JP2021060385A - Gas sensor and protective cover - Google Patents

Abstract

To reduce decrease in responsiveness of a gas being measured during low velocity time.SOLUTION: A gas sensor comprises a sensor element 110, and an inside protective cover 130 having a first member 131 in which one or more element chamber inlets 127 are disposed and a second member 135, and an outside protective cover 140 in which one or more outside inlets 144a are disposed. A first gas chamber 122 between the outside protective cover 140 and the inside protective cover 130 includes a first space 122a between the outside protective cover 140 and the second member 135 and a second space 122b that functions as a measured-gas passage from the first space 122a to the element chamber inlets 127. A cross-section area Cs of the second space 122b that is a passage cross-section area when the gas being measured passes through directly above the second member 135 from an outside of the second member 135 toward an inside, is 14.0 mm2 or greater, and a cross-section area Ds of the second space 122b that is a cross-section area perpendicular to a circumferential direction of the inside protective cover is 0.5 mm2 to 6.4 mm2, inclusive.SELECTED DRAWING: Figure 7

Description

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

Conventionally, a gas sensor that detects a predetermined gas concentration such as NOx or oxygen in a gas to be measured such as an exhaust gas of an automobile has been known. For example, Patent Document 1 describes a gas sensor including a sensor element, an inner protective cover in which the tip of the sensor element is arranged inside, and an outer protective cover arranged outside the inner protective cover. .. Further, in Patent Document 1, the total cross-sectional area S1 of one or more outer inlets arranged on the outer protective cover and being the inlets of the gas to be measured from the outside and the outside of the gas to be measured arranged on the outer protective cover By setting the cross-sectional area ratio S1 / S2, which is the ratio of the total cross-sectional area S2 of one or more outer outlets, to the value 2.0 exceeding the value 5.0 or less, the responsiveness of gas concentration detection can be improved. It is stated to increase.

JP-A-2017-223620

By the way, the responsiveness of gas concentration detection also changes depending on the flow velocity of the gas to be measured flowing around the gas sensor, and there is a problem that the responsiveness tends to decrease when the flow velocity is low (for example, less than 2 m / s).

The present invention has been made to solve such a problem, and an object of the present invention is to reduce a decrease in responsiveness of a gas to be measured at a low flow velocity.

The present invention has taken the following measures to achieve the above-mentioned main object.

The gas sensor of the present invention
A sensor element having a gas introduction port 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 inside from the gas introduction port.
It has a sensor element chamber in which the tip of the sensor element and the gas introduction port are arranged inside, and is one or more element chamber inlets which are inlets to the sensor element chamber and outlets from the sensor element chamber. A tubular inner protective cover in which one or more element chamber outlets are arranged, and
One or more outer inlets which are inlets of the gas to be measured from the outside and one or more outer outlets which are outlets of the gas to be measured to the outside are arranged and arranged outside the inner protective cover. With a tubular outer protective cover
With
The outer protective cover and the inner protective cover are a first gas chamber that functions as a flow path of the gas to be measured between the outer inlet and the element chamber inlet as a space between the two, and the outer outlet. A second gas chamber that functions as a flow path for the gas to be measured between the element chamber outlet and the first gas chamber and does not directly communicate with the first gas chamber is formed.
The inner protective cover has a tubular first member surrounding the sensor element and a tubular second member surrounding the first member.
The first member and the second member form the element chamber entrance as a gap between the first member and the second member.
The first gas chamber is parallel to the axial direction of the inner protective cover and the direction from the front end to the rear end of the sensor element is upward, and the direction from the rear end to the front end of the sensor element is downward. Is a space between the outer protective cover and the second member, which functions as a flow path of the gas to be measured upward from the outer inlet, and more than the upper end of the second member. It has a second space above and between the outer protective cover and the first member, which functions as a flow path for the gas to be measured from the first space to the entrance of the element chamber.
The cross-sectional area Cs, which is the cross-sectional area of the flow path when the gas to be measured passes directly above the second member from the outside to the inside of the second member in the second space, is 14.0 mm ² or more. ,
The cross-sectional area Ds, which is the 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 a thing.

In this gas sensor, the gas to be measured flowing around the gas sensor flows into the first space of the first gas chamber from the outer inlet of the outer protective cover, flows upward in the first space, and reaches the second space. , It flows in the second space from the outside to the inside of the second member, reaches the element chamber entrance, passes through the element chamber entrance, and reaches the gas inlet in the sensor element chamber. Here, when the flow velocity of the gas to be measured is low, the flow rate of the gas to be measured flowing from the outer inlet is small, so that the flow rate of the gas to be measured flowing into the device chamber through the inlet of the element chamber is also small. The responsiveness of specific gas concentration detection tends to decrease. On the other hand, in the gas sensor of the present invention, when the cross-sectional area Cs is 14.0 mm ² or more, the gas to be measured easily moves from the outside to the inside of the second member in the second space. That is, the gas to be measured in the first space easily passes through the second space and heads toward the entrance of the element chamber. As a result, the flow rate of the gas to be measured reaching the inlet of the element chamber can be increased, and the decrease in the responsiveness of the specific gas concentration detection when the gas to be measured has a low flow velocity can be suppressed. Further, when the cross-sectional area Ds is 6.4 mm ² or less, it is possible to suppress a decrease in responsiveness due to the gas to be measured flowing in the second space along the circumferential direction of the inner protective cover. Here, when the gas to be measured flows in the second space along the circumferential direction of the inner protective cover, the time until the gas to be measured passes through the second space and reaches the entrance of the element chamber becomes long and responsive. May decrease. On the other hand, when the cross-sectional area Ds is 6.4 mm ² or less, it becomes difficult for the gas to be measured 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 due to the above-mentioned gas to be measured 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 the decrease in responsiveness of the gas to be measured at a low flow velocity. The cross-sectional area Ds preferably has a small value as described above, but 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 mm ² or more. By doing so, the gas to be measured is more easily moved from the outside to the inside of the second member in the second space, so that the decrease in the responsiveness of the gas to be measured at a low flow velocity can be further suppressed.

In the gas sensor of the present invention, the cross-sectional area Ds may be 5.0 mm ² or less. By doing so, it is possible to further suppress the flow of the gas to be measured along the circumferential direction of the inner protective cover in the second space, so that it is possible to further suppress the deterioration of the responsiveness of the gas to be measured at a low flow velocity.

In the gas sensor of the present invention, the cross-sectional area is the total cross-sectional area of the second space inlet, which is the inflow port of the gas to be measured from the first space to the second space, and the one or more element chamber inlets. The cross-sectional area ratio As / Bs with Bs may be 1.41 or more and 4.70 or less. Here, if the cross-sectional area As is too small, the gas to be measured in the first space is less likely to flow into the second space, and as a result, the gas to be measured is less likely to flow into the inlet of the element chamber. Further, if the cross-sectional area Bs is too small, it becomes difficult for the gas to be measured in the second space to flow into the inlet of the element chamber. On the other hand, when the cross-sectional area ratio As / Bs is 1.41 or more and 4.70 or less, the size of the cross-sectional areas As and Bs is well-balanced, so that the gas to be measured in the first space is in the second space. Since it easily flows into the inlet of the element chamber, it is possible to further suppress a decrease in the responsiveness of the gas to be measured at a low flow velocity.

In the gas sensor of the present invention, the cross-sectional area As of the second space inlet, which is the inflow port of the gas to be measured from the first space to the second space, ^{may be 47.3 mm 2} or more and 68.1 mm ² or less. .. Further, the one or more cross-sectional area Bs is the total cross-sectional area of the element chamber inlet may be 14.5 mm ² or more 33.4 mm ² or less.

In the gas sensor of the present invention, the first member and the second member are such that the element-side opening, which is the opening on the sensor element-chamber side of the element-chamber inlet, opens downward. It may form a room entrance. By doing so, it is possible to prevent the gas to be measured flowing out from the opening on the element side from vertically hitting the surface of the sensor element (the surface other than the gas inlet), or to introduce the gas after passing over the surface of the sensor element for a long distance. It can prevent it from reaching the mouth. Thereby, the coldness of the sensor element can be suppressed. Moreover, the coldness of the sensor element is suppressed by adjusting the direction of the opening on the element side, and the flow rate and flow velocity of the gas to be measured in the inner protective cover are not reduced, so that the specific gas concentration is detected. The decrease in responsiveness can also be reduced. As a result, it is possible to suppress a decrease in the heat retention of the sensor element while suppressing a decrease in the responsiveness of the sensor element. Here, "the element-side opening opens downward" means that the opening is parallel to the downward direction and that the opening is inclined from the lower direction so as to approach the sensor element as the downward direction. Including the case where.

