JP7465739B2 - Gas sensor and protective cover - Google Patents

Description

The present invention relates to a gas sensor and a protective cover.

Conventionally, gas sensors that detect the concentration of a predetermined gas, such as NOx or oxygen, in a measurement gas, such as automobile exhaust gas, are known. For example, Patent Document 1 describes a gas sensor that includes a sensor element, an inner protective cover in which the tip of the sensor element is disposed, and an outer protective cover disposed on the outside of the inner protective cover. Patent Document 1 also describes that the responsiveness of gas concentration detection is improved by setting the cross-sectional area ratio S1/S2, which is the ratio between the total cross-sectional area S1 of one or more outer inlets, which are disposed in the outer protective cover and serve as inlets from the outside of the measurement gas, and the total cross-sectional area S2 of one or more outer outlets, which are disposed in the outer protective cover and serve as outlets to the outside of the measurement gas, to a value exceeding 2.0 and not exceeding 5.0.

JP 2017-223620 A

However, the responsiveness of gas concentration detection also varies depending on the flow speed of the measured gas flowing around the gas sensor, and there is a problem in that the responsiveness is easily reduced when the flow speed is low (for example, less than 2 m/s).

The present invention was made to solve these problems, and its main objective is to reduce the decrease in responsiveness when the flow rate of the measured gas is low.

The present invention takes the following measures to achieve the above-mentioned main objective.

The gas sensor of the present invention comprises:
a sensor element having a gas inlet for introducing a gas to be measured and capable of detecting a specific gas concentration of the gas to be measured that has flowed into the sensor element through the gas inlet;
a cylindrical inner protective cover having a sensor element chamber therein in which the tip of the sensor element and the gas inlet are disposed, the sensor element chamber having one or more element chamber inlets which are inlets to the sensor element chamber and one or more element chamber outlets which are outlets from the sensor element chamber;
a cylindrical outer protective cover provided with one or more outer inlets which are inlets for the measurement gas from the outside and one or more outer outlets which are outlets for the measurement gas to the outside, the outer protective cover being disposed outside the inner protective cover;
Equipped with
the outer protective cover and the inner protective cover define, as a space therebetween, a first gas chamber which functions as a flow path for the measurement gas between the outer inlet and the element chamber inlet, and a second gas chamber which functions as a flow path for the measurement gas between the outer outlet and the element chamber outlet and does not directly communicate with the first gas chamber,
the inner protective cover has a cylindrical first member surrounding the sensor element and a cylindrical second member surrounding the first member,
the first member and the second member define the element chamber inlet as a gap therebetween,
a direction parallel to the axial direction of the inner protective cover and from the front end to the rear end of the sensor element is defined as an upward direction, and a direction from the rear end to the front end of the sensor element is defined as a downward direction, and the first gas chamber has: a first space which is a space between the outer protective cover and the second member and functions as a flow path of the measurement gas from the outer inlet toward the upward direction; and a second space which is a space above an upper end of the second member and between the outer protective cover and the first member and functions as a flow path of the measurement gas from the first space to the element chamber inlet,
a cross-sectional area Cs of the second space, which is a flow path cross-sectional area when the measurement gas passes directly above the second member from the outside to the inside of the second member, is 14.0 ^mm2 or more,
A cross-sectional area Ds, which is a cross-sectional area perpendicular to the circumferential direction of the inner protective cover in the second space, is 0.5 mm ² or more and 6.4 mm ² or less.
It is something.

In this gas sensor, the measurement gas flowing around the gas sensor flows from the outer inlet of the outer protective cover into the first space of the first gas chamber, flows upward in the first space to reach the second space, flows in the second space from the outside to the inside of the second member to reach the element chamber inlet, and reaches the gas inlet in the sensor element chamber through the element chamber inlet. Here, when the flow rate of the measurement gas is low, the flow rate of the measurement gas flowing in from the outer inlet is small, so that the flow rate of the measurement gas flowing into the element chamber through the element chamber inlet is also small, and the response of the specific gas concentration detection is likely to decrease. In contrast, in the gas sensor of the present invention, the cross-sectional area Cs is 14.0 mm ² or more, so that the measurement gas moves easily from the outside to the inside of the second member in the second space. That is, the measurement gas in the first space passes through the second space and easily moves toward the element chamber inlet. This makes it possible to increase the flow rate of the measurement gas reaching the element chamber inlet, and suppress the decrease in the response of the specific gas concentration detection when the measurement gas flows at a low flow rate. In addition, by making the cross-sectional area Ds 6.4 mm ² or less, it is possible to suppress a decrease in responsiveness caused by the measurement gas flowing in the second space along the circumferential direction of the inner protective cover. Here, if the measurement gas flows in the second space along the circumferential direction of the inner protective cover, the time it takes for the measurement gas to pass through the second space and reach the inlet of the element chamber may be extended, and the responsiveness may decrease. In contrast, by making the cross-sectional area Ds 6.4 mm ² or less, it becomes difficult for the measurement gas to flow in the second space along the circumferential direction of the inner protective cover. Therefore, it is possible to suppress a decrease in responsiveness caused by the measurement gas flowing in the second space along the circumferential direction of the inner protective cover. As described above, the gas sensor of the present invention can reduce a decrease in responsiveness when the measurement gas flows at a low flow rate. Although the cross-sectional area Ds is preferably small as described above, the cross-sectional area Ds may be 0.5 mm ² or more.

In the gas sensor of the present invention, the cross-sectional area Cs may be 22.9 ^mm2 or more. This allows the measurement gas to move more easily from the outside to the inside of the second member in the second space, thereby further suppressing a decrease in responsiveness when the measurement gas flows at a low flow rate.

In the gas sensor of the present invention, the cross-sectional area Ds may be 5.0 ^mm2 or less. This can further prevent the measurement gas from flowing in the second space along the circumferential direction of the inner protective cover, thereby further preventing a decrease in responsiveness when the measurement gas flows at a low flow rate.

In the gas sensor of the present invention, the cross-sectional area ratio As/Bs between the cross-sectional area As of the second space inlet, which is the inlet for the measurement gas from the first space to the second space, and the cross-sectional area Bs, which is the total cross-sectional area of the one or more element chamber inlets, may be 1.41 or more and 4.70 or less. Here, if the cross-sectional area As is too small, the measurement gas in the first space does not easily flow into the second space, and as a result, the measurement gas does not easily flow into the element chamber inlet. Also, if the cross-sectional area Bs is too small, the measurement gas in the second space does not easily flow into the element chamber inlet. On the other hand, if the cross-sectional area ratio As/Bs is 1.41 or more and 4.70 or less, the cross-sectional areas As and Bs are well balanced in size, so that the measurement gas in the first space passes through the second space and easily flows into the element chamber inlet, and the decrease in responsiveness at low flow rates of the measurement gas can be further suppressed.

In the gas sensor of the present invention, a cross-sectional area As of a second space inlet, which is an inlet for the measurement gas to flow from the first space to the second space, may be 47.3 mm2 ^or more and 68.1 ^mm2 or less. Also, a cross-sectional area Bs which is a total cross-sectional area of the one or more element chamber inlets may be 14.5 mm2 ^or more and 33.4 ^mm2 or less.

In the gas sensor of the present invention, the first member and the second member may form the element chamber inlet such that the element side opening, which is the opening on the sensor element chamber side of the element chamber inlet, opens toward the downward direction. In this way, it is possible to prevent the measured gas flowing out from the element side opening from hitting the surface of the sensor element (surface other than the gas inlet) perpendicularly, or from passing a long distance on the surface of the sensor element before reaching the gas inlet. This can prevent the sensor element from cooling down. Moreover, since the sensor element is prevented from cooling down by adjusting the opening direction of the element side opening, and the flow rate or flow speed of the measured gas in the inner protective cover is not reduced, the deterioration of the responsiveness of the specific gas concentration detection can also be reduced. As a result, the deterioration of the responsiveness of the sensor element can be prevented while the deterioration of the heat retention of the sensor element can be prevented. Here, "the element side opening opens toward the downward direction" includes the case where it opens parallel to the downward direction and the case where it opens at an angle from the downward direction so as to approach the sensor element as it goes downward.

In the gas sensor of the present invention, the first member has a first cylindrical portion surrounding the sensor element, the second member has a second cylindrical portion having a larger diameter than the first cylindrical portion, and the element chamber inlet may be a cylindrical gap between the outer peripheral surface of the first cylindrical portion and the inner peripheral surface of the second cylindrical portion.

The protective cover of the present invention is
A protective cover for protecting a sensor element having a gas inlet for introducing a measurement gas and capable of detecting a specific gas concentration of the measurement gas flowing into the sensor element from the gas inlet,
a cylindrical inner protective cover having a sensor element chamber therein for arranging the tip of the sensor element and the gas inlet therein, the sensor element chamber having one or more element chamber inlets which are inlets to the sensor element chamber and one or more element chamber outlets which are outlets from the sensor element chamber;
a cylindrical outer protective cover provided with one or more outer inlets which are inlets for the measurement gas from the outside and one or more outer outlets which are outlets for the measurement gas to the outside, the outer protective cover being disposed outside the inner protective cover;
Equipped with
the outer protective cover and the inner protective cover define, as a space therebetween, a first gas chamber which functions as a flow path for the measurement gas between the outer inlet and the element chamber inlet, and a second gas chamber which functions as a flow path for the measurement gas between the outer outlet and the element chamber outlet and does not directly communicate with the first gas chamber,
The inner protective cover has a cylindrical first member and a cylindrical second member surrounding the first member,
the first member and the second member define the element chamber inlet as a gap therebetween,
a direction parallel to the axial direction of the inner protective cover and from the bottom of the outer protective cover toward the opposite side of the bottom is defined as an upward direction, and a direction from the opposite side of the outer protective cover toward the bottom is defined as a downward direction, the first gas chamber has: a first space which is a space between the outer protective cover and the second member and functions as a flow path of the measurement gas from the outer inlet toward the upward direction; and a second space which is a space above an upper end of the second member and between the outer protective cover and the first member and functions as a flow path of the measurement gas from the first space to the element chamber inlet,
a cross-sectional area Cs of the second space, which is a flow path cross-sectional area when the measurement gas passes directly above the second member from the outside to the inside of the second member, is 14.0 ^mm2 or more,
A cross-sectional area Ds, which is a cross-sectional area perpendicular to the circumferential direction of the inner protective cover in the second space, is 0.5 mm ² or more and 6.4 mm ² or less.
It is something.

