion and the inner side portion and connected to the intermediate chamber, the intermediate passage functions as a flow path for the measurement gas flowing downward, with a direction parallel to the axial direction of the inner body portion and a direction from the rear end to the front end of the sensor element being the downward direction, the intermediate protective cover and the inner protective cover form a gas passage that is part of the intermediate chamber and is configured as a space between the step portion and the bottom portion, the gas passage is a flow path for the measurement gas located between the intermediate passage and the intermediate chamber outlet, and functions as a flow path for the measurement gas from the intermediate passage side toward the central axis of 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 cross-sectional area S1 of the flow path of the intermediate passage at an outlet of the measurement gas to the intermediate chamber and a cross-sectional area S2 of the flow path of the gas passage at an inlet of the measurement gas from the intermediate passage side, the ratio S2 / S1 being 1.00 or less; It is something.

[0008] In this gas sensor, when the cross-sectional area of ​​the intermediate passage at the outlet of the measurement gas to the intermediate chamber is defined as S1 and the cross-sectional area of ​​the gas passage at the inlet of the measurement gas from the intermediate passage side is defined as S2, the ratio S2 / S1 is 1.00 or less. This enables the gas sensor to improve the responsiveness of the sensor element in detecting the concentration of a specific gas. The inventors have confirmed this through experiments and analyses.

[0009] [2] In the gas sensor described above (the gas sensor described in [1] above), the ratio S2 / S1 may be 0.80 or less, which can further improve the response in detecting the measurement gas.

[0010] [3] In the gas sensor described above (the gas sensor described in [1] or [2] above), the ratio S2 / S1 may be 0.20 or more.

[0011] [4] In the gas sensor described above (the gas sensor described in any one of [1] to [3]), the cross-sectional area S2 is 11 mm 2 It may be more than that.

[0012] [5] In the gas sensor described above (the gas sensor according to any one of [1] to [4] above), the element chamber inlet may open midway through the intermediate passage.

[0013] [6] In the above-described gas sensor (the gas sensor according to any one of [1] to [5]), 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 can further improve the responsiveness of the sensor element in detecting the concentration of a specific gas. [Brief explanation of the drawings]

[0014] [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] FF cross section of Figure 3. [Figure 9] Enlarged view of a portion of Figure 3. [Figure 10] 10 is a graph showing the relationship between the ratio S2 / S1 and the response time for each of Experimental Examples 1 to 5. DETAILED DESCRIPTION OF THE INVENTION

[0015] 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 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 line E in FIG. 3. FIG. 8 is a cross-sectional view taken along line FF in FIG. 3. FIG. 9 is a partially enlarged view of 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. 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.

[0016] As shown in FIG. 1, the gas sensor 100 is mounted 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 between the central axis of the gas sensor 100 and the horizontal direction in the inclined state is defined as angle θm. The angle θm is, for example, between 10° and 40°. Note that the angle θm may be 90°. That is, the gas sensor 100 may be attached to the pipe 10 so that the axial direction (up-down direction) is parallel to the vertical direction, rather than being inclined.

[0017] 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.

[0018] 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 .

[0019] 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 porous, the gas to be measured can flow through the inside of the porous protective layer 22 and reach the gas inlet 21.

[0020] 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 a side portion 136a of the intermediate body portion 136 of the intermediate protective cover 135 and a side portion 134a of 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).

[0021] 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 (an example of an inner side portion) and a bottom portion 134b. 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 portion 134b has a protruding portion 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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 (an example of an intermediate side portion) 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.

[0026] 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. The intermediate chamber 125 has a gas passage 151.

[0027] 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.

[0028] 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.