In the gas sensor of the present invention, the first member has a first cylindrical portion surrounding the sensor element, and the second member has a second cylindrical portion having a diameter larger than that of the first cylindrical portion. The element chamber entrance 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
A protective cover for protecting a sensor element that has a gas inlet for introducing a gas to be measured and can detect a specific gas concentration of the gas to be measured that has flowed into the inside from the gas inlet.
It has a sensor element chamber inside for arranging the tip of the sensor element and the gas introduction port inside, and at one or more element chamber inlets which are inlets to the sensor element chamber and outlets from the sensor element chamber. A tubular inner protective cover in which one or more element chamber outlets are arranged, and
One or more outer inlets which are inlets of the gas to be measured from the outside and one or more outer outlets which are outlets of the gas to be measured to the outside are arranged and arranged outside the inner protective cover. With a tubular outer protective cover
With
The outer protective cover and the inner protective cover are a first gas chamber that functions as a flow path of the gas to be measured between the outer inlet and the element chamber inlet as a space between the two, and the outer outlet. A second gas chamber that functions as a flow path for the gas to be measured between the element chamber outlet and the first gas chamber and does not directly communicate with the first gas chamber is formed.
The inner protective cover has a tubular first member and a tubular second member surrounding the first member.
The first member and the second member form the element chamber entrance as a gap between the first member and the second member.
The direction parallel to the axial direction of the inner protective cover and from the bottom of the outer protective cover to the side opposite to the bottom is upward, and the direction from the side opposite to the bottom of the outer protective cover to the bottom is downward. As a direction, the first gas chamber is a space between the outer protective cover and the second member, and functions as a flow path of the gas to be measured from the outer inlet to the upward direction. A second space above the upper end of the second member and between the outer protective cover and the first member, which functions as a flow path for the gas to be measured from the first space to the entrance of the element chamber. And have
The cross-sectional area Cs, which is the cross-sectional area of the flow path when the gas to be measured passes directly above the second member from the outside to the inside of the second member in the second space, is 14.0 mm ² or more. ,
The cross-sectional area Ds, which is the 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 a thing.

By arranging the tip of the sensor element and the gas inlet in the sensor element chamber of the protective cover, the effect of reducing the decrease in responsiveness of the gas to be measured at a low flow velocity can be obtained as in the case of the gas sensor of the present invention described above. Be done. In the protective cover of the present invention, various aspects of the gas sensor described above may be adopted.

The schematic explanatory view of the attachment state of the gas sensor 100 to the pipe 20. FIG. 1A is a cross-sectional view taken along the line AA of FIG. BB sectional view of FIG. FIG. 3 is a sectional view taken along the line CC of FIG. FIG. 3 is a cross-sectional view taken along the line CC of the outer protective cover 140 of FIG. FIG. 3D view of FIG. FIG. 6 is an enlarged cross-sectional view of a part of the EE cross section of FIG. The vertical sectional view of the gas sensor 200 of the modification. FIG. 8 is a sectional view taken along line FF of the outer protective cover 240 of FIG. G view of FIG. The cross-sectional view which shows the element chamber entrance 327 of the modification. The vertical sectional view of the gas sensor 400 of the modification. The graph which shows the relationship between the flow velocity of each of Experimental Examples 1 to 4 and the response time. The graph which shows the relationship between the height C, the cross-sectional area Cs, Ds, the volume V of each of Experimental Examples 1 to 4 and the response time at a flow velocity of 1 m / s.

Next, a mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a schematic explanatory view of a state in which the gas sensor 100 is attached to the pipe 20. FIG. 2 is a cross-sectional view taken along the line AA of FIG. FIG. 3 is a cross-sectional view taken along the line BB of FIG. FIG. 4 is a cross-sectional view taken along the line CC of FIG. FIG. 5 is a cross-sectional view taken along the line CC of the outer protective cover 140 of FIG. Note that FIG. 5 corresponds to a diagram in which the first cylindrical portion 134, the second cylindrical portion 136, the tip portion 138, and the sensor element 110 are excluded from FIG. FIG. 6 is a view D of FIG. FIG. 7 is an enlarged cross-sectional view of a part of the EE cross section of FIG. The direction parallel to the axial direction of the protective cover 120 and from the front end to the rear end of the sensor element 110 (upward in FIGS. 3 and 7) is upward, and parallel to the axial direction of the protective cover 120 and behind the sensor element 110. The direction from the end to the tip (downward in FIGS. 3 and 7) is the downward direction.

As shown in FIG. 1, the gas sensor 100 is mounted in a pipe 20 which is an exhaust path from the engine of the vehicle, and NOx, ammonia, O _2, etc. contained in the exhaust gas as the gas to be measured discharged from the engine. The specific gas concentration, which is the concentration of at least one specific gas among the gas components of the above, is detected. As shown in FIG. 2, the gas sensor 100 is fixed in the pipe 20 in a state where the central axis of the gas sensor 100 is perpendicular to the flow of the gas to be measured in the pipe 20. The central axis of the gas sensor 100 may be fixed in the pipe 20 in a state of being perpendicular to the flow of the gas to be measured in the pipe 20 and tilted by a predetermined angle (for example, 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, O 2,} etc.) in the gas to be measured, and a protective cover for protecting the sensor element 110. It is equipped with 120. Further, the gas sensor 100 includes a metal housing 102 and a metal bolt 103 having screws on the outer peripheral surface. The housing 102 is inserted into a fixing member 22 welded to the pipe 20 and provided with a female screw on the inner peripheral surface, and the housing 102 is inserted into the fixing member 22 by further inserting the bolt 103 into the fixing member 22. It is fixed in 22. As a result, the gas sensor 100 is fixed in the pipe 20. The direction in which the gas to be measured flows in the pipe 20 is the direction from left to right in FIG.

The sensor element 110 is an elongated plate-shaped element, 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 introduction port 111 that introduces the gas to be measured into its own interior, and is configured to be able to detect a specific gas concentration of the gas to be measured that has flowed into the inside from the gas introduction port 111. In the present embodiment, the gas introduction port 111 is assumed to be open to the front end surface of the sensor element 110 (the lower surface of the sensor element 110 in FIG. 3). The sensor element 110 includes a heater inside which plays a role of temperature control for 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 known, and are described in, for example, Japanese Patent Application Laid-Open No. 2008-164411. The sensor element 110 has a tip (lower end in FIG. 3) and a gas introduction port 111 arranged in the sensor element chamber 124. The direction from the rear end to the tip of the sensor element 110 (downward direction) is also referred to as the tip direction.

Further, the sensor element 110 includes a porous protective layer 110a that covers at least a part of the surface. In the present embodiment, the porous protective layer 110a is formed on five of the six surfaces of the sensor element 110 and covers most of the exposed surfaces 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 introduction port 111 is formed. Further, the porous protective layer 110a covers the side of the four surfaces (upper, lower, left and right surfaces in the sensor element 110 in FIG. 4) connected to the tip surface of the sensor element 110, which is closer to the tip surface of the sensor element 110. .. The porous protective layer 110a plays a role of suppressing, for example, moisture in the gas to be measured from adhering to the sensor element 110 to cause cracks. Further, the porous protective layer 110a plays a role of suppressing the oil component or the like contained in the gas to be measured from adhering to the electrode or the like (not shown) on the surface of the sensor element 110. The porous protective layer 110a is made of, for example, an alumina porous body, a zirconia porous body, a spinel porous body, a cordierite porous body, a titania porous body, a magnesia porous body, or the like. The porous protective layer 110a can be formed by, for example, plasma spraying, screen printing, dipping, or the like. The porous protective layer 110a also covers the gas introduction port 111, but since the porous protective layer 110a is a porous body, the gas to be measured circulates inside the porous protective layer 110a and flows through the gas introduction port. It is possible to reach 111. The thickness of the porous protective layer 110a is, for example, 100 μm to 700 μm.

The protective cover 120 is arranged so as to surround the sensor element 110. The protective cover 120 has a bottomed tubular inner protective cover 130 that covers the tip of the sensor element 110, and a bottomed tubular outer protective cover 140 that covers the inner protective cover 130. Further, the first gas chamber 122 and the second gas chamber 126 are formed as a space surrounded by the inner protective cover 130 and the outer protective cover 140, and the sensor element chamber 124 is formed as a space surrounded by the inner protective cover 130. ing. 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 (for example, stainless steel such as SUS310S).