By arranging the tip of the sensor element and the gas inlet in the sensor element chamber of this protective cover, the effect of reducing the decrease in responsiveness when the flow rate of the measured gas is low can be obtained, similar to the gas sensor of the present invention described above. Various aspects of the gas sensor described above may be adopted in the protective cover of the present invention.

FIG. 2 is a schematic explanatory diagram of a state in which the gas sensor 100 is attached to a pipe 20. 2 is a cross-sectional view taken along line AA in FIG. 1 . 3 is a cross-sectional view taken along the line B-B of FIG. 2 . 3C-C cross-sectional view of FIG. 4 is a cross-sectional view of the outer protective cover 140 taken along the line CC of FIG. 3. FIG. FIG. 5 is an enlarged cross-sectional view of a portion of the E-E cross section of FIG. 4. FIG. 4 is a vertical cross-sectional view of a gas sensor 200 according to a modified example. 9 is a cross-sectional view of the outer protective cover 240 taken along the line FF in FIG. 8 . FIG. FIG. 13 is a cross-sectional view showing a modified example of an element chamber inlet 327. FIG. 11 is a vertical cross-sectional view of a gas sensor 400 according to a modified example. 1 is a graph showing the relationship between flow rate and response time in each of Experimental Examples 1 to 4. 1 is a graph showing the relationship between height C, cross-sectional area Cs, Ds, volume V, and response time at a flow velocity of 1 m/s for each of Experimental Examples 1 to 4.

Next, the embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic explanatory diagram of the state in which the gas sensor 100 is attached to the pipe 20. FIG. 2 is a cross-sectional view taken along the line A-A in FIG. 1. FIG. 3 is a cross-sectional view taken along the line B-B in FIG. 2. FIG. 4 is a cross-sectional view taken along the line C-C in FIG. 3. FIG. 5 is a cross-sectional view taken along the line C-C of the outer protective cover 140 in FIG. 3. FIG. 5 corresponds to a view in which the first cylindrical portion 134, the second cylindrical portion 136, the tip portion 138, and the sensor element 110 are removed from FIG. 4. FIG. 6 is a view taken along the line D in FIG. 3. FIG. 7 is a cross-sectional view in which a part of the cross section E-E in FIG. 4 is enlarged. The direction parallel to the axial direction of the protective cover 120 and from the tip to the rear end of the sensor element 110 (the upward direction in FIGS. 3 and 7) is defined as the upward direction, and the direction parallel to the axial direction of the protective cover 120 and from the rear end to the tip of the sensor element 110 (the downward direction in FIGS. 3 and 7) is defined as the downward direction.

As shown in Fig. 1, the gas sensor 100 is attached in a pipe 20 which is an exhaust path from a vehicle engine, and is adapted to detect a specific gas concentration, which is the concentration of at least one specific gas among gas components such as NOx, ammonia, _O2, etc. contained in exhaust gas as a measurement gas discharged from the engine. As shown in Fig. 2, the gas sensor 100 is fixed in the pipe 20 with the central axis of the gas sensor 100 perpendicular to the flow of the measurement gas in the pipe 20. The gas sensor 100 may be fixed in the pipe 20 with the central axis perpendicular to the flow of the measurement gas in the pipe 20 and tilted at a predetermined angle (e.g., 45°) with respect to the vertical direction.

As shown in Fig. 3, the gas sensor 100 includes a sensor element 110 having a function of detecting a specific gas concentration (concentration of NOx, ammonia, _O2 , etc.) in a measurement gas, and a protective cover 120 for protecting the sensor element 110. The gas sensor 100 also includes a metal housing 102 and a metal bolt 103 having a male thread on its outer circumferential surface. The housing 102 is inserted into a fixing member 22 which is welded to the pipe 20 and has a female thread on its inner circumferential surface, and the housing 102 is fixed in the fixing member 22 by inserting the bolt 103 into the fixing member 22. In this way, the gas sensor 100 is fixed in the pipe 20. The direction of flow of the measurement gas in the pipe 20 is from left to right in Fig. 3.

The sensor element 110 is an element in the shape of a long and thin plate, and has a structure in which a plurality of oxygen ion conductive solid electrolyte layers such as zirconia (ZrO ₂ ) are laminated. The sensor element 110 has a gas inlet 111 for introducing a measurement gas into itself, and is configured to be able to detect a specific gas concentration of the measurement gas that flows into the inside from the gas inlet 111. In this embodiment, the gas inlet 111 is opened on the tip surface of the sensor element 110 (the lower surface of the sensor element 110 in FIG. 3). The sensor element 110 has a heater inside that plays a role in adjusting the temperature by heating and keeping the sensor element 110 warm. The structure of such a sensor element 110 and the principle of detecting a specific gas concentration are publicly known, and are described in, for example, Japanese Patent Application Laid-Open No. 2008-164411. The sensor element 110 has a tip (the lower end of FIG. 3) and the gas inlet 111 arranged in a sensor element chamber 124. The direction from the rear end of the sensor element 110 toward the front end (downward direction) is also referred to as the front end direction.

The sensor element 110 also includes a porous protective layer 110a that covers at least a portion of the surface. In this embodiment, the porous protective layer 110a is formed on five of the six surfaces of the sensor element 110, covering most of the surface exposed in the sensor element chamber 124. Specifically, the porous protective layer 110a covers the entire tip surface (lower surface) of the sensor element 110 on which the gas inlet 111 is formed. The porous protective layer 110a also covers the side closer to the tip surface of the sensor element 110 among the four surfaces (upper, lower, left, and right surfaces of the sensor element 110 in FIG. 4) connected to the tip surface of the sensor element 110. The porous protective layer 110a, for example, plays a role in suppressing the occurrence of cracks in the sensor element 110 due to the adhesion of moisture in the measured gas. The porous protective layer 110a also plays a role in suppressing the adhesion of oil components contained in the measured gas to electrodes (not shown) on the surface of the sensor element 110. The porous protective layer 110a is made of a porous body such as alumina, zirconia, spinel, cordierite, titania, or magnesia. The porous protective layer 110a can be formed by, for example, plasma spraying, screen printing, or dipping. The porous protective layer 110a also covers the gas inlet 111, but since the porous protective layer 110a is a porous body, the gas to be measured can flow through the inside of the porous protective layer 110a and reach the gas inlet 111. The thickness of the porous protective layer 110a is, for example, 100 μm to 700 μm.

The protective cover 120 is arranged to surround the sensor element 110. The protective cover 120 has a cylindrical inner protective cover 130 with a bottom that covers the tip of the sensor element 110, and a cylindrical outer protective cover 140 with a bottom that covers the inner protective cover 130. A first gas chamber 122 and a second gas chamber 126 are formed as spaces surrounded by the inner protective cover 130 and the outer protective cover 140, and a sensor element chamber 124 is formed as a space surrounded by the inner protective cover 130. The central axes of the gas sensor 100, the sensor element 110, the inner protective cover 130, and the outer protective cover 140 are coaxial. The protective cover 120 is made of metal (e.g., stainless steel such as SUS310S).

The inner protective cover 130 includes a first member 131 and a second member 135. The first member 131 includes a cylindrical large diameter portion 132, a cylindrical first cylindrical portion 134 having a smaller diameter than the large diameter portion 132, and a step portion 133 connecting the large diameter portion 132 and the first cylindrical portion 134. The first cylindrical portion 134 surrounds the periphery of the sensor element 110. The second member 135 includes a second cylindrical portion 136 having a larger diameter than the first cylindrical portion 134, a tip portion 138 located in the tip direction (downward direction) of the sensor element 110 than the second cylindrical portion 136, a step portion 139 connected to the upper end of the tip portion 138 and protruding outward from the outer circumferential surface of the tip portion 138, and a connection portion 137 connecting the lower end of the second cylindrical portion 136 and the step portion 139. The tip portion 138 has a side portion 138d and a bottom portion 138e. The tip portion 138 is formed with one or more element chamber outlets 138a which communicate with the sensor element chamber 124 and the second gas chamber 126 and serve as outlets for the measurement gas from the sensor element chamber 124. The element chamber outlets 138a have a plurality of (four in this embodiment) circular horizontal holes 138b formed at equal intervals on the side portion 138d. The element chamber outlets 138a are not provided on the bottom portion 138e of the tip portion 138. The diameter of the element chamber outlets 138a is, for example, 0.5 mm to 2.6 mm. In this embodiment, the diameters of the multiple horizontal holes 138b are all the same value. The element chamber outlets 138a are formed at a position toward the tip (downward) of the sensor element 110 relative to the gas inlet 111. In other words, the element chamber outlet 138a is located farther (downward) than the gas inlet 111 when viewed from the rear end of the sensor element 110 (the upper end of the sensor element 110, not shown in FIG. 3).

The large diameter portion 132, the first cylindrical portion 134, the second cylindrical portion 136, and the tip portion 138 share the same central axis. The large diameter portion 132 has an inner peripheral surface that abuts against the housing 102, thereby fixing the first member 131 to the housing 102. The second member 135 has an outer peripheral surface of a connection portion 137 that abuts against an inner peripheral surface of the outer protective cover 140 and is fixed by welding or the like. The outer diameter of the tip side (lower end side) of the connection portion 137 may be formed slightly larger than the inner diameter of the tip portion 146 of the outer protective cover 140, and the tip portion of the connection portion 137 may be press-fitted into the tip portion 146 to fix the second member 135.

On the inner peripheral surface of the second cylindrical portion 136, a plurality of protruding portions 136a are formed, which protrude toward the outer peripheral surface of the first cylindrical portion 134 and contact this outer peripheral surface. As shown in FIG. 4, three protruding portions 136a are provided and are evenly arranged along the circumferential direction of the inner peripheral surface of the second cylindrical portion 136. The protruding portions 136a are formed in an approximately hemispherical shape. By providing such protruding portions 136a, the positional relationship between the first cylindrical portion 134 and the second cylindrical portion 136 is easily fixed by the protruding portions 136a. It is preferable that the protruding portions 136a press the outer peripheral surface of the first cylindrical portion 134 toward the inside in the radial direction. In this way, the positional relationship between the first cylindrical portion 134 and the second cylindrical portion 136 can be more reliably fixed by the protruding portions 136a. It is preferable that the number of protruding portions 136a is not limited to three, but may be two or four or more. In addition, it is preferable to have three or more protrusions 136a, as this makes it easier to stabilize the fixation between the first cylindrical portion 134 and the second cylindrical portion 136.