[0029] 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 side portion 136a of the intermediate body portion 136 and the outer circumferential surface of the side portion 134a of the inner body portion 134. The intermediate passage 127 is a space from the upper end of the side portion 136a 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 side of the first gas chamber 122, which is the space in which the outer inlet 144a is disposed, and a lower opening 127b which is an opening on the side of the intermediate chamber 125. The upper opening 127a is a ring-shaped gap between the upper end of the inner circumferential surface of the intermediate body 136 and the outer circumferential surface of the inner body 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). 9, in the present embodiment, the connecting portion (corner) of the inner body portion 134 between the bottom portion 134b and the side portion 134a has an arc-shaped (R-shaped) cross section. This curved portion is not included in the outer peripheral surface of the side portion 134a, and the positions of the intermediate passage 127 and the lower opening 127b are defined.

[0030] 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.

[0031] As shown in FIG. 9, the gas passage 151 is part of the intermediate chamber 125 and is configured as a space between the stepped portion 136b of the intermediate body portion 136 and the bottom portion 134b of the inner body portion 134. More specifically, the gas passage 151 is configured as a gap between the upper surface of the stepped portion 136b and the lower surface of the bottom portion 134b (see FIGS. 8 and 9). The gas passage 151 has a gas passage inlet 151a, which is an opening on the intermediate passage 127 side, and a gas passage outlet 151b, which is an opening on the intermediate chamber outlet 138a side. The gas passage inlet 151a is a vertical gap between the outer circumferential edge of the lower surface of the bottom portion 134b and a portion of the stepped portion 136b that faces the outer circumferential edge of the lower surface of the bottom portion 134b in the vertical direction. Therefore, the gas passage inlet 151a has the same shape (here, the outline of a circle) as the outer circumferential edge of the lower surface of the bottom portion 134b when viewed from above (see FIG. 8). The gas passage outlet 151b is a vertical gap between the inner circumferential end of the upper surface of the stepped portion 136b and a portion of the bottom portion 134b that faces the inner circumferential end of the upper surface of the stepped portion 136b. Therefore, the gas passage outlet 151b has the same shape (here, the outline of a circle) as the inner circumferential end of the upper surface of the stepped portion 136b in a top view (see FIG. 8 ). In this embodiment, as shown in FIG. 9 , the connection portion (corner) between the bottom portion 134b and the side portion 134a of the inner body portion 134 has an arc-shaped (R-shaped) cross section. The positions of the gas passage 151 and the gas passage inlet 151a are defined without including this curved portion in the lower surface of the bottom portion 134b. Similarly, in this embodiment, the connection portion (corner) between the stepped portion 136b and the tip portion 138 of the intermediate body portion 136 has an arc-shaped (R-shaped) cross section. The curved portion is not included in the upper surface of the step portion 136b, and the positions of the gas passage 151 and the gas passage outlet 151b are defined in this manner. In this embodiment, the vertical height of the gas passage 151 is the same from the gas passage inlet 151a to the gas passage outlet 151b (slight differences due to manufacturing errors, etc., are allowed).

[0032] The gas passage 151 is a flow path for the measurement gas located between the intermediate passage 127 and the intermediate chamber outlet 138a. The gas passage 151 functions as a flow path for the measurement gas from the intermediate passage 127 side toward the central axis of the intermediate chamber 125. In this embodiment, the upper surface of the step portion 136b and the lower surface of the bottom portion 134b (the lower surface of the bottom portion 134b excluding the protruding portion 134c) are both surfaces perpendicular to the vertical direction. Therefore, the gas passage 151 serves as a flow path for the measurement gas perpendicular to the vertical direction (parallel to the horizontal direction).

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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 an internal heater in the sensor element 110 is controlled, for example, by a controller (not shown) to maintain a predetermined temperature. The measurement gas in the sensor element chamber 124 flows into the intermediate chamber 125 through the element chamber outlet 129. Meanwhile, the measurement gas flowing into the intermediate chamber 125 from the lower opening 127b is redirected by the upper surface of the stepped portion 136b from downward to toward the central axis of the intermediate chamber 125, as indicated by the white arrow in FIG. 9 , and then flows into the gas passage 151 through the gas passage inlet 151a. The measurement gas flowing into the gas passage 151 flows through the gas passage 151 in a direction parallel to the left-right direction and toward the central axis of the intermediate chamber 125, passing through the gas passage outlet 151b. The measurement gas that has flowed into the intermediate chamber 125 from the element chamber outlet 129 and the measurement gas that has passed through the gas passage outlet 151b flows through the intermediate chamber outlet 138a into the second gas chamber 126. The gas that has reached the second gas chamber 126 flows out through the outer outlet 147a.