The inner protective cover 130 includes a first member 131 and a second member 135. The first member 131 is a stepped portion connecting a cylindrical large-diameter portion 132, a cylindrical first cylindrical portion 134 having a diameter smaller than that of the large-diameter portion 132, and the large-diameter portion 132 and the first cylindrical portion 134. It has 133 and. The first cylindrical portion 134 surrounds the sensor element 110. The second member 135 includes a second cylindrical portion 136 having a diameter larger than that of the first cylindrical portion 134, a tip portion 138 located in the tip direction (downward direction) of the sensor element 110 from the second cylindrical portion 136, and a tip portion. It has a stepped portion 139 which is connected to the upper end of the 138 and protrudes outward from the outer peripheral surface of the tip portion 138, and a connecting portion 137 which connects the lower end of the second cylindrical portion 136 and the stepped portion 139. ing. The tip portion 138 has a side portion 138d and a bottom portion 138e. At the tip portion 138, one or more element chamber outlets 138a, which communicate with the sensor element chamber 124 and the second gas chamber 126 and are outlets for the gas to be measured from the sensor element chamber 124, are formed. The element chamber outlet 138a has a plurality of (four in this embodiment) circular lateral holes 138b formed at equal intervals on the side portion 138d. The element chamber outlet 138a is not arranged at the bottom 138e of the tip 138. The diameter of the element chamber outlet 138a is, for example, 0.5 mm to 2.6 mm. In the present embodiment, the diameters of the plurality of lateral holes 138b are all set to the same value. The element chamber outlet 138a is formed at a position in the tip direction (downward direction) of the sensor element 110 with respect to the gas introduction port 111. In other words, the element chamber outlet 138a is located farther (downward) from the gas introduction port 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 have the same central axis. The inner peripheral surface of the large diameter portion 132 is in contact with the housing 102, whereby the first member 131 is fixed to the housing 102. The outer peripheral surface of the connecting portion 137 of the second member 135 is in contact with the 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 is formed to be 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 is press-fitted into the tip portion 146. The second member 135 may be fixed.

On the inner peripheral surface of the second cylindrical portion 136, a plurality of protruding portions 136a are formed so as to project toward the outer peripheral surface of the first cylindrical portion 134 and are in contact with the outer peripheral surface. As shown in FIG. 4, three projecting 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 portion 136a is formed in a substantially hemispherical shape. By providing such a protruding portion 136a, the positional relationship between the first cylindrical portion 134 and the second cylindrical portion 136 can be easily fixed by the protruding portion 136a. The protruding portion 136a preferably presses the outer peripheral surface of the first cylindrical portion 134 inward 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 portion 136a. The number of protruding portions 136a is not limited to three, and may be two or four or more. Since the fixing between the first cylindrical portion 134 and the second cylindrical portion 136 is easy to stabilize, it is preferable that the number of protruding portions 136a is three or more.

The inner protective cover 130 forms an element chamber inlet 127 (see FIGS. 3, 4, 7) which is a gap between the first member 131 and the second member 135 and is an inlet of the gas to be measured to the sensor element chamber 124. ing. 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 is on the side of the sensor element chamber 124, which is the space where the gas introduction port 111 is arranged, and the outer opening 128, which is the opening on the first gas chamber 122 side, which is the space where the outer inlet 144a is arranged. It has an element-side opening 129, which is an opening. The outer opening 128 is formed on the rear end side (upper side) of the sensor element 110 with respect to the element side opening 129. Therefore, in the path of the gas to be measured from the outer inlet 144a to the gas introduction port 111, the element chamber inlet 127 becomes a flow path from the rear end side (upper side) to the tip end side (lower side) of the sensor element 110. ing. Further, the element chamber inlet 127 is a flow path parallel to the rear end-tip direction of the sensor element 110 (a flow path parallel to the vertical direction).

The element-side opening 129 opens in the direction from the rear end of the sensor element 110 toward the tip (downward) and parallel to the rear end-tip direction (vertical 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 arranged at a position other than the region in which the element chamber entrance 127 is virtually extended from the element-side opening 129 (the region directly below the element-side opening 129 in FIGS. 3 and 7). As a result, it is possible to prevent the gas to be measured flowing out from the element-side opening 129 from directly hitting the surface of the sensor element 110, and it is possible to suppress the cooling of the sensor element 110.

The outer peripheral surface of the first cylindrical portion 134 and the inner peripheral surface of the second cylindrical portion 136 are separated from each other by a distance A4 (see FIG. 7) in the radial direction of the cylinder at the element side opening 129, and the cylinder is formed at the outer opening 128. It is separated by a distance A5 in the radial direction of. Further, 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 a portion (cross section shown in FIG. 4) where the protruding portion 136a and the first cylindrical portion 134 are in contact with each other. ing. The distance A4, the distance A5, and the distance A7 are, for example, 0.3 mm to 2.4 mm, respectively. The distance A4, the distance A5, and the distance A7 may be 0.51 mm or more, or 1.18 mm or less. By adjusting the values of the distance A4 and the distance A5, the opening area of the element-side opening 129 and the opening area of the outer opening 128 can be adjusted. In the present embodiment, the distances A4, the distances A5, and the distances A7 are assumed to be equal, and the opening area of the element side opening 129 and the opening area of the outer opening 128 are equal. In the present embodiment, the distance A4 (distance A5, distance A7) is the same as half the difference between the outer diameter of the first cylindrical portion 134 and the inner diameter of the second cylindrical portion 136. Further, 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. Is. The distance L may be 3 mm or more, or 5 mm or less. Further, the minimum distance between the lower end of the first cylindrical portion 134 and the connecting portion 137 is defined as the distance A6 (see FIG. 7). The distance A6 may be a value larger than the distances A4, A5, and A7, may be the same value, or may be a smaller value.

As shown in FIG. 3, the outer protective cover 140 has a cylindrical large-diameter portion 142, a cylindrical body portion 143 connected to the large-diameter portion 142 and having a smaller diameter than the large-diameter portion 142, and a bottomed portion. It has a tubular tip portion 146 having an inner diameter smaller than that of the body portion 143. Further, the body portion 143 is a stepped portion that connects the side portion 143a having a side surface along the central axial direction (vertical direction) of the outer protective cover 140 and the side portion 143a and the tip portion 146 that are the bottom portion of the body portion 143. It has 143b and. 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 is in contact with the housing 102 and the large-diameter portion 132, whereby the outer protective cover 140 is fixed to the housing 102. The body portion 143 is located 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 portion 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 is in contact with the outer peripheral surface of the connection portion 137. The tip portion 146 has a side surface along the central axial direction (vertical direction) of the outer protective cover 140, a side portion 146a having an outer diameter smaller than the inner diameter of the side portion 143a, and a bottom portion 146b which is the bottom of the outer protective cover 140. And a tapered portion 146c that connects the side portion 146a and the bottom portion 146b and reduces the diameter from the side portion 146a toward the bottom portion 146b. The tip portion 146 is located on the tip direction side (lower side) with respect to the body portion 143. The outer protective cover 140 is formed on the body portion 143 and has one or more (plural, specifically 12) outer inlets 144a, which are inlets of the gas to be measured from the outside, and a tip portion 146. It has one or more outer outlets 147a, which are formed in the above and are outlets for the gas to be measured to the outside.

The outer inlet 144a is a hole leading to the outer side (outside) of the outer protective cover 140 and the first gas chamber 122. The outer inlets 144a are composed of a plurality of lateral holes 144b formed at equal intervals in the side portions 143a (six in the present embodiment) and a plurality of lateral holes 144b formed in the step portions 143b at equal intervals (six in the present embodiment). It has a vertical hole 144c (FIGS. 3 to 6). The outer inlet 144a (horizontal hole 144b and vertical hole 144c) is a hole formed in a circular shape (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 the present embodiment, the diameters of the plurality of horizontal holes 144b are all set to the same value, and the diameters of the plurality of vertical holes 144c are all set to the same value. Further, the diameter of the horizontal hole 144b was set to a value larger than the diameter of the vertical hole 144c. As shown in FIGS. 4 and 5, the outer inlet 144a is formed so that the horizontal holes 144b and the vertical holes 144c are alternately located at equal intervals along the circumferential direction of the outer protective cover 140. That is, the line connecting the center of the lateral hole 144b and the central axis of the outer protective cover 140 in FIGS. 4 and 5 and the center of the vertical hole 144c adjacent to the lateral hole 144b and the central axis of the outer protective cover 140 are connected. The angle between the cover and the line is 30 ° (360 ° / 12 pieces).

The outer outlet 147a is a hole leading to the outer side (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 portion 146b of the tip portion 146 (see FIGS. 3, 5 and 6). Unlike the outer inlet 144a, the outer outlet 147a is not arranged on the side portion of the outer protective cover 140 (here, the side portion 146a of the tip portion 146). The outer outlet 147a (here, the vertical hole 147c) is a hole formed in a circular shape (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 the present embodiment, the diameter of the vertical hole 147c is set to a value larger than the diameter 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 portion 143 and the inner protective cover 130. More specifically, the first gas chamber 122 is a space surrounded by a step portion 133, a first cylindrical portion 134, a second cylindrical portion 136, a side portion 143a, and a 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. Since the inner peripheral surface of the tip portion 146 is in contact with the outer peripheral surface of the connecting portion 137, the first gas chamber 122 and the second gas chamber 126 are not directly communicated with each other.