This inner protective cover 130 forms an element chamber inlet 127 (see Figs. 3, 4, and 7) which is a gap between the first member 131 and the second member 135 and is an inlet for the measured gas to the sensor element chamber 124. More specifically, the element chamber inlet 127 is formed as a cylindrical gap (gas flow path) between the outer peripheral surface of the first cylindrical portion 134 and the inner peripheral surface of the second cylindrical portion 136. The element chamber inlet 127 has an outer opening 128 which is an opening on the first gas chamber 122 side, which is the space in which the outer inlet 144a is arranged, and an element side opening 129 which is an opening on the sensor element chamber 124 side, which is the space in which the gas inlet 111 is arranged. The outer opening 128 is formed on the rear end side (upper side) of the sensor element 110 than the element side opening 129. Therefore, in the path of the measurement gas from the outer inlet 144a to the gas introduction port 111, the element chamber inlet 127 is a flow path from the rear end (upper side) to the tip end (lower side) of the sensor element 110. In addition, the element chamber inlet 127 is a flow path parallel to the rear end-to-tip direction of the sensor element 110 (a flow path parallel to the up-down direction).

The element side opening 129 opens in the direction from the rear end to the tip of the sensor element 110 (downward) and parallel to the rear end-to-tip direction (up-down direction) of the sensor element 110. That is, the element side opening 129 opens parallel to the downward direction. Therefore, the sensor element 110 is disposed at a position other than the region that is a virtual extension of the element chamber entrance 127 from the element side opening 129 (the region directly below the element side opening 129 in Figures 3 and 7). This prevents the measurement gas flowing out from the element side opening 129 from directly hitting the surface of the sensor element 110, and prevents the sensor element 110 from cooling down.

The outer peripheral surface of the first cylindrical portion 134 and the inner peripheral surface of the second cylindrical portion 136 are separated by a distance A4 (see FIG. 7) in the radial direction of the cylinder at the element side opening 129, and are separated by a distance A5 in the radial direction of the cylinder at the outer opening 128. The outer peripheral surface of the first cylindrical portion 134 and the inner peripheral surface of the second cylindrical portion 136 are separated by a distance A7 at the portion where the protrusion 136a and the first cylindrical portion 134 contact each other (the cross section shown in FIG. 4). The distances A4, A5, and A7 are, for example, 0.3 mm to 2.4 mm, respectively. The distances A4, A5, and A7 may be 0.51 mm or more, or 1.18 mm or less. By adjusting the values of the distances A4 and A5, the opening area of the element side opening 129 and the opening area of the outer opening 128 can be adjusted. In this embodiment, the distances A4, A5, and A7 are equal, and the opening area of the element side opening 129 is equal to the opening area of the outer opening 128. In this embodiment, the distance A4 (distance A5, distance A7) is equal to half the difference between the outer diameter of the first cylindrical portion 134 and the inner diameter of the second cylindrical portion 136. In addition, the vertical distance between the element side opening 129 and the outer opening 128, that is, the vertical distance L of the element chamber inlet 127 (corresponding to the path length of the element chamber inlet 127) is, for example, more than 0 mm and 6.6 mm or less. The distance L may be 3 mm or more, or 5 mm or less. The minimum distance between the lower end of the first cylindrical portion 134 and the connection portion 137 is the distance A6 (see FIG. 7). The distance A6 may be greater than, equal to, or smaller than the distances A4, A5, and A7.

As shown in FIG. 3, the outer protective cover 140 has a cylindrical large diameter portion 142, a cylindrical body portion 143 that is connected to the large diameter portion 142 and has a smaller diameter than the large diameter portion 142, and a tip portion 146 that is a bottomed tube with an inner diameter smaller than the body portion 143. The body portion 143 has a side portion 143a that has a side surface along the central axis direction (up and down direction) of the outer protective cover 140, and a step portion 143b that is the bottom of the body portion 143 and connects the side portion 143a and the tip portion 146. The central axes of the large diameter portion 142, the body portion 143, and the tip portion 146 are all the same as the central axis of the inner protective cover 130. The inner peripheral surface of the large diameter portion 142 abuts against the housing 102 and the large diameter portion 132, thereby fixing the outer protective cover 140 to the housing 102. The body 143 is positioned so as to cover the outer periphery of the first cylindrical portion 134 and the second cylindrical portion 136. The large diameter portion 142 and the body 143 may have the same diameter. The tip portion 146 is positioned so as to cover the tip portion 138, and the inner peripheral surface abuts against the outer peripheral surface of the connecting portion 137. The tip portion 146 has a side portion 146a having a side surface along the central axis direction (vertical direction) of the outer protective cover 140 and an outer diameter smaller than the inner diameter of the side portion 143a, a bottom portion 146b which is the bottom portion of the outer protective cover 140, and a tapered portion 146c which connects the side portion 146a and the bottom portion 146b and reduces in diameter from the side portion 146a to the bottom portion 146b. The tip portion 146 is positioned on the tip direction side (lower side) than the body 143. This outer protective cover 140 has one or more (in this embodiment, multiple, specifically 12) outer inlets 144a formed in the body 143, which are inlets for the measured gas from the outside, and one or more outer outlets 147a formed in the tip 146, which are outlets for the measured gas to the outside.

The outer inlet 144a is a hole that connects the outside (outside) of the outer protective cover 140 to the first gas chamber 122. The outer inlet 144a has a plurality of (six in this embodiment) horizontal holes 144b formed at equal intervals in the side portion 143a and a plurality of (six in this embodiment) vertical holes 144c formed at equal intervals in the step portion 143b (FIGS. 3 to 6). The outer inlet 144a (horizontal holes 144b and vertical holes 144c) are holes that are opened in a circular (perfect circle). The diameter of the 12 outer inlets 144a is, for example, 0.5 mm to 2 mm. The diameter of the outer inlet 144a may be 1.5 mm or less. In this embodiment, the diameters of the multiple horizontal holes 144b are all the same value, and the diameters of the multiple vertical holes 144c are all the same value. The diameter of the horizontal holes 144b is also set to a value larger than the diameter of the vertical holes 144c. As shown in Figures 4 and 5, the outer inlet 144a is formed such that the horizontal holes 144b and the vertical holes 144c are alternately positioned at equal intervals along the circumferential direction of the outer protective cover 140. That is, the angle between the line connecting the center of the horizontal hole 144b in Figures 4 and 5 to the central axis of the outer protective cover 140 and the line connecting the center of the vertical hole 144c adjacent to the horizontal hole 144b to the central axis of the outer protective cover 140 is 30° (360°/12 pieces).

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 vertical hole 147c formed in the center of the bottom 146b of the tip 146 (see Figures 3, 5, and 6). Unlike the outer inlet 144a, the outer outlet 147a is not disposed on 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 hole that is opened in a circular shape (a perfect circle). The diameter of the outer outlet 147a is, for example, 0.5 mm to 2.5 mm. The diameter of the outer outlet 147a may be 1.5 mm or less. In this embodiment, the diameter of the vertical hole 147c is set to a value larger than the diameters of the horizontal hole 144b and the vertical hole 144c.

The outer protective cover 140 and the inner protective cover 130 form a first gas chamber 122 as a space between the body 143 and the inner protective cover 130. More specifically, the first gas chamber 122 is a space surrounded by the step portion 133, the first cylindrical portion 134, the second cylindrical portion 136, the side portion 143a, and the step portion 143b. The sensor element chamber 124 is a space surrounded by the inner protective cover 130. The outer protective cover 140 and the inner protective cover 130 form a second gas chamber 126 as a space between the tip portion 146 and the inner protective cover 130. More specifically, the second gas chamber 126 is a space surrounded by the tip portion 138 and the tip portion 146. Note that since the inner peripheral surface of the tip portion 146 abuts against the outer peripheral surface of the connection portion 137, the first gas chamber 122 and the second gas chamber 126 are not directly connected.

7, the first gas chamber 122 has a first space 122a and a second space 122b. The first space 122a is a space between the outer protective cover 140 and the second member 135 of the inner protective cover 130, and functions as a flow path of the measurement gas from the outer inlet 144a upward. More specifically, the first space 122a is a space surrounded by the side portion 143a, the step portion 143b, and the second cylindrical portion 136, and is a space below the upper end of the second member 135 (here, the upper end of the second cylindrical portion 136). The first space 122a is a cylindrical gap between the inner circumferential surface of the outer protective cover 140 and the outer circumferential surface of the second cylindrical portion 136. The second space 122b is a space above the upper end of the second member 135 (here, the upper end of the second cylindrical portion 136) and between the outer protective cover 140 and the first member 131 (here, the first cylindrical portion 134). The second space 122b functions as a flow path for the measurement gas from the first space 122a to the element chamber inlet 127. The second space 122b is a cylindrical gap between the inner circumferential surface of the outer protective cover 140 and the outer circumferential surface of the first cylindrical portion 134.

The inlet of the measurement gas from the first space 122a to the second space 122b is called the second space inlet 122c. The second space inlet 122c is a ring-shaped gap between the inner circumferential surface of the outer protective cover 140 and the upper end of the outer circumferential surface of the second cylindrical portion 136. All of the outer inlets 144a are located below the second space inlet 122c. In other words, all of the outer inlets 144a are located below the upper end of the second member 135 (here, the upper end of the second cylindrical portion 136). The radial width of the second space inlet 122c, that is, the difference between the radius of the inner circumferential surface of the outer protective cover 140 and the radius of the upper end of the outer circumferential surface of the second cylindrical portion 136, is called the distance A1 (see FIG. 7). The cross-sectional area (opening area) of the second space inlet 122c is called the cross-sectional area As. The cross-sectional area As is the area of a surface perpendicular to the up-down direction. In this embodiment, the cross-sectional area As=(area of a circle having a diameter equal to the inner diameter of the side portion 143a)−(area of a circle having a diameter equal to the outer diameter of the second cylindrical portion 136). The distance A1 may be, for example, 1.18 mm or more, or 1.85 mm or less. The distance A1 may be a value equal to or greater than the distances A4, A5, and A7. The ratio A/A4 may be 1.0 or more and 3.63 or less. Similarly, the ratios A/A5 and A/A7 may be 1.0 or more and 3.63 or less. The cross-sectional area As may be, for example, 47.3 mm ² or more, or 68.1 mm ² or less.