[0038] Here, the cross-sectional area of ​​the flow path of the intermediate passage 127 at the outlet of the measurement gas to the intermediate chamber 125 is defined as S1. The cross-sectional area of ​​the flow path of the gas passage 151 at the inlet of the measurement gas from the intermediate passage 127 side is defined as S2. In this case, in the gas sensor 100 of this embodiment, the ratio S2 / S1 is 1.00 or less. The outlet of the measurement gas from the intermediate passage 127 to the intermediate chamber 125 is the lower opening 127b. Therefore, in this embodiment, the cross-sectional area S1 is the area of ​​the lower opening 127b. Specifically, the cross-sectional area S1 = (area of ​​a circle having the inner diameter of the side portion 136a as its diameter) - (area of ​​a circle having the outer diameter of the side portion 134a as its diameter). The inlet of the measurement gas from the intermediate passage 127 side of the gas passage 151 is the gas passage inlet 151a. Therefore, in this embodiment, the cross-sectional area S2 is the area of ​​the gas passage inlet 151a. Specifically, the cross-sectional area S2 is the same as the area of ​​the outer circumferential surface of a cylinder whose diameter is the diameter of the gas passage inlet 151a (i.e., the diameter of the outer circumferential end of the lower surface of the bottom portion 134b) and whose height is the height of the gas passage inlet 151a (i.e., the vertical distance between the lower surface of the bottom portion 134b and the upper surface of the stepped portion 136b). That is, the cross-sectional area S2 = (diameter of the gas passage inlet 151a) × π × (height of the gas passage inlet 151a). Note that the cross-sectional area S1 is the area of ​​a surface perpendicular to the vertical direction. The cross-sectional area S2 is the area of ​​a surface parallel to the vertical direction.

[0039] When the ratio S2 / S1 of the cross-sectional area S1 to the cross-sectional area S2 is 1.00 or less, in other words, when the cross-sectional area S2 is equal to or less than the cross-sectional area S1, the responsiveness of the sensor element 110 in detecting the concentration of a specific gas can be improved. The inventors confirmed this through experiments and analyses. The reasons for this are believed to be as follows. First, as described above, the measurement gas changes direction as it flows from the intermediate passage 127 toward the gas passage 151. This increases the risk of turbulence occurring in the measurement gas around the gas passage inlet 151a, which may decrease the flow rate. However, when the ratio S2 / S1 is 1.00 or less, this turbulence is suppressed, which increases the flow rate of the measurement gas passing through the gas passage 151. Furthermore, when the flow rate of the measurement gas passing through the gas passage 151 increases, the flow rate of the measurement gas around the element chamber outlet 129 in the intermediate chamber 125 also increases. This increases the likelihood of a gas flow from the sensor element chamber 124 through the element chamber outlet 129 toward the intermediate chamber 125. As a result, the measurement gas in the sensor element chamber 124 is more easily replaced with new measurement gas from outside the gas sensor 100, which is thought to improve the responsiveness of the sensor element 110 in detecting the concentration of a specific gas.

[0040] The ratio S2 / S1 is preferably less than 1.00, and more preferably 0.80 or less. The smaller the ratio S2 / S1, the higher the flow rate of the measurement gas passing through the gas passage 151 compared to the flow rate of the measurement gas passing through the intermediate passage 127, and the more suppressed the occurrence of turbulence, thereby further improving the responsiveness of the detection of the concentration of the specific gas.