Further, as shown in FIG. 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 gas to be measured upward from the outer inlet 144a. More specifically, the first space 122a is a space surrounded by a side portion 143a, a step portion 143b, and a second cylindrical portion 136, and is an upper end of the second member 135 (here, the upper end of the second cylindrical portion 136). It is the space below. The first space 122a is a cylindrical gap between the inner peripheral surface of the outer protective cover 140 and the outer peripheral 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). Is. The second space 122b functions as a flow path for the gas to be measured from the first space 122a to the device chamber inlet 127. The second space 122b is a cylindrical gap between the inner peripheral surface of the outer protective cover 140 and the outer peripheral surface of the first cylindrical portion 134.

The inflow port of the gas to be measured from the first space 122a to the second space 122b is referred to as a second space inlet 122c. The second space inlet 122c is a ring-shaped gap between the inner peripheral surface of the outer protective cover 140 and the upper end of the outer peripheral surface of the second cylindrical portion 136. The outer entrances 144a are all located below the second space entrance 122c. In other words, each of the outer inlets 144a is 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 peripheral surface of the outer protective cover 140 and the radius of the upper end of the outer peripheral surface of the second cylindrical portion 136 is referred to as a distance A1 (see FIG. 7). .. Further, the cross-sectional area (opening area) of the second space entrance 122c is referred to as a cross-sectional area As. The cross-sectional area As is the area of the plane perpendicular to the vertical direction. In the present embodiment, the cross-sectional area As = (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 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 of distances A4, A5, A7 or more. The ratio A / A4 may be 1.0 or more and 3.63 or less. Similarly, the ratio A / A5 and the ratio A / A7 may be 1.0 or more and 3.63 or less. Sectional area As, for example, may be 47.3 mm ² or more, may be 68.1Mm ² below.

The outer opening 128 described above is also an outlet (second space exit) from the second space 122b to the element chamber entrance 127. Further, the cross-sectional area (flow path cross-sectional area) of the element chamber inlet 127 is referred to as a cross-sectional area Bs. The cross-sectional area Bs is an area in the direction perpendicular to the direction (here, downward) of the gas to be measured passing through the element chamber inlet 127. If the cross-sectional area of the flow path of the gas to be measured in the element chamber inlet 127 is not constant, the minimum value thereof is defined as the cross-sectional area Bs. For example, in the present embodiment, since the distances A4 and A5 are equal, the outer opening 128 and the element side opening 129 have the same opening area (= flow path cross-sectional area), but the element chamber entrance 127 is larger than these opening areas. Of these, the cross-sectional area of the flow path in the portion where the protruding portion 136a exists is smaller. Therefore, in the present embodiment, the cross-sectional area of the element chamber inlet 127 in the cross section of the element chamber inlet 127 in which the protruding portion 136a is most protruding, that is, the cross section shown in FIG. 4 is defined as the cross-sectional area Bs. Therefore, in the present embodiment, the cross-sectional area Bs = (the area of the circle whose diameter is the inner diameter of the second cylindrical portion 136)-(the area of the circle whose diameter is the outer diameter of the first cylindrical portion 134)-(FIG. 4). The absolute value of the decrease in the cross-sectional area of the element chamber inlet 127 due to the protruding portion 136a in the cross section) × (the number of protruding portions 136a). Sectional area Bs, for example may be 14.5 mm ² or more, may be 33.4 mm ² or less.

In the second space 122b, the gas to be measured passes directly above the second member 135 (here, directly above the second cylindrical portion 136) from the outside to the inside of the second member 135 (passes from left to right in FIG. 7). ) Is referred to as a flow path cross section 122d. Further, the vertical length of the flow path cross section 122d is referred to as a height C, and the cross-sectional area of the flow path cross section 122d is referred to as a cross-sectional area Cs. The cross-sectional area Cs is the same as the area of the outer peripheral surface of a cylinder having a height C, which has the same diameter 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) × π × (height C). The flow path cross section 122d is a cross section of the second space 122b that is perpendicular to the radial direction toward the center of the inner protective cover 130 and that is directly above the second cylindrical portion 136, and is cut off directly above the second member 135. It is defined as the cross section at the position where the area is the smallest. For example, in the present embodiment, the cross-sectional area of the second space 122b, which is perpendicular to the radial direction, is smaller directly above the inner peripheral surface of the second cylindrical portion 136 than immediately above the outer peripheral surface of the second cylindrical portion 136. Therefore, the cross section of the second space 122b that is 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.

Of the second space 122b, the 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 (substantially rectangular area) of the second space 122b shown in the cross section of FIG. In the present embodiment, the cross-sectional area Ds = {(inner diameter of the side portion 143a) − (outer diameter of the first cylindrical portion 134)} ÷ 2 × (height C). In other words, the cross-sectional area Ds = {A + A5 + (thickness of the second cylindrical portion 136)} × (height C).

The volume V of the second space 122b ^{may be, for example, 43 mm 3} or more, ^{or 70 mm 3} or more. The volume V of the second space 122b ^{may be, for example, 223 mm 3} or less, ^{or 174 mm 3} or less. In the present embodiment, the volume V = {(the area of the circle whose diameter is the inner diameter of the side portion 143a)-(the area of the circle whose diameter is the outer diameter of the first cylindrical portion 134)} × (height C). ..

Here, the flow of the gas to be measured in the protective cover 120 when the gas sensor 100 detects the specific gas concentration will be described. The gas to be measured flowing in the pipe 20 first flows into the first gas chamber 122 through at least one of the plurality of outer inlets 144a (horizontal hole 144b and vertical hole 144c). Next, the gas to be measured flows into the element chamber inlet 127 from the first gas chamber 122 via the outer opening 128, flows out from the element side opening 129 via the element chamber inlet 127, and flows into the sensor element chamber 124. To do. At least a part of the gas to be measured that has flowed into the sensor element chamber 124 from the element-side opening 129 reaches the gas introduction port 111 of the sensor element 110. When the gas to be measured reaches the gas introduction port 111 and flows into the inside of the sensor element 110, the sensor element 110 generates an electric signal (voltage or current) according to the specific gas concentration in the gas to be measured, and this electricity is generated. A specific gas concentration is detected based on the signal. Further, 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 hole 138b), and then flows out from there through the outer outlet 147a. .. 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 gas to be measured, the flows in the first gas chamber 122 and the element chamber inlet 127 will be described in detail. The gas to be measured that has flowed 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. Subsequently, the gas to be measured reaches the inside of the second space 122b from the second space inlet 122c and flows in the second space 122b from the outside to the inside of the second member 135, that is, protects the inside of the second space 122b. It flows radially toward the central axis of the cover 120 and reaches the outer opening 128 of the element chamber inlet 127. Then, the gas to be measured flows downward from the outer opening 128 through the element chamber inlet 127 and reaches the sensor element chamber 124 from the element side opening 129.

Here, in general, when the flow velocity of the gas to be measured is low (for example, less than 2 m / s), the flow rate of the gas to be measured flowing in from the outer inlet 144a is small, so that the sensor element chamber passes through the element chamber inlet 127. The flow rate of the gas to be measured flowing into the 124 also becomes small, and the responsiveness of the specific gas concentration detection tends to decrease. On the other hand, in the gas sensor 100 of the present embodiment, since the cross-sectional area Cs described above is 14.0 mm ² or more, the gas to be measured moves from the outside to the inside of the second member 135 in the second space 122b. It will be easier to do. That is, the gas to be measured in the first space 122a easily passes through the second space 122b and heads toward the element chamber inlet 127. Thereby, the flow rate of the gas to be measured reaching the inlet 127 of the element chamber can be increased, and the decrease in the responsiveness of the specific gas concentration detection when the gas to be measured has a low flow velocity can be suppressed.