The outer opening 128 described above is also an outlet (second space outlet) from the second space 122b to the element chamber inlet 127. The cross-sectional area (flow path cross-sectional area) of the element chamber inlet 127 is referred to as the cross-sectional area Bs. The cross-sectional area Bs is an area in a direction perpendicular to the direction (here, downward) of the measurement gas passing through the element chamber inlet 127. In addition, when the flow path cross-sectional area of the measurement gas in the element chamber inlet 127 is not constant, the minimum value is taken as the cross-sectional area Bs. For example, in this embodiment, the distances A4 and A5 are equal, so that the outer opening 128 and the element side opening 129 have the same opening area (=flow path cross-sectional area), but the flow path cross-sectional area of the part of the element chamber inlet 127 where the protruding portion 136a exists is smaller than these opening areas. Therefore, in this embodiment, the cross-sectional area of the element chamber inlet 127 at the cross section where the protruding portion 136a of the element chamber inlet 127 is most protruding, that is, the cross-sectional area of the element chamber inlet 127 at the cross section shown in FIG. 4 is taken as the cross-sectional area Bs. Therefore, in this embodiment, cross-sectional area Bs = (area of a circle whose diameter is the inner diameter of second cylindrical portion 136) - (area of a circle whose diameter is the outer diameter of first cylindrical portion 134) - (absolute value of reduction in cross-sectional area of element chamber inlet 127 due to protruding portions 136a in the cross section of Figure 4) x (number of protruding portions 136a). Cross-sectional area Bs may be, for example, 14.5 ^mm2 or more, or 33.4 ^mm2 or less.

In the second space 122b, the cross section when the measurement gas passes from the outside to the inside of the second member 135 (here, directly above the second cylindrical portion 136) (passing from left to right in FIG. 7) is called the flow passage cross section 122d. The vertical length of the flow passage cross section 122d is called the height C, and the cross-sectional area of the flow passage cross section 122d is called the cross-sectional area Cs. The cross-sectional area Cs is the same as the area of the outer circumferential surface of a cylinder of height C whose diameter is the same as the inner diameter of the second cylindrical portion 136. That is, the cross-sectional area Cs = (inner diameter of the second cylindrical portion 136) x π x (height C). The flow passage cross section 122d is a cross section of a surface perpendicular to the radial direction toward the center of the inner protective cover 130 in the second space 122b and a surface directly above the second cylindrical portion 136, and is defined as the cross section at the position directly above the second member 135 where the cross-sectional area is the smallest. For example, in this embodiment, the cross-sectional area of the second space 122b perpendicular to the radial direction is smaller directly above the inner peripheral surface of the second cylindrical portion 136 than directly above the outer peripheral surface of the second cylindrical portion 136. Therefore, the cross section of the second space 122b perpendicular to the radial direction of the inner protective cover 130 and directly above the inner peripheral surface of the second cylindrical portion 136 is defined as the flow path cross section 122d. The height C may be, for example, 0.47 mm or more, or 0.75 mm or more. The height C may be 2.35 mm or less, or 1.87 mm or less.

Within the second space 122b, a cross-sectional area perpendicular to the circumferential direction of the inner protective cover 130 is referred to as a cross-sectional area Ds. The cross-sectional area Ds is the area of the second space 122b (the area of a substantially rectangular shape) shown in the cross section of Fig. 7. In this embodiment, the cross-sectional area Ds = {(inner diameter of the side portion 143a) - (outer diameter of the first cylindrical portion 134)} ÷ 2 x (height C). In other words, the cross-sectional area Ds = {A 1 + A5 + (thickness of the second cylindrical portion 136)} x (height C).

The volume V of the second space 122b may be, for example, ⁴³ mm3 or more, or 70 ^mm3 or more. The volume V of the second space 122b may be, for example, ²²³ mm3 or less, or ¹⁷⁴ mm3 or less. In this embodiment, volume V = {(area of a circle whose diameter is the inner diameter of the side portion 143a) - (area of a circle whose diameter is the outer diameter of the first cylindrical portion 134)} x (height C).

Here, the flow of the measurement gas in the protective cover 120 when the gas sensor 100 detects the specific gas concentration will be described. The measurement gas flowing in the piping 20 first flows into the first gas chamber 122 through at least one of the multiple outer inlets 144a (horizontal hole 144b and vertical hole 144c). Next, the measurement gas flows from the first gas chamber 122 through the outer opening 128 into the element chamber inlet 127, and flows out of the element side opening 129 through the element chamber inlet 127 and into the sensor element chamber 124. At least a portion of the measurement gas that flows into the sensor element chamber 124 from the element side opening 129 reaches the gas inlet 111 of the sensor element 110. When the measurement gas reaches the gas inlet 111 and flows into the inside of the sensor element 110, the sensor element 110 generates an electrical signal (voltage or current) corresponding to the specific gas concentration in the measurement gas, and the specific gas concentration is detected based on this electrical signal. The gas to be measured in the sensor element chamber 124 flows into the second gas chamber 126 through at least one of the element chamber outlets 138a (horizontal holes 138b), and then flows out through the outer outlet 147a to the outside. The output of the internal heater of the sensor element 110 is controlled by, for example, a controller (not shown) so as to maintain a predetermined temperature.

Among the above-mentioned flows of the measurement gas, the flows in the first gas chamber 122 and the element chamber inlet 127 will be described in detail. The measurement gas that flows into the inside of the outer protective cover 140 from the outer inlet 144a first flows into the first space 122a of the first gas chamber 122 and flows upward in the first space 122a. Next, the measurement gas reaches the second space 122b from the second space inlet 122c, flows in the second space 122b from the outside to the inside of the second member 135, that is, flows radially in the second space 122b toward the central axis of the protective cover 120, and reaches the outer opening 128 of the element chamber inlet 127. Then, the measurement gas flows downward from the outer opening 128 in the element chamber inlet 127 and reaches the sensor element chamber 124 from the element side opening 129.

Generally, when the flow rate of the measurement gas is low (for example, less than 2 m/s), the flow rate of the measurement gas flowing in from the outer inlet 144a is small, so that the flow rate of the measurement gas flowing into the sensor element chamber 124 through the element chamber inlet 127 is also small, and the response of the specific gas concentration detection is likely to decrease. In contrast, in the gas sensor 100 of this embodiment, the above-mentioned cross-sectional area Cs is 14.0 mm ² or more, so that the measurement gas is likely to move from the outside to the inside of the second member 135 in the second space 122b. That is, the measurement gas in the first space 122a is likely to pass through the second space 122b and move toward the element chamber inlet 127. This makes it possible to increase the flow rate of the measurement gas reaching the element chamber inlet 127, and to suppress the decrease in the response of the specific gas concentration detection when the measurement gas flows at a low flow rate.

In addition, in the gas sensor 100 of this embodiment, the cross-sectional area Ds is ^6.4 mm2 or less, so that the deterioration of the response caused by the measurement gas flowing in the second space 122b along the circumferential direction of the inner protective cover 130 can be suppressed. Here, generally, when the measurement gas flows in the second space 122b along the circumferential direction of the inner protective cover 130, the time until the measurement gas passes through the second space 122b and reaches the element chamber inlet 127 becomes long, and the response may be deteriorated. In addition, generally, when there are multiple outer inlets 144a, the measurement gas may flow out to the outside from the outer inlet 144a located near the downstream side of the measurement gas flowing around the outer protective cover 140 among the multiple outer inlets 144a. For example, in FIG. 3, the measurement gas flows from left to right around the outer protective cover 140, so that the horizontal hole 144b and the vertical hole 144c shown on the right side of the sensor element 110 in FIG. 3 correspond to the outer inlet 144a located near the downstream side. The greater the flow rate of the measurement gas flowing in the second space 122b along the circumferential direction of the inner protective cover 130, the greater the flow rate of the measurement gas flowing out from the outer inlet 144a located near the downstream side. When the measurement gas flows out from the outer inlet 144a, the amount of measurement gas reaching the element chamber inlet 127 decreases accordingly, and the response of the specific gas concentration detection decreases. In this way, generally, the greater the flow rate of the measurement gas flowing in the second space 122b along the circumferential direction of the inner protective cover 130, the more likely the response of the specific gas concentration detection decreases. In contrast, in the gas sensor 100 of this embodiment, the cross-sectional area Ds is 6.4 mm ² or less, so that the measurement gas does not easily flow in the second space 122b along the circumferential direction of the inner protective cover 130. Therefore, the decrease in response caused by the measurement gas flowing in the second space 122b along the circumferential direction of the inner protective cover 130 can be suppressed. As described above, the gas sensor 100 of this embodiment can reduce the decrease in responsiveness when the flow rate of the measurement gas is low. As described above, it is preferable that the cross-sectional area Ds is small, but the cross-sectional area Ds may be ^0.5 mm2 or more.

According to the gas sensor 100 of this embodiment described above in detail, by setting the cross-sectional area Cs to 14.0 mm ² or more and the cross-sectional area Ds to 6.4 mm ² or less, it is possible to reduce a decrease in responsiveness when the flow velocity of the measurement gas is low.