[0041] The ratio S2 / S1 may be 0.20 or more. The cross-sectional area S2 is 11 mm 2 The ratio S2 / S1 may be 0.20 or more, and / or the cross-sectional area S2 may be 11 mm 2 By setting the above, it is possible to prevent the cross-sectional area S2 from becoming too small, and it is possible to prevent the flow rate of the measurement gas passing through the gas passage 151 from becoming too small.

[0042] The cross-sectional areas S1 and S2 can be adjusted by adjusting the dimensions of the inner body portion 134 and the intermediate body portion 136. The height of the gas passage inlet 151a may be 0.5 mm or more. The inner diameter of the side portion 134a of the inner body portion 134 may be determined so that the distance between the side portion 134a and the sensor element 110 in a direction perpendicular to the axial direction is 0.05 mm or more. The flow path length of the gas passage 151, i.e., the difference in radius between the gas passage inlet 151a and the gas passage outlet 151b, may be, for example, 0.5 mm or more or 3.00 mm or less.

[0043] 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 that flows into the intermediate chamber 125 from the lower opening 127b and passes through the gas passage 151 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.

[0044] 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 from lower opening 127b into intermediate chamber 125 and passes through gas passage 151 to flow downward due to the shape of the lower surface of protruding portion 134c (particularly the lower surface of connecting portion 134d).

[0045] 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. FIG. 9 shows a plane H0 that passes through the lower end of the gas inlet 21 and is perpendicular to the vertical direction, 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 has no 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 upper end of the opening of each of the multiple horizontal holes 128b on the sensor element chamber 124 side, which is the upper end of the opening of the element chamber inlet 128 on the sensor element chamber 124 side, is referred to as the upper end of the opening. However, in this embodiment, the positions of the upper ends of the multiple horizontal holes 128b are all the same. The phrase "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. 9 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 further improved.

[0046] 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. 9 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. 9 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.

[0047] According to the gas sensor 100 of this embodiment described above, the cross-sectional area S2 / S1 is 1.00 or less, thereby improving the responsiveness of the sensor element 110 in detecting the concentration of a specific gas. Furthermore, the ratio S2 / S1 is 0.80 or less, thereby further improving the responsiveness of the sensor element 110 in detecting the concentration of a measured gas.

[0048] 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 can further improve the responsiveness of the sensor element 110 in detecting the concentration of a specific gas.

[0049] 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.

[0050] In the above-described embodiment, the gas passage 151 is a flow path for the measurement gas that is perpendicular to the up-down direction (parallel to the left-right direction), but this is not limited thereto. The gas passage 151 may be a flow path for the measurement gas that runs from the intermediate passage 127 side toward the central axis of the intermediate chamber 125. That is, the gas passage 151 may be a flow path that runs in a direction that intersects with the flow direction of the intermediate passage 127 (downward in this case). In other words, it is only necessary that the flow direction of the measurement gas changes between the intermediate passage 127 and the gas passage 151.

[0051] In the above-described embodiment, the intermediate passage 127 is a flow path for the measurement gas that runs from the rear end (upper side) to the front end (lower side) and is parallel to the vertical direction. However, the intermediate passage 127 is not limited to a flow path for the measurement gas that is parallel to the downward direction, as long as it functions as a flow path for the measurement gas that runs downward. For example, the intermediate passage 127 may be a flow path for the measurement gas that is inclined downward. For example, the intermediate passage 127 may be a flow path that is inclined downward so that the measurement gas approaches the central axis of the inner body portion 134 as it flows downward. Furthermore, such a flow path inclined downward may be present in a part of the intermediate passage 127.

[0052] 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.

[0053] In the above-described embodiment, the element chamber inlet 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 inlet 128 (horizontal holes 128b) be multiple, more preferably four or more, even more preferably six or more, and even more preferably eight or more.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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. [Example]

[0059] Specific examples of fabricated gas sensors will be described below as examples. Experimental Examples 1 to 3 correspond to examples of the present invention, and Experimental Examples 4 and 5 correspond to comparative examples. Note that the present invention is not limited to the following examples.