Further, in the gas sensor 100 of the present embodiment, when the cross-sectional area Ds is 6.4 mm ² or less, the gas to be measured flows in the second space 122b along the circumferential direction of the inner protective cover 130. It is possible to suppress the deterioration of sex. Here, in general, when the gas to be measured flows in the second space 122b along the circumferential direction of the inner protective cover 130, the time until the gas to be measured passes through the second space 122b and reaches the element chamber inlet 127. May become longer and the responsiveness may decrease. Further, in general, when there are a plurality of outer inlets 144a, the gas to be measured is sent to the outside from the outer inlet 144a located near the downstream side of the gas to be measured flowing around the outer protective cover 140 among the plurality of outer inlets 144a. The phenomenon of outflow may occur. For example, in FIG. 3, since the gas to be measured flows around the outer protective cover 140 from left to right, the horizontal hole 144b and the vertical hole 144c shown on the right side of the sensor element 110 in FIG. 3 are closer to the downstream side. It corresponds to the outer entrance 144a at the position. The larger the flow rate of the measured gas flowing in the second space 122b along the circumferential direction of the inner protective cover 130, the more the flow rate of the measured gas flowing out from the outer inlet 144a located closer to the downstream side. Is likely to increase. Then, when the gas to be measured flows out from the outer inlet 144a to the outside, the gas to be measured that reaches the element chamber inlet 127 is reduced by that amount, so that the responsiveness of the specific gas concentration detection is lowered. As described above, in general, the larger the flow rate of the gas to be measured flowing in the second space 122b along the circumferential direction of the inner protective cover 130, the more easily the responsiveness of the specific gas concentration detection tends to decrease. On the other hand, in the gas sensor 100 of the present embodiment, since the cross-sectional area Ds is 6.4 mm ² or less, it becomes difficult for the gas to be measured to flow in the second space 122b along the circumferential direction of the inner protective cover 130. Therefore, it is possible to suppress a decrease in responsiveness due to the above-mentioned gas to be measured flowing in the second space 122b along the circumferential direction of the inner protective cover 130. As described above, the gas sensor 100 of the present embodiment can reduce the decrease in responsiveness of the gas to be measured at a low flow velocity. The cross-sectional area Ds preferably has a small value as described above, but the cross-sectional area Ds ^{may be 0.5 mm 2} or more.

According to the gas sensor 100 of the present embodiment described in detail above, when 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 responsiveness of the gas to be measured at a low flow velocity is lowered. Can be reduced.

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

Further, the cross-sectional area ratio As / Bs of 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 gas to be measured in the first space 122a is less likely to flow into the second space 122b, and as a result, the gas to be measured is less likely to flow into the element chamber inlet 127. Further, if the cross-sectional area Bs is too small, it becomes difficult for the gas to be measured in the second space 122b to flow into the element chamber inlet 127. On the other hand, when the cross-sectional area ratio As / Bs is 1.41 or more and 4.70 or less, the size of the cross-sectional areas As and Bs is well-balanced, so that the gas to be measured in the first space 122a is the second. Since it easily flows into the element chamber inlet 127 through the space 122b, it is possible to further suppress a decrease in the responsiveness of the gas to be measured at a low flow velocity.

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 gas to be measured flowing out from the element-side opening 129 from vertically hitting the surface of the sensor element 110 (the surface other than the gas introduction port 111), or after passing over the surface of the sensor element 110 for a long distance. It is possible to suppress the arrival at the gas introduction port 111. Thereby, the coldness of the sensor element 110 can be suppressed. Moreover, the coldness of the sensor element 110 is suppressed by adjusting the direction of the opening of the element side opening 129, and the flow rate and the flow velocity of the gas to be measured in the inner protective cover 130 are not reduced. The decrease in responsiveness of gas concentration detection can also be reduced. As a result, it is possible to suppress a decrease in heat retention while suppressing a decrease in responsiveness of the sensor element 110.

Needless to say, the present invention is not limited to the above-described embodiment, and can be implemented in various aspects as long as it belongs to the technical scope of the present invention.

For example, the shape of the protective cover 120 is not limited to the above-described 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 appropriately changed. For example, the tip portion 146 of the outer protective cover 140 has a bottomed tubular shape and has a side portion 146a, a bottom portion 146b, and a tapered portion 146c, but the tapered portion 146c may be omitted. Further, the tip portion 138 of the inner protective cover 130 has a shape such that the outer diameter of the side portion 138d is constant and the side portion 138d and the bottom portion 138e have the same diameter. The shape may be such that the outer diameter of the side portion 138d becomes smaller as it approaches the bottom portion 138e. FIG. 8 is a vertical cross-sectional view (gas sensor 100) of the gas sensor 200 in which the tip portion 146 of the outer protective cover 140 has a cylindrical shape with the tapered portion 146c omitted, and the tip portion 138 of the inner protective cover 130 has an inverted truncated cone shape. BB cross-sectional view). FIG. 8 also shows an enlarged view around the second space 122b. 9 is a sectional view taken along line FF of the outer protective cover 240 of FIG. 8, and FIG. 10 is a G view of FIG. In FIGS. 8 to 10, the same components as those of the gas sensor 100 are designated by 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 has a tip portion 238 having an inverted truncated cone shape in place of the tip portion 138 and the step portion 139. Further, the tip portion 238 is formed with an element chamber outlet 238a which communicates with the sensor element chamber 124 and the second gas chamber 126 and is an outlet of the gas to be measured 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 portion 238. The outer protective cover 240 has a tip portion 246 having a bottomed tubular shape (cylindrical shape) and an inner diameter smaller than that of the body portion 143 instead of the tip portion 146. The tip portion 246 has a side surface along the central axial direction (vertical direction in FIG. 8) of the outer protective cover 240, and has a side portion 246a whose outer diameter is smaller than the inner diameter of the side portion 143a and a bottom portion of the outer protective cover 240. It has a bottom 246b and a certain bottom. Further, an outer outlet 247a, which is an outlet for the gas to be measured to the outside, is formed at the tip portion 246. The outer outlet 247a has a plurality of (here, 6) vertical holes 247c formed at equal intervals along the circumferential direction of the outer protective cover 240 at the bottom 246b of the tip portion 246 (FIGS. 8, 9, and 6). 10). Even in such a gas sensor 200, when 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 same effect as that of the above-described embodiment can be obtained.

In the above-described 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 present invention is not limited to this. The chamber entrance may have any shape as long as it is a gap between the first member 131 and the second member 135. For example, the entrance of the element chamber may be a gap inclined from the vertical direction in FIG. 3 (see also FIG. 12 described later). Further, the number of element chamber inlets 127 is not limited to one, but may be plural (see also FIG. 11 described later). The element chamber outlet 138a, the outer inlet 144a, and the outer outlet 147a are not limited to the holes, but may be gaps between a plurality of members constituting the protective cover 120, and the number of each may be one or more. Further, although the outer inlet 144a has a horizontal hole 144b and a vertical hole 144c, it may have only one of them. Further, in addition to or in place 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 square hole. Further, the outer outlet 147a may have a through hole provided in the tapered portion 146c.

In the above-described embodiment, the protruding portion 136a is formed on the inner peripheral surface of the second cylindrical portion 136, but the present invention is not limited to this. It suffices that at least one surface of the outer peripheral surface of the first cylindrical portion 134 and the inner peripheral surface of the second cylindrical portion 136 is formed with a plurality of projecting portions projecting toward the other surface and in contact with the surface. Further, in the above-described embodiment, as shown in FIGS. 3 and 4, the outer peripheral surface of the portion of the second cylindrical portion 136 in which the protruding portion 136a is formed is recessed inward, but the outer peripheral surface is not limited to this. Does not have to be dented. Further, the protruding portion 136a is not limited to the hemispherical shape and may have any shape. The protruding portion 136a may not 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-described embodiment, the element chamber inlet 127 is a tubular gap between the outer peripheral surface of the first cylindrical portion 134 and the inner peripheral surface of the second cylindrical portion 136, but the present invention is not limited to this. For example, a recess (groove) is formed in 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 entrance is the first cylindrical portion and the second cylindrical portion formed by the recess. It may be a gap with the cylindrical portion. FIG. 11 is a cross-sectional view showing the element chamber entrance 327 of the 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 (four in FIG. 11) outer peripheral surfaces of the first cylindrical portion 334 are in contact with each other. The recesses 334a are formed at equal intervals. The gap between the recess 334a and the inner peripheral surface of the second cylindrical portion 336 is the element chamber entrance 327. When there are a plurality of element chamber inlets (4 locations in FIG. 11) as in the element chamber inlet 327, the total cross-sectional area of each element chamber inlet, that is, the total cross-sectional area is defined 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-tip direction of the sensor element 110 (a flow path parallel to the vertical direction in FIG. 3), but the present invention is not limited to this. For example, the element chamber entrance 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 the gas sensor 400 of the modified example in this case. FIG. 12 also shows an enlarged view around the second space 122b. In FIG. 12, the same components as those of the gas sensors 100 and 200 are designated by 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. Compared to the first member 131, the first member 431 does not include the first cylindrical portion 134, but instead has a cylindrical body portion 434a and a cylindrical first cylindrical portion 434b whose diameter decreases downward. It has. The first cylindrical portion 434b is connected to the body portion 434a at the upper end portion. Compared to the second member 235, the second member 435 does not include the second cylindrical portion 136 and the connecting portion 137, but instead includes a cylindrical second cylindrical portion 436 whose diameter decreases downward. 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 both is the element chamber entrance 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. Due to the shapes of the first cylindrical portion 434b and the second cylindrical portion 436, the element chamber inlet 427 is inclined from the vertical direction so as to approach the sensor element 110 (approaching the central axis of the inner protective cover 430) as it goes downward. It is a flow path. Similarly, the element-side opening 429 is inclined from the vertical direction so as to approach the sensor element 110 as it goes downward (see the enlarged view of FIG. 12). When the element chamber inlet 427 is a flow path inclined in the vertical direction or the element side opening 429 is inclined in the vertical direction as described above, the sensor element chamber is formed from the element side opening 429. The direction in which the gas to be measured flowing out to 124 flows is a direction inclined from the vertical direction. As a result, the same effect as that of the element chamber entrance 127 and the element side opening 129 of the above-described embodiment can be obtained. That is, it is necessary to prevent the gas to be measured from vertically hitting the surface of the sensor element 110 (a surface other than the gas introduction port 111), or to reach the gas introduction port 111 after passing over the surface of the sensor element 110 for a long distance. Can be suppressed. Thereby, the coldness of the sensor element 110 can be suppressed. Further, in FIG. 12, the width of the element chamber entrance 427 becomes narrower toward the lower side 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 entrance 427 is smaller at the distance A4 than at the distance A5 described with reference to FIG. 7. As a result, the gas to be measured flows in from the outer opening 428 and flows out from the element side opening 429, so that the flow velocity of the gas to be measured at the time of outflow is higher than that at the time of inflow. Therefore, the responsiveness 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. Further, 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 is inclined from the vertical direction to open, and the opening area of the element side opening 429 is the outer opening. Although it is made smaller than the opening area of the portion 428, one or more of these three features may be omitted, or the gas sensor may have one or more of these three features. May be good. Even in such a gas sensor 400, when 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 same effect as that of the above-described embodiment can be obtained. In the gas sensor 400 of FIG. 12, like the gas sensor 200, the tip portion 246 of the outer protective cover 240 has a cylindrical shape with the tapered portion omitted, and the tip portion 238 of the inner protective cover 430 has a truncated cone shape. However, instead of this, the gas sensor 400 may have a tip portion 138, a step portion 139, and a tip portion 146 such as the gas sensor 100.