Moreover, the cross-sectional area Cs is preferably 20.0 mm ² or more, more preferably 20.9 mm ² or more, even more preferably 22.9 mm ² or more, even more preferably 30 mm ² or more, and even more preferably 40 mm ² or more. The larger the cross-sectional area Cs, the easier it is for the measurement gas to move from the outside to the inside of the second member 135 in the second space 122b, so the effect of suppressing the decrease in responsiveness at a low flow rate of the measurement gas is enhanced. Furthermore, the cross-sectional area Ds is preferably 6.0 mm ² or less, more preferably 5.9 mm ² or less, even more preferably 5.0 mm ² or less, and even more preferably 4.0 mm ² or less. The smaller the cross-sectional area Ds, the more it is possible to suppress the measurement gas from flowing in the second space 122b along the circumferential direction of the inner protective cover 130, so the effect of suppressing the decrease in responsiveness at a low flow rate of the measurement gas is enhanced. The cross-sectional area Cs may be, for example, 73.1 ^mm2 or less, 70.0 ^mm2 or less, 60.0 ^mm2 or less, or 57.0 ^mm2 or less. The cross-sectional area Ds may be, for example, 1.2 ^mm2 or more, 1.5 ^mm2 or more, or ^2.0 mm2 or more.

Furthermore, the cross-sectional area ratio As/Bs between the cross-sectional area As and the cross-sectional area Bs is preferably 1.0 or more, and more preferably 1.41 or more and 4.70 or less. Here, if the cross-sectional area As is too small, the measured gas in the first space 122a does not easily flow into the second space 122b, and as a result, the measured gas does not easily flow into the element chamber inlet 127. Also, if the cross-sectional area Bs is too small, the measured gas in the second space 122b does not easily flow into the element chamber inlet 127. On the other hand, if the cross-sectional area ratio As/Bs is 1.41 or more and 4.70 or less, the cross-sectional areas As and Bs are well balanced in size, so that the measured gas in the first space 122a passes through the second space 122b and easily flows into the element chamber inlet 127, and the decrease in responsiveness at low flow rates of the measured gas can be further suppressed.

Furthermore, in the gas sensor 100, the first member 131 and the second member 135 form the element chamber inlet 127 so that the element side opening 129 opens downward. Therefore, it is possible to prevent the measurement gas flowing out from the element side opening 129 from hitting the surface of the sensor element 110 (surface other than the gas inlet 111) perpendicularly, or to prevent the measurement gas from passing a long distance on the surface of the sensor element 110 before reaching the gas inlet 111. This can prevent the sensor element 110 from cooling. Moreover, the sensor element 110 is prevented from cooling by adjusting the opening direction of the element side opening 129, and the flow rate or flow speed of the measurement gas in the inner protective cover 130 is not reduced, so the decrease in responsiveness of the specific gas concentration detection can also be reduced. As a result, the decrease in responsiveness of the sensor element 110 can be prevented while the decrease in heat retention can also be prevented.

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

For example, the shape of the protective cover 120 is not limited to the above embodiment. The shape of the protective cover 120, the shape, number, arrangement, etc. of the element chamber inlet 127, the element chamber outlet 138a, the outer inlet 144a, and the outer outlet 147a may be changed as appropriate. For example, the tip 146 of the outer protective cover 140 is a bottomed tube having a side 146a, a bottom 146b, and a tapered portion 146c, but may be a cylindrical shape with the tapered portion 146c omitted. In addition, the tip 138 of the inner protective cover 130 is shaped so that the outer diameter of the side 138d is constant and the side 138d and the bottom 138e have the same diameter, but may be shaped so that the outer diameter of the side 138d becomes smaller as it approaches the bottom 138e, such as an inverted truncated cone shape. FIG. 8 is a longitudinal sectional view (corresponding to the B-B sectional view of the gas sensor 100) of the gas sensor 200 in which the tip 146 of the outer protective cover 140 is cylindrical with the tapered portion 146c omitted, and the tip 138 of the inner protective cover 130 is shaped like an inverted truncated cone. FIG. 8 also shows an enlarged view of the periphery of the second space 122b. FIG. 9 is a sectional view of the outer protective cover 240 of FIG. 8 along the line F-F, and FIG. 10 is a view seen from the direction G of FIG. 8. In FIGS. 8 to 10, the same components as those in the gas sensor 100 are given the same reference numerals, and detailed description thereof will be omitted. As shown in FIG. 8, the protective cover 220 of the gas sensor 200 includes an inner protective cover 230 instead of the inner protective cover 130, and an outer protective cover 240 instead of the outer protective cover 140. The second member 235 of the inner protective cover 230 includes a tip 238 shaped like an inverted truncated cone instead of the tip 138 and the step portion 139. The tip 238 is also provided with an element chamber outlet 238a which is connected to the sensor element chamber 124 and the second gas chamber 126 and is an outlet for the measured gas from the sensor element chamber 124. The element chamber outlet 238a has one circular vertical hole formed in the center of the bottom surface of the tip 238. The outer protective cover 240 has a tip 246 which is a bottomed tubular (cylindrical) shape and has a smaller inner diameter than the body 143, instead of the tip 146. The tip 246 has a side portion 246a which has a side surface along the central axis direction of the outer protective cover 240 (the vertical direction in FIG. 8) and has an outer diameter smaller than the inner diameter of the side portion 143a, and a bottom portion 246b which is the bottom of the outer protective cover 240. The tip 246 is also provided with an outer outlet 247a which is an outlet for the measured gas to the outside. The outer outlet 247a has a plurality of (six in this embodiment) vertical holes 247c formed at equal intervals along the circumferential direction of the outer protective cover 240 in the bottom 246b of the tip portion 246 (see FIGS. 8, 9 and 10). With this gas sensor 200 as well, the same effects as those of the above-described embodiment can be obtained by setting the cross-sectional area Cs to 14.0 ^mm2 or more and the cross-sectional area Ds to ^6.4 mm2 or less.

In the above embodiment, the element chamber inlet 127 is a cylindrical gap between the first cylindrical portion 134 of the first member 131 and the second cylindrical portion 136 of the second member 135, but the element chamber inlet may have any shape as long as it is a gap between the first member 131 and the second member 135. For example, the element chamber inlet may be a gap inclined from the vertical direction of FIG. 3 (see also FIG. 12 described later). The number of element chamber inlets 127 is not limited to one, but may be multiple (see also FIG. 11 described later). The element chamber outlet 138a, the outer inlet 144a, and the outer outlet 147a are not limited to holes, but may be gaps between multiple members constituting the protective cover 120, and each number may be one or more. The outer inlet 144a has a horizontal hole 144b and a vertical hole 144c, but may have only one of them. In addition to or instead of the horizontal hole 144b and the vertical hole 144c, a square hole may be formed at the corner of the boundary between the side portion 143a and the step portion 143b. Similarly, the element chamber outlet 138a and the outer outlet 147a may have one or more of a horizontal hole, a vertical hole, and a rectangular hole. The outer outlet 147a may have a through hole provided in the tapered portion 146c.

In the above embodiment, the protrusion 136a is formed on the inner peripheral surface of the second cylindrical portion 136, but this is not limited thereto. It is sufficient that a plurality of protrusions are formed on at least one of the outer peripheral surface of the first cylindrical portion 134 and the inner peripheral surface of the second cylindrical portion 136, protruding toward the other surface and contacting the surface. In addition, in the above embodiment, as shown in Figures 3 and 4, the outer peripheral surface of the second cylindrical portion 136 where the protrusion 136a is formed is recessed inward, but this is not limited thereto and the outer peripheral surface does not have to be recessed. In addition, the protrusion 136a is not limited to a hemispherical shape and may have any shape. Note that the protrusion 136a does not have to be formed on the outer peripheral surface of the first cylindrical portion 134 and the inner peripheral surface of the second cylindrical portion 136.

In the above embodiment, the element chamber inlet 127 is a cylindrical gap between the outer peripheral surface of the first cylindrical portion 134 and the inner peripheral surface of the second cylindrical portion 136, but is not limited thereto. For example, a recess (groove) may be formed on at least one of the outer peripheral surface of the first cylindrical portion and the inner peripheral surface of the second cylindrical portion, and the element chamber inlet may be a gap between the first cylindrical portion and the second cylindrical portion formed by the recess. FIG. 11 is a cross-sectional view showing an element chamber inlet 327 of a modified example. As shown in FIG. 11, the outer peripheral surface of the first cylindrical portion 334 and the inner peripheral surface of the second cylindrical portion 336 are in contact with each other, and a plurality of recesses 334a (four in FIG. 11) are formed at equal intervals on the outer peripheral surface of the first cylindrical portion 334. The gap between the recesses 334a and the inner peripheral surface of the second cylindrical portion 336 is the element chamber inlet 327. When there are a plurality of element chamber inlets (four in FIG. 11) like this element chamber inlet 327, the sum of the cross-sectional areas of the element chamber inlets, i.e., the total cross-sectional area, is taken as the cross-sectional area Bs.