[0060] [Experimental Examples 1-5] The gas sensor 100 shown in FIGS. 3 to 9 was fabricated and used as Experimental Example 1. In Experimental Example 1, the ratio S2 / S1 was set to 0.76. Furthermore, by shortening the vertical length of the side portion 136a of the intermediate body portion 136 compared to Experimental Example 1, the vertical heights of the gas passage inlet 151a were made different, and multiple gas sensors 100 having the same structure except for changing the cross-sectional area S2 and the ratio S2 / S1 were fabricated and used as Experimental Examples 2 to 5. In Experimental Example 2, the ratio S2 / S1 was set to 0.80. In Experimental Example 3, the ratio S2 / S1 was set to 1.00. In Experimental Example 4, the ratio S2 / S1 was set to 1.32. In Experimental Example 5, the ratio S2 / S1 was set to 2.45.

[0061] [Responsiveness evaluation] The gas sensors 100 of Experimental Examples 1 to 5 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. 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 varied. 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 1.1 seconds or less, the responsiveness was judged to be very high ("A"), if the response time was more than 1.1 seconds but less than 1.3 seconds, the responsiveness was judged to be high ("B"), and if the response time was 1.3 seconds or more, the responsiveness was judged to be low ("F").

[0062] Table 1 shows the evaluation results of the ratio S2 / S1, response time, and responsiveness for each of Experimental Examples 1 to 5. Also, Fig. 10 is a graph showing the relationship between the ratio S2 / S1 and the response time for each of Experimental Examples 1 to 5.

[0063] [Table 1]

[0064] As shown in Table 1 and FIG. 10, Experimental Examples 4 and 5, in which the ratio S2 / S1 exceeded 1.00, were evaluated as "F" in responsiveness, whereas Experimental Examples 1 to 3, in which the ratio S2 / S1 was 1.00 or less, were evaluated as "A" or "B" in responsiveness. These results confirmed that an S2 / S1 ratio of 1.00 or less improves the responsiveness of the detection of the specific gas concentration. Furthermore, Experimental Example 3, in which the ratio S2 / S1 was 1.00, was evaluated as "B" in responsiveness, whereas Experimental Examples 1 and 2, in which the ratio S2 / S1 was 0.80 or less, were evaluated as "A" in responsiveness. These results confirmed that an S2 / S1 ratio of 0.80 or less further improves the responsiveness of the detection of the specific gas concentration. [Explanation of symbols]

[0065] 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, 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, 151 gas passage, 151a gas passage inlet, 151b gas passage outlet.

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 an inner 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 body portion has an intermediate side portion and a step portion connecting the intermediate side portion and the tip portion, the intermediate protective cover and the inner protective cover form an intermediate passage configured as a space between the intermediate side portion and the inner side portion and connected to the intermediate chamber, the intermediate passage functions as a flow path for the measurement gas flowing downward, with a direction parallel to the axial direction of the inner body portion and a direction from the rear end to the front end of the sensor element being the downward direction, the intermediate protective cover and the inner protective cover form a gas passage that is part of the intermediate chamber and is configured as a space between the step portion and the bottom portion, the gas passage is a flow path for the measurement gas located between the intermediate passage and the intermediate chamber outlet, and functions as a flow path for the measurement gas from the intermediate passage side toward the central axis of 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 cross-sectional area S1 of the flow path of the intermediate passage at an outlet of the measurement gas to the intermediate chamber and a cross-sectional area S2 of the flow path of the gas passage at an inlet of the measurement gas from the intermediate passage side, the ratio S2 / S1 being 1.00 or less; Gas sensor.

2. 2. The gas sensor according to claim 1, The ratio S2 / S1 is 0.80 or less. Gas sensor.

3. 3. The gas sensor according to claim 1, The ratio S2 / S1 is 0.20 or more. Gas sensor.

4. 3. The gas sensor according to claim 1, The cross-sectional area S2 is 11 mm 2 That's all. Gas sensor.

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

6. 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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