In the above-described embodiment, the element-side opening 129 is opened downward, but the present invention is not limited to this, and the sensor element chamber 124 may be opened in a direction perpendicular to the downward direction, for example.

In the above-described embodiment, the surface defining the upper end of the second space 122b is the lower surface of the step portion 133 of the first member 131, but the present invention is not limited to this. For example, the lower surface of the housing 102 may be a 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 are integrated members. You may.

In the above-described embodiment, the gas introduction port 111 is open to the front end surface of the sensor element 110 (the lower surface of the sensor element 110 in FIG. 3), but the present invention is not limited to this. For example, it may be opened on the side surface of the sensor element 110 (the upper, lower, left and right surfaces of the sensor element 110 in FIG. 4).

In the above-described embodiment, the sensor element 110 includes the porous protective layer 110a, but the sensor element 110 may not include the porous protective layer 110a.

In the above-described embodiment, the protective cover 120 has been described as a part of the gas sensor 100, but the protective cover 120 may be distributed independently.

Although not described in the above-described 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 having a diameter of 1.5 mm can pass. The second condition is that the width of the flow path of the gas to be measured in the protective cover 120 is adjusted so that a sphere having a diameter of 0.8 mm can reach from the outer inlet 144a to the gas introduction port 111. The second condition is, in other words, the minimum value (referred to as the minimum flow path width) of the flow path width among the flow paths through which the gas to be measured must pass between the outer inlet 144a and the gas introduction port 111. , 0.8 mm or more. For example, in the gas sensor 100 of the above-described embodiment, when the distance A6 shown in FIG. 7 is smaller than any of the distance A4, the distance A5, and the distance A7 shown in FIGS. Is the value of. In this case, if the distance A6 is 0.8 mm or more, the second condition is satisfied. The gas to be measured flowing in the pipe 20 may contain soot, and by satisfying both the first condition and the second condition, the soot resistance of the gas sensor 100 is improved. For example, when the distance A6 is less than 0.8 mm, soot may be clogged in the gap between the lower end of the first cylindrical portion 134 and the connecting portion 137. On the other hand, when the distance A6 is 0.8 mm or more, such clogging of soot can be suppressed. The effect of improving the soot resistance by satisfying both the first condition and the second condition ^{is whether or not the above-mentioned cross-sectional area Cs is 14.0 mm 2} or more and the cross-sectional area Ds is 0.5 mm ² or more and 6.4 mm. Obtained regardless of whether it is ^{2 or less.} Further, not only the gas sensor 100 but also a gas sensor provided with a protective cover having another shape such as the above-mentioned various modifications, the effect of improving the soot resistance by satisfying both the first condition and the second condition. Is obtained. For example, when the minimum value of the distance A4, the distance A5, and the distance A7 is smaller than the distance A6 shown in FIG. 7 in the gas sensor 100, 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 distance A4, the distance A5, and the distance 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 the soot resistance can be obtained. When the outer inlet 144a has a plurality of holes, in order to satisfy the first condition, one or more holes having a diameter of 1.5 mm can pass through the plurality of holes, but the diameter is 1.5 mm. The number of holes through which the sphere can pass occupies 60% or more of the plurality of holes, or the total opening area of the holes through which the sphere with a diameter of 1.5 mm can pass is the total opening area of the plurality of holes. It is preferable that it occupies 60% or more of. The same applies to the element chamber outlet 138a and the outer outlet 147a. Further, in addition to the first condition and the second condition, it is preferable that the following third condition is also satisfied. The third condition is that the width of the flow path of the gas to be measured in the protective cover 120 is adjusted so that a sphere having a diameter of 0.8 mm can reach from the gas introduction port 111 to the outer outlet 147a.

Hereinafter, an example in which a gas sensor is specifically manufactured will be described as an example. Experimental Examples 2-4, 6-8, 10-12, 14-16, 18, 19 correspond to the examples of the present invention, and Experimental Examples 1, 5, 9, 13, 17 correspond to the comparative examples. The present invention is not limited to the following examples.

[Experimental Example 1]
The gas sensor 200 shown in FIGS. 8 to 10 was used as Experimental Example 1. Specifically, the first member 131 of the inner protective cover 230 has 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, and a large diameter portion 132. The outer diameter of the first cylindrical portion 134 is 14.4 mm, the axial length of the first cylindrical portion 134 is 8.4 mm, the outer diameter of the first cylindrical portion 134 is 8.48 mm, and the radius Br2 of the outer diameter of the first cylindrical portion 134 is 4. It was set to 24 mm. The second member 235 has 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, and a second member. 2 The radius Ar2 of the outer diameter of the cylindrical portion 136 is 5.15 mm, the radius Br1 of the inner diameter of the second cylindrical portion 136 is 4.85 mm, the axial length of the tip portion 238 is 4.9 mm, and the diameter of the bottom surface of the tip portion 238. Was 3.0 mm. The diameter of the element chamber outlet 238a was set to 1.5 mm. The outer protective cover 240 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, and a body portion. The axial length of the 143 is 9.0 mm (the axial length from the upper end of the body 143 to the upper surface of the step 143b is 8.7 mm), the outer diameter of the body 143 is 14.6 mm, and the inner diameter of the body 143. The radius Ar1 was 6.9 mm, the axial length of the tip portion 246 was 9.6 mm, and the outer diameter of the tip portion 246 was 8.7 mm. The outer inlet 144a was formed with six horizontal holes 144b having a diameter of 1.5 mm and six vertical holes 144c having a diameter of 1 mm, which were alternately formed at equal intervals (the angle formed by the adjacent holes was 30 °). The outer outlet 247a is not provided with a horizontal hole, but is provided with six vertical holes 247c, and the diameter of the vertical holes 247c is 1 mm. The material of the protective cover 220 was SUS310S. Further, 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 was made of an alumina porous body and had a thickness of 400 μm. The height C of the second space 122b is a 3.759Mm, the cross-sectional area As is a 66.2 mm ^2, the cross-sectional area Bs is set to 15.9 mm ^2, the cross-sectional area Cs is set to 114.5 mm ^2, the cross-sectional area Ds is 10. It was set to 0 mm ² . The cross-sectional area ratio As / Bs was set to 4.2, and the volume V of the second space 122b was set to 349.94 mm ³ .