In the above-described embodiment, the element chamber inlet 127 is a flow path parallel to the rear end-front end direction of the sensor element 110 (a flow path parallel to the vertical direction in FIG. 3), but is not limited thereto. For example, the element chamber inlet may be a flow path inclined from the vertical direction so as to approach the sensor element 110 as it goes downward. FIG. 12 is a vertical cross-sectional view of a gas sensor 400 of a modified example in this case. FIG. 12 also shows an enlarged view of the periphery of the second space 122b. In FIG. 12, the same components as those of the gas sensors 100 and 200 are given the same reference numerals, and detailed description thereof will be omitted. As shown in FIG. 12, the protective cover 420 of the gas sensor 400 includes an inner protective cover 430 instead of the inner protective cover 230. The inner protective cover 430 includes a first member 431 and a second member 435. The first member 431 does not include the first cylindrical portion 134 as compared to the first member 131, but includes a cylindrical body portion 434a and a cylindrical first cylindrical portion 434b whose diameter decreases toward the bottom. The first cylindrical portion 434b is connected to the body portion 434a at the upper end. The second member 435 does not include the second cylindrical portion 136 and the connecting portion 137 as compared to the second member 235, but includes a cylindrical second cylindrical portion 436 whose diameter decreases toward the bottom. The second cylindrical portion 436 is connected to the tip portion 238. The outer peripheral surface of the first cylindrical portion 434b and the inner peripheral surface of the second cylindrical portion 436 are not in contact with each other, and the gap formed by the two is the element chamber inlet 427. The element chamber inlet 427 has an outer opening 428 which is an opening on the first gas chamber 122 side, and an element side opening 429 which is an opening on the sensor element chamber 124 side. The element chamber inlet 427 is a flow path that is inclined from the vertical direction so as to approach the sensor element 110 as it goes downward (so as to approach the central axis of the inner protective cover 430) due to the shapes of the first cylindrical portion 434b and the second cylindrical portion 436. Similarly, the element side opening 429 opens at an incline from the vertical direction so as to approach the sensor element 110 as it goes downward (see the enlarged view of FIG. 12). In this way, when the element chamber inlet 427 is a flow path that is inclined with respect to the vertical direction or when the element side opening 429 opens at an incline with respect to the vertical direction, the flow direction of the measurement gas flowing from the element side opening 429 to the sensor element chamber 124 becomes an inclined direction from the vertical direction. This provides the same effect as the element chamber inlet 127 and the element side opening 129 of the above-mentioned embodiment. That is, it is possible to prevent the measurement gas from hitting the surface of the sensor element 110 (surface other than the gas inlet 111) perpendicularly, or to prevent the measurement gas from passing a long distance over the surface of the sensor element 110 before reaching the gas inlet 111. This prevents the sensor element 110 from cooling down. 12, the width of the element chamber inlet 427 narrows toward the bottom of the sensor element 110. Therefore, the opening area of the element side opening 429 is smaller than the opening area of the outer opening 428. In other words, the element chamber inlet 427 is smaller at the distance A4 than the distance A5 described with reference to FIG. 7. As a result, the measurement gas flows in from the outer opening 428 and flows out from the element side opening 429, so that the flow rate of the measurement gas increases when it flows out compared to when it flows in. Therefore, the response of the specific gas concentration detection can be improved. In this gas sensor 400, the space between the outer protective cover 240 and the second cylindrical portion 436 of the second member 435 is the first space 122a. Moreover, the space above the upper end of the second cylindrical portion 436 and between the outer protective cover 240 and the body portion 434a of the first member 431 is the second space 122b. In Fig. 12, the element chamber inlet 427 is a flow path inclined from the vertical direction, the element side opening 429 opens at an incline from the vertical direction, and the opening area of the element side opening 429 is smaller than the opening area of the outer opening 428, but one or more of these three features may be omitted, or the gas sensor may have one or more of these three features. In such a gas sensor 400, the same effect as the above-mentioned embodiment can be obtained by setting the cross-sectional area Cs to 14.0 mm2 ^or more and the cross-sectional area Ds to ^6.4 mm2 or less. In the gas sensor 400 in Fig. 12, the tip 246 of the outer protective cover 240 is cylindrical in shape without a tapered portion, and the tip 238 of the inner protective cover 430 is in the shape of an inverted truncated cone, as in the gas sensor 200, but instead, the gas sensor 400 may have the tip 138, the step portion 139, and the tip 146 as in the gas sensor 100.

In the above-described embodiment, the element side opening 129 opens downward, but this is not limited thereto, and it may open into the sensor element chamber 124 in a direction perpendicular to the downward direction, for example.

In the above embodiment, the surface that defines the upper end of the second space 122b is the lower surface of the step portion 133 of the first member 131, but this is not limited to this. For example, the lower surface of the housing 102 may be the surface that defines the upper end of the second space 122b.

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

In the above embodiment, the gas inlet 111 is open to the tip surface of the sensor element 110 (the bottom surface of the sensor element 110 in FIG. 3), but this is not limited to this. For example, it may be open to the side surface of the sensor element 110 (the top, bottom, left, and right surfaces of the sensor element 110 in FIG. 4).

In the above-described embodiment, the sensor element 110 is provided with a porous protective layer 110a, but may not be provided with the porous protective layer 110a.

In the above embodiment, the protective cover 120 is described as part of the gas sensor 100, but the protective cover 120 may be distributed separately.

Although not described in the above embodiment, it is preferable that the gas sensor 100 satisfies both the following first and second conditions. The first condition is that each of the outer inlet 144a, the element chamber outlet 138a, and the outer outlet 147a has at least one hole through which a sphere with a diameter of 1.5 mm can pass. The second condition is that the width of the flow path of the measurement gas in the protective cover 120 is adjusted so that a sphere with a diameter of 0.8 mm can reach from the outer inlet 144a to the gas inlet 111. In other words, the second condition is that the minimum value of the flow path width (referred to as the minimum flow path width) of the flow paths through which the measurement gas must pass between the outer inlet 144a and the gas inlet 111 is 0.8 mm or more. For example, in the gas sensor 100 of the above embodiment, when the distance A6 shown in FIG. 7 is smaller than any of the distances A4, A5, and A7 shown in FIGS. 4 and 7, the minimum flow path width is the value of the distance A6. In this case, if the distance A6 is 0.8 mm or more, the second condition is satisfied. The measurement gas flowing through the pipe 20 may contain soot, and by satisfying both the first and second conditions, the soot resistance of the gas sensor 100 is improved. For example, when the distance A6 is less than 0.8 mm, soot may clog the gap between the lower end of the first cylindrical portion 134 and the connecting portion 137. In contrast, when the distance A6 is 0.8 mm or more, such clogging by soot can be suppressed. The effect of improving the soot resistance by satisfying both the first and second conditions can be obtained regardless of whether the cross-sectional area Cs is 14.0 mm ² or more and whether the cross-sectional area Ds is 0.5 mm ² or more and 6.4 mm ² or less. In addition, not only the gas sensor 100 but also gas sensors equipped with protective covers of other shapes such as the various modified examples described above can have the effect of improving the soot resistance by satisfying both the first and second conditions. For example, in the gas sensor 100, when the minimum value of the distances A4, A5, and A7 is smaller than the distance A6 shown in FIG. 7, the minimum flow path width is the minimum value. In this case, if the minimum value is 0.8 mm or more (in other words, if the distances A4, A5, and A7 are all 0.8 mm or more), the second condition is satisfied. In this case, if the first condition is also satisfied, the effect of improving soot resistance can be obtained. In addition, when the outer inlet 144a has a plurality of holes, in order to satisfy the first condition, it is sufficient that one or more holes through which a 1.5 mm diameter ball can pass exist among the plurality of holes, but it is preferable that the number of holes through which a 1.5 mm diameter ball can pass occupies 60% or more of the plurality of holes, or that the total opening area of the holes through which a 1.5 mm diameter ball can pass occupies 60% or more of the total opening area of the plurality of holes. The same applies to the element chamber outlet 138a and the outer outlet 147a. In addition to the first and second conditions, it is preferable to also satisfy the following third condition. The third condition is that the width of the flow path of the measurement gas inside the protective cover 120 is adjusted so that a sphere having a diameter of 0.8 mm can reach from the gas inlet 111 to the outer outlet 147a.

Specific examples of gas sensors that have been fabricated are described below as examples. Experimental Examples 2 to 4, 6 to 8, 10 to 12, 14 to 16, 18, and 19 correspond to examples of the present invention, and Experimental Examples 1, 5, 9, 13, and 17 correspond to comparative examples. Note that the present invention is not limited to the following examples.

[Experimental Example 1]
8 to 10 was used as Experimental Example 1. Specifically, the first member 131 of the inner protective cover 230 had a plate thickness of 0.3 mm, an axial length of 10.2 mm, an axial length of the large diameter portion 132 of 1.8 mm, an outer diameter of the large diameter portion 132 of 14.4 mm, an axial length of the first cylindrical portion 134 of 8.4 mm, an outer diameter of the first cylindrical portion 134 of 8.48 mm, and a radius Br2 of the outer diameter of the first cylindrical portion 134 of 4.24 mm. The second member 235 had a plate thickness of 0.3 mm, an axial length of 11.5 mm, an axial length of the second cylindrical portion 136 of 4.941 mm, an inner diameter of the second cylindrical portion 136 of 9.7 mm, an outer radius Ar2 of the second cylindrical portion 136 of 5.15 mm, an inner radius Br1 of the second cylindrical portion 136 of 4.85 mm, an axial length of the tip portion 238 of 4.9 mm, and a diameter of the bottom surface of the tip portion 238 of 3.0 mm. The diameter of the element chamber outlet 238a was 1.5 mm. The outer protective cover 240 had a plate thickness of 0.4 mm, an axial length of 24.35 mm, an axial length of the large diameter portion 142 of 5.75 mm, an outer diameter of the large diameter portion 142 of 15.2 mm, an axial length of the body portion 143 of 9.0 mm (an axial length from the upper end of the body portion 143 to the upper surface of the step portion 143b of 8.7 mm), an outer diameter of the body portion 143 of 14.6 mm, an inner diameter radius Ar1 of the body portion 143 of 6.9 mm, an axial length of the tip portion 246 of 9.6 mm, and an outer diameter of the tip portion 246 of 8.7 mm. The outer inlet 144a had six horizontal holes 144b with a diameter of 1.5 mm and six vertical holes 144c with a diameter of 1 mm, which were alternately formed at equal intervals (an angle between adjacent holes of 30°). The outer outlet 247a does not have a horizontal hole, but has six vertical holes 247c, and the diameter of the vertical holes 247c is 1 mm. The material of the protective cover 220 is SUS310S. The sensor element 110 of the gas sensor 200 has a width (horizontal length in FIG. 4) of 4 mm and a thickness (vertical length in FIG. 4) of 1.5 mm. The porous protective layer 110a is made of alumina porous body and has a thickness of 400 μm. The height C of the second space 122b is 3.759 mm, the cross-sectional area As is 66.2 mm ² , the cross-sectional area Bs is 15.9 mm ² , the cross-sectional area Cs is 114.5 mm ² , and the cross-sectional area Ds is 10.0 mm ^2. The cross-sectional area ratio As/Bs is 4.2, and the volume V of the second space 122b is 349.94 mm ³ .

[Experimental Example 2]
Experimental Example 2 was a gas sensor 200 similar to Experimental Example 1, except that the height C was set to 2.2 mm by increasing the axial length of the second cylindrical portion 136 (6.5 mm). In Experimental Example 2, the cross-sectional area As was set to ^66.2 mm2, the cross-sectional area Bs was set to 15.9 ^mm2 , the cross-sectional area Cs was set to 67.0 ^mm2 , the cross-sectional area Ds was set to 5.9 ^mm2 , the cross-sectional area ratio As/Bs was set to 4.2, and the volume V was set to 204.80 ^mm3 .