[Experimental Example 2]
The same gas sensor 200 as in Experimental Example 1 was used as Experimental Example 2 except that the height C was made 2.2 mm by increasing the axial length of the second cylindrical portion 136 (6.5 mm). In Example 2, the cross-sectional area As is a 66.2 mm ^2, the cross-sectional area Bs is set to 15.9 mm ^2, the cross-sectional area Cs is the 67.0Mm ^2, the cross-sectional area Ds is set to 5.9 mm ^2, the cross-sectional area ratio As / Bs was set to 4.2, and volume V was set to 204.80 mm ³ .

[Experimental Example 3]
The gas sensor 100 shown in FIGS. 3 to 7 was used as Experimental Example 3. Specifically, the first member 131 of the inner protective cover 130 has 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, and a large diameter portion 132. The outer diameter of the first cylindrical portion 134 is 14.4 mm, the axial length of the first cylindrical portion 134 is 8.4 mm, the outer diameter of the first cylindrical portion 134 is 8.48 mm, and the radius Br2 of the outer diameter of the first cylindrical portion 134 is 4. It was set to 24 mm. The second member 135 has 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, and a second member 135. 2 The radius Ar2 of the outer diameter of the cylindrical portion 136 is 5.15 mm, the radius Br1 of the inner diameter of the second cylindrical portion 136 is 4.85 mm, the axial length of the tip portion 138 is 4.9 mm, and the side portion 138d of the tip portion 138. The outer diameter of was 5.6 mm. The element chamber outlets 138a were formed with four lateral holes 138b having a diameter of 1.5 mm 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, and a body portion. The axial length of the 143 is 9.0 mm (the axial length from the upper end of the body 143 to the upper surface of the step 143b is 8.7 mm), the outer diameter of the body 143 is 14.6 mm, and the inner diameter of the body 143. Radius Ar1 is 6.9 mm, the axial length of the tip 146 is 9.6 mm, the axial length of the side 146a of the tip is 6.9 mm, the outer diameter of the tip 146 is 8.7 mm, and the tip. The diameter of the bottom 146b of the 146 was set to 2.6 mm. The outer inlet 144a was formed with six horizontal holes 144b having a diameter of 1.5 mm and six vertical holes 144c having a diameter of 1.0 mm, which were 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. Further, the sensor element 110 of the gas sensor 100 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 was made of an alumina porous body and had a thickness of 400 μm. In Example 3, the height C is set to 1.374Mm, the cross-sectional area As is a 66.2 mm ^2, the cross-sectional area Bs is set to 15.9 mm ^2, the cross-sectional area Cs is set to 41.9 ^2, the cross-sectional area Ds is 3. It was 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]
The same gas sensor 100 as in Experimental Example 3 was used as Experimental Example 4 except that the height C was made 0.685 mm by increasing the axial length of the second cylindrical portion 136 (8.015 mm). In Example 4, the cross-sectional area As is a 66.2 mm ^2, the cross-sectional area Bs is set to 15.9 mm ^2, the cross-sectional area Cs is set to 20.9 mm ^2, the cross-sectional area Ds is set to 1.8 mm ^2, the cross-sectional area ratio As / Bs was 4.2 and volume V was 63.77 mm ³ .

[Experimental Examples 5-8]
The same gas sensors as in Experimental Examples 1 to 4 were used as Experimental Examples 5 to 8 except that the diameter of the second cylindrical portion 136 was changed so that the radius Ar2 was 5.3 mm and the radius Br1 was 5.0 mm.

[Experimental Examples 9-12]
The same gas sensors as in Experimental Examples 1 to 4 were used as Experimental Examples 9 to 12, except that the diameter of the second cylindrical portion 136 was changed so that the radius Ar2 was 5.45 mm and the radius Br1 was 5.15 mm.

[Experimental Examples 13 to 16]
The same gas sensors as in Experimental Examples 1 to 4 were used as Experimental Examples 13 to 16 except that the diameter of the second cylindrical portion 136 was changed so that the radius Ar2 was 5.6 mm and the radius Br1 was 5.3 mm.

[Experimental Examples 17-19]
The same gas sensors as in Experimental Examples 1 to 3 were designated as Experimental Examples 17 to 19 except that the diameter of the second cylindrical portion 136 was changed so that the radius Ar2 was 5.75 mm and the radius Br1 was 5.45 mm.

[Evaluation of responsiveness and heat retention]
The gas sensors of Experimental Examples 1 to 19 were attached to the pipes in the same manner as in FIGS. 1 and 1, respectively. A gas in which oxygen was mixed with the atmosphere and adjusted to an arbitrary oxygen concentration was used as a gas to be measured, and this gas to be measured was flowed through a pipe at a flow velocity of 0.73 m / s. Then, the time change of the output of the sensor element was investigated when the oxygen concentration of the gas to be measured flowing in the pipe was changed from 23.6% to 20.9%. The output value of the sensor element immediately before changing the oxygen concentration is set to 0%, the output value when the output of the sensor element changes and stabilizes after the change of oxygen concentration is set to 100%, and the output value exceeds 10%. The elapsed time until it exceeded 90% was defined as the response time (sec) for detecting the specific gas concentration. The shorter the response time, the higher the responsiveness of the specific gas concentration detection. The response time was measured a plurality of times for each experimental example, and the average value of each was taken as the response time for each experimental example. For each of Experimental Examples 1 to 19, the response time was measured in the same manner when the flow velocity of the gas to be measured was 1 m / s. For each of Experimental Examples 1 to 4, the response time was measured in the same manner when the flow velocity of the gas to be measured was 2 m / s and 4 m / s. Further, in Experimental Examples 1 and 2, the response time was measured in the same manner when the flow velocity of the gas to be measured was 8 m / s.

Table 1 shows the evaluation results of the radii Ar1, Ar2, Br1, Br2, height C, cross-sectional area As to Ds, cross-sectional area ratio As / Bs, volume V, response time, and responsiveness in the gas sensors of Experimental Examples 1 to 19. Was summarized. In Table 1, the response time when the flow velocity of the gas to be measured is 1 m / s is used for the evaluation of the responsiveness, and when the response time is 2.5 seconds or less, the responsiveness is very good (A), 3 It was determined that the response was good (B) when the time was less than 2 seconds and the response was poor (F) when the time was more than 3 seconds. Further, FIG. 13 is a graph showing the relationship between the flow velocity of each of Experimental Examples 1 to 4 and the response time. 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 approximate curve (approximate by a cubic polynomial) showing the relationship between the height C and the response time. Further, based on this approximate curve, a height C having a response time of 3 seconds and a height C having a response time of 2.5 seconds were calculated and shown together with FIG. Further, in Experimental Examples 1 to 4, since the cross-sectional areas Cs, Ds, and volume V are changed by changing only the height C, the cross-sectional areas Cs, Ds, and volume V are all set to height C. It is a proportional value. That is, the relationship between each of the cross-sectional areas Cs, Ds, and volume V and the response time is the same except that the values on the horizontal axis are different from the graph in FIG. Therefore, FIG. 14 also shows the values of the cross-sectional areas Cs, Ds, and volume V having a response time of 3 seconds, and the values of the cross-sectional areas Cs, Ds, and volume V having 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 (the responsiveness is lowered) as the flow velocity is lower. Further, when the flow velocity was 2 m / s or more, there was almost no difference in the response time between Experimental Examples 1 to 4, but when the flow velocity was less than 2 m / s, the difference in response time between Experimental Examples 1 to 4 was large. Further, as shown in Table 1 and FIG. 13, the response times of Experimental Examples 2 to 4 were shorter than those of Experimental Example 1, and the response time of Experimental Example 3 was the shortest. Further, as can be seen from the approximate curve of FIG. 14, it was found that the response time becomes long regardless of whether the values are too large or too small for any of the height C, the cross-sectional area Cs, the cross-sectional area Ds, and the volume V. .. It is considered that the reason why the response time becomes long when the height C, the cross-sectional area Cs, the cross-sectional area Ds, and the volume V are too small is that the cross-sectional area Cs is too small. That is, as described above, if the cross-sectional area Cs is too small, it is difficult for the gas to be measured to move from the outside to the inside of the second member in the second space 122b (it is difficult to move toward the inside in the radial direction of the protective cover). ) Therefore, it is considered that the responsiveness is reduced. Further, it is considered that the reason why the response time becomes long when the height C, the cross-sectional area Cs, the cross-sectional area Ds, and the volume V are too large is that the cross-sectional area Ds is particularly large. That is, as described above, if the cross-sectional area Ds is too large, the gas to be measured tends to flow in the second space 122b along the circumferential direction of the inner protective cover, and it is considered that the responsiveness is lowered. From the relationship between the approximate curve of 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. It is considered that the decrease in responsiveness of the gas to be measured at low flow velocity can be reduced. Further, when 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, the response time at a flow velocity of 1 m / s is 2.5 seconds or less, and the responsiveness of the gas to be measured at a low flow velocity. It is considered that the decrease in the amount can be further reduced.