[Experimental Example 3]
3 to 7 was used as Experimental Example 3. Specifically, the first member 131 of the inner protective cover 130 had a plate thickness of 0.3 mm, an axial length of 10.2 mm, an axial length of the large diameter portion 132 of 1.8 mm, an outer diameter of the large diameter portion 132 of 14.4 mm, an axial length of the first cylindrical portion 134 of 8.4 mm, an outer diameter of the first cylindrical portion 134 of 8.48 mm, and a radius Br2 of the outer diameter of the first cylindrical portion 134 of 4.24 mm. The second member 135 had a plate thickness of 0.3 mm, an axial length of 15.1 mm, an axial length of the second cylindrical portion 136 of 7.326 mm, an inner diameter of the second cylindrical portion 136 of 9.7 mm, an outer diameter radius Ar2 of the second cylindrical portion 136 of 5.15 mm, an inner diameter radius Br1 of the second cylindrical portion 136 of 4.85 mm, an axial length of the tip portion 138 of 4.9 mm, and an outer diameter of a side portion 138d of the tip portion 138 of 5.6 mm. The element chamber outlet 138a had four lateral holes 138b with a diameter of 1.5 mm formed at equal intervals. The outer protective cover 140 has a plate thickness of 0.4 mm, an axial length of 24.35 mm, an axial length of the large diameter portion 142 of 5.75 mm, an outer diameter of the large diameter portion 142 of 15.2 mm, an axial length of the body portion 143 of 9.0 mm (an axial length from the upper end of the body portion 143 to the upper surface of the step portion 143b of 8.7 mm), an outer diameter of the body portion 143 of 14.6 mm, an inner diameter radius Ar1 of the body portion 143 of 6.9 mm, an axial length of the tip portion 146 of 9.6 mm, an axial length of the side portion 146a of the tip portion 146 of 6.9 mm, an outer diameter of the tip portion 146 of 8.7 mm, and a diameter of the bottom portion 146b of the tip portion 146 of 2.6 mm. The outer inlet 144a has six horizontal holes 144b with a diameter of 1.5 mm and six vertical holes 144c with a diameter of 1.0 mm, which are alternately formed at equal intervals. The diameter of the outer outlet 147a (vertical hole 147c) was 2.0 mm. The material of the protective cover 120 was SUS310S. The sensor element 110 of the gas sensor 100 had a width (horizontal length in FIG. 4) of 4 mm and a thickness (vertical length in FIG. 4) of 1.5 mm. The porous protective layer 110a was made of alumina porous body and had a thickness of 400 μm. In the experimental example 3, the height C was 1.374 mm, the cross-sectional area As was 66.2 mm ² , the cross-sectional area Bs was 15.9 mm ² , the cross-sectional area Cs was 41.9 mm ² , the cross-sectional area Ds was 3.7 mm ² , the cross-sectional area ratio As/Bs was 4.2, and the volume V was 127.91 mm ³ .

[Experimental Example 4]
Experimental Example 4 was the same gas sensor 100 as Experimental Example 3, except that the axial length of the second cylindrical portion 136 was increased (8.015 mm) to set the height C to 0.685 mm. In Experimental Example 4, the cross-sectional area As was 66.2 ^mm2 , the cross-sectional area Bs was 15.9 ^mm2 , the cross-sectional area Cs was 20.9 ^mm2 , the cross-sectional area Ds was 1.8 ^mm2 , the cross-sectional area ratio As/Bs was 4.2, and the volume V was 63.77 ^mm3 .

[Experimental Examples 5 to 8]
Experimental Examples 5 to 8 were gas sensors identical to those of Experimental Examples 1 to 4, except that the diameters of the second cylindrical portion 136 were changed so that the radius Ar2 was 5.3 mm and the radius Br1 was 5.0 mm.

[Experimental Examples 9 to 12]
Experimental Examples 9 to 12 were the same gas sensors as Experimental Examples 1 to 4, except that the diameters of the second cylindrical portion 136 were changed to a radius Ar2 of 5.45 mm and a radius Br1 of 5.15 mm.

[Experimental Examples 13 to 16]
Experimental Examples 13 to 16 were gas sensors similar to those of Experimental Examples 1 to 4, except that the diameters of the second cylindrical portion 136 were changed so that the radius Ar2 was 5.6 mm and the radius Br1 was 5.3 mm.

[Experimental Examples 17 to 19]
Experimental Examples 17 to 19 were gas sensors similar to those of Experimental Examples 1 to 3, except that the diameters of the second cylindrical portion 136 were changed to set the radius Ar2 to 5.75 mm and the radius Br1 to 5.45 mm.

[Evaluation of responsiveness and heat retention]
The gas sensors of Experimental Examples 1 to 19 were attached to the pipes as in Figs. 1 and 2. The gas to be measured was a gas adjusted to an arbitrary oxygen concentration by mixing oxygen with the atmosphere, and this gas to be measured was flowed through the pipes at a flow rate of 0.73 m/s. Then, the change in the output of the sensor element over time was examined when the oxygen concentration of the measured gas flowing through the pipes was changed from 23.6% to 20.9%. The output value of the sensor element immediately before the oxygen concentration was changed was set to 0%, and the output value when the output of the sensor element changed and stabilized after the oxygen concentration change was set to 100%, and the elapsed time from when the output value exceeded 10% to when it exceeded 90% was set as the response time (sec) of the specific gas concentration detection. The shorter this response time, the higher the response of the specific gas concentration detection. The response time was measured multiple times for each experimental example, and the average value of each was set as the response time for each experimental example. For each of Experimental Examples 1 to 19, the response time was also measured in the same manner when the flow rate of the measured gas was set to 1 m/s. For each of Experimental Examples 1 to 4, the response time was also measured in the same manner when the flow velocity of the measured gas was set to 2 m/s and 4 m/s. For Experimental Examples 1 and 2, the response time was also measured in the same manner when the flow velocity of the measured gas was set to 8 m/s.

Table 1 summarizes the evaluation results of the radii Ar1, Ar2, Br1, and Br2, height C, cross-sectional areas As to Ds, cross-sectional area ratio As/Bs, volume V, response time, and responsiveness of the gas sensors of Experimental Examples 1 to 19. In Table 1, the response time when the flow velocity of the measured gas is 1 m/s is used to evaluate the responsiveness, and the response is judged to be very good (A) when the response time is 2.5 seconds or less, good (B) when the response time is 3 seconds or less, and poor (F) when the response time exceeds 3 seconds. FIG. 13 is a graph showing the relationship between the flow velocity and the response time of each of Experimental Examples 1 to 4. FIG. 14 is a graph showing the relationship between the height C of each of Experimental Examples 1 to 4 and the response time at a flow velocity of 1 m/s. FIG. 14 also shows an approximation curve (approximation by a third-order polynomial) showing the relationship between the height C and the response time. Based on this approximation curve, the height C at which the response time becomes 3 seconds and the height C at which the response time becomes 2.5 seconds were calculated, and are also shown in FIG. 14. In addition, in all of Experimental Examples 1 to 4, the cross-sectional areas Cs, Ds, and volume V were changed by changing only the height C, so the cross-sectional areas Cs, Ds, and volume V all have values proportional to the height C. In other words, the relationship between the cross-sectional areas Cs, Ds, and volume V and the response time is the same as that in the graph of FIG. 14, except that the values on the horizontal axis are different. Therefore, FIG. 14 also shows the values of the cross-sectional areas Cs, Ds, and volume V that result in a response time of 3 seconds, and the values of the cross-sectional areas Cs, Ds, and volume V that result in a response time of 2.5 seconds.

As shown in Table 1 and FIG. 13, it was found that in all of Experimental Examples 1 to 4, the response time tends to be longer (response is reduced) as the flow velocity is lower. In addition, there is almost no difference in the response time between Experimental Examples 1 to 4 when the flow velocity is 2 m/s or more, but the difference in the response time between Experimental Examples 1 to 4 becomes larger when the flow velocity is less than 2 m/ s . In addition, as shown in Table 1 and FIG. 13, the response time is shorter in Experimental Examples 2 to 4 than in Experimental Example 1, and in particular, the response time of Experimental Example 3 was the shortest. In addition, as can be seen from the approximation curve in FIG. 14, it was found that the response time becomes longer when the values of height C, cross-sectional area Cs, cross-sectional area Ds, and volume V are too large or small. The reason why the response time becomes longer when height C, cross-sectional area Cs, cross-sectional area Ds, and volume V are too small is thought to be due to the cross-sectional area Cs being too small. That is, as described above, if the cross-sectional area Cs is too small, the measurement gas does not easily move from the outside to the inside of the second member in the second space 122b (does not easily move toward the radial inside of the protective cover), and therefore the responsiveness is considered to be reduced. In addition, the reason why the response time is long when the height C, cross-sectional area Cs, cross-sectional area Ds, and volume V are too large is considered to be that the cross-sectional area Ds is particularly large. That is, as described above, if the cross-sectional area Ds is too large, the measurement gas tends to flow in the second space 122b along the circumferential direction of the inner protective cover, and therefore the responsiveness is considered to be reduced. And, from the relationship between the approximation curve in FIG. 14 and the response time, if the cross-sectional area Cs is 14.0 mm ² or more and the cross-sectional area Ds is 6.4 mm ² or less, the response time at a flow velocity of 1 m/s is 3 seconds or less, and the decrease in responsiveness at a low flow velocity of the measurement gas can be reduced. Furthermore, if the cross-sectional area Cs is 22.9 ^mm2 or more and the cross-sectional area Ds is ^5.0 mm2 or less, the response time at a flow velocity of 1 m/s is 2.5 seconds or less, and it is considered that the decrease in responsiveness when the flow velocity of the measured gas is low can be further reduced.

14, the numerical range of the height C corresponding to "cross-sectional area Cs is 14.0 ^mm2 or more and cross-sectional area Ds is 6.4 mm2 ^or less" was 0.46 mm or more and 2.40 mm or less, and the numerical range of the corresponding volume V was 43 mm3 ^or more and ²²³ mm3 or less. The numerical range of the height C corresponding to "cross-sectional area Cs is 22.9 mm2 ^or more and cross-sectional area Ds is 5.0 ^mm2 or less" was 0.75 mm or more and 1.87 mm or less, and the numerical range of the corresponding volume V was 70 mm3 ^or more and 174 ^mm3 or less.