As shown in FIG. 14, the numerical range of the height C corresponding to "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" is 0.46 mm or more and 2.40 mm or less. The numerical range of the corresponding volume V was 43 mm ³ or more and 223 mm ³ or less. The numerical range of the height C corresponding to "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" is 0.75 mm or more and 1.87 mm or less, and the corresponding numerical range of the volume V is It was 70 mm ³ or more and 174 mm ³ or less.

Similar to Experimental Examples 1 to 4, Experimental Examples 5 to 19 also tended to have a longer response time (decrease in responsiveness) as the flow velocity decreased. In Experimental Examples 5 to 19, the same tendency as in Experimental Examples 1 to 4 was confirmed between the values of the cross-sectional area Cs and the cross-sectional area Ds and the responsiveness at low flow velocity. For example, in Experimental Examples 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 response at a flow velocity of 1 m / s is obtained.} The time was 3 seconds or less (the evaluation of responsiveness was "B" or more). Further, when comparing between Experimental Examples 5 to 8 in which the cross-sectional areas As are the same and the values of the cross-sectional areas Bs are the same, the conditions are 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. Experimental Example 7 satisfying the above conditions had the shortest response time. Similarly, when compared between Experimental Examples 9 to 12, ^{Experimental Example 11 satisfying 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 has the shortest response time. Comparing between Experimental Examples 13 to 16, Experimental Example 15 satisfying the condition 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 has the shortest response time at a flow velocity of 0.73 m / s. It was. 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 is small and is considered to be an error. Comparing between Experimental Examples 17 to 19, the response time between Experimental Example 18 and Experimental Example 19 in which 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 is 1 m / s. Although the values were the same, the response time at a flow velocity of 0.73 m / s was the shortest in Experimental Example 19 among Experimental Examples 17 to 19. Therefore, as a whole, it was confirmed that Experimental Example 19 tended to have the shortest response time between Experimental Examples 17 to 19.

Further, among Experimental Examples 2 to 4,6 to 8,10 to 12,14 to 16,18,19 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, each other.} Experimental Examples 2 to 4 having the same cross-sectional area As and the same cross-sectional area ratio As / Bs are designated as the first group, and Experimental Examples 6 to 8 are similarly grouped as the second group, and Experimental Examples 10 to 12 are referred to as the third group. Experimental Examples 14 to 16 are referred to as a fourth group, and Experimental Examples 18 and 19 are referred to as a fifth group. Comparing the first to fifth groups, the cross-sectional area As of the first to fourth groups in the range of ^{47.3 mm 2} or more and 68.1 mm ^{2 or less is out of this range.} It was confirmed that the response time at low flow velocity tended to be shorter than that of the fifth group. 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 is "B", and the effect of reducing the decrease in the responsiveness of the gas to be measured at a low flow velocity is obtained.

20 Piping, 22 Fixing member, 100, 200, 400 Gas sensor, 102 housing, 103 volts, 110 sensor element, 110a porous protective layer, 111 gas inlet, 120, 220, 420 protective cover, 122 1st gas chamber, 122a 1st space, 122b 2nd space, 122c 2nd space inlet, 122d flow path cross section, 124 sensor element chamber, 126 second gas chamber 127,327,427 element chamber entrance, 128,428 outer opening, 129, 429 Element side opening, 130, 230, 430 Inner protective cover, 131, 431 first member, 132 large diameter part, 133 step part, 134, 334 first cylindrical part, 135, 235, 435 second member, 136 336, 436 Second cylindrical part, 136a protruding part, 137 connection part, 138, 238 tip part, 138a, 238a Element chamber outlet, 138b side hole, 138d side part, 138e bottom part, 139 step part, 140,240 outer protective cover , 142 Large diameter part, 143 body part, 143a side part, 143b step part, 144a outer entrance, 144b side hole, 144c vertical hole, 146,246 tip part, 146a, 246a side part, 146b, 246b bottom part, 146c taper part 147a, 247a outer outlet, 147c, 247c vertical hole, 334a recess, 434a body part, 434b first cylindrical part.

Claims (9)

A sensor element having a gas introduction port 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 inside from the gas introduction port.
It has a sensor element chamber in which the tip of the sensor element and the gas introduction port are arranged inside, and is one or more element chamber inlets which are inlets to the sensor element chamber and outlets from the sensor element chamber. A tubular inner protective cover in which one or more element chamber outlets are arranged, and
One or more outer inlets which are inlets of the gas to be measured from the outside and one or more outer outlets which are outlets of the gas to be measured to the outside are arranged and arranged outside the inner protective cover. With a tubular outer protective cover
With
The outer protective cover and the inner protective cover are a first gas chamber that functions as a flow path of the gas to be measured between the outer inlet and the element chamber inlet as a space between the two, and the outer outlet. A second gas chamber that functions as a flow path for the gas to be measured between the element chamber outlet and the first gas chamber and does not directly communicate with the first gas chamber is formed.
The inner protective cover has a tubular first member surrounding the sensor element and a tubular second member surrounding the first member.
The first member and the second member form the element chamber entrance as a gap between the first member and the second member.
The first gas chamber is parallel to the axial direction of the inner protective cover and the direction from the front end to the rear end of the sensor element is upward, and the direction from the rear end to the front end of the sensor element is downward. Is a space between the outer protective cover and the second member, which functions as a flow path of the gas to be measured upward from the outer inlet, and more than the upper end of the second member. It has a second space above and between the outer protective cover and the first member, which functions as a flow path for the gas to be measured from the first space to the entrance of the element chamber.
The cross-sectional area Cs, which is the cross-sectional area of the flow path when the gas to be measured passes directly above the second member from the outside to the inside of the second member in the second space, is 14.0 mm ² or more. ,
The cross-sectional area Ds, which is the 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.
The gas sensor according to claim 1. The cross-sectional area Ds is 5.0 mm ² or less.
The gas sensor according to claim 1 or 2. Cross-sectional area ratio of the cross-sectional area As of the second space inlet, which is the inflow port of the gas to be measured 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. As / Bs is 1.41 or more and 4.70 or less,
The gas sensor according to any one of claims 1 to 3. The cross-sectional area As of the second space inlet, which is the inlet of the gas to be measured from the first space to the second space, is 47.3 mm ² or more and 68.1 mm ² or less.
The gas sensor according to any one of claims 1 to 4. Said one or more element chamber inlet of total cross-sectional area Bs is the cross-sectional area is 14.5 mm ² or more 33.4 mm ² 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 entrance so that the element side opening, which is the opening on the sensor element chamber side of the element chamber entrance, opens downward. Yes,
The gas sensor according to any one of claims 1 to 6. The first member has a first cylindrical portion that surrounds the sensor element.
The second member has a second cylindrical portion having a diameter larger than that of the first cylindrical portion.
The element chamber entrance is a cylindrical gap between the outer peripheral surface of the first cylindrical portion and the inner peripheral 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 that has a gas inlet for introducing a gas to be measured and can detect a specific gas concentration of the gas to be measured that has flowed into the inside from the gas inlet.
It has a sensor element chamber inside for arranging the tip of the sensor element and the gas introduction port inside, and at one or more element chamber inlets which are inlets to the sensor element chamber and outlets from the sensor element chamber. A tubular inner protective cover in which one or more element chamber outlets are arranged, and
One or more outer inlets which are inlets of the gas to be measured from the outside and one or more outer outlets which are outlets of the gas to be measured to the outside are arranged and arranged outside the inner protective cover. With a tubular outer protective cover
With
The outer protective cover and the inner protective cover are a first gas chamber that functions as a flow path of the gas to be measured between the outer inlet and the element chamber inlet as a space between the two, and the outer outlet. A second gas chamber that functions as a flow path for the gas to be measured between the element chamber outlet and the first gas chamber and does not directly communicate with the first gas chamber is formed.
The inner protective cover has a tubular first member and a tubular second member surrounding the first member.
The first member and the second member form the element chamber entrance as a gap between the first member and the second member.
The direction parallel to the axial direction of the inner protective cover and from the bottom of the outer protective cover to the side opposite to the bottom is upward, and the direction from the side opposite to the bottom of the outer protective cover to the bottom is downward. As a direction, the first gas chamber is a space between the outer protective cover and the second member, and functions as a flow path of the gas to be measured from the outer inlet to the upward direction. A second space above the upper end of the second member and between the outer protective cover and the first member, which functions as a flow path for the gas to be measured from the first space to the entrance of the element chamber. And have
The cross-sectional area Cs, which is the cross-sectional area of the flow path when the gas to be measured passes directly above the second member from the outside to the inside of the second member in the second space, is 14.0 mm ² or more. ,
The cross-sectional area Ds, which is the 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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