As with Experimental Examples 1 to 4, Experimental Examples 5 to 19 also showed a tendency that the response time became longer (response decreased) as the flow velocity became lower. As with Experimental Examples 1 to 4, Experimental Examples 5 to 19 also showed a tendency between the values of the cross-sectional area Cs and the cross-sectional area Ds and the responsiveness at low flow velocity. For example, Experimental Examples 6 to 8, 10 to 12, 14 to 16, 18, and 19, in which the cross-sectional area Cs was 14.0 mm ² or more and the cross-sectional area Ds was 6.4 mm ² or less, had a response time of 3 seconds or less at a flow velocity of 1 m/s (response evaluation of "B" or more). In addition, when comparing Experimental Examples 5 to 8, which have the same cross-sectional area As and the same cross-sectional area Bs, Experimental Example 7, which satisfies the conditions that the cross-sectional area Cs is 22.9 mm ² or more and the cross-sectional area Ds is 5.0 mm ² or less, had the shortest response time. Similarly, when comparing Experimental Examples 9 to 12, Experimental Example 11, which satisfied the conditions that the cross-sectional area Cs was 22.9 mm ² or more and the cross-sectional area Ds was 5.0 mm ² or less, had the shortest response time. When comparing Experimental Examples 13 to 16, Experimental Example 15, which satisfied the conditions that the cross-sectional area Cs was 22.9 mm ² or more and the cross-sectional area Ds was 5.0 mm ² or less, had the shortest response time at a flow velocity of 0.73 m/s. Note that the response time at a flow velocity of 1 m/s was shorter in Experimental Example 14 than in Experimental Example 15, but this difference was small and considered to be an error. When comparing Experimental Examples 17 to 19, the response time at a flow velocity of 1 m/s was the same for Experimental Example 18 and Experimental Example 19, which satisfied the conditions that the cross-sectional area Cs was 22.9 mm ² or more and the cross-sectional area Ds was 5.0 mm ² or less, but the response time at a flow velocity of 0.73 m/s was the shortest among Experimental Examples 17 to 19. Therefore, overall, it was confirmed that among Experimental Examples 17 to 19, Experimental Example 19 tended to have the shortest response time.

In addition, among the experimental examples 2 to 4, 6 to 8, 10 to 12, 14 to 16, 18, and 19 in which the cross-sectional area Cs is 14.0 mm ² or more and the cross-sectional area Ds is ^6.4 mm 2 or less, the experimental examples 2 to 4 in which the cross-sectional area As and the cross-sectional area ratio As/Bs are the same are classified as the first group, the experimental examples 6 to 8 are classified as the second group, the experimental examples 10 to 12 are classified as the third group, the experimental examples 14 to 16 are classified as the fourth group, and the experimental examples 18 and 19 are classified as the fifth group. When comparing the first to fifth groups, it was confirmed that the first to fourth groups in which the cross-sectional area As is in the range of 47.3 mm ² or more and 68.1 mm ² or less tend to have a shorter response time at low flow rates compared to the fifth group in which the cross-sectional area As is outside this range. Therefore, it is considered that the cross-sectional area As is preferably 47.3 mm ² or more and 68.1 mm ² or less. However, even in the fifth group, the evaluation of the responsiveness was " A ", and the effect of reducing the decrease in responsiveness when the flow velocity of the gas to be measured is low is obtained.

20 piping, 22 fixing member, 100, 200, 400 gas sensor, 102 housing, 103 bolt, 110 sensor element, 110a porous protective layer, 111 gas inlet, 120, 220, 420 protective cover, 122 first gas chamber, 122a first space, 122b second space, 122c second space inlet, 122d flow passage cross section, 124 sensor element chamber, 126 second gas chamber, 127, 327, 427 element chamber inlet, 128, 428 outer opening, 129, 429 element side opening, 130, 230, 430 inner protective cover, 131, 431 first member, 132 large diameter portion, 133 step portion, 134, 334 first cylindrical portion, 135, 235, 435 Second member, 136, 336, 436 Second cylindrical portion, 136a Protruding portion, 137 Connection portion, 138, 238 Tip portion, 138a, 238a Element chamber outlet, 138b Horizontal hole, 138d Side portion, 138e Bottom portion, 139 Step portion, 140, 240 Outer protective cover, 142 Large diameter portion, 143 Body portion, 143a Side portion, 143b Step portion, 144a Outer inlet, 144b Horizontal hole, 144c Vertical hole, 146, 246 Tip portion, 146a, 246a Side portion, 146b, 246b Bottom portion, 146c Tapered portion, 147a, 247a Outer outlet, 147c, 247c Vertical hole, 334a Recess, 434a Body portion, 434b First cylindrical section.

Claims (9)

a sensor element having a gas inlet for introducing a gas to be measured and capable of detecting a specific gas concentration of the gas to be measured that has flowed into the sensor element through the gas inlet;
a cylindrical inner protective cover having a sensor element chamber therein in which the tip of the sensor element and the gas inlet are disposed, the sensor element chamber having one or more element chamber inlets which are inlets to the sensor element chamber and one or more element chamber outlets which are outlets from the sensor element chamber;
a cylindrical outer protective cover provided with one or more outer inlets which are inlets for the measurement gas from the outside and one or more outer outlets which are outlets for the measurement gas to the outside, the outer protective cover being disposed outside the inner protective cover;
Equipped with
the outer protective cover and the inner protective cover define, as a space therebetween, a first gas chamber which functions as a flow path for the measurement gas between the outer inlet and the element chamber inlet, and a second gas chamber which functions as a flow path for the measurement gas between the outer outlet and the element chamber outlet and does not directly communicate with the first gas chamber,
the inner protective cover has a cylindrical first member surrounding the sensor element and a cylindrical second member surrounding the first member,
the first member and the second member define the element chamber inlet as a gap therebetween,
a direction parallel to the axial direction of the inner protective cover and from the front end to the rear end of the sensor element is defined as an upward direction, and a direction from the rear end to the front end of the sensor element is defined as a downward direction, and the first gas chamber has: a first space which is a space between the outer protective cover and the second member and functions as a flow path of the measurement gas from the outer inlet toward the upward direction; and a second space which is a space above an upper end of the second member and between the outer protective cover and the first member and functions as a flow path of the measurement gas from the first space to the element chamber inlet,
a cross-sectional area Cs of the second space, which is a flow path cross-sectional area when the measurement gas passes directly above the second member from the outside to the inside of the second member, is 14.0 ^mm2 or more,
A cross-sectional area Ds, which is a cross-sectional area perpendicular to the circumferential direction of the inner protective cover in the second space, is 0.5 mm ² or more and 6.4 mm ² or less.
Gas sensor. The cross-sectional area Cs is 22.9 mm ² or more.
2. The gas sensor according to claim 1. The cross-sectional area Ds is 5.0 ^mm2 or less.
3. The gas sensor according to claim 1 or 2. a cross-sectional area ratio As/Bs of a cross-sectional area As of a second space inlet which is an inlet for the measurement gas from the first space to the second space to a cross-sectional area Bs which is a total cross-sectional area of the one or more element chamber inlets is 1.41 or more and 4.70 or less;
The gas sensor according to any one of claims 1 to 3. a cross-sectional area As of a second space inlet, which is an inlet for the measurement gas from the first space to the second space, is 47.3 ^mm2 or more and 68.1 ^mm2 or less;
The gas sensor according to any one of claims 1 to 4. a cross-sectional area Bs, which is a total cross-sectional area of the one or more element chamber inlets, is 14.5 mm2 ^or more and 33.4 ^mm2 or less;
The gas sensor according to any one of claims 1 to 5. the first member and the second member form the element chamber inlet such that an element side opening, which is an opening of the element chamber inlet on the sensor element chamber side, opens in the downward direction,
The gas sensor according to any one of claims 1 to 6. The first member has a first cylindrical portion surrounding the sensor element,
The second member has a second cylindrical portion having a larger diameter than the first cylindrical portion,
the element chamber inlet is a cylindrical gap between an outer circumferential surface of the first cylindrical portion and an inner circumferential surface of the second cylindrical portion;
The gas sensor according to any one of claims 1 to 7. A protective cover for protecting a sensor element having a gas inlet for introducing a measurement gas and capable of detecting a specific gas concentration of the measurement gas flowing into the sensor element from the gas inlet,
a cylindrical inner protective cover having a sensor element chamber therein for arranging the tip of the sensor element and the gas inlet therein, the sensor element chamber having one or more element chamber inlets which are inlets to the sensor element chamber and one or more element chamber outlets which are outlets from the sensor element chamber;
a cylindrical outer protective cover provided with one or more outer inlets which are inlets for the measurement gas from the outside and one or more outer outlets which are outlets for the measurement gas to the outside, the outer protective cover being disposed outside the inner protective cover;
Equipped with
the outer protective cover and the inner protective cover define, as a space therebetween, a first gas chamber which functions as a flow path for the measurement gas between the outer inlet and the element chamber inlet, and a second gas chamber which functions as a flow path for the measurement gas between the outer outlet and the element chamber outlet and does not directly communicate with the first gas chamber,
The inner protective cover has a cylindrical first member and a cylindrical second member surrounding the first member,
the first member and the second member define the element chamber inlet as a gap therebetween,
a direction parallel to the axial direction of the inner protective cover and from the bottom of the outer protective cover toward the opposite side of the bottom is defined as an upward direction, and a direction from the opposite side of the outer protective cover toward the bottom is defined as a downward direction, the first gas chamber has: a first space which is a space between the outer protective cover and the second member and functions as a flow path of the measurement gas from the outer inlet toward the upward direction; and a second space which is a space above an upper end of the second member and between the outer protective cover and the first member and functions as a flow path of the measurement gas from the first space to the element chamber inlet,
a cross-sectional area Cs of the second space, which is a flow path cross-sectional area when the measurement gas passes directly above the second member from the outside to the inside of the second member, is 14.0 ^mm2 or more,
A cross-sectional area Ds, which is a cross-sectional area perpendicular to the circumferential direction of the inner protective cover in the second space, is 0.5 mm ² or more and 6.4 mm ² or less.
Protective cover.

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